CA2091654A1

CA2091654A1 - Process and apparatus for cooling hot solids in a fluidized bed

Info

Publication number: CA2091654A1
Application number: CA002091654A
Authority: CA
Inventors: Michael Stroder; Johannes Albrecht; Klaus Janssen; Wladislaw Lewandowski; Hansjobst Hirschfelder
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1992-04-24
Filing date: 1993-03-15
Publication date: 1993-10-25
Also published as: SK282384B6; EP0567167B1; SK36093A3; JP3358632B2; FI107641B; CZ288550B6; CZ65993A3; HU9301202D0; EP0567167A1; HUT65400A; FI931845A; DE4213475A1; ES2092744T3; FI931845A0; JPH0626613A; DE59304075D1

Abstract

ABSTRACT
Hot granular solids are cooled in a fluidized bed under a pressure from 2 to 50 bars. The fluidized bed is dis-posed in a cooling chamber, which is provided with an inlet for solids and an outlet far solids. The solids move in the fluidized bed mainly in a vertical direction from the inlet for solids to the outlet for solids. Fluidizing gas is intro-duced into the lower portion of the fluidized bed end heat is indirectly dissipated by cooling means, which are flown through by a cooling fluid. The cooling means extend over at least one-half of the height of the fluidized bed. The flui-dized bed has a bed height from 2 to 20 meters and a ratio of bed height to average bed width from 2:1 to 10:1. The diffe-rence between the temperatures of the solids in the lower and upper portion of the fluidized bed is at least 80°C. The fluidized bed has preferably a bed height of at least 3 meters.

Description

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This invention relate~ to a procesa of coollng hot granular solids under a pres3ure from 2 to 50 bars in 8 fluidlzed bed, whlch i9 disposed in a coollng chamber provided with an inlet for solids and an outlet for solid~ and in which the solids move mainly in a vertical direction from the inlet for solids dispo3ed at one end of the fluldized bed through the tluldized bed to the outlet for ~olld~ dl~po~ed at the oppoalte eno of the fluldlzed bed, ~luldlzlng ga~es sre ln-troduced lnto the lower portion of the fluidized bed and heat i8 lndlrectly dlssipated by cooling means, ~hich are flown through by a cooling ~luid and extend over at least one-half of the height of the fluidized bed. The invention relates also to an apparatus ~or carrying out that process. The coollng mean~ may be disposed ln and/or surround the fluidized bed.
A process and an apparatus of that klnd, whlch are gultable al90 for an operatlon under increased pressure, are known from E~-A-0,407,730. It 19 an obJect of the inventlon so to improve the process and the apparatus that the structu-ral and operating costs are decisively reduced. It 18 parti-cularly desired to effect an intense cooling of the eolids and to reduce the demand for fluldizing gases.

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In the process desc~bed first hereinbefore the obJect ~ 5 accomplished ln accordance with the lnventlon ln that the ~luldlzed bed has a bed height from 2 to 20 me-ters, the ratio of the bed height ta the average bed wldth 19 between 2:1 and 10:1, the cooling fluid flo~s cocurrently or countercurrently to the sol~ds movlng from the inlet for solids to the outlet for solids, and the difference between the temperatures of the ~olids in the lower and upper por-tiongs of the fluidized bed is at least 80~0. The fluidizedbed is maintained under a superatmospheric pressure and i~
dlsposed in a tall and slender cooling chamber so that the 9paCe i9 effectlvely utlllzed and the demand for fluidlzlng gaoes 19 low. ~eo~u~e the sollds are constralned to ~low ~rom the lnlet through the Fluldized bed to the outlet, the ~avor-able condltlons exlstlng ln the fluldlzed bed for the dlssl-patlon of heat result ln the establishment of a distlnct tem-perature profile ln the fluldized bed. The same fluidized state 19 achieved as ln a statlonary fluldlzed bed.
Fluidized bed coolers which opsrate under atmos-pheric conditlons or under pressures below 2 bars can be ope-rated only with lo~ beds o~ing to a disturblng coalescence of bubbles. The process in accordance ~ith the lnventlon ~9 car-rled out under a pressure from 2 to 50 bars and preferably of at least 5 bars and the bed bo~ a helght of at least 2 meters and preferably of at lea~t 3 meter~ 90 that the b~se area un~
der the flu~dlzed bed and the demand for fluldizing gas are minimized.

