WO2023065031A1

WO2023065031A1 - Falling film evaporator system and method

Info

Publication number: WO2023065031A1
Application number: PCT/CA2022/051544
Authority: WO
Inventors: Colin DARCEL; Peter Palumbo; Lucas PALUMBO
Original assignee: Maratek Environmental Inc.
Priority date: 2021-10-19
Filing date: 2022-10-19
Publication date: 2023-04-27

Abstract

A falling film evaporator system includes falling film evaporator for separating solvent from a feed stream, a condenser for condensing and recovering the separated solvent, and a heat pump subsystem for transferring heat recovered from the condenser to the falling film evaporator.

Description

FALLING FILM EVAPORATOR SYSTEM AND METHOD

CROSS REFERENCE TO PRIOR APPLICATIONS

[0001] The present application claims priority to United States Application No. 63/257,472, filed October 19, 2021. The content of such prior application is incorporated herein by reference as if set forth in its entirety.

FIELD OF THE DESCRIPTION

[0002] The present description generally relates to systems and methods used in solvent extraction and recovery processes. More particularly, the description relates to a system integrating a falling film evaporator system to incorporate one or more heat pump sub-systems to improve energy efficiency.

BACKGROUND

[0003] Solvent extraction processes are commonly known, wherein solvents, typically comprising volatile alcohols or hydrocarbons, are used to extract desired components. One example where such processes are used is in the extraction of oils, resins, and/or other such components from plant or other organic material. In such processes, the organic material is first crushed and mixed with a suitable solvent (which may comprise one solvent or a solvent mixture) to enable the desired components from the organic material to be solubilized in the solvent. The solvent mixture is then drawn out and directed to an evaporator unit, wherein the mixture is heated in order to boil off the volatile solvent thereby leaving the extracted components as a concentrate. Such a process is often used for the extraction of oils and/or cannabinoids from cannabis plant material. In such case, a suitable solvent has been found to be ethanol.

[0004] Falling film evaporators are commonly used in both small-scale and large-scale solvent extraction applications for the separation of solvent from the oil phase. As known in the art, falling film evaporators generally comprise a plurality of tubes, which, in most instances, are vertically arranged within a chamber. A fluid to be separated is introduced to the tops of the tubes and allowed to flow as a film there-through. A heating medium, such as steam or the like, is introduced into the chamber so as to heat the tubes. Consequently, the volatile components, namely the solvent, of the liquid mixture is evaporated. Upon exiting the chamber, the evaporated solvent and remaining liquid components are separated. The separated solvent is then passed through a condenser to produce the solvent in liquid form, which can then be recycled for later use.

[0005] Typical falling film evaporator systems utilize a heating unit to heat the heating medium for the evaporation process and a cooling unit for the condensation process, which results in an energy intensive process. Attempts have been made to reduce the energy burden of such evaporator systems. One example is provided in US Patent No. 10,899,728, which comprises a heat exchanger for transferring heat from solvent recovered from a falling film evaporator to preheat an incoming liquid mixture.

[0006] There is a need for a more energy efficient falling film evaporator system that has a reduced need for external energy input.

SUMMARY OF THE DESCRIPTION

[0007] In one aspect, there is provided a falling film evaporator system comprising:

[0008] - a falling film evaporator having a feed inlet, a feed outlet, a heating fluid inlet, and a heating fluid outlet;

[0009] - a solvent condenser having a feed inlet, a feed outlet, a cooling fluid inlet and a cooling fluid outlet; and,

[0010] - a heat pump subsystem comprising:

[0011] - an evaporator unit in fluid communication with the solvent condenser through a first heat transfer fluid circuit, the evaporator unit serving to extract heat from the cooling fluid after exiting the solvent condenser;

[0012] - a condenser unit in fluid communication with the falling film evaporator through a second heat transfer fluid circuit, the condenser unit serving to heat the heating fluid entering the falling film evaporator;

[0013] - a refrigerant circuit for flowing a refrigerant between the condenser unit and the evaporator unit, the refrigerant circuit including a compressor for pressurizing the refrigerant, and, an expansion valve for depressurizing the refrigerant, whereby the refrigerant circuit transfers heat from the evaporator unit to the condenser unit. [0014] In another aspect, there is provided a method of operating a falling film evaporator system, for recovering solvent from a solvent extraction process, the method comprising:

