NL2016303B1

NL2016303B1 - Improved heat pump and process of heat pumping.

Info

Publication number: NL2016303B1
Application number: NL2016303A
Authority: NL
Inventors: Rexwinkel Glenn; Antonius Maria Ten Asbroeck Nick
Original assignee: Frames Renewable Energy Solutions B V
Priority date: 2016-02-23
Filing date: 2016-02-23
Publication date: 2017-09-07
Also published as: EP3420288B1; EP3420288A1; WO2017146570A1

Abstract

The heat pump comprises a closed circuit configured for flow of a solvent and a refrigerant, which closed circuit comprises an evaporator and an absorber, which are mutually interconnected with a first line configured for the transport of vapour from the evaporator to the absorber, a second line configured for the transport of a primarily liquid stream from the evaporator to the absorber, and a third line configured for transport of an enriched liquid from the absorber towards the evaporator, wherein said evaporator is typically in heat communication with an input stream for transmission of heat into the evaporator and wherein said enriched liquid being brought in heat communication with a output stream for transmission of heat thereto, particularly at high pressure, wherein a compressor is arranged in the first line and an expansion device is arranged in the third line. Herein, a first refrigerant inlet and a second refrigerant inlet are present and are configured for supply of a first and a second refrigerant. This is configured such that the first refrigerant and the second refrigerant react with each other in the absorber, leading overall to liberation of condensation heat and reaction heat.

Description

Improved heat pump and process of heat pumping

Field of the invention

The invention relates to a heat pump comprising a closed circuit configured for flow of a solvent and a refrigerant, which closed circuit comprises an evaporator and an absorber, which are mutually interconnected with a first line configured for the transport of vapour from the evaporator to the absorber, and second line configured for the transport of an enriched liquid from the absorber, wherein said evaporator is typically in heat communication with an input stream for transmission of heat into the evaporator and wherein said enriched liquid being brought in heat communication with a output stream for transmission of heat thereto, particularly at high pressure. The invention also relates to the use of said heat pump for pumping of heat from an input flow at a first temperature to an output flow at a second temperature.

The invention further relates to a process of heat pumping comprising the steps of

Heat exchanging an input stream with a circulating stream comprising a refrigerant; Evaporating at least part of the circulating stream;

Mixing the evaporated circulating stream with a solvent to dissolve the evaporated circulating flow and generate an enriched liquid stream;

Bringing the circulating stream at a higher pressure, and;

Heat exchanging the enriched stream with an output stream for transmission of heat thereto.

Background of the invention

Heat pumps are means for upgrading a first heat flow, typically a low temperature waste heat flow, to useful high temperature heat. The operating principle of a heat pump is based on the physical property that the boiling point of a fluid increases with pressure. By lowering the pressure, a medium can be evaporated at low temperatures, while an increase of pressure will lead to a high boiling point. At high pressure, the vapour is condensed, which results in a useful source of energy.

Different types of heat pumps exist, known in the art as the mechanical heat pump, the absorption heat pump and also a hybrid type of heat pump. The mechanical heat pump is the most widely used. Its operating principle is based on compression and expansion of a refrigerant. A mechanical heat pump thereto is provided with a compressor and an expansion device that are arranged upstream and downstream of a condenser.

In an absorption heat pump, the refrigerant is first evaporated, and then brought into contact with an absorption medium or solvent. The absorption process releases useful heat. In order to regenerate sufficiently pure refrigerant, the enriched liquid stream is then compressed and further heated in a generator. This results in evaporation of the refrigerant, which is subsequently condensed and expanded to bring it back in a liquid form ready for another cycle of evaporation. One example of such a heat pump is for instance disclosed in GB2169069A.

In a hybrid heat pump, the input stream is first heat exchanged and warmed up, so as to extract waste heat. The mixture of refrigerant and solvent is then separated, to form a vapour stream primarily or substantially comprising refrigerant and a liquid stream primarily comprising solvent. The vapour stream and the liquid stream are compressed and pumped to higher pressure respectively, after which both are combined and useful heat is released. Finally, the resulting stream is expanded and the input stream is again obtained.

For use in these type of heat pumps, several refrigerants are known. All refrigerants are known with an R number. Well-known refrigerants include R134a, an organofluor compound, R600 and R600a, being butane and isobutane, R717 or ammonia, R744 or carbon dioxide. The latter is particularly used for low temperature freezer applications, and in applications wherein a potential user allows for heating at non-constant temperatures, as condensation above the transcritical temperature of 31°C occurs over a temperature range. A well-known solvent is water. For absorption and hybrid heat pumps, ammonia is the most common refrigerant.

Heat pumps are normally reviewed on the basis of their efficiency, which is expressed as the coefficient of performance (COP). It is determined by the rate of the energy usage (particularly for compressor and/or pump) and the amount of useful heat or cooling released from the condenser or absorber. The COP depends on several factors. Especially the temperature difference between waste heat source and potential user is an important factor: the smaller the temperature difference between condensation and evaporation temperature, the higher the efficiency. It is observed that these condensation and evaporation temperatures can often not be chosen freely, but depends on the process of use. A most interesting application for a heat pump is the heat pumping from for instance an input temperature in the range of 50-90°C to an output temperature in the range of 100-150°C, preferably at least 110°C. The temperature of 100-150°C is often needed as process water. These processes generally produce vapors which have to be condensed destroying partly the valued heat into lower grade heat. Typical processes are distillation, refining stripping of C02 and the like. The net consumption of heat in the 100-150 °C range is a large part of the costs of these industrial processes. In addition most often this heat is produced from high valued primary energy sources like e.g. natural gas employing not to its full potential the exergy to make also electricity. These processes produce large amounts of waste heat in the range of 70-95°C which typically can only be used for local heating purposes but often because of the large amounts available needs to be destroyed in cooling equipment, requiring further resources like water and electricity. Furthermore, this input temperature represents the temperature of cooling water in industry, but also cooling water output of diesel generators.

