US3572588A

US3572588A - Condensate and heat recovery system

Info

Publication number: US3572588A
Application number: US813161A
Authority: US
Inventors: John S Hamilton Jr
Original assignee: Boiler Equipment and Controls Inc
Current assignee: Boiler Equipment and Controls Inc
Priority date: 1969-04-03
Filing date: 1969-04-03
Publication date: 1971-03-30
Anticipated expiration: 1988-03-30

Abstract

A trapless condensate and heat recovery system is provided for use with a plurality of parallel connected steam heating coils, each of which is provided with an individual temperature control valve at its inlet side. The coils are connected without the use of traps to a common condensate recovery tank which is provided with pressure and level controls. In one embodiment, the tank is provided with a vent orifice sized to provide adequate venting of noncondensible gases. Alternatively, the tank may be provided with pressure responsive means to bleed off flash steam to a point in a condensate return line from the tank. The condensate return line is coupled either to a deaerating heater or to a makeup storage tank depending on the temperature of the condensate in the line. Live makeup steam is fed into the deaerating heater in response to the pressure within the heater, and excess flash steam within the heater is automatically transferred to the makeup storage tank in response to excess pressure within the heater. In the event that the temperature within the makeup storage tank is excessive, temperature control means responsive to the temperature within the makeup storage tank is employed for controlling an atmospheric vent coupled to the excess steam line to the makeup storage tank. The deaerating heater is provided with level controls to control the feed of water to and from the makeup storage tank.

Description

United States Patent [72] Inventor John S. HamiltonJr.

Monroe, La.

[54] CONDENSATE AND HEAT RECOVERY SYSTEM 23 Claims, 4 Drawing Figs.

[52] US. Cl 237/9 [5 l Int. Cl t F24d 1/02 [50] Field of Search 237/9, 67,

[5 6] References Cited UNITED STATES PATENTS 2,055,033 9/1936 Kingsland 2,493,365 1/1950 Schramm 2,515,650 7/l950 Hunt et al.

Primary Examiner-Edward J. Michael AttorneyRaphael Semmes Atmospheric out '34 I06 "6 Vent Daoaratlnq I32 I08 ea or '00 as v Make-up Water ABSTRACT: A trapless condensate and heat recovery system is provided for use with a plurality of parallel connected steam heating coils, each of which is provided with an individual temperature control valve at its inlet side. The coils are connected without the use of traps to a common condensate recovery tank which is provided with pressure and level controls. In one embodiment, the tank is provided with a vent orifice sized to provide adequate venting of noncondensible gases. Alternatively, the tank may be provided with pressure responsive means to bleed off flash steam to a point in a condensate return line from the tank. The condensate return line is coupled either to a deaerating heater or to a makeup storage tank depending on the temperature of the condensate in the line. Live makeup steam is fed into the deaerating heater in response to the pressure within the heater, and excess flash steam within the heater is automatically transferred to the makeup storage tank in response to excess pressure within the heater. In the event that the temperature within the makeup storage tank is excessive, temperature control means responsive to the temperature within the makeup storage tank is employed for controlling an atmospheric vent coupled to the excess steam line to the makeup storage tank. The deaerating heater is provided with level controls to control the feed of water to and from the makeup storage tank.

To other 30 From other Heaters Heaters Live Steam Make-up 4 42 Steam 64 Supply 56 IZO 9 96 Make-up Storage Tank 94 l j Condensate 88 62 6o Re ieiling CONDENSATE AND HEAT RECOVERY SYSTEM BACKGROUND OF THE INVENTION This invention relates to steam systems and, more particularly, to a condensate andheat recovery system therefor.

In systems of the prior art employing a plurality of steam heating units in parallel, it has been customary to provide each unit with an individual trap to pass condensate but to prevent the passage of steam. In such systems, there is a tendency for air to become trapped in the units and interfere with proper heating by the steam. Such systems also provide nonuniform heating and tend to require a considerable length of starting time after a shutdown because of the time required for the traps to pass condensate and for air in the units to work its way out.

There have been a number of proposals in the prior art of steam heating systems in which parallel connected steam heat ing units do not employ steam traps. However, it has been difficult to provide efi'ectiv'e control of such systems. There is a tendency for steam to appear in the condensate recovery and return equipmentmaking it difficult to prevent the loss of condensate and heat. Noncondensible gases which cause corrosion have not been disposed of efiectively. The heat output of the heating units has usually been constant rather than controlled.

