CA1079577A - Boiler cold start using pulverized coal in ignitor burners - Google Patents
Boiler cold start using pulverized coal in ignitor burnersInfo
- Publication number
- CA1079577A CA1079577A CA299,030A CA299030A CA1079577A CA 1079577 A CA1079577 A CA 1079577A CA 299030 A CA299030 A CA 299030A CA 1079577 A CA1079577 A CA 1079577A
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- coal
- air
- nozzle
- furnace
- ignitor
- Prior art date
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Abstract
BOILER COLD START USING
PULVERIZED COAL IN IGNITOR BURNERS
Abstract of the Disclosure:
An ignition, warm-up and low-load-stabilization system for furnaces fired by pulverized coal. In conjunction with a system in which pulverized coal is sent directly from a coal mill to a load-bearing nozzle and in which combustion air is brought to the nozzles from an air preheater that uses hot furnace gases to warm the combustion air, ignitor nozzles are provided that are supplied by pipes bearing coal from which the drying air has been separated. Combustion air for the ignitor nozzles is heated by an independent heat source that heats the combustion air or a portion thereof to a temperature higher than that of the air supplied by the air preheater. Such a coal-fired ignitor burner can replace oil or gas-fired ignitors and warm-up guns and thereby reduce the amount of oil or gas used in ignition, warm-up, and low-load stabilization.
PULVERIZED COAL IN IGNITOR BURNERS
Abstract of the Disclosure:
An ignition, warm-up and low-load-stabilization system for furnaces fired by pulverized coal. In conjunction with a system in which pulverized coal is sent directly from a coal mill to a load-bearing nozzle and in which combustion air is brought to the nozzles from an air preheater that uses hot furnace gases to warm the combustion air, ignitor nozzles are provided that are supplied by pipes bearing coal from which the drying air has been separated. Combustion air for the ignitor nozzles is heated by an independent heat source that heats the combustion air or a portion thereof to a temperature higher than that of the air supplied by the air preheater. Such a coal-fired ignitor burner can replace oil or gas-fired ignitors and warm-up guns and thereby reduce the amount of oil or gas used in ignition, warm-up, and low-load stabilization.
Description
. . ' ~ ~ .
Backqround of the Invention:
The present invention relates to the field of coal-fired furnaces. It relates particularly to a furnace that can ... .
-se coal for ignition, warm-up, and low-load stabilization.
S It is sometimes desirable to use coal rather than gas or oil in electrical generating facilities. In those si~uations, the utility will naturally hava a coal-fired unit built rather than an oil-fired unit. However, even in coal-fired units, substantial quantities of gas or oil are oten u9ed. In a typioal coal-fired unit, coal to be burned in the furnace is dried and pulverized in a coal mill and delivered directly from the coal mill to the load-carrying coal no2zles in the furnace. Operation of the coal mills requires that heated air be supplied to the mills for drying and conveying the coal. This air is supplie~ by a forced-draft fan that forces the air through an air preheater, a de-vice that uses the hot products of combustion in the furnace - to preheat the air. This preheated ~ y aiL, the air used for drying and conveying coal, is delivered with the coal to ~e coal nozzles and used to support combustion. The primary air is typically not sufficient in quantity to support combustion of all the coal, 50 secondary air is brought directly from the air preheater to the furnace to supply the rest of the air needed for combus~ion. The coal thus supplied with air is caused to burn due to ignition enexgy from the primary air, the secondary air, the heat in the coal itself, radiation and conduction from flame in thP furnace, and radiation ~rom furnare walls~
:
It is to he noted that almost all of these combustion 30 , energy sources presuppose that the furnace has already been
Backqround of the Invention:
The present invention relates to the field of coal-fired furnaces. It relates particularly to a furnace that can ... .
-se coal for ignition, warm-up, and low-load stabilization.
S It is sometimes desirable to use coal rather than gas or oil in electrical generating facilities. In those si~uations, the utility will naturally hava a coal-fired unit built rather than an oil-fired unit. However, even in coal-fired units, substantial quantities of gas or oil are oten u9ed. In a typioal coal-fired unit, coal to be burned in the furnace is dried and pulverized in a coal mill and delivered directly from the coal mill to the load-carrying coal no2zles in the furnace. Operation of the coal mills requires that heated air be supplied to the mills for drying and conveying the coal. This air is supplie~ by a forced-draft fan that forces the air through an air preheater, a de-vice that uses the hot products of combustion in the furnace - to preheat the air. This preheated ~ y aiL, the air used for drying and conveying coal, is delivered with the coal to ~e coal nozzles and used to support combustion. The primary air is typically not sufficient in quantity to support combustion of all the coal, 50 secondary air is brought directly from the air preheater to the furnace to supply the rest of the air needed for combus~ion. The coal thus supplied with air is caused to burn due to ignition enexgy from the primary air, the secondary air, the heat in the coal itself, radiation and conduction from flame in thP furnace, and radiation ~rom furnare walls~
:
It is to he noted that almost all of these combustion 30 , energy sources presuppose that the furnace has already been
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s~
operating, and, in the large furnaces used in power generat~
it presupposes that the furnace has been operating for a fairly long time. Accordingly, in order to sause and sustain comhustion of the coal, it is necessary to use an auxiliary ~uel for warming up the furnace walls, for providing ignition flame, and for warming up the air preheater. This is usually the function o oil- or gas-fired ignitors and warm-up guns.
In a typical installa-tion, a relatively high-capacity oil bùrner is started by an ignitor, and this starts the process or warming up the furnace walls and the heat-exchange surfaces of the air preheater. This can take some time, and the use of 70,000 gallons of oil in a SOO-megawatt unit for one startup alone is not uncommon. In addition, there is considerable capital expense involved in providing the hard-ware that is used for supplying oil. Once the furnace has been brought up to temperature, the coal noz21es are ignited by oil- or gas-fired ignitors or by thewarm-up guns themselves.
The use of auiliary fuel is not necessaril~ over when the coal nozzles have started to supply coal. At high boiler loads--that is, when the amount of coal supplied by the no2zles is great--the furnace can typically maintain stable combustion of the pulverized coal. However, when the load goes down and the coal supply is thereby decreased, the stabLlity of the pulverized coal flame is also decreased, and it is therefore common practice to use the ignitors or w~rm-up guns to maintain flame in the furnace, thus avoiding , , .
the accumulation o unburned coal dust in the furnace and the associated danger of explosion.
All of these functions of the oil- or gas-fired hurners rely on the greater ease of ignition of these fuels; less `~ _3_ ~ 3~
heat LS re~uired, fro~ whatevex s.ouxce., to liberate the volatiles and there~y in~.t~ate or sus:tain combustion.
Conversely, the ~reater d~.fficulty encountered in i.gniting coal is the reason wh.y ~t has typically not been used for the ignition, warm~up and low~load-stabilizati~on functions. An incidental advantage of oil and gas that also contributes to the greater des~ra~.ili`t~ of the~i`~ us-e fo~ these. ~unctions is that it i5 possi~file to suppl~ th.em ~n relati~ely small pipes, there~y~ keep~ng t~eir contri~ut~on to the congestion in the :
fuel-nozzle area to a minimum. The us~lal method of supplyiny coal to nozzIes h~s ~e~u~æed rat~:e~ large p~ping~ and the addition of more large~si`ze p~p~ng would not he we.lcome in the area i:mmed~ately ~eh~nd th.e. ueI nozzles.
Summary of the In~ent~on:
It ~s accord~ngl~ an o~ject of the present invention to accompl~sh th.e ~unctions of ignition t warm-up r and low-load ! stabilization ~th the use of a minimum of auxiliary fuel.
