US2544884A - Steam generator - Google Patents

Description

March 13, 1951 e. P. JACKSON 2,544,884

STEAM GENERATOR Filed Aug. 16, 1944 6 Sheets-Sheet 1 v INVIfiNTOR Egg; rib,

ATTORNEYS March 13, 1951 Filed Aug. 16, 1944 G. P. JACKSON STEAM GENERATOR 6 Sheets-Sheet 2 jimm ATTORNEYS March 13, 1951 Filed Aug. 16, 1944 e. P. JACKSON 2,544,884

STEAM GENERATOR 6 Sheets-Sheet 3 ATTORNEYS March 13; 1951 e. P. JACKSON 2,544,884

STEAM GENERATOR Filed Aug. 16, 1944 6 Sheets-Sheet 4 TOR 7 ATTORNEYS March 13, 1951 a. P. JACKSON STEAM GENERATOR 6 Sheets-Sheet 6 Filed Aug. 16, 1944 LilLikll lillllll Illll IN 45a BY F v ATToRNEYs Patented Mar. 13, 1951 STEAM GENERATOR George P. Jackson, Flushing, N. Y., assignor to Combustion Engineering-Superheater, Inc., a

corporation of Delaware Application August. 16, 1944, Serial No. 549,719

. f This invention relates to steam generators and particularly to those operating at high capacities and under high pressures. It is a continuation in part of my application Serial No. 499,530, filed August 21, 1943', now abandoned.

It has long been recognized in the steamgen- I circulation equipment far outweighing the savings effected in the steam generating plant' proper by the use of the forced circulation, not to mentionthe high cost of maintenance. In other words, the cost of such, installations has been much higher than the cost of an installation of the same capacity and pressure designed to secure adequate circulation by natural circulation. There have been many proposals in the art which have never gone into use because, although, the cost of the circulation equipment was not excessive, they were ineffective for one reason or another. Therefore, natural circula tion systems have been generally employed in high pressure boilers, despite the fact that they are very sensitive and subject to circulation interruption and overheating.

To the best of my knowledge, I am the first to provide. an arrangement whereby adequate circulation can be provided not only at low cost of initial installation but also with low cost of maintenance. Stated. in another way, I believe that I am the. first to provide an installation with cir ul ion e uipm nt at a co u .very sl g t y inexcessof e o t oia installation of th .same capacity and. pressure having adequate natural circulation. Moreover, in myinvention the costs of maintenance are very low.

In carrying. out my invention, I employ the feed water to operate the pumps for augment.- ing the natural. circulation. I have discovered that if I combine this with a boiler operating at. a pressure of substantially 900 lbs. per square inch upward (but short. of critical pressure) I will be enabled to increase the circulation and secure. a, ratio of. water .to. steam, such as will protect the tubes against unduly high temperatures and consequent internal stresses, while at the same time I am enabled to use much smaller tubes than would be required if natural circulation alone were relied upon, which, in turn,

p 2 Claims. (01. 122-4 11) means that the weight and the cost of the boiler installation is greatly reduced. So much so is this the case, that the cost of my improved installation, inclusive of the circulating equipment, will be only in the neighborhood of about 2% to about 2 /2% more than the cost of the same installation constructed on the basis of natural circulation. The advantages gained far outweigh this relatively slight increase in cost. In the combination, I also employ a type of boiler in which by far the greatest portion of the steam is generated by evaporating surfaces subject to radiant heat, the amount of convection surface,

any, beingrelativel-y small so that, at best,

only a relatively small portion of the steam generated is generated from surfaces subject to convection heat. The invention is practically only applicable to boilers of relatively high pressures where the heating surfaces of the furnace generate the major portion of the steam, and where the ratios of requisite water circulated to steam generated become relatively low. I have discovered that for such boilers the feed water can be economically used to drive the augmented circulation pumps efficiently.

In the accompanying drawings I have shown an installation, designed for approximately 1400 lbs. pressure per square inch and a capacity of about 500,000 to 550,000 lbs. of steam, as illustrative of how my invention may be employed.

