WO2014154869A1

WO2014154869A1 - Cryogenic heat engine

Info

Publication number: WO2014154869A1
Application number: PCT/EP2014/056293
Authority: WO
Inventors: Jean THIESSARD
Original assignee: Thiessard Jean
Priority date: 2013-03-29
Filing date: 2014-03-28
Publication date: 2014-10-02
Also published as: FR3003897A1

Abstract

The invention relates to a cryogenic heat engine comprising a heat pump (230) and a steam engine (210) with cryogenic fluid, both connected via a counter-flow heat exchanger (235) forming an element of the very-high-pressure chamber of the steam engine and an element of the high-pressure chamber (232) of the heat pump.

Description

CRYOGENIC THERMAL MACHINE

The present invention relates to a cryogenic thermal machine which comprises a heat pump and a cryogenic fluid steam machine connected through a countercurrent heat exchanger.

Its possible application is the production of a Cryogenic injection engine whose purpose is, for example, to co-generate cold and mechanical energy from ambient thermal energy.

Rankine cycle steam engines are Carnot machines for which a fluid passes alternately from the liquid phase to the vapor phase and thus comprises isobaric heating and cooling. By adding a step of steam overheating in the Rankine cycle, Hirn showed a noticeable improvement in yield. The yield limit values of Carnot machines, which include Rankine cycle machines, are expressed as the ratio of absolute temperatures of cold and hot sources. For simplicity, engine manufacturers prefer to use the compression ratio, it is a tautology because the pressure of a gas is directly related to its temperature. Guy Nègre filed patent applications for a cryogenic engine with ambient thermal energy and constant pressure and its thermodynamic cycles, these patent applications being published under the numbers FR2904054A1 and WO2008009681 A1. This invention replaces the cold source of the thermal machines with a low pressure chamber self regenerated by a heat pump. Several features of this invention oppose its industrialization. In the energy balance of the engine, some posts are ignored:

the inertia of the piston whose kinetic movement is reversed twice per cycle;

- the work of the cams for the opening and closing of the piston chamber;

- the alternation of hot and cold temperatures in the piston chamber causes losses of heat energy. This to the detriment of the portion converted into mechanical energy;

- gas leaks between the piston and its envelope.

This last point limits the potential refrigerants mentioned in a large scale use:

- for helium, leakage represents a significant cost;

- for hydrogen leakage induces a significant risk of explosion;

- For all potential gases the leak induces a decline in the working gas stock, and therefore a limitation of autonomy.

We will see in the present invention how to overcome these disadvantages and how to increase the list of potential refrigerants.

In steam engines using organic compounds, authors have replaced the turbine with a screw expander or a cascade of pressure reducers. Documents EP0803639, WO2011035073 and WO9527179 describe such embodiments.

The amount of mechanical energy to be subtracted from the Rankine machine to introduce the fluid into the very high pressure chamber will be smaller in the form of liquid than in the form of compressed gas. But this is paid energetically by a very large amount of heat, because it is necessary to heat and especially to vaporize the liquid after introducing it into the very high pressure chamber. Anyway, it is possible to reduce the energy consumed by the pump. An invention dating back more than 140 years, the injector Giffard (May 8, 1858) has the advantage of using no mechanical part. In the past it was the most economical way to reinject the condensate into the high pressure chamber of a steam engine. Today a hydropneumatic system could possibly compete with it.

The Scottish William Cullen showed in 1755 that water vapor injected under a vacuum bell gave a little ice. The expansion of a compressed gas after the gas has returned to room temperature can produce partial liquefaction of the gas. Thanks to a counter-current heat exchanger in 1871 Linde was able to produce liquid air much more easily. The cooling is even more intense if mechanical energy is provided by the expansion of the gas. This principle was used by Georges Claude in 1902 to perfect the Linde machine with a piston regulator. With a piston regulator there are energy losses. On the contrary with a screw regulator the trigger is perfectly controlled and almost all the energy of the trigger can be used for practical purposes. For example Yo Shiotani in EP2224093A1 decreases the external energy to be supplied to a compressor by mechanically coupling it with a screw expander. See also EP0004609A2 which relates to a cooling device compressor / pressure regulator screw. It is possible to operate a screwless expansion valve, for example in order to liquefy a gas such as nitrogen as described for example in EP0566126. Gas leaks do not prevent a fraction of the gas from liquefying. But this loss reduces the efficiency of a Rankine cycle machine. Because a gas that relaxes without providing work, if only against the atmospheric pressure, sees its temperature increase. This was revealed by the experience of the Modane wind tunnel, air at atmospheric pressure at 300 K is introduced into an empty gas tank. The temperature measured after stopping the turbulence is 500 K.

