GB2132327A - Heat transfer apparatus - Google Patents

Abstract

An absorption type heat pump or chiller includes various heat exchanger and other plant stages. In order to economise on space, it is proposed in accordance with the present invention that the heat exchange stages should be plate heat exchangers mounted in a common frame. Other plant stages such as the absorber are also mounted in the frame. In order to provide a suitable absorber, the absorber comprises a body 41 with means 55 for suspending the body from the body top bar of a heat exchange frame. An upper corner port 45 admits vapour to a flow zone 44 within the absorber. Baffles 46 provide a tortuous flow path for the vapour passing down through the flow zone 44, and an inlet pipe 47 for liquid is also provided near the top of the flow zone 44 so as to contact and absorb the vapour while both are following paths formed by the baffles 46. The liquid with absorbed vapour is drawn off via a line 51. <IMAGE>

Description

SPECIFICATION Heat transfer apparatus This invention relates to heat transfer apparatus of the heat pump or chiller type.

Heat transfer apparatus of this type is in commercial use and may for instance operate on the absorption principie. It functions to transfer heat from one stream to another in an indirect manner and may for instance be used to chill water or a product stream or as a heat pump to raise the temperature of a low grade heat source, such as a river, industrial effluent or waste water to a higher and more useful level. Such apparatus is used when normal heat exchange would not be available, owing to the temperatures of the streams.

One problem of this type of heat transfer apparatus is that the use of multiple stages of heat transfer between the streams, via an absorbent medium, requires the use of a number of heat exchangers and other pieces of plant, so that the apparatus tends to be not only expensive, but also requires a great deal of space.

According to one aspect of the invention, there is provided a heat pump or chiller in which the heat exchange stages are formed by plate heat exchangers.

It is particularly advantageous if the heat exchangers are mounted in a common frame and preferably an absorber is also mounted in the frame.

According to a second aspect of the invention, there is provided an absorber for mounting in the frame of a plate heat exchanger, comprising a body with means for suspending the body from a top bar of a heat exchanger frame, an upper corner port for admitting vapour from an adjacent heat exchanger section in the frame, a chamber formed within the body and including means for providing a tortuous liquid path from a liquid inlet to the bottom of the chamber, the said chamber being in communication with the corner port to admit vapour to the chamber for contacting with and absorption into the liquid following the said tortuous path, and means for withdrawing liquid from the chamber.

In order to enable the absorber also to act as a connection to adjacent heat exchanger sections, the body may include a lower section having connections therein to enable supply and discharge of media to and from sections of the plate heat exchanger adjacent to the absorber.

The tortuous path for the liquid may be formed by baffles affixed to facing plates secured to the body and bounding the said chamber.

The invention will be further described with reference to the accompanying diagrammatic drawings, in which: Figure 1 illustrates the components of a heat transfer apparatus of the absorption type adapted for mounting in a common heat exchanger frame; Figure 2 illustrates the basic components of a heat exchanger frame; Figure 3 is an elevation of an absorber; and Figure 4 is a section of the line IV--IV of Figure 3.

The flow diagram of Figure 1 shows five flows streams related to a typical generally conventional absorption type heat pump or water chiller, using a lithium bromide/water system as the absorbent/refrigerant pair and low pressure steam or hot water as the driving heat source. The arrangement is drawn up in such a way that it can be incorporated in the frame of a heat exchanger, of which a follower is shown at 1 and a head at 2.

The flow of a heat source, which is chilled in operation, is shown by the chain dotted line 3. The flow of liquid, such as the product to be warmed, is shown by the dashed line 4. The flow of lithium bromide solution is shown by the full line 5 and the flow of water derived from and reabsorbed into the flow of lithium bromide solution is shown by the line of long dashes 6. A further chain dotted line 7 illustrates the flow of the driving steam or hot water.

The heat exchanger frame contains five heat exchanging sections denoted by the reference numerals 11, 12, 13, 14 and 15. Physically between the sections 11 and 1 2 there is located an absorber 1 6 also mounted in the heat exchanger frame. Between the sections 12 and 1 3 there is located a connection grid or intermediate header 17, and between the sections 13 and 14 there is a further similar connecting grid or intermediate header 1 8. Between the sections 14 and 1 5 there is located a vapour separator 19, also mounted in the heat exchanger frame.

In connection with the separator, attention is drawn to our copending application number 8235606 filed simultaneously herewith and entitled "Vapour Separator." Dealing first with the flow of water, this first arises as vapour separated from the lithium bromide solution in the separator 19, and it is passed from there to the heat exchange section 14 where it is condensed and warms the stream 4 just prior to the withdrawal of that stream from the system in its fully warmed state. The water is fed by a pump 21 through an expansion valve 22 and arrives at the heat exchanger section 11, which acts as an evaporator operating at low pressure (in the region of 20 mm mercury).This evaporation is achieved by extracting heat from the heat source stream 3, which has this as its only active involvement in the system, and is thus cooled, thereby feeding energy into the system.

The water vapour from the evaporator is then fed into the absorber 1 6 where it is condensed into the circulating lithium bromide solution and raises the temperature thereof.

The thus warmed and diluted lithium bromide solution is fed by a pump 23 into the heat exchanger section 1 2 in heat exchange with the stream 4 which is thus heated. It will be appreciated that the stream 4 is further heated in the condensation stage 14 before leaving the system. The lithium bromide solution passes from the heat exchanger section 12 to the heat exchanger section 1 3 where it is regeneratively heated by the concentrated lithium bromide solution fed from the separator 19 by a pump 20.

