US2854959A - Furnace arrangement - Google Patents

Description

Oct. 7, 1958 WQJUNKERMANN FURNACE ARRANGEMENT Filed Deo. 15. 1953 w TZ ATTORNEY United StatesI PatentOfice 2,854,959 Patented Oct. 7, 1958 FURNACE ARRANGEMENT Wolfgang Junkermann, Oberhausen, Germany, assignor `to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application December 15, 1953, Serial No. 393,356

8 Claims. (Cl. 122--235) The present invention relates to the construction and operation of furnaces wherein a pulverized slag-forming solid fuel is burned in suspension under slagging temperatures, and particularly to fuel burningapparatus of the character described in which high temperature gaseous products of combustion are generated, and discharged substantially free of entrained slag or ash particles over a wide load range.

In modern high capacity steam generating units, for example, pulverized coal is burned in suspension in a furnace and the path of the burning fuel and gaseous products of combustion therein is such that normally a relatively high percentage of the incombustible dry ash residue is carried out of the furnace by the gases and into contact with the convection heated tubes of the steam generator. A lower dust load in the gases can be obtained by the burning of coarsely pulverized or granular fuel in a whirling fuel-air stream in a cyclone type furnace of circular cross-section in which the fuel is burned under slagging' temperature conditions partly in suspension and partly in place on the slag covered peripheral wall of the cyclone. The size of such cyclone furnaces, however, is limited, so that for high fuel burning capacities it would be necessary to provide a number of such cyclone furnaces arranged to discharge into a common secondary furnace chamber. One minor disadvantage of such an arrangement is the necessity of simultaneously controlling combustion conditions in the individual cyclones or alternatively cutting in and out of individual cyclones, in accordance with changes in the load.

When a pulverized slag-forming fuel is burned Vin suspension in the usual type of pulverized fuel furnace under a mean furnace temperature above the ash fusion temperature, and the fuel stream directed to facilitate the separation of the molten slag particles in suspension, a substantial proportion of the ash content can be separated in the furnace and removed as a molten slag. There is, however, a substantial portion of the molten slag left in the discharging furnace gases and it is important that this be largely eliminated before the gases reach the convection heated tubes. Slag screens have been provided for this purpose in the path of the gases and when high ash fuels are burned, such slag screens are frequently overburdened with slag and the openings between the tubes thereof become clogged.

stream and gases. In accordance with this invention, the secondary combustion chamber is in the form of one or more vertically arranged cyclone chambers having a tangential inlet connection from the main furnace chamber, a slag outlet at the bottom thereof, and an upper axially arranged outlet opening for the discharge of the relatively clean heating gases. Also in accordance with the invention both the main furnace chamber walls and the walls of the cyclone secondary combustion chamber or chambers are lined with uid cooling tubes covered with refractory material and/or deposited slag. The invention thus comprises a method of and apparatus for burning a pulverized slag-forming fuel over a Wide range of loads wherein the ash content of the fuel is effectively separated in the furnace and discharged separately from the heating gases.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated and described.

Of the drawings:

Fig. l is a sectional elevation, taken on the line 1 1 of Fig. 2, of the main furnace chamber and secondary combustion and separating chamber of a pulverized coal tired steam generating unit constructed in accordance with the invention; and

Fig. 2 is a sectional plan view of the construction taken on the line 2-2 of Fig. 1.

The steam generating unit illustrated comprises in general a primary furnace 30 in which a combustible mixture of a pulverized slag-forming fuel, such as pulverized bituminous coal and air is burned, and which is arranged to direct combustion constituents tangentially into two vertically elongated cylindrical cyclone-type separating and combustion chambers, l0 and l2 respectively, which are positioned at each side of one end of the primary furnace 3th. The cylindrical separating and combustion chambers are arranged lbelow a vertically elongated radiation chamber 2li into which clean gases from the combustion constituents are passed upwardly from the separating and combustion chambers, while the solid slag forming particles impinge along the cyclone walls in the form of a molten mass. This molten mass flows by gravity into` bottom openings 74 and 76 in each separating and combustion chamber.

The primary furnace 30 is substantially L-shaped in vertical section, and comprises: a vertical upper rear wall 36, having a plurality of openings therein for pul- In accordance with the present invention a pulverized ration of a substantial portion of the molten slag particles t therein and their discharge from the furnace chamber into a secondary combustion chamberwherein combustion of the fuel particles is completed and most of the ,remaining slag particles separated from the burning fuel verized coalv and air nozzles 38, and secondary air nozzles 4G; a forwardly sloping roof 42; a vertical front or face wall 44; a lower rear wall 46; a furnace oor 48; side walls 50 and 52; and a lower rear roof 66. The side walls Stb and 52 are lined with a plurality of fluid cooled stud-tubes 54 which extend from a lower header 56, located below the outside of the furnace floor 48, to an upper header 5S located above the outside of roof 42; and thence upwardly into the radiant chamber 20 to form part of the cooling tubes therein. The floor is also lined with cooling tubes 60 which extend from a lower header 62, subjacent the rear wall 46, along the oor 48, front wall 44, and roof 42 to the outside header S8. Additional cooling tubes 64 lining the lower rear ceiling 66, and vertical tubes 68 lining rear wall 46 and extending upwardly from header 62 also form part 0f the circulating system of the steam generator. All of the cooling tubes lining the primary furnace and the ,separating and combustion chambers are spaced with refractory in a manner which will give furnace wall `3 temperatures which will maintain any slag forming thereon in a molten state.

