GB2470278A

GB2470278A - Heat engine and refrigerating heat pump

Info

Publication number: GB2470278A
Application number: GB201007884A
Authority: GB
Inventors: Naji Amin Atalla
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-05-11
Filing date: 2010-05-11
Publication date: 2010-11-17
Also published as: GB201007884D0; WO2010130981A3; WO2010130981A2; GB0908063D0

Abstract

A heat engine 200 or refrigerating heat pump, comprising equipment 205 for dissolving in a solvent a waste working medium produced by the engine or heat pump, a separator 201 arranged to receive the dissolved waste working medium and to separate it into a gaseous working medium and a solvent. Preferably the dissolving equipment dissolves the waste working medium in a solvent to form a rich solvent and the separator separates the dissolved waste working medium into a gaseous working medium and a lean solvent, wherein the concentration of the working medium is lower in the lean solvent than in the rich solvent. The engine may include a turbine (203). There may be heat exchangers to heat rich solvent from the dissolving equipment with heat from lean solvent received from the separator. Preferably the working medium is methane and the solvent is toluene.

Description

Heat engine for producing mechanical work and a refrigerating heat pump This invention relates to a heat engine systems and plants for producing mechanical work or other forms of energy and more particularly to power generation apparatus for producing electrical energy. In addition, this invention relates a refrigerating heat pump.

Current electrical power generation plants use heat engines and systems, often based on closed-loop Rankine cycles, with water as a working medium. In such plants, a fuel is burnt to produce thermal energy and heat the pressurised water in a boiler, thereby producing a high pressure and high temperature water vapour. The thermal energy of this high temperature and high pressure water vapour is then converted into a mechanical output, typically using a turbine. After the turbine has extracted energy from the high pressure and high temperature water vapour, a lower temperature and lower pressure water vapour leaves the turbine and is condensed in a condenser to form liquid water. This condensation step is necessary so that the liquid water can be pumped and pressurized for recycling back to the boiler to complete the closed-loop cycle of the heat engine.

The need for the condensation stage results in a loss of a significant portion of the energy used to heat the working medium. This energy is lost to cooling agents such as sea water or river water, which are used to cool the condenser.

Furthermore, conventional power generating plants use very high fuel combustion temperatures of over 1473 K (1200 °C) to vaporize the working medium under very high pressures of over 4.00 MPa and at temperatures of over 750 K (480 °C). Operating power generating plants at such a high temperature requires the conventional power plants to be constructed robustly. This means the initial cost of building the power plant is relatively high.

Therefore, the inventor has appreciated that it is advantageous to provide a heat engine system which is able to operate at a lower working medium vaporisation temperature than conventional power generating plants but under the same or even higher pressures, but under the same or even higher pressure.

Furthermore, the inventor has appreciated that it is advantageous to provide a heat engine which is also able to operate without the need for a condensing step.

Summary of the Invention

The invention is defined in the independent claims to which reference should now be made.

Advantageous features are set forth in the dependent claims.

According to a first aspect of the present invention, there is provided a heat engine for producing mechanical work, or other forms of energy, comprising means for dissolving in a solvent a waste working medium produced by the engine as a result of the production of mechanical work; and a separating means arranged to receive and to separate the dissolved working medium from the solvent wherein the separating means separates the dissolved working medium into a gaseous working medium and a solvent of the working medium.

When the waste working medium is dissolved in the solvent it forms a rich solvent having a first concentration of working medium. Once separated by the separating means the rich solvent becomes a gaseous working medium and a lean solvent of the working medium having a concentration of working medium lower than the rich solvent. A pumping/pressurization means may be provided to pump/pressurize the rich solvent and the separated gaseous working medium and lean solvent may also be pressurized.

By having such a heat engine comprising a dissolving means, and separating means this avoids the need for a prior art condenser, and hence the efficiency of the heat engine is improved compared to that of conventional heat engines. This is because energy is not lost due to the use of a condenser.

Preferably, the separating means is a fractional distillation means such as a fractional distillation column or flashing means.

Usually, the waste working medium produced by the engine, is a gaseous waste working medium.

However, the waste working medium may be partially condensed to liquid and partially gaseous.

Embodiments of the invention operate at a lower temperature mode in a less harsh environment than that of conventional power plants. Further, conventional power plants may be readily modified to include a heat engine according to embodiments of the invention.

Brief Description of the Drawings

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic diagram of a thermodynamic cycle used in a conventional power plant; Figure 2 shows a simplified schematic diagram of a heat engine according to an embodiment of the invention; Figure 3 shows a detailed schematic diagram of an example of a heat exchanger used by heat engines and heat pumps embodying the invention; Figure 4 shows a detailed schematic diagram of a heat engine according to a further embodiment of the invention comprising a reflux pump; Figure 5 shows a detailed schematic diagram of a heat engine according to another embodiment of the invention comprising a recycle booster pump; Figure 6 shows a detailed schematic diagram of a heat engine according to another embodiment of the invention comprising other heat exchangers; Figure 7 shows a detailed schematic diagram of a heat engine according to another embodiment of the invention also comprising additional other heat exchangers; Figure 8 shows a schematic diagram of a multi-stage turbine which may be used by embodiments of the invention; Figure 9 shows a simplified schematic diagram of a refrigerating heat pump according to another embodiment of the invention; and Figure 10 shows a simplified schematic diagram of another variation of a refrigerating heat pump according to a further embodiment of the invention.

Detailed Description of the Preferred Embodiments of the Invention In the drawings, like features have been given like reference numerals. Referring now to figure 1, the main steps performed by a conventional power generation plant will now be described. Liquid water is first pumped by a pump 107 from a low pressure to a sufficiently high pressure by inputting energy using the pump 107. The high pressure liquid water enters a boiler 101 and is then vaporized under high pressure and at high but constant temperature by inputting energy released from fuel 108. This results in a phase change of the water from a liquid to a high pressure and high temperature saturated water vapour, which typically at this stage has a temperature of 370 to 400 degrees Celsius and pressure of 10 to 22 MPa, The saturated high pressure and high temperature water vapour produced in the boiler 101 is further superheated to a higher temperature of about 750 K (480 °C) at the same pressure of 10 to 22 MPa. The superheated high pressure and high temperature water vapour 102, is fed into a turbine 103. In the turbine 103, the water vapour undergoes adiabatic expansion and a portion of its internal thermal energy is converted to mechanical work. The lower pressure and lower temperature water vapour leaving the turbine, which typically at this stage has a temperature of 100 degrees Celsius, and a pressure of 0.IMPa, is then condensed into a liquid in condenser 105 resulting in a phase change and energy rejection or loss. In the condenser water vapour condenses from a volume of I.7m3 per kg to a liquid volume of 0.001 m3 per kg, and this process results in the loss of the latent energy of vaporization of about 2267 kJ per kg of water.

Referring now to figure 2, a heat engine 200 according to an embodiment of the invention will be described. The heat engine 200 uses a liquid or gaseous working medium 202, (204), and a solvent 206a (206) of the working medium 206a (206). Examples of suitable working media 202 and solvents 206 will be described in further detail below.

The heat engine 200 comprises a separating means, such as a fractional distillation column 201, an absorber 205, and lines, or pipes or tubes or another means for conveying the working medium 202, or solvent 206, from the separation column 201 to the absorber 205 or from one component of the heat engine 200 or heat pump 400 to another component of the heat engine 200 or heat pump 400 embodying the invention.

The absorber 205 is arranged to receive the working medium 204 from the separation column 201.

In one example, a line, or pipe, or tube or other means for conveying the working medium connects the separation column 201 to the absorber 205. The absorber 205 is also arranged to receive, the solvent 206 from the separation column 201.

The function of the absorber 205 is to dissolve in the solvent 206 the gaseous working medium 204 which is output from the separation column 201, through the turbine 203. Further, the function of the separation column 201 is to split or separate the working medium 202, 204 from the solvent 206, 206a in which it is dissolved.

Separation column As mentioned above, the function of the separation column 201 is to split or separate the working medium 202, from the solvent 206, in which it is dissolved. The separation or distillation column 201, may have trays or other types of packing to assist and control separation of the working medium 202 from the solvent 206. The volume of the separation column 201 is sufficiently large to provide suitable space for ready separation of working medium in a gaseous or vapour phase from the solvent.

Turbine In the embodiment shown in figure 2, the heat engine comprises a turbine 203 for producing mechanical work or kinetic energy, although this is optional. Gaseous working medium 202, is withdrawn from the top or a suitable location of the distillation or separation column 201, and is fed to the turbine 203 via a line, pipe or tube, or a means for conveying the gas 202 from the separation column 201 to the turbine 203. The gas entering the turbine 203 is usually a high pressure gas 202 having typical pressure P1 of above 4.0 MPa (40 bar) and a temperature TI of above 450 K (177 DC) The gaseous working medium is allowed to expand in the turbine 203 under controlled conditions, and provides rotational mechanical work, or other types of mechanical work, which may be used to generate electrical power in a generator 215, or perform other type of work.

