US1614295A - Furnace construction - Google Patents

Description

Jan. 11 1927. 1,614,295 y' A. E. GRUNERT ET AL FURNACE CONSTRUCTION Filed Nov. 24, 192s 2 sheets-sheet 2 Patented Jan. 11, 1927.E

UNHTED STATES PA TENT oFFicE.

ARTHUR E. GRUNERT AND ALEX D. BAILEY. OF CHICAGO. ILLINOIS.

FURNACE CONSTRUCTION.

Application filed November 24. 1923. Serial No. 676,744.

ough and continuous mixture of air andsaid gases so as to complete-the combustion ofv same earlier and substantially completely,

also consume substantially completely the V unburned particles of free carbon or coal,

thus increasing the efiiciency of combustion of the fuel and substantially preventing the formation of smoke.

4It has been found that where the natural 2U draft is depended upon for mixing airover the fire with the volatile combustible gases driven off by the heat fromthevfuel bed that no matter hou7 the openings are arranged nor how many openings are pro- '-5 yvided there will not be a uniform mixture of air and combustible gases throughout the furnace but the air will tend to travel more along the Walls ofthe furnace than toward the center thereof Where the volatile comm bustiblev gases ,are banked and there Will be a region in which there -Will be an insufficient supply of oxygen to cause the proper combustion to take place. This uneven stratification not only takes place longitudif" nally vWith the fuel .bed but also tends to unevenness in mixture in a transverse direction. Due, therefore, to the tendency of gas streams toward parallel flow, a condition exists resulting in a dela-y in the combustion, tl and incomplete combustion with resulting smoke. This condition is what is ordinarily lreferred to as long flaming or delayed combustion, and the degree of pre-valence tends in general to increase with the propor- 15 tion of volatile constituents of the fuel. This flaming is partially reducing and causes an increase in the slagging and fouling of the heating surfaces. This is true even Where a forced draft is provided such as in thev case of mechanical l-stokerswhere air under pressure is blown through the fuel bed. These volatile gases' are of the same kind as are ldriven off from coal -in a gas retort Where illuminating gas is formed from the destructive distillation of coal. The

`burning or ignited in the presence of insuffigases are colorless and do not of themselves either constitute nor form smoke. It is only u'hen these gases are burned in an incomplete manner as, for example, chilled While to cient air, or the air is not sufficiently mixed with or distributed throughout the gases, that the phenomenon of formation of smoke occurs. Formation of smoke results from a breaking up of the'hydrocarbon gas. It appears that the hydrogen part of the gas will dissociate from the carbon and will combine With'oxygen more readily than vthe carbon, leaving the carbon in the form of a fine amorphous powder suspendedV in the gas and4 termed smoke. The dissociation of the hydrogen may be carried on at a temperature below the ignition temperature of lthe said carbon with oxygen With which it may be 1n contact. Y

By applying the air under pressure above the bed of burning fuel and injecting it at a suficient velocity so that a stream of air Will be projected into the furnace a sufficient distance to reach that portion of thefurnace 'where a large amount of distillation o f gases occurs, which portion but little airV reaches, due to natural draft, thus bringingabout an intimate mixture of oxygen with the partiallv burned combustible gases at a -point much earlier than would ordinarily occur, and as a result practically all these gases are burned and a much greater'etiiciency is obtained from the furnace than Where the draft is blown through the fuel bed or the natural draft is depended upon through openings inthe sides or front of the furnace. Proper combustion of the large amounts of combustible gases which are released from. bituminous coals such as We findl in the Chi.- cago region, presents a very difficult problem. The difficulty is not so muchin getting sufficient air into the furnace, for thatis easy enough. Merely forming an opening in the walls of the fire-box will, by natural 1Q0 draft, admit any required amount of air. But that will not do.

