US3135252A - Recirculation system for steam generator - Google Patents

Recirculation system for steam generator Download PDF

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US3135252A
US3135252A US127395A US12739561A US3135252A US 3135252 A US3135252 A US 3135252A US 127395 A US127395 A US 127395A US 12739561 A US12739561 A US 12739561A US 3135252 A US3135252 A US 3135252A
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Prior art keywords
pump
flow
water
recirculating
tubes
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US127395A
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English (en)
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Willburt W Schroedter
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Combustion Engineering Inc
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Combustion Engineering Inc
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Priority to BE620762D priority Critical patent/BE620762A/xx
Application filed by Combustion Engineering Inc filed Critical Combustion Engineering Inc
Priority claimed from US127176A external-priority patent/US3202138A/en
Priority to US127289A priority patent/US3135250A/en
Priority to US127395A priority patent/US3135252A/en
Priority to CH881962A priority patent/CH402001A/de
Priority to CH883162A priority patent/CH394249A/de
Priority to DES80569A priority patent/DE1253723B/de
Priority to FR905222A priority patent/FR1334598A/fr
Priority to ES0279529A priority patent/ES279529A1/es
Priority to FR905223A priority patent/FR1416315A/fr
Priority to GB2903462A priority patent/GB1008795A/en
Priority to GB29028/62A priority patent/GB1008793A/en
Priority to SE8314/62A priority patent/SE308529B/xx
Priority to US331196A priority patent/US3202135A/en
Publication of US3135252A publication Critical patent/US3135252A/en
Application granted granted Critical
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22G—SUPERHEATING OF STEAM
    • F22G5/00—Controlling superheat temperature
    • F22G5/02—Applications of combustion-control devices, e.g. tangential-firing burners, tilting burners
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B29/00—Steam boilers of forced-flow type
    • F22B29/02—Steam boilers of forced-flow type of forced-circulation type
    • F22B29/023—Steam boilers of forced-flow type of forced-circulation type without drums, i.e. without hot water storage in the boiler
    • F22B29/026—Steam boilers of forced-flow type of forced-circulation type without drums, i.e. without hot water storage in the boiler operating at critical or supercritical pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B29/00—Steam boilers of forced-flow type
    • F22B29/06—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes
    • F22B29/12—Steam boilers of forced-flow type of once-through type, i.e. built-up from tubes receiving water at one end and delivering superheated steam at the other end of the tubes operating with superimposed recirculation during starting and low-load periods, e.g. composite boilers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B35/00—Control systems for steam boilers
    • F22B35/06—Control systems for steam boilers for steam boilers of forced-flow type
    • F22B35/10—Control systems for steam boilers for steam boilers of forced-flow type of once-through type
    • F22B35/12—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating at critical or supercritical pressure
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
    • F22B35/00—Control systems for steam boilers
    • F22B35/06—Control systems for steam boilers for steam boilers of forced-flow type
    • F22B35/10—Control systems for steam boilers for steam boilers of forced-flow type of once-through type
    • F22B35/12—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating at critical or supercritical pressure
    • F22B35/125—Control systems for steam boilers for steam boilers of forced-flow type of once-through type operating at critical or supercritical pressure operating with superimposed recirculation during starting or low load periods, e.g. composite boilers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22G—SUPERHEATING OF STEAM
    • F22G5/00—Controlling superheat temperature
    • F22G5/06—Controlling superheat temperature by recirculating flue gases
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F22—STEAM GENERATION
    • F22G—SUPERHEATING OF STEAM
    • F22G5/00—Controlling superheat temperature
    • F22G5/10—Controlling superheat temperature by displacing superheater sections

