US2869517A - Once through steam generating plant - Google Patents

Description

Jan. 20, 1959 A LIEBERHERR ones THROUGH STEAM GENERATING PLANT Filed June 4, 1954 NEK ARTHU/FL/EBERHERR 4 /1/44? United States Patent ONCE THROUGH STEAM GENERATING PLANT Arthur Lieberherr, Winterthur, Switzerland, assignor to Sulzer Freres, Societe Anonyme, Winterthur, Switzerland, a corporation of Switzerland Application June 4, 1954, Serial No. 434,616

Claims priority, application Switzerland September 26, 1953 10 Claims. (Cl. 122-406) The present invention relates to a forced flow steam generator ofthe once through type in which water is circulated from a feed water storage tank through the tube system, and back into the tank during the heating-up period 'of the generator. 7

Although, during the heating-up period, i. e. from the moment the fire in the combustion chamber is lighted t the moment the generator has reached normal operating temperature, no steam can be produced for outside purposes, an operating medium must nevertheless be forced through the tube system to avoid objectionable heat stresses in the latter. If water is circulated during this period, the heat transmitted to the water during the heating-up period is not lost but can be accumulated. Proposals made so far for accomplishing this called for a superheater design which must take into account not only the steam flow during normal operation but also the flow of the steam-water mixture during the heatingup period. It was necessary to ensure that all water pockets in the superheater tubes be completely removed already before reaching normal operating conditions and that no unstable conditions in the flow of the steam-water mixture could occur. The superheater tube system had to be so. constructed that it did not only answer the requirementsof superheated steam flow, but also of flowing a steam-watermixture. I e p v The present invention overcomes the aforementioned disadvantage by connecting a recirculating conduit between the evaporating or steam-generating part and the superheater part of the tube system, for conducting water back to the feed water tank during the heating-up period, and by shielding the superheater against tl-ame radiation. This provides considerable freedom in the construction and particularly in the arrangement of the superheater tubes, because at no time does water or a steam-water mixture flow through the superheater. The superheater need not be cooled during the heating-up period because the superheater tubes are shielded from the flame radiation.

A water separator is preferably arranged in a conduit connecting the steam generator and the superheater be tween the outlet of the evaportor and the point where the recirculating conduit is connected with the aforesaid connecting conduit. 7 p

It is of advantage to provide a valve in the conduit between the water, separator and the superheater and also in the recirculating conduit. These valves make it possible to conduct theoperatingmedium-through the superheater during normal operation and back into the feed water tank during the heating-up period without passing the medium through the superheater.

These valves may be adjustable by hand or they may operate semior fullyautomatically. They maybe constructed as overflow valves which maintain the pressure at the valve inlet. The valve in the conduit connecting the. water trap and the superheater is preferably provided with an adjusting deviee by means of which the pressure can be adjusted in accordance with requirements The valve in the conduit between the water trap and the superheater may be actuated by a device which is responsive to the condition of the medium entering the water trap. This device may alternatively be responsive to the condition of the medium leaving the water trap or to the water level in the trap. Likewise, the valve in the recirculating tube may be controlled by a conventional device which is responsive to the condition of the medium in the water trap.

The term overflow valve used in the present specification defines a valve which allows overflowing of water and/or steam from a zone of relatively high pressure into a zone of relatively low pressure.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself however and additional-objects and advantages thereof will best be under stood from the following description of embodiments there-of when read in conjunction with the accompanying drawing in which Fig. lis a diagrammatic illustration of a steam generating plant according to the invention;

Figs. 2.to 7 illustrate six modifications of valve arrangements and control means therefor in the plant shown in Fig. 1.

The same numerals designate the same parts in all fig ures.

During normal operation, the operating fluid of the steam or vapor generator is forced by a pump 2 from a feed water tank 1 into an economizer 3 and through-an evaporator 3 tube system. The wet steam leaving the evaporator or steam generator part 3 of the tube system is conducted through a water separator or trap 4 from which saturated steam flows through an overflow valve 5 into a superheater 7 which is shielded by a baflle 6 against flame radiation, the superheated steam leaving the plant through an outlet conduit 8.

