US3007456A - Apparatus for and method of generating and superheating steam - Google Patents

Description

1961 J. R. MURRAY ETAL 3,007,456

APPARATUS FOR AND METHOD OF GENERATING AND SUPERHEATING STEAM Filed July 13, 1956 LOW PRESS. STM.SOURCE INVENTORS Jullan R. Murray 42 BY Jackson E. O'Connell ATTORNEY 3,007,456 APPARATUS FOR AND METHOD OF GENER- ATING AND SUPERHEATING STEAM Julian R. Murray, Skokie, and Jackson E. OConnell, Elmhurst, 11]., assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed July 13, 1956, Ser. No. 597,655 8 Claims. (Cl. 12233) This invention relates to the art of steam generation and steam superheating. More particularly, the invention relates to the generation of high pressure (i.e. 2400 psi) steam in a fuel fired unit including *a gas heated steam superheater, the initial superheating of relatively low pressure steam (350 psi.) by indirect heat transfer involving the condensing 'of all of the high pressure steam, the return of the condensate to the high pressure steam generation, the subsequent superheating of the low pressure steam in a plurality of stages in the gas heated superheater of the unit, and provisions whereby the gas heated superheater of the unit may, alternatively, superheat the high pressure steam when low pressure steam is not available, the latter provisions functionally eliminating the initial superheating by indirect heat exchange and effecting steam flow directly from the zone of generation of high pressure steam to the gas heated superheater of the unit.

The steam generating and steam superheating unit of the invention is particularly applicable to a power plant having a plural pressure stage steam turbine means with a lower pressure stage of the turbine means receiving 1100 F. steam at a relatively low pressure (i.e. 350 p.s.i.a or 600 p.s.i.a.) and generated by a nuclear reactor, and with the high pressure stage of the turbine receiving relatively higher pressure steam.

The invention is exemplified in a steam generating and superheating unit in which relatively low pressure steam derived from a source independent of the unit is superheated in a plurality of stages in a separately fired superheater. The latter preferably includes a high pressure steam generating section in which the steam is generated predominantly in the wall tubes of a fuel fired furnace, Saturated steam from this high pressure source is adapted to transmit heat by indirect heat exchange to the low pressure steam to superheat the latter in a first stage of superheating, with high pressure steam being condensed in this superheating stage. The low pressure steam heated in this initial superheating stage then passes through successive other superheating stages formed by the gas heated superheating means of the separately'fired superheater, or high pressure steam unit. v

The invention may be regarded as including a separately fired superheater burning a fossil fuel or a slag forming fuel at combustion temperatures in excess of 2200 F. and having a high capacity for superheating relatively low pressure steam. The separately fired superheater of the invention is characterized by high availability and low furnace chamber wall maintenance by its inclusion in the furnace chamber walls adjacent the active combustion zone of steam generating tubes operating at the saturation temperature of the high pressure steam, while the wall portions of the fumaoe chamber beyond the active combustion zone in a gas flow sense contain radiant superheater wall tubes forming one stage or part of the superheating means and normally receiving the low pressure steam from the independent steam generating source.

The invention particularly involves means whereby the power plant may be operated solely by steam generated in the unit when the nuclear reactor or other independent source of relatively low pressure steam is shut down.

Under these circumstances, the steam generated in the unit flows directly through the gas heated superheater means of the unit, the normal communication between the gas'heated superheater means and the independent source of relatively low pressure steam being shut off, and the normal conmiunication for high pressure steam flow to the initial superheating stage and the normal communication for the flow of condensate from the initial superheating stage of the relatively low pressure steam being likewise shut off. Under these circumstances the non-radioactive steam generated in the normally high pressure steam generating section may act as a washing agent to wash out or dilute radioactive deposits in the superheating means and other parts of the power plant such as the condenser and feed-water heaters. The invention, as indicated immediately above, may be considered as providing for the continuous service of the unit involving the high pressure steam generator and the gas heated superheating means normally for superheating relatively low pressure steam, rather than necessarily shutting down the whole power plant when the reactor is shut down. This decreases the chance of oxygen pickup in the system, and resulting corrosion. The invention may thus involve a substantial decrease in the original cost of the power plant by permitting the use of carbon steel in the feedwater heaters and associated equipment, in place of stainless steel, the cost of which is many times that of the carbon steel.

