WO2007113330A1

WO2007113330A1 - Process for producing electrical energy from biomass

Info

Publication number: WO2007113330A1
Application number: PCT/EP2007/053397
Authority: WO
Inventors: Philippe Daverat; Nicolas Millet
Original assignee: Eneria
Priority date: 2006-04-05
Filing date: 2007-04-05
Publication date: 2007-10-11
Also published as: EP2016158A1; FR2899596B1; FR2899596A1

Abstract

The present invention relates to a process for producing electrical energy from biomass, comprising the following successive steps: a) autothermal gasification of the biomass in the presence of air in a reactor, under a slightly reduced pressure, advantageously at a temperature greater than 800°C, in order to obtain a syngas, b) cooling of the syngas at a temperature of not less than 300°C, c) washing of the syngas in order to substantially remove the tars and/or the ammonia, d) injection of the washed gas into at least one gas engine coupled to an electrical generator, making it possible to produce electrical energy. The invention also relates to a plant for the production of electrical energy from biomass, which is suitable for the implementation of said process.

Description

Process for producing electrical energy from biomass

The present invention relates to the general technical field of valorization of biomass, in particular of vegetable and / or animal waste or by-products, in order to produce electricity and heat.

In particular, the present invention relates to a method of producing electrical energy from biomass including autothermal gasification of biomass to produce synthesis gas, treatment of this synthesis gas, and injection of the gas into at least one an internal combustion engine coupled to an electric generator, for producing electrical energy. The process according to the present invention also advantageously makes it possible to produce thermal energy. The present invention also relates to an installation for producing electrical energy from biomass suitable for implementing such a method. The installation according to the present invention also advantageously makes it possible to produce thermal energy.

Today, diversification of energy resources is a challenge for most countries. Oil and natural gas reserves are dwindling, and we risk missing these fossil fuels in the near future. Moreover, the majority of Western countries, including France, have few fossil resources to produce electricity, and the need to import fossil fuels represents a considerable cost for these countries, in a context where the price oil is on the rise.

The desire to develop environmentally friendly energy sources, coupled with the constant concern for economic efficiency, has made renewable energies a full and integral component of French energy policy.

Unlike fossil fuels, such as oil, natural gas, and coal, which increase the amount of CO ₂ in the atmosphere and have catastrophic effects on the greenhouse effect, renewable energy contributes to sustainable energy development. since they do not emit greenhouse gases. The development of renewable non-fossil energy sources is therefore a major environmental issue.

Bio-mass and bio-fuels have the dual advantage of being high-quality fuels and fuels, and not adding to the greenhouse gas emissions. Indeed, biomass contributes to the fight against global warming, since the _CO2 generated by the combustion of bioenergy is offset by the _CO2 absorbed by the plants during their growth.

As a result, there was a need to develop a new process for generating electricity from non-fossil fuels. In addition, there was also a need to develop biomass, particularly waste and by-products, particularly green waste.

The present invention satisfies this need. The Applicant has thus discovered a new method of producing electrical energy and thermal energy from biomass by gasification of said biomass. Furthermore, the process according to the present invention allows the treatment and recovery of all kinds of biofuels, such as vegetable waste, not requiring a prior step of extraction of particular plant compounds or isolation of specific plant parts. . Thus, all the biomass such as plant biomass can be used in the context of the present invention, and the whole mass of plants, including by-products of plants, such as stems, leaves, shells, herbs. needles, or straw, which are generally rejected, can be energetically enhanced in the process according to the present invention.

In addition, the method of producing electrical energy from biomass according to the present invention is relatively inexpensive, since the starting compounds are biomass such as waste or by-products of industries. Furthermore, the method according to the present invention makes it possible to contribute to the reduction of fossil fuel imports contributing to a significant saving in Tonnes of Petroleum Equivalent (PET). Finally, the method of producing electrical energy according to the present invention, comprising the gasification of the biomass to obtain a synthesis gas, the washing of the gas, and then the injection of the synthesis gas into at least one gas engine. coupled with an electric generator, is an environmentally friendly process, since it contributes to the reduction of greenhouse gas emissions. No atmospheric pollutant is released during the gasification stage. In addition, there is no CO ₂ emission during the gasification of plant biomass and the production of CO ₂ by the gas engine is compensated by the fixation of carbon dioxide during the period of growth of the plants. because of the phenomenon of photosynthesis. The theoretical balance on the carbon dioxide produced is therefore neutral. The use of plant biomass as a source of energy thus enters the natural carbon cycle. Vegetable biomass is thus considered as a neutral renewable energy with respect to the greenhouse effect.

The subject of the present invention is therefore a method for producing electrical energy from biomass comprising the following successive steps: a) autothermal gasification of the biomass in air in a reactor, under low vacuum, advantageously at a temperature greater than 800 ^° C., to obtain a synthesis gas, b) cooling of the synthesis gas at a temperature of not less than 300 ^° C., (c) washing of the synthesis gas in order to eliminate substantially the tars and / or the ammonia, d ) injection of the washed gas into at least one gas engine coupled to an electric generator, for producing electrical energy.

Advantageously according to the present invention, the bio mass is at least one vegetable waste, such as agricultural or forestry waste, or a by-product or co-product of agro-food industries of the distilleries type. In particular, the biomass may contain grape marcs and / or wood chips, or bark.

In a particular embodiment of the present invention, the method further comprises a step of drying the biomass in order to obtain a mass moisture content of less than 25% on total mass, prior to the gasification step a) biomass. According to a particular feature of the present invention, the method further comprises a step of grinding and / or calibration of the biomass, prior to the gasification step a) of the biomass. Advantageously according to the present invention, water vapor is also injected into the gasification reactor a) of the biomass in order to increase the gasification yield.