SUMMARY OF THE INVENTION It is a further object of the invention to provide meansfor relieving noneondensible gases, which have a tendency to produce or cause corrosion, at a point near the admission of condensate to the system.

It is an additional object of the invention to provide a trapless condensate and heat recovery system with control of the discharge'of condensate to a tank in which complete and final deaeration to levels acceptable to the industry are maintained for all conditions for operation.

It is another object of the invention to provide a trapless condensate and heat recovery system with maximum recovery of the heat from the condensate consistent with overall operating requirements and conditions.

Another object of the invention is the provision of a trapless condensate and heat recovery system in which loss of condensate is prevented within limits consistent with continuous operation and protection of piping and equipment.

Still another object of the invention is to provide an automated trapless condensate and heat recovery system.

Yet another object of the invention is the provision of a trapless condensate recovery system witha plurality of parallel connected steam heating coils each of which is individually controlled by the provision of a temperature responsive control valve at its inlet side.

Briefly, the invention contemplates the provision of a plurality of steam heating coils connected in parallel with a common steam supply, each of the heating coilsbeing provided with an individual control valve on its inlet side. Trapless connections are provided from the heating coils to a common condensate recovery tank which includes means for controlling the pressure within the tank as some of the condensate received from the coils flashes to steam. This means may take the form of a vent orifice sized to provide adequate venting of noncondensible gases and may also include a high condensate level sensing device to close the valve in response to a high condensate level within the tank to prevent loss of condensate for surge loads or startup operation. In another embodiment, the pressure within the tank is controlled by pressure sensing means to bleed off flash steam to a point in a condensate return line from the tank. In addition, the tank is provided with means to maintairi the level of condensate within the tank constant by controlling a-valve in the condensate return line. Alternatively, a pump may be provided in the return line and be associated with a recirculation line and recirculation orifice for returning a portion of the pump flow to the condensate receiving tank to avoid flashing in the pump when the valve in the condensate return line is closed. The condensate in the return line is fed either, to a deaerating feedwater heater or to a makeup water storage tank, depending upon the temperature of condensate within the return line. The pressure within the deaerating heater is maintained constant by controlling the feed of live steam to the heater in response to the pressure therein. If excess flash steam is developed in the heater, a pressure controller controls a valve to feed excess steam to the makeup storage tank. If the temperature within the makeup storage tank is excessive, a temperature controller, responsive to the temperature in the makeup storage tank, controls a valve from the excess steam line to an atmospheric vent. Level controls are provided for feeding makeup water from the storage tank to the deaerating heater in the event that the level falls or, in the event that the level is excessive, to return water' from the deaerating heater to the makeup storage tank. In addition, a level sensor senses the level in the makeup storage tank to supply makeup water from a water supply source as needed. Water is returned from the deaerating heater to the boilers which supply steamto the system.

Theforegoing and other objects, advantages, and feature of the invention and the manner in which the same are accomplished will become more readily apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, which illustrate preferred and exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of a condensate and heat recovery system of the invention;

FIG. 2 is a cross section view of a structural detail of the invention;

FIG. 3 is a partial schematic diagram showing an embodiment of the invention; and

FIG. 4 is a partial schematic diagram showing another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning to FIG. 1, it will be seen that a steam heating system employing the condensate and heat recovery system of the invention includes a steam supply line 10 which provides steam from a steam supply, which typically will be one or more boilers (not shown). Steam from steam supply line It) is suppliedto a plurality of steam heating coils 12, I4 and I6 connected in parallel. Although three coils are shown, any number might be employed. Each of the steam heating coils is provided with an individual control valve on its inlet side.