The working medium 204 exits the turbine 203 under significantly reduced but controlled pressure P2, for example, 0.16 to 0.5 MPa (1.60 to 5 bar), and at a temperature T2, for example 177 K (-96 °C), or any other suitable temperature.

Heat exchanger After leaving the turbine, the working medium 204 is conveyed by a line, pipe or tube, to a first heat exchanger 203a, although the first heat exchanger 203a is optional. The working medium 204, which may be partially or completely condensed, is then heated and partially or completely vaporized in the first heat exchanger 203a, preferably by means of a source of low level thermal energy, such as ambient temperature water 203b, for example river water or sea water. The ambient temperature water may have typically a temperature of between 5 and 25 °C although this is dependent upon the geographical location of the heat engine.

The first heat exchanger 203a has two inputs and two outputs. The working medium leaving the turbine 203 is fed into one of the inputs of the first heat exchanger 203a. Ambient temperature water is then fed into the other input of the first heat exchanger 203a. The low pressure working medium 204 received from the turbine 203 is then heated in the first heat exchanger 203a by the ambient temperature water. The heated low pressure working medium exits the first heat exchanger 203a via the corresponding output. The ambient temperature water 203b is cooled by the low pressure working medium in the first heat exchanger 203a and the cooled water exits the first heat exchanger 203a via the corresponding output. Usually, the first heat exchanger 203a comprises two lines, pipes or tubes which are arranged in close proximity to each other to allow heat to pass between the pipes, without physical mixing of the fluids flowing along the pipes, and this is described in further detail below with reference to figure 3.

Absorber The low pressure working medium 204 leaving the first heat exchanger 203a, which may be partially condensed, is then fed or conveyed by a line, or pipe, or tube, or another means for conveying the working medium into the bottom or a suitable point or points of the absorption vessel 205 or absorber.

The absorber 205 also receives via a line, pipe, or tube lean solvent 206a from the separation column 201 which is pumped into the absorber via a second heat exchanger 210a and a third heat exchanger 210 using a dual liquid operation pump (dual effect pump) 207. The dual liquid operation pump 207 simultaneously pumps two separate liquids from separate tubes, or lines or pipes or conveying means without mixing of liquid which is contained in each of the lines. The dual liquid pump 207 receives low pressure rich solvent 208 from the absorber and pumps it via the second and third heat exchangers 210, 210a to the separation column 201.

The dual liquid pump 207 utilizes the potential energy of the high-pressure lean solvent coming from the bottom of the separation column to minimize the system's overall losses to reduce the amount of energy required by the pump 209 to pump the low pressure solvent 208. In this way, the dual liquid pump (207) pumps the solvent received from the dissolving means using the solvent received from the separation column (201).

If the energy recovered from the high pressure lean solvent is not sufficient to pump the low pressure solvent 208, then an electrical motor or other driving means may be used to drive another pump 209 to provide the additional energy required to pump the low pressure solvent.

Alternatively, instead of a dual liquid pump 207, two separate pumps may be provided. One pump may pump the rich solvent from the absorber 205 via the second and third heat exchangers 210, and 210a to the separation column. Energy of the high pressure lean solvent 206 from the separation column via the second and third heat exchangers 210, 210a can be used to drive a liquid generator and generate electrical power, and then fed to the absorber. However, such arrangement may prove less efficient.

In this way, the absorber 205 receives simultaneous feeding of the working medium from the turbine 203 and lean solvent from the separation co'umn 201. By lean so'vent, we mean a solvent that has less than approximately 1% to 3% by weight of working medium is dissolved in it, although the lean solvent can in principle have no working medium dissolved in it.

In the embodiment shown in figure 2, the absorber 205 comprises a sparger 205a which distributes and forces the gaseous working medium 204 through the liquid solvent 206a thereby introducing the gaseous working medium into the liquid solvent, although the sparger 205a is optional. In the sparger, the gaseous working medium bubbles through the liquid solvent 206a. This improves the contact of working medium 204 with solvent 206a and speeds up the dissolution process of the working medium 204 in the lean solvent 206a to form a rich solvent 208.

By rich solvent, we mean a solvent which has approximately over 12%, for example from 23% to 28%, by weight of working medium dissolved in it, although in principle, it is sufficient for the rich solvent to have at least some (i.e. more than 0% by weight) of working medium 204 dissolved in it.

In the embodiment shown in figure 2, the rich solvent 208, withdrawn from an appropriate point of the absorption vessel 205, is pumped using a pump 209 (in addition to pump 207) to a predetermined pressure and fed into the separation column 201 via the second and third heat exchangers 210, 210a. The pump 209 may be driven by an electric motor. However, having an additional pump 209 can be optional if sufficient pumping may be achieved by dual liquid pump 207.

The pumps 207, 209 increase the pressure of the rich solvent 208 to a pre-determined pressure which is higher than the pressure P1 of the high pressure gas leaving the separation column 201 to ensure the flow of fluid through the second and third heat exchangers 210, 210a and flushing into the separation column 201. The one or more of the pumps 207, 209 may be driven by a motor powered by electricity.

As previously mentioned, low pressure rich solvent 208 is pumped via the second and third heat exchangers 210, 210a to the separation column while high pressure lean solvent flows from the separation column via the second and third heat exchangers 210, 210a and the dual effect pump 207, to the absorber. The operation of the second and third heat exchangers 210, 210a operate in a manner similar to the first heat exchanger 203a.

The high pressure rich solvent 208a is conveyed from pumps 207, 209 by a line, or pipe or tube and enters the second heat exchanger 210 at one input a. In the second heat exchanger 210, the high pressure rich solvent 208a is in close proximity to a hotter lean solvent 206 at high pressure which enters the second heat exchanger 210 at the second input b. In the second heat exchanger 210, heat flows from the hotter lean solvent 206 to the cooler rich solvent 208a. The cooled lean solvent leaves the second heat exchanger 210 at one output c, for input into the absorber 205 via a line, tube or pipe and dual effect pump 207, while the heated rich solvent leaves the second heat exchanger 210 at output d which is then fed to the third heat exchanger 210a and enters the third heat exchanger 210a at input e of the third heat exchanger 210a via a line, tube or pipe. Output g of the third heat exchanger 210a is connected via a line, pipe or tube to the input b of the second heat exchanger 210.

Rich solvent then enters the third heat exchanger 210a at the input point e. In the third heat exchanger, the rich solvent is in close proximity to a hotter lean solvent at high pressure which enters the third heat exchanger at input f via a line, pipe or tube connected to the separation column 201. In the third heat exchanger 210a heat flows from the hotter lean solvent to the cooler rich solvent. The cooled lean solvent leaves the third heat exchanger 210a at one output g for entry into input b of the second heat exchanger 210 while the heated rich solvent leaves the third heat exchanger 210a at another output h for input into the separation column 201 via a line, pipe or tube.

Heat exchanger Referring now to figure 3, an example of the detailed structure of a heat exchanger, such as the heat exchangers 203a, 210, 210a will now be described. As previously described, each of the heat exchangers 203a, 210, 210a has two inputs b, f and a, e and two outputs c, g and d, h. The heat exchanges 203a, 210, 210a are arranged to heat one liquid using hotter liquid without physical mixing of the two liquids. The operation of the heat exchangers will be described with particular reference to heat exchanges 210, and 210a.

Each of the heat exchangers comprises an outer line, tube or pipe 301 and an inner line, tube or pipe 303. For the sake of clarity, these will be referred to as pipes, although the heat exchanger can comprise two or more means for conveying a liquid. The outer pipe 301 surrounds the inner pipe 303, and the inner 303 and outer 301 pipes are arranged so that a fluid can flow between the inner pipe 303 and outer pipe 301. As can be seen in figure 3 on the left hand side which shows a section through the heat exchanger shown on the right hand side of figure 3, the inner pipe 303 also acts as a wall which separates any fluid flowing between the outer pipe 301 and inner 303 pipe and fluid flowing along the inner pipe 303.

As shown in figures 2 and 3, lean solvent enters the heat exchanger 210 or 210a at a temperature T2a or T3 at input b or f and exits the heat exchanger 210, 210a at a cooler temperature T4 or T2a at output c or g. In the heat exchanger shown in figure 3, the lean solvent flows in the space in the heat exchanger between the outer pipe 301 and the inner pipe 303. Further, rich solvent enters the heat exchanger 210 or 210a at a temperature T5 or T5a at input a or e and exits the heat exchanger at a cooler temperature T5a or T6 at output d or h. The rich solvent flows inside the inner pipe 303. In the heat exchanger shown in figure 3, the direction of flow of the rich and lean solvents are substantially opposite to one another. The temperature of the solvent leaving the heat exchanger 203a is cooler than the temperature of the solvent entering the heat exchanger 203a.

Further, the temperature of the lean solvent entering the heat exchangers 210, 210a is hotter than the temperature of the lean solvent leaving the heat exchangers 210, 210a while the rich solvent entering the heat exchanger 210 is cooler than the rich solvent leaving the heat exchangers 210, 210a.