In a particular embodiment of the present invention, the gasification a) of the biomass is carried out in a non-fluidized moving bed gasifier, with stirring in order to avoid stagnation of the ash in the gasification reactor.

According to a particular characteristic of the present invention, the cooling b) of the synthesis gas is carried out by passage of said gas in a thermal recuperator containing a thermal fluid, such as thermal oil. Advantageously, said heat recovery unit is coupled to a vaporizer for producing steam, said water vapor being then advantageously used to drive a steam turbine to produce electrical energy.

In a particular embodiment, the method according to the invention makes it possible to produce thermal energy in the form of hot water or of water vapor during the cooling step b) of the synthesis gas using thermal recuperator. In this case, water vapor is not recovered in a steam turbine.

According to a particular embodiment of the present invention, at least a portion of the ashes and dusts entrained in the synthesis gas are separated from the gas by passage in at least one cyclone, downstream of the gasification a) of the biomass, prior to the washing step c) synthesis gas.

Advantageously according to the present invention, the process also comprises at least one step of compressing the synthesis gas downstream of the gasification a) of the biomass, advantageously before and / or after the washing step c) of the synthesis gas . In a particular embodiment of the present invention, the washing c) of the synthesis gas is carried out in at least one organic liquid washer by counter-current organic liquid spraying, in order to purify the gas by trapping the heavy tar. and / or light in the organic liquid.

The organic liquid is typically selected depending on the tars produced according to the type of biomass. Advantageously, this specific organic liquid can be called synthetic oil. Advantageously according to the present invention, the purification of heavy tar is carried out in a first organic liquid scrubber stage by trapping heavy tar in this organic liquid, then the heavy tar is separated from the organic liquid, for example by centrifugation, before being reinjected as fuels in the gasification reactor.

Even more advantageously according to the present invention, the purification of light tars is carried out in a second organic liquid scrubber stage by trapping light tars in this organic liquid, this organic liquid being identical to or different from the organic liquid used for purifying the heavy tars, then the light tars are separated from the organic liquid in an air / liquid organic air separator by hot air injection against the current, and the hot air charged with light tars is then reinjected into the oxidation zone of the gasification reactor.

Advantageously according to the present invention, the washing c) of the synthesis gas is carried out in at least one water washer by countercurrent water spraying, in order to purify the gas by trapping ammonia in water, advantageously after washing the gas of heavy and / or light tar.

Even more advantageously according to the present invention, the ammonia is separated from the water in an air / water separator by injection of hot air against the current, and the hot air charged with ammonia is then reinjected into the reactor. gasification.

In a particular embodiment of the present invention, following the washing step c) of the synthesis gas, and prior to its injection d) in the gas engine, said gas has a lower heating value between 4 and 7. MJ / Nm ³ , is at a pressure between 60 and 100 mbar, and at a temperature between 40 and 80 ⁰ C, preferably between 40 and 60 ⁰ C.

In a particular embodiment of the present invention, following the injection d) of the gas in the gas engine, the energy of the exhaust gases from the combustion in said gas engine is recovered in order to supply a fuel. boiler for producing water vapor, said water vapor being then advantageously used to drive a turbine coupled to a generator to produce electrical energy. In a particular embodiment, the energy of the gases exhaust from combustion in said gas engine can also be recovered as thermal energy.

The subject of the present invention is also an installation for the production of electrical energy from biomass comprising, in series, an autothermal gasification reactor (1) for the biomass containing means for continuously injecting air throughout the entire period of time. duration of the gasification reaction, generating a synthesis gas, a cooling device (2) of the synthesis gas, - a washing device (3) of the synthesis gas in order to eliminate substantially the tars and / or the ammonia , and at least one gas engine (4) coupled to an electric generator, for producing electrical energy.

This installation is suitable for implementing the method according to the present invention.

Advantageously according to the present invention, the installation also contains a means (5) for drying the biomass, such as a low-temperature dryer, upstream of the biomass gasification reactor (1).

According to one particular characteristic, the plant according to the present invention further contains a grinding means and / or a means for calibrating the biomass, upstream of the biomass gasification reactor (1).

In a particular embodiment of the present invention, the biomass gasification reactor (1) is a non-fluidized moving bed gasifier containing counter-current air injection means. Advantageously according to the present invention, the reactor (1) for gasification of biomass further contains means for injecting water vapor.

In a particular embodiment of the present invention, the reactor (1) for gasification of the biomass contains, in its lower part, at least one stirring means, such as a rotary stirring arm provided with deflectors. In the context of the present invention, the cooling device (2) of the synthesis gas is typically a thermal recuperator containing a thermal fluid, such as thermal oil, said thermal recuperator being advantageously coupled to a vaporizer for producing water vapor, said vaporizer itself being advantageously coupled to a steam turbine (6) in order to produce electrical energy.

In a particular embodiment, the plant according to the present invention also contains at least one cyclone (7), downstream of the reactor (1) for gasification of the biomass.

According to a particular characteristic, the installation according to the present invention also contains at least one compression device (8) for the synthesis gas downstream of the reactor (1) for gasification of the biomass, advantageously upstream and / or downstream. of the washing device (3) of the synthesis gas.

Advantageously according to the present invention, the washing device (3) of the synthesis gas contains at least one tar washing means (3a), such as an organic liquid scrubber, in order to extract the tars from the synthesis gas. Advantageously, the organic liquid is synthetic oil. Typically, the synthesis gas washing device (3) contains two series-associated organic liquid washers (3a), in particular a first organic liquid washer for trapping heavy tar in the organic liquid, followed by a second scrubber with organic liquid to trap light tar in the organic liquid.

