US2745364A

US2745364A - Combustion air supply through grates and grate construction

Info

Publication number: US2745364A
Application number: US118418A
Authority: US
Inventors: Martin Johannes Josef
Original assignee: Individual
Current assignee: Individual
Priority date: 1948-10-01
Filing date: 1949-09-28
Publication date: 1956-05-15
Anticipated expiration: 1973-05-15

Description

May 15, 1956 J. J. MARTIN 2,745,364

COMBUSTION AIR SUPPLY THROUGH GRATES AND CRATE CONSTRUCTION Filed Sept. 28, 1949 i a Sheets-Sheet 1 a in 7 25 /2 "9 y 1956 J. J. MARTIN 2,745,364

COMBUSTION AIR SUPPLY THROUGH GRATES AND GRATE CONSTRUCTION Filed Sept. 28, 1949 3 Sheets-Sheet 2 INVENTOR L/ZJE/v/w': Jd JEF Mwr/A/ BY/(JAL ATTORN May 15, N56 J. J. MARTIN 2,745,354

comaus'rzom AIR SUPPLY THROUGH GRATES AND GRATE CONSTRUCTION Filed Sept. 28, 1949 5 Sheets-Sheet 3 iifiglk INVENTO R Joly/W55 c/ZJifW87/A4 BY Wfl W ATTORNE U ed S e Pw COMBUSTION AIR SUPPLY THROUGH GRATES AND GRATE CONSTRUCTION The present invention relates to an'improved method of supplying combustion air through fuel-burning grates and particularly the individual bars thereof, and to the construction of suchgrates and elements or grate bars therefor.

With the conventional operating'methods and constructions of fuel-burning grates, removal of the heat trans- 2,745,364 Patented May.15, 1956.

or transverse ribs and the air may be additionally thronice ' tled at the end of the channels before entering the dis:

ferred to the grate elements by radiation and contact'f particularly when burning fuel of high heat value or when operating with highly preheated air, is difficult and the life of the grate bars is short.

For better cooling of the grate, narrow bat-shaving high cooling ribs have been used. Since the amount of air available perunit of grate surface is limited, agrate fuel spread on the grate. The flow of air therefore de-' pends chiefly on the resistance of the fuel layer, and, at portions of the grate which are covered by liquid slag, the flow of air is much reduced or completely interrupted, sothat the grate is overheated and damaged.

Conventional methods and constructions do not produce a flow of air which assures continuous and efiicient cooling of all parts of the grate and which is independent of'the different conditions of the fuel layer at various portions of the grate. ance of the fuel layer to the flow of air is low, the velocity of the air flowing underneath and at the flanks of the grate bars is not more than 9 to 15 feet per second and the heat transfer is therefore insuffieient. Only at the flanks where the air leaves the slots between the bars, the heat transfer is somewhat greater, but these surfaces are too insignificant to efiect appreciable cooling.

Although the temperature of the grate bars of conventional grates is sometimes higher than 1500 degrees Fahrenheit, the temperature increase of the air is not much more than, say, 200 degrees Fahrenheit, and the cooling efiect is insufiicient.

It is an object of the present invention to provide an improved method of operating and an improved construction of grates consisting of a plurality of bars, wherebythe heat transfer from the grate to the combustion air is substantially increased at all parts of the grate, and, not only wear and the cost of upkeep is reduced, but also the temperature of the air reaching the fuel is considerably increased, greatly improving combustion conditions According to the invention all or at least a large portion of the air does not just pass along the grate bars but is conducted through cavities in the individual bars at high velocity and in streams moving back and forth and may be further accelerated to a predetermined degree at the points of its discharge into the fuel. For this purpose, one or more channels are provided on the under: side of the bars which are formed by suitable longitudinal Even at portions where the resistcharge openings toward the fuel layer. All this causes a highly turbulent flow of the air, which is due to the great pressure reduction and efiects not only efiicient cooling of the grate bars but aslo stabilization of the combustion process .by equalization of the air flow to.the various zones of the fuel bed; this effects better drying ofQthe fuel and improved ignition particularly if wet and low grade coals are burned.