The embodiment shown in figure 2 has two heat exchangers 210, 210a. Each heat exchanger 210, 210a may have a structure like that shown in figure 3, with the two heat exchangers being interconnected by two connecting lines, or pipes or tubes. One pipe connects the output g of the third heat exchanger 210a to the input b of the second heat exchanger 210. Similarly, a second connecting pipe connects the output d of the second heat exchanger 210 to the input e of the third heat exchanger 210a.

Heat exchanger 203a works in a similar way to the heat exchanger shown in figure 3 with working medium leaving the turbine 210 entering the heat exchanger 203a via one input of the heat exchanger 203a, The working medium input into the heat exchanger 203a is heated by ambient temperature water which enters the heat exchanger 203a at another input and exits the heat exchanger at one output. The water leaving the heat exchanger 203a is cooler than the ambient temperature water entering the heat exchanger 203a. Heat is transferred from the ambient temperature water to the working medium as previously described with reference to figure 3. The heated working medium leaves the heat exchanger 203a via another output.

After rich solvent has been heated by heat exchangers 210, 210a, the heated rich solvent 208 is then flushed into the separation or distillation column 201, to separate the dissolved working medium from the liquid solvent, under predetermined conditions of temperature and pressure. The separation column may comprise a heat source to allow the separation of the solvent from the working medium.

High pressure gas is then collects at the top of the separation column due to its lower density, while more dense solvent collects at the bottom of the separation column 201. The high pressure gas 202 separated by the separation column is fed to the turbine 203 to complete the cycle. In this way, the heat engine embodying the invention may be said to be a closed-loop heat engine.

In the heat engine shown in figure 2, the separation column 201 comprises a re-boiler 211, to increase or maintain the temperature of the lean solvent at the bottom of separation column at the required level, and enhance separation of the dissolved working medium from the solvent 208b.

However, the re-boiler 211 is optional. The re-boiler 211 may be heated with any heat source or by using low or medium pressure water vapour or steam 21 Ia or other sources of energy to provide a suitable temperature for the solvent to gather at the bottom of separation column and ensure the proper separation of working medium from solvent.

The re-boiler 211 receives lean solvent which has gathered at the bottom of the separation column 201, reheats this using the heat source thereby vaporising the lean solvent, which usually comprises some dissolved working medium. The vaporised solvent and working medium are fed back to the separation column 201 where the solvent and working medium are separated, as previously described.

Having a re-boiler has the advantage that better separation of the rich solvent 208b into a lean solvent 206 and a gaseous working medium is achieved.

Reflux In an alternative embodiment shown in figure 4, the heat engine 400 further comprises a reflux line 412 and a reflux pump 412a. Some or all of the gaseous working medium which has condensed to a liquid working medium as it passes through the turbine 203 may be pumped from the turbine 203 using a reflux pump 412a to pressurize the liquid and then return it via a line, or pipe or tube or another means for conveying the condensed liquid working medium to a suitable point of the separation column 201 as a primary or an additional reflux step. Having this additional step has the advantage that this minimizes concentration of vaporized solvent in the working medium and hence maximises efficiency of the heat engine. The reflux option is particularly important for heat engines where the operation conditions are below the critical characteristics of the working medium.

In an alternative embodiment shown in figure 5, the heat engine 500 further comprises a reflux line 512 and a recycle booster pump 512a. Some of the lean solvent leaving the heat exchanger 210 or 210a may be conveyed by a line or pipe or tube back to the separation column and pumped into the separation column using a recycle booster pump 512a as a reflux 512.

Pumping the lean solvent 206 from the heat exchanger 210 or heat exchanger 210a back to the distillation column 201 allows for the temperature within the separation column to be controlled and reduced and for the composition of the gaseous working medium leaving the separation column 201 to be controlled.

In an alternative embodiment shown in figure 6, the heat engine 600 further comprises an additional dual liquid pump 607, an additional heat exchanger 610c an additional compressor 613, a further additional heat exchanger 614 and a further additional dual liquid pump 611, to improve efficiency of the heat engine system. This arrangement operates as a heat pump.

The dual liquid operation pump 607 simultaneously pumps two separate tubes, or lines or pipes or conveying means without mixing of liquid which is contained in each of the lines. One line of the dual liquid operation pump 607 runs between heat exchangers 210 and 210a, on a solvent rich high pressure line between the two exchangers 210 and 210a. The second line of the dual liquid operation pump 607 runs between output c of heat exchanger 210 and the absorber 205 feeding lean low pressure solvent to the absorber 205. The dual liquid operation pump 607 uses the high pressure line to fully or partially pump the low pressure line.

The dual liquid operation pump 611 simultaneously pumps two separate tubes, or lines or pipes or conveying means without mixing of liquid which is contained in each of the lines. One line of the dual liquid operation pump 611 runs between heat exchangers 210a and 610c, on a solvent rich high pressure line between the two exchangers 210a and 610c. The second line of the dual liquid operation pump 611 runs between output c of heat exchanger 210 and the absorber feeding lean low pressure solvent to the absorber 205. The dual liquid operation pump 611 uses the high pressure line to fully or partially pump the low pressure line.

The heat exchanger 610c has two inputs and two outputs. Further heat exchanger 614 has two inputs and two outputs. High pressure rich solvent received from the dual liquid operation pump 611 enters the heat exchanger 610c at one input. The high pressure rich solvent heats cooler liquid which enters heat exchanger 610c at the other input of heat exchanger 610c. The liquid which has been heated by the rich solvent received from the dual operation pump 611 then leaves heat exchanger 610c via one output of heat exchanger 610c and is fed to heat exchanger 614 to enter the heat exchanger 614 via one input of heat exchanger 614. This liquid is used to heat a lean solvent which is received via one input of heat exchanger 614 from the bottom of the separation

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column. The lean solvent, which is heated by the liquid received from heat exchanger 610, then leaves heat exchanger 614 for input into heat exchanger 210a.

The selected liquid for the heat pump flowing between heat exchangers 610c and 614 operates in a closed loop which is fed from one output of heat exchanger 614 via the compressor 613 to one input of heat exchanger 610c. The other output of heat exchanger 614 is fed into input f of heat exchanger 210a. With this arrangement, some thermal energy of the high temperature lean solvent is transferred from heat exchanger 614 to heat exchanger 610c. The purpose of this loop is to preserve as much as possible of the high temperature thermal energy from the distillation column and return it to the column by heating the rich solvent 208b to the highest possible level.

In this way heat exchanger 610c heats rich solvent received from heat exchanger 610a using the heat transferred from heat exchanger 614, by the heat pump fluid. Further, heat exchanger 614 cools the lean solvent received from the bottom of separation column 201 to vaporize the heat pump fluid, using the higher temperature of the lean solvent, and transfers heat energy to heat exchanger 610c.

In an alternative embodiment shown in figure 7, the heat engine 700 comprises a two-stage turbine 703. High pressure gaseous working medium 202 is fed from separation column 201 into a first stage of the two-stage turbine 703. Lower pressure working medium, which may be partially condensed, leaves the first stage of the two-stage turbine and is conveyed via a line, or pipe or tube to a heat exchanger 703c. Working medium in the heat exchanger 703c can be heated by the ambient temperature water, or other suitable means, and the heated working medium leaves the heat exchanger 703c via the corresponding output of the working medium input into the heat exchanger, and the heated and vaporized working medium is returned back into the second stage of the two-stage turbine. Heat exchanger 703c may completely vaporise any condensed liquid working medium and superheat it. The cooled ambient temperature water leaves heat exchanger 703c via the other output for outlet of the cooled water. The working medium performs mechanical work in the first and second stages of the two-stage turbine, and leaves the turbine for input into heat exchanger 203a as previously described with reference to figure 2, and completes the heat engine cycle.

Referring now to figure 8, a multi-stage turbine 701 which may be used by embodiments of the invention is now described. High pressure gaseous working medium 202 enters a first stage I of the multi-stage turbine. After it has performed mechanical work through each stage of the turbine, working medium may condense and is fed to the corresponding knock out tanks 703, 705 and 707, to separate the liquid and direct the gaseous portion to the subsequent stage. To minimize the working medium condensation, vapour from the knock out tank may be superheated as described earlier for the two stage turbine. Liquid portions may be fed to the subsequent knock out tank to vaporize some portion and be fed with the uncondensed portion of the working medium of that stage to the next stage, and complete the heat engine cycle.

Working medium then leaves the final fourth stage 4 of the multi-stage turbine where it is conveyed by a line, pipe or tube to a further knock out tank 709, where liquid working medium is separated from gaseous working medium. The liquid working medium in the knock out tank 709 is then fed to a further working medium vaporizer 715, or used as reflux as described earlier. In the embodiment shown in figure 8, the vaporizer is a heat exchanger which uses ambient temperature water to heat the condensed liquid working medium. The heat exchanger has two inputs and two outputs.

Ambient temperature water may be used which enters the heat exchanger via one input where it heats liquid working medium which enters the heat exchanger via the second input. Heated and vaporized working medium leaves the heat exchanger via one output, while water which has been cooled by the liquid working medium leaves the heat exchanger via the second output. The gaseous working medium is then conveyed from heat exchanger 715 to be input into the absorber 205, as previously described with reference to figure 2, and complete the heat engine cycle.

