US1920817A - Fire box construction - Google Patents

Description

1 mg. 1, 1933.. M VAN WQERT E,92,8fi7

FIRE BOX CONSTRUCTION Filed Dec. 6. 1929 2 Sheets-Sheet l INV QMM ZM ATTORNEYS 3- M. P. VAN WOERT 1,920,817

FIRE BOX CONSTRUCTION Filed Dec. 6, 1929 2 Sheets-Sheet 2 CID BUD um um um 28 3/ uu'uoun uuunuunun 2 Z uuouuuunuu EIEI UDEID 30 uunuuuuuun an 00 4/ /48 lNVE 10 ATTORN EY5 Patented Aug. 1, 1933 I 1,920,817 FIRE BOX CONSTRUCTIQN Application December 6, 1929. Serial No. 412,115

rarest easier 7 Claims.

This invention relates to furnace grates and is concerned more particularly with a grate construction especially adapted for heavy duty use as in locomotives, marine boilers and the like.

In locomotive fire-boxes, the grate extends the full length of the fire-box and below the grate is an ash pan with openings along the sides of the fire-box through which air is admitted beneath the grate. Above the grate is the usual brick 10 arch supportedon water tubes and there is an opening through the arch near the front end of the fire-box through which the gases of combustion pass on their Way to the fire tubes, the area of the exit opening being relatively small compared to the area of the grate. As the'opening lies above one end of the grate, the draft exerts its greatest pull on the fuel bed beneath or near the opening. If a fuel bed of uniform thickness from end to end and from side to side 29 is maintained on the grate, a greater amount of air is drawn through that portion of the fuel bed near the exit opening and a lesser amount through the remainder of the bed, little air passing through the grate at the end remote from the exit opening. Similarly more air passes through the sides of the fuel bed adjacent the lateral air admission openings than through the middle and this uneven distribution of air causes inefficient combustion and poor operating condi- 30 tions. The fuel at the end of the grate near the exit opening burns rapidly While that at a distance from the opening is consumed slowly and possibly with insufficient air forcombustion. A r similar uneven distribution of air occurs with respect to the side portions of the fuel bed and the portion which lies along the middle of the grate. In order to overcome these difficulties, the fireman ordinarily tries to maintain a relatively thick bed of fuel on the grate near the fire door and a thinner layer further back and beyond the rear edge of the exit opening through the arch. Similarly, he tries to keep a thicker layer along the sides of the grate than at the middle. This expedient, however, is unsatisfactory since in order to approximate an even distribution of the air to the fuel in this manner, the fuel bed is usually maintained at such a thickness near the fire door and along the sides that the fire burns sluggishly on this part of the grate an is likely to be choked with ashes. Also, it'is extremely difficult for thefireman to, attain a distribution of the fuel which will result in even a close approach to ideal conditions.

In Scotch marine boilers, the same difficulties are encountered though in the fire-boxes of such boilers, the exit opening for the gases liesabove the top of a bridge wall at the rear. end of the grate. Here the greatest pull of the draft is' on that part of the fuel bed nearest the bridge wall and on this part of the grate the deepest bed of fuel is usually maintained with a relatively thinner bed elsewhere.

The present invention is directed to the provision of a grate in which the difficulties above mentioned are overcome and on this grate a bed of fuel of uniform depth may be maintained from one end to the other and from side to side regardless of the differences of the pull of the draft on different portions of the'fuel bed. The grate is so constructed as to insure a thorough distribution of the air to all parts of the fuel bed, and the flow of air through the fuel on those parts of the grate where the pull of the draft is greatest is restricted to compensate for the decreased pull through the fuel on other portions of the grate. With this construction, the entire fuel bed burns at a substantially uniform rate and good combustion is obtained throughout, this result being dependent only to a slight degree on the skill of the fireman.

For a better understanding of the invention, reference may be made to the accompanying drawings, in which 7 Fig. 1 is a longitudinal sectional View through a locomotive fire-box showing the grate of the present invention;

Fig. 2 is a longitudinal section through a boiler of the Scotch marine type showing the application of the new grate;

Fig. 3 is a view illustrating one type of grate bar used in the new grate and showing the supporting member in section and a cross-bar in elevation;

Fig. l is a fragmentary plan view of a portion of the grate made up of the bars illustrated in Fig. 3;

Fig. 5 is a fragmentary plan View illustrating a portion of the grate constructed in accordance with my invention;

Fig. 6 is a view similar to Fig. 3 showing a different type of bar useful in the new grate; and

Fi '7 is a plan view of a portion of a grate bar which may be used in practising the invention.

