DESCRIPTION

Technical field of the invention

The present invention pertains to the field of energy conversion plants and, specifically, concerns a plant that can be reversibly used according to two alternative operational modes. The first mode entails operation as a co-tri-generation plant, supplying the end-user with electrical/mechanical power and simultaneously heating power and/or cooling power by converting thermal power derived from any type of heat source (renewable or non-renewable). The second mode involves operation as a high- temperature heat pump, supplying the end-user with high-temperature heating power by converting thermal power at low-to-medium temperature derived from the aforementioned heat source, and without any electrical/mechanical power supplied from an external source.

Background of the invention

Italian patent no. 102016000027735, issued in the name of the present applicant and to be considered fully incorporated herein by reference, describes a plant for supplying the end-user simultaneously with electrical and/or mechanical power, heating power, and cooling power (in the operational sub-mode referred to as "Heating-Cooling" or CCHP), or simultaneously with electrical and/or mechanical power and heating power (in the operational sub-mode referred to as "Heating" or CHP), or simultaneously with electrical and/or mechanical power and cooling power (in the operational sub-mode referred to as "Cooling" or CCP), by converting thermal power derived from any type of heat source (including traditional sources such as gas, petroleum derivatives, coal, and renewable sources such as biomass, solar, geothermal).

The operation of the plant, according to each of the aforementioned three operational sub-modes, is accomplished by controlling and regulating several on-off valves and a fluid flow control/regulation valve. The unique configuration of the plant, implementing two-phase fluid expanders and compressors, enables supplying the enduser with the requested mechanical and/or electrical power, heating power, and/or cooling power through the regulation of several process parameters. In particular, this supply is achieved with significantly greater flexibility, compared to previously commercialized CCHP plants and to similar plants operating with two-phase fluid expanders and/or compressors as described in the prior art, as the plant under consideration allows supplying the end-user with the requested values of electrical and/or mechanical power, heating power, and/or cooling power within respective broader ranges (broadness understood both in terms of power values and in terms of corresponding temperature values for the heating and cooling powers requested by the end-user), without deficit or surplus in any of the aforementioned powers. Furthermore, the plant under consideration enables the attainment of high thermodynamic performance.

The prior art also involves heat pumps for supplying the end-user with heating power. Heat pumps currently available in the market are classified into the following two types:

1) Compression: they use thermal power at low-to-medium temperature derived from the heat source and mechanical (or electrical) power supplied from an external source.

2) Absorption: they use low-temperature thermal power (derived from a first heat source), medium-temperature thermal power (derived from a second heat source), and very modest mechanical or electrical power supplied from an external source.

In particular, high-temperature heat pumps provide heating power to the end-user at temperatures exceeding 100 °C. Such heating requirements are typical in industries such as chemical, mining, food, metallurgical, textile, etc.

Heat pumps for the supply of thermal power in the temperature range T = 100 - 140 °C are in the prototyping phase, while in the range T = 140 - 180 °C, they are still in the laboratory research phase. Recent projects (such as the Free2Heat project funded by the Norwegian government) have explored the development of a heat pump capable of delivering heat up to 180 °C (the highest temperature value achieved worldwide using this technology), utilizing waste heat from industrial processes.

There are still known examples of empirically studied reversible plants [Dumont O, Quoilin S, Lemort V. Experimental investigation of a reversible heat pump organic Rankine cycle unit designed to be coupled with a passive house to get a Net Zero Energy Building, I nt. Journal of Refrigeration 54 (2015) 190-203], which would aim to operate according to the following two alternative operational modes:

1) Organic Rankine Cycle (ORC): this mode is used for electricity generation; 2) Heat Pump (HP): this mode is used for supplying the end-user with high- temperature heating power, being fed by electrical/mechanical power provided by an external source.

The reversible plant layout involves two heat exchangers, a circulation pump, and a single-phase fluid machine. From an operational perspective, in the operational mode of electricity production, the following processes can be distinguished: increase in pressure of the working fluid in liquid phase through the circulation pump operating unit; heat transfer from the heat source to the working fluid, occurring in the first heat exchanger (functioning as an evaporator); single-phase expansion for electricity generation taking place in the single-phase fluid machine (acting as a single-phase expander); heat transfer from the working fluid to the low-temperature heat source, occurring in the second heat exchanger (functioning as a condenser).

With the same reversible plant layout, but with the working fluid not circulating through the circulation pump operating unit (which is bypassed), but instead circuiting through a lamination valve arranged in parallel to the aforementioned pump, the operational mode of a heat pump can be realized, through the following processes: heat transfer from a low-temperature heat source to the working fluid, occurring in the aforementioned second heat exchanger (functioning as an evaporator); increase in pressure of the single-phase working fluid occurring in the abovementioned single-phase fluid machine (functioning as a single-phase compressor); high-temperature heat transfer from the working fluid to the end-user, taking place in the aforementioned first heat exchanger (functioning as a condenser); decrease in pressure of the working fluid, occurring in the abovementioned lamination valve.

In summary, in the reversible plant under consideration, the following operating units are used: one single-phase fluid machine, which operates as a single-phase compressor (in the HP operational mode) or as a single-phase expander (in the ORC operational mode); two heat exchangers, each capable of functioning for heat absorption (evaporator) or for heat transfer (condenser); one circulation pump that operates exclusively in the ORC operational mode, and finally, one lamination valve that operates exclusively in the HP operational mode. It follows that in the reversible plnat under consideration: i) some operating units work in one of the two operational modes while non work (namely they are bypassed) in the other operational mode. In other words, each operating unit does not work in both operational modes; ii) in the HP operational mode, the plant is fed by electrical/mechanical power provided by an external source to the single-phase fluid machine operating as a single-phase compressor; iii) adiabatic single-phase fluid machines are used, wherein the same machine is capable of working as a single-phase compressor (in the HP operational mode) or a single-phase expander (in the ORC operational mode).