However, many heat pumps are not suitable for such an output temperature range. Absorption heat pumps for instance are suitable for delivering useful heat at a maximum temperature of 70°C, and cooling of the condenser with water or air. Then the efficiency can be approximately 150% (COP 1.5).

One example is for instance a heat transformer. Such a system is known from DE3140013A1. Herein, a two-step heat transformer is combined with a turbine from a power generator. The vapour from the turbine is led directly into the absorber, that is integrated with either an evaporator into an absorber-evaporator unit or with a “austreiber”. On the one hand, the absorbed vapour is, as in an absorption heat pump, brought to higher pressure, and then the sent to a condenser, and is thereafter returned to a heating vessel of the power generator turbine. Another part is used via further circuits to win back part of the energy of the waste; depending on the input temperature, a high output temperature may be achieved. However, such a system is intended as part and improved of a power generator, rather than as a separate heat pump. Moreover, the system does not appear very simple.

Another example is known from Y. Kubo and S. Seichima, “High temperature heat pump research and development”, 1986, International Refrigeration and Air Conditioning Conference, Paper 30. Herein, normal pentane was selected as the best refrigerant and a polyglycol synthetic oil was used as lubricating oil. Use was made of a mechanical heat pump, using a 75kW pilot plant. While the results appeared promising, it was added that pentane is flammable. An incombustible refrigerant would therefore to be reviewed.

Summary of the invention

It is therefore an object of the invention to provide an improved heat pump that is feasible to give an output temperature in the range of 100-150°C, preferably 110-140°C, more preferably 120- 135°C, that is acceptable for use in industrial environments, in terms of complexity, maintenance and efficiency.

It is another object to provide an improved process of pumping heat.

According to a first aspect, the invention provides a process of pumping heat from an input stream to an output stream, comprising the steps of: (1) heat exchanging the input stream with a circulating stream comprising a refrigerant; (2) evaporating at least part of the circulating stream to obtain a vapour stream and an - at least primarily - liquid stream; (3) compressing the vapour stream; (4) adding the compressed vapour stream and the liquid stream to an absorber; (5) operating the absorber to generate an enriched liquid stream; (6) transmitting heat from the absorber to the output stream, and (7) transporting the enriched liquid stream for reuse as circulating stream. The circulating stream comprises a first and a second refrigerant, and wherein the first and the second refrigerant in the vapour stream are dissolved in the absorber into the solvent and react with each other to generate a pair of a positively and negatively charged ions.

According to a second aspect, a heat pump is provided that comprises a closed circuit configured for flow of a solvent and a refrigerant, which closed circuit comprises an evaporator and an absorber, which are mutually interconnected with a first line configured for the transport of vapour from the evaporator to the absorber, a second line configured for the transport of a primarily liquid stream from the evaporator to the absorber, and a third line configured for transport of an enriched liquid from the absorber towards the evaporator, wherein said evaporator is typically in heat communication with an input stream for transmission of heat into the evaporator and wherein said enriched liquid being brought in heat communication with a output stream for transmission of heat thereto, particularly at high pressure, wherein a compressor is arranged in the first line and an expansion device is arranged in the third line. Herein, a first refrigerant inlet and a second refrigerant inlet are present and are configured for supply of a first and a second refrigerant.

In the present invention heat is generated by the heat of absorption followed by the heat of reaction released at high pressure while the reverse reaction and subsequently desorption occurs at low pressure. The reactive medium can be composed of 2 or more components of which at least 2 react together reversibly releasing the heat of reaction. The reaction should be exothermic as not to counteract the temperature increase due to compression.

Preferably, the first refrigerant is a source of acid and the second refrigerant is a source of base. Such a combination is a good choice of a reversible reaction, wherein the difference in pressure contributes to shift the equilibrium. An example of such a system is a mixture of water, ammonia and C02. Ammonia and C02 react together to form the carbamate ion in water. Next to the heat of absorption of NH3 and C02 in water this reaction releases on average 75 kJ/mole of carbamate formed. This heat of reaction would be absent when C02 is absent in the mixture and in that case the system is reduced to an absorption heat pump. The working liquid may contain 30-65 wt% of NH3, 30-65 wt% H20 and 5-40 wt%.

The here proposed heat pump will use the thermal energy inside these 60-100°C waste streams to be upgraded to the range of 100-150 °C for reuse in the processes lowering significantly the total heat demand. The heat pump works at high Coefficient of Performance (COP) with typical COP from 2-4, which is higher than known heat pumps for pumping heat to temperatures above 100°C. An improvement of 10-30% is deemed feasible without too many further optimizations. Unique of this heat pump is its environmentally friendly working fluid of H20, C02 and NH3. The typical reactions involved in this system allow highly efficient pumping of heat in small equipment.