Referring now to the drawings, the new grate fuel with a fuel bed of uniform thickness.

air.

customary elongated form and extending lengthwise of it are water tubes 11 on which are mounted fire brick 12 forming the usual arch. This arch extends from the rear end of the fire-box to a point near the front end at which the fire door 13 is located, the front edge of the brick being spaced from the front Wall of the fire-box to form an exit opening for the gases. The grate consists of a plurality of bars 14 extending across the fire-box from side to side, these bars being of the shaker type and mounted on trunnions in a suitable supporting frame. In a large fire-box, there will be two rows of such grate bars, the trunnions at the outer ends of the bars of the two rows beingsupported in a suitable frame member at the sides of the fire-box and the trunnions at the inner ends of the bars being supported in a suitable frame member extending lengthwise of the fire-box along its median line. The bars are provided with individual shaker arms 15 connected by a shaker rod 16 which leads to a point at the front of the fire-box where it is connected to a shaker handle, not shown.

In a fire-box of this construction, it will be seen that the exit opening for the gases of combustion through the arch is of much less size than the area of the grate and it lies over the front end of the grate. Accordingly, the draft exerts its greatest pull on the fuel bed supported on that portion of the grate which lies nearest the opening, that is, on grate bars which lie directly beneath the opening. The pull of the draft on the bed of fuel on the grate bars at the rear end of the fire-box beneath the arch is relatively less and the pull increases as the opening is approached. Similarly, since the air flows into the space beneath the grate through openings, one on each side of the fire-box, more air flows through the grate along the sides of the fire-box than at the middle.

Grate bars of standard constructionhave air openings therethrough for the passage of air to the fuel and in the ordinary grate the bars are all alike so that the total cross-sectional area of the openings per unit of grate area is the same regardless of where the unit is located in the grate. In a standard grate bar the combined areas of the air openings is equal to approximately 50% of the total top area of the bar. The remainder of the top area of the bar is solid metal and consists of a fuel-supporting surface. In such a bar, the area of the total fue1 supporting surface varies inversely with the combined areas of'the air openings and, while in some bars used, for example, for burning lignite or similar fuels, fewer openings are provided than is customary for other fuels, the decrease in the combined areas of the air openings results in an increase in the total fuel-supporting surface.

In a grate of standard construction used in a fire-box of the type illustrated in Fig. 1, it is not possible to obtain good combustion of the This is due to the variation in the pull of the draft on different parts of the fuel bed. The fuel on that part of the grate which lies nearest the exit opening may receive an amount of air which is in excess of that required for good combustion,

while the fuel on other portions of the grate more remote from the exit opening receives less The fuel on that part of the grate which lies directly beneath the exit opening, therefore,

. burns .more rapidly and the burning gases are drawn into the fire tubes 18 and are likely to pass out the stack before they are completely consumed. The fuel on a bar, such as that designated 19, which is remote from the opening, is supplied with less air than is desirable and the fuel consequently burns sluggishly.

In order to overcome the non-uniform combustion conditions in different parts of the fuel bed on a standard grate as above described, it is the practice to maintain a bed of fuel of greater depth on that part of the grate which 'lies adjacent the exit opening, the thickness of the bed of fuel on this part of the grate being indicated by the broken line A. Similarly the deeper bed of fuel is maintained along the sides of the fire-box than in the middle. Such a fuel bed is maintained on the grate in the hope that the increased resistance to flow of air through the deeper part of the bed will overcome the increased pull of the draft thereon, to the end that substantially the same volume of air will pass through a unit area of the grate regardless of where the area is located. In actual practice, this result is not obtained but, on the contrary, the thick burning mass on those parts of the grate near the exit opening and along the sides is likely to become choked with ashes, so that ideal conditions are by no means closely approached. A skillful fireman will perhaps obtain better results than one of less ability, but under any circumstances, the difficulty of firing and maintaining a bed of fuel of the proper graduated thickness from one end of the grate to the other causes faulty combustion and waste of fuel.