Even more advantageously according to the present invention, the synthesis gas washing device furthermore contains, at the bypass outlet of the first organic liquid washer (3a), a means for separating heavy tar from the organic liquid, as well as means for recirculating the heavy tars recovered at the outlet of the separation means to the gasification reactor (1).

In a particularly advantageous manner according to the present invention, the washing device of the synthesis gas further contains, at the bypass outlet of the second organic liquid washer (3a), an air / organic liquid separator containing air injection means. counter-current hot for separating light tars from the organic liquid, as well as means for recirculating the hot air charged with light tars recovered at the outlet of the air / liquid organic separator to the reactor (1) for gasification.

In a particular embodiment of the present invention, the washing device (3) of the synthesis gas contains at least one means for eliminating ammonia (3b), such as a water scrubber, for purifying the gas by trapping ammonia in the water.

In this embodiment, the synthesis gas washing device furthermore advantageously contains, at the bypass outlet of the water washer (3b), an air / water separator containing means for injecting hot air against the current. for separating the ammonia from the water, as well as means for recirculating the hot air charged with ammonia recovered at the outlet of the air / water separator to the reactor (1) for gasification.

According to a particular characteristic of the present invention, the installation furthermore contains, at the outlet of the gas engine (4), means for recovering the exhaust gases from the combustion in said gas engine in order to supply a boiler to produce water vapor, and the installation further contains, at the outlet of the boiler, a turbine (6) coupled to a generator to produce electrical energy.

Various objects and advantages of the present invention will become apparent to those skilled in the art by way of reference to the following illustrative drawing: FIG. 1 is a schematic view of an electrical power generation plant from biomass comprising associated with series: - means for drying (5) the biomass, an autothermal gasification reactor (1) partially dried biomass, containing means for continuous air injection to generate a synthesis gas, a cooling device (2) synthesis gas, said device (2) being coupled in parallel with a steam turbine (6), - a cyclone (7) to separate from synthesis gas a portion of the ashes and dusts entrained in the gas, a first booster (8) for compressing the synthesis gas prior to washing the gas, a washing device (3) of the synthesis gas to extract gas tars and ammonia, said device (3) contena in series a tar washing means (3a) and an ammonia washing means (3b), a second booster (8) for compressing the synthesis gas after washing the gas, and a gas engine (4) coupled to an electric generator, for producing electric energy, said gas engine (4) being further coupled in parallel with a steam turbine (6).

The installation also comprises a flare (9), at the bypass outlet of the two boosters (8), in order to periodically burn off the surplus synthesis gas if necessary, and thus to regulate the flow of gas before it enters the system. gas engine.

Advantageously, the heat produced by the hot water circuit and the residual energy of the engine fumes are used for the drying of the biomass.

The method according to the present invention makes it possible to produce electrical energy by gasification of the biomass.

By the term "biomass" is meant in the sense of the present invention any organic matter biodegradable from a natural process, capable of energy recovery. Thus, biomass can be any biodegradable carbonaceous waste. Biomass can be of plant or animal origin, or can be produced by human activity.

Biomass can be: - wood, for example in the form of logs, pellets and platelets; wood by-products which cover all the waste produced by logging (branching, bark, sawdust ...), sawmills (sawdust, chips, etc.), by the wood-processing industries ( joineries, furniture manufacturers, flooring) and panel manufacturers, as well as packaging such as pallets; by-products of the industry, such as sludge from pulp (black liquor) and waste from agri-food industries (grape and coffee grounds, pulp and grape seeds, etc.); products from traditional agriculture (cereals, oilseeds), residues such as straw, rice husks, bagasse (ligneous residues from sugar cane) and new energy plantations such as short rotation coppices (willow, miscanthus, etc.); organic waste such as urban waste including sewage sludge, household waste, and waste from agriculture such as agricultural effluents; or waste from livestock such as manure, litter, dung, slurry, etc. Typically, the biomass in the context of the invention is a waste or a plant by-product, which can decompose, including agricultural waste or forest, such as leaves, stems, pods, pods or shells, barks, needles, straw, grasses, and mixtures thereof. In particular, grape marcs, wood chips, or mixtures thereof can be used. By way of example, it is thus possible to use all the agricultural plants, and in particular all the remains or by-products of these plants, in particular roots such as endive roots, flax waste, fruit stones, bagasse, etc.

By way of example, it is also possible to use slurry of pigs, animal meal, or composts, such as sewage sludge mixed with green waste.

Different types of waste can be used in the process according to the present invention.

Advantageously according to the present invention, the biomass is dried prior to the gasification step a) of the biomass. Generally, all of the biomass products naturally have a moisture content of approximately 35 to 55% on total material, for example of the order of 40% on total material.

Typically, the biomass is dried in order to obtain a mass moisture content of less than 25% on total material, advantageously less than 20% on total material, before being introduced into the reactor (1) for gasification. Drying is advantageously carried out by injection of hot air. In a particular embodiment of the present invention, the drying of the biomass is carried out at low temperature, ie at a temperature of less than 100 ^° C., in particular of approximately 80 ° to 95 ° C., in a low temperature dryer. For example, the dryer contains a micro-perforated belt that transports the product from the feed silo to the point of discharge of the product. Hot air is advantageously injected onto the micro-perforated carpet, thereby plating the product to be dried on the carpet, and therefore avoiding the flights at the end of drying.