If the air isadmitted in large quantities it will tend naturally to cool-the walls of the fire-,box with which it is in contact. It will also cool the boiler and instead of securing the desired effect it merely decreases the efliciency of the furnace and Yof the boiler.V But `the large volumes of combustible gas require correspondingly large voll .i

umes of air to complete the reaction of combustion. This is the first condition which must be fulfilled for complete and satisfactory chemical union between the oxygen of 'the air and the hydrogen carbon sulfur, etc.,

of the combustible gases.

'lhe next consideration is that it is .not suflicient merely to supply the proper amounts tw form the right proportions, but the. proper amounts must first be provided and then they must be mixed so thoroughly that each particle of combustible material has, in sufficiently -close relation'thereto, the proper amount of oxygen t-o permit of chemical union. This is difiicnlt to attained because of the peculiar but wellknown tendency of the gases in the furnace to flow'in parallel streams andv to diffuse only very slowly into each other. The more rapid the passage of the gases through the furnace, the less time and tendency is there for them to diffuse and intermingle. i

The best way known to the prior art to secure the desired diffusion and intermingling was to provide a long fire-box giving the gases a maxnnum of time to intermingle and burn before they struck the boiler tubes.

The next consideration is that such intermingling alone is not sufficient. The gases, after they are intermingled, must be ignited continuously and not chilled, otherwise the chemical reaction is retarded or prevented from being completed.

le secure the desired effect of completing the chemical reaction of burning of the gases by fulfilling the above recited and other incidental requirements by our methodv of combustion.

7e introduce the proper amount of air by proportioning the air introduced over the fire to the amount passing through the fuel bed. Next, we deliver the air into the gases vto be burned at the point where tliey are formed, i. e., immediately above the incandescent fuel bed. NeXt,-we deliver the air injets of such size and velocity as to produce a violent turbulence and' mixing of the air and fuel-gases. This turbulent miX- ing of the fuel gases and air stirs. them thoroughly into each other. -Thisis done in a region where ignition is maintained first, by the incandescent fuel bed and, second, by the hot walls ofthe arch and adjacent furnace walls. The turbulence and mixing of the gases is comparable to stirring of two reagents together to secure`completion of a chemical reaction.

In the form of the invention shown in the drawings the air blast means is shown as being applied to a furnace having what is known asa flat arch in which the air under pressure is injected under the arch and well above the bed of fuel. It has also been found to be desirable in some cases to inject air under pressure into the furnace at the front wall thereof rearwardly of said flat archand this is also shown 1n the form of the invention illustrated. It 1s of course to be understood that while a flat arch is shown, the device could be applied as well to a furnace having any form of arch desired.

Preferably, the air is injected over the bed of fuel through nozzles which are arranged in spaced relation so.as to properly distribnte the air among the distilled off gases and these nozzles arc preferably so constructed as to obtain a high velocity from the nozzle to thus inject the air as far as possible into the furnace. The desired object of high `velocity injection nozzles is penetration of within the scope of the claims.

In the drawings:

Fig. 1-is a vertical, longitudinal, section-al view of a furnace showing our improvements applied thereto;

Fig. 2 is a transverse, sectional view taken on the line 2 2 of Fie. 1;

Fig. 8 is a fragmentary enlarged vertical sectional view showing one of the nozzles; and

Fig. 4 is a fragmentary face view, partly in section, showing the compressed air means, the refractory material through which the nozzles extend being omitted for purposes of clearness.

Referring in detail to the drawings, in Figs. 1 and'2 is shown a furnace comprising a rear wall portion 10, a side wall portion 11 and partitions 12 between adjoining furnace portions. Only one furnace portion is shown inthe drawingsd as the furnace portions are, of course, duplicates. The furnace is also provided with a front wall 13 which comprises a substantially vertically extending portion 14 extending to the curved rear end portion 15 of the fiat arch 16 which extends from the forwardly projected portion 17 of the front wall of the furnace to the portion 14 thereof. Thefurnace is also provided witli a baffie wall 18 below the tubes 19, the boiler shown being a vwell known form of water tube boiler and the. furnace construction referred to above being a well known type of furnace construction. The function of arch 16 is primarily to hold and reflect heat upon the entering fuel for the purpose of igniting the same. The space under the arclLis the chief region where the combustible gases ai'e driven ofi', audit is here that combustion of the gases should take place in order to secure the most etfectire use of the space aild of the fuel. By introducing the proper amount of air into the bank of gases and securing turbulence in this hot chamber, the reactionof coinbust ion is carried out quickly and completely with resulting increase of etlciencytand the elimination of smoke formation.