The invention will be clearly and concisely set forth in the claims appended hereto, but for a more complete understanding of the invention, its advantages and uses, reference should be had to thefollowing description'which refers to the attached drawing, showing a preferred embodiment of apparatus involved in the invention.

The drawing is a somewhat diagrammatic side sectional view indicating the high pressure condensing steam generating unit involving gas heated steam superheating means which normally functions solely to superheat relatively low pressure from an independent source.

In normal operation of the unit shown in the drawing, low pressure (i.e., 350 p.s.i.-a. or 600 p.s.i.a.) steam from an independent source 10, such as a nuclear reactor, passes through the line 12 to the inlet 14 of the first superheating stage. Here the relatively low pressure steam is superheated by indirect heat transfer in the heat exchanger 16. This heat exchanger receives, through the conduit 18, high pressure steam (i.e. 2400 p.s.i.a.) from the steam and water drum 20 of the high pressure steam generating system or section, of the fuel fired superheater. This high pressure steam passes to the inlet chamber 22 of the heat exchanger 16, and then through a plurality of spaced tubes 24 having their inlet ends fixed within the tube sheet 26 and their outlet ends fixed within the tube sheet 28. The outlet ends of these tubes communicate with the intermediate high pressure steam chamber 29 from which the high pressure steam (or its condensate) passes through a series of spaced tubes 30 to the condensate outlet chamber 32. The condensate of the high pressure steam flows from the chamber 32 through one or more conduits 34 to the Water space of the drum 20.

The tubes 24 and 30 are disposed within a hollow cylinder shell 36 which receives the low pressure steam through the inlet 14. This low pressure steam is initially superheated in the heat exchanger 16 from which it is conducted through one or more conduits 38 to a second superheating stage. The shell 36 of the heat exchanger 16 is in pressure-tight relationship with the tube sheets 26 and 28 at the opposite ends of the heat exchanger.

The steam initially superheated in the heat exchanger 16 passes through the conduits 38 to the horizontal header 40. From this header the steam flows through a row of of the horizontalgas pass 44 of thelunit. The flow then continues through the upright and widely spaced screen sections 46 and 48 between which the heating gases exit from the gas pass and then how past the dampers 50 into the flue '52 leading to the air heater/54. From-the upright screen sections 46 and 48, the steam flowrcontinues through the gas pass floor tube sections 56 to the header '58. From this header, the steam flows through a series of connecting tubes such as 60'to sidewall headers, one of which is indicated at 62. Leading upwardly from each of the side wall headers such as 62,.there' is a row of superheater wall tubes '64. The upper and outlet ends of these tubes are connected to dischargeinto'one of the upper sidewall headers 65. Fromthesesidewall headers, the steam passes through connecting tubes 66 and 68i to the header 70 from which the steam flows downwardly through the inlet tubular sections 72 of closely spaced and serially connected return bend tubes. constituting the banks 74 and 78 of convection superheater tubes; the outlet sections 80 of which are in-communication with the.

header 82.

From the header 82, thesteam flow continues downwardly through one or more conduits 84 to-the header means or header section 86. This header means may include four connected header sections one 'of which is located along each of the 4 sides of the furnace chamber 88. 'I'hese header sectionsare preferably connected so that they all receive steam through the conduits 84,

one of the header sections being indicatcd"a t st the front wall 9210f the furnace'chamber and opposite'the header section 86 disposed adjacent the rear furnace tubes, the first sections 42 of which extend along the roof the separated water passes header 142;

- 'The lower headers for the cyclonefurnace; such as l r the header 152, are directly connected by circulators 154,

that the tubes forming parts of the walls of thecyclone furnace havetheir outlet ends connected to one 'or more chamber wall 94. From the header sections suchv as 86 and 90,, the steam flows upwardly through radiant. superheater 'wall tubes alongthe walls ofthe furnacechamber 88,-some of these tubes being indicated at 96 and 98.

