US2730971A - Furnace and boiler plant - Google Patents

Description

Jan. 17, 1956 M. BIRKNER FURNACE AND BOILER PLANT Filed Aug. 29, 1950 I II Ill:

H IJ I I IJI I IQ 112, 0 enter ..5 zLI'nkIz 61 F; 421E 0 l United States Patent FURNACE AND EBOILER PLANT Max Birkner, Koln-Dellbruck, Germany Application August 29, lssmsenal No. 132,075

Claims priority, application Germany September 15, 1949 Claims. (Cl. 110-40) The present invention relates to improvements in a method and apparatus for the burning of solid fuel in boiler plant installations and more particularly to improvements in the method and apparatus described and claimed in my co-pending application Serial No. 123,515, filed October 25, 1949, entitled Burning Solid Fuel as modified by my further co-pending application Serial No. 168,925, filed June 19, 1950, and entitled Apparatus for Burning Solid Fuel.

More particularly this invention is concerned with the regulation and the operation of the boiler plant installation and more particularly to the regulation of the combustion occurring therein and likewise to the adjustment of the combustion to suit the properties of the ash content of the fuel and further, by means of such regulation of combustion to regulate the output of the plant. As clearly set forth in my co-pending applications, the lower portion of the furnace that is beneath the partition means and thus beneath the radiation section comprises two primary furnace areas. ln the lowermost area immediately superjacent the traveling grate the major portion of fuel is consumed in what may be termed more or less coarse combustion which provides for combustion and gasification of the fuel. However, absolute complete combustion does not occur in this furnace portion and in the upper portion of the furnace beneath the partition the complete combustion of the yet unburnt fuel particles occurs in suspension and any particles elevated into this portion from the lowermost portion are gasified into the gases coming from the lower portion. With the furnace operating in such a fashion no regulation or at most rather a coarse regulation of combustion is necessary in the lower portion, that is that area immediately above the traveling grate. However, in the upper portion a very fine regulation to the extent of providing a small excess of air is effected by controlling the CO2 and CO contact of the products within this upper portion.

By thus dividing the furnace area into two portions with a separate regulation of combustion in each, combustion can be effected with the highest efiiciency in a very simple manner and at all boiler loads and firing rates. In connection with this invention 1 utilize a feature known per se in the art for conveying combustion gases back into the furnace. In this connection the return of such combustion gases does not adversely affect the air excess in the furnace gases. The return has an inert effect and is adapted to reduce the furnace temperature and also the intensity of combustion. According to this invention the return of combustion gases provides an additional effect in that it enables the kinetic process of returning incandescentparticles to the lower portion of the furnace to be fully maintained even when operating under a low output, under which conditions the air supply would be reduced.

It is therefore an object of the instant invention to provide for regulation of combustion in the various combustion zones in a furnace of the type referred to in my co-pendiug applications and more particularly to provide for separate regulation of combustion in the various zones. It is an additional object to provide in connection with such regulation the return to the furnace of combustion gases withdrawn from stack areas of different temperatures, and if desired, to mix. with the combustion gases air heated by heat exchange by the gases passing through the stack.

Further and more specific objects will be apparent from the accompanying drawings, in which:

Figure 1 is a longitudinal view partly in section and partly in elevation of a boiler plant embodying the invention,

Figure 2 is a fragmentary view partly in section and partly in elevation taken on line 2-2 in Figure 1,

" is a similar view taken along line 3-3 of Figure 5 Figure l, and

Figure 4 is a fragmentary cross-sectional view taken along the lines 44 of Figure l. y

in the drawings there is disclosed wall means which define a vertically disposed combustion zone including a lower section U, a superposed upper section 0, and a radiation zone is defined above the combustion zone by the wall of the stack 01' tower and by partition means PT which extend transversely through the cross-sectional area of the walls to a difl'user element DP having a sleeve member SL projecting beneath the partition means so that products of combustion from the combustion zone constituted by the superposed sections U and 0 pass through the sleeve SL and are diffused into the radiation section A.

