US3240187A

US3240187A - Method of starting once-through type boilers

Info

Publication number: US3240187A
Application number: US327639A
Authority: US
Inventors: Tamura Zensuke
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1962-12-04
Filing date: 1963-12-03
Publication date: 1966-03-15
Anticipated expiration: 1983-03-15
Also published as: GB1055989A; DE1248677B

Description

March 15, ZENSUKE TAMURA METHOD OF STARTING ONCE-THROUGH TYPE BOILERS Filed Dec. 5, 1963 Fig.

VALVE TURBINE DETECTOR 1 m CONDENSER 2 I F H I I 5% 5 L I .J I BOILER DEAERATOR Fig. 2

Flowouf rafe 0f flu/0 Time Fig. 3 F ue/ rafe ATTORNEY United States Patent Olhce 3,24%,187 Patented Mar. 15, 1966 METHOD OF STARTHNG flNCE-TERQUGH TYPE BOILERS Zensulre Tamara, Hitachi-sin, Japan, assignor to Hitachi, Ltd Tokyo, Japan, a corporation of Japan Filed Dec. 3, 1963, Ser. No. 327,639

Claims priority, application Japan, Dec. 4, 1962,

$763,658 2 Claims. (Cl. 122-406) This invention relates to once-through type boilers, and more particularly to method or process of starting operation of such type of boiler plants.

As is well-known, in starting operation of boiler plants of once-through type, the so-called water swelling phenomena is inevitable, and necessitates the use of piping of larger capacity than that required during normal operation when such phenomena does not occur at all, resulting in poor economy.

An object of the present invention is to provide method or process of starting operation of boiler plants of the kind specified, in which the water swelling phenomena is substantially prevented from occurring.

Another object of the present invention is to provide method or process of starting operation of boiler plants of the kind specified, wherein peak values in the rate of water flowing out during the water swelling phenomena are so low that the capacity of the bypass piping can be remarkably smaller than ever.

There are other objects and particularities of the present invention, which will best be understood from the following detailed description of the invention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a boiler plant of through-flow type, in which the present invention is carried out;

FIG. 2 is a curve diagram showing relations between the flowing-out rate of water or working medium and the fuel rate during starting of the boiler plant shown in FIG. 1, as well as the plant modified according to the present invention; and

FIG. 3 shows characteristic curves of the boiler plants embodying the present invention.

A typical boiler plant of once-through type is schematically shown in FIG. 1 of the accompanying drawings, and comprises a feed water pump 1 for supplying highpressure water to a boiler 2, a secondary superheater 3 for generating high-pressure steam, a turbine 11 actuated thereby, a condenser 12, a condenser pump 13, and a deaerator 14 connected before the pump 1. Though not illustrated, there may be provided a feed-water heater before the pump 1 for preheating feed water by utilization of exhaust steam.

The boiler plant shown in FIG. 1 is also provided with a superheater bypass circuit and a turbine bypass circuit connecting the inlet and outlet or" secondary superheater 3 with the condenser 12, and these comprising a superheater bypass valve 5, a turbine bypass valve 7, pipe 6', a flash tank 8, a path 18 including a dump valve 9 for passing steam from flash tank 8 to the steam chamber of condenser 12, and a path 19 including a drain valve for passing saturated water from flash tank 8 to the hot well of condenser 12.

During the period of starting of the once-through type boiler plant as shown in FIG. 1, when the boiler output is low and steam cannot be generated in a predetermined state, the turbine, or the superheater and turbine, are usually by-passed by way of the above-referred circuits for circulating generated steam directly through the condenser 12. In such a type of boiler plants, undesirable water swelling occur during starting operations.

At the start of such a type of boiler plant, the heat absorption rate is generally first maximum in the waterwall portion of the boiler, so that the temperature of the water rises very quickly at the outlet of the water wall, and before the water at the outlet of boiler would have reached saturation temperature, the water in the waterwall portion reaches saturation temperature, resulting in undesirable expansion of water therein, which forces a large amount of water at undersaturation temperature to flow into the bypass circuit through the valve 5.

In avoiding serious problems resulting from this water swelling phenomena a superheater bypass valve 5 and a turbine bypass valve 7 are utilized for maintaining the pressure of circulatory system constant. Thus, when the system pressure rises, the condition is detected by pressure detector 20 and the opening of valves 5 and 7 will be increased to prevent the pressure rise, so that they serve as safety valves during normal operation of the boiler plant. Consequently, when the flow-out rate of water is extraordinarily increased as in the case of the water swelling phenomena, the valves 5 and 7 are caused to increase their opening for preventing pressure rise in the system, but in order to enable such a pressure rise to be prevented, the valve opening, as well as, the piping should be remarkably large, resulting in poor economy.

The present invention proposes to provide means in connection with the method or process of starting such a type of boiler plant, whereby the peak value of flow-out rate of water is decreased during the period when the water swelling would otherwise occur, so that the bypass piping and the bypass valves required by virtue of such phenomena may be of decreased capacity.

The superheater bypass valve 5 and the tunbine bypass valve '7 increase their opening automatically when the system pressure rises in response to control from pressure detector 2%, such action being of particularly increased speed or response and of increased opening when water swelling occurs. The present invention provides for control between the bypass valves 5 and '7 and the fuel regulating valve 16, so that the tension of increased pressure due to water swelling by valves 5 and 7 results in an automatic decrease in the rate at which fuel is supplied to the burner 15, and when the valve-closing actuation is commenced, the fuel system is returned to normal automatically.

