US2424755A - Method and apparatus for burning solid fuels - Google Patents

Description

muy 29, WM R. c. JOHNSON 2,424,755

METHOD AND APPARATUS FOR BURNING SOLID FUELS Filed Sept.4 8, 1944 /4 l f2 FUEL LcoMBusT|onLAsH /0 /3 I Y 2/ N f 3 22 g@ 32 l MEDIUM T0 BE Patented`July-29, 1947 METHOD AND APPARATUS FOR BURNING' SOLID FUELS Raymond C. Johnson, Philadelphia, ra., assignor,

by mesne assignments,V to Anthracite ,Equipment Corporation, New York,lN. Y., a corporation of Delaware Application September 8, 1944, Serial No. n'553,193-

9 claims'. L l The present invention relates to heating apparatus and more particularly to a compact unit operating at high eihciency for burning solid fuels, such as anthracite coal.

Heating units, as heretofore constructed, all

` follow conventional lines, the general characteristics of which are large fuel beds burning at slow rates per unit area. Thus, there is a large volume of fuel surrounded by a heat absorbing surface, the area of which is relatively small compared to the volume of fuel. As a consequence, only about twenty to forty percent of the heat contained in the fuel is absorbed by the surrounding heat absorbing surface. Most of the remaining heat leaves the fuel bed as sensible or undeveloped heat in the combustion gases. Therefore, such heating units are necessarily large and cumbersome because in an attempt to gain elciency it is necessary to provide space to complete combustion of the incompletely burned gases and large secondary heat absorbing surfaces to extract the heat from the gases. A considerable portion of the fuelis converted to carbon monoxide in the fuel bed, and this carbon monoxide is burned with air introduced above the fuel bed in the combustion space. Therefore, .only a part of the heat in the fuel is liberated in the fuel bed itself because the reaction from carbon to carbon monoxide liberates approximately one-third of the heat that is liberated when the. reaction is carried from carbon to carbon dioxide. In the present day conventional burning equipment, it is essential for any degree of efficiency that these large volumes of fuel be burned at relatively slow rates in order to obtain emcient absorption of the large amount of fuel converted to combustible gases and burned above the primary combustion chamber.

Some of the objects of the present invention are: to provide an improved combustion unit for solid fuel; to provide a unit wherein the fuel is burned in such a manner that complete heat liberation will take place in the fuel bed; to provide a heating unit wherein the heat of the fuel will be efficiently absorbed; to provide a heating unit wherein thenecessity of a secondary heat ab# sorbing surface is eliminated; to provide a heatsurface is large as compared to the volume of fuel; and to provide other improvements as will hereinafter appear.

In the accompanying drawing, Fig. l represents a longitudinal section of a combustion unit embodying one form of the present invention; Fig, 2 represents a section on line 2-2 of Fig. 1; and Fig. 3 is a diagrammatic representation of one form of installation using the unit of the present invention.

Referring to the drawing, one form of the present invention comprises a metal tube l0, open at both ends and suitably supported to form a passage and combustion chamber Il for fuel,

preferably'anthracite coal. This fuel is arranged' to be fed into and along the tube, in the present instance, by a Worm l2 driven at a selected or predetermined rate by a pulley i3 fast tothe worm shaft I4, and driven by a belt |'5 from a pulley I6 fixed to a shaft I 1 projecting from a gear box lI8 in which suitable ratio of gears are driven by an electric motor 20. As shown, a fuel feed conduit 2l leads from the fuel supplyl and houses a second fuel feed worm 22 for delivering the fuel to the worm I2..The shaft 23 of the worm 22 is arranged to be driven by a pulley 24,

belt 25 and pulley 26 from the motor 20. This worm arrangement and motor driven pulley sys.. tem are shown merely as one example of progressively feeding fuel to the tubev I0 and various other mechanical means. can be used, aswill be y understood.

For supporting combustion and removing combustion gases, the fuel inlet end of the tube communicates with a conduit 21 leading to the inlet of an exhaust fan 28 which has its outlet 30 leading to a stack (not shown). The fan- 28 is arranged to be driven by an electric motor 3|.