Fuel is fed to the furnace from a hopper H to a conveyor indicated at B to fall by gravity upon the front portion of a traveling grate W. This grate W is movable from front to rear. At the rearmost end of the grate there is provided an ash or slag shaft R for completing the combustion of particles of fuel or coke that may adhere to the ash or slag.

As indicated in my co-pending application Serial No. 123,515, filed October 25, 1949, primary air or oxidizing medium is admitted beneath the traveling grate with the incoming pressure of this air or oxidizing medium increasing from front to rear. Dampers DP are provided in the respective air inlets beneath the grate and the position of these dampers obviously controls the degree of pressure in the areas beneath the grate. Thus the grate portion is divided into three longitudinally aligned portions W1, W2, and W3. The fuel is deposited upon the front portion W1 in the form of a falling curtain of fuel. Under the middle portion W2 the pressure of the introduced medium is sufficient to fluidizethe fuel thereon and under the third or final portion W the pressure of the introduced medium is at a greater pressure so that it will pick up and fling incandescent particles upwardly from the bed to tend to burn these particles in suspension. In the area 0 constituting the upper portion of the combustion zone are provided in superposed banks tertiary air or oxidizing medium nozzles d1, dz, d3, and dr and tr, t2, and ta, as referred to hereinafter. These nozzles, as described in both of my referred to co-pending applications, are tangentially arranged so as to provide a whirling action and burning of particles in suspension. In Figure 4 the uppermost bank of nozzles d1 is depicted. The walls defining the superposed sections are provided with protecting tube walls PTW, PTW1, and PTWz, as described in my copending applications. As shown in the drawing the radiation or cooling section A of the boiler plant is in communication with the upper portion of the combustion zone 0 by means of the diffuser DF terminating in a lower s1eeve-like member SL projecting down into the upper furnace area and terminating beneath the partition PT.

Above the radiation section A of the boiler there is provided feed preheaters SV; and SV: which are in the 3 form of serpentine tubes. and arev spaced alongthe stack or flue ST, and beneath the. lowermost or first preheater is mounted an air heater LI and between the respective feed preheaters' is an air heater L2. These heaters L1 and L2 are connected by a conduit or tube [1. The struc ture thus presents a vertically arranged boiler or stack tower. The vertically arranged structure thus constituting confining means for the products of combustion.

Regarding the regulation of combustion in this boiler and as shown in Figure 1, a cold air blower FG leads air through branch pipes f and g. The pipe f is branched toward the bottom into the superposed branches a and b, the branch a providing primary air or oxidizing medium beneath the grate W and the branch b which is provided with a regulating valve or throttle Z conveys air to the ash or slag shaft R for completing the combustion of any residual fuel or coke adhering to the ash. The main cold air branch g leads to the air heater L where the air is heated by the products of combustion passing through the stack ortower and conveyed through the conduit or tube It to the air heater L2 where its temperature is again raised by heat exchange with the gases or combustion products in the tower. From the air heater L2 air flows through a duct 1' which is divided into two branches i1 and is which are respectively continued by ducts cc and dd as indicated in Figure 2. One of these ducts dd is longer than the other and has extending therefrom ducts c which terminate in tuyeres or nozzles c1 and c2 for the secondary oxidizing medium supply. The tuyeres are located in the rear wall of the furnace, and as described in my said co-pending applications, provide for the projection of the lifted incandescent particles from the rear of the lower portion U of the combustion zone toward the front thereof to intermingle these incandescent particles with the incoming curtai'nof fuel. The shorter'duct cc has plural ducts d extending therefrom and terminating in the tangentially arranged tertiary tuyeres dl, d2, d3, and d4 which supply additional hot oxidizing medium above the fuel bed on the grate for the combustion of fuel and suspension in for the combustion of gases. Valves s and v are respectively provided in the ducts cc, dd. These for example may constitute flap valves pivoted about axes st and v1 respectively andthey regulate the flow through these ducts.

