LV12095B

LV12095B - METHOD AND DEVICE FOR CHILDREN'S FLOWER TEMPERATURE CONTROL

Info

Publication number: LV12095B
Application number: LVP-98-71A
Authority: LV
Inventors: Markku Raiko; Seppo Hulkkonen; Jukka Hirvenoja
Original assignee: Imatran Voima Oy
Priority date: 1995-10-20
Filing date: 1998-04-16
Publication date: 1998-09-20
Also published as: EE9800118A; HUP9903894A3; SK48798A3; FI100064B; FI955011A; FI955011A0; PL326315A1; HUP9903894A2; EP0856129A1; WO1997015784A1; CZ117198A3; LV12095A; AU7301796A

Description

1 LV 12095

METHOD AND APPARATUS FOR CONTROLUNG THE TEMPERATURE OF THE BED OF A

BUBBLING BED BOILER

The invention relates to a method according to the pre-amble of claim 1 for controlling the bed temperature in a fluidized-bed boiler, particularly in boilers fired with coal or other fuels of high heat value but difficult to gasify.

The invention also concerns an assembly suited for imple-menting the method. A fluidized-bed boiler is a boiler structure in which the fuel is combusted and partially gasified substantially above the boiler bottom in a fluidized bed layer formed by the mixture of incombustible particulate bed material with the fuel. The bed is ķept fluid by high-velocity injection of a fluidizing gas, usually air, thereto from nozzles placed in the boiler bottom. Fluidized-bed boilers are intended for firing solid fuels, and they are particularly efficient in firing easily gasifiable fuels such as wood and peat, whereby the bed temperature can be controlled by adjusting the degree of gasification through controlled air distribution. The present invention is applicable to a bubbling fluidized-bed boiler, usually operated with two zones, the lower one being formed by an approx. 1 m high bed in which the fuel is combusted and partially gasified. The upper zone is the freeboard for postcombustion. Fuel gasified in the fluidized bed risēs up to the freeboard zone, where the fuel is combusted completely, whereby the postcombustion process is controlled by means of blowing secondary air into the postcombustion zone to ensure complete burning of the fuel. The valis of the freeboard zone are conventionally vater-cooled and heat transfer to the waterwalls occurs mainly by absorption of radiation emanating from the gases of the combustion process. 2

HEI II

The temperature within the fluidized bed is approx. 750 - 900 °C. On one hand, to avoid loss of combustion efficiency, the bed temperature must not fall too low. On the other hand, if the bed temperature is allowed to rise above a certain upper limit, sintering will occur rapidly in the bed as the melting ash binds the bed material into clumps. When burning easily gasifiable fuels, the bed temperature can be controlled by altering the flow rāte of air injected into the bed, whereby a smaller air flow favours fuel gasification to its combustion in the bed, resulting in a lower bed temperature. Then, a larger portion of the fuel is combusted in the freeboard zone. Because fuels of problematic gasification properties such as coal often cause uncontrolled temperature rise in the bed, these fuel types cannot be used as the main fuel. Problems in bed temperature control will also occur when fuel quality and boiler output vary. Therefore, coal is conventionally combusted in a circulating fluidized-bed boiler, where a portion of the bed material and fuel are returned via the boiler top part back to the bed. As this arrangement requires a cyclone or other efficient par-ticle collector to capture the circulating bed material from the flue gases, its construction becomes more expen-sive than that of conventional fluidized-bed boilers. Circulating fluidized-bed boilers are discussed in, e.g., US Pat. Nos. 5,054,436 and 4,766,851.

Conventionally, bed temperature control has been imple-mented by, e.g., altering the air coefficient through ad-justing the air feed rāte to the fluidized bed or circulating flue gases back to the boiler bottom in order to cool down the bed. In some cases, heat exchangers im-mersed in the bed have been used, whereby problems arise from their rapid erosion. From the standpoint of wear of boiler components, the bed is an extremely harsh site, the conditions in the bed varying from reducing to oxi-dizing, causing extremely strong erosion and corrosion. 3 LV 12095

Particularly, the combination of heat and the above-mentioned factors with the erosive effect of fuel and bed material circulation results in fast wear of structures located in the bed. Due to the multifaceted nature of the 5 different wear mechanisms acting in the bed, it is almost impossible to find a material for heat exchangers that would resist the combination effect of ali the above-mentioned wear mechanisms and simultaneously could offer a sufficiently high heat transfer efficiency. Use of 1ū additional air injection is hampered by the limited control range of bed temperature available thereby. While a satisfactory result of combustion parameter control can be achieved by flue gas circulation, this arrangement requires the erection of a separate circulation system. 15

