US2931344A - Closed condensate return and boiler feed system - Google Patents

Description

v. E. STIERS 2,931,344

CLOSED CONDENSATE RETURN AND BOILER FEED SYSTEM April 5, 1960 Filed Oct. 4, 1956 L lll l I l I I I l l VERN E. STIERS AI'TTORNEYS CLOSED CONDENSATE RETURN AND BOEER FEED SYSTEM Application October 4, 1956, Serial No. 614,902

11 Claims. (Cl. 122-1) The present invention relates to a closed condensate return and boiler feed system. It consists of the combinations, constructions, and arrangement of parts, as hereinafter described and claimed.

An object of my invention is to provide a system which will strip condensate from process units without the necessity of providing any kind of trap, temperature control, or orifice in the return line. A high velocity in the removal of the condensate from the process units is developed in order to prevent even the slightest waterlogging and therefore increase heat-transfer in the process units. A rapid and complete removal of insulating gases such as oxygen, nitrogen, and carbon dioxide is performed by my system and will also increase the heat transfer.

A further object of my invention is to provide a system of the type described that will handle all flows with full-sized lines regardless of the amount produced due to start-up loads or overload.

The system is intended to return all condensate to the boiler without heat or water loss due to flashing to a lower pressure. All condensate is taken from the process units and is returned to the boiler at temperatures and pressures approximating boiler temperatures and pressures.

The system is intended to provide eflicient deaeration and degasification of both condensate return and raw makeup. It is particularly efficient in removing dissolved carbon dioxide gas from the condensate, and preventing the gas from re-dissolving at a later or cooler -point in the system. A good removal of oxygen from the raw makeup is obtained in the primary receiver.

A further object of my invention is to provide a system of the type described in which the temperature of the feedwater for the boiler is kept as close as possible to the temperature of the water in the boiler.

This will increase the boiler output and make the boiler more responsive to load changes while stabilizing its performance.

Other objects and advantages will appear as the specification continues. The novel features will be set forth in the claims hereunto appended.

Drawing ceiver, and is taken along the line 2--2 of Figure 1.

Description While I have shown only the preferred form of my invention, it should be understood that various changes,

L or modifications, may be made within the scope of the annexed claims without departing from the spirit thereof.

In carrying out my invention, I show a boiler A, and

i this boiler has a steam outlet pipe 1 that has two or nited tates Patent O more branches 2 and 3. The steam flowing through the branch pipe 3 is used for any desired purpose and is not returned to the system. Therefore a hotwell B or raw water supply is used for adding water to the boiler to take the place of steam that flows through the pipe 3 and is lost so far as the system is concerned. One of the objects of the invention is to heat the water from the raw water supply or hotwell B, to a point which is close to the temperature of the water in the boiler A, before the water is admitted into the boiler. The means for accomplishing this will be described hereinafter.

The branch pipe 2 conveys steam at the desired temerature and pressure to one or more process units .C. The steam condensate is conveyed from these units C to a unit receiver D, by pipes 4. Normally the process units C are placed at a higher level than the unit receiver D, and the condensate will flow by gravity through the pipes 4. If gravity flow for the condensate, cannot be used, pumps, not shown, could be placed in the lines 4 and force the condensate therealong.

One or more unit receivers may be used in the system. Each one is a pressure vessel coded to or above boiler pressure. Only one is shown in the schematic drawing in order to make the system as simple as possible for disclosure. The unit receiver D is illustrated as being a horizontal cylinder with a collector E mounted in the unit receiver D, and also extending in a horizontal direction. The collector E is positioned in the upper half of the unit receiver D and it is tubular in shape.

The collector E is a manifold considerably larger than the total diameters of all condensate lines 4 that communicate with it as shown in the drawing. The left hand end of the collector manifold is shown closed in Figure l, and the lines 4 connect with the collector near to this closed end. Between the point where the condensate lines 4 enter the collector, and where the collector emerges from the unit receiver D, the top of the collector is slotted at 5, see Figure 2, to permit ample space for overflow of the condensate from the manifold into the interior of the unit receiver D.

lt will be seen from Figure 1, that the collector E is reduced in diameter at a point to the right of the slot 5 and before the collector emerges from the unit receiver D. The conduit or reduced portion 6 has a crosssectional area equivalent to the sum of the cross-sections of the condensate lines 4, or of a suflicient diameter to handle all of the condensate without any restriction that is to flow back to the boiler A. A check valve 7 is placed in the reduced portion 6 of the collector that projects clear of the unit receiver D and prevents backflow of water into the collector E. The reduced portion 6 communicates with a return pipe 8 that leads toa primary receiver F. A second pipe 8a also communicates with the bottom of the unit receiver D and has a pump G for delivering condensate from the unit D to the return pipe 8 and to the primary receiver F, when the water level in the receiver D reaches a certain level. The unit receiver D contains a level control D an adjustable orifice deaerating vent D and a Water gauge glass D At no time will the water level in the unit receiver D, rise above the collector E.