Summary of the invention

Taking into consideration this state of the art, and in particular revealing a surprising potential of the co-tri-generation plant described in the aforementioned patent, the applicant has now arrived at an innovative solution that enriches the range of available plants. Through the same plant configuration, that simultaneously ensures a first operational mode as a co-tri-generation plant and, alternatively, a second operational mode as a high-temperature heat pump capable of working without electrical/mechanical power supplied from an external source. Consequently, unlike the aforementioned reversible plants currently present in the state of the art, in the reversible plant under consideration: i) each operating unit works in both operational modes; ii) in the HP operational mode, the plant is not fed by electrical/mechanical power provided by an external source; iii) adiabatic two-phase fluid machines are used, wherein each machine exclusively works as an adiabatic two-phase compressor to determine the pressure increase of the two-phase working fluid (via conversion of mechanical/electrical power) or exclusively works as an adiabatic two-phase expander to determine the pressure decrease of the two-phase working fluid (generating mechanical/electrical power). The plant and method according to the present invention has the essential features defined by the attached independent claims. Other significant secondary features are defined in the dependent claims.

Brief description of the drawings

The features and advantages of the plant and method according to the invention will become apparent from the following description of its embodiments, with reference to the attached drawings in which:

Figure 1 is a circuital scheme of a plant according to the invention;

Figures 2 and 3 depict the scheme of Figure 1 with functional indications referring respectively to the first operational mode (co-tri-generation plant) and the second operational mode (high-temperature heat pump system operating without electrical/mechanical power supplied from an external source);

Figures 4, 5a, and 5b are temperature - specific entropy qualitative diagrams representing the operation of the plant respectively in the first operational mode, i.e. , co- tri-generation plant (Figure 4), and in the second operational mode, i.e., high-temperature heat pump plant operating without electrical/mechanical power supplied from an external source (Figures 5a and 5b, referring to respective variations).

Detailed description of the invention

With reference to said figures, and particularly Figure 1, from the perspective of the overall layout, the plant according to the invention follows that of the plant known from Italian patent no. 102016000027735, to which reference is made, noting that in terms of nomenclature there is a correspondence among the three indicated circuits (Ci , C2, C3), while for the individual operating units updated indices are used, with a correspondence nevertheless readily reconstructible by an expert in the field, considering the use of standard symbols, which are not analytically expressed here.

Regarding the aforementioned known layout, however, in the illustrated embodiment, the addition of the following operating units must be noted (Figure 1):

In the first circuit Ci, operating units enclosed in the dashed box B, which consists of (first) spillover means of the working fluid flow (BI,Q) functionally associated with (first) adiabatic two-phase compression means (TCI.M) and (first) adiabatic two-phase expansion means (TEi.o) to promote the circulation of a portion of the working fluid flow between said (first) adiabatic two-phase compression means (TCI.M) and said (first) adiabatic two-phase expansion means (TEi.o) through interposed (first) connection means or through interposed (first) isobaric heat exchange means (HEI.N);

In the second circuit C2, operating units enclosed in the dashed box C, which consists of (second) isobaric thermal regeneration means (TR2,P) and (second) spillover means of the working fluid flow (62,0*), where TR2,P and 62,0* are functionally associated with (second) adiabatic two-phase compression means (TC ₂ ,M*) and (second) adiabatic two-phase expansion means (TE2,o*). In particular, TR2,P promote the heat transfer between the working fluid circulating downstream of at least one stage of the (second) adiabatic two-phase expansion means (TE2,o*) and the same working fluid circulating downstream of at least one stage of the (second) adiabatic two-phase compression means (TC ₂ ,M*). Furthermore, B2,Q* promote the circulation of a portion of the working fluid flow between said (second) adiabatic two-phase compression means (TC ₂ ,M*) and said (second) adiabatic two-phase expansion means (TE2,o*) through interposed (second) connection means or through interposed (third) isobaric heat exchange means (HES,N*).

For the first operational mode, as a co-tri-generation plant in the operational submodes of CCHP, or CHP, or CCP, reference can be made to that described for the previous plant and is explicitly illustrated by the schemes and diagrams in Figures 2 and 4.

In particular, this operational mode enables the simultaneous supply to the end-user of electrical power, heating power, and cooling power (“CCHP sub-mode”), or electrical power and heating power (“CHP sub-mode”), or electrical power and cooling power (“CCP sub-mode”) through the conversion of the thermal power provided by any heat source (renewable or non-renewable).

Compared to the layout of the plant known from Italian patent no. 102016000027735, the addition of the abovementioned operating units implies the following three modifications for the plant operating in the first operational mode (co-tri- generation plant).