Further and other objects of the present invention will be hereinafter set forth in the accompanying specification.

and claims, and are shown in the drawings which, by way of illustration, show. what I now consider to be preferred embodiments of the invention. In the. drawings: V v v I Fig. 1 is a longitudinal part sectional view through a step grate according to the invention; v

Fig. 2' is a bottom view of a grate bar according. to the invention with a portion of the .cover plate removed;'

Fig. 3 is a cross-section of the grate bar shownin Fig. 2, the section being taken along line IlIIII of Fig.2; e 7

Fig.4 is a bottom view of a modified grate bar according to the invention with the cover plate removed; I

Fig...5 is a cross-section of the bar shown infFig. 4

I F taken along line V Y- of Fig. 4; V

' Fig. 6 is a bottom view of a further modificationof three juxtapositioned grate bars according to. the I inven: tion with the cover platesremoved;

'Fig. T is. a cross-section through. the bars showninf Fig. 6 taken along line VII-VII of said figure; j i

I Fig. 8 is a bottom view of still another modification of a grate bar accordingto the invention with a part of the cover plate removed;

Fig. 9 is a cross-section of the bar shown in Fig. 8 taken along line IX-IX of said figure;

Fig. 10 is a bottom view of another modification of three juxtapositioned grate bars according to the invention with the cover plates removed;

Fig. 11 is a cross-section through the grate bars shown, in Fig. 10 taken along line XIX[;

Fig. 12 is a bottom view of still, another modification of a grate bar according to the invention with the cover plate removed;

Fig. 13 is a cross-sectionof the bar shown in Fig. 12

taken along line X[IIX[II of said figure; v

' Fig. 14.is a diagrammatic bottom view of three juxtapositioned grate bars provided with hold-down means ac-.. cording to the invention; I f

Fig. 15 is a cross-section of the gratebars shown in Fig. 14 takenalong line XV-XV of Fig. 14.

Fig. 16 is a diagrammatic longitudinal sectional view of a modified grate bar construction according .tothe invention; I

Fig. 17 illustrates in top .view a grate bar arrangement. according to the invention; 7 p

Fig. 18 illustrates in top view the grate bar arrangement shown in Fig.' 1;

Fig. l9 is a longitudinal sectional view. of a further modification of a grate bar construction according to the invention; V

Fig. 20 is a sectional view of the grate bar shown in Fig. 19 taken along line XXXX and looking in the direction of the arrows inFigure 19; V

Fig. 21 is a bottom view of the cover plate used inthe construction shown in Figs. 19 and 20.

Like parts are designated by like numerals in all figures of the drawings.

In the embodiment of the invention shown in Figures 1 to 9, the underside of the grate bars 1 isprovided with a plurality of walls or bafiies 20 forming channels or conduits 3 which may be either fully cast in the bars or open at one side and covered by a plate 10, as illustrated. The plate 10 which forms the bottom wall of the grate bar may be cast of a material having the same heat expansion coeflicient as the grate bars or may be made of annealed sheet iron spot-welded to the grate bars either at its circumference and/or in the center through holes positioned adjacent to the ribs, and its ends may rest slidably on suitable supports 22 to permit expansion as shown in Fig. 16.

Instead of providing four parallel channels longitudinally of the grate element, as shown in Figures 2 and 3,,

three adjacent parallel conduit portions may be arranged as shown in Figures 4 and 5. In the first case, the air enters at 16 through an opening in the bottom of the front portion of the bar, and in the latter case the air enters through an opening 17 in the side wall atthe rear portion of the .bar. The flow of the air is indicated by fine lines and arrows in the drawings.

In the modification illustrated in Figures 6 and 7, two longitudinal channels only are provided, and the air enters through openings 18 in the bottom of the front end of the bar.

Instead of introducing the air at one side of the bars and conducting it in a meandering conduit to the other side as in Figures 1 to 7, the air may enter in the middle of the bar. and move in two symmetrical serpentine streams toward both sides of the bar as shown in Figures 8 and 9.

The channels may be superimposed as shown in'Figures 10 and 11 instead of juxtapositioned as per Figures 1 to 9.

Baflies 21 may be arranged transversely to the longitudinal axis of the bars and extend only over a part of the width of the bars as shown in Figures 12 and 13, whereby the air stream is forced to. asume a meandering configuration.

It is desirable to increase the flow area of the conduits in accordance with the increase in the volume vof the air due to heating This is indicated in Figure 12.