The flow of steam continues through these tubes to the V header 100 from which thejsteam flows as indicated by nace chamber-88;. r

headers such as 156, the :latterfbeing directly connected and water mixture receiving by the risers'158 to the steam space of the drum20k V t a The refractory covered floor 160 of the primary furnace chamber 1-361includes1 the floor tube sections 162 of some of the steam generating tubes leading directly from the drum or headeri1 42 along the floor and then along the wallcornponent 164 'of the primary furnace chamber} Thence these, tubeslead through the walls of the threat 1 134 and then through the wall component 1660f the primaryfurnacejchamber. Other-tubes directly connecting the drum or header 142 and the header means 144 involve the screen sections 138 and also successive tubular sections in the wall l68 separating the primary furnace chamber 136 from the lower part of the secondary furu;ThesidewallEheaders/170 for the primary furnace chamber and;;the1lower'part of 'thersecondary furnace chamber are appropriately connected by circulators 172 with-theheader:orqdrumi142, and the wall tubes extending upwardly from the headers. 170 to sidewall" headers such as the header sections i144-and 146 adjacent the level 140 .are preferably covered on their furnace sides with high temperature refractory thermally and mechanically maintained therein by metallic studs secured tothetubes in;-good-heat transfer relationship and extending into the refractory metalin the manner, indicated in the patentto Bailey 2,239,662 of April 22, 1941. i o

Others bf'the tubes leading upwardly from the lower drum or header 142 include the wall tube sections-174 disposed along the rear wall 176 of the lower portionofe the secondary furnace chamber 88 and joined at their upper ends to'ithe header section '146. r

a The superheater headers above thefurnace chamber 88 then flows, as indicated by the arrow 11 2.,to the header 1 108 through the connecting tubesf114. From the header 103, the steam flows through a multiplicity of spaced and serially connected return bend tubes constituting the banks of secondary superheateru tubes 116-1-18. The

outlet ends of these tubes are connected to the header 120 from which the highly heated superheated steam flows through one or more conduits 122, to a stage of a steam turbine. I v

The unit shown in the drawings includes a coal-fired cyclone furnace preferably of the type shown in the US. Patent to Kerr et al. 2,594,312 of April 29, 1952. High temperature furnace'gases pass from this furnace and above the horizontal 'gaspass44, and the tubular-connections between thoseheaders' are enclosed within a cas- V ingwhich is preferably gas tight and which is constructed.

sons to aiford thermal insulation. This casing is indicated 1 in the drawing as having a' roof section 200, a rear wall section 202,' drum enclosing sections 204 and 206, the section 208 at the base of the horizontal gaspass, and other 7 sections including those along the'walls 92-and 94 and the sections above'the lowerlpa'rt of the ,unit including the through its throat 134 into the primary'furnace chamber 136 and thence across the steam generating screen tubes the lower rear wall of the secondary furnacev including steam generating tubes. Above the level 140, the walls of the secondary'furnace chamber are lined with radiant steam superheater tubes'as previously indicated, and below the level 140' the Walls of the primary furnace cham-' 138 into the secondary furnace chamber 88, the walls of l the cyclone furnace, the primary furnace chamber 136 and.

cyclone furnace and the primary furnace chamber 136. The enclosure-for the'pressure parts is supported from steel 7 work including such elements as the columns 220' and 222 and the; girder'224. i The pressure parts such as the drum,

headers and tubes are supported on the steel workin manners well known in the art, by means of hangers and drum straps. V o I r The normal operation of the described unit involves the flow of steam at pressures such as 350 'p,s.i,a. or 600 p.s.i.a'; from a nuclear-reactor, the, flow of steam continu ing through the different stages of superheating including the initial superheating in the heatexchanger 16 and the subject to the fluid separating action of steam and water 7 separators preferably of the type shown in the U.S. Patent to Rowand et a1. 2,289,970 of July 14, 1942, and,

subsequent super'heating changes inthe gas heated superheater components subj'ect to the heat of the gases originating in the cyclone furnace; 130. The steam superheated to a temperature of-the order of'1,100'F. passes'to a stage "of'a plural stage steam turbine for producing power. l