Acco~dingl~, in a furnace s~stem that i.ncludes a l furnace, a ma~n coal nozzIe arranged to direct coal into the :
;l 20 furnace, an air preheater ha~ing a flue yas inlet, an air j inlet, and an a~r outlet and being connected to receive flue .
gas:es from th.e furnace at its flue gas i`.nlet and transfer heat from the 1ue gases to a~.r enteri.n~ the ai.x i.nlet and leaving the air outlet, a main pul~erizer, condu~t.means connected to conduct coal -from t~e pulYerizer outlet to the m~i.n coal nozzle, means for forci:ng a ~irst air stream thxough the p~eheater . ;
from its aIr ~nlet to its ai.r outle.t, and from the ~ir outlet . -~
through the pulYer~zer and into t~e: main coal nQzzle, and ~ :
~eans for forcing ~ second air stream f~om the preheater outlet
s~
operating, and, in the large furnaces used in power generat~
it presupposes that the furnace has been operating for a fairly long time. Accordingly, in order to sause and sustain comhustion of the coal, it is necessary to use an auxiliary ~uel for warming up the furnace walls, for providing ignition flame, and for warming up the air preheater. This is usually the function o oil- or gas-fired ignitors and warm-up guns.
In a typical installa-tion, a relatively high-capacity oil bùrner is started by an ignitor, and this starts the process or warming up the furnace walls and the heat-exchange surfaces of the air preheater. This can take some time, and the use of 70,000 gallons of oil in a SOO-megawatt unit for one startup alone is not uncommon. In addition, there is considerable capital expense involved in providing the hard-ware that is used for supplying oil. Once the furnace has been brought up to temperature, the coal noz21es are ignited by oil- or gas-fired ignitors or by thewarm-up guns themselves.
The use of auiliary fuel is not necessaril~ over when the coal nozzles have started to supply coal. At high boiler loads--that is, when the amount of coal supplied by the no2zles is great--the furnace can typically maintain stable combustion of the pulverized coal. However, when the load goes down and the coal supply is thereby decreased, the stabLlity of the pulverized coal flame is also decreased, and it is therefore common practice to use the ignitors or w~rm-up guns to maintain flame in the furnace, thus avoiding , , .
the accumulation o unburned coal dust in the furnace and the associated danger of explosion.
All of these functions of the oil- or gas-fired hurners rely on the greater ease of ignition of these fuels; less `~ _3_ ~ 3~
heat LS re~uired, fro~ whatevex s.ouxce., to liberate the volatiles and there~y in~.t~ate or sus:tain combustion.
Conversely, the ~reater d~.fficulty encountered in i.gniting coal is the reason wh.y ~t has typically not been used for the ignition, warm~up and low~load-stabilizati~on functions. An incidental advantage of oil and gas that also contributes to the greater des~ra~.ili`t~ of the~i`~ us-e fo~ these. ~unctions is that it i5 possi~file to suppl~ th.em ~n relati~ely small pipes, there~y~ keep~ng t~eir contri~ut~on to the congestion in the :
fuel-nozzle area to a minimum. The us~lal method of supplyiny coal to nozzIes h~s ~e~u~æed rat~:e~ large p~ping~ and the addition of more large~si`ze p~p~ng would not he we.lcome in the area i:mmed~ately ~eh~nd th.e. ueI nozzles.
Summary of the In~ent~on:
It ~s accord~ngl~ an o~ject of the present invention to accompl~sh th.e ~unctions of ignition t warm-up r and low-load ! stabilization ~th the use of a minimum of auxiliary fuel.
Acco~dingl~, in a furnace s~stem that i.ncludes a l furnace, a ma~n coal nozzIe arranged to direct coal into the :
;l 20 furnace, an air preheater ha~ing a flue yas inlet, an air j inlet, and an a~r outlet and being connected to receive flue .
gas:es from th.e furnace at its flue gas i`.nlet and transfer heat from the 1ue gases to a~.r enteri.n~ the ai.x i.nlet and leaving the air outlet, a main pul~erizer, condu~t.means connected to conduct coal -from t~e pulYerizer outlet to the m~i.n coal nozzle, means for forci:ng a ~irst air stream thxough the p~eheater . ;
from its aIr ~nlet to its ai.r outle.t, and from the ~ir outlet . -~
through the pulYer~zer and into t~e: main coal nQzzle, and ~ :
~eans for forcing ~ second air stream f~om the preheater outlet
3~ into th.e furnace, there. i~ provided ~ccording to one aspect of ' ~ .:
_ ' "'' " ' ' ~-, the present inye.ntion an i.gnito.r nozzle posi.ti.oned for ignition of coal leaving the main coal nozzle, an ignitor pul~erizer for pulverizing coal, a separator for separating coal from aîr, me~ns for conveying coal ~ixed with air from the ignitor pulverizer to t~e separator, means for conveying coal fxom the separator to the ~gnitor nozzle, means. for causing a third air stream hav~.ng a temperature higher th.an the te~pe.rature of either the first or the: second air stream to flow to the ignitor nozzle, and a li~h.ter, posi~tiona~le near the outlet o~ the ignitor nozzle, ~or ~gniting coal issuing from the ignitor nozzle.
According to anothex en~od~ment o~ the invention t~ere is provi~ded an i~gnitor nozzIe po$it~oned or igniti.on of coal leaving the:`coal nozzle, an ign~tor pulverizer for pulverizing coal, a s.ep~ato~`fo~ sepa~atin~ coal from air, means fox conYey~ng coal mi`xed ~th'a~r from the ~:~ni.tox ':
: pulveri.zer to the' s:epar~tor, means ~or co~veylng coal from the separator to the i~gnitor nozzIe,`means ~or trans~erring heat tQ a thi`.rd air stre~m from a sQurce other than the com~us.tion products, means for causi~ng the' th~rd air s.tream to flo~ into '~ the furnace`at the i`gni~tor nozzle, and a ligh.ter, positionable .
ne.a~ the outlet of the lgnitox`nQzzle~` fo~ ~gnit~ng coal issuing from the ignitor nozzle.
Accordin~ to a furthe~ em~odiment~ the. inventi.on resides in an ~mproved ~arm-up sys-tem for a ~urnace. system of the type described, whi'ch ~arm-up ~s.tem comprise~ :
an i.~ni:tor nozzle., means ~or stox~n~ ~ suppl~ of pul~er~zed coal during normal furnace opexat~on, ~ean~-for esta~ hi.n~ a second air ~tream, 3Q means for cont~oll~Iy re.le~in~ pulverized coal from , .
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said storing means into a stream of primar~ air to form a fuel stream, means for trans:ferr~ng heat to the second air stream from a source other th~n the furnace flue gas, means for causing the heated second a~r stream and the fuel stream to flow into the furnace at the i~nitor nozzle, said flow causing means dividing the heated second air stream i~nto a pair of streams coax~l wi~t~ the fuel s~tre~m, and a l~hter, position-a~le near the outlet of the ~gnitor nozzle, for igniting coal ~ulng f~om t~e i`gni~tor nozzle w~erefi~ i~niti.on energy ~ill be. s~ppl~.ed b~ said l~hter and ~e~t tr~ns~r mean~.
In a further aspect, the i.n~enti.on broadly resides in a method of operating a coal-fired furnace that includes heating a first air stream ~ transferring heat from combustion products of the furnace to the air in the firs.t air ~tream, :~ usiny the first air stream to entra~.n coal ground i.n a main pulverizer and convey ~t to the furnace, heating a second air stream ~y transfe.rri`ng heat from combust~on products of the furnace to the air ~n the s~cond ~ix stream, and conducting it to the furnace, the improve~ent compri.s~n~ steps of .; 2Q separ~ting pul~erized coal f~om a ~xture of pul~erized :~
coal and air, s:upplying the sepa~ated coal to an ignitor nozzle poslti.oned to ;~.gnite the coal entrained in the fir~t air s.tream as it enters the furn~ce, he.atlng a th~rd air s-tream to a temperature high.ex than t~.e temperatu~e of both the fir~t and second air stxeam~, cau~ng the thi.rd air stream to flow to the furnace at the: ignitor nozzle, and igniting the coal lea~lng the l~nitox nozzle.