According to a further aspect, the invention provides a heat pump comprising a closed circuit configured for flow of a solvent and a refrigerant, which closed circuit comprises an evaporator and an absorber, which are mutually interconnected with a first line configured for the transport of vapour from the evaporator to the absorber, a second line configured for the transport of a primarily liquid stream from the evaporator to the absorber, and a third line configured for transport of an enriched liquid from the absorber towards the evaporator, wherein said evaporator is typically in heat communication with an input stream for transmission of heat into the evaporator and wherein said enriched liquid being brought in heat communication with a output stream for transmission of heat thereto, particularly at high pressure, wherein a compressor is arranged in the first line and an expansion device is arranged in the third line. The absorber is configured to have a first outlet to the third line and a second outlet to a fourth line, said outlet and said fourth line being configured for vapour transport back to the evaporator. The absorber and the evaporator, each having a first inlet for a predominantly liquid stream and with a second inlet for the vapour stream, are configured such for at least partially countercurrent flow of vapour and liquid.

According to a fourth aspect, the invention provides use of the heat pump of the invention for pumping of heat from an input flow at a first temperature to an output flow at a second temperature, particularly to a second temperature in the range of 100-150°C, such as 120-130°C.

According to a fifth aspect, the invention provides a process of pumping heat from an input stream to an output stream, comprising the steps of: (1) heat exchanging the input stream with a circulating stream comprising a refrigerant; (2) feeding a diluted vapour stream to the circulating stream; (3) evaporating at least part of the circulating stream to obtain a vapour stream and an - at least primarily - liquid stream; (4) compressing the vapour stream; (5) adding the compressed vapour stream and the liquid stream to an absorber; (6) operating the absorber such as to create countercurrent flow of liquid and vapour, resulting in an enriched liquid stream for use as the circulating stream and the diluted vapour stream; (6) transmitting heat from the absorber to the output stream, and (7) transporting the circulating stream and the diluted vapour stream for reuse.

In the absorber, the one or more refrigerants in vapour form, are absorbed in the solvent. Because of countercurrent vapour and liquid, a large contact area is obtained resulting in an effective dissolution process, with the concomitant release of heat. Due to the dissolution and condensation of the vapour stream the stream leaving the absorber in vapour form is diluted in refrigerant, i.e. it is a diluted vapour stream, which thus contains comparatively high amounts of solvent, typically water. By combining this diluted vapour stream into the evaporator, evaporation is herewith further stimulated. Reasons for this stimulation may be due to better mixing, facilitating nucleation of vapour bubbles and/or adding of energy.

Particularly, the absorber is configured, for instance by means of its inlets and outlets that, under stationary operation, an upper side of the absorber has a lower content of the first and/or second refrigerant than a lower side thereof. Conversely, the evaporator is configured such that, in use under stationary operation, an upper side of the evaporator has a higher content of the first and/or the second refrigerant than a lower side thereof. This is deemed beneficial to create countercurrent flows in the evaporator and the absorber, but it further is deemed beneficial for the setting of the partial pressures in the vapour stream and diluted vapour stream that leave the evaporator and the absorber respectively. It will be understood that the size of the absorber and the evaporator vessels are designed in dependence of the mass flow rates of the entering and leaving streams, and in order to achieve a residence time that is sufficient for the desired mass transfer between vapour and liquid and any concomitant reactions. A bubbling reactor is a preferred implementation, so as to create a large vapour-liquid interface and to reduce a thickness of a boundary layer between the concentrations of refrigerants in vapour and liquid. The principles of the mass and heat transfer and the consequences for reactor design and operation are known per se to the skilled person in chemical engineering, as described in handbooks such as R.B. Bird, W.E. Stewart and E.N. Lightfoot, Transport Phenomena (Wiley, 1960, see f.i. section 22.5) and Westerterp, Van Swaaij and Beenackers, Chemical Reactor Design and Operation (Wiley, 1988).

In the context of the present application, the term ‘ diluted vapour stream’ refers to a vapour stream wherein the effective mass transfer of the first and/or the second refrigerants is lower than in the vapour stream. The lowered mass transfer may result therein that the mass flow rate of the diluted vapour stream is smaller than that of the vapour stream. Simultaneously, the concentration of refrigerants, particularly refrigerant ions or reaction products in the circulating stream from absorber to evaporator is higher than that in the liquid stream from the evaporator to the absorber.

Preferably, this heat is transmitted to an output stream by means of a heat exchanger that is integrated into the absorber. This enables a better process control, and may prevent that the temperature would increase too much in the absorber, which counteracts the process of dissolution and condensation of the refrigerant.

Herewith higher temperatures above 100°C are achievable for the second temperature (i.e. of the output stream). The higher second temperature, together with a first temperature of 60-100°C is deemed particularly beneficial for the operation of the heat pump and process of the invention, as it implies that the working liquid (i.e. the combination of solvent and refrigerant(s)) is continuously just below boiling temperature, such that the phase transition can be achieved relatively easily.