As shown in FIG. I, steam flows from steam supply header 10 into coil 12 through a control valve 18, into coil 14 through a control valve 20, and into coil 16 through a control valve 22. These valves may be on-off valves, but more accurate control is obtained when modulating control valves are employed. In either event, the valves are controlled in response to the temperature in the space, device or process receiving heat from the corresponding coil. To this end, temperature sensors 24,

26 and 28 are positioned so as to monitor the temperature in the space, device or process supplied with heat by coils l2, l4 and 16, respectively, and provide control signals through temperature controllers 30, 32 and 34 to control the

corresponding valves

18, 20 and 22. When modulating control valves are used, a signal from a temperature controller would continue to force the corresponding valve open, if suflicient heat were not supplied with the valve opening initially called for by the temperature controller. In the case of a coil filled with condensate, there is little heat transfer to further condense the steam: and with a small valve opening, the steam would generate enough pressure to remove the condensate. In order to permit condensate to be forced out, as steam is introduced into the heating coils, and not be forced back into adjacent coils,

check valves

36, 38 and 40 arerespectively provided at the outlet sides of

heating coils

12, 14 and 16. It is to be noted that the steam traps which are conventionally employed in this location have been omitted. Instead, the check valves directly lead to a common condensate receiving header 42.

The header 42 conducts condensate received from the heating coils to a condensate receiving tank 44. Upon entering tank 44, some of the condensate will flash to steam. This steam is vented with noncondensible gases through a vent orifice 46. As shown more clearly in FIG. 2, orifice 46 is connected at the end of a pipe 48 leading from tank 44 and comprises a fitting 50, having a tapered passageway 52 terminating in the orifice opening 54. This opening is sized for the particular application to provide adequate venting of noncondensible gases and to provide a control of pressure in tank 44 at a level consistent with the requirements for returning the balance of the condensate to the heat recovery equipment, which will be presently described.

A constant level of condensate water is maintained in condensate receiving tank 44. This is accomplished by employing some conventional form of level sensor coupling 56, which may include a pair of level sensing connections. for transferring the level to a level sensor and controller 58 which serves to control the position of level control valve 60. Valve 60 is located in the condensate return line 62 leading from tank 44. When the condensate level in tank 44 becomes too high as sensed by level coupling 56, controller 58 will provide a signal causing valve 60 to open. On the other hand, if the condensate level as sensed by sensor coupling 56 falls below the desired level, controller 58 will provide a signal to close valve 60. In this way, the level within tank 44 will be maintained substantially constant.

There is a possibility that some condensate may be lost through orifice 46 when the system is started up or in response to surge loads. In order to prevent this condensate loss, a high level control 64 is employed for sensing a sudden high condensate level, which appears too rapidly for adequate control by controller 58. The controller 64 provides a signal to operate a vent control valve 66 closing vent 46 in the presence of these unusually high surges to prevent condensate from passing through orifice 46.

In another embodiment as illustrated in FIG. 3, the pressure within receiving tank 44 may be controlled by providing a pressure sensing connection 68 and an associated pressure controller 70 for controlling the opening of a pressure control valve 72 located in a bleed line 74. As will be seen from FIG. 3, bleed line 74 feeds into condensate return line 62 at a point downstream from level control valve 60. In this way, flash steam within tank 44 which causes the pressure within tank 44 to be excessive may be bled off to return line 62 to reduce the pressure within tank 44.

Although, as shown in FIGS. 1 and 3, condensate from receiving tank 44 is fed through valve 60 directly into condensate return line 62, it is sometimes desirable to provide power means for discharging the condensate from the receiving tank. If, for example, it is desired to pump the condensate directly to a steam boiler, a pump may be needed to augment the pressure. Thus, as shown in FIG. 4, a pump 76 is placed in condensate return line 62 at a point upstream of level control valve 60. This pump will provide a higher discharge pressure than is obtainable from the receiving tank 44 directly, and this discharge pressure will now be sufficient to return the condensate to any point desired. A recirculation line 78, including a recirculation orifice 80, is provided to return a portion of the pump flow to receiving tank 44 in order to avoid flashing in the pump when control valve 60 is in its closed position.

Returning to FIG. 1, it will be seen that condensate in condensate return line 62 will be fed either to a deaerating feedwater heater 82 or to a makeup water storage tank 84. It may happen during startup of the steam heating system, or because one or more of the units of the system had been cooled to a very low temperature, that the temperature of the condensate leaving the receiving tank 44 will be below that allowing satisfactory operation for a given operating pressure in the deaerating heater 82. It has been found, for example, in a particular system, that condensate temperatures below 230 F. would not be acceptable within deaerating feedwater heater 82. Thus, the present system is provided with a temperature controller 86 for sensing the temperature of condensate in condensate return line 62 to develop a control signal for controlling a three-way valve 88. In addition, a thermometer 90 may be provided so that the temperature of the condensate may be monitored. When the temperature of the condensate drops below the acceptable level for the heater pressure, temperature controller 86 will actuate three-way valve 88 to allow condensate to return directly to makeup storage tank 84 through a perforated pipe 92 contained therein. The condensate water will then be returned to the deaerating heater 82 through a makeup water pump 94 connected in a makeup pump line 96 through a deaerating heater level control valve 97. In order to avoid flashing within pump 94. a recirculation line 98, containing a recirculation orifice 99, is provided to return some of the output from pump 94 to makeup storage tank 84 in the event that valve 97 is closed. However, when the temperature of the condensate in condensate return line 62 is above the acceptable level, temperature controller 86 will actuate valve 88 to return all of the condensate directly to deaerating heater 82.