An important property of the selected solvent (liquid) is to readily dissolve gaseous working medium under suitable conditions and also permit ready separation under other suitable conditions.

The working medium may react with solvent to form a compound, which then decomposes with increased temperature, and separate the working medium from solvent, such as the dissolution of hydrogen sulphide (H2S) or carbon dioxide (C02) in Mono Ethanol Amine (MEA).

A number of materials may be used as working media. Such working media preferably have a boiling point significantly below 273 K (0 °C), which allow them to be more readily separate from their associated solvents at wide ranges of suitable temperatures. In contrast the suitable solvents are preferably liquids with a boiling temperature, which is preferably significantly higher than 273 K (0°C) and with sufficiently lower solidification or freezing temperature which is preferably significantly below 273 K (0°C).

Preferably, the difference between the boiling temperature of the working medium and solvent is more than 100 K. Preferred working medium may be selected from the group comprising the following gases: Ammonia, Methane, Nitrogen, Hydrogen, Neon, Argon, Helium, Carbon Monoxide, Carbon Dioxide, Hydrogen Bromide, Hydrogen Iodide, Hydrogen Sulphide, Hydrogen Chloride, and Chlorine gas, and others.

These gases have suitable thermodynamic properties (adiabatic exponent), in terms of ratio of specific heats of gas under constant pressure (Cp) to specific heat of the said gas under constant volume (Cv), and expressed as k: k=CIC Eq. 1 For all these gases the value of k is more than 1.3 in conditions of temperature at 290 K (17 °C) under pressure of about 0.10 MPa (1.0 bar). The value of k is an important factor for extracting thermal energy from the employed gaseous working medium, when it expands through the turbine.

It is an indicator of how much thermal energy can be extracted from a specific weight, for example 1kg or 1 Tonne, of that working medium gas, white expanding across the turbine, under the selected operation conditions of the heat engine.

Suitable solvents are those liquids such as organic or inorganic materials, which are preferably non-corrosive, in which the selected working medium is sufficiently soluble or reacts under certain suitable conditions and the resulting compounds can be easily decomposed and separated from the solvent under other suitable and desirable conditions. There are many such liquids for all the above mentioned gases as working media. The table below lists suitable working media and solvents for use with heat engines according to embodiments of the invention.

Working medium Solvent Ammonia gas Methanol, Ethanol, Butanol, Ethylene Glycol, Organic Ethers, etc Methane gas Benzene, Toluene, Mixed Xylenes Carbon dioxide MEA, DEA, TEA Hydrogen Sulphide MEA, DEA, TEA Table 1: Selected working media and associated solvents for use with heat engines embodying the invention.

Referring now to figure 9, a heat pump 900 embodying refrigeration function of the invention will be described. For the sake of clarity, like features have been given like reference numerals, and will not be described again.

High pressure working medium 202 is conveyed from the separation column 201 to a working medium condenser 903. In the embodiment shown in figure 9, the condenser is a heat exchanger with two inputs and two outputs. The high pressure working medium gas is condensed in the condenser 903 and is ready to be fed to the refrigeration element 903b.

Condensing effect is produce by the ambient temperature water, which enters the condenser 903 at one input and is heated by the condensed and cooled gas in the condenser to liquid. The heated water then leaves the condenser 903 at one output while the condensed working medium leaves the condenser 903 at the other output. The advantage of having the working medium condenser 903, is that the flow rate of the working medium input into a refrigeration element 903b can be

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controlled and also to control the vaporization pressure of working medium in refrigeration element 903b, through the pressure reducers (903c and 903d) and then vaporized working medium in the refrigeration element 903b under significantly lower pressure to produce the required refrigeration effect.

For example, vaporization temperature of the working medium in the element 903b can be controlled at about -15°C by controlling the required reduction and controlling the vaporization pressure through the valves (903c and 903d), to a level which is suitable for producing that level of refrigeration in the element 903b of a freezing apparatus.

The refrigeration element 903b then cools a space which surrounds the refrigeration element with the flow heat from the hotter space to the cooler refrigeration element 803b.

After leaving the refrigerating element 903b, the gaseous working medium passes through a pressure regulation valve 903c and then into the absorber 205, as previously described with reference to figure 2, and completes the heat engine cycle. The pressure regulation valve controls vaporization pressure of working medium liquid in the refrigeration element, and produces refrigeration, as well as controlling working medium pressure required for the absorption process.

An alternative embodiment is shown in figure 10, in which a heat pump 1000 comprises a turbine 203 for producing mechanical work and refrigerating element 903c for providing cooling. As previously described with reference to figure 2, gaseous working medium is fed from the separation column 201 to a turbine where it performs mechanical work on the turbine 203. Cold and low pressure gaseous working medium leaving turbine 203 is fed directly to a refrigeration element 903c through the pressure control valve 903d. Temperature of the low pressure working medium leaving the turbine 203 may be about -95°C. The refrigeration element 903c may be a line or pipe or tube which is in close proximity to an enclosure which is being cooled. The working medium may also expand in the refrigeration element 903c to provide additional cooling. After leaving the refrigerating element, the working medium is conveyed to a pressure regulation valve 903b, which controls pressure inside the refrigeration element, via a suitable line, pipe or tube.

After leaving the pressure regulation valve 1003b the working medium is fed to a heat exchanger 1004 which uses ambient temperature water to heat and vaporize the working medium so that it can be fed back into the absorber 205, as previously described with reference to figure 2, and complete the heat engine cycle.

Analysis of operational steps of the system An analysis of the main operational steps performed by embodiments of the invention will be made assuming that the working medium is Methane Gas (CH4), and that the solvent is Toluene (C6H5-CH3).

Properties of Methane gas (CH4) Methane gas is a stable organic material widely available in nature as natural gas and huge amounts are produced worldwide. It is used mainly as fuel gas for power generation, domestic fuel and as feedstock for manufacturing of many products, particularly ammonia, urea, amino products and Nitric acid. It is a non-corrosive material, with following properties: * Molecularweight 16.042 * Solidification (freezing) point 91.0 K (-182.6°C) * Boiling point 111.6 K (-161.6 °C) * Critical pressure 4.599 MPa (45.99 Bar) * Critical Temperature 190.6 K (-82.9 °C) * Specific Heat Cp, (heat capacity) under constant pressure expressed as JIkg.K, At constant pressure of 0.100 M Pascal (1.0 bar abs) and from 250 K to 360 K: Cp is 2280 J/kg.K, .( 0.545 kcallkg,°C) * Specific Heat Ci,, (heat capacity) under constant volume expressed as J/kg.K * Ratio of specific heats C / Ci,, is expressed as k and, value of k for methane gas at 288 K (15 °C)and under 0.100 M Pa(1.0 bar abs) k = 1.31 CC/1.31 = 2280/1,31 = 1740J/kg.K (0.415 kcal/kg.°C) * If operating conditions of the heat engine embodying the invention are chosen to be in a temperature range from 150 K to 500 K and pressure range from 0.500 MPa to 22.000 MPa, which is above the critical conditions of methane gas. Average ratio of specific heats C / C is expected to be low at: k = 1.20 to 1.45 * Solubility of Methane gas in Toluene: Sufficiently soluble to over 15 % wt, under pressure of about 0.5 MPa g (5.0 Bar abs) and temperature of 293K (20 °C), and is separable by heating, flashing and distillation, Properties of Toluene (Methyl Benzene) C6H5-CH3 Toluene is a very stable petrochemical (aromatic), widely available in world market, very important solvent for a wide variety of materials, with following properties: * Molecular weight 92.14 * Solidification (freezing) point 178 K (-95.0 °C) * Boiling point 384 K (110.7°C) * Critical Temperature 591.7 K (318.3 °C), * Critical pressure 4.06 MPa (40.6 Bar) * Specific heat, in a temperature range: From 283 to 360 K, 2000 J/kg.K (0.478 kcal/kg.°C) * Density 0.8666 kg/L * Widely used as solvent * Readily dissolves methane gas when brought into contact at low temperatures of say 270 to 300 K (-3 to +20 °C). Solubility of methane gas increases with increased pressure of methane gas over toluene.

Example Followed For the System Analysis The most convenient point of the power system to be taken as the start point is the point of working medium entrance to the turbine. At this point, operation parameters of the system are most suitable for precise definition. This point is referred to as step number 1, with the remaining steps being sequentially referred to in the order that they occur after entry of the working medium into the turbine.

Step No 1: Turbine and Power Generation Energy release from the working medium The separated and superheated gaseous working medium is withdrawn from top, or any suitable point, of splitting (distillation) column at the predetermined high pressure P1 and suitable predetermined temperature Ti, and is fed to the turbine/generator system. Working medium expands adiabatically across the turbine and uses its internal thermal energy for expansion and can perform mechanical work. Such expansion results in a significant decrease of temperature of the gaseous working medium by the time it reaches the outlet point of turbine. Outlet pressure of the expanded working medium P2, is controlled at a level which is suitable for the subsequent steps of heating and absorption in the absorber vessel. Outlet temperature is determined by the outlet pressure and working medium gas properties.

