US2087801A - Furnace - Google Patents

Description

H. J. KERR FURNACE 3 Sheets-Sheet 1 Filed March 23, 1937 INVENTOR.

Howard J'Kerr IR ATTORNEY.

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5 SheetsSheet 3 INVENTOR. Howard] Kerr 5 ATTORNEY.

H. J. KERR July 20, 193 7.

FURNACE Filed March 23, 1937 Patented July 20, 1937 UNITED STATES FoaNAcE I Howard J. Kerr,

Westfleld; N. J.,'assignor to The Babcock & Wilcox Company, Newark, N. 1., a corporation of New Jersey Application March 23,

1937,- Serial No. 132,480

' The present invention relates in. general to the construction and operation of furnaces for buming pulverized fuel in pension, and more particularly to multi-stage furnaces of this type especially adapted for use. in a steam boiler unit.

Pulverized fuel furnaces have heretofore been developed in which a stream of pulverized fuel and air for combustion is introduced into and burned in suspension in a furnace chamber in which a normal mean temperature above the fuel ash fusion temperature is maintained. Under such conditions the particles of incombustible fuel "residue separating from the fuel and flame stream will be in a molten condition and tend to 15 deposit as molten slagon the furnace bottom.

The accumulating slag is continuously or intermittently removed in a molten condition through openings in the furnace bottom or side walls.

When a furnace chamber of the character deg scribed forms the primary or high temperature stage of a two-stage furnace, the second or low temperature furnace stage is substantially shielded from the radiant heat of the primary section by a separating baille or partition below which the fuel and flame stream from the primary section passes through a screen formed by spaced water tubes. Combustion is completed in the second furnace section at a normal mean furnace temperature below the fuel ash fusion temperature so that the ash particles separating in that section will be mainly in a solid or dry condition. The ash separating in the second section is separately removed.

The main object of my invention is the provision of an improved construction and method of operation of a pulverized fuel burning furnace which is characterized by its capacity for use with fuels having a wide range of ash fusion temperatures whilemaintaining high heat release rates in the furnace, separation of a high percentage of the ash constituents in the furnace, and continuous removal of the separated ash or slag over a wide range of operating conditions. A further and more specific object is the provision of a pulverized fuelfurnace of the two-stage type which is characterized by the removal of all the ash separating in the furnace through the portion of the furnace bottom below the second or low temperature section. A further object is the provision of a steam boiler unit with a-water cooled furnace of the type described which is further characterized by a relative arrangement of the furnace chamber and boiler generating surface which shields the boiler gen- 66 crat ng tubes from he furnace radiant heat and minimizes the deposition of slag on the boiler tubes.

The various features of novelty which characterize my invention are pointed out with particularity inthe claims annexed to and forming a part of this specification. Fora better understanding of the invention, its operating advantages and specific objects attained by its'use, ref erence should be had to the accompanying drawings and descriptive matter in which I have 11- lustrated and described a preferred embodiment of my invention. Y

Of the drawings: a Fig. 1 is a sectional elevation taken on the line l-llf Fig. 2 illustrating a two-drum integral furnace type steam boiler constructed in accordance with my, invention; Fig. 2 is a horizontal section takenon the line 22 ofFig. 1; p

Fig. 3 is a longitudinal vertical section taken on'the line 3-3 of Fig. 2; and

Fig. 4 is an enlarged sectional view of a por-- tion of the furnace slag screen taken on the line 4-4 of Fig; 3. i

The steam boiler illustrated comprises an upper steam and water drum I0 and a parallel lower water drum ll slightly offset therefrom and connected thereto by an inclined bank of vertically disposed steam generating tubes l2.

; The drums and tube bani: are arranged along one .side of a setting of rectangular horizontal crosssection formed by a vertically disposed front wall l3, rear wall l4, and side walls l5 and Hi. The setting space laterally adjoining the tube bank is occupied by a pulverlzed.fuel burning furnace.