In an alternati`~e em~odi.~ent, a third a;r stream `
m~y be heated f~o~ a source oth.er than th.e co~bustion products, 3~ and us:ed fox th.e purpose$ descr~.bed In the p~eceding paragraph. -- --5a- :
^ :
t~
~rief Description of the Dr'awin~:
These and further features and advantages of the invention become evi~dent ~n the descripti.on of the embodiment shown in the dra~ngs attac~ed, where~n:
FIGURE 1 i.s a diagrammatic ~iew o~ fuel system for the load-carrying nozzIes;
FI~URE 2 is a diagrammat~c vi.ew o~ the ~uel system for the ignitor nozzle of the presen-t invent~on; and FIGURE.3 i.s a side'elevatlon, partly a cross section, lQ of a typical ignitor nozzIe for use with the present invention.
'~ De:tai:led:De:s:cript:ion:'o:f::t:h'e: pre::~e:rr'e'd Embod~ment:
FIGURE 1 sho~s the system for s.uppl~.ng air and fuel to the load-carr~ing nozzles of a pulverized~coal boi.ler. The furnace is generally sho~n at lQ. A conduit 36 connects the outlet o~ th.e furnace to the ~lue gas ~nlet of ai.X preheater . `
38. Condui.t 4Q conne.ct~ the'flue-gas outlet to a stack, not f sh.own, th~t reIeases th.e products of combusti.on to the atmosphere. A fan 42 draws ~rom the ~tmpsphere and blows . I
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- ~' air through the air inle~ of air preheater 38, Conduit 34 connects the air outlet of air preheater 38 to windboxes 12 and 30 located on either side cf the furnace. The typical furnace would actually have four windboxes, one at each corner, but, for the sake of simpLicity, only two are shown.
Another conduit 32 conducts air from conduit 34 to the air inlet of pulverizer 22. The outlet of pulverizer 22 is con-nected by conduit 21 to exhauster 20, whose outlet communi-cates with several conduits. Conduits 18 and 24 lead from the ~xhauster outlet to coal nozzles 19 and 25, which are arranged so as to direct coal fed to them into the interior of furnace 10. ~ozzles 16 and 26 are fed by a second pulverizer-exhauster combination that is not shown in the drawing, while a third pulverizer-exhauster combination, ! 15 also not shown, feeds nozzles 14 and 28. Again, for each pair of nozzles shown there is typically another pair of nozzles not shown that is fed by the same pulverizer.
Windboxes 12 and 30 communicate with the interior of the furnace through openings in the vicinity of the nozæles.
Dampers, not shown in the drawing, control the allocation o~ air from the windbox among the openings.
In normal operation, coal and air enters furnace 10 through one or more elevations of nozzles. Combustion takes plaoe in the interior of furnace 1~, producing hot flue gases that flow out conduit 36, through air preheater 38, and i through conduit 40 to a stack. Air preheater 38 has moving heat-exchange surfaces that alternately contact the hot flu2 gases and the air enteriny the preheater from fan ~2. The surfaces thus absorb heat from the flue gases and release i 30 it to the air from fan 42. Part of the heated air leaving .
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~ ~,,..~..~,al!.d~l~S~J~ .
57~7 air preheater 38 passes throuyh conduit 32 ~nd into pulverizer 22. Pulverlzer 22 is an apparatus for drying and crushing coal, and the hot air brought by conduit 32 is used to dry the coal~ The air stream ~lowing in conduit 32 and pulverizer 22 also flows through con~uit 21, exhauster 20, and conduits 18 and 24 to the associated nozzles. In flowing through pulverizer 22, the air stream entrains thP coal that has been sufficiently pulverized and carries it to nozzles 19 and 25. Since fan 42 and exhauster 20 both provide motivating force for this motion, it can be seen that together they constitute means for forcing a first air stream from the air - outlet of preheater 38, through pulverizer 22, and into either nozzle 19 or nozzle 25.
The air forced by fan 42 and exhauster 20 through pulverizer 22 is referred to as primary air and is delivered ~ with the coal to main coal nozzles 19 and 25. However, - there is not usually enough primary air to support co~bustion of all of the coalt so some of the air leaving air preheater 38 goes through conduit 34 to windboxes 12 and 30. Windboxes 12 and 30 supply the secondary air, the remainder of the air reguired to support combustion of all the coal~ ~ :
It is evident `that the above discussion presupposes ~.
that hot flue gases are flowing through conduit 36. Of course, ~5 at the beginning of furnace operation, the gases flowing through the conduit 36 are relatively cooI. A typical coal-~ired unit includes supplementary burners that burn oil or natural gas, and it is the func~ion of these hurners to .. . .
; operate when the gases coming through conduit 36 are relati~ely 30 cool. This is because pulverized coal is relatively difficult . . .
to ignite, and ~table combustion cannot be guaranteed unless .
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a5~
~ignificant amounts of heat energy are present in the combustion area~ Th_s heat energy that is used to start or maintain combustion comes from many sources. It could come directly by radiation from flame that is already in the furnace, by radiation from the walls of the furnace, by conduction from the generally hot gases in the furnace, or by conduction from the primary and secondary air flowing into ~e the furnace. In actuality, all of these sources contribute to the ignition energy, and at high-load conditions 10 they all add up to a sufficient amount of .ignition energy ~ for stable combustion of the coal. However, in many situa-; tions the com~ination of these energy sources is not sufficient to guarantee stable combustion. One of these situations is that of a cold furnace, in which there is 15 little radiation from the furnace walls and little energy transferred to the primary and secondary air by the air preheater. In such cases the supplementary burners are used.
Another situation in which supplementary burners are used ; is the case in which the furnace is operated at a relatively - 20 low load, when the amount of reactants burniny is sufficiently low to cause a redu~tion~in the energy derived ~rom the various sources. In this case again, supplementary burners arc used to maintain stable combustion. In the past, these supplementary burners have all burned oil or natural gas.
,- 25 Thi~ is a natural choice, since oil and natural gas are much easierJto light than pulverized coal is~
FIGURE 2 shows a system that enables the supplementary burner~ tQ be fired by pulverized coal. An iynitor pulverizer 110 receives air at inl~t 112 from air preheater 38 of E'IGURE 1. Conduit 100 conducts the coal=air mixture leaving , .
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pulverizer 110 to exhauster 102, and conduit 98 connects the outlet of exhauster 102 to further conduits 96. Conduits 96 lead to cyclone separators such as separator 65. The number of such separators deponds on the designer; only one is necessary, but more could be used The outlet ~f separator 65 is connected by an air line 62 to a point in the interior of the furnace remote from the fuel nozzles~ Bin 66 is positioned to receive the coal leaving separator 65, and the outlet of the bin is controlled by valve 67. Coal from bin .
66 is fed through coal pipe 70 to appropriately valved coal pipes 74, 78, and 82, each of which terminates in coal nozzles not shown in. FIGURE 2. Similar coal pipes 86, 90, and 94 also receive coal either from coal bin 66 or another coal bin not shown and feed it to nozzles positioned at their exits.
Those skilled in the art will recognize that it is not : essential that pulverizer 110 ~e a separate pulverizer.
The functions o~ pulverizer 110 and pulverizer 22 could be combined in the same pulverizer, the output being divided between a direct connection to the furnace and a connection to a separator 65. Accordingly, the main pulverizer and the ignitor pulverizer in the claims can be embodied in the same hardware.