The first modification (enclosed in box B in Figure 1) allows for the execution (Figure 2) of the extraction (in circuit Ci) of a portion of the working fluid flow from first adiabatic two-phase expansion means (TEi, ₂ in this case) through first spillover means (Bi,i in this case). This portion of the working fluid flow is then circulated to first adiabatic two-phase compression means (TCi,i in this case) through interposed first connection means or through interposed first isobaric heat exchange means (HEI , ₂ in this case). In particular (Figure 4), the portion of the working fluid flow is extracted from TEi, ₂ at intermediate section 5** and then circulates in HEi, ₂ to execute the supply of heating power to the enduser at the respective temperature value. The portion of the working fluid flow exiting HEi, ₂ (point 5***) enters TCi,i where it is isobarically mixed with the working fluid flow circulating therein (point 1*). In particular, the quality of the working fluid (i.e. , the ratio of vapor phase mass to two-phase fluid mass) at point 5*** is lower than the quality of the working fluid at point 1*. Due to said isobaric mixing, the overall working fluid flow (point 1** with lower quality compared to point 1*) undergoes the compression process 1** - 2 (in the same TCu). The first modification of the plant layout known from Italian patent no. 102016000027735 (described up to this point) implies several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) consists of reducing the mechanical power required in the compression process 1 - 1* (due to the decrease in the circulating working fluid flow rate) and further decreasing the mechanical power required in the compression processes 1** - 2 and 2* - 3 (due to the decrease in the specific enthalpy difference in the respective processes 1** - 2 and 2* - 3). The second effect (disadvantageous for the thermodynamic performance of the plant) consists of reducing the mechanical power produced in the expansion processes 5** - 6 and 7 - 8 (due to the decrease in the circulating working fluid flow rate) and increasing the thermal power supplied by the heat source to the working fluid in the transformation 3 - 4 at the same working fluid flow rate circulating in circuit Ci (due to the decrease in specific enthalpy at point 3). Under certain operating conditions, the first effect prevails over the second effect, resulting in an increase in the thermodynamic performance of the plant. Conversely, the first modification under consideration can be implemented according to the variant described below. In particular, the extraction of a portion of the working fluid flow is performed (in circuit Ci) from first adiabatic two-phase compression means (TCu in this case) through first spillover means (Bi ,1 in this case). This portion of the working fluid flow is then circulated to first adiabatic two-phase expansion means (TEI,2 in this case) through interposed first connection means or through interposed first isobaric heat exchange means (HEI ,2 in this case). In this variant, HEi, 2 allows the heat transfer from an additional heat source to the working fluid at the respective temperature value. Further details associated with the implementation of this variant are omitted for brevity, as they can be readily inferred by an expert in the field following the above description. Under certain operating conditions, the first modification (implemented according to the aforementioned variant) leads to an increase in the thermodynamic performance of the plant.

The second modification (enclosed in box C in Figure 1) allows the extraction (shown in Figure 2) of a portion of the working fluid flow from the second adiabatic two-phase expansion means (TE2,2 in this case) through the second spillover means (62,1 in this case) in the C2 circuit. This portion of the working fluid flow is then circulated to the second adiabatic two-phase compression means (TC2,I in this case) through interposed second connection means or through interposed third isobaric heat exchange means (HEs.i in this case). In particular (Figure 4), the portion of the working fluid flow is extracted from TE2.2 in the intermediate section 10** and then circulates in HEs.i (to provide cooling power to the end-user at the respective temperature value). The portion of the working fluid flow leaving HEs.i (point 10***) enters TC2,I where it is isobarically mixed with the working fluid flow circulating there (point 12*). In particular, the quality of the working fluid at point 10*** is lower than the quality at point 12*. Due to said isobaric mixing, the overall working fluid flow rate (point 12** with lower quality than point 12*) undergoes the compression process 12** - 13 (within the same TC2,I). The second modification to the plant layout as known from Italian patent no. 102016000027735 (described so far) entails several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) consists of a decrease in the mechanical power required in the compression process 12 - 12* (due to the decrease in the circulating working fluid flow rate) and a decrease in the mechanical power required in the compression processes 12** - 13 and 13* - 14 (due to the decrease in the specific enthalpy difference in the respective processes 12** - 13 and 13* - 14). The second effect (disadvantageous for the thermodynamic performance of the plant) consists of a decrease in the mechanical power produced in the expansion process 10** - 11 (due to the decrease in the circulating working fluid flow rate) and an increase in the mechanical power required in the compression process 12 - 12* at the same cooling power provided to the end-user in the process 11 - 12 (due to the increase in the specific enthalpy at point 12 resulting from the decrease in the circulating working fluid flow rate in the process 11 - 12). Under certain operating conditions, the first effect prevails over the second effect, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, the second modification under consideration can be implemented according to the variant described below. In particular, a portion of the working fluid flow is extracted (in the C2 circuit) from the second adiabatic two-phase compression means (TC ₂ ,I in this case) through the second spillover means (62,1 in this case). This portion of the working fluid flow is then circulated to the second adiabatic two-phase expansion means (TE2.2 in this case) through interposed second connection means or through interposed third heat exchange means (HEs.i in this case). In this variant, HEs allows the heat transfer (thermal power dissipation) from the working fluid to the external environment at the respective temperature value. Further details associated with the implementation of this variant are omitted for brevity, as they can be easily inferred by an expert in the field, similarly to the description provided above. Under certain operating conditions, the second modification (implemented according to the aforementioned variant) results in an increase in the thermodynamic performance of the plant.

