US2833230A - Pulverized coal firing system - Google Patents

Description

J. KRUG PULVERIZED COAL FIRING SYSTEM Filed April 22. 1954 fr l FIG. 3

2 Sheets-Sheet 2 l A f /lllll` .INVENTORZ v JULIUS KRUG ATTORNEY Unite States 2,833,230 y Puri/unizar) coat HIRING SYSTEM Julius Krug, Stuttgart, Germany, assigner to- Kohlenscheidungs-Gesellschaft, m. b. H., a corporation of Germany Application April A22', 1954, Serial No. 425,007

` 6 Claims. (Cl. 110-28) ln a steam generator of this type the furnace is generally lined with fluid cooled tubes. The gas carrying the pulverized fuel and the secondary air is usually introduced separately into the Cyclonic slagging chamber by streams which are directed tangentially to an imaginary firing circle concentrically located within the slagging chamber.

The carrier gas by means of which fuel is thus introduced into the furnace may be preheated air, furnace gas or a mixture of both depending on whether preheated air, furnace gas or a mixture of both is utilized for. drying the moisture laden fuel as it is pulverized in the mill. This carrier gas and fuel when entering the furnace chamber has a-temperature of between 200 and 240 F. which ternperature signicantly affectsy the ignition and combustion of the fuel within the furnace. Moreover, in cases where the furnace gases are used for drying and transporting the fuel'an additional difliculty is presented. by the fact that these oxygen poor furnace gases render it more difiicult kto attain satisfactorymixingk of fuel with oxygen rich combustion air.

According to the invention a considerable improvement in this respect can be achieved by dividing the, fuel carrying gases into separate streams of different dust density and/or particle nenessand introducing these streams intof'the combustion chamber at separate locations in the peripheral wall thereof and directed to. separate firing circles having diameters of different size. Inthisrespect it wasfound to be of considerableadvantage-to direct the .stream having lthe greater density or carrying. fuel of larger sizing tangentially to a small ring circle whilerthe other streams carrying lesser fuel or fuel oflner sizing are directed -tangentially to successively larger ring circles.

In this manner a gas and fuel stream containing n relatively small dust quantities and/ or particles of'smallfsize followsa spiral path adjacent the peripheral walls of the slagging chamber within a yzone of the chamber Where the' cooling effect of the wall tubes is most effective. Moreover, a comparatively large quantity ofrcombustion air is injected into this zone through secondary air nozzles thus causing the fuel in that zone to ignite easily and to burn more completely. The other separate streams containing large quantities of fuel and/or larger size follow a path which'is within the flame zone of the outer above mentioned stream. Consequently ignition of the coarser fuelv is also easily accomplished and any fuel'particles which fail to burn Withinsaid flame zone are carried therethrough outwardly by centrifugal force to establish contact with additional air for complete combustion in the outer ignition zone.

The herein disclosed invention is of particular importance when applied to the burning of coal in cyclone 'ice furnaces because, as is well known, the amount of heat radiated from the peripheral walls of these furnaces `to the entering fuel is comparatively small rendering it diiiicult lto quickly ignite and completely burn some types of fuels.

In accordance with the invention the separate ring circles mentioned above can be arranged in series with respect to the direction of ame travel in which case the stream having a lower dust density and/ or carrying fuel of finer sizing, would be directed into the slagging chamber through the peripheral wall thereof preferably ahead of the other streams. VThese separate streams as above described could be produced by various well known means such as for example by means of a reverse ow classifier in which the various layers of classified material having different neness are separately maintained.

lt is accordingly one object of the invention to provide a pulverized fuel tiring system having a furnace with a Cyclonic slagging combustion chamber in which the fuel is introduced through the peripheral wall thereof in separate streams and directed to ring circles of ydifferent diameters.

lt is another object of the invention to introduce the fuel'into a cyclone furnace through the peripheral wall thereof in separate streams and directed to separate firing circles of different diameters, one of said streams containing fuel in large quantities aud/or coarser iineness than the remaining streams.

