CA1151874A - Process for thermal treatment of finely divided solid fuel - Google Patents

Abstract

Abstract of the Disclosure The process for a thermal treatment of a finely divi-ded solid fuel according to the present invention comprises drying said fuel and a two-step pyrolysis thereof, followed by separation of the resulting vapour-gas products and coke fines. According to the invention, drying of said fuel is effected using a portion of said hot coke fines; at least a portion of the remaining coke fines is additionally heated to a temperature of from 800 to 1,500°C by gases and/or a partial combustion of said coke fines, whereafter said heated coke fines are separated from the gases and gasified with steam resulting from drying of said fuel; thereafter the resulting gasification products are separated from the coke fines which are employed as a heating agent supplied to the first step of pyrolysis.

Description

Field of the Invention The present i~nvention relates to the art of a comprehen-sive processing of fuels and, more specifically, it relates to a process ~or a the~mal treatment o~ a finel~ divided solid uel.

The process of the present invention is useful in the production of transportable fuels, including synthetic liquid fuels, electric power, as well as in the manufacture of chemical and industrial starting stock.

Background of the Invention Known in the art is a process for a thermal treatment of a solid fuel, wherein as the heat-transfer agent for heating of the fuel use is made of corundum beads with a diameter of 10 to 12 mm heated in the first chamber of a two-chamber reactor by means of flue gases. In the second chamber, whereinto a solid hot heat-transfer agent is con tinuously supplied from the top there are effected such stages as heating, post-drying, coking and a partial gasifi-cation of the finely divided solid fuel ascending in a mix-ture with gas and vapour upwardly through a dense bed of the heat-transfer agent. ~s commercial products there are obtained hot coke fines, resin and gas. (Cf. A. L. Perepe-litsa et al.

~i '.

' '' : ' ' :, ' ~1874 "Use of Solid Heat-Transfer A~ent in Rrocess of Continuous Coking of Irkutsk Field Coals"l.

Known in the art is a process ~or a thermal treatment of a solid fuel, where~n supplièd upwardly is a current of a gaseous suspension of a solid fuel which is heated at the account of heat o~ the moving downwardly counter current of larger part;cles of a ~ot solid heat-transfer agent (sand, pellets and ~he like) irnmiscible with the fuel. Along with the solid fuel charged into the reactor is steam and, simul-taneously with pyrolysis, the process of coal gasification also occurs. The heat-transfer a~ent is heated by flue gases immiscible with the products of pyrolysis and gasification.
(Cf. USSR Inventor~s Certificate No. 82492 published January, 1967 to Z. F. Chukhanov).

This prior art process features dilution of the pyroly-sis products with steam and water gas thus complicating puri-fication and utilization of the pyrolysis products and neces-sitating the use of sophisticated process equipment.

Known is a process for pyrolysis of a solid fuel, i.e.coal, which involves pre-dyring of the coal, heating thereof to the temperature of 500C in the first zone of pyrolysis by the heat of flue gases to give coke fines, followed by supplying said coke fines to the second zone of pyrolysis and heating thereof to the temperature of l,000C by a gase-ous heat-transfer medium with the recovery of the residual pyrolysis products, followed by separation thereof and re-moval as comrnercial products ~Cf. USSR Inventor's CertificateNo. 335267 published July, 1972 to Z. F. Chuklanov).

s`*1 , ~L~IL5~874 ..

This prior art process is charac~erized by that -the solid residue of the ~uel9 i.e. coke ~ines produced as a result of pyrolysis and gasification) is generall~ used~
alo~g with ash, in combustion chambers of boilers of a pov~er unit thus causing troubles in the operation o~ ~he unlt (boiler) by slagging and pollu~ing the environme~-ts with har-mful o~ides of sulphur and ~itrogen as well as ash particle~9 the yield of valuable organic produc~s in the process is 1O~J
and bhese products are diluted with non-useful contaimina~ts.

