AU6980496A - Fluidized bed lime kiln - Google Patents

Description

ΗTLE : FLUIDIZED BED LIME KILN

Field of the Invention

This invention relates to the cooling and recovery of heat from finely divided solid product, and to an apparatus for continuously reacting or treating finely divided solids with an incoming gas in a fluidized bed which is able to cool and recover heat from product streams.

Solid gas chemical reactions are customarily conducted in shaft furnaces, kilns or mechanically stirred furnaces. Such reactors have disadvantages associated with the particle size-reaction velocity relationship as well as temperature-corrosive atmosphere relationships. Some of these problems have been overcome by the use of fluid-bed reactors. Background of the Invention

In a fluidized bed reactor, a bed of solid particles is treated or reacted with a fluidizing gas supplied under pressure through a wind box which supports the bed in a state of fluidization above the gas distribution means. From the wind box, the gases rise into a reaction chamber receiving a continuous supply of the material to be treated, while the solids and gaseous reaction products are continuously removed.

The behaviour, appearance and physical characteristics ofthe bed of fluidized material are comparable to those of a body of boiling liquid, the specific gravity of which depends on the density at which the bed is maintained by the up-flowing fluidizing gas.

The spent hot gases resulting from the chemical reaction or other fluidizing treatment operation, with entrained dust particles blown from the bed, escape through the gas outlet of the reactor unit where the dust particles are usually trapped in a gas solid separator such as a cyclone.

Depending on the volume of the reaction and the solid product, the product is taken off above the wind box and gas distribution means, or in the case of a solid product having a higher specific gravity than the raw materials, the solid product may be permitted to fall pass the gas distribution means and collected under the wind box.

In many applications, the fluidized bed reactor usually operates at high temperatures and so the outgoing reaction gas and solid product have a large amount of sensible heat which can be recovered and used to improve the energy efficiency of the operation.

Furthermore, if the recovered heat is used to preheat reactants before entering the reaction chamber, greater energy efficiencies can be achieved. Brief Summary of the Invention

It is an object of the invention to provide an apparatus to cool and recover heat from finely divided solid product and an apparatus for continuously reacting or treating finely divided solids in which the heat of the outgoing products is effectively utilized.

In one aspect of the invention there is provided an apparatus for reacting a finely divided solid in a fluidized bed including a fluidized bed reactor having an upright outer housing, a gas distribution arrangement dividing the housing into a fluidized bed reaction chamber above the gas distribution arrangement and a wind box and product chamber below, said gas distribution arrangement being adapted to support a bed of fluidized finely divided solid for at least partial reaction of said solid, a supply means for feeding the raw finely divided solid to said fluidized bed chamber, a gas inlet for supplying fluidizing gas to the gas distribution arrangement, a product cooler extraction system, beneath said gas distribution arrangement into which product cascades towards a product hopper a gas outlet for discharging spent fluidizing gases from the reactor housing, and a raw materials preheater to preheat the solid finely divided raw material by heat exchange with a portion of the spent fluidizing gas and a recuperater for preheating the fluidizing gas by indirect heat exchange with the remainder of the spent fluidizing gas.

In a preferred form of the invention, the spent fluidizing gases from the gas outlet in the reaction housing pass to a gas solid separation means such as a cyclone to remove fine solid product entrained in the spent fluidizing gas. After the gas- solid separator, the spent gas stream may then be split into a solids preheater stream and a gas preheater stream.

The apparatus of the invention is able to utilize heat from the spent fluidizing gas by direct heat exchange with the solid raw materials before these materials are charged to the fluidized bed. Additionally, the spent fluidizing gas is used to preheat the incoming fluidizing gas by indirect heat exchange. At least a potion of the incoming fluidizing gas may be further preheated by heat exchange with the solid product in the product cooler extractor system.

The raw material preheater may include a chamber having an inlet and outlet for spent fluidizing gas and a plurality of conduits extending into said chamber, the spent fluidizing gas directly and indirectly transferring heat to raw materials passing through the conduits.