Fan 118 draws air from the air preheater shown in FIGURE 1, and this air stream is divided among conduits 119, 120 and 122. Conduit 119 feeds an in-duct air heater, possibly an electric heater, and the output of air heater 116 is sent by means of conduit 114 to the ignit~r no~zles at the ends of coal pipes 82 and 94. The temperature of the a-ir leaving 30 air heater 116 is preferably between 300E and 1000F. A
~imilar heater and similar connections exist between conduit 120 and th~ noz~les at the end of coal pipes 78 and 90 and between conduit 122 and the nozzles at the ends of coal pipes 74 and 86.
FIGURE 3 shows an ignitor nozzle of the type that would be fed by coal pipe 82. The ignitor nozzle is actually made of three concentric nozzles 128, 130 and 134. ~ozzles 128 and 134 are both fed by conduit 80, which is attached to noæzle 128 by flexible connector 126. Coal pipe 82 is connected through ball joint 138 to coal-pipe extension 1440 Interior to and concentric with coal pipe 82 and coal-pipe extension 144 is lighter 142. Lighter 142 may be a small version of an ordinary coal-/or gas-fired ignitor, or it may be a high-energy arc ignitor. In either case, the ignitor is flexible at least thrvugh the area of the ball joint in order to allow it to move with coal-pipe extension 144. Air conduit 124 communicates with windbox 12 of FIGURE 1 and has nozzl~ 130 fitted on its exit~ Accordingly, no~zle 130 is ' in communication with windbox 12. A typical unit would have 1 20 a discriminating flame detector 132 of any desired type in order to determine whether or not there is flame at the end of the ignitor nozzle.
To start up the furnace when it is cold, pulverizer 110 i9 ~tarted, receiving coal at i~s inlet and crushing it~
The air inlet of pulverizer 110 receives air that has been blown through air preheater 38 by fan 42. In a cold start up, this air is still relatively cool. The cool air-is blown through pulverizer 110, conduit 100, exhauster 102, and conduits 98 and 96 to separator 65. Separator 65 removes the ~oal that has been entrained by the air blown through pulver-.. :
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~g~
izer 110, and it drops it into bin 66. Simulatan~ously, the air separated from the coal is exhausted into the furnace through line 62. Alternately, bin 66 could be a storage bin larye enough to hold the amount of coal needed for a startup.
I~ such a case, the pulverized coal left in bin 66 from previous oper~tion of the furnace would fuel the operation until the furnace has heated up. Inerting line 64 is used to maintain an atmosphere in bin 66 during storage that dis-courages spontaneous combustion. Af~er the furnace has heated up, ignitor pulverizer 110 starts to work, replenishing the supply of stored coal in bin 66.
Whichever method is used, coal is supplied by bin 66.
Valve 67 regulates the amount of coal that is allowed to ~all from bin 66, and this coal is forced by appropriate means through conduits 70 and 82 and out the ignitor nozæleO
Similarly, coal is also forced through coal pipe 94 and through the nozzle fitted at its exit. Due to the fact that the coal is sent to conduits 82 and 94 with almost no air, coal pipes 82 and 94 can be made relatively small, so they do not contribute to the congestion in the furnace corners. At the same time that the coal is being delivered to the ignitor nozzles, air from preheater 38 is drawn by fan 118 through ~onduit 119 to heater 116. Heater 116 heats the air to a temperature high enough to provide stable combustion. Without heater 116, the only heat in the air would be that imparted to it by air preheater 38, and on a cold start this is not very much heat. The hot air leaving heater 116 is fed by conduit 114 to conduits 80 and 92. Part of the air flowing through conduit 80 passes through nozzle ~34 of FIGURE 3~
According to the present state of the art, nozzle 134 may have `'''' ' ` ' '`
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vanes 136 to properly direct the air flow, and this air flow imparts an appropriate flow pattern to the coal that l~aves the openings of coal-pipe extension 144.
It is to be noted that th~ present system allows ~he a~nount of heat introduced by air heater 116 to be kept to a minimum. Since the air that is heated is used only to add to the ignition energy at the ignitor nozzle, the n~cessity of adding heat to the entire volume of air flowing through preheater 38 i5 avoided. Furthermore, since the inert water vapor that result~ from the drying of the coal has been separated from the coal before the coal reaches the ignitor nozzles, none of the energy supplied by air heater 116 is used up in he-ating inerts. The rest of the air that ~lows through conduit 80 is conducted through nozzle 128 and past vanes 140, which also impart a flow pattern appropriate for stable combustion. Though the amount of air heated by heater 116 will normally be kept as low as possible, system designs may provide suf~icient capacity to heat 100 per cent stoichiometric air if required. Thus, the amount of air supplied through nozzles 128 and 134 may be stoichiometrically sufficient for combustion of the coal. If it is not, windbox air will be introduced through nozzle 130 Even if the amount of heated air introduced through no2zles 128 and 134 is suf~icient for combustion o~ all the coal, however, it may be desirable, depending on the characteristics of nozzles 128 and 134 and vanes 136 and 140, to introduce windbox air in order to cause a flow pattern adapted to feeding hot combustion products back into the combustion zone, thereby ~ontributing t~ ignition energy and the stability of the ignitor flame.
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Typically, the coal leaving coal-pipe extension 144 would have its volatiles liberated by liyhter 142, and combustion of some of the coal would also be started in the presence of the air flowing through ignitor 134. The remainder of the air needed for combustion would be supplied by nozzle 128, so combustion is completed after the coal and air leaving nozzle 134 meets the air in nozzle 128. As was noted before, the air coming throuyh conduit 80 is hot enough so that its ~ontribution to ignition energy pro-vides for a stable flame~
It is to be understood that the nozzle of FIGURE 3 is .. . ..
merely illustrative; it merely shows the functions that would - typically be performed by a nozzle used with the present invention.
The stable flame at the outlet of the ignitor nozzle begins to warm the furnace walls and steam pipes, and as they warm up, the flue-gas temperature increases. Eventually, the air preheater becomes hot enough for operation o~ the ` main coal no~zles, and their pulverizers are started. The coal issuing from the main coal nozzles is ignited by flame from the ignitor nozzles, and normal operation begins. If the urnace is operating at low loads, the ignitor nozzles remain on, providing low-]oad stabilization. It may ~e determined that the cost penalty in leaving the ignitors in operation is minor, so they may be left operating even at high loads.
While the invention has been described in terms of a ~pecific embodiment, the use o~ a specific embodiment is by no means meant as a limitation. Accordingly~ any modification . . ..
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within the scope of the appended claims that is apparent to those skilled in the art in light of the foregoing descrip-tion is meant to be included in the invention.
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_ ' "'' " ' ' ~-, the present inye.ntion an i.gnito.r nozzle posi.ti.oned for ignition of coal leaving the main coal nozzle, an ignitor pul~erizer for pulverizing coal, a separator for separating coal from aîr, me~ns for conveying coal ~ixed with air from the ignitor pulverizer to t~e separator, means for conveying coal fxom the separator to the ~gnitor nozzle, means. for causing a third air stream hav~.ng a temperature higher th.an the te~pe.rature of either the first or the: second air stream to flow to the ignitor nozzle, and a li~h.ter, posi~tiona~le near the outlet o~ the ignitor nozzle, ~or ~gniting coal issuing from the ignitor nozzle.
