US2022913A - Aerator for furnaces - Google Patents

Description

Dec. 3, 1935. D HQFFMAN 2,022,913

AERATOR FOR FURNACE 5 Filed Sept. 25, 1951 5 Sheets-Sheet l Dec. 3, 1935. F. o. HOFFMAN 2,022,913

AERATOR FOR FURNACES 5 Sheets-Sheet 2 Filed Sept. 23, 1931 Dec, 3, 1935.- F, H MAN 2,022,913

AERATOR FOR FURNACES Filed "s t. 25, 1951 s Sheets-Sheet s Patented Dec. 3, 1935 UNITED STATES Omar.

2,022,913 AERATOR FOR FURNACES Fred DQ Hoffman, levcland, u Ohio, assignmto Scientific CombustionLaboratories; Inc., Painesville, Ohio, a corporation of Qhio Application September 23,1931; Serial No. 564,537 1 cla m; 7 (01; 110-74) My invention relates to a method'andiappa ratus for burning coal, coke or other solid fuels and is particularly concerned with a combustion chamber for effi cientburning of such fuels and thorough utilization of the resultant heat;

Heretofore in the burning of coal and solid fuels, a very large percentage of the heat units of the fuel has been lost and wasted. This loss results not only from failure to free properly the 10' volatile content of the fuelbut also from improper aeration of the matter that is volatilized. The former failure is evidenced by the unduly large proportion of ash residue and the latter by the large volumeof smoke and size and yellow color of the flame. Further evidence may be found by examination of the grate bars which will usually be found to be cakecl with carbonaceous deposits due to poor combustion or be urned badly or warped due to excess heat or toorapid and localized combustion.

The burning of solid fuels in the manner de fined by my process frees all of the volatile and combustible matter from the fuel and complete- 1y aerates the gases and burns the resultant mix-,

ture and at the same time eliminates the difficulties above enumerated.

Thecombustion chamberand apparatus hereinafter described enables meto practice my proce'ssfin any of the present types of furnaces withs A more specific object of my invention is to mmaintain thevfire so as to form a largeheat radiatingsurface thus effectively utilizing the heat units of the fuel. H V Numerous advantages result from. the practice of the method of my invention among. which are th e..complete combustion of the, cheapest and lowest grades of coal of either largesize lump or exceedingly small particles and ocal dust.

,Another advantage of my invention resides in the fact that the rate of burning may be accu rately controlled throughout a wide range. and

instantaneous circulation of air and gases obtained'so that the heat can be quickly increased or decreased;

Another advantage of my'invention 55 from more nearly perfect combustion is the elimination of smoke and a great reduction in the cinders and ash residue.

. A very' im portant object of my invention is to correlate the rate of evolution of the volatile gases from the fuel and the volume and dis- 5 tribution of secondary airto cause complete aeration and burning of the resultant mixture so that no combustible gas is lost and the cooling or conveying effects of excessive air are eliminated.

Another specific object is to preheat the air thatis mixed with the evolved gases so that the gases maybe burnedquickly and close to the fuel bed andto direct the heat against the furnace Walls so that stack losses are eliminated. 15

Another object of my invention is to burn the fuel evenly throughoutthe fire box and as effectively adjacent .the furnace or retort walls as toward the central portion of the fire bed.

Another object of my invention is to burn the 26 fuel in a manner such that .excessive localized heats on the grate: bars are eliminated.

Another important object is to protect the grate bars byconveying the heat away therefrom and completely recuperating the heat so con- 25 veyed awa v 7 Still another object of my invention is to provide an inexpensive and durable apparatus for obtaining these results which may be easily and quickly installed in furnaces of the present type 30 with slight or no change inthe furnace structure, and which requires neither special skill for installation or operation, nor accessory equipment. Y s v v I Another specific but important object of my invention is to maintain free circulation of air and gasesin the furnace and to eliminate the danger of explosions due to accumulated gases in furnaces of; the present type. 7

[Other objects and advantages will become ap- 40 parent from the following specification in which reference is. made to the drawings by the use of reference numerals.