In these drawings:

Figure 1 is a vertical section through a steam generator embodying my invention, the same being taken onthe line l-l of Figure 2; I

Figure 2 is a rear elevation of the steam generator, showing in greater detail, the means for augmenting the natural circulation;

Figure 3 is an enlarged vertical section through the circulator pump employed in carrying out my invention; i

Figure '4 is a sectional view Figure 3 butillustrating a modified form of circulation pump; and

Figures 5 and 6 are more or less diagrammatic views illustrating modifications of the hook-up shown in Figures l and 2. u Referring now to Figures 1 and 2, the furnace I is provided withthe usual fuel burners 2 (such, for example, as 'powderedco'al, oil or gas burners) which project through the front wall.

The front, rear and side walls of the furnace are faced or lined with water wall tubes 3 such, for'example, as 2" tubes on about 2 /8" centers, swedged or stag ered at the bottom and the top for connection to the headers to bev described.

similar to that of a It will be seen that these tubes are relatively small diametered, long, tubes of relatively thin wall thickness as compared with the tubes customarily employed in a natural circulation boiler of corresponding pressure. (From the floor level to the center line of the boiler is 88' 9", in the installation shown.) Assuming a pressure of 1400 lbs. p. s. i., the tubes customarily employed in a natural circulation boiler would be approximately 3" in diameter on 3 centers. The wall and roof tubes in my boiler are subject to radiant heat.

The side water wall tubes 3 are connected at their bottom ends to headers 4 and 5 which are in turn connected to the drum or large header 6 by means of tubes 1 and 8. The front and rear water wall tubes 3 are connected at their bottom ends to the drum 6. Thus drum or header 6 serves as a common supply for all of the water wall tubes.

All of the wall tubes 3 deliver into the steam and water drum 9; the front wall tubes via the radiant heat screen tubes In which shield the superheater l5, the rear water wall tubes via the radiant heat roof tubes II, and the side water wall tubes via headers l2 and tubes 13.

The products of combustion leave the furnace I through the offtake [4 after first passing over the screen tubes l0 and the suspended superheater 15. Upon leaving the offtake Hi the combustion gases pass downwardly through flue 1-8 in which is suspended a superheater l1, and thence pass upwardly through flue IS in which the economizer I9 is hung. Optionally, for reasons which will hereinafter appear, a secondary economizer or evaporator 20 may be placed in the flue [8 in advance of the economizer i9 with respect to gas flow.

Suspended from the steam and water drum 9 and connected therewith are a plurality of socalled downcomer tubes 2| which are connected to a plurality of pumps 22, as will further appear. (For this installation, four 10" tubes 2| are employed.) The pumps 22 discharge into 10" tubes 23 which are connected to the drum 6. As will further appear, the pumps 22 augment the natural circulation of the boiler producing what may be termed an augmented natural circulation boiler.

Referring now to Figure 3, the construction of the pumps 22 will now be described. This pump is hydraulically driven and comprises a turbine or an impeller wheel 24 mounted to rotate with shaft 25 within the housing 26. Peripherally surrounding the wheel 24 is an inlet volute passage 21 and axially adjacent to the wheel 24 is an outlet conduit 28. Fastened to the wheel housing 26 through the medium of flange 29 and flange 32 and bolts 30 is a pipe elbow 3!. The vertical leg 33 of the elbow 3| is fitted with a sleeve 34 within which the water pump propeller 35 rotates with the shaft 25 driven by the wheel 24. A cage 36 is supported concentrically with shaft 25 by means of the flange 31 which is clamped between flanges 29 and 32. The cage 36 is so formed as to support bearings 38 and 3811 which in turn position and support the shaft 25, wheel 24 and impeller 35. The free area in sleeve 34 which surrounds the impeller is relatively large. The vertical leg 33 of the elbow is connected to one of the pipes 23, and the horizontal leg to one of the downcomer pipes 2 I.

When fluid under pressure is delivered into the volute passage 21 it reacts on wheel while flowing therethrough, causing it to rotate, after which it is discharged through outlet conduit 28. For operational reasons which will later appear, a check valve 39 is located in the horizontal portion of elbow 3|.

