CA1076422A - Coal burning arrangement - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Pyrolyzing pulverized coal to form char and volatiles, separating the char from the volatiles, burning the char in heat-transfer relationship with a stoichiometric excess of air, forming thereby ash and a mixture of gases, the excess of air being chosen to produce in the ash a temperature below the fusion temperature thereof, separating the mixture of gases from the ash, and thereafter burning the volatiles in the mixture of gases. Also, coal burning apparatus which comprises, in combination a spouted bed pyrolyzer, a fluidized bed combustor, a first cyclone, a second cyclone, and an after-burner, the pyrolyzer being connected to accept pulverized coal and to dis-charge char to the combustor and gaseous materials with entrained particulate material to the first cyclone, the first cyclone being connected to deliver gases to the afterburner, the combustor being connected to accept also a combustion supporting gas and to deliver to the second cyclone gaseous materials with entrained particulate material, and the second cyclone being connected to deliver gaseous material to the afterburner.

Description

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This invcntion relates to burning powdered coalO
The advantages of coal as an energy source need no elaboration here~
at this historical juncture. However~ burning coal has also had its dis-advantages such as initial handlinga handling of waste products of combus-tion~ equipment corrosion~ and pollution.
In recent years~ fluidized bed combustors have been developed that solve most of these problems~
Cyclones can be used with fluid beds because of the ash-coarsening agglomeration that occurs~ as is shown in U.SO Patent 3~431~892 (Godel) and UOS. Patent 3~171~369 (Stephens et al)O me emission of no~ious trace elements~ (e.gO3 beryllium~ cadmium and mercury) is minimized in fluidized beds by their far_lower operating temperatureO
Yet, the low outlet temperatures of conventional fluidized beds outlet gases cannot be used to provide heat for high-temperature furnaces~
Such low temperatures also create excessive stack-gas losses if conventional fluidized-bed combustors are retrofitted to existing boilers and space-heat-ing furnacesc The present invention overcomes these objections by providing a system with high outlet temperatures that nevertheless permits the char combustor to be operated at low temperaturesO One prior art system that also produces outlet temperatures appreciably higher than the char-burner temp- -erature is found in U.S~ Patent No. 3~358~624 (~ay)O The system uses a pyrolyzer to separate coal into char and volatiles~ a burner for the char cooled by excess air~ but only to keep the ash molten so that it will form as slag on the walls rather than be vaporized~ and a second burner for the volatiles and combustion products and excess air of the first burner~ giving a high output temperature.
Numerous pyrolyzers have been developed over the years to remove volatiles from coalO One requirement is for a pyrolyzer that can handle caking coals without foulingO The design perfected by the ~OSo Bureau of Mines ~Bureau of Mines Report of Investigation 7843, 1973), is particularly ~76422 suitable for the nee~s of the present invention. The design has been modified to withdraw solicl materials in a standpipe, instead of by gas entrainment from the top, thereby reclucing particle attrition. This modiEicatioll is suggested in "Spouted Becls," Kishan B. ~lathur, Norman epstein, Academic Press, New York, 1974.
Tlle invention permits coal to be burnt with great eEEiciency and witll very greatly reduced corrosion, pollution, and products handling problems, all with simplicity, capability of automatic operation) and adaptability to the widest range of installation sizes. Either wet or dry crushed coal, with or without additives, may be burned. Combustion is quiet and uniform, and at a closely controllable burning temperature. Furthermore, near stoichiometric flame temperatures are achieved with little excess oxygen.
Even fine fly ash is removed, along with sulfur, with great efficiency; and there is minimum formation of trace elements and N0x compounds. Corrosion of equipment is minimized. Retrofitting existing equipment is practical. -Altogether, the invention promises to be the lowest cost method of using coal in an environmentally acceptable manner in high temperature furnaces and in boilers retrofitted from other fuels.
The present invention provides the method of burning coal which comprises the steps of: pyrolyzing coal to form char and volatiles, contact-ing and reacting said volatiles with a sorbent at a zone before or after separating said char from said volatiles, separating said char from said volatiles, transferring reacted sorbent from said zone to a burner, burning said char in heat-transfer relationship with a stoichiometric excess of air in said burner, forming thereby ash and spent sorbent and a mixture of gases, said excess of air being~chosen to produce in said ash and spent sorbent a temperature below the fusion temperature of said ash, separating said mixture of gases from said ash, and thereafter burning said volatiles in said mixture `~
of gases.
0 In another aspect, the invention provides coal burning apparatus which comprises, in combination: means for pyrolyzing coal to form char and volatiles, means for separating sai char from said volatiles, means for ~ .

