EP0395619A1 - Process for treatment and use of pyrolysis and bombustion products from a gasifier and plant for carrying out this process - Google Patents

Abstract

Process for the treatment and use of pyrolysis and combustion products obtained in a gasifier (1) containing a fluidised bed (2) charged with fuel originating from urban refuse and/or industrial waste, which consists, on the one hand, in separating from the gas phase carrying solid particles and escaping at the top of the fluidised bed, at a higher temperature at which all the pyrolysis gases are in vapour form, the inert particles and the carbon particles of a size which is too great for them to ignite instantly in air and, on the other hand, in employing the gas phase freed from these particles, while it is maintained at a temperature above 300 DEG C, as fuel in a boiler (4). <IMAGE>

Description

The subject of the present invention is a process for the treatment and use of the pyrolysis and combustion products obtained in a fluidized bed reactor or gasifier supplied with make-up air and loaded with biomass fuel or the like, constituted in particular by combustible residues from urban garbage and / or similar industrial waste, and composed of a gaseous phase escaping at the top of the fluidized bed and two solid phases, the first of which, consisting essentially of non-carbonated carbon particles and particles or inert dust coming from loads of cardboard, paper and other combustible waste, is, given the low density of said particles, dispersed in the aforementioned gas phase and entrained by the latter in its upward movement, while the second solid phase, formed by heavy residues, such as gravel, glass, etc ..., remains at the base of the fluidized bed from where it e can be evacuated by gravity.

It is well known that the pyrolysis and combustion products obtained by gasification of urban garbage or industrial waste are difficult to use as an energy source, on the one hand because of their low calorific value and on the other hand because of their toxicity due to the formation of toxic gaseous compounds such as nitrogen oxides and dioxin.

The object of the invention is to provide a process for the treatment and use of said products which allows them to be used directly as fuel and to replace, for example, natural gas or fuel oil, in boilers or ovens, without significant transformation. of these. This job is allowed thanks to a significant increase in the calorific value of said products compared to that of products generally from gasifiers using a fuel consisting of garbage or waste. Said method further allows the use of said products without risk of formation of toxic products and without dispersion of dust.

To this end, according to the invention, said method consists, on the one hand, in separating from the gaseous phase charged with the above-mentioned first solid phase, at a temperature above which all the pyrolysis gases are in the form of vapor, the aforementioned inert particles and the carbon particles whose particle size is too high for them to ignite instantly in air and, on the other hand, to use the gas phase, rid of these particles by maintaining it at a temperature above 300 ° C, as fuel in an oven or boiler.

According to an advantageous embodiment of the invention, the gasifier is supplied with fuel by introducing the latter at the base of the fluidized bed and near the zone or zones for introducing make-up air supplied to said fluidized bed.

According to a particularly advantageous embodiment of the invention, the fuel / make-up air weight ratio is between 1 and 1.5 for a fluidized bed volume between 0.5 and 1.5 m3 per tonne of fuel introduced per hour in the gasifier to obtain a carbon content of between 75 and 250 kg / m3 of bed volume, having observed that this carbon is an essential intermediate for chemical reactions.

The invention also relates to a simple and compact installation for the implementation of the above process.

According to the invention, said installation comprises at least one fluidized bed gasifier, a boiler or oven, powered by the gas phase freed from the aforementioned part of the first aforementioned solid phase, associated with the gasifier, a collector connecting the gasifier to the boiler and through which the aforementioned gas phase charged successively laden with the first aforementioned solid phase then the gas phase rid of said part of the first solid phase, at least one separator device interposed in the collector for separating the aforementioned particles from the gas phase, means associated with said device and arranged, on the one hand, to evacuate the inert particles and , on the other hand, to recycle in the fluidized bed carbon particles of too large particle size and separated from the gas phase in the aforementioned device and means provided for thermally insulating at least the collector and the separating device and arranged to maintain the gas phase charged with particles at a temperature above 300 ° C until entering the boiler or oven.

• La figure 1 est une vue schématique, en élévation, partiellement en coupe et avec brisures partielles, d'une installation pour la mise en oeuvre du procédé susdit.
• La figure 2 est une vue partielle, analogue à la figure 1, montrant une variante de l'installation illustrée à ladite figure 1.

