US2939434A - Pulverized fuel furnace of the cyclone type - Google Patents

Description

June 7, 1960 G. STEINERT 2,939,434

PULVERIZED FUEL FURNACE OF THE CYCLONE TYPE FiledFeb. 6, 1958 2 Sheets-Sheet 1 FIG. I

5r INVENTOR: 46 j GERHARD STEINERT June 7, 1960 e. STEINERT PULVERIZED FUEL FURNACE OF THE CYCLONE TYPE Filed Feb. 6, 1958 2 Sheets-Sheet 2 FIG. 5

INVENTORZ GERHARD STEINERT kin 4M 15/ AGENT Filed Feb. 6,1958, Ser. No. 713,592

8 Claims. .(Cl.122-235) This invention relates to improvements in a pulverized fuel burning furnace having an upright cyclone type combust'ionchamber designed for removing the ashes'en trained in the combustion gases in a fluid state. The invention specifically relates to'a cyclone type furnace having'fluid cooled walls and a top gas outlet from which ice . '2 nearlymatching thewidth and depth respectively of the radiationchamber.

Itis another important object of the invention to provide a cyclone chamber with an inwardly extending gas outlet "sleeve which is of elliptical, oblong or similar shape, the long and short axes thereof substantially matching the width and depth respectively of the topa gas duct sleevejcoaxially extends downwardly into the interior-"of the cyclone chamber. In addition the invention applies toa cyclone combustion chamber as aboveidescribed having a t'op-jacently adjoining radiation chamber of a generallyrectangular cross section, and

jacently adjoining radiation chamber.

t A further object of the invention is the provision of a cyclone'combustion chamber and internal gas outlet sleeve, one or both 'being of elliptical, oblong or other similar shape that is not circular, and in which the ratio of the long and short axes of one or both of the above elliptical or like configurations substantially equal the ratio of the width and depth of the adjoining radiation chamber.

' A stillfurther object of the invention is the provision in an upright furnace of a cyclone chamber and gas outlet sleeve both having elliptical or oblong cross sectional configuration, an adjoining radiation chamber having a'lower portion that is alsoof elliptical or oblong shape which either matches the combustion chamber or the gas is' mor'e' particularly concerned with the relative shapes of the-outlet gas duct sleeve, the cyclone chamber and the radiation chamber.

"-Heretofore,--the' furnaces of the above described cy clone type have been equipped with gas outlet sleeves and-combustion chambers of circular cross section and 'slop-ing' transition surfaces connecting the rectangularly shaped radiation chamber with the circularly shaped gas out-let sleeve. Cyclone furnaces as heretofore employed in the fuel burning field and designed as hereinabove outlined are beset with slagging difficulties in the radiation chamber especially when operated with fuels having a high ash content. These difliculties arise because the residual ash still entrained in the combustion gases when leaving the circular gas, outlet sleeve and following a spiral path at high velocity is expelled from the gas stream outlet by centrifugal force and deposited in a liquid or soft state on the sloping transition surface. The cooling action of the tubes of which these surfaces are constructed causes solidification of the liquid ash and formation of slag deposits; These deposits'inter-fere-with the heat transfer efficiency of the tubular surfacesiand the jflow of hot combustion gases leaving the "gas outlet. They cause a rise in furnace gas temperature entering the convection heating surfaces, slag deposit on these surfaces and a lowering of the efficiency of th ehoiler due to higher gas outlettemperatures.

Furthermore in furnaces of the cyclonic type it is highly desirable to provide an adjoining radiation chainber of rectangular cross' section having a width substantially largerthan the depth thereof, in order most ecoinomically'to accommodate the convection heating surfaces such'as superheater, reheater and economizer that areldi'sposedin gas passages adjoining the furnace offtake. It has been common practice to provide the; rectangularly shaped radiation chamber with acyclone combustion chamber having a circular cross section. Suchv a construction fails to make the fullest useof the space and area available beneath the radiation chamber forproviding maximum furnace volume and heating surshape, 'the.'long and-shor.t axes thereof matching or outletsle eve; andhaving an upper portion of rectangular cross section the width and depth thereof corresponding to the long and. short axes respectively of the lower portion. An additional object of -the invention is to improve ignition,' con1bust-ion of the fuel and separation of liquid ash from the combustion gasesby providing a relatively large flow area immediately. afterthe point of discharge of fuel and air into the furnace, and a relatively small flow area at the location where the flame subsequently undergoes a sharp change in flow direction.

