FR2874023A1 - Preparation of combustible gas from organic material in water uses thermal plasma immersed in the water - Google Patents

Abstract

The procedure for making a combustible gas from an organic material in water inside a gasification reactor (1) consists of employing a thermal plasma immersed in the water for an adequate period of time to produce the gas. The organic material can be, according to its nature, in the form of a solution, emulsion or suspension, and the gas produced can be carbon monoxide, hydrogen or a light hydrocarbon such as methane or acetylene, and the plasma is a partially ionised electrically conducting gas heated to a temperature of 3000 - 14000 degrees C. Since the walls (5, 7, 9) of the reactor chamber (3) are kept cool it can be made from a metal such as stainless steel or a polymer such as a plastic or resin-based material. The plasma arc can be transferred between two or more immersed electrodes, and it can be produced by induction or a blown plasma arc torch (11).

Description

2874023 1

  PROCESS FOR THE PRODUCTION OF A COMBUSTIBLE GAS BY ACTION OF AN IMMERSE PLASMA ON ORGANIC MATTER IN

AQUEOUS ENVIRONMENT

DESCRIPTION TECHNICAL FIELD

  The present invention relates to a method for producing a combustible gas from an organic material.

  This process is particularly likely to be used for the treatment of biomass, such as organic sludge, waste oil, plastic materials, agricultural waste.

  STATE OF THE PRIOR ART Currently, the depletion of fossil fuel resources poses a fundamental problem with regard to the supply of fuel to technological systems.

  A particularly attractive method for replacing conventional sources of fuel (such as coal, oil) is the gasification of solid or liquid organic materials, which provides an energy fuel gas transformable into mechanical or electrical energy. The organic material that can be used for fuel gas can come from biomass, such as domestic, industrial and agricultural waste, the volume of which is constantly increasing over the years.

  The processes for the gasification of known organic materials are currently mainly derivatives of incineration processes of organic materials, allowing both the destruction of organic materials and the production of fuel gas. These methods operate in a pyrolytic mode, that is to say in a low oxygen atmosphere.

  Conventional gasification processes are carried out in simple furnaces, among which are fixed grate furnaces, mechanical grate furnaces, heating taking place by means of a fuel, such as wood or coal. . These processes essentially concern the treatment of solid organic waste.

  Single grate ovens are rustic fireplaces that can be used to process a variety of heterogeneous materials such as wood, cardboard, packaging, mostly in bulk and with high humidity levels. Inclined grids automate the extraction of ashes. These ovens have the advantage of being simple to use and require only a small investment. However, the grids operate discontinuously and therefore limit the material processing capacity to 50 to 1000 kg per hour.

  Mechanical grate furnaces are generally dedicated to the treatment of fairly coarse waste, such as household waste. Among the mechanical grate furnaces, there may be mentioned: - furnaces comprising mobile carpet grids generally used for coals, household waste granules, vegetable waste; furnaces comprising grids with tilting bars which make it possible to treat household refuse in bulk, without prior sorting; - Furnaces comprising rotating soles, which are cylindrical trays driven periodically in rotation which ensure the mixing of waste.

  The efficiency of such furnaces is much higher than that of fixed grate furnaces. However, the risks of blockage or deterioration of the grate during the incineration of organic matter must be taken into account.

  Other known organic material gasification processes employ arc electric heating in an arc furnace. In these processes, the gasification is obtained by subjecting the organic material to an electric arc, vector of very high temperatures (of the order of 3000 C or more), said electric arc being obtained by passing a current between two electrodes in an ionized gaseous medium. Currently, the use of arc furnaces is mainly found in the metallurgical industry, for example, for the elaboration of electrofusion. The implementation of this type of process for the incineration of waste still has many disadvantages, such as the erosion of refractory materials constituting the walls of the furnace.

  Finally, when the organic material is in the form of sludge, it is common to incinerate in fluidized bed furnaces. This type of oven is well suited to the incineration of industrial and urban sludge. A fluidized bed furnace is in the form of a closed vertical enclosure, of cylindrical shape, containing a bed of very hot sand (between 750 C and 850 C) kept in suspension by an updraft of air injected at its base. through a distribution grid. The waste is injected directly into the bed itself or introduced into the upper part of the oven. A flow of air ensures both the fluidization of the bed and the input required for combustion. This technique ensures a good transfer of matter and energy. However, these ovens have strict use constraints. Thus, the waste, when solid, must have a particle size of the same order of magnitude as the material constituting the bed. The high particle content requires large dusting equipment. In addition, it is formally forbidden to reach the softening point of the ash, which could lead to the setting of the fluidized bed. The gases thus produced are thus loaded with a large quantity of ash.