'l`he furnace is shown as being provided willi a mechanical stoker having a chain grate D which may be provided with forced dra-ft means 2t) blowing through the grate and through the hed of fuel thereon. 'l`he bed of fuel is indicated by the numeral 21 in the drawings and, as is well known, the fuel 22 at the end of the stoker, where the same enters the furnace, isinot yet ignited while that intermediate 'the length of the stoker at the region indicated by the numeral 23, is coking and is giving off a large amount of hydro-.carbon gas oi' what 4is known as volatile mat-ter which is highly combustible and renders a very hot flame provided the proper amount of air or oxygen is mixed with the saine to obtain the full heat valuev thereof and a condition'of ignition ismaintained. After the fuel has been thoroughly coked-th'e same is made uplargely of carbon and contains but very little of volatile matter, this condition existing in the region indicated by the numeral 24. The amount of air supplied through the grate at this point is generally in practice more than sufficient for burning the coked fuel.

However, in the region above the portion 23 of the fuel bed where coking occurs and where the volatile matter is being driven off it has been found to be very difficult to supply the proper amount-and distribution of air even where forced draft is provided through the fuel bed as the fuel, of course, offers considerable resistance to the air blast and the ability of the force of the air to cause thorough mixing-of the oxygen with the gasesis lost because the chemical reaction known as combustion taking place due to a flow of air through an incandescent fuel bed is in the presence of an excess of carbon, hydrogen and sulphur, Wherefore it is highly improbable that sulficient oxygen to complete the combustion' could .be forced through the fuel bed itself in the zone 23 Where theie conditions prevail.

This is true because of theyolatile contents of the fuel. The oxy n of the air tends to combine at once witi the incandescent carbon of the fuel bed to form carbon dioxide andto give of hea-t. The heat in turn drives off volatile gases. Hence the faster that heatis liberated the faster Ywill the coal be coked by driving off volatile conmonoxide.

stituents. Since the fuel bed is fairly thick at this point, the carbon dioxide in passing through the incandescent mars of fuel tends to be reduced` at least in part, to carbon loth of these-etl'ccts result in the'formation of large amounts` of combustible gases in the coking region of the furnace. Also, in supplying ail-.through draft openings in the walls of the furnace above the fuel bed where the natural draft of the furnace is depended upon for mixing the air with the volatile matter. it has Abeen found that most of the,air follows' thewalls` of the furnace'toward the smoke vstack following the path of lea-st resistance and the shortest path. Thisl causes a condition where the air is arranged in substantially one stratum while the volatile matter is in another stratum and the same are not properly mixed to obtain the best combustion. lt is -a well known phenomenon that in a flowing tluid there is a tendency for the particles to more in so called stream lines, that is to say, in smooth curves, and the tendency of these particles is, furtliermore, to move in generally parallel lines.

Ditfusion which includes a lateral movement requires time for its accompli-shmeut. lVhere the lateral distance that must be traveled is appreciable, and the velocity fairly high, it can be seen that' the gases may y pass out of the tire-box before diffusion can occur; 1t is because of this fact that the prior art has provided long'ordeep tireboxes in an attempt to prov 1de a length of path great enough to secure the desired lateral travel of the gases to secure diffusion or interminglinv. l

This invention also applies t'o the prevention of smoke, inasmuch as smoke is a distilling out of minute carbon particles in a reducing medium which condition is prevalent to a varying degree in zone 23. The air injection as described above supplies the necessary oxyo'en for consuming this smoke dust and carbon particles Which together are known as smoke, which in itself improves, combustion efficiencywhen air in proper amounts is supplied.

