US3130715A - Anti-flash control system - Google Patents

Description

April 28, 1964 D. ARONSON 3,130,715

ANTI-FLASH CONTROL SYSTEM Original Filed June 23, 1960 0 To BOILER DAVID ARo NSON INVEN TOR.

United States Patent 3,130,715 AYTI-FLASH CONTROL SYSTEM David Aronson, Upper Montclair, N.J., assiguor to Worthington Corporation, Harrison, N.J., a corporation of Delaware Continuation of application Ser. No. 38,224, June 23, 1960. This application Feb. 27, 1962, Ser. No. 175,971 8 Claims. (Cl. 122-451) This invention relates generally to boiler feedwater systems of the closed type and more particularly contemplates the embodiment of means in such a system which prevent flashing of feedwater in the event of failure of feedwater to the suction of the feed pump. This application is a continuation of my copending application Serial No. 38,224, filed June 23, 1960, now abandoned.

In open feedwater systems, with a direct contact heater at the suction of the boiler feed pumps such as is shown in Patent 2,372,087, failure of the condensate pump does not present an urgent or immediate problem, as the direct contact heater contains an adequate storage of emergency feedwater which will normally permit the boiler feed pumps to continue operating for a limited period.

In closed feedwater systems, there is no such safety measure, and complete failure of feedwater supply at the suction of the boiler feed pumps would seriously damage the pumps.

Various systems have been incorporated into the construction of power plants to provide emergency feedwater at a predetermined pressure to the suction of the boiler feed pump in the event of failure of the condensate pump.

One such system is disclosed in United States Patent 2,840,052 and overcomes the foregoing problems by providing a surge tank arrangement in a closed feedwater system adapted to deliver emergency feedwater at a predetermined pressure directly to the suction of the boiler feed pump, the surge tank being pressurized to a predetermined pressure by steam, gas, or the like to cause said tank on failure of adequate feedwater supply to the feed pump to supply emergency feedwater thereto.

An analysis of foregoing patent indicates that the problem relating to providing pressurized emergency feedwater in the event of upset in the system is solved but there still remains some hazard associated with the fact that there is an inherent time delay between the time of the upset and the time water becomes available at adequate pressure at the boiler feed suction.

The present invention meets the time delay problem set out above with the provision of a sensing means taking the form of a surge tank of relatively limited capacity which is continuously floating on the line leading to the pump suction to therefore instantaneously provide emergency water of proper pressure in the event of system upset.

Accordingly, it is one object to provide an improved anti-flash control system.

It is another object to provide a sensing means which includes a surge tank and operates to both provide emergency feedwater on failure and actuate a second surge tank into operation when the fluid level in said first surge tank or sensing means falls a predetermined amount.

With these and other objects in view, as may appear from the accompanying specification, the invention consists of various features of construction and combination of parts which will be first described in connection with the accompanying drawings, showing an anti-flash control to prevent flashing of feedwater delivered to boiler feed pumps in a closed type feedwater system of a preferred form embodying the invention and the features forming the invention will be specifically pointed out in the claims.

Patented Apr. 28, 1964 Referring to the drawings, there is shown a closed feedwater cycle generally designated 1 which includes a condensate pump 2 for extracting condensate from hot well 3 of the condenser 4 and delivering it through one or more closed heaters 5 to the boiler feed pump 6 through suction line 7 connected therebetween. This arrangement is well known in the art and accordingly is not more fully discussed herein. Furthermore, it is believed clear that if failure of the condensate pump 2 occurs for any reason or should there be a lack of properly pressurized feedwater supply to the boiler feed pump 6 the unit must be stopped or emergency feedwater fed thereto to prevent mechanical failure.

In a commercial installation it is highly desirable to keep the entire system in operation. The present invention illustrates an arrangement of anti-flash control which permits continued operation or provides for continuous operation until the deficiency is corrected in the event of a failure by providing means which supply pressurized water to the line 7 as soon as a drop-off of pressure occurs in line 7.

Generally a sensing means taking the form of a first surge tank 8 is connected to line 7 and preferably between closed heater 5 and boiler feed pump 6 and the sensing means 8 normally pressurized as by pressure fluid passed thereto through line 9 as will be described in detail hereinafter passes pressurized liquid to the suction of pump 6 in the event of a pressure drop caused by condensate pump failure or system upset.

A second surge tank 10 also connected to line 7 and preferably between condensate pump 2 and heater 5 is maintained normally out of communication with line 7 by check valve 11 and provides pressurized water to line 7 and pump 6 through line 12 when the fluid level in surge tank 8 falls below a predetermined level to thusly provide the required emergency feedwater.