The hot air is typically generated by the passage of ambient air from an air / water exchanger preferably located in the upper part of the dryer. A fan usually circulates this air inside the dryer.

In a particularly advantageous manner according to the present invention, hot water and / or fumes recovered from gas engines (4) are used in order to provide the energy necessary to heat the air which will be used for drying the biomass.

The air saturated with water can then be rejected by an exhaust duct (chimney) at the top of the dryer.

A regulation system can be used to follow and adapt the operating speed of the dryer to guarantee a constant humidity rate at the outlet, ie of the order of 20% or 25% moisture content. total.

Advantageously, the outlet air is not odorous: in fact, the temperature being low and the air flow important, no combustion of the biomass is carried out during the drying, and the discharges are very diluted (dilution of VOC exiting the dryer).

The dried products then generally transit to a buffer silo pending conversion to synthesis gas in the gasifier. The transport of the dried biomass to the buffer storage silo can be carried out by a mechanical conveyor.

Before drying, the biomass can be ground if necessary, especially when the biomass contains platelets or bark of plants. Generally, grinding is carried out in order to calibrate the biomass. The crushed particles typically have a particle size of less than 1 cm ³ .

After drying, the biomass is advantageously weighed by a metering unit, in order to constantly supply the gasification reactor (1).

Typically, the product is conveyed continuously to the gasification reactor (1), for example by means of a variable speed feed screw and a bucket elevator. A last feed screw advantageously brings the fuel to the reactor core (1). During the gasification step a), the biomass which is a solid fuel is converted into syngas.

In the reactor (1), the gasification is typically carried out in a poor atmosphere O ₂ . The admission of the products and the evacuation of ashes are generally carried out continuously. Thus, the synthesis gas produced is generally sucked up and evacuated continuously. The injection of air into the reactor is advantageously carried out by air injection continuously throughout the duration of the gasification reaction for generating the synthesis gas.

Advantageously according to the present invention, the gasification a) of the biomass is carried out at a gas outlet temperature of greater than 700 ^° C., still more advantageously at a temperature above 800 ^° C., still more advantageously at a temperature above 850 ^° C. C, still more advantageously at a temperature above 900 ^° C., in particular at a temperature above 950 ^° C. The temperature of the biomass bed can reach and exceed 1100 ^° C. The gasification reactor (1), that can also be called gasifier, advantageously operates at a pressure close to atmospheric pressure. In particular, the gas generator operates under a low vacuum, which limits any risk of leakage to the outside. The pressure in the reactor (1) is typically of the order of -10 to -5 mbar. This depression is preferably maintained by a booster fan (8) placed after the gasification reactor (1). This fan is typically driven by a variable frequency motor.

During a cold start, the temperature of the reactor (1) can be done through a gas burner, which is preferably installed at the bottom of the reactor for the duration of the heating phase of the hearth. The burner is equipped with its ignition and flame detection system and generally runs on propane gas. It makes it possible to heat the reactor to a necessary and sufficient temperature (self-ignition temperature of the order of 500 ^° C.) so that the gasification can begin alone.

According to the invention, the gasification a) of the biomass is advantageously an autothermal gasification, in air, unlike allothermal gasification requiring external heat input. The gasification a) of the biomass is a combustion of the biomass, taking place by controlled admission of air into the reactor (1). The injected air flow rate is typically of the order of 1.5 to 2.5 relative to the biomass flow rate at 20% by total mass (MT). For example, the injected air flow rate is of the order of twice the mass flow rate at 20% by total mass (MT).

The gasification is advantageously controlled by the gasification temperature in the reactor (1). This gasification temperature is advantageously adjusted by regulating the amount of air introduced preferably by a supply air fan located in the lower part of the reactor (1). The distribution of air in the reactor is advantageously carried out through a perforated support plate. Depending on the size of the gasifier, several air intakes can be provided in order to evenly distribute the air injection. Manually adjustable valves can be installed at each air injection point. In a particularly advantageous manner according to the present invention, the gasifier contains countercurrent air injection means constituted by a multitude of nozzles distributed homogeneously under the surface of the bed.

The gasification temperature makes it possible to reach a stage of "cracking" the carbon chains to generate a gas mainly containing nitrogen, CO ₂ , carbon monoxide, hydrogen, methane, etc. This poor gas, called synthetic gas, is of low energy value, but is compatible with the use of an internal combustion engine. Moreover, the synthesis gas is advantageously free of dioxins and furans.

Advantageously, during the gasification in the reactor (1), the residence time of the biomass in the moving bed at a temperature typically greater than

1050 ^° C., and in particular of the order of 1100 ^° C., is greater than 10 seconds, typically of the order of 10 to 15 seconds, and the residence time of the synthesis gas is generally greater than 3 seconds, typically of the order of 3.5 seconds.

The gasification reactor (1) is for example a vertical reactor, of the order of 15 to 20 m. The gasification reactor (1) is advantageously a non-fluidized moving bed gasifier of constant height for a given fuel. It advantageously contains means for injecting air against the current. Biomass is typically introduced in the middle and central part of the reactor (1) gasification, while the injection of air is performed in the lower part of the reactor (1).

The gasification reactor (1) is advantageously equipped with an agitator, preferably in its lower part. It allows mixing the product, maintain a bed of fuels of constant height (approximately twenty centimeters), and conveys the ashes to the low point or points of ash recovery at the bottom of the reactor (1).

The rotational speed of the stirrer and the rate of ash removal can affect the gasifier's performance. This agitator is typically powered by a variable speed motor. The operating mode can be automatic or manual.

