CN203420766U - Waste heat comprehensive utilization system of CNGE - Google Patents

Abstract

The utility model discloses a compressed natural gas engine (CNGE) waste heat comprehensive utilization system, which relates to a new energy-saving technology of the engine. It adopts a waste heat heat exchanger to use tail gas and/or cylinder jacket water waste heat to heat high-pressure gas output from a high-pressure gas cylinder. , using at least two-stage expander devices (one stage is a variable expansion ratio expander, and the other stage is a constant expansion ratio expander) to depressurize the high-pressure gas to achieve the gas pressure required for engine combustion, and at the same time use the expander to Comprehensive utilization of pressure energy and waste heat increases engine output shaft work, improves engine system efficiency, increases mileage, and saves natural gas consumption. The device of the utility model has compact structure and reliable performance, recovers 80% of the energy consumed in the gas compression process, and significantly improves the advantage of natural gas as engine fuel.

Description

A comprehensive utilization system of compressed natural gas engine waste heat

technical field

The utility model relates to the technical field of waste heat comprehensive utilization and energy saving, in particular to a waste heat comprehensive utilization system using a compressed natural gas engine (Compressed Natural Gas Engine, CNGE).

Background technique

With the rapid development of the world economy, the number of cars has increased sharply. Cars have brought great convenience to people's travel and made great contributions to human development. However, at the same time, they consume a lot of oil resources and emit a lot of harmful gases. important source. Statistics show that in the air pollution of large and medium-sized cities in western developed countries, about 54% of carbon monoxide CO, 41% of nitrogen oxides _NOx , and 28% of carbon oxides _COx come from automobile exhaust. In my country, automobile exhaust has also become the chief culprit of air pollution. Studies have shown that the main sources of air pollution in Guangzhou are: motor vehicle exhaust accounting for 22%, industrial pollution accounting for 20.4%, and dust pollution from construction sites accounting for 19.2%. Vehicle exhaust is rated as "the most intolerable pollutant" by citizens. In order to solve this problem, people have been working hard to change the energy structure and use low-pollution/no-pollution automobile engines to replace fuels.

The new energy that has been used in automobile engines mainly includes liquefied petroleum gas, fuel and electric hybrid, pure electric, fuel cell, alcohol fuel and compressed natural gas. The main disadvantage of the promotion of liquefied petroleum gas is that the construction investment of liquefied petroleum gas is huge, 1/3 of the gas source is imported by sea, and with the rise of oil prices, the use price is also increasing. Hybrid and pure electric power sources are mainly limited by battery capacity and life issues that cannot be well resolved, resulting in excessively high value of bicycles, making it difficult to promote them on a large scale in a short period of time. Fuel cells mainly refer to hydrogen fuel cells. The biggest problem is that the cost of the whole vehicle is high, and the basic construction of hydrogen refueling stations cannot keep up. In addition, the battery life is short and the economy is not good. Alcohol fuels are mainly methanol and ethanol. It is relatively easy to obtain materials, mainly grains, but the fuel itself is too corrosive to equipment, resulting in a short service life of related storage and filling equipment, making it difficult to promote on a large scale. Correspondingly, compressed natural gas (CNG) fuel is cheap, has a single composition, large reserves, less harmful emissions, high safety and reliability, and good anti-knock performance. It has attracted much attention and has become the best alternative fuel for automobile engines. The market Wide range of applications and broad prospects.

Natural gas, coal and petroleum are listed as the three pillars of world energy. At present, the total proven reserves of natural gas in the world are about 140 trillion cubic meters, which is equivalent to 123.2 billion tons of oil, and it is expected to be exploitable for 200 years. At the same time, my country has abundant reserves of natural gas resources, with proven reserves of 3.8 trillion cubic meters. At present, an annual production capacity of 323 billion cubic meters has been formed in Sichuan Province, the central and western provinces and the sea. With the continuous increase of proven natural gas reserves, its application will become more and more extensive, and its position in the energy structure will become more and more important. As a clean fuel, CNG (compressed natural gas) has increasingly obvious advantages in terms of price and environmental protection, and has been widely used in automobile engines, especially taxis and buses.