In accordance with the invention, the rear wall 46 of the primarylfurnace is provided with vertically extending wedge-shapedpassages 32 and 34 adjacentside walls 50 and '52 rcspectively These passages are normally arranged 'to extend from the lower portion of the lloor 43 to a position subjacent the lower roof 466. Each wedgeshaped passage leads through narrow high-velocity venturi-type throat sections v70 `and 72 tangentially into the cylindrical separating and combustion chambers 1Q and l2 respectively. The throat portions are arranged so that combustion constituents exiting therefrom enter tangentially into the cyclones at high velocities. y

The separating land combustion chambers 19 and 12 are arranged with axes vertical .and are laterally spaced from each other. -Their Acylindrical walls are lined on the inside with stud- tube cooling tubes 14 and 16, in chambers and 12 respectively. VThe walls are arranged with a rcfractory'composition between each tube to give wall temperatures `which will keep any slag forming thereon in a molten state. The walls extend outwardly and upwardly at :the top of each chamber to form the walls of the radiation chamber 20. VThe tubes of each chamber form part of the group of radiant chamber cooling wall tubes, and connect into the circulation systern of the boilers. The outside portion of these tubes is lined by a layer of insulating bricks -22 with an outer metal casing24 `outside these bricks.

Radiation chamber lis similar to that shown in the patent to H. 1.4Kerr et al. Number 2,594,312 which issued on April 29, 1952. Itis part of the steam generator, having its walls lined with cooling tubes 26. Between each secondary combustion chamber and the main radiation chamber is a plurality of cooling tubes larranged to form a slag and ash screen 28 which aids in preventing the entrance of any ash which may possibly carry over with the combustion gases which move upwardly in the separating and combustion chambers.

In operation the combustion constitutents enter the furnace chamber 30 from nozzles 38 and 40, located `in the upper rear wall 36, and are ignited and directed against the face wall 44. Slag particles contained therein impinge against the face wall and floor, and the molten slag formed thereon flows downwardly along wall 44, and floor 48, through the lower portion of the inlet passages 32 `and 34, to the cyclone chambers 10 and 12. In the cyclone chambers the slag falls downwardly through air sealed openings 74'aud 76 into a water trough (not shown) where the ash is conducted away on a conveyor.

The combustion constituents generated in the furnace chamber 30 are directed back from wall 44 where they continue to burnas they pass into the lower portion of the furnace. Combustion is substantially completed when the combustion constituents enter the cyclone chambers 10 and 12. These constituents then pass through the narrow passages 32 and 34 where the gas velocity is increased by the venturi-like passages, and then into the separating and combustion chambers where the gases are `separated from the ash particles. The gases are given a cyclonic upward whirling motion whereby thc remaining constituents are burned completely or the solids which will -not burn are separated from the gases as lthey are hurled against the walls of the cyclone chambers.

lIn the embodiment shown the slag flows downhill from the furnace avallfl, the lloor 48, and the passages 32 and 34, out the hopper openings 74 and 76. However, the invention also contemplates slag removal by means of an opening in chamber 30 at the lower end of floor which would be connected 'below the wedge shaped passages to the bottom of .the Vcyclone separating and combustion chambers, 'or Jdirectly -to 'a water trough 'or `4 hopper in a known manner. In such a case, the passages 32 and 34 would not extend even to the oor '48, and the combustion constituents which have been separated from some of their slag contents by the impingement of the furnace walls would be directed upwardly from the furnace chamber lloor before entering the passages 32 and 34. In which event, further separation of the solid particles from the gases would occur in the furnace chamber due to the upward gas ow from the `furnace floor.

The invention herein disclosed provides an effective means for burning a pulverized fuel of the character 'described. Stable ignition conditions are achieved with the invention by heating the combustion constituents to above ignition temperatures in the primary furnace, so that substantially complete ignition is accomplished therein and a large portion of the slag is separated onto the walls before passing the constituents into separating chambers where substantially all the solid particles are removed. The invention lprovides means for materially lessening the expense of cleaning ash from the surfaces of the main radiation chamber by insuring that only clean heating gases sweep through the radiation chamber.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention maybe embodied otherwise without departing from such principles.