According to anothex en~od~ment o~ the invention t~ere is provi~ded an i~gnitor nozzIe po$it~oned or igniti.on of coal leaving the:`coal nozzle, an ign~tor pulverizer for pulverizing coal, a s.ep~ato~`fo~ sepa~atin~ coal from air, means fox conYey~ng coal mi`xed ~th'a~r from the ~:~ni.tox ':
: pulveri.zer to the' s:epar~tor, means ~or co~veylng coal from the separator to the i~gnitor nozzIe,`means ~or trans~erring heat tQ a thi`.rd air stre~m from a sQurce other than the com~us.tion products, means for causi~ng the' th~rd air s.tream to flo~ into '~ the furnace`at the i`gni~tor nozzle, and a ligh.ter, positionable .
ne.a~ the outlet of the lgnitox`nQzzle~` fo~ ~gnit~ng coal issuing from the ignitor nozzle.
Accordin~ to a furthe~ em~odiment~ the. inventi.on resides in an ~mproved ~arm-up sys-tem for a ~urnace. system of the type described, whi'ch ~arm-up ~s.tem comprise~ :
an i.~ni:tor nozzle., means ~or stox~n~ ~ suppl~ of pul~er~zed coal during normal furnace opexat~on, ~ean~-for esta~ hi.n~ a second air ~tream, 3Q means for cont~oll~Iy re.le~in~ pulverized coal from , .
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~ 5~ ..
said storing means into a stream of primar~ air to form a fuel stream, means for trans:ferr~ng heat to the second air stream from a source other th~n the furnace flue gas, means for causing the heated second a~r stream and the fuel stream to flow into the furnace at the i~nitor nozzle, said flow causing means dividing the heated second air stream i~nto a pair of streams coax~l wi~t~ the fuel s~tre~m, and a l~hter, position-a~le near the outlet of the ~gnitor nozzle, for igniting coal ~ulng f~om t~e i`gni~tor nozzle w~erefi~ i~niti.on energy ~ill be. s~ppl~.ed b~ said l~hter and ~e~t tr~ns~r mean~.
In a further aspect, the i.n~enti.on broadly resides in a method of operating a coal-fired furnace that includes heating a first air stream ~ transferring heat from combustion products of the furnace to the air in the firs.t air ~tream, :~ usiny the first air stream to entra~.n coal ground i.n a main pulverizer and convey ~t to the furnace, heating a second air stream ~y transfe.rri`ng heat from combust~on products of the furnace to the air ~n the s~cond ~ix stream, and conducting it to the furnace, the improve~ent compri.s~n~ steps of .; 2Q separ~ting pul~erized coal f~om a ~xture of pul~erized :~
coal and air, s:upplying the sepa~ated coal to an ignitor nozzle poslti.oned to ;~.gnite the coal entrained in the fir~t air s.tream as it enters the furn~ce, he.atlng a th~rd air s-tream to a temperature high.ex than t~.e temperatu~e of both the fir~t and second air stxeam~, cau~ng the thi.rd air stream to flow to the furnace at the: ignitor nozzle, and igniting the coal lea~lng the l~nitox nozzle.
In an alternati`~e em~odi.~ent, a third a;r stream `
m~y be heated f~o~ a source oth.er than th.e co~bustion products, 3~ and us:ed fox th.e purpose$ descr~.bed In the p~eceding paragraph. -- --5a- :
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t~
~rief Description of the Dr'awin~:
These and further features and advantages of the invention become evi~dent ~n the descripti.on of the embodiment shown in the dra~ngs attac~ed, where~n:
FIGURE 1 i.s a diagrammatic ~iew o~ fuel system for the load-carrying nozzIes;
FI~URE 2 is a diagrammat~c vi.ew o~ the ~uel system for the ignitor nozzle of the presen-t invent~on; and FIGURE.3 i.s a side'elevatlon, partly a cross section, lQ of a typical ignitor nozzIe for use with the present invention.
'~ De:tai:led:De:s:cript:ion:'o:f::t:h'e: pre::~e:rr'e'd Embod~ment:
FIGURE 1 sho~s the system for s.uppl~.ng air and fuel to the load-carr~ing nozzles of a pulverized~coal boi.ler. The furnace is generally sho~n at lQ. A conduit 36 connects the outlet o~ th.e furnace to the ~lue gas ~nlet of ai.X preheater . `
38. Condui.t 4Q conne.ct~ the'flue-gas outlet to a stack, not f sh.own, th~t reIeases th.e products of combusti.on to the atmosphere. A fan 42 draws ~rom the ~tmpsphere and blows . I
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, `:
- ~' air through the air inle~ of air preheater 38, Conduit 34 connects the air outlet of air preheater 38 to windboxes 12 and 30 located on either side cf the furnace. The typical furnace would actually have four windboxes, one at each corner, but, for the sake of simpLicity, only two are shown.
Another conduit 32 conducts air from conduit 34 to the air inlet of pulverizer 22. The outlet of pulverizer 22 is con-nected by conduit 21 to exhauster 20, whose outlet communi-cates with several conduits. Conduits 18 and 24 lead from the ~xhauster outlet to coal nozzles 19 and 25, which are arranged so as to direct coal fed to them into the interior of furnace 10. ~ozzles 16 and 26 are fed by a second pulverizer-exhauster combination that is not shown in the drawing, while a third pulverizer-exhauster combination, ! 15 also not shown, feeds nozzles 14 and 28. Again, for each pair of nozzles shown there is typically another pair of nozzles not shown that is fed by the same pulverizer.
Windboxes 12 and 30 communicate with the interior of the furnace through openings in the vicinity of the nozæles.
Dampers, not shown in the drawing, control the allocation o~ air from the windbox among the openings.
In normal operation, coal and air enters furnace 10 through one or more elevations of nozzles. Combustion takes plaoe in the interior of furnace 1~, producing hot flue gases that flow out conduit 36, through air preheater 38, and i through conduit 40 to a stack. Air preheater 38 has moving heat-exchange surfaces that alternately contact the hot flu2 gases and the air enteriny the preheater from fan ~2. The surfaces thus absorb heat from the flue gases and release i 30 it to the air from fan 42. Part of the heated air leaving .
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~ ~,,..~..~,al!.d~l~S~J~ .
57~7 air preheater 38 passes throuyh conduit 32 ~nd into pulverizer 22. Pulverlzer 22 is an apparatus for drying and crushing coal, and the hot air brought by conduit 32 is used to dry the coal~ The air stream ~lowing in conduit 32 and pulverizer 22 also flows through con~uit 21, exhauster 20, and conduits 18 and 24 to the associated nozzles. In flowing through pulverizer 22, the air stream entrains thP coal that has been sufficiently pulverized and carries it to nozzles 19 and 25. Since fan 42 and exhauster 20 both provide motivating force for this motion, it can be seen that together they constitute means for forcing a first air stream from the air - outlet of preheater 38, through pulverizer 22, and into either nozzle 19 or nozzle 25.
The air forced by fan 42 and exhauster 20 through pulverizer 22 is referred to as primary air and is delivered ~ with the coal to main coal nozzles 19 and 25. However, - there is not usually enough primary air to support co~bustion of all of the coalt so some of the air leaving air preheater 38 goes through conduit 34 to windboxes 12 and 30. Windboxes 12 and 30 supply the secondary air, the remainder of the air reguired to support combustion of all the coal~ ~ :
It is evident `that the above discussion presupposes ~.
that hot flue gases are flowing through conduit 36. Of course, ~5 at the beginning of furnace operation, the gases flowing through the conduit 36 are relatively cooI. A typical coal-~ired unit includes supplementary burners that burn oil or natural gas, and it is the func~ion of these hurners to .. . .
; operate when the gases coming through conduit 36 are relati~ely 30 cool. This is because pulverized coal is relatively difficult . . .
to ignite, and ~table combustion cannot be guaranteed unless .