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contacting and reacting said volatiles with a sorbent at a zone before or aTfter separating saicl char from said volatiles, means for transferring reactecl sorbent from said zone to a burnerJ a burner for burning said char in heat-transfer rclationsh:ip with a s-toichiometric exccss of air, form:ing thereby ash ancl spent sorbent ancl a mixture of gases, means for separating said mixture of gases from said ash, and means for thereafter burn:ing said volatiles in said m:ixture of gases.
The invention also provides coal burning apparatus which comprises, in combination, a spouted fluidized bed pyrolyzer, a fluidized bed combustor, a first cyclone, a second cyclone, and an afterburner, the pyrolyzer being connected to accept pulverized coal and to discharge char to the combustor - 2a -1076~ZZ

and gaseous mateFials with entrained particulate material to the first cyc~
lone~ the first cyclone being connected to deliver gases to the afterburner~
the combustor bei.n~ connected to accept al90 a combustion supporting gas and to del:iver to the second cyclone gaseous materials with entrained particu-late material~ and the second cyclone being connected to deliver gaseous material to the afterburner In preferred embodiments, the invention features also bringing the stoichiometric excess of air into contact with the char in pyrolyzing, providing in the pyrolyzer specific characteristics, carrying out the solid~
gas separations in cyclones~ burning char in a solids-recirculating fast fluidized bed combustor, providing in the combustor specific characteristics~
providing heat in the pyrolyzer by burning therein a portion of the combus-tibles thereinto, varying fusion temperature by adding a temperature varying material3 adding a diluent gas to volatiles before burning them~ adding water at the pyrolyzer~ adding sorbent at the pyrolyzer~ and adding oil at the afterburner.
Other advantages and features of the present invention will be :
apparent from the following speci:Eic description of preferred embodiments thereof given by way of example only and with reference to the accompanying drawings, in which:
Figure 1 is a diagrammatic flow chart illustrating a preferred ~:
embodiment of the invention;
: Figure 2 is a table showing temperatures and throughputs at various places in said embodiment;
Figure 3 is the preferred embodiment of pyrolyzer used therein, shown in vertical section;
Figure 4 is a vertical section of the preerred embodiment of fluidized bed combustor for use therein;
Figure 5 is a partial sectional view taken at 5-5 of Figure 4;
Figure 6 is a vertical sectional view of the afterburner preferred ' : .:' ' ' for use therein:
Figure 7 is a vertical sectional view of the preheaters preferred for use therein; and ~ igure 8 is a somewhlt diagrammatic view in perspective of the preferred embodiment of the inventionO
Turning now to my presently preferred embodiment~ and describing it in a manner enabling to those skilled in the art, there is shown in Figure 1 a diagrammatic flow chart illustrating a combination of elements arranged to burn coal according to my novel inventionO
In this embodiment~ I burn Illinois high volatile bituminous Grade B coal with 3.0% sulfur content~ ash content of 1005%~ and a heating value of 11,300 BTU/lb. The coal is dried and crushed to pass 8 mesh at the mineO
Dry limestone crushed to pass 8 mesh is m1xed (not shown) with the coal just upstream of mixed-coal-and-limestone feed line 10 (Figo 1)~ by dropping each from its separate screw feeder into a venturi for transport air (not shown), the two venturis discharging into a common zoneO Downstream of this~ but just upstream of feed line 10~ bleed air is introduced. (The compressor for the transport air has a capacity of 40 psi~ and supplies the transport air for each purpose hereinafter mentioned~ m e blower for the bleed air has a capacity of 2 psi). Coal~ limestone, transport air~ and bleed air enter pyrolyzer 12 through line lOo Gaseous products move through refractory lined line 14 into char cyclone 16~ which removes entrained particles-O The cleaned gases are then introduced through refractory lined line 18 into afterburner 200 Most of the char produced in pyrolyzer 12 pass~s through standpipe 22 into inlet line 24~ me char discharged from cyclone 16 through line 26 also enters line 24 (A venturi in each of l~ne 22 and 26~ each cooperating with transport air from the transport air compressor, blows the two together in a Y the single outlet of which is line 24; venturis and compressors are not shownO) Line 24 discharges into fast fluidized-bed combustor 28, which serves as the : ' ` . , 3~07~Z2 prcferred char burncrO ~lso di.scharging into the fast fluidized-bed combustor (transfer l:ine reactor with solids rec:irculat:ion) 28 is combustion air blown through l:ine 30 by blower 320 Al:L the products of combustion~ nitrogen~ and remaining oxygen flow through refractory lined line 34 into ash cyclone 36 in which most of the ash (with spent limestone) is removed through line 420 Most of the residue (ash ~ spent limestone) leaving the fluid bed combustor 28 does so through standpipe 400 Residue leaving through standpipe 40 is mixed with residue leaving ash cyclone 36 through line 42, each of lines 40 and 42 including a venturi (not sho~n) cooperating with transport air~ mixed residue emerging in line 440 Hot gases leave ash cyclone 36 through refractory insulated line 46, and mix and burn with gases from line 18 in :
after burner 200 Hot products of combustion leave afterburner 20 and enter : a furnace (not shown).
This preferred embodiment provides an energy output of 10,000,000 BTU per hour. Input flow rates are 930 pounds per hour of coal transport .:
air, 1380 pounds per hour of bleed air, and 9010 pounds (130% of stoichio- .
metric) of combustion airO ~ines are of piping as follows:
ine No~Standard Pipe Size/I~DO Nonstandard ¦Inches)