It is an object of the present invention to provide a method capable of controlling the temperature of a fluid-ized bed in a superior manner with respect to the conven-tional methods described above. 20

The goal of the invention is achieved by arranging a cooling zone above the bed, but below the freeboard, and then feeding the fluidizing gas into a portion of the bed with an excess rāte per unit area, whereby over the area 25 of increased fluidizing gas injection rāte, the bed is expanded upward frora teh bubbling bed into said cooling zone, wherefrom unburned combustible material and the particulate matter of the bed can fall back in the bed. 30 In particular, the gas injection with the higher flow rāte is arranged to the center of the fluidized bed, whereby the return circulation can occur past the water-wall portions enclosing the cooling zone, thus facilitat-ing efficient heat transfer from the bed material in the form of radiation absorbed by the heat transfer surfaces of the cooling zone waterwalls. 35 4

liti VI

More specifically, the method according to the invention is characterized by what is stated in the characterizing part of olaim 1. 5 Furthermore, the asseinbly according to the invention is characterized by what is stated in the characterizing part of claim 8.

The invention offers significant benefits. 10

The invention makes it possible to combust fuels of high heat value in a fluidized-bed system without the need for expensive particulate matter collectors such as those used in circulating fluidized-bed techniques. Temperature 15 in the postcombustion zone, that is, the freeboard zone above the fluidized bed can be elevated sufficiently high thus permitting elimination of obnoxious nitrogen com-pounds such as nitrous oxide from flue gases of a normai fluidized-bed combustion process. Hence, the present 20 method is excellently suited for, e.g., converting pul-verized-coal fired boilers into fluidized-bed boilers. Without compromising a sufficient cooling rāte, installa-tion of expensive and rapidly wearing heat exchangers into the fluidized bed zone becomes unnecessary. Due to 25 the variable air injection rāte in the different zones of the fluidized bed, the combustion process parameters can be controlled easier and over a wider range by this method than by prior-art arrangements. In the high-velocity fluidization domain of the fluidized bed, oxi-30 dizing conditions are formed that facilitate. desulfuriza-tion with limestone in the same manner as in a circulating fluidized-bed boiler. With the help of secondary-air injection or circulating gas, or both, the cooling zone can be provided with a gas vortex that stabilizēs the gas flow pattern of the boiler. Resultingly, among other things, nitrogen oxides are reduced. The size of the gasification region of the fluidized bed can be made 35 5 LV 12095 smaller and the maximum temperature in the boiler lowered owing to the improved heat transfer rāte. This factor, too, contributes to easier removal of nitrogen and sulfur oxides.

In the following the invention is described in greater detail by making reference to the appended drawings in which

Figurē 1 is a schematic block diagram of a fluidized-bed boiler arrangement according to the invention; and

Figurē 2 is a more detailed illustration of the fluidized bed of the boiler arrangement according to the invention.

Referring to the diagrams, the boiler arrangement according to the invention is basically similar to that of con-ventional fluidized-bed boilers. The boiler 1 has a furnace region 1 above which is located a heat transfer region 2 in which the heat released by the combustion of the fuel is transferred by means of heat exchangers 3 into the heat conveying medium. The heat conveying medium conventionally is water which is evaporated and super-heated in the heat exchangers for use in steam turbines and other equipment. From the heat transfer region 2, the cooled flue gases are taken to the stack either directly or via cleaning equipment, depending on the need for additional cleaning. According to the present method, nitrogen and sulfur oxides can be substantially removed already in the boiler 1 during the combustion process.

The furnace region of the boiler 1 is divided into a number of zones. Lowermost in the boiler 1 are located fluidizing gas injection nozzles 4, 5, above which is maintained the fluidized bed 6. Above the fluidized bed 6 is provided a cooling zone 7 according to the invention, and above that, a freeboard 8 for postcombustion. The 6 fluidizing gas, conventionally air or flue gas or a mixture thereof, is blown to the nozzles 4, 5 by means of a fan 10 along a duct 11. The duct 11 is on its way branched into a channel 12 leading to the lateral nozzles 5 and into a channel 13 leading to the center nozzles 4. The fuel is fed into the bed via a duct 14 using a con-ventional feed arrangement. Into the region between the cooling zone 7 and the freeboard 8 are adapted secondary air nozzles 15, whose function may be complemented by additionally placing in the cooling zone 7 a return nozzle 16 for circulating flue gas or particulate matter from the region of the boiler 1 following the heat transfer region 2.

