WO2005116523A1

WO2005116523A1 - Method of generating electrical power from non-traditional fuels

Info

Publication number: WO2005116523A1
Application number: PCT/ES2005/000285
Authority: WO
Inventors: Jeronimo Angulo Aramburu
Original assignee: Sener Grupo De Ingenieria, S.A.
Priority date: 2004-05-24
Filing date: 2005-05-20
Publication date: 2005-12-08
Also published as: ES2221816A1; ES2221816B1

Abstract

The invention relates to a method of generating electrical power from non-traditional fuels. The inventive method comprises the following steps consisting in: (a) combusting the non-traditional fuel in a combustion oven, with recovery of the heat in order to generate and/or superheat water vapour; and (b) supplying the water vapour from step (a) to a steam turbine which is connected to an electrical generator in order to produce electrical power. According to the invention, some of the power requirements in step (a) are satisfied using the waste heat from a motor-generator unit. In this way, it is possible to optimise the electrical yield of low-medium power electricity generating stations using non-traditional fuels.

Description

PROCEDURE FOR THE GENERATION OF ELECTRICAL ENERGY FROM NON-TRADITIONAL FUELS

FIELD OF THE INVENTION

The present invention belongs to the field of electricity generation from non-traditional fuels such as primary forest or plant biomass, secondary biomass (sawdust, bark, etc.), urban waste or similar products, industrial waste, waste from the agricultural or agricultural sector or from effluent treatment, etc.

These fuels usually have a low heat of combustion, often due to the percentage of water they contain, which often reaches proportions of 15-75% by weight.

The usual scheme of electricity generation from these non-traditional fuels consists in their combustion in a furnace equipped with a steam boiler and an electric turbogenerator driven by steam. The energy yields of these systems generally do not exceed 25% (expressed as a percentage of electrical KWh generated with respect to the thermal KWh contained in the primary fuel), very unfavorable compared to those of the combined natural gas citrus that reach yields of the order 50% or more.

These low energy yields are due not only to the limitations of the steam turbine system, but also to the fact that a significant part of the combustion heat is consumed in the drying of the non-traditional fuel as well as in the heating of the combustion air. Some of these non-traditional fuels, such as urban waste or certain plastic waste containing chlorinated derivatives, produce very toxic chemical compounds (dioxins, furans, etc.) that pollute chimney fumes. In addition, hydrogen chloride is generated in combustion that attacks the tubular beams of steam generation, when the temperature is raised to achieve supersaturated steam.

BACKGROUND OF THE INVENTION Some of the aforementioned problems of electricity generation with non-traditional fuels (humidity, low energy efficiency, production of toxic chemical compounds, corrosivity, etc.) have been addressed through the use of traditional fuels (natural gas, diesel, fuel oil, etc.) as auxiliary fuels for non-traditional ones.

Thus, for example, raising the temperature of the combustion gases of the furnace above 900 ° C, generally at 1000-1200 ° C, by a post-combustion of a traditional fuel, allows to destroy the toxic compounds, avoiding their poured into the atmosphere by the fireplace.

Likewise, the generation of high-pressure saturated steam in the boiler's tubular beam and its overheating in an external exchanger with fumes from a traditional fuel burner, allow to eliminate corrosion problems in said tubular beam and improve energy efficiency of the steam cycle (patent ES 2006059, SENER

1989). Energy efficiency is further improved if the traditional fuel fumes that overheat saturated steam come from a turbogenerator (ES patent 2010890, SENER 1989). Natural gas has also been used as auxiliary fuel in turbogenerators, using hot fumes to dry the fuel non-traditional (US patent 4957049, ELECTRODYNE RESEARCH CORP, 1990) and to replace cold combustion air of the furnace (US patent 4882903, CH GUERNSEY CO, 1989). On the other hand, the use of natural gas, as auxiliary fuel in turbogenerators to generate hot fumes and provide heat to a non-traditional fuel electric generation system, has been described by various authors (those already mentioned above; and WO 90/00219 , IMATRAN VOIMA OY, 1990; US 4852344, ENERGY ECONOMICS AND DEVELOPMENT, 1989; US 5623822, MONTENAY INTERNATIONAL

CORP, 1997; US 5724807, MONTENAY INTERN. CORP., 1998, etc.), since this improves the energy efficiency of natural gas combustion by generating electricity and hot gases simultaneously. However, the electrical performances of gas turbines decrease significantly with their size, so they are not very suitable for supplying auxiliary heats in non-traditional low-medium power (5-25 MWe) non-traditional fuel generation facilities, as is the case frequently in the case of biomass, industrial, agricultural or livestock waste, where the availability of fuel or waste is limited.