2 (standard) 14 10 (I ~Do nonstandard) 18 6 (IoDo nonstandard) 22 2 (IoDo nonstandard) : 24 12 (IoDo nonstandard) :~ 26 2 (IoDo nonstandard) 8 (IoDo nonstandard) 34 22 lIoD~ nonstandard) 2 (IoDo nonstandard) 42 2 (IODg nonstandard) 44 3/4 (I~Do nonstandard) - 5 _ ~7f~42Z

ine NoO Standard Pipe Size/IOD, Nonstandard (Inches) 46 12 (I~Do nonstandard) Only enough air i.s provided in the W rolyzer to b:ring its temp-erature to 1600 F.~ be].ow the fus:ion point of the ash of the particular coalO
Tcmperature in the upper zone of the fast fluidized-bed combustor 28 is held at 1570Fo (In both the pyrolyzer and the fluidized-bed combus-tor temperature :i9 maintained by a sensor working with a controller to regu-late air flow to the respective unitO) If the temperature in the pyrolyzer falls unduly, less volatiles are produced; this means more combustion in the fluidized-bed combustor, with consequent increased necessary excess air there and thus overall lower temperature at the afterburnerO Also~ unduly lower temperature in the pyrolyzer causes less fuel-nitrogen compound break-down, compromising what is otherwise one of the advantages of my invention making possible burning coal with low production of NO compoundsO On the other hand~ unduly high temperatures in the pyrolyzer and fluidized-bed combustor result in undesirable slagging and structural problemsO Unduly high temperature in the fluidized-bed combustor also causes excess lime-stone useO Unduly low temperatures in the fluidized-bed combustor both cause excess limestone use and require use of more excess air, and thus lower afterburner temperature undesirablyO Detailed flow rate data and transport air quantities are shown in the chart of Figure 20 To start up, when a thermostat moves to call for heat~ the pneumatic air transport compressor and the air blower turn on. The compressor purges lines during preheating, while the blower blows air through the preheatersO
Three preheaters (not shown), one for each of the pyrolyzer 12, char cyclone 16, and fluidized-bed combustor 28 are then turned on ~unless a thermo-couple, carried by each of them, in one or more of them senses that the respective element is still hot from a recent run)O Each turns off when the component it is heating reaches the predetermined temperature (minimum operating temperature), 1200 Fo Gas temperatures out of preheaters are 1300 Fo into the pyrolyzer and fluidized-bed combustor and 1800Fo into the char cyclone~

