US2643520A - Feed-water control system for steam power plants - Google Patents

Description

Patented June 30, 1 953 FEED-WATER CONTROL SYSTEM FOR STEAM POWER PLANTS William Powell, Jr., Llanerch, Pa., assignor to Bailey Meter Company, a. corporation of Delaware I Application January 6, 1949, Serial No. 69,529 8 Claims. (01. 60-107) My invention relates to control systems and it may be said that the rate of discharge of particularly to providing method and apparatus for controlling variable conditions in the operation of power producing or utilizing apparatusresponsive to one or more variable conditions of the operation.

In present day steam generating stations the arrangement may be of the unit type wherein one or more vapor generators supply steam to a single turbine from which the condensate returns as feed water to the same boilers. In other stations the header system may be employed wherein a steam header is common to all boilers and supplies all turbines; the turbine condensate cycles all leading into a feed water header common to all boilers. Often the equipment is so arranged that through the manipulation of header sectionalizing valves the operation may selectively be of the unit or header type.

With either type of system the boilers must be operated to supply sufiicient steam to maintain desired pressure at the inlet of the turbines regardless of the number of turbines taking steam or the proportioning of load between the turbines. The rate of available condensate from each turbine unit will depend upon the rate of steam flow to the respective turbine, but the operation of the deaerators, heaters, makeup, feed pumps, etc., must be kept within safe limits and the feed water header must be supplied with large enough total and at satisfactory pressure to properly supply the boilers at their individual and selective rates of operation.

The rate of water supply to the feed; water header system from each turbine cycle is usually about 10% greater than the weight rate of supply of steam to the turbine, the difference supplied from makeup within the cycle to balance the weight of steam lost through leakage, diversion from the cycle and for other reasons. Modern stations have a plurality of heaters and storage systems in the cycle between the hotwell of the turbine condenser and the feed headers to which the water is supplied at an elevated pressure by one or more centrifugal feed water pumps. Usually stage heating is employed wherein steam from one or more stages of the turbine is diverted to heat condensate and/or makeup liquid prior to the high pressure feed water pumps. It is apparent that for most economical operation each turbine cycle must be kept substantially in balance so that the various heaters and storage tank systems will not be run dry or flooded but will be operated in consonance with the load on the prime mover. In general then water by the high pressure pumps to the feed water system should be proportioned at all times to the weight rate of supply or steam to the turbine with minor or temporary fluctuations absorbed within the cycle apparatus. Such is the desideratum regardless of operation as a unit sys tem or as a header system.

My invention is primarily concerned with operation as a unit system, although it is equally applicable to the header system, and is mainly concerned with the proper balancing of operation of the high pressure feed water pumps or control of their discharge in desired proportionality to the weight rate of supply of steam to the turbine inlet for that particular cycle. This regardless of whether the cycle is operated as a unit or is one of several such cycles operated between a common steam header and a common feed water header.

In the particular embodiment which I have chosen to illustrate and describe I have shown in diagrammatic fashion two complete cycles with provision that they may be operated as individual units or as a header system. In either event the turbines may be of different capacity or may be operated at unequal loading by choice, either from a standpoint of economy or of necessity for some reason, or because one turbine may have an inherent tendency to hog the load from the other turbine and thus to operate on an unequal load basis between the two. Again, it may bemore economical to operate one or more of the turbine cycles at a uniform most economical loading and take the station deviations in load upon another turbine.

In addition to the loading upon the turbine unit there may be unequal, unexpected or emergency variations in demand upon the feed water system as imposed by the boilers and this may occur for one or more boilers of a single cycle or may occur by some of the boilers of a header system.

Variations, other than load, which may occur at the boilers and thus be effective upon the feed water supply system are changes in blowdown rate, the rupturing of ,a boiler tube or the like, leakages, etc., all tending to upset the'steamwater proportioning and in some instances to place demand upon the feed water header which might normally seriously deplete the storage of condensate and/ or makeup in one or more of the cycles. This would be'particularly true if the sudden demand upon the feed water header were not evenly or proportionately distributed among the various turbine cycles. If through unequal loading or hogging of load upon the cycles or units the maximum of such sudden demands were felt on a single turbine cycle the effect might snowball to the point of putting that cycle completely out of service or rendering it not only inefiicient but unable to satisfy the demand for change in the feed water system.