Definitions

  • FIG-8 w. w. SCHROEDT'ER RECIRCULATION SYSTEM FOR STEAM GENERATOR 1961 5 Sheets-Sheet 4 INVENTOR WILLBLJRT W. SCHROEDTER ATTORNEY conditions at all loads.
  • An object of this invention is an improved recirculating system for a once-through steam generator for operation in the supercritical pressure region.
  • custom and experience has dictated that a minimum rate of circulation of the water or working mediumin the heating tubes must be maintained at all times while there is fire in the furnacedn order to prevent the burning of the tubes forming the walls of the furnace, commonly known as the water walls, and containing the working medium, usually purified water.
  • Custom and experience has indicated that an average velocity of about 3 feet per second for example at the entrance to the water wells is the 'minimum safe velocity at all operating conditions of the generator to provide the turbulent flow required to prevent localized heating and burning of the tubes. This velocity is a criteria which determines many of the other constructional features of the steam generator.
  • the object of circulation is to assure continuous removal of the heat absorbed so as to i keep the tubes'from exceeding their designed temperatures.
  • This circulation must produce therequired fluid flow in the tubes at the most economical balance between tubing cost and available or required pressure drop and also provide proper distribution of the fluid among multiple tube circuits with suflicient stability against transient Modern steam generators, regardless of pressure level, have by'their very nature, (1) a water heating section or economizer, (2) an evaporator or at supercritical pressures,'an intermediate section,
  • furnace walls which by convention is commonly termed furnace walls, and finally (3 a superheater.
  • the pressure level or working pressure at which the steam generator operates influences particularly the relative size of these sections and the temperature level.
  • a In natural circulation water is heated and boils in the heat-absorbing riser tubes and the mixture of water and steam rises upward into a drum located above the riser tubes where the steam separates from the water and flows on into the superheater.
  • the incoming feed water is fed into the drum and mixes withithe water in the drum and is returned through a downcomer to the lower end of the heat absorbing riser tubes.
  • Circulation is by a thermal pump deriving its power from the heat absorbed and 7 depends upon the large change in volume between saturated water and steam at sub-critical pressures andmust provide a substantial ratio of saturated'water to steam in order to assure adequate cooling of all evaporator tubes.
  • Both the natural and the controlled circulation method recirculate fluid through the evaporator or furnace wall section. Both of these methods require a drum for separating the recirculated fluid, in the form of water, from i the steam passing through the system to the turbine.
  • feed Water pump only supplies feed water to the drum and pressure to the system but does not participate in the circulation of fluid through the furnace wall.
  • the control device may be responsive to any of several variables which are dependent upon the load, for instance, on the pressure drop occurring within a predetermined section of the fluid heating device, to variations, in the speed of the feed pump, or to the electrical output of a turbo-generator, the turbine of which is supplied with steam from the steam generator.
  • the regulating device may take several forms, for instance a throttle valve in the recirculating, system controlled by the control device or, in the case where the recirculating pump is driven by a variable speed motor, it may comprise speed adjusting means for this motor controlled. by the control device. This publication indicates also that this particular recirculating system can be applied to steam generators operating in the supercritical pressure range.
  • the present invention relates to a once through steam generator in which the through-flow consists of the feedwater and its vapor which continuously passes through the generator to the point of use.
  • a recirculation system having a recirculation passageway including a selected portion of the generator, such as the water walls, is superimposed on' the through-flow and provides recirculation through the selected portion of the generator in addition to the through-flow and is particularly adapted for operation in the supercritical pressure range and is an improvement over any of the devices shown in either of the above mentioned British publications.
  • control and eventual elimination of the recirculatien in the supercritical system is automatically obtained without the head limiting means of the one publication or the control and regulating devices of the other publication.
  • the heat and pressure characteristics peculiar to the supercritical operation are ultilized to automatically balance the output of a free-running, uncontrolled centrifugal pump in the recirculating system to maintain a sufiicient but limited recirculation flow at partial power conditions and where desired to automatically block the recirculation flow at load conditions above a preselected amount.
  • FIGURE 1 is a diagrammatic representation of forced flow once-through steam generating power plant embodying the invention
  • FIGURE 2 is a diagrammatic representation of a steam generator of the forced flow once-through type operating in the supercritical pressure range, and having in accordance with the invention a recirculation circuit superimposed upon the water heating tubes, the flow therethrough being automatically controlled by a constant speed, uncontrolled recirculating pump floating on the once-through flow circuit; the gas duct containing the superheater has been moved from the rear to the side of the furnace, and the economizer has been omitted for clarity;
  • FIGURE 3 is a graph showing the relation between temperature and specific volume (cubic feet per pound) in a fluid (water and steam) maintained at supercritical and subcritical pressure;
  • FIGURE 4 is a graph showing the fluid temperatures in the furnace walls including the center Walls and water walls of a steam generator operating at supercritical pressures;
  • FIGURE 5 is a graph of the pump characteristics and the system curves forthe system of FIG. 2;
  • FIGURE 6 is a graph of the recirculation flow for various percentages of the total feed water flow
  • FIGURE 7 is a graph showing the water wall velocities produced with the recirculating flow pump operating at various percentages of feed water flow
  • FIGURE 8 shows the head produced by the recirculating pump in a graph similarto FIG. 7 but plotted in feet of Water being pumped at various percentages of feed Water flow; 7
  • FIGURE 9 shows a modification of the structure shown in FIG. 2, in which the recirculating pump location has been changed from a position in the inlet to a position in the outlet of the mixing vessel 20;
  • FIGURE 10 is a graph similar to FIG. 5 but showing the pump characteristics and system curves for the mixed flow pump
  • FIGURE 11 is a graph similar to FIG. 8 but showing the head in feet of water being pumped by the mixed flow recirculating pump;
  • FIGURE 12 shows a further-modification of the structure. shown in FIG. 2 in which the recirculating pump is located between the center and water walls;
  • FIGURE 13 shows a still further modification of the structure shown in FIG. 2 in which the recirculating pump is inserted in the through flow line at the outlet of the water walls.
  • FIGURE 1 there is illustrated in diagrammatic form'the basic circuit of a forced flow once-through steam generator power plant operating in the supercritical pressure range.
  • a feed pump F takes water from a water tank W and delivers this water under pressure to an economizer E wherein the water is first heated.
  • economizer E the water flows through additional heating tubes H which serve as a lining for the walls of the furnace and also may constitute convection heating surface exposed to the combustion gases after they have left the furnace.