[0015] - providing a feed to the falling film evaporator system, wherein the feed comprises a mixture of solvent and extracted compounds resulting from the solvent extraction process, and wherein the falling film evaporator system comprises:

[0016] - a falling film evaporator having a feed inlet, a feed outlet, a heating fluid inlet, and a heating fluid outlet;

[0017] - a solvent condenser having a feed inlet, a feed outlet, a cooling fluid inlet and a cooling fluid outlet; and,

[0018] - a heat pump subsystem comprising:

[0019] - an evaporator unit in fluid communication with the solvent condenser through a first heat transfer fluid circuit, the evaporator unit serving to extract heat from the cooling fluid after exiting the solvent condenser;

[0020] - a condenser unit in fluid communication with the falling film evaporator through a second heat transfer fluid circuit, the condenser unit serving to heat the heating fluid entering the falling film evaporator;

[0021] - a refrigerant circuit for flowing a refrigerant between the condenser unit and the evaporator unit, the refrigerant circuit including a compressor for pressurizing the refrigerant, and, an expansion valve for depressurizing the refrigerant, whereby the refrigerant circuit transfers heat from the evaporator unit to the condenser unit;

[0022] - extracting heat from the solvent condenser with the first heat transfer fluid;

[0023] - transferring, with the heat pump subsystem, heat from the first heat transfer fluid to the second heat transfer fluid;

[0024] - heating the falling film evaporator with the heated second heat transfer fluid. BRIEF DESCRIPTION OF THE FIGURES

[0025] The features of certain embodiments will become more apparent in the following detailed description in which reference is made to the appended figures wherein:

[0026] Fig. 1 is a schematic illustration of a known falling film evaporator system.

[0027] Fig. 2 is a schematic illustration of a falling film evaporator system according to an aspect of the description.

[0028] Fig. 3 is a schematic illustration of a heat pump illustrated Fig. 2 according to an aspect of the description.

DETAILED DESCRIPTION

[0029] For the purpose of the present description, the term “oil” will be used to describe the organic components extracted using a solvent extraction process. As indicated above, the solvent extraction step is utilized to extract oils or other desired components from organic matter. The term “oil” as used in such context will be understood to mean an oil or some oilcontaining mixture that is desired to be extracted from organic matter. The term “oil” is not intended to be limiting in any way of the scope of the present description.

[0030] The term “solvent” as used herein will be understood to mean any solvent or mixture of solvents that can serve the purpose of extracting desired components, generally hydrophobic components, from organic matter in a solvent extraction process. Various solvents, such as alcohols, or other volatile hydrocarbons, will be known to persons skilled in the art. The present description is not limited to any particular solvent.

[0031] As used herein, the terms “comprise”, “comprises”, “comprised” or “comprising” may be used in the present description. As used herein (including the specification and/or the claims), these terms are to be interpreted as open-ended terms and as specifying the presence of the stated features, integers, steps or components, but not as precluding the presence of one or more other feature, integer, step, component or a group thereof as would be apparent to persons having ordinary skill in the relevant art. Thus, the term "comprising" as used in this specification means "consisting at least in part of”. When interpreting statements in this specification that include that term, the features, prefaced by that term in each statement, all need to be present but other features can also be present. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner.

[0032] The phrase “consisting essentially of’ or “consists essentially of” will be understood as generally closed terms, with the exception of allowing inclusion of additional items, materials, components, steps, or elements, that do not materially affect the basic and novel characteristics or function of the item(s) used in connection therewith. When using an open-ended term, such as “comprising” or “including”, it will be understood that direct support should be afforded also to “consisting essentially of’ language as well as “consisting of’ language as if stated explicitly and vice versa. In essence, use of one of these terms in the specification provides support for all of the others.

[0033] The term "and/or" can mean "and" or "or".

[0034] Unless stated otherwise herein, the articles “a” and “the”, when used to identify an element, are not intended to constitute a limitation of just one and will, instead, be understood to mean “at least one” or “one or more”.

