CA1156465A - Method for processing pulverized solid fuel - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

There is provided a method for processing a pulverized solid fuel by heat, which comprises the steps of drying said fuel and subjecting the latter to two-stage pyrolysis with the resulting formation of vapour, gaseous products and small coke, according to the invention, at least a part of said small coke is additionally heated to a temperature of 800 to 1500°C by combustion gas and/or by partial burning of the small coke, whereafter the heated small coke is separated from the combus-tion gas, fed at the first stage of pyrolysis and for drying said fuel; whereas the heated small coke is gasified by steam and the resultant gasification products are separated from the small coke which is then fed as the heat carrier at the first stage of pyrolysis.

Description

1 158~65 BACKGRO~N~ O~' THE INVENT~ON

1. Field of the Invention The present invention relates to comprehensive process-ing of various fuels, and more in particular to a method for processing pulverized solid fuel by heat.

This invention finds wide application in the production of transportable fuels, electric power, chemical and commer-cial materials.

2. Description of the Prior Art There is known in the art a method for processing a solid fuel, wherein corundum balls of 10 to 12 mm in diameter are used as the heat carrier for heating the fuel, which balls are preheated in the first chamber of a two-chamber reactor by furnace gases. The second chamber, having a heated solid heat carrier continuously fed thereinto from top, is used for heating, drying, coking and partial gasi-fication of a pulverized solid fuel which, in admixture with gas and vapour, flows upwardly through a dense layer of the heat carrier. The resultant commercial products are hot coke small, tar and gas (cf. Perepelitza A.L. et al.
"Utilization of Solid Heat Carrier in the Flow Process of Continuous Coking of Coals in the Coal Fields of Irkutsk Region").

There is also known a method for processing a pulveriz-ed solid fuel, wherein a flow of pulverized fuel is fed upwardly. The fuel is heated by a downward countercurrent flow of larger-in-size particles of a solid hcat carrier (sand, shot, etc.) immiscible with the fuel. Fed together with the solid fuel to the reactor is water vapour; pyroly-- sis is effected simultaneously ,, 115~5 with the co~l æasification process. The heat carrier is heated by combustion ~as im~iscible with the products o~ pyrolgsis ~nd gasilification.
~ he above me~hod is ch~racterize~ b~ ~at the products of p~rolysis mi.~ with ste~n and blue gas, whic~ comp~icate the clean-up and use o~ pyrolysis products~as well as the apparatus c onstructionO
There is known a method for pyrolysis o~ pulverized solia fuel, such as coal, vJherei~ the fuel is ~irst, dried and the~
heated to a temperature of 500C in the ~irst zone of p~rolysis b~ the heat evolved ~rom combustion gas with the resulta~t formation of small coke a~d pyrolysis products, the small co~e being fed to the second zone of pyrolysis to be heated therein to a temperature o~ 1000C by gaseous heat carrier with the resulta~t ~ormation of residual products o~ p~rol~sis and small an~
coke,~their subsequent separation and collection as commercial products (cf. U~SoSoR~ Inventor's Certificate Mo 335,267) .
~ he abo7e-described method is characterized b~ that the solid residue of fuel and small coke, resu~tant from p~rolysis a~d gasification, is normally used together with tar i~ fur~aces o~ a boiler incorpora~ed in a power p~ant, and thus causes e2cessive slagging in the boiler and adds to tne pol~ution of env~ronment as harmful refuse of sulfur, nitrogen oxides, as well as ash particles are disposed of; the ~ield o:E valuable products is negligible and, to make things worse, the products contain inert admi~ures.

SUMMAR~ OF THE INVENTION

It is an object of the .invention to enhance the ope~at-ing process slmultaneously with an i,ncrease in the yield and im-proved quality oE the end product.

Another object of the invention is to eliminate thepossibility of slagging due to occur in boilers of power plants and to reduce the amount of harmful gases vented to the atmos-phere.