The third modification already mentioned (enclosed in box C) allows for thermal regeneration in circuit C2. In fact, the working fluid on the hot side (13 - 13*) of the second isobaric thermal regeneration means (TR2,I in this case) transfers thermal power to the same working fluid on the cold side of TR2 (10 - 10*). The third modification of the plant layout known from Italian patent No. 102016000027735 (described so far) entails several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) involves a decrease in the mechanical power required in the compression process 13* - 14 (due to the decrease in the specific enthalpy difference in the same 13* - 14 process) and an increase in the mechanical power produced in the expansion process 10* - 11 (due to the increase in the specific enthalpy difference in the same 10* - 11 process). The second effect involves an increase in the circulating working fluid flow rate in circuit C2, necessary for supplying the end-user with the fixed cooling power (in the third isobaric heat exchange means HEs,2) (due to the decrease in the specific enthalpy difference in the aforementioned HE ₃ ,2 resulting from the increase in specific enthalpy in point 11). In turn, the increase in the circulating working fluid flow rate in circuit C2 leads to an increase in the overall mechanical power required by the second adiabatic two-phase compression means in C2 (disadvantageous effect for the thermodynamic performance of the plant) and an increase in the overall mechanical power produced by the second adiabatic two-phase expansion means in C2 (advantageous effect for the thermodynamic performance of the plant). Under certain operating conditions, the aforementioned advantageous effects prevail over the aforementioned disadvantageous effects, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, the third modification under consideration can be implemented according to the variant described below. In particular, the working fluid on the hot side (10 - 10*) of the second isobaric thermal regeneration means (TR2,I in this case) transfers thermal power to the same working fluid on the cold side of TR2.1 (13 - 13*). Further details associated with the implementation of this variant are omitted for brevity, as they can be readily inferred by an expert in the field, similarly to the description provided above. Under certain operating conditions, the third modification (implemented according to the aforementioned variant) results in an increase in the thermodynamic performance of the plant.

The transformations of the process according to the first operational mode as a co- trigeneration plant are depicted in the self-explanatory temperature (T) - specific entropy (s) diagram in Figure 4, as previously described in the previous patent, except for the modifications (thoroughly described above) associated with the transformations related to the spillover means in circuits Ci and C2 and the thermal regeneration in circuit C2. However, it is worth emphasizing that, similarly to the plant known from the Italian patent no. 102016000027735, the plant of the present invention (operating according to the first operational mode as a co-trigeneration plant) provides thermal power to the end-user at the first temperature value (transformation 6 - 7), cooling power at the first temperature value (transformation 11 - 12), and finally dissipates thermal power to the external environment (transformations 15 - 1 - 9). On the other hand, compared to the plant known from the Italian patent no. 102016000027735, the plant of the present invention is characterized by the spillovers in circuits Ci and C2 (described above). These spillovers, in addition to enhancing the thermodynamic performance of the plant (explained above), also enable the supply of thermal power to the end-user at the second temperature value (transformation 5** - 5***) and the supply of cooling power to the end-user at the second temperature value (transformation 10** - 10***).

The basis of this invention therefore consists of two aspects. The first aspect involves the understanding that a plant with the same layout under consideration (usable in the first operational mode as a co-trigeneration plant) can be surprisingly functional for a reversible use in the second operational mode as a high-temperature heat pump capable of operating without electric/mechanical power provided by an external source. In other words, each operating unit works in both of the aforementioned operational modes. The second aspect, which however can be pursued independently of the first one that will be explained shortly, involves the aforementioned options for modifying the plant layout known from Italian patent No. 102016000027735 in order to enhance its thermodynamic performance.

In the alternative (second) operational mode, the plant is capable of providing the end-user with high-temperature heating power without the need of electric/mechanical power provided by an external source, by converting the low-to-medium temperature thermal power supplied from any heat source (renewable or non-renewable). In other words, the same plant (without any change of its configuration, i.e. , requiring the operation of each operating unit in both of the aforementioned operational modes) can be reversibly used according with said two alternative operational modes (i.e., the first mode as a co- trigeneration plant and the second mode as a high-temperature heat pump without external electric/mechanical power provided by an external source).

In a version of the plant operating according with the second operating mode (Figure 3 and Figure 5a), heating power is supplied from the plant to the end-user at three distinct temperature values (transformations 3 - 4, 1* - 1**, and 6 - 7), with the heat transfer from the heat source to the working fluid in transformations 15 - 1 - 9.

In more detail, the operating units and corresponding transformations of the thermodynamic cycle according to this version of the second operational mode, as represented in the plant scheme of Figure 3 and the T-s diagram of Figure 5a, can be indicated as follows in the circuits Ci , C2, and C3 that constitute the thermodynamic cycle:

• First and second adiabatic two-phase compression means TC1 ,1 , TCI ,2, TC2,I , and TC2, 2 (transformations 1 - 2, 2* - 3, 12 - 13, and 13* - 14, respectively): in each of these, an increase in pressure (and consequent increase in temperature) of the working fluid is achieved due to the supply of mechanical power (provided by the first and second adiabatic two-phase expansion means of the same plant) to the aforementioned first and second adiabatic two-phase compression means;

• First isobaric thermal regeneration means TRu (cold side transformation 2 - 2* and hot side transformation 5 - 5*): the heat transfer is accomplished from the working fluid on the hot side of TR1 ,1 to the same working fluid on the cold side of TR1 ,1 ;

• First, second, and third isobaric heat exchange means HE1 ,1 , HEI,2, and HEI,3 (transformations 3 - 4, 1* - 1**, 6 - 7, respectively): in each of them, the supply of heating power from the working fluid to the end-user (useful effect) is achieved at the respective temperature value. Therefore, the plant depicted in Figure 5a allows the supply of heating power to the end-user at three distinct temperature values;

• First and second adiabatic two-phase expansion means TEi,i, TEI ,2, TEI ,3, TE2.1, and TE2.2 (transformations 4 - 5, 5* - 6, 7 - 8, 9 - 10, and 10* - 11 , respectively): in each of them, a decrease in pressure (and consequent decrease in temperature) of the working fluid is achieved, resulting in the generation of mechanical and/or electrical power. Furthermore, the overall mechanical (or electrical) power produced by the aforementioned first and second adiabatic two-phase expansion means is used for the operation of said first and second adiabatic two-phase compression means within the same plant, and any surplus of the aforementioned mechanical (or electrical) power is supplied to the end-user;