The pump G is electrically started and stopped and is controlled by the water level control D mounted in the unit receiver. A dotted line 9 indicates wires that electrically connect the pump G to a source of current when the float it; rises to a predetermined point. This starts the pump G, and the pump will continue to operate until a the float 10 again drops to a predetermined position and collector E, discharge the condensate into the top and near the left hand end of the primary receiver F.

The primary receiver F, also contains a raw makeup discharge'header H, that is placed near the bottom of the receiver, and has a plurality of outlet openings 11 on its sides. The header H, is in communication with the source of raw Water supply B, by means of a pipe 12, and any suitable'pump J. The header H is placed at the left .hand end of the primary receiver F, and delivers ;raw water at the same end that receives the condensate from the return pipe 8. The header H, delivers its water 7 along the bottom of the primary receiver F.

A vertical bafiie 13 extends transversely across the primary receiver'F, from the bottom 'of the receiver up to a horizontal baflie 14 that extends to the right of the "batlle 13. Any condensate received from the pipe 8, or raw water received from the header H, will fill the com-. partment F formed by the bafile 13, before it will flow over the horizontal battle 14, and into the right hand end of the primary receiver. Two other pipes 15 and 16 areshown communicating withthe primary receiver F at points adjacentto where the return pipe 8 enters the compartment F These two pipes indicate that process units,

other than the units C, may form a part of the system and deliver their condensate into the compartment F,

' .steam near the makeup discharge header H. A valve, not shown, controls the fiow of steam through the pipe 17.

Another transversely extending battle 18 is mounted in the-primary receiver F, and is placed to the left of the baffle 13, and is parallel therewith. The lower edge of the bafile 18 is positioned above the header H, while the "upperedge extends above the horizontal baffie 14. All

of the condensate received from the pipes 8, 15 and 16,

'must flow under the baffle 18, before it can flow out of ithe compartment F and over the baffle 14. This will insure adequate mixing of the condensate with the raw water delivered by the header H. The water in flowing over the baffle 14, insures surface film exposure for deaeration. Additional horizontal baffles, not shown, could be provided in the primary unit F to receive the "filmof 'water from the bafile 14, and cause the water to 'remain in a film as it flowed over these other bafiies. This would result in further deaeration of the water.

The compartment F of the primary receiver F, which is'downstream from the bafi'les 13 and 14, contains a level control K, and an adjustable deaerating vent L. A water outlet pipe 19, leads from the bottom of the compartment F to a special pump M, that in turn pumps the water to a pipe 20, that delivers it to the boiler A. A

return automatic by-pass pipe 21, branches from the pipe 20, and leads to the top of the primary receiver F, for delivering the water to the compartment F if the boiler does not need any additional water. The pump M, nor mally operates continuously and delivers water either to the boiler A, or to the automatic by-pass pipe 21. The

boiler A, may be provided with a level control N, that is 'eiectrically connected to the pump M by wires indicated by the dotted lines 22. When the boiler needs additional water, the level control N would close an electric circuit 'htothe pump M, and start it operating.

The priniary receiver F, has a valve-controlled drain 23 for the compartment F ,'arida sample cookie, com- "municating withthe drain pipe .23 at a point above the walveifonthe'pipe. Also the primary receiver F,. has a 4 pressure gauge 25, and a temperature gauge 26, com municating with the compartment F 'A'water guage glass 27 is placed at the right hand end of the primary unit F, and it will indicate the water level in the compartment F 7 A The special pumps G and M, are located at the bottom of each receiver D and F, respectively. The pump M may replace the boiler feed pumps'. .Also,-1if the unit receiver D is not used, the pump 6' may be used to pump the condensate directly from the process units C, to the primary receiver F. When the unit receiver 'D,andithe collector E, are used, the pump G will remain idle most of the time because the differential in pressure between the unit receiver D, and the primary receiver F, will be sufiicient to force the water from the receiver D, to the receiver F. The pump G will only operate when water spills out the slot 5 in the collector E, and fills the unit receiver D, to a point where the water level control D will close a circuit to the pump for starting it.

