US2840052A - Control means to prevent flashing of emergency feedwater delivered to boiler feed pumps in a closed type feedwater system - Google Patents

Description

June 24, 1958 J. KARASSIK 2,840,052

CONTROL mums TO PREVENT FLASHING OF EMERGENCY FEEDWATER DELIVERED TO BOILER FEED PUMPS IN A CLOSED TYPE FEEDWATER SYSTEM Filed Aug. 1'7, 1954 STEAM PRESSURE REDUCING VALVE WATER SURGE INLET TANK VALVE FLOAT CONTRDL Z9 CONDENSER CHECK 3 H01 WELL VALVE 5 FE-SSURE IMPULSE Z I I 9 9 2' WW- Q 6 CONDENSATE c'zuosso PUMP HEATERS BOILER FEED PUMP as 0 I4 5 WATER PUMP FIG l I 7 zs 2 IGOR J'QKARASSIK INVENTOR.

I 2 BY United States PatentO CONTROL MEANS TO PREVENT FLASHING .OF EMERGENCY FEEDWATER. DELIVERED TO BOILER FEED PUMPS IN A CLOSED TYPE FEEDWATER SYSTEM Igor J. Karassik, Maplewood, N. J.

. Application August 17, 1954, Serial No. 450,463

3 Claims. (Cl. 122-451) emergency feedwater which will normally permit the boiler feed pumps to continue operating for a limited period. i

In closed feedwater cycles, there is no such safety measure, and complete failure of feedwater supply at the suction of the boiler feed pumps would seriously damagethe pumps. I 5

Accordingly, some protective measure must be provided to avoid and overcome this condition.- In the early days when the operating temperatures of the feedpumps were relatively moderate, it was possible to install a surge tank in the suction line containing a reasonable .volume of cold Water storage ready to supply emergencyfeedwater to the feed pump on failure of the condensate supply. For example, if the feed pump handled feedwater at 240 F. (vapor pressure equal to 10.2 p. s. i. .g.) and if the minimum net positive suction head were feet (10.2 p. s. i. g.), the water level in the surge tank could .be held at about 50 feet which would be equivalent to :20.4 p. s. i. g. minimum suction pressure. A check valveinstalled in the line between the surge tank and the suction header would open at 20.4 p. s. i. g. and thecold water from the surge tank would flow to the boilerfeed pump, acting as a protective measure.

Two separate factors, however, have made this solution 2 feed pump, the surge tank being pressurized to the predetermined pressure by steam, gas or the like when failure of the condensate pump occurs for any reason, such failure being signalled by suitable automatic control means to actuate the pressurizing of the surge tank.

Accordingly, it is an object of the present invention to preventfiashing of'feedwater delivered to the boiler feed pump in'aclosed type feedwater cycle. f 'It is another object of the present invention to provide a system wherein the surge tank is pressurized only when the emergency requires or demands it thereby minimizing heat loss and/or other costs for this system.

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 a control means 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.

In the drawings:

Figure 1 is .a diagrammatic sketch of a boiler feed system showing the invention associated therewith.

'Figure'Z is a diagrammatic illustration of the anti-flash control;

Referring to the drawings, Figure 1 shows a closed feedwater cycle generally designated 1 which includes a condensate pump 2 for extracting condensate from the 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 thereoetween. This at} rangement is well known in the art, hence is not more fully discussed. However, it is believed clear thatjif failure of the condensate pump 2 occurs for any reason that thebo'ilerjfeed pump must be stopped, or emergency feedwater .fed thereto prevent mechanical failure. I

Ina commercial installation it is highly desirable to keep the entire system in operation. Accordingly, the present invention illustrates an arrangement which will produce this result. i I

Thus a surge tank 8 is shown as connected to the suction line 7 by means of a connecting pipe 10 having a check valve 9 disposed therein which will open when the pressure in the surge tank 8 rises above the pressure in the suction line" 7 developed by pump 2 during normal inapplicable to the systems which are in operationtoday:

placedat the highest elevation consistent with sound ina. Boiler feed pump capacities have increased sothat the minimum net positive suction head required may be as high as 40 and even 60 feet. I

b. Operating temperatures have increased.

These factors have combined to increase the minimum suction pressure to a point where the high water levelrequired in thestorage tank is beyond practicality.

