A heat pump and a process for producing a heated first medium and a cooled second medium Introduction

The present invention relates to a heat pump plant comprising an expander circuit, a compressor circuit, and an exhaust gas source

Background art

Cogeneration or combined heat and power (CHP) uses a combustion engine to generate electricity and a waste heat stream at the same time. Trigeneration or combined cooling, heat and power (CCHP) refers to the simultaneous generation of electricity, heating, and cooling from the combustion of a fuel or a solar heat collector.

Cogeneration is a thermodynamically efficient use of fuel. In separate production of electricity, some energy must be discarded as waste heat, but in cogeneration some of this thermal energy is put to use. All thermal power plants emit heat during electricity generation, which can be released into the natural environment through cooling towers, flue gas, or by other means. In contrast, CHP captures some or all of the by-product for heating, either very close to the plant, or— especially in Scandinavia and Eastern Europe— as hot water for district heating. This is also called combined heat and power district heating (CHPDH). Small CHP plants are an example of decentralized energy production.

In cogeneration, the supply of fuel first drives a combustion engine powered generator and the resulting low-temperature waste heat is then used for water or space heating . At smaller scales (typically below 1 MW) a gas engine or diesel engine may be used. Trigeneration differs from cogeneration in that the waste heat is used for both heating and cooling, typically in an absorption refrigerator. CCHP systems can attain higher overall efficiencies than cogeneration or traditional power plants. In the United States, the application of trigeneration in buildings is called building cooling, heating and power (BCHP). Heating and cooling output may operate concurrently or alternately depending on need and system construction.

The present invention provides an improved heat pump and a process, which uses the waste heat streams from a combustion engine to drive a heat pump. The heat pump will deliver a first heated medium and a second cooled medium. Summary of the invention

The present invention relates to a heat pump comprising a combustion engine, an expander circuit and a compressor circuit, wherein

a. the combustion engine is configured for producing an exhaust gas,

b. the expander circuit comprises

i. a boiler configured for producing a stream of saturated steam from water,

ii. a boiler heat exchanger configured for superheating the stream of steam from the boiler and cooling the exhaust gas,

iii. a first expander configured for receiving the stream of superheated steam from the boiler heat exchanger and for transferring mechanical energy to a shaft,

iv. an expander heat exchanger configured for heating the stream of steam from the first expander and for cooling a stream from the compressor circuit,

v. a second expander configured for receiving the stream of steam from the expander heat exchanger and for transferring energy to a shaft,

vi. an expander circuit condenser configured for receiving the stream of steam from the second expander, and for producing water, and

vii. a pump configured for transferring water from the expander circuit condenser to the boiler, c. the compressor circuit comprises

I. an evaporator configured for producing a stream of steam from water,

II. a compressor configured for receiving the stream of steam from the evaporator and compressing the stream of steam using mechanical energy from the shaft of the first and/or the second expander,

III. an inlet to the expander heat exchanger for cooling the compressed stream of steam and an outlet for the cooled stream of steam,

IV. a compressor circuit condenser configured for receiving the cooled stream of steam from the expander heat exchanger for producing water, and

V. a valve configured for receiving the water from the condenser and reducing the pressure thereof before the water is entered into the evaporator,

wherein the expander circuit condenser and/or the compressor circuit condenser are configured for heating a first medium and the evaporator is configured for cooling a second medium.

The invention also relates to a process for producing a heated first medium and a cooled second medium, comprising the steps of:

a. Producing an exhaust gas from a combustion engine, b. Providing an expander circuit comprising the steps of: i. Producing a stream of saturated steam from water in a boiler,

ii. superheating the stream of steam from the boiler and cooling the exhaust gas in a boiler heat exchanger iii. transferring mechanical energy to a shaft by a first expander receiving the stream of superheated steam from the boiler heat exchanger,

iv. heating the stream of steam from the first expander and cooling a stream from the compressor circuit in an expander heat exchanger

v. transferring energy to a shaft by a second expander receiving the stream of steam from the expander heat ex- changer