Primarily the demand for Water upon each cycle should be related to the availability of condensate at the outlet of the particular turbine with minor variations in feed water demand, or emergency variations, applied among the cycles in desired proportion to their loading.

With basically different loading on the units,

the pumps of one unit may be handling a lower flow than for another unit and due to the pump characteristic curves, this may tend to build up a higher discharge pressure. If pressure in the header decreases for anyreason such as an increased demand thereon, the tendency will be for the pumps of the less loaded unit to hog the water demand and abstract from that unit at a rate greater than the rate of condensate supply with consequent depletion of storage. At the same time the more highly loaded unit will not take its share of increase and may be sending excess condensate to its own storage system.

It is therefore a primary object of my invention, regardless of operation as a unit system or as a header system, to control the discharge of water from each unit to the feed water system by proportioning the water flow rate to the steam demand of that unit (and thus to the condensate availability) with readjustment on all units in desired proportion to their loading. Such proportioning may be set up to be equal among the cycles or in direct proportion to the cycle loading.

Another object is to compare the rate of water supplied to the feed water system from each cycle to the weight rate of steam flow admitted to the turbine of that cycle and upon departure from desired proportionality to control the discharge from the feed water pumps to bring the weight rate of Water supply into desired proportionality with the steam supply.

Another object, in connection with the header system, is to proportion the water discharged to the steam for each individual cycle and to readjust the rate of water discharge on all cycles proportionately among the cycles in accordance with their basic loading.

- With these and further objects in mind reference will now be made to the single sheet of drawing on which I diagrammatically show a preferred embodiment of my invention.

Referring now in particular to the drawing I indicate at I a steam header having a sectionalizing valve 2 and supplied with steam from boilers 3, 4, 5, 6 which are representative of any plurality of vapor generators which may be supplying steam to the header I. The feed Water header I has a sectionalizing valve 8 and is arranged to supply feed Water to the boilers 3, 4, 5, 6 serving the steam header I.

Steam turbine #I is connected to steam header I by a conduit 9 and exhaust steam from the turbine passes by way of a conduit I0, condenser IA, heaters II, conduit I2, feed pumps I3, I4, I5, and conduit I6 to the feed water header I. In similar manner turbine #2 is connected to the header I by a conduit I1 and discharges through a conduit I8, condenser 2A, heaters I9, conduit 20, feed pumps 2|, 22, 23, and a conduit 24 to 4 the header I. I do not feel it necessary to go into particular detail as to the usual equipment whereby the steam exhaustion from the turbines #I and #2 is condensed and the condensate then passes through the various heaters and deaerators prior to joining the feed water conduit I under elevated pressure. It seems sufiicient to indicate that the turbines impose a steam demand upon the header I and eventually separately discharge their condensed steam (either with or without the addition thereto of makeup) to the feed water header I.

The arrangement in general may be operated as a unit system if the sectionalizing valves 2 and 8 are closed, or as a header system if the valves 2 and 8 are open. With the valves 2 and 8 closed, it will be seen that #I turbine is supplied with steam by boilers 3 and 4 and discharges to that portion of the feed water header I which is feeding boilers 3 and 4. Likewise turbine #2 takes its steam from boilers 5 and 6 and discharges to that portion of the feed water header I which is supplying feed water to the boilers 5 and 6.

When operating as a header system, with sectionalizing valves 2 and 8 open, all boilers discharge their generated steam into the common header I and take feed water from the common supply header 1. In similar fashion the steam using turbines #I and #2 draw from the header I and discharge their condensate to the feed waconditions have been already mentioned, namely,

unequal loading upon the turbines may result in incorrect loading of the various feed water pumps which inequalities may accentuate or snowball under certain operating conditions.

