US2806453A - High pressure vapor generators - Google Patents

Description

I 17, Q I G TROUTMAN HIGH PRESSURE VAPOR GENERATORS Filed May 7, 1953 F i G 1 INVENTOR lows G Zmumarz ATTORNEY United States Patent O Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application May 7, 1953, Serial No. 353,503 2 Claims. or. 122-459 This invention relates to a fuel burning natural circu- Iati-on high pressure vapor generating and vapor superheating installation wherein heat transferred from furtrade heating gases to fluid in the circulatory system results in an optimum degree of vaporization and thereby anoptimum thermo-syphonic circulatory effect.

More particularly, the invention is directed to a natural circulation steam generating and steam superheating unit havingsteam and water separating provisions in an elevated steam and water drum from which the separated water is conducted by downwardly extending Water supply conduits to the lower inlet ends of upwardly extending furnace heat absorbing steam generating tubes.

This invention is exemplified in a steam generating and superheating installation wherein the operating pressure is in excess of 2000 p. s. i. and/ or high proportion of the heat is absorbed in superheating high pressure and reheating low pressure steam. The invention is particularly advantageous where the feed water for the unit 'is supplied at atemperature substantially below the saturated steam temperature corresponding to the operating steam pressure.

The invention is especially advantageous in the described type of high pressure natural circulation vapor generating unit where heat absorbing tubular elements of difierent circulatory flow paths are so arranged and subject to different intensities of heat input that "attainment of the maximum thermo-syphonic circulation head is essential.

By the utilization of the invention it is possible to .provide a natural circulation steam generating and superheating unit operating at a pressure as high as 2700 p. s. i. with a thermo-syphonic circulation which will cause steam and water mixtures to flow through highly heated furnace heat absorbing tubes at optimum rates.

The invention provides an "arrangement whereby feed water, introduced into the circulatory system of the vapor generator at a temperature substantially below the saturated temperature, is quickly raised to the saturated steam temperature corresponding to the'pressure at the zone of introduction, so that when *the mixture of recirculated water and added feed water fiows from .the steam and water drum to the downcomer or supply conduits it will be at a uniform temperature corresponding to the saturation temperature at that pressure. Modern high capacity steam generators, :particularly of the natural circulation type, frequently have furnace wall watertubes, suppliedfrom an elevated steam and water drum, exposed to the heat of the furnace over an extent of, :forexa-mple 100 'ft. or more 'at elevations below the elevation of steam andwater drum. With'such a construction in aunit having a drum pressure of 270.0 s. .i;, .the water pressure at the lower un et thefexposed .portions :of the furnace Wall tubes will be Jof the orderof 22.5 p. -s. i. about the drum pressure. This increased @pressure gives a F. saturation terriperatu'rewhic is only slightly above the temperature at which thewater is supplied to that zone, and thereby only 3106B. 't. 511.7 lb. o'fwat'erwill ice need to be supplied to bring the water to a saturation temperature. Vaporization will therefore begin in the furnace wall tubes promptly after heat absorption by those tubes has been initiated.

The invention is thus directed to a particularly advantageous arrangement for the introduction of sub-saturated temperature feed water to the circulation system of a large capacity high pressure vapor generating and super-heating unit whereby the maximum available thermosyphonic circulation head may be made available, for the attainment of optimum design relationship.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings:

Fig. l is a partly diagrammatic sectional elevation of a steam generating and superheating unit incorporating the present invention;

Fig. 2 is an enlarged transverse section through the steam and Water drum of the Fig. 1 unit, showing the drum internals particularly pertinent to the invention;

Fig. 3 is a fragmentary transverse section through the steam and water drum of the Fig. 1 unit, taken at the position of a large downcomer; and

Fig. 4 is an enlarged View of one of the feed water conduits.