The means for supplying fluid pressure for driving the pump will now be described, reference being had to Figures 1 and 2. The boiler feed pump 48 which may be of the conventional construction ordinarily employed in feed water pumps is connected by a pipe or pipes 49 to the header 50 which is in turn connected by means of pipes 5| to the volutes 21 of each of the pumps 22. Thus the boiler feed water discharge from the feed water pump enters the volutes 21, drives the wheels 24 and leaves through the outlet conduits 28, each of which is connected by means of a pipe 5 la to a common header 52. This header 52 in turn is connected by a pipe orpipes 53 with the economizer 19. Thus the feed water, after having performed its T'function of driving the pumps, is led to the economizer and after passing through the economizer, it flows through pipe or pipes 54 into the boiler drum 9. 1

Since each of the downcomer tubes 2! leads .to a pump 22 (specifically to the horizontal leg of the elbow 3| of each pump), the pump propellers augment the natural circulation by forcing the water in downcomers 2| into the header 6 (through pipes 23 connected to the vertical leg 33 of the elbows 3|), and from. header 6 through the tubes which connect the water wall tubes 3 with header-B. v V

Thus the boiler has augmented natural circulation. At from approximately 900 lbs. p. s. i. and upward in boiler pressure, I have found that the feed water driven pumps will augment the circulation to the point that the ratio of water to steam entering the boiler (say about 10 to 1 at 900 lbs. with decrease as pressure rises), will adequately cool the tubes. At such pressures per square inch, the pumps are so eflicient that the desired results can be obtained with a feed water pump but slightly larger than would be employed where the natural circulation is not augmented.

In this connection. feed water pumps are designed to operate at a pressure somewhat in excess of the boiler pressure, usually somewhere about 200 lbs. in excess. For example, at 1400 p. s. i., I need a feed water pump giving about 10% higher excess than customary or about p. s. i. excess.

It will be seen that the hydraulic motors, the water pump propellers, and the interconnecting drive means, are wholly contained within the fluid circuit pressure parts, as are the bearings for the drive means. Inasmuch as there is greater pressure in the volutes 21 than exists in the elbow 3|, the bearings will be lubricated by the feed water, which is clean. To this end the holes 2411 are provided. Thebearings may be made of any suitable bearing metal. There are no stuffing boxes.

It will be evident that the pum s are of simple, inexpensive construction. and will have relatively long life. As stated, well known forms of feed water pumps of at most but slightly greater power than customary. may be employed. Hence it will be seen that I have provided an installation for augmenting the natural circulation, the cost of which and the maintenance costs of which are very low. This coupled with the fact that I am thereby enabled to use small diametered evaporating tubes of thin wall thickness, produces a high pressure installation of relatively low weight and cost as comparednwithhigh pressure natural circulationboilers.- The use of radiant heat tubes in the boiler which produce by far the most (or all?) ofthesteam generated, also tends toward In the event that the temperature of the gases passing upwardy through fiue I8 is so high that steam may occur in the lower tubes of the economizer l9, it may be desirable to include the secondary evaporating or economizer surface in order to moderate this temperature and to ensure the absence of any appreciable amount of steam. Where such a secondary economizer is used, a circuit is provided from drum 9 through the evaporator and back to drum 9, as, for example, by means of pipes 55, 51 and 58 shown in Figure 2. Since the resistance of such a circuit would be relatively high, I place a circulating pump 55 in this circuit (see Fig. 2), which pump is a duplicate of the pumps 22 hereinbefore referred to. This pump 55 would be supplied with feed water for driving the motor thereof by means of pipe 59 leading from header 50, and the feed Water discharged from such pump would be led to header 52 by means of the pipe 60.

Again referring to Fig. 2, a feed water regulating valve 5| is placed in the pi e 53 leading from the header 52. In order to maintain circulation by means of the pumps 22 and 55, when the feed water regulating valve 6! is partially or completely closed, I provide a relief valve 62 connected by pipe 63 to the suction side of the feed water pump as or to some other suitable point in advance thereof, such as to a feed water heater in advance of the feed water pump.

Since all pumps 22 run in parallel, and should one of the pumps fail to rotate, the water from drum 6 being maintained under the pressure of the remaining pumps 22. mi ht flow upwardly through a pipe 23 and through the pump that failed, which might disturb the circulation. It is for this reason that check valve 39, hereinbefore referred to, is located in the horizontal leg of elbow 3| of each pump. Should such a reverse flow as described occur through failure of a ump, its check valve 39 would close and stop such flow.

