GB1580198A

GB1580198A - Method of feeding a closed loop system with utilizable or consumable vaporizable liquid and devices therefor

Info

Publication number: GB1580198A
Application number: GB4731676A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-05-12
Filing date: 1977-05-12
Publication date: 1980-11-26

Description

(54) IMPROVEMENTS IN OR RELATING TO A METHOD OF FEEDING A CLOSED LOOP SYSTEM WITH UTILIZABLE OR CONSUMABLE VAPORIZABLE LIQUID AND DEVICES THEREFOR (71) I, PIERRE EUGÈNE REGAMEY, a Swiss citizen, residing at 35 Le Calabert, 69130 Ecully, France, do hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention is concerned with a method of feeding a closed-loop system with utilizable or consumable vaporizable liquid and devices for carrying out the method.

The subject matter of this Specification is allied to that of the Specifications of copending Applications 79.19104 (Serial No.

1,580,199 and 79.19401 (Serial No.

1,580,200).

According to a first aspect of the invention there is provided a method of feeding with utilizable or consumable vaporizable liquid' to be renewed periodically, a fluid-containing closed-loop system of generation and distribution of condensable vapour, having at least one condensable vapour generator, at least one evaporating boiler and at least one condensate storage reserve and wherein at least a major part of the said fluid is binary consisting of a gaseous phase (vapour) and a liquid phase (condensate) at pressures and temperatures which are approximately constant and wherein, diregarding local flow-pressure losses, the pressure values and temperature values are substantially the same at all points between the point of supply of vapour under the pressure of utilization and the point of delivery of the condensates, with recovery of at least part of the condensates discharged from the system by directed, substantially dry and mostly or wholly natural, gravitational return-flow, the method including replenishing the or each boiler from at least two sources of make-up liquid used simultaneously or separately and constituted respectively by:: (i) a supply or reserve or external input feed-liquid providing a supply flow-rate controllable automatically, and (ii) by the direct reintroduction into the or each boiler, by forced circulation, of the recovered condensates collected and accumulated in one main storage reserve, forming a buffer tank, said supply or feed liquid supplying directly into said main storage reserve in which said feed liquid is admitted and mixed according to an intermittent flow rate which is controlled automatically in dependence on the amount of stored liquid in said buffer tank, said buffer tank providing a make-up liquid flow rate to the or each boiler automatically according to the level of liquid at any instant in the or each boiler.

Preferably the rate of inflow of said make-up liquid into the or each boiler is automatically controlled by the movement of a float in the or each boiler to effect a control of the on-off type or of the gradual modulating action type and wherein a continuous flow of make-up liquid is furnished from said buffer tank and part of which is diverted and recovered in the form of a diverted permanent leakage current of make-up liquid with a continuous, relatively low and selectively controllable flow-rate, wherein said leakage current mixes with the inflow of feed liquid or returns directly to said buffer tank.

Expediently the said feed liquid inflow into the said main storage reserve is dependent on and controlled by a predetermined minimum amount of liquid maintained in the said main storage reserve in order to heat a cold inflow of feed liquid by dispersion in this minimum residual mass of hot liquid.

According to a second aspect of the invention there is provided a device for carrying out the method of the invention comprising at least one vapour producing boiler, at least one closed-loop system of condensate discharge and return lines leading to at least one condensate recovery collector, said collector leading to one main condensate storage reserve forming a main buffer tank, and connected to the or each boiler by at least one direct-reintroduction piping provided with at least one main pump so as to constitute in combination with said buffer tank a pumping sub-station for the delivery of said condensates into the or each boiler and at least one feed tank for the supply of external input feed liquid, connected by at least one supply conduit to said storage reserve, said supply conduit being provided with a power-drivable feed pump, wherein there are provided automatic control means when in use for the flow-rate of direct reintroduction of said make-up liquid and the supply of input feed liquid, in direct dependence on the level of vaporizable liquid remaining in the or each boiler and the amount of available condensates in said buffer tank at any instant respectively.

