US 20100154304 A1
The present invention provides a gasifier comprising one or more fluid conduits for converting carbonaceous feedstock into an off-gas and residual solid material. The gasifier comprises a refractory-lined processing chamber having one or more fluid conduits located therein to facilitate the passage of fluid material such as gas into and/or out of the chamber. For example, a conduit facilitates the input of process additives and/or the exit of steam and/or off-gases from the processing chamber. The gasifier comprises one or more input(s) for receiving feedstock, one or more residue outlets, and heating means to facilitate the conversion process and a control system for controlling various aspects of the gasification process. Optionally, the gasifier may be configured for recycling steam and/or off-gas and/or recycled heat back into processing chamber. Optionally, the gasifier may further comprise one or more material displacement control modules, and mixing means.
1. A gasifier comprising one or more fluid conduits for converting carbonaceous feedstock into an off-gas and residual solid material, the gasifier comprising a refractory-lined processing chamber having one or more fluid conduits located therein to facilitate the passage of fluid;
at least one input for receiving feedstock;
at least one residue outlets; and
a heating means to facilitate the conversion process, and a control system for controlling various aspects of the gasification process, wherein the conduit facilitates the input of process additives and at least one of the exit of steam and off-gases from the processing chamber.
2. The gasifier of
3. The gasifier of
4. The gasifier of
5. A gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising:
a refractory-lined processing chamber comprising one or more fluid passage conduits located therein;
at least one additive inputs for input of additives into the processing chamber;
at least one gas outputs for output of the off-gas from the processing chamber;
at least one feedstock inputs for input of the carbonaceous feedstock into the processing chamber; and
at least one residue outputs for output of the solid residue from the processing chamber, wherein the at least one additive inputs and the at least one gas outputs is provided via the at least one or more fluid passage conduits.
6. The gasifier of
7. The gasifier of
8. The gasifier of
9. The gasifier of
10. The gasifier of
11. The gasifier of
12. The gasifier of
13. The gasifier of
14. The gasifier of
15. The gasifier of
16. A vertically oriented gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising:
a descending bed processing chamber comprising one or more fluid conduits located therein, one or more vertically successive processing regions being distributed within the chambers, within each one of which a respective process selected from the group consisting of drying, volatilization and carbon conversion is at least partially favoured, the processing regions being identified by chemical conditions respectively enabling each of the respective process;
one or more material displacement control modules adapted to control a vertically downward movement of the feedstock through said processing regions to enhance each of the at least partially favoured process;
at least one additive inputs for input of additives into said processing regions;
at least one gas outputs for output of gas from the gasifier;
at least one feedstock inputs located near a first of the processing regions; and
at least one residue outputs;
wherein one or more of the at least one additive inputs and the at least one or more gas outputs is provided via the one or more fluid conduits.
17. A horizontally oriented gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising:
a processing chamber comprising one or more fluid conduits located therein, one or more horizontally successive processing regions being distributed within the chambers, within each one of which a respective process selected from the group consisting of drying, volatilization and carbon conversion is at least partially favoured, the processing regions being identified by chemical conditions respectively enabling each of the respective process;
one or more material displacement control modules adapted to control a horizontal movement of the feedstock through the processing regions to enhance each of the at least partially favoured process;
one or more additive inputs for input of additives into the one or more processing regions;
one or more gas outputs for output of gas from the gasifier;
one or more feedstock inputs located near a first of the processing regions; and one or more residue outputs;
wherein one or more of the one or more additive inputs and/or the one or more gas outputs is provided via the one or more fluid conduits.
18. The gasifier of
19. The gasifier of
20. The gasifier of
The invention pertains to the field of gasification, and, in particular, to a gasifier comprising one or more fluid conduits.
Gasification is a process that enables the conversion of carbonaceous feedstock, such as municipal solid waste (MSW), biomass or coal, into a combustible product gas. The product gas can be used to generate electricity or as a basic raw material to produce chemicals and liquid fuels.
Generally, the gasification reaction consists of feeding carbonaceous feedstock into a heated gasifier along with a controlled and/or limited amount of oxygen/air and optionally steam. In contrast to incineration or combustion, which operates with excess oxygen to produce CO2, H2O, SOx, and NOx, gasification reactions produce a raw gas composition comprising CO, H2, H2S, and NH3. After clean-up and appropriate processing, the primary gasification products of interest are H2 and CO.
Possible uses for the product gas from the gasification reaction include: the combustion in a boiler for the production of steam for internal processing and/or other external purposes, or for the generation of electricity through a steam turbine; the combustion directly in a gas turbine or a gas engine for the production of electricity; fuel cells for the production of electricity and/or steam (heat); the production of methanol and other liquid fuels; as a further feedstock for the production of chemicals such as plastics and fertilisers; the extraction of both hydrogen and carbon monoxide as discrete industrial fuel gases; and other industrial applications.
A number of systems have been proposed for capturing heat produced by the gasification reaction and utilising such heat to generate electricity, generally known as combined cycle systems. The energy in the product gas coupled with substantial amounts of recoverable sensible heat produced by the process throughout the gasification system can generally produce sufficient electricity to drive the process, thereby alleviating the expense of local electricity consumption.
Useful feedstock can include any municipal waste, waste produced by industrial activity and biomedical waste, sewage sludge, coal, heavy oils, petroleum coke, heavy refinery residuals, refinery wastes, hydrocarbon contaminated soils, biomass, and agricultural wastes, forestry wastes and/or by-products, tires, and other hazardous waste. Depending on the origin of the feedstock, the volatiles may include H2O, H2, N2, O2, CO2, CO, CH4, H2S, NH3, C2H6, unsaturated hydrocarbons such as acetylenes, olefins, aromatics, tars, hydrocarbon liquids (oils) and char (carbon black and ash).
The means of accomplishing a gasification reaction vary in many ways, but rely on four key engineering factors: the atmosphere (level of oxygen or air or steam content) in the gasifier; the configuration and dimensions of the gasifier; the internal and external heating means; and the operating temperature for the process. Factors that affect the quality of the product gas include: feedstock composition, preparation and particle size; gasifier heating rate; residence time; material feeding method (dry or slurry feed system), the feedstock-reactant flow arrangement, the design of the dry ash or slag removal system; whether it uses a direct or indirect heat generation and displacement method; and the syngas cleanup system. Gasification is usually carried out at a temperature in the range of about 650° C. to 1200° C., either under vacuum, at atmospheric pressure or at pressures up to about 100 atmospheres.
As the feedstock is heated, water is the first constituent to evolve. As the temperature of the dry feedstock increases, volatilization takes place. During volatilization, the feedstock is thermally decomposed to release tars and light volatile hydrocarbon gases, with the formation of char, a residual solid consisting of both organic and inorganic materials. At high temperatures (such as above 1200° C.), inorganic mineral matter is fused or vitrified to form a molten glass-like substance called slag. The slag is usually found to be non-hazardous and may be disposed of in a landfill as a non-hazardous material, or sold as an ore, road-bed, or other construction material.
If the gas generated in the gasification reaction comprises a wide variety of volatiles, such as the kind of gas that tends to be generated in a low temperature gasifier with a “low quality” carbonaceous feedstock, it is generally referred to as off-gas. If the characteristics of the feedstock and the conditions in the gasifier generate a gas in which CO and H2 are the predominant chemical species, the gas is referred to as syngas. Optionally, the raw gas or the raw syngas is converted to a more refined gas composition in a gas reformulating system (GRS) prior to cooling and cleaning through a gas conditioning system (GCS).
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the invention.
The object of the invention is to provide a gasifier comprising one or more fluid conduits.
In accordance with an aspect of the invention, there is provided a gasifier comprising one or more fluid conduits for converting carbonaceous feedstock into an off-gas and residual solid material, the gasifier comprising a refractory-lined processing chamber having one or more fluid conduits located therein to facilitate the passage of fluid; one or more input(s) for receiving feedstock; one or more residue outlets; and heating means to facilitate the conversion process; and a control system for controlling various aspects of the gasification process; wherein the conduit facilitates the input of process additives and/or the exit of steam and/or off-gases from the processing chamber. Optionally, the gasifier is configured for recycling steam and/or off-gas and/or recycled heat back into the processing chamber.
In one embodiment, the gasifier further comprises one or more material displacement control modules for facilitating movement of the reactant material through the gasifier, agitation or mixing means to facilitate mixing of reactant material with process additives. Optionally, the material displacement control modules and/or the agitation or mixing means is operatively coupled to the control system.
In accordance with another aspect of the invention, there is provided a gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising a refractory-lined processing chamber comprising one or more fluid passage conduits located therein; one or more additive inputs for input of additives into the processing chamber; one or more gas outputs for output of the off-gas from the processing chamber; one or more feedstock inputs for input of the carbonaceous feedstock into the processing chamber; and one or more residue outputs for output of the solid residue from the processing chamber; wherein the one or more additive inputs and/or the one or more gas outputs is provided via the one or more fluid passage conduits. In one embodiment of the invention, the gasifier comprises two or more fluid passage conduits.
