A coal bed methane liquefaction device

Abstract

The present invention aims to develop an energy efficient and cost-effective coal bed methane (CBM) liquefaction plant that integrates the CBM liquefaction process with liquid air energy storage (LAES) system and active magnetic refrigeration (AMR) to facilitate co-production of electricity. This integration approach aims to address the energy efficiency and economic challenges in the conventional CBM single mixed refrigerant (SMR) liquefaction process. The integration of LAES and AMR technologies with the conventional CBM-SMR process provides a novel solution to enhance the CBM liquefaction process. AMR based on the magnetocaloric effect provides an environmentally friendly refrigeration method; and provides an efficient cold heat in the pre-cooling stage of CBM liquefaction. LAES stores energy in the form of liquid air and provides cold heat in its discharge mode to assist the liquefaction stage of CBM, which can improve the overall energy efficiency. The power from the discharge stage of LAES can also be used as the input power for the air turbine that can be used as the compressor in the CBM liquefaction process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy, in particular to a coal bed gas liquefaction device. BACKGROUND

[0002] Coal bed gas (CBM) exists in coal seams, with methane as the main component. It is mainly adsorbed on the surface of coal matrix particles, and part is free in coal pores or dissolved in coal seam water. Coal bed gas is a byproduct of coal mining and is a non-conventional natural gas. Coal bed gas is a self-generating and self-storing energy source, and coal seams are both gas source rocks and reservoir rocks. Coal bed gas mainly exists in coal pores in adsorbed state (70-95%), a small amount exists in other fractures or pores in free state (10-20%), and a very small amount exists in groundwater in coal seams in dissolved state.

[0003] China has a large coal reserve, so optimization of coal bed gas extraction methods is of great significance to China. Compared with traditional coal mining, coal bed gas extraction is a more environmentally friendly option because it releases less carbon dioxide and other pollutants during the extraction process. For China, the use of coal bed gas resources is in line with the energy strategy, can reduce dependence on coal, and is less polluting and less greenhouse gas.

[0004] In recent years, research in this field has focused on exploring various strategies to improve the energy efficiency of coal bed gas liquefaction. Existing technologies mainly focus on optimizing refrigeration cycle layout, adding pre-cooling cycles, and using mixed refrigerants to reduce energy consumption. According to the 27th United Nations Framework Convention on Climate Change (COP27) conference, in order to limit the rise in global average temperature to within 1.5°C, coal bed gas extraction and utilization technologies are crucial.

[0005] The main challenges in current coal bed gas liquefaction technologies include two aspects: the need for high energy input, and the unstable and dispersed source of coal bed gas, as well as unstable production and methane concentration.

[0006] Traditional coalbed methane liquefaction processes involve two steps: cooling and condensation. Due to its good safety and simple process, the nitrogen reverse Brayton cycle (N2-RBC) method is generally popular for small-scale liquefaction plants. When using the nitrogen reverse Brayton cycle as the refrigeration cycle, its use of nitrogen as the working fluid ensures a high level of safety and durability. Furthermore, its booster connected to the expander can partially reuse the shaft work generated by the expander. In addition, its operating and maintenance costs are low. Despite these advantages, liquefaction systems using the nitrogen reverse Brayton cycle typically exhibit a higher specific energy consumption (SEC) than systems based on mixed refrigerants. The irreversible heat transfer and high SEC of the nitrogen reverse Brayton cycle limit its application.

[0007] Coalbed methane wells are typically located in remote areas. Converting pure natural gas (NG) in coalbed methane into a liquid form, namely liquefied natural gas (LNG), is an efficient method for storing and transporting coalbed methane. This technology provides a simple solution for obtaining coalbed methane products in the field.

[0008] Due to the unique characteristics of coalbed methane, such as its remote and dispersed distribution, unpredictable production and methane concentration, and the fact that liquefaction equipment must be constantly moved to different gas reservoirs when the reservoir is depleted or for other practical purposes, those skilled in the art have made the following attempts to provide better liquefaction technology.

[0009] Chinese utility model patent CN205448491 U discusses a coalbed methane liquefaction system utilizing an expander and a liquefaction separator. The expander's expansion end cools and depressurizes the nitrogen and oxygen tail gas from the liquefaction separator and recovers it, while its pressure-enhancing end compresses regenerated gas for a drying device. This system efficiently utilizes the tail gas, enhancing energy conservation and environmental protection.

[0010] Chinese invention patent application CN105605883A introduces a liquefaction and separation system and technology for oxygen-containing coalbed methane using a plant and an expander. It involves expanding nitrogen and oxygen tail gas from the plant to reduce its temperature and pressure, then recirculating it for further cooling, while compressing regenerated gas from a drying tower for recovery. This process emphasizes the efficient utilization of tail gas, enhancing energy conservation and environmental benefits.