• Third isobaric heat exchange units HEs and HEs,2 (transformations 10** - 10*** and 11 - 12, respectively): in each of them, the heat transfer (thermal dissipation) from the working fluid to the external environment is achieved at the respective temperature value;

• Second isobaric thermal regeneration units TR2,I (hot side transformation 13 - 13* and cold side transformation 10 - 10*): the heat transfer is accomplished from the working fluid on the hot side of TR2,I to the same working fluid on the cold side of TR2,I ;

• Mixing means Ml (transformation 8 - 14 - 15): isobaric mixing is achieved between the working fluid exiting circuit Ci (point 8) and the working fluid exiting circuit C2 (point 14);

• Fourth (HE4) and second (HE2) isobaric heat exchange means (transformations 15 - 1 and 1 - 9, respectively): the heat transfer from the low-to-medium temperature heat source to the working fluid exiting the mixer (point 15) is accomplished.

Similarly to the first operational mode, in this different (second) operational mode as well, the plant (box B in Figure 1) allows for the spillover (in circuit Ci) of a portion of the working fluid flow from first two-phase adiabatic compression means (TCi,i in this case) through first spillover means (Bi ,1 in this case). This portion of the working fluid flow is then circulated to first two-phase adiabatic expansion means (TEI ,2 in this case) through interposed first connection means or through interposed first isobaric heat exchange means (H EI ,2 in this case). In particular (Figure 5a), the portion of the working fluid flow is withdrawn from TCi,i in the intermediate section 1* and then circulates through HEi,2 (to provide the end-user with heating power at the respective temperature value). The portion of the working fluid flow exiting HEi,2 (point 1**) enters TEI,2, where it is isobarically mixed with the working fluid flow here circulating (point 5**). In particular, the quality of the working fluid at point 1** is higher than the quality of the working fluid at point 5**. Due to the aforementioned isobaric mixing, the overall flow rate of the working fluid (point 5*** with higher quality than that of the working fluid at point 5**) undergoes the adiabatic two- phase expansion process 5*** - 6 (in the same TEi, 2 operating unit). The transformation (described so far) implies several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) involves a decrease in the mechanical power required in the two-phase adiabatic compression processes 1* - 2 and 2* - 3 (due to the reduction in the working fluid flow rate here circulating), an increase in the mechanical power produced in the two-phase adiabatic expansion processes 5*** - 6 and 7 - 8 (due to the increase in specific enthalpy difference in the respective processes 5*** - 6 and 7 - 8), and a reduction in the thermal power supplied from the heat source to the working fluid in both HE4 and HE2 at the same circulating working fluid flow rate (due to the increase in specific enthalpy at point 8 and consequently also at point 15). The second effect (disadvantageous for the thermodynamic performance of the plant) involves a decrease in the mechanical power produced in the two-phase adiabatic expansion processes 4 - 5 and 5* - 5** (due to the reduction in the working fluid flow rate here circulating). The third effect (disadvantageous for the thermodynamic performance of the plant) involves, at the same heating power supplied from the working fluid to the end-user in the process 3 - 4, a decrease in the circulating working fluid flow rate in process 3 - 4, resulting in an increase in the mechanical power required in the two-phase adiabatic compression process 2* - 3 (due to the increase in specific enthalpy difference in the two-phase adiabatic compression process 2* - 3) and a decrease in the mechanical power produced in the two-phase adiabatic expansion processes 4 - 5 and 5* - 5** (due to the decrease in specific enthalpy difference in the two- phase adiabatic expansion processes 4 - 5 and 5* - 5**). Under certain operating conditions, the advantageous effects are predominant over the disadvantageous ones, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, the spillover in the Ci circuit of the plant in the second operational mode under consideration can be implemented according to the variant described below. In particular, the withdrawal (in circuit Ci) of a portion of the working fluid flow from first two- phase adiabatic expansion means (TEi, ₂ in this case) is carried out through first spillover units (Bi ,1 in this case). This portion of the working fluid flow is then circulated to first two- phase adiabatic compression means (TCi,i in this case) through interposed first connection units or through interposed first heat exchange means (HEI, ₂ in this case). In this variant, HEI, ₂ enables the heat transfer from an additional heat source to the working fluid at the respective temperature value. Further details associated with the implementation of this variant are omitted for brevity, as they can be readily inferred by an expert in the field, similarly to the description provided above. Under certain operating conditions, the spillover in the Ci circuit of the plant in the second operational mode (implemented according to the aforementioned variant) results in an increase in the thermodynamic performance of the plant.