The pressurizing of both surge tanks 8 and 9 is necessary to provide the head required to prevent the hazardous flashing discussed above. This is accomplished by providing a pressurized source of fluid to the surge tanks through lines 9 and 18 and by setting a first valve 13 in line 18 in normally closed position and setting a second valve 14 in line 9 in a normally open position, and functioning as a three way valve either to admit steam to surge tank 8, to bleed steam from surge tank 8 to condenser 4 through line 20, or to close oif flow either in or out, all as determined by the level controller 16. Under normal conditions of essentially constant pressure discharge from condensate pump 2, a small flow of steam is passed to surge tank 8, to provide for makeup of steam condensed in the surge tank by reason of heat loss from the tank 8 to the surroundings. On increase of pressure at the discharge of the condensate pump 2, the level in surge tank 8 will rise, due to the compression of the steam above the liquid, and additional steam will have to be admitted to restore the liquid level to the control position. Conversely, on decrease of pressure at the discharge of pump 2, the steam above the liquid will expand and the level of liquid will tend to fall. Action of the controller 16 will then move valve 14 to such position as to bleed steam from the surge tank 8, and therefore allow the liquid level to rise to the control point. As will be obvious to one skilled in the art, such restoring action will hold the liquid level within such limits as to preclude a false signal being sent by level control 17.

Where there is a drastic and sudden decrease in the discharge pressure of pump 2, as occurs when said pump becomes inoperative, then the restoring action of level control 16 setting the position of three-way valve 14 is inadequate to keep the level from falling below the setting of level control 17, and accordingly a true signal is sent by level control 17 to actuate valve 13 which admits steam to surge tank 10.

The possibility of having a mechanism which can distinguish between moderate decreases in pump discharge pressure, and the rapid decrease associated with pump failure, is inherent in the nature of the system. So long as the pump is running and subject only to changes in pressure associated with the characteristic pressure-flow relationship of the pump, the liquid will be at a pressure substantially above saturation. However, on pump failure, the pressure falls to that related to the temperature of the water in the uppermost portion of surge tank 8. Due to the physical elevation of the surge tank 8 above the inlet of the boiler feed pump 6, there will be sulficient pressure to avoid cavitation at the boiler feed pump suction, and also, the steam liberated by the hot water in the uppermost portion of the surge tank 8 will be in such volume as to exceed the bleed-off capability of threeway valve 14, and so cause the level to fall below the setting of level control 17, thus correctly initiating the opening of control valve 13. One skilled in the art will design control valve 14 to have the flow characteristics which will handle the routine variations in discharge pressure of condensate pump 2, bleeding oli steam at an adequate rate, but not having such a large capacity as to vitiate the desired emergency performance of surge tank 8 on failure of condensate pump 2.

More particularly to transfer the operation from surge tank 8 to surge tank 10 to provide a reservoir having greater capacity of fluid, actuating means such as the usual diaphragm in valves 13 and 14 are moved by a signal from control means shown as liquid level responsive controls 16 and 17 to permit flow of pressure fluid to surge tank 10 by opening valve 13 and to prevent flow to surge tank 8 by closing valve 14.

Controls 16 and 17 are set at a point about 75% and 70% of the way from bottom of the tank, and these controls may be of the type shown in Mason-Neilan Division of Worthington Corporation Instructions No. 4003, dated September 1955, and copyrighted 1948, entitled Ball Float Pilot Operated Liquid Level Controllers.

Thusly it is evident that on initial failure of required fluid flow to pump 6, surge tank 8 instantaneously supplies same and as soon as liquid level in said tank drops below a predetermined level control means 16 and 17 signal valves 13 and 14 to transfer their operative relation relative lines 18 and 9 to therefore cause emergency pressure fluid to be supplied .to pump 6 from surge tank 10.

It will be understood that the invention is not to be limited to the specific construction or arrangement of parts shown but that they may be widely modified within the invention defined by the claims.

What is claimed is:

1. Means for preventing flashing of feedwater in a boiler feed system of the closed type including, a condensate pump, a boiler feed pump having a suction inlet and conduit means interconnecting said condensate pump and the suction inlet of the boiler feed pump, said means including, sensing means comprising a surge tank connected to said conduit means, a second surge tank connected to said conduit means, said sensing means connected downstream from said second surge tank, pressure fluid supply means connected to said second surge tank and sensing means, control means connected to said pressure fluid supply means to normally maintain flow of pressure fluid to said sensing means and normally prevent flow of pressure fluid to said second surge tank, and actuating means interconnecting said sensing means and control means, and said actuating means including means responsive to fluid level in said sensing means to cause said control means to prevent flow of pressurized fluid to said sensing means and provide flow of fluid to said second surge tank when the fluid level in said sensing means falls a predetermined amount.

2. Means for preventing flashing of feedwater in a boiler feed system of the closed type including, a condensate pump, a closed heater, and a boiler feed pump having a suction inlet, said means including, a sensing means comprising, a first surge tank connected to the suction inlet of said boiler feed pump for delivering emergency feedwater thereto at a pressure exceeding the pressure at the suction inlet in the event of failure of the condensate pump, and a second surge tank connected to the suction inlet of said boiler feed pump operative to deliver emergency fluid thereto at a pressure exceeding the pressure at the suction inlet when the level in said first surge tank falls a predetermined amount, pressure fluid supply means connected to the sensing means and second surge tank, control means connected to said pressure fluid supply means to normally maintain flow of pressure fluid to said sensing means and normally prevent flow of pressure fluid to said second surge tank, and actuating means interconnecting said sensing means and control means and said actuating means including means responsive to fluid level in said sensing means to cause said control means to prevent flow of pressurized fluid to said sensing means and provide flow of fluid to said second surge tank when the fluid level in said sensing means falls a predetermined amount.