It may be desirable to divide the interior of drum 6 into compartments 64 by means of partitions 65 whereby each compart ent will be served by one of the pumps 22 via the respective connection 23. In this way the amount of flow to these water walled tubes connected to the respective compartments 64, may be regulated by varying the speeds of the respective pumps. This would be of advantage in ca e that some of the groups of wall tubes 3 are heated to a greater extent than others and would therefore require proportionately more water in their circuit. Regulation of the speed of the respective pumps may be had by regulating the valves shown in the pipes 51a which lead from the pumps, which valves can be used to control the amount of feed water passing through each pump and therefore the speed of the pump.

The pump shown in Figure 4 is substantially the same in construction as that shown in Figure 3, except that the wheel 24 is inverted and the outlet 23 of Figure 3 is omitted. In Figure 4 the outlet 46 is formed in cage 4! and the fluid leaving the wheel 24 flows downwardly through outlet and joins with the water coming from the downcomer tube 2| into elbow 3| on its way to the pump propeller 35. Optionally, the dis.- charge of fluid from outlet 28 of Figure 3 may be connected into the elbow 3| on the inlet side of the impeller, with respect to the direction of the fluid flow.

Optionally, the boiler feed pump may be. connected directly to the economizer in the usual fashion, and the discharge from the economizer -connected into the header 50. The header 52 would then be directly connected to boiler drum 9. This arrangement is shown in Figure 5. Such a hook-up would be particularly applicable in case the pump of Figure 4 were employed as illustrated in Figure 6. Thus in Figure 6 the header to the pump 48, with a relief valve 62.

The secondary evaporator surface 20, shown in Fig. 2, may be advantageously applied to Figs. 5 and 6, in the event that the temperature of the water leaving the economizer IQ for the pumps 22 should be heated to a steaming temperature and found to be undesirable for use in said pumps.

While the invention is particularly applicable to high pressure boilers of the order of 1800 lbs. or more p. s. i. it may be used to advantage in any natural circulation boiler of about 900 lbs. p. s. i. or more, wherein the capacity and pressure are such, in the absence of my improved augmentation, as would compel the use of relatively large thick walled tubes.

Since numerous changes may be made without departing from the spirit and scope of the invention, it is to be understood that the above description and the drawings are to be interpreted as illustrative and not limiting.

I claim:

1. In a high capacity steam generating unit, the combination of a natural circulation boiler of the type in which the steam is generated at least in ma or part in a multiplicity of generally vertical boiler tubes subject to radiant heat and which has a steam and water drum, said boiler operating at a pressure of about 900 lbs. p. s. i., and upward, but short of critical pressure, a downcomer lea-ding from the drum, 2. pump for augmenting natural circulation located in said downcomer, a water turbinefcr driving said circulation pump during steam generation, a feed water pump operating at a pressure exceeding the sum of the boiler pressure and the pressure drop through the turbine, a first line for delivering feed water from the feed water pump to the turbine inlet, and a second line for delivering feed water from the turbine outlet to the boiler at a rate equal to the rate of steam generation.

2. In a high capacity steam generating unit, the combination of a natural circulation boiler of the type in which steam is generated at least in major part in a multiplicity of generally vertical boiler tubes subject to radiant heat and which has a steam and water drum, said boiler operating at a pressure of about 900 lbs. p. s. i., and upward, but short of critical pressure, a multiplicity of downcomers leading from the drum, a pump located in each downcomer for augmenting natural circulation, means for checking the upward flow of water in each of said downcomers, a water turbine for driving each pump during steam generation, a feed water pump operating at a pressure exceeding the sum of the boiler pressure and the pressure drops through said turbines whereby to provide discharge of water from said turbines at a pressure exceeding said boiler pressure, first lines Ior delivering feed water from the feed water pump to 8 REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 4 Number Name 7 Date 744,341 Hodge Nov. 1'7, 1903 1,109,882 Tull Sept. 8, 1914 1,859,857 Whittam May 24, 1932 2,296,426 Coutant Sept. 22, 1942 Frisch Aug. 13, 1946 the turbine inlets, and second lines for deliver- 1 ing feed water from the turbine outlets to the boiler at a rate equal to the rate of steam generation. GEORGE P. JACKSON.

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