In the drawings, which illustrate a preferred form of apparatus suitable for carrying out my process: i v

Figure 1 is a side elevation of a furnace, a portion of the wall being cut away to show the interior of the firebox and the aerator with r0 which my invention is particularly concerned; 0

Figure 2 is a reduced partial cross sectional view through the furnace taken on a plane indicated by the line 2-2 of Figure 1;

Figure 3 is an enlarged plan view of a form of aerator embodying the principles of my in- Vention;

Figure 4 is a front elevation of the aerator illustrated in Figure 3, the two separate sections in which the aerator is made being unbolted and separated for purposes of clearness in illustration;

Figure 5 is a cross sectional view of the aerator illustrated in Figure 3, taken on a plane indicated by the line 55;

Figure 6 is a cross sectional view of the aerator illustrated in Figure 3, and is taken on a plane indicated. by the line 6-6 thereon; V

Figure 7 is a perspective view of the aerator illustrated in Figures 3 and 4;

Figure 8 is a'plan View of the fire combustion chamber of the furnace showing the general direction of the air current, the position of the aerator being shown in dot-dash line.

The furnace includes a combustion chamber 2 enclosed in an air chamber 4 in which the air is circulated and heated, and from which it is passed out through the usual conduits to various rooms or points of application. The bottom of the combustion chamber is spanned by agrating of bars 6 of any of the well known types. The combustion chamber is provided with a passage 8 for feeding fuel thereinto. This passage extends through the air chamber 4 and. may be closed by a door 9. The lower wall of the passage forms a coking plate Iii of the furnace.

An air chamber I2 is positioned below the grates 6 and is of sufiicient depth to retain a large volume of ashes or cinders without restriction of the passage of air through a passage M, the size of the opening being controlled by means of a door 55. I have found it eifective to locate the opening l4 well below the grates 6 for purposes later to be described.

The aerator with which my invention is more 1 particularly concerned may be formed in two separate pieces, as illustrated in Figures 3 and 4, overlapping in the center so as to be slid relatively apart and together for convenience in fitting them into various sizes of combustion chambers. These sections may have complementary slots adapted to receive a bolt It for securing the two pieces in a fixed relative position. i

The assembled aerator roughly is a frustropyramidal or frustro-conical shell or hood I 8, surmounting a somewhat cylindrical or polygonal base, the walls of which base may be substantially vertical and comparatively low;

The particular form shown by way of illustration has a base 25 which is semi-circular in outline. The front face 22 of the aerator slopes inwardly of the base and upwardly. The adjacent faces 24 and 25 likewise slope toward the axis of the base and upwardly from the base so that the shell forms a surface substantially one half of a frustrum of a six faced pyramid. It should be noted, however, that this specific number of walls or shape of faces is not necessary, the important feature being that the faces slope downwardly and outwardly so that the aerator is considerably larger at the base than at the top. The reason for these features will later be described.

Secured to or forming the top of the aerator is a head .32 which extends rearwardly of the body l8 and is preferably horizontal.. The head 32 may be covered by a plate 33, shown particularly in Fig. '7. The height of this head above the base of the aerator is such that the aerator is installed, as illustrated in Figure 1. The faces of the body t are each providedwith a large her 2 of the furnace.

the body and exposes the grating bars 30'to the i0 air evenly on each of their sides.

v A distance back from the body [8 on the underside of the head 32 is a box-like chamber 34 hav ing in the base a passage 38 which communicates the chamber with the space beneath the hood l and between the body l8 and the adjacent walls of the combustion chamber 2. The chamber 34 7 opens into the combustion chamber 2 of the furnace forming an elongated horizontal 'tuyere. The central portion of this opening may be closed, however, thus forming tuyeres 38 and 40 near each end of the chamber 34. On each side of the body I8 are wings 42 and 44 which slope backwardly from the faces 24 and respectively and upwardly to the head 32. These wings are pro- 25 vided with tuyres 46 which may be positioned as illustrated. These tuyeres'likewise communicate the space beneath the body 18 of the aera- V tor and the remainder of the combustion cham- Superimposed upon the head 32, preferably at the outer ends and above the wings 42 and. 44 are tuyeres 48 and 58' which likewise communicate with the chamber .34 and through the'chamber 34 with the space between the walls of the com- 85 48 and 50 may discharge into the combustion chamber horizontally. 'Ihe'tuyeres 48 and 50, as illustrated tend to discharge downwardly due to the air currents impinging on the upwardly sloping top walls 52 and deflecting, though such is not noticeable in case of light drafts.