[0035] Fig. 1 , as indicated above, illustrates a falling film evaporator system as generally known in the art. As illustrated, the system 10 comprises a falling film evaporator (FFE) 12, which is typically vertically oriented. A feed stream 14 is introduced into the FFE 12, generally at an upper end thereof. The feed stream 14 may be an effluent of a solvent extraction process and would comprise a fluid mixture of the solvent and extracted oil (as described above). A heating fluid 16 is introduced into the FFE 12 and serves to heat the feed stream that is introduced into the FFE. As known in the art, and as discussed above, the heating fluid 16 is passed through the interior of the FFE 12 vessel, while the feed stream 14 is passed through tubing contained within such vessel. In this arrangement, the heat from heating fluid 16 is transferred to the stream within the FFE. In the result, the heating fluid condenses to form a condensate 18, which is then removed from the FFE 12.

[0036] The heat from the heating fluid 16 transferred to the feed stream 14 results in partial or complete evaporation of the solvent component within the feed, whereby the effluent 20 from the FFE 12 comprises a mixture of solvent vapour and oil, which is separated into a liquid oil stream 22 and a vapour stream 24. The liquid oil component 22 is conveyed (such as by pumping, gravity, or any other means) to a receiving vessel or tank etc. (not shown). The vapour component 24 may be further processed by conveying (such as by venting, pumping, or any other means) the vapour stream to a vapour/liquid separator 26, where the vapour stream 24 is subjected to a further separation process to extract any residual oil. The resulting oil 28 may be combined with the oil 22, as illustrated. The further purified vapour 30 may be diverted to a solvent condenser 32 to provide a liquified solvent 34, which may be stored or recycled as needed.

[0037] As discussed above, in conventional or known falling film evaporation systems, such as shown in Fig. 1 , two separate systems are used, one for heating the FFE 12 and one for cooling the solvent condenser 32. Consequently, energy is input into the system to heat the evaporator and further energy is input to remove such heat at the condenser, with such heat being released the environment.

[0038] Fig. 2 illustrates an aspect of the present description that provides at least some energy demand mitigation over known systems. Elements in Fig. 2 that are similar to those described in Fig. 1 are identified with similar reference numerals but with the prefix “1” added for clarity. As illustrated, Fig. 2 depicts a system 110 comprising a falling film evaporator (FFE) 112 to which is supplied a heating fluid 116, which, after heating, results in a condensate 118. The effluent stream 120 from the FFE 112 is directed into a vapour/liquid separator 125, where the stream 120 (comprising solvent vapour and oil) is separated into a liquid oil stream 122 and a vapour stream 124. The separator 125 may be any known separator such as a centrifugal separator etc. In one aspect, the vapour stream 124 from the separator 125 may optionally, or preferably, be subjected to a further vapour/liquid separation in separator 126 thereby resulting in a further residual oil stream 128. As will be understood, such two-stage separation may not be needed in all circumstances, in which case separator 126 would not be needed.

[0039] The purified vapour 130 (or 124 if optional separator 126 is not present) is introduced into a solvent condenser 132 to condense the solvent into stream 134 that is conveyed to a storage tank or the like 208.

[0040] Optionally, and as shown in Fig. 2, the solvent stream 134 exiting the condenser 132 may be further subjected to a vacuum separation process in a tank 200, wherein a vacuum pump 202 serves to create a vacuum environment to reduce the solvent’s boiling point. A vapour product 204 from such process may be vented and the remaining liquid solvent 206 pumped to the tank or the like 208. A pump 210 may be used for this purpose. [0041] The extracted oil streams 122 and 128 are combined into stream 212, which may then be conveyed, such as by means of a pump 214, to a tank 216 or other such container.

[0042] A feature of the present description is an integrated heat pump 300, which forms a part of the system described herein. In general, the heat pump 300 serves to move heat from condensing vapour in the solvent condenser 132 and to transfer such heat to the FFE 112. As illustrated in Fig. 2, the heat pump 300 comprises a condenser unit 310 and an evaporator unit 312, which are associated, respectively, with the FFE 112 and the solvent condenser 132. These components of the heat pump 300 are connected to the components of the falling film evaporator system by means of fluid transfer lines, which are discussed further below.