The pumps G and M, are specially designed to handle the temperatures and pressures involved in moving the heated water. At the present time, the pumps G and M, are a two-stage-in-series turbine type pump with water cooled seals and bearings, and are known as 'HP-HT pumps, manufactured by the Pacific Pumping Co., Oakland, California. ther pumps may be used for special applications; however, in no case will the "pump be a standard conventional pump because of the'temperatuies and pressures involved.

Operation the hotwell B will have to deliver water .to the boiler sulficient to make up for the 30% steam loss;

The 70% of steam flowing to the process 'umts C, through the branch pipe 2, will be theoretically .at a pressure of 200 p.s.i. and 'a temperature of 388 F., less any line'losses. The condensate from the process units .Cywill flow through the pipes 4 and will enter the collector ,E at the same pressure of 200 p.s.i. and the .sametemperature of 388 F. At the start of the operation, :the primary receiver P, will be at atmospheric pressure, or zero reading on the pressure gauge 25. The initial differential in pressure therefore, between the unit receiver-D, and the primary receiver F, is 200 p.s.i., and the hot water at 388 R, will quickly flow into the primary receiver F, by means of the return pipe 8, until the gauge pressure reads 241 30 p.s.i., and the temperature is 388 F., disregarding line losses. The system isnow static. 1

However, 30% of the steam, lost .throughthe pipe .3, must be made up by adding raw water into the system. The hotwell B delivers this raw water at a temperature of about 220 F., to theheader H, by means of the pipe 12 and pump I. When this relatively colderraw water ,at 220 F., mixes with the hotter Water in the compartment F the pressure will drop one half, from 200 p.s.i., to p.s.i., and the temperature willdrop 50 .F., from 388 F., to 338 F. This pressure drop of 100 p.s.i., between the unit receiver D and the primary receiver F, is sufiicientto make the :system operate continuously so long as any condensate is in theprocess units C. Even a "ten pound pressuredrop. is enough to cause the'system to function.

, is ,deaeratecl. The mixture of condensate 'and' raw' water in the primary receiver R, at a temperature of 338 F., and a pressure of 100 p.s.i., is fed back into the boiler A, by the pump M, as the boiler needs the water. All the boiler A need do is to raise the water temperature to again make steam at a temperature of 388 F., and a pressure of 200 p.s.i. This completes the cycle of operation.

It will be seen that a pressure drop is created across the closed system by the addition of makeup water to the primary receiver F. The manner of adding this makeup water near the bottom of the compartment F in the primary receiver F, gives a readily controllable pressure drop, sufiicient to cause a rapid flow of the condensate and the gases from the process units C, through one or more unit receivers D, to the primary receiver F; but still not enough pressure drop to cause steam collapse in the primary receiver and subsequent loss of suction head on the boiler feed pump M, regardless of the quantity of raw makeup water being added. On very high makeup systems, steam would be added to the primary receiver F, through the steam pipe 17, to keep the pressure drop at optimum levels. As low as 2% makeup water to the closed system is sufficient to provide an adequate pressure drop for a good operation of the system. Since almost no boiler plant uses less makeup water than this, the system is universally applicable.

The collector E in the unit receiver D, allows most of the condensate to flow directly to the primary receiver F. It is not necessary to have gravity flow from the unit receiver D, to the primary receiver F. Entrained and dissolved gases can separate out through the slot in the collector E, and are ejected through the controlled vent D On the start-up of the cold process units C, the flow of condensate may over-capacitate the collector E, in

which case an overflow will take place through the slot 5 and into the unit receiver D. When the water level in the receiver D, reaches a certain point, the water level control D will start the pump G, and the latter is sized to handle maximum condensate flow. The check valve 7 prevents backfiow of the condensate into the collector E from the second pipe 8a and the conduit 6 when the pump G is operating.

As soon as the system settles down to an operating load, the collector E stops overflowing and most of the condensate will flow directly from the collector into the return pipe 8 because of the pressure drop between the primary receiver F, and the collector E. This will give maintenance-free pump life on the special pump G, because the pump will not have to operate continuously.

' In addition, there is a better stripping action on the condensate through the collector E than can be provided by using only the pump G. The pump G may also be operated on tapering the shutdown load. When this happens, little or no makeup water may be required and therefore the pressure drop to the primary receiver may be too small for adequate flow from the collector E. As the condensate flows by gravity to the collector E, and overflows into the unit receiver D, the pump G will operate when the water level reaches a predetermined height, to transfer the water from the receiver D, to the receiver F. The pump G will also take care of any condensation moisture developing in the unit receiver D.