In order to prevent flow of incoming cool air alongside the grate bars and into the stream of hot air leaving an element, the recesses 23 in the side walls or the passages 14 at the bottom of thegrate bars in which the cool air flows to the air inlet are separated from the recesses through which the hot air leaves the'bars, by sealing ribs or air flow blocking means 4 projecting laterally from the side walls of the grate bars. From the rib 4 a horizontal rib extends along the longitudinal upper edge of the grate bar which horizontal rib in cooperation with the adjacent horizontal rib of a juxtapositioned gratebar constitutes also a means for blocking air flow between the bars so that the air must flow through the bars. 9 leaking between the sealing ribs assumes high velocity, 60 to 140 feet per second, and contributes eflfectively to the cooling of-the ribs. This leakage air unites at the air outlets with the main air streams 12.

Air discharge recesses 13 may be provided in both side walls of the grate bars as shown in Figures 1 to' and 8 i and 9 or on one side only as in Figures 6 and 7 and to 15 where they are designated by numeral 19.

The flow of'hot air leaving the internal channels 3 may be substantially so guided that it cannot escape other than by flowing olf to the fuel layer 2 at the air discharge zone 5 formed. by adjacent bars.

However, an arrangement may also be provided in such a manner that the air leaving the channels 3 of each bar may flow ofi in part at said discharge zone 5 and in part enter a chamber 14, the bottom of which is formed by the top of the underlying bars, the transverse direction of The air stream the chamber 14'. This arrangement permits intercommunication of air heated in several bars ofv the same step of the grate. It equalizes air flow through all elements of one step and also. assures cooling of those elements whose proper air discharge is blocked, for example, by liquid slag. I v

The web 4' may form an integral part of the grate bar 1; it can, however, also be attached to or form a part of the cover plate 10', as shown in Figs. 19 and 21.

The superimposed bars of a grate maybe in alignment, as shown in Fig. 17, so that the air outlets 13 of superimposed bars are all placed in the same verticaluplane; or they may be offset by one half of their widths,;as shown in Fig. 18, for distributing the air in the fuel more equally;

With this novel manner of admitting air to the fuel through the grate bars, the number of points where air is admitted to a given zone can be mademuch smaller and the velocity of the air can be made much greater than in conventional grates. The invention is not limited to the illustrated application to stoker grates but may be used.

as well in plane grates and chain grates.

Due to the high velocity of the 'air in a grate according I to the invention which is substantially independent of the.

resistance to air flow caused by the fuel layer, the grate bars and clearances therebetween are kept cleaner than is This cleaning effect.

possible with conventional systems. can be further improved by a gradually downward'widening of the nozzle spaces between relatively moving bars as is indicated in Figures 3, 5 and 7, i. e. by'u'pwardly,

diminishing the depth of the recesses 13-. The sealing webs 7 (Fig; 6) of movable bars are preferably made thicker than those (4) of the juxtapositioned bars to such an extent that they have a closing effect during the whole relative movement of the bars.

In order to prevent rising of individual bars due to heat expansion and eventual warping, hold-down projections'8 may be provided which extend under the side walls of the small number of discharge nozzles through which the air flows at high velocity, cause heat absorption by the combustion air and consequently cooling of the grate which cooling is-considerably increased relative to the conditions in conventional grates where the air flows in one direction only in open channels and directly'into the fuel.

Due to the increased length and reduced'flow-area of the conduits through which the air passes in a grate according to the invention, a great pressure drop amounting to 4 inches of water and more is produced in each grate bar which considerably exceeds the pressure drop in the fuel bed which is only 1.1 to 2.4 inches of water, so that the amount of air passing into the fuel is practically independent of changes in the resistance of the fuel to air flow. This improves combustion and makes it uniform in all zones of the grate; it also increases the drying effect of the air and improves ignition, particularly when damp and low grade fuel is burned.

With the system according to the invention and normal air flow resistance of the fuel bed, only a small portion of the initial pressure of the air, say 8 inches of water, is.

say 10 to 15 per cent, and no craters are formed in the fuel bed. This is of particularimportance with coarse-.

grained fuels which offer little resistance to air flow, as

well as with coal having a tendency to develop an aero dynamically unstable layer.