In one preferred embodiment, the absorber and suitably also the evaporator are embodied as a column into which a heat exchanger is integrated. Thus rather than sequentially heating and vaporizing respectively absorbing, the heat exchange and mass transfer from one phase to the other phase occurs simultaneously. Therewith, the heat is more quickly absorbed, facilitating a larger heat transfer out of the input stream and into the output stream. The heat exchanger may be embodied in that the absorber and/or evaporator contains a plurality of stages, each with a mass transfer section and a heat exchanger section.

In a further, preferred implementation, use is made of heat exchanger tubes that are distributed within the absorber and/or the evaporator. The tubes are in use filled with a heat exchanging liquid, more particularly the output stream. The tubes may be arranged in any suitable orientation, thus horizontal, vertical and/or under a suitable angle upwards or downwards. An orientation that is substantially horizontal is deemed particularly beneficial. For sake of clarity, such substantially horizontal orientation is understood to be an arrangement with an angle between -30 and +30 degrees, suitably with an angle between -15 and +15 degrees or even between -5 and +5 degrees. It is understood by the inventors, that such heat exchanger tubes result in an increase of mass transfer, such the liquid may flow on the tube surface, enlarging the interface between gas and liquid. As a consequence, such tubes that are arranged substantially horizontal do not need to be provided with a packing. If the orientation is different than substantially horizontal, such a packing, either random or structured, is suitably applied.

Particularly suitable is the use of the heat pump in combination with a first and a second refrigerant. Most suitably the first refrigerant is a source of acid, and the second refrigerant is a source of base. The use of carbon dioxide as the first refrigerant and ammonia as the second refrigerant is preferred, as both refrigerants are commonly available, and carbon dioxide is not or not substantially corrosive. Moreover, both refrigerants are sufficiently volatile. It is to be understood that the refrigerants as mentioned here are in the form as they are present in the vapour phase. In the liquid phase, a reaction will typically occur. This is more particularly an acid-base interaction. Suitably, the refrigerants are also supplied into the system in pure form and/or as diluted with water, either in vapour phase or in liquid phase. For carbon dioxide supply in the vapour phase appears most beneficial. Ammonia may be supplied as a vapour or as a liquid. Particularly in the latter case, it may be diluted.

The use of a first and a second refrigerant that are capable of reacting with each other in a reversible manner, particularly with water, is advantageous, as the heat capacity will therewith further increase; not merely the heat of absorption is released, but also heat of reaction. The heat pump has been found to work at high Coefficient of Performance (COP) with typical COP from 2-4. Moreover, the friendly working fluid of H20, C02 and NH3 is environmentally friendly, and the typical reactions involved in this system allow highly efficient pumping of heat in small equipment. Ammonia and C02 react together to form the carbamate ion in water. Formation of bicarbonate and/or carbonate ions is not excluded, particularly not as a side product. Next to the heat of absorption of NH3 and C02 in water this reaction releases on average 75 kJ/mole of carbamate formed. This heat of reaction would be absent when C02 is absent in the mixture. Suitably, the working liquid may contain 30-65 wt% of NH3, 30-65 wt% H20 and 5-40 wt%.

Moreover, it is believed that the presence hereof is also beneficial for the operation of the evaporator. As mentioned before, the stream in the fourth line is a diluted vapour stream, implying that it contains relatively more water than the circulating stream. The diluted stream thus contains a lower concentration than the circulating stream, which is the enriched liquid stream. The addition thereof, as a vapour form to the circulating stream, thus generates the interaction between two phases with a different composition. As a consequence, it may stimulate diffusion between the two phases, and therewith acceleration of refrigerant molecules.

In again a further embodiment, the compressor is provided with an inlet for a lubricant, said lubricant being supplied via a further line, and wherein said further line is divided from either the second line or the third line. Most preferably, the further line is divided from the third line. In this manner, it is foreseen that the conditions in the compressor may be controlled, and particularly the temperature be limited, so as to prevent the formation of urea and/or other side products. The formation of urea, that typically occurs at 140°C and higher is better prevented, as urea cannot be decomposed easily and therefore does not contribute to the heat pumping function. Moreover, urea may contaminate the compressor, and even may precipitate, which hampers long term operation.

It is understood that any further embodiment specified in the dependent claims and/or discussed hereinabove or in the following figure description may be combined with any of the aspects of the invention.

Brief introduction of the figures

These and other aspects of the heat pump and the process of the invention will be further elucidated with reference to the Figures, that are purely schematical and not drawn to scale, and wherein same reference numerals in different Figures refer to equal or corresponding elements, wherein:

Figure 1 shows schematically a first embodiment of a reactive heat pump according to the invention;

Figure 2: shows schematically a second embodiment of a reactive heat pump, wherein the absorber and the evaporator are emboded as two-stage countercurrent contactors with intermediate heat exchange;

Figure 3 shows schematically a third embodiment of a reactive heat pump, wherein the absorber and the evaporator are embodied as countercurrent (packed) columns with heat exchange means installed inside the columns;

Figure 4 shows schematically a fourth embodiment, which constitutes a further improvement of the third embodiment.

Detailed description of illustrated embodiments

Figure 1 shows the reactive heat pump system of the invention according to a first embodiment.