Tubes l2 of the innermost row of the tube bank are spaced from the remaining. portion of the bank and provided with a multiplicity of projecting metallic studs for anchoring initially plastic refractory material which fills the intertube spaces and covers the furnace side of the tubes I2 to define a'refractory faced partition ll extending from the front wall rearwardly along the tube bank and separating the tube bank for. a. major portion of its length from the furnace. a t

A row of substantially horizontal water tubes I8 extends laterally from the lower drum to a longitudinal header l9 at t e base of the side wall l5, with the spaces between the tubes l8 being closed by suitable metallic tube blocks 20 to form a-flat floor for the furnace chamber ex-- tending from the front wall to a point adjacent the rear end of the partition l1. 7 A row of stud tubes 2| extends upwardly along the side wall l5 and inclined across the arch 22 to the upper drum Ill. The stud tubes along the forward portion of the side wall have refractory material filling the intertube spaces and covering the furnace side of the tubes, while the tubes 2| in' the rear section are partly studded, with the refractory material only in the intertube spaces and a portion of the tube surface directly exposed to the furnace chamber. A row of fully studded tubes 25 covered by refractory extends upwardly along the front wall |3 from a transverse header 26 connected to the lower drum. The upper ends of the tubes 25 are connected to a similar transverse header (not shown) connected to the upper drum.

The arch sections of some of the tubes 2| have their studs and refractory omitted to define a fuel burner port 29 in the arch. Suitable pulverized fuel burners 30 discharge a multiplicity of thin streams of finely divided solid fuel and air for combustion downwardly through the intertube spaces into the furnace chamber. A row of stud tubes 3| similar to the tubes 2W extends upwardly from a transverse header 32 along the rear wall H with their upper port-ions connected to an inclined header 33 leading to the upper drum.

The furnace chamber is thus defined by fluid cooled walls throughout its length, with the inner wall surface-of the front section of the furnace chamber being mainly refractory-faced thus contributing to the maintenance of high temperatures in the front section, which in view of the fuel introduction into that section will be the zone of most active combustion, while the inner wall surface ofthe rear section contains a large amount of exposed metallic heat absorbing surface which facilitates the maintenance of a lower temperature in that section.

The tubes |2 in the innermost row of the tube bank beyond the end of the partition I! are spaced to provide a slag screen across the space between the end of the partition I1 and 'the reartube bank. Transverse baflies 36 and 31 cooperate with the partition I! and side wall Hi to provide a plurality of serially connected transverse gas passes across the tube bank leading to a stack connection at thefront end of the same.

In accordance with my invention the front and rear sections of the furnace chamber are separated by a refractory covered screen extending across the furnace chamber from the partition to the side wall IS. The furnace screen 40 is formed by two staggered rows of vertically disposed stud tubes 4| with corresponding tubes in the two rows arranged in pairs and each tube covered by refractory material 42 held in posi tion by studs 4|.of different lengths on the tube periphery. The studs of greatest length on each tube extend toward the other tube of the pair and with the refractory coveringform a built-up tube structure of generally ovate cross-section with its smaller end slightly separated from the corresponding end of the other tube. The major axis of each tube structure is arrang d b q y to the plane of the tube row, so that adjacent pairs of tubes define gas flow passages directed outwardly and rearwardly. The'upper portions of the screen tubes 4| are bent outwardly and substantially parallel to the partition tubes I2. The passages between the upper bent portions of the screen tubes willbe narrower than between the lower straight portions. This arrangement of the screen tubes and passages also provides an effective shield for the rear end of the main tube bank from radiant heat from the front section of the furnace chamber. The tubes 4| extend between a transverse lower header 43 and an inclined upper header 44 connected to the upper drum II]. A cooling fluid circulation is thus provided through the screen tubes. The cooling effect provided is such that in operation the exposed surface of the supported refractory material is at-a temperature approaching the fuel ash fusion temperature.

As shown in Fig. ,3, the furnace floor terminates a short distance rearwardly of the furnace screen and above the front end of a fluid cooled hopper extending across the rear end of the furnace chamber. The rear wall of the hopper 50 is formed by a row of steeply inclined tubes 5| hav ing their lower ends rounded and connected to a header 52 and their upper ends connected to the rear wall header 32. The tubes 5| are covered by metallic blocks 53 forming a smooth inclined fluid cooled floor leading to a transverse pit 54 from which the depositing material is removed in any suitable manner. The front wall of the hopper is similarly constructed and symmetrically K headers 52 and 56 are connected in any suitable manner to the lower drum I to provide a cooling fluid circulation through the hopper, rear wall and furnace screen tubes. Breaker blocks 51 at the nose of each hopper .inclined wall facilitate the discharge of deposited material. The inner side wall of the hopper is cooled by the lower portions of the slag screen tubes l2 The rea-rmost partition tubes l2 are also extended down along this wall to the header 34. Additional cooling tubes 58 extend from the lower drum to the header 34 along the extended partition tubes. Tubes 59 provide a water supply to the header 34 from the lower drum. The opposite vertical wall of the hopper is cooled by corresponding side wall tubes 2 which are extendeddownwardly to a longitudinal header 6!! connected to the lower drum.