  All of these incineration processes described above are based on the pyrolysis of the organic materials to be gasified, which consists of subjecting the material to thermal degradation accompanied by the production of the following main elements: a carbon residue ( coke) containing the initial mineral materials; condensable gases containing heavy hydrocarbons (such as tars, oils); - incondensable combustible gases (CO, CO2r H2 ...). Combustible gases, before being used, must be separated from uncomfortable combustion products such as soot, tar or dust in suspension in the gases.

  The condensable gases as well as the carbonaceous residues can be subsequently converted into fuel gas during a steam reforming operation at high temperature (for example of the order of 900 ° C.). Pyrolysis gasification can also lead to the formation of toxic products, such as dioxins, which must be separated from the combustible gases formed, either by controlled cooling of the gases or by purification of gases on special filters.

  As is apparent from the above discussion, the gasification of the material by pyrolysis requires the setting up of complex equipment (ovens, separation units, post-treatment units, etc.) to obtain a fuel gas of quality.

  In order to overcome problems related to the formation of troublesome by-products such as tars, soot and in order to simplify gasification plants, some authors have proposed to bring the organic matter to be gasified at much higher temperatures than temperatures typically achieved in gasification furnaces. To do this, these authors have proposed to use as heating means a plasma torch in a reducing medium. However, if such heating can largely prevent the formation of tars and soot, it does not eliminate the presence of a large amount of dust in the formed fuel gases.

  For all the incineration processes described in the prior art, from an economic point of view, it is necessary to proceed to a drying of the charge to be incinerated, when it comprises a too high humidity rate . The prior drying of the organic material proves to be a particularly expensive step.

  Thus, the gasification processes of the organic material exposed in the prior art have one or more of the following disadvantages: they cause the formation of annoying by-products such as tars, soot; they do not allow maximum recovery of the energy contained in the organic matter in the form of combustible gas; - they implement complex installations; They cause a degradation over time of the reactors in which they are used; they require a drying pretreatment of the material to be gasified.

  DISCLOSURE OF THE INVENTION The object of the present invention is precisely to provide a method of manufacturing a combustible gas that makes it possible to overcome the drawbacks of the prior art, and in particular that makes it possible to obtain a combustible gas without ash. .

  The object of the present invention is to provide a method of manufacturing a fuel gas, which can be implemented in a reactor by keeping the walls thereof cold.

  The objects mentioned above are achieved by the present invention which relates to a process for preparing a combustible gas from an organic material, wherein said organic material is subjected to a medium comprising water to a thermal plasma immersed in said medium.

  In other words, the organic material included in an aqueous medium is subjected, in a gasification reactor, to a thermal plasma immersed in said aqueous medium, for a suitable time until a combustible gas is obtained.

  It is specified that the organic material may be, depending on its nature, in solution, in emulsion or in suspension in the medium comprising water.

  By combustible gas is meant, in the foregoing and the following, a gas or a mixture of combustible gas in the presence of air or oxygen. The combustible gas may be carbon monoxide, hydrogen, light hydrocarbons (methane, acetylene, etc.). It is specified that, by thermal plasma, is meant, in what precedes and what follows, a gaseous medium partially ionized conducting electricity brought to temperatures of the order of 3000 C to 14 000 C.

  Thus, thanks to this method, the fact that the heat input required for the gasification is provided by a submerged thermal plasma makes it possible to keep the reactor generally cold, except in the very localized immersed treatment zone, which makes it possible to minimize the corrosion problems encountered in the prior art, where the furnaces operated at very high average global temperatures. It is thus possible to implement the process of the invention in reactors whose walls are not made of a refractory material. By way of examples, suitable reactors for carrying out the process of the invention may be reactors whose walls are made of metal such as stainless steel, or of a polymer material / such as a material plastic or resin-based (s).

  The use of a thermal plasma as a heat source makes it possible to reach very high local temperatures, which makes it possible to avoid obtaining undesirable by-products, such as tars, as is the case. methods known from the prior art.

  Finally, the fact that gasification takes place in a submerged environment makes the treatment of the gases produced extremely simple. Indeed, the washing of the gases (such as the cleaning of the dust) is carried out in situ, by the inherent capacity of the liquid media to retain the solid particles. The very rapid quenching of the gases produced, thanks to the surrounding aqueous medium, also makes it possible to avoid the reformation of toxic products, such as dioxins.

  According to the invention, the thermal plasma used in the context of the invention may be an arc plasma, such as a non-transferred arc plasma (hereinafter referred to as blown arc plasma), or arc transferred between at least two electrodes, the two electrodes being immersed in the aqueous medium. The thermal plasma can also be an induction plasma, the induction being an alternative means to the arc to obtain a thermal plasma.