In accordance with another aspect of the invention, there is provided a vertically oriented gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising a descending bed processing chamber comprising one or more fluid conduits located therein, one or more vertically successive processing regions being distributed within the chambers, within each one of which a respective process selected from the group consisting of drying, volatilization and carbon conversion is at least partially favoured, the processing regions being identified by chemical conditions respectively enabling each of the respective process; one or more material displacement control modules adapted to control a vertically downward movement of the feedstock through the processing regions to enhance each of the at least partially favoured process; one or more additive inputs for input of additives into the one or more processing regions; one or more gas outputs for output of gas from the gasifier; one or more feedstock inputs located near a first of the processing regions; and one or more residue outputs; wherein one or more of the one or more additive inputs and/or the one or more gas outputs is provided via the one or more fluid conduits.
In accordance with another aspect of the invention, there is provided a horizontally oriented gasifier for conversion of carbonaceous feedstock into off-gas and solid residue, the gasifier comprising a processing chamber comprising one or more fluid conduits located therein, one or more horizontally successive processing regions being distributed within the chambers, within each one of which a respective process selected from the group consisting of drying, volatilization and carbon conversion is at least partially favoured, the processing regions being identified by chemical conditions respectively enabling each of the respective process; one or more material displacement control modules adapted to control a horizontal movement of the feedstock through the processing regions to enhance each of the at least partially favoured process; one or more additive inputs for input of additives into the one or more processing regions; one or more gas outputs for output of gas from the gasifier; one or more feedstock inputs located near a first of the processing regions; and one or more residue outputs; wherein one or more of the one or more additive inputs and/or the one or more gas outputs is provided via the one or more fluid conduits.
Embodiments of the present invention will now be described, by way of example only, by reference to the attached Figures, wherein:
As used herein, the term ‘about’ refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.
The terms ‘carbonaceous feedstock’ and ‘feedstock’, as used interchangeably herein, are defined to refer to carbonaceous material that can be used in the gasification process. Examples of suitable feedstock include, but are not limited to, hazardous and non-hazardous waste materials, including municipal wastes; wastes produced by industrial activity; biomedical wastes; carbonaceous material inappropriate for recycling, including non-recyclable plastics; sewage sludge; coal; heavy oils; petroleum coke; heavy refinery residuals; refinery wastes; hydrocarbon contaminated solids; biomass; agricultural wastes; municipal solid waste; hazardous waste and industrial waste. Examples of biomass useful for gasification include, but are not limited to, waste wood; fresh wood; remains from fruit, vegetable and grain processing; paper mill residues; straw; grass, and manure.
The term ‘reactant material’ is defined to refer to any feedstock, including but not limited to partially or fully processed feedstock.
The term ‘residue ’ generally refers to the residual material produced during processes for the gasification or incineration of carbonaceous feedstocks. These include the solid and semi-solid by-products of the process. Such a residue generally consists of the inorganic, incombustible materials present in carbonaceous materials, such as silicon, aluminum, iron and calcium oxides, as well as a proportion of un-reacted or incompletely converted carbon. As such, the residue may include char, ash, and/or any incompletely converted feedstock passed from the gasification chamber. The residue may also include materials recovered from downstream gas conditioning processes, for example, solids collected in a gas filtering step, such as that collected in a baghouse filter. The residue may also include solid products of carbonaceous feedstock incineration processes, which may come in the form of incinerator bottom ash and fly ash collected in an incinerator's pollution abatement suite.
As used herein, the term “sensing element” is used in the broadest sense to describe the aspect of any element related to the gas reformulation system that is configured to sense, detect, read, monitor, etc. one or more characteristics, parameters, and/or information of the system, inputs and/or outputs.
As used herein, the term “response element” is used to describe the aspect of any element related to the gas reformulation system that is capable of responding to a signal.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The gasifier comprises a refractory-lined processing chamber having one or more fluid conduits located therein to facilitate the passage of fluid material such as gas into and/or out of the chamber. For example, a conduit facilitates the input of process additives and/or the exit of steam and/or off-gases from the processing chamber. The gasifier comprises one or more input(s) for receiving feedstock, one or more residue outlets, and heating means to facilitate the conversion process and a control system for controlling various aspects of the gasification process. Optionally, the gasifier may be configured for recycling steam and/or off-gas and/or recycled heat back into processing chamber.
Optionally, the gasifier may further comprise one or more material displacement control modules for facilitating movement of the reactant material through the gasifier, agitation or mixing means to facilitate mixing of reactant material with process additives. The material displacement control modules and/or the agitation or mixing means may be operatively coupled to the control system.
Generally, the gasification of the carbonaceous feedstock can be subdivided into three stages, namely, drying, volatization and char-to-ash conversion. Accordingly, one or more processing regions may optionally be defined within the gasifier within each one of which a certain process such as drying, volatilization or carbon conversion or combinations thereof may be at least partially favoured.
(a) Drying of the Material
The feedstock delivered into the gasifier undergoes a drying process under a temperature range between about 25° C. and about 200° C., for example. In this temperature range, drying may also be accompanied by minor amounts of volatilization.
(b) Volatilization of the Material
This process occurs mainly between about 350° C. and about 800° C., for example, and may also be accompanied by a small remainder of the drying operation as well as a substantial amount of carbon conversion. The composition of air supplied in this region is typically varied depending on the feedstock supplied (e.g. oxygen enriched or depleted air).
(c) Carbon Conversion
At temperatures between about 900° C. and about 1000° C., for example, the main process reaction occurring is that of carbon conversion with the remainder of volatilization. By this time most or all of the moisture has been removed from the material. The flow rate of air supplied can be varied depending on the reactant material supplied. Steam is also optionally added in this region.
A worker skilled in the art would readily appreciate that in a given chemical condition (e.g. temperature range), all of the three processes are occurring somewhat simultaneously and continuously, though, depending on the chemical condition, one of the processes is at least partially favoured.
A worker skilled in the art will understand that the gasifier can in general comprise of a large number of processing regions with a different proportion of drying, volatilization or carbon conversion occurring in each processing region. Thus, the number of processing regions can be as many or as few as desired, without loss of generality.
Different embodiments are shown in
As mentioned above, the gasifier comprises one or more fluid conduits and optionally, one or more input elements and/or one or more output elements operatively disposed around a periphery of the chamber. These cooperate to facilitate the addition of process additives and/or the exit of steam and/or off-gases therefrom. The additives injected into the processing chamber determine the chemical conditions therein and thus promote the determination of one or more processing regions within the gasifier within which a certain process such as drying, volatilization or carbon conversion may be at least partially favoured.
A worker skilled in the art will readily understand that the location and shape of the fluid conduits can vary and is not limited to any shape explicitly mentioned herein. In one embodiment, the fluid conduit is a cylindrical tube centrally located within the processing chamber. In one embodiment, the fluid conduit is centrally located within the processing chamber but has a rectangular cross-section. In one embodiment, the fluid conduit has a tear drop shape. The various shapes of the fluid conduits may be designed to optimize the dispersion of the process additives into the gasifier.
A worker skilled in the art will readily understand that even within the same processing chamber, the different fluid conduits can vary in shape and size and can also be used for different functions. For example, the gasifier may comprise a first fluid conduit used for outputting off-gases and/or steam, and a second fluid conduit used for injecting additives.
For embodiments where the off-gas is outputted using the one or more fluid conduits, the off-gas can be drawn out at either or both ends of the processing chamber by appropriate placement of a blower or other suction means as known in the art.
Additionally, the multiple fluid conduits can be nested within one another, (e.g. concentric cylindrical tubes can be used for exit of off-gases and/or the entry of additives into the different processing regions) and/or distinctly located. Multiple fluid conduits can also be positioned and designed to act as stirring/mixing means.
In one embodiment of the invention, the gasifier comprises three processing regions with the first processing region at least partially favouring drying, the second processing region at least partially favouring volatilization and the third processing region at least partially favouring carbon conversion. In one embodiment and referring to
It will be appreciated that several fluid conduits may be provided for supplying additives to and/or removing off-gases from (optionally for use in heat and/or by-product recycling, as discussed further below) the gasifier, in accordance with different embodiments of the present invention, as can any number or group of these fluid conduits may be provided with a header and be configured to be removed and/or replaced for maintenance and/or cleaning.
A worker skilled in the art will readily understand that the exact location, size, use (e.g. exit of off-gases, entry of additives, etc.) and the direction of gas flow within the fluid conduits are not limited to those exemplified in the embodiments of
It will be appreciated that cross-flow conditions may be promoted by careful design of the gasifier, and in particular, the design of the boundary zones between adjacent processing regions. These boundary zones do not have any additional reactions occurring, such as injection of process additives and/or off-gas extraction. As such, the boundary zones may be designed to have no holes in the wall and fluid conduit(s).
To reduce the proportion of gas and/or additives passing from one processing region to another and thus, promote cross-flow operation, it is essential that the pressure drop across a processing region be less than the pressure drop from one processing region to another. Referring to Figure shown below, this implies that the following equations be satisfied:
Under conditions that satisfy the above equations, there is very minimal active flow of gases along the flow lines indicated by subscript A, B, C, and D. Note that these equations assume that there are no holes in the wall or conduit(s) in the boundary zones. The minimal flow in the boundary zones may occur due to superficial gases caught between the solid materials and/or gases which go with the flow of the solid material.
