US2879751A - Forced flow steam generator and method of starting same - Google Patents

Description

March 31, 1959 A. LlEBERHERR FORCED FLO-W STEAM GENERATOR AND METHOD OF STARTING SAME Filed June :5o. 1954 lll/lll IN V EN TOR.

ARTHUR L :Esser/sek. BY

ArraR/vfn nited States FORCED FLOW STEAM GENERATOR AND METHOD F STARTING SAME Application June 30, 1954, Serial No. 440,392

Claims priority, application Switzerland September 26, 1953 2 Claims. (Cl. 122-406) The present invention relates yto a forced liow steam generator and a method for starting the generator which method includes the rstep of circulating water from v' 1 feed water accumulator through a portion of the tube system of the generator and back into the feed water accumulator.

The present application is a continuation-in-part of my copending application Serial No. 434,616, filed June 4, 1954.

Although, during the heating-up period, i.e. from the moment the fire in the combustion chamber is lighted to 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 of the generator to avoid objectionable heat stresses in the latter. If water is circulated during this period, the heat transmitted to the water dur.- ing the heating-up period v is not lost but can be accumulated.

Conventional arrangements of the type set forth above impair the freedom in constructing the superheater because the tube system forming the latter must be so designed that not only does it produce the desired flow conditions of the superheated steam during normal operation but that it also produces the desired flow conditions of the steam-water mixture during the heating-up period of the steam generator. It is neces-sary to completely eliminate all water from the superheater tubes before normal operation begins and to ensure a steady flow of the steam-water mixture during the heating-up period.

It has been proposed to return, during the heating-up period, the water circulating through the tube system to the feed water 'accumulator by connecting a conduit to the pipe connecting the tube system of the evaporator 'and that of the superheater, and to shield the superheater from flame radiation. ln many cases it is difficult to arrange the superheater so that it is protected from flame radiation, land the superheater` is damaged by thermal stresses, if there is no satisfactory cooling of the superheater.

To avoid the aforedescribed disadvantages, it is proposed to remove the circulating water from the tube system of the generator at a point located between the evaporator and the superheater, after having filled the superheater with Water which evaporates in the superheater during the heating-up period, and towithdraw from the superheater the steam thus produced. This affords a much greater freedom in the construction of the superheater tube system, because it is not necessary to circulate water or a steam-water mixture through the superheater during the heating-up period or to shieldthe superheater from fiame radiation and/or combustion gases. The superheater accordingto the invention `is so constructed that its water content is equal to the amount of water which can be evaporated during the heating-up period, i.e. that all Water is evaporated by the time the steam generator is ready for normal operation.

atent A water separator is interposed between the evaporator and the superheater and to connect a return conduit with the water separator for returning water to the feed' water accumulator during the heating-up period.

It is recommended to arrange a first valve between the water rseparator and the superheater, a second valve in the return conduit, and a third valve in a conduit branched-off from the steam main at the outlet of the superheater -for removing the steam produced in the superheater during the heating-up period. The first two valves afford conducting the working medium through the superheater during normal operation and returning it to the feed water accumulator during the heating-up period, so that the medium does not liow through the superheater during the heating-up period. The third valve affords blowing-off of the steam produced in the superheater during the heating-up period.

The valves may be designed for manual operation or for fullor semi-automatic operation. Particularly the first two valves may be constructed as overow valves for maintaining a desired pressure at the valve inlets. The first valve is preferably provided with conventional adjustment means by which the pressure can be `adjusted during operation of the Valve.

The first valve may be actuated by a control device which is responsive to the condition of the operating medium entering the water separator. The first valve may also be actuated in dependence on the condition of the operating medium leaving the water separator or in dependence on the Water level in the water separator. Similarly, the second valve may be actuated by a conventional device which is responsive to the condition of the operating medium entering the water separator, or to the condition of the operating medium leaving the water separator, or which may be responsive to the water level in the water separator.

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 bestbe understood from the following description of embodiments thereof when read in conjunction withv the accompanying drawing in which:

Fig. l is a diagrammatic illustration lof 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 figures.

During normal operation the operating medium is pumped by a feed pump 2 from a feed waterstorage tank 1 into an economizer 3 and therefrom through an evaporator portion 3 of the tube system of the generator. The wet steam leaving the evaporator passes through a water separator 4 from which ysaturated steam fiows through a valve 5 into a superheater 6, the superheated steam leaving the superheater through an outlet conduit v7.

