US2186581A

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Publication number: US2186581A
Authority: US
Publication date: 1940-01-09
Anticipated expiration: 1957-01-09

Description

&anan n; 9, 1940 Unirea, STATES PATENT- e es V asass' ;arratis ron BUBNING soam I :Gunnar Ganner, Lidingo, Sweden, assignor to Sv Aktiebolaget Gasaccmnlator, Stockholm, sweden, a co'poration of Sweden Application March 4, 1937. Serial No. 128389 In Sweden March 7, 1936 v Claim.

The present invention relates to apparatus for burning solid fuel and has particular reference to apparatus 'for burning solid fuel continuously over long periods of time. Still more particulargg ter, much is demanded in the wayof reliability ofoperation and ease of handling. These factors have been brought to a state of development :such that ordinarily all of the attention that is required is limited to supplying the apparatus x ith fuel and shaking down and removing the hes at regular intervals. The' necessity for aking down'the ashes is an undesirable feaure of the operation of solid uelburning apmratus since' it is practically impossible to prevent the formation of dust and dirt'in the place where the apparatus is located 'The general object of the present invention ic *e improveapparatus of the kind above referred z and to provide n'ovel apparatus constructed in auch manner that continuous combustion may be maintained without the necessity for shaking down ashes. A further object is to provide ap- 'paratus of the character under .consideration having greater reliability of operation than has g@ heret'ofore been obtainable, and insuring con-- fuel has' been made with relatively large grate' bar area and relatively small spaces between the 45 grate bars, inorder to prevent unconsumed pieces of fuel from falling through the grate'into the ash bed. Because of this the grate bars have taken up a relatively large part of the total area of the grate. As a consequence, the grate has a 50 relatively' large heat 'conducting capacity, thusconducting heat away 'from the layer of fuel lying `closest to the grate.. Also, radiatlon of heat downwardlyl from the fuel bed' has been screened to a large extent so that substantlally pl p .combustion that will reliably continue so long as 55 55, no preheating of the combustion air due to heat vcombustion air actually enters the fuel.

from the fuel bed can be obtained before the such prevention of downward radlation to the ash bed is usuallydeliberately intended, inorder to avoid loss of heat' to the greatest possible extent due to radiation to the ashpit. The net result of these factors is that in the usual form of combustion apparatus the layer of fuel lying nearest to or on the grate, is chilled to an extent such that combustion in this layer i oj is retarded or ceases to an extent producing a bed of unconsumed fuel hindering the ashes from falling through the grate. Above this lower layer thereis. however, a high rate of combustion and as the condustion of heat from this layer is rela- '15 tively siight, the temperature rises to such an extent that the sinters or fuses into slag or clinker which eventualiy may shut off all further supply of air te the combustion zone and thus cause thefire to go out. A further disadvantage go 'of' slag is that unconsumed fuel particles are often imbedded n' 'the slag or clinker and shut oil' from combustion air so that low 'combustion emciency results. Also, slag formation frequently prevents ash from being removed from thegrate by ordinary shaking of the grate, ,r'equiring breaking up by the .use -of a slice bar before it .can be removed.

In accordance with the present invention, the above' described phenomena are prevented from taking place, and the resultant disadvantages avoided by regulating combustion in such a way that it will take place only in a thiri layer immediately above the grate. In general it may be said that this is attained by providing apparatus which will operate to cause preheating .of the air so` that it will have a high temperature when striking the fuel bed and in which the minimum fconbustion temperature is limited to preventit from risin'g to a temperature resulting 40 I -in slagging or clinkerlng of the ash. i

In 'order to eflect this, the grate is formed and arranged in such a way that an effective radiation of 'heat downwardly from the fuel bed on the grate is obtained. This is done by proportioning the ratio of the spaces between the grate bars to the width of the bars so that the total portion of the grate area formed by the spaces between the 'grate bars is large as comparedt the portion of the space occupied bythe bars themselves. This general character of grate Construction,'combined with other features of construction, 'as will hereinafter be more fully pointed out,

has been found to provide for a character of Fig. 1 is a vertical section through combustion apparatus embodying the invention;

Fig. 2 is a section taken on the line 2-2 o! Flg. 1; and

Fig. 3 is a section similar to Fig. 1 showing another form of apparatus.