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In the process in accordance wlth the lnventlon the ratlo of the bed helght to the average bed wldth i9 from 2:1 to 10:1 and preferably amounts to at least 3:1. The ave-r~ge bed width is calculated aa the mean of the large~t and smallest wldths measured on a horlzontal plane that extend~
through the fluldlzed bed, unle~s the croas-sectlon is clr-cular. If the cross-~ectlon of the bed varles over the height of ~he bed, the average bed wldth wlll be the mean of average vslues of various bed cross-sectlons, which extend through the fluidlzed bed on dlfferent levels spaced, e.g., 50 cm spQrt.
In dependence on the locatlons of the lnlet for sollds and the outlet for sollds the sollds to be cooled wlll be constralned to rise or descend ln the fluidized bed and an intense mixing of the solids ln the vertlcsl direction cannot be expected 90 that the temperature of tne solids varies ac-cording to a profile over the height of the bed. For thi3 resson the cooling fluid, which flows upwardly or downwardly in lines of the cooling.means in the fluidized bed, may be caused to flow consistently countercurrently or cocurrently to the solids. Particularly during a countercurrent operation this fact will result in a strong heat transfer from the so-llda to the cooling fluid. Advantage~ will be afforded by a cocurrent operatlon if it i9 desired to qulckly cool the ao-llds immedlately after they have entered the fluldlzed bed or lf the solids rise and it 19 deslred to evaporate the cooling fluid.

., The cooling fluid msy con~ist of a liquid or of a fluld ln the form of a gas or vapor. Suitable known coDling llqulds lnclude, e.g., water, oil9 or molten ~alts. The heat moy alternatlvely be dls~ipated, e.g., by water vapor or by various gaoes (such as nltrogen).
The hot sollds are supplied at temperatures from about 300 to 1200C, u3ually at temperatures in the range from 400 to 1000~. In the fluidlzed bed formed ln accordance wlth the lnventlon the dlfference between the temperatures of the sollds ln the upper and lower portlons of the fluldlzed bed may amount to 150C and more.
In the tall fluldlzed bed havlng a small cross-sectlonal area which 19 provlded ln accord~nce wlth the in-ventlon the dem~nd for fluldlzlng gases 19 relatlvely low.
300 to 750Q sm3 (sm~ standard cublc meter) o~ fluldlzing gases per cublc meter of the fluldlzed bed volume snd per hour wlll be sufflclent.
A dl t f th embodiment f th 1 tl the hot sollds are lnltlally precooled ln a precedlng fluldlzed bed dl~posed ln a precedlng aecond cooling chamber, ln whlch the sollds move also from an lnlet for sollds at one end of the second coollng chamber malnly ln a vertlcal dlrectlon through the precedlng fluldlzed bed to an outlet for sollds at the opposlte end of the second coollng chamber. Approxlmstely the same pressure 19 maintalned ln the precedlng fluidlzing chamber as in the succeedlng fluldlzed bed. In the precedlng .. ,., , . . ., .. ,~ .. i.. - .! ... .... .