According to the invention, the fluidizing gas injection nozzles 4, 5 are divided into two domains.· In a certain domain of the boiler 1, advantageously in the center as illustrated in this embodiment, the nozzles are grouped denser than in the periphery, whereby more air will be injected centrally into the bed 6 in proportion to the greater number of the nozzles 4, 5 in the center. The amount of air to the nozzles 4, 5 may be regulated by means of control dampers 17 located in the air duets 12, 13. When both dampers 17 are fully open, the amount of air injected into the bed 6 will be determined by the numerical ratio of the center domain nozzles to the peripheral ones. If the flow rāte of air taken to the center domain nozzles 4 is regulated smaller than that taken to the peripheral domain nozzles 5 in inverted proportion to the number of nozzles in the two domains, the air flow injected into the entire area of the fluid-ized bed 6 will behave as in a conventional fluidized-bed boiler. The nozzles can be located so that, e.g., the number of nozzles is the same in the center and peripheral domains, but the area of the high-velocity fluid-ization domain is designed to be approx. 1/9 of the peripheral domain area. However, the invention must not 7 IM Ul. LV 12095 be understood to be limited by the proportion of the nozzles in the different areas of the bed.

When air is injected into the fluidized bed 6, the opera-tion of the boiler is as follows. The overali flow rāte of air injected into the fluidized bed can be regulated equal to that used in conventional fluidized-bed combus-tion, As more air is now injected into the domain of high-velocity fluidization, the bed material will therein rise up as a center pillar 9 reaching into the cooling zone 7. The cooling zone 7 is the region formed above the fluidized bed, but below the freeboard 8, whereby the height of this zone is determined by the maximum height from the top surface of the fluidized bed 6 reached by the pārticies thrown upward therefrom. In the boiler 1, this zone extends partially to the upper part of the protective lining 18 of the fluidized-bed zone 6, par-tially above that. Above the protective lining 18, the walls of the boiler according to the invention are formed into heat-transferring walls 19 cooled. with water or steam. The secondary-air nozzles 15 are located in the region of the heat-transferring walls 18.

In the fluidized bed 6 and the cooling zone, the internai circulation occurs in the fona of a center pillar rising from the Central high-velocity fluidization domain of the bed 6, whereby the pillar is formed by combustibles and gases entrained with the bed particulate matter. In that domain, where the particulate matter risēs above the bubbling bed, the air feed rāte is adjusted so that the pārticies can attain at least their termiņai velocity. In the present context, the term termiņai velocity refers to that velocity at which the particulate matter of the bed in the furnace starts rising up entrained with the upward moving gas flow. The particle size of the bed material is selected such that the pārticies can fall back in the bed without totally becoming carried up in the furnace. Thus, 8 IIIIIIJ, the bed material is forced to rise as a center pillar 9 upward and then is returned back in the bed as a reflow along the inner valis of the boiler 1, thus efficiently transferring heat by radiation to the heat-transferring wall surfaces 19 of the cooling zone. As the emittivity of the bed material is approximately three-fold in com-parison to that of furnace gases, the internai circula-tion of the bed material provides extremely efficient cooling of the bed.

The temperature in the cooling zone 7 is approx. 850 °c, while the temperature in the freeboard 8 is approx. 1100 °C. These values are only given as an example eluci-dating the operating conditions used in the invention. Obviously/ each boiler design will have different optimal temperatures for its components and operating conditions.

Secondary air required to assure complete combustion of the fuel is injected into the boiler 1 advantageously tangentially in the region of the cooling zone 7, whereby its flow will cause a corresponding vortex in the center pillar and the reflux passing down along the boiler walls. The thus induced vortical flow forces the pārticies of the refluxed bed material close to the heat-transferring surfaces 19, whereby improved heat transfer is attained. Additionally, the vortex equalizes the par-tial gas flows in the different parts of the furnace. The injection of secondary air may be complemented with injection of flue gas that also can be injected into the cooling zone when additional cooling is desired.