It is preferable that the raw material which passes through the preheater be nonvolatile.

The plurality of conduits may be in the form of hoppers extending into said preheat chambers. The solids preheater gas stream preferably circulates around said hoppers for indirect heat exchange with said finely divided raw material before contacting the raw materials for direct heat exchange.

The hoppers are preferably shaped to cause some hold up of the raw material and thereby increase the residence times in the hoppers. The hoppers are preferably in the shape of an inverted truncated pyramid or pyramids.

In one form of the invention, each hopper includes at least two converging ducts preferably in the form of inverted truncated pyramid shaped ducts, one duct being supported within the other, said ducts being arranged to provide flow channels between said ducts for the gas stream to flow into said hoppers and contact the raw material passing therethrough.

In another aspect of the invention there is provided a solid product cooler/extractor for solid product said cooler/extractor including a top plate having a plurality of apertures arranged in rows and a bottom plate having a plurality of apertures arranged in rows, each row of apertures in the bottom plate being aligned with a row of apertures in the top plate, the apertures in the bottom plate being displaced from the apertures in the top plate, at least one apertured beam between the top and bottom plates, said apertured beam reciprocating between a first and second position, the apertures of the beam being aligned with at least one row of apertures in the top plate when the apertured beam is in the first position, and the apertures of the beam being aligned with at least one row of apertures in the bottom plate when the apertured beam is in the second position, such that when the apertured beam is in the first position, solid product passes through the apertures in the top plate into chambers defined within the apertured beam below each aperture, said apertured beam reciprocating to the second position to enable the solid product to pass through the aperture in the bottom plate.

To extract solid finely divided product using the product extraction system, the apertured beam is in the first position such that the apertures of the top plate correspond with the apertures of the beam. The solid particles pass through the top plate into the apertures of the beam. The beam then moves to its second position where the apertures of the beam correspond with the apertures in the bottom plate and the solid product is able to fall from the apertures in the beam to a product collection bin.

Further included is at least one gas plenum adjacent the at least one apertured beam having a gas inlet connected to a gas source and a gas outlet the at least one gas plenum being positioned below and communicating with a row of apertures in the top plate above the plenum.

The gas plenum is able to not only provide a means of cooling the product by indirect heat exchange between the gas in the plenum and the solid product in the apertured beam, and on the top plate but also provides a means to reduce blockages occurring in the apertures in the top plate.

The gas pressure in the plenum must be sufficient to prevent product from falling through the apertures in the top plate into the plenum and also prevents the build up of large particles around the apertures above the adjacent apertured beam.

Preferably there are a plurality of apertured beams and a plurality of plenum chambers alternately positioned between the top and bottom plate beneath coπesponding rows of apertures in the top plate. The plurality of beams and plenum may be arranged such that each beam has a plenum on either side.

The product cooler/extraction system of this aspect of the invention may be incorporated into the continuously operating fluidized bed apparatus to cool and extract heat from product of the fluidization chamber.

Brief Description of the Drawings

Figure 1 is a sectional elevational view of a fluidized bed apparatus in accordance with the invention,

Figure 2 is an enlarged sectional view of the upper section of the apparatus shown in Figure 1 along line 2-2,

Figure 3 is an enlarged sectional view of the lower section of the apparatus shown in Figure 1,

Figure 4 is a sectional view through line 4-4 of Figure 2,

Figure 5 is a sectional view of the bubble cap through line 5-5 of Figure 3,

Figure 6 is a sectional view through line 6-6 of Figure 5,

Figure 7 is a sectional view through line 7-7 of Figure 6,

Figure 8 is a sectional view through line 8-8 of Figure 3,

Figure 9 is a cut-away plan view of an extractor plate shown in Figure 8,

Figure 10 is a sectional view through line 10-10 of Figure 9,

Figure 11 is a sectional view through line 11-11 of Figure 9,

Figure 12 is a sectional view through line 12-12 of Figure 9,

Figure 13 is a sectional view through line 13-13 of Figure 9,

Figure 14 is a cut-away perspective view of an extraction plate shown in

Figure 8, and

Figure 15 is an enlarged sectional view of the upper section of the apparatus shown in Figure 1 along line 2-2 showing an alternative embodiment of raw materials preheater.

