GB2063444A

GB2063444A - Absorption Type Heat Pumps

Info

Publication number: GB2063444A
Application number: GB7938917A
Authority: GB
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1979-11-09
Filing date: 1979-11-09
Publication date: 1981-06-03

Abstract

An absorption type heat pump, for example air conditioner, suitable for operation by a solar collector incorporates a turbine. It comprises an evaporator (1), an absorber (3), a pump (5) for pumping refrigerant-rich absorbant from the absorber (3) to a generator (6) which can be heated by a solar collector, (8), an impulse turbine (9), a throttling valve (11), a condenser (12) and a throttling valve (15). <IMAGE>

Description

SPECIFICATION Absorption Type Heat Pumps This invention relates to absorption type heat pumps for example air conditions or refrigerators especially those operated by a solar collector.

It is a feature of absorption type air conditioners that the coefficient of performance (C.O.P.) which is the ratio of the heating effect to the energy supplied is not greatly improved when the heat input temperature is raised above about 900C. However, the C.O.P.'s which are achieved (0-6-0.8) are as good as those achieved by Rankine cycle/compression refrigeration systems using much higher heat input temperatures.

Simple concentrating solar collectors can provide solar energy efficiently at temperatures much higher than 90 C, and the absorption unit does not take full advantage of the useful energy which is theoretically available at these high solar collector temperatures.

We have now devised an absorption type heat pump, for example an air conditioner, which can utilise this useful energy and which can be used for example to provide electrical power to operate the circulation pump and to operate the fans which move air over the heat exchangers.

According to this invention an absorption type heat pump comprises: (1) an evaporator for vaporising a refrigerant, (2) an absorber into which vapor from the evaporator can enter and be absorbed by an absorbant, (3) a pump capable of pumping refrigerant- rich absorbant from the absorber to (4) a generator which is heated by heat from a solar collector or from a source of fossil fuel, (5) an impulse turbine into the nozzle of which vapour and liquid phases from the generator can enter, (6) a throttling valve in a conduit connecting the liquid outlet of the turbine with the absorber, (7) a condenser into which vapour from the turbine can pass and (8) a throttling valve in a conduit connecting the liquid outlet of the condenser with the liquid inlet of the evaporator.

A suitable combination of refrigerant and absorbant is ammonia and sodium thiocyanate; other suitable combinations are water and lithium bromide or ammonia and water.

In the evaporator where heat is added at low temperature the refrigerant enters as a liquid and is vaporised therein. The heat may be supplied by means of heat exchange with circulating air in the case of air conditioners or with brine in the case when the heat pump is used for refrigeration, and a typicai temperature range is OOC to 1000, e.g.

about 70C.

Vaporised refrigerant leaves the evaporator at a temperature of for example 70C and enters an absorber where by means of ambient air or a cooling tower heat is removed. In this absorber refrigerant is dissolved by the absorbant rejecting the heat of absorption at a temperature typically in the range 350C to 450C, for example about 4000. The pressure within the absorber will be substantially equal to that within the evaporator, and when ammonia is used as refrigerant and sodium thiocyanate used as absorbant the pressure will be in the range 500-550 kPa e.g.

about 525 kPa.

Liquid refrigerant dissolved in the absorbant leaves the absorber and is pumped by a liquid pump to the generator, where heat is added at high temperature by means of a solar collector or by a source of fossil fuel. Here the temperature is typically in the range 11000 to 1300C, for example about 1200C. The concentration of refrigerant in absorbant leaving the generator has to be lower than that in the absorber and the pressure within the generator should preferably not be high enough to retain substantially all the refrigerant in solution within the generator. It is desirable to evaporate some of the refrigerant within the generator since this uptake of energy at the peak temperature improves the thermal efficiency of the cycle.

It is preferable if heat from the vapour and liquid phases leaving the turbine is recovered by the solution passing from the absorber to the generator.

The mixture of vapour and liquid phases from the generator passes through the nozzle of an impulse turbine where vapour is generated within the body of the liquid as the pressure falls on passage through the nozzle. No mixer is required and the transfer of momentum is efficient.

It is preferable if the nozzle of the impulse turbine is designed so that the temperature of the nozzle wall is kept as high as possible so as to encourage the formation of a vapour film between the wall and the liquid passing through the nozzle.

When ammonia and sodium thiocyanate are used as refrigerant and absorbant, the vapour and liquid phase mixture enters the impulse turbine at a temperature of about 1200C and about 4% of the heat input is available as shaft power at about 8000 r.p.m. when a 6" (12.7 mm) diameter impulse turbine is used and when operating the unit at a C.O.P. of about 0.7.

