US3338033A

US3338033A - Boiler feed water system with vacuum deaeration

Info

Publication number: US3338033A
Application number: US571072A
Authority: US
Inventors: Gene W Ross
Original assignee: Sybron Corp
Current assignee: Sybron Transition Corp
Priority date: 1966-08-08
Filing date: 1966-08-08
Publication date: 1967-08-29
Anticipated expiration: 1984-08-29

Description

s- 29, 96 G- w. Ros 3,338,033

BOILER FEED WATER SYSTEM WITH VACUUM DEAERATION Filed Aug. 8, 1966 INV ENT OR f/l f 2053 ATTORNEYS United States Patent 3,338,033 BOILER FEED WATER SYSTEM WITH VACUUM DEAERATION Gene W. Ross, Lorain, Ohio, assignor, by mesne assignments, to Ritter Pfaudler Corp., Rochester, N.Y., a

corporation of New York Filed Aug. 8, 1966, Ser. No. 571,072 7 Claims. (Cl. 55-464) This invention relates to steam boiler feed systems and in particular to vacuum deaeration equipment for removing dissolved gas from the steam condensate before the latter is returned to the boiler for reuse.

The concept of deaerating steam condensate and makeup water before use in a boiler for the purpose of reducing the corrosive effect of dissolved gases is well known. One type of known vacuum deaerating equipment operates by enclosing a charge of water in a sealed chamber and subsequently pumping some of the Water out of the chamber so as to reduce the pressure in the tank. The vacuum produced by this means is equal to the vapor pressure of the water at the temperature of the water. The water is thus at its boiling point, and since the solubility of gases is zero under this condition, a high percentage of dissolved gases come out of solution and collect above the water surface. The deaerated Water is then supplied to a boiler as feed water.

It is the primary object of the present invention to provide a steam boiler feed water system having simplified, low-cost vacuum deaerating and storage equipment and a novel piping arrangement for connecting the equipment into the boiler system.

It is another object of the invention to provide a compact, low-cost vacuum deaerator for use in treating steam condensate and makeup water, the deaerator being adapted to be constructed as a complete unit at its place of manufacture and subsequently connected into a boiler feed system with a minimum of expense.

The invention will be further understood from the following description of an illustrative embodiment taken with the drawing in which the sole figure is a diagrammatic elevational view, partly in section, of a steam boiler system having a feed water system embodying the principles of the invention.

The illustrated boiler system comprises a conventional steam-generating boiler 10 having a feed water inlet pipe 12 leading from a boiler feed pump 14 and a steam discharge pipe 16 which supplies steam to steam-consumption equipment, such as radiators 20 employed to heat a building. Condensate from the steam-consumption equip ment passes into armain condensate line 22 which leads to a combined feed water accumulator and deaerator 24 located adjacent the boiler 10. As is conventional, a steam trap 20a is associated with each radiator 20. The com bined accumulator and deaerator 24, which performs the known functions of condensate deaeration and storage of the deaerated condensate, is novel in its construction and in the manner in which it is connected into the boiler system.

As shown, the combined accumulator and deaerator 24 includes a single upright tank 26 which is divided by a plate 28 into a large upper accumulator storage chamber 30 and a lower, vacuum deaerating chamber 32 of smaller volume than the upper chamber. Water enters and leaves the deaerating chamber 32 through a pipe 34 which connects at one end with the lowermost part of the deaerating chamber 32 and at its other end with the suction side of a pump 36, the latter being driven by a motor 38. As will be more fully described hereinafter, periodic operation of the pump 36 will produce a deaerating vacuum in the deaerating chamber 32 and will deliver deaerated water to the accumulator chamber 30. At the uppermost part of the deaerating chamber 32 is a sealing and vent arrangement for sealing the chamber when under vacuum and for venting gases to the atmosphere by displacement when water enters the chamber. The arrangement includes a check valve 41 in the vent lines which closes upon the lowering of the pressure in the deaerator chamber 32 below atmospheric pressure and opens when the water and gas flowing into the chamber through the pipe 34 increases the pressure over atmosphere.

The pump motor 38 is provided with a control circuit which starts the motor when condensate has filled the deaerating chamber 32 and stops the motor when the chamber level drops to predetermined elevation. As shown, the control circuit includes upper and lower probes 42 and 43 inside the chamber 32 and electrically connected to the motor 38.