Thus, the need continues to exist in the state of the art to optimize the non-traditional low-medium power non-traditional fuel generation facilities in terms of their electrical performance.

The present invention is based on the fact that internal combustion engines that run on traditional fuels such as natural gas, gas-oil, fuel-oil, etc., are machines that achieve high electrical yields (up to 45-48%), also providing of usable residual heats from combustion fumes and water from cooling of shirts and turbochargers. Unlike turbines, internal combustion engines are applicable to the low power range achieving high power generation yields. The utilization of the residual heats of the engines allows not only to generate steam that can be reheated with the furnace fumes to move a steam turbine, but preferably to provide heat in lower temperature ranges such as fuel drying, heating of the combustion air of the furnace or the heating of boiler water.

OBJECT OF THE INVENTION

The present invention, therefore, is intended to increase the energy efficiency of electricity generation from non-traditional fuels, such as biomass, urban waste, etc., using a traditional fuel such as liquid or gaseous hydrocarbons as auxiliary fuel. fossil origin, for example. It is also an object of the present invention to integrate an electric generation system by means of internal explosion engines with another generation system of the combustion furnace-steam boiler type, so that the residual heats of the first are used in the second, resulting in better efficiency than would be produced with the two systems separately.

It is also an object of the present invention that the residual heats of the motor generator be used in the energy needs of the auxiliary or low temperature services of the furnace-boiler system, so that the combustion heat of this second system is preferably used in the high temperature services such as generation and steam overheating, which results in better use of residual heats.

It is also an object of the present invention to achieve maximum utilization of the heat contained in the combustion fumes and in the cooling water of the engines that burn the auxiliary fuel.

It is also an object of the invention to make the improvement in energy efficiency applicable to low-medium power generation facilities, especially in the range of 5 to 25 MWe in which gas turbines lose performance.

It is also an object of the invention to make compatible the energy efficiency improvements produced by the motor generator in the low temperature areas, with which they can be achieved with other systems known in the area of the generation of high pressure saturated steam and its subsequent overheating, which act in high temperature areas.

Finally, it is the object of the invention to have a sufficiently flexible process and adaptable to the particularities of the various non-traditional fuels.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for generating electric energy from non-traditional fuels comprising the following steps:

(a) combustion of non-traditional fuel in a combustion furnace with heat recovery to generate and / or overheat water vapor, and (b) supply of the water vapor of step (a) to a steam turbine coupled to an electric generator to produce electrical energy;

characterized in that the residual heat of a motor generator is used to satisfy part of the energy demands of stage (a).

In a particular embodiment, the process of the invention comprises, prior to the combustion stage (a), a previous stage of drying the wet non-traditional fuel, characterized in that the residual heat of the motor generator is used to satisfy part or all of the energy demands of said previous stage.

In another embodiment of the process of the invention, the residual heat of the motor generator is used in the heating of the combustion air of stage (a), or in the heating of the water intended for steam generation of stage (a), or in the generation of water vapor of stage (a), or in the drying of the non-traditional fuel of the previous stage, or in a combination thereof.