However, to provide fora supply of steam from mama to the turbine for power generating purposes when the nuclear reactor is shut down,the invention involves means wherebyusteam generated in the lower part of the unit is passed directly to the gas'heated superheater components and thence to 'the turbine. The means for accomplishing this involves one or more conduits such as 250 arranged through one or more large diameter down'comers such as to the lower drumor to conduct steam from the drum 20 to the superheater inlet header 40. As shown, the conduit 250 leads from the conduit 18 at a position between the drum 20 and the valve 252 which is closed when the nuclear reactor is shut down. Under these circumstances, the valve 254 in the line 34 and the valve 256 in the line 38 are closed and the valve 258 in the line 250 is open. Under these circumstances, the pressure of the steam leaving the drum 20 is reduced to a pressure as that corresponding to the normal pressure of the steam from the nuclear reactor. In addition to providing for the production of power when the nuclear reactor is shut down, the method of operation of the invention provides for advantageous utilization of non-radioactive steam generated by the unit. This steam may act as a washing agent to wash out or dilute radioactive deposits in the superheaters, turbine, condenser and feedwater heater. It also decreases the chance of oxygen pickup in the system, and resulting corrosion and thereby provides for a substantial saving in the original cost of the system in that carbon steel may be used in place of stainless steel for the feedwater heaters and associated equipment.

' When the steam from the fuel fired generator passes to the turbine, the furnace wall steam generating tubes are supplied with feed water at an appropriate temperature. This may be attained by a convection-economizer interposed relative to the air heater 54 and the convection superheater, the flow of feed water from the economizer being directed to the nuclear steam generator when the superheaters receive only steam from the latter generator.

Whereas the invention has been described with reference to the details of a specific embodiment, it is to' be appreciated that the invention is not to be considered as limited to all of the details thereof. It is rather to be considered as of a scope commensurate with the scope of the subjoined claims.

What is claimedis:

1. A method of operating a nuclear steam generating plant including a fuel fired unit normally generating steam at a much higher pressure than the nuclear produced steam and superheating the nuclear produced steam in an initial stage by condensing the high pressure steam and utilizing the heat of the combustion gases to superheat the nuclear produced steam in plurality of later stages to a high temperature, comprising the steps of reducing the pressure of the steam generated at the high pressure, bypassing the reduced pressure steam around the initial stage of the superheating of nuclear generated steam when the generation of nuclear produced steam is ceased, and conducting the steam of reduced pressure directly through the gas heated superheater to wash the gas heated superheater free of any radioactive particles deposited therein during the final superheating stage of the nuclear generated steam.

2. In the operation of a power plant including nuclear means for normally generating relatively low pressure steam, a fuel fired steam generator and superheater for normally generating high pressure steam and condensing that steam in an initial stage of superheating the nuclear generated steam in its passage to a point of use, the fuel fired superheater also involving a gas heated second stage of superheating the nuclear generated steam; the method of operation which includes supplying steam from the high pressure steam generating section of the fuel fired superheater directly to its gas heated superheating section and bypassing an initial and steam condensing stage of initial superheating when the nuclear steam generator is inoperative to effect a washing of the gas heater superheating section free of any radio-active particles deposited therein during the second stage of superheating the nuclear generated steam.

3. In a method of operating a power plant including a low pressure steam generating nuclear reactor, a fuel fired high pressure steam generator for normally superheating the nuclear generated steam by heat transfer from the condensation of high pressure steam and from the gases of the fuel fired component, comprising effecting combustion Within a confined zone by burning a fossil fuel at temperatures in excess of 2200 F., transmitting heat predominantly by radiation from the active combustion zone to confined water streams thereby generating steam at a pressure much higher than the pres sure of the steam from the nuclear steam generator, transmitting heat by indirect heat exchange from the high pressure steam to the much lower pressure steam from the nuclear reactor, said transmission of heat involving the condensing of the high pressure steam, returning the condensate to the inlets of the water streams subject to the heat of the active combustion zone, further superheating the low-pressure steam from the condensing zone by heat transmission from the combustion gases to confined streams of the lower pressure steam in a heating zone beyond the active combustion zone in a gas flow sense, and when the nuclear reactor is shut down, by passing the condensing zone and superheating the steam from the normally high pressure steam generator by passing it through the gas heated superheating zone.

4. In apparatus of the character described, means for generating relatively low pressure steam, said means being a steam generating nuclear reactor, high pressure steam generating means including a fuel fired furnace having steam generating wall tubes, means for initially superheating the lower pressure steam from the nuclear reactor by condensing the saturated steam from the high pres sure steam generating means, a condensate line for returning the condensate from said superheating stage to the Water space of the high pressure steam generating means, means including a separately fired gas heated superheater incorporated as a unit with the high pressure steam generating means and subject to the heat of the gases from the fuel firing, a superheated steam supply line leading from the first superheating stage to the sep: arately fired superheater, means for conducting the superheated steam to a point of use, and means bypassing the initial superheating stage and conducting steam from the high pressure steam generator directly through the separately fired superheater to said point of use when the supply of steam from the nuclear recator steam generator is shut off.