  • tubes H transition takes place from the liquid phase to the vapor phase of the Working fluid before the steam is conducted to superheater S wherein the steam is superheated *to a fi'nal temperature of say 1000 F.
  • the steam Upon leaving the superheater S the steam is conveyed to a point of use such as turbine T where the thermal energy of the steam is converted into mechanical energy for driving an electric generator 'G.
  • the feed pump pressurizes the entire generator system from the entrance of economizer E to the usual control valve for turbine T with a pressure known as working pressure. This pressure varies from one end to the other of the'system due to friction and other loses incident to forcing the fluid through the system and is usually measured at the turbine control valve or the superheater discharge end of the system.
  • the steam exhausted from the turbine T is condensed in condenser C and returned to water tank W by way of condensate pump P.
  • recirculating circuit pump R is arranged in parallel with the pump F and may take working fluid from the outlet of tubes H andreturn it to the inlet thereof.
  • the invention will be described particularly in connection with the operation of this pump R in which fluid taken from the outlet of the heating tubes H which will be called the center walls and water walls and returned to a mixing chamber M at the entrance to'the furnacewalls where the recirculated fluid is mixed with the feed water fluid to provide a mixed fluid which is fed to thefurnace walls.
  • FIGURE 2 shows a specific embodiment of the invention in which the amount of working fluid recirculated through the heating tubes 12, forming a center wall in the furnace, and tubes 14, forming the water walls in the furnace, is automatically regulated by the pump 1% driven by the constant speed electric motor 16.
  • the pump 1 takes fluid from the header 18, connecting the tops of the tubes forming the water walls 14, and delivers it to the mixing chamber 29, which also receives water from the feed pump 22.
  • the chamber has a discharge connection 200 to the header 24 connecting the bottom of the tubesforming the center wall 12.
  • the chamber 2% is normally located near the top of the steam generator in order to obtain the benefit of the pressure differential between the cold water in line 2% and the heated fluid'in the fluid passes to the header 24 and then tmough panels of parallel heating tubes, with the panels formed of tubes 12 and 14, being connected in series and forming radiant and/or convection heating surfaces exposed to the heat of the hot gases in the furnace.
  • These tubes 12 and 14 may form water wall linings within the furnace chamber 32 as shown in more detail in my application for Furnace Wall Arrangement for Vapor Generator Serial No. 127,-
  • the amount of working fluid recirculated through the tubes 12 and 14 is controlled entirely by the free running
  • the centrifugal pump 10% is driven by a substantially constant speed mechanism shown as a constant speed electric motor 16 having an onand off-switch 84 in the power lines 86 for the purposeof starting and stopping the recirculating pump'10.
  • the conduit 60 including conduit 20d. is provided with a check valve 88 preferably at the pump 7 outlet and if desired may be provided with a throttle the usual slight expansion and contraction with pressure and temperature changes.
  • the fuel supply and the feed water supply of the steam generator may becontrolled by any conventional control system to provide fuel and feed water supply in accordance with load.
  • control system may be divided generally into two control systems.
  • One system controls the-turbine output and pressure by heat input.
  • the other system controls feedwater flow and steam temperature in response to heat ab sorption. Both systems are intermeshed by a load output signal to the feedwater control and by a steam temperature signal to the heat input.
  • the one system is controlled generally by the load regulating computer 741 which provides error signals from desired load, pressure and frequency, to regulate and maintain the proper required output over the full load range.
  • Computer output signals are sent to the control system for feedwater 49, fuel and air 38 and turbine governor 72.
  • the control action for fuel and air is accomplished by the computer 70, so that fuel input through line 39 is regulated by valve 38 to maintain the proper steam generator output.
  • Feed water control is accomplished by a feed water valve 40 in-conjunction with a flow meter 74.
  • Feed water valve 40 is adjusted in accordance with heat input which in turn is adjusted by load. Heat input is sensed by water wall temperature.
  • the feedwater controller receives a signal from the combustion control system to maintain the proper fuel and feed water relationship.
  • the water wall temperature is also adjusted to maintain a proper ratio of injection to the superheater, for steam temperature control (not shown), to total feed water flow.
  • the pump is pumping very hot fluid received from the header 18 at the top of the water walls and is delivering it to a mixing chamber 20 where it is mixed with the relatively cool feed water to provide a cooler mixture which is fed through the center wall where some heat is added and the temperature is raised before the mixture is fed to the header 30 at the entrance to the water walls.
  • a mixing chamber 20 where it is mixed with the relatively cool feed water to provide a cooler mixture which is fed through the center wall where some heat is added and the temperature is raised before the mixture is fed to the header 30 at the entrance to the water walls.
  • this temperature increases from about 731 at 5% load to about 758 at 100% load. This is the temperature of the water that is being pumped by the recirculating pump 10.
  • Line 96 indicates the temperature of the water leaving the center wall which would be the temperature of the water in the header 26 and as this header is connected by a 'downcomer 28 directly with the header 30 at the inlet of the water walls 14 this center wall outlet temperatureis also the water wall inlet temperature and is the temperature of the water which establishes the three feet per second flow at the water wall inlet. It will be noted that although the recirculating water temperature increases with load the water wall inlet temperature decreases with load. This is due to the addition of the cold feed water from the feed pump 22 to the mixing vessel 20.
  • Line 08 represents the temperature of the water at the center wall inlet header 24 and shows how the water leaving the mixing vessel has its temperature reduced with increasing loads due to the increased quantity of feed water and the reduced quantity of recirculating water being fed to the mixing vessel.
  • Line 100 is an indication of the temperature of the feed water being fed by the feed pump 22 to the mixing vessel 20 to be combined with the recirculating water whose temperature is indicated by the line 94. The above temperatures are established by the furnace and water wall designs and are a function of the load.
  • FIGURE 3 the condition afiecting the pump operation attention is called to FIGURE 3 in which the line 102 represents the changes in specific volume, that is, cubic feet per pound, at different temperatures at supercritical pressure.
  • the line 102 represents the changes in specific volume, that is, cubic feet per pound, at different temperatures at supercritical pressure.
  • the temperature range of the water wall outlet namely, between 731 and 752 at the supercritical pressure indicated that there is a rather sharp change in specific volume for a 'comparatively small change in temperature although there is only a single'phase fluid and each unit of heat added or subtracted will change the temperature of the fluid.
  • the line 108 indicates a system resistance curve, which is an indication of the flow in gallons per minute at a selected water wall outlet temperature and at a selected percentage of feed water flow in the parallel recirculating system.