Brie~ ~ummary of the Invention I~ is an ob ject of the present i~ention to increase the efficiency factor of the thermal treatme~t proeess a~d in-tensification thereo~' simultaneousl~ Yii~h increasi~g ~he yi-eld of the desired products a~d improve quality thereof.
It is a~other objec~ of the present invention to eliIsi-nate slagging of` boilers of po~er units and prevent pollutio~
of tho atmosphere with har~ul off-gases.
This object is accomplishad by a process for a -thermal treatment of a finely divided solid fuel which invol~es the stage of drying of said fueld and a two-step ~yrolysis ~here-of followed by separa~ion of the resulting gas-vapour produc~s~
wherein, in accorda~ce ~ith the present invention~ d~yi~g of said fuel is ef~ected by means of a portion of said ho-~ coke fi~es; ~herewith9 a~ least a portion of the remaining coke ~15~L87~

~ines is addi~ionally ileated to a tempexature within the range of from 800 to 1j500C by gases and/or b~ a partial combustion o~ said coke fines 7 whereaLter the heated coke fines are separated ~ro~ t~e gases and ~asi~`ied by means o~ steam produced in dryin6 of said fuel7 then the resultinO
gasification products are separated ~rom thc- coke f'i~es which are supplied to the ~'irst step o~ pyrolysis as a heat-transfer medi~wm~
The process accordinO to ~he present inv~ntio~ fea~ures a high efficiency 9 i.e~ it has a high (up to 84-~8%) power e~flciency factor due to the utilization of` col~e ~ es and production of steam from the ~uel moisture which steam is then used in the gasification process; the advantage o~ the process according to the present i~vention also resides in a comprehensive utilization of the fuel Lor the manu~ac-ture o~ chemical~ process and po~er starting materials. ~urt-hermore 9 the process accordin~ to the prese~t invention makes ,~
it possible to ensure a rational use of the hea-ti~g potenl~
lities of the heat~transfer medium and7 thereby~ i~crease the process efficiency~ ~he use of a solid heat-transfer agent for pyrol~sis~ i.e. col~e f'ines cooled upo~ gasifica~
tion ma~es it possible to per~orm ~yrolysis u~der ~ild tem~
perature conditio~s 7 i~e. with reduced temperature drop of the heat;~ransf'er agent i~ the f`irst step OL' the pyrolyzerg thus en~bling a higher yield of' most valuable liquid products obtained in a rapid pyro~sis 9 ~15~8~4 Due to the fact that coke fines are supplied t-o gasifica-tion in an excessive amount~ which is associated ~Nith the thermal balance of the water-gas reaccor~ steam has a higher de~ree a~d i~ensity o~ decompositio~ and the e~ciency ~ C r f~OS e factor o~ the production o~ water was i~7Kke~.
It is advisable, ~or intensification and better control o~ the processes of heating of the fuel and dxying thereof that these processes be efIected in a curre~t o~` an overheated steam, and supplied to the first step of ~yrolysis should be a portion o~ the gases separated from the heated coke ~ines.
For the pu.rpose of the process in~ensi~ication a~d inc-rease of the yield of valuable vapour~gas products of ~ro-lysis it is advisable that a solid fuel~ be ~inely divided .
to particles with a size o~ ac most 1.5 mm~ it is also desirable that the gases supplied to the`~irst step of py-rolysis contain at most 2~o by volu~e of free oxygen~