Other details and particularities of the invention will emerge from the description of the appended drawings which illustrate the above process and which represent, by way of non-limiting example, a particular embodiment of the installation according to the invention.

• Figure 1 is a schematic view, in elevation, partially in section and with partial broken, of an installation for the implementation of the above method.
• FIG. 2 is a partial view, similar to FIG. 1, showing a variant of the installation illustrated in said FIG. 1.

In the various figures, the same reference notations relate to identical or analogous elements.

The process according to the invention and illustrated in the drawings is intended for the treatment and the use of the pyrolysis and combustion products obtained in a reactor 1 or fluidized bed gasifier supplied with air. make-up and loaded with biomass fuel or the like, consisting in particular of combustible residues from urban waste and / or similar industrial waste. These products are composed of a gas phase escaping from the top of the fluidized bed 2 and two solid phases. The first of these phases, which is essentially formed of non-carbonated carbon particles and inert particles or dust coming from cardboard, paper and other combustible waste loads, is, given the low density of said particles, dispersed in the aforementioned gas phase and driven by the latter in its upward movement, while the second phase, formed by heavy residues, such as gravel, glass, etc., is maintained at the base of the fluidized bed 2 from where it can be evacuated by gravity .

To impart a calorific value to the aforementioned products which makes them usable as a single fuel or as an auxiliary fuel in ovens or boilers, said method consists, on the one hand, in separating from the charged gaseous phase from the first solid phase aforementioned, at a temperature above which all of the pyrolysis gases are in the form of vapor, the above-mentioned inert particles and the carbon particles whose particle size is too high for them to ignite instantly in air and, d on the other hand, to use the gas phase, freed from these particles by maintaining it at a temperature above 300 ° C, as a single or additional fuel in an oven or a boiler.

Given that it is advantageous to obtain as fuel a gas rich in CO, H₂ and CH₄, it is preferable to ensure in the reactor 1, as a first reaction time, local partial combustion in the presence of air d '' a local pyrolysis in the absence of air, which generates tar and hydrocarbons difficult to decompose, the method according to the invention provides to supply the gasifier 1 with fuel by introducing it at the base of the fluidized bed 2 and near the introduction areas 3 make-up air which is supplied to this fluidized bed. In a second step, the CO₂ and H gazO gases locally produced by combustion are reduced by residual carbon, also produced by this combustion to in turn form CO, H₂ and CH₄ while thus reducing the quantities of tars and hydrocarbons. emerging at the pyrolysis stage.

As the production of combustible and oxidizing gas must advantageously be as constant as possible, the method according to the invention provides, taking into account that the phenomenon of reduction of CO₂, and H₂O in the absence of air is significantly slower than CO₂ production during partial combustion, a fuel / make-up air weight ratio which is between 0.4 and 0.75 for a fluidized bed volume between 0.5 and 1.5 m3 per ton of fuel introduced per hour into the gasifier.
This way of doing things leads, as indicated above, to a fluidized bed 2 whose carbon content is such that it compensates for the slow reaction in the aforementioned second time and thereby self-regulates the total reaction in order to finally produce, at a given temperature, a combustible gas of determined and substantially constant composition.

To enrich the combustible gas as much as possible with carbon particles capable of igniting instantly in air, the gas phase, charged with the aforementioned first solid phase, is subjected to at least one acceleration and one before the above-mentioned separation. successive expansion in an area where the above particles, and in particular the carbon particles, transported by the gas phase are subjected to impacts to reduce their particle size, so that the dimensions of at least 80% of the particles are equal or less than 200 µm, a condition which allows them to ignite on contact with air.

The carbon particles whose dimensions could not be reduced during the aforementioned impact treatment are collected and recycled in the fluidized bed 2, while the inert and carbon particles coming from the above separation are collected and either evacuated or used as fuel in a heat exchanger 5 used to at least partially dry the fuel supplied to the gasifier 1.

To avoid the formation of toxic products during the reaction, the biomass fuel is transformed in a homogeneous manner into the gaseous phase and into the abovementioned solid phases at a temperature of between 650 ° and 850 ° C.