In the operation of the steam boiler unit described, streams of pulverized coal surrounded by sufficient air for its combustion are downwardly discharged at the front end of the furnace chamber and the fuel ignited and burned in suspension in the front section. Due to formation of the parts defining the frontsection of the furnace chamber with a large percentage of exposed refractory area and the burning of the pulverized fuel at a high heat release rate, a high temperature may be easily maintained'therein. A rate of heat absorption is maintained in these parts providing a normal mean temperature above the.

As the burning fuel streams pass rearwardly they contact with the furnace screen elements. The screen elements cause further mixing of the burning gases and air and insure the section adjacent the furnace screen. Ash particles in suspension in the fuel stream contact with the refractory covering on the screen tubes and rapidly accumulate as slag thereon, providing sticlw surfaces on which additional particles impinge and collect. The heat insulating characteristics of this refractory and the relatively low cooling effect of the screen tubes on the outer surface of the refractory causes the slag deposits to remain in a molten condition and continuously flow downwardly to the furnace floor. The molten slag accumulated in the front furnace chamber section and that collected by the screen tubes. flows along the furnace floor through the passages in the furnace screen to the rear edge of the furnace floor.

Only a small portion of the furnace floor extends beyond the furnace screen so that the moiten slag passingthrough the furnace screen passages is not cooled to any substantial extent by the lower temperature conditions in the rear furnace section before reaching the rear edge of the floor. rear end contributes to the discharge therefrom of the molten slag in a multiplicity of small thin streams which rapidly break up into separate drops or globules falling onto the inclined front wall of the hopper. The slag globules are rapidly cooled while falling to and sliding or rolling down the hopper front wall, so that on reaching the pit 5! the globules will no longer be in a molten condition.

The heat absorbing surface in the rear section V is arranged andlproportioned to maintain a rate of heat absorption therein providing a normal mean temperature therein below the fuel ash fusiontemperatuf'e, whereby ash particles separating therein will be or rapidly become chilled and deposit on the inclined hopper walls in a dry condition. The asliparticles depositing on the inclined hopper floors roll or slide into the pit 54 from which they are removed with the slag descending .from the rear edge of the floor.

The heating gases turn in, the rear section of the furnace chamber around the rear end of the partition and enter ,the space occupied by the main tube bank. The heating gases initially pass across the boiler slag screen tubes, which cool the remaining ash particles in suspension. Slag collecting on the boiler slag'screen tubes may fall or be blown off the tubes into the hopper-'50. The gas stream thenflows across the rearend of the tube bank and superheater tubes and forwardly through the transverse gas passes over the remaining portion of the tube bank.

The two-stage furnace construction described permits a highly effective use of radiant heat in efficiently and rapidly burning a slag-forming fuel and separating most of the ash constituents of-the fuel before the heating gases leave the furnace. The radiant heat effect is almost wholly confined to the first or high temperature stage of the furnace chamberlwhere combustion is ini- The described arrangement -of the floor cordingly will be shielded from radiant heat and slag deposits, thus reducing the cost of operation considerably. These results can be maintained with a wide range of fuels of varying ash charac'terlstics and over a wide range of combustion ra es. V

While in accordance with the provisions of the statutes I have illustrated and described herein one form of my invention, those skilled in the art completion of combustion of the fuel in the rear will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features. In the claims the term slagfis used to denote molten ash particles which have agglomerated or fused may The tubes in the main bank and superheater acfrom the point of fuel introduction and' having slag flow passages therein adjacent the floor, level of the portion of said furnace chamber in front .of said screen, said furnace chamber front port on having a closed floor therein constructed to support a. layer of slag in a molten condition, and an ash receiving space below the portion of said furnace chamber at the rear of said screen constructed to receive slag flowing through said screen passages from said front furnace chamber portion. V

2. ,A furnace for burning finely divided solid fuel comprising walls defining a furnace cham-. ber, means for introducing a stream of finelydivided solid fuel and air for combustion into said furnace chamber, means forming a fluid cooled screen extending across said furnace chamber at a point spaced from the point of fuel introduction and having slag flow passages therein adiacent the floor level of the portion of said furnace chamber in front of said screen, heat absorbing surface lining said furnace chamber front portion and constructed to maintain a normal mean temperature therein above the fuel ash fusion temperature including a closed fluid cooled floor therein constructed to-support a layer of 3. A furnace for burning finely divided solidfuel comprising vertically disposed walls defining -a furnace chamber, means at the front end of said furnace chamber for introducing a stream of finely divided solid fuel andair for combustion, a group of vertically disposed refractorycovered tubes arranged to form a slag collecting screen extending across said. furnace chamber,

