US2290991A - Fuel combustion method and means - Google Patents

Description

y 23, 1942- R. w. PAl QRY FUEL COMBUSTION METHQD AND MEANS Filed Oct. 5. 1938 mv smox Richard Wparr y.

BYQWJ A'rroRNEYJ.

Patented July 28 1942 UNITED STATES PATENT OFFICE FUEL COMBUSTION METHOD AND- MEANS Richard w. Parry, Cincinnati, Ohio Application October 5,. 1938, Serial No. 233,428

7 Claims.

The present invention relates to the art of efficient combustion of solid fuels, and particularly to the burning of fuels containing volatiles andhas for an object the provision of simple and relatively inexpensive means whereby the eflic-iency of fuel burning furnaces is enhanced and whereby the objectionable products of improper or incomplete combustion are largely eliminated.

Another object of the invention is to, provide a novel and easily practiced method of providing for optimum efficiency in furnaces of .various types to the end that proper adjustment to the individual characteristics of any furnace is automatically attained. Still further, the invention has for an object a provision for a method and means affording uninterrupted and more complete consumption of liberated gases in the combustion zone witheut increase in stack draft of the furnace and with great reduction in excess air.

These and other objectsare attained by the methods and means herein described and exemplified in the accompanying drawing, in which:

Fig. l is a vertical section through a furnace solid fuel particles and fly ash into the atmosphere, and frequent smoky conditions in the fire box and offensively smoky and sooty stack discharges. 7

In order to overcomeall of these objections, I have foundthat it is necessary to avoid a condition which has heretofore received little or no attention, namely, the unsuspected interruption of the burning process in the fire box and the combustion zone. It is known to those versed in the art that incompletely burned solids may lose is ,not increased by the introduction. of the air. jets or streams. Since the total air required is reduced, the stack draft is automatically desome of their temperature and thereafter become from the combustion zone before attaining ignition temperature, and that burnable gases may stratify and escape before proper mixture with air can take place;

To accomplish this I have devised a novel f the latter istaken largely in the activity of method of procedure applicable, with predictable results, to various fumaces and preferably employin-g means which are inexpensive to the extent that the cost of equipping a furnace therewith is quickly recovered in. reduced fuel consumption cost.

The invention consists in introducing into the zone of flame and rising gases of a furnace fire box jets of air which is preheated to approximately ignition temperature'or greater and at such velocity and in such directions as to substantially exhaust the kinetic energy of the air streams in so mixing and churning the flame, liberated gases, and the introduced air at ignition temperature, as to foster instantaneous explosive ignition and rapidly ensuing combustion of various quantities of solid small fuel particles and of the proper mixture of air and volatiles as rapidly as the combustible mixtures are made. The effect of the foregoing eliminates the necessity for the travel of combustible gases in the flame zone in order to attain ignition temperature, The further effect is to increase the distance travel of the bumingcgases in a given unit of time within the flame zone and to produce a churning reverberatory action of the fiame between the various air jets. .Since the kinetic energy of the air stream movement and of the explosions of the various. quantities of combustible gaseous mixtures is beneficially utilized and substantially exhausted' in the combustion zone, the stack draft creased; It follows then that the liberated volatiles including the black smoky carbonaceous substances have no opportunity to pass beyond the combustion zone before they are intimately mixed with the air at. ignition temperature and ignited. The characteristic appearance of the interior of afurnace fire box when operated by the means and methods of the invention is one of transparent flame in a state of rapid reverberation and a simultaneous. chaotic sinuous flow. By the proper adjustment of the volume of air introducedat ignition temperature, with relation to the total combustion air employed, the total air may be appreciably reduced with the result that excess air in the fire box is materially lowered and a milder reducing flameis produced. The walls of the fire box are therefiirerelieve-d of the detrimental effects of an oxidizing name and they are furthermore relieved of the attrition'bf the gases and fuel particles because the energy breaking down and mixing the stratum which tend'to form-by reason of relatively low stack draft.