The valve 5 is closed during the heating-up period and the operating medium is returned through a second overflow valve 9 and a bypass conduit 10 to the feed water tank 1. The circulated water is gradually heated, a steamwater mixture emerging from the outlet of the steam generator after some time, the water content of the mixture gradually diminishing. The water separator 4, which is initially swamped with water, is able to separate water from the steam after a certain period of time. The separated water may be removed from the separator 4 through a conduit 11. When saturated steam emerges from the separator, the valve 5 may be opened. It is not necessary to wait until the medium at the outlet of the tube system 3' has normal dryness.

In the plant shown in Fig. 1, the valves 5 and 9 are constructed as pressure actuated overflow valves which are actuated by a conventional pressure responsive regulator 12 for maintaining the pressure at the valve inlet at a predetermined value. The valves 5 and 9 are opened whenever the pressure upstream of the valves exceeds a predetermined value. Valve 5 is adjusted by means of an adjustment device 13 for closing the valve or for causing greater flow resistance than that in valve 9, to produce, during the heating-up period, the circulation of the operating medium according to the invention. As soon as the water separator 4 is able to separate the entire Water content from the steam-water mixture flowing through'the separator, the valve 5 may be opened partially or entirely by means of the adjustment device 13, so that all or part of the saturated steam leaving the separator flows into the superheater 7. Partial opening of the valve 5 is desirable, for example, if a turbine receiving steam through the conduit 8 is to be warmed up or driven at low load.

The -valve 5 may be automatically regulated, for eX' ample, as shown in Fig. 2 in which the valve is actuated by a conventional control device 14 which is responsive to the condition of the fluid entering the separator 4.

In the modification shown in Fig. 3, the valve 9 is actuated by a control device 14 which is responsive to the condition of the fluid entering the separator. 4.

If both valves 5 and 9 are overflow valves, and the valve 5 offers greater flow resistance thanthe valve 9 during the heating-up period, the operating fluid will be circulated during the heating-up. period in the desired manner. If valve 5 is fully opened and valve 9 is fully closed, the steam will flow through the superheater.

In the modification shown in'Fig. 4 the valve 5 is actuated by a conventional control device which is responsive to the condition of the operating fluid leaving the separator 4. Likewise, the valve 9 may be regulated by a control device 15 which is responsive to the condition of the fluid leaving the separator 4 (Fig. 5). The valve 5 may be fully closed during the heat-.- ing-up period, and the valve 9 may be fully closed during normal operation of the plant. Automatically controlled valves may be so adjusted'that the inlet pressure which opens the valve in the circuit to be held open is lower than the inlet pressure which opens the other valve.

Fig. 6 shows an arrangement in which a control device 16 actuating. the valve 5 is responsive to the water level in the separator 4 to close the valve 5 when the water level is above a predetermined locality, whereas Fig. 7 shows a control device 16' which actuates the valve 9 according to the water level in the separator 4 to open the valve 9 when the water level rises beyond a predetermined point.

The choice. of the most suitable control arrangement will depend on the individual operating conditions. It will be of. advantage in many cases to combine several of the illustrated arrangements.

The superheatermay be shielded from the flame radiation in any suitable manner, for example by means of baffles or by placing the superheater in the gas flue, or a suflicient distance away from the combustion chamber, or at least from the grate or burners.

The recirculation of the operating fluid may be effected not only during the heating-up period but also under other operating conditions. For example, the amount of steam needed at the generator outletat low loads may be so small that the generator heating surfaces would be burnt if no additional operating fluid were circulated through the generator tubes in the proposed manner. In this case, 'the valve 5 is opened so far that only the actually needed amount of steam enters the superheater. The circuit according to the invention may also be used when shutting down the boiler, after the prime mover which normally receives steam from the generator has been stopped. During this period the heat radiating from the brickwork or from the grate may damage the unprotected heating surfaces.

While specific embodiments of. the invention have been shown and described, it will be apparent to those skilled in the art that various changes, modifications, substitutions, additions and omissions may be made therein without departing from the spirit and scope of the in: vention as set forth in the appended claims.