vi. condensing the stream of steam from the second expander for producing water in an expander circuit condenser, and vii. transferring water from the expander circuit condenser to the boiler by a pump,

c. providing a compressor circuit comprising the steps of: i. producing a stream of steam from water by an evaporator, ii. compressing the stream of steam from the evaporator using mechanical energy from the shaft of the first and/or the second expander,

iii. cooling the compressed stream of steam in the expander heat exchanger,

iv. condensing the stream of steam from the expander heat exchanger for producing water in a compressor circuit condenser,

v. reducing the pressure of the water from the condenser by a valve and

vi. introducing the water into the evaporator, wherein a first medium is heated by the expander circuit condenser and the compressor circuit condenser, and a second medium is cooled in the evaporator.

Combustion engines are readily available on the market and may be selected as internal or external combustion engines. Generally, internal combustion engines are preferred to the present invention, such as piston engines, Wankel rotary engines, or gas turbines. The combustion engine is generally connected to a generator for converting power to electricity. By the combustion an exhaust gas is generated, which is used in the present heat pump.

The piston engines may be driven by a suitable combustible fuel, such as natural gas, gasoline, diesel fuel, fuel oil, biodiesel fuel, (bio)ethanol, methane, propane, hydrogen etc. and are generally preferred because the cooling water needed for cooling the engine may be used in the heat pump. Furthermore, piston engines tend to be more energy effective than gas turbines. A preferred piston engine is the gas engine, which runs on e.g . coal gas, producer gas, biogas, landfill gas, liquid natural gas (LNG), or compressed natural gas (CNG). Compared to diesel engines, the gas engine exhaust gases are much hotter for a given output, which is considered an advantage for the present invention. Gas engines produce a higher a Generally, the term gas engine refers to a heavy-duty industrial engine capable of running continuously at full load for periods approaching a high fraction of per year. Typical power ranges from 10 kW to 18 MW. Manufacturers of applicable gas engines include Hyundai Heavy Industries, Rolls-Royce with the Bergen-Engines AS, Kawasaki Heavy Industries, Liebherr, MTU Friedrichshafen, GE Jenbacher, Caterpillar Inc., Perkins Engines, MWM, Cummins, Wartsila, GE Energy Waukesha, Guascor Power, Deutz, MTU, MAN, Fairbanks Morse, Doosan, and Yanmar.

The boiler is boiling water to steam. In some embodiments of the invention the boiler is heated by an external source. However, in a suitable embodiment, the boiler is configured for receiving the partly cooled exhaust gas from the boiler heat exchanger for heating of the water to produce steam. The boiler may also be referred to as a steam generator or stationary steam engine.

The steam leaving the boiler is generally saturated. In the boiler heat exchanger, the steam becomes superheated whereas the exhaust gas is cooled. A number of heat exchangers are suitable for the purpose, including shell and tube heat exchangers, plate and shell heat exchangers, plate fin heat exchangers, etc. A preferred heat exchanger is of the type often referred to as waste heat recovery units (WHRU).

The superheated steam inters the expander, which is a centrifugal or axial flow turbine through which a high pressure gas is expanded to produce work. The expander may also be referred to as turbo-expander or expansion turbine and comprises an expander wheel coupled to a shaft. The expander extracts work from the expanding high pressure gas and exhaust gas from the turbine at a lower temperature and pressure. Each of the expanders used in the present invention may be coupled to a separate shaft, which may be combined through a suitable gearing . In a preferred aspect, however, the expand- ers are sharing a common shaft.

The expanded gas leaving the expander is usually at or close to its saturation point. In the expander heat exchanger, the steam is superheated, while a stream from the compressor circuit is cooled. The expander may be of the same or similar type as the one used as the boiler heat exchanger.

In some embodiments, one or more additional expander(s) are used, wherein the outlet of a preceding expander is connected to a heat exchanger for heating the steam which subsequently is connected to the inlet of a subsequent expander. The use of one or more additional expanders increases the energy efficiency. While the heat exchanger may receive heat from various sources it is generally preferred that the heat exchanger receives heat from the expander circuit and/or the exhaust gas.