In the practice of the invention I have not overlooked the fact that different furnaces exhibit widely different burning characteristics and efficiency due to causes which are in some instances the fire attains some initial preheat, taking the same from the brick work of the furnace if de sired. The conduit will desirably but not absolutely necessarily lead to a plenum conduit from which suitably arranged nozzle supply pipes are led. The supply pipes have spaced apart ofitake outlets arranged at intervals and these are suitably adapted to receive the blast nozzles which extend into the combustion zone. Preferably the conduit, plenum and supply pipes are protected to some degree against the direct action of flame and the connecting ends of the blast nozzles are also thus protected in order to facilitate the eventual replacement of any blast nozzle. The exact distance to which any given blast nozzle must extend into the combustion zone in order to assure preheating of the issuing air to at least ignition temperature is not accurately determinable as a general proposition, due to the heretofore mentioned different burning characteristics in various furnaces. Furthermore there is no easily practiced mode of determining that distance in an existing furnace wherefore the following mode of installation is resorted to with notable success. When preparing the blast nozzles for installation in a given furnace, pipes, such as sections of wrought iron pipe are cut to such lengths that they will extend from their supply pipes well over the fire bed and into the combustion zone sufficiently far to insure the heating of the metal to incandescence. When the furnace is initially placed in operation after the installation of the nozzles and air under suitable pressure is being discharged through the nozzles, the total forced air supply under and over the fire is materially reduced with relation to the amount previously used in the normal operation of the furnace and the reduced total air supply is proportioned between the nozzles as a group and the primary air under the'fire, whereupon excessive length of metal piping forming the nozzles will rapidly burn away, thereby causing the action of the furnace itself to automatically shorten the individual blast nozzles to such lengths that the air passing through said air nozzles will preclude further burning away. It has been found that with such adjustment the issuing air is at ignition temperature or slightly higher. Thereafter, the destruction of the free ends of the nozzles is negligible because the rate of air movement through the nozzles varies as the total combustion air varies, as will be hereinafter more fully understood.

The foregoing mode of disposing nozzles for preheated air is entirely distinct from heretofore known modes of installation of nozzles for preheated air in that the latter have been invariably terminated at the side walls of the furnace with a. surrounding protection of fire clay, tile, or the like. The effectiveness of an air stream issuing from a perforation in a flat surface is of itself considerably less than that of a stream issuing r-mma :nozzle, particularly forthe purposes of the present invention. Furthermore it is highly impractical, if not indeed impossible, to attain preheat of air to ignition temperature from an orifice in the furnace wall.

Reference is now made to the drawings which show one embodiment of the invention, it being understood that the invention is in no wise restricted to the specific details of construction there illustrated.

In Fig. 1 there is shown an existing stoker fed furnace installation wherein an air duct l0, providing air beneath the fire through the way ll under control of a permanently adjusted valve or damper I2, is tapped at I3 with a conduit 14 of which the sections 15 and I6 run along and over the furnace side wall and back wall respectively. The section I6 is connected into a plenum pipe II which desirably restson top of the back wall It. From opposite ends of pipe ll nozzle supply pipes l9 are housed in the brick work of the side walls. Nozzles 20, desirably consisting of lengths of wrought iron pipe are coupled into the supply pipes l9 and, in the present embodiment, have their free ends lowered slightly below the horizontal so that air streams issuing therefrom will traverse the general upper direction of movement of rising flames and gases from the fire bed. Nozzles 20 shown in Fig. 2 as of substantially uniform length although in practice this need not necessarily be the'case so long as each of the pipes is initially at least long enough.

In the operation of the device the air from duct I0 is carried through conduit M, I5 and I6, to

' plenum pipe I1 and acquires an initial preheat invention is installed and tested.

' temperature. The volume of pressure air passing into plenum pipe I! is divided between the nozzle supply pipes I9 from which it issues through the several blast nozzles 20. As hereinbefore indicated the additional heat imparted to the air as it passes through the nozzle supply pipes and nozzle raises the temperature of the air to 700 F. or more and the individual jets of air at ignition temperature set up a reverberatory action of the flame and gases ina zone between the ends of the nozzles and above the fire bed. It will be understood therefore that the intense transparent flame thus generated absorbs the kinetic *energy of the air jets and that any portion of the It will be noted that air duct 10 supplies pres-.

sure air beneath the fire and also to the blast nozzle system. This arrangement is considered preferable to separate air sources and controls in all cases where duct 10, or its equivalent, provides sufficient air pressure or where it can be made to do so. In such a case an initial proportioning of the air available above and below the fire can be made when the apparatus of the Thereafter the blast nozzle pressure will remain proportionate under possible fluctuations of the source pressure during operation of the furnace. The balance between the air through the fire and over the fire is automatically maintained.