The thermodynamics of the expanding working medium gas, across the turbine, are described according to the following equations: Ti 1V2 k-1.0 = _ Equation 2 12 LVIJ And: P1 1-V2 -k = !::,-. Equation 3 P2 LV1J Where: TI, is temperature of working medium at the inlet into the turbine, T2, is temperature of working medium at the outlet of the turbine, VI, is volume of working medium at the inlet into the turbine, V2, is volume of working medium at the outlet of the turbine, P1, is pressure of working medium at the inlet into the turbine, P2, is pressure of working medium at the outlet of the turbine, and k, is the exponent expressed as C/C, of the involved gas, The working medium and solvent are selected to permit operation of the heat engine according to embodiments of the invention in a manner such that the resulting temperature T2 at the outlet of turbine is, preferably but not necessarily, much lower than 273 K (0 °C), to allow the use of low temperature levels of natural energy. Some amounts of working medium may condense through the turbine, a portion of which can be used as a reflux and recycled back to the splitting column, as previously described.

Assuming that the operating conditions of working medium at the designated point of entry into the turbine and across the turbine are: P1 = 22.00 MPa (220 Bar) P2 5.00 MPa (5.00 Bar) Ti = 500 K (227°C) The value of k for methane gas within the pressure and temperature operation ranges of this

example at: k 1.33

In these conditions: h1 is enthalpy of methane gas at 500 K and 22.00 MPa is 1650 kj/kg (394.36 kcal/kg) s1 is entropy of methane gas at 500 K and 22.00 MPa is 9.95 kj/kg.K (2.378 kcal/kg.°C) The working medium, which in this example is methane gas, will expand adiabatically across the turbine, per equations I and 2. The temperature and pressure decrease and volume increase of the expanding methane gas across the turbine is as follows: 22.0 fV2.33 0.5 1V1 f Log (22.00 / 0.5) = 1.33 x Log (V2NI) 1.643 = 1.33xlog(V2NI) V2NI = 17.21 Calculations show that working medium (methane gas) will expand through the turbine from volume Vi to volume V2 by a factor of 17.21, or each one m3 of methane gas entering into the turbine will expand to 17.21 m3 at the outlet from the turbine.

The temperature decrease across the turbine is: 500 17.21 1.331.O T2 1.00 500 /12 = (17.21) ° 500 = T2 X 2.557 T2 = 500 / 2.557 = 195.5 K (-77.46 °C) Therefore, the theoretical temperature decrease across the turbine is: TI -T2 = 500-195.5= 304.5 K (304.5°C) The combined specific heat of methane gas under these conditions is about 2280 J/kg (0.545 kcallkg). Then theoretical specific energy extraction (release) from one kg of methane gas (working medium) expressed as kJ/kg, (kcallkg), is: 304.5 x 2280 = 694,260 J/kg (165.93 kcalfkg) Calculation shows that thermodynamic conditions of methane gas at the outlet of turbine, at 0.5 MPa and 195.5 K, are still at the superheated state and no condensation of methane gas is therefore expected.

Energy released (work performed) by one kg of methane gas, according to the Second Law of Thermodynamics is: Wcyce = h1 -h2 Where: Wcycie is the work performed by the cycle, expressed as the energy extracted from the h1 is enthalpy of methane gas at conditions of inlet point into the turbine at temperature and pressure of 500 K and 22.0 MPa respectively and is 1650 kj/kg (394.36 kcal/kg) h2 is the enthalpy of methane gas at the outlet point from the turbine at temperature and pressure of 195.5 K and 0.5 MPa respectively and is 960 kJ/kg (299.45 kcal/kg) Wcycie = h1 -h2 = 1650-960 = 690 J/kg (164.91 kcal/kg) The calculated value of the specific energy extraction from this method is very close to the value estimated from the adiabatic expansion method. This value of the calculated theoretical energy extraction is considered more accurate and representative of the actual operation conditions of the cycle and is taken as the actual amount of energy which is released by each one kg of methane in the turbine, It is taken also for calculation of energy balance of the heat engine embodying the invention.

Enthalpy of the working fluid medium (methane gas) through the sysytem will be followed and analysed, as the main reference for the energy situation of the heat engine embodying the invention.

Calculation also shows an important factor that temperature of the exhausted methane gas from the turbine exit, is significantly lower than the prevailing atmospheric and sea water temperature, which are normally about 280 to 300 K (7 to 27 °C.

The difference, for example of the ambient temperature of 280 K, is: 280-195.5 = 84.5 K (84.5 °C) Such favourable temperature difference conditions allow for extraction significant amount of thermal energy from lower temperature sources of energy such as sea water, and add to the amount provided by higher temperature sources such as fossil fuel combustion.

Some toluene will also be vaporized and accompany methane working medium from exit of the splitting column and through the turbine. Toluene has low exponent k, and will produce some energy. Presence of toluene is discussed in the separation step No 5 also but is not analysed in

this example.

Step No 2, Energy input a-From Sea Water Heater' As shown in above step No 1, the adiabatically expanded working medium (methane gas) cools down across the turbine, from 500 K to about 195.5 K, which is still at superheated conditions and no condensation of methane gas is expected. The expanding working medium uses significant amount of its internal thermal energy to produce electromechanical work as useful work (output energy). The very cold working medium (methane gas) can be heated by sea water in a suitable heat exchanger from 195.5 K to a temperature which is close to the sea water temperature of, say, 280 K as a portion of input energy to the working medium. If the average annual sea water temperature at that location is, say, 288 K (15 00), the very low temperature of the working medium of 195.5 K, will provide an effective temperature difference (delta) for heat exchanger of more than K, which will allow to reduce the required surface area of the heat exchanger (economic factor).

The pre-heated working medium is fed to the absorption vessel at a pre-determined and controlled temperature, which is suitable for absorption in the selected solvent.

Difference between temperature of the exhausted gas from the turbine and the average temperature of the sea water temperature, is.

288-195.5 = 92.5 K Specific heat of methane gas under conditions of constant pressure Cp, at temperature range of 110 K to 295 K, including some minimal vaporization of any condensed methane gas, averages to about 2280 j/k, (0.545 Kcal / kg).

The amount of thermal energy that one kg of methane gas can absorb (potentially) from the sea water heater will be about: 92.5 x 2280 = 210,900 j/kg, about (50.41 kcal/kg) This is a very significant amount of thermal energy input per one kg of working medium, which will be converted to useful energy output across the turbine/generator, and increase the efficiency on the involved power system.

However, in practice this may not be possible to fully achieve. Dissolution process of methane gas in toluene is expected to generate some heat which will need to be absorbed by the cold methane gas (as will be shown in Stage 3 below).

These conditions can generally be further harnessed to: > Control absorption temperature and exit temperature of the rich solvent from absorber, > Control pumping and pressurization of the rich solvent and ) Control of delta temperature (Delta T) for heat transfer through the heat exchangers, > Reduce requirement for fossil fuels energy, > Control energy balance of the entire system * Step No 3: Absorption process of working medium -Absorption Vessel After the sea water heater, the gaseous working medium (methane gas), ideally but not necessarily, at about 273 K to 283 K, is fed and sparged at controlled pressure to the bottom section of absorption vessel.

Simultaneously the cooled and lean solvent (toluene with small amount of dissolved methane gas) is fed to the top section of the absorption vessel at, preferably but not necessarily, similar pressure and similar or close temperature. For the necessary fast rate of dissolution of methane in toluene, the preferred temperature range is 283 K to 293 K (10 to 20 00). Effective contact between the gas and solvent is needed, to achieve the desired dissolution rate and resulting concentration of working medium in the solvent. It can be achieved by sparging and bubbling of working medium gas into the liquid in the absorption vessel, and/or providing effective agitation (stirring) while eliminating or minimizing, as far as possible, formation of gas phase over liquid phase at the top section of absorption vessel (bubbling state). As the dissolution of methane gas in toluene takes

I

place at higher temperature than the critical temperature of methane gas (of about 280 to 290 K), then it is not expected that condensation of methane can take place and remains in the gas form but dissolved in toluene.

Dissolution concentration conditions of working medium in solvent, preferred at: -Lean solution, solvent (toluene) is fed to the absorption vessel with ideally less than 1% to 3 % dissolved working medium (methane gas), and: Is concentrated at the end of dissolution process to: -Rich solution: solvent (toluene) with ideally 12% wt, to 25% wt, or in the region thereof, of dissolved gas methane and is achievable under a suitable pressure, selected to readily dissolve working medium and maintain the concentration, Such a concentration level of methane gas at the outlet of absorber vessel permits the separation or splitting of sufficient amount of working medium of at least 12% wt, to 18% wt, from the rich solvent in the subsequent stages No 4 and No 5, by the combined effect of: -Heating rich solution in a series of heat exchangers prior to feeding to splitting column and applying re-boiler at the bottom of splitting column to raise the bottom temperature of lean solvent to a sufficiently high level, which will substantially reduces solubility of working medium in the solvent, -Providing a sufficiently large volume in the splitting column, which allows ready separation of working medium from solvent leading to formation of two phase liquid-vapor or liquid-gas status, and, -Augmentation of separation process in the splitter column, with bubble trays, suitable packing, direct contact scrubbing, etc. With 12% to 18% dissolution concentration of working medium in the solvent, it is expected that the desired separation rate (effect) in the absorber can be achieved. Assuming the net separation rate of the working medium methane gas from toluene at 12% wt, the amount of lean solvent G required for dissolution of each one kg of methane gas is: 1.0 G= 1.07.3kg 0.12 Ratio of lean solvent weight, to working medium weight, expressed as R, is: Weight of circulating lean solvent (Gig) R =

I

Weight of separated circulating working medium (G wm) (G) If the ratio R = = 1.0 (G wm) Theoretically, this means that, one kg of working medium (methane gas) will be dissolved in one kg of the lean solvent (toluene with traces of dissolved methane gas) to form a concentration of about 50%.