Deaerating heater 82 has the principal function of removing all noncondensible gases from water to be used for boiler feed. It is necessary that the pressure within deaerating heater 82 be maintained constant. To this end, a pressure controller 100 senses the pressure within the deaerating heater 82 and develops a control signal for controlling a valve 102 which regulates the feed of live steam from a live steam makeup line 104 connected to a source (not shown) of high pressure steam into deaerating heater 82. In this way, sufficient steam is fed into deaerating heater 82 to maintain the pressure therein constant. Noncondensible gases will be vented through vent 106, the flow through which may be controlled by a manual vent valve 108.

When the system is operating under normal conditions, the high temperature condensate being returned to deaerating heater 82 will be at a temperature above the saturation temperature at the pressure within the heater. This will cause at least some of the condensate entering heater 82 to flash to steam with a consequent reduction of the condensate temperature to the operating temperature of the deaerating heater. The effect of the flash steam is to provide necessary additional heat to makeup water supplied to the deaerating heater from makeup storage tank 84 through valve 97. Since the additional steam within deaerating heater 82 will raise the pressure therein, pressure controller I00 will then reduce or shut off the supply of live steam through live steam makeup valve 102. At times the flash steam provided may exceed the steam requirement for heating the incoming makeup water. The pressure in deaerating heater 82 will rise to, first, cause shutoff of valve 102 by operation of pressure controller 100; and then, at a slightly higher pressure, excess steam will be relived through an excess steam control valve 114 which is controlled by a pressure controller 116 responsive to excessive pressure within deaerating heater 82. The excess steam is fed to makeup storage tank 84 through an excess steam line 118 which is connected to the perforated pipe 92 at an end opposite to the end connected to valve 88.

A constant condensate level is maintained in deaerating heater 82 by providing a level sensor coupling which develops a control signal in level controller 112 for operating level control valve 97. Thus, makeup water from makeup storage tank 84 will be admitted through valve 97 only when the condensate level within heater 82 drops below a predetermined level as sensed by level sensor coupling 0.

A constant level is maintained in makeup storage tank 84 by providing a level sensor coupling 120 for developing a signal in a level controller 122. This signal is employed for controlling a makeup water valve 124 connected in a makeup water line 126 which may be connected to a cold water supply supplied under pressure from a community water supply, well, reservoir or other source which might be available.

In the event that the amount of excess steam returned through excess steam return line 118 is sufiicient to heat the water in makeup storage tank 84 to a temperature in excess of the maximum allowable temperature in makeup water pump 94, a temperature sensor 128 causes a temperature controller 130 to provide a control signal opening an atmospheric vent valve 132 leading to an atmospheric vent 134 from excess steam line 118. Excess steam will thus be relieved to the atmosphere. A thermometer 129 may be provided to monitor the temperature in tank 84.

Condensate accumulating in deaerating heater 82 is returned to one or more steam boiler or boilers through a boiler return line 142. in order to assist this return and to insure that it is at adequate pressure, a boiler return pump 144 is provided in boilenreturn line 142. It is to be understood that various controls may be provided further along boiler return line 142 to regulate the flow of water returned to the boiler or boilers. In the event that such controls may unduly restrict flow from deaerating heater 82 and cause undue pressure within pump 144, a recirculation line 146, having a recirculation orifice 148, is provided forreturning some of the flow from pump 144 to deaerating heater 82. I

At times, the volumes of condensate returning from the system to the boiler or boilers may exceed the amount required for operation of the boiler or boilers. The level in deaerating heater 82 may then rise to a point at which all incoming makeup water is shut off by controller 112 and above an overflow level. An overflow controller or trap 136 will then open to allow return of excess condensateto makeup storage tank 84 through a condensate return pipe v138 to pipe 140 discharging below the normal water line or through perforated pipe 92.

