JP2011094942A - Gas cycle type external combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and feasible consumer-use heat engine capable of using a high efficient heat engine durable at a middle and high temperature for power generation or cogeneration by using a refrigerant such as HFC, HC or CO<SB>2</SB>widely used for refrigeration and air conditioning as an operation medium. <P>SOLUTION: The operation medium such as HFC is compressed in a superheated state by a compressor, and is heated by a middle and high temperature heat source, and then, adiabatically expanded in an expander to obtain power. Net output power is obtained by subtracting input required for compression from the obtained power. As a compression process approaches isothermal compression, the power required for driving is reduced to improve the heat efficiency, and thereby, a multistage compressor with intermediate cooling or a single-stage compressor with special structure improvement is used. As the practical application, a two-stage compressor with an intermediate cooler is used, the whole of a driving part such as the expander is integrally stored in a pressure container to be easily used, and heat efficiency is improved further by a heat regenerator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

Since the present invention is difficult to use in the past, the external combustion type heat generated by a completely new gas cycle that effectively recycles the medium-to-high temperature heat source (mid-high temperature heat) around 200 ° C. to 300 ° C., which has been discarded. Regarding the engine (external combustion engine). Based on volumetric compression mechanisms for refrigerants (working media) such as HFC (fluorocarbon), HC (hydrocarbon), or carbon dioxide (CO2), which are conventionally used in conventional home or small business or vehicle air conditioning equipment Combined with a positive displacement expander capable of operating at high temperatures, a highly energy-saving consumer heat engine that mainly constitutes a 1 to 10 kW class output system is realized. This heat engine adiabatically expands the working medium in the superheated steam (gas) state to obtain the maximum driving force, and at the same time, the compression is performed in the superheated steam (gas) state in a substantially isothermal or isoenthalpy state to minimize the required power and improve the efficiency. Configure a gas cycle that produces a high net output. For this reason, not only exhaust heat exhausted from internal combustion engines such as vehicles and gas engine heat pumps (GHP), micro gas turbines, high-temperature fuel cells such as SOFC or factories, but also mid-high temperature heat obtained from solar heat, biofuel combustion heat, etc. It can be widely used as a high-efficiency clean energy-related device such as co-generation that can be used as a heat source for heating from outside the system to obtain output such as power generation and shaft power, and at the same time use the exhaust heat also for hot water supply and heating.

External combustion engines such as Stirling engines and Rankine engines are known as heat engines that drive various medium and high temperature waste heat as a heat source for high temperature side heating. However, practically none of them are practically used in the consumer market. The former Stirling engine uses high-pressure hydrogen, helium, etc. as the working medium, so the structure for preventing leakage inside and outside the housing and improving heat transfer is complicated, and the working medium is not suitable for high speed due to reciprocating motion. Therefore, it is difficult to reduce the size and the casing is large and heavy, so that it is likely to be expensive and difficult to spread. The latter Rankine engine has been regarded as unsuitable for medium to high temperatures due to the matching of the working medium and the expansion mechanism, and requires a special pump to raise the pressure of the liquid working medium from low pressure to high pressure. Application to heat is not progressing. Recently, attempts have been reported to recover the exhaust heat of vehicles and generate electricity, but they have not been put into practical use.

The conventional Rankine engine converts the enthalpy difference of the working medium when the working medium is heated to the maximum temperature in the heat cycle with a high-pressure heater and adiabatic expansion with an expander to low pressure and low temperature, and then cools. It is composed of a heat cycle that is liquefied and increased from a low pressure to a high pressure by a liquid pump and returned to the heater again. When this is used as a medium / high temperature heat source, refrigerants (working media) such as HFC (fluorocarbon), HC (hydrocarbon) or carbon dioxide (CO2), which are conventionally used in refrigeration and air conditioning, are adiabatically compressed as a superheated gas in a normal refrigeration cycle. In order to reach a higher enthalpy state than that achieved by this, and to be liquefied after expansion, a large cooling step is required. In order to efficiently perform this cooling process, it is possible to exchange heat by using a heat regenerator and exchanging heat with the pressurized working medium in a liquid state, instead of being cooled only when it is at a low temperature, to exchange heat. It is effective only for a part of the process where there is a temperature difference. The same applies to the heating process, and only part of the process is improved. Also, a large capacity is required in proportion to the maximum temperature reached by the heat regenerator itself. In addition, the liquid pump has a theoretical equal enthalpy change and energy input to the working medium is unnecessary. However, in the actual machine, mechanical friction loss and fluid loss are large, and durability and efficiency are practically difficult. As a result, there is no effective and practical means that can regenerate power by using medium and high temperatures as a heat source.