On the .other hand, if there is a tendency to increase air resistance of the fuel 'layer on top of a grate bar, the

throttling efiect f the bar is considerably reduced and the air pressure available for piercing through the fuel is correspondingly increased and combustion of the flowresisting portion of the fuel layer sped up. With the system according to the invention, the range of fuel which can be efiiciently burned is widened with regard to the size and shape of the grain, as well as with respect to the fusing point of the fuel.

If the increase of the air flow resistance of the fuel layer extends over whole zones of the grate or large portions thereof, the air pressure under the zones increases due to the characteristic of the air-blower which causes quick return to normalcy of the air supply conditions in the fuel layer.

The higher combustion air temperature caused by the system according to the invention improves drying and ignition of damp fuel or of fuel of low heat value. A grate according to the invention has a heat accumulating and recuperative effect, and if the character of the coal tends to interrupt combustion locally and the fire must be forced temporarily, the heat accumulated in the grate is quickly transferred to the coal whereby the ignition temperature is maintained, combustion is stabilized, reliable combustion of low heat value fuels is assured, and the heat liberated per unit of grate surface is increased.

While I believe the above described embodiments of my invention to be preferred embodiments, I wish it to be understood that I do not desire to be limited to the exact details of method, design and construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. A fuel burning grate receiving combustion air from below the grate and comprising a plurality of juxtapositioned longitudinal hollow grate bars, each of said grate bars having a forward and a rearward portion, each of said grate bars having an air inlet opening and two parallel side walls, an air discharge opening in at least one of said side walls at the forward portion of the grate bar, and air flow blocking means projecting laterally from at least one of said side walls in the rear of said discharge opening, said air flow blocking means of one of two neighboring grate bars being adjacent to the other grate bar and being adapted to block flow of air between the neighboring bars all along the length of the neighboring bars in the rear of said discharge opening, said blocking means leaving an air flow passage between the side walls of the forward portions of two neighboring grate bars, said passage receiving air from the inside of the grate bar through said discharge opening.

2. A fuel burning grate according to claim 1, in which said air flow blocking means include a rib extending substantially transversely to the longitudinal extension of the bar.

3. A fuel burning step grate receiving combustion air from below the grate and comprising a plurality of stepwise superimposed rows of juxtapositioned longitudinal hollow grate bars, eachof said grate bars having a forward and a rearward portion, the forward portions of a row of juxtapositioned bars resting on top of the rearward portions of the underlying row of grate bars, each of said grate bars having an air inlet opening and having two parallel side walls and a bottom wall, an air discharge opening in at least one of said side walls at the forward portion of each grate bar, and air flow blocking means projecting laterally from said side walls and downwardly from said bottom wall and including portions extending transversely to the longitudinal axis of said grate bars, said blocking means, being in the rear of said air discharge opening and forward of said inlet opening, said air flow blocking means projecting laterally from the side walls of a bar being adjacent to the juxtapositioned bar and said air flow blocking means projecting downwardly from the bottom wall of a bar being adjacent to the top of an underlying grate bar, said air flow blocking means being adapted to block flow of air between neighboring and superimposed bars all along the length of the neighboring and superimposed bars in the rear of said air discharge opening, said blocking means leaving an air flow passage between the side walls of two neighboring grate bars at the forward portion of said grate bars, said passage receiving air from the inside of the grate bar through said discharge opening.

4. A fuel burning grate as defined in claim 3, in which said grate bars have a forward wall having a bottom surface resting on the underlying grate bar, said forward Walls of a plurality of juxtapositioned grate bars forming with the air flow blocking means projecting downwardly from the bottom walls of a plurality of juxtapositioned grate bars and with the bottom Walls of the forward portions of a plurality of juxtapositioned grate bars and with the tops of the rear portions of a plurality of underlying juxtapositioned grate bars an air chamber extending transversely of the longitudinal axes of the grate bars and receiving air from a plurality of air discharge openings, equalizing the pressure in said air flow passages.

References Cited in the file of this patent UNITED STATES PATENTS 641,124 Lee Jan. 9, 1900 1,481,366 Herkenrath Jan. 22, 1924 1,513,987 Hare Nov. 4, 1924 1,925,840 Marx Sept. 5, 1933 FOREIGN PATENTS 103,999 Germany July 12, 1899 104,822 Austria Nov. 25, 1926 110,389 Germany May 10, 1900 370,781 Germany Mar. 7, 1923