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fluldized bed, heat is also indlrectly dissipated by caoling mesnsf which are flown through by a cooling fluld and whlch extend over at least one-half 1~ the height o~ the preceding fluidized bed. The bed height of the preceding fluidized bed 19 ln the range from 2 to 20 meters ~nd preferably amounts to st least 3 meters. The ratio of the bed helght to the average bed width of the precedlng fluidized bed is from 2:1 to 10:1 and preferably amaunts to at least 3:1. In the preceding flui-dlzed hed the cooling fluld i9 al90 caused to flow cocurrently or countercurrently to the solids moving from the inlet for solids to the outlet for solids, and the difference between the temperstures in the lower and upper partions of the pre-ceding fluidized bed is at le0~t ~0C and prefersbly ln excess of 200C. The solids which hcve been precooled in the preced-lng fluidized bed move from the outlet for slids directly to the lnlet for sollds assoclated wtih the succeedlng fluidized bed, in which the cooling i9 continued.
The salids preferably movedgwtwerednYthe 1 1 t f sollds and the outlet for sollds in the preceding fluidized bed and rise during the contlnued cooling ln the succeedlng fluldlzed bed to the outlet for sollds assoclated wlth the fluidized bed.
The inventlon provldes also to an apparatua for cooling hot granular solids under a pressure from 2 to 50 bars ln a cooling chamber, whlch contalnR a fluidlzed bed formed by the solids and i9 provided with an inlet for solids and an outlet for sollds and contains cooling means for indlrectly cooling the solid~ and i9 provided in its lower portion with means for supplying fluidizing gases. The cooling chamber i9 de31gned to accommodate a fluldized bed having a bed height from 2 to Z0 meters and a ratlo of the bed height to the average bed width ~rom 2:1 to 10:1.
embodiment A ~urther of so~d cooling spparatus re-sides in that the cooling chamber (first coollng chamber) i8 preceded by a second cooling chamber, which has an inlet for aolids and an outlet ~or sollds, whlch iB cannected to the inlet for sollds associated with the fIrst cooling chamber.
Embodiments of the process and appa-ratus will be explained with reference to the drswing, in which Figure 1 is a schematlc longltudinal sectional view showing a first cooling apparatus, Figure Z is a longitudinal sectlonal view showlng a second coallng apparatus, Figure 3 is a graph lndlcatlng the demand for fluldlzlng gas, and Figure 4 19 a longitudlnal sectlonal vlew showlng a known fluldlzed bed cooler.
The apparatus shown ln Flgure 1 comprlses a tall and slender cooling chamber 1, whlch is provided with an ln-let 2 for solids and an outlet 3 ~or solids. During operation the cooling chamber 1 contalns a fluidized bed, not shown, which conslsts of granular solids, which are cupplled through llne 4. The flui~i~ed bed extends from a nozzle grate 5 to the outlet 3 and surrounds the helical line of cooling means 6, through whlch a cooling fluid for dlssipatlng heat 19 con-ducted. Fluldlzlng gas i~ supplled through line 8 ~nd flrat enters a dlstributlng chamber 9 and then rlse~ through the nozzle grate 5 0nd fluidizes the ~uidlzed bed. The fluidiz-ing gases which hsve left the fluidized bed first flow inbo an enlarged stllllng space 10 and then lea~e the coollng appa-ratus through an outlet 11, which may be connected to mesns for a further processing, which ~re not shown and may consist, e.g., of dedustlng means.
The cooling chamber 1 i9 80 de3igned that the fluldlzed bed contained ln the chamber has a height from 2 to 20 meters and preferably of at least 3 meter~. Under the ac-tion of the fluidlzing 939, such as alr, the granulQr sollds to be cooled rlse in the coollng chamber 1 from the inlet 2 for sollds and leave the fluidlzed bed through the outlet 3.
Owing to that predetermined movement o~ the sollda the coollng fluld can be conducted ln the cooling means 6 cocurrently or countercurrently to the sollds. The rate at which solids enter the fluidized bed may be controlled by a gas which is fed through a llne 13 to the lnlet 2. The coollng chamber 1 and the stllling space 10 are enclosed by a pressure-reslstant vessel 12.
The coollng apparatus ehown in Figure 2 comprises a flrst coollng chamber 1a and a second coollng chamber 1b.
~ partitlon 7 is dlsposed between the coollng chambers 1a and ,: : . - :,,, ,: . - - . , 1b, and an openlng 15 i9 left between the nozzle grate 5 and the bottom edge of the partition 7. The cooling chambers are enclosed by a ~ressure-resistant houslng 16, whlch i9 provlded wlth an lnlet 22 for solids snd an outlet 23 ~or sollds. The top edge 7a of the partltlan 7 i9 dlsposed above the inlet 22 and the outlet Z3. Fluidizing gases leave the houslng through the outlet 11.
Hot ~olids are supplied through the inlet 22 and initially enter the second cooling chamber 1b, which contains a fluidlzed bed, which i9 deacribed here as the "preceding fluidized bed". Fluidizing gas for the preceding fluldized bed is supplieo through line 19 and enters the distributing cham-ber 20 and then rises through the second cooling chamber 1b to the outlet 11. The solids descend in the precedlng fluidized bed in the second cooling chamber 1b and through the openlng 15 enter the fluldlzed bed ln the fir~t cooling chamber 1a.
The space which i9 constltuted by the opening 15 ls supplied wlth fluldizing gas through a line 24 and a dlstributlng cham-ber Z5, which i~ disposed under the nozzle grate 5. The rate at which sollds mo~e through the openlng 15 can be influenced by a change of the rate at which gas ls supplled through line 24. In that way the rate at whlch solids are supplied to the flrst cooling chamber 1a can be controlled by a fluld-dynamic valve.
The opening 15 serves a~ an inlet for ~o~ds en-tering the fluidized bed in the first cooling chamber 1a, in which the sollds rise in a stationary fluidized bed until they ,: . . ' . :: . .: . ' -' :: ' . . , ~: ;, : , ~ , ;!, :, : ~ : :
' ~ ' ' . . . ' . ' ' : . ' . . . ::: . , ' ' . : .: . ' ': : - "