Referring to Figure 1, a fluidized bed apparatus 1 in accordance with the invention is shown comprising a raw materials preheater 2 which receives nonvolatile raw materials from a conveyor 3. When volatile solids are being fed to the apparatus, the feed is diverted prior to the preheater into storage hoppers 4 on either side of the apparatus. The flow of solid is controlled from the hopper by a screw conveyor which supplies the solid via conduit 5.

When nonvolatile solids are supplied, these solids pass by the solids diverter 9 into a solid raw material preheater 2 where the solids are preheated by heat exchange with outgoing process gases. In the raw material preheater 2, the nonvolatile raw material stream is fed through a plurality of conduits 10 to raw material preheat hoppers 11 where the solids are retained for a short period of time. The inlet to the conduits or hoppers are preferably wider than the exit to encourage hold-up in the hoppers. Preferably the hoppers are in the shape of inverted truncated pyramids or cones. The hoppers feed solids onto a conveyor 12 which supplies nonvolatile solids to conduit 13. The volatile solids conduit 5 joins with nonvolatile solids conduit 13 to combine the two solids streams before being injected into the fluidized bed chamber 7 within the outer upright housing 8 with air supplied by blower 6 through duct 6a.

The refractory lined upright outer housing 2 is divided by a gas distribution arrangement 14 into a fluidized bed chamber 7 above the gas distribution arrangement and a product chamber 17 below. The housing 2 has a gas inlet duct 15 for supplying fluidizing gas to the gas distribution arrangement 14 and a gas outlet duct for discharging spent fluidizing gases from the housing 2. The gas distribution arrangement 14 continuously supplies fluidizing gas to the fluidized bed chamber 7 to fluidize the solids in the fluidized bed.

As the reaction between the solids and fluidizing gas in the fluidized bed approaches completion, the solids increase in density, migrate to the bottom of the bed and eventually cascade through the gas distribution arrangement 14 towards a product cooler/extraction system in product chamber 17.

The spent fluidizing gas is preferably passed to a gas solids separator 18 such as a cyclone separator to remove fine particles entrained in the gas stream. The resulting gas stream is then split into a solids preheater gas stream and a recuperater waste gas stream. The solids preheater gas stream passes via a duct 19 into the raw materials preheater 2 for heat exchange with the incoming raw materials after which the gas is then exhausted to the atmosphere through duct 20.

The recuperater waste gas stream passes via duct 21 to a recuperater where the waste gas stream exchanges heat with the incoming fluidizing gas entering the recuperater by duct 24 by direct heat exchange. The incoming fluidizing gas then passes via a duct 23 to the gas inlet 25 in the upright housing 2 and the outgoing waste gas is exhausted through duct 25.

The product cascades through gas distribution arrangement 14 into a product cooler/extractor 30. A stream of gas from a separate positive displacement blower may be fed to the product cooler/extractor 30 for direct heat exchange with the solid product. The blower provides air at a known volumetric rate and the volume of gas flowing through the solid product is regulated by controlling the gas flow flowing from the outlet of the cooler/extractor through a control valve (not shown).

The product is then removed from beneath the product cooler/extractor into a product hopper 31. The product is removed from the product hopper by a conveyor 32 to storage.

Referring to Figure 2, finely divided volatile and nonvolatile solids are fed to the apparatus by conveyor 3 into solids inlet 40. The volatile solids are periodically fed to the apparatus 1 and diverted by solids diverter 9 down conduits 41 into volatile solids hoppers 4.