The present invention solves the problems of the conventional heat engine as described above with a completely new heat cycle (gas cycle) in which the working medium always operates under a heated gas state. The heat cycle is basically heated from the outside of the cycle with medium and high temperature heat, then adiabatically expanded, cooled and compressed again. The output obtained by subtracting the power required for compression from the output obtained by expansion becomes the net output of this thermal cycle, and a simple system is realized based on the existing equipment technology. In order to obtain approximately isothermal compression, the compressor is provided with a cooling mechanism inside or outside, or has an intermediate cooler in the middle of each stage in multistage compression, and the required amount of compression power is minimized. In order to improve the thermal efficiency, the expansion can be obtained by adiabatic expansion to obtain the maximum amount of expansion power. If necessary, a heat regenerator is provided to heat the lower temperature superheated gas after compression with the heat of the expanded superheated gas. At the same time, the former superheated gas itself is further cooled by the latter superheated gas. It is also possible to obtain a high thermal efficiency improvement.

The present invention can solve the conventional problems by using the above-described means. Specifically, since all the working medium that forms the basis of the present plan is in a superheated gas state, even if medium and high temperature heat is applied to the expander, the temperature difference from the compressor is not as great as in a Rankine engine that requires liquefaction. Therefore, the heat regeneration capacity may be minimized, and the temperature of the working medium supplied to the compressor may be, for example, 100 degrees or more necessary for hot water supply, so that the cooling process can be used as it is for heating hot water in the co-generation system. The main components of the system, the compressor, expander, motor and generator, can be coaxially connected and housed in a common container, which can be handled as a high-pressure gas container and can be made compact and convenient. . Especially when using a rotary type such as a rolling piston type, swing piston type, etc. for a compressor or an expander, a rotary type such as a multi-vane type or a scroll type is easy to connect, and the speed and phase can be adjusted between the drive shafts of each mechanism element. If each device is provided, capacity matching and freedom of control are improved. In addition, it is possible to share the lubrication mechanism or store the lubricant in the same container. Since it is an external combustion engine, not only can the heat source be selected variously as described above, but the working medium is a closed cycle, so there is no exhaust as in the open cycle, and the operation is quiet and the internal combustion engine is used when combustion heat is used as the heat source. Exhaust discontinuous combustion like the above, but the exhaust gas is cleaned to the maximum in the continuous combustion state in the optimum state like a general combustor, and can greatly contribute to environmental measures.

A rotary compressor is used in two stages, the suction working gas of the first stage compressor is the main cooler, and the suction working gas of the second stage compressor is intermediate compression provided between the first stage and second stage compressors. Each is cooled by a machine and compressed by suction. The high pressure gas discharged from the second stage compressor is heated by the heat regenerator and the heater and enters the expander. Here, the heat regenerator heats the high-pressure gas with the heat of the working gas discharged from the expander after the expansion stroke is completed, and the heater further heats the high-pressure gas with a medium / high temperature heat source. The expander is a rotary type, sucks the working gas, adiabatically expands at a predetermined expansion ratio, generates shaft power, and discharges the working gas at a low pressure. Although this working gas temperature has decreased considerably due to adiabatic expansion, it can be utilized if there is a temperature that can be sent to the heat regenerator and used for heating the working gas immediately after compression. After that, it enters the main cooler, is cooled, returns to the compression process again, and completes the cycle. In order to minimize the power required for this compression process, compression is performed in two stages as described above, and the amount of compression, compression ratio, and amount of cooling are greatly reduced so that each stage is cooled in advance and approaches thermal isothermal compression. The temperature difference between the working gas suction temperature to the first stage compressor and the second stage discharge working gas (the temperature obtained by subtracting the former temperature from the latter temperature) is minimized. When the compressor and the expander are combined together and the rotating mechanism such as the electric motor and the generator or the electric motor / generator are connected coaxially and the driving mechanism is integrated and housed in the pressure vessel, the handling becomes easy and convenient. It is also possible to connect and connect devices between the shafts so that the mutual capabilities can be converted as required and the output can be changed in response to load fluctuations. Note that the compressor and electric motor, and the expander and generator may be combined and stored in separate containers depending on the peripheral pressure, temperature, lubrication mechanism, and production convenience of each drive mechanism. This is particularly convenient when diverting existing container-housing equipment.