Detailed Description of the Inventio~
The process accordi~g to the present invention will now be more fully apparent from the following detailed descri-ptiOll with reference to the accompa~ying drawing, whexein a preferable flow-sheet o~ the process is shown.
In accordance with the drawin~ a finely divided solid fuel with a particle size of not more than 1~o5 mm is fed~ ~
from a bin 1, to a shaft mill 2 ~ whereinto :Eor grinding and d~yinç~; a portion of coke fines resulting from p;yrolysis Sl!374 is fed throu~h a~ inlet pipe 3 via lines 4 and 5; s-team is supplied to the sha~t mill through a blower 6. The gaseous suspension is fed i~to a cyclona 8 via a line '~; in said cyclone 8 said dr~ ~`uel is separated and the overheated stearn ~ormed fro~ the fuel moisture is delivered b~ the blower 6 via a line 9 through a grate 10 to a xeactor 11 of water gas and partly to the mill ~ Eowevex~ said opera~io~s of drying and heating of the fuel can be performed without the steam sup~ly~
~! ~ .' 9 Said d~y fuel is deliver~d, ~æeug~ an intermediate bin-aispenser 129 to a firststep p~rolyzer 13, wherei~to a solid heat-t~a~s~er agent~ i.e. coke ~ines 9 or a mixed (solid and gaseous) heat-transf`er agent is admitted via a line 14 which heats the ~uel to a temperature wi-thin the ra~ge of fxom 500 to 800C. r~he pyrolysis products along with a small por-tion of th~ entrai~ed dust~ e coke ~i~es are discharged into the c~Jclone 15j wherein said coke fines are separated and delivered to intermediat~ bins 16~ nd 17 and there~ter used either as a heat-trans~er agent ~ pyrolysis, or as a commercial transportable fueld product~
r~he va~our-gas mixture ~rom the cyclone 15 via the li~e 18 is withdrawn to the system o~ purifica~ion and condensa-tio~ 9 wherein valuable liquid com~ercial products and gas are produced.
A portion of hot coke fi~es ~rom ~he pyrolyzer 1~ is fed via the line 4 through the pipe ~ to the mill 2; the remaining ~ 8 por-tion of said coke fi~es is ~ed to th~ second-step p~ro~-1 z~r 'l9~ wherein these are hea-ted to a tempexature within the range o~ ~rom 600 to 1~100C by means of a ~as burner 20 ope-ting on the gas supplied along wi-th air via inlet pipes 21.
~he gas from the seco~d-step pyrolyzer 19 and bin 17 is with-drawn throu~h outlet pipes via g~as ducts 220 A portion of hot coke ~ines from the second-step pyroly-zer 19 into a process combustion chambex 23 comlllanicating with a cyclone 24. It is also possible to suppl~ only a por~
tion of hot coke fines from the seco~d-step p~rolyzer 19 i~to the process combustion chamber 23; the remainlng portion of the coke finas is withdrawn from the process as ~ commer-cial product along a line 33. The main (second~ portion of the gaseous heating agent is fed into the process combustion cham-ber 23 through the burner 25 operating on the gas supplied along with the aix through inlet pipes 26; this heating agent serves to heat and transport the coke fines 7 i.e~ a solid heat transfer agent, through the process combustion chamber 23 to the cyclone 24.
~ he coke fines separated i~ the c~clone 24 at a tempera- .
ture withi~ the range of ~rom 800 to 1~500C is passed~
.
through an intermediate bin 27~ i~to the water ~as reactor 119 ~herein the re~uired predetern1ined ,~part o~ ~aid coke fines is subjected to gasi~ication by steam supplied via the line 9 through the grate 10; this steam is produced from moisture ~ 5~ 4 contained in the ~uel and in the case o~ sho~tage of this mois~ure, s-team is additionally admitted along the lina 280 S~eam in the water gas reactor 11 is converted to a highly calorific gas which is a valuable chemical feedstocl~ and f'uel. ~he gas~suspension of -the Y~ater gas anà coke fines ~rom the wat0r gas reactor 11 is fed into a cyclone ~9 wherein the coke fines are separated from the water gas and~
as the solid heat-trans~er agent9 is fed through a bin ~0 to the line 14, wherein it is mixed with a portion o~ the gas ef`flue~.t ~rom the cyclone ~4. The mai~ po~tion ol the gas is withdrawn via the li~le ~ for purification and suppl~ to the power u~it. II1 said mixing o.~ -the solid heat-transfer agent with the portion of ~he g~s, the resulting mixed heating agent is fed to the first-step p~rol~zer 13.
There~ore, in -the process according to the present i~ven--tion9 due to the provision of a clos~d cycle of p~rolysis, gasification and drying 7 harmful exhausts to the atmosphere axe eliminated, since fed ~o combustion cha~bers of pov~er units are purified p~rol~sis gas, water gas and mixed gas.
~'or this reason, the height of boilers of` said power units and overall dimensions thereof can be minimized and operation of said boilexs can be substantially simplifled.
~ urthermore, si~ce in the process accordi~ to the pra-sent inventio~ steam is used for gasil`ication which steam is pxoduced upo~ dr~ing the fuel 9 there is no need in additional fuel, This inc.Leases, by ~5%~ ~he power e~ficie~cy of the fuel utilizatio~.