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When the elements are tlp to temperature, coal and limestone feed is begunO
Blower air is then redirected from the preheaters to the pyrolyzer and the s fluidized-bed combustorO Blower air at room temperature is also introduced tnot shown) into line 18~ just downstream of char cyclone 16~ and with volatiles (not shown) at the entrance of line 18 to heat ito (This prevents ~mwanted condensation~ as well as unwanted soot build-up, in line 180) When the downstream end of line 18 reaches its minimum operating tcmperature of 1000F.~ as indicated by a thermocouple~ air to line 18 is shut offO
Lines 24 and 44 are water-cooled.
When the system is shut down the compressor runs for a short further time, to make sure lines are clear.
Many variations within the spirit and scope of my invention will be apparent to those skilled in the art. m us, as examples only, the char burner may be a slow Eluidized-bed combustor or a gas-turbine-type (dilute phase) combustorO Again~ if low-sulfur coal is used, a single-~one combustor, for example, can be run at ash agglomerating temperatures Ifrom 1900F. to 2200F~)~ causing agglomeration and permitting efficient flyash removal by cyclone. A fines separator may be added to the system downstream of the ash cyclone and upstream of the afterburner (a sand bed filter) or downstream of the furnace or boiler (various low-temperature filters)O A desulfurizing chamber may be added, also, as a separate piece of equipment, downstream of the agglomerating combustor, both upstream of the char cycloneO Pyrolysis could be achieved by recycling some hot products rather than directly from a part of the coal, as in the preferred embodimentO Any coal of rank hvAb or lower may be usedO Or, cooling air or water could be used through a heat exchanger at the combustor rather than added as combustion air. The sorbent material for the capture of sulfur compounds may be lime~ half-calcined lime-stone, or dolomite, rather than limestone. Fluxes may be mixed with the feed to the pyrolyzer or char burner to lower the ash fusion point; soda ash ~Na20)~ borax (B203), or potash (K20) may be added to reduce the fusion ~L~7t~422 temperature, thereby increasing the tendency to agglomerate and improve collection efficiencyO Conversely, addition of silica will increase the fusion point, if desired to prevent slagging. If desired, diluent gases~
such as steam or recirculated products of combustion~ may be added to line 14~ to reduce hydrocarbon concentration in Line 14 and downstream elements~
thereby inhibiting the cracking of saturated hydrocarbons and PoulingO Water may be added to the pyrolyzer to gasify some of the char~ principally by the steam-carbon reaction (H20 + C -~ C0 + H2)o This reduces char to the char burner and increases volatiles to afterburner 200 This reduces needed com-bustion air (through line 30), and makes possible adding preheated air to afterburner 200 mis reduces system fuel consumption and increases the flame temperature and furnace output, permits use of coals with lower volatile-matter content without reducing outlet flame temperature, and allows the use of water slurry coal feed--which simplifies coal handling, storage, and trans~
portation--, and eliminates the need for coal drying, and reduces system size and cost, since the combustion air added at the afterburner bypasses re-; actors and cyclone)O
If9 as mined~ the coal contains pyrite in amount to give a sulfur content over three percent, any excess thereover is removed, at the mine Turning now to a description of each of the elements of Figure 1 in more detail~ there is shown in Figure 3 pyrolyzer 12~ comprising inlet 50~ tank 52, deflector 54, standpipe outlet 56~ and upper outlet 58. Pyro-lyzer 12 is 12 feet 7 inches high, Pyrolyzer 12 is refractory lines (TmaX-1800 Fo for tank 52)~ and has an outer wall of carbon steel.
In operation, the pyrolyzer 12 is first filled with powdered material. In a new system, the material may be any non-melting substance such as sand; after run-up~ the char and limestone from the previous run is used insteadO
m e pyrolyzer contents and walls are heated during start-up by .

~7~;Z;2 combustion products entering at inlet pipe 10~ as has been previously describedO When the temperature :in pyroly~er 12 is brought to 1200 Fo by preheating as previ.ous.Ly described, coal~ limestone~ transport air~ and bleed air enter inlet 50 from line lOo Conical deflector 54 prevents, on start-up, jetting of the feed materia.ls through tank 52 and out through outlet 580 The feed materials accumulate within tank 52 by virtue of the spouted fluidi7ed bed created by interaction of the incoming stream transport air, coal, lime-stone~ and bleed air on the char and limestoneO Thus the feed spouts up the ~ .
center of tank 520 Char produced by pyrolysis, along with the limestone, ~
circulates by flowing downward in the annulus~ then being entrained at the ~ -bottom of tank 52 by the incoming stream, before showering back to the an-nulusO Pyrolysis of the coal occurs as the incoming particles of coal are heated by the recirculating char and limestoneO Each particle of incoming coal is immediately surrounded by several particles of inert, non-sticky~
char and limestone. (This is important if the incoming coal is of the caking type; without the dilution effect, the incoming coal would agglutinate into a large lump. The narrowness of the cone, of only 20~ helps promote the rapid mixing of recirculating solids with incoming coal.) Combustion of the incoming air with the coal, char~ and volatile matter heats the solid materials in the pyroly~er by combustion, only enough air is supplied to create 1600Fo Lime (the reaction products of which are elsewhere herein referred to as "spent limestone") produced from the thus-calcined limestone reacts with the emitted sulfur compounds in the volatiles (primarily H2S), -;
thereby scrubbing the gas stream while forming spent sorbent, primarily CaS
(calcium sulfide).
The char and spent limestone pass through standpipe 56 to line 24 and then to combustor 28, as above describedO Gaseous products and entrained : char and limestone fines pass out through upper outlet 58, through line 14 to char cyclone 16~
Char cyclone 16 is a quite standard cyclone separator designed for ':'' ' : ~ ' .