The heat pump comprises an evaporator 1 and an absorber 2. The evaporator 1 and the absorber 2 are herein embodied as columns suitable for bubbling, for instance as flash vessels known per se. A first line 101 configured for transport of a vapour stream leaves the evaporator 1 at its first outlet 121, in this embodiment exactly at the top of the evaporator 1 and is coupled to the absorber 2. The first line 101 enters the absorber 2 via its first inlet 211. A compressor 3 is arranged in the first line 101. A second line 102 configured for liquid transport leaves the evaporator 1 at its second outlet 122, arranged at a bottom of the evaporator. The second line 102 enters the absorber at its second inlet 212, A pump 4 is arranged in the second line 102. The second inlet 212 is arranged higher than the first inlet 211 so as to stimulate countercurrent flow of liquid and vapour in the absorber 2.

The exact location of the first inlet 211 and the second inlet 212 is open for further design and optimization, as can be accomplished by a skilled person. It is observed for clarity, that the second line 102 is configured for an at least primarily liquid stream. In other words, it is not excluded that this stream also contains vapour bubbles. It is further observed that the term ‘vapour’ as used in the context of the invention does not exclude that the vapour is physically a gas being present above its critical temperature

Figure 1 further shows a first heat exchanger 7 that is arranged within the evaporator 1 and a second heat exchanger 8 that is arranged within the absorber 2. Although it is suitable that the heat exchangers 7, 8 are physically integrated into the evaporator 1 and the absorber 2, it is feasible that the heat exchangers 7, 8 or at least one thereof is coupled in series with the evaporator 1 and the absorber 2 respectively. Rather than a single heat exchanger 7, 8 they may be arranged in series. The first heat exchanger 7 enables heat communication of the input stream with the circulating stream of refrigerant and solvent. The second heat exchanger is configured for heat exchange between the circulating stream in the absorber 2 and the output stream.

Figure 1 also shows a third line 103 and a fourth line 104 that are configured for leading respectively a enriched liquid stream and a diluted vapour stream from the absorber 2 to the evaporator 1. More specifically, the diluted vapour stream leaves the absorber via its first outlet 221, and enters the evaporator at the first inlet 111. The enriched liquid stream leaves the absorber via the second outlet 222 and enters the evaporator 1 at the second inlet 112. An expansion device 5, as known per se, is present in the third line 103. A pressure reducing valve 6 is arranged in the fourth line 104

In operation, a vapour stream from the evaporator vessel 1 is compressed and sent to absorber vessel 2 over the first line 101. Simultaneously, a liquid stream is pumped from the evaporator vessel 1 to the absorber vessel 2 over the second line 102. Since the pressure in the absorber vessel 2 is higher than in the evaporator vessel 1, refrigerants in the vapour stream are absorbed in the absorber 2 into the lean liquid stream running downwards. Heat is being generated by the heat of absorption (due to condensation and/or dissolution of refrigerant into the solvent) and reaction. The reaction occurs between the first and second refrigerants. The streams in absorber vessel 2 are cooled by heat exchanger 8. The temperature in the absorber vessel 2 is therein maintained between 100 and 150°C, preferably between 110 and 140°C.

While it is foreseen that both the first and the second refrigerant, more specifically carbon dioxide and ammonia, are present in the vapour stream and then selectively absorbed in the liquid in the absorber, it is not excluded that merely one of the first and second refrigerant is evaporated into the vapour stream in the evaporator and then - selectively - absorbed into the liquid in the absorber. Still a reaction may occur, if the other reactant remains in the liquid and is transported between evaporator and absorber via the liquid streams. While it may be that substantially all, for instance more than 90% of the first and/or second refrigerant are absorbed in the liquid, such that the ratio of mass flow rates of the first and/or the second refrigerants between the vapour stream and the diluted vapour stream is at least 10, this is not needed. This may be implemented in accordance with the requirements on output temperature (i.e. to be supplied via the heat exchanger coupled to the absorber), input temperature (to be obtained via the heat exchanger coupled to the evaporator), the flow rates of fluids (for instance process water) to be heat exchanged with the absorber and evaporator, investments into the apparatus, type of refrigerants etc. Said ratio of refrigerant mass flow rates between vapour stream and diluted vapour stream could be as low as 1.3. Preferably, the ratio of refrigerant mass flow rates is at least 2.

The enriched liquid that is generated in the absorber vessel 2 is transported back to the evaporator vessel 1 via the third line 103. The liquid level in the absorber vessel 2 is controlled by the valve 5. The pressure in the absorber vessel 2 is controlled by a reducing valve 6 which is arranged within the fourth line 104 and allows the diluted vapour stream to move to the evaporator vessel 1. In operation, the enriched liquid stream - also referred to as circulating stream - running through the third line 103 will flash in the evaporator vessel 1 due to the lower pressure present in this vessel 1. This flashing causes the temperature of the enriched liquid to decrease. The stream in the evaporator vessel 1 has to be heated using the first heat exchanger 7 to maintain constant temperature between 70 and 100°C.

As explained herein, the vapour streams and the liquid streams are transmitted separately from each other. This is deemed beneficial to maintain differences in composition. Moreover, it allows to inject vapour stream and liquid stream at different locations within the evaporator and absorber (vessels). It is believed that the system of the invention may be considered to work such that any water vapour in the vapour stream and the diluted vapour stream is a carrier gas, with in the case of C02, NH3 and water also having some catalytic properties at least. Furthermore, effects of flow behavior are believed to help in setting up a system beneficial for working as a heat pump. For instance, the diluted vapour stream may contribute to transmission of heat and bubbling so as to increase the evaporation rate of the refrigerants. Furthermore, the entering of the vapour stream into the absorber may contribute to distribution of the refrigerants. It is believed that both due to an increase of the vaporization in the evaporator and a better and quicker absorption of the vapour stream in the absorber, the effective heat transfer from the input stream to the output stream can be increased further.

