US2754778A - Furnace for burning wet fuels - Google Patents

Description

July 17, 1956 E. DENNIS FURNACE FOR BURNING WET FUELS 2 Sheets-Sheet l Filed May 22, 1952 f f/v INVENTOR Eow//v L. DENN/.5

BY M 5M ATTORNEY Fig. l

United States Patent i" FURNACE FOR BURNING WET FUELS Edwin L. Dennis, New Orleans, La., assignor to Riley Stoker Corporation, Worcester, Mass., a corporation of Massachusetts Application May 22, 1952, Serial No. 289,371

3 Claims. (Cl. 110-7) This invention relates to furnaces and more particularly to the construction and arrangement of furnaces for burning waste materials such as bagasse, wood refuse, and the like, which are relatively high in moisture content.

Heretofore it has been a common practice to burn such fuels in a so-called horseshoe furnace from which the hot gases travel over the top of a bridge wall and thus into a main combustion chamber formed by the setting of a steam boiler. The fuel-burning capacity of such a construction is decidedly limited. Furthermore, large quantities of fly ash are carried over the bridge wall and accumulate on the oor of the main combustion chamber, Where they fuse into aphard glassy mass. A great amount of labor is required for the removal of this mass, and it is necessary to shut down the boiler and allow the setting to cool before such work can be started. Accordingly, the boiler may be out of service for long periods at rather frequent intervals.

These difficulties have been recognized, and an attempt has been made to overcome them by burning the fuel within the boiler setting and directly beneath the boiler tubes. However, such arrangements as heretofore employed have proven to be incapable of burning suicient fuel to operate the boiler at more than a relatively small fraction of its full capacity. Thus, it has been necessary to install more boilers than would be required if each boiler could be depended upon to generate its full quota of steam. Furthermore, it is important to provide for tiring the boiler with an auxiliary fuel, such as oil, in order to maintain a supply of steam during a temporary shortage of the waste fuel. Oil and similiar fuels, however, are burned in suspension and require considerable furnace volume and provision for ample flame travel. With the prior constructions it has not been found possible to comply with these requirements, and the oil burning capacity has been extremely limited. The construction described in my copending application Serial Number 81,699, tiled March 16, 1949, which issued on July 8, 1952, as Patent No. 2,602,409, obviates some of the ditliculties encountered in the prior art devices. The present invention is an improvement on that construction.

It is accordingly one object of the invention to provide a furnace construction and arrangement adapted for use with a steam boiler and capable of burning high-moisture solid fuels at rates suiiciently high to operate the boiler at its maximum steam generating capacity.

It is a further object of the invention to provide a furnace construction and arrangement adapted to burn high moisture solid fuels at rates required for the operation of an associated steam boiler at its maximum steam generating capacity, the furnace also being capable of burning oil in amounts required for the generation of large quantities of steam when the principal fuel is in short Supply- With these and other objects in view, as will be apparent Patented July 17, 1956 to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

Referring to the drawings illustrating one embodiment of the invention, and in which like reference numerals indicate like parts,

Figure 1 is a vertical sectional view through a steam generating furnace, taken on the line 1 1 of Figure 4,

Figure 2 is a partial sectional view of the furnace embodying the invention taken on the line 2-2 of Figure l,

Figure 3 is a partial sectional view taken on the line 3-3 of Figure 1,

Figure 4 is a sectional view taken on the line 4-4 of Figure 1, and

Figure 5 is a partial sectional view taken on the line 5--5 of Figure 1.

The embodiment illustrated comprises a steam generator having an upper transverse steam-and-water drum 10 and a lower transverse water drum 11 therebeneath, the drum 11 being located a substantial distance above a floor 12. The drums 10 and 11 are connected by a rear bank of upright water tubes 14. A transverse front drum 16 is mounted at a substantial distance in front of the upper drum 10. The lower drum 11 is connected to the front drum 16 by a bank of generally L.-shaped tubes 18 arranged in several transverse rows. These tubes 18 have substantially horizontal upper portions 20 which preferably slope slightly upwardly toward the front drum 16. Several rows of tubes 22 connect the front drum 16 to the steam-and-water drum 10.

The steam generating parts as so far described are mounted within a setting constructed largely of refractory material. This setting includes a front wall 24 adjacent to the front drum 16, a rear wall 25 behind the tubes 14, two side walls 26, and a roof 28. This roof is supported by one of the upper rows of tubes 22.

The space 30 beneath the upper portions 20 of the tubes 18 forms a combustion chamber of considerable height and volume from which hot gases may flow upwardly. To direct these gases in a desired path, a wall or baille 31 extends upwardly in front of the lower drum 11'. With this construction the gases flow upwardly from the combustion chamber 30 through the tubes 18, swirl around the tubes 22, and then pass rearwardly to an outlet duct 32.