The working process of a CNG engine car: flush high-pressure compressed natural gas into the cylinder, the pressure in the cylinder should not exceed the nominal pressure of 20Mpa, to prevent the pressure from being too high, and the temperature will rise dangerously; it should not be less than 3Mpa, to prevent the pressure from being too small, and the occurrence of Insufficient air supply. The high-pressure compressed natural gas is output from the gas storage cylinder, and enters the three-stage pressure reducing valve through the high-pressure solenoid valve. The switch of the high-pressure solenoid valve is controlled by the ECU. The pressure is adjusted to between 0.1Mpa and 0.5Mpa. During the decompression process, high-pressure natural gas needs to absorb a large amount of heat due to decompression and expansion. In order to prevent the decompression valve from freezing, the engine coolant is led out to the decompressor to heat the gas. The decompressed natural gas enters the electronic control regulator, and the electronic control regulator accurately controls the injection amount of natural gas according to the engine operating conditions. After the regulated natural gas and air are fully mixed in the mixer, they enter the engine cylinder and are ignited by the spark plug for combustion. The ignition of the spark plug is controlled by the ECU. The oxygen sensor monitors the oxygen concentration of the exhaust gas after combustion in real time to calculate the air-fuel ratio. The feedback signal of the oxygen sensor corrects the injection quantity of natural gas in time.

In order to improve the energy utilization efficiency of CNG engines, experts and scholars at home and abroad have done a lot of work in recent years, such as in-cylinder direct injection technology, coolant heating pressure reducer technology, etc., but most of them focus on in-cylinder combustion technology. Energy and exhaust waste heat utilization is less. Due to the high energy consumption (0.3-0.5kWh/kg) in the process of producing compressed natural gas for vehicles, while the high-pressure gas output by the conventional engine through the gas cylinder is depressurized through the pressure reducing valve, and the throttling loss is serious. In the prior art, a CNGE residual pressure energy recovery device has also appeared. Although CNGE has been utilized to a certain extent, there are a series of problems in the use process. Low, not conducive to the full use of pressure energy. Another is that there are major defects in the pressure energy release process of CNG. The expander is directly used for decompression. There are no pressure stabilization measures during the decompression process. Working at a variable expansion ratio all the time makes the energy output by the expander unstable, and makes the outlet pressure of the expander unstable, affecting the normal and stable operation of the downstream CNGE.

Contents of the invention

The purpose of this utility model is to address the above-mentioned shortcomings and deficiencies of the prior art, and propose a compressed natural gas engine (CNGE) waste heat comprehensive utilization system. and jacket water waste heat. Specifically, the CNGE tail gas and jacket water waste heat are used to depressurize the high-pressure gas. The depressurization of the high-pressure gas is achieved by using an expander device with a variable expansion ratio combined with a constant pressure ratio and a pressure stabilizing device. The stable utilization of high-pressure gas improves engine output and efficiency, and is suitable for various CNG engines.

For achieving the above object, the technical solution of the utility model is:

A compressed natural gas engine (CNGE) waste heat comprehensive utilization system, including a CNG gas storage device connected through a gas pipeline, a solenoid valve, a heat exchanger group, an expansion unit, a pressure stabilizing valve group, a gas nozzle, a gas mixer, and CNGE, It is characterized by:

The expansion unit includes a variable expansion ratio expander and a constant expansion ratio expander connected in series; the heat exchanger group includes at least heat exchangers I and II; the pressure stabilizing valve group includes at least pressure stabilizing valves I and II; A supercharger unit is provided in the tail gas pipeline of the CNGE, and the supercharger unit includes a supercharger turbine and a supercharger compressor; wherein,

The gas pipeline between the gas outlet of the CNG gas storage device and the air inlet of the variable expansion ratio expander is at least provided with the electromagnetic valve and heat exchanger I, and the gas outlet of the variable expansion ratio expander and the gas pipeline At least the heat exchanger II and the pressure stabilizing valve I are arranged on the gas pipeline between the expanders with a fixed expansion ratio, and at least a pressure stabilizing valve is arranged on the gas pipeline between the gas outlet of the expander with a fixed expansion ratio and the gas nozzle II,

The supercharger turbine drives the supercharger compressor, and the supercharger compressor boosts the air and delivers it to the gas mixer. The supercharger turbine is driven by the exhaust gas flow of the CNGE. Each of the heat exchangers The cold fluid inside is compressed natural gas, and the hot fluid is CNGE tail gas.

Preferably, the CNG gas storage device injects CNG into it through a gas filling valve, and stores compressed natural gas not higher than 20MPa.

Preferably, the solenoid valve is used to control the on-off of the CNGE air supply system, and is controlled by the engine electronic control unit ECU to switch the fuel supply.

Preferably, each pressure stabilizing valve is installed behind each expander to stabilize the pressure reduced from the outlet of the expander.