The method according to the invention for cooling the fluidized bed is thus based on concentrated injection of the air flow taken into the bed so that a certain domain of the bed is formed into a high-velocity fluidization area in vhich the particulate matter is ejected upvard substantially higher than the pārticies of the surround- 9 II1IIJI. LV 12095 ing bed surface. By arranging above the bed a tangential flow with the help of gas jets, which may be fed with secondary air or circulating gas, the overall gas flow in the furnace is forced into a vortical motion that conveys 5 the entrained pārticies in the gas flow to the inner walls of the boiler. Then, the lower portion of the furnace is provided in the vicinity of its water-cooled walls with a domain of dense suspension in which the fluidized bed material is cooled efficiently during its 10 downward flow. In this fashion, into the fluidized bed is formed a vigorous internai circulation in which the pārticies located in the center area of the bed are forced to rise higher and return back in the bed after being cooled in a reflux occurring close to the furnace 15 walls, thereby lowering the bed temperature particularly when fuels of high heat value are combusted. Resultingly, the bed temperature can be regulated by āltering the internai reflux circulation, whereby with an increased gas injection at the center of the bed, a higher cooling 20 effect is attained. In the above-described embodiment, the bed temperature control occurs via position adjust-ment of the dampers 17 in the air duets 12, 13.

In the method, the primary air flow through the fluidized 25 bed is ķept essentially equal to that in a typical bubbling fluidized-bed boiler. Under favourable condi-tions, the system may be deactivated, whereby fuels of high moisture content may be fired as in a conventional fluidized-bed process. Thus, the invention makes it 30 possible to fire a number of different fuels in a single boiler. As the need for the bed temperature control arises, a major portion of the injection gas is directed into the center area of the fluidized bed, simultaneously reducing the flow through the peripheral areas of the bed. However, such a minimum flow rāte of fluidizing gas must at ali times be maintained in ali parts of the bed that is sufficient to keep the bed in a fluidized State. 35 10

Besides those described above, the present invention may have alternative embodiments. In principle, the injection nozzles of the fluidizing gas could be divided into a larger number of control dūmains, but such an arrangement is hardly practical due to the complicated construction and minimal extra benefit involved. The gas being inject-ed into the separate nozzle domains may be taken using separate main duets and fans, whereby air and circulating flue gas can be mixed. The principle of the invention based on regulated injection of different amounts of air to the different domains of the bed can be implemented in varied manners. When using equal-size nozzles distributed homogeneously, the injection pressure at some nozzles may be fed with a higher pressure, whereby the air flow rāte therethrough is inereased. Alternatively, larger-diameter nozzles may be used in certain areas of the nozzle field or a higher density of nozzles can be arranged through complementing a conventional nozzle system in a certain domain with circulating gas nozzles, whereby the fluid-ized bed is operated in a conventional raanner, while the particulate matter reflux is driven with circulating gas. The cooling zone can be formed in existing boilers by adjusting the height of the fluidized bed center pillar at the lower part of the freeboard, whereby the cooling effect is accomplished via the cooled walls of the freeboard. 11 LV 12095

Claims: 1. A method of controlling the bed temperature in a bubbling fluidized-bed boiler, in which method, - upward from the bottom of a boiler (1) containing bed material is injected fluidizing gas via fluidizing gas nozzles (4, 5) in order to suspend the bed material as a fluidized layer (6) above the boiler bottom, - into the fluidized bed (6) is fed fuel which is allowed to partially gasify and combust in this bed, - the gasified fuel and emerging combustion gases are allowed to rise upward in the boiler (1) into a freeboard (8) for postcombustion, and - above the fluidized bed into the boiler (1) is injected air in order to effect complete combustion of the gasified fuel in the freeboard (8), c. haracterized in that - the fluidizing gas is injected into the boiler (1) so that the amount of injected gas per unit area is over at least one domain (4) of the area equipped with the fluidizing gas injection nozzles (4, 5) larger than on the other domains equipped with the fluidizing gas injection nozzles (5), and bed pārticies located above said domain (4) of higher gas injection rāte are given at least such a termiņai speed that makes the pārticies to rise up (9) from the fluidized bed (6) proper, - the amount and injection velocity of the fed fluidizing gas are ķept such that the higher rising 12

lllil I bed material pārticies fall back in the fluidized bed (6) after being carried to an area (5) fed with a smaller amount of the fluidizing gas, and - at least a portion of the inner wall of the boiler (1) is used as a heat exchanger over a furnace region extending from the top surface of the fluidized bed (6) up to the Ievel of the maximum rising height of bed material pārticies in order to enable heat transfer from the bed through the rising pārticies for controlling the temperature of the bed. 2. A method as defined in claim 1, character-i z e d in that a relatively larger amount of the fluidizing gas is injected through a domain located in the center of the boiler (1). 3. A method as defined in claim 1 or 2, charac-terized in that air is injected into the furnace of the boiler (1) tangentially from the inner walls of the boiler. 4. · A method as defined in claim l or 2, charac-terized in that circulating gas is fed to the furnace region remaining between the top surface of the fluidized bed (6) of the boiler (1) and the Ievel of the maximum rising height of the bed material pārticies. 5. A method as defined in claim 2, character-i z e d in that the fluidizing gas is air. 6. A method as defined in claim 2, character-i z e d in that the fluidizing gas is air and circulating gas. 7. A method as defined in any of the claims 1, 2, 5 or 6, characterized in that into the area 13