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highly efficient removal of the entrained particles from the gases leaving W rolyzer 12. Gases with a velocity oP 50 feet per second enter tangentially into the side of thc cyclone adjacent its wider top; particles are whirled to the outsicle~ and spin downwardly until they fall through an outlet in the bottom connected to line 26. Transport air (from a compressor not shown) keeps the particles ~oving out of cyclone 16 and through lines 26 and 22 by ejector actionO Cleaned gases leave through an outlet in the top of the cyclone connected to line 180 Cyclone 16 is 14 feet high and is lined with

3/4 inch refractory-filled hexagonal steel honeycomb (TmaX-1800F.) anchored with studs~ surrounded by 3 inch heat insulating refractory and an outer carbon steel casingO
Char and limestone from line 24 enter fast fluidized-bed combus-tor 28 (Figo 4)9 where combustion of the char takes placeO Combustor 28 comprises concentric tubes 100 and 102~ which form the main body of the combustor and define both annular burner zone 104 between the tubes and inner chamber 106 within tube 1020 Combustor base 108, mounted on struts 105~ has hollow conical portion 109 projecting upward into chamber 1067 a tapered annulus 106a thereby being defined be~een tube 102 and conical portion lO9o Annulus 104 is divided into a lower fast fluidized bed ash-agglomerating combustion zone at 2000F. and an upper fast fluidized beddesulfurizing zone at 1570F. by air entering manifold 113 and through circumferential slot 115 into annular zone 1040 Deflector rings ll9a and ll9b prevent solids backflow and assist in defining the two zonesO Tube 102 is spaced above base 108 to define, at the bottom of combustor 28~ zone 107~ which connects ~one 104 with annulus 106a and chamber 106. Circular char inlet manifold 110 connects l;ne 24 to burner zone 104 by eighteen tubes 111 fitted through holes in the walls of tube 100 and spaced circum ferentially thereabout. Air inlet 112 connects line 30 with circular mani-fold 114~ located within conical portion 109 near its bottom~ and manifold 114 in turn is connècted by twenty-four circumferentially spaced ejector -- 10 _ .

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tubes 116 to zone 107, ejcctor tubes 116 being fitted through holes in conical portion 1090 Also fitted through conical portion lOg is ash outlet pipe 117, which connects annular zone 106a near the top of conical portion 109 with standpipe 400 Flue 118 connects chamber 106 with line 34. Connect-ing burner zone 10~ and chamber 106 at the top of combustor 28 is vaned separator 120, which has twelve equally spaced (75) vanes 121 (Figo 5).
Combustor cover 122 overlies separator 120 and tube 102, connected at its top to separator 120~
Combustor 28 is 17 feet 8 inches higho Tube 100 has an outer steel casing (1/4 inch thick)~ which surrounds a 3 inch thick castable refractory3 which in turn surrounds a 3/4 inch refractory-filled hexagonal steel honeycombO Tube 102 is composed of an outer wall of 3/4 inch refrac-tory-filled hexagonal steel honeycomb and an inner wall of the same 3/4 inch refractoryO ~etween the inner and outer honeycombs is 3/16 inch thick steel tube running the length of tube 102 and welded to the honeycombs on 6 inch centersO Slot 115 is 3/16 inch.
In operation~ preheating of combustor 28 is accomplished~ as above described9 with preheated air entering through inlet 112 to bring combustor 28 to 1200Fo Combustion air from blower 32 then directly passes to com-bustor 28 through inlet 1120 Char and limestone from pyrolyzer 12 and char cyclone 16~ carried by transport air~ enter manifold 110 from line 24~ and : are distributed through tubes 111 into the bottom portion of burner zone 1040 Air blown from inlet 112 into manifold 114 distributes through ejector nozzles 116 into zone 107~ and from there sweeps char and limestone upward through burner zone 104~ Combustion begins in zone 104, ignited by the heat of recirculating solidsO Combustion continues in an upward directi~n through zone 104 in the form of a fast fluidized bed composed of char~ limestone~
and combustion air. The products of combustion move upwards with a super-ficial velocity of 18 feet per secondO Products of combustion7 excess oxygen~ and unburned char rise up to separator 120~ which~ in conjunction ~ 11 --.. . . . .
. . : .