Still another object of the invention is to direct through the peripheral wall of a cyclone chamber a rst fuel carrying gas stream containing a large quantity of fuel and/ or large sizing toward a firing circle of comparatively small diameter Vand directing at least one other stream containing fuel of lesser quantity and/or finer sizing toward a tiring circle that is larger than said first fuel carrying gas stream.

It is a further object of the invention to provide a fuel burning system of thetype above `described in which the stream containing the lower dust density and/ or finer sizing is `directed into the slagging or combustion chamber through the peripheral wall thereof at .a location with respect to ame travel ahead of the point lof introduction of the other streams having higher dus-t density and/or carrying fuel of coarser sizing.

With these and other objects in view which will become apparent from the following `description reference is 1 made to the accompanying drawing forming a part of this specification and illustrating my invention as `applied to a pulverized coal ring lfurnace without intention of limitl ing the invention to any particular form or use.

-In the drawings:

Figure l is :a vertical section throng-h the lower portion of a radiant boiler equipped with -a cyclone furnace taken on line 1 1 of Fig. 2.

Figure 2 is a horizontal cross section through the cyclone furnace of lFig. l taken on line 2 2.

Figure 3 is a section similar to Fig. 2 but of an embodiment having four burners.

Asy shown in Fig. l the furnace is equipped with a cyclone slagging chamber l the circiunference of which being lined with fluid cooling tubes 2 which are fed `from 4a ring header 3. The water -for coolingy and generating steam is supplied to the ring header 3 from a downcomer header 6 lfrom which the water flows through connecting tube 7 into ringlheader 3. Projecting into the cyclone combustion chamber is a cylindrical gas outlet 8k formed by spirally arranged tubes through which waterismade lto circulate from afsource not shown'.

The steam generating tubes 2 extend from the cyclonic combustion chamber .l upwardly into the upper radiant portion of the furnace chamber 0l and terminate in a steam and water drum, not shown, wherein separation of steam and water takes place. Downcomer pipes 5 of which only the lower portion is shown carry water from the drum downwardly into header 6. In addition some of the water passes from the drum .through tubes 9 which line'the outer surface of the furnace portions 4 `and 1 forming, wall 22 `and terminate in ring header 3. This wall 22 is provided with fire-proof'material arranged between steam generating tubes 2 and feeder tubes or downcomer tubes 9. In Iaddition the cyclone furnace chamber is surrounded by an outside wallr10 having a metallic outer casing `11. 1

-In the preferred embodiment of my invention illustrated in Fig. l the fuel carrying gas and fuel enters the millv from :a source not shown. After grinding to a suitable tneness thefuel and gas enters a separator or classifier 26 wherein it is separated into two streams and delivered to the cyclone Achamber 1 `by way of two fuel nozzles 12 and 13. The air Vfor combustion is introduced by way of secondary air nozzles 14 receiving preheated air from a source not shownby wayof air duct 15. The fuel carryinggas stream 16 issuing from nozzle12 con` tains a fuel and gas mixtureof relatively low density and/ orsmall particle size. This stream isV directed tangentially to a comparatively large ring circle 17. #Fuel nozzle 13 carrying, on the other hand, a fueland gas stream 18 of higher density -and/ or a coarser fuel sizing is directed tangentially to a firing circle 19. According to therinvention the fuel issuing from nozzle 12 enters the furnace chamber ahead of 4the fuel passing through fuel nozzle 13 with respect to the travel of the tiame which follows a spiral path iirstin a generally downward direction. This is accomplished in the embodiment shown inFig. l by locating the firing circle 17 which is associated with fuel nozzle 12 :above the firing circle 19 associated with fuel nozzle 13.

Or, as illustratively shown in Fig. 3 the Ifuel nozzle 12 may be arranged so that it discharges fuel into the furnace chamber ahead of the point of discharge of nozzle 13 `in a circumferential direction. In `the design of Fig. 3 two pairs of fuel nozzles 12 and 13 are preferably used diametrically positioned with respect to each other.