  • the line 108 indicates the head produced between the mixing tank and the water wall outlet header 18 by a flow of a selected number of gallons per minute through the recirculating piping 60 at a temperature of 750F. when the feedwater pump is delivering 60% of its fullcapacity.
  • the position on the curve marked by the reference numeral indicates the volume in gallons per minute in the recirculating system at 750 F. which will produce a flow of three feet per second at the water wall inlet.
  • the curve 128 may be plotted from the intersection points of 118, 120 and 122 of FIGURE 5.
  • the three feet per second curve 130 may be plotted from the three feet per second points in FIG- URE 5 or may be calculated, and the curve 132 indicating the head developed between the mixing tank 20 and the outlet header 18 by the feed water pump might also be calculated or determined from the selected feed water and temperature conditions.
  • the pump performance curve 134 may be picked off from the intersection points 118, 120 and 122 of FIGURE 5.
  • FIGURE 6 and FIGURE 8 show that the uncontrolled self-regulating recirculating pump which has the characteristics of a reduced flow when the head pumped against is increased will produce the required three feet per second flow at the water wall inlet at about 30% load and will automatically cease delivering any recirculating flow when the feed water flow reaches approximately 88% of full load.
  • FIGURES 6 and 8 also show that the water wall flow area in a once-through system can be made large enough so that the feed water pump will not produce the three feet per second flow at the water wall inlet until it has attained about 70% of capacity and that the uncontrolled recirculating pump will maintain that three feet per second flow automatically under all conditions and will even increase the flow rate at the higher firing rates accompanying the increased feed water flow which is a preferred condition.
  • the performance of the uncontrolled pump can be illustrated in another manner by plotting the water wall inlet velocity against the percent of the feed water flow as shown in FIGURE 7.
  • the velocity may be figured from the recirculation flow in gallons per minute at points 118, 120 and 122 of FIGURE 5 corrected for the temperature at the water Wall inlet and added to the feed water flow.
  • Line 136 shows the three feet per second line below which the velocity at the water wall inlet should not drop.
  • 'Line 138 shows the velocity produced by the feed water pump without assistance from the recirculating pump and line 140 shows the velocities obtained with both the feed water and the recirculating I once-through flow only.
  • FIGURES 6, 7 and 8 and particularly FIGURES 7 and 8, show that the recirculating pump may be stopped at 70% load and from there on to the higher loads the feed pump alone'will maintain the required safe flow at the water wall inlet. However, the recirculating pump may be allowed to continue to operate and will automatically cease delivering at about 88%. This emphasizes another safety feature, concerning the temperature fluctuation at the inlet of the hot fluid, emanating from the pump, into the nnxing vessel 20.
  • the steam generator operates at a fluctuating load of or l% or so around the no delivery point of the pump then the temperatures of the nozzle will flucmate in a similar manner between the hot fluid temperature and the mixed temperature in the vessel as the pump alternately delivers and then stops delivering. This is an undesirable condition because the temperature fluctuation thus produced in heavy Wall piping can lead in time to fatigue failure.
  • the operator may shut down the circulating pump, if the load as reflected in the percentage of feed water flow starts fluctuating about this point, and particularly if the fluctuation is expected to continue.
  • the check valve 88 will then close and the piping and nozzle and the mixingvessel will be cooled to the least temperature and remain there while the feed water pump will supply all of the flow necessary to maintan the three feet per second at the water wall inlet.
  • Acheck valve 202 is placed in the conduit forming line 200 and a branch 204 leadingto the intake of the pump 210 is connected to the line 200 1G upstream of the check valve 2il2 between the valve 202 and the mixing tank 20 and a pump discharge line 206 connects the pump discharge with the line 200 downstream of the check valve 202 between the valve 202 and the header 24.
  • a shut-oi? valve 212 can be placed in the line 204 and a shut-off valve 214 can be placed in the line 206 to isolate the pump 210 from line 200.
  • the check valve 202 will prevent short circuiting of the pump 210 and will permit feedwater flow to bypass pump 210 and thus prevent excessive economizer pressure if either or both valves 212 and 214 are inadvertently closed.
  • the connections 206 and 200 between the recirculating pump'outlet and the header 24 connected to the bottom of the heating tubes is uncontrolled and has a passageway of normally fixed dimensions.
  • the valve 214 is not a control valve but is an isolating valve for use in isolating the pump for repairs and renewal. As with the device shown in FIG. 2, the
  • recirculation system conduit or passageway 60 including the conduits 2%, 204, and 2% may contain check valve 83 and isolating valves 212 and 214 but is otherwise of fixed or generally constant fluid flow area and .thus will provide a recirculation passageway or conduit it becomes progressively cooler as the load increases while the water from the water wall outlet becomes progressively hotter.
  • the pump 216 being in series with the feed pump must now handle not only the recirculating water but also all of the feed water as well. However, because of the dilference in temperature of the water being handled the total capacity of the pump and the head of the pump as measured does not have to be as large as the recirculating pump required for pumping the hot fluid in line 69 as shown in FIGURE 2.
  • the pump 210 will create suflicient head between the water wall outlet 18 and the center wall inlet header 24 to force recirculating water through the center walls and water walls and thefeed water pump 22 will supply enough additional water to satisfy the load requirements of the turbine. It will be understood that if desired the pump 216 can be placed directly in the line 2% andthe valve 2612 closed or omitted.
  • the pump 210 as shown in FIGURE 9 with the valve 2tl2 and its connections omitted will be designed to have enough free flow space through the centrifugal pump to permit passage of all or part of the feed water through the pump 210 with the pump shut down without material pressure drop through the idle pump.
  • the pump characteristic curve of pump 210 is shown in FIGURE 10 and the system characteristic curve with 5, 30 and 60% of the feed water flow are shown intersecting the pump characteristic curve.
  • the pressure drop can not be readily applied to the pump curve as it is in FIGURE 5.
  • the system resistance curves are first established without the recirculating piping and then corrected for theh ead lost in the recirculating piping.
  • the pump curve 216 intersects the system curve 218, representing the system characteristics for 5% of feed water flow, will establish a point indicating the gallons per minute and the head of mixed water being pumped by the circulating pump 210 under the temperature and head conditions for 5% of feed water flow.
  • the intersection of the line 216 withthe line 229 indicating the system characteristics for 30%:of flow will establish the pump head and volume characteristics under the conditions of 30% of feed water flow and similarly, the inter- 1 1 section of the 'line 216 with the line 222 showing the system characteristics at'60% flow will establish a point indicating the head and volume characteristics of the pump at the 60% feed water flow condition.