When the volatile solids hoppers are not being replenished, nonvolatile solids are allowed to move past solids diverter 9 into nonvolatile solids chamber 42. The nonvolatile solids then pass through a plurality of conduits 10 into a preheat chamber 43 of the raw materials preheater 2. The preheater 2 is preferably refractory lined to reduce heat loss through the walls of the preheat chamber 43.

The preheat chamber 43 is supplied with spent fluidizing gas through inlet 44 fed by duct 19. Due to the high temperature of the spent fluidizing gas, the inner surface of the preheat chamber 43 is preferably formed from stainless steel.

The solids in conduits 10 fall into a plurality of preheat hoppers 11 preferably formed of stainless steel. Figure 4 is a plan view of one of the hoppers showing cross supports Ila. The cross supports Ila, act as flow retarders to slow the progress of the finely divided nonvolatile solids through the preheat chamber 43 of the preheater. The solids falling from the conduits 10 into hoppers 11 contact the gas entering through inlet 44 and undergo direct heat exchange with the gas to heat - 8 - the solids. After a short residence time in the hoppers where the solids undergo indirect heat exchange through the hopper walls with the incoming preheater gas, the solids then pass from hoppers 11 to conveyor 12 which is preferably a screw conveyor to feed the preheated nonvolatile solids to conduits 13.

Figure 15 shows an alternative embodiment of preheater hoppers in preheat chamber 43a. In the embodiment shown in Figure 15, each hoppers 60 are formed from at least two converging ducts 61, 62 preferably in the shape of inverted truncated pyramids.

First duct 61 is supported within the second duct 62 by a number of spaced support members 63 extending in the direction from the entrance to the exit of the hopper 60. These support members define flow channels 64 between the first and second ducts for the passage of preheat gas into the hopper for contact and direct heat exchange with the raw materials. The preheater gas then flows out of the solids entrance of the hopper into the upper region of preheat chamber 43 before being discharged through conduit 20.

As in the embodiment of Figure 2, solids enter the preheat chamber through conduits 10 into the preheat hoppers 60. The hoppers 60 which optionally may be formed with flow retarders to hold-up the flow of the finely divided non-volatile raw materials through the hoppers to increase the residence time in the hoppers 60 and the preheat chamber 43a.

The solid raw material contacts the gas in the upper region of the preheat chamber 43a and the gas exiting the hoppers for direct heat exchange therewith. Within the hopper the solids contact gas flowing into the hopper through flow channels 64 and is help up in the second duct 62 where indirect heat exchange with the incoming preheater gas through the hopper wall occurs.

While the invention has been described with reference to only two converging ducts, it would be appreciated by those skilled in the art that the hoppers 60 may include more than two converging ducts supported to provide flow channels at a number of levels where the ducts overlap.

By providing hoppers formed by at least two converging ducts, forming flow channels hoppers 60 at the level where the ducts overlap, a greater contact time O 97/12188 PC17AU96/00606

- 9 - between the gas and solids is provided for direct heat exchange.

Volatile solids in conduit 6 are mixed with preheated nonvolatile solids in conduit 13 before being fed into fluidized bed chamber 7. The solids are fluidized by fluidizing gas from gas distribution aπangement 14. As shown in Figure 5, the gas distribution aπangement preferably includes a plurality of gas distribution beam 30 equally spaced across the fluidized bed chamber 7, each beam traversing substantially the width of the chamber 7. Each gas distribution beam 50 consists of two substantially vertical sides 51 and two ends 52 defining a space therebetween. The bottom end 54 of the space 53 communicates with a wind box 55 which provides fluidizing gas to the gas distribution beams 50. The top end of defined space 53 is provided with a bubble cap 56 and is provided with apertures 57 for the discharge of fluidizing gas. As the gas departs the gas distribution beam 50 is preferably provided with a swirling motion which imparts the necessary fluidizing motion to the finely divided solids in the fluidized bed chamber.

Figure 7 shows a cross sectional view of one of the bubble caps illustrating the apertures for the fluidizing gas spaced along wall 51 of the gas distribution beam 50.

In Figure 5, eleven gas distribution beams 50 are shown connected to a wind box 55 which is supplied with fluidizing gas by duct 15.