Preferably, an air filter is provided at the inlet end of the supercharger compressor.

Preferably, a filter is also arranged on the gas pipeline before the gas nozzle.

Preferably, the pressure ratio of the variable expansion ratio expander is variable, with a working range of 3-20, and the pressure ratio of the constant expansion ratio expander remains constant during operation, and the pressure ratio is 5-20.

Preferably, a heat exchanger III is also arranged on the gas pipeline between the gas outlet of the constant expansion ratio expander and the gas nozzle, the cold fluid in the heat exchanger is compressed natural gas, and the hot fluid is CNGE tail gas.

Preferably, the cylinder liner cooling water of the CNGE is provided with an external circulation pipeline, and the inlets on the hot fluid side of each heat exchanger are connected to the external circulation pipeline or the tail gas of the CNGE.

Preferably, each heat exchanger can be designed as two different thermal fluids connected in series or in parallel, and the same natural gas is heated by the two thermal fluids. Preferably, the tail gas of the CNGE first partially or completely passes through each heat exchanger, and then collectively or separately passes through the turbocharger turbine, so as to heat the natural gas at a higher temperature, thereby obtaining higher expansion work, It is better to utilize the pressure energy of natural gas, or, the tail gas of the CNGE first flows through the turbocharger turbine, and then is split to each of the heat exchangers.

Preferably, the thermal fluid of the heat exchangers I and II is provided by the CNGE tail gas, the thermal fluid of the heat exchanger III is provided by the CNGE cylinder liner cooling water, or the thermal fluid of the heat exchangers I and II is provided by CNGE cylinder liner cooling water is provided, and the heat fluid of heat exchanger III is provided by the CNGE exhaust gas.

Preferably, in the system, the components before the constant expansion ratio expander are connected through a high-pressure gas pipeline, and the components after that are connected through a low-pressure gas pipeline.

Preferably, each expander can be a multi-stage combined expander, and each expander can be a piston type, screw type, vane type or mixed type expander, and the fixed expansion ratio expander can also be a miniature centripetal type expander.

Preferably, each heat exchanger can be of a shell-and-tube type, a plate-fin type, and a spiral tube type.

The waste heat comprehensive utilization system of the compressed natural gas engine (CNGE) of the utility model has a work flow as follows: when the engine using the compressed natural gas fuel works, the high-pressure gas flowing out from the compressed gas cylinder first passes through the solenoid valve and enters the heat exchanger I to absorb the engine Exhaust gas or cylinder jacket water waste heat heats up; the high-pressure gas after heat exchange and temperature rise is expanded to do work through the first-stage variable expansion ratio expander, and the gas pressure of 20MPa is reduced to a certain design pressure between 0.5 and 2MPa. As the working time goes by, The pressure in the gas storage tank keeps decreasing, so the working process of the first-stage expander is in a state of variable expansion ratio; the high-pressure gas after the first pressure reduction and temperature reduction passes through the heat exchanger II and the pressure stabilizing valve I to absorb the exhaust heat of the engine exhaust or the cylinder jacket water again, and the temperature rises. Then enter the second-stage expander to expand and do work, reducing the pressure from the outlet pressure of the first-stage expander to about 0.05-0.2MPa. The pressure at the inlet and outlet of the second-stage expander is stable during the working process, which is an expander with a fixed expansion ratio; after expansion, pressure reduction and cooling The normal-pressure gas passes through the pressure-stabilizing valve II and heat exchanger III to further absorb waste heat, which not only prevents the phenomenon of "freezing" of the pipeline, but also increases the temperature of the gas entering the engine cylinder, saving heat energy; The filter filters out the liquid droplets and fine solid particles in the gas, and then injects the air through the turbocharger into the pre-mixer of the engine cylinder through the gas nozzle for mixing, and finally enters the engine combustion chamber. After the combustion works, the exhaust gas of the engine passes through the exhaust gas of the turbocharger and the high-temperature cylinder jacket water to be used as the heat source of the heat exchanger groups I, II, and III. For the engine without a turbocharger, the exhaust gas of the engine is directly used as The heat sources of heat exchanger groups I, II, and III can also be eliminated according to different engine designs, and the normal-pressure and normal-temperature gas enters the mixer after being filtered and burns in the engine to perform work.