Refrigerant heat pumps are nowadays a consumer product. Their coefficient of performance or energy efficiency ratio (EER) is generally between 3 and 5. This is an average value given for operation between certain limits.

The rotary piston blowers are industrialized since 1868 (Aerzen) they are able to brew very large quantities of air or gas without lubricant with a positive pressure of the order of 1000 millibars, or to cause a depression of the order 500 millibars. The volumes of gas transferred per kW supplied are in the range of 480 liters to 768 liters per minute.

In parallel flow heat exchangers the fluid outlet temperatures are near and intermediate between the fluid inlet temperatures. At best 50% of the heat can be transferred. With countercurrent heat exchangers the exchange rate is lower for the same area, but the amount of exchangeable heat is much higher. In addition, the outlet temperature of the initially "hot" fluid is close to and slightly greater than the inlet temperature of the "cold" fluid, and the outlet temperature of the fluid initially "cold" is near and slightly lower than the inlet temperature of the fluid "hot". At equal performance, plate heat exchangers are more compact and cheaper than other types of countercurrent heat exchangers. Typically with a plate exchanger, it is possible to obtain deviations of the order of 3 ° C. on each of the input / output pairs. For the same flow rate by increasing the surface of the plates and / or the number of plates the difference can go down to 2 ° C or lower, a limit of the difference is due to the loss of pressure, called pressure drop which is proportional to the number of plates. Many of the industrialized plate heat exchangers can work in temperature ranges from 200 ° C to -200 ° C under pressures up to 30 bar.

Since the preliminary work to the Kyoto Protocol, most states have realized the interest in limiting CO2 emissions and not using greenhouse fluids.

Like all thermal machines, cryogenic engines are subject to the second principle of thermodynamics. Solutions envisaged in conventional thermal machines for reducing energy losses can be applied to cryogenic machines.

In view of this prior art, the present invention proposes a cryogenic thermal machine comprising a heat pump and a cryogenic fluid steam machine connected through a first heat exchanger connected to a very high pressure chamber of the steam engine. an outlet, said first exchanger enclosing a high pressure chamber element of the heat pump, for which the heat pump comprises an evaporator constituting a very low pressure chamber, a condenser constituting said high pressure chamber, an insulated gas booster and a pressure regulating device, the steam engine comprising an insulated condenser constituting a low pressure chamber of the steam engine.

Advantageously, the first heat exchanger consists of a heat-insulated evaporator.

The very high pressure chamber preferably comprises a radiator superheater cryogenic fluid.

The machine advantageously comprises an adjustable pressure regulator, a pressure regulator or several screw regulators connected in series and an injector of liquid cryogenic fluid between the low pressure chamber and the very high pressure chamber.

According to a particular embodiment, the machine comprises several screw expander and a mechanical connection between at least one of the screws of each screw expander and a mechanical transmission shaft.

The evaporator of the heat pump advantageously constitutes a second heat exchanger between the low pressure chamber of the steam engine and the very low pressure chamber of the heat pump.

The "heat pump evaporator-steamer condenser" pair is preferably defined to have selected working pressures such that the steamer's refrigerant liquefaction temperature is above the boiling temperature. refrigerant heat pump, and that out of the first countercurrent type heat exchanger, the liquid refrigerant of the heat pump is at the lowest possible temperature.

The machine preferably comprises a fan present in the low pressure chamber and adapted to stir the cryogenic gas fluid against the evaporator of the heat pump.

The very high pressure chamber of the steam engine is preferably insulated and includes a heat exchanger regulated to control the influx of calories from a hot source supplying the radiator of said very high pressure chamber.

The steam engine preferably comprises a starting system provided with a device for low temperature setting insulated areas of the machine, a transfer gas pump or cryogenic gas fluid from the low pressure chamber to the very high pressure chamber until reaching a stabilized service pressure.

The steam engine advantageously comprises an electric starter.

The invention furthermore relates to a method for implementing a cryogenic thermal machine according to the invention for which working pressures are chosen in the different chambers so that for the couple 'condenser of the steam engine - evaporator of the heat pump »the liquefaction temperature of the refrigerant of the steam engine is higher than the boiling point of the refrigerant of the heat pump.

The method advantageously comprises a thermodynamic cycle according to the following six phases:

- Injection of a high pressure liquid cryogenic fluid;

- Vaporization of the liquid cryogenic fluid by the heat pump;

- Overheating of the cryogenic gas fluid at the operating pressure;

- Relaxation producing work and lowering temperature;

- Exhaust in closed cycle in the low pressure chamber;

- Liquefaction of the cryogenic gas fluid by the heat pump.