In a boiler of the Scotch marine type such as that illustrated in Fig. 2, the exit opening for the gases is defined in part by a bridge wall 19 and the greatest pull of the draft is exerted on the fuel nearest the bridge wall, so that a greater amount of air than is required is supplied to that portion of the fuel bed, while the fuel at a distance from the bridge wall receives substantially less air. Here again in practice, the fireman attempts to maintain a thick bed of fuel of the depth indicated at the broken line B on that part of the grate which is nearest the bridge wall, but,'as is the case inthe locomotive boiler, this expedient is at best only a make-shift.

In order to overcome these difficulties, I have devised a grate which is made up of a plurality of individual bars having fuel supporting surfaces and openings for the passage of air, and the openings in the bars nearest the exit opening are smaller in size than the openings in bars disposed at a distance from the exit opening. Similarly, if desired, the openings through the ends of the bars adjacent the sides of the fire-box are smaller in size than those in portions of the bars which lie spaced from the sides of the fire-box. Since the bars are so disposed that the smaller openings lie where the pull of the draft is greatest, the amount of air supplied to the fuel may be made substantially uniform throughout the fire-box.

While a grate embodying the principles of this invention may be made of bars of numerous kinds, I prefer to employ the bar shown in the co-pending applications of Buckley, Serial No. 338,352, filed February 8, 1929, and of Thompson, Serial No..406,558, filed Nov. 12, 1929. The bar of the Buckley appli ation includes a supporting member 20 provided at its ends with trunnions 21 and on this member are mounted a plurality of cross-bars 22, each of which is formed with spaced lugs 23 on its opposite faces: Extending upwardly from the tops of the bars are tapering projections 24, these projections having flat tops which serve as fuel-supporting surfaces. Adjacent lugs on thecross-bars define air passages 25 and these lugsare preferably of increasing width from bottom to top so that the effective cross-sectional area of each passage is .in part determined by the distance between adjacent lugs at the point 26. The projections are preferablyformed in groups of four, as indicated in Fig. 4, and in each group of projections, such as that designated 27, the projections 28 may lie above the top of a lug, while the projections 29 may lie above the main body of the cross-bar adjacent this lug. The projections of each group are separated by intersecting channels 30 and 31 and there is a central channel 32 extending along the top of a cross-bar between groups of projections. The cross-bars on the supporting member 20 are separated-to form an air space 33 between them, the amount of separation being determined by spacing projections 34 on certain of the lugs 23. Y

The bars are mounted side by side'with their trunnions received in suitable sockets in a frame and there is a space 35 between the ends of aligned cross-bars on adjacent supporting members, as illustrated in Fig. 4. With this arrangement, the fuel is supported on the tops of the projections 24 and is supplied with air which passes up through the spaces 33 and 35 and through the passages 25. The air enters the several channels 30, 31, and 32 and flows around the projections so that it reaches all parts of the fuel except such as are directly in contact with the tops of the projections. As these projections are of relatively small area, there is little dead space at the bottom of the fuel bed where air cannot reach the fuel.

In one form of grate constructed in accordance with the invention oi the Buckley application, the top of'each projection may be one-quarter inch on each side, each cross-bar carrying 96 projections, with 18 cross-bars on each supporting member. The dimensions of the outline of the top of the grate may be 12" by 36 and the width'of the spaces between adjacent crossbars on the same bar and between the ends of aligned cross-bars on adjacent supporting members may be one-quarter inch. In a grate bar of the dimensions specified, the aggregate area of the tops of the projections is about 25% of the total top area ofthe bar and the total air space area including the space between adjacent cross-bars on one supporting member and be tween the ends of aligned cross-bars on adjacent supporting members is in the vicinity of 30% of the total top area of a single bar. The total fuel supporting area and total air space area of this grate are, therefore, both substantially less than the corresponding values in a standard grate bar where the total air space area approximates 50% of the total top area of the grate. However, it has been found that better combustion results are obtained with a grate made of bars of this type than of standard bars, even though less air is conducted through the grate to the fuel, this result being obtained because of the superior distribution of air and the elimination of dead space on the bottom of the fuel bed.