The present inventions offer the advantages of improved, efficient and reliable working procedure and operation, of an organically simple and lasting structure, therefore of a relatively economical construction or manufacture and mounting requiring only reduced supervision and maintenence, as well as of a very economical working ensuring high energetic efficiency as a result of substantial gains in motive power, fuel and other kinds of employed and consumed energy, resulting in substantially increased rentability.

Preferred forms of the invention will now be described, by way of example, with reference to the accompanying drawings wherein: Figure 1 illustrates a circuit diagram of an embodiment of the invention' showing a feed system for the supply of a boiler with vaporizable make-up liquid by a pumping sub-station fed from a feed-tank, the said circuit including an economizer; Figure 2 is a modification of the circuit of the foregoing Figure, in which no economizer is used and two boilers are mounted in parallel; Figure 3 is an enlarged isolated sectional diagrammatic view of the main buffer-tank of Figure 2, illustrating the various characteristic levels in the latter; Figure 4 shows a modified embodiment of the circuit of Figure 2, with auxiliary pumping sub-stations feeding the main pumping sub-station;; The embodiment according to Figure 1 illustrates a method and a device for refeeding or replenishing at least one boiler with vaporizable make-up liquid (e.g.

water) composed of external fresh liquid admitted from a feed-liquid reserve and/or of condensates admitted from a condensate storage reserve. Means are provided for a common pre-heating of the said make-up liquid, prior to its admission into the boiler, by the hot combustion gases after their exit from the said boiler, in a manner known per se. The said pre-heating acts upon an ascending flow of said make-up liquid arriving from below and leaving from above.

Figure 1 illustrates the application of the method to a continuous flow of said make up liquid supplied from the said condensate storage reserve and part of which is diverted and recovered in the form of a diverted permanent leakage current of make-up liquid with a continuous, relatively low and possibly selectively controllable flow-rate. The said leakage current is composed of the already preheated make-up liquid returning directly to the said condensate storage reserve and the said reserve of external feed liquid (feed water) discharges directly into the said condensate storage reserve to which the said feed liquid is conveyed and mixed according to an intermittent flow-rate controlled automatically in interlocked follow-up relationship to the present amount of stored liquid.

The said pre-heating is performed generally, in installations such as, for example, boiler vapour-heating plants, by means of at least one economizer which is a heat exchanger traversed by the boiler combustion gases after their exit from the said plant, as well as by the make-up-liquid, such as water, before its admission into the boiler, so that the economizer operates as a water heater by recovering the residual sensible heat of the burnt gases or the hot combustion products. A device embodying the invention serving to carry out the aforesaid method, is mainly applicable to condensable vapour production and distribution systems in which the temperature and pressure are substantially constant everywhere and identically the same at all points of the system, except for the flow pressure losses, and such a system, provided with an economizer, requires a certain number of precautions, the main ones of which are the maintenance of a minimum water flow-rate through the economizer and the elimination of a certain quantity of heat by the said economizer, therefore the passage through the latter of relatively cold water as compared with the temperature of the water contained in the boiler.The embodiment of the device according i,' Figure 1, which is of the type defined previously, comprises at least one feed-tank 10 connected by a conduit 69, equipped for example with a float valve controlled by the water level in the tank 10, to a source of fresh water and constantly communicating with the surrounding atmospheric air through a vent or the like 13. Starting from the tank 10 is at least one teed water supply conduit 11 containing a power-driven piloted feed pump 12 sucking under a static head from the lower part of the tank 10 through the bottom of the latter, the said feed pump being mounted between a down-stream isolating valve 57 and an upstream isolating valve 57' and delivering the feed water through a downstream check valve or the like 56.Boiler 8 produces condensable vapour which, through a main feed-line 9, reaches at least one system of vapour-utilizing apparatuses (not shown) operating by way of heat exchange with heat absorption by condensing the vapour (such as, for example, ambient space heating radiators or heat exchangers), the condensates thus produced being discharged through at least one network of return lines leading to at least one condensate-recovery collector forming a general gravity-return conduit 15 leading to an opening into the upper part of at least one main buffer-tank 14 located at a general low point of the installation.In Figures 1, 2 and 4, although not shown in the drawings, the feed tank 10 provides a liquid supply flow-rate automatically according to the level of liquid at any instant in the or each boiler 8 with a defined range of controlled values between an upper or feed shut-down limit and a lower or maximum feed flow-rate limit. The supply conduit 11 opens into the bottom of the buffer-tank 14, the lower part of which is connected to the boiler 8 by at least one condensate direct-reintroduction piping 16' forming a common pipe 88 for the supply of the said make-up liquid and advantageously containing a shut-off valve or the like 90.