According to a particular embodiment, the machine comprising screw expander is introduced a very high pressure cryogenic gas at the inlet of pressure regulators simultaneously with a lubricant at the same pressure as the gaseous cryogenic fluid at very high pressure .

Advantageously, the lubricant is recycled to a storage location before the liquefaction of the cryogenic gas fluid.

The machine of the invention is preferably composed of elements adapted to maintenance, safety and compliance with the legislation on refrigerants and in particular:

- special valves for evacuation of engine chambers and the introduction of cryogenic fluids;

a sufficient dimensioning of the low pressure chamber of the steam engine and safety valve between the very high pressure chamber and the low pressure chamber of the steam engine so that the cryogenic fluid can equilibrate without risk of leakage in the event of stopping the machine;

- A very low pressure chamber of the heat pump of sufficient volume so that the cryogenic fluid can equilibrate without risk of leakage in case of stopping the machine.

In order to reduce the mechanical and heat losses with respect to a piston, the invention provides for the use of a rotary lobe screw expander. As the movement is rotary and continuous, the energy to move the inertial parts is spent once at startup and not twice per cycle. On the other hand at the operating equilibrium the temperature variations for each zone delimited between the lobes is much weaker. It is the variation between two contiguous zones, that is to say the total variation divided by the number of zones delimited between high and low temperature. There is therefore less heat loss than in a piston expander. Another energy advantage is that there are no valves controlled by cams.

The refrigerant gas is fed into the pressure reducer via a manually operated or digitally controlled pressure regulator which is located between the high pressure chamber of the steam engine and the inlet of the pressure reducer. screw. The setting of this regulator makes it possible to increase, decrease or block the power delivered by the liquid injection engine.

As far as refrigerant gas leaks to the outside are concerned, they are limited to the space between the mechanical transmission shaft and its casing. These leaks become unlikely if the pressure of the low pressure chamber is chosen close to the atmospheric pressure. It is possible to add the step sealing system which is used in gas screw compressors on the high pressure side.

There is a second way to consider the losses produced by a refrigerant gas leak that is purely energetic. This is the loss of charge by diffusion between two compartments separated by the rotating lobes. There are two ways to fix it:

- By reducing the pitch of the screws so that the pressure difference between two compartments separated by the rotary lobes is lower.

- Or by adding a liquid lubricant to the gas. By capillarity the lubricant will enhance the sealing of the compartments with each other.

In the case where the first solution does not give satisfaction, it is possible to perform the second in the following manner. The lubricant possibly freed of traces of refrigerant is stored at the pressure of the high pressure chamber. A carburetor reservoir accepts the lubricant in a venturi where the gaseous refrigerant passes between the high pressure chamber and the pressure regulator. There is lubricant spray at the inlet of the screw regulator.

Finally, the low temperature zones are insulated to reduce warming to ambient temperature which is one of the causes of particular losses to cryogenic engines. The machine of the present invention therefore consists of a Rankine cycle steam engine, a heat pump and insulated enclosures.

The steam engine converts the caloric energy of a gaseous refrigerant into mechanical energy by means of a screw regulator. In the low pressure chamber of this machine, the heat exchanger of the heat pump absorbs the calories of the gas cooled by the expansion in order to liquefy it. A Giffard injector or a hydropneumatic pump, controlled by the level of the liquid refrigerant and actuated by the gaseous refrigerant under high pressure, injects the liquid refrigerant into the countercurrent heat exchanger for this liquid refrigerant to be heated by the pump. heat. Driven by successive liquid injections, the vaporized refrigerant is overheated by a circuit containing a fluid at room temperature until the refrigerant is at the working pressure for the next cycle.

The heat pump comprises a regulator constituted as we have seen by a heat exchanger located in the low pressure chamber of the steam engine, a fan present in the low pressure chamber of said machine circulates the gaseous refrigerant on the expander until 'to its liquefaction. A rotary lobe booster creates a vacuum in the expander and propels the gaseous refrigerant from the heat pump into the condenser which is the other circuit of the countercurrent heat exchanger common to the steam engine.

A valve, a throat slowing the flow of liquid, or a pressure regulator regulate the maximum pressure difference between the expander and the condenser. For example one can choose a difference of 0.5 bar. The liquefied refrigerant from the heat pump returns to the regulator to restart the heat pump cycle. To distinguish the very high relative pressure of the heat pump from the higher pressure of the high pressure chamber of the steam engine, this chamber will be more readily referred to as a "very high pressure chamber", even if this high pressure does not occur. is only relative.