Particularly advantageously according to the present invention, the gasification reactor (1) contains, in its lower part, a rotary agitator arm provided with deflectors. The baffles are advantageously arranged along the arm. A slow and steady movement of the ash bed from the center to the periphery of the gasifier thus avoids the stagnation of the ashes, their agglomeration and therefore their vitrification.

This embodiment is particularly suitable when the biomass contains grape marc. Indeed, the marc of grapes contains a significant part of potassium (about 2%), unlike other fuels such as wood that contain much less. This portion of potassium adversely affects the ashes which have a strong tendency to vitrify (caking with formation of glass). This vitrification disrupts airflow by blocking air inlets and therefore degrades the operation of the gasifier. The use of a rotary agitator arm provided with deflectors in the gasifier thus makes it possible to avoid vitrification of the ashes.

Advantageously according to the present invention, steam is injected into the reactor (1) during the step of gasification a) of the biomass. The Applicant has discovered that the injection of water vapor into the gasification reactor (1), in particular into the intake air, tends to "crack" the last% of carbon contained in the ashes, and thus significantly improve the gasification efficiency. Without addition of water vapor in the gasification reactor (1), the yield of the gasifier is typically of the order of 60 to 75%, for example around

70%.

With the addition of small quantities of water vapor in the gasification reactor (1), the yield of the gasogen is typically of the order of 70 to 80%, in particular of the order of 75 to 80%, for example around 77%.

The gasification reactor (1) essentially generates the synthesis gas, which is preferably discharged by a sheath placed in the upper part of the reactor and connected to the gas washing device. The reactor advantageously does not have a chimney in the exhaust rejection sense. The temperature of the gas leaving the reactor is typically about 700 to 1000 ^° C., for example of the order of 850 ^° C.

At the outlet of the reactor (1), the synthesis gas mainly contains carbon monoxide, carbon dioxide, methane, hydrogen and nitrogen. Advantageously according to the invention, the synthesis gas is devoid of dioxins and furans. Typically, the synthesis gas contains (% by volume): 10 to

20% of CO, for example of the order of 15% of CO, 10 to 20% of CO ₂ , for example of the order of 15% CO ₂ , 2 to 8% of CH ₄ , for example order of 5% of CH ₄ , 5 to 15% of H ₂ , for example of the order of 10% of H ₂ , and 45 to 55% of N ₂ , for example of the order of 50% of N ₂ . The synthesis gas is suitable for combustion in internal combustion engines, and advantageously has a methane number greater than 70.

In a particular embodiment of the present invention, the synthesis gas has the following composition (% by volume):

Methane (CH ₄ ): 4.26%

Ethane (C ₂ H ₆ ): 0.21% Propane (C ₃ H ₈ ): 0.03%

Butane (C ₄ H ₀ ): 0.03%

Pentane (C ₅ Hi ₂ ): 0.01%

Ethylene (C ₂ H ₄ ): 1.11%

Propylene / Propene (C ₃ H ₆ ): 0.13% Benzene (C ₆ H ₆ ): 0.13%

Carbon Dioxide (CO ₂ ): 12.05%

Carbon monoxide (CO): 14.07% Hydrogen (H ₂ ): 4.25% Nitrogen (N ₂ ): 48.57% Water vapor (H ₂ O): 14.74% Sulfur dioxide (SO ₂ ): 0.06% Ammonia: 0, 35%

The gas is also loaded with tars that will be removed during the washing phases.

The ash collected at the bottom of the gasifier (1) is advantageously cooled and then transported, for example in a closed conveyor, to a silo for storing bottom ash. These ashes can then be used for agricultural application or for agricultural amendments.

Following the gasification a) of the biomass, the gas can be advantageously subjected to primary purification by controlled air injection into the gasogen, typically at the top of the gasifier. In particular, the air injection is performed in the upper part of the gasifier, typically above the feed screw of the biomass. The injected air can be heated or at room temperature. Most of the air is injected into the reactor, but it can also be enriched in O ₂ and / or steam. The primary purification of the synthesis gas makes it possible to crack the tars generated in the bottom of the reactor to unload the downstream gas scrubber, to react the carbon of the ash entrained by the generation of the gas to transform it into a combustible gas (improvement of the yield), and reduce the amount of ash collected by the cyclone (7).

Following the gasification a) of the biomass and optionally following the primary treatment, the synthesis gas obtained is subjected to a cooling step b), typically using a heat exchanger (2). During cooling b), the gas advantageously passes through a thermal recuperator (2), like countercurrent flue gas tubes. This recuperator (2) makes it possible to cool the synthesis gas to a temperature greater than 300 ^° C., advantageously greater than about 320 ^° C., in particular greater than about 350 ^° C., for example using a fluid thermal such than thermal oil. The temperature of the synthesis gas after cooling b) must not be too low, in order to prevent the tars from settling and clogging the circulation lines.

Advantageously, the cooling device (2) of the synthesis gas is specific to the product gas. It is typically a vertical device, in which the gas passes from top to bottom, and the thermal fluid from bottom to top.

Temperature sensors make it possible to control the temperature of the thermal oil in the recuperator and at the outlet of this recuperator.

Particularly advantageously according to the present invention, the cooling device (2) of the synthesis gas is coupled to a vaporizer to produce steam driving a steam turbine (6), to produce electrical energy. The cooling device (2) of the synthesis gas can also make it possible to produce thermal energy in the form of hot water or steam. According to one particular characteristic of the present invention, at least part of the ashes and dusts entrained in the synthesis gas are separated from the gas by passage through at least one cyclone (7), downstream of the gasification a) of the biomass, beforehand in the washing step c) synthesis gas.

