US1773088A - Power plant - Google Patents

Description

Aug. 19, 1930. w. H. ARMACCVJST POWER PLANT Filed Jan. 5, 1928 2 Sheets-Sheet l A TTORNEY.

Patented Aug. 19, 1930 UNITED STATES PATENT OFFICE WILBUR H. ARMACOST, OF NEW YORK, N. Y., ASSIGNOR TO THE SUPERHEATER GOM- IPANY, OF NEW YORK, N. Y.

POWER PLANT Application filed January 3, 1928. Serial No. 244,180.

This invention relates to steam power plants and is concerned particularly with reheating the steam coming from a high pressure turbine. The present day trend is toward steam pressures of the order of v1300 to 1400 lbs. per square inch. This steam is of course superheated before being used inthe turbines or other prime movers. On account of the limitations imposed by the materials of which the superheater, the turbine, the valves and other parts are made, the total temperature to which this superheating can be carried is in the neighborhood of 750 F. With an initial pressure of 1350 pounds per square inch the superheat will disappear by the time the steam has been allowed to expand down to 300 or 400 lbs. of pressure. Should the steam be used expansively from this point on without reheating it, the presence of the moisture that won d be precipitated would more than offset the economy gained by the initial high pressures. It is therefore essential that the steam after having expanded down to the point mentioned be reheated.

One way in which this reheating is accomplished is'by carrying it back to a reheater located in the boiler setting itself. The reheater may be exposed to the radiant heat in the fire-box or it may absorb its heat from the current of hot gases somewhere in the setting beyond the fire-box. My invention relates to the case where the reheating is done in a reheater of the first class mentioned, that is, in a reheater absorbing its heat by radiation in the fire-box. The characteristics of these so-called radiant type superheaters or reheaters are well known and one of their leading features is that. as the rating of the boiler is raised, that is, as the firing is increased because the load is heavier and the boiler has to supply more steam, the steam passing through the radiant superheater or reheater is heated to a lower degree.

In some plants using these high pressures, the exhaust from the high pressure turbine is led to a main to which steam from other boilers operating under lower pressure is also carried. The pressure in these mains is of course kept as nearly constant as possible and the high pressure turbines therefore exhaust against what is practically constant back pressure. In other plants, and this will be true particularly of plants in the future which are independently designed and not designed to supplement existing low ressure power plants, the exhaust from the liigh pressure stage is used directly in a low pressure stage. The back pressure for the high pressure turbine may vary considerably in such installations. The variation may in some cases be as much as 200 lbs. which may correspond to a temperature variation of 8090 F. In other cases it may vary to a slighter degree. Where the load on the plant is comparatively constant, this variation may remain within quite narrow limits.

In those plants where the variation spoken of is large, a radiant type reheater of the ordinary type may be the best one to use. This is true because the characteristics of the reheater are in exactly the opposite direction from those of the turbine variations and the two offset each other. As the load goes up and the boiler is worked harder, the temperature of the exhaust from the high pressure turbine rises and this is offset by the fact that the temperature of the steam flowing through the radiant reheater drops off at the higher boiler ratings. A fairly constant temperature of the steam supplied to the low pressure turbine may therefore be obtained in this way with the proper designs.

My invention relates to plants which, while utilizing the steam from a high pressure turbine directly in a low pressure turbine, operate under conditions such that the variations of the steam temperatures from the high pressure turbine stage are small and to plants in which the steam from the high pressure turbine exhausts against a substantially constant back pressure because it is carried to a steam main where such constant pressure is maintained. It has for its purpose an improvement in connection with the reheating, whereby the temperature of the steam flowing to the low pressure turbine will more or less diagrammatically an installation according to my invention; Fig. 2 is a plan view on an enlarged scale of a detail of the invention; Fig. 3 is a view in elevation of the same detail, and Fig; 4 shows some curves used in the explanation of the invention.