Accordin~ to the present invention there is provided amethod for processing a ~ulverized solid fuel comprising: (a) drying said fuel wikh a hot gas introduced at a rate sufficient to form a gaseous suspension containing a dry particulate fuel fraction and a volatile moisture-co.ltaining fraction; (b) separat-ing and remQving the entire volatile moisture-containing frac-tion from the gaseous suspension and feeding it to a power plant fuel supply, thereby leaving a residue of dry particulate fuel;
~c) subjecting the residue of dry particulate fuel to a first stage pyrolysis to form a first gas-vapor product, which is se-parated, remoyed and condensed, and a first residue of small coke; (d~ subjecting the first residue of small coke from step (c) to a second stage pyrolysis to form a gaseous product which is separated and remo~ed, and a .second residue of small coke; (e) introducing ~ portion of the~ second residue of small coke from step (d) into a gas-fired furnace and heating to a temperature of about ~oao _ 15Q0C to form a third residue of heated small coke and a hot flue gas; the'remaining portion of said second residue of small coke from step ('d.) ~eing removed as a product; (f) separati.ng the third residue of heated small coke in step (e) from the hot flue ga,s; (,g) recycling a portion o~ said hot flue : gas, as ~ ga,seous heat source, to the first stage pyrolysis in step (c~ and recycling the remaining portion to step (a) to serve as the hot drying gas; (h.~ introducing said third residue of heated small coke from step (f) to a water-gas gasifier wherein a ... .. .

4 ~ ~

suspension consisting essentially of volatile water-gas and a fouxth residue ~f heated srnall coke are fortned; and ~i) separa-ting and removing the water-gas, and recycliny the fourth residue of coke from s-tep (h) to the f.irst s~age pyrolys.is in step (c) to serve as a solid heat source for said pyrolysis.

The method according to the invention for processing pulverized solid fuel is highly effectiVe, featuriny enhanced power efficiency (up to 84-88~) with the comprehensive utiliza-tion of fuel as the starting material for chemical, industrial andpublic-utility use. In addition, the method of the invention permits the temperature potential of the heat carrier to be effec-- 4a -1~5~S

tivel~ used, thereby enh~cing the proce~ ef~iciencg. The u,~s o~' æma~l coke, cooled during gasif~ication, as ~he so~id he~t carrier th ~ l~n~er ~,,,,~t for~pyrolysis makes it possible to co~duct pyrolysis ~ more favou.rable temperature condit.ions, i.e, at a lower drop o~' tempe-rature betwee~ the heat carrier and t~e apparatu~ for effecting the first stage of pyrolysis, which, in turn~ results in a hi$her yield of the most valuable liquid product3 of a high-speed p~ro-lysis.
Since the amou~t of small coke fed ~or gasi~ication is determined by the heat balance o~ the water-gas gasiYier, water vapour has a high degree of decomposition, resulting in a~ anhan-ced efficiency oY wa~er ~a~.
It is advantageous to use pulverized solid fuel with the particle size thereof being not more than 1.5 mm, which makes it'possible to i~te~si~y the operating process and improve aua-lity o~ pyrolysis products. '~he gasification process is prefe-rab~y carried out with the,controlled ~low rate of water vapour, which allows for auto~atic control of the water-gas discharge, elimination o~ excessive consumptio~ and u~desired accumulation o~ small coke in an apparatus~
~ he invention will now be descxibed b~ way of example onl~
with reference to the accompanging drawing which æhows schemati-càll~ the pre~erred process flow of a method ~or processing pulYerized solid fuel.
~ eferri~g now to the drawing, there is shown ther~in the process flow according to which a finely divided solid fuel, such as coal, ~Jith a particle size of preferabl~ 1.5 mm is fed 1 ~5f~46r~
from a bin 1 to a shaft mill ~ to be dried th(reirl by a dryirlg gaseous agent, preferably free frorn ox~yen, ~/hich is introduced to t,he mill 2 through a connecti,ny pipe 3. The gaseous suspen-sion flows through a pipe ~ to a cyc].one 5 wherein the dry fuel is separated and the dus-t~f:rec drying agent with the fuel mois-ture is introduced throu~h a ventilator 6 to the furnace of a boiler 7 of a power plant.

The dry fue] is introcluced throuyh a dust-controlled intermediate bin gate 8 to a first-stage apparatus 9 for pyroly-sis, wherein the fuel is heated to a temperature of 500 to 800C
; by a mixed (solid and gaseous) heat carrier fed thereinto throllgh a pipe 10. Pyrolysis products together with a small amount of entrained small coke dust then pass to a cyclone 11 wherein the small coke dust is separated to be thereafter delivered to in-termediate bins 12 and 13 for further use as the heat carrier for pyrolysis or else as commercial fuel product.

A gas-vapour mixture is removed from the cyclone 11 through a pipe 14 to be thereafter passed to a consendation and purification system wherein valuable commercial liquid products and gas are collected for further use.

