HEAT EXCHANGE SYSTEM AND METHOD OF CONTROLLING THE ALTERNATION AND REDUNDANCY BETWEEN HEAT EXCHANGERS THEREIN

Abstract

The heat exchange system is for heating water from a water source and comprises first and second flooded heat exchangers that have steam sides that are each independently fed with steam, but water sides that are serially fed with water through the first heat exchanger then through the second heat exchanger. The system also comprises first and second control valves located at or downstream of subcooled condensate outlets of the first and second heat exchangers, first and second water temperature sensors at or downstream of the heated water outlets of the first and second heat exchangers, and a control device for receiving temperature data from the first and second water temperature sensors and for controlling the first and second control valves. The proportions of the first and second steam sides that are flooded are respectively selectively adjusted by controlling the debit of condensate allowed through the first and second subcooled condensate outlets with the first and second control valves, for allowing heat exchange to the water to be adjusted as a result of the water temperature measured by the first and second water temperature sensors. The first and second control valves are set in one of a first state in which they are both at least partly opened to allow effective heat exchange from the steam to the water in both first and second heat exchangers, and a second state in which one of them is closed while the other is at least partly opened to have an effective heat exchange from the steam to the water in only one of the first or second heat exchangers while the first and second steam sides remain both supplied with steam.

Claims

1. A heat exchange system for heating water from a water source, comprising: a first flooded heat exchanger comprising: a first steam side extending through said first heat exchanger between a first steam inlet and a first subcooled condensate outlet, said first steam inlet for receiving steam and for allowing steam to flow through said first steam side and to condense to form condensate that at least partly floods said first steam side and that flows out through said first subcooled condensate outlet; and a first water side in heat exchange relationship with said first steam side and extending through said first heat exchanger between a first cold water inlet and a first heated water outlet, said first cold water inlet being connected to said water source for receiving water and for allowing water to flow through said first water side, to be heated therein by heat exchange with said first steam side and to flow out through said first heated water outlet; a second flooded heat exchanger comprising: a second steam side extending through said second heat exchanger between a second steam inlet and a second subcooled condensate outlet, said second steam inlet for receiving steam and for allowing steam to flow through said second steam side and to condense to form condensate that at least partly floods said second steam side and that flows out through said second subcooled condensate outlet; and a second water side serially connected to said first water side, said second water side being in heat exchange relationship with said second steam side and extending through said second heat exchanger between a second cold water inlet and a second heated water outlet, said second cold water inlet being connected to said first heated water outlet for receiving water and for allowing water to flow through said second water side, to be heated therein by heat exchange with said second steam side and to flow out through said second heated water outlet; a first control valve located at or downstream of said first subcooled condensate outlet; a second control valve located at or downstream of said second subcooled condensate outlet; a first water temperature sensor at or downstream of said first heated water outlet, albeit upstream of said second heat exchanger; a second water temperature sensor at or downstream of said second heated water outlet; and a control device for receiving temperature data from said first and second water temperature sensors and for controlling said first and second control valves; wherein the proportions of said first and second steam sides that are flooded are respectively selectively adjusted by controlling the debit of condensate allowed through said first and second subcooled condensate outlets with said first and second control valves, for allowing heat exchange to the water to be adjusted as a result of the water temperature measured by said first and second water temperature sensors; and wherein said first and second control valves are selectively set in one of a first state in which they are both at least partly opened to allow effective heat exchange from the steam to the water in both first and second heat exchangers, and a second state in which one of them is closed while the other is at least partly opened to have an effective heat exchange from the steam to the water in only one of said first or second heat exchangers while the first and second steam sides remain both supplied with steam.

2. A heat exchange system as defined in claim 1, further comprising isolation valves upstream and downstream of each of said first and second steam sides and of each of said first and second water sides, such that said first and second steam and water sides can be independently shut off to allow maintenance or replacement of one of said first and second heat exchangers while the other remains operational.

3. A heat exchange system as defined in claim 1, further comprising a first recirculation line connecting said second heated water outlet to said first cold water inlet for allowing water to be at least partly recirculated therebetween, and a second recirculation line connecting said second heated water outlet to said second cold water inlet for allowing water to be at least partly recirculated therebetween.