The piping 16' contains at least one powerdriven pump 17 advantageously mounted in series between an up-stream isolating valve 18 and a down-stream isolating valve 21 and sucking under static head from the buffer-tank 14 through the bottom of the latter and delivering preferably through a check valve or the like 20. An automatic control valve 46 is mounted in series in the common pipe 88 near the inlet of the latter into the boiler, advantageously between an up-stream isolating valve 91 and a downstream isolating valve 95 with preferably a down-stream check valve or the like 96 placed in the pipe 88 between the boiler 8 and the valve 46. The servo-motor of the valve 46 is connected through a remotecontrol transmission 47 to the pilot member of a liquid level detector or controller 37 associated with the boiler 8.At least one economizer 84 is intercalated in series in the common piping 88 before the control valve 46 and the economizer 84 is so mounted as to have its inlet and its outlet connected to the up-stream or incoming portion and to the down-stream or outgoing portion, respectively, of the common pipe 88.

The individual servo-motor of the feedpump 12 is connected by a remote-control transmission 54b to a liquid level detector or controller 53 associated with the buffer tank 14. The said common pipe 88 is connected, at a piont 40' located before the automatic control valve 46 and the isolating valve 91, to one of the aforesaid two makeup liquid sources through a branch conduit 39 forming an escape path opening preferably into the upper portion of the said source and containing a valved member 43 producing high pressure losses, notably by a restriction or a reduction of the free crosssectional area of passage with a substantially constant, preferably selectively variable opening. The branching point 40' is located after the water outlet of the economizer 84, and the aforesaid source, into which the branch conduit 39 opens at 41, is constituted by the main buffer-tank 14.

In order that, in case the economizer 84 should be put out of service by simultaneous closing of its up-stream and down-stream isolating valves 90 and 91, the make-up liquid may nevertheless reach the boiler 8, there is advantageously provided a by-pass conduit 92 containing an isolating valve 94 and connecting the condensate reintroduction piping 16' to the down-stream portion of the common pipe 88 after the economizer 84 by being connected at a point 87' to the piping 16' and at a point 93' to the common pipe 88 (between the control valve 46 and the isolating valve 91 of the latter). An isolating valve 44 is advantageously provided in the escape conduit 39.

The embodiment of Figure 1 offers the following features:- The condensates to be reintroduced directly into the boiler 8 are delivered into a flow-line after being mixed with the makeup water proceeding from the feed-tank 10.

The operation of the condensate direct.

reintroduction pump 17 is continuous or permanent.

The periodical operation of the feed water pump 12 is controlled by the water level in the buffer-tank 14 by means of a level detector or controller 53 which starts the pump 12 when the said level falls below a minimum value, and then stops the said pump when the admissible maximum level is reached.

The liquid level detector or controller 37 regulates the feeding of the boiler with make-up water by acting upon the single automatic-control valve 46.

The economizer 84 may be isolated and put out of service by means of the valves 90, 91 and the boiler 8 is then fed directly with the condensates to be reintroduced and with make-up water through the shorting or by-pass conduit 92.