It is believed that the operation of the system just described will be readily apparent. A system of this character has been employed for heating dry kilns of the type employed in sawmill operations and has been operated very satisfactorily in this application.

While preferred embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims. For example, instead of employing pressure controller 100, the feed of live steam through valve 1102 might be controlled by means of a temperature sensing element, located within the water storage area of heater 82 below the water level, and temperature controller. Accordingly, the foregoing embodiments are to be considered illustrative rather than restrictive of the invention, and those modifications which come within the meaning and range of equivalency of the claims are to be included therein.

lclaim: 1. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side;

trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils and said tank, said means being unregulated in the direction of flow to said tank;

means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and

means to maintain the level of condensate within said tank substantially constant.

2. A steam heating system as recited in claim l,wherein said means for controlling pressure within said tank comprises a vent orifice sized to provide adequate venting of noncondensible gases and to control the pressure within said tank at a level consistent with the return of condensate from said tank to heat recovery equipment of said system.

3. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side; trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and

means to maintain the level of condensate within said tank substantially constant, said means for controlling pressure within said tank'further comprising a vent control valve and high condensate level sensing means to close said valve in response to a high condensate level within said tank to prevent loss of condensate for surge loads or startup operation. 4. A steam heating system as recited in claim 1 wherein said means for controlling pressure within said tank comprises pressure sensing means and valve means responsive to said pressure sensing means to bleed off flash steam to a point in a condensate return line from said tank.

5. A steam heating system as recited in claim 1 wherein said means to maintain the level of condensate within said tank constant comprises means for sensing the level of condensate within said tank, a condensate return line from said tank, and level control valve means in said condensate return line responsive to said means for sensing the level of condensate withinlsaid tank.

6. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side;

trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and I means to maintain the level of condensate within said tank substantially constant, said means to maintain the level of condensate within the tank constant comprising means for sensing the level of condensate within said tank, a condensate return line from said tank, level control valve means in said condensate return line responsive to said means for sensing the level of condensate within said tank, a pump in said return line at a point upstream from said level control valve means, and a recirculation line in cluding a recirculation orifice for returninga portion of the pump flow to said condensate receiving tank to avoid flashing in said pump when said level control valve means is closed. 7. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side;

trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank;

means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; I

means to maintain the level of condensate within said tank substantially constant;

a return line from said condensate recovery tank;

a deaerating feedwater heater;

a makeup water storage tank; and

control valve means responsive to the temperature of condensate within said return line for feeding condensate from said return line to said makeup storage tank when said temperature is below a predetermined value and to said deaerating heater when said temperature exceeds said predetermined value.

8. A steam heating system as recited in claim 7, further comprising means to maintain a constant pressure in said deaerating heater.

9. A steam heating system as recited in claim 8 wherein said means to maintain a constant pressure in said deaerating heater comprises means for sensing the pressure within said deaerating heater and means, including a valve responsive to said means for sensing the pressure within said heater, for feeding live steam from a high pressure source into said heater.

10. A steam heating system as recited in claim 9 wherein said deaerating heater includes heater level sensing means and a control valve responsive to said heater level sensing means for feeding makeup water from said makeup storage tank.

H. A steam heating system as recited in claim 10, wherein said deaerating heater includes means responsive to pressure within said heater to relieve excess steam, flashed from high temperature condensate entering said heater, through a valve to the makeup storage tank.

12. A steam heating system as recited in claim 11, wherein said excess steam is fed to a perforated pipe within said makeup storage tank to heat the water stored therein.

13. A steam heating system as recited in claim 11, wherein said makeup storage tank includes means to maintain a constant water level therein by controlling a supply of makeup water thereto.

14. A steam heating system as recited in claim 11, further comprising means responsive to excess temperature within said makeup storage tank for venting said excess steam to atmosphere.

15. A steam heating system as recited in claim 7. wherein said deaerating heater includes excess level responsive means to return condensate to said makeup storage tank.

16. A steam heating system as recited in claim I. wherein said individual control valves are responsive to a temperature condition in the space'affected by its corresponding heating coil.