In the above-mentioned CNGE waste heat efficient utilization system, there are mainly four schemes for the heat exchange cycle of the heat exchanger: Scheme 1, for a turbocharged engine, the exhaust gas of the engine cylinder after the supercharger turbine depressurizes the exhaust gas, part or All of them enter the heat exchanger as a thermal fluid to provide a heat source for the natural gas fuel to heat up; option 2, for a turbocharged engine, part or all of the engine cylinder exhaust first enters the heat exchanger as a thermal fluid to provide a heat source for the natural gas fuel to heat up, and then enters the turbocharged engine. The compressor turbine continues to expand; Option 3, for a non-turbocharged engine, part or all of the exhaust gas from the engine cylinder enters the heat exchanger as a thermal fluid to heat the natural gas; Option 4, part or all of the cooling water of the engine cylinder liner enters the heat exchange The heater acts as a thermal fluid to heat natural gas. The above four schemes can also be combined, that is, the heat of each heat exchanger can come from engine exhaust or cylinder jacket water alone, or it can be mixed and heated.

According to another aspect of the utility model, a method for comprehensive utilization of compressed natural gas engine (CNGE) waste heat is also provided. Using the system for comprehensive utilization of compressed natural gas engine (CNGE) waste heat of the utility model, it is characterized in that the gas supply of the CNGE A variable expansion ratio expander and a constant expansion ratio expander are arranged in series on the pipeline, a heat exchanger is installed in front of each expander, a pressure stabilizing valve is installed behind each expander, and the pressure stabilizing valve of the last stage expander can be optionally A heat exchanger is arranged, a supercharger turbine is arranged in the tail gas pipeline of the CNGE, the cold fluid in each heat exchanger passes through CNG, and the CNGE tail gas before or after the supercharger turbine is passed in as a hot fluid In each of the heat exchangers, the jacket cooling water of the CNGE can be selectively cut into the thermal fluid side of each of the heat exchangers.

The comprehensive utilization system of compressed natural gas engine waste heat of the utility model adopts a heat exchanger group and an expansion unit to replace the pressure reducing valve, and utilizes a first-stage variable expansion ratio expander and a first-stage constant expansion ratio expander to cooperate to maximize The pressure energy of natural gas and the waste heat of exhaust gas and cylinder jacket water are effectively utilized, and the structure is relatively simple and reasonable, which can effectively realize the comprehensive cascade utilization of waste heat and pressure, and the engine output and efficiency increase by an average of 5-10% during operation.

Description of drawings

Fig. 1 is the structural schematic diagram of embodiment 1 of the waste heat comprehensive utilization system of compressed natural gas engine of the present invention;

Fig. 2 is the structural schematic diagram of embodiment 2 of the waste heat comprehensive utilization system of compressed natural gas engine of the present invention;

Fig. 3 is a structural schematic diagram of embodiment 3 of the comprehensive utilization system for compressed natural gas engine waste heat of the present invention;

Fig. 4 is a structural schematic diagram of Embodiment 4 of the comprehensive utilization system for compressed natural gas engine waste heat of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the utility model clearer, the utility model will be further described in detail below with reference to the accompanying drawings and examples.