In this first embodiment, the two vessels 1, 2 are constructed as bubble columns where the vapour streams enter at the bottom of the vessels. The vapour streams move virtually in plug flow from the bottom to the top within the evaporator 1 and the absorber 2. The vessels 1,2 are preferably designed so as to have sufficient residence time and interfacial area between liquid and vapour for the heat and mass exchange. This is beneficial to increasing the COP (coefficient of performance) of the heat pump.

Fig. 2 shows a process diagram of a second embodiment of the heat pump according to the invention, which is configured so as to get, as much as possible and preferably substantially, outgoing vapour streams in thermodynamic equilibrium with ingoing liquid streams. This distinguishes operation in according with the second embodiment from that of the first embodiment, in which the outgoing vapour streams are more in thermodynamic equilibrium with the outgoing liquid streams.

In the more complex configuration of the second embodiment the evaporator 1 and the absorber 2 are not implemented as simple flash vessels, but as two stage contactor columns. Each stage contains a mass transfer section and a heat exchanger 7A, 7B; 8A, 8B. The mass transfer sections may be equipped with structured or random packing. Furthermore, a recycle circuit is added per stage. In other words, liquid coming from a single mass transfer section is collected in a collector and pumped through a heat exchanger by pumps 11 A, 1 IB, 12A and 12B and recycled to the top of the mass transfer section of the same stage. Fresh liquid is continuously added to the top of the columns (i.e. absorber or evaporator). In this implementation, an overflow mechanism is applied for the transfer from the first stage to the second stage. Liquid from the collector of a first stage starts to overflow to the next stage and subsequently to the sump when the hold-up of the collectors have reached their maximum. However, an alternative transfer mechanism from the first to the second stage is not excluded.

The use of a first and a second mass transfer section, wherein liquid and vapour are contacted counter currently improves the mass transfer efficiency considerably. A much richer liquid after the high pressure column and a much leaner liquid after the low pressure column can be achieved. The effect is estimated to further improve going from 2 to 3 or more stages, each with a mass transfer section. Adding more stages, however, will increase the investment cost of the heat pump of figure 2. Its commercial viability is thus still to be evaluated.

The operation of the heat pump of this second embodiment is otherwise comparable to the operation of the heat pump of the first embodiment. Similar to the simple case gases from column 1 are compressed and sent to column 2. At the same time the liquids are pumped from the sump of column 1 to the top of column 2. Since the pressure in column 1 is higher than in column 2 the gases are absorbed into the lean liquid coming from column 1. Heat is being generated by the heat of absorption and reaction. The liquid in column 2 is cooled by heat exchangers 8A and 8B. The temperature in column 2 is maintained between 100 and 140°C by exchangers 8A and 8B. The rich liquid from the sump of column 2 is transported to the top of column 1. The liquid level in the sump of column 2 is controlled by valve 5. The pressure in column 2 is controlled by reducing valve 6 which allows gases to move to column 1. The rich liquid coming from column 2 flashes in column 1 due to the lower pressure present in column 1. This causes the temperature of the rich liquid to decrease and the liquid in column 1 has to be heated using heat exchangers 7 A and 7B to maintain constant temperature between 70 and 100°C.

It is observed that it appears beneficial that the evaporator 1 and the absorber 2 are embodied in the same way. However, this is not strictly necessary, and the evaporator shown in Fig 1 may be combined with the absorber shown in Fig. 2 or vice versa. Furthermore, the liquid recycle circuit may also be used for a column shown in Fig. 1.

Fig. 3 shows a process diagram of a third embodiment of the heat pump of the invention, wherein the absorber and the evaporator are embodied as a column with a single mass transfer section with heat transfer means that are distributed inside the column. The heat transfer means are preferably embodied as heat exchanger tubes 7C, 8C, through which a heat exchanging medium flows. The heat exchanging medium is suitably the output stream, however, an intermediate cycle with a heat exchanging medium with a high heat capacity and/or non-corrosive and predefined composition may be used alternatively. For instance, the heat exchanging medium could be an oil. In the latter case, the output stream is again heat exchanged with the intermediate cycle.

The mass transfer section is in this embodiment, as in any other embodiment suitably provided with mass transfer promoting internals. These internals could be structured or random packing. However, the internals may even be omitted when the heat transfer means have sufficient mass transfer promoting capabilities of their own. When embodying the heat transfer means as heat exchanger tubers that are substantially horizontally arranged, the internals could be omitted. Liquid from the top trickles down across the heat exchanger tubes while the vapour flow up in the column. The heat exchanger tubes promote the mass transfer between the liquid and the gas and the heat of absorption and reaction is transferred by the heat exchanger tubes.

As a consequence, the column is effectively subdivided by the heat exchanger tubes in a plurality of mass transfer stages. In an alternative embodiment of heat transfer means, wherein heat exchanger tubes are installed vertically, the heat exchanger tubes are not foreseen to have any positive effect on mass transfer, and are then not feasible to replace random or structured packing or any other mass transfer promoting internals.