  • line 224 to FIG- URE 6 which will'show the gallons per minute of recirculating flow and show how it compares with the recirculating 'flOW required to maintain the necessary three feet per second at the water wall inlet.
  • the gallons per minute indicated by line 224 arethe gallons indicated by the intersectionpoints on FIGURE 10 minus-the quantity of 'feed water flow.
  • the pump 210 establishes the minimum safe flow of three feet per second at the start up feed water flow of say about and will maintain a slight excess over the required three feet per second up to approximately 80% of the feed water flow at which point the feed water establishes a head across the center and water walls sufficiently high to block any further pumping of recirculating fluid by the pump 210. Above this point the pump 210 may be shut down and the feed water fiow allowed-to flow through the pump or through the by-pass around the idle pump 210 and through the check valve 202 if such a check valve is utilized. As indicated above, if the load is fluctuating about the 80% point the pump 210 may be shut down to avoid the-thermal stresses in the nozzles of the mixing tank 20 and the necessary flow of three feet per second will be maintained by the feed water pump.
  • FIGURE 11 is another chart showing the characteristics of the system by plotting the head in feet or" the mixed fluid pumped against the percentage of feed water flow.
  • the percentage of feed water increases the head as measured in the feet of Water pumped by pump 21 0 decreases to maintain the three feet per second flow. This is because the quantity of cool feed water is increasing and the quantity of hot recirculated water is decreasing so that the mixed fluid has a decreasing temperature and is consequently heavier and will require a smaller number of feet of that fluid to produce the same pressure, or pounds per square inch.
  • the head in feet of fluid pumped by the pump 210 as indicated by line 226 also decreases it does not decrease as rapidly as the required head as indicated by line 223 so that a safe margin is maintained above the required head, as the feed water flow and the corresponding firing rate increases giving rise to more severe conditions, in which the slight increase in' flow will provide an additional safety feature at the higher firing rates.
  • this second embodiment utilizing the constant speed free running pump floating on the through-flow system and located in the line 205 in series with the feed pump, presents characteristics differing somewhat from those of the FIGURE '2 embodiment in which the recirculating pump is arranged in parallel with the feed pump but retains the very important features of being self-regulating Without any outside control mechanism and without any of the mechanism for limiting the pump flow except its inherent self-limiting features.
  • Still another position in which the pump could be placed and provide satisfactory performance and regulation would be to place the pump 21h 'in series with the feed pump by placing it in the downcon'ier 28' as shown in FIGURE 12 between the center wall outlet header 26 and the water wall inlet header 30.
  • Stillanother position in which the recirculating pump may be placed is in the through-flow line 300, as shown in FIGURE 13, at the outlet of the water Walls 14.
  • this modification shows the free running recirculating pump in series with the feed pump and pumping the mixed flow and providing the head for recirculating flow and providing mixed flow of at least the critical velocity in the heating tubes at loads below the cut-off point of the recirculating pump.
  • Free-running as used in this specification and claims is limited to mean running free without separate control mechanism responsive to any parameter of the fluid pumped for controlling either the pump, pump inlet means, pump outlet means or the motor.
  • the freerunning pump in the specific embodiment disclosed would be a pump driven by a motor connected to a power source, such as the usual alternating current electric power line having a substantially constant voltage and frequency, hence running at substantially constant speed without motor performance control or regulating mechanism between the motor and the source and with the pump operating free of controls in the pump circuit.
  • Floating as used in this specification and claims is limited to means connected across or in a line, passageway or circuit without controlling mechanism in the connec. tion for limiting or controlling the inlet or discharge flow of thepump, so that the full pump pressure is applied across or in the line whenever the pressure across or in the line would otherwise fall below the pump pressure.
  • the pump output is self-regulating and uncontrolled by control mechanism and dependent only on the pump characteristics and the line conditions.
  • a forced flow once-through steam generator having means for supplying hot gases and having working fluid heating tubes having an inlet, an outlet and an intermediate portion therebetween exposed to said hot gases, feed pump meansuconnected to said inlet of said tubes and supplying a positive, once-through flow of Working fluid to the heating tubes at super-critical pressure, recirculating means including a passageway having generally constant recirculating fluid flow area during normal recirculation fluid flow throughout a range of operation of the generator connecting the outlet to the inlet of the fluid heating tubes and including a free running, self regulating recirculating pump having the inherent characteristic of decreasing pumped volume with increasing pumped head and establishing a positive recirculation of the working fluid through the heating tubes and the recirculation means in addition to the once-through flow.
  • a furnace having walls formed by a plurality of tubes and having means for heating a working medium in said tubes for supplying avarying working medium demand, said tubes having an inlet and an outlet and requiring a predetermined velocity flow rate of said medium in said tubes for safe operation, feed water pump means connected with said inlet and supplying said medium to said tubes at supercritical pressure and at a rate to satisfy said demand whichrate, at times, is insufflcient to produce said predetermined velocity in said tubes,
  • a free running recirculating pump having the inherent characteristic of decreasing pumped volume with increasing pumped head, means connecting said recirculating pump in fluid flow relationship directly across said tubes to recirculate the working medium through said tubes in addition to the medium pumped by said feed pump to thereby maintain said predetermined safe velocity flow rate.
  • a combination as claimed in claim 4 in which the recirculating pump is connected directly across said tubes in series with said feed pump.
  • said recirculating pump is a pump having an output varying inversely with pumped head and having a minimum head under operating conditions sufficient to maintain said predetermined velocity flow rate at said times when the through flow through the tubes is at a rate less than said predetermined rate and having a no recirculating flow delivery head greater than the feed pump means head required to maintain said flow rate alone.
  • a forced-flow once-through vapor generator means for supplying hot gases and having working fluid heating tubes having an inlet, an outlet and an intermediate portion between said inlet and outlet exposed to said heated gases, a mixing chamber, feed pump means supplyingthrough-flow working fluid first to said chamber and then to said inlet of said tubes at a rate to satisfy the vapordemand, recirculation means comprising a recirculation passageway including said mixing chamber, a connection from said chamber to the inlet of said tubes, said tubes, and an outlet connection connecting the outlet er said tubes with said-chamber, the improvement comprising a free-running recirculating pump in said passage- Way, said passageway includingmeans connecting said recirculating pump in fluid flow relation across said tubes and conducting working fluid from said outlet to the inlet of said recirculating pump, said pump forcing working fluid through said tubes in addition to said through-flow fluid to provide a combined flow of working fluid, means preventing flow from said chamber to said outlet in said outlet connection, said free-running pump having the inherent self-regulating characteristic ofautomatically varying