From the apparatus 9 the small coke is transferred to a second-stage apparatus 15 for pyrolysis to be heated therein to a temperature of 600 to 1100C by a gas burner 16 operating on gas fed together with the air through inlets 17. Gas is dis-charged from the second stage pyrolysis apparatus 15 and bin : 30 ~r ~1~

1 1S6~

13 through connecting pipes and gas vents 18, 19.
The ho-t small coke is passed from the second-sta~e pyro-lysis apparatus 15 ~o a process ~urnace 20 connect~d ~ith a cyc-lo~e 21~ It is possible to supply o~l~ a par-t of hot small coke ~rom the second-stage p~rol~sis apparatus 15 to the process fur-nace 20, wi-th the remainder part o~ the hot small coke be~ng removed th~ough the bin 13 for use as commercial product. The lh amount of gaseous heat carrier, which heats and delivers the small coke - solid heat carrier - through the furnace 20 to a cyclone 21, is fed to the furnace 20 through a burner 22.
The small coke, separated at a temperature of 800-1500C
i~ the cyclone 2~, is fed via an intermediate bin 23 t~ a water-gas gasifier 24 wherein a predetermined amount thereof is ~asi~ied by means of used water vapour introduced therein alo~g a pipe 25 through a baffle 25, this being e~ected by means of a regulator 27 in a manner well known to those skilled in the art a~d as described in the book ~nder the title "Puel Contro~
at Power Plants" by A.A.Andreev,tB.C.Beloselskiy, M.N.Krasno~, ~ergia Publishers? ~oscow, 1973. Steam is converted in the gasifier 24 ~ to water gas having a high calorific value and, ~ g~seO.~s therefore, bein~ ~aluable chemical material and ~uel. ~Mh~
suspe~sion of water ga~ and smal~ coke.i~ ~ed ~rom the gasifier 24 to a ¢yclone 28 wherein the small coke.is separated from the water ~as a~d is then pas~ed as the solid heat carrier through a bi~ 29 to the pipe 1Q to be mixed therein with the first por-1 ~ Sg~

c~ y tiOIl of gas dlscharged from the cyclone 21. ~he ~d~ELpor-tion of gas is passed from the cyc~one 21 through the co~necting pipe 3 for use as a drying agent ~or dryi.n~ the solid .fuel.
This mixture, which can be other~ise term0d as mixed heat carrier, is ~ed to the ~irst-stage pgxolysis apparatus 9, therebg closinO the entire cgcle. Small coke and combustion gas ca~ be ~ed separatel~ to the first-stage pyro~gsis apparatus 9.
Water gas ~mainl~ hydrogen and carbon oxides) is passed ~rom the cyclone 28 along a pipe~ine 30 for puri~ication, where-after it is de~iuered ~o 3. user~ for e~ample, such as power pl~nt, chemical reactor ~or the production of hydrogen, s~nthesis gas methanol or other products, With the method of the inve~tion it becomes possible to produce e~tremely cheap ~ater gas, sinca an excessive amount of small coke in the gasifier 24 e~ab~es a ~i~h degree of steam decomposition (up to 80-95%) and a high power e~ficienc~ thereof, therebg simplifging the entire system.
~utomatic control over the gas-making process, process temperature and contro~ over the amount of the circulating solid heat carrier is effected b~ alteri~g the way in which ~he small coke is re--moved from the process through the intermediate ~in 13 a~d ~urther along a pipe line 31 and b~ passing steam to the gasi-~ier 24 with due regard to a possible change in the quality of fuel and operating conditions of a power unit. '~he distinctive ~eature o~ the inventio~ lies in that passing to the boiler ~urnace o~ a power unit together with a d~ing agent i9 not only a flow o~ pulverized solid ~uel but gases as well which are ~156~