The gas distribution aπangement is particularly suitable for reacting or treating finely divided raw materials which have a lower density than the finally reacted product of the reaction or treatment. Accordingly, the velocity of the fluidizing gas should be sufficient to maintain the raw materials in a fluidized state but not high enough to maintain the final product in a fluidized state. Consequently, once the solid product approaches complete reaction, the solid migrates to the bottom of the bed and eventually cascades between the gas distribution beams 50.

The solid then falls to a product cooler/extractor 30. The preferred embodiment of the cooler/extractor 30 is shown in Figures 8 to 14.

Two similarly constructed cooler/extractors 30 are shown mounted on a framework 305. Each cooler/extractor includes a top plate 303 and a bottom plate 304. A plurality of apertures 301, 302 are arranged in rows on the top plate 303. The bottom plate is also provided with a plurality of apertures 306 aπanged in rows and aπanged such that each row apertures in the bottom plate 304 is aπanged below a row of apertures in the top plate 303. The apertures within each row of apertures in the bottom plate 304 are displaced longitudinally from the apertures 302 in the coπesponding row in the top plate 303 such that the apertures within each row of the bottom plate 304 are not aligned with the apertures 302 in the coπesponding row in the top plate 303.

Preferably the spacing between each of the apertures 306 in the rows in the bottom plate 304 is the same and substantially the same as the spacing between the apertures 302 in the coπesponding row of the top plate 303. At least one apertured beam 307 is provided between the top and bottom plates 303, 304 respectively. The at least one apertured beam 307 extends beneath a row of apertures 302 in the top plate 303 and above a row of apertures 306 in the bottom plate and reciprocates between two positions. The apertures in the at least one beam 307 are spaced substantially the same distance apart as the apertures 302 in the top plate and in an embodiment (not shown) may be separated by spacers which define chambers in said at least one beam 307.

In the first position of the at least one apertured beam 307, the apertures of the beam aligned with at least one row of apertures in the top plate. Solid product passes through the apertures 302 in the top plate and through the apertures of the at least one apertured beam 307.

In the second position of the apertured beam 307, the apertures of the beam are not aligned with the apertures in the top plate and the shear forces created by the movement of the reciprocating beam 307 from the first to the second position causes the solid product to move along the bottom plate and fall through apertures 312 in the bottom plate into a product hopper 31. Alternatively, the apertured beam may have a plurality of transverse bars which separate the channel of the apertured beam into a number of product chambers. Thus, with the movement of the apertured beam from the first position to the second, the product is urged towards the apertures in the bottom plate 304. The cooler/extractor 30 may further include at least one gas plenum chamber adjacent the at least one apertured beam 307 having a gas inlet 309 connected to a gas source (not shown) and a gas outlet 310. The at least one gas plenum chamber is positioned below and communicates with a row of apertures 301 in the top plate 303.

Gas entering is able to flow through the plenum chamber, exiting the plenum through apertures 301 and gas outlet 310. The gas pressure in the gas plenum chamber must be sufficient so that gas exiting through the apertures 301 prevents product falling through the top plate 303 into the plenum. The top plate 303 is provided with caps 311 which cover apertures 301 and has apertures directing the flow of gas from apertures 301 towards apertures 302.

In the embodiment shown, a plurality of apertured beams and a plurality of plenums are provided alternately positioned between the top and bottom plate beneath rows of apertures 302, 301 respectively in the top plate. The plurality of beams and plurality of plenum may be aπanged such that each beam has a plenum on either side.

Since product can only pass the extractor by moving through the apertures 302 in the top plate, apertures 306 in the beam 307 and apertures 312 in the bottom plate, the gas diverters or caps 311 direct the gas from the plurality of plenum chambers towards the exiting apertures 302 for the product. The flow of gas is able to cool the solid product by direct heat exchange and if travelling at a sufficient velocity is able to prevent and clear blockages in exit apertures 302 caused by agglomerated or oversized product.