Briefly, my method includes continously passing a relatively small volume of air slowly through the fuel bed to maintain the under stratum in a state of combustion and thus slowly to heat the upper stratum and evolve the combustible gases therefrom. The gases so evolved are regurgitated by a secondary stream or streams of preheated air of suflicient volume to permit complete combustion of the gases. The secondary air mixes with the gases easily, and, since it is preheated 55 the resulting mixture ignites and burns rapidly. In order to utilize the resulting heat effectively, the secondary air currents are of such volume and so directedinto the combustion chamber that slight pressure may result, forming a blanket over the fuel bed and preventing the gasesfrom passing directly to the flue and escaping. Since air is an insulatoror a poor conductor of heat, 7 in the sense that whileheat will not pass readily therethrough by conduction, it is a very efficient conveyor of heat, the secondary air is directed across the fuel bed so as to carry the burning mixture to and-cause it to impinge upon the walls of the combustion chamber and follow therealong with a swirling motion and to deliver its heat directly against the'combustion chamber walls. This same action renders the'path of the burning stream through the combustion chamber'rnore tortuous, thus allowing a longer period. of time for the gases to burn therein.

My method further contemplates controlling the relative proportions of the primary and secondary volumes of air and the temperature of the latter by the shape of the under surface of the fire bed and particularly by maintaining the under surface sloped upwardly to the point of discharge of the secondary air.

The manner in which the aerator above described efiects these results is as follows:

Assuming the fire bed within the combustion chamber 2 to extend from the grates 6 to the dot-dash line, indicated at 54, and the lower stratum of the fuel to be in a state of fusion, the rate of combustion is controlled by the size of the passage i l. The cool outside air flows in along the bottom of the air chamber l 2 following a path approximately as indicated by the arrows, to the rear end of the chamber l2. As it strikes the rear end of the chamber l2, it is deflected against the heated grates 6 and its temperature increased, the grates 6 being cooled thereby. Part of this air infiltrates into and through the burning stratum maintaining combustion thereof to heat the upper stratum and evolve the gases. Due to the upward slope of the aerator walls, however, less resistance is offered to the normal tendency of the heated air to rise. Consequently a large proportion of the air stream follows along the underside of the grates i5 and up under the aerator, the portion of the grates 5 extending beneath the aerator being comparatively open and permitting free passage therethrough.

As the air rises along the under side of the aerator, a part of it passes through the passages 28 and through the fuel bed, maintaining the under stratum along the aerator in a state of combustion. The longitudinal grate bars 26 of the aerator permit easy upward flow of the air and are in turn maintained at a lower temperature by giving up part of their heat to the air. The air is thus preheated to a higher degree. The grate bars of the aerator may extend in another direction than longitudinally but the flow of air is retarded somewhat as a result of passing over a roughened surface. Furthermore, the bars are cooled more on the side toward the oncoming air than on the opposite side and there is a tendency to deflect more air through the fuel bed and cause eddy currents.

The air continues rising rapidly due to the preheating and passes into the openings 36 and out of the central tuyeres 38 and 4H and the outer tuyres 48 and 59 into the combustion chamber. Part of the air also passes out of the tuyeres 4B in the wings 42 and 44. The streams of air have considerable force as a result of thermal convection and issue from the tuyeres as comparatively forcible streams. The streams of air from the central tuyeres 38 and 40 may issue from the central tuyeres substantially horizontally across and close to the surface of the fuel bed, following a slightly upcurved path due to the natural tendency of heated air to rise. The walls of the combustion chamber 2 preferably slope inwardly and upwardly away from the plane defined by the tuyeres 3B and 43. This current of air passes over and close to the fire bed, as described, and is restricted by the opposite wall of the combustion chamber 2. In doing so part of the air stream bends back above the original stream and part below as indicated by the arrows 56 and 58 respectively. Part also tends to follow back along the walls of the chamber 2.