Cross-flow operation can be achieved in both horizontally and vertically oriented embodiments of the present invention, as shown in the Figure below.
In one embodiment and referring to
In one embodiment and referring to
For embodiments using a plurality of fluid conduits, one or more of the fluid conduits may be in a nested configuration.
In one embodiment and referring to
In one embodiment and referring to
As mentioned earlier, the fluid conduits may be configured so that the process additives may be injected into each processing region independently, or in a coordinated fashion.
In one embodiment and referring to
In one embodiment and referring to
In one embodiment and referring to
The independent extraction of off-gases from and/or the independent injection of the process additives to each of the processing regions promote the enhanced control of the gasification reaction. Referring to
An important challenge in the design of gasifiers is the plugging of the holes used for entrance/exit of additives/off-gases due to its proximity with the reactant material. Various aspects of the designs of these holes are described in
For embodiments where the fluid conduits of the inner volume are used for injection of additives, the holes on the fluid conduits do not plug as much since they are now injecting air rather than being the exit point. The holes distributed around the processing chamber will have lower flow rates (more holes); so the pressure drop and velocity will not be as great, resulting in reduced plugging. In addition, cleaning plugged holes is easier for holes distributed around the processing chamber than on the inside. Different techniques for clearing plugged holes include: (a) a pressure spike to clear the holes; (b) scraping the holes with the agitator or other device; and (c) use of a small piston push though the holes from the outside jacket.
Three additional design options for the holes are shown in
To further reduce plugging and/or collecting of ash, a protector (cap or cover) may be needed.
Due to different temperatures in the gasifier and the fact that a fluid conduit may extend the entire length of the gasifier, there will be significant temperature effects on the conduit (from 25° C. to 1000° C.). It will be appreciated that the fluid conduit(s) will require careful engineering of sections (generally in the boundary zones) where the conduit material either changes or has an expansion joint to relieve the stresses; and also where the fluid conduit(s) intersects with the gasifier wall, to ensure that the conduit connection does not leak. Such engineering solutions would be known by one skilled in the art. It will be appreciated that refractory lining may not be necessary on these fluid conduit(s) as temperatures on either side thereof will be substantially similar.
In one embodiment, the processing chamber of the gasifier comprises an outer wall and a refractory-lined inner wall defining an inner volume, within which the one or more fluid conduits are located. In general, the carbonaceous feedstock is fed into the inner volume between the inner wall and the one or more fluid conduits. Optionally, one or more input elements and/or output elements, or groups thereof, are disposed on the inner wall, around the processing chamber for facilitating the entry/exit of additives/off-gases to/from the inner volume. The inner walls may vary in shape so long as the inner volume can accommodate the appropriate amount of reactant material for the designed residence time, and allow for a reasonable off-gas superficial velocity to be attained.
The outer walls can also vary in shape. A worker skilled in the art will readily understand that mechanical considerations for operational stability and support may be important in determining appropriate designs for the outer wall. In one embodiment of the invention, the outer wall defines a cylinder whose length is between about 1 and 6 times its diameter. In one embodiment, the cylinder's length is between about 1 and 2 times its diameter. In one embodiment, the length is about 1.5 times its diameter.
In one embodiment of the invention, a refractory lining protects the processing chamber from the effects of high temperatures and corrosive gases and minimizes unnecessary loss of heat from the process. The refractory material is a conventional refractory material, which is well-known to those skilled in the art and which is suitable for use for a high temperature e.g. up to about 1800° C., un-pressurized reaction. Examples of such refractory material include, but are not limited to, high temperature fired ceramics, i.e., aluminum oxide, aluminum nitride, aluminum silicate, boron nitride, zirconium phosphate, glass ceramics and high alumina brick containing principally, silica, alumina, chromia and titania. To further protect the processing chamber from the impact of corrosive gases, it may be lined with a membrane. Such membranes are known in the art and as such a worker skilled in the art would readily be able to identify appropriate membranes based on the gasifier requirements.
The physical design characteristics of a processing chamber are determined by a number of factors that can be readily determined by one skilled in the art. For example, the internal configuration and size of the processing chamber can be dictated by the operational characteristics through analyses of the chemical composition of the input feedstock to be processed.
Gasification requires heat and an oxidant such as oxygen and/or steam. Heating can occur directly by the heat released due to partial oxidation of the feedstock or indirectly by use of one or more heat sources known in the art.
Therefore, other design factors include the type of heating means used and the position and orientation of the heating means used. These heating means are generally positioned within the processing chamber at the desired depth in order to concentrate the high temperature processing region where it is most effective, while simultaneously minimizing heat losses.
In one embodiment of the invention, the heat source is pre-heated air injected into the processing chambers either obtained from air heaters or heat exchangers, both of which are known to a worker skilled in the art and fed through to each processing region using an independent air feed and distribution system, provided for example by an air box. The air could also be injected through the fluid conduits. Alternatively, the indirect heat source could either be circulating hot sand or an electrical heating element. The heat required for gasification may also be obtained by recycling (discussed in detail below) sensible heat present in the output gas streams of the gasification and/or gas reformulation processes.
Various computer-based simulation and modeling tools can facilitate the physical design of the processing chamber by taking into account factors such as efficient heat transfer, gas flow, mixing of additives, etc. Computer-based tools virtually eliminate the need for experimentation prior to preliminary system design and provide rapid confirmation of process characteristics and efficiency with any input waste stream. They also permit interactive iteration to optimize operational characterization for any particular system prior to system commissioning and facilitate real-time optimization of processes for non-homogeneous materials based on product gas characterization as input.
One such simulator is the Chemical Process Simulator, as detailed in U.S. Pat. No. 6,817,388 (incorporated by reference). It uses the principle of minimization of Gibb's free energy to allow prediction of the product gas components at a specific temperature and specific set of input parameters.
In addition to using the Chemical Process Simulator, flow modeling of the processing chamber may also be used in the design process to ensure proper mixing of the process inputs, to analyze impact of the kinetic effects, and to adjust the reaction temperature profile within the simulator. Flow modeling results also assist refractory design since all operating characteristics at the refractory surface can readily be identified.
The processing chamber design may incorporate various design features of various types of processing chambers known in the art, including but not limited to descending bed processing chambers, fixed-bed processing chambers, gravity-assisted vertical processing chambers, mechanically-assisted flow processing chambers, entrained flow processing chambers, and fluidised bed processing chambers, to name a few.
In addition, the processing chambers can further comprise one or more service ports to allow for entry for maintenance and repair. Such ports are known in the art and can include sealable port holes of various sizes. In one embodiment, access to a processing chamber is provided by a manhole at one end which can be closed by a sealable refractory lined cover during operation. In one embodiment of the invention, a manhole is placed on both ends of a processing chamber for maintenance.
In order to facilitate initial start up of the gasifier, the processing chambers can include access ports sized to accommodate various conventional burners, for example natural gas or propane burners, to pre-heat the gasifier.
Additives may be input at multiple locations within the processing chamber to promote definition of each processing region therein and to facilitate efficient conversion of the feedstock into gas. The type and quantity of the additives is selected to optimize the process reactions while maintaining adherence to regulatory authority emission limits and minimizing operating costs.
The different types of additives include but are not limited to air, oxygen-enriched air, nitrogen, oxygen, steam and ozone. The injected additives play a key role in determining the chemical conditions (e.g. temperatures) within the processing chambers and thus the extents of the processing regions wherein different processes are at least partially favoured.
Additives fed into the processing chamber can include steam, pre-heated air etc, and serve to improve the quality of the product syngas. The position, orientation and number of the injection ports for these additional additives also have to be considered in the design of the processing chamber to ensure that they are injected where they will promote efficient reaction to achieve the desired conversion result.
Air or oxygen input can be used to maximize carbon conversion (i.e., minimize free carbon) and to maintain the optimum processing temperatures while minimizing the cost of input heat. The quantity of both additives can be established and rigidly controlled as identified by the outputs for the feedstock being processed. The amount of air injection is established to minimize the cost of heating while ensuring the overall process does not approach any of the undesirable traits associated with incineration (such as unwanted dioxins, furans, NOx, SOx in product gas, metals in ash and lower carbon conversion), and satisfies the emission standards requirements of the local area.
Steam inputs promote sufficient free oxygen and hydrogen to maximize the conversion of decomposed elements of the feedstock into product gas and/or non-hazardous compounds. As the conversion of the reactant material to gas via reaction with steam is an endothermic one, it can serve to balance out the endothermic nature of the reaction via air. In addition, steam provides additional hydrogen for the proper balancing of C, H, O reactions.
In some embodiments of the invention, a secondary feedstock stream is also introduced as a process additive. This feedstock stream can be dynamically manipulated by the global control system depending on the downstream parameters of the gasifier such as the quality of the product gas, pressure etc as sensed by the sensing elements. A typical secondary feedstock is high carbon feedstock such as plastics, rubber such as tires and the like, and other such feedstock as will be readily apparent to the person of skill in the art.