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lea~e the cooling apparatus thrcugh the uutlet 23. Fluidlz-lng gas 19 supplled through llne 26 and throuqh the dlstri-buting chamber 27 and the grate 5 enters the fluldlzed bed.
The arrangement shown in Flgure 2 may be modlfied in that the two coollng chambers 1a and 1b are arranged in a hnusing which i8 not de~igned to wlthstnnd a relatively high pre~sure and which la disposed ln a separate pressure housing as shown ln Figure 1.
The remarks made hereinbefore in connection wlth a single fluidized bed regarding the bed height, the ratio of the bed height to the average bed width and the dlfference between the temperatures in the lower and upper portlons of a fluldlzed bed are appllcable to the flrst cooling chamber 1a, the second coollng chamber 1b, and the ~luldized beds con-talned thereln. It la apparent thst the sollds snd the cool-lng fluld may be conducted cocurrently or countercurrently in the precedlng fluldlzed bed and ln the succeedlng fluidized bed and the coollng fluid flo~s through the cooling means 6a and 6b.
In numerous applications the veloclties of the fluidizinq gas lie in the range ~rom O.Z to 0.~ meters per -second and may be regarded as belng substantially lndependent o~ pres~ure.
In the graph shown as Figure 3 the ascertained dependence of the demand V for fluidizing gas (ln sm~ per hour and per cubic meter of fluidized bed volume) on the pres~ure p .. , , , . , .. ~ ~ .: , :

- ~, , . . . . . .- ., ": , ,.,. : , ~: :
- ; . j: :- :. . ~ , -... . . .. . ...

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19 represented for vsrious bed heights h (h = 1, 2, 5, 10 and 20 meters) far a fluldlzing gss ~lowing at a velocity of 0.5 meter per second and a temperature of 500C and particle slze~ of the solids from 100 to 400 mlcrometers in the flul-dized bed. It is apparent, e.g., from the point A that V = 6500 will be required at p = 10 b~rs and a height h = 1 meter whereas V = approximately 1300 will be ~ufficient if the pressure is the same and the bed height h is 5 meters (point E).
Compa~ative . Example In the partly calculsted comparison described herelnafter a conventlonal known flat fluldized bed cooler, tall as shown in Figure 4, is compared with a fluldized bed cooler as shown in Figure 1. The ~luidlzed oed cooler shown in Fi-gure 4 comprl~e5 o housing 30 provlded with an inlet 31 for sollds, an outlet 32 for so~ds and a sys~em 33 for fluidizing gases and 19 divlded by three welrlike partitlons 34 lnto four chambers 35, 36, 37 and 3B. Each chamber contalns a flui-dized bed, and the sollds move from the inlet 31 over the partitions 34 and through the fluldlzed beds to the outlet 32. Each fluidized bed is indlrectly cooled by coollng means 39, whlch are supplied with cooling water. Fluidizing gasea are wlth-drawn ir line 40.
In the P example each chamber of the sppa-ratus shown ln Figure 4 has a horizontal cross-sectional are~
of O.BB m2 and the fluidized bed shown in Figure 1 has also a~