4. A heat exchange system as defined in claim 3, wherein said first and second recirculation lines comprise respective first and second recirculation pumps.

5. A heat exchange system as defined in claim 1, wherein steam flowing to said first and second steam inlets is fed from a same steam source.

6. A heat exchange system as defined in claim 1, wherein condensate flowing out from said first and second subcooled condensate outlets is merged and discharged through a same condensate return.

7. A method of controlling the alternation and redundancy, in a heat exchange system as defined in claim 1, between the first and second heat exchangers, comprising: continuously supplying with steam the first and second steam sides that are connected in parallel; continuously circulating the water through said first and second water sides that are connected in series; selecting one of the first and second states of the first and second valves, wherein: in the first state the first and second heat exchangers both provide effective heat transfer to the water, and in the second state a single one of the first and second heat exchangers provide effective heat transfer to the water; and in the second state the method further comprising alternating the effective heat transfer between the first and second heat exchangers by alternately opening the first and second control valves at selected time intervals.

Description

DESCRIPTION OF THE DRAWINGS

[0037] In the annexed drawings:

[0038] FIG. 1 is a schematic view of the heat exchange system of the present invention; and

[0039] FIGS. 2 and 3 are enlarged schematic cross-section views of the areas respectively circumscribed by circles II and III in FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] The present invention proposes the use of dual flooded heat exchangers with the water to be heated running serially through both flooded heat exchangers at all times, while the steam is continuously supplied in both heat exchangers but, by selectively closing one condensate outlet valve, the effective heat transfer only occurs at one of the two heat exchangers. Both heat exchangers being operative at all times means that either both heat exchangers can be used in alternation, wherein no initialisation of the other heat exchanger when a switch occurs and consequently the invention has the advantages of both equal run time alternation and no initialisation of heat exchangers; or both heat exchangers can be used simultaneously, notably under high load periods, again without initialisation of the second heat exchanger.

[0041] As mentioned above, although water is mentioned as the liquid to be cooled, any other liquid can also be circulated such as glycol for example.

[0042] More particularly, the present invention comprises a heat exchange system 10 as shown in FIGS. 1-3 for heating water from a water source 12. Depending on the application for which heated water is required, the water source can be tap water, or water returning through a circuit to the heat exchange system 10 after having been circulated in a closed loop through application segments for example for heating rooms in a building.

[0043] Heat exchange system 10 comprises one or more pumps to help circulate the water in the heat exchange system 10, with two pumps 14, 16 here being shown for redundancy but a single one would suffice. Pump 14 or 16 pumps water from water source 12 through a first water inlet line 18 that is connected to a first flooded heat exchanger 20 as described hereinafter. The pump or pumps could alternately be located downstream of heat exchangers 20, 40, or outside the heat exchange system 10 itself, i.e. the heat exchange system 10 can be retrofitted in a circuit where water is circulated with existing pumps, for instance by using municipal tap water.

[0044] First flooded heat exchanger 20 comprises a first steam side 21 in the exchanger shell side, extending through first heat exchanger 20 between a first steam inlet 22 and a first subcooled condensate outlet 24. First steam inlet 22 is for receiving steam and for allowing steam to flow through first steam side 21 and to condense to form condensate that at least partly floods first steam side 21 to a variable level of flooding F and that is subcooled by additional heat transfer to the water before flowing out through first subcooled condensate outlet 24. Steam is fed from a steam source 26, such as a boiler for example, through a main steam inlet line 28 that splits into first and second steam inlet lines 30, 32, with first steam inlet line being connected to first steam inlet 22.

[0045] First flooded heat exchanger 20 also comprises a first water side 34 in the exchanger tube side, in heat exchange relationship with first steam side 21 and extending through first heat exchanger 20 between a first cold water inlet 36 and a first heated water outlet 38, first cold water inlet 36 being connected to the water source and more particularly to first water inlet line 18 for receiving water and for allowing water to flow through first water side 34, to be heated therein by heat exchange with first steam side 21 and to flow out through first heated water outlet 38.