17. A steam heating system comprising:

a return line for returning condensate from said system;

a deaerating feedwater heater;

a makeup water storage tank; and

valve means responsive to the temperature of said condensate in said return line for feeding condensate from said return line to said makeup storage tank when said temperature is below a predetermined value and to said deaerating heater when said temperature exceeds said predetermined value.

18. A steam heating system as recited in claim 17 wherein said deaerating heater includes means responsive to the pressure therein for feeding steam under pressure thereto.

19. A steam heating system as recited in claim l8 wherein said heater includes level responsive means for feeding makeup water from said makeup tank to said heater.

20. A steam heating system as recited in claim 19, wherein means responsive to pressure within said heater relieves excess flash steam to said tank.

21. A steam heating system as recited in claim 20 wherein said excess steam is fed to one end of a perforated pipe within said tank, the other end of said pipe being connected to said valve means.

22. A steam heating system as recited in claim 20, further comprising means responsive to excess temperature within said tank for venting said excess steam to atmosphere.

23. A steam heating system as recited in claim [9. further comprising means responsive to overflow of condensate within said heater for returning condensate to said tank.

Claims

1. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side; trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils and said tank, said means being unregulated in the direction of flow to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and means to maintain the level of condensate within said tank substantially constant.

2. A steam heating system as recited in claim 1, wherein said means for controlling pressure within said tank comprises a vent orifice sized to provide adequate venting of noncondensible gases and to control the pressure within said tank at a level consistent with the return of condensate from said tank to heat recovery equipment of said system.

3. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side; trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and means to maintain the level of condensate within said tank substantially constant, said means for controlling pressure within said tank further comprising a vent control valve and high condensate level sensing means to close said valve in response to a high condensate level within said tank to prevent loss of condensate for surge loads or startup operation.

4. A steam heating system as recited in claim 1 wherein said means for controlling pressure within said tank comprises pressure sensing means and valve means responsive to said pressure sensing means to bleed off flash steam to a point in a condensate return line from said tank.

5. A steam heating system as recited in claim 1 wherein said means to maintain the level of condensate within said tank constanT comprises means for sensing the level of condensate within said tank, a condensate return line from said tank, and level control valve means in said condensate return line responsive to said means for sensing the level of condensate within said tank.

6. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side; trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; and means to maintain the level of condensate within said tank substantially constant, said means to maintain the level of condensate within the tank constant comprising means for sensing the level of condensate within said tank, a condensate return line from said tank, level control valve means in said condensate return line responsive to said means for sensing the level of condensate within said tank, a pump in said return line at a point upstream from said level control valve means, and a recirculation line including a recirculation orifice for returning a portion of the pump flow to said condensate receiving tank to avoid flashing in said pump when said level control valve means is closed.

7. A steam heating system comprising: a plurality of steam heating coils connected in parallel with a common steam supply, each of said heating coils having an individual condition responsive control valve on its inlet side; trapless means for connecting said heating coils to a common condensate recovery tank to feed condensate forced by steam from said coils to said tank; means for controlling the pressure within said tank as some of said condensate received from said coils flashes to steam; means to maintain the level of condensate within said tank substantially constant; a return line from said condensate recovery tank; a deaerating feedwater heater; a makeup water storage tank; and control valve means responsive to the temperature of condensate within said return line for feeding condensate from said return line to said makeup storage tank when said temperature is below a predetermined value and to said deaerating heater when said temperature exceeds said predetermined value.

11. A steam heating system as recited in claim 10, wherein said deaerating heater includes means responsive to pressure within said heater to relieve excess steam, flashed from high temperature condensate entering said heater, through a valve to the makeup storage tank.

15. A steam heating system as recited in claim 7, wherein said deaerating heater includes excess level responsive means to return condensate to said makeup storage tank.

16. A steam heating system as recited in claim 1, wherein said individual control valves are responsive to a temperature condition in the space affected by its corresponding heating coil.

17. A steam heating system comprising: a return line for returning condensate from said system; a deaerating feedwater heater; a makeup water storage tank; and valve means responsive to the temperature of said condensate in said return line for feeding condensate from said return line to said makeup storage tank when said temperature is below a predetermined value and to said deaerating heater when said temperature exceeds said predetermined value.

19. A steam heating system as recited in claim 18 wherein said heater includes level responsive means for feeding makeup water from said makeup tank to said heater.

23. A steam heating system as recited in claim 19, further comprising means responsive to overflow of condensate within said heater for returning condensate to said tank.