Thus, with the fan 28 in operation, air is drawn into the fuel exit end of the tube l0, traverses the ignited fuel therein, also that portion of the fuel entering the tube I0, and exhausts by Way of the conduit 21. Thus, in addition to supporting the required combustion, the air delivers col lectedheat units to the incoming fuel to thereby preheat it on its way to the combustion area. A further benefit of this construction resides in the fact. that the incoming fresh coal functions to filter outy ash from the air and thereby materially reduces its discharge to the stack. v

In order to utilize the heat generated in the tube IIJ, a jacket 32 encircles the tube l0, and

is provided with an inlet pipe 33 and outlet pipe 34 for circulating a medium to be heated. In this instance. by'way of example, the motor 20 oper- 2,424,755 v g y ates a pump 35 as a means of maintaining circulation through the Jacket l2.

The installation of Fig. 3 is housed in a casing 35 having provision for admitting the fuel feed conduit 2l, and such other pipes as lead to the outside of the casing. An ash receptacle 31 is positioned below the tube l to receive ash discharged from the exit end of the tube I0, and the l casing 36 has a door or other opening (not shown) to allow access to the receptacle 31 for emptying the ashes-as required. A deflecting plate 38 may be attached to the inner wall of the casing 36 in position to direct the falling ashes into the receptacle 31.

In operation the fuel is fed into the tube I0, ignited intermediate the ends of the tube, and combustion maintained by a counter flow of air which latter leaves the tube I0 at a point beyond the burning area and coincident with .the area of the entering fresh fuel. The speed of the exhaust fan 2B and the rate of travel of the worm I2 gases are hotter. The amount of carbon monoxide leaving the fuel bed is only a small fraction of that found in heating units having large fuel beds in which the wall area of the fuel bed container to the volume of the burning fuel is much smaller.

In accordance with the present invention it has been found that tubes forming a combustion chamber ranging from two inches. to eight inches in diameter will burn fuel, such as anthracite coal,

l0 at rates as high as or higher than 100 lb./sq. ft./hr.,

are correlated and so proportioned as to maintain f a substantially constant fuel bed. Thus, as the ash residue is discharged at one end of the tube I0, aA

deinite incremental area is added 'so that the effective action is a continuous moving column of fuel composed of fresh fuel, preheated fuel,

burningfuel and ash or unburned residue. While l for purposes of illustration the tube l0 is cylindrical in shape, the invention is not limited to any particular configuration, the essential consideration being that the ration of the volume of the burning fuel to the heat absorbing surfaces be low. Such ratio is maintained by providing a tube having a relatively small diameter or of such `dimensions as will provide a cross-sectional area of minimum size. `As illustrative, a tube of six inch diameter provided a cross-sectional area of approximately of a square foot. This crosssectional area may be varied by adjusting the width and length of the tube to produce the desired economical result'. By the present invention a secondary heat absorbing surface is not` required because substantially complete oxidation of the carbon to carbon dioxide takes place in the fuel bed itself. In conventional heaters the large fuel bed causes a considerable portion of thefuel to be converted into carbon monoxide which is burned with air introduced above the bed in the combustion chamber. Hence only part of the heat in the fuel is liberated in the fuel bed itself because the reaction from carbon to carbon monoxide liberates approximately one-third of the heat that is liberated when the reaction is carried from carbon to carbon dioxide. Thus, in these conventional heating units the rates of heatl liberation seldom exceed 15,000 B. t. u./cu. ft./hr.,

and this is accomplished without the heretofore serious disadvantages of clinkering the extraneous materials contained in the fuel. Clinkering and removal of the ash are a very limting factor in the economical operation of'conventional heaters and restrict the use of the desirable high burning rates. At high rates of heat liberation the temperature of the fuel bed becomes very high so that the ash tends to soften and fuse together, forming a clinker, which is the cause of much dissatisfaction with coal burning equipment. Also, a high fuel bed temperature causes an increase in the rate of formation of carbon monoxide, with a corresponding reduction in the amount of carbon dioxide. Furthermore, at high combustion rates the gas velocity through the fuel bed is much greater, and carries with it small particles of fuel and ash, known as y ash, which when deposited in the flue passes reduces the emciency of the heat absorption and increases the losses up the chimney.