3. Means for preventing flashing of feedwater in a boiler feed system including, a condensate pump, a closed heater, a boiler feed pump having a suction inlet, and fluid flow means connecting said condensate pump, closed heater and boiler feed pump in closed circuit relation; said means for preventing flashing of feedwater including, a sensing means comprising, a first surge tank connected to said fluid flow means between said closed heater and suction inlet and for delivering emergency feedwater thereto at a pressure exceeding the pressure at the suction inlet in the event of failure of the condensate pump, a second surge tank connected to said fluid flow means between said condensate pump and closed heater to provide emergency fluid to said suction inlet when the level in said first surge tank falls at predetermined amount, pressure fluid supply means connected to the sensing means and second surge tank, control means connected to said pressure fluid supply means to normally maintain flow of pressure fluid to said sensing means and normally prevent flow of pressure fluid to said second surge tank, and actuating means interconnecting said sensing means and control means and said actuating means including means responsive to fluid level in said sensing means to cause said control means to prevent flow of pressure fluid to said sensing means and provide flow of fluid to said second surge tank when the fluid level in said sensing means falls a predetermined amount.

4. The apparatus claimed in claim 3 wherein the control means comprises, a first control valve, and a second control valve.

5. The apparatus claimed in claim 4 wherein said actuating means comprises, a first and second liquid level control, operatively associated with the first and second valves.

6. Means for preventing flashing of feedwater in a boiler feed system of the closed type including, a condensate pump, a closed heater, a boiler feed pump having a suction inlet, conduit means interconnecting said condensate pump and said closed heater to the suction inlet of said boiler feed pump, said means comprising, a first surge tank connected to said conduit means for delivering emergency feedwater to the suction inlet of said boiler feed pump, a second surge tank connected to said conduit means and operative for delivering emergency feedwater to said boiler feed pump when the level in said first surge tank falls a predetermined amount, said first surge tank connected downstream from said second surge tank, pressure fluid supply means connected to said first and second surge tanks, first means connected to the first surge tank and said pressure fluid supply means for normally maintaining pressure fluid flow to said first surge 8. The apparatus claimed in claim 7 wherein the first tank, second means connected to said pressure fluid supand second valves are actuated into operation by a liquid ply means and responsive to fluid level in said first surge level control connected to the first surge tank. tank to normally prevent flow to said second sur e tank and cause pressure fluid flow to said second surge tank 5 References Cited In m6 file of thls patent when the level in said first surge tank falls said predeter- UNITED STATES PATENTS mined amount, and said first means to prevent flow of 2,314,899 Samiran Man 30, 9 pressure fluid to said first surge tank when the level in 2,840,052 Rarassik June 24 1953 said first surge tank falls said predetermined amount.

7. The apparatus claimed in claim 6 wherein the first 10 FOREIGN PATENTS and second means include, a first and a second valve. 531,062 Great Britain Dec. 27, 1940

Claims (1)

1. MEANS FOR PREVENTING FLASHING OF FEEDWATER IN A BOILER FEED SYSTEM OF THE CLOSED TYPE INCLUDING, A CONDENSATE PUMP, A BOILER FEED PUMP HAVING A SUCTION INLET AND CONDUIT MEANS INTERCONNECTING SAID CONDENSATE PUMP AND THE SUCTION INLET OF THE BOILER FEED PUMP, SAID MEANS INCLUDING, SENSING MEANS COMPRISING A SURGE TANK CONNECTED TO SAID CONDUIT MEANS, A SECOND SURGE TANK CONNECTED TO SAID CONDUIT MEANS, SAID SENSING MEANS CONNECTED DOWNSTREAM FROM SAID SECOND SURGE TANK, PRESSURE FLUID SUPPLY MEANS CONNECTED TO SAID SECOND SURGE TANK AND SENSING MEANS, CONTROL MEANS CONNECTED TO SAID PRESSURE FLUID SUPPLY MEANS TO NORMALLY MAINTAIN FLOW OF PRESSURE FLUID TO SAID SENSING MEANS AND NORMALLY PREVENT FLOW OF PRESSURE FLUID TO SAID SECOND SURGE TANK, AND ACTUATING MEANS INTERCONNECTING SAID SENSING MEANS AND CONTROL MEANS, AND SAID ACTUATING MEANS INCLUDING MEANS RESPONSIVE TO FLUID LEVEL IN SAID SENSING MEANS TO CAUSE SAID CONTROL MEANS TO PREVENT FLOW OF PRESSURIZED FLUID TO SAID SENSING MEANS AND PROVIDE FLOW OF FLUID TO SAID SECOND SURGE TANK WHEN THE FLUID LEVEL IN SAID SENSING MEANS FALLS A PREDETERMINED AMOUNT.

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