'~'Jater gas (mainl1 hydro~en and carbon o~ides) ~rom the cyclone 29 via the line ~2 are f'ed to purification and then to the user; as the latter there may be a power plant inclu-din~ a gas t~rbinc or ~ chemical reactor ~OI' the prod~ction of` hydro~en, synthesis gas, methanol and other products.
'l`he process accoxding to the present i~vention makes it possible to produce a ve~y cheap water gas; since the excess o~ coke fi~es in the water gas xeactor 11 ma~es it possible to ensure a high (to 80-95~o) de~rree O~ decomposition o~ steam and a high power efficiency factor, as well as simpli~y the entire system. Automated control o~ the manufacture o~ the re~luired amount o~ water gas, process temperature and the amount o~ circulating solid heating agent 9 i.e. coke fi~es;
is e~fected by va~ying the withdrawal o~ the coke ~ines thro-ugh the inte~mediate bin 17 and via the line ~3 ~rom the pro-cess and supplying steam to the ~ater-gas reactor 11 with the account o~ a possible variation o~ ~he ~uel amount and operation conditions of the power unit~ '~he necessarJ control valves for corresponding streams o~ steam, gas 9 gas-suspensi-on and solid particles are not shown in the dra~ving~
A ve~y important feature charac~erizi~g the new process resi~des in that fe~ into the heating chamber o~ the power unit are gases completely puri~ied ~rom sulphur solid ~uel and asa, thus tra~s~orming the boilers i~to gas-heated ones a~d eliminating slagging of the hea-ting sur~aces. l'his - 10 - ' " '.

~lS~87~L

process provides high economic parameters of the process on such fuel as turf, including high-moîsture turf. ~he overall dime~sions of the boiler units are substanti~lly decreased.
q'empera~ure conditions o~ pyrolysis and gasi~ication are controlled also b~ var~ing the ~uan~ity and temperature of the gaseous heating agent produced i~ gas burners 20 and 25 and in the process combustion chamber 23.
Since into the combustion chamber of the power plant t~ere~ s fed9 along with gases, a great amount of a low-ca-~3 lo~irio gas produced i~ the process combustion chamber 23 andbur~ers 20 and 25, the burning temperature in the combustion chamber of the power unit is reduced a~d the conte~t of harm-ful nitrogen oxides in the gases effluent from the power unit is considerably lo~ered both in respect o~ the external (formed in the combustion chamber upon burning o~ nitroge~
and internal (~romed from the fuel nitrogen) oxides produced in processing of said fuels at the power plant9 This makes it possible not only to ensure a aeep comprehensive utilization of the fuel on power plants7 but substan-tiall~ comple-tely eliminate pollution of the environments with the of~-gases of the power units in respect of both gaseous (oxides of sul-p~ur and nitrogen) ~nd solid (ash particles) compone~s ex-hausted to the atmosphere.
~ he process according to the present i~ve~tion also enables utilizatio~ o~ low-Quality power liquid l~uels by :
, . . .

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in~roducing them into a process combustio~ chamber or i~ a water-gas reactor dependi~g o~ the ~inal applicatio~ o~ the pIoduced water gasO
~ ox a botter understandi~g of the present invention7 some speeific examples are given hereinbelow by way o~ illust~
ration of the process for a thermal treatment of a finel~
divided solid fuel~
Exa~ple 1 In this Example operation of a po~er~process plant (PPP) with a thermal processing o~ coal is described. Ca~acity o~
o~e unit is 500 tons o~ Grude coal per hour. r~he an~ual capa-city of the plant is 50 mln.to~ of coal; electric power capa~
city o~ the plant is 32 bln.kW.hr/year.
Subjected to thermal processi~ is crude coal ~vith the ;
calirifi^ capacity o~ ~,560 kCal/kg containing 36~o of moisture 9 ."~
6.5~o by weigh~ of ash, and 4~% b~ weigh-t of volatile matter per the combustible mass. Coal ~rom the bi~ (1) is supplied to a drying mill (2), whereinto through the i~let pipe (3) a circulati~ mixture is ad~itted consisting of 120 kg o~
coke fines (solid heating agent) and 80 kg o~ ste~m heated respectively to the temperature of 780 and 580C pe~ ever~
100 kg of the coal. The product ob-tained after dIying 9 i~e.
64 kg o~ a dust-like d~y coal (~esidue on the sieve with 100 mcm i~ 10% by weight) and ~6 kg of steam at the temperatu- ;
re of 250C are passed, along with the heating agent9 through the cyclo~ 8, wherei~ coal a~d coke ~ines-are separated ~rom steam.