In practice, the ratio (R) may be different and could be up to 18 or 20.

In this example:

Weight of circulating lean solvent (C Is) 7.3 R= = =7.3 Weight of separated circulating working medium (G wm) 1.0 This ratio means that, one kg of working medium (methane gas) will be dissolved in 7.3 kg of the lean solvent (toluene with traces of dissolved methane gas) to increase its concentration by about 12%. With affecting dissolution pressure of 0.5 MPa (5 bar), it is expected that the solubility of methane gas in toluene to achieve this concentration would be in accordance with Henry's and Raoult Laws.

The dissolution process of working medium in the solvent takes place in an energy exchange neutral conditions and no energy exchange takes place with surrounding ambient. Ideally no significant temperature increase of the lean solvent will occur at the end of dissolution. It may be useful to actually have a decrease of temperature after dissolution, which can help the heat exchange process in the subsequent stage.

Dissolution of methane gas in toluene takes place also without reaction, dissociation or ionization of methane gas in toluene. It is generally a dispersion of methane gas molecules within the toluene liquid molecules. Both materials are stable hydrocarbons and generally retain their chemical, physical and thermodynamic properties in the dissolution conditions.

When one kg of methane gas, at a temperature of 195.5 K about (-77.5 °C), is dissolved in 7.3 kg of toluene at temperature of about 293 K (20 °C), to form rich solution, the resulting final temperature of rich solvent changes slightly. Depending on the heat of dissolution' of methane gas in toluene, the temperature of rich solution may decrease from 293 K (20 °C) to about 290 K (17 °C).

During the dissolution process, the significant shrinkage of methane gas volume takes place. As the dissolution temperature of about 293 K, is significantly higher that its critical temperature of 190.6 K, methane will remain in the gaseous form, but dissolved, and no condensation is expected.

Thermodynamic properties of methane gas and the resulting solution also remain un-changed by the effect of dissolution, as no reaction is involved.

This process is important for the subsequent step No 4, to provide the adequate temperature delta (delta T) for heat exchange process. The required and adequate average temperature difference (Delta T) across the length of the heat exchanger(s) 210, 210a, 611c, etc, is about 12 to 22 degrees K, for the efficient and economic heat exchanging process. If the: -Amount of circulating lean solvent (toluene) entering the absorption vessel per one kg of working medium (methane gas) is 7.3 kg Ratio of the: solvent /working medium = 7.3/1 = 7.3 -Temperature of the lean solvent at the inlet to absorber is 290 K -Required temperature of rich solvent at the outlet of absorption vessel is 290 K -Pressure of the absorption process 0,50 MPa (5 bar abs) There are two contrasting thermal effects which take place during the dissolution process of working medium in the solvent in the absorption vessel, which are: a-Release of energy during dissolution of working medium methane gas in solvent under constant pressure, which leads to increasing temperature of the resulting rich solvent.

b-Energy absorption by the very cold working medium, while dissolving in the solvent, leading to decrease temperature of the rich solvent (two materials), The aim in this step is to control the final temperature at the predetermined level, which is required in the subsequent step No 4, and also to eliminate or minimize the need for any energy rejection.

When methane gas dissolves in toluene it's volume shrinks from about 0.3 m3/kg to about 0.0056 m3/icg (toluene volume) under constant pressure of 0.5 MPs (5.0 bar). Dissolution process will perform mechanical work of approximately: I x 0.5 x 100 x (0.3-0.0056) x 10,000 = 147,200j /kg (35.18 kcal/kg) To avoid temperature increase of the resulting rich solvent, release of this thermal energy will need to be countered with the cold temperature of methane gas. Hence, the required methane gas temperature to act as a thermal sink below the dissolution temperature of 285 K (12 °C), which is sufficient to absorb this amount of thermal energy is: 147,200 / 2280 = 65.8 K (64.56 °C) Assuming this is the total amount of dissolution heat, temperature of methane gas entering to the absorption vessel is: 290 -65.6 = 224.4 K (-48.6 °C) Hence, the net thermal energy input from the sea water heater to one kg of methane gas needs to be: (224.4 -195.5) x 2280 = 65,890 j/kg (15.75 kcal/kg) At the same time, when the high pressure lean solvent is depressurized from 22.00 MPa to 0.5 MPa, each one kg of the lean solvent will lose significant amount of potential thermal energy, equal to: (22.00-0.5) x 100 x 10 = 21,500 j/kg (5.14 kcal/kg) This leads to cooling of the lean solvent by: 21500/1870= 11.5 K Where, 1870 kj/kg is the specific heat of toluene at 280 to 300 K, Hence, to provide suitable delta-T for heat transfer in the lean-rich solvents heat exchangers of about 10 to 15 K, and act as suitable heat sink for the released energy from methane dissolution in the solvent, inlet temperature of the cold methane gas to the absorber will be restricted to about 215 to 230 K. This process (step) permits to keep the latent heat of vaporization (or condensation) of the working medium methane within the system, and avoid the costly process of condensation of the working medium by an outside agent and significant energy losses. Latent heat will no longer be a problematic factor and will circulate within the rich solvent. No condensation process is required.

Control and regulation of the dissolution conditions in the absorption vessel are also driven by the needs of the process conditions of the pumping and heat exchange step No 4 below * Step No 4: Pumping and heat exchangers Rich and cold solvent, toluene with dissolved methane gas (in liquid phase) is withdrawn from absorption vessel at temperature of 290 K (17 °C) and pressure of 0.5 MPa (5.0 bar abs), and is pumped and pressurized progressively to about 22.20 MPa (Pla) or to higher pressure if required by operation conditions and flashing (for example to 30 MPa). Rich solvent is also progressively heated in a series of suitable heat exchangers from about 290 K (17 °C) (T5), to temperature T6, by the effect of hot and lean solvent from bottom of splitting column. Rich solvent is then fed to the splitting column Simultaneously, the lean solvent at a predetermined temperature of T3, for example, 525 K (252 °C) and pressure of 22.00 M Pa, flows from bottom of the splitting column and is passed in a counter current direction through the heat exchangers. Flow rates of both rich and lean solvents are reasonably close and therefore, the temperature of the rich solvent at the outlet of the final heat

I

exchanger T6, is close to temperature of the hot lean solvent from the bottom of the splitter column T3, as shown in figure 3.

Enthalpy of methane gas changes significantly during the pressurization and heating of the rich solvent, and provides possibility to control the process in a manner to have the most preferable operation and economic conditions.

Controlled conditions of pressurization and heating process allow preserving most of the thermal energy introduced into the system within the system, while providing suitable operation conditions to: -Cool down the hot lean solvent from bottom of splitting column to a temperature, which is suitable for absorption process in the absorber vessel, -Heat the cold rich solvent from absorption vessel to highest possible temperature which is suitable for splitting and separation of working medium from solvent in the splitting column, -Establish a high temperature reservoir of rich and lean solvents in the splitting column, Pumping involves input of a small portion of energy into the system by pressurizing the rich solvent toluene and the dissolved methane gas, to a very high pressure.

When the cooled lean solvent is fed to the dual liquid pumps at a high pressure of 22.0 M Pa (220 bar) and depressurized to only 0.5 MPa (5.0 bar abs), it loses significant amount of potential energy which is converted to kinetic energy, and will therefore cool down. Each one kg of the lean solvent loses (about): 1 x(22-0.5)x 1,000 21,500 J/kg (5.14 kcal/kg) If temperature of the lean solvent at the inlet into the absorber is controlled at 293 K, which is also temperature of the lean solvent from the dual pumps, then temperature of the cold solvent at the inlet into the dual pumps (and at the outlet of last heat exchanger T4), is: 293 + ((22 -0.5) x 1000/1850)) 304.62 K (31.62 °C) Where: 1850/kg.K: is the specific heat of toluene at 290 to 310 K Temperature of the rich solvent T5, at the inlet into the first heat exchanger 10, should be sufficiently lower than 304.62 K (31.62 °C), for example about 290 K (17 °C). As mentioned earlier this temperature will depend also on the dissolution heat of methane gas in toluene.