  • the rerecirculating means including means connecting the outlet of said tubes with the inlet of said tubes and also including a substantially constant speed recirculating pump having the inherent characteristic of pumped flow varying inversely'with pumped head floating on the through flow line' for establishing a positive recirculation flow of the working fluid through 'said heating tubes and the recirculating means.
  • a generator as claimed in claim 9 in which the recirculating pump is in the through-flow passageway in series with said feed pump means.
  • a generator as claimed in claim 11 including a mixing chamber connected with the inlet of said tubes and receiving both the once-through and the recirculating flow and in which the recirculating pump is located between the chamber and said inlet.
  • a generator as claimed in claim '11 including'a by-pass around said recirculating pump and a check valve in said. by-pass preventing short-circuiting of said recirculating pump.
  • a forced flow once-through steam generator for supplying a variable steam demand and having a once-through flowpassageway including vertically arranged parallel flow working fluid heating tubes having an inlet, feed water pump means connected with said inlet of said tubes for establishing the working pressure and a positive oncethrough flow of working fluid to said tubes at supercritical pressure and at said demand rate, said through flow passing through said tubes creating a pressure drop across said tubes increasing with said demand, recircu-' lat1ng mean comprising a recirculating pump floating on the once-through passageway and connected in fluid flow relation across said tubes by conduit means unobstructed by variable control mechanism during recirculation operation, means driving said pump at a substantially constant speed, said recirculating pump pumping against said pressure drop and having theinherent characteristic of reducing volume pumped with increase in head across said tubes and having sufiicient capacity to provide with said through flow, a preselected critical velocity of working fluid in said generator at a selected steam demand substantially less than that necessary to provide'a critical velocity of through flow alone and provide a higher
  • a forced flow once-through steam generator for supplying a varying steam demand and having means for creating hot gases and having working fluid heating tubes having an inlet, an outlet and an intermediate portion between said inlet and said outlet exposed to hot gases and in which the temperature of fluid discharged from said tubes increases with increased steam demand
  • through-flow means including said tubes and feed pump means connected to said inlet and supplying through flow fluid cooler than said discharged fluid for supplying a positive once-through flow of working fluid at supercritical pressure and in'accordance with'said demand, said tubes requiring a predetermined velocity flow rate of said working fluid for safe operation
  • recirculation means connected to the said inlet and said outlet of said fluid heating tubes and including a substantially constant speed recirculating pump, having an output inherently varying inversely with pumped pressure, floating on the throughflow means for establishing a positive recirculation of the working fluid through the heating tubes, means combining said through flow and the recirculation flow to provide a combined flow of at least said predetermined velocity, the temperature of recirculation fluid discharge
  • a forced flow once through vapor generator having means for generating hot gases and having-a through flow passageway including working fluid heating tubes having an inlet, an outlet and an intermediate portion,
  • feed pump means connected to said inlet establishing the Working pressure and a positive once through flow of working fluid through the passageway, a check valve in said passageway preventing reverse flow in said passageway, recirculating means including means connecting the outlet of said tubes with the inlet of said tubes and also including a recirculating pump having an inlet and located in said passageway in series assisting relation with said feed pump and means connecting said pump across said check valve with the inlet of said recirculating pump connected upstream of said check valve, and an isolation valve on each side of said recirculation pump in said pump'connecting means.
  • a forced-flow once-through steam generator for supplying a variable steam demand and having vertically arranged working fluid heating tubes having an inlet and an outlet, feed water pump 'istic of decreasing recirculation flow less than the inmeans, means connecting said pump means to the inlet of said tubes, for establishing the Working pressure and supplying a positive once-through upward flow of working fluid to said tubes at supercritical pressure and at the demand rate, said connecting means including a mixing vessel at an elevation substantially equal to the top of said tubes, connected with said inlet by a downwardly directed conduit, and receiving the feed pump discharge, a recirculating system connecting the outlet of said tubes with said inlet and including a self regulating recirculating pump connected in fluid flow relation with said mixing vessel and said tubes for establishing a positive recirculation of heated fluid through said tubes and mixing vessel, said recirculating pump floating in the connecting means between the mixing vesseland the inlet of said tubes, the pressure differential between the comparatively cool fluid in said conduit and the heated fluid in said tubes assisting said recirculation.
  • a forced flow once-through steam generator having a safe minimum velocity of the working fluid and in which the once-through flow varies with the load and hot Working fluid is recirculated, through a portion of the generator, to provide said safe velocity at loads below that at which the through flow alone provides said safe velocity, by a pump, floating on the oncethrough circuit through said portion, and having a no delivery condition at a load above that at which the through flow alone provides the minimum safe velocity of the working fluid, the steps of recirculating hot fluid at loads above that at which the once-through flow alone provides the minimumsafe velocity, and'in the event of a fluctuating load fluctuating both sides of said no delivery condition, discontinuing recirculation and operating with the through flow alone.
  • a method of operating a once-through vapor generator supplying a variable demand and having working fluid heating tubes and a recirculating system recirculating fluid through said tubes and recirculating means conmeeting the outlet with the inlet of said tubes and having in said connecting means an upstream portion and a downstream portion, the step of withdrawing fluid from said tubes through said upstream portion at a reduced pressure and supplying 'fluid to said tubes through said downstream .portion at an increased pressure to recirculate fluid through said tubes, supplying a through flow of working fluid through said tubes in accordance with said demand, mixing said through flow 'fluid with said reduced pressure recirculating fluid while supplying the through flow fluid at a rate which will maintain the pressure at the mixing point of said through flow and recirculating fluids below the pressure at said tube outlet, increasing the rate of through flow supply to increase the pressure at said mixing point to a pressure greater than the pressure at said outlet, to block flow of recirculating fluid from said outlet to said mixing point and thereafter maintaining a safe rate of flow through said tubes by said through