Still referring to the deaerating portion of the equipment 24 it will be seen that the deaerating pump 36 includes a casing 44 and a rotor 46, the pipe 34 connecting with the suction side of the casing 44 and a separate pipe 48 connecting with the pressure side of the casing 44. A deaerated water discharge pipe 50 connects with the pipe 48 and extends upwardly and then laterally into the accumulator chamber 30 where it terminates in a spray header 52. A check valve 54 in the deaerated water discharge pipe permits flow of deaerated water into the accumulator chamber 30 and prevents flow in the opposite direction. The check valve 54 is spring biased toward a closed position.

On the upstream side of the check valve 54 is a holdup tank 56 the lower portion of which is connected to the discharge line by a line 58.- The holdup tank 56 forms a sealed chamber having a gas cushion 60 which overlies the liquid in the lower portion of the chamber. The upper portion of the tank, which contains the gas cushion 60, is provided with a normally closed valve 62 through which gas may be introduced or withdrawn for the purpose of adjusting the volume of the gas cushion 60. In operation, described in detail hereinafter the holdup tank 56 receives and holds the first portion of water pumped out of the deaerating chamber 32 by the pump 36 and returns the holdup portion to the chamber 32 when the pump 36 stops.

The deaerating portion of the system also includes a scavenging line 64 which periodically draws a vacuum in the storage chamber 30. As shown, the scavenging line 64 connects at one end with the pipe 48 through a check valve 66 which permits fluid flow only into the pipe 48. The other end of the line 64 terminates inside the storage chamber 30 where it is provided with a floating heavy gas skimmer 69. :In the illustrated embodiment the skimmer 69 is constructed in the form of a funnel 68 which is connected to the line 64 by means of a flexible line 70. The funnel 68 is maintained with its upper end just above water level by means of a suitable buoyancy chamber 72. A cap 74 is secured to the funnel 68 to prevent water from the spray header 52 from entering the latter. An annular space between the cap 74 and the top of the funnel 158 provides a path for the periodic flow of gases into the funnel 68, these gases being the residual gases liberated in the storage chamber 30. The storage chamber 30 is provided with a heater, in this case a finned steam coil 76, for the purpose of heating the condensate. The coil 76 is connected to a steam supply line 80 leading from the main steam line 16. One supply line 80 includes a temperature controlled valve 82 which receives its operating signal from a temperature sensor 84 in the storage chamber 30. The arrangement is constructed so as to maintain suflicient steam flow into the coil to heat the condensate in the chamber 30 to a temperature above the temperature of the condensate in the chamber 32 and preferably to a temperature slightly below its boiling point.

The pipe 48 also connects with the main condensate return line 22, the latter containing a check valve 86 which permits flow only into the pipe 48. A makeup water line 88 is also provided for adding water to the system through a valve 90 which is normally in a closed position. Operation of the valve may be manual or automatical in response to a low liquid level sensor 91 in the chamber 30.

The operation of the system, assuming that the deaerating pump motor 38 is off, is as follows. Condensate which forms in the radiators 20 flows by gravity into the main condensate return line 22 and then through the check valve 86 into the pipe 48. From the pipe 48 the condensate flows through the casing 44 of the pump 36 and through the pipe 34 into the deaerating chamber 32. The check valve 41 is open at this stage owing to the pressure head of the condensate in the return line 22. Simultaneously, the probe 42 activates the pump motor 38 with the result that the pump 36 starts pumping water out of the lower end of the deaerating chamber 32 into the pipe 48. At this time the check valve 41 closes and thereby seals the deaerating chamber 32. Continued operation of the pump 36 immediately lowers the pressure in the chamber 32 to value equal to the vapor pressure of the condensate in the latter. This boiling-point vacuum causes dissolved gases in the condensate to come out of solution, rise to the surface in the form of small bubbles and collect in the upper part of the chamber 32. When the level of condensate reaches the lower probe 43, the pump 36 stops thereby permitting any condensate in the main return line 22 to again flow through the check valve 86, the pipe 48, the pump casing 44 and into the deaerating chamber 32. The gas which was liberated from the previous batch of condensate is thereby forced out the vent arrangement 41 to the atmosphere. From the above description it will be apparent that the condensate which is pumped out of the deaerating chamber 32 by the deaerating pump 36 has been subjected to a vacuum for a period of time ranging upwards from zero. That is, the first-pumped fraction will have been subjected to a vacuum for substantially zero time; whereas the last-pumped fraction will have been subjected to a vacuum for the time required to pump the condensate down to the level of the lower probe 43. Since gas liberation is very rapid once a boiling point vacuum has been established, all but the first-pumped portion of condensate will be substantially completely deaerated by the time it passes into the pipe 48.