The operation of the heat pump is again otherwise identical to the embodiments shown in Fig. 1 and Fig. 2

Fig. 4 shows a process diagram of a fourth, preferred embodiment of the heat pump of the invention, wherein the compressor is lubricated by the process mixture. C02 and NH3 can react together at high temperature and pressure to form Urea and water. Urea is a solid and therefore highly undesirable as it may damage the compressor. The formation of Urea needs to be avoided, even small amounts. Fortunately the reaction of ammonia and C02 to form Urea is an equilibrium reaction. The presence of water (vapor) will prevent the formation of Urea. It is understood by the inventors that the presence of water during compression is beneficial and therefore as part of the invention the compressor is preferably lubricated by the process mixture. Suitably, the enriched liquid running through the third line 103 is used. In one embodiment, a branch towards the compressor is split off and provided with a valve for determining the flow rate towards the compressor.

Otherwise, the implementation shown in Fig. 4 is identical to the third embodiment shown in Fig. 3. It is to be understood that the lubrication of the compressor by means of the process mixture can alternatively be implemented in the first and the second embodiments shown in Fig. 1 or 2 or in any further embodiment, not shown herein.

While not shown in the schematic representations of Fig. 1-4, the heat pump suitably comprises one or more inlets for the refrigerants and the solvent. In order to ensure that the composition of the fluid does not deviate over time, it is further foreseen to include any outlet. The inlets and the outlet can further be used for start up and/or interruption. It is deemed preferable that separate inlets are present for the different refrigerants, which can be connected to supplies thereto, that are well known in the art. Nonetheless, it is not excluded that a pre-mixing chamber is provided, in combination with one or more inlets. Such pre-mixing chamber avoids generation of variations in composition that, like waves, are damped out merely slowly. Rather than implementing a premixing chamber outside the closed circuit, such a pre-mixing chamber is in one embodiment arranged within the closed circuit, for instance upstream of the evaporator, more particularly in the low temperature domain.

Furthermore, it is foreseen that the heat pump of the invention is further provided with one or more sensors and a controller. The controller is configured for control of the operation of the heat pump, such as the liquid level in the absorber, the temperature in the absorber, as arranged by the flow rate of heat exchanging medium etc. Furthermore, the controller may be arranged to control inflow of fresh refrigerant and/or fresh solvent. Typical sensors that are envisaged are pressure sensors, temperature sensors, flow sensors and/or pH sensors.

While the invention has been elucidated with reference to water as a solvent, it is not excluded that another solvent or a mixture of solvents is used as the solvent. For instance, water could be mixed with methanol, ethanol or the like. Also, salts could be added into the water to achieve a background level of salt concentration, and/or predefine a pH level. The latter is however suitably not too high, so as to avoid unexpected crystallization in the course of time.

Example

Several cases for the system presented in figure 1 are simulated using a medium with only water and NH3 and a medium with water, NH3 and C02. The thermodynamic properties of the mixture are calculated with the extended UNIQUAC activity coefficient method for the liquid phase and the Soave-Redlich-Kwong equation of state for the vapor phase. The code for this method was developed as an extension to Aspen Plus. When a limited amount of C02 is added to the ammonia water mixture the COP of the cycle increases when sufficient amounts of ammonia are present so that the C02 can fully react with the ammonia and water in the liquid phase. Then the cycle does not only benefits from the heat of absorption as in the case with an ammonia water mixture but additionally the heat of reactions. The increase in COP for the cases is approximately 5-10 %. In contrast to the ammonia water mixture results have not been fully optimized for the NH3 - H20 -C02 mixture and therefore the potential of the mixture are likely even more favorable than these first results. Additional benefits of the NH3 - H20 - C02 mixture is that the pressure ratio for each case decreases which results in less stages needed for the compression.

Claims

A method for pumping heat from an incoming stream to an outgoing stream, comprising the steps of: exchanging heat between the incoming stream with a circulating stream comprising a coolant; Evaporating at least a portion of the circulating stream to obtain a vapor stream and an - at least primary liquid stream; Compressing the vapor stream (compression); Adding the compressed vapor stream and the liquid stream to an absorption unit; Operating the absorption unit to provide an enriched liquid stream; Passing on the heat from the absorption unit to the outgoing stream, and Moving the enriched liquid stream for reuse as a circulating stream, wherein the circulating stream contains a first and a second refrigerant, and in which the first and the second refrigerant are dissolved in the absorption unit and react with each other to provide heat.

The method of claim 1, wherein the first coolant is an acid source and the second coolant is a base source.

The method of claim 2, wherein the first coolant is carbon dioxide and the second coolant ammonia, wherein the coolants react in the absorption unit, at least in part, to positively charged ammonium ions and negatively charged bicarbonate, carbonate and / or carbamate ions .

A method according to claims 1-3, wherein the first coolant is used at a level of 30-65 weight percent and the second coolant is used at a level of 5-40 weight percent, and wherein the solvent is present at a level of 30-65 weight percent 65% by weight, which percentages relate to the total amount of coolant and solvent added to the heat pump.

A method according to claims 1-4, wherein a diluted vapor stream is brought outside the absorption unit and added to the circulating stream at a pressure that is lowered with respect to the pressure in the absorption unit.

The method of claims 1-5, further comprising controlling the pH of the reaction mixture in the absorption unit.