The valve 5 is closed during the heating-up period and the operating medium is returned through a second valve 8 and a by-pass or return conduit 9 tothe feedwatertank 1. v The circulated water is gradually heated, a steam water mixture emerging from the outletof the steam gem erator after some time, thewater content of the mixture gradually diminishing. The water separator 4, which is initially swamped with water, isk able to separate water from the` steam after a certain period of time. The sep arated water may be removed from the separator 4 through a conduit 10. When saturated steam emerges from the separator, the valve 5 is opened. It is not necessary to wait until the medium at the outlet of the tube system 3 is in the form of dry saturated steam.

the meantime, the water which has been introduced into the superheater 6 prior lto starting the generator or partly during the heating-up period has been completely evaporated. A valve 11 provided in a conduit 12 branched ot from the steam main 7 at the outlet of the superheater, which valve was open during the heatingup period for relieving the steam generated in the superheater during this period, may now be closed, whereby the boiler plant is made ready for normal operation. The valve 11' is preferably actuated by a conventional device 11 which is responsive to the pressure in the pipe 7 so that the valve 11' acts as an overflow valve maintaining a predetermined pressure in the superheating tube system 6.

In the plant shown in Fig. 1, the valves 5 and 8 are constructed as pressure actuated overflow valves which are actuated by a conventional pressure responsive regulator 13 Afor maintaining the pressure at the valve inlet at a predetermined value. Valve is adjusted by means of an adjustment device 14 for closing the valve or for causing greater flow resistance than that effected by the valve 8, 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-waterl ple, as shown in Fig. 2 in which the valve 5 is actuated.

by a conventional control device 15 which is responsive to the condition for example the pressure of the tluid entering the separator 4.

In the modification shown in Fig. 3, the valve 8 is actuated by a control device 15 which is responsive toY the condition of the fluid entering the separator 4.

If both valves 5 and 8 are overow valves, and the valve 5 oiers greater ow resistance than the valve 8 during the heating-up period, the operating iluid will be circulated during the heating-up period in the desired manner. If valve 5 is fully opened and valve 8 is fully closed, the steam will ow through the superheater.

In the modification shown in Fig. 4 the valve 5 is actui ated by a conventional control device 16 which is responsive to the condition of the operating fluid leaving the separator 4. Likewise, the valve 8 may be regulated by a control device 16 which is responsive to the condition of the fluid leaving the separator 4 (Fig. 5). The valve 5 may be fully closed during the heating-up period, and the valve 8 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 17 actuating the valve 5 is responsive to the water level inthe separator 4, whereas Fig. 7 shows a control device 17 which actuates the valve 8 according to the water level in the separator 4.

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

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

What is claimed is: l

1. The method of starting a forced ow steam generator in which, during normal operation, the water is forced from a source of supply through an evaporating tubesystem and the resulting steam is forced through a water separator and therefrom through a superheating tube system, including the following steps: forcing water from the source of supply consecutively through the evaporating tube system, through the water separator, and through the superheater until the latter is flooded; thereupon stopping the flow of operating medium from the steam space of the water separator to the superheater and returning the operating medium from the steam space of the water separator to the source of supply; applying of feed water supply, an evaporating tube system connected with said source for receiving feed water therefrom, a water separator connected with the outlet of said evaporating tube system for receiving operating medium from the latter, a superheating tube system, a iirst conduit connected with the steam space of said water separator and with said superheating tube system for conducting operating medium from the steam space of said water separator into said superheating tube system, a,

rst valve interposed in said rst conduit, a second conduit connecting said rst conduit upstream of said irst valve with said source for returning operating medium from said rst conduit to said source, a second valve interposed in said second conduit, a relief pipe connected with the outlet of said superheating tube system for relieving operating medium therefrom, a valve in said relief pipe, and valve actuating means connected with said first and second valves and including means connected with and being responsive to the pressure of the operating medium in said conduits upstream of said first and second valves for opening said first valve and closing said second valve when the pressure of the operating medium exceeds a predetermined value and for closing said rst valve and opening said second valve when the pressure of the operating medium is below said predetermined value.

References Cited in the tile of this patent UNITED STATES PATENTS 1,898,196 Lucke Feb. 21, 1933 2,035,879 Gleichmann Mar. 3l, 1936 2,065,782 Wood Dec. 29, 1936 2,202,507 Swietochowski May 28, 1940 2,324,513 Junkins July 20, 1943 FOREIGN PATENTS 1,703,228 France Feb. 26, 1929 503,072 Great Britainl Mar. 30, 1939 458,717 Great Britain Dec. 24, 1936 OTHER REFERENCES Steam Boilers (Fowler). Published by Scientific Publishing Co. (Manchester, England), 1908. (Pages 383-384 and 398-399.)

Images