Provision is made for burning waste solid fuel directly beneath the combustion chamber 3S. For this purpose there are provided a plurality of fuel burning cells arranged in two transverse rows in the lower part of the boiler setting. As shown, there are two front cells 38 and two rear cells 39, each cell having a restricted gas outlet opening or throat 40 at its upper end communicating directly with the combustion chamber 30 thereabove. The front walls of the front cells 38 are formed by the lower portion of the front wall 24, and the outer side walls of all four cells are formed by the lower portions of the side walls 26. The rear walls of the rear cells 39 are formed by a wall 42 which is a downward extension of the baille 31. The front cells 38 are separated from the rear cells 39 by a transverse wall 43, and the right hand cells 38-39 are separated from the left hand cells 38-39 by a longitudinal wall 44. Fuel is supplied to the cells 38 and 39 through chutes 46 which lead to openings 47 in the walls of the cells. More specifically, the openings 47 are located exactly on the portion of minimum diameter in the throat 40 of the cells. Ashes are removed from the cells through openings 48 in front wall 24 and the side walls 26 at the bottom of the cells, these openings being normally closed by suitable doors 49 The piles of fuel in the cells 38 and 39 are burned by means of air which is directed against each pile through openings in the cell walls. For this purpose the walls of each cell are made hollow to provide a primary air chamber 51 which extends around the cell and for a substantial distance upwardly above the level of the cell floor. The several air chambers 51 are separated from one another by upright metal plates 52 with their edges embedded in the adjacent brickwork. A row of air nozzles 54 are built into the refractory walls of each cell to conduct air from the corresponding chamber Si into the cell interior. These nozzles may be metal castings and, as shown in Figure 5, they are of square crosssection and have tapered passages of circular cross-section therethrough. Furthermore, the axes of the passages are directed at a substantial angle to a radial line so as to give a tangential motion to the air.

The hot gases from the burning fuel travel upwardly through the restricted throats 4t) of the cells. ln order to ensure complete combustion of these gases, jets of secondary air are discharged in tangential directions into each throat, these air jets tending to whirl the gases and create considerable turbulence therein. As shown, the wall around each throat 4t) is made hollow to provide an annular air chamber 5'7 which is connected to the throat by tangentially arranged nozzles 5S. These may be of similar construction to the nozzles 54. The secondary air chambers 57 are separated from one another by the solid walls of the cell structure.

Air under pressure is supplied to each of the air chambers 51 and 57, with independent manual control, not shown, of the air supply to each chamber.

The large combustion chamber 3i) may be used to burn an auxiliary fuel in suspension. For this purpose the front wall 24 may be provided with an opening, not shown, for a suitable oil or gas burner, also not shown, above each of the front cells 38. There is ample space available for the llames from these burners to travel rearwardly and complete the combustion of the fuel before reaching the first row of tubes i8.

The operation of the invention will now be apparent from the above disclosure. Each of the cells 38 and 39 will be supplied with fuel such as bagasse, wood refuse, or the like through the chutes 46 and the openings 47 by gravity. Each cell will contain a fuel pile generally conical in shape, with jets of primary air from the nozzles 54 directed against the sides of the pile to maintain combustion. The air streams will strike the pile in a tangential direction and will form a swirl of the lighter particles and of the gases; the turbulence thus produced results in a more complete combustion because of the better mixing between combustibles and air. The hot gases from each burning pile will travel upwardly through the restricted throat 40 thereabove, where secondary air jets from the nozzles 58 will enter the gases from tangential directions. This will further whirl the gases, creating extreme turbulence and promoting a rapid and thorough mixture which will ensure substantially complete combustion before the gases reach the horizontally inclined portions of the tubes 18. The gases will thereupon travel across the tube portions 20 and then rearwardly across the tubes 14 into the outlet duct 32. Steam will be generated in a well-known manner in the water tubes, the steam being discharged into the drum 10 and withdrawn therefrom for use. By use of the manual air control, not shown, the operator can control the air to each fuel burning cell independently of the others, and he can also vary the ratio of the primary air to the secondary air. After a considerable quantity of fuel has been burned in any particular cell, the fuel supply thereto will be stopped and the pile allowed to burn down, whereupon the incombustible residue will be raked out through the door opening 48 and the cell can again be placed in service. The boiler can be fired with oil by means of the burners, not

shown, whenever there is an insufiicient supply of bagasse or other solid fuel to meet the demand for steam.