Other and further objects of the invention'willb'ecome apparent to those skilled in the art from the detailed description thereof when taken in conjunction with the accompanying drawings wherein: v

Fig. 1 is an elevational section of a steam generator having a furnace of the cyclone type equipped with my inventive improvements;

' Fig. 2 is a plan section through the cyclone furnace chamber when taken on line 2-2 of Fig. 1;

Fig. 3 is a plan section similar to that of Fig. 2 taken through a furnace chamber wherein the ratio of the large axis to the short axis of the gas outlet duct is greater than that of the combustion chamber.

' i Fig. 4 is a plan section through a cyclone combustion chambersimilar to that illustrated in Fig. 2, however showing a chamber of circular cross section in conjunction' with an oblong gas outlet duct sleeve;.

.Fig., 5 is an elevational section of a steam generator similar to that illustrated in Fig. 1 but having a radiation chamber of outside width anddepth substantially equal to the long and short axes respectively of an elliptically shaped combustionchamber. r

Fig. 6 is a plan section taken through the combustion chamber generally on lines 6-6 of Fig. 5;

Fig. 7 i s a plan section through the radiation chamber when taken on line 7-7 of Fig. 5;

'Fig. 8 is a plan section through therupper portion of the radiation chamber and the parallelly downwardly. extending convection gas passwhen taken on line 8-8 of Fig. 5. V

Referring now to the drawings wherein like reference characters are used throughout to designate likeuelements, Fig. 1 schematically represents a pulverizedfcoal fired steam generator having a furnace 10 water cooled throughout and comprising a radiation chamber 12 and. a subadjacently adjoining cyclone type combustion chamber 14. Fuel and air are discharged into combustion chamber '14 by way of burners 16 in directions generally "tangential to air-imaginary firing circle coaxially located within the combustion chamber 14" The temperature maintained in the combustion chamber is such that the ash is expelled by centrifugal force from the rotating gases While t l in fl d; ta fl w do n hewalls he chamber and is discharged through a slag;qut-let;18;een y located n h ot om Qfthe u ac The amp o r gases still rotating a ishe oeit n a duet sleeve 20 extending downwardly intothe interior of the cyclonic combustion chamber {14 from a gas outlet open; ing 22 formed in the; roof of combustion chamber 14;. Sleeve 20 is constructed of upnight steamgenerat-ing-itubes 23 originating in headers 24. Thewalls of the combnsmentq E g- Zthe ong and short. axes, o gas dnet. a e. shown equal to the width and depth respectively of the tion chamber 14 are linedwithsteamgeneratingtuhesfi originatingin headers 26; Eachtube 23-joinsa tu e- 5a;

the periphery of gas ou'tlet22 by means of' a bifurcateand continues upwardly as tube 27- to form the liningfor radiation chamber 12 andto terminate in a steam and water drum 28. A mixture of steam and water is thus discharged by way of tubes 27 into drum 28, the steam being separated from the water by conventional means, not shown. The. water flows downwardly through tubes 30 which terminate. in. headers 26 thereby completing the water circulation circuit of the steam generator. Saturated steam flows from drum 28 to a low temperature convection. superheatersection 32 by way of connecting pipes 34, and after being pre-superheated proceeds to a panel type. high temperature superheater section, 36 loradiation chamber 12.

This construction affords the advantage of greatly diminishing the sloping transition surfaces to restricted residual areas 55 in the corners of the chamber 12, and accordingly offers to the entrained ash particles only a small surface upon which. to settle. The lower portions of water wall tubes 27 of the radiation chamber 12 remain therefore in; a relatively clean condition without heavy accumulation of slag. Reduction of the heat absorbing capacity of these tubes is accordingly largely avoided and the temperature of the gases can be held at the design value to maintain the efiici'ency of the steam generator. Furthermore the bending of the water wall tubes is greatly simplified offering substantial savings in fabrication costs of the furnace walls.