Similarly to the first operational mode, in this different (second) operational mode as well, the plant (box C in Figure 1) is capable of performing (Figure 5a) the withdrawal (in the C ₂ circuit) of a portion of the working fluid flow from second two-phase adiabatic expansion means (TE ₂ , ₂ in this case) through second spillover means (B ₂ ,I in this case). This portion of the working fluid flow is then circulated to second two-phase adiabatic compression means (TC ₂ ,I in this case) through interposed second connection means or through interposed third isobaric heat exchange means (HEs.i in this case). In particular (Figure 5a), the portion of the working fluid flow is withdrawn from TE ₂ , ₂ in the intermediate section 10** and then circulates through HEs (in order to execute the dissipation of thermal power from the working fluid to the external environment at the respective temperature value). The portion of the working fluid flow exiting from HEs (point 10***) enters TC ₂ ,I where it is isobarically mixed with the working fluid flow already here circulating (point 12*). In particular, the quality of the working fluid at point 10*** is lower than that of the working fluid at point 12*. Due the aforementioned isobaric mixing, the overall working fluid flow (point 12** with lower quality than point 12*) undergoes the two- phase adiabatic compression process 12** - 13 (in the same TC ₂ ,I). The transformation (described so far) implies several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) consists of a decrease in the mechanical power required in the two-phase adiabatic compression process 12 - 12* (due to the reduction in the working fluid flow rate here circulating) and a decrease in the mechanical power required in the two-phase adiabatic compression processes 12** - 13 and 13* - 14 (due to the reduction in the specific enthalpy difference in the respective processes 12** - 13 and 13* - 14). The second effect (disadvantageous for the thermodynamic performance of the plant) involves a decrease in the mechanical power produced in the two-phase adiabatic expansion process 10** - 11 (due to the reduction in the working fluid flow rate here circulating) and an increase in the thermal power supplied by the heat source to the working fluid in both HE4 and HE2 at the same working fluid flow rate here circulating (due to the reduction in the specific enthalpy at point 14 and consequently also at point 15). Under certain operating conditions, the first effect prevails over the second effect, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, the spillover in the C2 circuit of the plant in the second operational mode under consideration can be implemented according to the following variant. In particular, a portion of the working fluid flow is withdrawn (in the C2 circuit) from the second adiabatic two-phase compression means (TC2,I in this case) through second spillover means (62,1 in this case). This portion of the working fluid flow is then circulated to the second adiabatic two-phase expansion means (TE2.2 in this case) through interposed second connection means or through interposed third isobaric heat exchange means (HEs.i in this case). In this variant, HEs enables the heat transfer from an additional heat source to the working fluid (for example, supplying the end-user with cooling power) at the respective temperature value. Further details associated with the implementation of this variant are omitted for brevity, as they can be readily inferred by an expert in the field, similarly to the description provided above. Under specific operating conditions, the spillover in the C2 circuit of the plant in the second operational mode (implemented according to the aforementioned variant) leads to an increase in the thermodynamic performance of the plant.

Similarly to the first operational mode, in this different (second) operational mode as well, the plant allows for thermal regeneration in the Ci circuit (Figure 5a). In fact, the working fluid on the hot side (5 - 5*) of the first two-phase isobaric thermal regeneration means (TRu in this case) transfers thermal power to the same working fluid on the cold side of TRu (2 - 2*). Such thermal regeneration in the Ci circuit of the plant in the second operational mode entails several effects that are contrasting with each other, as described below. The first effect involves the reduction in the working fluid flow rate circulating in the Ci circuit, necessary to supply (in the first isobaric heat exchange means HEu) to the enduser the fixed thermal power (due to the increase in the specific enthalpy difference in the aforementioned HEu as a result of the increase in specific enthalpy at point 3). In turn, the reduction in the working fluid flow rate in the Ci circuit leads to a decrease in the overall mechanical power required by the first two-phase adiabatic compression means in Ci (advantageous effect for the thermodynamic performance of the plant) and a decrease in the overall mechanical power produced by the first two-phase adiabatic expansion means in Ci (disadvantageous effect for the thermodynamic performance of the plant). The second effect (disadvantageous for the thermodynamic performance of the plant) involves an increase in the mechanical power required in the two-phase adiabatic compression process 2* - 3 (due to the increase in the specific enthalpy difference in the same process 2* - 3) and a decrease in the mechanical power produced in the two-phase adiabatic expansion process 5* - 5** (due to the increase in the specific enthalpy difference in the same process 5* - 5**). Under certain operating conditions, the aforementioned advantageous effects prevail over the mentioned disadvantageous effects, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, thermal regeneration in the Ci circuit of the plant in the second operational mode under consideration can be implemented according to the variant described below. In particular, the working fluid on the hot side (2 - 2*) of the first two- phase isobaric thermal regeneration means (TRu in this case) transfers thermal power to the same working fluid on the cold side of TRu (5 - 5*). Further details associated with the implementation of this variant are omitted for brevity, as they can be easily inferred by an expert in the field, similarly to the description provided above. Under specific operating conditions, the thermal regeneration in the Ci circuit of the plant in the second operational mode (implemented according to the aforementioned variant) leads to an increase in the thermodynamic performance of the plant.

Similarly to the first operational mode, in this different (second) operational mode as well, the plant allows the thermal regeneration in the C2 circuit (Figure 5a). In fact, the working fluid on the hot side (13 - 13*) of the second two-phase isobaric thermal regeneration means (TR2,I in this case) transfers thermal power to the same working fluid on the cold side of TR2,I (10 - 10*). Such thermal regeneration in the C2 circuit of the plant in the second operational mode implies several effects that are contrasting with each other, as described below. The first effect (advantageous for the thermodynamic performance of the plant) involves a decrease in the mechanical power required in the two-phase adiabatic compression process 13* - 14 (due to the decrease in specific enthalpy difference in the same process 13* - 14) and an increase in the mechanical power produced in the two-phase adiabatic expansion process 10* - 11 (due to the increase in specific enthalpy difference in the same process 10* - 11). The second effect (disadvantageous for the thermodynamic performance of the plant) consists of an increase in the thermal power supplied from the heat source to the working fluid both in HE4 and HE2 at the same working fluid flow rate here circulating (due to the decrease in specific enthalpy in point 14 and consequently also in point 15). Under certain operating conditions, the aforementioned advantageous effects prevail over the mentioned disadvantageous effects, resulting in an increase in the thermodynamic performance of the plant.