The expanded gas from the second expander is condensed in a condenser. Typically, the condenser is of the shell-and-tube type. The first medium to be heated flows through the tube side and the steam enters the shell side where the condensation occurs on the outside of the heat transfer tubes. The condensate drips down and collects at the bottom, often in a built-in pan called a hotwell. The shell side often operates at a vacuum or partial vacuum, produced by the difference in specific volume between the steam and condensate. Conversely, the vapor can be fed through the tubes with the first medium flow- ing around the outside. Other types of condensers may also be used, such as the Liebig condenser, Graham condenser, or Allihn condenser.

The first medium extracting the heat from the condensation process may be used for various purposes, including district heating systems, process water for industrial processes, including diary processes, etc.

The condensate is usually recycled to the boiler by a pump. The pump may be selected according to the specific need of the pressure in the boiler. Typically, the pump if of the positive displacement type, however, centrifugal pumps may also be applicable. Specific types of positive displacement types include gear pumps, screw pumps, and rotary vane pumps.

While the expander circuit has been described using water as the working fluid, the person skilled in the art will understand that other working fluid can be used instead. Alternative working fluid for the expander circuit include ammonia, propane, butane, pentane, cyclopentane, toluene, Chlorofluorocar- bons, hydrochlorofluorocarbons, fluorocarbons, propane, butane, isobutane, ammonia, and sulfur dioxide.

The compressor circuit comprises an evaporator configured for producing a steam from water. Usually, the steam is at a relative low pressure and temperature. The heat needed for evaporation is obtained from a second medium, which may be chosen according to the available heat streams, such as cooling water or sea water. In other instances, the second medium is used for refrigeration or storage of cooling e.g. for used in air conditioning .

The steam from the evaporator is directed to the compressor. In some embodiments, the outlet of the evaporator is connected to an evaporator heat exchanger for heating the stream of steam before its enters the compressor, said evaporator heat exchanger receives heat from the exhaust gas and/or a cooling medium for the combustion engine. The heating of the steam before it is compressed recovers further heat energy from the exhaust gas and/or a cooling medium for the combustion engine.

The compressor is usually of the centrifugal type. Centrifugal compres- sors use a rotating disk or impeller in a shaped housing to force the steam to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. Generally, axial- flow compressors are preferred . They are dynamic rotating compressors that use arrays of fan-like airfoils to progressively compress a fluid.

In a certain embodiment of the invention, one or more additional compressors) are used for step-wise increase of the pressure, wherein the outlet of a preceding compressor is connected to inlet of a subsequent compressor. The application of one or more additional compressor may be referred to herein as multiple staging, i.e. two or more compressors are used consecutively to increase the pressure of the steam.

In an axial flow compressor, the arrays of airfoils are usually set in rows, usually as pairs: one rotating and one stationary. The rotating airfoils, also known as blades or rotors, accelerate the fluid. The stationary airfoils, also known as stators or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage. Axial compressors are usually multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. The compressor may be fitted with features such as stationary vanes with variable angles (known as variable inlet guide vanes and variable stators), to allow some air to escape part-way along the compressor (known as inter-stage bleed) and being split into more than one rotating assembly (known as twin spools, for example).

In a certain embodiment of the invention, a heat exchanger is provided between the outlet of a preceding compressor and inlet of a subsequent com- pressor for cooling the partly compressed steam and heating an expander circuit stream. The step-wise cooling in more than one step ensures a higher energy efficiency.

The compressed steam is directed to a heat exchanger for heating the expanded steam from an expander as explained above. The cooling of the com- pressed steam may be performed in a single step, or in two or more steps between consecutive expanders, before the steam enters the compressor circuit condenser. Generally, the compressor circuit condenser is of the same type as the expander circuit condenser. The first medium heated in the compressor circuit condenser may be used as such or directed to the inlet of the expander circuit condenser for further heating .