completely free of sulphur and solid jnclusiona of ~ueL~ thUS
enabling boilers to operate on gas ~nd, practically, eliminating the possib:ilil"y o~ ~lagging vn ~hc heating suxfaces. This method is e~ceptional1J ef`f~ective where peat a~ well as high-moisture peat i.s utilized. In addition, it becomes possible to conside-rabl~ reduce the boilers in size.
Temperature conditions of pyro~ysis and gasification are controlled by alterin~ the amount a~d temperature of the ~aseous heat carrier obtained in the gas burners 21, 16.
nce the drying agent fed to the boiler 7 together with rg e, gases contains a ~re~ amount of steam ~ormed in the course o~
drying of` the above fuel, the combustion temperature is lowered, and the content of harmful nitrogen oxides i~ combustion gas e,~pen5 e sharply decreases at the 4x~iu~} of both internal (produced in the fur~ace during combustion of nitrogen) and ex~,ernal (produced ~rom the nitrogen contained in f`uel) nitro~e~ o~ides produced in the course of processing o~ the above fuels at a power and process f'uel treatment plant. This factor makes it possible not only to assure comprehensive utilization of the fuel, but to almost completely eliminate the possibility o~
e~vironme~t contam~ation by waste products, both gaseous (sulphur and nitrogen oxides) and solid (ash particles), vented to the atmosphere f'rom such'a p~ant.
~ he method o~ the present invention permits the use of low-grade liquid fuels which are introduced either into a _ g _ process f~lrnace or water~gas gasificlr deper)dirlg or, t~e ultimate use of water ~as.

1'he invelltlor) wi11 be f~rther described with refererlce to the following i]lu.c;trative cxarnples.

Example 1 Considering the operation of a power and process fuel treatment plant utilizing coal. The production capacity of a single unit is 500 t of raw coal per hour.

Raw coal with a calorific power of 3560 kcal/kg, con-taining 35 percent by weight of moisture, 6.5 per cent by weight of ash and ~8 per cent by weight of volatile matter, was subject-ed to processing by heat treatment. Coal was fed from the bin /I/ to the dryer (2) with 95 ky of hot (at 1050C) oxygen-free drying agent being introduced therein through the connecting pipe (3) per each 100 kg of coal. The coal was dried and finely divided (with a mesh size of 100 microns, 20 wt.%). At a tem-perature of 200C the dry coal was separated in the cyclone (5) from gas containing 35 kg of coal moisture vapour, 95 kg of dry-ing agent and 0.3 kg of coal dust.

The dry coal in an amount of 65 kg was fed through the intermediate bin 8 to the first-stage pyrolysis apparatus 9 to be heated therein to a temperature of 700C by a mixed (small coke and gas) heat carrier passing from the cyclones 21, 28 of the process furnace (20) and the water-gas gasifier (24), respec-tively. Small coke in an amount of 156 kg at a tem-1 1$64B5 perature of 850C and 32.5 kg of gaseous hea~ carrier nire fed to the first-stage pyrolysi~ apparatus (9)~ The final stage of the coal pyrolysis proce5s wa5 conducted at a tem-perature of 780C in the second-stage pyrolysis ~yparatus (15)~
Produced from 65 kg o~ coa~ fed to khe apparatu~ for pyro-lysis are 29.8 kg of gas-vapour ~ix*ure and 35~2 kg of small cokeO The small coke is separated from the gas-~apour mi~ture to be thereafter delivered to a co~densatio~ and purification system.
Also produced in the course of pyrol~sis of coal are 18~3 k~
of pyrolysis gas, 8 kg of tar, 0.5 kg of gas benzine ~ld ~ kg OI pyrogenic water.
The pyrolysis ~as has a heating value of 4~50 kcal/m3 and the following composition, i~ volume percentage: C02, 2~; C0, 27;
~2~ 20; CH4, 21; a~d other hydrocarbons, 10. Converted i~to p~rolysis gas are 81200 kcal, and into tar and gas be~zine, 6780 kcal. Converted into the small coke 35.2 kg, formed during the coal p~rolysis, are 63 per cent of potential heat evolved from the coal or 58 per cent of the heat supplied to a power unit.
Final heating of the small coke in the second-stage pyrolysis apparatus (15) is ef~ected by bu~ning gas taken in anamou~t of 1.5 kg and small coke in an~mount of 2.2 k~. Commercial small coke was produced in an amount of 14.4 kg (12 kg of cæbon-~.
I~ additio~, to the he~t carrier (small coke) ~ed to the pyro-lysis apparatus in an amount of 156 kg, the furnace receives 8.3 kg of small coke while 6.7 kg of the-~w~produced small .

coke are heatecl i:o a tcmL~eraturc o~ ~300"C.