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~ignificant amounts of heat energy are present in the combustion area~ Th_s heat energy that is used to start or maintain combustion comes from many sources. It could come directly by radiation from flame that is already in the furnace, by radiation from the walls of the furnace, by conduction from the generally hot gases in the furnace, or by conduction from the primary and secondary air flowing into ~e the furnace. In actuality, all of these sources contribute to the ignition energy, and at high-load conditions 10 they all add up to a sufficient amount of .ignition energy ~ for stable combustion of the coal. However, in many situa-; tions the com~ination of these energy sources is not sufficient to guarantee stable combustion. One of these situations is that of a cold furnace, in which there is 15 little radiation from the furnace walls and little energy transferred to the primary and secondary air by the air preheater. In such cases the supplementary burners are used.
Another situation in which supplementary burners are used ; is the case in which the furnace is operated at a relatively - 20 low load, when the amount of reactants burniny is sufficiently low to cause a redu~tion~in the energy derived ~rom the various sources. In this case again, supplementary burners arc used to maintain stable combustion. In the past, these supplementary burners have all burned oil or natural gas.
,- 25 Thi~ is a natural choice, since oil and natural gas are much easierJto light than pulverized coal is~
FIGURE 2 shows a system that enables the supplementary burner~ tQ be fired by pulverized coal. An iynitor pulverizer 110 receives air at inl~t 112 from air preheater 38 of E'IGURE 1. Conduit 100 conducts the coal=air mixture leaving , .
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pulverizer 110 to exhauster 102, and conduit 98 connects the outlet of exhauster 102 to further conduits 96. Conduits 96 lead to cyclone separators such as separator 65. The number of such separators deponds on the designer; only one is necessary, but more could be used The outlet ~f separator 65 is connected by an air line 62 to a point in the interior of the furnace remote from the fuel nozzles~ Bin 66 is positioned to receive the coal leaving separator 65, and the outlet of the bin is controlled by valve 67. Coal from bin .
66 is fed through coal pipe 70 to appropriately valved coal pipes 74, 78, and 82, each of which terminates in coal nozzles not shown in. FIGURE 2. Similar coal pipes 86, 90, and 94 also receive coal either from coal bin 66 or another coal bin not shown and feed it to nozzles positioned at their exits.
Those skilled in the art will recognize that it is not : essential that pulverizer 110 ~e a separate pulverizer.
The functions o~ pulverizer 110 and pulverizer 22 could be combined in the same pulverizer, the output being divided between a direct connection to the furnace and a connection to a separator 65. Accordingly, the main pulverizer and the ignitor pulverizer in the claims can be embodied in the same hardware.
Fan 118 draws air from the air preheater shown in FIGURE 1, and this air stream is divided among conduits 119, 120 and 122. Conduit 119 feeds an in-duct air heater, possibly an electric heater, and the output of air heater 116 is sent by means of conduit 114 to the ignit~r no~zles at the ends of coal pipes 82 and 94. The temperature of the a-ir leaving 30 air heater 116 is preferably between 300E and 1000F. A
~imilar heater and similar connections exist between conduit 120 and th~ noz~les at the end of coal pipes 78 and 90 and between conduit 122 and the nozzles at the ends of coal pipes 74 and 86.
FIGURE 3 shows an ignitor nozzle of the type that would be fed by coal pipe 82. The ignitor nozzle is actually made of three concentric nozzles 128, 130 and 134. ~ozzles 128 and 134 are both fed by conduit 80, which is attached to noæzle 128 by flexible connector 126. Coal pipe 82 is connected through ball joint 138 to coal-pipe extension 1440 Interior to and concentric with coal pipe 82 and coal-pipe extension 144 is lighter 142. Lighter 142 may be a small version of an ordinary coal-/or gas-fired ignitor, or it may be a high-energy arc ignitor. In either case, the ignitor is flexible at least thrvugh the area of the ball joint in order to allow it to move with coal-pipe extension 144. Air conduit 124 communicates with windbox 12 of FIGURE 1 and has nozzl~ 130 fitted on its exit~ Accordingly, no~zle 130 is ' in communication with windbox 12. A typical unit would have 1 20 a discriminating flame detector 132 of any desired type in order to determine whether or not there is flame at the end of the ignitor nozzle.
To start up the furnace when it is cold, pulverizer 110 i9 ~tarted, receiving coal at i~s inlet and crushing it~
The air inlet of pulverizer 110 receives air that has been blown through air preheater 38 by fan 42. In a cold start up, this air is still relatively cool. The cool air-is blown through pulverizer 110, conduit 100, exhauster 102, and conduits 98 and 96 to separator 65. Separator 65 removes the ~oal that has been entrained by the air blown through pulver-.. :
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~g~
izer 110, and it drops it into bin 66. Simulatan~ously, the air separated from the coal is exhausted into the furnace through line 62. Alternately, bin 66 could be a storage bin larye enough to hold the amount of coal needed for a startup.
I~ such a case, the pulverized coal left in bin 66 from previous oper~tion of the furnace would fuel the operation until the furnace has heated up. Inerting line 64 is used to maintain an atmosphere in bin 66 during storage that dis-courages spontaneous combustion. Af~er the furnace has heated up, ignitor pulverizer 110 starts to work, replenishing the supply of stored coal in bin 66.
Whichever method is used, coal is supplied by bin 66.
Valve 67 regulates the amount of coal that is allowed to ~all from bin 66, and this coal is forced by appropriate means through conduits 70 and 82 and out the ignitor nozæleO
Similarly, coal is also forced through coal pipe 94 and through the nozzle fitted at its exit. Due to the fact that the coal is sent to conduits 82 and 94 with almost no air, coal pipes 82 and 94 can be made relatively small, so they do not contribute to the congestion in the furnace corners. At the same time that the coal is being delivered to the ignitor nozzles, air from preheater 38 is drawn by fan 118 through ~onduit 119 to heater 116. Heater 116 heats the air to a temperature high enough to provide stable combustion. Without heater 116, the only heat in the air would be that imparted to it by air preheater 38, and on a cold start this is not very much heat. The hot air leaving heater 116 is fed by conduit 114 to conduits 80 and 92. Part of the air flowing through conduit 80 passes through nozzle ~34 of FIGURE 3~
According to the present state of the art, nozzle 134 may have `'''' ' ` ' '`
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vanes 136 to properly direct the air flow, and this air flow imparts an appropriate flow pattern to the coal that l~aves the openings of coal-pipe extension 144.
It is to be noted that th~ present system allows ~he a~nount of heat introduced by air heater 116 to be kept to a minimum. Since the air that is heated is used only to add to the ignition energy at the ignitor nozzle, the n~cessity of adding heat to the entire volume of air flowing through preheater 38 i5 avoided. Furthermore, since the inert water vapor that result~ from the drying of the coal has been separated from the coal before the coal reaches the ignitor nozzles, none of the energy supplied by air heater 116 is used up in he-ating inerts. The rest of the air that ~lows through conduit 80 is conducted through nozzle 128 and past vanes 140, which also impart a flow pattern appropriate for stable combustion. Though the amount of air heated by heater 116 will normally be kept as low as possible, system designs may provide suf~icient capacity to heat 100 per cent stoichiometric air if required. Thus, the amount of air supplied through nozzles 128 and 134 may be stoichiometrically sufficient for combustion of the coal. If it is not, windbox air will be introduced through nozzle 130 Even if the amount of heated air introduced through no2zles 128 and 134 is suf~icient for combustion o~ all the coal, however, it may be desirable, depending on the characteristics of nozzles 128 and 134 and vanes 136 and 140, to introduce windbox air in order to cause a flow pattern adapted to feeding hot combustion products back into the combustion zone, thereby ~ontributing t~ ignition energy and the stability of the ignitor flame.