In the preferred embodiment of Fig.- 2 thefuel and primaryair is introduced through burners 16 in. directions paralleltothe long axis La. The gases generated immediately after the fuel enters the furnace chamber arethus permitted; to travel ina substantially straightpath througha flow-area 56 before they app oach therounded I end portions a and b of the; oblong shaped gas outlet duct cated in the upper portion ofthe radiation chamber 12 v v Having been heatedto the desired temperaturerthe steam passes out of superheater section36by-way ofsteam pipe 38 and valve 40 and is ldelivered to apoint of use,- such as a turbine, not shown. Thereare provided within the radiation chamber '12; radiant steam generating tube panels 42 whichreceivea water and steam mixture from headers 44 disposeddirectly above the roof of combustion chamber 14. Only a limitednumber of tubes 25 lining the wall of combustion chamber 14 join tubes 23 liningthe gas outlet sleeve20 to form tubes 27 lining the radiation chamber 12. The remaining tubes 25 terminate inheaders 44 to supply panels 42.with a steam and watermixture. vAny water separated from the steam in headers 44 is drainedofi via tubes 46 to headers. 24, which, in turn, supply water to tubes 23 forming gas outlet sleeve 20.

The gases generated in the combustionchamber 14 by tangential firing are-given a strong rotational flow and fol; low a spiral upwardly directed path when passing through gas outlet sleeve 20. While flowing upwardly through furnace 10 these gases give upheat to water wall tubes 25 and 27, panels 42 andsuperheaterpanels 36 and enter a horizontally adjoiningv gas 'offtake 50in whichthe convection superheater 32 is located. The gases are subsequently conducted over other heating surfaces suchas econom'izer and air heater, not shown, and are eventually discharged into the atmosphere by way of an induced draft fan and a stack. The furnace '10 is walled in by refractory 52 and insulation 53 which is covered with a metallic outside casing 54. 7

Referring now to Fig. 2, in accordance with the invention, the gas outlet sleeve 20 is of a prolate,- elliptical,

oblong or other similarshape, elongated along a long axis La having rounded ends a and b, connected with side portions c and d symmetrically located along a short axis Sa.

The invention also discloses a combustion chamber 14of prolate, elliptical, oblong or other elon- '1 gated shape havinga long axisLb and a short axis Sb. In the preferred embodiment of Fig. 2 the ratio of the long axis La to-the short axis Sa of thegas outlet-sleeve 20 is equalor-approximately equal to theratio of the haiah tlh. More s si isa ly,, atQePr te Ies srnQQsIi:

width and depthof'the radiationlchamber .12is substan- 2!). In this; manner separation; of the fuel particles from the airdueto. centrifugal force-is avoided before ignition of'the fuel takes place. Accordingly the burning of the fnelis; rapid, the flame. temperature, is raised and early forming of liquid ash encouraged; thereby increasingthe slag remgving f i i cy of the-furnac E rthermorethe furnace can now safely be operated at; lower loads since the combustion ofi the-fuelisefiected at higher temperatures. v

As illustratively shown in Fig. 3- and in accordance withthe invention, the ratio of the long axis L0 to the short axisSa-of the gas outlet sleeve may preferably be chosen to be larger than the corresponding ratio of' the axesof the cyclone chamber 14. A restriction of the flow "area 57 near the end portions a and b of the gas outlet duct20,,is; thereby achieved with respect to the flow area provided at 56 between the straight wall portions of the gasoutlee duct 20 andcyclone chamber 14.

I Onto gain the s-ameends, the combustion chamber 14 can-bejgiyen a circular shape58 as shownin, Fig. 4. In both designsasdepicted, in Figs. 3 and 4, the velocity of thecornbustiongasesiproduced at 56 in the combustion chamber 14.is substantially increased as. these gases approach area 57 adjacent the-rounded endportionsa and]? oftheelongated gas outletsleeve 20. Aperiodic increase and decrease ofthevelocityof the; gases accordingly takes place which encourages coagulationof'the liquid ash para ticles entrained in the gasesand increasesthe efiiciencyof thecyclonechamber in separating the ashes from the gases before; these gases leave the combustion chamber 14.