Preferably I primarily control the output of the feed water pumps in each turbine cycle to proportion the water supplied thereby to the header I to the steam taken by the related turbine from the steam header I and secondarily to readjust all cycles so that they will proportionately absorb fluctuating demands made upon the feed water system to which they discharge.

Located in the conduit 9 is an orifice 30 producing a pressure differential representative of rate of steam flow to the #I turbine and arranged to actuate a steam flow meter 3! having a pilot valve 32 continually establishing in a pipe 33 a fluid loading pressure representative of steam flow to the #I turbine. In similar fashion a steam flow meter 34 is connected across an orifice 35 in the steam conduit I! and is arranged to position a pilot valve 36 continually establishing in a pipe 31 a fluid loading pressure representative of the rate of steam flow supplied to the #2 turbine.

Located in the conduit I6 is an orifice 4U arranged to actuate a water flow meter II which positions a pilot 42 continually establishing in a pipe 43 a fluid loading pressure representative of the rate of water fiow through the conduit I5 from the pumps I3, I4, I5 to the feed water header 7. In like manner an orifice 5B is located in the conduit '24 and is arranged to actuate a feed water flow meter 5| which positions a pilot 52 continually establishing in a. pipe 53 a fluid loading. pressure representative of the.

rate of water fiow through the conduit 24 to the header l.

It will be understood that, for turbine cycle iii, any combination of. the pumps I3, l4, l5 may be operated as chosen manually, or automatically, in accordance with the load. expected. for turbine #E. It only being essential that sufiicient pumping capacity be continually available to exceed the expected water handling capacity of the cycle. At the discharge of the pumps 13, I4, [5, in the conduit I6, I show a diaphragm actuated regulating valve 00 arranged to regulate or throttle the flow of water discharged from the pumps. is, i l and/or as through the conduit [0 to the feed water header '7.

In similar manner the diaphragm actuated valve 09 is located in the conduit 24 between the pumps El, 22, 20 and the conduit 24. Preferably, in each cycle, sufficient pumping capacity is continually available so that the regulating valve 60 and/or L l will be operating in a throttling or regulating condition and thus controlling the rate of fiow or water through the conduits it and 2 1.

I preferably operate the system being described as a header ystem with the sectionalizing valves- 2 and 3 open. lhus variations in demand upon the feed water header 7 will apply to the supply conduits it and 0 and will abstract from the cycles in desired proportion.

[it I show an averaging relay having four expansible-contractible chambers. The pipe 33 joins the A chamber while the pipe 43 joins the B chamber. The C chamber is open to the atmosphere, while the D chamber contains a loading pressure resultant of the forces within chamhers A and B. The arrangement, capacities and adjustments of meters 3!, ll, pilot valves 32, 32, and relay iii are such that the pneumatic loading pressure in the D chamber of relay l0 may have a predetermined value whenever a certain desired proportionality exists between weight rate of ilow or" steam through orifice 30 and of water through orifice 50. For example, the relay '10 may be in a balanced condition, and the output loading pressure in pipe ll be of desired value, under an operating condition of 100,000 lbs. per hr. of steam through orifice 30 and 110,000 lbs. per hr. of water through orifice 40. Likewise, the ad justinents may be arranged to give the same output loading pressure under a condition of 200,000

and 220,000 water if desired.

In 'lar manner an averaging relay 72 has its A chamber subjected to the pressure in .pipe 3i and its 3 chamber subjected-to the pressure in pipe 233 for producing in a pipe it an output load ing pressure representative of relation between steam flow through orifice 3:3 and water flow through orifice 50.

If desired proportionalityexists between steam rate through orifice 30 and water rate through orifice 50; and desired proportionality exists be tween steam rate through orifice 35 and water rate through orifice til; then the pressures in pipes H and I3 will be equal, even though the #l and turbines are carrying decidedly different loads.