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Combustion Of Fluid Fuel (AREA)
  • Pipeline Systems (AREA)
  • Control Of Steam Boilers And Waste-Gas Boilers (AREA)
  • Engine Equipment That Uses Special Cycles (AREA)
  • Jet Pumps And Other Pumps (AREA)
  • Fluidized-Bed Combustion And Resonant Combustion (AREA)
US127395A 1961-07-27 1961-07-27 Recirculation system for steam generator Expired - Lifetime US3135252A (en)

Priority Applications (13)

Application Number Priority Date Filing Date Title
BE620762D BE620762A (d) 1961-07-27
US127289A US3135250A (en) 1961-07-27 1961-07-27 Steam generator utilizing a recirculating system
US127395A US3135252A (en) 1961-07-27 1961-07-27 Recirculation system for steam generator
CH881962A CH402001A (de) 1961-07-27 1962-07-20 Zwanglaufdampferzeuger
CH883162A CH394249A (de) 1961-07-27 1962-07-23 Verfahren zum Betrieb eines Zwanglaufdampferzeugers und Zwanglaufdampferzeuger zum Durchführen des Verfahrens
DES80569A DE1253723B (de) 1961-07-27 1962-07-24 Zwangdurchlaufdampferzeuger fuer Betrieb mit ueberkritischem Druck
FR905222A FR1334598A (fr) 1961-07-27 1962-07-26 Procédé de réglage de la température de la vapeur de générateurs
ES0279529A ES279529A1 (es) 1961-07-27 1962-07-26 Generador de vapor de paso forzado y procedimiento para el funcionamiento del mismo
FR905223A FR1416315A (fr) 1961-07-27 1962-07-26 Générateurs de vapeur et en particulier systèmes de recirculation de générateurs de vapeur hypercritique
GB2903462A GB1008795A (d) 1961-07-27 1962-07-27
GB29028/62A GB1008793A (en) 1961-07-27 1962-07-27 Improvements in and relating to forced flow vapour generators
SE8314/62A SE308529B (d) 1961-07-27 1962-07-27
US331196A US3202135A (en) 1961-07-27 1963-12-17 Vapor temperature control method