The hold-up tank 56 accepts this first-pumped, slightly deaerated portion and prevents it from passing to the storage chamber 30 thereby assuring that the latter will receive only substantially deaerated condensate. Considering the flow of condensate out of the pump 36 more specifically it will be apparent that the pressure in the pipe will maintain the check valves 66 and 86 closed and will tend to force the condensate upwardly through the pipes 50 and 58 against the biasing spring of the check valve 54 and against the gas cushion 60, respectively. The biasing force tending to maintain the check valve 54 closed is pre-selected at a value such that the valve will not open until the pressure builds up somewhat in the pipes 50 and 58. During this build-up of pressure the gas cushion 60 becomes compressed and allows condensate to enter the hold-up tank 56. When the pressure in the tank 56 equals the biasing force on the check valve 54, the latter opens and passes substantially completely deaerated condensate into the accumulator chamber 32 through the spray header 52. The amount of condensate retained in the hold-up tank 56 depends on the volume of the tank and the volume of the overlying gas cushion '60 and on the biasing force on the check valve 54.

When the deaerating pump 36 stops as a result of the condensate levels dropping to the probe 43, the vacuum 4 in the deaerating chamber 32 pulls raw condensate from the line 22 through the check valve 86. At the same time the check valve 54 closes, and condensate passes out of the holdup tank 56 until the pressure of the gas cushion 60 falls to a value in equilibrium with the pressure in the pipes 48 and 50. As previously stated, this flow of condensate into the deaerating chamber 32 continues until the level rises to the probe 42.

A further effect of the vacuum in the deaerating chamber 32, when the deaerating pump 36 stops, is the opening of the check valve 66 and the pulling of a vacuum on the condensate in the accumulator section 30. This sequential vacuum together with the fact that the stored condensate is only slightly below its boiling point, reduces or prevents redissolution of any gases which may be present owing to leaks or the production of incompletely deaerated condensate. In addition, the spraying of the incoming condensate into a vacuum aids in liberating residual dissolved gases. It is important that any gas in the accumulator section 30 should not be permitted to stagnate, because in time a high concentration of carbon dioxide may develop. Carbon dioxide, as an example, having a greater density and solubility than oxygen or nitrogen, will tend to collect in a thin layer just above the liquid surface and will tend to re-dissolve in the liquid, thereby creating severe corrosion problems in the boiler 10. However, the heavy gas skimmer 69 which floats on the liquid surface intermittently skims any gas present and thereby prevents accumulation of carbon dioxide. As described previously, this skimming effect is produced by connecting the funnel-shaped part 68 to the line 64 so that the periodic vacuum which is drawn on the latter draws gas into the funnel through an annular slit between the top of the funnel 68 and the cap 74.

The condensate-handling equipment, which includes the deaerator tank 26, deaerating pump 36, the holdup tank 56, the heater 76 and associated valving and piping, may be pre-assembled as a unit and easily incorporated in an existing boiler feed system. The deaerating pump 36 need not be of large capacity, because its only function is to pull a vacuum on the small deaerating chamber 32. The deaerating pump 36 is not required to have a pumping capacity suflicient to establish a high vacuum in the storage chamber 30 for several reasons. First, the water in the chamber 30 has been substantially deaerated before it enters the chamber 30. Therefore, the gas scavenger 69 need pull out only a small amount of residual gas in order to fulfill its function of preventing re-dissolution of the heavy corrosive gases. Thus, the vacuum line 64 for the scavenger 69 is not connected to the suction line of the deaerating pump 36 but rather is connected to make use of the residual vacuum in the deaerating chamber 32 after the pump 36 has stopped operating. Second, the condensate in the storage chamber 30 is maintained near its boiling point by the heater 76 so that only a very small vacuum established in the chamber 30 will assure complete deaeration. It will be appreciated, of course, that the system is not rendered inoperative by omitting the heater 76, although in this event it would be desirable to employ a deaerating pump of greater capacity.