The present machine has some common characteristics with the Cryogenic Engine of Guy Nègre and in particular:

- At the outlet of the screw regulator the gas enters the low pressure chamber with insufficiently low temperature to liquefy spontaneously;

- In the low pressure chamber, the heat pump removes the remaining calories until the refrigerant liquefies, which can start a new cycle again;

the working gas is a cryogenic fluid used in a closed cycle stored in the liquid phase, working in the gaseous phase and brought back to the stock in the liquid phase;

- The gas under very high pressure is admitted to the inlet of a screw expander whose screws are connected to a motor shaft, which is similar in purpose.

He distinguishes himself by several others:

- The fluid in the liquid state and at low temperature is injected into the lower part of the very high pressure chamber;

- In the lower part of the very high pressure chamber constituted by one of the two circuits of a countercurrent heat exchanger the liquid fluid is heated by the heat pump whose fluid passes into the other circuit;

- In the upper part of the very high pressure chamber the fluid is vaporized and superheated to the operating pressure by a parallel flow heat exchanger where circulates a fluid at room temperature.

The temperature of the gas may remain deliberately below the ambient temperature;

- The expansion of the gas causes the rotation of the screws and the energy of the gas is transformed into mechanical work which decreases its temperature. (similar on the purpose).

Now back on the heat pump. The different parts of the heat pump are located in insulated enclosures near the boiling point of the refrigerant. When the booster works, a flow of gaseous refrigerant circulates and a balance is established. Per unit of time, equivalent amounts of refrigerant vaporize in the expander, are pulsed by the booster in the gaseous state, liquefied in the exchanger against the current and return in liquid form in the expander. The quantity of refrigerant transported depends on the efficiency of the booster under the difference of chosen pressure. The efficiency of commercial blowers ranges from 480 liters per kW for flow rates of 3 to 4 m3 / minute and can reach 768 liters per kW for flow rates of the order of 30 to 75 m3 / min. Knowing the difference in pressure between the regulator and the condenser, the density of the gaseous refrigerant and the heat of vaporization, it is easy to calculate the EER of a particular refrigerant. There are values between 3.8 and 6.5.

The refrigerants of the heat pump and the steam engine can be identical. If they are of a different nature, the boiling point at atmospheric pressure of the refrigerant of the heat pump must imperatively be less than or equal to the point of liquefaction at atmospheric pressure of the refrigerant of the steam engine, in order to allow the heat transfer from the low pressure chamber of the steam engine to the very low pressure chamber of the heat pump. The heat transfer from the high pressure chamber of the heat pump to the evaporator seems to never pose a question, since at constant volume and double pressure, the absolute temperature of the refrigerant will double. The issue is actually different. The energy from the hot source is sufficient to evaporate and overheat the refrigerant of the steam engine. What the whole system needs is to ensure that the liquefied refrigerant of the heat pump is at the lowest possible temperature before coming into the evaporator of the heat pump, It is achieved by causing the booster to work in depression, because under very low pressure the evaporation temperature of the refrigerant of the heat pump is lower than the liquefaction temperature of the refrigerant of the heat pump expanded to a higher pressure

Let's calculate the energy transformations of the Cryogenic Thermal Machine. A volume of pressurized gas at the operating temperature enters the screw expander at each turn. During the same turn, the expansion of the gas is carried out all along the regulator and during this same turn the same amount of gas exits at the other end of the regulator under a larger volume and a lower temperature. See Figure 1 which schematizes the volume variations between two "pinches" corresponding to the screw of the regulator for each fraction of a turn.

As we work at low temperatures increasingly closer to the point of refrigerant liquefaction, perfect gas equations are no longer usable. The heat capacity of the gas must be taken into account. Cv is the heat capacity at constant volume and Cp the heat capacity at constant pressure. The transferable heat energy from the gas is therefore at the beginning:

Hgaz = n .R.Ti + n. Cv. Ti = (R + Cv). not . Ti

More simply by noting that Cp = Cv + R:

Hgaz = Cp. not . Ti

This heat capacity itself varies with the temperature in a calculable manner generally presented in the form:

Cp = a + b. T + c. T ² + ...

If a lubricant is present in a certain proportion, it removes as much proportion of gas. The lost momentum outweighs the gain that the enthalpy of the gas lubricant can give. The volume still accessible by the gas will be taken into account when lubricant is present.

Since there are volume variations throughout the regulator that induce pressure variations that induce temperature variations, a static formula is not suitable. We must integrate the consequences of infinitesimal variations.