The system will operate when there is a 2% raw water makeup, and it will operate from this point on up to an 80% raw water makeup. There will be an acceptable pressure drop within these limits for a proper operation of the system. However, where a minimum or a maximum pressure drop is necessary, this can be controlled by utilizing pressure sensitive controls to regulate either the amount of raw water makeup added to the primary receiver F, or the amount of steam added through the steam pipe 17, or both.

Theoretically, it would be possible to use the system on plants utilizing up to 100% raw water makeup, however, the economics of operation make this less practical return branch for returning the water to the second I mas the raw water makeup approaches Since the condensate is being returned to the primary receiver F at close to boiler temperatures, the, water in the compartment F is much hotter (usually over 300 F.), than that found in ordinary deaerating heaters, and for this reason adequate degasification can be secured with less mechanical difiiculty. The baffies 13, 14' and 18, in the primary receiver F, insure adequate mixing of raw water from the supply B, with the hot condensate from the pipes 8, 15 and 16, and they also insure surface film' exposure for degasification. The controllable vent L, removes these gases. The location and design of the vent, prevent steam or water loss.

The pressure in the primary receiver is rarely over 50 p.s.i. below the boiler pressure, and the differential may go as low as 10 p.s.i. The temperatures may go to 400 F., or higher. These temperatures and pressures are handled by the special pump M, which in most cases has replaced the boiler feed pump. The pump M, is controlled by the boiler level controi N. When the boiler A does not require water, the automatic by-pass 21 allows the pump M to circulate the water back to the primary receiver F.

The water level control K is electrically connected to the pump J by wires indicated by the dotted lines 28. When the water level in the compartment F reaches a predetermined point, the electric circuit to the pump 5, is opened and the pump will cease deliveringraw makeup water from the supply B to the compartment F by means of the pipe 12. As soon as the water in the compartment F drops below the predetermined level, the pump I will automatically start operating again.

I claim:

1. The combination with a steam boiler which will convert water into steam under pressure; at least one processing unit communicating with the boiler to receive steam therefrom under pressure; means coupledyto the boiler to convey part of the steam therefrom,- which part will not reach the processing unit; of a collector having at least one pipe leading therefrom to the process ing unit to receive steam condensate from said unit, for conveying the condensate to the collector, said collector being mounted in a unit receiver and-having an opening for permitting excess condensate to overflow from the collector into the unit receiver; a primary receiver hav ing a first compartment with a return pipe leading therefrom to the collector for conveying the condensate from the collector to the first compartment; a check valve mounted in the return pipe for preventing a reverse flow from the pipe back to the collector; a pipe leading from the bottom of the unit receiver and communicating with the return pipe at a pointy beyond the check valve; a float-controlled pump in said last-named pipe for. automatically pumping the condensate from the unit receiver into the first compartment of the primary receiver when the water level in the unit receiver reaches a predetermined level; a source of makeup water; a second pump and a conduit for delivering makeup water into the bottom of the first compartment for mixing with the condensate received by the first compartment; said primary receiver having a second compartment for receiving the mixture of condensate and makeup water from the first compartment; 21 third pump and a conduit for'delivering the water in the second compartment, back to the boiler; and automatic means controlled by the Water level in the boiler for connecting the third pump to a source of electric power for operating the pump when the water-level in the boiler drops below a-predetermined point.

2. The combination as set forth in claim 1: and in which the conduit for the third pump has an automatic partment when the w'ate'r level in the boiler re predetermined pjOiintLf' 1 3. The combination as set forth in claim 1: and in v 7 which the said unit receiver has a vent for permitting the escape of gases from the receiver. a

4. The combination as set forth in claim 1; and in which the said unit receiver and said primary receiver, each has a vent for the escape of gases from the receiver.

'5. The combination as set forth in claim 1: and in which there is a water level control in the second compertinent for stopping the second pump from operating when the water level in the second compartment reaches a predetermined point.

6. in a device of the type described: a collector for receiving a condensate; a unit receiver housing the colleci to'r; said collector having an overflow slot therein for permitting excess condensate received by the collector, to overflow into the receiver; a primary receiver having a pipe communicating therewith and with the collector; means for creating a lower pressure in the primary receiver than in the unit receiver for causing the condensate to flow from the collector into the primary receiver; a

water level control for the unit receiver; a second pipe tending from the bottom of the unit receiver and communicating with the first pipe; and a pump mounted in the second pipe and connected to a source of current by the water level control for operating it when the water in the unit receiver rises above a predetermined level.