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Typically, the coal leaving coal-pipe extension 144 would have its volatiles liberated by liyhter 142, and combustion of some of the coal would also be started in the presence of the air flowing through ignitor 134. The remainder of the air needed for combustion would be supplied by nozzle 128, so combustion is completed after the coal and air leaving nozzle 134 meets the air in nozzle 128. As was noted before, the air coming throuyh conduit 80 is hot enough so that its ~ontribution to ignition energy pro-vides for a stable flame~
It is to be understood that the nozzle of FIGURE 3 is .. . ..
merely illustrative; it merely shows the functions that would - typically be performed by a nozzle used with the present invention.
The stable flame at the outlet of the ignitor nozzle begins to warm the furnace walls and steam pipes, and as they warm up, the flue-gas temperature increases. Eventually, the air preheater becomes hot enough for operation o~ the ` main coal no~zles, and their pulverizers are started. The coal issuing from the main coal nozzles is ignited by flame from the ignitor nozzles, and normal operation begins. If the urnace is operating at low loads, the ignitor nozzles remain on, providing low-]oad stabilization. It may ~e determined that the cost penalty in leaving the ignitors in operation is minor, so they may be left operating even at high loads.
While the invention has been described in terms of a ~pecific embodiment, the use o~ a specific embodiment is by no means meant as a limitation. Accordingly~ any modification . . ..
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within the scope of the appended claims that is apparent to those skilled in the art in light of the foregoing descrip-tion is meant to be included in the invention.
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Claims (25)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a furnace system that includes a furnace, a main coal nozzle arranged to direct coal into the furnace, an air preheater having a flue-gas inlet, an air inlet, and an air outlet and being connected to receive flue gases from the furnace at its flue-gas inlet and transfer heat from the flue gas to air entering the air inlet and leaving the air outlet, a main pulverizer, conduit means connected to conduct coal from the pulverizer outlet to the main coal nozzle, means for forcing a first air stream through the preheater from its air inlet to its air outlet and from the air outlet through the pulverizer and into the main coal nozzle, and means for forcing a second air stream from the preheater outlet into the furnace, the improvement comprising:
a. an ignitor nozzle positioned for ignition of coal leaving the coal nozzle;
b. an ignitor pulverizer for pulverizing coal;
c. a separator for separating coal from air;
d. means for conveying coal mixed with air from the ignitor pulverizer to the separator;
e. means for conveying coal from the separator to the ignitor nozzle;
f. means for heating a third air stream to a temper-ature higher than that of the first and second air streams;
g. means for causing the third air stream to flow to the furnace at the ignitor nozzle; and h. a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle.
a. an ignitor nozzle positioned for ignition of coal leaving the coal nozzle;
b. an ignitor pulverizer for pulverizing coal;
c. a separator for separating coal from air;
d. means for conveying coal mixed with air from the ignitor pulverizer to the separator;
e. means for conveying coal from the separator to the ignitor nozzle;
f. means for heating a third air stream to a temper-ature higher than that of the first and second air streams;
g. means for causing the third air stream to flow to the furnace at the ignitor nozzle; and h. a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle.
2. An apparatus as recited in claim 1, wherein the means for conveying coal comprises a bin connected to receive coal from the separator and to supply coal to the ignitor nozzle, for storing coal separated from air by the separator.
3. An apparatus as recited in claim 1 wherein the lighter is an arc ignitor.
4. An apparatus as recited in claim 3 wherein the means for conveying coal comprises a bin connected to receive coal from the separator and to supply coal to the ignitor nozzle, for storing coal separated from air by the separator.
5. An apparatus as recited in claim 4 wherein the means for heating a third air stream is a means for heating a third air stream to a temperature between 300° and 1000°F.
6. In a method of operating a coal-fired furnace that includes heating a first air stream by transferring heat from combustion products of the furnace to the air in the first air stream, using the first air stream to entrain coal ground in a main pulverizer and convey it to the furnace, heating a second air stream by transferring heat from combustion products of the furnace to the air in the second air stream, and conducting it to the furnace, the improvement comprising steps of:
a. separating pulverized coal from a mixture of pulverized coal and air;
b supplying the separated coal to an ignitor nozzle positioned to ignite the coal entrained in the first air stream as it enters the furnace;
c. heating a third air stream to a temperature higher than the temperature of both the first and second air streams;
d. causing the third air stream to flow to the furnace at the ignitor nozzle; and e. igniting the coal leaving the ignitor nozzle.
a. separating pulverized coal from a mixture of pulverized coal and air;
b supplying the separated coal to an ignitor nozzle positioned to ignite the coal entrained in the first air stream as it enters the furnace;
c. heating a third air stream to a temperature higher than the temperature of both the first and second air streams;
d. causing the third air stream to flow to the furnace at the ignitor nozzle; and e. igniting the coal leaving the ignitor nozzle.
7. A method as recited in claim 6 wherein the igniting step comprises causing an electric spark to occur near the outlet of the ignitor nozzle.
8. A method as recited in claim 6 further comprising the step of storing the separated coal until it is supplied to the ignitor nozzle.
9. A method as recited in claim 8 wherein the igniting step comprises causing an electric spark to occur near the outlet of the ignitor nozzle.
10. A method as recited in claim 9 wherein the step of heating a third air stream comprises heating a third air stream to a temperature between 300° and 1000°F.
11. In a furnace system that includes a furnace, a main coal nozzle arranged to direct coal into the furnace, an air preheater having a flue-gas inlet, an air inlet, and an air outlet and being connected to receive flue gases from the furnace at its flue-gas inlet and transfer heat from the flue gas to air entering the air inlet and leaving the air outlet, a main pulverizer, conduit means connected to conduct coal from the pulverizer outlet to the main coal nozzle, means for forcing a first air stream through the preheater from its air inlet to its air outlet and from the air outlet through the pulverizer and into the main coal nozzle, and means for forcing a second air stream from the preheater outlet into the furnace, the improvement comprising:
a. an ignitor nozzle positioned for ignition of coal leaving the coal nozzle;
b. an ignitor pulverizer for pulverizing coal;
c. a separator for separating coal from air;
d. means for conveying coal mixed with air from the ignitor pulverizer to the separator;
e. means for conveying coal from the separator to the ignitor nozzle;
f. means for transferring heat to a third air stream from a source other than the combustion products;
g. means for causing the third air stream to flow into the furnace at the ignitor nozzle; and h. a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle.
a. an ignitor nozzle positioned for ignition of coal leaving the coal nozzle;
b. an ignitor pulverizer for pulverizing coal;
c. a separator for separating coal from air;
d. means for conveying coal mixed with air from the ignitor pulverizer to the separator;
e. means for conveying coal from the separator to the ignitor nozzle;
f. means for transferring heat to a third air stream from a source other than the combustion products;
g. means for causing the third air stream to flow into the furnace at the ignitor nozzle; and h. a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle.
12. An apparatus as recited in claim 11, wherein the means for conveying coal comprises a bin, connected to receive coal from the separator and to supply coal to the ignitor nozzle, for storing coal separated from air by the separator.
13. An apparatus as recited in claim 12, wherein the lighter is an arc ignitor.
14. An apparatus as recited in claim 13, wherein the means for conveying coal comprises a bin, connected to receive coal from the separator and to supply coal to the ignitor nozzle, for storing coal separated from air by the separator.
15. An apparatus as recited in claim 14, wherein the means for heating a third air stream is a means for heating a. third air stream to a temperature between 300° and 1000°F.