It will now be apparent that a complete unitary heating unit has been devised wherein the in which the rate of heat absorption will not be over 4500 B. t. u./sq. ft. of heat absorbing surface/hour. In accordance with the present invention, it is possible to obtain rates of heat liberation of 500,000 B. t. u./cu. ft./hr. or higher heat and absorption of 40,000 to 50,000 B. t. '1L/sq. ft. of heat absorbing area/hr. with absorption emciencies as high as 87% or higher. The new result is readily apparent when compared to absorption rates of 40% to 50% in conventional heating units. The increase in efficiency is due to the increased area of the surface containing the fuel bed in relation to the volume of the burning fuel. This permitsalmost complete combustion of any CO formed in the fuel bed by excess air which passes along the side walls more freely than through the center of the bed where the passages are more tortuous and the heat available in the fuel is developed in a very small fuel bed, all parts of which are in such close proximity to heat exchange surfaces as to cause the heat to be removed as rapidly as developed. Therefore, since the center of the fuel bed is only a very few inches from the water cooled heat exchange surface even extremely high burning rates do not produce a temperature high enough to cause softening and cohesion of the ash. Thus, the combustion air can flow evenly through the fuel bed without interference from clinkers and produce a uniformly high burning rate and maximum output. Also, the ash delivered from the combustion space will be of uniform size. It should also be noted that the induced airhas a counter-flow to the incoming fuel, and since it passes through the burning area, heat units absorbed thereby will be transferred to the incoming cool fuel and preheat it for delivery to that area. In the illustrative example heretofore mentioned, a tube forming a fuel bed but six inches in diameter and about eighteen inches in length gave heat outputs of about 100,000 B. t. u. per hour at an efiiciency of 67%. Present day commercial equipment eapable of an output of 100,000 B. t. u. per hour would require a boiler forty-eight inches high and thirty inches in diameter and operating at less than 50% eiciency.

In such equipment the ratio of the total heat absorbing surface to the volume of the fuel bed is approximately fifteen to one. The secondary heat-absorbing surfaces employed in such equipment for extracting heat from the combustion gases which leave the fuel bed are of extensive area, while the direct heat-absorbing surfaces (i. e., those extracting heat directly from the burning fuel bed) are of much less area; Athe ratio of the area of the direct heat-absorbing surface to fuel bed volume frequently being approximately one to five. In contrast, by the .method and apparatus of the present invention this ratio is much nearer unity being in the case denominator of said ratio representing substantially the maximum distance in-inches from the central longitudinal axis of the tube to any point on the inner tube surface in a plane perpendicular to the tube axis. This definition regarding the denominator of the ratio applies wherever the ratio is referred to in the appended claims.

By a ratio of not substantially less than two to. three and one-half as specified in various claims, applicant does not mean to exclude a denominator of four inches, since the new result attained by the present invention is due to the restricted distance from the burning area to the heat exchange wall, which in dimensions brings all of the burning area within four or less inches from that wall. In termsv of coal this distance may be measured as four -peces of radially disposed anthracite. Thus, it will be seen that the restricted cross-sectional area of the heat exchange element results in a fuel column formed of a plurality of transverse planar fuel areas, each composed of maximum fuel rows of ten aggregates each. For different coal sizes the diameter of the tube is varied accordingly to obtain the best eihciency, for example, a tube diameter of seven inches for chestnut coal; two inches for barley coal; six inches for pea; and four inches for buckwheat. In other words, the fuel bed can be dimensioned for different fuels so that predetermined amounts of coal can 'be ignited in proportion to the air admitted. J

As has been pointed out, the velocity of the air plays an important part in producing the new re sult, since this not only traverses the fuel bed to promote combustion and also carry heat units to the incoming fuel, but also produces a' scrubbing action upon the heat absorbing walls to keep them clean for maximum absorption.

It will be understood that the unit of 'the present invention can be equipped with automatic controls responsive to room temperature, stack temperature, and control for fuel feed as a means of obtaining uniform operation with low fuel consumption.

Having thus described my invention, I claim:

1. The method ofburning solid fuel in aggregate form utilizing a furnace having a combustion chamber perimeter proportioned to crosssectional area in a ratio of not substantially less than two to three and one half, comprising the steps of causing fuel aggregates to travel through such combustion chamber in a circumferentially engaged column, igniting a portion of the column, and inducing a ilow of air counter to the aggregate travel to successively traverse the ignited and un- `ignited portions of the column, whereby complete combustion takes place in the ignited portion by reason of the predetermined ratio.

imity to said outlet for combustion and another portionacross said inlet to be preheated, said fuel completely filling the combustion portion 0f said tube, means to induce a flow of air successively through the combustion portion and the portion to be preheated for combustion and preheating purposes and means to extract the heat absorbed by said tube.