5. The combination of claim 4 wherein said last named means includes the shut-off valves in the high pressure steam line leading to the initial superheating stage and in the condensate return line from the initial superheating stage to the high pressure steam generator, and a valve in the by-pass line leading directly from the highpressure steam generating section to the gas heated superheater.

6. In an apparatus of the character described, means for generating relatively low pressure steam, another steam generating means including a furnace for effecting the combustion of a fossil fuel to generate a relative high pressure steam, a heat exchange means connected to said lower pressure and high pressure steam generating means wherein the low and high pressure steam generated by said steam generating means, respectively, are brought into indirect heat exchange relationship whereby said low pressure steam is superheated and said high pressure steam condensed, a secondary superheating means exposed to the products of combustion of said fossil fuel, said secondary superheating means being connected with said heat exchanger means to receive the low pressure superheated steam from said heat exchanger means and expose said low pressure superheated steam in heated transfer relationship with the products of said fuel combustion so as to highly superheat said low pressure superheat steam; and a valved bypass means disposed between said high pressure steam generator and said heat exchange means and connecting said high pressure steam generating means to said secondary superheating means whereby steam generated by said combustion of fossil fuel is selectively directed through either said heat exchanger means or said secondary superheating means.

7' a 7,. In a steam generating and heating arrangement, a first steam generating means adapted 'to selectively pro duce relatively high pressure steam and low pressure steam and including 'a furnace chamber having walls of steam generating tubes, fossil fuel burning means arranged to discharge heating products of combustion into said furnace in heat absorbing relationship with said generating tubes, a steam and water separating drum connected to said generating tubes for receiving either the high pressure or low pressure saturated steam generated in said tubes, said drum having a steam outlet, a second steam generating means producing relatively low pressure saturated steam, said second generating-means being adapted to be operatively' or inoperatively connected into said arrangement, a' heat exchange means in commu 'nieation with said drum outlet-and said'second' generating means, said heat exchange means adapted to receive in indirect heat tr-ansfer'rel ationship the high pressure steam of said'first generator means and the relatively low pressure steam of said second generator means whereby said low pressure steam is initially superheated and said high pressure steam condensed, a secondary superheating means exposed -to the combustion products of said furnace and heated thereby, a first means con necting said secondary superheater in communication with said heatexch-ange means whereby said superheated low pressure steam from said heat exchanger is delivered to said secondary superheater means to be highly superheated therein, a second means directly connecting said drum outlet to said secondary superheating means, and

valve means operatively disposed in saidfirst and second s nace for effecting the combustion of a fossil fuel to gen erate a relative high pressure steam, 3' heat exchange means connected to said low pressure and high pressure steam generating means wherein the low and high pres surefste-am generated by saidstearn generating means respectively are brought-into indirect heat exchange-relationship whereby said low pressure nuclear react'ongen erated steam is superheated and said fossil generated'high pressure steam condensed, a secondary 'superheating means exposed to the products of combustion of said fossil fuel, said secondary supe'rheating means being con nected with said heat exchanger means to receive 7 superheated steam therefrom and to 'expose said superheated steam in heated transfer relationshipwith theproducts offsaid fuel combustion so as to be highly superj heated thereby, and bypass means directly connecting i said second mentioned steam generating means to said, secondary superheating means whereby the steam genenated by said combustion of fossil fuel is directed there to, and means for rendering saidbypass operative when said nuclear reactor means is rendered inoperative wherebythe flow of the fossil generated steam through the secondary superheater'effectsa cleansing action of said secondarysuper'heating means, 7

References Cited in file of this patent UNITED STATES PATENTS FOREIGN PATENTS, Great Britain 1Sept; 10,1952

679,083 V OTH ER REFERENCES Nucleonics, pp. 42-43, January 1953. a v

Facts About Con. Edisons lndian Point Nuclear El ectric Generating Station; September 19 55, pp; 1- 4. (Copy.

in Class 204193.2R.)

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