Once the product falls from the apertures 312 in the bottom plate 304, it is directed by product hopper 31 towards a conveyor such as a screw conveyor 32.

The above described apparatus is particularly useful for the production of lime. In the production of lime (calcium oxide), a finely divided calcareous material and a finely divided carbonaceous material are mixed under conditions such that combustion of the carbonaceous material occurs and the calcareous material decomposes. An excess of air is provided to ensure that complete combustion of the carbonaceous material occurs. In most commercial operations, the calcareous material is limestone and the carbonaceous material is coal preferably with a low ash content.

To operate the apparatus in accordance with the invention, it is preferable for the limestone and coal to be finely divided and in particles of 16 millimeters or less.

To maximise the efficiency of the reaction, it is desirable to preheat the nonvolatile solids (limestone) as much as possible prior to introduction into the reaction chamber. To avoid premature combustion of finely divided volatile solids (coal) only limited heating of these solids is prefeπed prior to being fed to the reaction chamber.

Fluidizing gas which is preferably air enters the fluidized bed chamber 7 through the gas distribution beams 50 and supports the fluidized bed where the carbonaceous material undergoes complete combustion and the calcareous material decomposes to lime. The temperature in the fluidized bed chamber is generally in the range of 920°C to 960°C. The temperature in the fluidized bed chamber is preferably maintained within the desired temperature range by varying the feed rate of limestone to the chamber while maintaining a substantially constant coal feed rate. The apparatus of the invention is particularly suited to the production of 50 to 90 tones per day of lime from limestone and coal. While the apparatus is running, the production rate of lime is preferably varied within that range by varying the feed rate of coal to the fluidized bed chamber. This causes an increase in heat and temperature to the bed thereby requiring an increase in the limestone feed rate to utilize the increased heat and maintain the bed temperature within the operating range. In this way the reaction rate of lime production is increased. Fluidizing air is supplied to the fluidized bed chamber 7 in excess quantities to ensure complete combustion of the coal.

The product, calcium oxide, settles towards the bottom of the fluidized bed chamber and eventually cascades through the gas distribution arrangement 14 as material is removed through the product cooler/extractor 30 due to the reciprocating action of beams 306.

Spent fluidized air rises to the top of the fluidized bed 7 and is removed from the housing by duct 16. The hot spent gas then enters a gas solids separator 18 which is preferably a cyclone separator where fine product particles entrained in the spent gas stream are separated. The fine product is then taken off as fine product stream 26.

The hot spent gas stream leaving the separator is then split with one stream passing through duct 19 to the preheater 2 and the other stream passing to a recuperater 22 through duct 21. The recuperater is essentially a U-shaped gas/gas shell-in-tube heat exchanger in which the hot spent gases pass through the tube side and the fresh fluidizing air supplied by a source such as a fan (not shown) passes on the shell side.

In the recuperater 22, sensible heat from the spent gases is transfeπed to the incoming fluidizing gas.

The hot spent gases entering the preheater through duct 19 exchange heat with the incoming finely divided limestone by direct contact before being exhausted through duct 20.

At the product cooler/extractor 30 in accordance with the invention, a stream of air is supplied to the air inlet 309 of the plurality of plenum chambers 308. This stream may be from a separate source of air.

The gas passes along the plenum chamber 308 and exits through outlet 310 or through apertures 301. The gas exiting through apertures 301 is diverted by gas diverters or caps 311 towards the apertures 302 through which solid product passes. Since there is preferably a plenum chamber on either side of each reciprocating beam 306, the product in the vicinity of apertures 302 are contacted by gas from at least two directions. The gas in the plenum chamber 308 initially undergoes indirect heat exchange with hot product in the adjacent reciprocating beam and then mixes with the solid product once it leaves aperture 301. This results in the solid product being cooled and the heated gases moving counter cuπent to the solid product to be used in the fluidizing chamber.

Since the reaction in the fluidizing chamber requires excess air to ensure complete combustion of the coal, the energy required to heat the air is reduced further improving the energy efficiency of the process.

