US2363875A

US2363875A - Combustion zone control

Info

Publication number: US2363875A
Application number: US420356A
Authority: US
Inventors: Kreisinger Henry; Virginius Z Caracristi
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1941-11-25
Filing date: 1941-11-25
Publication date: 1944-11-28
Anticipated expiration: 1961-11-28

Description

NOV. 28, 1944. H KRElslNGER TAL 2,363,875

COMBUSTION ZONE CONTROL 3 Sheets-Sheet l Filed Nov. 25, 1941 fof NOV- 28, 1944. H. KRElslNGER r-:TAL 2,363,875

COMBUSTION ZONE CONTRL Filed NOV. 25. 1941 5 Sheets-Sheet 2 IN V ENT 0K5 HTTORNEY Nov'. 28, 1944. H. KREISINGER r-:T AL 2363875 COMBUSTION ZONE CONTROL'V 'Filed Nov. 25, 1941 v 5 Sheets-Sheet 3 lNlfEq/ToRs @my Krezsngge WI/4r mms Z. faraffh v mmm/EY Patented Nov..-28, 1944 UNITED STATES PATENT oEFlcE COMBUSTION ZONE CONTROL Henry Kreisinger, Piemont, and Virginlus Z. aracristi, Bronxville, N. Y., asslgnors to Combustion Engineering Company, Inc., New York,

Application November 25. 1941. Serial No. 420,356

2 Claims.

This invention relates to an improvement in the regulation of the temperature of steam leavingv a superheater. It is particularly applicable to a superheater so located in a boiler that substantiallyall of the heating effect is by convection from the products of combustion from a furnace whose walls are lined with water cooled surfaces and in which turbulent ring is employed.

It is well known that in the operation of such a steam generating unit the temperature of the superheated steam varies with fluctuations in steam output, a reduction in superheat occurring with a reduction in rating. Because this is undesirable various means have been devised to correct for steam temperature variations.

One method. of regulating the temperature of superheated steam is to cause a variation in the heat absorption within the furnace from the fuel burnt therein so that the gases passed over the superheater surface are at a temperature capable of producing the desired degree of superheat. A method of this nature is dis closed in the patent to Kruger, No. 2,243,909, of June 3, 1941. It has been found, however, that Krugers method is inadequate to meet the large variations of superheat control now required in boilers of great steam generating capacity and, accordingly, it is an object of this invention to provide an improved method of regulating'the heat absorption within the furnace so as to obtain the desired steam temperature from the superheater.

How the foregoing together with other objects and advantages as may hereinafter appear or are incident to our invention are realized is illustrated in preferred form in the accompanying drawings wherein:

Figure 1 is a sectional elevation of a steam generating unit embodying the invention;

Figure 2 is a sectional elevation showing a modifled form for the lower part of the furnace of Fig. 1;

Figure3 is an enlarged vertical sectional View through a typical set of fuel burners shown in Fig. 1; I l

Figure 4 is a horizontal schematic view, taken through the furnace on the line 4-4 in Fig. l; and

Figure 5 is a vertical sectional view of a modifled form for the burners shown in Fig. 3.

In Figure l the boiler illustrated includes a lower water drum I0 and upper steam and water drum II interconnected by steam generating tubes I2. A superheater I3 receiving the saturated steam generated is located in the llrst pass of the boiler and balilesA I4 and I5 cause the gases from the ofltake of furnace I6 to pass serially over superheater I3, a tube bank I I and on to the boiler offtake.

In Figure 1 the furnace IB has its walls lined with water cooled tubes 20. The bottom of the furnace is suitably constructed to 'retain slag in a fluid condition, the slag overflowing through an opening 2l. Near the bottom of the furnace burners 22 are arranged preferably at the corners as illustrated in Fig. 4.