at a point spaced from the point of fuel introduc tion and having slag-flow passages therein adjacent the floor level of the portion of said furnace chamber'in front of said slag screen,'heat absorbing surface lining said furnace chamber front portion and constructed to maintain a normal mean temperature therein abov the fuel ash fusion temperature including a closed fluid cooled floor therein constructed to support a layer of slag in a molten condition, and a fluid cooled hopper in the rear portion of said furnace chamber and constructed to receive slag flowing through said screen passages from said front furnace chamber portion over the rear end of said floor.

4. A furnace for burning finely divided solid fuel comprising walls defining a furnace chamber, means for introducing a stream of finely divided solid fuel and air for combustion into said furnace chamber, means forming a slag collecting 4 screen extending across said furnace chamber at a point spaced from the point of fuel introduction and having slag flow passages therein adjacent the floor level of the portion of said furnace chamber in front of said screen, heat absorbing surface lining said furnace chamber front portion and constructed to maintain a normal mean temperature therein above the fuel ash fusion temperature including a closed fluid cooled floor therein constructed to support a layer of slag in a molten condition, heat absorbing surface lining the rear portion of said furnace chamber and constructed to maintain a normal mean temperature therein below the fuel ash fusion temperature, and an ash receiving space in the rear portion of said furnace chamber constructed to receive ash separating in said rear portion and slag flowing through said screen passages from said front furnace chamber portion over the rear end of said floor.

5. A furnace for burning finely divided solid fuel comprising vertically disposed walls defining a furnace chamber, means at the front end of said furnace chamber for downwardly discharging a stream of finely divided solid fuel and air for combustion, a; group of vertically disposed refractory-covered tubes arranged to form a slag collecting screen across said furnace chamber at a point spaced from the point of fuel introduction and having slag flow passages therein adjacent the floor level of the portion of the furnace chamber in front of said screen, heat absorbing surface lining said front portion and constructed to maintain a normal mean temperature therein above the fuel ash fusion temperature including a closed fluid cooled floor constructed to support a layer of slag in a molten condition and extending rearwardly of said screen, heat absorbing surface lining the rear portion of said furnace chamber and constructed to maintain a normal mean temperature therein below the fuel ash fusion temperature, and a. fluid cooled hopper in the rear portion of said furnace chamber and constructed to receive dry ash separating in said rear portion and slag flowing through said slag screen passages over the rear end of said-floor.

6. A steam generator comprising vertically disposed walls defining a furnace chamber having a heating gas outlet, means. for introducing a stream of finely divided solid fuel and air for combustion into said furnace chamber, means forming a slag collecting screen across said furnace chamber at a point between the point of fuel introduction and said gas outlet and having lining the portion of said furnace chamber infront of said slag screen and constructed to maintain a normal mean temperature therein above the fuel ash fusion temperature includinga fluid cooled floor constructed to support a layer of slag in a molten condition, heat absorbing surface. lining the rear portion of said furnace chamber and constructed to maintain a normal mean temperature therein below the fuel ash fusion temperature, a hopper in the rear portion of said furnace chamber and constructed to receive ash separating in said rear portion and slag flowing through said screen passages over the rear end of said floor, means defining a heating gas pass connected to said gas outlet, and steam generating surface arranged in said gas pass so as to minimize radiant heat absorption from said front section.

'7. A steam generator comprising a pair of upper and lower horizontally arranged drums, a bank of vertically disposed steam generating tubes extending between and connected to said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end, means at the front end of said furnace chamber for introducing a stream of finely di-' vided solid fuel and air for combustion, means forming a screen extending across said furnace chamber at a point spaced from the point of fuel introduction and having slag flow passages therein adjacent the floor level of the portion of said furnace chamber in front of said screen, a fluid cooled floor for said front portion constructed to support a layer of slag in a molten condition, and a hopper at the rear of said slag screen constructed to receive ash separating in said rear portion and slag flowing through said screen passages.