While preferred embodiments of the present invention have been described, further modifications may be made without departing from the scope of the invention. Therefore, it is to be understood that the details set forth or shown in the drawings are to be interpreted in an illustrative, and not in a limiting sense, except as they appear in the appended claims.

What is claimed is:

1. A boiler feed system for supplying degasified water for use in a boiler comprising: a deaerator tank; means including a conduit for periodically introducing water into said tank; means for periodically degasifying water in said deaerator tank including a pump having an inlet and an outlet disposed below the level of water in said deaerator tank, said inlet being in communication with the interior of said tank below the level of Water therein, said degasifying means further including vent and valve means associated with said deaerator tank for Venting gases from said tank upon introduction of water into said tank and for subsequently sealing said tank whereby operation of said pump produces a degasifying vacuum in said tank and pumps degasified water through said outlet; a degasified water storage tank; conduit means connecting said pump outlet with said storage tank; a holdup tank of lesser capacity than said deaerator tank for receiving and holding the first pumped portion of water pumped by said pump, said holdup tank having an upper portion containing a compressible gas cushion and a lower water containing portion in communication with said conduit means intermediate said deaerator tank and said storage tank; valve means in said conduit means intermediate said holdup tank and said storage tank for passing water only into said storage tank; means for periodically removing gas from said storage tank including a scavenging conduit communicating at one end with said storage tank above the level of water therein and communicating at its other end with said conduit means intermediate said pump outlet and said holdup tank, said scavenging conduit including a valve for passing gas only out of said storage tank whereby when said pump stops, vacuum in said deaerator tank causes gases to pass from said storage tank into said scavenging conduit, then into said conduit means and then through said pump in a reverse direction into said deaerator tank; and a second pump operatively associated with said storage tank for delivering degasified water to a boiler from said storage tank.

2. Apparatus as in claim 1 including heating means associated with said storage tank for maintaining the water therein at a temperature above the temperature of the water in said deaerator tank whereby the low solubility of gases in water at high temperature together with the vacuum periodically pulled on said storage tank through said scavenging conduit maintains the water in said storage tank substantially gas-free.

3. Apparatus as in claim 1 wherein said means for periodically introducing water into said deaerator tank includes a water supply conduit communicating with said conduit means intermediate said pump outlet and said holdup tank and further includes valve means in said supply conduit operable to pass water only into said conduit means whereby when said pump stops, the vacuum in said deaerator tank draws water from said supply conduit into said conduit means, through said pump in a reverse direction and into said deaerator tank.

4. Apparatus as in claim 1 wherein said scavenging conduit includes a vertically adjustable end portion disposed within said storage tank, said apparatus further comprising means within said storage tank for moving said adjustable end portion of said scavenging conduit so as to remain continuously at a small fixed distance above the water surface whereby heavy gases will be removed periodically from said storage tank.

5. A combined accumulator and deaerator for use in treating steam condensate before the latter is returned to a boiler comprising: a tank having an internal imperforate partition dividing the interior of said tank into a storage chamber and a deaerating chamber; a deaerated condensate outlet associated with said storage chamber; a

deaerating pump adjacent said tank, said pump having an inlet and an outlet disposed below the level of water in said deaerating chamber, said inlet being in communication with the interior of said deaerating chamber below the level of the water therein; pump control means associated with said deaerating chamber and with said deaerating pump for turning the latter on and off at predetermined high and low water levels, respectively, in said deaerating chamber; vent and check valve means associated with said deaerating chamber for venting gases from said chamber upon introduction of water into said chamber and for subsequently sealing said chamber upon operation of said deaerating pump whereby operation of the latter produces a degasifying vacuum in said tank and pumps degasified water through said pump outlet; conduit means connecting said pump outlet with said storage chamber; a water holdup tank of lesser capacity than said deaerating chamber for receiving and holding the first pumped portion of water pumped by said deaerating pump, said holdup tank having an upper portion containing a compressible gas cushion and a lower water containing portion in communication with said conduit means intermediate said deaerating chamber and said storage chamber; one-way valve means in said conduit means intermediate said holdup tank and said storage chamber for passing water only into said storage chamber; means for removing gas periodically from the upper portion of said storage chamber including a scavenging conduit having one end connected to said conduit means intermediate said pump outlet and said holdup tank whereby when said pump stops, vacuum in said deaerating chamber produces a vacuum in said scavenging conduit, the other end of said scavenging conduit terminating in a gas collecting device located in said storage chamber at the level of water therein, said gas collecting device including a float riding on the water surface and a gas inlet opening buoyantly supported just above the water surface by said float so as to rise and fall with changes in water level; one-way valve means in said scavenging conduit for passing gas only into said conduit means whereby when said pump starts, water is prevented from passing from said conduit means into said scavenging conduit.