and thus flow to the branch ducts d and c leading to the tuyeres. may each be provided with a valve. An additional branch conduit e provided with a valve x conveys hot air to the fuel supply shaft behind the fuel conveyor B as described in my co-pending application Serial No. 123,515. According to the present invention an additional blower RG is provided for withdrawing combustion gases from the tower. The inlet to this blower'includes a control valve or regulator which provides for separate withdrawing of combustion gases to duct 1 from an area k behind the warm air heater L1 and/ or through a duct n from a point In behind the hot airheater L2. These combustion gases after leaving the blower are conveyed through a duct p to mixing points controlled by the valves s and v. As indicated in- Figure 3, the duct p is branched into branches Pl, p2, which is shown in Figure l merging to the respective ducts cc and dd. It follows that the valves s and v can control flow through the ducts cc, dd so that, as viewed in dotted lines in Figure l, with the valves moved to the left only combustion gases pass from pipe 2 and past the valve through ducts cc, dd or, when the valves are moved to the right, this flow is shut off and hot air flows through the conduit i audits branches i1, i2. With the valves in an. intermediate position a mixture of hot air and combustion gases flows through ducts cc, dd. Thus the valves s and. v are mixing valves and. flow control valves. The duct p is provided with a further branch or conduit (1 which leads combustion gases to the regulator orvalve r disposed in the branch conduit use that, the primary oxidizing mediumfsupplied beneath the: traveling grate W can comprise a mixture of'cold air and warm or Alternatively the individual branches c and d hot combustion gases. Finally, as indicated in Figu e 1, an additional combustion gas branch t provided with a regulator member or valve u extends from the duct 2 in a series of branches leading to the nozzles t1, tz,.and t3 in the upper part 0 of the furnace area, which last mentioned nozzles are arranged in spaced planes between the planes containing the tertiary nozzles d1, d2, ds, and d4.

It is therefore clear that with the structure described the operation of the furnace can be effected so that the incandescent particles picked up from the rear of the grate can be blown toward the front thereof by the medium issuing from the duct c with the same intensity as at full load, even though a low firing rate is utilized. This is effected by maintaining the pressure and speed of the medium flowing through branch duct 0 by adding combustion gases in the duct p when the hot air supply through duct i is cut down. The regulation of oxygen and increase of inert gas in the mixture bring about a slackening of combustion and a reduction of the furnace temperature.

The same regulation effect is applicable in connection with the. tertiary tuyeres for introducing turbulence in the upper part 0 of the funiace. This turbulence separates the ash particles from the gases, as described in my c0- pending application Serial No. 123,515.

It is also possible to throttle the supply of cold air through the traveling grate at low loads. This throttling can be effected by the structure of the present invention without undesirably affecting the kinetic action over the grate, since combustion gases can be admixed with the cold air. Additionally, when the ash content of the fuel is such to require reduction of the temperature in the upper part 0 of the furnace even under high load conditions, this reduction of furnace temperature can be elfected by separate injection of combustion gases only through the nozzles 21, t2, and is communicating with the conduit t.

In all instances of regulation due to the disposition of the regulator member or valve 0, the supply of combustion gases to the blower RG can comprise gases of higher or lower temperature depending on which of the ducts n or I are placed in communication with the blower. This affords an additional means for controlling the temperature in various parts of the furnace. More particularly,

it enables the mixture of combustion gases with hot air,

and which gases have substantially the same temperature as the hot air.

Automatic regulations of the installation can be effected very economically and simply, coarse regulation in the lower part of the furnace being etfected by means of the regulating members u, r, and x which control the supply of combustion. gases over the grate, under the grate and to the. fuel supply respectively. The signal can advantageously be given by the rate of takingsteam. from the boiler, that is, the loading. Suitablev instrumentalities known in the art for signalling the rate of steam withdrawal are utilized to initiate this, regulation. The regulating member or'valveZ in the conduit b does not require any automatic control and can be manually adjusted periodically. This valve controls air flow to the ash or slag shaft R, and an excess or a lack of air in the shaft does not have'any serious effect on the operation of the furnace. This is due to the fact that the gases from this shaft pass upwardly into the lower portion U of the combustion zone and only play a very subordinate part in the combustion. The main function of the air flow through duct b is to assure the burning of any fuel particles that. may happen to accompany the, slag or ash. as it falls into the shaft R. As a desirable feature, the dampers controlling the. under gratev oxidizing medium supply are of the type. which can be adjusted. either manually or semiautomatically by suitable. control means.