If the flow rates of the rich and lean solvent are known, they allow the following parameters to be defined: a-Required surface Area of the heat exchangers, b-Final temperature of rich solvent at the outlet of the heat exchanger(s) 210, 210a For one kg of working medium (methane): If: -T3is 525K -T4is 304.62 K T5is29OK -T6 is slightly lower than temperature of rich solvent at the inlet into the first heat exchanger, -Average Delta-T along the series of heat exchangers is about 15 to 25 K, (due to differential temperatures along the length of heat exchangers 10, lOa, lOb, etc), -Specific heat of toluene (C01) is 2000 JIkg.K. (0.478 kcal/kg.°C) in the temperature range of 290 to 400K + Enthalpy hex of expanded and superheated methane gas at temperature of 290 K, under pressure of 0.5 MPa, (start of pressurization process) is about 1165,000 J/kg (278.44 kcal/kg) + Enthalpy hpr of pressurized methane gas at temperature of 490 K, under pressure of 22.20 MPa is about 1550,000 J/kg (370.46 kcal/kg) Further, if: -p is the heat exchange coefficient between the hot lean and cold rich solvents, and is about 3350 kj/m2.K.h (800 kcal/m2.°C.h) -No losses of thermal energy = 0.0 J/h To improve heat exchange process by providing a wider delta T across the heat exchangers, it is advisable to conduct heat exchange process from start pressure of 0.5 MPa, to 15.00 MPa to 22.00 MPa (or 300 MPa if required).

In this pressure range, enthalpy of gaseous methane increases with increased temperature and requires increased thermal energy.

The pumping and heat transfer process through the heat exchangers is explained as follows: Total amount of thermal energy (Qs) released by one kg of toluene (hot lean solvent), when cooled through the heat exchangers, while cooling down from 525 K to 304.62 K, is: = 1 x (525 -304.62) x 2000 = 440,760 J/kg (105.34 kcal/kg) Total energy transferred from 7.3 kg of hot lean solvent, per one kg circulating working medium (methane gas) is: 440,760 x 7.3 3.217.550 J/kg (6777.185 kcal/kg) Enthalpy of methane gas at the start of pumping rich solvent is about 1165,000 J/kg and at the end of 3d stage pumping and heating at about 490 K, under pressure of 22.00 MPa is about 1,550,000 J/kg,

Q

Average energy received by the rich solvent, per one kg of working medium methane, at the end of 3d stage of pumping is: 3.2 17.550 / 8.3 = 387,660 J/kg (92.65 kcal/kg) Assuming average specific heat of the rich solvent (Toluene and methane) at 2060 i/kg (0.49 kcal/kg), temperature rise of the rich solvent is: 387,660 / 2060 = 188 K (188 °C) Re-pumping of the rich solvent from 0.5 MPa to 22.00 MPa will result in increasing temperature of the rich solvent by nearly the same amount as that it lost during depressurization at the outlet of the last heat exchanger, which is estimated at: (22-0.5) x 100 x 10 = 21,500 j/kg (5.14 kcal/kg) This will lead to cooling of the lean solvent by: 21500/1870 = 11.5 K Final temperature of the heated rich solvent at the outlet of the final heat exchanger will be: 290+188+11.5= 489.5 K (216.5°C) If reflux is also used, then its flow rate and temperature will be included in these calculations and allowance will need to be made for heat balance of the system.

To preserve energy at this high temperature level, an additional heat exchanger 610c may be added with a suitable compressor to vaporize a suitable liquid (fluid) at, say, 475 K to 490 K, and condense at elevated temperature of, say, 515 K. Such a system minimizes the requirement of fossil fuels, by initially heating the reflux to the highest possible temperature: With the heat exchange and recovery system, the average Delta T (TdeI) for the heat transfer across the entire length of the heat exchangers is expressed as: ((13 -T4) + (T2 -T5))12 ((305 -290) + (525 -489.5))/2 = (15 + 37.5)/2 = 26.25 K (26.25 °C).

The required heat exchange surface area for all heat exchangers will be: 3.217.550/(26.25 x 3350 x 1000) = 0.0366 m2 /kg WM With requirement for the heat recovery and vaporization in the heat exchange system, total requirement for more heat exchange surface, say at 20 to 25% 1.25 x 0.0366 = 0,0457 m2/kg WM Pumping Energy:

Q

Net energy input required for rich solvent pressurization is only that amount required for methane pumping and to compensate for the mechanical losses (due to equipment efficiency, liquid viscosity, etc.) for pumping the rich solvent from 0.5 MPa (1.6 bar abs) to 22.00 M Pa (220 bar).

Although a significant amount of energy is required to pressurize the rich solvent from 0.5 MPa to 22.2 MPa, net energy input into the solvent (toluene) by pumping is close to zero, as the inlet pressure into the splitter column equal to the outlet pressure from the last heat exchanger, which is 22.00 M Pa (220 bar). Net amount of the required energy for pumping is estimated as follows: Energy input from pumping into one kg of rich solvent is: I x (22.2-0.5) x 1000 = 21,700 J/kg (5.19 kcallkg) Energy input per one kg of working medium (8.3 kg of rich solvent) is: 21,700 x 8.3 = 180,110 J (43.05 kcal) Power required to pump this amount of liquid per one kg of working medium methane gas, is about: 8.3 x 1000 x (22,2 -0.5)/ 3600x1 000 = 0.05 KW power, However, about 77 to 82% of pressure energy of the lean solvent is recovered in the dual effect liquid pumps, to pump and pressurize a significant portion of the rich solvent. The net required energy input into the system from outside is only about 18% to 23% of the total required pressurization energy.

Overall required pumping energy per one kg of working medium, which also is the net required pressurization energy for this case, is as follows: Potential pressure energy of the lean solvent per one kg of working medium is: (0.05/8.3) x 7.3 = 0.043 KW Expected energy loss at 80% pump efficiency is: 180,110 x 0.2 = 36,022 J (8.61 kcal) In terms of power, the required power is: 0.043 x 0.20 = 0.0086 KW Without reflux, the net amount of energy required for pumping is: (0.05/8.3)/i.0 (for methane gas) + 0.0086 = 0.0157 KW If reflux is used then, in addition, about 0.0012 KW is required to pump and pressurize reflux from 0.5 MPa to 22.2 M Pa.

The overall energy required for pumping per one kg of working medium, is: (0.05/8.3)/i.0 (for methane gas) + 0.0086 + 0.0012 = 0.0157 KW Net energy required for pumping the full amount of rich solvent of 8.3 kg/kg working medium needs to be included in the overall thermal efficiency of the system which is assumed at about 80%.

Overall energy losses from the system, account for all the expected unavoidable losses, such as: -Pressurization of the rich solvent (pumps efficiencies), -Boosting pump of the reflux lean solvent (if required) -Natural heat losses, -Friction losses, Etc.

Depressurization energy (cooling of the solvent), is accounted for in estimation of the temperature of lean solvent at the end of the last heat exchanger and energy of re-pressurization is also accounted for in the overall energy balances of the system.

a. Step No 5: Splitting (Distillation) and separation of working medium -Re-boiler energy input Heated rich solvent in the heat exchangers, as per step No 4 above, to the maximum temperature possible of 480 K to 495 K, is flashed into the splitting (or distillation) column at a pre-selected point. High temperature of the rich solvent entering the splitting column, combined with the large volume of the splitting column permit to separate and distil working medium, methane gas, from toluene. The column is provided with a reboiler as previously described, which increases solvent temperature at the bottom of splitting column to the required level, and in this example to about 525 K (252 °C) to further augment separation. This temperature is little lower than the critical temperature of toluene, which is 591.7 K (318.3 °C), and at which solubility of methane in toluene is significantly reduced and helps the separation process.

If separation process of methane gas from toluene requires a higher temperature of the lean solvent toluene at the bottom of splitting column, the reboiler is capable to provide it, without significant change to the heat balance of the splitting column.

As mentioned earlier, the dissolved methane gas in toluene is in the superheated state (but dissolved in toluene). Then, another option for separation of methane gas may also achieve the desired result, by: -Further pressurising the rich solvent after the last heat exchanger to about 30 MPa (300 bar) in the pumping step -Further heating the rich solvent in a higher temperature heat exchanger, to about 500 to 510 K, which may create effective bubbling of the working medium -Flushing the bubbling rich solvent into the separation column (201) (or tank) at a reduced pressure of 22 MPa (220 bar) to flush and separate as much as possible working medium from solvent A reboiler (211b) is needed to control the bottom temperature of the separation column and introduce any deficit thermal energy needed by the system for working medium flashing and separation and establish energy balance.

If a suitable separation of the working medium from solvent is achieved by flashing Top temperature of the column (also of the exiting methane gas) is expected to be close to the bottom temperature (of the lean solvent).

Combination of the two options for separation of working medium from the solvent may also be a viable and suitable option.

In practice, it may be advisable also to heat the lean solvent at the bottom of the splitting column to near critical temperature of toluene, which will significantly decrease methane solubility in toluene.

However, this may require large amount of reflux to control the top temperature of the splitting column at 500 K and result in the loss of thermal energy. For the flashing option, this may be desirable, if concentration of the vaporized solvent in the gaseous working medium can be controlled at an acceptable level.