Fig. 1 is embodiment 1 of the present utility model. The CNGE waste heat efficient utilization system of the present utility model includes an inflatable valve 1, a gas cylinder 2, a solenoid valve 3, heat exchangers 4, 5, 8, pressure stabilizing valves 6, 7, a filter 9, a gas nozzle 10, a mixer 11, Engine combustion chamber 12, air filter 13, natural gas source A, air B, expansion unit E1/E2, turbocharger turbine T1, supercharger compressor C. The expansion unit E1/E2 includes a first-stage variable expansion ratio expander E1 and a second-stage constant expansion ratio expander E2. The pressure ratio of the first-stage expander E1 is variable, and the working range is 3 to 20. The inlet passes through the heat exchanger 4 It is connected to the gas source of the gas storage cylinder; the pressure ratio of the secondary expander E2 is 5-20, which is stable during the working process, and the outlet enters through the pressure stabilizing valve 7, heat exchanger 8, filter 9, gas nozzle 10, etc. Gas mixer 11 and enters engine cylinder 12. The heat exchanger group includes at least two sets of heat exchangers 4 and 5 matched with the expansion unit E1/E2. The heat exchanger 4 is used to heat high-pressure gas in front of the expander E1, and the heat exchanger 5 is in front of the expander E2. It is used to heat the high-pressure gas after expansion and cooling. The heat exchanger 8 is used to heat the low-pressure gas in front of the filter 9. The heat exchanger groups are connected in series at different positions of the system pipeline. The heat exchanger groups are connected to the engine exhaust port or the engine The turbine outlet of the supercharger with the belt or the cylinder jacket of the engine are connected with water, and the heat medium is provided by it. The engine cylinder exhaust gas can also go through the heat exchangers 4, 5, 8 for heat exchange to heat the natural gas before entering the supercharger turbine T1 and then discharging. The expansion unit, heat exchanger group, engine, turbocharger, etc. are connected through high-pressure/low-pressure gas pipes and valves. A is a gas filling station or other gas source, which is filled into the compressed natural gas storage cylinder 2 through the gas filling valve 1. The gas cylinder stores compressed natural gas not higher than 20MPa, and the specific pressure is determined by the inflation pressure of the gas filling station; the solenoid valve 3 is used to control the on-off of the air supply system, and at the same time, it is controlled by the engine electronic control unit ECU to switch the fuel supply; the pressure stabilizing valves 6 and 7 are installed behind the expander to stabilize the pressure reduced from the outlet of the expander; The natural gas from the valve 7 passes through the filter 9 to filter out the liquid droplets and fine solid particles in the gas, and sprays it into the mixer 11 through the gas nozzle 10; B is the outside air, which passes through the air filter 13 and enters the supercharger compressor At the inlet end of C, the supercharger turbine T1 is driven coaxially with the supercharger compressor C, and the filtered air enters the mixer 11 after being pressurized by the supercharger compressor C. The mixed air and natural gas mixture enters the engine 12, and the exhaust gas of the engine or the exhaust gas of the turbocharger or the cylinder jacket water enters the heat exchanger 4, 5, 8 to cool and exchange heat; in the system 1, 2, 3, 4, 5 , 6, E1, E2 are high pressure parts, connected by high pressure pipelines; 7, 8, 9, 10, 11, 12, 13, T1, C are normal pressure parts, connected by low pressure pipelines

Its working process is as follows: the high-pressure gas flowing out of the compressed gas cylinder 2 first passes through the solenoid valve 3 and enters the heat exchanger 4 to absorb the exhaust gas of the engine or the waste heat of the cylinder jacket water to raise the temperature; Engine E1 expands to do work, reducing the gas pressure of 20MPa to a certain design pressure between 0.5 and 2MPa. As the working time goes on, the pressure in the gas storage tank continues to decrease, and the working process of the first-stage expander is variable expansion ratio; After cooling down, the high-pressure gas passes through the heat exchanger 5 and the pressure stabilizing valve 6 to absorb the waste heat of the engine exhaust or cylinder jacket water to raise the temperature again, and then enters the second-stage expander E2 to expand and do work, reducing the pressure from the outlet pressure of the first-stage expander to 0.05~ At about 0.2MPa, the inlet and outlet pressure of the secondary expander is stable during the working process, which is an expander with a fixed expansion ratio; the atmospheric pressure gas after expansion, decompression and temperature reduction passes through the pressure stabilizing valve 7 and heat exchanger 8 to further absorb waste heat, which prevents the road "icing" phenomenon, and increase the temperature entering the engine cylinder; the heated atmospheric pressure high-temperature gas passes through the filter 9 to filter out the liquid droplets and fine solid particles in the gas, and then passes through the gas nozzle 10 and the turbocharger The air is injected into the engine cylinder pre-mixer 11 for mixing, and finally enters the engine combustion chamber. After the combustion works, the exhaust gas of the engine passes through the exhaust gas of the turbocharger and the high-temperature cylinder jacket water to be used as the heat source of the heat exchanger groups 4, 5, and 8. For the engine without a turbocharger, the exhaust gas of the engine is directly used as The heat source of heat exchanger group 4,5,8, according to different engine design, heat exchanger 8 also can be canceled, and normal pressure normal temperature gas enters mixer 11 after entering the combustion work in engine.

Fig. 2 is the second embodiment of the utility model, its main structure is the same as that of the first embodiment, only the connecting part of the heat exchanger is changed. The cylinder liner cooling water of the compressed natural gas engine is respectively connected to the heat exchangers 4, 5, and 8 through pipelines to provide a heat source to heat the natural gas and complete the waste heat utilization cycle.

Fig. 3 is Embodiment 3 of the present utility model, its main structure is the same as Embodiment 1, only the connecting part of the heat exchanger is changed. The thermal fluids of heat exchangers 4, 5, and 8 can come from engine exhaust gas and cylinder liner cooling water. The heat exchangers can be designed as two different thermal fluids in series or in parallel, and the same natural gas is heated by the two thermal fluids.