The heated solution is then passed into the heat exchanger section 1 5 where it comes into heat exchange with the driving heat source stream 7 to raise the temperature still further and enable the absorbed water to be flashed off in the separator 19.

The concentrated solution then returns to the heat exchanger section 1 3 as already described and then to the absorber 16. As indicated above, the absorption cycle is substantially conventional, and the description of it is included to indicate how the necessary equipment to carry out this complex cycle can be incorporated into the frame of a plate heat exchanger.

For completeness, Figure 2 illustrates a typical plate heat exchanger frame which has the head 2 already referred to and an end stop member 31.

These are interconnected by a top rail 32 and a bottom rail 33. The follower 1 already referred to is suspended on the top rail 32 and supported by the bottom rail 33 and the pack of plates and other equipment, including the absorber 1 6, the separator 1 9 and the intermediate headers 1 7 and 18, is compressed between the follower 1 and the head 2 and the whole pack is secured in position after compression by means of tie bars illustrated at 34 and extending between the head 2 and follower 1.

The grids or intermediate headers 17 and 18 are currently available commercial pieces of equipment which are provided with corner porting to cooperate with the corner ports of the adjacent packs of plates, and also provided with external connections for supply and discharge of media to and from these corner ports.

Turning now to Figures 3 and 4, the absorber 1 6 is illustrated in rather more detail and will be seen to comprise a body 41 which, with facing sheets 42 and 43, defines an absorption chamber 44. A corner port 45 communicates with the adjacent porting of the evaporator section 11 to act as a feed for vapour to the chamber 44, and it will be seen that this corner port has been enlarged to a "D" section to allow greater flow area. It is preferred that the vapour port corresponding is of similar section.

This port 45 communicates with the chamber 44 to feed the vapour in for absorption. The facing sheets 42 and 43 each carry a series of baffles 46 as illustrated to provide a tortuous or zig-zag path for the lithium bromide solution which is fed in via a perforated pipe 40. The solution is distributed by the perforations and cascades off the baffles 46 successively for efficient contact with the vapour.

The body 41 is also provided with two strengthening ribs 48 and these ribs have holes 49 in them so that they do not present a substantial barrier to the lateral flow of vapour. The lithium bromide solution, augmented by condensed (ie.

absorbed) vapour, is collected in the bottom of the chamber 44 as indicated at 49, and is drawn off via a line indicated at 51 leading to the pump 23 shown in Figure 1.

In order to maintain a minimum liquid level to maintain the required low pressure conditions in the chamber 44, there is shown a float 52 which detects if the liquid level falls to a predetermined minimum and operates a valve 53 to prevent discharge of liquid.

The absorber 16 is shown as being provided with a roller 55 to enable it to be suspended from the top bar 32 of the frame, and attached to the lower end of the body 41, there is a standard lower end portion 56 containing porting illustrated at 57 and connection unions 58 to enable this lower portion 56 to be used for connection of supply and discharge to the adjacent heat exchanger sections. The portion 56 is provided with a recess 59 to cooperate with the bottom rail 33.

In order to enable the system to be purged of non-condensibles, a vent 61 is shown to enable the chamber 44 to be connected to a vacuum pump when required for purging the system and, if required, on start up.

The facing sheets 42 and 43 may be welded to the body 41 if required, but if access to the interior of the absorber is required for cleaning or other purposes, they may be removably secured and sealed by gaskets. Part of a gasket is indicated by the reference numerals 62.

Corrosion by the lithium bromide solution may be prevented by suitable coating on the metal parts. The pipe work carrying the lithium bromide is preferably in a suitable plastics material, as are the pumps. The plates in the heat exchanger sections in contact with the lithium bromide solution are preferably of titanium.

Various modifications may be made within the scope of the invention.

Claims (13)

1. An absorber for mounting in the frame of a plate heat exchanger, comprising a body with means for suspending the body from a top bar of a heat exchanger frame, an upper corner port for admitting vapour from an adjacent heat exchanger section in the frame, a chamber formed within the body and including means for providing a tortous liquid path from a liquid inlet to the bottom of the chamber, the said chamber being in communication with the corner port to admit vapour to the chamber for contacting with and absorption by the liquid following the said tortuous path, and means for withdrawing liquid from the chamber.

2. An absorber as claimed in claim 1, comprising a lower section having connections therein to enable supply and discharge of media to a frame section of the plate heat exchanger adjacent to the absorber.

3. An absorber as claimed in claims 1 dr 2, in which the chamber is defined by facing sheets.

4. An absorber as claimed in claim 3, in which the facing sheets are welded to the body.

5. An absorber as claimed in claims 3 or 4, in which the tortuous flow path is defined by baffles attached to the facing sheets.

6. An absorber as claimed in claims 3, 4 or 5, in which strengthening ribs extend between the facing sheets and are provided with holes to permit vapour flow through the ribs.

7. An absorber as claimed in any of claims 1 to 6, including a liquid level detection arrangement to prevent withdrawal of liquid if the liquid level falls below a predetermined level.

8. An absorber as claimed in any of claims 1 to 7, including a vent connectable to a vacuum pump to purge the chamber of non-condensibles.

9. An absorber substantially as hereinbefore described with reference to the accompanying drawings.

1 0. Heat transfer apparatus of the absorption type for use as a heat pump or chiller in which heat exchange stages are formed by plate heat exchangers.

11. Heat transfer apparatus as claimed in claim 10, in which the plate heat exchangers are mounted in a common frame.

1 2. Heat transfer apparatus as claimed in claim 11, in which an absorber for absorbing water vapour in the absorption solution is mounted in the same frame.

13. Heat transfer apparatus for the absorption type substantially as hereinbefore described with reference to the accompanying drawings.