A bar of the type illustrated in Fig. 3 may be used in such portions of the new grate as lie remote from the exit opening, while the bars usedin that part of the grate nearthe exit opening aresimilar in construction but the lugs on the cross-bars are larger so as-to reduce the size of the passages between them and thus reduce the amount of .air flowing through the grate bar. By the use of suitable patterns, grate bars may be made giving the desired air flow for different parts of the grate- The grate bar illustrated in Fig. 6 is of the Thompson type and includes a carrier member 20 and a plurality of cross-bars 22 mounted thereon. Each cross-bar is made with a plurality of spaced lugs 23 on its opposite faces, but the top of the cross-bar and the tops of the lugs are provided with channels 23"which subdivide'the top of the cross-bar and lugs into a plurality of smaller fuel supporting surfaces on all sides of which the air is free to flow. In the Thompson bar, the air passages 25 between adjacent lugs are of decreasing cross section from bottom to top and the channels 23 communicate with the air passages below the point of maximum restriction thereof. The tops of the passages constitute orifices at which an eifective pressure drop takes place and at the points where the channels 23 communicate with the air passages, minor orifices are formed at which a pressure drop occurs. As a consequence of this construction, the air drawn up through the grate by the pull of the draft increases in velocity as it approaches the top of the grate and the air is discharged from the grate through orifices so disposed that the air enters the fuel bed supported on the grate at high velocity 1 and with a wide distribution.

In constructing the new grate of either type of bar above described, it would be desirable theoretically to form each bar with air passages of different sizes, the bars nearest the exit opening having the smallest portion and the crosssectional area of the passages increasing with the distance of the bars from the exit opening. Similarly, it would be desirable to. construct each bar with openings of greater size in those parts of the bar which lie near the air admission openings alongthe sides of the fire-box. It is possible with the grate bar as above described toobtain this desirable result, since each grate baris made up of a plurality of crossbars which are detachable therefrom so that cross-bars of different constructions providing different air passages maybe mounted on the single carrier bar. As a practical matter, it is usually sufficient to form the grate of two groups of bars, the first group lying near the opening and having air passages about half the size of those through the bars of the second group which lie farther from the exit opening. Similarly, each bar may be madeup of a carrier member and cross-bars of two different kinds, those cross-bars which lie on the carrier member adjacent the air admission openings'defin ing smaller air passages than the cross-bars which lie on the carrier bar near the middle of the fire-box. 'Due to the excellent air distribution which is obtained with the bars ofthe construction described by reason of the fuel-supporting surface being sub-divided into a multiplicity of small areas, excellent results are obtained from a grate made up of the bars of the two kinds mentioned. i

In Fig. 7 there is illustrated in plan view a portion of a grate bar made up of cross-bars of different types. The cross-bar 35 is placed on the carrier member20 adjacent the side of the fire-box and it will be observed" that the air 1 It will be apparent, thereforefthat the new and from side to side. It is not necessary for passage 36 between'adja'cent lugs on the. crossbar is relatively small. The cross-bar 37 is similar in construction to the cross-bar 35 and they two'cross-bars are spaced apart'on the carrier member to define a relatively narrow. air passage 38 between the ends of opposed lugs. The crossbars 39 have lugsspaced apart to define air passages 40 between them which are wider than the passages 36, and these cross-bars are spaced from the nextcross-bar 39 to define an air passage 41 which is wider than the air passage 38; By this arrangementthe pull of the draft on the cross-bars 35 and 37 produces a flow of air which is about the vsame as that drawn through the passages defined by cross-bars 39. As a consequence, auniform bed of fuel may be maintained on the grate bar of which cross-bars 35,37 and 39 form a partand all parts of the fuel receive air in proper amounts for combustion.

In Fig. 5, there is illustrated a portion of the grate including portions of a pair of grate bars near one end of the fire box and portionsof another pair of grate bars near the other end of the fire box. The grate bars near one end have cross bars 41 having lugs 42 defining air passages 43 between them, certain of the lugs having spacing lugs 44. The I cross bars of adjacent grate bars define an air passage 45' between their ends. The cross bars 41 have relatively large lugs 42 defining relatively small air passages 43 and the spacing lugs 44 are of a size such that the air passage 46 between adjacent cross bars of a single grate bar is relatively small. Also, the crossbars are of .a length such that the passage between the ends of cross bars of two adjacent grate bars is relativelysmall.