Accordingly, ,'where the condensate pumps, 7 their drivers or the power supply to the drivers fail in a closed type feedwater cycle, the problem is once agaiupresented to provide protective means to prevent damage to the boiler feed pumps on failure of the-condensate pumps.

In theory, it is believed that a flashing condition at the pump suction of a very limited duration will not neces-' sarily cause undue damage to the boiler feed pumps; howoperation. i

,The pressuri zing of the surge tank 8 is necessary to theoretically raise the static elevation of the surge tank 8' because as a general rule while the surge tank will be 's'tallation costs, such actual elevation under normal conditions would: not give suflicient net positive suction head to the emergency feedwater to prevent flashing of the feedwaterbe'ing delivered from the condensate pump 2 to the boiler feed pump 6 in the event of a failure of the condensate pump for any reason.

Pressurizing of the surge tank 8 is accomplished by delivering steam under pressure to the surge tank 8 through a line'11 connected to any suitable source. It willbe understood that while steam is illustrated in the present'invention that gas or other suitable pressurizing vapor might be utilized for this purpose. A control and steam pressure reducing valve 12 is provided in the line 11 for regulating the flow and the pressure of the stearn delivered to the surge tank 8 whenever failure occurs for any reason.

The control and steampressurereducing valve 12 is opened by operation of a'diaphragm motor 13 which type v'alves. are well ,known and easily purchasable on the open market, the type valve shown in the present installation being of the normally closed type which is opened when the diaphragrn is actuated by air and pressure fed thereto through line 14 under controlof the air valve 15. 7 l v The air line valve is opened "and closed by operation of the solenoid 16 in turn operated by an anti-flashcontrol generally designated 17 and more fully discussed hereinafter. It will be understood that the control and steam producing valve 12 could be directly operated by the solenoid if it is desired v to eliminate the air pressure operation means indicated in the present structure.

Thus, the anti-flash, control mechanism includes, a temperature sensitive bulb 18 disposed at any suitable point in line 7 adjacent the suctionof the boiler feed pump to measure the temperature variations of the feedwater passed from condensate pump, 2 to-boiler feed pump 6.

Temperature sensitivebulb 18 is connected to capillary tube 19 and calibrated bellows 20 having a pointer '5 21 atone end movable with the expansion and contrac-' tion of the bellows 20. The bulb; 18, capillary tube 19 and bellows 20 are filled with any suitableffluid so that temperature variations at the bulb will cause corres ponding changes in the pressure of the internal fluid thereby actuatingthe bellows 20 and pointer 21 to, fluctuate sub stantially' in accordance with the vapor pressure of the feedwater at the measured temperature.

A similar pointer 22 fluctuates in accordance with the variations in absolute pressure. This pointer is connected 4:.

to bellows 23, capillary tube 24 and. connection 25 disposed adjacent the suction .of the boiler 'feed pumpf6. The actual pressure of the feedwaterbeing pumped from condensate pump 2 to boiler feed pump 6 will actuate the pointer 22 directly through these connections.

The distance between the pointers 21 and 22 asthey move towards and away from eachotherfrepresents" at all temperatures and pressures, the net difference between the vapor pressure of'the feedwater at the temperature measured and the actual pressure of the feedwater, all taken at the critical point in the system.

The pointers 21 and 22 act as asw itch when brought into contact with each other, acontact arm 21dbeing provided. to open and close the circuit through'the electrical lines 26 and .27 so that the control of current from any suitable source to actuate the solenoid 16 of the valve 15 may be controlled in accordance with the requirements of the system.

' Operation In this closed type boiler feed system, as long as the suction pressure is higher than the vapor pressure by a predetermined minimum pressure representing the re quired net positive suction headv at the boiler feed pump, the anti-flash control mechanism 17 will not open the air control valve 15 in the air line 14,and since the valve 85 open market will control the flow of water delivered to the surge tank 8 by the level of its float 31 disposed in the tank 8.

When the condensate pump 2 is reactivated the suction pressure will be built up thereby and the resultant pressure change will actuate the bellows to separate the pointers 21 and 22 thereby opening the circuit to the solenoid closing the valve 15 and the air line 14 which renders the diaphragm motor 13 inactive and allows the valve 12 also to close. The valve 12 will, of. course, remain closed until this above described procedure occurs once again when the condensate pump fails for any reason.