l~S~874 .
~ eam i~ the a~ount of 36 kg is introduced into the reac~or 11 o~ water gas and 80 kg are suppli~d for circulatio~
to the mill (2).
With the excessive amoun-~ o~ steam produced in this Example from coal in the amou~t o~ 18 kg, it can be fed -to the combustion chamber OL the power u~it~ ~he ~ry coke in the amount of 64 kg~ coke fi~es (120 kg) a-t the temperature o~' 250C are fed, through the inter mediate bi~ (12) to the first-step pyrol~zer 13 and heated to the tem~erature of 680C by means of a mixed heating age~t (coke ~i~es with the te~perature of 850C a~d a gas containing not more tha~ 1%
by volume of free oxygen at the temp~rature o~ 1~050C) sup-plied from cyclones (24, 29) respectively of the process combus-tion chamber 23 and the water-gas reactor 14~ Into the ~irst--step pyrolyzer (1~) there are supplied 160 kg of coke fines and ~2.5 kg~ of a gaseous heating agent. Completio~ of p~roly-sis of the coal is carried out at the temperature of 780C in the second-s-tep pyrolyzer (19)o The e~cessive gas is withdraw~
via the line 31~ puri~ied a~d supplied to the power unit. V1ith increased circulation ratio of coke ~ines a the amount thereof supplied to the pyrolyzer is 203 kg9 whereas ~he gaseous hea-ting agent is totally withdraw~ via the line 31J
In the pyrolyzer, from 64.0 kg of dry coal and circulat-i~g coke ~ines there arQ produced: 29.5 kg of a vapour-gas mixture (VGM) and 35.2 kg o~ coke fines. ~he latter are sepa-- 13 - . .

~7 ~

ated from the VGM which is delivered to purification and condensation sys~em.
l~part ~rom commercial coke ~ines, said pyrolysis and heating of the coal gi~es: 18.0 k~ of pyrol~sis gas (pyrogas) 9 8.6 kg o~ resin and gas naphtha, 2.9 kg of pyrogene liquor and the heating age~t.
The pyrogas has a calirific capacity of 4,840 kcaljm3 and the following compositio~9 pex cent ~ volume: C02 - 22~
C0 - 27; H2 ~ 20; CH4 - 21; other hydrocarbons - 10. Convert-ed to pyrogas are 81.000 Kcalg i.e. 23% of the potential coal heat, while to the resin a~d gas naphtha there are co~
verted 67,500 Kcal9 i.e. 1~o of the potential coal heat. '~o the coke fines obtained in the pyrolysis of coal there are converted 63% of the potential coal heat or 58% of the heat supplied to the unit.
An embodiment of the plant is possible 9 wherein the total amount of the semi-gas obtained after the process combustion chamber (23) is supplied to the power unit via the line 31 i~creasin~ therewith the rats o~ supply of the solid heating age~t, i.eO coke fines, to the pyrolyzer by about the same weight amount.
Commercial coke fines are produced in the amount o~ 14~4kg including 12 kg o~ carbon and 002 kg of hydrogen. In the se-cond-step pyrolyzer and in the process chambex respectively thexe are converted to gas and semi gas 2.2 and 8~3 kg o~ coke ~ines. With the coke fines and sla~s there are withdrawn 6.5 kg of the fuel ash.
. . .

.. .