The condensate leaving the condenser is subjected to pressure reduction in a suitable valve before it enters the evaporator. Alternatively, the evaporator and the valve is combined so that the pressure release occurs in a container, i.e. a flash tank.

Summary of the drawings

The present invention will now be described in greater detail based on preferred embodiments with reference to the drawings on which :

Figure 1 discloses a heat pump comprising an expander circuit and a compressor circuit.

Figure 2 shows a heat pump as outlined in figure 1, further provided with additional compressors.

Figure 3 shows a heat pump as outlined in figures 1 and 2, further provided with an additional expander.

Figure 4 discloses a heat pump as outlined in figures 1 to 3, further provided with an evaporator heat exchanger for heating the vapour from the evaporator before it enters the compressor section.

Fig. 5 discloses a heat pump as outlined in Figure 3, however, with the change that the second expander heat exchanger receives heat from the com- pressor circuit instead of the exhaust gas from the boiler.

Figure 6 discloses a heat pump as outlined in Figure 1 further provided with a motor heat exchanger, which heats the steam from the evaporator before it enters the compressor. Detailed description

Figure 1 discloses a heat pump comprising an expander circuit 200 and a compressor circuit 300. In addition, the figure shows a waste heat stream 100 embodied as an exhaust gas (EG) entering at 101 from a combustion engine (not shown), a first medium 500 to be heated entering at 501, and a second medium 400 to be cooled entering at 401. The expander circuit 200 comprises a boiler 201 for boiling water to steam. The water is heated by the exhaust gas from the combustion engine. Usually, the water is at a pressure higher than the ambient pressure, such as above 2 bar, preferably above 5 bar. The steam generated in the boiler will be saturated at the selected pressure. The generated steam leaves the boiler at exit 202 and is transferred to the entrance 211 of the boiler heat exchanger 210. In the boiler heat exchanger, the saturated steam from the boiler is superheated, i.e. heated above its saturation point by a waste heat stream from the combustion engine, which enters the boiler heat exchanger at 101 and exits at 102. The partially cooled exhaust gas is then transferred to the boiler and enters at 103 for further cooling . The twice cooled exhaust gas leaves the boiler at exit 104.

The superheated steam leaves the heat exchanger at exit 212 and is transferred to the first expander (El) 220 at entrance 222. In the expander 220 the superheated stream of steam is converted to mechanical energy, which is transferred to the shaft 223, and the stream of steam now depleted in pressure and temperature leaves at outlet 224 and is directed to entrance 213 of an expander heat exchanger 215. In the expander heat exchanger, the stream is heated and a stream from the compressor circuit is cooled . Usually, the stream to be cooled comes from the compressor. The heated stream exits the expander heat exchanger at 215 and is conveyed to the entrance 226 of the second expander 225. In the second expander the superheated stream of steam is converted to mechanical energy, which is transferred to the shaft 223, and the stream of steam now depleted in pressure and temperature is directed to entrance 231 of an expander circuit condenser 230.

In the expander circuit condenser, the steam is condensed to a liquid and exits at outlet 232. By the condensing process heat is evolved, which is transferred to a medium to be heated. The medium to be heated enters at inlet 503 and leaves the condenser at exit 504. By way of example, the medium to be heated may water in a district heating system.

The condensed stream of water is pumped by pump 233 to inlet 203 of the boiler 201.

The compressor circuit 300 comprises an evaporator 310. In the evaporator water is evaporated, usually under a pressure lower than the ambient pressure, to produce a stream of steam, which leaves the evaporator at outlet 311. The evaporation is effected by cooling a second medium 400, which enters the evaporator at inlet 401 and exits at 402. The second medium may for instance be sea water, which is returned to the sea after cooling or it may be a medium used for cooling or air conditioning of office spaces or homes.