The high pressure high capacity natural circulation steam generating and superheating unit illustrated has a fluid circulation system which includes an upper steam and water drum 18, and a series of vertical external water downco'mer pipes 42 connected at longitudinally spaced positions to the bottom of the drum and to a transversely extending bottom junction header 82. The housing for the unit is vertically elongated and .a vertical front Wall 11, side Walls 13, and a rear wall 15 define a housing of horizontal rectangular cross-section. The bottom header 82 functions to supply water to upright rear furnace Wall steam generating tubes 10., front wall tubes 10' and side Wall tubes 10" connected at their lower ends to the junction header and at their upper ends to the steam and water drum. In addition to the wall tubes, supply tubes 83 conected to the junction header 8-2 furnish water to the lower headers 34 of the wall cooling systems of fuel burning cyclone furnaces 72 and 74, and riser tubes 85 and 86 from the upper header 87 of each cyclone furnace discharge into the steam and water drum 18.

The unit is fired by two vertical spaced rows of coal burning cyclone furnaces 72 and 74 constructed and-operated similarly to those disclosed in the Kerr et 'al. Patent 2,594,312, granted April 27, 1952. The products of combustion flow from the cyclone furnaces through tapered throats 102 into a primary furnace chamber :68, from which separatedmolten fuel ash drains through a floor opening into a slag pit 80. Gaseous products of combustion i l ow between spaced screen tubes 76 below the target baffle 66 and upwardly through the secondary furnace chamber 12 to pass sequentially 'u-pward through gas pass 108 and'downwardly through a connecteddownfloiw gas pass 110, the passes being separated by a 'bafile 128 formed by tubes 104 extending inwardly and upwardly from the rear wall 15 with the intertube spaces closed by refractory except at their upper'ends. From the latter pass the gases flow through a connecting .duct 106 to a tubular air preheater (not shown) and then through a stack'to the atmosphere.

The saturated steam generated in the -wall and baflle tubes is delivered to the steam and water drum 18 as hereinafter described and the saturated steam is superheated in convection heated surface located in the upflow and downflow gas passes. team reheating surface is also located in these passes. The saturated steam passes through conduits 60 and 62 to the primary superheater inlet header 152. A counterflow primary superheater is positioned in gas pass 110 and comprises a plurality of transversely spaced superheater tubes arranged in superposed banks 140-145, with the heated steam flowing from an outlet header 150 through a conduit connection 146 to the inlet header 122 of a secondary superheater comprising banks of tubes 112-116 in the upfiow gas pass 108, the superheated steam being passed to a point of use from an outlet header 120.

A reheater for partially expanded low pressure steam from a turbine has an inlet header 132 at the rear of the unit and connecting tubes 130 extend across the upper end of gas pass 110 and about the outside walls of the gas cavities above both passes 198 and 110 into a reheater tube bank 124 positioned across the upper end of gas pass 108, so that it will be positioned between the primary and secondary superheaters in respect to the gas flow path. The tube bank 124 consists of a plurality of transversely spaced multiple loop elements, and alternate elements are connected to outlet headers 125 and 126 respectively from which the superheated low pressure steam is directed back to the low pressure stages of the turbine for expansion.

With the operation of the unit by supplying water to the circulation system as will be hereinafter described and the burning of fuel in one or more cyclone furnaces, heat will be absorbed so that the upper ends of the steam generating tubes 10, 10", 85, 36 and 104, which open into the .drum as indicated in Fig. 2, will discharge mixtures of water and steam into Opposite peripheral spaces 14 and 16 connected by a curved section 30 of restricted cross-section, the spaces, or collection zones, 14, 16 and 39 being separated from the central portion of the drum by an inner imperforate compartment wall made up of plates 3236. The wall plates are supported from the drum shell by spaced brackets 38 and 40. The peripheral compartment defined by the spaces 14, 16 and 3t) extends longitudinally throughout substantially the entire length of the drum and is closed at its ends by correspondingly curved plates. Horizontal plates close the upper ends of the spaces 14 and 16.

