FI89074C - FOER REFRIGERATION FOER FOERGASNING ELLER FOERBRAENNING AV FAST KOLHALTIGT MATERIAL - Google Patents

Description

1 89074

METHOD AND APPARATUS FOR THE GASIFICATION OR COMBUSTION OF SOLID CARBONATED MATERIAL

FARRING REQUIREMENTS FOR THE PRODUCTION OF ELECTRIC EQUIPMENT FOR FOLLOWING MATERIAL 5

The present invention relates to a process for gasifying or burning a carbonaceous substance in a Lei jet jet reactor, the reactor chamber of which produces gases from combustion or gasification to one or more gas purification steps separating ash and residual coal-containing fine dust, followed by separated fine dust. at least a portion of the ash contained in the fine dust is melted at an elevated temperature in the presence of an oxygen-containing gas and from which the fine dust containing molten ash is further passed through a return passage to the reactor chamber.

The invention also relates to an apparatus for gasifying or burning a solid carbonaceous substance in a Lei jet reactor, comprising - a reactor chamber and an associated carbonaceous material inlet, a fluidizing gas supply means and a degassing duct, - a particle separator for separating fine dust from a melt introduced into it to melt the ash contained in the fine dust separated in the particle separator, and - a return duct for returning the fine dust from the ash fume chamber to the reactor chamber.

The invention is particularly suitable for use in the gasification or combustion of solid carbonaceous material in circulating jet reactors which maintain such a high gas flow rate that a substantial portion of solid particles exits the gas-driven reactor chamber. solid particles into the reactor chamber. From the particle separator, the gases are further passed to a second gas cleaning stage, in which fine dust, ash and non-combustible carbon, which cannot be separated by the particle separator, are separated from the gas.

There are several different methods for gasifying carbonaceous solid fuels, the most important of which are 10 different gasifiers based on the fluidized bed principle. A problem in all carburetor solutions, as well as in fluidized bed carburetors, is to achieve a very high carbon conversion. This problem is accentuated when gasifying poorly reactive fuels such as coal. Achieving high carbon conversion with finely divided fuel such as milled peat is also difficult.

Poor carbon conversion is basically due to the relatively low reaction temperature of fluidized bed 20 carburetors, which is limited by the melting temperature of the fuel ash. By increasing the gasification reaction time, i.e. by returning the escaped unreacted fuel back to the reactor, the carbon conversion can be significantly increased.

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The circulating fluidized bed gasifier or boiler has such a high upward gas flow rate that a large amount of solid bed material rises out of the reactor with the product or flue gases. Most of this effluent bed material is separated from the gas in separators and returned to the reactor. The finest fraction leaves with the gas. In the reactor, the circulating mass is ash, coke and any other solid introduced, such as lime, which acts as a catalyst for the desired reactions.

However, the resolution of separators normally used in fluidized bed reactors, such as cyclones, is limited for small 3,69074 particles. Normally, hot cyclones can only separate particles in the size range of 50-100 pm, and the finer fractions tend to escape with the gases. Since the unreacted fuel leaving the reactor with the gas is mainly coke, from which the volatile (reactive) parts have already been removed, it would require a longer lag time in the reactor when returned to the reactor than the "fresh" fuel itself. However, due to the fine grain size of the recovered coke, the recovered fine fraction immediately flies out again out of the reactor chamber, leaving the reaction time too short and the carbon conversion low. The grain size of the coke decreases continuously during the process, increasing the dust emission from the cyclone, leading to low carbon conversion.

15 Using new ceramic filters, even small coke particles can be separated from the gases, but new problems are encountered. Solid fuels always contain ash, which must be removed from the system when producing pure gas. This should be done in such a way that large amounts of unreacted carbon are not removed with the ash in order to achieve the highest possible carbon conversion. However, the grain size distribution of the ash is always quite wide, and the fine ash tends to fly out of the reactor with a fine coke residue.

Achieving high carbon conversion therefore requires solving the following twofold problem: 30 1. It must also be possible to separate fine dust from the gases and return them to the reactor.

2. The carbon in the recovered dust must be reacted and the ash separated from the system.

However, efforts have been made to solve the problem satisfactorily without success.