Owing to the possibility of closing the isolating valves 90 and 91 of the economizer 84, the latter is necessarily provided with a safety member such as a safety valve or the like 97 mounted on the common pipe 88.

The escape conduit 39 connected to the output of the economizer 84 allows a permanent minimum flow through the economizer to be obtained in the form of an escape flow ending into the buffer-tank 14.

Since the passage of the condensates through the economizer 84 may result in vaporizing part of the said condensates, the passage of the liquid through the economizer is advantageously directed from bottom to top, for the vapour which is thus produced and tends to rise has no undesirable effect and the heated condensate as well as the vapour possibly produced are thus recovered from the top of the economizer.

The vapour which may thus be produced sometimes by the possible vaporization of the condensates is not lost, since it reaches and is collected in the buffer-tank 14 from which it may be conveyed to the utilizers.

The feed water is not delivered directly to the boiler 8, but is supplied to the buffertank 14 in order to be mixed with the stored condensates.

This principle is also applied in the forms of embodiment of Figures 2 to 4 which result from an application of the principle of Figure 1 to the multiple boiler system, optionally without economizer. It is known that, in a plant involving direct reintroduction of the condensates into several boilers, the admission of the condensates to be reintroduced into each boiler should be controlled. It is also necessary to be able to control individually the admission of make-up water every time the water level in each boiler considered individually reaches a lower limit value. A drawback to this is that it requires the adjunction, to the existing plant of'a second control of the water level in the boiler, or in each new plant, the provision of two independent controls for each boiler.

Advantageous forms of the present invention allow this drawback to be removed in the case of a system with, for example, several boilers forming a set of vapour generators, and a preferred method embodying the invention is characterized in that the aforesaid permanent leakage current which is returned to one of the two make-up liquid sources with the feed liquid supply flow or is returned directly to the single main condensate storage reserve which is common to all the boilers, whereas the said feed liquid reserve, which also is a single reserve common to all the boilers, discharges directly into the said condensate storage reserve to which the said feed liquid is supplied and mixed according to an intermittent flow controlled automatically in interlocked follow-up relationship to the present amount of stored liquid.According to another preferred feature of the invention the admission flow of the said feed liquid into the said main storage reserve is dependent on and controlled by a predetermined minimum amount of liquid maintained in the said storage reserve to heat the said flow entering the cold feed liquid by being dispersed in this residual minimum mass of hot liquid.

The device according to the embodiments of Figures 2 and 4 is characterized in that the permanent leakage conduit 39 opens either into the feed water supply conduit 11 after the feedpump 12 (through a length of conduit 39' indicated by a dotted line in Figure 4), or in the upper portion of the single main buffertank 14 (as indicated by a continuous plane line in Figure 2 and a length of conduit shown by a dotted line in Figure 4), whereas the common pipe 16 for direct reintroduction of the condensates is connected in parallel with several (e.g. two) boilers 8, 8a through conduits 88, 88a, respectively, each of which contains an automatic control valve 46, 46a, and the feed water supply conduit 11 opens, as in the case of Figure 1, into the bottom portion of the main buffer-tank, the liquidlevel detector or controller 53 of which is connected by a remote-control transmission 54b to the feed-pump 12, the main pump 17 for direct reintroduction of the condensates being, in this case, a continuously operating pump. According to another feature of this device, the suction pipe of the main pump 17 passes through the lower bottom of the main buffer-tank 14 and enters the latter substantially vertically, up to a height corresponding to the minimum amount of liquid to be maintained in the buffer-tank 14.