  Whether for plasma arc or induction plasma, there is always generation of a plume of plasma (or plasma flow) immersion, which will be used to manufacture the fuel gas from an organic material .

  Advantageously, the plasma flow is located generally in the center of the zone defined by the medium comprising water.

  In the case of a plasma arc or induction plasma, it is generated in the form of a plasma flow from a plasma torch immersed in the aqueous medium comprising the organic material to gasify.

  In the case of an arc plasma transferred between at least two electrodes, that is generated by the action of an electric arc between said two electrodes, on the aqueous medium, which is in this case, the plasmagene element.

  In the case of transferred arc plasma, the submerged electrodes may be either metal, such as copper or a non-metallic material, such as graphite. When the electrodes are made of a metallic material, they will advantageously be protected from oxidation by a sheathing of neutral gas, for example. The electrodes between which the plasma is produced can be fed either by a direct current or by an alternating current.

  Preferably, the current supplying the electrodes is an alternating current. It allows, when the electrodes are in a consumable material, such as graphite, to limit and evenly distribute the wear of the electrodes. Indeed, during operation, positively charged ions go to the cathode where they form a conductive deposit, while the anode is consumed by destruction of material passing in solution. When the current is alternating, the deposit is formed and destroyed alternately on each of the electrodes.

  Preferably, the medium comprising water is a stirred medium. Thus, this medium may be subjected to mechanical stirring, magnetic stirring or thermal agitation due to the natural convection generated by the localized heating induced by the submerged thermal plasma. The mechanical stirring can be obtained by means of a mechanical stirrer placed in the gasification reactor or withdrawal means, as explained below.

  Advantageously, this medium is a circulating medium.

  The process of the invention finds application in the field of the treatment of carbonaceous organic materials generated in large quantities but also in small quantities.

  The process can therefore find its application in the conversion of biomass on a small scale (for example for the supply of a combustion engine) or on a larger scale, especially when it comes to converting surplus production. sugar or dedicated biomass.

  It is specified that biomass means, in the foregoing and the following, all organic matter produced by plant and animal growth, or by human or animal activity, which can be used for the production of energy or for other purposes.

  As biomass capable of being treated by the process of the invention, mention may be made of the following organic materials: - various organic sludges (wastewater treatment plants, etc.); - agricultural waste; agricultural production (such as sugar production); - used oils; - materials based on cellulose or plastic materials; the chemical products in solution or suspension.

  These organic materials can be in the form of solutions, suspensions, emulsions.

  Other features and advantages of the invention will appear better on reading the additional description which follows, which is given of course by way of illustration and not limitation, and with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

  FIG. 1 schematically represents a gasification reactor operating with a blown arc or induction plasma (the representation being the same) for the implementation of the method of the invention.

  FIG. 2 schematically represents a gasification reactor operating with a transferred arc plasma for the implementation of the method of the invention.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Referring first to FIG. 1, which represents, in a schematic form, a gasification reactor 1 in which the method of the invention can be implemented.

  The gasification reactor 1 comprises an enclosure 3, cylindrical in shape, having a bottom wall 5, a side wall 7 and an upper wall 9, the enclosure being made of a non-refractory material.

  This reactor comprises, in its lower part, a blown arc plasma torch 11.

  Conventionally, a blown arc plasma torch comprises two electrodes, a negative called cathode and a positive called anode. The anode is pierced with a central hole serving as a nozzle for ejecting the plasma flow. A plasmagene gas is injected around the cathode, passes through the electric arc generated by passing a direct current between the two electrodes, and escapes in the form of plasma through the anode nozzle. The plasma gas may be any type of gas and in particular a neutral gas, such as argon, nitrogen, helium or a gas chosen from H2, CO, CO2, H2Og and mixtures of those -this. In the context of the invention, it can be very advantageous to recycle a portion of the combustible gas obtained at the end of the process as a plasma gas, which makes it possible to avoid the introduction of gases different from the synthesis gas and subsequent separation steps so as to remove these different gases from the synthesis gas produced.

  In the reactor shown in FIG. 1, the plasma torch is arranged so that the plasma flow or plume 13 is generally at the center of the zone defined by the aqueous medium comprising the material to be gasified. such arrangement of the torch makes it possible to maintain the reactor and in particular the enclosure thereof at a relatively low temperature. This avoids the corrosion problems encountered in the prior art in furnaces whose walls are subjected to a temperature equivalent to that required for the gasification of the material.

  The bottom wall 5 of the reactor comprises withdrawal means 17 of the liquid medium comprising the organic material to be gasified. These withdrawal means may be in the form of a conduit provided with a valve.

  These withdrawal means can operate continuously or discontinuously.