[0043] As illustrated in Fig. 2, the evaporator unit 312 of the heat pump 300 is connected to a first heat transfer fluid line 314, which circulates a first heat transfer fluid between the heat pump 300 and the solvent condenser 132. As shown, the first heat transfer fluid within the first fluid line 314 circulates through the solvent condenser 132. As would be understood, the first heat transfer fluid within the first fluid line 314 would enter the solvent condenser 132 at a first temperature sufficient to cool and thereby absorb heat from the hot solvent vapour 130 exiting the falling film evaporator 112. In the result, the first heat transfer fluid is heated to a second temperature as it circulates through the solvent condenser 132 and exits with the absorbed heat. The first heat transfer fluid, thus heated, is then directed to enter the evaporator unit 312 of the heat pump 300 where, as discussed below, the absorbed heat is removed, thereby cooling the first heat transfer fluid and reducing its temperature prior to being circulated back to the solvent condenser 132. In one example, the first temperature of the first heat transfer fluid as it enters the solvent condenser 132, at a flow rate of 45 U.S. gal/min, may be 40°F and its second temperature, as it exits the solvent condenser 132, may be 50°F. It will be appreciated that these temperatures are only provided by way of example and will vary based on the fluid flow rate, size of equipment, and desired heat load to be absorbed.

[0044] The condenser unit 310 of the heat pump 300 is connected to a second heat transfer fluid line 316, which circulates a second heat transfer fluid between the condenser unit 310 and the FFE 112. As shown, the condenser unit 310 comprises an outlet connected to second heat transfer fluid line 316 that is in fluid communication with the heated fluid line 116 for supplying heat to the FFE 112. The second heat transfer fluid line 316 is also in fluid communication with the condensate line 118 connected to the FFE 112. The second heat transfer fluid enters the FFE 112 through the second fluid transfer line 316 and heated fluid line 116 at a first, heated temperature. As would be understood, the temperature of the second heat transfer fluid entering the FFE 112 would be at a temperature sufficient to heat and vaporize the solvent in the feed 114 entering the FFE 112. In this way, the heat energy of the second heat transfer fluid is transferred to the feed stream flowing through the FFE 112 and, consequently, the temperature of the second heat transfer fluid is reduced from the first temperature to a second temperature after which it exits the FFE through condensate stream 118. The cooled second heat transfer fluid is then returned to the condenser unit 310 by means of second fluid transfer line 316. In one example, at a flow rate of 45 U.S. gal/min, the first temperature of the second heat transfer fluid, as it enters the FFE 112, may be 140°F, and its cooled temperature, as it exits the FFE 112, may be 130°F. As noted above, these temperatures and flow rates are intended to be examples and would vary based on the specific system design parameters.

[0045] As illustrated in Fig. 3, the components of the heat pump 300 are illustrated. As shown, the evaporator unit 312 of the heat pump 300 is fluidly connected to the solvent condenser 132, by means of first heat transfer fluid line 314. In addition, the condenser unit 310 of the heat pump 300 is fluidly connected to the FFE 112 by means of second heat transfer fluid line 316. As shown in Fig. 3, a refrigerant fluid line 318 connects the evaporator unit 312 and the condenser unit 310 for transferring heat from one to the other. The refrigerant fluid line 318 further includes a compressor 320 and an expansion valve 322.

[0046] In operation, the compressor 320 pressurizes the refrigerant in fluid line 318, thereby heating such fluid. The pressurized and heated fluid is conveyed by fluid line 318 to the condenser unit 310 which transfers the heat from the refrigerant to the first heat transfer fluid in fluid line 316. As discussed above, the heated first heat transfer fluid is flowed to the FFE 112, where heat is transferred to the incoming feed 114. The heat transfer fluid is then returned to the condenser unit 310. In this way the refrigerant flowing in refrigerant line 318 experiences a net loss of heat energy as it flows through condenser unit 310. In a preferred aspect, the refrigerant entering the condenser unit 310 is in gas form and exits the condenser unit 310 in liquid form after transferring its heat energy to the FFE 112.

[0047] The refrigerant is then conveyed to the expansion valve 322 to reduce the pressure of the refrigerant. At this stage, the refrigerant is converted to its gaseous state. Following the expansion valve, the refrigerant is transferred to the evaporator unit 312, where the refrigerant absorbs heat from the second heat transfer fluid line 314 connected to the solvent condenser 132. The now heated refrigerant is circulated back to the compressor 320.

[0048] As will be understood, the refrigerant line 318, the first heat transfer fluid line 314 and the second heat transfer fluid line 316 are separate fluid circuits and, therefore, would comprise the same or different fluids for performing the heat transfer operations discussed above. For example, the refrigerant, as noted above, is preferably reversibly convertible from a gas to a liquid based pressure variation. In this regard, the refrigerant can comprise any known fluid, such as, but not limited to, fluorocarbons (including chlorofluorocarbons, hydrochlorofluorocarbons, fluorocarbons), hydrocarbons, ammonia, carbon dioxide, etc.