In one embodiment, a plurality of steam and/or air streams may be injected into the one or more processing chambers. These streams are strategically oriented to direct steam and/or air into the high temperature regions. In embodiments in which pre-heated air is used as the gasifier heating means, additional air/oxygen streams may optionally be injected. In one embodiment, nitrogen is used as an additive instead of air in the processing region promoting drying to avoid the possibility of combustion.
In one vertically oriented embodiment of the invention, the input elements distributed around the processing chamber are used for injection of additives into the reactant material contained within. The resulting off-gases in the different processing regions are collected using the one or more fluid conduits located in the inner volume of the processing chamber. In one embodiment of the invention and referring to
In one vertically oriented embodiment of the invention and referring to
For the embodiments where additives are added using input elements distributed around the processing chamber, even distribution of additives and hence more stable reactions may be promoted. This design evens out the processing regions and may reduce the concentration of some additives (such as oxygen or ozone), thus avoiding localized combustion or agglomeration. To reduce the possible occurrence of bed fluidization and/or the creation of hot spots, agitators can be used to promote mixing of the reactant material. The actual location of the input elements around the processing chamber may be determined based on one or more of the following factors: (a) maximize heat transfer; (b) maximize contact with carbon; (c) minimize pressure loss; (d) avoid plugging; (e) minimize potential for gas channelling; (f) maximize ease of replacement and clean-up.
In the embodiments where the additives are injected into the reactant material using the fluid conduits located within the inner volume of the processing chamber, the additives expand outwards in the bed to the outside edge of the processing chamber where the resulting gas is collected and piped off. The gases can then pass to a reformulation chamber, or handled in a similar manner to alternative designs. Good mixing promotes an even treatment of the reactant material with additives and avoid combustion and around the one or more processing chambers, bridging/agglomeration in the regions contiguous to the input of the additives where the concentration of oxygen is higher. As the gas expands outward from the center it will react with the reactant material producing more gas resulting in an even gas flow.
The input of additives may be actively controlled by a common response element configured to provide a pre-selected quantity or input rate of additives (e.g. set absolute or relative input) for a given sensed process characteristic (e.g. process temperature, pressure, throughput, etc.; product gas quality, quantity, composition, pressure, flow, heating value etc.; feedstock input rate, quality, composition, etc; and the like), or again controlled by distinct response elements, possibly operatively linked via a same local, regional and/or global control system.
The movement of the reactant material through the gasifier may optionally be facilitated via one or more material displacement control modules, thus allowing the overall gasification process to be enhanced, if not optimized for a given set of process conditions.
In addition to controlling the displacement of material through the gasifier, the material displacement control module can also be specifically optimized to minimize the carbon content in the residue. In one embodiment of the invention, this is achieved using a plug flow pattern for the movement of the reactant material and a total control over the residue removal rate. It may also optionally incorporate means to break up residue agglomerates that can cause jamming at the residue outlets of the gasifier.
In one embodiment, one or more material displacement control modules operatively control one or more process devices and/or mechanisms configured to control a displacement or a rate of displacement of the reactant material through the processing regions, thereby promoting the efficient processing of the material therein.
The material displacement control module may further be associated with, or integrated within a local, regional and/or global control system adapted to actively control various elements of the gasifier in response to sensing one or more process characteristics, either within the gasifier, or external thereto, for example, in a downstream process or application of the product gas. In such an embodiment where the material displacement control module is actively operated in conjunction with a local, regional and/or global process control system, further refinement of the material processing may be achieved to meet downstream needs, for example, when the product gas, or a further processed derivative thereof, is used for a selected downstream application. Alternatively, or in combination therewith, the combined control of the gasification process may be implemented so to maximise gasification of the material, for example, to meet environmental regulations where such regulations exist, and/or to minimise an energetic impact of the process.
In general, the material displacement control module may be configured to operate under pre-set operational parameters, for example, allowing for a substantially constant residence time of the material in each processing region, or again, may be configured to operate under dynamically updated or generated operational parameters adapted to optimise processing of the material to achieve a given result. In either scenario, the material displacement control module, and any control system operatively coupled thereto, may comprise one or more sensing elements for sensing one or more process characteristics, such as process temperature(s), pressure(s), reactant composition, product gas composition, and adjust one or more process devices, such as mechanisms and/or devices operatively controlled by the material displacement control module for enabling a controlled displacement of the material through the processing regions within the gasifier, in response to these characteristics.
In one embodiment, a vertically oriented gasifier comprises one or more material displacement control modules that actively control the downward movement of the reactant material through the various processing regions of the gasifier. This is in contrast to standard descending bed gasifiers that rely on the gradual consumption of the reactant material in the gasifier to move the reactant material downwards.
For the vertically oriented embodiments of the present invention, various cooperative devices and/or mechanisms may be controlled by the one or more material displacement control modules to implement a downward displacement of the material, either by direct control of material displacement between each processing region, or by controlled extraction of reactant material from a lowermost processing region thereby indirectly controlling a downward displacement of the reactant material from an uppermost processing region toward the lowermost processing region under gravity, or using any combination thereof. As will be described below with reference to a number of illustrative embodiments, the material displacement control module will be adapted for a given embodiment to enable the controlled displacement of material through the one or more processing regions.
A worker skilled in the art will readily understand that in the vertically oriented embodiments of the present invention, the use of a single device at the bottom of the processing chamber will both directly control the rate of movement of the reactant material out of the lowermost processing region of the processing chamber and also indirectly control the rate of movement of the reactant material through all the prior processing regions of the processing chamber, as the reactant material in those processing regions will experience a downward displacement by the action of gravity, as reactant material is removed from the lowermost processing region. Thus, the use of a single device at the bottom of a processing chamber results in an in-built relationship between the values of the residence times for all the processing regions defined therein. A worker skilled in the art will readily understand that in vertically oriented embodiments where multiple processing chambers are operatively coupled, a rotating paddle may be used at the bottom of only the lowermost processing chamber and the reactant material passes from the uppermost processing chamber to the lowermost processing chamber by the action of gravity.
The material displacement control module can be configured to operate one of a variety of mechanisms or devices known in the art for enabling displacement of material from one region to another. Examples include, but are not limited to rotating arms, rotating wheels, rotating paddles, moving shelves, pusher rams, screws, conveyors, and combinations thereof.
The factors involved in the choice of a particular type of device or mechanism operated by the material displacement control module include but are not limited to: (a) controllability & speed: how well can the flow of the reactant material through the vertically oriented gasifier be controlled accurately; (b) variance in reactor flow: if additives are added below the material displacement control module, is there a disruption to the flow and is the disruption manageable; and/or (c) power requirements and durability: how much energy and maintenance is required for proper operation of the device or mechanism, e.g. rotating grates require more maintenance than screws and pusher rams when properly designed.
In one vertically oriented embodiment of the invention, the material displacement control module may comprise an array of one or more devices (e.g. pusher rams) within each processing chamber, each of which is used to actively control the movement of the reactant material from one processing region to the next until the final pusher ram pushes the residue out of the processing chamber. Thus, the reactant material is actively controlled through the entire height of the processing chamber. A worker skilled in the art will understand that such a material displacement control module can enable setting up of independent residence times in the different vertically successive processing regions within the same processing chamber.
In vertically oriented embodiments of the invention where the material displacement control module comprises a moving element and a guiding element, suitable moving elements include, but are not limited to, a shelf/platform, pusher ram, plough, screw element or a belt. The guide element can include one or more guide channels located in the bottom wall of the processing chambers, guide tracks or rails, guide trough or guide chains. Alternatively, the guide element can include one or more wheels or rollers sized to movably engage the guide element. In one embodiment, the guide engagement member is a sliding member comprising a shoe adapted to slide along the length of the guide track. Optionally, the shoe further comprises at least one replaceable wear pad.
The material displacement control module may be powered using a motor and drive system, or other such means as readily known in the art. In one embodiment the motor means is an electric variable speed motor which drives a motor output shaft selectably in the forward or reverse directions. Optionally, a slip clutch could be provided between the motor and the motor output shaft. The motor may further comprise a gear box.
Alternatively, operation of the material displacement control module can be implemented by a hydraulic or pneumatic system, chain and sprocket drive, or a rack and pinion drive. These methods of translating the motor rotary motion into linear motion have the advantage that they can be applied in a synchronized manner at each side of the material displacement control module (e.g. a pusher ram) to assist in keeping the mechanism aligned and thus minimize the possibility of jamming. In one embodiment, the use of two chains provides a means of maintaining angular alignment without the need for precision guides.
For the vertically oriented embodiments using two processing chambers,
A worker skilled in the art will appreciate that material displacement control modules can also be appropriately designed for horizontally oriented embodiments of the present invention. In one embodiment, the processing chamber is substantially horizontal and the material displacement control module is a plurality of rollers with horizontal and parallel axes in an inclined plane. An example of a plurality of rollers is the Dusseldorf/Babcock grate. See, for example, U.S. Pat. No. 5,967,064 and U.S. Pat. No. 5,448,957.