3. In an apparatus for burning solid fuel in aggregate form comprising the' combination of means forming aconduit for the passage 0f fuel, a flue communicating with said conduit, means for feeding fuel through said conduit, a tube arrangedto receive fuel discharged from said conduit and form a laterally confined column of fuel completely llling the combustion space of said tube and said tube having a perimeter pro-. portional .to cross-sectional area in a ratio of not substantially less than two to three and onehalf,

said tube also having an outlet for consumed fuel,

means for inducing a flow of air into said outlet to pass through said column into said conduit, and out through said flue, whereby combustion is completed in said column and the fuel in said tube is preheated, and means to extract the heat absorbed by said tube.

4. Apparatus for burning solid fuel in aggregate form to produce combustion with substantially no CO in the Waste gases, said apparatus comprising a heat-exchange element arranged to tially no CO in the waste gases, said apparatus 2. A combustion heater comprising a tube havcomprising a heat exchange element arranged to receive said solid fuel at one end and to circumferentially contact and confine said fuel as an elongated column having a portion forming a combustion bed, said element having an opening at its opposite end for the discharge of consumed fuel, said element `further providing a ratio of heat absorbing surface to volume of burning fuel not substantially less than two to three and one half, means to feed said fuel towards said discharge opening as a continuous column, and means to induce a flow of air in counter flow to said column. I

6. Apparatus for burning solid fuel in aggregate form to produce combustion with substantially no CO in the `waste gases, said apparatus comprising a heat exchange element arranged to receive said solid fuel at one end and to circumferentially contact and confine said fuel as an elongated column having a portion forming a combustion bed, said element having an opening at its opposite end for the discharge of consumed fuel, and means providing for flow of air through said combustion bed in quantity suiflcient to eiiect substantially complete combustion of said fuel in said heat exchange element, said element pro-v receive said solid fuel and to circumferentially 'ilne the same as an Aelongated column having a contact and confine the same as an elongated column having a portion forming a combustion bed, the inner confining periphery of said heat exchange element being at most four inches from the longitudinal axis of said combustion bed. said element providing a ratio of heat absorbing surface to volume of burning fuel not substantially less than two to three and one half.

8. Apparatus for burning solid fuel in aggregate form to produce combustion with substantially no CO in the waste gases, said apparatus comprising a heat exchange element arranged to receive said solid fuel at one end and to cireumferentlally contact and confine said fuel as an elongated column having a portion forming a combustion bed. the inner confining periphery of said heat exchange element being at most four inches from the 1ongitudinal axis of said combustion bed, said element having an opening at its opposite end for the discharge of consumed fuel, and means pro--v viding for 110W of air through said combustion bed in quantity sumcient to effect substantially complete combustion of said fuel in said heat exchange element, said element providing a ratio of heat absorbing surface to volume of burning fuel not substantially less than two to three and one half.

9.' Apparatus for burning solid fuel in aggregate form, said apparatus comprising a heat-exchange element arranged to receive said solid fuel and to circumferentially contact and conportion forming a combustion bed, the inner oon.

iining surface of said heat exchange element being at most four inches from the central 10u81- tudinal axis thereof, means to feed fuel through said element as a continuous column, and means to induce a ilow of air in counter ilow to said column.

RAYMOND C. JOHNSON.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 153,128 Stevens July 14, 1874 166,336 Bonta Aug. 3, 1875 182,056 Bonta Sept. 12; 1876 1,800,105 Rainchon Apr. 7, 1931 491,359 Ketchum Feb '7, 1893- 2,126,104 Fulton Aug. 9, 1938 2,151,642 Rose Mar. 21, 1939 399,798 Taylor v Mar. 19, 1889 FOREIGN PATENTS Number Country Date '174,722 France Dec. 12, 1934 617,308 Germany Aug. 16, '1935 Y 30,578 'rneNetherlands July o, 1931 486,183 AFrance Mar.4, 1918 '159,153 France oct. 24, 1932

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