1 is a Mollier diagram (pressure-enthalpy diagram) of the working medium of FIG. 1, a basic structure and system diagram of FIG. 2, and a basic structure and system diagram of FIG. 3 (based on the example of FIG. 2). A description will be given based on a changed example. The numbers from (1) to (8) and (9) and so on in the respective figures indicate the working gas state during each step in the thermal cycle of the present invention and the corresponding position in the system. FIG. 1 shows an example of a gas cycle, which is the gist of the present invention, using a Mollier diagram of HFC-134a (Freon) as a working medium. The vertical axis represents the pressure (P) of the working medium, and the horizontal axis represents the same enthalpy. (H) is shown, and the saturated vapor curve of the working medium is shown on the left side. The closed rectangular similar diagram shown on the right side of the diagram represents the state change of this gas cycle (1), (2), (3), (4), (5), (6), (7) , Change to (8), return to (1) again and complete a round. This embodiment uses substantially isothermal compression by two-stage compression. (1) is the starting point of the first-stage compression, and the state is the lowest pressure P1, the enthalpy is the minimum h1, and this is the first-stage compression. Adiabatic compression is performed by the machine (1), and the working medium is changed to the intermediate pressure P2 and the enthalpy h4 in the state (2). The state of (2) is slightly higher than the absolute temperature T1 in the state of (1), but this is passed through the intercooler (7) to cool, and the pressure remains at P2 as indicated by (3). Only the temperature is reduced to about the initial T1. At this time, the enthalpy is approximately equal to h1, but differs depending on the characteristics of the working medium. The working medium in the state (3) is adiabatically compressed again by the second stage compressor (2), and the pressure is increased to the maximum pressure P4 in the state (4). As a result, the enthalpy increases but is adjusted to about h4. As a result, the temperature of the working medium rises to T4. The power required for compression corresponds to the difference between the enthalpies h4 and h1, except for various losses such as friction and leakage. This working medium is led to the heat regenerator (12) and heated to the temperature T7 vicinity of (5). This heat source is so-called by heat exchange with the working medium at the temperature T7 discharged from the expander (3) described later. This corresponds to preheating for subsequent heating. Thereafter, the working medium is further heated from the state (5) to the state (6) by the heater (5), and exhaust heat or combustion heat having medium to high temperature heat outside the system is used for this heat source. The working medium in state (6) has the maximum energy of enthalpy h6 at pressure P4 and temperature T6, enters the expander (3), and is adiabatically expanded to change to pressure P1, temperature T7, and enthalpy h7 in state (7). . The reduction from the enthalpy h6 to h7 is converted into the power for output except for various losses. After that, the working medium is preheated with the heat regenerator (12) by exchanging heat with the working medium of (4) as described above from the state of (7) to the temperature of about (8) to about T4. This is cooled, that is, precooled and reaches the cooler (7). Since mutual heat exchange requires a difference in temperature between gas and sensible heat, (5) is slightly lower than T7, and (8) is slightly higher than T4, but this heat regenerator (12 ) Heat transfer in (5) to (6) and cooling heat (8) to (1) can be saved greatly by the transfer of heat in this case, and the contribution to efficiency improvement is great. In FIG. 2 and FIG. 3, the heat regenerator (12) is shown separately in the drawing, but is substantially configured integrally. Further, when the temperature difference between T7 and T4 is small due to the heat cycle configuration, the heat regenerator (12) may be omitted.

なお本熱サイクルではシステムの簡略化のため熱再生器（１２）を用いないものとしている。この熱サイクルにおける理論熱効率は（（膨張機出力）−（圧縮機入力））÷（熱入力）なので（ｈ６−ｈ７）−（ｈ４−ｈ１）／（（ｈ６−ｈ４）＝（６０５−５５０）−（５５０−５２０）／（６０５−５５０）＝２５／５５＝０．４５とほぼ４５％程度が期待できる。実用機においては機械摩擦や漏れ損失、熱損失、電動機あるいは発電機系の電気損失等が不可避のため前記効率への達成率は通常５０％程度の２０％強程度と見込まれるが、従来ランキン熱機関で報告されている例は最高温度が同程度では１４％前後で本熱機関は十分高効率で大きな優位性を有している。For reference, the thermal cycle described above is shown in the table below with the main state points of the design example using Freon HFC-134a as the working medium.