An extractor screw, as shown in
In a horizontal (or gravity sloped) embodiment of the gasifier, a screw is used to move the reactant material from one end of the chamber to the other. This screw and the outer walls of the chamber may be partially perforated to allow the gas to cross the reactant material, as shown in
Gases would cross from the holes in the conduit-screw to the walls or ceiling of the reactor (not the bottom of the reactor) or vice versa. These holes in the wall and screw would be similar in design as to the air-boxes used in our previous design and/or the would have covers where necessary on the holes so that material did not plug them.
Three alternate injection options are shown in
Optionally, and as mentioned earlier, the one or more processing chambers of the gasifier may comprise a mixing/agitation means for promoting efficient exposure of the reactant material to the additives thus promoting efficient gasification. The mixing means reduces gas channelling, a condition where the additives such as pre-heated air burns a path through the bed, resulting in more additives travelling down that ‘channel’ avoiding the reactant material completely. The passage of additives such as pre-heated air into the gas phase, also called ‘breakthrough’, can cause rapid combustion with gas phase combustibles, agglomeration of the reactant material and channel burning. Good mixing also stabilizes the gas composition and reduces the risk of downstream gas explosion.
Agitation/mixing can be achieved though various mechanical and/or sonic means known to one skilled in the art, whereby part of the reactant material is moved in relation to the rest of the reactant material. Such agitation results in better bed settling and movement of the material to avoid localized melting or slagging when not ideal.
Such agitation means may comprise, for example, a rotating shaft controlled using a motorized drive. These agitator shafts can also be operated, in one embodiment, as a sensing element of an integrated global control system wherein torque measurements on these shafts can serve as an indicator of the pile height, especially if the agitator has multi-level flights. To reduce false reports due to the formation of agglomeration on the flights, two agitator shafts may be used which clean each other as they rotate, thus knocking off agglomeration.
In one embodiment, agitation is achieved using a rod or a specially shaped metal tool that is mechanically driven to move in a pattern or random path through the bed material. It is generally thin and aerodynamic enough that reactant material does not get jammed on the agitator and the agitator does not get stuck on the reactant material.
As the off-gas produced in the gasifier is generally at high temperatures, different techniques described herein can be used to capture the sensible heat present in the off-gas and recycle it to the gasification system to enhance the thermodynamic efficiency of the overall gasification process. For example, in one embodiment of the invention, the captured heat can be used to heat the additives injected into the different processing regions. Referring to
With reference to the embodiment of
With reference to the embodiment of
With reference to the embodiment of
A selection of the most effective heat exchange scheme between input and output gaseous flows depends on the composition of the solid material and gaseous additives employed for the gasification process considered.
With reference to the embodiment of
The completeness of the gasification process is enhanced by an increase in the temperature of the additives and the concentration of steam (or carbon dioxide) in it. In one embodiment of the invention and referring to
In one embodiment where by-product recycling is optionally enabled, the gases from an earlier processing region(s) are used as additives in a later processing region(s) of the gasifier. In one embodiment referred to in
In one embodiment of the invention comprising three processing regions, and in reference to
The gasifier includes a material feeder system comprising one or more input feed ports catered to any physical characteristics of the input feedstock, each of which feed directly into the gasifier. In one embodiment of the invention, the material feeding subsystem consists of a feed hopper and a screw conveyor used to transport feedstock to the gasifier. In some embodiments of the invention, the material fed into the gasifier can be partially processed reactant material from an upstream gasifier. The feed hopper acts as a buffer for the material ready to be fed into the gasifier. The hopper can optionally have high and low level indicators that control the flow into the hopper and are optionally under the control of the process controller to match the feed rate to process demands.
Optionally, referring to
In one embodiment of the invention, the material feeding system consists of a rectangular feedhopper and a hydraulic assisted ram. A gate may be installed in the middle of the feed chute to act as a heat barrier between the processing chamber and the feedhopper. Limit switches on the feeder control the length of the ram stroke so that the amount of material fed into the processing chamber with each stroke can be controlled.
In one embodiment of the invention, the primary material feeding system may also be modified to accommodate the feeding of boxes, the form in which hospital biomedical type waste is provided for processing. A rectangular double door port will permit the boxes to be fed into the primary feed hopper where the hydraulic ram can input them into the processing chamber.
In one embodiment of the invention, an auger can be inserted hydraulically into the processing chamber to provide a granular waste material feed. In addition, ram, rotary valve, top gravity feed, are examples of other feeders that can be used in the present context to facilitate the introduction of desired feedstocks. In addition, liquids and gases can be fed into the processing chamber simultaneously through their own dedicated ports.
Optionally, the feedstock will pass through a pre-processing system before being fed into the feedstock input means. The pre-processing subsystem may comprise a shredder to reduce the as-received feedstock to a size more suitable for processing. As, components of the feedstock may include materials large enough to jam the shredder, the shedder is optionally equipped to stop when a jam is sensed, automatically reverse to clear the jam and then restart. If a jam is still detected the shredder will shut-down and send a warning signal to the controller. Appropriate shedder and shedder designs are known in the art.
The pre-processing subsystem may also include a magnetic pick-up located above the conveyor to avoid the undesirable feeding of excessive amounts of metal through the gasifier. Appropriate magnetic pick-ups are known in the art and consist of a powerful magnet over a pick conveyor belt to attract any ferrous metal that may be present in the shredded waste. Optionally, a non-magnetic belt can run across the direction of the pick conveyor, between the magnet and the feedstock so that any metal attracted to the magnet gets moved laterally away from the feedstock stream. When the metal has been moved away from the magnet it can be dropped onto a pile that is either disposed or sold.
The off-gas streams from the different processing regions may be kept separate or merged before being sent to a storage tank for future use or for further processing in a gas reformulating system (GRS).
Off-gases generated in the gasifier may need to be reformulated to obtain a gas of a desired composition, for compatibility with either downstream applications, environmental regulations or other factors. In one embodiment of the invention, the gasifier is connected to a gas reformulating system (GRS) either directly or via piping for the reformulating of off-gas 2 derived from gasification of carbonaceous feedstock 4 into a reformulated gas of a defined chemical composition 99.
In one embodiment, the GRS uses heat from one or more plasma torches to dissociate the gaseous molecules thereby allowing their recombination into smaller molecules useful for downstream application, such as energy generation. The air or other gases entering the plasma torch pass through the high potential electrical field and are heated to temperatures of 3000-5000° C. As a result of the high potential electrical field application, the plasma torch gas contains highly reactive free radicals and ions which together with the high temperature promote the gas reformulation process. The GRS may also comprise gas mixing means, process additive means, and a control system with one or more sensors, one or more process effectors and computing means to monitor and/or regulate the reformulating reaction.
The off-gas from the gasifier can be sent to other treatment processes to improve its quality (e.g. lower the quantity of tars) and to maintain heating value. In one embodiment of the invention, a low temperature GRS is used, which may not result in cracking of any tars present therein, but results in the conversion of the gas to a different composition tailored for a particular downstream application.
In one embodiment, a hydrogen burner is used to react oxygen and hydrogen to produce ultra-high temperature steam (>1200° C.). This steam can be applied to the off-gas to achieve gas reformulation and increase its heating value. This technique has similar energy efficiency as a plasma torch. As mentioned earlier, hydrogen burners can also be used to produce the additives to the lowermost processing region of the gasifier, than to the off-gas stream itself.
In one embodiment, a chemical scrubber is applied to remove tars, if present, from the off-gas. Once in the liquid phase they could be collected or chemically treated for disposal/sale. In one embodiment, a catalytic bed (fluidized or fixed) is used for gas reformulation with the addition of reactive additives.
In one embodiment, a cold fluidized sand bed is used. Here, a material such as sand, ceramic etc is used to allow the warm off-gas to cool just enough so that tars, if present, condenses. The condensed tars collects on the particle surface and the particle gets heavier and falls out of fluidization. Optionally the fluidized bed or fixed tower is cleaned/cooled using water which can wash off the tars to be processed later. The sand can also be cooled and recycled back into the process while the tars can be recycled back into the gasifier to stabilize the gas stream composition or sent to post-processing/sale/disposal. If the former, additional steam/air is injected with the tars to convert them into useable syngas. The response of the gas stream composition may be faster than if the feed is changed suddenly.
In one embodiment, the obtained syngas after the plasma-based reformulator is directed into a heat recycling system before it may be sent to a gas conditioning system and/or a gas homogenization system and/or a storage tank. The heat recycling system captures the sensible heat present in the syngas stream and recycles this heat to the gasification process to enhance the efficiency thereof.
The gas conditioning system serves to remove particulate matter and other impurities from the syngas while the gas homogenization system serves to smooth out any time variations in the composition and pressure of the syngas by providing adequate mixing means and residence time within a homogenization chamber. A storage tank is optionally used if the conditioned, homogenized syngas needs to be stored for future use. Otherwise, the conditioned, homogenized syngas can be used for downstream applications such as gas engines, boilers etc. Excess syngas can also be disposed of safely using a flare stack.
One or more residue outlets are used to remove the residue out of the final processing region of the gasifier. The configurations in which the residue exit the processing chamber are dependent on the design and function of the subsequent process and can be readily determined by one skilled in the art.