In another embodiment of the process of the invention, the residual heat of the motor generator comes from the combustion fumes or the cooling water thereof, or both. In the present invention, the integration of an internal combustion engine, fed with traditional fuel and coupled to an electric generator, with a furnace combustion system with heat recovery (an oven-boiler system, for example) that uses non-combustible traditional, it is achieved by releasing the heat of the combustion fumes and the cooling water of liners and turbochargers of the engine to the combustion air of the furnace, or to the water destined for steam generation (by boiler water, for example), or the generation of medium pressure steam, or the drying of traditional fuel or, preferably, a combination of these services. Depending on the size of the installation, one or more motor generators can be used. Alternators connected to the steam turbine and internal combustion engine produce the electrical energy of the integrated system of the invention. The present invention allows various particular embodiments to optimize the type and characteristics of the non-traditional fuel, the size in the plant, the type of traditional fuel and other circumstances of the specific implementation, without the descriptions made below being able to constitute limitations of the scope of the procedure

In a particular embodiment of the process object of the invention, the residual heat of the engine is used in the drying of non-traditional fuel and in the heating of combustion air and water destined for steam generation (FIG 1).

Thus, in a particular embodiment of the process of the invention, the drying of the previous stage is carried out in a dryer by direct contact of the non-traditional wet fuel with the combustion fumes, or by direct or indirect contact of the non-traditional wet fuel. with an intermediate fluid.

The nature and characteristics of the non-traditional fuel to dry determine the drying system. Thus, in a particular embodiment of the invention, the fumes of the traditional fuel do not come directly into contact with the non-traditional fuel in the dryer, but rather do so with an intermediate fluid, such as steam or thermal oil, which transfers its heat through exchangers or through oxygen depleted air that in direct circuit comes into direct contact with the product to be dried. In this way, the fumes of the traditional fuel are contaminated and the collection of water from the non-traditional fuel for recovery or treatment and disposal is facilitated.

In a particular embodiment of the process, applicable for example to urban waste, the dryer's exhaust gases are sent to a washing tower to eliminate odoriferous emissions before being emitted by the chimney (not shown in the figures).

In another particular embodiment of the process, part of the combustion fumes of the motor generator or part of the combustion fumes of the furnace are introduced into the combustion furnace (not shown in the figures). In this way, part of the residual heat of said fumes is used, thus increasing the energy efficiency of the system of the invention.

In another particular embodiment of the process object of the invention, applicable to non-traditional fuels with low water content, the residual heat of the engine is used in generating medium pressure steam (for example 10 Kg / cm ² ) and in heating the air of the oven (FIG. 2).

In a particular embodiment of the process object of the invention the heat of the motor generator is applied only to the drying of the fuel or to the heating of the combustion air or both (FIG. 3). In this case, the heating of the water destined to the steam generation can be carried out in an installation external to it in which, in addition, the water vapor is superheated using part of the traditional fuel. By overheating the steam generated in the oven outside it prevents unwanted corrosion problems. In a particular embodiment of the present invention, part of the traditional fuel is used in burners to increase the temperature of the combustion fumes of the motor generator or to increase the temperature of the combustion fumes of the furnace (not shown in the figures). Also, part of the traditional fuel can be used in burners to heat the water destined for steam generation or to overheat the saturated or slightly superheated steam generated in the combustion furnace before it is supplied to the turbogenerator of stage (b).

Thus, in a preferred embodiment of the process, the heat of the motor generator is applied to the drying of the fuel and to the heating of the air of a furnace-boiler-steam turbine system of greater performance, characterized in that saturated steam is generated at high pressure in the boiler (around 100 atm) that overheats to about 500 ° C with the heat of combustion of natural gas or other traditional fuel before turbinating it. In this case, the preheating of boiler water is integrated in the high pressure steam superheat system. In another preferred embodiment of the invention, part of the traditional fuel is used in a turbogenerator or in an additional motor generator whose fumes are used to overheat the saturated or slightly overheated steam generated in the combustion furnace before being supplied to the turbogenerator of the step (b) (not shown in the figures). In this way, by attaching a turbogenerator or motor generator additional to the system of the invention, the energy efficiency thereof is increased.

In a particular embodiment, the non-traditional fuel is primary or secondary biomass or a material assimilable to it (forest biomass, plant biomass, energy crops, sawdust, bark, etc.); or an urban waste or an assimilable material, or an industrial waste or a material assimilable, or a product or by-product of the wastewater treatment, or a residue of agricultural origin (sludge, slurry, chicken manure, buckwheat, alperujo, etc.) or an assimilable material, or an automotive waste or an assimilable material (tires outside used, slight fraction of car fragmentation, etc.), or a combination thereof.