What is claimed is: V

1. A forced flow steam generating plant of the onee through type, comprising, in combination, a feed water reservoir, a combustion chamber, a steam generating tube system adapted to be heated by heat produced in said combustion chamber, a feed water pump connected with said reservoir and with said tube system for pumping feed water from the former into the latter, a super.- heatena steam conduit connecting said tube system with said superheater, a steam and water separator inter; Posed in d m. wed e i epa at r-han sa water outlet for removing the separated water from the plant, a first valve interposed in said steam conduit between said separator and said superheater, actuating means connected with said first valve for varying the degree of opening of said first valve and for closing said first valve during the heating-up period of the plant, a return conduit connected with said steam conduit be tween said first valve and said separator and connected with said reservoir for returning operating fluid to said reservoir during heating up of the plant, a second valve in said return conduit/actuating means connected with said second valve for varying the degree of opening of said second valve and for closing said second valve during normal operation of the plant, and means for shielding said superheater from flame radiation and preventing burning of said superheater when no steam flows therethrough during the heating-up period of the plant.

2. A forced flow steam generating plant as defined in claim 1 including pressure sensitive means connected to and being responsive to the pressure of the operating fluid in said steam conduit and being connected with said actuating means to open one of said valves when the pressure of the operating fluid in said steam conduit exceeds-a predetermined value and to close the other valve when the pressure of the operating medium in said steam conduit drops below said value.

3. A forced flow steam generating plant as defined in claim 1 including pressure sensitive means connected to and being responsive to the pressure of the operating fluid in said steam conduit and being connected with said actuating means to close said first valve when the pressure oi the operating medium in said steam conduit drops below a predetermined value and to open the second valve when the pressure of the operating fluid in said steam conduit exceeds said value.

4. A forced flow steam generating plant as defined in claim 1 including pressure sensitive means connected with and being responsive to the pressure of the operating fluid in said'steam conduit and being connected with the actuating means of the first valve to open said first valve when the pressure of the operating fluid in said steam conduit exceeds a predetermined value.

5. A forced flow steam generating plant as defined in claim 1 including means connected with and being responsive to the pressure of the operating fluid in said steam conduit upstream of said separator and being connected with the actuating means of said first valve for actuating said first valve toward a closed position when the pressure of the fluid entering said separator drops below a predetermined value and toward an open 'positionwhen the pressure of the fluid entering said separator increases beyond a predeterminedvalue.

6. A forced flow steam generating plant as defined in claim 1 including means connected with and being responsive to the pressure of the operating fluid. in said steam conduit upstream of said separator and being connected with the actuatingrneans of said second valve for actuating sa id'second valve towardja closed position when the pressure of; the fluid entering said separator increases above a predetermined value and toward an open position when the pressure of the fluid entering said separator decreases below a predetermined value.

7. A forced flow. steam generating plant as defined in claim 1 including means connected with and being responsive to the pressure of the operating fluid in. said steam conduit downstream of said separator and upstream of said first valve and being connected with the actuating means of 'saidfirst valve'ffor actuating said first valve toward a closed position. when thepressure'of the fluid leaving said separator drops below a predetermined value and toward an open position when the pressure of the fluid leaving said separator increases beyondja predc: emitted a ue A. or ed. aw. steam. ne atin .plaat. as. d fine n 8-. na ted. w th 35 ll-8.59

sponsive to the pressure of the operating fluid in said steam conduit downstream of said separator and upstream of said second valve and being connected with the actuating means of said second valve for actuating said second valve toward a closed position when the pressure of the fluid leaving said separator increases beyond a predetermined value and toward an open position when the pressure of the fluid leaving said separator decreases below a predetermined value.

9. A forced flow steam generating plant as defined in claim 1 including means connected with said separator and being responsive to the water level in said separator and being connected with the actuating means of said first valve for actuating said first valve toward a closed position when the water level in said separator rises be yond a predetermined value and toward an open position when the water level in said separator falls below a predetermined value.

10. A forced flow steam generating plant as defined in claim 1 including means connected with said separator and being responsive to the water level in said separator and being connected with the actuating means of said second valve for actuating said second valve toward a closed position when the water level in said separator falls below a predetermined value and toward an open position when the water level in said separator rises beyond a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS

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