In order to avoid entraining in the gas phase a quantity of particles of too large dimensions which would complicate the above-mentioned impact treatment and separation, as well as to preserve in the fluidized bed the above-mentioned accumulated carbon content, ascending speeds of make-up air and, from there, the gaseous phase, between 0.25 and 1.5 m / sec.

By way of nonlimiting example, the gasifier operated with an ascent rate of 0.8 m / sec in zone 11 of the fluidized bed and 0.4 m / sec in zone 12 of Figures 1 and 2. The ratio weight of fuel (dry and without ash) to make-up air was 0.6, which made it possible to maintain a content of 100 kg of carbon per m3 of fluidized bed. The volume of the fluidized bed was 0.35 m3. The weight of the fine inert particles, which accompanied the gas at the outlet of the gasifier and retained in the cyclone, was equal to 20% of the weight of the fuel. The user device 4 of FIG. 1 could thus be supplied at 400 ° C with gas charged with microscopic particles of carbon and tar vapors, which brought the lower calorific value of the gas to 10 megajoules per Nm3 of gas instead of 4 to 5 megajoules / Nm3 normally obtained in lean gases.

The installation according to the invention, illustrated in the drawings, comprises, for the implementation of the above process, a gasifier 1 with a fluidized bed 2 and a boiler or oven 4 which is associated with said gasifier and supplied by the phase gaseous above after it has been freed of inert particles and carbon particles too large to be able to ignite directly on contact with air. The gasifier 1 and the boiler 4 are connected by a manifold 6 through which flows successively, in 6 ′ the gas phase charged with the first solid phase and then, in 6˝, the gas phase rid of the aforementioned inert particles and carbon. To get rid of the gaseous phase of these latter particles, at least one separating device 7 is interposed in the reader neck 6 and means 8, 9 are associated therewith for respectively removing, by gravity, the inert particles and for recycling, by gravity and in the fluidized bed, carbon particles whose dimensions are too large to ignite directly on contact with air. Means 10 are provided for thermally insulating the reader neck 6 and the separator device 7 and maintaining, until the inlet of the boiler 4, the gas phase at a temperature above 300 ° C. Finally, means 11 are arranged, at the base of the gasifier 1, for collecting and discharging the aforementioned second solid phase, which consists of heavy residues, such as gravel, glass, etc., and which, by its weight , is maintained at the base of the fluidized bed 2.

As shown in the drawings, the installation advantageously comprises a gasifier 1 of the single fluidized bed reactor type 2 which is essentially constituted, for ensuring combustion and pyrolysis of the biomass fuel, by two coaxial chambers 11 and 12 of vertical axis, these chambers 11 and 12 communicating with each other from below, at 13. The fuel supply 14 is effected either by a non-illustrated conduit extending along the axis of the chambers and opening out above the central chamber which serves, in this case, from the pyrolysis chamber, the combustion taking place in the peripheral chamber, either, as shown in the drawings, by a conduit 15 extending along the axis of the chambers and opening at the base from the central chamber 12 which serves as a combustion chamber (see FIG. 2) or also by at least two diametrically opposite conduits opening at the base of the peripheral chamber 11 which serves as the combustion chamber (see FIG. 1). The fuel is entrained in these conduits 15 in a regular and homogeneous manner by an endless screw arranged in the conduit, coaxial with the latter. A supply of make-up air 16, 17, possibly combined with a supply of water vapor or combustible gas, is provided at the base of each of the chambers 11 and 12 and controlled by valves 16 ′ and 17 ′. The means 18 for the evacuation of the aforesaid second solid phase comprise a collecting tank 19 disposed at the base of the chambers 11 and 12 and which communicates with the latter.