We have provided means whereby the air is injected into the furnace in such a manner as to reach the portion of the furnace above the fuel bed at the coking portion 23 thereof, the air entering in the proper volume and at suolil a velocity that the same penetrate .the bank of combustible gases and vvmixes thoroughly with them. While it has been found to be particularly advanta eous to use this arrangement with 'the nozz es supplying the air under an arch, yet considerable advantage results in any case where the air is su plied under ypressure at a high enough ve ocity` and in pro er volume to cause the same to mix thoroug 1- ly with the combustible gases immediately soy shown in the drawings, comprises an air pressure' box 25 which extends along the front of the furnace and to which air under pressure is supplied by means of the supply pipe 26. A plurality of nozzles 27 is connected with said air pressure box and said nozzles, as will be clear from Figs. 1 and 3, preferably extend at an oblique angle downwardly from a point above the fuel bed toward-said fuel bed so; as to throw a stream of air from the same downwardly toward the upper surface of the fuel bed where the gases are being distilled ofi", said nozzles being directed so as to project a stream of air into the region immediately above' the coking portion of the fuel bed. The nozzles gradually diminish in diameter to a point intermediate the length thereof indicated by the numeral 31, and then again increase to provide a gradually flaring mouth28, as

` will be clear from Figs. 1 and 3, thus causing the airto pass from the same at a high velocity and projecting the air deep into .the furnace, as will be clear from Fig. 1, the stream of air from the nozzle 27 being indicated by the numeral 29. The nozzles 27 are distributed at' substantially spaced distances along the front wall of the furnace, as willbe clear from Fig. 2. In the casewhere a flat arch isused it will be noted that the nozzles are placed very near the bottom face of said arch. The location of the injection nozzles may be variedfrom the position shown as it may be'under certain conditions .advisable to locate them in other relations to the arch and furnace walls than that shown.

It has sometimes been found to also be desirable to inject air at a somewhathigher point into the furnace, particularly Where a furnace of the type shown in the drawings is used, so as to supply additional air to the distilled off gases after the same have risen a .considerable distance above the fuel bed.

This means comprises a pipe or duct 30 lead# ing from the compressed air supply box 25 which is provided with a nozzle 31 which is directed at an oblique angle downwardly intol the furnace, as clearly shown in Fig. 1,

, said nozzle 31 passing through lthe straight wall portion 14 of the furnace above the fiat arch 16 and a slight' distance above the mediately above the bed of fuel in the region where the volatile matter is distilled off.

While a coal burning furnace having a grate is shown in the drawings, it is evident that-air under pressure maybe applied yto the combustion chamber of the furnace vto obtain 'a more uniform supply of oxygen thereiu when other fuels suchV as gas, oil or powdered coal are used. The air may be supplied at room temperature or a higher temperature if desired.

Having thus described our invention, what we desire to claim and secure by United States Letters Patent is: A

y 1. The process'of burning fuel in a closed furnace which consists in moving the fuel in a bed along a definite path through the furnace, igniting the entering fuel, creating a flow of air through the ignitedfuel to support combustion of the fuel in the bed, driving'otf the volatile combustible constituents ficient amount above the fire to support subl stantially complete combustion oftheV volatile combustible constituents, by projecting said air into lthe region of formation of the volatile lcombustible constituents and with sutlicient velocityV to stir the air and combustible 'constituents together thoroughly, and maintaining said stirred air and combustible constituentsV atthe temperature of ignition until the reaction of combustion is substantially. completed.

2. In combination, a furnace equipped with 'an arch, means for maintaining a. travelling fuel bed in the furnace,'mean's for admitting air through `the fuel bed, 'means for projecting. a stream of high velocity 'air into the furnace vabove/the fuel bed forwardly and diagonally downward toward the fuel bed, and below the arch into the combustibley ARTHUR E. GRUNERT. ALEX D. BAILEY.

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