Thus, owing to this arrangement, the use of a double control for each boiler is avoided by returning into the buffer-tank 14 located up-stream of the direct condensatereintroduction pump 17, not only the condensates to be reintroduced, but also the make-up water proceeding from the feed-tank 10. It is understood that, in this case, the operation of the pump 17 must be continuous so as to allow the boilers to be fed according to their respective needs. The operation of the feed-pump 12 allowing the admission of fresh make-up water into the buffer-tank 14 will therefore be linked up with the lowering of the water level in the buffer-tank 14 to an admissible minimum value below which there may be the risk of having no more available condensates nor make-up water to deliver to the boilers.The permanent leakage conduit 39 continuously returning into the buffer-tank 14 a small portion of the condensates withdrawn down-stream of the delivery pump 17 eliminates the risk of operating the latter with no possibility of delivery, i.e. with a zero output, in the case of absence of water requirements of the boilers, in particular during the simultaneous closing of the control valves 46, 46a.

Figure 3 illustrates the special design of the buffer-tank 14 of Figure 2, in such a manner that, at any moment, a certain minimum amount of water of a height h remains in the lower portion of the tank and rises above the bottom level No of the latter up to the level N, (so that h=N1-N0). This is obtained by providing the upper suction orifice 16" of the piping 16 located at least at the said level Nl or above this level of the minimum water volume. This allows the normally cold make-up feed water to be admitted through the feed water supply conduit 11 by way of dispersion in this minimum volume of relatively hot or hightemperature condensates, thus preventing the occurrence of a pressure surge or hammering of thermal origin.The liquidlevel detector or controller 53 so acts as to start the feed-pump 12 when the level of the condensates in the buffer-tank 14 has lowered to the minimum level N1 and to stop the feed-pump 12 in case the condensates in the buffer-tank should reach a higher level, e.g. an intermediate level N2.

In case the discharge conduit 39, 39' returns the condensates (delivered by the pump 17 and not admitted into the boilers 8, 8a) into the conduit 11 supplying the feed water to the buffer-tank 14, these condenstes are dispersed in the water of the latter by the feed-pump or iniector 12. This results in a saving in the power or energy (in particular electrical energy) consumption of the motors of both pumps 12, 17.

Figure 4 illustrates a variant of application of the method of the invention, of the type using at least one auxiliary storage reserve of condensates collected by free or natural gravitational flow and delivered by forced mechanical supply into the aforesaid main storage reserve. This variant is characterized in that the said delivery of condensates takes place under a pressure approximating to the one existing in the said boilers.The device for carrying out the method comprises at least one and preferably several auxiliary pumping substations, e.g. two such pumping substations, each constituted by an auxiliary buffer-tank 105, 1OSa into which opens a condensate gravity-discharge collector 121, 121a and by an auxiliary pump 103, 103a maintained under static head by the associated auxiliary buffer-tank from which it sucks and the delivery conduit 118, 118a of which opens into the upper portion of the main buffer-tank 14 owing to the fact that the respective delivery conduits 118, 118a of these auxiliary pumping substations unite into a common conduit 15 opening into the buffer-tank 14.These auxiliary pumping sub-stations deliver their condensates, under a pressure approximating to the one existing in the boilers, into the main buffer-tank which also receives the make-up feed water proceeding from the tank 10 and where the pump 17 sucks these condensates to deliver the same to the boilers. There may then be a risk of possible abnormal increase in pressure in the main buffer-tank 14. This increase in pressure may result from the delivery of the condensates by the individual pumps of the various auxiliary pumping sub-stations notably when the boilers at a given instant do not need any water admitted thereto, therefore in the absence of a lowering of the level of the condensates in the buffer-tank 14 of the boiler plant.This risk of undesirable overpressure can be eliminated, according to a preferred form of the invention, by providing at least one safety valve 97' connected to the upper portion of the main buffer-tank 14 or the to delivery conduit 15 of the various auxiliary pumping substations, the outlet orifice of this safety valve being advantageously connected by a discharge pipe 30, for example to the upper portion of the feed-tank 10. In such a case, the various pumps operate with a momentarily zero or almost zero output and a maximum delivery head, so that the pressure in the main buffer-tank 14 may rise to a value exceeding the admissible limit determined by the setting of the safety valve 97' which then opens to release the excess pressure towards the feed-tank.