With each infinitesimal variation of the volume corresponds a transferred mechanical energy:

dE = dV. P

This energy is subtracted from the energy present at the previous moment:

H (t + dt) = H (t) - (dV P)

The new temperature is calculated from the new volume

If there is a lubricant, the temperature is corrected in proportion to the heat capacities of the liquid and the gas and the quantities involved.

Finally the new pressure is calculated according to the new volume and the new temperature.

Integration stops, or has to be discussed, when one of the conditions that limit energy transformation appears. These conditions are as follows:

- all available energy has already been converted into mechanical energy;

the temperature of the lubricant approaches the freezing temperature of the lubricant; - the expansion of the gas reaches the limit of the screw expander, or screw regulators placed in series;

- The pressure of the gas in the low pressure chamber becomes close to the pressure of the gas in the pressure regulator of the heat pump. The transfer of heat can be done only if the pressure in the regulator is lower in the case where the refrigerant used is of the same chemical nature;

the temperature of the gas approaches the liquefaction temperature of the gas for the pressure obtained;

Regarding these last two points, it is possible to know them by looking at the Mollier chart of the refrigerant used. Unfortunately, Mollier's graphics are not available for all refrigerants or sometimes the lower part of the curve is missing if it does not really interest the refrigeration specialists. More advantageously we can estimate it using the Trouton-HildeBrand rule:

dSHild / R = dSebul / R-ln (Tebul / 373)

The number obtained is generally close to 10.5 but it can vary from 7.4 to 13.2. The interest of this rule is to know this coefficient from the boiling temperature and the heat of vaporization.

References :

- Wikipedia: Trouton Rule.

- Trouton showed first that the entropy of boiling of most liquids was of the order of (10; 5 +/- 0.5). R where R is the constant of perfect gases

- F. Trouton, Philosophical Magazine, 1884, 18, p.54.

- Hildebrand has made a correction with the boiling temperatures that makes the rule of Trouton-Hildebrand is verified throughout the field of boiling temperatures

J. Hildebrand, J. Am. Chem. Soc., 1915, 37, p.970, 1918, 40, p. 45.

- J. Hildebrand and RL Scott, The Solubility of Nonelectrolytes, Dover Publications, ^3rd ed, 1964, p.. 79.

The following transposition of this rule:

Pébul = exp (dSHild / R ^* (Tdét-Tebul at 1 bar) / Tdét))

gives the boiling pressure for a given temperature with usually a good enough precision. It is possible with a spreadsheet to reconstruct the left part of Mollier's graphs and to check the value of the calculation on the portions of the graphs available.

Other features and advantages of the invention will become apparent on reading the following description of non-limiting exemplary embodiments of the invention with reference to the drawings which represent:

in Figure 1: a simplified diagram of operation of a screw expander. This diagram serves as a support in the method of calculating the effects of a screw expander; in FIG. 2: a simplified diagram of a device according to the invention;

in Figure 3: a diagram of an embodiment of the invention operating without lubricant. The reference numbers of the form 3xx signal changes with respect to Figure 2;

in Figure 4: a diagram of a variant of the invention operating with a lubricant. The reference numbers of the form 4xx indicate modifications with respect to FIGS. 2 and 3.

According to the thermal machine of FIG. 2, in the heat-insulated lower part 232 of a high-pressure chamber, the counter-current heat exchanger 235 of a heat pump heats a liquefied refrigerant.

The ambient air, pulsed by a pump 251 inside a radiator 252, vaporizes and overheats the refrigerant. A pressure regulator 204 transfers the refrigerant to the inlet of a screw expander 210 connected to a mechanical transmission shaft 219. The expanded refrigerant escapes into an insulated low-pressure chamber constituted by the condenser constituting a low-pressure chamber 220 where the aerial part of the heat pump 230 liquefies the refrigerant. When the liquid level is correct 224, a float 221 triggers the operation of a pump 225 which injects the liquid refrigerant into the heat exchanger 235 to cool the heat pump fluid and complete the cycle.

The thermal machine of FIG. 3 consists of a very high pressure chamber 301 containing in its upper part a refrigerant in the gaseous state 302. A pressure regulator 204 controlled by a manual device or by a numerical control causes the refrigerant gas in a screw regulator 311. At the outlet of the screw expander 311, the partially expanded gas passes into an expander 312. A regulator screw 311 and a regulator screw 312 are mechanically connected to a transmission shaft 319 which can be the source of a mechanical movement directly used by a propeller, a driving wheel or by a conversion system such as a gearbox, an electric generator, various pumps.