At I show a differential standardizing relay such as is disclosed and claimed in the patent to Gorrie Re. 21,004. Ihe pipe 713 joins the Achamher while the pipe ll joins the B chamber, to '19 end that the pressures in said pipes are compared in relay l l. Any unbalance between the pressures results in a' change'in the'output con- 6,. trol pressure in the D chamber and. in output pipe 15. The latter joins amanual-automatic. selector valve 76 as well as the B chamber of a reversing relay H whose output pipe 18 leads to a selector valve 19.

Selector valve 16 provides the possibility of disconnecting diaphragm valve 6 I. from the eiiect of relay l4 and manually controlling the valve opening. In similar manner the selector valve "l0 provides the choice of placing the valve 80 under the control of relay M or of positioning it' through manual control.

Basic loading of the turbine cycles is accomplished by stopping or starting the desired number of pumps !3, it, [5, 2!, 2 2, 23 and positioning valves 00, 8i 1 anually through the agency of selector valves l9, it. When the desired proportioning of load between turbines and #2, as well as the desired proportioning between steam rate and water rate (-for each turbine cycle) is attained, the selector valves is and 19 are moved to automatic position and thereafter valves 00, 6| are controlled from relay M.

If #2. turbine tends to hog the load, steam fiow through orifice 35 increases as does the representative loading pressure in pipe 3! and chamber A of i2. and chamber A of I l; The output of 14 (in pipe l5) temporarily increases, opens valve SI and, through reversing relay li'l, closes down on valve E0. The increased fiow through 0|, increases pressure in E3 and chamber B of 12 opposing the pressure in pipe 3?, until relay I2 is again in balance. bine has dropped (by the amount that #2- increased) and. the system balances out with the stearn-water ratio of the individual cycles at the desired values.

Sudden water demands upon. header 1 will be applied equally to both cycles on the assumption that the basic storage capacities of the two cycles are the same. Such abnormal and relatively temporary demands upon header '1! may be caused by blow-down, leaks, burst boiler tubes, or similar conditions. By dividing the temporary demand equally, neither storage facility will be un-= duly depleted.

The operation as follows:

(initial) Because:

Water pressure on inlet side of valve 03 (and of Si) is unchanged.

The area opening of the valves remain unchanged.

Water pressure in header 1 and thus at outlet of valves til, 61 is lowered with the sudden de mand.

Thus the pressure differential is' changed across the fixed opening areas of the valves and, due to the 1-2 loading ratio, the 30,000 lbs. per 111'. demand will be split 10,000 to #l and 20,000 to #2.

However Immediately the water rates change there is a.

change in the pressures in pipes 43 and '53 and the change is notof the same magnitude becausev the actual change in rate ofwater flow is 10,000.

and-20,000 respectively.

This increases the pressure in pipe '13 In the meantime the. load on it! tur-- Thus, while the change in loading pressures is in the same direction, that in pipe 13 will be to a greater extent than that in pipe H and relay M will produce in pipe a change which will be applied directly to valve 6| and inversely to valve 60.

The system will balance out at 125,000 Water Rate 235,000 15,000 Increase 15,000

and the sudden demand of 30,000 lbs. per hr. will be split evenly between the cycles because of the readjustment of the valve opening areas.

The arrangement described acts to maintain desired proportionality between steam rate and water rate for each cycle separately and divides equally between the cycles sudden demand increases upon the feed water header.

It will be appreciated that usua1 and known means permit capacity, range, sensitivity and other adjustments of the variou measuring and controlling instrumentalities. Furthermore, that changes in loading pressures, w-hile described as sequential, are, in fact, substantially simultaneous, so that many individual demands for change in opening of valves 60, 6| may be cancelled out or modified before ever reaching the valves, thus avoiding hunting and overtravel.