The stream of steam exiting the evaporator is directed to inlet 321 of the compressor 320. The compressor is driven by the shaft 223, which receives the mechanical energy from the first and/or the second expander(s) . The compressed steam leaves the compressor at exit 322 and is transferred to the heat exchanger 215, where it enters at inlet 225 and exits at 226. In the heat ex- changer the compressed stream of steam is cooled and the heat is transferred to the expander circuit. The cooled stream of steam from the compressor enters the compressor circuit condenser 330 at inlet 331. In the compressor circuit condenser 330 the steam is condensed to a liquid and exits at outlet 332. By the condensing process heat is evolved, which is transferred to a medium to be heated . The medium to be heated enters at inlet 501 and leaves the condenser at exit 502. In the embodiment shown on figure 1, the medium to be heated is first heated in the compressor circuit condenser and subsequently heated in the expander circuit condenser. The two step heating of the medium enhances the efficiency.

The condensed water leaving the compressor circuit condenser 330 at outlet 332 is directed to a valve 340 for reducing the pressure before the liquid is fed to the evaporator 310 at entrance 312.

In an exemplary embodiment of the heat pump illustrated in figure 1, the pressure of the boiler 201 is adjusted to 10 bar by the pump 233. At this pressure the temperature of the saturated steam is around 180°C. The saturated steam is further heated in the boiler heat exchanger 210 to 395°C. The exhaust gas emanates from a Rolls-Royce gas engine having 6 cylinders (engine type C26 : 33L6PG) . The exhaust gas enters the boiler heat exchanger at a temperature of 405°C. In the boiler heat exchanger, the exhaust gas is cooled to 300°C and in the boiler the exhaust gas is further cooled to 190°C.

The superheated steam at 295°C (10 bar) leaving the boiler heat exchanger is fed to the first expander 221, in which mechanical energy is transferred to the rotating shaft 223 and the pressure is reduced to around 5 bar and the temperature is reduced to about 151°C at the outlet 224, i.e. close to or at its saturation point. In the expander heat exchanger 215, the steam from the first expander is again superheated to about 340°C by a stream from the compressor circuit 300. The stream from the compressor circuit is reduced in temperature from 350°C to 160°C in the expander heat exchanger. The superheated steam from the expander heat exchanger 215 is fed into the second expander at entrance 226. In the second expander pressure is reduced to 0.3 bar, corresponding to a temperature of about 73°C, and delivered to the expander circuit compressor. In the expander circuit condenser 230, the steam is condensed to water having a temperature of 57°C. The energy provided by the condensation process is delivered to a medium to be heated, which enters the expander circuit condenser at a temperature of 55°C and leaves at 70°C. The medium is used for heating a district heating system. The condensed water having a temperature of 57°C is returned to the boiler by the pump 233.

In the expander circuit, the evaporator 310 receives water, which is evaporated at 0.01 bar to obtain a saturated steam of a temperature around 6.7°C. Excess process water at a temperature of around 20°C is used for the evaporation. The process water is cooled to around 10°C in the evaporator and is discarded to a suitable recipient. The steam leaving the evaporator is delivered to the inlet 321 of the compressor. The compressor increases the pressure to 0.18 bar and the temperature to about 350°C. In the expander heat ex- changer, the temperature is lowered to 160°C, which is supplied to the compressor circuit condenser 330. In the compressor circuit condenser, the steam is condensed to a temperature of 38°C and a pressure of 0.18 bar. In the condensation process a medium is heated from 35°C to 55°C. The heated medium is conveyed to the expander circuit condenser, in which it is further heated as described above to 70°C. The medium is suitably water in a district heating system. The water exiting the compressor circuit condenser is reduced in pressure in the valve 340 to 0.01 bar before it enters the evaporator 310.

Figure 2 shows a heat pump as outlined in figure 1, further provided with additional compressors. In addition to what already has been described for figure 1, the steam leaving the evaporator 310 is compressed in three further steps before it enters the first compressor CI . Thus, the steam leaving at outlet 311 is conveyed to the inlet of the fourth compressor C4, in which the steam is partially compressed . The steam leaving the fourth compressor subsequently enters the third compressor C3, in which it is further compressed . The steam leaving the third compressor subsequently enters the second compressor C2, in which it is further compressed . Finally, the steam from the second compressor is compressed in the first compressor CI .