The streams of air from the tuyeres 48 and 5B tend to pass along and close to the upper surface of the fuel bed, following along the walls of the chamber, as illustrated in Figure 8. These streams of air meet each other and the air from the tuyres 38 and 40 and form in the horizontal plane reversely rotating swirls. same time there is a tendency for all the air to swirl in a vertical plane, the underside of the swirl being directed toward the rear wall of the combustion chamber and the upper returning. Thus the gases are pulled into the air streams and forcibly impinged against and rolled along the combustion chamber walls. The air from the tuyres 46 has a tendency to assist this effect of the streams from the tuyres 48 and. 50.

Since part of the fire bed rests against the tuyeres 46, part of the air therefrom passes through the fuel, causing combustion thereof and thus evolving gases near the feeding door of the furnace. These gases are blanketed down by the incoming air streams and caught in the swirling streams and burned as described. Dueto the steepness of the under slope of the wings 42 and 44, only a small proportion of the secondary air stream passes therethrough. into the fuel bed. However, due to the sloping outer surface of the aerator, the fuel bed is comparatively shallow and sufficient air will pass therethrough to coke the fuel. It should be noted that this aerator is preferably placed adjacent to the feeding door 9 and fuel fed into the furnace is merely shoveled onto the plate 32. As the fuel is shoved off from the plate 32, it falls onto the sloping surface of the aerator which causes it to spread outwardly as it progresses downwardly. Thus as fresh fuel is heated and volatilized, the gases pass across the entire combustion chamber and are burned. Furthermore, fusing and burning embers instead of fresh fuel are presented to the combustion chamber Walls. Thus at no time is fresh fuel against the walls which would carry away the heat rapidly and prevent ignition.

The inward slope of the upper portion of the fire box tends to reflect radiated heat onto the fuel bed, thus assisting in burning the gases.

In summation of some of the effects of the sloping surface of the aerator it should be noted that the fresh fuel is spread over a large area and is supplied with air to thoroughly coke it and at the same time a large surface of glowing embers is left uncovered away from the door so that the heat may be effectively radiated and conveyed and the evolved gases burned.

Another important reason for sloping outwardly the walls of the aerator resides in the fact that the thickness of the fuel bed and direction of air therethrough are such as to maintain efficient combustion and effectively apply the resultant heat. For example, the aerator illustrated in Figure 1 projects Well out into the combustion chamber, the base extending to or slightly past the center thereof. In many cases the base 20 should extend about two-thirds to threefourths of the way across the combustion chamber.

The fuel bed is then of much less thickness toward the bottom, especially in the direction of flow of air through the fuel bed from the aerator. Therefore, the already glowing embers may be more efficiently burned and the heat directed against the combustion chamber walls and utilized-rather than pass out of the stack and be lost.

In this manner a somewhat hood-shaped bed of fuel is maintained. If a more intense heat is desired, it is only necessary to p the Passage At the M and permit more air to enter the chamber 12. This causes more rapid combustion and consequently tends to heat the aerator and grates more. Concurrently with the rise in temperature of the grates, the air is preheated more and tends to rise more rapidly and draw in a larger volume. Thus the primary and secondary air currents are correlated and the use of a check draft is unnecessary, the air always circulating freely regardless of volume.

Thus far I have described my invention in conjunction with a manually fired furnace and natural draft. Obviously it is very effective when used with an automatic stoker, the fuel being fed onto the plate 33 continuously and consequently continuously progressing downwardly and outwardly from the plate and burning'as described. If the stoker is of the forced draft type, the air conduit may discharge into the chamber beneath the member Ill. The use of such stokers with my invention is sufficiently clear without illustration.

It is apparent that I have invented a method and apparatus for burning solid fuels which I have found may be used effectively with numerous devices employing heat other than the particular furnace shown by way of illustration I claim:

A supplementary grate for use in a furnace having a horizontal grate and a fire box rising grate having tuyere-like orifices opening over the 7 fuel bed, and from which air is discharged from said passage, said sections being secured together and relatively adjustable to increase or decrease the width of the same, and the cone sector surface having upright slot-like openings through which air may pass to the fuel bed.

FRED D. HOFFMAN.

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