The outlet 318 of the screw expander 312 opens into a low-pressure heat-insulated chamber constituted by the condenser constituting the low-pressure chamber 220. At the bottom of the low-pressure chamber, a contact 321 moved by a float opens a valve 327 when the level 224 liquefied refrigerant exceeds a ceiling value. This valve 327 holds the refrigerant gas under pressure from a pipe 360 of the upper part of the very high pressure chamber. This opening triggers the operation of a Giffard injector 225 to introduce through a check valve 326 the refrigerant in the lower part of the very high pressure chamber which is placed in a heat-insulated enclosure 232. The pipe 323 which connects the valve 327 and the Giffard injector 225 is insulated to prevent the refrigerant gas under pressure from condensing at the bottom of the pipe 360. A hydro-pneumatic pump driven by the refrigerant gas under pressure can replace the Giffard injector.

A heat pump is imbedded in both chambers of the steam engine. In the low pressure chamber of the steam engine resident a fan 337 and a radiator producing an evaporator 331 which is the very low pressure chamber of the heat pump. In insulated enclosure 232 an additional insulated wall 338 isolates a gas booster 334 and the uppermost part of the countercurrent heat exchanger from all other parts that reside there and work at a lower temperature:

the lower input / output torque of the heat exchanger 235

a chamber 333 sized to accept all the refrigerant in the gaseous state in the event of prolonged stopping of the engine,

a valve which opens when the pressure of the liquid at the outlet of the heat exchanger 235 reaches a set value, or else a constriction of a pressure regulator device 336 which limits the flow of liquid in such a way that there is a pressure difference. All or part of this pressure difference may result from the loss of load related to the number of plates of the heat exchanger 235. - The pipes that join the evaporator 331, the very low pressure chamber 333 and the gas booster 334.

Another insulated pipe joins the pressure regulator device 336 to the radiator constituting the evaporator 331.

The high pressure chamber of the heat pump is located between the gas booster 334 and the valve or necking of the pressure regulating device 336 and includes one of the two circuits of the counterflow heat exchanger 235. The other circuit of the heat exchanger goes from the non-return valve 326 to the exit 340 from which escapes the refrigerant of the vapor machine in gaseous form and some liquid refrigerant if the refrigerant could not be totally vaporized. These fluids are brought into the upper part of the very high pressure chamber by a pipe. Inside the upper part of the very high pressure chamber a radiator 252 will vaporize the remaining liquid refrigerant and superheat the gas obtained at the ambient ambient temperature. An ambient fluid 350 is drawn by a pump 351 inside the radiator 252, and the cooled fluid is discharged into the environment at 359.

The heat pump cools the refrigerant of the steam engine in the condenser constituting the low pressure chamber 220 to complete the liquefaction of this refrigerant and warms it in the heat exchanger 235 to dissipate the calories it has acquired so as to to be able to continue his mission in the next cycle

To start the system, the insulated enclosures 232 and 220 are brought to a low temperature, and a pump (not shown) transfers the refrigerant gas contained in the low pressure chamber constituted by the condenser constituting the low pressure chamber 220 to the very high pressure chamber 301 and optionally an electric starter gives a pulse on the drive shaft to move the screw regulator or regulators.

The embodiment of Figure 3 is suitable if the leaks between the different bearings of the screw regulators are negligible. Let's look at the case where a lubricant is absolutely necessary. In the embodiment of Figure 4, the very high pressure chamber 401 of the steam engine has a cell 403 for storing the lubricant. A valve 405 controlled by filling a tank in the manner of a carburetor releases the lubricant into a venturi 406. The Very high pressure refrigerant gas jet released by the pressure regulator 204 nebulizes the lubricant. The refrigerant gas and lubricant mixture enters a first screw expander 311 or the refrigerant expands by imparting mechanical energy to the transmission shaft 319. The refrigerant gas and lubricant mixture then enters the second screw expander 312 for continue the expansion of the refrigerant gas and transmit mechanical energy to the transmission shaft 319. In the case where the liquefaction temperature of the refrigerant is lower than the lubricant melting temperature such as with the isopentane for the When the lubricant temperature is still slightly above the melting temperature of the lubricant, the expansion is stopped. The lubricating refrigerant gas mixture passes into a heat-insulated 444 U-tube in an enclosure 420. The lubricant drips onto grids and accumulates at the bottom of the U-tube and the liquid level 442 rises. A contact 441 connected to a float pilot the operation of a pump 445. When the level 442 is sufficient, the pump 445 is turned on. The lubricant is injected through a check valve 446 into the lubricant reservoir 403. The pump 445 may be replaced by a hydropneumatic pump.