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Also in boiler plants, fluidized bed combustion, fly ash tends to be easily transported by non-combustible carbon, especially when low reactive fuel is used or when the boiler plant is operated with a low load 5 or when the load is at its maximum. Fly ash may contain more than 10% carbon, up to 20%, which degrades boiler efficiency. It is known that returning fly ash back to the furnace would give a lower carbon content in the fly ash and thus better efficiency in the boiler.

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Fly ash is also a problematic product in itself. For example, in the USA, only 20% of fly ash is used in the construction industry and road construction. End-of-life storage causes problems for power plants. Fly ash is a rather light substance with a bulk density of 15, so that the disposal of the ash requires quite a large space. This has become a problem in densely populated areas. In addition, it should be noted that the ash must be stored so that it does not come into contact with groundwater. The problem of fly ash-20 has been exacerbated by the recent introduction of ammonia for flue gas cleaning. Ammonia-treated fly ash is not suitable for the concrete industry.

Since the combustion temperatures in fluidized bed boilers are clearly lower than in e.g. dust combustion boilers, the properties of the ash are completely different. The ash from such low temperature incineration is not stable but can, under suitable conditions, release gaseous, liquid or dusty emissions into its environment.

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U.S. Patent No. 4,315,758 discloses a method and apparatus for solving a problem. In this process, the finest gas-separated dust is returned to the bottom of the reactor so that oxygen-containing gas is introduced to this same point in the reactor so that a high temperature zone is formed where the fine, recovered dust agglomerates with the granules in the fluidized bed. This method presents an improvement in the so-called U-gas Process method.

British Patent 6B 2065162 discloses a method and apparatus in which fines separated from a gas are directed to the top of a fluidized bed, where fine dust agglomerates into particles contained in the fluidized bed when said. oxygen-containing gas is introduced into the reactor.

10 There is a clear problem with process control in both of these methods. Both methods aim to agglomerate the separated fines into a fluidized bed characterized by very good heat and mass transfer properties. Since it is of paramount importance for the main process itself to be able to operate at the optimum temperature for it, the main process is easily disturbed when the temperature required for agglomeration in the reactor chamber is different from that required for the main process. Due to the good heat transfer in the fluidized bed, the temperatures tend to level off-20, resulting in new problems. On the one hand, the temperature in the fluidized bed tends to fall below the optimal agglomeration temperature at the agglomeration site, on the other hand, the temperature of the entire fluidized bed tends to rise above the optimal temperature of the main process.

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In addition, because the fluidized bed contains particles of very different grain sizes, it is difficult to control agglomeration in the reactor so that the formation of too large ash agglomerates could be prevented. The sticky ash 30 adheres to both large and small bed particles, resulting in the formation of too large ash agglomerates, making ash removal difficult or impeded, and the gasification process having to be interrupted. In addition, agglomeration in the reactor itself causes local overheating, which easily wears away.

U.S. Pat. No. 3,874,566 discloses a solution for high carbon efficiency by burning 6,89074 fines escaping from a carburetor in a separate incinerator in which the heat released from the combustion is used to heat a coarser carbonaceous pulp from the fluidized bed reactor to the reactor. In this way, by heating the bed material outside the fluidized bed, the heat required for gasification is generated. The gases released from combustion and gasification, flue gas and product gas, have to be removed from the system in two separate processes 10, each with a separate gas cleaning equipment. The solutions presented in the method thus lead to quite complex hardware solutions and also to a process that is difficult to control.

The problem with the presented methods is thus the difficult process conditions in which the above-mentioned agglomeration conditions have to be controlled. This requires expensive materials and cooled constructions.

One way to improve carbon conversion without the aforementioned disadvantages is disclosed in U.S. Patent No. 4,929,255, which discloses agglomeration of fine dust separated in a circulating fluidized bed reactor at an elevated temperature to circulating bed material 25 prior to reacting the solid particles.

It is an object of the present invention to provide a simple method and apparatus solution for improving carbon conversion.

It is also an object of the invention to provide a method and apparatus by which fine carbonaceous dust 35 separated from product or flue gases can be optimally returned to the reactor in such a form that the carbon contained in the dust can be utilized and the ash separated from the process.