The aforementioned separator device 7 comprises, as shown in FIG. 1, a cyclone 20 arranged to, on the one hand, essentially retain the inert particles entrained by the gas phase produced by the gasifier 1 and coming from the cardboard, paper and other charges combustible waste and the residual carbon particles of the non-gasified fuel which are too large to be instantly flammable in air and, on the other hand, to remain in the gas phase, to increase its calorific value, the carbon particles residual whose dimensions are such that they are instantly flammable on contact with air. Said separator device 7 comprises, upstream of the cyclone 20, considering the direction of flow of the gas phase shown diagrammatically by the arrow 21, an apparatus 22 constituted for example by an impact separator or a lamella filter and which aims to reduce the particle size of the particles entrained by the gas phase, in particular the non-carbonated carbon particles, before they are entrained in the cyclone 20. This device 22 is arranged so that the gaseous phase charged with the above-mentioned first solid phase, made up of inert particles and carbon particles, is successively accelerated and relaxed so that said particles are subjected to impacts so that the major part of these particles, which will be entrained by the gas phase in cyclone 20, have dimensions which are at most equal to 200 um. The larger particles are collected by gravity in an expansion zone provided in the device 22 and recycled by gravity in the fluidized bed 2 of the gasifier 1 using a pump 23 constituting the means 9 above.

As shown in FIG. 1, the cyclone 20 comprises, at its base, on the one hand, means 24 for collecting inert particles and carbon particles, separated from the gas phase in said cyclone, which consist of a tank 26 and, on the other hand, means 25 for evacuating said particles which are constituted by a conduit 27, connected to the aforementioned tank 26, in which the particles flow by gravity, their flow rate being regulated by a valve 28 .

The above installation advantageously comprises, as shown in FIG. 1, a heat exchanger 5 in which the fuel to be introduced into the gasifier 1 is previously and at least partially dried. This exchanger 5 comprises, for its fuel supply, means 29 constituted by a grid in the form of an endless band, driven in a continuous movement according to arrow 30, on the upper strand of which are uniformly distributed by the conduit 27, either as fuel or as supplementary fuel, the particles collected in the collection tank 26 provided at the base of the cyclone 20.

It should be understood that the invention is in no way limited to the embodiments described and that many modifications can be made to these without departing from the scope of this patent.

Claims (14)