Once heated in the process ~urnace (~0), the srnall coke i5 then separated Erorrl the yaseows heat carrier to be fed to the water-gas ~asifJer (~4) wherein ~ kg of water vapour (according to reaction ll2O -~ C) are produced frorn ~Jater vapour [18 kg] and an excessive amoun-t [156-~6] of 162 kg of srnall coke.
Water vapour is separated in the cyclone (2g) from the small - coke and is then cooled to be af-terwards delivered for purifica-tion and further use in a power and processing plant as a com-mercial product for the produc-tion of hydroyen, reduciny yas and synthesis yas.

The gaseous heat carrier (serniwater-yas) is produced in the process furnace [20] wherein 43 ky of air are introduced throuyh the burner 22 to enable combustion of yas and small coke.
After the solid heat carrier is separated in the cyclone [21], the semiwater~gas is used as the yaseous heat carrier. Depend-ing on the controller flow rate of water gas, a part of semiwater-gas in an amount of 19 kg is fed as the drying yas to the drying chamber 2 through the connecting pipe 3. I'he drying agent is fed to the furnace of the boiler 7 in an amount of 95 kg, of which 19 kg constitutes semiwater-gas and 76 kg of combus-tion gas from the power plant boiler.
Produced from 100 kg of coal, 18 kg of water vapour, 76 kg of drying ayent and 43 kg of air are 8.5 kg of tar and benzine yas, 18.3 ky of pyrolysis gas, 24 kg of water yas, 52 kg of semiwater-yas, 14.4 kg of pyrogenic water, 35 ky of coal moisture, 95 ky of drying ayent/inclusive of 19 kg obtained X

1 l ~ B4 6 S

~rom 52 kg o~ semiwatex~gas), and 4.1 kg o~ ~lag ~ith ash.

Example 2 This example is given to illustrate the embodimen~ o~
~he inventio~ pIeferable ~or u~e where the productio~ o~
commercial small coke is undesirable b~ reaso~ o~ its high content of ash~ sulphur3 etc. ~ his end, water vapour is ~ed to ~he water-gas gasi~ier ln a~ amount exceeding two-~old that ~iven ~ Example 1, wherea~ the small coke is ~o lo~ger removed as commercial product through the o~
let 31. ~he small coke is heated in the process fu~nace7~
to a temperature o~ 1500C. ~ed per 100 kg o~ coal are 76 kg o~ drying agent and 82 kg o~ air. ~he resulta~t outp~t of the power-and-process unit amounts to 8.5 kg o~ tar and gas benzine, I8.3 ~g o~ p~rolysis gas, 48 kg of water ~as, 95 kg of dr~ng agent, 3 ~g o~ pyrogenic water, ~5 kg o~ coal moistura and 6.5 kg of ~lag with tar. Ecologicall~, this e~ample is more ~ffectiveO ~here is no alternative for ~uels high i~ ash conten~.

'

Claims (2)

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

1. A method for processing a pulverized solid fuel comprising; (a) drying said fuel with a hot gas introduced at a rate sufficient to form a gaseous suspension containing a dry particulate fuel fraction and a volatile moisture-containing frac-tion; (b) separating and removing the entire volatile moisture-containing fraction from the gaseous suspension and feeding it to a power plant fuel supply, thereby leaving a residue of dry par-ticulate fuel; (c) subjecting the residue of dry particulate fuel to a first stage pyrolysis to form a first gas-vapor product, which is separated, removed and condensed, and a first residue of small coke; (d) subjecting the first residue of small coke from step (c) to a second stage pyrolysis to form a gaseous product which is separated and removed, and a second residue of small coke; (e) introducing a portion of the second residue of small coke from step (d) into a gas-fired furnace and heating to a tem- .
perature of about 800° - 1500°C to form a third residue of heated small coke and a hot flue gas; the remaining portion of said se-cond residue of small coke from step (d) being removed as a pro-duct; (f) separating the third residue of heated small coke in step (e) from the hot flue gas; (g) recycling a portion of said hot flue gas, as a gaseous heat source, to the first stage pyro-lysis in step (c), and recycling the remaining portion to step (a) to serve as the hot drying gas; (h) introducing said third residue of heated small coke from step (f) to a water-gas gasi-fier wherein a suspension consisting essentially of volatile water-gas and a fourth residue of heated small coke are formed, and (i) separating and removing the water-gas, and recycling the fourth residue of coke from step (h) to the first stage pyrolysis in step (c) to serve as a solid heat source for said pyrolysis.

2. A method as claimed in claim 1, wherein the pul-verized solid fuel used has a particle size of not more than 1.5 mm.