Thus, in a preferred embodiment, said non-traditional fuel is a material selected from among forest biomass, plant biomass, energy crops, sawdust, bark, sludge, slurry, chicken manure, alpechín, alperujo, unused tires, light fraction of the car fragmentation, or a combination thereof.

In another particular embodiment, the traditional fuel is a gaseous or liquid hydrocarbon of fossil origin, preferably gas-oil, fuel-oil or natural gas.

In another particular embodiment, said traditional fossil fuel is partially or totally replaced by a traditional non-fossil fuel such as biogas, poor gas, synthesis gas, bioethanol, biofuel or other assimilable internal combustion engine fuel.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 represents a scheme of the process of the invention in which the residual heat of the engine is used in the drying of non-traditional fuel and in the heating of combustion air and water destined for steam generation.

Figure 2 represents a scheme of the process of the invention in which the residual heat of the engine is used in the generation of medium pressure steam and in the heating of the oven air. Figure 3 represents a scheme of the process of the invention in which the heat of the motor generator is applied to the drying of the fuel or to the heating of the combustion air or both, while the heating of the water destined for the generation of steam is carried out in a external installation to it in which, in addition, water vapor is superheated using part of the traditional fuel.

PREFERRED EMBODIMENTS OF THE INVENTION Figure 1 illustrates the process of integrating a traditional fuel motor generator (natural gas or fuel, for example) with a non-traditional fuel electric generation system (forest biomass, for example). The combustion furnace of non-traditional fuel is in this case a furnace-boiler system.

The biomass (1), stored in the silo (A), is dried in the dryer (B) reducing its humidity to values below 15% of water by weight. The drying is carried out by contacting the biomass with the fumes (7), from the combustion of the traditional fuel (6) in the motor generator (H), which have previously transferred part of its calorific content to the combustion air (10) in the heat exchanger (I) and the boiler water (5) in the changer (J).

The dried biomass (2) is burned in the oven (C), recovering the heat of its combustion in the form of steam (4) produced in a tubular beam in the convection zone, fed with the boiler water (5) preheated in the changer (J).

The steam (4) moves the steam turbine (F), condenses in (G) and recirculates the changer (J) and the boiler. Fumes from non-traditional fuel (3) are purified in (D) (in this case dust removal, mainly) and together with the fumes of the traditional fuel (8) they are emitted by the chimney (E).

The combustion air of the oven (10) is preheated in the exchanger (K) taking advantage of the engine cooling water.

As previously mentioned, depending on the size of the installation, one or more motor generators can be used. Alternators connected to the steam turbine and the engine produce electric power (9).

In Figure 2, the fumes (7) of the engine (H) generate medium pressure steam in (J) and heat the combustion air (10) in (I) before leaving the chimney (E2); while the combustion heat of the non-traditional fuel (1) generated in the furnace (C), is used to generate high pressure steam that is turbined in (F1) and to overheat the medium pressure steam generated in (J) which is turbined in (F2). As in other particular embodiments, the electric power (9) is generated in the alternators coupled to the steam turbines (F) and the engine (H), which can be one or several units in parallel.

Figure 3 represents a particular embodiment in which the heat of the fumes (7) generated in an engine (I) with traditional fuel (6) is used to preheat the air (10) in the exchanger (J) and to dry the non-traditional fuel (1) in the dryer (B). The preheating of the water destined to the steam generation is integrated in a system of superheating of the saturated or slightly superheated steam generated in the oven (C) as is the changer (H), in which the steam is superheated with the heat of a burner that uses part of the traditional fuel (6) before moving the steam turbine (F). The example described below serves to illustrate the process of the invention, without implying limitations on its possibilities.

EXAMPLE 1 (according to figure 1)

30t / h of urban waste, with 40% humidity and a lower calorific value of 2000 Kcal / Kg, are processed in a technology unit prior to the present invention consisting of a grill oven with superheated steam recovery and turbine condensation, generating 17,300 KWh / h with a 25% yield.