The action of the air jets originating in the nozzles 58 on the incoming fuel is of utmost importance. The fuel is introduced through the openings 47 which are situated at the restricted throats 40 of the cells. This means that the fuel, which is a mixture of coarse and tine particles, enters at a region of high upward gas velocity; in addition, to the upward ow of gases, the air jets from the nozzles 53 create a swirling action. The net result is that the fine particles are carried upwardly into the combustion chamber 30 where they burn in suspension. The coarse particles fall into the cell where they burn in the ordinary manner under the action of the air jets originating in the nozzles The structure of the furnace is such that the fine particles, after arriving in the combustion chamber .'59, do not move up into the region occupied by the tubes l5, since the gas velocity is not great enough. Instead, they float under the opposite actions of the gas iiow and gravitational pull and are able to burn completely.

lt will now be apparent that the invention provides a furnace in which the fuel burning capacity is in much better proportion to the capacity of the associated steam boiler than has been the case with any construction heretofore available for use with wet fuels such as bagasse, wood refuse, and the like. The four or more vertical cells will burn suicient fuel to operate the associated steam boiler at substantially its full capacity, and the cells can easily be cleaned one at a time, whenever required, without any necessity for shutting down the boiler or for allowing the setting to cool off. These results are facilitated by the novel construction of the individual fuel burning cells and their arrangement in two transverse rows beneath the associated tubes 18. By this means the large furnace volume is provided which is essential to complete the combustion of the gases and solid combustible particles carried upwardly with them through the throats 4t). This combustion space is also available for the burning Of oil in adequate amounts to produce large quantities of steam whenever the principal fuel is for any reason in short supply. Furthermore, the shape of the tubes is such as to reduce the absorption of heat radiating from the cells, and this aids combustion by increasing the temperature within the cells. The restricted throats 40 further contribute to this result by appreciably shielding the cell interiors from the water tubes. The tangentially positioned air nozzles 58 cause the gases flowing upwardly from the cells to enter the combustion chamber 3i) with very pronounced whirling movements, so that the gases within the said chamber are in a very turbulent condition which is conducive to rapid and efficient combustion.

The invention having thus been described, what is claimed as new and desired to secure by Letters Patent 1s:

l. A furnace comprising upright walls forming a combustion chamber of considerable height having a gas outlet adjacent its upper end, walls forming a fuel burning cell directly beneath the combustion chamber and having an outlet throat which is smaller in cross-section in all lateral dimensions than the corresponding dimensions of the cell at its upper end for the upward discharge of hot gases, and means to supply fuel to the cell and form a pile of fuel therein, the walls of the cell having openings adjacent the lower portion of the cell for the discharge of air tangentially against the said pile, and other openings adjacent the throat for discharge of air tangentially into the hot gases flowing upwardly through the throat, the said openings being directed tangentially of the vertical axis of the cell and of the throat respectively, the said fuel-supplying means being located at said outlet throat.

2. A furnace as recited in claim 1, in which the walls are of hollow construction to provide one air chamber communicating with the openings adjacent the lower portion of the cell and another air chamber communicating with the openings adjacent the throat.

3. A furnace comprising upright walls forming a combustion chamber of considerable height having a gas outlet adjacent its upper end, walls forming two transverse rows of fuel burning cells directly beneath the combustion chamber and opening upwardly into the combustion chamber, means to supply fuel to each cell and form a pile of fuel therein, the walls of each cell having openings therein for the discharge of air tangentially into the cell to burn the fuel, each cell being provided with an outlet throat at its upper end which throat is smaller in cross-section in all lateral dimensions than the correspond ing dimensions of the cell, the walls of the throat being provided with tangentially directed openings for the discharge of air jets into the gases flowing upwardly through the throat to whirl the gases, the said openings being directed tangentially of the vertical axis of the cell and of the throat respectively, said fuel-supplying means introducing the fuel directly into said outlet throat.

References Cited in the file of this patent UNITED STATES PATENTS 17,842 Longacre July 2l, 1857 196,321 Arbogast Oct. 23, 1877 264,735 Monsanto Sept. 19, 1882 484,507 Reynolds Oct. 18, 1892 638,689 Archer Dec. 12, 1899 1,435,297 Heimbach Nov. 14, 1922 1,603,601 Hejma Oct. 19, 1926 1,952,010 Gregory Mar. 20,1934 2,114,619 Ward Apr. 19, 1938 2,602,409 Dennis July 8, 1952

Claims (1)

1. A FURNACE COMPRISING UPRIGHT WALLS FORMING A COMBUSTION CHAMBER OF CONSIDERABLE HEIGHT HAVING A GAS OUTLET ADJACENT ITS UPPER END, WALLS FORMING A FUEL BURNING CELL DIRECTLY BENEATH THE COMBUSTION CHAMBER AND HAVING AN OUTLET THROAT WHICH IS SMALLER IN CROSS-SECTION IN ALL LATERAL DIMENSIONS THAN THE CORRESPONDENCE DIMENSIONS OF THE CELL AT ITS UPPER END FOR THE UPWARD DISCHARGE OF HOT GASES, AND MEANS TO SUPPLY FUEL TO THE CELL AND FORM A PILE OF FUEL THEREIN, THE WALLS OF THE CELL HAVING OPENINGS ADJACENT THE LOWER PORTION OF THE CELL FOR THE DISCHARGE OF AIR TANGENTIALLY AGAINST THE SAID PILE, AND

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