' Furthermore, in accordance with the invention, the peaksof. the thusly established gas velocity pulsation can be increased byintroducing secondary air through nozzles 60 at locations intermediate the-pointsof fuel entry and immediately before thegases approach the'restricted flow areas 5 7, as shown in Fig. 3. In this mannerthe gas quantity is suddenly increased at the points where the flow area begins to decrease, which greatly enhancesthe beneficial; eifectof velocity pulsation on the ash' separation efficiency of. the cyclone furnace;

In Fig.1 a furnace is illustratively shown inwhich the tia'llyequ al to the width and depth of-the gas-outlet sleeve 20. Tliisconstruction offers theeconomic advantage of permitting the use of many tubes which aregenerally straight throughoutthelength thereof-from the-lower edgeofigaszduct 20 to thereof offfurnacer 10.

Obviously the above; introduction of the-secondaryair can bezuseda with equally beneficial. results in. a furnace .having ani oblong .gfls: outlet; sleeve- 20;. employed in coniunst ien:wither yclcaelmmhustion.chamherzfifl. t-cit:

- cular configuration "as illustratively shown in'Fig. 4; In Fig. :5 there is schematically shown a steam generator having a cyclone type furnace? generally similar to' that illustrated in Fig. 1. It comprises a combustion chamber and gas outlet sleeve of elliptical or near-elliptical cross-sections, wherein the-longan'dshort axesrespectively of the combustion chamber 14 are'equal to or-approxi: mately equal to the width-and depthflof the rectangular upper portion of radiation chamber 12, as illustratively shown in Figs. 6 and 8. The lower portion 62 of the radiation chamber 12' is preferably formed of upright tubes arranged to, produceta crosssection of an oblong or elliptical shape which matches that ofnhe combustion chamber 14. The height of the transition section,64 which is also generally of "elliptical configuration" is such that the tubes lining this section are very steeply sloped offering little if any support to the ash particles ejected by the rotating combustion gases that leave gas duct 20. Furthermore by giving the combustion chamber an elliptical or oblong form the periphery of which is tangent to the sides of the upper rectangular portion of the radiation chamber 12 as shown in Fig. 7, economical use is made of the space below chamber 12 as concerns the combustion space and heating surface incorporated in cyclone chamber 14-.

The gases generated in cyclone chamber 14 of furnace by the burning of fuel pass upwardly through the radiation portion 12 and through a row of widely spaced tubu-' lar panels 66 which in the embodiment of Figs. 5 and 8 represent steam generating and steam heating surfaces. Having given up heat to these surfaces the gases enter furnace ofltake 68 as indicated by the arrow and flow downwardly through a convection gas pass 70 in which are disposed banks of tubes representing steam heating surface 72 and economizer heating surface 74. The gases thereupon leave the boiler proper by way of duct 76, pass through an air heater and are discharged into the atmosphere by way of induced draft fan and stack, not shown.

The walls throughout the furnace of Fig. 5 are lined with water carrying and steam generating tubes 78 receiving water from a drum 80 all in a conventional and well known manner as earlier herein described in connection with the apparatus of Fig. l.

Although the herein disclosed invention has been described in connection with a natural circulation steam generator of the radiant type, being fired preferably with pulverized coal, this invention can with equally beneficial results be used in connection with a controlled circulation unit or with a once-throughtype steam generator. Furthermore, the invention could also be applied to a heat exchanger in which other fluids besides water and steam are heated, such as air or gases. Also, the invention could be employed in connection with furnaces burning such fuel as black liquor or other comminutedfuelsfi Furthermore the invention can also be' practiced with equally beneficial results in a heat exchanger apparatus operating under pressurized firing.

Although the invention as herein described is used in connection with a steam generator having but one combustion chamber discharging combustion gases into a radiation chamber, several of. such combustion chambers can be employed, discharging their gases into one or more radiation chambers.