  They can fulfill several functions: they allow to purge the reactor of the liquid medium; they make it possible to ensure the circulation of this liquid medium, and thus facilitate the maintenance of a relatively low temperature in the parts, which are not in contact with the plasma flow, such as the walls of the reactor.

  On its upper wall 9, the reactor comprises means 19 for supplying the aqueous medium comprising the organic material to gasify. These supply means may be in the form of supply ducts.

  Finally, the upper wall 9 is provided with means for extracting the produced fuel gas 21, occurring under a conduit extending inside the reactor and being immersed in the aqueous medium, the submerged end 22 of the conduit being located just above the dart of the plasma flow. These extraction means make it possible to convey the gases produced to the outside of the gasification reactor.

  According to a variant shown in FIG. 2, the reactor is the one described above, with the exception of the means for generating the plasma. It is specified that the same references were used for elements identical to those of the reactor shown in FIG.

  According to this variant, the plasma generation means are constituted by a pair of electrodes 23 arranged face-to-face immersed in the aqueous medium comprising the organic material to gasify 15. This pair of electrodes 23 is connected to a source of DC or AC current not shown in the figure. An adjustment device, not shown in this figure, makes it possible to adjust the length of the electric arc. When current flows through this pair of electrodes, an electric arc is triggered and through the temperature it conveys, causes the formation of a plasma from the aqueous medium, which constitutes the plasmagenic element.

  The immersed electrodes can be advantageously mobile, in order to evenly distribute their wear. The face-to-face configuration as mentioned above is not the only possibility.

  For these two embodiments presented above, the temperatures reached in the plasma immersed in the liquid allow the reforming reactions of the organic carbonaceous materials in the presence of water, which reforming reactions result in the formation of a fuel gas essentially comprising carbon monoxide, dihydrogen, and carbon dioxide. The fact that the reaction takes place in an aqueous medium flowing through the withdrawal means 17 allows an immediate cooling of the gases as soon as they are formed and thus to avoid a reaction of reformation of troublesome byproducts such as dioxins.

  It is specified that the atmosphere of the reactors can be, during the course of the gasification, maintained under pressure, namely a pressure of up to a few bars, and this so as to be able to do without a pump usually used to put in pressure a buffer storage volume, for example, for direct use of the gas produced in an internal combustion engine.

  The gases formed escape through the extraction means 21. At the outlet of the gasification reactor or any heat exchangers, the produced fuel gases can be directly used, as required, by an internal combustion engine, by a turbine or by a burner. They can also be stored for later use.

  The invention will now be described with reference to an exemplary implementation given by way of illustration and not limitation.

EXAMPLE

  In this example, the organic material is an aqueous glucose solution having a concentration of 200 g / liter simulating a residue from the biomass.

  The gasification reactor is a cylindrical reactor having a diameter of 300 mm and a height of 400 mm.

  This reactor is provided at mid-height with a device with graphite electrodes arranged face-to-face and horizontally. This device is powered by a direct current. Means for adjusting the spacing of the electrodes make it possible to adjust the length of the electric arc.

  Above the arc establishment zone is arranged a conduit for conveying the produced gas to a sampling system.

  The reactor is filled with 10 liters of the aforementioned glucose solution.

  The arc is started by contact of the two electrodes, then the spacing makes it possible to stabilize the voltage and current parameters. The electric generator used allows regulation of the arc current.

  In this example, the electrodes were subjected to a current having a voltage of 35 volts and an intensity of 225 amps. The submerged arc plasma is approximately 5 mm in size.

  It has been measured a flow of gas produced of the order of 600 liters / hour. The gases produced contain hydrogen, CO, acetylene and also a small amount of CO2, oxygen. This gas mixture is perfectly combustible in the air.

Claims (8)

  A process for preparing a combustible gas from an organic material, wherein said organic material comprised in a medium comprising water is subjected to a thermal plasma immersed in said medium.   The process for preparing a fuel gas according to claim 1, wherein the organic material is biomass.   3. A method of preparing a fuel gas according to claim 1 or 2, wherein the thermal plasma is an arc plasma.   4. A method for preparing a fuel gas according to claim 3, wherein the arc plasma is an arc plasma transferred between at least two electrodes immersed in the medium.   The process for preparing fuel gas according to claim 3, wherein the arc plasma is a blown arc plasma.   6. Process for the preparation of fuel gas according to claim 1 or 2, wherein the thermal plasma is an induction plasma.   7. Preparation process according to any one of claims 1 to 6, wherein the medium comprising water is a circulating medium.   8. A method of preparation according to any one of claims 1 to 7, wherein the thermal plasma is generated so that the plasma flow is located generally in the center of the zone defined by the medium comprising water.