In this heat cycle, the heat regenerator (12) is not used to simplify the system. Since the theoretical thermal efficiency in this thermal cycle is ((expander output)-(compressor input)) / (heat input), (h6-h7)-(h4-h1) / ((h6-h4) = (605-550) -(550-520) / (605-550) = 25/55 = 0.45, which is expected to be about 45% .In practical machines, mechanical friction, leakage loss, heat loss, electric loss of electric motor or generator system The achievement rate for the efficiency is usually expected to be about 20%, which is about 50%. However, the example reported in the Rankine heat engine is about 14% at the same maximum temperature. Is sufficiently efficient and has great advantages.

References

Research paper “Study on in-vehicle waste heat regeneration system using Rankine cycle” Vol. 38, no. 4, July 2007.

FIG. 2 shows a configuration example embodying the thermal cycle shown in FIG. The drive parts of the first stage compressor (1), the second stage compressor (2), and the expander (3) are connected to each other by a common shaft (8), and an electric motor / generator (4) is also coupled thereto. . At this time, if it is necessary to adjust and control the working medium drive capability of each drive mechanism section by changing the rotational speed, phase, etc., a control mechanism (11) is interposed in each connecting portion. For example, in general, the compression ratio P2 / P1 of the first stage compressor is set to be substantially equal to the compression ratio P4 / P2 of the second stage compressor. At this time, the compression according to the specific volume of the suction working medium in each stage The capacity is set, but when the same rotation is performed on the same axis, if the difference between the suction volumes of the first stage and the second stage is excessive and inconvenient in configuration, the required volume becomes larger. Adjustment control is performed by making the volume smaller than the second stage, or conversely decelerating the second stage and adapting the effective volume to the first stage. In general, unlike a compressor having a discharge valve, an expander expands at a constant expansion ratio of one stage, so that the displacement volume tends to be large, and it is convenient that the rotational speed can be adjusted and controlled for miniaturization. Here, each drive mechanism is based on the rotary type described above, and the compressor can use almost the same conventional compression mechanism, and the expander acts to reverse the compression by eliminating the discharge valve of the rotary compressor. In principle, it can be obtained by supplying a working medium of high pressure (P4 in this example) from the discharge side, but it is necessary to consider lubrication and heat resistance at medium and high temperatures. FIG. 2 shows that these drive mechanisms are housed in a single pressure-resistant vessel (9) and are connected to the heat exchange device through the vessel wall through a working medium pipe so that the inside of the vessel (9) has a minimum pressure P1. It is a thing. The working medium, which has been cooled after expansion and brought to the state (1), returns to the container (9) and is then sucked into the first stage compressor (1) inside the container (9). The outlets are each connected by a pipe penetrating the wall surface of the container (9). Lubricating oil (not shown) can be enclosed in this container (9) and supplied in common to the drive equipment. In the expander (3), since the medium and high temperature working medium flows in, the surroundings are likely to be heated to a relatively high temperature and there is a concern that the compressor and the motor / generator (4) may be heated. 10) should be provided between the two to cut off the heat. The motor / generator (4) mainly generates the driving force of the compressor as the starting motor when the heat engine is started. As the heat system approaches the rating, the power generated by the expander increases and the net shaft output increases. If generated, it will generate electric power as a generator, and of course the same function can be achieved even if the motor and generator are provided separately. The partition wall (10) is also provided as a pressure partition wall when the pressure environment is to be separated from other drive mechanisms only around the expander (3).

FIG. 3 shows an example in which the pressure in the container (9) in the example of FIG. 2 is changed to an intermediate pressure of the pressure P2 of the return working medium from the first stage compressor (1). In conventional refrigeration and air conditioning applications, when compressing CO2 or the like as a working medium to a high pressure of 10 MPa or more, a rotary or scroll type two-stage compressor is used and the inside of the container (9) is kept at an intermediate pressure as in this example, and the ambient atmospheric pressure There is an example in which the pressure resistance is improved to improve the internal lubrication and the cooling performance of the electric motor or the like, but the purpose in this example is also the same, and the system configuration can be simplified.