While I have described my invention as preferably so adjusted as to evenly divide sudden water header demands between the cycles, it will be understood that the system may be so adjusted as to divide such sudden demands in desired proportionality between the cycles.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. The method of operating the turbine cycles of a steam-electric generating station having a plurality of steam generators discharging to a common header, 9. pair of steam turbines taking steam from said header, a feed water header feeding all of said boilers and receiving water principally as condensate from the turbines, which includes, separately measuring the rate of supply of steam to each turbine, separately measuring the rate of discharge of water from each turbine cycle to the water header, normally continuously controlling the rate of flow of water from each cycle to maintain a predetermined ratio between the measurements of steam and water for that cycle, and continuously readjusting the rate of discharge of water from both of the cycles to maintain a predetermined ratio between the steam and water ratios of each cycle.

2. Apparatus adapted to control the operation of a steam-electric generating station having a steam header supplied by steam generating boilers, a pair of steam turbines taking steam from said header, a feed water header supplying all of said boilers and receiving water principally as condensate from the turbines, including in combination, a device for each turbine establishing a fluid pressure representative of steam flow rate thereto, a device for each turbine establishing a fluid pressure representative of water flow rate therefrom, and separate control means for each turbine regulating the rate of water from that turbine to the water header, said separate control means positioned conjointly by the fluid pressures established as representative of the steam flow rate and water flow rate for that turbine.

3. Apparatus adapted to control the operation of steam-electric generating station turbine cycles having a steam header supplied by steam generating apparatus, a pair of steam turbines taking steam from said header, a feed Water header supplying all of said boilers and receiving water principally as condensate from the turbines, including in combination, a device establishing a first fluid loading pressure continuously representative of the rate of flow of steam to one turbine, a device establishing a second fluid loading pressure continuously representative of the rate of discharge of water from that turbine cycle to the Water header, means for that turbine cycle continuously responsive to said first and second loading pressures and establishing a third fiuid' pressure representative of the ratio of said steam flow rate and water flow rate, similar devices and means for the other turbine cycle, comparing means to which both third fluid pressures are applied, and regulating means for the discharge of water from the cycles to the water header under the control of said comparing means.

4. The combination of claim 3 wherein the regulating means comprises a separate regulator for the discharge from the two cycles and wherein the two regulators are operated in unison.

5. The combination of claim 4 including means whereby the regulator for one cycle tends to increase the rate of water discharged to the header from that cycle as the regulator for the other cycle decreases the rate of Water discharged to the header from its cycle.

6. Apparatus adapted to control the operation of a steam-electric generating station having a steam header supplied by steam generating boilers, a pair of steam utilizing and condensing prime movers taking steam from said header, a feed water header supplying said boilers and re ceiving feed water principally as condensate from the prime movers, including in combination, separate fluid pressure actuated regulating means for each prime mover controlling the discharge of feed water to the header, and fluid pressure actuated means responsive to steam flow and Water flow of each prime mover establishing a fluid pressure representative of the ratio of said flows associated with each prime mover individually positioning said regulating means in direction and magnitude to maintain said ratios between steam ilow to the prime mover and water flow from the prime mover for each prime mover separately.

'7. Apparatus adapted to control the operation of steam-electric generating station prime mover cycles having a steam header supplied by steam generating boilers, a pair of steam utilizing and condensing prime movers taking steam from said header, a feed water header supplying said boilers and receiving water principally as condensate from the prime mover cycles, including in combination, separate fluid pressure controlled regulating means controlling the rate of discharge of water to the header from the two cycles, and fluid pressure operated means positioning said regulating means in proper direction and amount to maintain predetermined ratio between steam rate to the prime mover and water rate from the same prime mover cycle for each cycle separately, the fluid pressure operated means including relays for comparing the ratios and positioning the regulators simultaneously in opposite directions.

8. The method of operating steam-electric generating station turbine cycles having a plurality of steam generators discharging to a common header, 2. pair of steam turbines taking steam from said header, a feed water header supplying 10 rately from each cycle, and controlling the two discharge rates to increase one as the other is decreased.

WILLIAM POWELL, JR.

References ()itel in the file of this patent UNTTED STATES PATENTS Name Date Smoot July 3, 1934 Number

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