At the other end of the fire box, the grate bars have cross bars 47 provided with lugs 48 smaller l than the lugs-42".and defining. air passages 49 larger than the passages 43. Also, the spacing lugs 50 are larger than the lugs 44 so as toprovide air passages 51 between adjacent cross bars which are larger than theair passages 46. Also,

3 the cross bars 47 areslightly shorter than the cross bars 42, thus providing air passages 52 between the ends of cross bars of adjacent grate bars which are larger than the air passages 45. With this arrangement, more air will pass through the grate in those areas where cross bars 47 are employed than throughrthose areas where bars 41 are used. Cross bars 41 willbe employed near the exit openings and cross bars 47 farther from the exit openings. I

In the newgrate, variations in the flow of air through the grate bars near and. more remote from the exit opening, due to-the varying effect of the pull of the draft, are compensated for by employing cross-bars of appropriate dimensions.

grate may be so constructed that substantially uniform air fiow takes place therethrough and as a consequence, the fireman may maintain. a

bed of fuel of uniform thickness from end to end the fireman to attempt to equalize the pull of the draft by varying the thickness of the fuel bed on different parts of the grate, firing is simplified and better results are obtained. In some fire boxes, grate barsin two groups of varying of bars in a grate, particularly whenthe bars are of the Thompson and Buckley types, due to the excellent air distribution throughout the bed of fuel which is obtained by bars of those constructions.

. It will be apparent that in the type of fire-box illustrated in Fig. 2, those bars which lie nearest to the bridge wall will have the smaller air openings, while the bars more remote from the bridge wall will have the larger ones.

What I claim is:

1. In a fire-box having an exit opening for gases of combustion, a grate made up of a plurality of individual grate bars, each of which has a fuel-supporting surface made up of a plurality of minor areas and also a plurality of openings for the passage of air around all sides of said minor areas, the aggreate areas of the fuel-supporting surfaces of the several bars being the same, with the aggregate areas of the air openings in a unit of grate surface adjacent the exit opening being less than those in a unit of grate surface more remote from said exit opening in a direction lengthwise of the grate.

2. In a fire-box having air admission openings along its sides and near the bottom thereof, a grate made up of a plurality of individual grate bars extending transversely of said firebox, said bar being spaced apart and providing air openings between parts thereof and between adjacent bars, the total area of the openings per unit of grate area being greater at the middle of the grate than along the sides adjacent the air openings in said ash pan.

3. In a fire-box having an exit opening, a grate made up of a plurality of individual grate bars extending transversely of said fire-box, said bars being spaced apart and providing air openings between parts thereof and between adjacent bars, the total area of the openings per unit of grate area increasing with the remoteness of said unit from said exit opening and also from the lateral sides of said fire-box.

4. In a fire-box having an exit opening, a grate made up of a plurality of grate bars, each of which includes a carrier member and cross bars mounted thereon, said cross bars having lugs on their opposite faces defining air passages. the cross-bars near said exit opening having relatively large lugs and being spaced close together on said supporting member to permit a restricted flow of air to the fuel supported thereon and said cross bars remote from said exit opening having smaller lugs and being spaced relatively far apart to permit a greater volume of air to pass to the fuel supported thereon.

5. In a fire box having an exit opening for gases of combustion, a grate made up of a plurality of individual grate bars extending across the fire box, each bar providing a plurality of passages for air within the outlines thereof and adjacent bars being spaced to provide air passages between them, the total cross-sectional area of said passages in a'unit of grate surface increasing with the remoteness of said unit from the exit opening.

.6. In a fire box having an exit opening, a grate made up of separate grate bars providing fuel supporting areas and passages for air, the total fuel-supporting area per unit of grate surface being substantially constant throughout the fire box, and the total cross-sectional area of the air passages differing in different units of grate surface and increasing with the remoteness of said units from the exit opening.

7. In a fire box having an exit opening at one end and near its top and air admission openings along its sides near its bottom, a grate between the admission openings and. exit opening and made up of individual grate bars, each providing fuel-supperting areas and passages for air, the total cross-sectional area of the air passages per unit of grate surface increasing with MYRON P. VAN WOERT.

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