11111IIĪJ LV 12095 injected with a relatively larger amount of the fluidizing gas is fed limestone for sulfur removal. 3. An assembly for controlling the bed temperature in a fluidized-bed boiler, said assembly comprising - a boiler (1) containing bed material - fluidizing gas nozzles (4, 5) adapted to the bottom of the boiler (1) for injecting fluidizing gas into the bed material in order to suspend the bed material as a fluidized layer (6) above the boiler bottom, - means (14) for feeding fuel into the fluidized bed (6) / - a freeboard (8) for postcombustion located above the fluidized bed (6) of the boiler (1), and - at least one nozzle (15) for feeding secondary air into the freeboard (8), characterized by - means for controlling the amount of injected fluidizing gas by domains so that the amount of injected gas per unit area over at least one domain (4) of the area equipped with the fluidizing gas injection nozzles (4, 5) is larger than on the other domains equipped with the fluidizing gas injection nozzles (5), whereby bed pārticies located above said domain (4) of higher gas injection rāte are given at least such a termiņai speed that makes the pārticies to rise up (9) from the fluidized bed (6) proper, and - the particle size of the bed material is selected such that the higher rising pārticies can fall back 14 IIVI! ftl. in the bed (6) after being carried to an area (5) fed with a smaller amount of the fluidizing gas. - at least one heat transfer surface (19) formed to that furnace wall of the boiler (1) which extends from the top surface of the fluidized bed (6) up to the Ievel of the maximum rising height of bed material pārticies, for enabling heat transfer from the bed through the rising pārticies for controlling the temperature of the bed. 9. A method as defined in claim 8, character- i z e d in that said means for controlling the amount of injected fluidizing gas comprise a first nozzle domain (4) in the center of the boiler bottom and a second nozzle domain (5) in the peripheral areas of the boiler bottom and that the density of the nozzles per unit area in the centra! domain of high-velccity fluidization is relatively larger than in the peripheral domain of low-velocity fluidization. 10. A method as defined in claim 8, character- i z e d in that said means for controlling the amount of injected fluidizing gas comprise a first nozzle domain (4) in the center of the boiler bottom and a second nozzle domain (5) in the peripheral areas of the boiler bottom and that the gas injection flow rāte through the nozzles per unit area in the Central domain of high-velocity fluidization is relatively larger than in the peripheral domain of low-velocity fluidization. 11. A method as defined in claim 8, character-i z e d in that said means for controlling the amount of injected fluidizing gas comprise a first nozzle domain (4) in the Central high-velocity fluidization area of the boiler bottom and a second nozzle domain (5) in the peripheral areas of the boiler bottom, additionally IIII111; LV 12095 15 complemented with means for regulating the pressure of the gas fed to the nozzles. 12. A method as defined in any of foregoing claims 5 8-12, characterized in that the nozzles for feeding secondary air are adapted to the boiler (1) tangentially approximately to the Ievel of the irtaximum rising height of the bed material pārticies. 10 13. A method as defined in any of foregoing claims 8-12, characterized in that at least one nozzle (16) for feeding circulating gas is adapted to the boiler (1) in the region between the top surface of the fluidized bed (6) and the Ievel of the maximum rising height of the bed material pārticies. 15

Claims

A method for controlling the temperature of a layer of bubbling fluidized bed boilers, wherein - upstream of the bottom of the boiler (1) containing layer material, pseudo-liquefied gas is bubbled through the nozzles (4, 5) to suspend the layer material as a boiling layer (6) above the bottom of the boiler, - in the boiling layer (6), to introduce fuel that can be partially gasified and burned in this layer, - to the gasified fuel and fuel gases to rise up in the coolant zone (8) of the boiler (1) for further combustion, and - above the boiling layer Boilers (1) blowing air to promote complete combustion of gasified fuel in the coolant zone (8), characterized in that - the pseudo-liquefied gas is inflated by the boiler (1) so that the amount of gas injected per unit area above the supply area of at least one of the pseudo-liquefied gas nozzles the places (4) are larger than the others with the pseudo the atomised gas supply nozzles (5) are provided with at least one end velocity that causes the particles to rise (9) from the fluidized bed (6) in the required manner, to the sites and layer particles disposed above said largest gas feed point (4); the amount of injected pseudo-liquefied gas and the rate of injection is maintained such that the particles of the above-elevated layer material fall back into the boiling layer (6) and at least a portion of the inner wall of the boiler (1) after being fed into the area (5) of the pseudo-liquefied gas. over the furnace area, which stretched from the top of the surface of the fluidized bed (6) up to the maximum elevation height of the bed material particles, is used as a heat exchanger, allowing the heat to pass from the layer through the raised particles to regulate the temperature of the layer.