Vice versa, thermal regeneration in the C2 circuit of the plant in the second operational mode under consideration can be implemented according to the variant described below. In particular, the working fluid in the hot side (10 - 10*) of the second isobaric thermal regeneration means (TR2,I in this case) transfers thermal power to the same working fluid on the cold side of TR2 (13 - 13*). Further details associated with the implementation of this variant are omitted for brevity, as they can be easily inferred by an expert in the field, similarly to the description provided above. Under certain operating conditions, thermal regeneration in the C2 circuit of the plant in the second operational mode (implemented according to the above described variant) leads to an increase in the thermodynamic performance of the plant.

According to the variant shown in Figure 5b, the supply of thermal power to the enduser occurs at two temperature values, namely in the transformations 1* - 1** and 3 - 4. For operation according to this variant as a high-temperature heat pump, the bypass (i.e. , deactivation) of the first isobaric heat exchange means (HEi.s) is used by activating their respective first bypass means, enclosed in the small circle (DM1,3) in Figure 3. In particular, the working fluid downstream of the first two-phase adiabatic expansion means (TEI,2) at point 6 circulates through the aforementioned DM1,3 to the first two-phase adiabatic expansion means (TEi.s), thus avoiding circulation through said HEI,3. Similarly, all other isobaric heat exchange means in the Ci and C2 circuits can be deactivated (bypassed) (by activating corresponding bypass means analogous to the aforementioned DM1,3 bypass means), except for the first isobaric heat exchange means H Ei ,1 (transformation 3 - 4) and the third isobaric heat exchange means HEs,2 (transformation 11 - 12), otherwise the closed sequence of transformations in the thermodynamic cycle cannot take place.

In all the aforementioned variants of the second operational mode as a high- temperature heat pump, the plant operates without any mechanical and/or electrical power supplied from an external source, as the overall mechanical (and/or electrical) power produced by the two-phase adiabatic expansion means is used for the operation of the two-phase adiabatic compression means within the same plant, and any possible surplus of the aforementioned mechanical (and/or electrical) power produced is supplied to the end-user.

The advantages offered by the proposed plant (Figure 1) are described below.

1) Reversibility of the plant:

The same plant configuration (without any modifications, i.e., requiring the operation of each operating unit in both of the aforementioned operational modes) can be used reversibly according to the two aforementioned alternative operational modes (i.e., the first mode as a co-tri-generation plant and the second mode as a high-temperature heat pump plant operating without electrical/mechanical power provided by an external source).

In order to enable the same plant configuration to operate reversibly according to the two operational modes described above (either as a co-tri-generation plant or as a high-temperature heat pump plant without electrical/mechanical power provided by an external source), it is necessary to use adiabatic two-phase fluid machines (compressors, expanders) and heat exchangers with specific characteristics. In particular, the adiabatic two-phase fluid machines must be able to work with working fluid in their respective inlet sections with variable quality over a wide range. Furthermore, the heat exchangers must be able to operate as condensers (i.e., with the working fluid having decreasing quality between the respective inlet and outlet sections due to the heat transfer from the working fluid to the thermal fluid circulating in the same condensers) or as evaporators (i.e., with the working fluid having increasing quality between the respective inlet and outlet sections due to the heat transfer from the thermal fluid circulating in the same evaporators to the working fluid). In particular, as mentioned above, the adiabatic two-phase fluid machines must be able to operate with working fluid in their respective inlet section with variable quality over a wide range:

• First operational mode (co-tri-generation plant): in circuit Ci, each adiabatic two-phase compressor operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to zero in the limit condition, where in this limit condition, the said two-phase working fluid is predominantly composed of the liquid phase; and each adiabatic two-phase expander operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to one in the limit condition, where in this limit condition, the said two-phase working fluid is predominantly composed of the vapor phase. Conversely, in circuit C2, each adiabatic two-phase compressor operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to one, and each two-phase expander operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to zero.

• Second operational mode (high-temperature heat pump plant without electric/mechanical power provided by an external source): in circuit Ci, each adiabatic two-phase compressor operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to one, and each two-phase expander operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to zero. Conversely, in circuit C2, each adiabatic two-phase compressor operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to zero, and each adiabatic two- phase expander operates with working fluid in its respective inlet section with variable quality in a wide range, approaching values close to one.

Only for the sake of example, in order to operate with working fluid in the respective inlet section with variable quality in a wide range, two-phase fluid machines can be realized with variable geometry according to solutions already extensively tested on single-phase fluid machines, as well-known, for example, from [Haglind F. Variable geometry gas turbines for improving the part-load performance of marine combined cycles - Gas turbine performance, Energy 2010;35:562-570] and from [Herbst F, Eilts P. Experimental investigation of variable geometry compressor for highly boosted gasoline engines, SAE Technical Paper 2015-01-1289, 2015],

Again just for the sake of example, in order to operate as condensers or as evaporators, heat exchangers can be realized using solutions that have been widely experimented with and as known, for instance, from [Kelvion https://www.kelvion.com/products/product/td-series/] and [Swep https://www.swep. net/refrigerant-handbook/7.-condensers/asd1/].

Furthermore, all the other aforementioned operating units are to be considered inherently known in their nature and construction by the skilled person.