The residue is removed from the gasifier by the one or more material displacement control modules. In different embodiments of the invention, the residue can be removed into, for example, an ash collection gasifier or to a water tank for cooling as is known in the art, from where it is transmitted through a conduit under control of a valve, to a point of discharge. In one embodiment of the invention, the residue from the gasifier is sent to another gasifier for further gasification. This is particularly useful if the gasifier is not able to achieve thorough volatilization and carbon conversion.
In one embodiment, the residue is moved to a residue conditioning system which is either directly connected to the gasifier or connected via a conveyor. In the residue conditioning system, plasma arc heating is used to convert the residue (char, ash) to slag by raising the temperature of the residue to the level required for complete melting and homogenization to guarantee trouble free, continuous and automatic (i.e. unattended) slag removal. Other heating mechanisms can also be used in other embodiments of the residue conditioning system, but usually result in a slag of poor quality. The molten slag is quenched in a water tank to form a vitreous, solid slag that can either be used in the construction industry or disposed off in a non-hazardous manner in landfills. The slag contains heavy metals and other pollutants and is non-leaching. Product gases generated in the residue conditioning system is sent to the gas conditioning system either after passing through the gas reformulating system or otherwise. These gases are generally high in CO concentration from the fixed carbon in the residue
The residual particles collected in the gas conditioning system, can be sent back to the residue conditioning system for conversion to molten slag and quenching. For the case of the transfer of the product gas from the residue conditioning system to the gas conditioning system without passing through the gas reformulating system, the gas can reach the gas conditioning system either directly or through a secondary gas conditioning system.
As mentioned earlier, the gasifier of the invention can be combined with various other systems, such as a residue conditioning system, gas reformulating system, gas conditioning system, gas homogenization system, to form a complete gasification facility. This facility will take in carbonaceous feedstock and convert it into a refined, conditioned and homogenized syngas that can be used for various downstream applications. The overall gasification facility can be controlled using a global control system to ensure that the overall process meets the requirements set by the particular downstream application and by the relevant regulatory standards. One, embodiment of a control system 98 for an overall gasification facility is shown in
A worker skilled in the art will understand that while we have described the gasifier of the present invention as taking in carbonaceous feedstock and outputting a residue, it can also take in partially processed carbonaceous reactant material from another gasifier and/or output its partially processed reactant material to another gasifier. These upstream or downstream gasifiers can be horizontally or vertically oriented, as shown in the two embodiments of
An optional control system may be provided to control one or more processes implemented in, and/or by, the gasifier, or affecting any downstream process or application of the gas produced thereby, and/or provide control of one or more process devices contemplated herein for affecting such processes. In general, the control system may operatively control various processes related to the gasifier and/or related to one or more global, upstream and/or downstream processes implemented within a gasification system comprising such a gasifier, and thereby adjusts various control parameters thereof adapted to affect these processes for a defined result. Various sensing elements and response elements may therefore be distributed throughout the controlled system(s), or in relation to one or more components thereof, and used to acquire various process, reactant and/or product characteristics, compare these characteristics to suitable ranges of such characteristics conducive to achieving the desired result, and respond by implementing changes in one or more of the ongoing processes via one or more controllable process devices.
The optional control system generally comprises, for example, one or more sensing elements for sensing one or more characteristics related to the system(s), processe(s) implemented therein, input(s) provided therefor, and/or output(s) generated thereby. One or more computing platforms are communicatively linked to these sensing elements for accessing a characteristic value representative of the sensed characteristic(s), and configured to compare the characteristic value(s) with a predetermined range of such values defined to characterise these characteristics as suitable for selected operational and/or downstream results, and compute one or more process control parameters conducive to maintaining the characteristic value within this predetermined range. A plurality of response elements may thus be operatively linked to one or more process devices operable to affect the system, process, input and/or output and thereby adjust the sensed characteristic, and communicatively linked to the computing platform(s) for accessing the computed process control parameter(s) and operating the process device(s) in accordance therewith.
In one embodiment, the control system provides a feedback, feedforward and/or predictive control of various systems, processes, inputs and/or outputs related to the conversion of carbonaceous feedstock into a gas, so to promote an efficiency of one or more processes implemented in relation thereto. For instance, various process characteristics may be evaluated and controllably adjusted to influence these processes, which may include, but are not limited to, the heating value and/or composition of the feedstock, the characteristics of the product gas (e.g. heating value, temperature, pressure, flow, composition, carbon content, etc.), the degree of variation allowed for such characteristics, and the cost of the inputs versus the value of the outputs. Continuous and/or real-time adjustments to various control parameters, which may include, but are not limited to, heat source power, additive feed rate(s) (e.g. oxygen, oxidants, steam, etc.), feedstock feed rate(s) (e.g. one or more distinct and/or mixed feeds), gas and/or system pressure/flow regulators (e.g. blowers, relief and/or control valves, flares, etc.), material displacement within the gasifier (e.g. between vertically successive processing regions), and the like, can be executed in a manner whereby one or more process-related characteristics are assessed and optimized according to design and/or downstream specifications.
Alternatively, or in addition thereto, the control system may be configured to monitor operation of the various components of a given system for assuring proper operation, and optionally, for ensuring that the process(es) implemented thereby are within regulatory standards, when such standards apply.
In accordance with one embodiment, the control system may further be used in monitoring and controlling the total energetic impact of a given system. For instance, a given system may be operated such that an energetic impact thereof is reduced, or again minimized, for example, by optimising one or more of the processes implemented thereby, or again by increasing the recuperation of energy (e.g. waste heat) generated by these processes. Alternatively, or in addition thereto, the control system may be configured to adjust a composition and/or other characteristics (e.g. temperature, pressure, flow, etc.) of a product gas generated via the controlled process(es) such that such characteristics are not only suitable for downstream use, but also substantially optimised for efficient and/or optimal use. For example, in an embodiment where the product gas is used for driving a gas engine of a given type for the production of electricity, the characteristics of the product gas may be adjusted such that these characteristics are best matched to optimal input characteristics for such engines.
In one embodiment, the control system may be configured to adjust a given process such that limitations or performance guidelines with regards to reactant and/or product residence times in various components, or with respect to various processes of the overall process are met and/or optimised for. For example, an upstream process rate may be controlled so as to substantially match one or more subsequent downstream processes. Namely, the residence time of the material within the gasifier, and/or processing regions thereof, may be set and/or dynamically adjusted by a material displacement control module, which may operate independently, cooperatively and/or as a submodule of an overall or global control system, to meet certain preferences and/or requirements of downstream processes and/or applications.
The control system can be adapted for maintaining conditions suitable for local and/or downstream needs, e.g., temperature, feedstock input rate, displacement of material, etc. can be controlled to meet local needs, such as fast processing of waste, and/or to meet downstream needs such as suitable gas composition.
In addition, the control system may, in various embodiments, be adapted for the sequential and/or simultaneous control of various aspects of a given process in a continuous and/or real time manner.
In one embodiment, the control system controls (among other aspects of the process) the input of additives into the gasifier. As mentioned earlier, the off-gases and/or steam can be recycled back into the gasifier as part or whole of an additive stream.
In embodiments where the recycled stream contains a large amount of water vapour or steam, such as when the off-gases are extracted for recycling from the processing region(s) at least partially promoting drying, the control system may utilize a steam recycling control strategy to determine the addition of the steam. Addition of steam to high temperature areas may have two effects: (a) cools the area due to endothermic gasification reactions with steam, absorbs excess heat and stabilizes the area to avoid melting/slagging from occurring within the gasifier; (b) improves the quality of the gas and helps remove fixed carbon from the solids. Such a control strategy may use either feedback/feed-forward control and may utilize fuzzy logic.
A worker skilled in the art will understand that the “quality of a gas” is based on the downstream application (e.g. gas engine, chemical production facility etc.) for which the gas is used. Generally if the gas has a very high CO to CO2 ratio and low H2, steam addition from recycling will improve the quality of the gas, resulting in higher heating value and higher H2 vs CO). This improvement in the CO to H2 ratio is achieved with steam by moving the water-gas shift reaction equilibrium to produce more H2 by converting CO to CO2 and converting H2O to H2.
In one embodiment, a feedback control system may utilize temperature measurements made by thermocouples placed at various locations throughout the gasification facility, and particularly in areas where steam may be added. When the temperature gets too high in an area, part of the off-gases and/or steam from the processing regions promoting drying is diverted to that area using either piping to the walls/jacket or through a fluid conduit.
In one embodiment utilizing a feed-forward control system, if the gas quality is too low, steam from the processing region at least partially promoting drying is added into the processing region at least partially promoting carbon conversion. This may result in enhanced carbon conversion and thus, improve the heating value of the gas.
The control schemes (feed-forward and/or feedback) may be automated, and may utilize fuzzy logic to ensure that the steam is applied in the correct amounts and to the correct location within the system for the optimal results.
When steam recycling is done primarily for gas quality and not temperature, the recycled stream can be heated in a heat exchanger to help improve the reaction rates of the system to produce higher quality gas with less recycling. This approach also helps with pressure drops and other parasitic loads.