In addition to the water-steam mixture discharged from the furnace heated tubes, the feed water to the unit is inroduced at a rate corresponding to the steam discharge from the drum through two feed water distributing pipes 26 and 28 extending longitudinally within the peripheral compartment, the pipes being bracket supported in the upper portions of the side spaces 14 and 16. The pipes 26 and 28 extend through the wall of the steam and water drum 18 to a controlled source of feed water at suitable pressure and have a longitudinally extending series of relatively small diameter holes 26 and 28 opening inwardly at an angle of 30 degrees from the vertical, whereby the jets of feed water issuing therefrom will impinge upon the opposing legs of angle plates 26 and 28*, as shown in Fig. 4, and be broken up into inwardly and downwardly directed streams so as to enhance intimate mixing of the feed water with the mixture of water and steam in the upper portion of spaces 14 and 16. By such mixing and in subsequent flow through the cyclone type steam and water separators 20 and 22, as hereinafter described, the feed water is brought up to the saturated steam temperature corresponding substantially to the pressure in drum 18, so that all of the water discharged from the separators to the central water space 44 will be at saturated temperature.

The fluid entering the spaces 14, 16 and 30 as described is discharged therefrom through two longitudinal rows of vertically arranged steam and water cyclone separators 20 and 22, which as shown are of the type shown and described in the Rowand et al. Patent 2,321,628, granted June 15, 1943. The steam and water mixture from spaces 14 and 16 enters the whirl chambers of the separators 20 and 22 tangentially, and a centrifugal separation of water and steam is accomplished in accordance with the well-known operation of such separators. The separated water is discharged downwardly from the bottom of the separators to the water space 44 at a level below the normal water level indicated by the line 46, while the separated steam passes upwardly through corrugated plate scrubbers 52 and 54 arranged across the top of the individual separators. The separated steam is subjected to a further separation in a twin arrangement of corrugated plate separators 56 and 58 before passing out through the discharge pipes 60 and 62.

in the described heating of the sub-saturated temperature feed water to saturated temperature, the necessary heat is supplied from some of the steam of the mixtures flowing from the furnace heated steam generating tubes. The quantity of steam flowing from the separators 20 and 22, and from the drum to the superheater, will therefore be less than that delivered in the mixture to spaces 14, 16 and 30 from the furnace heated tubes, and conversely the quantity of water discharged from the bottom of separators to the water space 44 will be greater than the quantity of water in the mixtures delivered to the spaces 14, 16 and 30 from the furnace heated tubes. Water from the space 44 passes downwardly through the plurality of longitudinally spaced downcomers 42, which are connected to the water space 44 through passages in the peripheral compartment formed by circular plates 31 concentric with the upper ends of the downcomers, as shown in Fig. 3.

The advantageous manner of operation by the use of the above described arrangement of feed water introduction to the natural circulation system of the unit will now be described. As is well known, the circulatory movement of water from the water space 44 of the steam and water drum through the downcomers 42 and the serial flow through a junction header such as 82 and return upward through heated steam generating tubes lying in heat absorption relation to the heat of the furnace, is a function of the relationship of the fluid (water) density in down-flow leg to the fluid (a mixture of water and steam) density in the upfiow leg. This relationship or function will be of greatest value when there is the greatest difference in the weights of similar columns of the fluids in the two legs, and the attainment of such a value is accomplished in the present invention by initiating vaporization, and thus lowering the density of the fluid in the upfiow legs of the circulatory system, as represented by furnace tubes ltl, 10, 10", etc, promptly after they are exposed to heat absorption from the furnace. This is accomplished while insuring, through adequate preheating of the feed water, that the water delivered to the upfiow leg by the down-flow leg is substantially at the saturation temperature corresponding to the pressure at the entrance to the up-flow leg. Thus generation of vapor with a corresponding reduction in density follows promptly upon absorption of heat from the furnace gases and substantially the entire vertical height of the heat receiving up-flow leg is assured of a lower density fluid than exists in the down-flow leg of the circuit.