Top temperature of the distillation column is an important parameter and in embodiments of the invention, it is selected and controlled at a level which is suitable for operation, based on characteristics of the solvent and working medium. It is preferable, but not essential that the top temperature of the distillation column, which may also be the inlet temperature of working medium to the turbine (as in this example), is selected to be higher than critical temperature of the working medium. In cases where the top temperature of the splitting column is a saturation temperature of the working medium, then it is advisable that the working medium is further heated after exiting the splitting column to the desired superheated status, to improve efficiency of the power engine system.

Despite control of the top temperature of the separation column, there will always be some solvent vapours in the working medium. Amount of solvent vapours in the working medium depends on the solvent physical and thermodynamic properties and operation conditions, such as, for example only: boiling point, molecular weight, operation pressure and operation temperature.

In this example, at top temperature of splitting column of 500 K, the corresponding vapour pressure of toluene is about 1.20 Mpa (12 bar), and it is expected that mol concentration of toluene in methane gas to be about 4 to 5%. This concentration is not expected to significantly affect turbine operation, but it needs to be taken into consideration in the actual practice.

However, current analyses are made only for the pure methane gas.

Energy input and energy balance of the splitting column is conducted, based on the selected operation parameters, and also to ensure the: -Outlet temperature of working medium from splitting column at the predetermined level of 500 K, and, -Outlet temperature of lean solvent from bottom of the column at the predetermined level of 525K.

-Temperature difference between the bottom and top temperatures of the splitting column at: 525 -500 = 25 K (25 °C), Overall energy balance of the splitting column is achieved and controlled by the reboiler at the bottom of the column, which provides the required (deficit) thermal energy to column. Energy balance is determined according to the First Law of Thermodynamics, for one kg of the circulating Energy input = Energy output If there is a liquid reflux employed, it can be the lean solvent (toluene) which is diverted from the outlet of a suitable heat exchanger (after cooling) to a suitable temperature of, say, 450K. It is fed to the splitting column to condense and scrubbed as much as possible of the vaporized toluene in gaseous methane.

Assuming operation without reflux.

Energy input from reboiler to splitting column is required and calculated to achieve the most efficient conditions. For one kg of working medium, the corresponding weight of the solvent, in this

example 7.3 kg.

Hence, energy gain per 7.3 kg of solvent (for every one kg of working medium methane gas), through heating from the inlet temperature of 489.5 K to 525 K = 2000 x (525-489.5) x7.3 = 51,830 J/kg of working medium (WM) (12.39 KcaI) Dissolved methane gas in the rich solvent enters the splitting column at 489.5 K (215.5 °C) and leaves top of the column at 500 K (227 °C). Temperature difference between the inlet and outlet of methane gas into the splitting column of about 10 K (10 °C), is significant and the associated thermal energy requirement by one kg of methane gas through the heating stage is: (500 -489.5) x 2280 = 23,940 J/kg (5.71 kcal/kg) The decreased solubility of methane gas due to the high temperature of the rich solvent causes separation of the dissolved methane from toluene.

Total energy input into the splitting column by reboiler to heat up the solvent toluene from 489.5 K to 525 K and working medium methane gas per one kg of working medium from 489.5 K to 500 K, respectively, is: (525-489.5) x 2150 x 7.3 + (500-489.5) x 2380 = 557,170 + 24,990 582,160 J/kg (139.14 kcal/kg) The separated working medium exits column top at superheated state of 500 K and under pressure of 22.0 MPa, and is fed to the turbine generator step and repead the cycle.

Energy Balance of the System (full power cycle): Overall energy balance of the system, estimated for one kg of the circulating working medium (methane gas) per the above described steps No 1 to No 5, will be: According to the First Law of Thermodynamics: Energy input = Energy output + 0 loss Equation 4 Where: Q is the energy input into the system Q0 is energy output from the system Q0 is all energy losses due to rejection (if applied), equipment efficiencies and natural causes If the energy losses are assumed = zero, then: Equation 5 * Energy output Q -Theoretical energy output from one kg of working medium ammonia: By methane gas (working fluid) 690 J/kg (164.91 kcal/kg) * Energy input a-By Sea Water (liquid vaporization) 65,890 j/kg (15.75 kcal/kg) From pumping of rich solvent 36,022 J/kg (8.61 kcal/kg) b-From splitting column reboiler Balance 582,160 J/kg (139.14 kcal/kciL.

Total energy input 684,070 j/kg (163.50 kcal/kg) These values of energy input and output to the heat engine (system) are reasonably close and within the limits of estimate errors from different sources.

Actual amount of required energy from the splitting column reboiler is expected slightly higher to account for the natural (unavoidable) losses. This source of energy is very important as it will define the efficiency of the system, and the system will optimize and maximize energy input from the non fossil sources, if possible by all means.

Claims

CLAIMS1. A heat engine (200, 300, 400, 500, 600, 700) for producing mechanical or other forms of means for dissolving (205) in a solvent a waste working medium produced by the engine as a result of the production of mechanical work; and separating means (201) arranged to receive the dissolved waste working medium and to separate the dissolved waste working medium; wherein the separation means (201) separates the dissolved waste working medium into a gaseous working medium and a solvent of the waste working medium.
2. A heat engine (200, 300, 400, 500, 600, 700) according to claim 1 wherein: the dissolving means dissolves the waste working medium in a solvent to form a rich solvent having a first concentration of working medium, and the separation means separates the dissolved waste working medium into a gaseous working medium and a lean solvent of the waste working medium having a second concentration of working medium being lower than the first concentration of the rich solvent.
3. A heat engine (200, 300, 400, 500, 600, 700) according to claim I or 2 further comprising a turbine (203) arranged to receive gaseous working medium from the separating means (201).
4. A heat engine (200, 300, 400, 500, 600, 700) according to claim 1, 2 or 3 further comprising a heat exchanger (203a) arranged to receive working medium output from the turbine (203) or from the separating means (201) and to receive a heating agent for heating the working medium received from the turbine (203).
5. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising a dual liquid pump (207), the dual liquid pump arranged to receive solvent from the separating means (201) and to receive solvent from the dissolving means (205), the dual liquid pump arranged to pump the solvent received from the dissolving means (205), which has a pressure which is lower than the pressure of the solvent received from the separating means (201), using the solvent received from the separating means (201).
6. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising additional heat exchangers (210, 210a) arranged to receive a rich solvent from the dissolving means (205) and to receive a lean solvent from the separating means (201), the heat exchanger arranged to heat the rich solvent received from the dissolving means (205) using the lean solvent received from the separating means (201).S
7. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising lines for conveying working medium and solvent between components of the heat engine.
8. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising a reflux line for conveying liquid working medium leaving the turbine (203) via a reflux pump (4I2a) to the separation means (201).
9. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising a re-boiler arranged to receive a lean liquid solvent from the separation means and to heat the received solvent thereby vaporizing the solvent partially or fully, the liquid and vaporized solvent preferably being fed into the separation means (201) by a line.
10. A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising a reflux line or lines for conveying lean solvent from a heat exchanger (210) via a booster pump (512a) to the separation means (201).
11.A heat engine (200, 300, 400, 500, 600, 700) according to any preceding claim further comprising one or more lines for conveying working medium and solvent between components of the heat engine.
12.A heat engine (200, 300, 400, 500, 600, 700) according to any one of claims Ito 11 wherein one or more materials are employed as working mediums.
13.A heat engine (200, 300, 400, 500, 600, 700) according to any one of claims 1 to 12 wherein one or more materials are employed as one or more solvents.
14.A heat engine (200, 300, 400, 500, 600, 700) according to claim 12 wherein the working medium is methane.
15. A heat engine (200, 300, 400, 500, 600, 700) according to claim 13 wherein the solvent is toluene.
16. A refrigerating heat pump (900), (1000) comprising: dissolving means (205) for dissolving in a solvent a waste working medium produced by the pump as a result of the refrigeration; and separation means (201) arranged to receive the dissolved waste working medium, the separation means being arranged to separate the dissolved waste working medium into a gaseous working medium and a solvent of the waste working medium; wherein the separation means (201) separates the dissolved waste working medium into a gaseous working medium and a solvent of the waste working medium.
17. A refrigerating heat pump (900), (1000) according to claim 16 wherein: the dissolving means dissolves the waste working medium in a solvent to form a rich solvent having a first concentration of working medium, and the separation means separates the dissolved waste working medium into a gaseous working medium and a lean solvent of the waste working medium having a second concentration of working medium being lower than the first concentration of the rich solvent.
18. A refrigerating heat pump according to claim 16 or 17 further comprising a working medium condenser (903) arranged to receive working medium from the separation means (201) and to condense the working medium.
19. A refrigerating heat pump according to claim 16, 17 or 18 further comprising a refrigeration element (903b) arranged to receive working medium from the separation means (201) to cool the refrigeration element (903b). 1.
20. A method of operating a heat engine (200, 300, 400, 500, 600, 700) or a heat pump (900, 1000) comprising the steps of: dissolving in a solvent a waste working medium produced by the engine or heat pump as a result of the production of mechanical work; and separating the dissolved waste working medium into a gaseous working medium and a solvent of the waste working medium.