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It is a further object to provide a method and apparatus for gasifying or burning a solid carbonaceous substance in which the above-mentioned process control disadvantages are minimized.

5

The method according to the invention for gasifying or burning a solid carbonaceous substance in a fluidized bed reactor, in which fine dust separated from the exhaust gases is heated in an ash heating chamber and returned to the reactor chamber via a return duct 10, is characterized by introducing a cooling gas or liquid.

Correspondingly, the device according to the invention for gasifying or burning a carbonaceous substance in a fluidized bed reactor is characterized in that means for supplying a cooling gas or liquid to the return duct are arranged in the return duct leading from the separate ash heating chamber to the reactor chamber.

Cooling is preferably provided by passing a cooling gas or liquid into the return duct through its walls, thereby forming a protective gas or liquid film on the walls which prevents the molten ash from adhering to the walls. The coolant can be passed through the walls, e.g. through openings formed therein, or by forming at least a part of the return channel of a gas- or liquid-permeable porous material.

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In the ash heating chamber, the temperature of the fine dust is raised to more than 1000 ° C, preferably 1000 to 1300 ° C / by introducing an oxygen-containing gas into the dust stream and burning the residual carbon contained in the dust. If necessary, other fuel can be burned during heating. Thus, at least a portion of the ash contained in the fine dust forms sticky dust particles which are agglomerated, i.e. granulated, before being returned to the reactor chamber.

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The ash heating chamber can advantageously be formed as an uncooled structure with a dust outlet at the bottom so that the molten ash formed in the chamber flows by gravity from the chamber directly to the return pipe, where the melt droplets are cooled by mixing cooling gas or liquid.

The granulation and recovery of fine dust according to the invention is particularly suitable for use in fluidized bed reactors in which a particle flow of 2 to 10 m / s, a temperature of 750 to 1000 ° C and a gas pressure of 1 to 50 bar are maintained.

For example, the gasification in a circulating fluidized bed reactor differs in some respects substantially from the gasification in a conventional bubbling fluidized bed reactor. In the circulating jet reactor, the upward flow rate of the gas is so high that a large amount of solid petima material rises with the gases to the top of the reactor and out of the reactor 20, to which it is returned after gas separation. In this reactor, important reactions between gases and solids take place throughout the reactor, with a suspension density of 0.5 to 30 kg / kg of gas, most commonly 2 to 10 kg / kg of gas, even at the top of the reactor. In the bubbling fluidized bed, where the gas flow rates are typically only 0.4-2 m / s and the suspension densities at the top of the reactor about 10-100 times lower than in the fluidized bed reactor, the gas / solid reactions, on the other hand, mainly take place only in the bottom of the reactor.

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The coarse solids entrained in the reactor chamber are separated in the reactor separator and returned, at least for the most part, directly in the return pipe as untreated circulating mass 35 to the reactor chamber. Thereafter, in the second stage, mainly finer carbonaceous dust is separated from the gases leaving the first separator, e.g. as a filter, of which at least a part of the fine dust is returned to the reactor chamber agglomerated at an elevated temperature according to the invention.

The agglomeration increases the grain size of the fine dust so much that the dust delay time in the reactor increases and the carbon conversion improves. If the grain size of the recovered dust is increased to a sufficient size, the ash particles can be removed from the reactor at an optimal stage, whereby the carbon contained in the ash granule has reacted almost completely.

10

By agglomerating the dust outside the actual Lei bed reactor, where the size of the largest particles circulating is considerably smaller than the size of the largest particles floating in the reactor itself, the formation of too large particles is avoided, which could leave the reactor with the ash without reacting completely.

In processes where it is more advantageous the higher the temperature at which the gases can be purified, the fine dusts can be separated using a series of cyclones, cyclone batteries or high temperature resistant filters or the like which are also capable of separating hot particles.

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On the other hand, in combination with a combined cycle power plant process, for example, it is advantageous to use the produced hot gas at a pressure of 1-50 bar to superheat the steam and to purify the produced gas from fine dust only after the gas has reached a lower temperature, e.g. 850 ° C. In this case, gas cleaning is also easier to carry out. At lower temperatures, fine, difficult-to-separate fumes are no longer present in the gas to a detrimental extent, which easily clogs the pores of, for example, ceramic filters. In addition, hot fumes are chemically very aggressive and place high demands on materials. The method according to the invention is thus very well suited for combined cycle power plant applications, because the carbon conversion of the fuel is high, the gas produced is 8,89074 clean and suitable for gas turbines, and in addition the overall energy economy can be improved by superheating steam.