As mentioned previously, there are known examples of reversible plants capable of operating according to two alternative operational modes, namely the first operational mode (ORC) for supplying the end-user with electrical power and the second operational mode (HP) for supplying the end-user with heating power. However, in the aforementioned known reversible plants: i) some operating units work in one of the two operational modes while they do not work (i.e. , they are bypassed) in the other operational mode. In other words, each operating unit does not work in both operational modes; ii) adiabatic singlephase fluid machines are used, where the same machine can work as an adiabatic singlephase compressor (in the HP operational mode) or as an adiabatic single-phase expander (in the ORC operational mode). Conversely to the present invention, there is no known reversible plant where: i) each operating unit works in both the first operational mode (as a plant for supplying the end-user with electrical power or as a co-trigeneration plant) and the second operational mode (as a high-temperature heat pump plant); ii) two-phase fluid machines (compressors and expanders) are used, where each machine exclusively works as an adiabatic two-phase fluid compressor to increase (via conversion of the mechanical/electrical power supplied from an external source) the pressure of the two- phase working fluid, or exclusively works as an adiabatic two-phase expander to decrease (in order to produce mechanical/electrical power) the pressure of the two-phase working fluid. Furthermore, each two-phase fluid machine works with variable quality over a wide range in its respective inlet section to allow the operation of the plant in both the first mode (as a plant for supplying the end-user with electrical power or as a co-trigeneration plant) and the second mode (as a high-temperature heat pump plant).

2) High thermodynamic performance of the plant: In the first operational mode (co-trigeneration plant), circuit Ci works according to a suitable combination of direct Carnot thermodynamic cycles (i.e., in order to produce mechanical/electrical power) using a two-phase fluid. Similarly, circuit C2 works according to a suitable combination of reverse Carnot thermodynamic cycles (i.e., using mechanical/electrical power supplied from an external source) using a two-phase fluid. As well-known in the literature, direct and reverse Carnot thermodynamic cycles represent cycles with maximum efficiency. Consequently, the plant layout known from Italian Patent No. 102016000027735 is characterized by high thermodynamic performance. In addition, the three modifications to the aforementioned plant layout (extensively described earlier, i.e., spillovers of the working fluid in circuits Ci and C2 and thermal regeneration in circuit C2) allow for an increase in the (already high) thermodynamic performance of the plant operating in the first operational mode. Therefore, these modifications can be advantageously applied to a co-trigeneration plant regardless of its predisposition (also) for switching to the second operational mode. In other words, while supplying the enduser with the same powers (mechanical/electrical, heating, and/or cooling), the thermal power supplied by the heat source to the working fluid is reduced. Alternatively, at the same thermal power supplied by the heat source to the working fluid, the powers (mechanical/electrical, heating, and/or cooling) provided by the plant to the end-user are increased.

Similarly, in the second operational mode (high-temperature heat pump), the Ci and C2 circuits work as an appropriate combination of inverse and direct Carnot thermodynamic cycles using a two-phase fluid, respectively, which represent thermodynamic cycles with maximum efficiency, as well known in literature. In addition, both in the Ci and C2 circuits, thermal regeneration and spillovers (described extensively before) contribute to enhancing the (already high) thermodynamic performance of the plant operating in the second operational mode. In other words, at the same high- temperature heating power provided from the plant to the end-user, there is a reduction in the low-to-medium-temperature thermal power supplied from the heat source to the working fluid. Conversely, at the same low-to-medium-temperature thermal power supplied from the heat source to the working fluid, there is an increase in the high- temperature heating power supplied from the plant to the end-user. 3) Use of the plant in the second operational mode (high-temperature heat pump) without mechanical/electrical power supplied from an external source:

The mechanical/electrical power required to operate the entire set of two-phase adiabatic compressors in the plant is provided by the two-phase adiabatic expanders within the same plant. Therefore, the plant solely relies on being fed by a low-to-medium- temperature heat source, namely it does not require any mechanical/electrical power supplied from an external source. This implies that the plant can be used in locations without connection to the electrical grid (stand-alone plant). In addition, the plant can generate surplus mechanical/electrical power (beyond what is strictly necessary for driving the two-phase adiabatic compressors in the same plant), which can be supplied to the end-user (in particular, the electrical power can be fed into the electrical grid).

In contrast to the present invention, no heat pump (both compression and absorption types) is known capable to operate without mechanical/electrical power supplied from an external source. In fact, currently known heat pumps require the mechanical/electrical power supplied from an external source.

4) High flexibility of the plant in the second operational mode (high- temperature heat pump):

The plant according to the present invention in the second operational mode (high- temperature heat pump) allows the supplying the end-user with several required values of heating power within a significantly wider range (wideness to be understood both in terms of heating power values and their corresponding temperatures) compared to currently known high-temperature heat pumps. This is achieved without any deficit or surplus of the aforementioned heating power provided from this plant to the end-user. The remarkable flexibility of the plant’s usage according to the present invention enables the fullfilling of the energy requirements of the end-user that are variable over time (in terms of heating powers and respective temperatures). This considerable flexibility arises from the control/regulation of the following multiple independent process parameters: each of the two portions of the working fluid circulating in Ci and C2, the outlet quality from each HE2, HE4, HEI.N, HES.N*, TRI.P, and TR2,P, and the outlet pressure from each TEi.o, TE2,o*, TCI.M, and TC ₂ ,M*. The control/regulation of the aforementioned process parameters is carried out through means and methods accessible to an average technician and is therefore not further detailed here. Variations and/or modifications can be brought to the high-temperature heat pump plant without mechanical/electrical power supplied from an external source, which can be reversibly used in an alternative operational mode as a co-trigeneration plant according to the present invention, without departing from the scope of protection defined by the attached claims.