Heretofore, in steam generating units having unheated or outside downcomers from an upper steam and water drum to supply water to the lower ends of heat absorbing tubes of an up-fiow leg, it has been customary to introduce feed water directly into or above the water collecting space in the drum. When the feed water, so introduced, is at a temperature below the saturated steam temperature corresponding to the pressure, an appreciable reduction of the temperature below saturated temperature results in the water flowing into the downcomer pipes. When the downcomer pipes are not subjected to any heating action, the water flowing into the up-flow leg, such as the furnace wall tubes, will be still substantially below the temperature corresponding to the saturated steam temperature at the drum pressure. The heat absorbed by the fluid flowing in the first part of heat ex-' posed flow path in the tubes, is utilized first in raising the water temperature up to the saturated temperature. In some such steam generating units the water may not reach saturated temperature until it has traversed a vertical heat absorbing flow path of as much as 30 ft, and an effective lowering of the density in the up-flow leg by vaporization of a portion of the water therefore would not occur below that level. Units of the type under discussion are frequently so proportioned that the entrance to lowermost heat exposed tubes in the up-flow leg as much as 130 ft. below the steam and water drum, and the avoidance of delayed vaporization in the up-flow leg by the feed heating arrangement of the invention provides the maximum of available thermo-syphonic circulatory head, and thus is an important factor in the design of the fluid flow circuits of natural circulation boilers designed to operate at high steaming pressures, particularly at and above 1500 p. s. i., with a feed water supply at substantially below the temperature corresponding to the designed steam pressure.

While in accordance with the provisions of the statutes I have illustrated and described herein the best form of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. In a high pressure steam generating unit having a circulation system, including a steam and water drum, means forming a first chamber in the drum normally receiving steam and water mixtures, means forming a second chamber in the drum normally having a water level therein, steam generating tubes having their outlet ends communicating with the first chamber and normally discharging steam and water mixtures into the first chamber at saturation temperature, steam and water separating means connecting said chambers and normally receiving the mixtures from the first chamber and separately discharging separated steam and separated water into different parts of the second chamber, feed water supply means normally discharging at least a predominant proportion of the total feed water into the first chamber at a position ahead of the inlet of the separating means in a fluid flow sense and at one side of the direct flow path of fluid from the outlet of the steam generating tubes to the inlet of the separating unit, the separating means having a steam and water mixture inlet near its upper part and having a separated water outlet at its lower end and beneath said water level, the feed water supply means also having its outlet in the first chamber and at a level above the level of the inlet to the separating means.

2. In a high pressure steam generating unit having a unitary circulation system including a steam and water drum, means forming a first chamber in the drum receiving steam and water mixtures from the risers, means forming a second chamber in the drum normally having a water level therein, steam generating tubes having their outlet ends communicating with the first chamber and normally discharging steam and water mixtures into the first chamber at saturation temperature, steam and water separating means connecting said chambers and normally receiving the steam and water mixtures from the first chamber and separately discharging separated steam and separated water respectively into upper and lower parts of the second chamber, and feed water supply and mixing means arranged to discharge at least a greatly predominant proportion of the total feed water into the first chamber to heat the feed water to saturation temperature in the first chamber before the mixed feed water and steam and water mixture enters the separating means, the separating means having its steam and water mixture inlet at its upper part and having a separated water outlet at its lower end and beneath said water level and relatively remote from the inlet of the separating means, the feed water supply means also having its outlet in the first chamber spaced from the inlet of the separating means and arranged at a level above the level of the inlet to the separating means.

References Cited in the file of this patent UNITED STATES PATENTS 2,058,239 Kerr Oct. 20, 1936 2,402,154 Fletcher June 18, 1946 2,594,490 Patterson Apr. 29, 1952 2,669,976 Frisch Feb. 23, 1954

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