1. Process for the treatment and use of the pyrolysis and combustion products obtained in a reactor or gasifier (1) with a fluidized bed (2) supplied with make-up air and loaded with biomass fuel or the like, constituted in particular by residues fuels from urban garbage and / or similar industrial waste, and composed of a gaseous phase escaping at the top of the fluidized bed (2) and two solid phases, the first of which, which is formed essentially of non-carbonated carbon particles and inert particles or dust coming from loads of cardboard, paper and other combustible waste, is, given the low density of said particles, dispersed in the abovementioned gas phase and entrained by the latter in its upward movement, while the second solid phase, formed by heavy residues, such as gravel, glass, etc ..., stays at the base of the fluidized bed (2) from where it can be evacuated by gravity, said process being characterized in that it consists, on the one hand, in separating from the gaseous phase charged with the above-mentioned first solid phase, at a temperature above which all of the pyrolysis gases are in the form of vapor , the above-mentioned inert particles and the carbon particles whose particle size is too high for them to ignite instantly in air and, on the other hand, to use the gas phase freed from these particles, keeping it at a temperature above 300 ° C, as fuel in an oven or boiler (4). 2. Method according to claim 1, characterized in that the gasifier is supplied with fuel by introducing the latter at the base of the fluidized bed and near the introduction zone or zones (3) of make-up air. supplied to said fluidized bed. 3. Method according to claim 2, characterized in that the fuel / make-up air weight ratio is between 0.45 and 0.75 for a bed volume fluidized between 0.5 and 1.5 m3 per tonne of fuel introduced per hour into the gasifier to obtain a carbon content of between 75 and 250 kg / m3 of bed volume. 4. Method according to any one of claims 1 to 3, characterized in that, before the above-mentioned separation, the gaseous phase, charged with the above-mentioned first solid phase, is subjected to at least one successive acceleration and relaxation in a area where the above particles, and in particular the carbon particles, transported by the gas phase are subjected to impacts to reduce their particle size, so that the dimensions of at least 80% of the particles are equal to or less than 200 μm . 5. Method according to any one of claims 1 and 4, characterized in that, during the above-mentioned separation, the above-mentioned inert particles are dissociated, which are evacuated by gravity of carbon particles of high particle size which are directed into the fluidized bed. 6. Method according to any one of claims 1 to 5, characterized in that one transforms, in a homogeneous manner, the biomass fuel into the gaseous phase and into the above-mentioned solid phases at a temperature between 600 ° C and 900 ° C . 7. Method according to any one of claims 1 to 6, characterized in that the ascending speeds of the above-mentioned gas phase and of the make-up air supplied to the fluidized bed are maintained between 0.25 and 1.5 m /dry. 8. Installation for implementing the method according to any one of claims 1 to 7, characterized in that it comprises at least one gasifier (1) with a fluidized bed, a boiler or oven (4), supplied by the gas phase freed from the above-mentioned part of the first aforementioned solid phase, associated with the gasifier, a collector (6) connecting the gasifier (1) to the boiler (4) and through which successively circulates the aforementioned gaseous phase charged with the aforesaid first solid phase then the gaseous phase rid of said part of the first solid phase, at least one separator device (7) interposed in the reader neck (6) to separate from the gaseous phase the aforementioned particles, means (8, 9) associated with said device (7) and arranged respectively to evacuate the inert particles and to recycle, in the fluidized bed, the carbon particles of excessively large particle size and separated from the gas phase in the aforementioned device, means (10) provided for thermally insulating at least the reader neck and the separating device and arranged to maintain the gas phase charged with particles at a temperature above 300 ° C until the inlet of the boiler or oven (4) and means (18) arranged at the base of the gasifier for evacuating by gravity the aforementioned second solid phase. 9. Installation according to claim 8, characterized in that the aforesaid gasifier (1) is of the single fluidized bed reactor type (2) which, to ensure pyrolysis and combustion of the biomass fuel, consists essentially of two coaxial chambers ( 11, 12), with a vertical axis, communicating from below, a fuel supply (14) being provided to open out above the central chamber where the pyrolysis takes place, the combustion taking place in the peripheral chamber, said gasifier (1) comprising, at the base of each of the chambers, a supply of make-up air (16, 17) optionally combined with a supply of water vapor or combustible gas. 10. Installation according to claim 8, characterized in that the aforesaid gasifier (1) is of the single fluidized bed reactor type (2) which, to ensure combustion and pyrolysis of the biomass fuel, consists essentially of two coaxial chambers ( 11, 12), of vertical axis, communicating from below, at least one fuel supply (14) being provided to lead to the base of one of said chambers while a supply of make-up air (16, 17), possibly combined with a supply of water vapor or combustible gas, is provided at the base of each of the chambers. 11. Installation according to any one of claims 6 to 11, characterized in that the aforementioned separator device (7) comprises a cyclone (20) arranged to, on the one hand, essentially retain the inert particles entrained by the gas phase and from charges of cardboard, paper and other combustible waste and the residual carbon particles of the non-gasified fuel which are too large to be instantly flammable in air and, on the other hand, allow the particles to remain in the gas phase residual carbon whose dimensions are such that they are instantly flammable on contact with air. 12. Installation according to claim 11, characterized in that it comprises, upstream of the cyclone considering the direction of flow of the gas phase, an apparatus (22), such as impact separator, lamella filter, arranged for that the gas phase charged with the first solid phase be successively accelerated and relaxed so that the particles are subjected to impacts so that the major part of said particles, which will be entrained by the gas phase in the cyclone (20), have dimensions all at most equal to 200 μm, the larger particles being collected, by gravity, in an expansion zone provided in the apparatus and which is connected to the gasifier (1) to allow recycling of these particles in the fluidized bed (2) . 13. Installation according to either of claims 11 and 12, characterized in that the aforementioned cyclone (20) comprises, at its base, means for collecting (24) and evacuating (25) inert particles and carbon particles which are separated from the gas phase charged with particles during the passage of the latter in said cyclone. 14. Installation according to claim 13, characterized in that it comprises a heat exchanger (5) in which the fuel is dried, at least partially, before its introduction into the gasifier (1) and means (29) arranged for supply this exchanger (5) either with fuel or with additional fuel, from the means for collecting and evacuating (24, 25) the abovementioned particles provided at the base of the cyclone (20).

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