[0049] Similarly, the first and second heat transfer fluids may be the same or different and may comprise any known fluid for conveying heat. Such heat transfer fluid may, for example, comprise water, glycol, oil, etc. The present description is not limited to any specific refrigerant or heat transfer fluid.

[0050] As would be understood, upon start up of the aforementioned FFE system, heat must be initially provided to bring the FFE to the required temperature. For this stage, and in one aspect, the heat pump 300 would initially be started and simultaneously a separate heater 325 may be used to heat one or more of the heat transfer fluids to a level sufficient for functioning of the FFE. In one aspect, as discovered by the present inventors, the heater is preferably used to heat the heat transfer fluid 314 that is introduced into solvent condenser 132. As the heat pump runs without solvent feed 114 to the falling film system, the second heat transfer heating loop 316 will therefore increase in temperature as the added heat (from the heater 325) is not absorbed by the incoming feed. Once the second heat transfer loop 316 has reached a sufficient operating temperature to boil solvent, feed is then introduced to the FFE and the heater is switched off. From there, the heat pump system 300 would be sufficient to run without the addition of external heat. While this additional heating method has been found by the inventors to be best suited for the present system, it would be understood that the separate heater 325 may also be used to heat the second heat transfer fluid 316, or both fluids 314 and 316. It will be appreciated that the heater 325 may comprise any heat source, or equipment that is suitable for heating a fluid, including but not limited an electric heating element, a fuel powered heating system, or the like. The present description is not limited to any particular heater. It will also be understood that the actuation of the heater 325 may be controlled by a temperature sensor, whereby the heater 325 is activated when the temperature of either the first heat transfer fluid 314 or second heat transfer fluid 316 is below a predetermined threshold value. This situation would arise, for example, upon start up of the system. Once the temperature sensor registers that the threshold value has been reached, i.e., the fluids in the system have reached the desired or required temperatures, a controller would then automatically switch off the heater.

[0051] As would be understood, during normal operation, the heat pump 300 may generate more heat than it absorbs from the condenser heat transfer loop 314, if this is not managed the heating side of the heat pump 300 will continue to increase in temperature unit the heat pump is forced to shut down because of excessively high discharge pressure from the compressor 320. To mitigate against this possibility, a temperature monitoring and control subsystem may be incorporated into the system described above. This is illustrated in Fig. 2, where a bypass line 324 is shown for diverting a portion of the second heat transfer fluid 316 prior to such fluid entering the FFE 112. The bypass line 324 includes a cooling unit 326, which serves to cool the second heat transfer fluid flowing in fluid line 316, and therefore the heat pump. The cooling unit 326 may comprise any cooling system as would be known to persons skilled in the art, such as a fan cooled heat exchanger, an air radiator, or a refrigerating device. As would be appreciated, the bypass line 324 would be provided with one or more of temperature sensors, flow control valves, flow meters, and other control devices to allow an operator to monitor and control the system as necessary. For example, in one aspect a temperature sensor may be provided for monitoring the temperature of the fluid flowing in the second heat transfer fluid line 316 prior to entering the FFE 112. If the temperature of the second heat transfer fluid exceeds a pre-determined threshold value, as measured for example by the temperature monitor, a control circuit may be programmed to open a valve allowing at least a portion of the second heat transfer fluid to flow into bypass line 324 and thus be cooled by the cooling unit 326. The fluid, thus cooled, would then be reintroduced to the condenser unit 310 as shown in Fig. 2.

[0052] As would be understood from the foregoing, the heat pump 300 system discussed above effectively moves heat from the solvent condenser 132 to the FFE 112 thereby reducing or eliminating the need to generate heat externally to heat the falling film evaporator. Integration of a heat pump 300 into a falling film evaporator system 110 therefore aids in reducing the total energy consumption of the system as well as the amount of heat energy exhausted compared to conventional systems.

[0053] Although the above description includes reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art. Any examples provided herein are included solely for the purpose of illustration and are not intended to be limiting in any way. Any drawings provided herein are solely for the purpose of illustrating various aspects of the description and are not intended to be drawn to scale or to be limiting in any way. The scope of the claims appended hereto should not be limited by the preferred embodiments set forth in the above description, but should be given the broadest interpretation consistent with the present specification as a whole. The disclosures of all prior art recited herein are incorporated herein by reference in their entirety.