The fine regulation in the upper part of the furnace. is advantageously efliecte d independence on the air excess. in; the combustion gases (CO content with complete absence of CO) by actuating the throttle member s, means known in the art being used to determine the air excess in the combustion gases. j

A considerable increase in the economy of this furnace and boiler plant is obtained if the blower pressures are made so high that they suffice not merely to supply the furnace itself with air and gases, but also to drive these right through the whole boiler plant without the interposition of a suction fiue section. If in the normal combustion process due to the high air and gas speeds used at various points there is a substantial pressure above atmospheric which calls for a completely tight enclosure, the pressure in the furnace is increased by the amount necessary to overcome the resistance presented by the heating surfaces above the furnace and to achieve the necessary speed ofdischarge of the combustion gases through the chimney, so that the entire boiler must be enclosed and the pressure increased in the furnace, which is equivalent to a loading even if but a small one, improves the heat intake. The exclusion of inward air leaks in the whole boiler installation also improves the efficiency.

What I claim is:

j 1. A method of burning solid fuel comprising delivering fuel solely by gravity onto the front portion of a fire bed traveling from front to rear of a combustion zone in the form of a free falling downwardly flowing curtain of fuel extending substantially coextensive in width with the width of the combustion zone, introducing oxidizing medium from beneath the bed, increasing the pressure of the introduced medium successively from front to rear of the bed so as to respectively fluidize the fuel on the bed and to pick up and fling incandescent particles upwardly from the rear of the bed, injecting additional hot oxidizing medium at the rear of the combustion zone, above the bed and directed toward the front of the zone to project the lifted incandescent particles from the rear to the front of the bed to intermingle the same with the downwardly flowing curtain of incoming fuel, supplying additional hot oxidizing medium in the form of jets in a plurality of vertically spaced planes above the bed and above the path of flow of the injected hot oxidizing medium and directing the jets to provide turbulence about the vertical axis of the combustion zone at an area above the path of flow of the injected additional hot oxidizing medium to separate fume borne ash from the gases and to burn gases and fuel particles in suspension, and separately regulating the temperature and supply of the introduced medium at all points of introduction.

2. In a boiler plant installation, the combination of means defining a vertically disposed combustion zone constituting a lower and an upper section, means defining a communicating radiation zone above the upper section of said combustion zone including apertured means through which combustion gases pass, nozzles directed into the upper section and arranged tangentially to a common circle about the axis thereof, a stack tower extending above said radiation section, heat exchange means in the tower above the radiation section for heating air by heat exchange with the combustion gases issuing from said radiation zone, means for drawing oft combustion gases from spaced areas above said radiation section, and means for mixing the heated air and the combustion gases including conduit means conveying the mixture to said nozzles and means for regulating the proportion of the mixture.

3. In a boiler plant installation as defined in and by claim 2, wherein the means for drawing ofl combustion gases includes conduits communicating with the tower at the spaced areas, said areas having considerably dif ferent temperatures therein and the means for regulating the proportion of the heated air and drawn-off gases includes means for regulating the proportions of different temperature combustion gases to be mixed with the heated air.

4. In a boiler plant installation the combination of means defining a combustion zone, said zone constituting a lower and an upper section, means defining a radiation section above said zone, a traveling grate movable from front to rear beneath said lower section, means for feeding solid fuel to fall by gravity upon the front portion of said grate, means for supplying air beneath said grate at pressure increasing from the front to the rear thereof, nozzles above the grate and directed toward the front thereof, means for confining combustion gases leaving the radiation section,heat exchange means within said confining means for heating air by heat exchange with the combustion gases, means for drawing off cornbustion gases from the confining means at at least one area above the radiation section, means for mixing heated air with the drawn-oif gases including conduits cornmunicating with said nozzles and means for regulating the proportions of heated air and drawn-off gases discharged through the nozzles.