~076~Z2 with chamber 106~ acting as a conventional cyclone separator~ causes the oncoming mass of solids and gases to swirlO Swirling solids comprising ash~
spent ~imestol-e~ and some unburned char enter chamber 106 and fall along the :inner walls o.f tube 102 into tapered annulus 106aO The swirling action assures that only ~ery small particles of ash and still-burning coal can escape from the burnerO
The ejec-tor action caused by air flow from properly dimensioned ejector tubes 116 draws some of the first to fall solids out through zone 107 and recirculates them back up through zone 104 for burning of any un-burned char. In spite of the ejector action~ solids so accumulate in annu-lus 106a in the form of a slow fluidized bedO Nhen the bed reaches the level of ash outlet pipe 117~ pipe 11? acts as a weir to draw off the excess solids~
made up of ash and spent limestone, and carry them down to standpipe 40;
from there the solids go to line 44~ and finally are flushed out by trans-port air~ to an ash hopper (not shown).
The maintenance of a stoichiometric excess of air in combustor .
28 holds combustor temperature at 1570F.~ which is the temperature at which desulfurification by limestone occurs with the least use of the sorbent~
Yet it is desirable to operate a portion of the annulus 104 at a higher temperature~ 2000Fo~ in order to maximize the agglomeration of fine flyash particlesO It becomes desirable to operate burner 28 with two temperature zones~ the lower zone at the higher temperatureO
me two zones are created by placement of a fluid-dynamic check :
valve~ placed in the middle of annulus 10~. The opposing rings forming the check valve retard slippage of solids by mechanically blocking their flow.
~he check flow action is enhanced by the introduction of the air stream through slot 115~ which air is also used to cool the gases from the optimum .
ash-agglomerating temperature (2000Fo) to the optimum desulfurification temperature (1570 F~). me relative amount of air entering through air inlet 112 and slot 115 is controlled by two temperature sensors~-one in each ' : - 12 _ , ~.~7~22 annular fast fluidized bed zone; a sensor in the lower zone regulates air through air inlet 112 to fix lower zone temperature at 2000Fo~ and a sensor in the upper zone regl~ates air througll slot 115 to maintain the proper upper zone temperatureO
Similar to char cyclone 16 is ash cyclone 36~ two of which connec~
ted in parallel I use in ny presently preferred embodimentO Ash cyclone 36isa quite standard cyclone separator proportioned for highly efficient particle removala and is composed of generally the same materials for refractory and casing as is cyclone 160 Cyclone 36 is 15 feet 10 inches high~
and has a tangential inlet on its side near the top. Upper and lower outlet configurations are substantially the same as in cyclone 160 In operation~
hot gases from combustor 28 having an inlet velocity of ~5 feet per second enter through the tangential inletO Ash and spent limestone are centrifu-gally whirled~ fall downward~ and finally pass through the bottom outlet . connected to line 42 and then to line 44O Transport air flushes these solid products out through lines 42 and 44O Clean combustion gases (1570Fo) leave by the top outlet, and pass through line 46 to afterburner 200 Receiving clean combustible gases from char cyclone 16 through line 18 and clean combustion gases as well as nitrogen and remaining oxygen from ash cyclones 36 -through line 46 is afterburner 20 (Figo 6)o Gases from : line 46 pass axially into cylindrical afterburner 20 through inlet 130n Gases from line 18 under press~e enter tangentially through inlet 132 into annular chamber 134~ from which they are uniformly introduced radially into the flow of gases from inlet 130 for eYen mixing thereof by distributor 136, a ring having a series of circumferential ports 136a fitted within after-burner 20 downstream of inlet 130 and concentrically within annular chamber 1340 In operation~ gases from inlets 130 and 132 are hot enough to initiate combustion in combustion chamber 138 between the combustible gases from inlet 132 and the unconsumed oxygen from inlet 1300 The afterburner 20 discharges directly into a furnace (not shown)~