The curve in Fig. 4 marked Total temperature is a typical curve representing the variation of the total temperature of the steam coming from a high pressure turbine with only slightly va ing loads. The loads are plotted horizontaly, increasing toward the right, the temperature being plotted vertically, increasing in upward direction. The curve illustrates the variations in the temperature of the steam in which the exhaust from the high pressure turbine is not carried into a steam main of constant back pressure but where it is carried directly to a low ressure turbine or a low pressure stage 0 the same turbine. The load on the boiler is here assumed to correspond to the load on the plant and therefore on the turbine. With the slight increase of the load on the boiler, the temperature of the exhaust steam. from the high pressure turbine also goes up slightly. Should this steam be carried to a pure radiant reheater, that is to say to a reheater which gets substantially all of its heat from the radiant heat of a furnace and substantially none by convection from the hot gases, the total temperature so obtained might be represented by the curve marked Curve from ure radiant heating. The amount of heatlng which the radiant reheater'is able to add drops with the increase in the load and the resulting total temperature still has a dropping characteristic. The third curve in Fig. 1 marked Curve, addin convection heating represents a curve whic I am enabled to et by my improvement, and as will be note is a flat substantially horizontal curve, representing the desirable state of affairs where the exhaust from the high pressure turbine is reheated to a constant temperature before being delivered to the low pressure turbine.

Referring now to Fig. 1, the boiler housing 1 encloses a boiler comprising upper drums 2 and 3 and a lower drum 4 connected by banks 5, 6 and 7 of boiler tubes. The upper drums are connected to each other by steam circulators 8 and water circulators 9. A superheater 10 located among the tubes of bank 5 receives its steam from drum 3 by means of pipe 11, and delivers it to high pressure turbine 12 by means of pipe 13. The furnace 14 is shown as having its side walls lined with a water screen 15. Projecting its flame into the furnace space is the burner 16 which is for purposes of illustration shown as an ordinary type of liquid fuel burner modified, however, for my purpose as described below. The radiant superheater is shown at 17 against the wall facing the burner 16. It is of an ordinary type comprising an upper horizontal header 18, a lower horizontal header 19 and the reheater elements 20 connecting them. The exhaust from high pressure turbine 12 is carried to the upper header 18 through the pipe 21, while the lower header 19 delivers the reheated steam to ipe 22 which carries it to the low pressure tur ine 23. 24 represents a condenser to which the exhaust from low pressure turbine 23 is'conveyed by pipe 25.

Should the reheater 17 receive only radiant heat at all ratings of the boiler and no convection heat, the temperature of the steam in pipe 22 would be represented by the middle of the three curves of Fig. 4 as explained above. To add the varying amounts of heat to bring the total temperature up to the uppermost of the three curves, I adopt the following arrangement. I place the burner 16 opposite the reheater 20 as above described, the dimensions and proportions of the firebox and the distance between the burner and the reheater being such that at low ratings the flame from the burner will not extend much beyond the central portion of the furnace space and at any rate substantially out of contact with the reheater. This is indicated b the lines made up of short dashes. l/Vhen t e boiler is forced, however. the flame, on acount of the relative location of the parts, distinctly impinges more against the reheater, as indicated by the lines made up of long dashes. The result is that at low ratings substantially all of the heat absorbed by the reheater is radiant heat while as the rating increases the reheater absorbs increasingly large proportions of its heat by convection. This convection heat, added to the radiant heat brings the total heat of the steam delivered by the reheater up so that this resulting temperature is represented by a curve like the top curve in Fig. 4.

The principle of my invention will be clear from the above. Other means may be used for causing more absorption of convection heat as the ratings rise. I illustrate one other such means, combined with the means already described. This consists in feeding the burner 16 so it can be swung into different positions resulting in a varying degree of impingement of the flame against the radiant reheater. The point about which it pivots is 26. Referring to Fig. 2, the short shafts 27 and 28, fixed to the burner 16, rotate in the trunnion bearings 29 and 30 respectively.