=7. The combination with a steam boiler; at least one processing unit communicating with the boiler to receive steam therefrom under pressure; a primary receiver; a unit receiver having a pipe communicating with the primary receiver; :1 amp mounted in the pipe; a condensate collector mounted in the unit receiver and having a conduit communicating with the pipe at a point between the pump and the primary receiver; a check valve in the conduit; an unrestricted pipe for conveying condensate from the processing unit to the collector; said collector "having a slot for permitting excess condensate therein to overflow into the unit receiver; automatic means for starting the pump to deliver condensate from the unit receiver to the primary receiver when the level of the condensate in the unit receiver reaches a predetermined point; a source of makeup water; means for delivering water from said source to a point in the primary receiver below the water level when it becomes necessary to add makeup water thereto; and means for delivering water from the primary receiver to the boiler as needed; the lowering of the temperature of the condensate in the primary receiver caused by the introduction of make-up water below the water level, creating a pressure differen- -tial between the primary receiver and the collector, sufthe first compartment and with the co'llecto'r; a check valve placed betweenithe collector and the pipe to prevent backfiow of water into the collector; means for creating a lower pressure in the primary receiver than in the unit receiver for causing the condensate to flow from the collector into the first compartment; a water level control forthe unit'receiver; a second pipe leading frcm the bottom of the unit receiver and communicating with the first pipe at a point between the check valve and the first compartment; a pump'mounted in the second ,pipe and connected to a source of current by the water level control .for operating it when the water in the unit receiver rises above a predetermined level; and a baffle disposed between the two compartments and determining the water level in the first-compartment; said baffle causing anywaterfiowlng from *the first to the second compartment, to spread out in a thin film fordeaerating the water. I a

; '9. The combination with a steam boiler of at least one processing unit communicating with the boiler to receive steam therefrom, a receiver, said boiler, processing unit and receiver constituting a closed system, said receiver having a baffie' forming a first water receiving compartment in said receiver and a second water receiving compartment spaced to one side of and separated from said first water receiving compartment by said baflie, said bafiie extending between said compartments upwardly in said receiver but stopping short of the receiver top so as to provide a common steam chamber above said water receiving compartments extending across the tops of both of said compartments and communicating therewith, condensate conveying means'arranged for conveying condensate from the processing unitinto the top of said first compartment, a source of makeup water colder than said condensate, means for delivering water from said source into the said first compartment at a point below the top of said bafiie and the water level in said first compartment, means for delivering water from said second compartment to the boiler, means in said second compartment for controlling the delivery of make-up water to said first compartment by said means for delivering Water from said source and for causing operation or" the latter means when the water level in said second compartment drops below a predetermined level below the top of the baflle, the construction being such that the water in said first compartment flows over said bafile into said second compartment whenever the water level in said first compartment rises above said bafiie, said ba fle being so positioned that introduction of feed water in said first compartment will cause a reduction of temperature in the water in said first compartment and thus a reduction of the pressure in said steam chamber sufficient to cause the fiow of condensate from said processing unit into said first compartment. 1

10. The combination of claim 9 including a horizontal bafiie connected to the top of the first mentioned baflie and providing a horizontal surface extending between said first and said second compartment at the top of said first mentioned bafiie, said surface extending substantially across the full width of the latter bafile, said horizontal surface providing for the flow, of water from said first compartment into said second compartment over said surface in; a substantially thin film exposed to said steam chamber to facilitate deaeration of'said'water.

11. The combination of claim 9 including a second oafile position in said first water receiving compartment, said second bafile extending parallel to said first baffie and extending completely across said receiver, and having its bottom spaced above the bottom of said receiver, said second bafiie being positioned adjacent the first mentioned bafiie, said second bafile extending from substantially below said water level to a substantial distance above the top of the first mentioned bafile and being spaced laterally thereof, the top of said second baffle being spaced downwardly from the top of said steam chamber, said second bafile forming a water passage space with the first mentioned bafile, said condensate conveying means 7 through said passage.

References Cited in the file of this patent UNIT ED STATES PATENTS 07,459 Swaney May 3, 1955 FOREIGN PATENTS 7 ,675: Canada June 19, 1951

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