[0046] Heat exchange system 10 further comprises a second flooded heat exchanger 40 that is similar to first flooded heat exchanger 20. Second flooded heat exchanger 40 comprises a second steam side 42 in the exchanger shell side, extending through second heat exchanger 40 between a second steam inlet 44 that is connected to second steam inlet line 32 and a second subcooled condensate outlet 46, second steam inlet 44 being for receiving steam from the steam source 26 and for allowing steam to flow through second steam side 42 and to condense to form condensate that at least partly floods second steam side 42 at a level of flooding F (that may be the same as the level of flooding F of the first heat exchanger 20, but more probably not) and that is subcooled by additional heat transfer to the water before flowing out through second subcooled condensate outlet 46.

[0047] Second flooded heat exchanger 40 also comprises a second water side 48 in the exchanger tube side, in heat exchange relationship with second steam side 42 and extending through second heat exchanger 40 between a second cold water inlet 50 and a second heated water outlet 52. Second cold water inlet 50 is serially connected to first water side 34, and more particularly an intermediate line 54 extends and links the first heated water outlet 38 to the second cold water inlet 50, such that water can flow from first water side 34, through intermediate line 54 and into and through second water side 48, where it will be heated by heat exchange with second steam side 42 before flowing out through second heated water outlet 52.

[0048] Heat exchange system 10 also comprises a first control valve 56 located at or downstream of first condensate outlet 24; and a second control valve 58 located at or downstream of second condensate outlet 46. A first water temperature sensor 59 is provided at or downstream of first heated water outlet 38, albeit upstream of second heat exchanger 40; and a second water temperature sensor 60 is provided at or downstream of second heated water outlet 52. A control device 62 receives temperature data from first and second water temperature sensors 59, 60 and controls first and second control valves 56, 58.

[0049] First and second subcooled condensate outlets 24, 46 lead into respective first and second condensate outlet lines 64, 66 that merge into a main condensate outlet line 68 that leads to a suitable condensate discharge (not shown). For instance, main condensate outlet line 68 can lead back to a main condensate return line that in turn leads back to steam source 26, or could be discharged in a municipal sewer conduit.

[0050] Second heated water outlet 52 leads into a heated water line 70 that in turn conveys the water to applications where heated water is required. If the applications do not use the water itself, e.g. in building heating applications, then the water may be circulated back to water source 12 to be heated again.

[0051] In FIG. 1, a single tube is shown to represent the water side, but it is understood that numerous tubes normally form the tube side. Also, although a U-tube configuration is shown in FIG. 1, in an alternate embodiment (not shown), the tubes could be straight instead or other suitable tube configuration.

[0052] In another alternate embodiment (not shown), the water could circulated in the shell instead and the steam could be circulated in the tubes instead.

[0053] First and second condensate control valves 56, 58 are said to be located at or downstream of subcooled condensate outlet 38, 46 because any position along their respective lines 64, 66 is substantially equivalent as will be obvious for someone skilled in the art. Likewise, first and second water temperature sensors 59, 60 are said to be located at or downstream of heated water outlets 38, 52, albeit upstream of second heat exchanger 40 in the case of first sensor 59, because any position along their respective lines 54, 70 is substantially equivalent as will be obvious for someone skilled in the art.

[0054] In use, to heat water within heat exchange system 10 to a desired temperature, the proportions of each of first and second steam sides 21, 42 that are flooded can be respectively selectively adjusted by controlling the debit of subcooled condensate allowed through first and second subcooled condensate outlets 24, 46 with first and second control valves 56, 58, for allowing heat exchange to the water to be adjusted as a result of the water temperature measured by first and second water temperature sensors 59, 60.

[0055] More specifically, first and second control valves 56, 58 can be set in one of a first state in which they are both at least partly opened (at respective opening percentages, that can be identical or, more likely, different) to allow effective heat exchange from the steam to the water in both first and second heat exchangers 20, 40; and a second state in which one of them is closed while the other is at least partly opened to have an effective heat exchange from the steam to the water in only one of first or second heat exchangers 20, 40, while the first and second steam sides 21, 42 remain continuously supplied with steam.