A method according to claims 1-6, wherein the circulating stream is exchanged with the incoming stream when the circulating stream is within an evaporator for evaporation to the vapor stream and the liquid stream.

Method according to claims 1-7, wherein the heat pump according to claims 9-23 is used.

A heat pump comprising a closed circuit for flowing a solvent and a coolant, said closed circuit comprising an evaporator and an absorption unit which are interconnected by a first line adapted for transporting vapor from the evaporator to the absorption unit , a second line adapted for transporting a mainly liquid stream from the evaporator to the absorption unit, and a third line adapted for transporting an enriched liquid stream from the absorption unit to the evaporator, the evaporator usually in heat exchange with a incoming stream, so heat is transferred to the evaporator and the enriched liquid is brought into heat exchange with an outgoing stream to transfer heat there, particularly at high pressure, with a compressor placed in the first line and an expansion unit is placed in the third line, and wherein an inlet for a first refrigerant and an i are provided for a second coolant and are arranged for supplying a first and a second coolant.

A heat pump comprising a closed circuit for flowing a solvent and a coolant, said closed circuit comprising an evaporator and an absorption unit which are interconnected by a first line adapted for transporting vapor from the evaporator to the absorption unit , a second line adapted for transporting a mainly liquid stream from the evaporator to the absorption unit, and a third line adapted for transporting an enriched liquid stream from the absorption unit to the evaporator, the evaporator usually in heat exchange with a incoming stream, so heat is transferred to the evaporator and the enriched liquid is brought into heat exchange with an outgoing stream to transfer heat there, particularly at high pressure, with a compressor placed in the first line and an expansion unit is placed in the third line, the absorption unit having a first one outlet to the third line and from a second outlet to a fourth line, which second outlet and which fourth line are adapted for vapor transport back to the evaporator; The absorption unit and the evaporator each have a first inlet for a substantially liquid flow and a second inlet for the vapor flow, and are arranged such that vapor and liquid flow in counter-flow with each other.

A heat pump according to claim 9 or 10, wherein at least one of the absorption unit and the evaporator is designed as a column, preferably as a bubbling column.

A heat pump according to claims 9-11, wherein the absorption unit comprises a column with a heat exchanger for heat exchange with the outgoing stream, wherein liquid leaving the column is returned to a top of the same column.

A heat pump according to claim 12, wherein the absorption unit comprises a first and a second column, each with a heat exchanger and with means for returning liquid from an outlet to a top of the same column.

A heat pump according to claim 12 or 13, wherein the heat exchanger is designed as a plurality of heat exchange tubes.

The heat exchanger according to claim 14, wherein the heat exchange tubes are arranged horizontally.

16. Heat pump as claimed in any of the foregoing claims 9-15, wherein the compressor is provided with an inlet for a lubricant, which lubricant is added via a further line and wherein said further line is tapped from the second line or the third line .

The heat pump according to any of the preceding claims 9-16, further comprising at least one solvent and / or coolant inlet.

A heat pump according to claim 17, wherein an inlet for a first cooling means and an inlet for a second cooling means are present and are adapted for supplying a first and a second cooling means.

A heat pump according to claim 18, wherein the first coolant is a source of base, preferably ammonia, and wherein the second coolant is an acid source, preferably carbon dioxide.

A heat pump according to any of the preceding claims 9-19, further comprising at least one sensor and a controller suitable for controlling the heat pump based on an input from the at least one sensor.

The heat pump of claim 20, wherein the sensor is a pH sensor.

The heat pump of claim 21, further comprising a means for supplying a base or an acid to adjust the pH value in at least a portion of the heat pump during use.

A heat pump according to any one of the preceding claims 9-22, wherein a pressure-reducing valve is present in the fourth line.

Use of the heat pump according to any of claims 9-23 for pumping heat from an incoming stream at a first temperature to an outgoing stream at a second temperature.

The use of claim 24, wherein the second temperature is in the range of 100-150 ° C.

The use according to claim 24 or 25, wherein the first temperature is in the range of 50-100 ° C, and wherein the second temperature is higher than the first temperature.

The use according to any of claims 24-26, wherein the heat pump is operated with a first coolant, a second coolant and a solvent.

The use of claim 27, wherein the first coolant is ammonia and the second coolant is carbon dioxide, and wherein the solvent is or contains water.

Use according to claim 27 or 28, wherein the first coolant is used at a level of 30-65 weight percent, the second coolant at a level of 5-40 weight percent and the solvent at a level of 30-65 weight percent, which percentages relate to to the total amount of solvent and coolant that is supplied to the heat pump.

A method for pumping heat from an incoming stream to an outgoing stream, comprising the steps of: exchanging heat between the incoming stream with a circulating stream comprising a coolant; Supplying a diluted vapor stream to the circulating stream; Evaporating at least a portion of the circulating stream to obtain a vapor stream and an - at least primary liquid stream; Compressing the vapor stream (compression) Adding the compressed vapor stream and the liquid stream to an absorption unit; Operating the absorption unit with vapor and liquid flowing in counter-flow with each other, resulting in an enriched liquid stream for use as a circulating stream and diluted stream; Passing on the heat from the absorption unit to the outgoing stream, and Moving the diluted stream and the circulating stream for reuse.

The method of claim 30, wherein the heat pump of claims 9-23 is used.