The fuel supply coming through flexible pipe 31 is controlled by the valve 32. The stem 33 of this valve is equipped with a hand-wheel 38 and has fixed toit the sprocket wheel 3-1 from which a chain 35 extends around the fixed sprocket wheel 36 attached to the setting by bracket 37. It is obvious that a rotation of the hand-Wheel 38 for the purpose of changing the fuel supply causes a rotation bined as described.

of the burner about the axis of the shafts 27 and 28. The arrangement is such that during low ratings the burner points horizontally or perhaps a little upward, and that to increase the length of the flame the hand-wheel 38 is rotated in such a direction that the burner assumes a more downward inclination asin dicated by the dotted line in Fig. 3 and like the one shown in Fig. 1. The result is that at low ratings the flame from the burner and the resulting hot'gases are substantially out of contact with the reheater, which therefore receives heat practically only by radiation, and that as the rating increases and the burner is tipped, the flame and hot gases come more and more into contact with the reheater and therefore the reheater absorbs more'convection heat not only because the flame is longer but also because of its change of direction.

The two means for effecting the variation in the relative amount of heat supplied by convection with variations in the rating may be used separately from each other, or com- In plants where the steam from ahigh pressure boiler is used in a high pressure turbine and exhausted into a steam main of constant lower pressure, and it is desired to give it a constant temperature, irrespective of the variations of the load on the turbine, before putting it into the main, the same arrangement is used. Instead of delivering the steam to a low pressure turbine, pipe 22 would then merely lead it to a low pressure main.

While I have described my invention in the above only as applied to a reheater, I wish to point out that it can also be made use of in connection with superheaters. Where these are of radiant type they have the characteristic that the total temperature of the steam delivered by them drops with increased ratings. This can be remedied in exactly the same way as is pointed out above in connection with the reheater described. In other words, the reheater 17 of Fig. 1 might be a superheater and my inventive idea would be carried out in precisely the same way.

As already suggested above, other variations will readily be made by those interested in practising this invention.

I claim:

1. The method of operating a boiler equipped with a radiant type superheater which comprises the steps of generating steam, superheating it in the superheater at all times in part by radiant heat, and adding the remaining part of the desired superheat by causing-the hot gases to come into contact with the superheater, the relative amount of heat added by the gases coming into contact with the superheater being caused to increase with the amount of steam generated and flowing through the superheater.

2. The method of operating a boiler equipped with a radiant type superheater and burning fuel in suspension in the furnace, comprising the steps of generating steam and superheating it in the superheater at all times partly by radiant heat and partly by convection, and causing the flame to be directed against the superheater more in proportion as the boiler is forced.

3. The method of operating a boiler according to claim 2, the variation of the extent to which the flame is directed against the superheater being caused by the greater or lesser forcing of the burner.

4. The method of operating a boiler according to claim 2, the variation of the extent to which the flame is directed against the superheater being caused by varying the direction in which the burner points.

5. In apparatus of the class described the combination of a furnace always exposed to radiant heat, a superheater in the furnace, and a burner so arranged that the more it is forced the more will its flame impinge against the superheater.

6. In apparatus of the class described-the combination of a fire-box, a boiler heated by the gases from the fire-box, a. superheater arranged in proximity toone of the firebox walls, a burner opposite the superheater and projecting a flame in a'direction toward the superheater, the arrangement being such that when the burner is not forced the flame substantially does not come into contact with the superheater, the superheating being substantially all by radiant heat, but in proportion as the burner is forced more of the gases come into contact with the superheater.

'7. In apparatus of the class described the combination of a furnace, a superheater in the furnace adjacent to one of the walls, and a burner arranged in the opposite wall and pointing generally toward the superheater, the burner being mounted so it can be pointed more or less directly at the superheater.

8. In apparatus of the class described the combination of a furnace, a superheater in the furnace adjacent to one of the walls, a burner arranged in the opposite Wall and pointing generally toward the superheater, a valve controlling the fuel supply to the burner, the burner being mounted so it can be pointed more or less directly at the super= heater, and means to swing the burner automatically to point more directly at the superheater in proportion as the valve is opened.

WILBUR H. ARMACOST.

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