In Figure 2 the lower part of the furnace BBA has two opposed sides sloping toward a throat 23 and Afaced with water cooled tubes fil. The two remaining side walls also are lined with water cooled' tubes extending downwardly to the throat 23. 'I'he bottom and side walls above the throat thus form a water cooled hopper into which ash particles, gravitating from the fuel burning within the furnace, fall and, while falling, cool to a state in which they will not adhere to the sides of the hopper. The burners 22 in Fig. 2 are arranged somewhat above the hop- 25 per bottom and, as in Fig. 4, preferably at the corners.

Figure 4 shows the burners 22 arranged at the corners of the furnace projecting their streams of fuel and air into the furnace in directions tangential to the surface of an imaginary cylin-l der "C located vertically in the furnace, preferably in its center. Each set of burners in Fig. 1 discharges three fuel streams into the furnace while each set of burners in Fig. 2 disl end of section 32. The tip 34 and section 33 are formed at their juncture into a cylinder and sockl et joint. The nozzle tip 34 is rectangular and located within and connected to a tubular air deflecting vane 36, the whole, when turned up. wardlv or downwardly directing the fuel and air stream accordingly. The tip 34 and vane are rotated by means of a. rod 31 connected at one end to the tip by an arm 40 fixed to a. pin 4I.

At its other end rod l1 carries apin 4I located in the slot 44 of a cam 45. The cam 45 is mounted by a in 46 on a vertically movable bar 41 so it may ro te. An adjusting screw 48 which holds cam 45 at a. suitable angle with respect to bar 41 is fixed in its longitudinal movement by pivot block'll hinged. to the bar 41 by pin 50a. The screw 48 may be adjusted to draw the lower end of cam 45 closer to, or push it away frombar 41, thereby changing the angularity of the cam with respect to the fbar. 'I'he bar 41 is limited to vertlcal movement by bearings El. A change in angularlty of the cam 45 changes the movement of related connecting rod 31 and the fuel nozzle tip 34 connected thereto. As shown in the drawings, the pin 43 is in mid-position in slot 44 and the connecting rod 31 holds the tip 34 in position for horizontal discharge of the fuel and air. When the bar 41 is moved down, carrying cam 45 with it. the tip 34 directs the fuel and air stream upwardly. Conversely an upward movement of bar 41 directs the fuel and air stream downwardly. The ba:- 41 may be moved to adjust the nozzle tip by a motor controlled from the switchboard for firing control.

Above and below each fuel nozzle 3l there are pivoted air deilectors 60 that may be turned to direct the air horizontally, upwardly or down.- wardly. As shown, deectors are interconnected in pairs and operating rods Bl are provided, the construction, operation and adjustments for the respective deectors being the same as that dei scribed above for rotating the nozzle tips 34.

' Figure 5 shows a modified form of the end section for the nozzle. The nozzle end section SIA itself is formed to direct the fuel and air stream upwardly at half of the maximum angle through which the tip 34A moves from the horizontal. For example, if the tip 34A is movable through 45 deg., the inner end of section 3lA is turned upwardly 22% deg. This construction permits a greater vertical angle of discharge for the fuel and air stream and yet provides a relatively smooth flow through the fuel nozzle for all angles.

The construction shown in Figure 5 may advantageously be used in a slagging bottom furnace such as shown in Figure 1. In this adaptation three fuel burners are shown, the upper two of which may be made adjustable upwardly to an angle of 45 deg. while the bottom one may be .adjustable 22l/2 deg. from the horizontal both.

upwardly and downwardly as provided for in Figure 3.

It is contemplated that the fuel nozzles may in addition be adjustable horizontally as is shown in the patent to Kruger mentioned above.