5. In a boiler plant installation as defined in and by claim 4, wherein the means for drawingoif the combustion gases comprises conduits communicating with the confining means at areas of considerably difierent temperatures, and regulating means regulating the pro portion of the drawn-01f gases of different temperatures to be admixed with the heated air.

6. In a boiler plant installation the combination of means defining a combustion zone constituting superposed lower and upper sections, means defining a radiation section above said upper section, a plurality of superposed spaced series of nozzles directed into the upper section tangentially of a common circle about the axis of the combustion zone, confining means for confining combustion gases to discharge in a path extending above said radiation section, heat exchange means located within said confining means for heating air with the combustion gases, means for drawing off combustion gases including at least one conduit communicating with the confining means, said last mentioned means includ ing further conduits communicating directly with at least.

some of said nozzles so that the same discharge only combustion gases into the combustion zone, and means for mixing heated air and drawn-01f gases including conduits communicating with others of said nozzles for discharging a mixture of heated air and gases into said zone, said last mentioned means including means regulating the proportion of drawn-off gases and heated air.

7. In a boiler plant installation as defined in and by claim 6, in which the means for drawing off combustion gases includes conduits communicating with the confining means at areas of considerably different temperatures and means for regulating the proportion of combustion gases of different temperatures.

8. A method of burning solid fuel in a vertically extending combustion zone having an upper outlet and a fire bed travelling from front to rear thereof at the bottom of the zone and which fire bed embodies plural aligned portions including at least front, middle and rear portions comprising continuously dropping solely by gravity all fuel to be burnt upon the front portion of the fire bed from an inlet in the front of the zone at a height substantially midway of the height of the zone in the form of a falling curtain of fuel of narrow extent with relation to the direction of travel of the bed and of a width substantially coextensive in width with the width of the zone, introducing primary oxidizing medium under pressure from beneath the bed under all portions thereof, increasing the pressure of the medium introduced under the middle portion of the bed to a pressure suflicient to fluidize and stir the fuel thereon and to elevate fine incandescent particles therefrom, increasing the pressure of the medium introduced under the rear portion of the bed to a pressure higher than that required for fluidization and sufficient to elevate and fling fuel particles and larger incandescent particles upwardly from the bed, supplying additional oxidizing medium above the rear portion of the bed in the form .at a level beneath the fuel inlet and under a pressure sufiicient to entrain and project the fuel and incandescent particles elevated from the bed across the bed to the front of the zone to intermingle the same with the incoming curtain of fuel, and to provide a horizontal stream substantially throughout the zone separating the same into a coarse combustion zone portion beneath the .stream and a combustion completing portion above the stream, and supplying still additional hot oxidizing medium above the bed and above the inlet in the form withdrawal and varying the temperature and quantity of a the medium introduced through the jets in dependence upon'the air excess in the combustion gases.

10. A method of burning solid fuel as claimed in 7 claim 1, in which a mixture of hot air and combustion gases are injected through the jets, supplying additional 'of jets directed to provide turbulence about the vertical axis of the combustion completing portion of the comcombustion gases in the form of additional jets arranged in a plurality of vertically spaced planes, each of said planes being between the planes containing the first mentioned jets and directing the last mentioned additional jets to provide turbulence about the vertical axis of the combustion zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,624,908 Bowman Apr. 19, 1927 1,678,827 Schillinger July 31, 1928 1,713,817 Cotton May 21, 1929' 1 ,714,678 Kreisinger Aug. 28, 1929 1,771,989 Barker- Aug. 5, 1930 1,8l9',174 Jacobus Aug. 18, 1931 1,829,996 Lysholm et a1. Nov. 3, 1931 1,837,713 Jacobus Dec. 22, 1931 1,863,541 Lucke June 14, 1932 1,898,479 Coghlan et' a1 Feb. 21, 1933 1,943,949 Coghlan et a1 Jan. 16, 1934 2,216,809 Derby 4-0 Oct. 8, 1940 2,380,169 Gygi July 10, 1945 2,424,587 Smith et a1. July 29, 1947 2,483,728 Glaeser Oct. 4, 1949 FOREIGN PATENTS 302,471 Great Britain Dec. 20, 1928 342,885 Italy Aug. 26, 1936

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