-~L15~L~374 The coke fi~es heated to the tem~erature of 1~G50C i~
the pI'OCeSS combustion cham~er (23) is separated from the gaseous heating- agent and supplied to -the water-gas reactox hexein from the overheated steam (18 kg) and dust-like coke fines (166 ~g) there are produced 24 kg of water gas as a result of the reaction beGween I120 and C. 'I'he water gas in the cyclo~e (29) is separated from the coke fines (160 kg with the tempèrature of 850C), dischargea via the line (3~) and, after cooling, delivered to purificatio~ and utilization in the power unit and as a commercial produc-t ~or the produc-tion of hydro~en, reducing gas or sy~thesis-gas.
The coke fi~es comprising the heati~g a~ent are ~ed, through the bin 30, to the line 1L~, wherein these are mixed with a gas (semi-gas) Irom the cyclone 24 and then this mixture is supplied to the first-step pyrolyzer for pyrolysis;
~he process scheme is closed, ile. it has no ope~ harm~ul exnausts to the atmosphere in the process ox`power units~
Example 2 'I'his ~xample illustrates an embodime~t of the process according to the present invention, wherein the production o~
commercial coke fines is undesirable due to its i~creased ash-co~tent, sulphur content and other reasons. Process is effected with the crude coal of the same compositio~ as that in the fregoing ~xample 1~ In the water gas reactor t~ere is decomosed a twi~e larger amount o~' steam (36 kg) evaporated .

, 1: L5~L~37~

from 100 kg of coal and reacting with 12~6 kg of coke ~i~e~
here are produced ~ kg OL wa-ter gas, 8.5 k~ o~ gasoline and resinj 18.3 l~g of p~rolysi.s gas~ 3 kg o~ p,~rogene liquox, 6.5 kg o~ ash and sl~g, 105 kg OL` semi-gas. All the moisture o~ the working fuel (36 kg per 100 kg of the coal) is gasi~ied i~ this embodiment o~ the process according to the present invention, i.e. converted to water gas. q'his gives economic effect o~ about ~o of the coal heat saved 9 thus increasing the efficiency ~actor of processing and utilization o~ coal~
In the case o~ steam shortage due -to practically possible variations and the moisture content and composition of coal9 or reduced activi~y o~ carbon9 the controlled amou~t o~ steam is supplied to the apparatus via the line 28 ~rom the ou~side~
'l'he process of coal drying can be ef~ected9 when required9 without steam supply, i.e. onLy with the suppl~ of a solid heating agent to the mill (2~.
Example 3 I'his E~ample illustrates an embodiment of the process according to the present invention~ wherein coke fines have ', a low activity of the reaction thereof with steam or feature a particular compositio~ of the ashO I~ this case the heating agent has a high starting temperature, just as the coke fines reacting with steam~
Processes is the coal having the same compositio~ as des-cribed in the foregoi~g Example 1. ~`he coal moisture co~tent - ~6 -~lS~
iS 27~o~ the ash co:lltent is 2'1.95~o. Into the process coMbustLon chamber air is fed at the temperature o~ 700 heated 'Dy the gas dischurge~ via the li~e 31 an~ temperatu~e i~ said pro-cess combustion chamber i5 elevated to 1,500-1j600C; the ash is discharged as a li~uid slag. The products obtained are the same as i~ ~xample 2 hereinbe~ore, namel~. 36 Xg of water gas, 6.4 kg o~ resin a~d gasoline, 13~7 kg of p~rolysis gaS9 pyroge~e liquor ~.3 vol.%3 ash and slag~ 29.9 kg. ~his enables a complete conversion o~ coal to liquid and gaseous products thus excluding exhausts o~ ash a~d sulphur oxides to the atmosphere .

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for a thermal treatment of a finely divid-ed solid fuel comprising the stage of drying of said fuel, its two-step pyrolysis and a subsequent separation of the resulting vapour-gas products and hot coke fines; supplying a portion of said hot coke fines to the stage of drying and additional heating of at least a portion of the remaining coke fines to a temperature within the range of from 800 to 1,500°C by means of hot gases and/or partial combustion of said coke fines; separating the heated coke fines from the gases supplied to the first step of pyrolysis, gasification of the heated coke fines with steam produced upon drying of said fuel; separation of the coke from gasification products;
supplying coke fines as a heating agent to the first step of pyrolysis.

2. A process according to claim 1, wherein use is made of a finely divided solid fuel with a particle size of at most 1.5 mm.

3. A process according to claim 1, wherein drying of said fuel is effected in a current of superheated steam.

4. A process according to claim 1, wherein a portion of gases separated from the heated coke fines is supplied to the first step of pyrolysis.

5. A process according to claim 4, wherein gases sup-plied to the first step of pyrolysis contain at most 2 vol.
% of free oxygen.