The gaseous refrigerant escapes from the second leg of the U-tube 444 and enters the upper zone of the low-pressure chamber where there is a second U-shaped tube 449. Thanks to the heat pump the temperature of the chamber Low pressure is much lower than the expanded gas outlet. The second U-tube is also at this very low temperature which freezes on the grids the few drops of lubricant that may have escaped the first tube U. This device thus acts as a lubricant trap. The gaseous refrigerant continues its route in the middle part of the low pressure chamber to be liquefied in contact with the condenser of the heat pump. There is no difference with the embodiment of Figure 3 until the return of the liquid refrigerant mixture, gaseous refrigerant in the middle part of the very high pressure chamber 401. It is interesting to control the pressure and the temperature inside the very high pressure chamber 401. Too little airflow or heat transfer fluid in the radiator will induce a drop in pressure and a decrease in available power. Conversely in case of heat wave, or if the ambient fluid is warmed, the temperature and the pressure will rise. If the lubricant is volatile, it could vaporize and disrupt the operation of the screw regulators. For this reason, the very high pressure chamber 401 is insulated and the pressure switch 457 will regulate the pressure and the temperature by controlling the pump 351 for circulating air or ambient heat transfer fluid.

The hot source can be any natural environment, or any private or industrial heating source whose temperature is higher than the boiling temperature of the cryogenic fluid used. The hot source may also consist of beams of light or electromagnetic radiation concentrated by reflectors.

The cold source is created artificially at startup by pumping calories through a heat pump, or using a refrigerant such as liquid nitrogen for example. This cold source is then maintained by the heat pump using part of the energy provided by the machine. As the heat pump is able to pump more calories than it consumes energy to operate, the enthalpy lost to liquefying the refrigerant will be divided by the energy efficiency ratio (EER) of the heat pump.

The sum of all the energy losses including the maintenance energy of the heat pump must be less than the energy supplied by the cryogenic thermal machine for the said machine to operate after the start-up period. If the enthalpy of liquefaction of the refrigerant is sufficiently low, then it is possible that the energy balance is favorable to the Cryogenic Thermal Machine.

The energy balance = the available power - the consumption of the heat pump which boils down to the consumption of the gas booster 334 - the consumption for the injection of the liquid refrigerant - the possible consumption for the injection of the lubricant - the consumption for external and internal breakdowns.

If the balance is positive, the machine provides energy as long as the heat source provides calories.

If the balance is negative, the machine stops very quickly after stopping the starting system, even if there are calories available in the hot source. We are now able to simulate refrigerant behavior in a thermal machine according to the invention, to compare them, if the conditions may be similar, or to discuss the advantages and disadvantages.

The lubricant proposed here is iso pentane, because it is liquid on a large scale: +28 ° C to -160 ° C. For the di-nitrogen this lubricant does not cover the scale - 160 to -196 ° C. It largely covers the use of tetrafluorocarbon (R14) but is not miscible to it. For these two reasons, if the presence of a lubricant proves unavoidable, it is necessary to modify the Cryogenic Thermal Machine to provide a distribution of the lubricant and a lubricant trap. Also to fix the ideas, we suppose here that the first regulator with screw of the series of the regulators with screw necessary would be able in reverse mode to compress 1700 liters of air per minute. Finally the ambient temperature is 28 ° C and the starting pressure is 30 bar.

R14 is tetrafluoromethane (CF4), R23 is trifluoromethane (CHF3). We see that dinitrogen and R14 can be selected as refrigerants for the thermal machine of the invention. On the other hand, the R23 which differs from the R14 only by an atom can not be selected.

Since the machine consists of two refrigeration systems, all elements required by those skilled in the art and by legislation must be present. Without being exhaustive the list of these elements must provide:

valves for evacuating and filling the steam engine and the heat pump with refrigerant;

- low pressure chambers, or maintenance tanks large enough to accept all the refrigerant under pressure in case of heat wave;

- safety valves;

To start the system it is also necessary to have a low temperature setting of the chambers, a pump to transfer the refrigerant from the low pressure chamber of the steam engine to the very high pressure chamber of the steam engine and possibly an electric starter as on conventional heat engines.

A Cryogenic Injection Engine (MCAI) based on the cryogenic thermal machine of the present invention can be used by directly using the mechanical force to propel marine, aquatic, submarine, underwater, ground or underground vehicles by cooling the propulsion medium.

Coupled with an electric generator the MCAI provides electricity in situations where the supply of fuel is difficult or expensive, from natural sources of heat such as the ambient atmosphere, the sun, geothermal energy, so-called Provencal wells or Canadian, the water of oceans, seas, rivers, rivers or lakes, geysers.

MCAI is used to convert the heat dissipated in all machines used to compress gases for pneumatic machines or gas-liquefying machines into electricity or mechanical energy.