For example, following cooling b) and / or prior to cooling b), the synthesis gas passes through a cyclone (7) to remove the fine dust contained in the gas.

The synthesis gas is then advantageously compressed, prior to the washing step c). Typically after having passed through the cyclone (7), the gas is sucked by a first booster (8), making it possible to maintain the gasifier (1) in slight depression (of the order of -5 mbar), and thus to suck the gas through the heat recuperator (2) and the cyclone (7).

At the outlet of the booster (8), the gas is compressed between approximately 50 and 75 mbar, advantageously between 60 and 70 mbar, above atmospheric pressure, in order to operate at a slight overpressure in the washing system (3) of the gas .

The gas, advantageously compressed, is then washed to substantially remove tars and / or ammonia. The tar content at the entrance to washing is typically 25 g / Nm ³ and is reduced to 100 mg / Nm ³ at the end of the wash. The ammonia content at the inlet of the scrubber is typically 4000 to 5000 mg / Nm ³ and is reduced to 40-50 mg / Nm ³ at the outlet.

The washing c) of the gas advantageously comprises a first tar extraction step in at least one tar washing device (3a). The washing of the tars is typically carried out in at least one oil scrubber by spraying synthesis oil (organic liquid) in countercurrent. For reasons of simplification, the synthesis oil will be described as oil below.

According to a particular characteristic of the present invention, the heavy tar are first removed in a first scrubber stage, typically at a temperature of the order of 300 to 350 ^° C. The oil scrubber ( scrubber) is typically supplied with oil from a small buffer storage tank.

In this oil scrubber, preferably vertical, the gas enters the lower part and circulates from bottom to top, while the oil is sprayed through nozzles, against the current, in the upper part of the column. The synthesis gas is thus purified of most of the heavy tar which is trapped in the oil.

The oil loaded with heavy tar is then sent to a means for separating heavy tar from the oil, this separating means being connected to the bypass outlet of the oil scrubber. The means for separating heavy tar from the oil may for example be a centrifuge. The oil is then generally re-injected into the buffer storage tank.

Recovered tars, for their part, are advantageously reinjected as fuels in the reactor (1) for gasification to be burned completely.

Following the washing of the heavy tar, the light tars are advantageously washed. The synthesis gas is thus transferred to a second scrubber, placed downstream of the first oil scrubber that was used to purify the heavy tar. In the same way as in the first oil scrubber, an organic liquid (synthetic oil) is sprayed against the current in this second oil scrubber to extract the light tar from the gas. The oil may be the same as or different from the oil used to purify heavy tar.

Following the passage in this second oil scrubber, the synthesis gas is thus purified of most of the light tars which are trapped in the oil. The oil loaded with light tar is then sent to a means for separating the light tars from the oil, this separation means being connected to the bypass outlet of the second oil scrubber. The means for separating the light tars from the oil is typically an air / oil separator (air / oil stripper) into which hot air is injected countercurrently. The hot air is typically injected into this air / oil separator at a temperature of the order of 160 to 200 ^° C., in particular at a temperature of between 180 ^° C. and 190 ^° C.

The hot air is preferably injected at the bottom of the air / oil separator, while the oil is injected at the top. The tars are then transferred to the air, and the clean oil can then be returned to the second stage of the oil scrubber. The column of the air / oil separator is advantageously filled with packing to maximize the exchange surface.

The hot air charged with light tars can then be reinjected into the gasification reactor (1) as combustion air.

The purified gas of the tars is then advantageously directed to a washing system (3b) in order to remove a large part of the NH ₃ (ammonia).

Prior to introducing the gas into the ammonia washing device (3b), the gas is advantageously cooled to a temperature of the order of 20 to 30 ^° C., for example around 25 ° C. for example in a double-stage condenser. Condensate charged with NH ₃ can then be sent to an air / water separator (air / water stripper) for pre-treatment of this deconcentration water.

In a particular embodiment of the present invention, the ammonia washing device (3b) is a washing device with water, such as a water scrubber (water scrubber), by water spraying against a current. The principle of water washing involves absorbing the ammonia (NH ₃ ) contained in the gas with water.

As in the oil scrubber (scrubber), the oil being here replaced by water, the gas advantageously circulates upwards in the water scrubber, while the water is sprayed against the current. The column of the water washer is advantageously equipped with a lining (small elements arranged in an ordered structure) which allows better absorption of NH ₃ by water: the gas is then obliged to borrow from sinuous paths, and therefore more in contact with water (increase of the exchange surface).

Typically, the water washing system (3b) makes it possible to reduce the concentration of NH ₃ in the gas from approximately 4000 - 5000 mg / Nm ³ of gas to 25 mg / Nm ³ of gas.

Following the passage in this water washer (3b), the synthesis gas is thus purified of most of the ammonia which is trapped in water. Thus, at the outlet of the water washer (3b), the clean gas can then be sent to the power plant, also called cogeneration plant, for the supply of gas engines (4). Prior to the injection d) of the gas in the gas engines (4), the gas is compressed using a booster (8) at a pressure greater than atmospheric pressure, typically at a pressure of between 50 and 50.degree. 140 mbar, advantageously between 60 and 100 mbar.

The water charged with ammonia is then sent to a means for separating ammonia and water, this separation means being connected to the bypass outlet of the water scrubber. The means for separating the ammonia from the water is typically an air / water separator (air / water stripper) into which hot air is injected countercurrently. The hot air is typically injected into this air / water separator at a temperature of the order of 30 to 70 ^° C., in particular at a temperature of between 35 ° C. and 55 ° C.