The advantages of the method according to the invention are e.g. the following: - The method achieves a high degree of carbon conversion.

- Agglomeration of fine coal can be carried out in a controlled manner without disturbing the process conditions in the carburettor or boiler.

10 - When using the circulating fluidized bed principle, the reactor section can be constructed with a clearly smaller cross-section than when using the so-called bubbling fluidized bed reactor.

- Due to the smaller cross-section and better mixing conditions, the need for fuel supply and ash removal devices is substantially less than the so-called in the case of a bubbling bed.

- The binding of the sulfur contained in the fuel to the cheap lime can be carried out in the process.

- The reactions between the solid and the gases take place in the entire area of the reactor section and the separator.

- The devices shown do not require expensive special materials.

- Since the different process steps, e.g. gasification and agglomeration, are performed in different devices, it is possible to make the process control 25 optimal for the overall result.

- The ash can be removed inert.

- Fly ash storage problems are reduced.

The invention will now be described in more detail with reference to the figures, which show two embodiments of the invention.

Figure 1 is a schematic diagram of a gasification device according to the invention and Figure 2 is a schematic diagram of a combustion device according to the invention.

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The gasification plant 10 shown in Fig. 1 comprises a circulating fluidized bed reactor chamber 12, a circulating mass separator 14, a circulating mass return pipe 16 and a fine dust agglomeration device 18. At the bottom of the reactor chamber 28.

The circulating mass separator is connected to the upper part of the reactor chamber by an outlet duct 30. The separator is in the form shown in the figure a so-called flow cyclone, but other types of separators are suitable for use. The bottom 32 of the flow-through cyclone is oblique and the lower part of the bottom is connected to the circulating mass return pipe 16. A gas-15 outlet pipe 34 is arranged in the bottom of the separator.

The fine dust agglomeration device 18 comprises a cylindrical ash heating chamber 36 arranged on the side of the reactor chamber, which is formed as an uncooled structure 20, e.g. of a ceramic material or a masonry structure. A fine dust supply connection 38, an oxygen-containing gas supply connection 40 and possibly an additional fuel supply connection 42 are arranged in the upper part of the chamber. The connections 38, 40 and 42 can be arranged elsewhere in the chamber, if desired. An opening 44 is formed in the lower part of the ash heating chamber, which is connected to the return duct 46, which in turn is connected to the reactor chamber.

The walls 48 of the return channel 46 are formed of a gas and / or liquid permeable porous material. The material can be e.g. porous collected. If a liquid, e.g. water, is used as the cooling medium, the walls of the return duct can also be formed of metal in which openings have been formed. A gas-tight housing 50 is arranged around the return duct, into which a coolant inlet connection 52 is arranged.

The gasification plant according to the invention operates in such a way that a second carbonaceous solid to be gasified is fed to the reactor chamber via a joint 26 and the substance is fluidized by a fluidizing gas flowing through the distribution plate 22, which may be e.g. air, the fluidizing gas also forming a gasification medium. In the reactor chamber, the temperature 5 is maintained at about 750 to 1000 ° C.

A high particle flow rate of e.g. 2-10 m / s is maintained in the reactor chamber, whereby part of the bedding material contained in the chamber travels with the gas 30 through the channel 10 to the separator 14. The bedding material comprises e.g. inert bedding material, ash, coke and any gas cleaning reagents. In the separator, the coarse solid is separated from the gas and returned in a return pipe 16 to the lower part of the reactor chamber. The structure of the reactor chamber 15 and the separator are preferably internally masonry structures. The hot gases and the small amount of dust they contain, which typically accounts for about 0.1 to 2% of the solids stream from the reactor chamber, are passed through line 34 to a potential heat recovery unit.

20

Partially purified and possibly cooled gases contain both ash harmful to further processes and non-combustible carbon. This so-called fly ash is separated from the gas by filters or other separators capable of separating 25 also fine dust. This is not shown in Figure 1. The gas thus purified is led to the application.