Rei'erring to Fig. 1, the apparatus illustrated shows the invention embodied in a cook stove of the heat accumulating magazine type but it will be understood that the invention is equally,

applicable to other specific forms of heating apparatus. In this figure the outer shell or casin'g of the stove is indicated at u, the "top plate of the stove being indicated at l2. A cylindrical metal member !4 acts as a fuel magazine and in the' form shown is of heavy section to provide heat storing capacity, the upper face of the member providing a hot plate for cooking purposes and being fitted with a central fuel charging opening closed by ,lid IE. `The walls of an outer casing a surround the walls of the member M in spaced relation to provide an annular flue space 20 communicating with the ofitake flue 22 The bottom oi' the combustion space is formed by the grate indicated generally at 24 and provided, in the. form shown, with a plurality ot relatively narrow longitudinally extending grate bars 26. The bars 26 are spaced'trom each other so that the total area of 'the spaces formed between the bars is at least twice and preierably three or more times as large as the total part of the grate area occupied by the grate bars. Advantageously, the grate is made from a material e having poor heat conducting characteristics such for example as an alloy of iron and chromium. When the grate is made of such material, chilling of the fuel particles lying closest to the grate bars due to conduction oi heat therefrom by the grate bars is reduced. In order further to reduce conduction of'heat from the fuel bed through the grate structure, the grate is advantageously supported by means of narrow projections 28, hav--..

' ing small contact areas, resting on ledges 30 projecting from the walls 32 forming the ashpit 34. In the embodment illustrated, the ashpit walls are made integral with' walls s.

In the apparatus illustrated, the combustion chamber is restricted at a relatively short distance above the grate 24, such restriction being formed by the in'wardly projecting portions 38 of the outer casing wall structure.

combustion air is admitted to the ashpit 34 through the inlet opening 38, which is in communication with an air inlet passage 40. Flow of air through opening 38 is controlled by a thermostatically actuated v'alve 42 which is advantageously responsive to variations in temperature oi' that which it is desired to heat by means of the fire. chamber are surrounded by heat insulating material 44 to prevent less' of heat. In Fig. 2 the outer shell and'insulation have been omitted from the showing as well as the door tor 'closing the opening 46 for removing ashes from the pit.

The combustion air entering the ashpit through opening 38 is preheated to a high degree in the Both the ashpit and the combustion pit before reaching the grate and fuel bed. mostly by conduction and convection o! heat from the` ashpit walls which are heated to a high degree by radiation from the incandescent fuel bed immediately overlying ,the grate. The temperature of the ashpit walls is very high, owing to the fact that these walls are exposed to intense radiation of heat iromthe fire and are insulated against external loss of heat by the surrounding insulation.

In order to obtain eflective radiation of heat to the side walls of the ashpit as well as to the bottom. the grate is advantageously bulged downwardly as shown in Fig. 1, thus making a so-called "hanging" grate. Heat may also be transmitted to the ashpit walls by conduction from the heated walls of the'combustion chamber, with which they may be made integral as in Fig. 1 or ar- 4 ranged :in some other suitable heat conducting relation. I

Owing to the preheating or the combustion air before it reaches the fuel bed, a high rate ot combustion will be developed as soon as the air strikes the fuel in the layer lying immediately on the grate and ash released 'as a result of this combustion will fall through the grate without necessity for the grate to be Shaken If combustion should extend so as to take place in'higher portions of the fuel column, the removal of the ash thereby released is more diilicult since such ash is prevented from falling freely from the fuel bed by the underlying unconsumed fuel. It is therefore desirable that the layer in which active combustion takes place shall be as thin as possible. A high degree of preheating of the combustion air attains this object' since with highly preheated air, the rapid combustion occurring in the lowermost layer oi' the fuel bed acts to rapidly consume the oxygen content of the, air, so that little ii' any oxygen is available for combustion in the portions above the lowermost layer.