[0056] The heat exchange system 10 consequently allows controlling both the alternation and the redundancy between first and second heat exchangers 20, 40, by continuously supplying with steam the first and second steam sides 21, 42 that are connected in parallel, namely in two parallel branches of the steam circuit; and by continuously circulating the water through both the first and second water sides 34, 48 that are connected in series, namely the water circulates through the first and then the second heat exchangers 20, 40 one after the other.

[0057] In the first state of control valves 56, 58 where both are opened and effective heat exchange occurs between steam and water in both heat exchangers 20, 40, there is effective heat transfer in both the first and second heat exchangers 20, 40 between the steam and the water. This allows usage of heat exchange system at peak demand times where high hot water debit is required.

[0058] In the second state of control valves 56, 58 where one is open and the other is closed, a single one of the first and second heat exchangers 20, 40 provides effective heat transfer between the steam and the water. Here, it becomes possible to alternate the effective heat transfer between the first and second heat exchangers 20, 40 under equal run time procedures, by alternately opening the first and second control valves 56, 58 at desired time intervals, e.g. alternation can occur every day or every week. However, the steam remains continuously supplied to the heat exchanger 20 or 40 that is not operatively transferring heat, this heat exchanger does not need to be initialized when alternation occurs. The mechanical stress on it is reduced because of this warm start.

[0059] Heat exchange system 10 of course allows each heat exchanger 20, 40 to be used alone in case of maintenance or replacement of the other. To this end, isolation valves 72, 74, 76, 78, 80, 82 are provided on inlet water line 18, intermediate water line 54, outlet water line 70 and on dedicated isolation lines 84, 86, 88. In normal operation of heat exchange system 10, valves 76, 82 are closed and water is circulated in series through both heat exchangers 20, 40 as described above. By closing isolation valves 72, 74 and opening valve 76, water can bypass the first heat exchanger 20 entirely; or by closing valves 78, 80 and opening valve 82, water can bypass second heat exchanger 40 entirely.

[0060] Control valves 56, 58 if closed can be used to isolate their respective heat exchanger 20, 40, in conjunction with first and second steam shut-off valves 90, 92 that are provided on the steam inlet lines 30, 32 respectively. Steam shut-off valves 90, 92 are required on any steam exchanger 20, 40 as normal components, to allow steam to be selectively shut off or automatically shut off in case of system failure. Here, they further serve to isolate the steam sides 21, 42 in conjunction with control valves 56, 58.

[0061] First and second and water sides 34, 48 and first and second steam sides 21, 42 can consequently be shut off to allow maintenance or replacement of one of first and second heat exchangers 20, 40 while the other remains operational. The usual redundancy of heat exchangers 20, 40 consequently exists with the present invention.

[0062] Heat exchange system 10 optionally comprises, as shown in FIG. 1, a first recirculation line 94 equipped with an optional first recirculation pump 96 connecting second heated water outlet 52 to first cold water inlet 36 for allowing water to be at least partly recirculated therebetween, and a second recirculation line 98 equipped with an optional second recirculation pump 100 connecting second heated water outlet 52 to second cold water inlet 50 for allowing water to be at least partly recirculated therebetween. In heat exchangers 20, 40 where effective heat transfer occurs, a portion of the heated water is optionally advantageously recirculated to the cold water inlet to increase temperature stability at times of varying demand.

[0063] First and second steam inlet start-up valves 102, 104 are advantageously provided to allow low debit and low pressure gradual injection of steam when the corresponding first and second heat exchangers 20, 40 are initialized (e.g. after initial installation or maintenance).

[0064] First and second security flow sensors 106, 108 are provided at first and second cold water inlets 36 and 50 to detect the eventual absence of water running into the first and second heat exchangers 20 and 40. Control device 62 would then command the closure of shut-off valves 90, 92 to avoid the heat exchangers 20, 40 from overheating. Flow sensors 106, 108 could alternately be installed at the heat exchanger outlets 38, 52 instead.

[0065] In an alternate embodiment (not shown), the heat exchange system of the present invention includes three or more heat exchangers instead of two, where the water sides of all heat exchangers are in series and the steam sides, in parallel.