- 13 _ 1~76422 through a 24 inch ~iameter openingO Afterburner 20 is fitted into a hole in the furnace wall, by attaching flange 142 to the furnace casing. In this configuration~ combustion chamber 138 is 4 feet long. Alternatively~ a flange 142a may be attached to the afterburner as sho~n, and attached to the Eurnacc~ In the latter case~ the afterburner casing downstream of flange L42a is removed. In this configuration, combustion chamber 138 is 1015 feet longO With the collfiguration of flange 142~ combustion is essentially completed within the afterburnerO ~ith the configuration of flange 142a, combustion is completed within the furnace. The former configuration may improve the completeness of combustion, particularly with boilers and other furnaces where the walls are relatively cold. The latter configuration is more compact and is cheaper to buildo ~n element used in start-up~ as described above7 is preheater 150 (Figo 7)3 two of one size being used for pyrolyzer 12 and char cyclone 16 and a larger one being used for combustor 28. For each start-up in which preheating is required, blower 32 blows air (60 Fo) into each preheater 150 through inlet 1520 The air passes into vaned chamber 154~ where it separ-ates, part flowing axia~Ly through center conduit 156, and part being swirled outwardly through vanes 155 (approximately 45) into the annuLar spaced surrounding chamber 154 and then into combustion chamber 158. Natural gas is admitted through inlet 160 into manifold 162, and issues therefrom into the annuLar space space surrounding chamber 154, thereby mixing with the swirl-ing air and burning upon ignition initially by a spark plug (not shown) located in chamber 1580 Air passing through conduit 156 is swirled by vortex generator 164, and~ upon leaving conduit 156~ mixes with the gases passing through chamber 158, which are products of combustionO
~he air passing through vanes 155 is the primary air, and is approximately the amount required for complete combustion of the gas~ The air entering through duct 156 is the secondary air~ and is used to cool the products of combustion to the temperature needed to preheatO ~ithout this ~764;~2 cooling air~ products of combustion leaving the burner 150 would be too hot~
causing structural damage to the piping of lines 109 14~ and 30. ~irflow through tube 156 a]so cools the tube7 and prevents structural damage that would otherwLse occur due to the heating by hot gases in combustion zone 1580 Cond~it 156 and chamber 158 are made of stainless steelO The smaller version of preheater 150 i9 17 inches longO Natural gas flow into inlet 160 iY 200 standard cfh~ and airflow into inlet 152 is 7200 standard cfh for pyrolyzer 12 and 4800 standard cfh for char cyclone 160 The larger version of pre-heater 150, for combustor 28~ is 42 inches long. Natural gas flow into inlet 160 is 1000 standard cfh~ and airflow into inlet 152 is 36~000 stand-ard cfho The heated air passes from outlets 166~ and enters pyrolyzer 12 char cyclone 16, and fluid bed combustor 28 in their usual air entrancesO
~ inally~ there is shown in Figo 8 a burner station such as could be used in a factory or power plant. Preheaters 150 are not shown in this figure. ~ compressor 31 is shown adjacent blower 32~ The various elements are mounted on foundations 6 and 8 ~braces and other supports not shown). A
system of valves (not shown) can be used to coordinate coal~ limestone7 air~
and water feeds for the station, an operator at a central control panel (not shown~ effectively running the burnerO Hoppers to store powdered coal~
ash~ and limestone are not shownO

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Claims (22)

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

1. The method of burning coal which comprises the steps of: pyrolyzing coal to form char and volatiles, contacting and reacting said volatiles with a sorbent at a zone before or after separating said char from said volatiles, separating said char from said volatiles, transferring reacted sorbent from said zone to a burner, burning said char in heat-transfer relationship with a stoichiometric excess of air in said burner, forming thereby ash and spent sorbent and a mixture of gases, said excess of air being chosen to produce in said ash and spent sorbent a temperature below the fusion temperature of said ash, separating said mixture of gases from said ash, and thereafter burning said volatiles in said mixture of gases.

2. Coal burning apparatus which comprises, in combination: means for pyrolyzing coal to form char and volatiles, means for separating said char from said volatiles, means for contacting and reacting said volatiles with a sorbent at a zone before or after separating said char from said volatiles, means for transferring reacted sorbent from said zone to a burner, a burner for burning said char in heat-transfer relationship with a stoichiometric excess of air, forming thereby ash and spent sorbent and a mixture of gases, means for separating said mixture of gases from said ash, and means for thereafter burning said volatiles in said mixture of gases.

3. Coal burning apparatus according to claim 2, wherein said pyrolyzer comprises a lower entrance passage progressively changing in direction from transverse to longitudinal, a cylindrical chamber portion is defined by a line rotated about the longitudinal axis of said pyrolyzer, a conical transition portion is between said entrance passage and said cylindrical chamber portion, an outlet passage of smaller diameter than said cylindrical chamber portion is disposed above said cylindrical chamber portion, a deflector is positioned in said cylindrical chamber portion to bar flow directly along a parallel to said longitudinal axis from the lower portion of said cylindrical chamber portion into said outlet passage, and a standpipe emerges from said cylindrical chamber portion upstream of said deflector.