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horizontal cross-sectional area of 0.88 m2: Further datn are apparent form the following Table.
'.!i Figure 4 Figure_1 Height of ~luidi~ed bed 0;5 m 2.0 m Total fluidlzed bed volume 1.76 m3 1.76 m~
Surface area of cooling mean~ 36 m2 36 m2 Presaure 10 bars 10 bars Solids rate 2500 kg/h 2500 kg/h Cooling water rste ~000 kg/h 8000 kg/h Fluidlzlng gas rate 4B,000 kg/h 12,000 kg/h Temperatures Solids at lnlet 700C 700C
Solids at outlet 126C 123C
Coollng wster at lnlet 30C 30~C
~oollng water at outlet 9ZC 9~C
Fluidlzlng gas at lnlet 150C 150C
Fluldlzlng gas at outlet 146C 123C

The data have been calculated ln part and sre based on ~olid~ which conslst o~ coal ash and have par-ticle sizea ln the range from 0.1 to 1 mm. Air ia ueed as a fluidlzlng gas and i8 conducted through the fluidized beds ln all case~ at a velocity of 0.4 to 0.7 meters per second.
It i~ apparent from the Table that for a glven fluidlzed bed volume, given cooling means, a given cooling water rate and a glven veloclty of the ~uidizlng gaa the tall Pluidlzed bed of Figure 1 require~ only one-fourth of the rate . ~. ;. , , . - , - , .. . . " ,,, ~, ", . :

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of ~luldizlng gag that i~ requlred ln the apparatus shown ln Flgure 4 and the structural expendlture ls lower. The ln-Pluence of dead corners, whlch by experience are ~ound in ~lat fluldized bed coolers as shown ln Flgure 4 and addltlo-nally reduce thelr efficlency have not been taken into ac-count ln the calculatlons.

Claims

1. A process of cooling hot granular solids un-der a pressure from 2 to 50 bars in a fluidized bed, which is disposed in a cooling chamber provided with an inlet for solids and an outlet for solids and in which the solids move mainly in a vertical direction from the inlet for solids dis-posed at one end of the fluidized bed through the fluidized bed to the outlet for solids disposed at the opposite end of the fluidized bed, fluidizing gases are introduced into the lower portion of the fluidized bed and heat is indirectly dissipated by cooling means, which are flown through by a cooling fluid and extend over at least one-half of the height of the fluidized bed, characterized in that the fluidized bed has a bed height from 2 to 20 meters, the ratio of the bed height to the average bed width is between 2:1 and 10:1, the cooling fluid flows cocurrently or countercurrently to the solids moving from the inlet for solids to the outlet for solids, and the difference between the temperatures of the solids in the lower and upper portions of the fluidized bed is at least 80°C.

2. A process according to claim 1, characterized in that the fluidized bed has a bed height of at least 3 me-ters.

3. A process according to claim 1 or 2, characte-rized in that the ratio of the bed height of the fluidized bed to its average width is at least 3:1.

4. A process according to claim 1, 2 or 3, characterized in that the cooling fluid flows countercurrent-ly to the solids moving from the inlet for solids to the out-let for solids.

5. A process according to claim 1, 2 or 3, characterized in that the difference between the temperatures of the solids in the lower and upper portion of the fluidized bed is at least 200°C.

6. A process according to claim 1, 2 or 3, characterized in that a pressure of at least 5 bars is main-tained in the fluidized bed.

7. A process according to claim 1, 2 or 3, characterized in that the fluidized bed is supplied with 300 to 7500 sm3 of fluidizing gas per cubic meter of the fluidized bed volume and per hour.

8. A process according to claim 1, 2 or 3, characterized in that the solids to be cooled are supplied to the lower portion of the fluidized bed and withdrawn from the upper portion of the fluidized bed.