8. A steam generator comprising a pair of upper and lower horizontally arranged drums, a bank of vertically disposed steam generating tubes extending between and connected to said drums, means defining a furnace chamber laterally adjoining the space containing said tube bank and communicating therewith adjacent its rear end,

means at the front end of said furnace chamber for introducing a stream of finely divided solid fuel and air for combustion, a group-of vertically disposed refractory-covered tubes arranged to form a slag collecting screen extending across said furnace chamber at a point spaced from the point of fuel introduction and having slag flow passages therein adjacent the floor level of the portion of said furnace chamber in front of said slag screen, heat absorbing surface lining said furnace chamber front portion'and constructed to maintain a normal. mean temperature therein above the chamber divided into communicating front and rear sections separatedbya fluid cooled screen, the method of burning a finely divided solid fuel and separating ash constituents of the fuel in the furnace which comprises introducing a stream of the fuel and air for combustion into the front section'of the furnace chamber and burning the said screeninto said rear section, and causing the slag in said front section to pass through said screen into said rear section,

10. In a furnace having a two-stage furnace -,5 chamber divided into communicating front and rear sections separated by a refractory covered screen, the method of 'burhinga'finely divided solid'fuel and separatingash constituents of the fuel in the furnace which comprises introducing a stream of the fuel and air for combustion into the front section of the furnace chamber and burning, the fuel in suspension therein at a relatively high rate of heat release, maintaining a rate of heat absorption in said front section providing a normal mean temperature therein above the fuel ash'fusion temperature, whereby ash particles separated therein will-be in-a molten condition, collecting and maintaining a layer of molten slag on the portion of the furnace bottom 0 below said front section, directing the burning --me1 stream through said refractory-covered screen to effect the removal of ash-particles in suspension, and causing the slag formed in said front section to pass thr ugh said screen into the portion of the furnace bottom below said rear section. 1

11. In a furnace having a two-stage furnace chamber divided into communicating front and rear sections separated by a refractory-covered screen, the method of burning a flnelydivided solid fuel and separating ash constituents of the fuel in-the furnace which comprises introducing a stream of the fuel and air for combustion into the front section of the furnace chamber and burning the fuel in suspension therein at a relatively high rate of heat release, maintaining a rate a of heat absorption in said front section providing a normal mean temperaturetherein above the fuel ash fusion temperature, maintaining a rate in a molten condition, and collecting the ash separating in said rear section and the slag collected by said screen in the portion of the furnace bottom at the rear of said screen.

chamber divided into communicating front and rear sections separated by a refractory-covered screen, the method of burning a finely divided solid fuel and recovering ash constituents of the fuel in the furnacewhich comprises downwardly maintaining a rate of heat absorptionin said front section providing a normal mean temperature therein above the fuel ash fusion temperature, whereby ash particles separating therein will be in a molten condition, collecting and maintaining a layer of molten slag von the portion of the furnace bottom below said front section, main- "ace-7,501

'taining a rate of heat absorption in said rear section providing a normal meantemperature therein below the, fuel ash fusion temperature,

whereby ash separating therein will be in a dry condition, directing the burning fuel stream through said screen to effect the removal of ash particles in suspension in a molten condition, and collecting the slag and ash separating in said front and rear sections and the slag collected by said screen in-the portion of the furnace bottom at the rear of said screen.

ducing a stream of finely-divided solid fuel and I combustion air into said high temperature sectionand burning-the fuel in suspension therein, heat section and constructed to maintain a'norm'al mean temperature therein above the fuel ash fusion temperature, a closed fluid cooled 'floor forming the bottom of said high temperature sec- .tion and constructed to support separated slag depositing thereon in a molten condition and discharge the same over its rear end, heat absorbing surface lining said low temperature section and constructed to maintain a normal mean temperature therein below the fuel ash fusion temperature, and a hopper at the bottom of said low -temperature section extending below the level of saidfloorand arranged to receive ash separating in said low temperature section and slag flowing over the rear end of said floor.

absorbing surface lining said high temperature 14. A furnace for burning afinely divided solid fuel comprising walls defining a furnace chamber,

means including a vertically disposed row of [water tubes arranged to ,divide said furnace chamber into a front high temperature section and a rear low temperature section, said sections commun eating at their lower portions, means for intro ucing a stream of finely. divided solid fuel and combustion air into said high temperature section and burning the fuel in suspension at a relatively high rate of heat release 'while traveling therein, heat absorbing surface lining Y said high'temperature section and-constructed 12. In a furnace having av two-stage furnace the bottom of said high temperature section and constructed to support a layer of slag depositing thereon in a molten condition and'discharge the same over its rear end, heat absorbing surface,

lining said low temperature section and constructed to maintain a normal mean-temperature.

therein below the fuel ash fusion temperature, and a fluid cooled'ash hopper at the bottom of said low temperature section extending below the level of said floor and arranged to receive ash separating in said low temperature section and nowam: J.

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