The same amount of urban waste is processed in a unit as shown in Figure 1, in which the auxiliary fuel (6) is natural gas (35,500 KWh / h), of whose residual heats (fumes and cooling water) are they recover 9,650 KWh _t / hour, in the drying of the residue in (B) (whose humidity drops below 20%) and in the preheating of the combustion air in (K) and in (I). The electrical energy obtained in the steam turbine is 19,700 KWh / h, to which we must add 16,000 KWh / hour generated by the gas engine, that is, a total of 35,700 KWh / hour.

With the process of the invention, electricity generation with non-traditional fuel has increased by 14%. The electric power efficiency of both machines with the process of the invention is 29.2%, whereas if the motor's residual heats had not been used in the services (B), (K) and (I), of In accordance with the present invention, the overall yield of both unintegrated generation systems would have been 27.2%.

Claims

1. Procedure for generating electric energy from non-traditional fuels comprising the following stages: (a) combustion of non-traditional fuel in a combustion furnace with heat recovery to generate and / or overheat water vapor, and ( b) supply of the water vapor of step (a) to a steam turbine coupled to an electric generator to produce electrical energy; characterized in that the residual heat of a motor generator is used to satisfy part of the energy demands of stage (a).

2. The method according to claim 1, which comprises, prior to the combustion stage (a), a previous stage of drying the non-traditional wet fuel, characterized in that the residual heat of the motor generator is used to satisfy part or all of the energy demands of said previous stage.

Method according to claims 1 and 2, characterized in that the residual heat of the motor generator is used in the heating of the combustion air of stage (a), or in the heating of the water destined for the generation of steam of the stage (a ), or in the steam generation of stage (a), or in the drying of non-traditional fuel from the previous stage, or in a combination thereof.

Method according to claim 3, characterized in that the residual heat of the motor generator comes from the combustion fumes or the cooling water thereof, or both.

5. Method according to claims 2-4, characterized in that the drying of the previous stage is carried out in a dryer by direct contact of the non-traditional wet fuel with combustion fumes, or by direct or indirect contact of the non-traditional wet fuel with an intermediate fluid.

Method according to the preceding claims, characterized in that part of the combustion fumes of the motor generator is introduced into the combustion furnace.

Method according to the preceding claims, characterized in that part of the combustion fumes of the furnace is introduced into said combustion furnace.

Method according to the preceding claims, characterized in that part of the traditional fuel is used in burners to increase the temperature of the combustion fumes of the motor generator, or to increase the temperature of the combustion fumes of the furnace, or to heat the water destined to steam generation, or to overheat the saturated or slightly overheated steam generated in the combustion furnace before it is supplied to the stage turbogenerator (b).

Method according to the preceding claims, characterized in that part of the traditional fuel is used in a turbogenerator or in an additional motor generator whose fumes are used to overheat the saturated or slightly overheated steam generated in the combustion furnace before being supplied to the turbogenerator. of stage (b).

Method according to the preceding claims, characterized in that the non-traditional fuel is primary or secondary biomass or a material assimilable to it, or an urban waste or an assimilable material, or an industrial waste or an assimilable material, or a product or by-product of wastewater treatment, or a residue of agricultural origin or an assimilable material, or an automotive waste or an assimilable material, or a combination thereof.

11. Method according to claim 10, characterized in that the non-traditional fuel is a material selected from among forest biomass, plant biomass, energy crops, sawdust, bark, sludge, slurry, chicken manure, alpechín, alperujo, unused tires, light fraction of car fragmentation, or a combination thereof.

Method according to the preceding claims, characterized in that the traditional fuel is a gaseous or liquid hydrocarbon of fossil origin, preferably gas-oil, fuel-oil, or natural gas.

13. A method according to claim 12, characterized in that the traditional fossil fuel is partially or totally replaced by a traditional non-fossil fuel such as biogas, poor gas, synthesis gas, bioethanol, biofuel or other assimilable internal combustion engine fuel.