Fig. 4 is Embodiment 4 of the present utility model, its main structure is the same as Embodiment 1, only the heat fluid flow process of the heat exchanger is changed. That is, in a turbocharged engine, the exhaust gas from the cylinder of the engine partly or completely passes through all or some of the heat exchangers 4, 5, 8, and then collectively or separately passes through the turbocharger turbine T1, so that It is used to heat natural gas at a higher temperature, so as to obtain higher expansion work and make better use of the pressure energy of natural gas.

The above-mentioned embodiment can also be changed, and a combined arrangement is adopted. For example, the hot fluid of heat exchangers 4 and 5 is provided by engine exhaust gas, the hot fluid of heat exchanger 8 is provided by cylinder jacket cooling water, or the hot fluid of heat exchange 4 is provided by The cylinder liner cooling water is provided, and the heat fluid of the heat exchangers 5 and 8 is provided by the exhaust gas of the engine.

The above descriptions are only preferred embodiments of the present utility model, and are not intended to limit the present utility model. Any modifications, equivalent replacements, improvements, etc. within the spirit and principles of the present utility model shall include Within the scope of the present utility model.

Claims (10)

1. The utility model provides a Compressed Natural Gas Engine (CNGE) waste heat comprehensive utilization system, includes Compressed Natural Gas (CNG) gas storage device, solenoid valve, heat exchanger group, expander set, steady voltage valves, gas nozzle, gas mixer, CNGE through gas pipe connection, its characterized in that:

the expansion unit comprises a variable expansion ratio expansion machine and a fixed expansion ratio expansion machine which are connected in series; the heat exchanger group at least comprises a heat exchanger I and a heat exchanger II; the pressure stabilizing valve group at least comprises pressure stabilizing valves I and II; a supercharger unit is arranged in a tail gas pipeline of the CNGE, and comprises a supercharger turbine and a supercharger compressor; wherein,

the gas pipeline between the gas outlet of the CNG gas storage device and the gas inlet of the expansion ratio-variable expansion machine is at least provided with the electromagnetic valve and the heat exchanger I, the gas pipeline between the gas outlet of the expansion ratio-variable expansion machine and the expansion ratio-constant expansion machine is at least provided with the heat exchanger II and the pressure stabilizing valve I, the gas pipeline between the gas outlet of the expansion ratio-constant expansion machine and the gas nozzle is at least provided with the pressure stabilizing valve II,

the turbocharger turbine drives a turbocharger compressor, the turbocharger compressor boosts air and then conveys the air to a gas mixer, the turbocharger turbine is driven by CNGE tail gas flow, cold fluid in each heat exchanger is compressed natural gas, and hot fluid is CNGE tail gas.

2. The system of claim 1, wherein a filter is further disposed on the gas line before the gas burner.

3. The system according to claim 1, wherein a heat exchanger III is further arranged on the gas pipeline between the gas outlet of the expansion machine with the fixed expansion ratio and the gas nozzle, the cold fluid in the heat exchanger is compressed natural gas, and the hot fluid is tail gas of CNGE.

4. The system of claim 1, wherein the cylinder jacket cooling water of the CNGE is provided with an external circulation pipeline, and the heat fluid side of each heat exchanger is connected with the external circulation pipeline or the tail gas of the CNGE.

5. The system of claim 1, wherein each heat exchanger can be designed as two different thermal fluids in series or in parallel, and the two thermal fluids heat the same natural gas.

6. The system of claim 1, wherein the CNGE exhaust gas passes partially or completely through each heat exchanger before being combined or passing through the supercharger turbine separately, or wherein the CNGE exhaust gas passes through the supercharger turbine before being split to each heat exchanger.

7. The system according to claim 3, wherein the hot fluid of the heat exchangers I and II is provided by the CNGE tail gas, and the hot fluid of the heat exchanger III is provided by CNGE cylinder jacket cooling water, or the hot fluid of the heat exchangers I and II is provided by CNGE cylinder jacket cooling water, and the hot fluid of the heat exchanger III is provided by the CNGE tail gas.

8. The system as claimed in claim 1, wherein the components before the constant expansion ratio expander are connected by a high pressure gas line, and the components after the constant expansion ratio expander are connected by a low pressure gas line.

9. The system of claim 1, wherein each expander is a multi-stage combined expander, each expander is a piston, screw, vane or hybrid expander, and the constant expansion ratio expander may be a micro radial expander.

10. The system of claim 1, wherein each heat exchanger is a shell and tube, plate fin, or spiral tube.

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