6. Apparatus as in claim 5 including heater means associated with said storage chamber for heating water therein to a temperature above the temperature of Water in said deaerating chamber.

7. Apparatus as in claim 5 wherein said conduit means extending between said pump outlet and said storage chamber includes a connection for receiving condensate from steam utilizing equipment, said connection being located intermediate said pump outlet and said holdup tank, said connection including a one-way valve for passing the condensate only into said conduit means whereby the condensate will enter said conduit means when said pump is not operating.

References Cited UNITED STATES PATENTS 6/1956 Day et al 55-193 X 9/1963 Baker 55164

Claims

1. A BOILER FEED SYSTEM FOR SUPPLYING DEGASIFIED WATER FOR USE IN A BOILER COMPRISING: A DEAERATOR TANK; MEANS INCLUDING A CONDUIT FOR PERIODICALLY INTRODUCING WATER INTO SAID TANK; MEANS FOR PERIODICALLY DEGASIFYING WATER IN SAID DEAERATOR TANK INCLUDING A PUMP HAVING AN INLET AND AN OUTLET DISPOSED BELOW THE LEVEL OF WATER IN SAID DEAERATOR TANK, SAID INLET BEING IN COMMUNICATION WITH THE INTERIOR OF SAID TANK BELOW THE LEVEL OF WATER THEREIN, SAID DEGASIFYING MEANS FURTHER INCLUDING VENT AND VALVE MEANS ASSOCIATED WITH SAID DEAERATOR TANK FOR VENTING GASES FROM SAID TANK UPON INTRODUCTION OF WATER INTO SAID TANK AND FOR SUBSEQUENTLY SEALING SAID TANK WHEREBY OPERATION OF SAID PUMP PRODUCES A DEGASIFYING VACUUM IN SAID TANK AND PUMPS DEGASIFIED WATER THROUGH SAID OUTLET; A DEGASIFIED WATER STORAGE TANK; CONDUIT MEANS CONNECTING SAID PUMP OUTLET WITH SAID STORAGE TANK; A HOLDUP TANK OF LESSER CAPACITY THAN SAID DEAERATOR TANK FOR RECEIVING AND HOLDING THE FIRST PUMPED PORTION OF WATER PUMPED BY SAID PUMP, SAID HOLDUP TANK HAVING AN UPPER PORTION CONTAINING A COMPRESSIBLE GAS CUSHION AND A LOWER WATER CONTAINING PORTION IN COMMUNICATION WITH SAID CONDUIT MEANS INTERMEDIATE SAID DEAERATOR TANK AND SAID STORAGE TANK; VALVE MEANS IN SAID CONDUIT MEANS INTERMEDIATE SAID HOLDUP TANK AND SAID STORAGE TANK FOR PASSING WATER ONLY INTO SAID STORAGE TANK; MEANS FOR PERIODICALLY REMOVING GAS FROM SAID STORAGE TANK INCLUDING A SCAVENGING CONDUIT COMMUNICATING AT ONE END WITH SAID STORAGE TANK ABOVE THE LEVEL OF WATER THEREIN AND COMMUNICATING AT ITS OTHER END WITH SAID CONDUIT MEANS INTERMEDIATE SAID PUMP OUTLET AND SAID HOLDUP TANK, SAID SCAVENGING CONDUIT INCLUDING A VALVE FOR PASSING GAS ONLY OUT OF SAID STORAGE TANK WHEREBY WHEN SAID PUMP STOPS, VACUUM IN SAID DEAERATOR TANK CAUSES GASES TO PASS FROM SAID CONDUIT TANK INTO SAID SCAVENGING CONDUIT, THEN INTO SAID CONDUIT MEANS AND THEN THROUGH SAID PUMP IN A REVERSE DIRECTION INTO SAID DEAERATOR TANK; AND A SECOND PUMP OPERATIVELY ASSOCIATED WITH SAID STORAGE TANK FOR DELIVERING DEGASIFIED WATER TO A BOILER FROM SAID STORAGE TANK.