16. In the method of operating a coal-fired furnace that includes the steps of pulverizing coal, supplying the pulverized coal to the furnace through a main coal nozzle, supplying a stream of secondary air to the furnace at the main coal nozzle to support combustion of the coal in the furnace, igniting the coal in the furnace, thereby producing combustion products, and using heat from the combustion products to heat the air supplied to the furnace, the improvement wherein the igniting step comprises the steps of:
a. providing a bin of pulverized coal;
b. supplying coal from the bin to the furnace through an ignitor nozzle positioned for ignition of coal issuing from the main coal nozzle, the coal being carried to the ignitor nozzle by a stream of primary air;
c. heating a third air stream from a source other than the combustion products;
d. supplying the third air stream to the furnace at the ignitor nozzle; and e. igniting the coal issuing from the ignitor nozzle, thereby providing an ignitor flame by which coal is ignited when it issues from the main coal nozzle.
a. providing a bin of pulverized coal;
b. supplying coal from the bin to the furnace through an ignitor nozzle positioned for ignition of coal issuing from the main coal nozzle, the coal being carried to the ignitor nozzle by a stream of primary air;
c. heating a third air stream from a source other than the combustion products;
d. supplying the third air stream to the furnace at the ignitor nozzle; and e. igniting the coal issuing from the ignitor nozzle, thereby providing an ignitor flame by which coal is ignited when it issues from the main coal nozzle.
17. A method as recited in claim 16, wherein the step of igniting the coal issuing from the ignitor nozzle comprises causing an electric spark to occur near the outlet of the ignitor nozzle.
18. A method as recited in claim 16 further comprising the step of storing the separated coal until it is supplied to the ignitor nozzle.
19. A method as recited in claim 18 wherein the igniting step comprises causing an electric spark to occur near the outlet of the ignitor nozzle.
20. A method as recited in claim 19 wherein the step of heating a third air stream comprises heating a third air stream to a temperature between 300°F and 1000°F.
21. A method of igniting a fuel stream comprising pulverized coal in an unheated furnace pursuant to initiating operation of the furnace comprising the steps of:
providing a supply of pulverized coal;
establishing a stream of primary air;
establishing a second air stream;
energizing a source of thermal energy located exteriorly of the unheated furnace;
heating the second air stream by transferring thermal energy thereto from the source of thermal energy, the second air stream thereby being heated with thermal energy which is not directly derived from furnace operation to a temperature substantially higher than that of the primary air;
entraining coal from the supply in the primary air stream to form a fuel stream;
simultaneously delivering the fuel stream and at least a first part of the heated second air stream to the interior of the furnace via a nozzle associated with a burner;
delivering additional hot air from the heated second air stream to the furnace at the nozzle and coaxially about the simultaneously delivered fuel stream and first part of the heated air whereby the additional hot air supports combustion of the fuel stream; and supplying ignition energy to the fuel stream at the nozzle to cause ignition thereof in the cold furnace to thereby initiate operation of the furnace.
providing a supply of pulverized coal;
establishing a stream of primary air;
establishing a second air stream;
energizing a source of thermal energy located exteriorly of the unheated furnace;
heating the second air stream by transferring thermal energy thereto from the source of thermal energy, the second air stream thereby being heated with thermal energy which is not directly derived from furnace operation to a temperature substantially higher than that of the primary air;
entraining coal from the supply in the primary air stream to form a fuel stream;
simultaneously delivering the fuel stream and at least a first part of the heated second air stream to the interior of the furnace via a nozzle associated with a burner;
delivering additional hot air from the heated second air stream to the furnace at the nozzle and coaxially about the simultaneously delivered fuel stream and first part of the heated air whereby the additional hot air supports combustion of the fuel stream; and supplying ignition energy to the fuel stream at the nozzle to cause ignition thereof in the cold furnace to thereby initiate operation of the furnace.
22. The method of Claim 21 wherein the step of providing a supply of pulverized coal comprises:
pulverizing coal during normal operation of the furnace;
diverting some of the pulverized coal to an air separator to remove transport air therefrom;
loading the pulverized coal into a storage bin; and controllably withdrawing pulverized coal from the storage bin.
pulverizing coal during normal operation of the furnace;
diverting some of the pulverized coal to an air separator to remove transport air therefrom;
loading the pulverized coal into a storage bin; and controllably withdrawing pulverized coal from the storage bin.
23. The method of Claim 21 further comprising:
pulverizing coal subsequent to ignition of the fuel stream and warming up of the furnace;
heating the air which subsequently forms the primary air stream by heat exchange with furnace combustion products;
supplying the pulverized coal to the furnace by means of entrainment in the heated primary air; and discontinuing heating of the second air stream upon initiation of pulverizing.
pulverizing coal subsequent to ignition of the fuel stream and warming up of the furnace;
heating the air which subsequently forms the primary air stream by heat exchange with furnace combustion products;
supplying the pulverized coal to the furnace by means of entrainment in the heated primary air; and discontinuing heating of the second air stream upon initiation of pulverizing.
24. The method of Claim 23 wherein the step of providing a supply of pulverized coal comprises:
diverting some of the coal pulverized subsequent to discontinuing heating of the second air stream to an air separator to remove transport air therefrom; and loading the diverted pulverized coal into a storage bin.
diverting some of the coal pulverized subsequent to discontinuing heating of the second air stream to an air separator to remove transport air therefrom; and loading the diverted pulverized coal into a storage bin.
25. In a furnace system that includes a furnace, at least a first main coal nozzle arranged to direct coal into the furnace, an air preheater having a flue-gas inlet, an air inlet, and an air outlet and being connected to receive flue gases from the furnace at its flue-gas inlet and transfer heat from the flue gas to air entering the air inlet and leaving the air outlet, a coal pulverizer, conduit means connected to conduct pulverized coal from the pulverizer to the main coal nozzle, means for forcing a first air stream through the preheater from its air inlet to its air outlet and from the air outlet through the pulverizer to entrain and transport coal through said conduit means and into the main coal nozzle, an improved warm-up system comprising:
an ignitor nozzle;
means for storing a supply of pulverized coal during normal furnace operation;
means for establishing a second air stream;
means for controllably releasing pulverized coal from said storing means into a stream of primary air to form a fuel stream;
means for transferring heat to the second air stream from a source other than the furnace flue gas;
means for causing the heated second air stream and the fuel stream to flow into the furnace at the ignitor nozzle, said flow causing means dividing the heated second air stream into a pair of streams coaxial with the fuel stream; and a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle whereby ignition energy will be supplied by said lighter and heat transfer means.
an ignitor nozzle;
means for storing a supply of pulverized coal during normal furnace operation;
means for establishing a second air stream;
means for controllably releasing pulverized coal from said storing means into a stream of primary air to form a fuel stream;
means for transferring heat to the second air stream from a source other than the furnace flue gas;
means for causing the heated second air stream and the fuel stream to flow into the furnace at the ignitor nozzle, said flow causing means dividing the heated second air stream into a pair of streams coaxial with the fuel stream; and a lighter, positionable near the outlet of the ignitor nozzle, for igniting coal issuing from the ignitor nozzle whereby ignition energy will be supplied by said lighter and heat transfer means.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA299,030A CA1079577A (en) | 1978-03-14 | 1978-03-14 | Boiler cold start using pulverized coal in ignitor burners |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA299,030A CA1079577A (en) | 1978-03-14 | 1978-03-14 | Boiler cold start using pulverized coal in ignitor burners |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1079577A true CA1079577A (en) | 1980-06-17 |
Family
ID=4111004
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA299,030A Expired CA1079577A (en) | 1978-03-14 | 1978-03-14 | Boiler cold start using pulverized coal in ignitor burners |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1079577A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114947166A (en) * | 2022-05-10 | 2022-08-30 | 贵州省烟草公司六盘水市公司 | Biomass baking deflagration-proof method |
-
1978
- 1978-03-14 CA CA299,030A patent/CA1079577A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN114947166A (en) * | 2022-05-10 | 2022-08-30 | 贵州省烟草公司六盘水市公司 | Biomass baking deflagration-proof method |
| CN114947166B (en) * | 2022-05-10 | 2023-05-30 | 贵州省烟草公司六盘水市公司 | Biomass baking explosion-proof method |
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