The separated fine dust is passed to an agglomerator 18 to granulate the ash to a more suitable grain size and recycle the residual carbon 30. The dust is fed by a feed connection 38 to an ash heating chamber 36, to which at the same time oxygen-containing gas is fed together by 40 to provide combustion and heating.

Additional fuel may be introduced into chamber 36 via line 42 if the recovered fine dust does not contain the necessary amount of carbon to provide an elevated temperature. This additional fuel can be, for example, 13,89074 carbonaceous substances to be gasified in the carburetor. Gas produced in gasification can also be used as additional fuel in the ash heating chamber.

5 Since the amount of fine dust is substantially smaller than the total amount of bed material and since only the temperature of the fine dust is raised in the agglomerator, it is possible to recover the fine dust in a controlled manner without disturbing the main process itself in the reactor chamber. Thus, by agerating Agglo-10 fine dust outside the reactor chamber, the agglomeration temperature can be freely selected according to the ash, without adversely affecting the gasification process in the boiler. In contrast, the temperature of the reactor chamber can rarely be adjusted to suit the agglomeration in the reactor chamber without adversely affecting the gasification process.

The molten fly ash from the ash heating chamber solidifies as it mixes with the colder cooling gas or liquid-20 and forms hard and dense, coarse particles, typically 2 to 20 mm in size. The ash agglomerated ash is fed into the reactor chamber through an opening 45 arranged in its wall 47. The coarse ash granules can be separated in the reactor chamber together with the normal bottom ash 25 out of the ash removal pipe 28.

Figure 2 shows a combustion plant in which carbonaceous fuel is burned in a fluidized bed reactor and the fly ash is returned agglomerated to 30 reactors according to the invention. In Figure 2, the same reference numerals as in Figure 1 have been used, where applicable.

The combustion plant according to Figure 2 comprises a reactor chamber 12, in which the fuel 35 fed to it by means of 26 is burned in a circulating fluidized bed. The reactor chamber is preferably formed as a water tube wall structure 13, and heat transfer surfaces 15 are further arranged in the upper part of the chamber. Coarse particles are separated from the gases leaving the reactor chamber in a separator 14 and gases 14 are fed 14 to a heat exchanger 52 to cool the gas. The cooled gas is passed to a filter 54 where the fly ash is separated from the gas. The gases cleaned from the filter are discharged from the system by a common 56.

5

The fly ash separated in the filtrate is led by a connection 38 to an ash heating chamber 36, where the addition of oxygen-containing gas from the connection 40 causes at least partial melting of the ash. The chamber 36 is formed as a masonry structure 10.

Molten ash and other fine dust flow down from the ash heating chamber to the return passage 46, the walls 48 of which are provided with openings 49 for conducting coolant from the housing 50 surrounding the return passage. A pressurized coolant is introduced into the housing by the connection 52. The coolant may be, for example, purified circulating gas from the connection 56 or another inert gas whose temperature is low enough to cool the gas. The coolant 20 may also be a liquid, e.g. water, which is injected through the openings 49 into the molten ash.

The ash to be agglomerated is thus heated by oxidizing the ash carbon residue or other additional fuel, e.g. the fuel used by the incinerator, in a separate chamber, preferably arranged on the side of the actual reactor chamber. In some applications, even all of the fuel can be introduced into the boiler through the agglomerator and the temperature in the agglomerator can be controlled by the amount of oxygen-containing gas 30. The ash melted in the chamber is cooled and granulated before being dropped into the reactor, e.g. with a gas or liquid film which enters the chamber, e.g. through a wall made of porous ceramic material.

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If desired, the ash heating chamber according to the invention can be used as a starting burner, in which case additional liquid or gaseous fuel is burned in the chamber under oxidizing conditions. Hot flue gases raise the temperature of the actual reactor chamber.

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The invention is not intended to be limited to the carburetor or incinerator shown as application example 5. The invention can be applied, for example, in such gasification reactors in which oxygen-containing gas is not used to effect gasification, but in which the temperature of the substance to be gasified is raised in some other way.