4. Coal burning apparatus according to claim 2, wherein said fluid-ized bed combustor being of fast, solids-recirculating character and said com-bustor includes a central recirculation chamber defined by a first portion cylindrical about the combustor longitudinal axis and a generally conical por-tion, an annular fast fluidized bed chamber is positioned around said central recirculation chamber, said central recirculation chamber and said fast fluid-ized bed chamber communicating beneath said first portion, said first portion defining with said generally conical portion a central recirculation chamber annulus, said generally conical portion being provided therethrough with a multiplicity of air jets, and said fast fluidized bed chamber being provided therethrough around a lower periphery thereof with a multiplicity of char in-let passages.

5. The apparatus of claim 4 in which said central recirculation chamber and said fast fluidized bed chamber communicate at their opposite ends around the other end of said first portion through a multiplicity vanes angled to provide materials moving from said fast fluidized bed chamber to said central recirculation chamber with a centrifugal movement to throw solids toward the inner wall of said first portion, and said generally conical por-tion includes a withdrawal standpipe.

6. The apparatus of claim 4 in which said air jets promote circula-tion from said central recirculation chamber to said fast fluidized bed chamber.

7. The apparatus of claim 4 in which said fast fluidized bed chamber is divided into a lower agglomerating chamber and an upper desulfurizing chamber.

8. The apparatus of claim 7 in which said agglomerating chamber and said desulfurizing chamber are separated by a fluid dynamic check valve.

9 The method of burning coal which comprises the steps of introduc-ing pulverized coal and sorbent into a fluidized bed pyrolyzer, carrying out in said pyrolyzer a reaction to produce char, desulfurized volatiles, and sulfur-bearing sorbent containing sulfur taken from said volatiles, separating the char and sorbent from the desulfurized volatiles, introducing the char and sulfur-bearing sorbent into a fluidized bed burner, introducing into the burner a stoichiometric excess of air, said excess of air being chosen to produce an ash temperature below the fusion temperature thereof, burning the char in con-tact with the sulfur-bearing sorbent and in heat-transfer relationship with the stoichiometric excess of air, forming thereby dry ash, a desulfurized mixture of gases, and sorbent-bearing sulfur in increased amount, separating said mixture of gases from said ash, and burning said desulfurized volatiles in said desulfurized mixture of gases.

10. The method of claim 9 in which said stoichiometric excess of air is brought into physical contact with said char.

11. The method of claim 9 in which said pyrolyzer is heated by burning a portion of the combustibles introduced there-into.

12. The method of claim 9 in which a diluent gas is added to said volatiles before burning said volatiles in said mixture of gases.

13. The method of claim 9 in which H20 is added at said pyrolyzer.

14. The method of claim 13 in which preheated air is added in burning said volatiles.

15. The method of claim 9 in which said coal is Illinois high volatile bituminous Grade B, and said ash temperature is 1600°F.

16. Goal burning apparatus which comprises, in combination: a spouted fluidized bed pyrolyzer, a fluidized bed combustor, a first cyclone, a second cyclone, and an afterburner, means for introducing pulverized coal and sorbent into said pyrolyzer, means for transferring char and sorbent from said pyrolyzer to said combustor, means for transferring gaseous materials with entrained particulate material from said pyrolyzer to said first cyclone, means for trans-ferring gaseous materials from said first cyclone to said afterburner, means for introducing a combustion supporting gas into said combustor in quantity sufficient to maintain a temperature of combustion products below the fusion temperature of ash from the char, means for transferring gaseous materials with entrained particulate material from said combustor to said second cyclone, and means for transferring gaseous materials from said second cyclone to said afterburner.

17. The apparatus of claim 16 in which said fluidized bed combustor is of fast solids-recirculating character.

18. The apparatus of claim 16 in which said pyrolyzer is a solids-recirculating device.

19. The apparatus of claim 16 in which said combustor includes a collector therein.

20. The apparatus of claim 16 in which ejector means promote recircu-lation in said combustor.

21. The apparatus of claim 16 in which said pyrolyzer includes a standpipe for removal therefrom therethrough of char.

22. The apparatus of claim 16 in which hot particles recirculated into a portion of said combustor adjacent an outlet thereof are passed over vanes positioned therearound to provide a whirling motion and reduce needed freeboard to prevent escape of too-hot particles.