In operation when all of the burners are adjusted to project the fuel and air stream in a "l` substantially horizontal direction tangent to the imaginary vertical cylinder C located centrally of the furnace, the burning fuel streams issuing from the four sets of corner located burners impinge upon one another resulting in a turbulent, rotating mixture with a consequent rapid rate of combustion. This rapid combustion produces a very high temperature in a zone A at the level of the burners near the bottom of the furnace so that there is a high rate of heat transfer from the flames to the water cooled wall tubes 20 in this zone both by radiation and by convection. Leaving this zone the hot products of combustion pass 4upwardly and continue giving off heat to the water cooled walls thereabove and exit from the furnace at a relatively low' temperature. When all of the burners are directed upwardly ascas'ns the streams of fuel are still tangent to an imagmary vertical cylinder in the furnace but the lmpingement of ne burning fuel streams upon one another is much less than when the burners are horizontally directed as above described. This results in but relatively little mixing and turbulence and consequent slower or delayed combustion. This delayed combustion occurs in a zone B, that is located higher in the furnace than the zone A, and extends well into the upper part of the furnace.' Consequently the temperature 'of the products of combustion leaving the furnace is relatively high because of the shorter path through which they pass from the combustion zone to the outlet of the furnace and because tbe heat transfer from the flames to the water cooled walls at the bottom of the furnace is substantially less than with horizontally directed streams. The change in the direction of the fuel streams from the horizontal to an upward inclination results in a. rise in the temperature of the gases leaving the furnace which has been found adequate to change the rate of heat absorption by the superheater I3 so that the steam temperature may be raised to that required for satisfactory operation over a. greater range of ratings of the steam generating unit than heretofore attainable.

This invention in effect reduces the size of the furnace at the lower ratings of the steam generating unit, where lthe temperature of the superheated steam is relatively low. For example, at half rating about half of the maximum amount of fuel that may be burned in the furnace is delivered to the furnace near the bottom and burned there in zone A; the products of combustionlikewise are about half and dwell within the furnace and are exposed to the cooled walls about twice as long as at full rating. The exit temperature of the gases may then be too low for superheating the steam to the temperature desired. By raising the zone of combustion within the furnace and delaying combustion by decreasing turbulence, the dwell of the products of combustion within the furnace is reduced as is the area. of cooled furnace walls exposed to the gases.

In Figure 2 the burners are located higher than in Figure l and the zone of most intense combustion may be moved below zone A to zone D, thereby increasing the range through which said zone of combustion may be moved vertically in the furnace. y

According to the invention. not all of the burners need be adjusted to a vertical angle; for example, the two upper burners 22 of each set may be so adjusted while the lower burner may be horizontal.

Any or all of the burners may also be made to be both vertically and horizontally adjustable. When the furnace is operated with a layer of 'molten lfluid slag on the furnace floor, it may bs advantageous to maintain the bottom burners in position to direct the flame streams horizontally or even downwardly over the slag so as to maintain it in a huid condition throughout the lower furnace' while the upper burners are used to control the superheated steam temperaof the furnace from a plurality of points remote from the furnace outlet in such directions as to create a turbulent gas mass burning in a zone in the lower part of the furnace to transmit heat to the water tubes therein; maintaining, for a given load, a substantially uniform rate of fuel firing; and altering the angle to the horizontal of the direction of the streams of fuel and air so as to lower or raise the vertical location of the combustion zone along the furnace axis as the. superheated steam temperature respectively increases or decreases to thereby alter the length of the path of gas travel through the furnace and the extent to which gases are cooled before reaching the superheater.

2. The method of regulating the temperature of steam derived from a superheater receiving its heat mainly by convection from gases flowing from the outlet at the upper part of a vertical furnace whose walls are lined with water circulating tubes comprising; introducing fuel and air into the furnace from a multiplicity of points near the bottom of the furnace and in directions substantially tangential to an imaginary vertical n cylinder located centrally in the furnace for creating a turbulent rotating gas mass in\a zone 1ocated in the lower portion of the furnace to transmit heat to the water tubes therein; maintaining, for a given load, a substantially uniform rate of fuel lring; and, as the supherheated steam temperature increases, decreasing the vertical angle of the directions of fuel introduction relatively to the furnace walls to thereby increase the extent to which gases are cooled before reaching the superheater.

HENRY KREISINGER.

VIRGINIUS Z. CARACRISTI. l