In the properly adjusted arrangement in a furnace embodying the method and means of the invention CO3 is produced without using the, customary large amount of excess air. For example, existing furnaces showing up to fifty percent (50%) or even sixty percent (60%) excess air in operation will, when-modified and operated according to the present invention, use from three percent (3%) to fivepercent (5%). excess air. The total amount of air used in the operation of the furnace thus improved is reduced approximately twenty-five percent (25%). Within the combustion zone the directed, high temperature air jets increase the length of travel of particles of gases and fuelin a given space and time from inches to feet. directed turbulence eifected under these conditions results in a very nearly equal high efficiency throughout the entire volume of furnace space. This is in strong contrast to commonly known variations of over fifty percent (50%) variations in the eiiiciency in different sections of the same furnace at a given time.

What is claimed is: 1. The method of permanently adjusting combustion in a forced draft mechanically fired solid fuel burning furnace which comprises the steps of initially adjustinggthe forced air draftentirely beneath the firebed to attain optimum combustion at a given rate of firing, then reducing said forced draft by approximately twenty-five percent (25%), then leading on a portion of the total air supply ahead of the firebox for sec-' ondary air of combustion and allowing the remainder of said forced air to pass beneath the fire while maintaining the given rate of firing,

then delivering said secondary air as two relatively opposed rows of spaced apart velocity-air jets issuing at ignition temperature from two sides only above the firebed traversing the zone ofcrising flame and gases below the top level of 0 the furnace bridgewall, then adjusting the flow of primary combustion .air beneath the fire to attain a balance between said primary combus-; tion air and said secondary combustion air indicated by and establishinga chaotic and rever- .beratory turbulence with transparentsmoke free flame close above the firebed and permanently fixing the-adjustmentof primary and secondary air proportions.

2.'The method of adjusting the combustion of solid fuel in a forced draft furnace which consists in establishing a total forced air supply. affording a relatively low theoretical percentage of excess-air atrany given firing rate,--and dividing said total air supply into complementary primary and secondary air supplies, introducing the secondary air as a plurality of jets of velocity air, preheated to issue at ignition temperature, from two opposite sides only of the firebox traversing the naturaldirectionmn rising flame and gases 00 above the'firebed and below thetop level of the furnace bridgewall whereby turbulent chaotic mixture of said secondary airand said flame and gases is effected and finally and;permanently apportioning the relative amounts of primary 65 and secondary combustion air by adjusting the flow of primary combustion air under the fire until the turbulent mixture assumes a reverberatory character accompanied by smoke-free transparent flame in the-firebox.

The positive and v15 in a furnace having forced air supply which comprises effecting a permanent selected apportionment of the total combustion air into primary and secondary air supplies with said secondary of the firebox only and at such volume and velocity with respect to the primary air as to effect action producing transparent yellow smoke-free flame in the firebox evolving above into clear colorless gas.

4. In'combination, a solid fuel burning furnace, a duct providing the total pressure air I to said furnace, a 'valve controlling the supply of air from said duct beneath the fire and a secondary air supply system communicating with said duct closely ahead of said valve and com-' prising supply pipes on two sides only of the firebox, and spaced apart and relatively opposed metallic nozzles projecting well over the firebed, said valve being adjustable to a permanent position effecting selected proportioning of the volume and velocity of said secondary air'jets with relation to the primary combustion supply under all operating conditions.

5. In a solid fuel burning furnace the combination withafurnace structure, of a .pressure air'supplymeansaffording the total air of combustion to the furnace, a valve controlling the flow of primary combustion air from said means beneath the fire, a secondary air system connectover the firebed on tWoopposed sides thereof only, said valve in selected adjustment serving to proportion the total air in substantially-uniform ratio between the secondary air and the air under the fire under varying pressures in said means.

6. In combination, a solid fuel burning furd nace, a duct providing the total pressure air to said furnace, a valve controlling the supply of air from said duct beneath the fire and a secondary air supply system communicating uncontrolledly with saidduct closely ahead of said valve and comprising supply pipes on two sides only of the firebox, spaced apart and relatively opposed metallic nozzles projecting well over the firebed, said valve being adjustable to a permanent position effecting selected proportioning'of the volume and velocity of said secondary air jets with relation to'the primary 7. In a solid fuel burning furnace the combi- & nation with a furnace structure, of a pressure air supply means affording the total air of combustion to the furnace, a'valve controlling the flow of primary combustion air from said means beneath the fire, a secondary air system con-.

necting-Fwithsaid means ahead of the valve and includingdzwo rows of directing nozzles extending over the 'firebed on two opposed sides thereof only below the top level of the furnace bridgewail, said valve in selected adjustment serving to proportion the total air in substantially uniform ratio between the secondary air and the air undervthe fire under varying pressures; in said means. i 3. The method ofefilciently burning .solid fuel w. PARRY.

a constant chaotic turbulent and reverberatory combustion supply under all operating conditions.

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