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US127289A US3135250A (en) 1961-07-27 1961-07-27 Steam generator utilizing a recirculating system
US127395A US3135252A (en) 1961-07-27 1961-07-27 Recirculation system for steam generator
US127176A US3202138A (en) 1961-07-27 1961-07-27 Vapor temperature control method
US331196A US3202135A (en) 1961-07-27 1963-12-17 Vapor temperature control method

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US3135252A true US3135252A (en) 1964-06-02

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US127395A Expired - Lifetime US3135252A (en) 1961-07-27 1961-07-27 Recirculation system for steam generator
US127289A Expired - Lifetime US3135250A (en) 1961-07-27 1961-07-27 Steam generator utilizing a recirculating system
US331196A Expired - Lifetime US3202135A (en) 1961-07-27 1963-12-17 Vapor temperature control method

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US127289A Expired - Lifetime US3135250A (en) 1961-07-27 1961-07-27 Steam generator utilizing a recirculating system
US331196A Expired - Lifetime US3202135A (en) 1961-07-27 1963-12-17 Vapor temperature control method

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US (3) US3135252A (d)
BE (1) BE620762A (d)
CH (2) CH402001A (d)
DE (1) DE1253723B (d)
FR (2) FR1416315A (d)
GB (1) GB1008793A (d)
SE (1) SE308529B (d)

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GB1030352A (en) * 1964-02-05 1966-05-18 Foster Wheeler Ltd Supercritical steam power plants
US3357407A (en) * 1965-01-14 1967-12-12 Struthers Thermo Flood Corp Thermal recovery apparatus and method
US3308792A (en) * 1965-08-26 1967-03-14 Combustion Eng Fluid heater support
US3307524A (en) * 1965-09-16 1967-03-07 Combustion Eng Fluid heater support

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GB719753A (en) * 1951-10-23 1954-12-08 Siemens Ag Improvements in or relating to forced through-flow boilers
GB818159A (en) * 1955-05-09 1959-08-12 Babcock & Wilcox Ltd Improvements in forced flow, once-through vapour generating and vapour heating units
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GB719753A (en) * 1951-10-23 1954-12-08 Siemens Ag Improvements in or relating to forced through-flow boilers
GB818159A (en) * 1955-05-09 1959-08-12 Babcock & Wilcox Ltd Improvements in forced flow, once-through vapour generating and vapour heating units
US3038453A (en) * 1957-02-07 1962-06-12 Combustion Eng Apparatus and method for controlling a forced flow once-through steam generator

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* Cited by examiner, † Cited by third party
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Also Published As

Publication number Publication date
GB1008793A (en) 1965-11-03
US3202135A (en) 1965-08-24
DE1253723B (de) 1967-11-09
SE308529B (d) 1969-02-17
FR1334598A (fr) 1963-08-09
FR1416315A (fr) 1965-11-05
CH394249A (de) 1965-06-30
CH402001A (de) 1965-11-15
BE620762A (d)
US3135250A (en) 1964-06-02

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