The hot air is preferably injected at the bottom of the air / water separator, while the water is injected at the top. The ammonia dissolved in the water is captured by the hot air, the hot air causing a fall in the partial pressure of the NH ₃ and thus allowing its degassing. The column of the air / water separator is advantageously filled with a porous lining, making it possible to increase the exchange surface as much as possible.

The hot air containing the NH ₃ then exits through the top of the column of the air / water separator before being reinjected into the gasification reactor (1) as combustion air. Particularly advantageously according to the present invention, the hot air charged with ammonia is first sent to the lower part of the air / oil separator (stripper air / oil) which is then used to separate the light tar from the oil. Then, the hot air charged with ammonia and light tar is reinjected into the gasification reactor (1).

The clean water recovered at the bottom of the column of the air / water separator is advantageously cooled, then reused in the water scrubber (scrubber water).

Prior to washing c) of the synthesis gas, preferably at the outlet of the first booster (8), a bypass system is installed in particular for the start-up phase of the installation. On this bypass system, a flare (9) can burn episodically excess synthesis gas if necessary. During the rise in temperature and power (0 to 100%) of the gasifier

(1), the first gases produced are advantageously burned by flaring until the gasifier has reached 70% load, the washing system (3) can function properly from this load. This bypass is also used in case of malfunction of the washing system (3) or the second booster (8). Following the washing system (3) of the synthesis gas, preferably at the outlet of the second booster (8), a second bypass system is installed in particular in the event of a partial or total shutdown of the booster unit. cogeneration (shutdown of engines). Indeed, the inertia of the gasification system is such that the system can not respond instantly. The gas produced in excess is then flared, thereby regulating the flow of gas before entering the gas engine (4).

A bypass duct is thus preferably connected to the bypass outlet of each of the two boosters (8) which are advantageously upstream and downstream of the washing device (3a, 3b) of the gas (see FIG. 1).

The flare (9) is a gas burning device used very episodically, a temporary solution necessary in the start-up phase or to compensate for the lack of reactivity of the gasifier (1) during an emergency stop or during sudden changes in the load of the motors (4).

After the washing c) of the synthesis gas, and prior to its injection d) in the gas engine (4), said gas has a lower heating value (PCI) of between 4 and 10 MJ / Nm ³ , advantageously between 4 and 6 MJ / Nm ³ . Then, the injection of the washed gas into at least one gas engine (4) coupled to an electric generator makes it possible to produce electrical energy. For example, lkg / h of biomass dried at 20% moisture on the total mass makes it possible to produce IkWh of electricity. Typically, the efficiency of the gas engine (4) is of the order of 32 to 38%, in particular of the order of 33 to 36%.

Typically, the efficiency of steam turbines (6) is of the order of 21 to 27%, for example of the order of 24 to 25%.

Typically, the overall efficiency of the process (electrical and thermal energy) is of the order of 75 to 85%, for example of the order of 80% with a turbine.

The engine (4) may be a spark ignition internal combustion engine or a pilot fuel injection engine.

Preferably, the installation according to the present invention contains several gas engines (4). According to a particular characteristic of the present invention, brine flows in a closed circuit in the pipes in order to cool the gas engines (4).

In a particularly advantageous manner according to the present invention, following the injection d) of the gas in the gas engine (4), the exhaust gases resulting from the combustion in said gas engine are recovered in order to supply a boiler for producing water vapor, said water vapor being then advantageously used to drive a turbine (6) coupled to a generator to produce electrical energy.

Claims

1. A method for producing electrical energy from biomass comprising the following successive steps: a) autothermal gasification of the biomass in air in a reactor, under low vacuum, preferably at a temperature above 800 ^° C., to obtain a synthesis gas, b) cooling of the synthesis gas at a temperature of not less than 300 ^° C., c) washing of the synthesis gas in order to eliminate substantially the tars and / or the ammonia, and d) injection of the washed gas in at least one gas engine coupled to an electric generator, for producing electrical energy.

2. Method according to claim 1, characterized in that the biomass is at least one vegetable waste, such as agricultural or forestry waste, in particular grape marc and / or wood chips.

3. Method according to claim 1 or 2, characterized in that it further comprises a step of drying the biomass to obtain a mass moisture content of less than 25% of the total mass, prior to the step of gasification a) biomass.

4. Method according to any one of claims 1 to 3, characterized in that it further comprises a step of grinding and / or calibration of the biomass, prior to the step of gasification a) biomass.

5. Method according to any one of the preceding claims, characterized in that water vapor is further injected into the gasification reactor a) bio mass to increase the gasification yield.

6. Process according to any one of the preceding claims, characterized in that the gasification a) of the biomass is carried out in a non-fluidized moving bed gasifier, with stirring in order to avoid stagnation of the ash in the gasification reactor. .

7. Process according to any one of the preceding claims, characterized in that the cooling b) of the synthesis gas is carried out by passing said gas into a thermal recuperator containing a thermal fluid, such as thermal oil, said thermal recuperator. being advantageously coupled to a vaporizer for producing steam, said water vapor being then advantageously used to drive a steam turbine to produce electrical energy.

8. Method according to any one of the preceding claims, characterized in that at least a portion of the ashes entrained in the synthesis gas are separated from the gas by passing through at least one cyclone, downstream of the gasification a) the biomass, prior to the washing step c) synthesis gas.

9. Method according to any one of the preceding claims, characterized in that it further comprises at least one compression step of the synthesis gas downstream of the gasification a) biomass, preferably before and / or after the washing step c) synthesis gas.