In an exemplary embodiment, the steam from the evaporator 310, having a pressure of 0.01 bar is compressed to around 0.02 in the fourth compressor, to around 0.04 bar in the third compressor, to around 0.08 in the second compressor, and finally to 0.18 bar in the first compressor. By performing the compression in multiple steps, the efficiency is increased.

Figure 3 shows a heat pump as outlined in figures 1 and 2, further provided with an additional expander. In addition to what already has been described for figures 1 and 2, the further expander E3 receives steam supplied from the second expander E2, which has been superheated in the second expander heat exchanger 218. The steam close to its saturation point from the second expander is received at inlet 216 of the expander and exits at the outlet 217 as a superheat steam. The partly cooled exhaust gas from the boiler is used as the source of energy and the exhaust gas enters the second expander heat expander at inlet 105 and exits as outlet 106. The superheated steam is delivered to the third expander 229 at inlet 227. In the expander E3, the pressure and temperature are decreased and the energy is converted to mechanical energy in the rotating shaft. At the outlet 228 of the third expander, the steam leaves the expander and is transferred to the expander condenser and treated as described above.

In an exemplary embodiment, the stream of steam from the first expander heat exchanger 215, having a temperature of 340°C and a pressure of 5 bar, is treated in the second expander (E2) 225 so that the steam exiting the second expander has a pressure of 1.2 bar and a corresponding temperature of around 105°C. This steam is fed to the second expander heat exchanger 218 for superheating of the steam to 180°C in heat exchange with the exhaust gas from the boiler having a temperature of 190°C at the inlet 105 and a tem- perature of 115°C at the out let 106. The superheated steam from the second expander heat exchanger is delivered to inlet 227 of the third expander E3. In the third expander the pressure is reduced at the outlet to 0.3 bar and a corresponding temperature of around 73°C. This stream of steam is fed to the expander condenser and treated as above.

Figure 4 discloses a heat pump as outlined in figures 1 to 3, further provided with an evaporator heat exchanger for heating the vapour from the evaporator before it enters the compressor section. The heating is performed in exchange for a cooling of the exhaust gas stream.

The exhaust gas stream exiting at 106 from the second expander heat exchanger 218 still comprises energy that can be used in the system. The exhaust gas enters the evaporator heat exchanger 315 at inlet 107 and delivers heat to the steam from the evaporator before the exhaust gas is discarded to the ambient air at outlet 108. The steam from the evaporator 310 exits at 311 and is delivered to the evaporator heat exchanger 315 at inlet 316. After having been transferred heat from the exhaust gas stream, the steam exits at outlet 317. The now superheated steam is delivered to the compressor section as described above.

In an exemplary embodiment, the exhaust gas from the second expander heat exchanger 315 having a temperature of 115°C is cooled in the evaporator heat exchanger 315 to 20°C before it is liberated to the air. The evaporated steam from the evaporator having a pressure of 0.01 bar and a temperature of 6.7°C is heated is superheated to 105°C in the evaporator heat exchanger. In the compressor section comprising C4 - CI the pressure is incremented stepwise as disclosed above.

Fig. 5 discloses a heat pump as outlined in Figure 3, however, with the change that the second expander heat exchanger receives heat from the compressor circuit instead of the exhaust gas from the boiler. Thus, the compressor circuit stream is cooled in two steps before it enters the compressor circuit condenser.

According to this embodiment, the stream of steam exiting the first expander heat exchanger 215 at out let 326 is conveyed to the inlet 327 of the second expander heat exchanger 218. In the second expander heat exchanger 218, the compressor circuit stream is cooled before it exits at outlet 328 and is treated in the compressor circuit condenser 331 as described above. The stream of steam exiting the second expander E2 enters the second expander heat exchanger 218 at inlet 216 where it is heated before it leaves at outlet 217. The heated stream from the second expander heat exchanger is then treated in the third expander E3, as disclosed elsewhere herein.