The gases from apertures 301 also clear and reduce the occuπence of - 14 - blockages caused by solid product agglomerating in apertures 302.

The reciprocating beam which may be a flat bar has apertures 306a equally spaced along its length, the spacing between the apertures being substantially identical to the spacing between the apertures 302 in the top place 303. Apertures 312 in the bottom plate are aπanged in rows aligned with rows of apertures 302 in the top plate. The position of the apertures in each row in the bottom plate is offset or laterally displaced from the coπesponding apertures 302 in the top plate.

When the apertures 306a in the beam are aligned with those in the top plate 302, solid product falls through the apertures in the top plate and into the apertures of the reciprocating beam 306. Transverse bars (not shown) may be provided to form a number of product chambers with the reciprocating beam. The reciprocating motion of the beam 306 moves the solid towards apertures 312 in the bottom plate 304. The solid product then falls through the bottom of the beam, through the apertures in the bottom plate into product hopper 31 which loads the product onto screw conveyor 32.

The solid product is then removed from the apparatus for storage. The above described apparatus in accordance with the invention has an improved energy efficiency compared to apparatus for reacting or treating solid particles with gas at relatively high temperatures. The apparatus of the invention is able to efficiently recover heat from not only the solid product stream but also the waste gas streams by preheating raw materials and gases prior to entering the fluidized bed chamber.

Claims (22)

CJLΔIMS

1. An apparatus for reacting a finely divided solid in a fluidized bed including a fluidized bed reactor having an upright outer housing, a gas distribution aπangement dividing the housing into a fluidized bed reaction chamber above the gas distribution aπangement and a wind box and product chamber below, said gas distribution arrangement being adapted to support a bed of fluidized finely divided solid for at least partial reaction of said solid, a supply means for feeding the raw finely divided solid to said fluidized bed chamber, a gas inlet for supplying fluidizing gas to the gas distribution aπangement, a product cooler extraction system, beneath said gas distribution aπangement into which product cascades towards a product hopper a gas outlet for discharging spent fluidizing gases from the reactor housing, and a raw materials preheater to preheat the solid finely divided raw material by heat exchange with a portion of the spent fluidizing gas and a recuperater for preheating the fluidizing gas by indirect heat exchange with the remainder of the spent fluidizing gas.

2. The apparatus according to claim 1 wherein the spent fluidizing gases from the gas outlet of the reactor housing passes to a gas solid separation means to remove fine solid product entrained in the spent fluidizing gas.

3. The apparatus according to claim 2 wherein the spent gas stream exiting said gas solid separation means is split into a solids preheater stream and a gas preheater stream.

4. The apparatus according to claim 3 wherein said raw materials preheater includes a preheat chamber, a plurality of conduits extending into said chamber, said conduits being for the passage of raw materials through said preheat chamber, a gas inlet for introducing said solids preheater gas stream and a gas outlet, said solids preheater gas stream contacting the finely divided raw material passing through said conduits for indirect heat exchange before being discharged through the gas outlet.

5. The apparatus according to claim 4 wherein the preheater hoppers are shaped to ensure that there is hold-up of the solid raw material passing therethrough.

6. The apparatus according to claim 5 wherein each preheat hopper includes at least two converging ducts, a first duct being supported with a second duct to provide flow channels between said ducts.

7. The apparatus according to claim 6 wherein gas said preheater circulates around said second duct before entering said hoppers through said flow channels for direct heat exchange with the solid raw material.

8. The apparatus according to claim 4 wherein the finely divided raw material exiting the raw materials preheater is fed to the fluidized bed reactor.

9. The apparatus according to claim 1 wherein the gas distribution aπangement includes a plurality of parallel spaced gas distribution beams extending across the reactor housing and connected to a wind box supplied with fluidizing gas, each of said gas distribution beams having a bubble cap to introduce fluidizing gas into the fluidized bed reactor and impart a fluidizing motion to the gas.