I claim:

l. An apparatus for burning a slag-forming fuel which comprises, a vprimary furnace chamber of substantially rectangular horizontal cross section having a oor and substantially vertical boundary walls, means for introducing a`fuelin-a 'finely pulverized condition in astream of combustion air into an upper yportion of said primary furnace chamber, means for burning the fuel in suspension, means for directing the burning lfuel stream against at least one wall whereby the direction of said fuel stream is reversed for continuation of flow in `the opposite direction at a lower elevation and molten ash ,particles in suspension separate therefrom and deposit .on said wall and oor of said primary furnace chamber, at least one cyclonic separating and combustion chamber, means for directing the'burning fuel stream and combustion gases generated thereby from said Vprimary furnace tangentially into said cyclonic chamber, means for withdrawing the clean gases lfrom one end of said Cyclonic chamber, and means for withdrawing the molten slag from said primary furnace chamber and said Cyclonic chamber, said last named means including a Vslag passage extending from adjacent the bottom of said primary furnace to said cyclonic chamber.

2. An apparatus for burning a slag-forming fuel which comprises, a primary furnace chamber of substantially rectangular horizontal cross section having a oor and substantially vertical boundary walls, means for introducing a fuel in a nely pulverized condition in a stream of combustion air into an upper portion of said primary furnace chamber, means for burning the fuel in suspension, means for directing the burning fuel stream forwardly against one of said walls whereby the direction of said fuel stream is reversed Aand molten ash particles in suspension separate therefrom and deposit on said one wall of said primary furnace chamber, two Cyclonic separatingand combustion chambers each having aninlet arranged tangential thereto and arranged near opposing side walls of said primary vfurnace chamber, means for directing the burning fuel stream and combustion gases generated thereby from said primary furnace tangentially into said cyclonic chambers, means for withdrawing the clean gases from one'end of said cyclonic chambers, and means for withdrawing the molten slag from said primary furnace chamber'and' from lower portions of 'said cyclonic chambers.

'3. An apparatus for burning a slag-forming fuel which comprises, a primary furnace chamber of substantially rectangular horizontal cross section having a floor and substantially vertical boundary walls, means for introducing a fuel in a finely pulverized condition in a stream of combustion air forwardly into an upper portion of said primary furnace chamber, means for burning the fuel in suspension, means for directing the burning fuel stream against the front wall whereby the direction of said fuel stream is reversed and molten ash particles in suspension separate therefrom and deposit on said front wall and oor of said primary furnace chamber, two cyclonic separating and combustion chambers arranged near opposing side walls of said primary furnace chamber each having an inlet arranged to connect tangentially into said chambers for inlet llow in opposite rotational directions within the respective cyclonic chambers, means for directing the burning fuel stream and combustion gases generated thereby from said primary furnace tangentially into said cyclonic chambers, means for withdrawing oppositely rotating clean gases from an upper portion of each of said cyclonic chambers, and means for withdrawing the molten slag from said primary furnace chamber and said cyclonic chambers, said last named means including a slag passage extending from said primary furnace to each of said cyclonic chambers and arranged below said burning fuel stream and combustion gas directing means.

4. An apparatus for burning a slag-forming fuel which comprises, a primary furnace chamber of substantially rectangular horizontal cross-section having a floor and substantially vertical boundary walls, means for introducing a fuel in a linely pulverized condition in stream of combustion air forwardly into an upper portion of said primary furnace chamber, means for burning the fuel in suspension, means for directing the burning fuel stream forwardly against the front wall whereby the direction of said fuel stream is reversed and molten ash particles in suspension separate therefrom and deposit on said front wall of said primary furnace chamber, two cyclonic separating and combustion chambers arranged near opposing side walls of said primary furnace chamber each having an inlet arranged to connect tangentially into said chambers for flow in opposite rotational ldirections within the respective cyclonic chambers, means for directing the burning fuel stream and combustion gases generated thereby from said primary furnace tangentially into the respective cyclonic chambers, means for withdrawing oppositely rotating clean gases from an upper portion of each of said cyclonic chambers, and means for withdrawing the molten slag from said primary furnace chamber and said cyclonic chambers, said last named means including a slag passage extending from said primary furnace to each of said cyclonic chambers.

5. An apparatus for burning a slag-forming fuel which comprises, a primary furnace chamber of substantially rectangular horizontal cross section having a oor and substantially vertical boundary walls, means for introducing a fuel in a nely pulverized condition in a stream of combustion air into an upper portion of said primary furnace chamber, means for burning the fuel in suspension, means for directing the lburning fuel stream forwardly against one wall whereby the direction of said fuel stream is reversed and molten ash particles in suspension separate therefrom and deposit on said one wall and the floor of said primary furnace chamber, two cyclonic separating and combustion chambers each having an inlet arranged tangential `thereto at a location adjacent a separate side wall of said primary chamber, means for direct ing the burning fuel stream and combustion gases generated thereby, from said primary furnace tangentially into said cyclonic chamber inlets, means for withdrawing the clean gases from one end of each of said cyclonic chambers, and means for withdrawing the molten slag from said primary furnace chamber and said cyclonic chambers.