In an industrial environment, MCAI can trap aerosols or polluting vapors by supplying mechanical or electrical energy.

The MCAI can be used to cool machinery or premises by providing mechanical or electrical energy, this concerns air conditioning, refrigeration, freezing, ice rinks.

MCAI coupled with a heat pump can be used to heat habitats. MCAI is particularly useful in case of heat wave or hostile environment such as desert areas or deep mines.

Claims

1 - cryogenic thermal machine comprising a heat pump and a cryogenic fluid steam machine connected through a first heat exchanger (235) connected to a very high pressure chamber (301) of the steam engine via an outlet ( 340), said first exchanger enclosing a high pressure chamber element of the heat pump, characterized in that the heat pump comprises an evaporator (331) constituting a very low pressure chamber, a condenser constituting said high pressure chamber, a booster insulated gas valve (334) and a pressure regulating device (336), the steam engine having an insulated condenser constituting a low pressure chamber (220) of the steam engine.

2 - cryogenic thermal machine according to claim 1 wherein the first heat exchanger consists of a heat-insulated evaporator (235).

3 - cryogenic thermal machine according to claim 1 or 2 for which the very high pressure chamber comprises a radiator (252) superheater cryogenic fluid.

4 - cryogenic thermal machine according to claim 1, 2 or 3 comprising an adjustable pressure regulator (204), a screw pressure regulator or several screw regulators connected in series (311, 312) and an injector (225) of liquid cryogenic fluid between the low pressure chamber (220) and the very high pressure chamber (301).

5 - cryogenic thermal machine according to claim 4 comprising a plurality of screw expander (311, 312) and a mechanical connection between at least one of the screws of each screw expander and a mechanical propeller shaft (319).

6 - Cryogenic thermal machine according to any one of the preceding claims wherein the evaporator (331) of the heat pump constitutes a second heat exchanger between the low pressure chamber (220) of the steam engine and the very low chamber pressure of the heat pump.

7 - Cryogenic thermal machine according to any one of the preceding claims for which the couple "condenser constituting the low pressure chamber (220) of the steam engine - evaporator of the heat pump (331) "is defined to have selected working pressures so that the liquefaction temperature of the refrigerant of the steam engine is greater than the the boiling point of the refrigerant of the heat pump, and that when leaving the first heat exchanger (235) type against the current, the liquid refrigerant of the heat pump is at the lowest possible temperature.

8 - Cryogenic thermal machine according to any one of the preceding claims comprising a fan (337) present in the low pressure chamber (220) and adapted to stir the cryogenic gas fluid against the evaporator (331) of the heat pump.

9 - Cryogenic thermal machine according to any one of the preceding claims, the very high pressure chamber (401) of the steam engine is insulated and includes a regulated heat exchanger (457, 351) to control the influx of calories from a hot source (350) supplying the radiator (252) of said very high pressure chamber.

10 - cryogenic thermal machine according to any one of the preceding claims for which the steam engine comprises a starting system provided with a device for setting low temperature insulated areas (220, 232, 301, 338, 401) of the machine, a gas pump for transferring the gaseous cryogenic fluid (s) from the low pressure chamber (220) to the very high pressure chamber (301, 401) until a stabilized operating pressure is reached.

11 - Cryogenic thermal machine according to any one of the preceding claims wherein the steam engine comprises an electric starter.

12 - Process for implementing a cryogenic thermal machine according to any one of the preceding claims for which operating pressures are chosen in the different chambers such that for the couple "heat-insulated condenser constituting the low-pressure chamber (220 ) of the steam engine - evaporator of the heat pump (331) »the liquefaction temperature of the refrigerant of the steam engine is higher than the temperature boiling of the refrigerant from the heat pump.

13 - Process for implementing a cryogenic thermal machine according to claim 12 comprising a thermodynamic cycle according to the following six phases:

- Injection of a high pressure liquid cryogenic fluid;

- Vaporization of the liquid cryogenic fluid by the heat pump;

- Overheating of the cryogenic gas fluid at the operating pressure;

- Relaxation producing work and lowering temperature;

- Exhaust in closed cycle in the low pressure chamber;

- Liquefaction of the cryogenic gas fluid by the heat pump.

14 - Process for implementing a cryogenic thermal machine according to claim 13 for which the machine comprises screw pressure regulators, a very high pressure cryogenic gas is introduced at the inlet of screw pressure regulators (311, 312) simultaneously with a lubricant (403) at the same pressure as the gaseous cryogenic fluid at very high pressure.

15 - Process for implementing a cryogenic thermal machine according to claim 14 wherein the lubricant is recycled (444, 446) to a storage location before the liquefaction of the cryogenic gas fluid.