The various foregoing forms of embodiment or parts of the latter, may of course be combined and associated with one another in different manners in closedcircuit vapour systems or networks with direct reintroduction of the condensates into the boilers, the working fluid being everywhere at a temperature and a pressure which are substantially or at least approximately constant and identically the same at all points of the said systems or networks (disregarding flow pressure losses and casual cooling) which are generally completely deprived of any vapour or condensate bleeder, drain or like phaseseparating devices.

WHAT I CLAIM IS: 1. A method of feeding with utilizable or consumable vaporizable liquid to be renewed periodically, a fluid-containing closed-loop system of generation and distribution of condensable vapour, having at least one condensable vapour generator, at least one evaporating boiler and at least one condensate storage reserve and wherein at least a major part of the said fluid is binary consisting of a gaseous phase (vapour) and a liquid phase (condensate) at pressures and temperatures which are approximately constant and wherein, disregarding local flow-pressure losses, the pressure values and temperature values are substantially the same at all points between the point of supply of vapour under the pressure of utilization and the point of delivery of the condensates, with recovery of at least part of the condensates discharged from the system by directed, substantially dry and mostly or wholly natural, gravitational return-flow to the or each storage reserve, the method including replenishing the or each boiler from at least two sources of make-up liquid used simultaneously or separately and constituted respectively by: (i) a supply or reserve or external input feed-liquid providing a supply flow-rate controllable automatically, and (ii) by the direct reintroduction into the or each boiler, by forced circulation, of the recovered condensates collected, and accumulated in one main storage reserve, forming a buffer tank; said supply or feed liquid supplying directly into said main storage reserve in which said feed liquid is admitted and mixed according to an intermittent flow rate which is controlled automatically in dependence on the amount of stored liquid in said buffer tank, said buffer tank providing a make-up liquid flow rate to the or each boiler automatically according to the level of liquid at any instant in the or each boiler.

2. Method according to Claim 1, wherein the rate of inflow of said make-up liquid into the or each boiler is automatically controlled by the movement of a float in the or each boiler to effect a control of the on-off type or of the gradual modulating action type and wherein a continuous flow of make-up liquid is furnished from said buffer tank and part of which is diverted and recovered in the form of a diverted permanent leakage current of make-up liquid with a continuous, relatively low and selectively controllable flow-rate, wherein said leakage current mixes with the inflow of feed liquid or returns directly to said buffer tank.

3. Method according to Claim 2, wherein the said feed liquid inflow into the said main storage reserve is dependent on and controlled by a predetermined minimum amount of liquid maintained in the said main storage reserve in order to heat a cold inflow of feed liquid by dispersion in this minimum residual mass of hot liquid.

4. Method according to Claim 2 or Claim 3, wherein at least one auxiliary supply or storage reserve for condensates collected by free or natural gravitational flow and delivered in a mechanically forced flow into the said auxiliary supply or storage reserve wherein the said delivery of condensates takes place under a pressure approximating to the one existing in the or each said boiler.

5. Method according to Claim 4, wherein the excess pressure of the liquid stored in the said main storage reserve is discharged automatically.

6. Method according to Claim 5, wherein the liquid stored in the said main storage reserve is discharged automatically into the said main storage reserve.

7. Method according to Claim 1 substantially as herein described with reference to any one of Figures 1 to 4 of the accompanying drawings.