A worker skilled in the art will understand that while steam recycling is specifically mentioned above, these strategies may also be applied to recycle other off-gases. Additional additives to the system may not be needed, in certain applications.
In general, the control system may comprise any type of control system architecture suitable for the application at hand. For example, the control system may comprise a substantially centralized control system, a distributed control system, or a combination thereof. A centralized control system will generally comprise a central controller configured to communicate with various local and/or remote sensing devices and response elements configured to respectively sense various characteristics relevant to the controlled process, and respond thereto via one or more controllable process devices adapted to directly or indirectly affect the controlled process. Using a centralized architecture, most computations are implemented centrally via a centralized processor or processors, such that most of the necessary hardware and/or software for implementing control of the process is located in a same location.
A distributed control system will generally comprise two or more distributed controllers which may each communicate with respective sensing and response elements for monitoring local and/or regional characteristics, and respond thereto via local and/or regional process devices configured to affect a local process or sub-process. Communication may also take place between distributed controllers via various network configurations, wherein a characteristics sensed via a first controller may be communicated to a second controller for response thereat, wherein such distal response may have an impact on the characteristic sensed at the first location. For example, a characteristic of a downstream product gas may be sensed by a downstream monitoring device, and adjusted by adjusting a control parameter associated with the converter that is controlled by an upstream controller. In a distributed architecture, control hardware and/or software is also distributed between controllers, wherein a same but modularly configured control scheme may be implemented on each controller, or various cooperative modular control schemes may be implemented on respective controllers.
Alternatively, the control system may be subdivided into separate yet communicatively linked local, regional and/or global control subsystems. Such an architecture could allow a given process, or series of interrelated processes to take place and be controlled locally with minimal interaction with other local control subsystems. A global master control system could then communicate with each respective local control subsystems to direct necessary adjustments to local processes for a global result.
The control system of the present invention may use any of the above architectures, or any other architecture commonly known in the art, which are considered to be within the general scope and nature of the present disclosure. For instance, processes controlled and implemented within the context of the invention may be controlled in a dedicated local environment, with optional external communication to any central and/or remote control system used for related upstream or downstream processes, when applicable. Alternatively, the control system may comprise a sub-component of a regional and/or global control system designed to cooperatively control a regional and/or global process. For instance, a modular control system may be designed such that control modules interactively control various sub-components of a system, while providing for inter-modular communications as needed for regional and/or global control.
The control system generally comprises one or more central, networked and/or distributed processors, one or more inputs for receiving current sensed characteristics from the various sensing elements, and one or more outputs for communicating new or updated control parameters to the various response elements. The one or more computing platforms of the control system may also comprise one or more local and/or remote computer readable media (e.g. ROM, RAM, removable media, local and/or network access media, etc.) for storing therein various predetermined and/or readjusted control parameters, set or preferred system and process characteristic operating ranges, system monitoring and control software, operational data, and the like. Optionally, the computing platforms may also have access, either directly or via various data storage devices, to process simulation data and/or system parameter optimization and modeling means. Also, the computing platforms may be equipped with one or more optional graphical user interfaces and input peripherals for providing managerial access to the control system (system upgrades, maintenance, modification, adaptation to new system modules and/or equipment, etc.), as well as various optional output peripherals for communicating data and information with external sources (e.g. modem, network connection, printer, etc.).
The processing system and any one of the sub-processing systems can comprise exclusively hardware or any combination of hardware and software. Any of the sub-processing systems can comprise any combination of none or more proportional (P), integral (I) or differential (D) controllers, for example, a P-controller, an I-controller, a PI-controller, a PD controller, a PID controller etc. It will be apparent to a person skilled in the art that the ideal choice of combinations of P, I, and D controllers depends on the dynamics and delay time of the part of the reaction process of the gasification system and the range of operating conditions that the combination is intended to control, and the dynamics and delay time of the combination controller. It will be apparent to a person skilled in the art that these combinations can be implemented in an analog hardwired form which can continuously monitor, via sensing elements, the value of a characteristic and compare it with a specified value to influence a respective control element to make an adequate adjustment, via response elements, to reduce the difference between the observed and the specified value. It will further be apparent to a person skilled in the art that the combinations can be implemented in a mixed digital hardware software environment. Relevant effects of the additionally discretionary sampling, data acquisition, and digital processing are well known to a person skilled in the art. P, I, D combination control can be implemented in feed forward and feedback control schemes.
In corrective, or feedback, control the value of a control parameter or control variable, monitored via an appropriate sensing element, is compared to a specified value or range. A control signal is determined based on the deviation between the two values and provided to a control element in order to reduce the deviation. It will be appreciated that a conventional feedback or responsive control system may further be adapted to comprise an adaptive and/or predictive component, wherein response to a given condition may be tailored in accordance with modeled and/or previously monitored reactions to provide a reactive response to a sensed characteristic while limiting potential overshoots in compensatory action. For instance, acquired and/or historical data provided for a given system configuration may be used cooperatively to adjust a response to a system and/or process characteristic being sensed to be within a given range from an optimal value for which previous responses have been monitored and adjusted to provide a desired result. Such adaptive and/or predictive control schemes are well known in the art, and as such, are not considered to depart from the general scope and nature of the present disclosure.
Sensing elements contemplated within the present context, as defined and described above, can include, but are not limited to, temperature sensing elements, position sensors, proximity sensors, pile height sensors and means for monitoring gas.
In one embodiment, the gasifier comprises a temperature sensor array of one or more removable thermocouples. The thermocouples can be strategically placed to monitor temperature at various points within each processing region of the gasifier. Appropriate thermocouples are known in the art and include bare wire thermocouples, surface probes, thermocouple probes including grounded thermocouples, ungrounded thermocouples and exposed thermocouples or combinations thereof.
In one embodiment of the invention, individual thermocouples are inserted into a processing chamber via a sealed end tube (thermowell) which is then sealed to the chamber's shell, allowing for the use of flexible wire thermocouples which are procured to be longer than the sealing tube so that the junction (the temperature sensing point) of the thermocouple is pressed against the end of the sealed tube to assure accurate and quick response to temperature change. Optionally, to prevent material from getting blocked by the thermocouple tube the end of the sealed tube cap can be fitted with a deflector. In one embodiment, the deflector is a square flat plate, with bent corners that contact the refractory and are in-line with reactant material flow to slip-stream particles over the thermowell.
In addition, the invention may comprise devices for monitoring the exit of product gas. These may include but are not limited to gas composition monitors and gas flow meters. For example, as depicted in
Similarly, a gas flow or pressure monitor may be used in an embodiment where a selected downstream application is adversely affected by variations and/or absolute fluctuations in gas flow/pressure. In response to a sensed variation in product gas pressure, for example, additive input feed rates may be adjusted, thereby adjusting the gas output of the gasifier. In response to such adjustment, other process characteristics, such as feedstock input rate, HCF input rate, process temperature, etc. may also be adjusted to rebalance the process and substantially maintain desired output characteristics.
Furthermore, by measuring process temperatures throughout the material pile, gas phase temperatures above the pile, and by measuring resultant gas flow rate and analyzing gas composition, the amount of air injected can be optimized to maximize efficiency and minimize undesirable process characteristics and products including slagging of ash, combustion, poor gas heating value, excessive particulate matter and dioxin/furan formation thereby meeting or bettering local emission standards. Such measurements can be taken during initial start-up or initial testing of the gasifier, periodically or continually during operation of the gasifier and may optionally be taken in real time.
In one embodiment of the invention, the gasifier can optionally comprise a pressure sensor or monitor within the gasifier.
The gasifier can further comprise level switches or monitors to assess pile height. Appropriate level switches, sensors and monitors are known in the art. In one embodiment of the invention, the level instrumentation comprises point-source level switches. In one embodiment of the invention, the level switches are microwave devices with an emitter on one side of the processing chamber and a receiver on the other side, which detects either presence or absence of reactant material at that point inside the processing chamber.
A worker skilled in the art would readily be able to determine the appropriate placement of level switches, sensors and monitors such that the desired reactant material pile profile can be obtained. In one embodiment, the gasifier further comprises proximity or position sensors.
Response elements contemplated within the present context, as defined and described above, can include, but are not limited to, various control elements operatively coupled to process-related devices configured to affect a given process by adjustment of a given control parameter related thereto. For instance, process devices operable within the present context via one or more response elements, may include, but are not limited to elements controlling chamber heating, elements controlling the input of additives, feedstocks and other process constituents, and elements of the material displacement control module, to name a few.
The material displacement control module may be used in such embodiments to regulate the pile height inside a given chamber of the gasifier. Low levels of the feedstock pile can result in fluidization of the reactant material from injection of pre-heated air while high levels of the feedstock pile can result in poor temperature distribution through the reactant material pile due to restricted airflow. Therefore, a level control system with the use of a series of level switches may be used to maintain stable pile height inside the gasifier. Maintaining stable level also maintains consistent residence time in the gasifier.