While I have illustrated and described preferred embodiments of my invention, it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes as fall within the purview of my invention.

I claim:

1. A 'fumace having a cyclone-type combustion chamber defined by fluid cooled walls. disposed about a generally upright longitudinal axis, burner means for tangentially discharging fuel and airinto said chamber for burning, means forming a constrictedz outlet centrally upright line moving generally parallel to said longitudinal axis and constantly meeting in a plane normal to said line a closed curve of oblong shape having a long and short axis of substantially the same length, respectively, as the wide and narrow side of said radiation chamber and including rounded convex end portions interconnected by side portions.

2. The 'fumace of claim 1 in which the cross-section of said combustion chamber is of circular shape.

3. A furnace having a cylone type combustion chamber defined by fluid cooled walls disposed about a generally upright, longitudinal axis, burner means for tangentially discharging fuel and air into said chamber for burning, means forming a constricted outlet centrally disposed in the top of said combustion chamber for evacuating the gases generated therein, a gas duct sleevehaving fluid cooled walls and extending coaxially from said opening downwardly 'into said combustion chamber for conducting the gases from the interior of said combustion chamber to said gas outlet, an upright radiation chamber having two wide parallel walls and two narrow parallel walls of fluid cooled construction, with the wide walls being substantially larger than the narrow walls, said radiation chamber top-jacently adjoining said combustion chamber for receiving said hot gases discharged from the outlet of said gas duct sleeve, said combustion chamber and said sleeve each being formed of an individual surface of revolution traced by a substantially straight and upright line moving generally parallel to said longitudinal axis and constantly meeting in a generally horizontal plane a closed curve of oblong shape having a long and a short axis and including rounded convex end portion interconnected by side portions, the long and short axes of said gas duct sleeve being substantially equal to the width of the wide and narrow walls, respectively, of said radiation chamber.

4. The furnace organization of claim 3 in which the ratio of the long and short axes of said combustion chamber and the ratio of thelong and short axis of said gas duct sleeve are substantially equal.

5. The furnace organization of claim 3 in which the ratio of the long and short axes of said gas duct sleeve is larger than the ratio of the long and short axes of said combustion chamber.

6. The furnace organization of claim 3 in which said burner means are disposed to. discharge fuel and air streams in directions parallel to said side portions.

7. The furnace of claim 6 additionally being provided with nozzle means located intermediate said burner means for discharging air into said combustion chamber.

8. A furnace having a cyclone type combustion chamber of oblong cross section and defined by fluid cooled walls disposed about a generally upright longitudinal axis, burner means for tangentially discharging fuel and air into said chamber for burning, means forming a constricted oblong outlet opening centrally disposed in the top of said combustion chamber for evacuating the gases generated therein, a gas duct sleeve having fluid cooled walls peripherally connected to said outlet forming means and extending co-axially from said outlet downma -asa- 7 wardly into said combustion chamber forconducting the-gases fron'rtlminterior; of said combustion chamber to said "g'asouflet; *an 'upright' radiation chamber -"liaving fluid cooledwalls and top-jacently adjoining said: combustion chamber forrecciving said hot gases discharged from the outlet. of said" gas'duct sleeve; said radiation chamber comprising an upper portion of-generally'rem tangular cross section having; two" wide parallel :walls and two. narrow parallel walls, with the-wide walls being substantially larger than.the ariaw. walls, and a lower portion of. an oblong .cross-s ection having a width and depth whichsubstantially equal the width and vdepth .tespectively, of the walls of the" upper portion, said lower portion and said sleeve and; said; combustion chamber each being formed of an. individual surface of: revolue ti'on traced} by==a substantially. straight and. upright line moving 'generally'panailel to said longitudinal axis; and constantly meeting in a plane normal to said line a closedcurvevofoblong shape having a: long and a; short including rounded"; convex" end portion. intercom nected j by side portions, the long and'short axes ro spectivelz of said" combustion chamber and of said lower portion being substantially of. equal length.

References Gited' in the file;of this patent FOREIGN PATENTS France.v Oct. 26,, 1955' Francev Oct. 22,1956

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