9. A process according to claim 1, 2 or 3, characterized in that the hot solids are precooled in a pre-ceding fluidized bed disposed in a preceding second cooling chamber, in which the solids move also from an inlet for solids at one end of the second cooling chamber mainly in a vertical direction through the preceding fluidized bed to an outlet for solids at the opposite end of the second cooling chamber, the solids from said outlet directly enter the fluidized bed of the first cooling chamber, approximately the same pressure is maintained in the second cooling chamber as in the first cooling chamber, fluidizing gas is fed into the lower part of the preceding fluidized bed, heat is indirectly dissipated by cooling means within said second chamber, said cooling means are flown through by a cooling fluid and which extend over at least one-half of the height of the preceding fluidized bed, the bed height of the preceding fluidized bed is in the range from 2 to 20 meters and preferably amounts to at least 3 meters, the ratio of the bed height to the average bed width of the preceding fluidized bed is from 2:1 to 10:1 and preferably amounts to at least 3:1, in the second cooling chamber the cooling fluid is also caused to flow cocurrently or countercurrently to the solids moving from the inlet for solids to the outlet for solids, and the difference between the temperatures of the solids in the lower and upper portions of the preceding fluidized bed is at least 80°C.

10. A process according to claim 9, characterized in that the solids descend between the inlet for solids and the outlet for solids in the preceding fluidized bed and the solids rise in the succeeding fluidized bed from the inlet for solids to the outlet for solids.

11. A process according to claim 10, characterized in that the rate at which solids are transferred from the preceding fluidized bed to the succeeding fluidized bed is fluid-dynamically controlled.

12. A process according to claim 1, characterized in that the cooling fluid flows countercurrently to the solids moving from the inlet for solids to the outlet for solids.

13. A process according to claim 12, characterized in that the difference between the temperatures of the solids in the lower and upper portion of the fluidized bed is at least 200°C.

14. A process according to claim 13, characterized in that a pressure of at least 5 bars is maintained in the fluidized bed.

15. A process according to claim 14, characterized in that the fluidized bed is supplied with 300 to 7500 sm3 of fluidizing gas per cubic meter of the fluidized bed volume and per hour.

16. A process according to claim 15, characterized in that the solids to be cooled are supplied to the lower portion of the fluidized bed and withdrawn from the upper portion of the fluidized bed.

17. A process according to claim 16, characterized in that the hot solids are precooled in a preceding fluidized bed disposed in a preceding second cooling chamber, in which the solids move also from an inlet for solids at one end of the second cooling chamber mainly in a vertical direction through the preceding fluidized bed to an outlet for solids at the opposite end of the second cooling chamber, the solids from said outlet directly enter the fluidized bed of the first cooling chamber, approximately the same pressure is maintained in the second cooling chamber as in the first cooling chamber, fluidizing gas is fed into the lower part of the preceding fluidized bed, heat is indirectly dissipated by cooling means within said second chamber, said cooling means are flown through by a cooling fluid and which extend over at least one-half of the height of the preceding fluidized bed, the bed height of the preceding fluidized bed is in the range from 2 to 20 meters and preferably amounts to at least 3 meters, the ratio of the bed height to the average bed width of the preceding fluidized bed is from 2:1 to 10:1 and preferably amounts to at least 3:1, in the second cooling chamber the cooling fluid is also caused to flow cocurrently or countercurrently to the solids moving from the inlet for solids to the outlet for solids, and the difference between the temperatures of the solids in the lower and upper portions of the preceding fluidized bed is at least 80°C.

18. A process according to claim 17, characterized in that the solids descend between the inlet for solids and the outlet for solids in the preceding fluidized bed and the solids rise in the succeeding fluidized bed from the inlet for solids to the outlet for solids.

19. A process according to claim 18, characterized in that the rate at which solids are transferred from the preceding fluidized bed to the succeeding fluidized bed is fluid-dynamically controlled.

20. An apparatus for cooling hot granular solids under a pressure from 2 to 50 bars in a cooling chamber, which contains a fluidized bed formed by the solids and is provided with an inlet for solids and an outlet for solids and contains cooling means for indirectly cooling the solids and is provided in its lower portion with means for supplying fluidizing gases, characterized in that the cooling chamber is designed to accommodate a fluidized bed having a bed height from 2 to 20 meters and a ratio of the bed height to the average bed width from 2:1 to 10:1.

21. An apparatus according to claim 20, characterized in that the cooling chamber is preceded by a second cooling chamber, which has an inlet for solids and an outlet for solids, said outlet connected to the inlet for solids associated with the first cooling chamber.