In FIG. 2, the solid-line curves show the relation between fuel rate and flow-out rate of fluid at the boiler outlet in old boiler plants, while dotted-line curves show the corresponding relation in a boiler plant embodying the present invention. The relation between fuel rate and superheater-bypass-valve opening obtained when the present invention is embodied is shown in FIG. 3. It will eadily be understood from these curve diagrams that, when the fuel rate is decreased, upon occurrence of water swelling according to the present invention the flow-out rate of fluid is remarkably decreased, and the maximum opening of bypass valve 5 and piping capacity may be decreased remarkably, resulting in good economy.

-In PEG. 1, a suitable control system for automatic starting operation according to the present invention is shown by dotted lines, whereby the opening degrees of bypass valves 5 and 7 are automatically detected by valve detectors 21 and 22, respectively, and only when their opening have increased extraordinarily or beyond predetermined degrees, the fuel supply is automatically decreased. In practice, such a control system as above outlined may be provided utilizing well-known control elements and combinations which are illustrated schematically in FIG. 1 as detectors 21 and 22. When the fuel system includes a relatively large operational time-lag, as when coal is used as the boiler fuel, the temperature of water wall or evaporator that would have reached the saturation temperature might be used as the control for decreasing the rate of supply of boiler fuel.

Thus, according to the present invention, the variation of flow-out rate of working medium is reduced, so that the piping capacity may be decreased remarkably with smallerdiameter pipes and smaller valves, resulting in good economy. In addition water swelling may be suppressed or prevented, so that starting operations can be effected in a stable and smooth manner.

What I claim is:

1. The method of controlling the starting operation to effectively reduce water swelling in a once-through type boiler circuit including a boiler having a burner, a turbine, a superheater connected between said boiler and the input side of said turbine, a condenser connected to the exhaust side of said turbine, and bypass means including a valve for connecting the output of said boiler directly to said condenser in response to detection of increased pressure in said boiler, the method comprising during passage of water through said bypass means with said valve in the open condition in response to the pressure of said water,

detecting the amount of water flowing through said bypass means by the degree of opening actuation of said valve,

decreasing the rate of fuel supplied to said burner only in response to detection of the amount of water flowing through said valve above a limit representing an indication of the initial stages of water swelling in said boiler, and

restoring the normal rate of fiow of fuel to said boiler upon reduction of said water flow below said limit as determined by the reduced degree of opening actuation of said valve.

2. The method of controlling the starting operation to effectively reduce water swelling in a once-through type boiler circuit including a boiler having a burner; a turbine, a superheater connected between said boiler and the input side of said turbine, a condenser connected to the exhaust side of said turbine, and bypass means for connecting the output of said boiler and said superheater directly to said condenser in response to detection of increased pressure in said boiler including first and second pressure responsive valves controlling the flow from said boiler and said superheater into said bypass means, respectively, the method comprising during passage of water through said bypass means with both said first and second valves in the open condition in response to the pressure of said water,

detecting the amount of water flowing through said bypass means by the degree of opening actuation of both valves, decreasing the rate of fuel supplied to said burner only in response to detection of the amount of water flowing through said valves above a limit representing an indication of the initial stages of water swelling in said boiler, and restoring the normal rate of flow of fuel to said boiler upon reduction of said water flow below said limit as determined by the reduced degrees of opening actuation of said valves.

References Cited by the Examiner UNITED STATES PATENTS 2,900,792 8/1959 Buri 122-406 3,035,557 5/ 1962 Litwinoff 122406 3,055,181 9/1962 Argesinger et al. 122406 FOREIGN PATENTS 879,032 10/ 1961 Great Britain.

OTHER REFERENCES German printed application No. 1,103,348, printed Mar. 30, 1961.

German printed application No. 1,109,705, printed June 29, 1961.

Publication: Large Sub and Supercritical Steam Generator Startup and Control System Integration with the Turbine Generator, by C. Strohrneyer, Jr. Reprint of paper represented at American Power Conference, Mar. 29, 1962, Chicago, Ill. (Pages 6-10 and Figs. 5-10, 4 pp. in particular) FREDERICK L. MATIESON, JR., Primary Examiner.

KENNETH W. SPRAGUE, ROBERT A. OLEARY,

Examiners.

Claims

1. THE METHOD OF CONTROLLING THE STARTING OPERATION TO EFFETIVELY REDUCE WATER SWELLING IN A ONCE-THROUGH TYPE BOILER CIRCUIT INCLUDING A BOILER HAVING A BURNER, A TURBINE, A SUPERHEATER CONNECTED BETWEEN SAID BOILER AND THE INPUT SIDE OF SAID TURBINE, A CONDENSER CONNECTED TO THE EXHAUST SIDE OF SAID TURBINE, AND BYPASS MEANS INCLUDING A VALVE FOR CONNECTING THE OUTPUT OF SAID BOILER DIRECTLY TO SAID CONDENSER IN RESPONSE TO DETECTION OF INCREASE PRESSURE IN SAID BOILER, THE METHOD COMPRISING DURING PASSAGE OF WATER THROUGH SAID BYPASS MEANS WITH SAID VALVE IN THE OPEN CONDITION IN RESPONSE TO THE PRESSURE OF SAID WATER, DETECTING THE AMOUNT OF WATER FLOWING THROUGH SAID BYPASS MEANS BY THE DEGREE OF OPENING ACTUATION OF SAID VALVE, DECREASING THE RATE OF FUEL SUPPLIED TO SAID BURNER ONLY IN RESPONSE TO DETECTION OF THE AMOUNT OF WATER FLOWING THROUGH SAID VALVE ABOVE A LIMIT REPRESENTING AN INDICATION OF THE INITIAL STAGES OF WATER SWELLING IN SAID BOILER, AND RESTORING THE NORMAL RATE OF FLOW OF FUEL TO SAID BOILER UPON REDUCTION OF SAID WATER FLOW BELOW SAID LIMIT AS DETERMINED BY THE REDUCED DEGREE OF OPENING ACTUATION OF SAID VALVE.