Limitation of the height oi the layer in which active combustion 'can take place 'is also contributed to byshaping the combustion chamber as shown in Flg. 1. As will be observed from the figure, the combustion gases leave the fuel bed laterally and escape into the flue 'space 20 at a distance not far above the grate. consequently, such gases, which are very hot, cannot operateto raise the temperature of the upper portions of the fuel bed to the ignition point. The interposition of the heavy heat absorbing member 'll between the passage 20 and the upper portions of the fuel stored in the magazine also tends to assist in maintaining the upper portion of the stored fuel below ignition temperature.

It is of substantial importance that heat shall not be carried away from the burning fuel nearest the grate at too great a rate. If the fuel nearest the grate is cooled by conduction or radiation of heat therefrom, at too great a rate, it may be cooled below ignition, temperature and remain in unburned or partially unburned state' on the grate, thus preventing the free dislodgement and fall of the ash that is released by combustion of the fuel. Accordingly, the grate is thereiore ar- .ranged with relatively small heat conducting asase the grate on projections of small area such as are indicated at 28.

In order to prevent pieces of fuel which are located along the edges of the grate from being unduly cooled by the walls of 'the combustion space these walls are constricted 'immediately above the grate as by means of a fiange 36 or the like so that fuel at the grate level does not come into contact with the side walls of the combustion chamber but is on the other hand maintained in appreciably spaced relation with re spectthereto.

On the other hand, if conduction of heat from the fuel is too low, the temperature in the combustion zone may rise to such high level that the ash will fuse and form clinkers, thus preventing,

maximum temperature t'o be attained in' the combustion zone can be controlled by proportioning the structure in accordance with' well known laws governing the rate of heat dissipation by radiation and convection.

In Fig. 3 there is illustrated another embodiment of the invention. In this figure the bottom and side walls of the ashpit areexposed to radiation from the incandescent tuel and heat may also be conducted theretoby conduction from the upper combustion chamber walls.

In this instance the air admission channel a, to which a controlledsupply of air is admitted through the valve 42, embraces the ashpit, air being admitted to the latter through the openings sia. i

In order to assist in preheating the air flowing bustion space and an ashpit below said combustion space, a grate for supporting fuel -above reaches the tuoi bed.

through passage daa, the ashpit walls may be advantageously provided with fiange's 48 providing extended heatexchange surface.

' In other respects,'the embodiment shown in Fig. 3 is,in general similar to that illustrated 5 in Fig. 1, although in the present ,instance the constriction above the grate is formed by an 1nward sweep of the walls at 36a rather than by the inwardly extending fiange as shown in Fig. 1.

It will be evident that the invention is not limited to the above described embodiments which have been shown by way of illustration only, but may .be varied widely with respectto the form and shape of the several elements and the specific manner in which the `greheating of 15 the air is accomplished.

While the invention is not limited to any specific forms of solid fuels, it is 'primarily intended for and particularly 'applicableto the combustion of relatively non-volatile fuels such asi an thracite, coke, or charcoal.

What I claim is:

-Apparatus for continuous combustion of solid fue] including casing structure providing a comsaid ashpit and means for supplying combustion air to said ashpit, said grate being made of material having a relatively low coemcient of heat condictivity andhaving supporting contact of relatively small area with said' casing structure,

'whereby to minimize conduction bi' heat through the grate from the overlying fuel bed, said grate v being proportioned so that the portion of the total grate area occupied by the gratebars is not more than one-half of the portion oi' the total grate area formed by. thespaces between the grate bars, whereby to provide a relativeiy high rate of heat radiation downwardly through the grate to heat the wails' of said ashpit and the 40 combustion air admitted thereto before said air emm emm.