There is a conduit connecting the liquid outlet of the turbine with the absorber. This conduit is provided with a throttling valve where the pressure of the liquid passing through is reduced.

The vapour from the turbine passes to a condenser where heat is removed by means of heat exchange, with for example air or a liquid such as water. Here the vaporised refrigerant condenses, rejecting its latent heat of condensation at a temperature in the range 2000 to 450C, for example about 4000.

Finally, the liquid refrigerant returns to the liquid inlet of the evaporator by means of a conduit provided with a throttling valve where the pressure of the liquid passing through is reduced.

As stated above heat for the generator may be provided by a source of fossil fuel. Preferably however it is provided by means of a solar collector. Suitable solar collectors include those described in our patent applications 79.19252, 79.31344 and 79.37864. These all comprise a plurality of units having a lens, a receiver and a reflector. The collector of U.K. 79.31344 involves the use of a material of high transparency (e.g. a plastics such as acrylic resin) having a refractive index of at least 1.35 and being able of withstanding temperatures of at least 750C, preferably at least 1500 C. U.K. 79.37864 (PM7925) involves the use of an orientating mechanism so that the maximum possible amount of solar radiation at the particular time of the year can be collected.There is also a fail-safe system whereby should the flow of heat transfer fluid through a receiver cease, the units are orientated so that substantially all the incoming radiation is outside the angle of acceptance of the collector.

Ali these solar collectors should be capable of providing temperatures of about 1 200C or higher.

The absorption type heat pumps of this invention can therefore produce their own ancillary power and this can be used for operating circulatory pumps and fans etc.

The invention is now described with reference to the drawing which is a flow diagram of an absorption type solar operated air conditioner.

Liquid ammonia as refrigerant enters the evaporator 1 and is vaporised therein at a temperature of 70C. The circuit 2 in which air is circulated, supplies heat to the liquid ammonia in the evaporator 1. From the evaporator 1 gaseous ammonia passes to the absorber 3 where it is dissolved by Na SCN as the absorbant rejecting the heat of absorption at 40 C. This heat of absorption is transferred to an air-cooled cooling tower or to a ducted air heating system in the circuit 4.

From the absorber 3 the refrigerant-rich absorbant (NH3 in NaSCN) is pumped by means of pump 5 into the generator 6 where the refrigerant NH3 is boiled off at 1200 C. Heat is supplied to the generator 6 by means of circuit 7 powered by solar cell 8. The peak pressure in the generator 6 will be of the order of 3150 kPa.

From the generator 6 the mixture of liquid and vapor phases of refrigerant and absorbant pass through the nozzle of an impulse turbine 9.

Through conduit 10 the liquid phase from the turbine 9 passes to the absorber 3 by way of a throttling valve 11 where the pressure of the liquid is reduced from 1 575 kPa to 525 kPa.

The vapour phase from the turbine passes to a condenser 12 where the vaporised refrigerant NH3 condenses, rejecting its latent heat of condensation at 400C which is heat exchanged in an air-cooled cooling tower or in a ducted air heating system in circuit 13.

Finally the liquid refrigerant NH3 passes through a conduit 14 in which there is a throttling valve 1 5 where the pressure is reduced from 1575 kPa to 525 kPa. After passing through valve 1 5 the liquid refrigerant enters the evaporator 1.

Claims

1. An absorption type heat pump comprising (1) an evaporator for vaporising a refrigerant, (2) an absorber into which vapour from the evaporator can enter and be absorbed by an absorbant, (3) a pump capable of pumping refrigerant-rich absorbant from the absorber to (4) a generator which is heated by heat from a solar collector or from a source of fossil fuel, (5) an impulse turbine into the nozzle of which vapour and liquid phases from the generator can enter, (6) a throttling valve in a conduit connecting the liquid outlet of the turbine with the absorber, (7) a condenser into which vapour from the turbine can pass and (8) a throttling valve in a conduit connecting the liquid outlet of the condenser with the liquid inlet of the evaporator.

2. A heat pump according to claim 1 wherein there are means for heat exchange between the vapour and liquid phase streams leaving the turbine and the solution passing from the absorber to the generator.

3. A heat pump according to either of claims 1 and 2 wherein the nozzle of the impulse turbine is designed so that the temperature of the nozzle wall is kept as high as possible so as to encourarFe the formation of a vapour film between the wall and liquid passing through the nozzle.

4. A heat pump according to any one of ehe preceding claims wherein the generator is Iwea ed by heat from a solar collector, said collector comprising a plurality of units each having a receiver and a reflector.

5. A heat pump according to claim I substantially as hereinbefore described with reference to the drawing.