6. Apparatus for burning an'ash-containing particulate solid fuel which comprises a combustion chamber defined by walls having an inner exposed refractory surface and iluid cooled tubes proportioned for the maintenance of a normal mean temperature in said combustion chamber above the fuel ash fusion temperature, means for introducing combustion air and ash-containing particulate solid fuel into said combustion chamber, said air and fuel introducing means and the walls defining said combustion chamber being relatively arranged to effect a horizontally elongated inverted burning fuel ow path in said combustion chamber causing the release of a substantial portion of the ash in the fuel in a molten condition for ow to the lower portion of said combustion chamber, walls including Huid cooled tubes defining a cyclonic separating chamber of substantially circular cross-section having a gas outlet and disposed laterally adjacent one end of said combustion chamber, means forming a restricted gas outlet at said one end of the combustion chamber opening tangentially to said cyclonic separating chamber for discharging the gases with slag particles in suspension into said cyclonic separating chamber and effecting a helical path of travel therein along the circumferential wall of the cyclone chamber of sucient length to cause release of substantially all of the remaining recoverable ash in the fuel, and means for withdrawing slag from the lower portion of said combustion and cyclonic separating chambers.

7. Apparatus for burning an ash-containing particulate solid fuel which comprises a combustion chamber defined by walls having an inner exposed refractory surface and fluid cooled tubes proportioned for the maintenance of a normal mean temperature in said combustion chamber above the fuel ash fusion temperature, means for introducing combustion air and ash-containing particulate solid fuel into said combustion chamber, said air and fuel introducing means and the walls defining said combustion chamber being relatively arranged to direct the burning fuel-air stream in impacting relation with one of said walls to effect a horizontally elongated inverted burning fuel iiow path in said combustion chamber and thereby cause the release of a substantial portion of the ash in the fuel in a molten condition for ow to the lower portion of said combustion chamber, walls including uid cooled tubes defining a cyclonic separating chamber of substantially circular cross-section having a gas outlet and disposed laterally adjacent one end of said combustion chamber, means forming a restricted gas outlet at said one end of the combustion chamber opening tangentially to said cyclonic separating chamber for discharging the gases with slag particles in suspension at an increased velocity into said cyclonic separating chamber and effecting a helical path of travel therein along the circumferential wall of the cyclone chamber of suflicient length to cause release of substantially all of the remaining recoverable ash in the fuel, and means for withdrawing slag from the lower portion of said combustion and cyclonic separating chambers.

8. Apparatus for burning an ash-containing particulate solid fuel which comprises a combustion chamber delined by walls having an inner exposed refractory surface and lluid cooled tubes proportioned for the maintenance of a normal mean temperature in said combustion chamber above the fuel ash fusion temperature, means for introducing combustion air and -ash-containing particulate solid fuel into said combustion chamber, said air and fuel introducing means and the walls delining said combustion chamber being relatively arranged direct to direct the burning fuel-air stream in limpacting relation with one of said walls to effect a horizontally elongated U-shaped burning fuel flow path in said combustion chamber and thereby cause the release of a substantial portion of the ash in the fuel in a molten conldition for ow to the lower portion of said combustion chamber, walls including fluid cooled tubes defining a cyclonic separating chamber of substantially circular 7 cross-section .having a gas 4,outlet at one end thereof kand disposed laterally adjacent one .end of said combustion chamber, means forming a restricted gas outlet at -said one -end `of the combustion chamber opening tangentially -to the circumferential wall of said Cyclonic separating kchamber for discharging -the gases with slag particles in suspension at an increased Velocity linto said cyclonic ,separating chamber andeiecting a helical path of travel therein along the circumferential wall of the cyclone chamber of sucient length to cause release of 'substan- 4tially all of the remaining recoverable ash in the fuel, and means for withdrawing slag from the lower portion .of said combustion chamber and from the .opposite .rend of said cyclonic lseparating chamber, said last named 1means including a .slag passage extending yfrom adjacent the bottom of said combustion chamber to Cyclonic separating'chamber.

vReferences Cited .inthe le of this patent UNITED STATES PATENTS Kinyon June 24, McDonald Aug, 17, Hawley Apr. 17, Brown Sept. 22, Cannon et a1 Feb, 12, Baumgartner Nov. 4, Robinson et al Nov. 4,

FOREIGN PATENTS Switzerland Oct. 15,

said

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