In an exemplary embodiment, the compressed steam leaving the first expander heat exchanger 215 has a temperature of 160°C. In the second expander heat expander 218 further heat is withdrawn from the compressor circuit and at the exit the temperature is 115°C. The now cooled gas from the compressor circuit is the entered into the compressor circuit condenser 330 as disclosed elsewhere. The stream of steam leaving the second expander is 105°C and has a pressure of 1.2 bar. In the second expander heat exchanger 218 the stream from the second expander is heated to 150°C before it enters the third expander and is treated as described elsewhere herein.

Figure 6 discloses a heat pump as outlined in Figure 1 further provided with a motor heat exchanger, which heats the steam from the evaporator before it enters the compressor.

According to this embodiment, the steam exiting at outlet 311 from the evaporator 310 is superheated by the cooling water from the motor or engine, usually a gas engine. The steam from the evaporator enters at inlet 318 to the motor heat exchanger. After heating of the steam in exchange for a cooling of the cooling water from the gas motor, the heated steam exits at outlet 319. The cooling water from the gas motor enters at inlet 111 and is cooled in the motor heat exchanger before it exits at outlet 112. The cooling water may be recirculated to the gas engine or discarded, whereas the heat steam is introduced in the compressor 320 at the inlet 321.

In an exemplary embodiment, the evaporated steam exits the evaporator 310 at a pressure of 0.01 bar and a temperature of about 6.7°C. In the engine heat exchanger 110, the steam is superheated to about 80°C. In exchange, the cooling water entering at 90°C is cooled in the motor heat ex- changer to 20°C. The cooling water is recirculated to the gas motor. The superheated steam exiting the motor heat exchanger is introduced into the compressor 320 at inlet 321 and treated as disclosed elsewhere herein. Reference numbers on the drawings :

Waste heat stream

Inlet for exhaust gas (EG) to boiler heat exchanger

Outlet from exhaust gas (EG) to boiler heat exchanger

Inlet for exhaust gas to boiler

Outlet for exhaust gas from boiler

Inlet for exhaust gas to heat exchanger

Outlet for exhaust gas from heat exchanger

Inlet to evaporator heat exchanger

Outlet from evaporator heat exchanger

Engine heat exchanger

Inlet medium carrying engine heat

Outlet of medium carrying engine heat

Expander circuit

Boiler

Outlet of steam from boiler

Inlet for water to boiler

Boiler steam exchanger

Inlet of steam to boiler heat exchanger

Outlet of steam from boiler heat exchanger

Inlet to expander heat exchanger

Outlet from expander heat exchanger

Expander heat exchanger

Inlet to second expander heat exchanger

Outlet from second expander heat exchanger

Second expander heat exchanger

First expander (E1 )

Inlet to first expander

Shaft

Outlet of frist expander

Second expander

Inlet to second expander

Inlet to third expander

Outlet for thrid expander

Third expander

Expander circuit condenser

Inlet of steam to expander circuit condenser

Outlet of steam from expander circuit condenser

Pump from expander to boiler

Compressor circuit

Evaporator

Outlet of steam from evaproator

Inlet of water to evaporatir

Inlet to evaporator heat exchanger

Outlet from expander heat exchanger

Inlet to heat exchanger 319 Outlet from heat exchanger

320 Compressor

321 Inlet to compressor

322 Outlet from compressor

325 Inlet to expander heat exchanger

326 Outlet from expander heat exchanger

327 Inlet to second expander heat exchanger

328 Outlet from second expander heat exchanger

330 Compressor circuit condenser

331 Inlet to compressor circuit condenser

332 Outlet from compressor circuit condenser

340 Valve

400 Second medium to be cooled

401 Inlet of second medium

402 Outlet of second medium

500 First medium to be heated

501 Inlet of first medium to compressor circuit condenser

502 Outlet of first medium from compressor circuit condenser

503 Inlet of first medium to expander circuit condenser

504 Outlet of first medium from the expander circuit condenser

EG Exhaust gas

C Compressor

E Expander

MH Motor heat