In both -arrangements (Fig. l and Fig. 3) the finely divided fuel enters the furnace chamber first -through nozzle 12, ignites and establishes favorable conditions for ignition `and burning of the coarser fuel entering the furnace chamber 1 through fuel nozzle 13.

The slag droplets formed by the combustion of the fuel CSX are thrown by centrifugal force towards the walls of the cyclone chamber from where they iiow downwardly towards the ash discharge -opening 21 located in the furnace bottom.

This bottom is cooled by water tubes 20 supplied with feed water by well known means not shown. The combustion gases leave the cyclone furnace through `gas discharge throat 8 and pass through the upper furnace chamber 4 from where they are conducted over additional heat absorbing surfaces, such as, superheater, reheater and air heater (not shown). i

Although the invention has herein been described in connection with a radiant heat steam boiler its application is not limited to this type of apparatus but could withan similar favorable results be applied to a heat exchanger heating other fluids such ras oil, air or other gases. Furthermore, the application ofthe hereinv disclosed invention is not limited to the burning of coal since it could also be utilized, for example, in the combustion of other solid or Xliquid fuels such as concentrated black liquor as employed in the recovery of chemicals in the field of paper manufacture.

I claim:

1. In a fuel burning system for burning finely divided fuel and in which the fuel residue is discharged in a molten condition, the combination of a Cyclonic furnace chamber having means forming an opening for discharging the molten fuel residue at one end thereof and means forming an opening for discharging the gases of combustion at. the opposite endthereof, first burner means located in the' periphery of said cyclone chamber for feeding a iirst mixture of fuel and fuel carrying gas and air for combustion into said furnace chamber in a direc tion tangential to a rst firing circle, second burner means located in the periphery of said cyclone chamber yfor feeding a second mixture of fuel and fuel carrying gas and air for combustion into said furnace chamber in a direction tangential to a second firing circle, said first tiring circle being of smaller diameter than said second tiring circle, and the total outer surface of the fuel for each unit of carrying gas and pound of fuel contained in said first mixture being smaller than the total `outer surface of the fuel for each unit of carrying gas and pound of fuel contained in said second mixture, whereby said first mixture is preheated by penetrating said burning second mixture, said second mixture being more readily ignitable by virtue of the larger surface thereof. Y

2. A fuel burning system as defined in claim l in which the point Aof entrance into said furnace chamber of said rst fuel and air mixture precedes in direction of iiame travel the pointof entrance of said second fuel and air mixture by a circumferential distance which is less than one half ofthe corresponding circumference of said cyclonic furnace chamber.-

3. The method of burning finely divided fuel in a cyclonic furnace chamber comprising the steps'of feedl ing into said chamber from the periphery thereof and burning therein a first mixture of fuel and carrying gas in a direction `tangential to a first imaginary firing circle concentrically arranged within said furnace chamber with respect to the longitudinal axis thereof, feeding into said chamber from they periphery thereof and burning `therein a `second mixture of fuel' and carrying gas in a direction tangential to a second imaginary firing circle concentrically arranged within said furnace chamber with respect to the longitudinal axis thereof said second tiring circle being Yof larger diameter than said first firing circle, `the total'outer surface of the fuel for each unit of carrying gas and pound of fuel contained in said first mixture" being smaller than'the total outersurface of the yfuel for each ufnit of; carrying gas and pound of fuel contained inv saidsecond mixture, preheating said first mixture by penetrating said burning secondmixture, feeding into said -chamber air for combustion, and discharg- Aing `theeresidue of combustion from the chamber in a K molten stage.

mixture contains fuel of larger particle size than said ,74. The method according to claim V3 wherein said first secondmixture.

5.1-The method accordingtoclaim 3 in which the first mixture has a higher density than said second mixture.

6. The method according to `claim 3 in which the admission of the second mixture into the furnace chamber takes place directlyiaheadof the admission of the first mixture with respect to flame travel. f

References Cited in the tile of this patent FOREIGN PATENTS 847,570 France July 3, 1939

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