8. A device for carrying out the method claimed in Claim 1, comprising at least one vapour producing boiler, at least one closed-loop system of condensate discharge and return lines leading to at least one condensate recovery collector, said collector leading to one main condensate storage reserve forming a main buffer tank, and connected to the or each boiler by at least one direct-reintroduction piping provided with at least one main pump so as to constitute in combination with the said buffer tank a pumping sub-station for the delivery of said condensates into the or each boiler and at least one feed tank for the supply of external input feed liquid, connected by at least one supply conduit to said storage reserve, said supply conduit being provided with a power-drivable feed pump, wherein there are provided automati control means when in use for the flow-rate of direct reintroduction of said make-up liquid and the supply of input feed liquid, in direct dependence on the level of vaporizable liquid remaining in the or each boiler and the amount of available condensates in said buffer tank at any instant res,,ectively.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. approximately constant and identically the same at all points of the said systems or networks (disregarding flow pressure losses and casual cooling) which are generally completely deprived of any vapour or condensate bleeder, drain or like phaseseparating devices. WHAT I CLAIM IS:

1. A method of feeding with utilizable or consumable vaporizable liquid to be renewed periodically, a fluid-containing closed-loop system of generation and distribution of condensable vapour, having at least one condensable vapour generator, at least one evaporating boiler and at least one condensate storage reserve and wherein at least a major part of the said fluid is binary consisting of a gaseous phase (vapour) and a liquid phase (condensate) at pressures and temperatures which are approximately constant and wherein, disregarding local flow-pressure losses, the pressure values and temperature values are substantially the same at all points between the point of supply of vapour under the pressure of utilization and the point of delivery of the condensates, with recovery of at least part of the condensates discharged from the system by directed, substantially dry and mostly or wholly natural, gravitational return-flow to the or each storage reserve, the method including replenishing the or each boiler from at least two sources of make-up liquid used simultaneously or separately and constituted respectively by: (i) a supply or reserve or external input feed-liquid providing a supply flow-rate controllable automatically, and (ii) by the direct reintroduction into the or each boiler, by forced circulation, of the recovered condensates collected, and accumulated in one main storage reserve, forming a buffer tank; said supply or feed liquid supplying directly into said main storage reserve in which said feed liquid is admitted and mixed according to an intermittent flow rate which is controlled automatically in dependence on the amount of stored liquid in said buffer tank, said buffer tank providing a make-up liquid flow rate to the or each boiler automatically according to the level of liquid at any instant in the or each boiler.

9. Device according to Claim 8 for

carrying out the method claimed in Claim 2, wherein said buffer-tank is provided with a liquid-level controller and wherein there is provided at least one automatic-control servo-motor valve mounted in series in the said reintroduction piping the servo-motor of which is connected by a remote-control transmission to a liquid-level controller of the said boiler, and including a leakage conduit connected to the said reintroduction piping between the said main pump and the said automatic-control valve and communicating with the said main buffer tank, wherein the said leakage conduit opens either into the said supply conduit downstream of the said feed pump, or into the top of the said main buffer-tank, the said reintroduction piping being connected in parallel with a plurality of boilers by, respectively, diverted conduits each of which contains an automatic control valve, and the said supply conduit opens into the bottom of the said main buffer-tank, the said feed pump being provided with a servo-motor connected by a remote-control transmission to the liquidlevel controller of the said main buffertank.

10. Device according to Claim 9, wherein the leakage conduit is a permanent leakage conduit.

11. Device according to Claim 9 or Claim 10, wherein the suction pipe of the said main pump passes through a lower or bottom portion of the said main buffer-tank and penetrates substantially vertically into the latter up to a height corresponding to the minimum amount of liquid to be maintained in the said buffer-tank.

12. Device according to any one of Claims 9 to 11, including at least one auxiliary pumping sub-station comprising an auxiliary buffer-tank into which opens an aforesaid condensate recovery collector and an auxiliary pump maintainable under a static head by the said auxiliary buffertank and whose delivery conduit opens into the top of the said main buffer-tank, wherein the top of the said main buffertank or the said delivery conduit is connected to a safety valve, the outlet orifice of which is connected by a discharge pipe to a suitable vessel.

13. Device according to Claim 12, wherein the suitable vessel is an upper portion of the aforesaid feed tank.

14. A device suitable for carrying out the method claimed in Claim 1 substantially as herein described and with reference to any one Figures 1 to 4 of the accompanying drawings.