The material displacement control module may be used as necessary to ensure that pile height is controlled at the desired level. To accomplish this in embodiments in which the material displacement control module comprise pusher rams, the pusher rams move in a series of programmed step of which there may exist a number of control parameters that may include, but are not limited to: specific movement sequence, speed, distance, and sequence frequency.
In some embodiments, the pusher rams move out to a set point distance, or until a controlling level switch is tripped; either at the same time or in a pre-determined sequence. The level switch control action can be based on a single switch, tripping either empty or full, or may require multiple switches tripping, empty or full, or any combination thereof. Afterwards, the pusher rams move back to end the cycle, and the process is repeated. There is an optional delay between cycles as required by the process and residence time requirements of the gasifier.
In one vertically oriented embodiment of the invention where the material displacement control module comprises an array of pusher rams in a processing chamber, the height of the reactant material pile in the processing chamber is a function of the input feed-rate and the pusher ram motion. Optionally, the processing chamber has three processing regions and the material displacement control module has three pusher rams with one pusher ram dedicated to each of the three processing regions for the movement of reactant material/residue out of that processing region. The third pusher ram controlling the movement of the residue out of the third processing region of the processing chamber sets the throughput by moving at a fixed stroke length and frequency to discharge the residue out of the processing chamber. The second pusher ram follows and moves as far as necessary to push reactant material onto the third processing region and change the third processing region's start-of-stage level switch state to “full”. The first pusher ram follows and moves as far as necessary to push reactant material onto the second processing region and change the second processing region's start-of-stage level switch state to “full”. All three pusher rams are then withdrawn simultaneously, and a scheduled delay is executed before the entire sequence is repeated. Additional configuration may be used to limit the change in consecutive stroke lengths to less than that called for by the level switches to avoid excess ram-induced disturbances. The pusher rams will always need to be moved fairly frequently in order to prevent over-temperature conditions at the bottom of the processing chamber. Appropriate pusher ram sequences can be readily developed for other embodiments of the gasifier and are considered to be within the scope of this invention.
As with controlled pusher ram sequences between processing regions, different material movement units (e.g. mechanisms, devices, etc.) may also be used in a given sequence and/or according to control parameters of the material movement control module at least partially influenced by pile height readings. For example, rotary arm configurations controlling movement of material may be used in step to adjust pile heights within respective processing regions, as can others of the above examples, as will be apparent to the person of skill in the art. The control system may be further configured to assess optimal processing characteristics, taking into account optimal residence times of material within each region, pile height restrictions and favourable conditions, as well as other characteristics as described herein for a given process result.
Optionally, the control system may further provide for the control of temperature within the gasifier. For example, to promote optimisation of the conversion efficiency, the feedstock should be kept at as high a temperature as possible, for as long as possible. However, at very high temperatures, the material begins to melt and agglomerate forming ‘clinkers’ which affects the gasification performance in multiple ways: (1) it reduces the available surface area and hence the conversion efficiency; (2) it causes the airflow in the reactant material pile to divert around the chunks of agglomeration, aggravating the temperature issues and further accelerating the agglomeration process; (3) it interferes with the normal operation of the material displacement control module; and (4) it can jam the residue removal mechanisms thus potentially causing a system shut down.
In order to get the best possible conversion efficiency, the temperatures in the gasifier and temperature distribution through the pile can be stabilized and controlled. Stable temperature distribution throughout the reactant material pile may also be used to prevent a second kind of agglomeration, in which plastic melts and acts as a binder for the rest of the reactant material.
In one embodiment, temperature control within the pile is achieved by changing the flow of process air into a given region (ie. more or less combustion). For example, the process air flow provided to each processing region in the gasifier may be adjusted by the control system to stabilize temperatures at that region. Temperature control utilizing displacement units may also be used to break up hot spots and to avoid bridging.
In one embodiment, the air flow at each processing region is pre-set to maintain substantially constant temperature ranges and ratios between processing regions. Alternatively, air input ratios may be varied dynamically to adjust temperatures and processes occurring within each processing region of the gasifier and/or within the GRS.
The means for controlling the reaction conditions to manage the chemistry and energetics of the gasification of a feedstock comprise a main integrated processor and a series of sensors for monitoring the state of the system and control systems for controlling various operational parameters, for example, the rate of addition of feedstock and/or additives, as well as operating conditions, such as pressure in the processing chamber. The main integrated processor receives data obtained from sensors relating to current states of the gasification reaction, and processes these data to generate an appropriate set of output instructions to manage the chemistry and energetics of the conversion reaction, whereby the optimal reaction set point is maintained.
In response to the information input, the conditions within the gasifier can be adjusted either manually or automatically. The gasifier can be regulated by a series of on/off switches and instruments. The computation means can optionally include various output means. Different types of control schemes, outlined below, can be used.
a. Fuzzy Logic Control and Other Types of Control
Fuzzy logic control as well as other types of control can equally be used in feed forward and feedback control schemes. These types of control can substantially deviate from classical P, I, D combination control in the ways the reaction dynamics are modeled and simulated to predict how to change input variables or input parameters to affect a desired outcome. Fuzzy logic control usually only requires a vague or empirical description of the reaction dynamics (in general the system dynamics) or the operating conditions of the system. Aspects and implementation considerations of fuzzy logic and other types of control are well known to a person skilled in the art.
b. Feed-Forward Control
Feed forward control processes input parameters to influence, without monitoring, control variables and control parameters. A gasification facility can use feed forward control for a number of control parameters such as the amount of power supplied to one of the one or more plasma torches in the gas reformulating chamber (GRS). The power output of the arcs of plasma torches can be controlled in a variety of different ways, for example, by pulse modulating the electrical current which is supplied to the torch to maintain the arc, varying the distance between the electrodes, limiting the torch current, or affecting the composition, orientation or position of the plasma.
The rate of supply of additives to the gasifiers and/or the gas reformulator in a gaseous or liquid form or a pulverized form which can be sprayed or otherwise injected via nozzles, can be controlled with certain control elements in a feed forward way. Effective control of an additive's temperature or pressure, however, may require monitoring and closed loop feed back control.
c. Feed-Back Control:
In feedback control the value of a control parameter or control variable is compared to a desired value. A control signal is determined based on the deviation between the two values and provided to a control element in order to reduce the deviation. For example, when the output gas exceeds a predetermined H2:CO ratio, a feedback control system can determine an appropriate adjustment to one of the input variables, such as increasing the amount of additive air to return the H2:CO ratio to the desired value. The delay time to affect a change to a control parameter or control variable is sometime called loop time. The loop time, for example, to adjust the power of the plasma arc, air or steam flow rate, can amount to 30 to 60 seconds.
Feed back control may be used for all control variables and control parameters which use direct monitoring or where a model prediction is satisfactory. There are a number of control variables and control parameters of the gasifier that lend themselves towards use in a feedback control scheme. Feedback schemes can be effectively implemented in aspects of the control system for those control variables or control parameters which can be directly sensed and controlled and whose control does not, for practical purposes, depend upon other control variables or control parameters.
Modulated plants are facilities where each function block is a pre-built module. Modules are built and tested in a factory setting and then sent out to the facility site. They include all the equipment and controls needed to be functional. Modules include Gasifier Block, Gas Conditioning System Block, Power Block, etc. On-site, these modules would only need to be connected to other modules and the control system to be ready for plant's commissioning. This design allows for shorter construction time and economic savings due to reduced on-site construction costs. There are different types of modular plants set-ups. Larger modular plants incorporate a ‘backbone’ piping design where most of the piping is bundled together to allow for smaller footprint.
One possible application of modular design in this technology is it allows more options in the gasification of multiple wastes. This technology can allow for multiple gasifiers to be used in a single high-capacity facility. This would allow the option of having each gasifier co-process wastes together or separately; the configuration can be optimized depending on the wastes.
If an expansion is required due to increasing loads, a modular design allows this technology to replace or add modules to the plant to increase its capacity, rather then building a second plant. Modules and modular plants can be relocated to other sites where they can be quickly integrated into a new location.
Modules can also be placed in series or parallel. Here similar tasked equipment can share the load or successively provide processing to the product stream. For example, product gas output from the plurality of gasifiers are not combined to pass through a single GRS and GCS but is split up into two parallel streams, each with its own GRS and GCS.
It is possible to combine the functions of different gasification trains (series of equipment) so that common functions can be carried out in function blocks that take in gases or material from more than one stream.
In these embodiments there are two trains shown although this set-up of combined functions between trains can occur for any number of trains and for any feedstock per train (even if one train has a combined feedstock). Once a stream has been combined one may still choose parallel handling equipment downstream; the parallel streams do not need to be of the same size even if handling the same gases.
For the following description and referring to
B. Residue Conditioning System
C. Gas Reformulating System
A worker skilled in the art will readily understand that while in the above section we have mentioned the gasification system as comprising of the function blocks A, B & C and the GCS, it can be further subdivided into other smaller function blocks. For example, the function block A, B & C could represent the drying region, volatilization region and the carbon conversion region respectively such that a single gasifier can be formed by the combination of these function blocks. A worker skilled in the art will readily appreciate that for each designation of function blocks, the trains can be combined in a larger family of schemes depending on where the combination of the trains is effected.
The embodiments of the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.