Claims

WE CLAIM:

1 . A falling film evaporator system comprising:

- a falling film evaporator having a feed inlet, a feed outlet, a heating fluid inlet, and a heating fluid outlet;

- a solvent condenser having a feed inlet, a feed outlet, a cooling fluid inlet and a cooling fluid outlet; and,

- a heat pump subsystem comprising:

- an evaporator unit in fluid communication with the solvent condenser through a first heat transfer fluid circuit, the evaporator unit serving to extract heat from the cooling fluid after exiting the solvent condenser;

- a condenser unit in fluid communication with the falling film evaporator through a second heat transfer fluid circuit, the condenser unit serving to heat the heating fluid entering the falling film evaporator;

- a refrigerant circuit for flowing a refrigerant between the condenser unit and the evaporator unit, the refrigerant circuit including a compressor for pressurizing the refrigerant, and, an expansion valve for depressurizing the refrigerant, whereby the refrigerant circuit transfers heat from the evaporator unit to the condenser unit.

2. The falling film evaporator system of claim 1 , wherein the heat pump subsystem further comprises a fluid bypass connected to the second heat transfer fluid circuit, the fluid bypass including a cooling unit, whereby the temperature of the second heat transfer fluid may be reduced.

3. The falling film evaporator system of claim 2 further comprising a temperature sensor provided on the second heat transfer fluid circuit for monitoring the temperature of the second heat transfer fluid.

4. The falling film evaporator system of claim 2 or 3 further comprising a bypass flow control system for opening the fluid bypass upon the temperature of the second heat transfer fluid reaching a threshold, whereby at least a portion of the fluid in the second heat transfer fluid circuit flows through the fluid bypass, through the cooling unit, and directly returned to condenser unit.

5. The falling film evaporator system of any one of claims 1 to 4, further comprising a heater to heat the first heat transfer fluid and/or the second heat transfer fluid.

6. The falling film evaporator system of claim 5, wherein the heater heats the first heat transfer fluid, and wherein the heater is provided between the evaporator unit of the heat pump subsystem and the solvent condenser.

7. The falling film evaporator system of claim 5 or 6, wherein the heater is controlled by a controller, whereby the heater is activated when the temperature of the first heat transfer fluid and/or the second heat transfer fluid falls below a threshold value.

8. The falling film evaporator system of claim 7, wherein one or more temperature sensors are provided on the first heat transfer fluid circuit and/or the second heat transfer fluid circuit.

9. A method of operating a falling film evaporator system, for recovering solvent from a solvent extraction process, the method comprising:

- providing a feed to the falling film evaporator system, wherein the feed comprises a mixture of solvent and extracted compounds resulting from the solvent extraction process, and wherein the falling film evaporator system comprises:

- a heat pump subsystem comprising:

- a refrigerant circuit for flowing a refrigerant between the condenser unit and the evaporator unit, the refrigerant circuit including a compressor for pressurizing the refrigerant, and, an expansion valve for depressurizing the refrigerant, whereby the refrigerant circuit transfers heat from the evaporator unit to the condenser unit;

- extracting heat from the solvent condenser with the first heat transfer fluid;

- transferring, with the heat pump subsystem, heat from the first heat transfer fluid to the second heat transfer fluid;

- heating the falling film evaporator with the heated second heat transfer fluid.

10. The method of claim 9, further comprising monitoring the temperature of the second heat transfer fluid.

11 . The method of claim 10, wherein, upon the temperature of the second heat transfer fluid reaching a threshold value, the method comprises diverting at least a portion of the second heat transfer fluid to a bypass circuit and a cooling unit prior to entering the falling film evaporator.

12. The method of claim 11 , wherein the bypass circuit returns the at least a portion of the second heat transfer fluid to the condenser unit of the heat pump subsystem.

13. The method of claim 11 or 12, wherein the bypass circuit is opened automatically.

14. The method of any one of claims 9 to 13, further comprising a heater for heating the first heat transfer fluid and/or second heat transfer fluid.

15. The method of claim 14, wherein the heater heats the first heat transfer fluid, and wherein the heater is provided between the evaporator unit of the heat pump subsystem and the solvent condenser.

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