10. The apparatus according to claim 1 wherein the raw material supplied to raw material preheater is a nonvolatile solid.

11. The apparatus according to claim 10 wherein the finely divided nonvolatile material is a calcarious material containing at least limestone.

12. The apparatus according to claim 11 wherein a separate supply conduit is provided to supply finely divided volatile material to the fluidized bed reactor.

13. The apparatus according to claim 12 wherein the finely divided volatile material is a carbonaceous material including at least coal.

14. The apparatus according to claim 13 wherein the volatile solid and the nonvolatile solid are mixed prior to being introduced into the fluidized bed reactor.

15. The apparatus according to claim 1 further including a solid product cooler/extractor for solid product which has cascaded through the gas distribution aπangement into the product chamber, said cooler/extractor including a top plate having a plurality of apertures aπanged in rows and a bottom plate having a plurality of apertures aπanged in rows, each row of apertures in the bottom plate being aligned with a row of apertures in the top plate, the apertures in the bottom plate being displaced firom the apertures in the top plate, at least one apertured beam between the top and bottom plates, said apertured beam reciprocating between a first and second position, the apertures of the beam being aligned with at least one row of apertures in the top plate when the apertured beam is in the first position, and the apertures of the beam being aligned with at least one row of apertures in the bottom plate when the apertured beam is in the second position, such that when the apertured beam is in the first position, solid product passes through the apertures in the top plate into chambers defined within the apertured beam below each aperture, said apertured beam reciprocating to the second position to enable the solid product to pass through the aperture in the bottom plate.

16. The apparatus according to claim 15 wherein the product cooler/extractor system further includes at least one gas plenum adjacent to the at least one apertured beam having a gas inlet connected to a gas source and a gas outlet, the at least one gas plenum being positioned below and communicating with a row of apertures in the top plate above the plenum.

17. The apparatus according to claim 16 wherein the gas pressure in the plenum is sufficient to prevent finely divided solid falling through the apertures in the top plate above the plenum and also prevents the build up of solid around the apertures above the adjacent apertured beam.

18. The apparatus according to claim 17 wherein there are a plurality of apertured beams and a plurality of gas plenum chambers alternately positioned between the top and bottom plate beneath coπesponding rows of apertures in the top plate, the plurality of beams and gas plenum are arranged such that each beam is adjacent a gas plenum.

19. A solid product cooler/extractor for solid product said cooler/extractor including a top plate having a plurality of apertures arranged in rows and a bottom plate having a plurality of apertures arranged in rows, each row of apertures in the bottom plate being aligned with a row of apertures in the top plate, the apertures in the bottom plate being displaced from the apertures in the top plate, at least one apertured beam between the top and bottom plates, said apertured beam reciprocating between a first and second position, the apertures of the beam being aligned with at least one row of apertures in the top plate when the apertured beam is in the first position, and the apertures of the beam being aligned with at least one row of apertures in the bottom plate when the apertured beam is in the second position, such that when the apertured beam is in the first position, solid product passes through the apertures in the top plate into chambers defined within the apertured beam below each aperture, said apertured beam reciprocating to the second position to enable the solid product to pass through the aperture in the bottom plate.

20. The apparatus according to claim 19 wherein the product cooler/extractor system further includes at least one gas plenum adjacent to the at least one apertured beam having a gas inlet connected to a gas source and a gas outlet, the at least one gas plenum being positioned below and communicating with a row of apertures in the top plate above the plenum.

21. The apparatus according to claim 20 wherein the gas pressure in the plenum is sufficient to prevent finely divided solid falling through the apertures in the top plate above the plenum and also prevents the build up of solid around the apertures above the adjacent apertured beam.

22. The apparatus according to claim 21 wherein there are a plurality of apertured beams and a plurality of gas plenum chambers alternately positioned between the top and bottom plate beneath coπesponding rows of apertures in the top plate, the plurality of beams and gas plenum are aπanged such that each beam is adjacent a gas plenum.