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

Whatis claimed is: 1. Means for preventing flashing of feedwater in a boiler feed system of the closed type including, in combination on the suction portion thereof, a condensate pump, a closed heater and a boiler'feed pump having a suction inlet, said means comprising a surge tank adapted for connection to said suction inlet for delivering emergency feedwater thereto at a pressure exceeding the suction pressure at the suction inlet of said boiler feed pump in the event of failure to the condensate pump, pipe means providing communication between said surge tankand said suction inlet, .valve means in said pipe line operative to preclude flow from said surge tank to said suction inlet when the condensate pump is operative in providing a predetermined fluid flow to said boiler feed pump, pressure fluid supply means connected to said surge tank to provide a source of pressure fluid thereto to increase the pressure in said surge tank, and means connected to said suction portion actuated by the temperature of the suction feedwater in terms of its vapor pressure at the suction inlet, means connected at another point in said suction portion actuated by the absolute and actuates the solenoid 16 to open the air valveil5 supplying air to the diaphragmniotor 13; The diaphra'gm motor 13 will then" actuate to open the control and steam pressure reducing valve 12 and steam under pressure will be delivered instantaneously to the surge tank 8. When the pressure in the surge tank 8 reaches the predetermined required pressure, the check valve 9 will open and deliver emergency. feedwater to the suction line7 of the boiler feed pump 6.

To insure a continued supply of emergency feedwater to the surge tank 8 during such emergencies, water from any suitable. source is delivered by the pump 28 and line 29 to the surge tank 8. Afloat controlled inlet valve 30 which is a standard unit easily purchasable on the pressure at the suction inlet, and means responsive to a predetermined pressure differential between said vapor pressure actuated means and said absolute pressure actuated means for actuating'said pressure fluid supply means.

,2. Means for preventing flashing of feedwater in a boiler feed system of the closedtype including, in combination on the suction portion thereof, a condensate pump, a closed heater and a boiler feed pump having a suction inlet, said means comprising a surge tank adapted for connection to said suction inlet for delivering emergency feedwater thereto at a pressure exceeding the suction pressure at the suction inlet of said boiler feed pump in the event of failure of the condensate pump, pipe means providing communication between said surge tank and said suction inlet, valve meansin said pipe line operative to preclude flow from said surge tank to said suction inlet when the condensate pump is operative in providing a predetermined fluidflow' to said boiler feed pump, pressure fluid supply'means connected to said surge tankto provide a source of pressure fluid thereto to increase the pressure in said surge tank, a diaphragm operated pressure reducing valve connected between said surge tank and said pressure fluid supply means, and means operatively connected to said suction inlet for actuating said pressure reducing valve responsive at a predetermined minimum pressure difierential between the temperature of the suction feedwaterin terms of its vapor pressure and the absolute pressure at the suction inlet including, means for determining the vapor pressure at the suction inlet, means for determining the absolute pressure at said suction inlet, and a switch mechanism actuated at said predetermined minimum pressure differential between said vapor pressure measuring means and said absolute pressure measuring means to actuate the diaphragm operated pressure reducing valve to open position.

3. Means for preventing flashing of feedwater in a boiler feed system of the closed type including, in combination on the suction portion thereof, a condensate pump, a closed heater and a boiler feed pump having a suction inlet, said means comprising a surge tank adapted for connection to said suction inlet for delivering emergcncy feedwater thereto at a pressure exceeding the suction pressure at the suctioninlet of said boiler feed pump in the event of failure of the condensate pump, pipe means providing communication between said surge tank and said suction inlet, valve means in said pipe line operative to preclude flow from said surge tank to said suction inlet when the condensate pump is operative in providing a predetermined fluid flow to said boiler feed pump, pressure fluid supply means connected to said surge tank to provide a source of pressure fluid thereto to increase the pressure in said surge tank, and means in said suction portion responsive to a predetermined minimum pressure difierential between the temperature of the suction feedwater in terms of its vapor pressure and the absolute pressure at the suction inlet of said boiler feed pump for actuating said pressure fluid supply means.

References Cited in the file of this patent UNITED STATES PATENTS 2,152,979 Schwander Apr. 4, 1939 2,372,087 Karassik Mar. 20, 1945 2,489,345 Welch Nov. 29, 1949 2,636,721 Spining Apr. 28, 1953

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