10. Process according to any one of the preceding claims, characterized in that the washing c) of the synthesis gas is carried out in at least one organic liquid washer by counter-current organic liquid spraying, in order to purify the gas. by trapping heavy and / or light tar in the organic liquid.

11. A method according to claim 10, characterized in that the purification of heavy tar is carried out in a first organic liquid scrubber stage by trapping heavy tar in this organic liquid, then the heavy tar are separated from the organic liquid before to be reinjected as fuels in the gasification reactor.

12. Method according to claim 11, characterized in that the purification of light tars is carried out in a second organic liquid scrubber stage by trapping light tars in the organic liquid, the organic liquid being identical to or different from the organic liquid used. for purifying the heavy tar, then the light tar is separated from the organic liquid in an air / liquid organic separator by injection of hot air against the current, and the hot air charged with light tar is then reinjected into the gasification reactor .

13. Method according to any one of the preceding claims, characterized in that the washing c) of the synthesis gas is carried out in at least one water washer by countercurrent water spraying, in order to purify the gas by entrapment of the ammonia in the water, advantageously after washing the gas of heavy and / or light tar.

14. The method of claim 13, characterized in that the ammonia is separated from the water in an air / water separator by injection of hot air against the current, and the hot air charged with ammonia is then reinjected into the gasification reactor.

15. Process according to any one of the preceding claims, characterized in that, following the washing step c) of the synthesis gas, and prior to its injection d) in the gas engine, said gas has a heating value. less than 4 and 7 MJ / Nif ³ , is at a pressure between 60 and 100 mbar, and at a temperature between 40 and 80 ⁰ C.

16. A method according to any one of the preceding claims, characterized in that, following the injection d) of the gas in the gas engine, the energy of the exhaust gases from the combustion in said gas engine is recovered to feed a boiler to produce steam, said water vapor is then advantageously used to drive a turbine coupled to a generator to produce electrical energy.

17. Installation for producing electrical energy from biomass comprising associated in series: a reactor (1) for autothermal gasification of the biomass containing means of continuous air injection throughout the duration of the gasification reaction generating a synthesis gas; - a synthesis gas cooling device (2), a synthesis gas washing device (3) for the substantial elimination of tars and / or ammonia, and at least one gas (4) coupled to an electric generator, for producing electrical energy.

18. Installation according to claim 17, characterized in that it further contains a drying means (5) of the biomass, such as a low-temperature dryer, upstream of the reactor (1) for gasification of biomass.

19. Installation according to claim 17 or 18, characterized in that it further contains a grinding means and / or a biomass sizing means, upstream of the reactor (1) for gasification of biomass.

20. Installation according to any one of claims 17 to 19, characterized in that the reactor (1) for gasification of biomass is a non-fluidized moving bed gasifier, containing means for injection of air against the current. .

21. Installation according to any one of claims 17 to 20, characterized in that the reactor (1) for gasification of the biomass further contains means for injecting water vapor.

22. Installation according to any one of claims 17 to 21, characterized in that the reactor (1) for gasification bio mass contains, in its lower part, at least one stirring means, such as an agitator arm rotary equipped with deflectors.

23. Installation according to any one of claims 17 to 22, characterized in that the cooling device (2) of the synthesis gas is a thermal recuperator containing a thermal fluid, such as thermal oil, said thermal recuperator being advantageously coupled to a vaporizer for producing water vapor, said vaporizer itself being advantageously coupled to a steam turbine (6) in order to produce electrical energy.

24. Installation according to any one of claims 17 to 23, characterized in that it further contains at least one cyclone (7) downstream of the reactor (1) for gasification of biomass.

25. Installation according to any one of claims 17 to 24, characterized in that it further contains at least one compression device (8) of the synthesis gas, downstream of the reactor (1) for gasification of bio mass , advantageously upstream and / or downstream of the washing device (3) of the synthesis gas.

26. Installation according to any one of claims 17 to 25, characterized in that the washing device (3) of the synthesis gas contains at least one organic liquid washer (3a), preferably two organic liquid washers in series, in particular, a first organic liquid washer for trapping heavy tar in the organic liquid, followed by a second organic liquid scrubber for trapping light tar in the organic liquid.

27. Installation according to claim 26, characterized in that the washing device (3) of the synthesis gas further contains, at the output of the first organic liquid washer (3a), a means for separating heavy tar from the organic liquid, and means for recirculating heavy tars recovered at the outlet of the separation means to the reactor (1) for gasification.

28. Installation according to claim 26 or 27, characterized in that the washing device (3) of the synthesis gas further contains, at the outlet of the second organic liquid washer (3a), an air / liquid organic separator containing means counter-current hot air injection system for separating the light tars from the organic liquid, as well as means for recirculating the hot air charged with light tars recovered at the outlet of the air / liquid organic separator to the reactor (1 ) gasification.

29. Installation according to any one of claims 17 to 28, characterized in that the washing device (3) of the synthesis gas contains at least one water washer (3b) for purifying the gas by trapping the ammonia in the water.

30. Installation according to claim 29, characterized in that the washing device (3) of the synthesis gas further contains, at the outlet of the water washer (3b), an air / water separator containing injection means of countercurrent hot air for separating the ammonia from the water, as well as means for recirculating the hot air charged with ammonia recovered at the outlet of the air / water separator to the reactor (1) for gasification.

31. Installation according to any one of claims 17 to 30, characterized in that it further contains, at the outlet of the gas engine (4), means for recovering the exhaust gases from combustion in said engine. gas generator for supplying a boiler for producing water vapor, and in that it also contains, at the outlet of the boiler, a turbine (6) coupled to a generator for producing electrical energy .