Method according to claim 1, characterized in that a relatively larger amount of pseudo-liquefied gas is introduced through a site located in the center of the boiler (1).

3. A method according to claim 1 or 2, characterized in that the air is blown into the boiler (1) tangentially from the internal walls of the boiler.

4. A method according to claim 1 or 2, characterized in that the circulating gas is supplied to the area of the furnace which remains between the top of the surface of the boiling layer (6) of the boiler (1) and the level of the maximum rise height of the bed material particles.

5. A method according to claim 2, wherein the pseudo-liquefied gas is air.

6. A method according to claim 2, wherein the pseudo-liquefied gas is air and circulating gas.

7. A method according to claim 1, 2, 5 or 6, characterized in that limestone is introduced into the area with a relatively large amount of pseudo-liquefied gas to remove sulfur.

8. A device for controlling the temperature of a layer of a boiler in a fluidized bed, said device comprising: - a boiler (1) comprising a layer of material, a pseudo-liquefied gas nozzle (4, 5) adapted to the bottom of the boiler (1) for introducing the pseudo-liquefied gas into the layer material, suspending the layer material as a boiling layer (6) above the bottom of the boiler, - means (14) for introducing fuel into the boiling layer (6), - for further combustion of the super-cooling zone (8) located above the boiling layer (6) of the boiler (1), and - comprising at least one nozzle (15) for supplying secondary air in the supercooling zone (8), comprising: means for adjusting the amount of injected pseudo-liquefied gas at the site locations so that the amount of gas injected per unit area above at least one of the pseudo-liquefied gas supply nozzles (4) (5) The areas of the supplied area (4) are larger than those of the other with pseudo-liquefied gas the supply nozzles (5) are provided at locations that result in at least the end velocity of the layer particles located above said largest velocity gas supply site (4), which causes the particles to rise up (9) from the fluidized bed (6) in the desired manner and - the particle size of the layer material is chosen such that the raised particles can fall back into the layer (6) after being introduced into the area (5) to which the smaller amount of pseudo-liquefied gas is supplied, - at least one heat transfer surface (19) is formed at its boiler (1) the walls of the furnace extending from the top of the surface of the fluidized bed (6) up to the level of maximum elevation of the particles of the layer material, allowing the heat to pass from the layer through upwardly raised particles to regulate the temperature of the layer.

Method according to claim 8, characterized in that said means for controlling the amount of injected pseudo-liquefied gas comprises a first nozzle location (4) at the center of the boiler bottom and a second nozzle location (5) in the peripheral area of the boiler bottom, and that nozzle density on the area the highest velocity pseudo-liquefaction of the units at the central site is relatively larger than the lower speed pseudo-liquefaction at the peripheral site.

10. A method according to claim 8, characterized in that said means for adjusting the amount of pseudo-liquefied gas introduced comprises a first nozzle location (4) in the center of the bottom of the boiler and a second nozzle location (5) in the peripheral zone of the boiler bottom, and that the gas supply flow the velocity through the nozzles to the unit at the central velocity of the highest velocity pseudo-dilution is relatively higher than the lower velocity pseudo-dilution peripheral.

11. The method of claim 8, wherein said injected pseudo-liquefied gas volume adjusting means comprises a first nozzle location (4) in the central high speed pseudo-dilution zone of the boiler bottom, and a second nozzle location (5) in the peripheral zone of the boiler bottom for addition. with means for regulating the gas supply pressure on the nozzles.

A process according to any one of claims 8 to 12. , characterized in that the secondary air supply nozzles are mounted tangentially to the boiler (1), at a level of maximum elevation of the particles of the layer material.

A method according to any one of claims 8 to 12. characterized in that at least one circulating gas supply nozzle is mounted on the boiler (1) in the area between the top of the surface of the fluidized bed (6) and the level of the maximum rise height of the bed material particles.