Claims (21)

A process for gasifying or burning a solid carbonaceous substance in a fluidized bed reactor, wherein - the carbonaceous substance is fed to and gasified or combusted in a fluidized bed reactor chamber, - the gases from gasification or combustion are passed from the reactor chamber to one or more degassing steps; carbon-containing fine dust, - the separated fine dust is passed to an ash heating chamber in which at least part of the ash contained in the fine dust is melted at an elevated temperature in the presence of oxygen-containing gas, 20 liquid melts to cool and granulate dust containing ash. A method according to claim 1, characterized in that the cooling gas or liquid is introduced as a gas or liquid film to the walls of the return duct. A method according to claim 2, characterized in that the cooling gas or liquid is introduced into the return duct through its porous walls. A method according to claim 2, characterized in that the cooling gas or liquid is introduced into the return duct through openings formed in its walls. n 89074 A method according to claim 1, characterized in that the fine dust containing molten ash is led from the uncooled ash heating chamber through an outlet 5 formed in its lower part to a return duct arranged below the ash heating chamber, from which the dust is allowed to drain into the reactor chamber by gravity. Process according to Claim 1, characterized in that the solid carbonaceous substance is gasified in a circulating fluidized bed reactor. Process according to Claim 1, characterized in that the solid carbonaceous substance is combusted in a circulating fluidized bed reactor. A method according to claim 1, characterized in that an oxygen-containing gas is introduced into the ash heating chamber for at least partial combustion of the residual coal contained in the fine dust and for at least partial melting of the ash. 25 Method according to Claim 8, characterized in that air is introduced into the ash heating chamber. A method according to claim 1, characterized in that the solid carbonaceous fuel which is gasified or combusted in the reactor chamber is introduced into the ash heating chamber. 35 A method according to claim 1, characterized in that the temperature of the fine dust, i.e. 89074, is raised to more than 1000eC in the ash heating chamber. Method according to Claim 1, characterized in that the purified and cooled flue gas generated in the fluidized-bed reactor is introduced into the return duct. A method according to claim 1, characterized in that the gas coming from the reactor chamber is cooled before the fine dust is separated from the gas. Process according to Claim 1, characterized in that - the solid carbonaceous substance is gasified or combusted in a circulating fluidized bed reactor, the reactor chamber of which maintains a particle flow rate of 2 to 10 m / s and a temperature of 750 to 1100 ° C and a gas pressure of 1 to 50 Bart; most of the coarse solids entrained by the gases leaving the reactor chamber are separated from the gases in the separator and returned untreated to the reactor chamber, - in the second step the fine dust is separated as a filter and the fine dust separated as a filter is passed to the ash heating chamber. An apparatus for gasifying or combusting a solid carbonaceous substance 30 in a fluidized bed reactor, comprising - a reactor chamber (12) and an associated carbonaceous material inlet (26), fluidizing gas supply means (24) and a degassing channel (30) for separating fine dust from a particle separator (14) gases, 19 89074 for at least partially melting the ash contained in the fine dust separated in the particle separator from the ash heating chamber (36) and returning the fine dust from the 5 ash heating chambers to the reactor chamber, characterized in that the return duct is provided with means (48.49) to direct the liquid into the return channel. 10 Device according to Claim 15, characterized in that the return duct (46) is formed at least in part by a porous material through which the cooling gas can be introduced into the return duct. Device according to Claim 15, characterized in that openings are formed in the walls of the return duct (46) through which cooling gas can be introduced into the return duct. Device according to Claim 15, characterized in that the ash heating chamber (36) is formed as an uncooled structure and in which oxygen-containing gas supply means (40) are arranged. Apparatus according to claim 15, characterized in that the fluidized bed reactor (12) is a circulating fluidized bed reactor, in which a separator for separating bed material from gases leaving the reactor chamber is connected to the reactor chamber degassing channel and a bed material return pipe (16) is connected to the separator. 20 89074 Device according to Claim 15, characterized in that the ash heating chamber is a substantially cylindrical chamber formed of ceramic material or in the form of a masonry structure, the upper part of which is provided with fine dust and oxygen-containing gas supply means (38, 40) and the lower part of which is connected to porous ceramic material. made return pipe. 21 89074