The change in the state of the working medium from (1) to (9) indicated by the broken line in FIG. 1 indicates the case where the enthalpy h1 is substantially constant and the isothermal compression is performed. Ideally, the compression along the broken line minimizes the power required for compression and maximizes the output of the heat engine, but it is difficult to realize this in an actual machine. Although some attempts have been made for this purpose, it is necessary to make a significant modification to the compression mechanism in order to cool the working medium in the middle of compression, and it is difficult to adapt to consumer equipment that should be small, simple, and inexpensive. As shown in the above-mentioned examples, the present invention is basically two-stage compression that can be realized by appropriately modifying, selecting, and combining conventional positive displacement compressors, and reducing the required driving power by approaching isothermal compression. Yes. Further, an expander at a medium to high temperature of about 200 ° C to 300 ° C is difficult to divert as it is because the heat resistance of a conventional compressor is less than 200 ° C. The scroll type has problems in blade deformation and lubrication mechanism, but the multi-vane type and rotary type can be realized by improving the material and structure. In addition, the working medium can be similarly applied in a superheated gas state using a chlorofluorocarbon, HC (hydrocarbon), or carbon dioxide (CO2) other than the above-described HFC-134a.
JP2009-185681 JP 2001-132675 A

Utility model literature

Actual application 2009-5754

As described above, a compressor and an electric motor and an expander and an electric generator may be combined and stored in separate containers as necessary, or only the compressor and the electric motor may be stored in a common container. Not shown). In particular, when the expander and the generator are integrally stored in a common container, the ambient temperature becomes a medium high temperature, and there is a concern that special consideration is required for heat resistance. At this time, the electric motor and the generator are coupled so as to be electrically controllable, and their functions are linked to start and stop operation from the start.

As described above, according to the present invention, a high-performance gas cycle type external combustion engine having a relatively simple structure and high practicality is possible, and medium-to-high temperature exhaust heat and combustion heat, which has been difficult to regenerate energy conventionally, are driven by power. As described in the introduction, it is possible to deploy to many clean and highly efficient consumer energy devices and their applied technology fields.

Mollier diagram of working medium (pressure-enthalpy diagram) Basic structure and system diagram Structure and application system diagram changed based on the system of FIG.

(1) First stage compressor (2) Second stage compressor (3) Expander (4) Motor / generator (5) Heater (6) Main cooler (7) Intermediate cooler (8) Shaft ( 9) Container (10) Bulkhead (11) Control mechanism (12) Heat regenerator

Claims (10)

The overheated working medium is compressed almost isothermally with a positive displacement compressor, heated with a heater, then substantially adiabatic expansion with a positive displacement expander, and then cooled to return to the original compression process again. A gas cycle type external combustion engine configured such that a shaft output of the expander exceeding a shaft power of the compressor can be taken out as a net shaft output. The working medium in an overheated state is compressed by a positive displacement multistage compressor that is cooled in two or more stages by providing an intermediate cooler in the middle of each stage, further heated by a heater, and then expanded by a one stage positive displacement expander A gas cycle system in which the heat cycle is cooled and then restored to the original compression process, and the shaft output of the expander exceeds the shaft power of the compressor so that the net shaft output can be taken out. External combustion engine. 3. The gas cycle type external combustion engine according to claim 1 and / or claim 2, wherein the compressor, the compressor driving motor, the expander, the expander output extraction generator, or the motor and the generator are replaced. In addition, a mechanism that combines an electric motor / generator that serves both functions with a common shaft is configured. The compressor, the expander, the electric motor, and the generator or the electric motor / generator coupled with a common shaft according to claim 3 are housed in a common container. A mechanism for appropriately connecting and connecting a device capable of converting and controlling the mutual rotational speed and / or phase between the shafts of the compressor, the expander, the electric motor and the generator or the electric motor / generator according to claim 3. Make up. The working medium cooled after being discharged from the expander is introduced into the container according to claim 4 so as to be used for suction of the compressor. When the multistage compression system according to claim 2 is provided in the container according to claim 4, the working medium that has been intercooled after discharge from the first stage of the compressor is guided to the second stage suction of the compressor. Configure to serve. 5. The partition according to claim 4, wherein only the expander is thermally and / or pressure-isolated from the other components in the container. The heat of the discharge working medium of the compressor and the heat of the discharge working medium of the expander in claim 1 and / or claim 2 are heat-exchanged by a heat regenerator, the latter preheats the former, and the former To be able to pre-cool. 5. The mechanism according to claim 4, wherein only the expander and the generator are excluded from the container, and the compressor motor is configured so as to be controlled by an electric circuit.

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