[0011] PCT international application WO2017121042A1 discloses a method for cooling a methane-rich gas mixture, removing heavy hydrocarbons, and separating the cooled gas into liquid and flash vapor via a throttling valve and separator. The liquid is collected, while the flash vapor is reheated, pressurized, and separated; a portion is mixed back into the methane-rich gas for recooling, while the other portion undergoes further cooling and expansion to provide refrigeration for the system, completing the cycle.

[0012] Rehman et al. proposed a biomethane liquefaction method for the subcooling and liquefaction stages of biomethane, improving refrigeration efficiency. This integration is supported by energy, exergy, and economic analyses, showing a 42% increase in exergy efficiency and a 33.5% reduction in total cost compared to conventional methods. Rehman et al.'s research involved nitrogen expanders and single-mix refrigerant processes in small-scale and offshore LNG production, using the Jaya optimization algorithm to improve their energy efficiency to 14.3% and 11.6%, respectively, significantly reducing operating costs. Rehman et al. also demonstrated a systematic approach to enhancing SMR processes, achieving significant energy savings and exergy efficiency using advanced exergy analysis and multivariate Coggin's optimization methods.

[0013] Existing technology also includes a two-stage nitrogen Rankine bottom cycle system in which nitrogen from the intermediate-pressure expander is cooled before entering the low-pressure expander. In this study, researchers enhanced a parallel nitrogen reverse Brayton cycle in a small-scale liquefied natural gas process.

[0014] Furthermore, Mofid et al. and Palizdar et al. enhanced the parallel nitrogen reverse Brayton cycle in the liquefied natural gas (LNG) process using a multi-objective particle swarm optimization algorithm and advanced thermal economic techniques, respectively. They investigated the impact of precooling on the efficiency of a pure natural gas liquefaction system using a two-stage nitrogen reverse Brayton cycle.

[0015] Other researchers have constructed pre-cooling refrigeration cycles based on the traditional nitrogen reverse Brayton cycle, using carbon dioxide and propane as working fluids respectively. Further research has explored and improved parallel nitrogen reverse Brayton cycle systems with R22 pre-cooling for use in liquefied natural gas (LNG) processes. This technology optimizes the system and achieves a 22.2% reduction in specific energy consumption compared to baseline. It should also be noted that efficiency can be improved by using a combination of nitrogen and methane (N2-CH4) as a refrigerant in the regenerative Brayton cycle; this method is known as the N2-CH4 expansion process. Moe in et al. optimized a parallel N2-CH4 reverse Brayton cycle system using a genetic algorithm and investigated the effect of methane concentration in the refrigerant on performance. Existing technologies have also investigated three two-stage reverse Brayton cycle systems: a nitrogen reverse Brayton cycle, a nitrogen reverse Brayton cycle with pre-cooled propane, and an N2-CH4 reverse Brayton cycle system with pre-cooled propane. Studies have shown that the N2-CH4 reverse Brayton cycle system using pre-cooled propane has the lowest specific energy consumption and the highest exergy efficiency.

[0016] In summary, the efficiency of the nitrogen reverse Brayton cycle in liquefied natural gas processes can be improved by implementing a precooling cycle, introducing methane or propane into the standard nitrogen refrigerant, or replacing the gas expander with a gas-liquid expander.

[0017] However, these improvements require significant costs and involve considerable complexity. Furthermore, the presence of flammable and high Global Warming Potential (GWP) refrigerants such as propane, methane, and combinations thereof reduces the feasibility of using nitrogen reverse Brayton cycles for various applications.

[0018] Considering the shortcomings of existing technologies, clean and green cold energy combined with the coalbed methane liquefaction process offers a more promising solution. For example, Liquid Air Energy Storage (LAES) and Active Magnetic Refrigerant (AMR) provide improved pathways to the pre-cooling and liquefaction stages, respectively, and reduce reliance on refrigerants with high global warming potential. Summary of the Invention

[0019] The problem addressed by this invention is how to provide a green and environmentally friendly coalbed methane liquefaction device to reduce dependence on refrigerants with high global warming potential. Furthermore, the coalbed methane liquefaction device provided by this invention has good energy-saving performance and low cost, and the method also has the advantages of high energy output and high exergy efficiency.

[0020] To address the aforementioned problems, this invention provides a coalbed methane liquefaction device, comprising: a precooling system; a coalbed methane pipeline, the end of which is provided with a storage tank for storing liquefied coalbed methane; a refrigerant circulation pipeline, in which refrigerant circulates; a first heat exchanger, wherein the coalbed methane pipeline and the refrigerant circulation pipeline exchange cold energy at the location of the first heat exchanger; and a fifth heat exchanger, located on the coalbed methane pipeline and preceding the first heat exchanger; wherein the coalbed methane pipeline and the precooling system exchange cold energy at the location of the fifth heat exchanger.

[0021] The coalbed methane liquefaction apparatus of the present invention involves at least two stages of cooling and liquefaction of the coalbed methane feed gas stream. In the first pre-cooling stage, the coalbed methane feed gas stream is pre-cooled at ambient temperature using a pre-cooling system in a fifth heat exchanger. In the second sub-cooling stage, the pre-cooled coalbed methane undergoes sub-cooling in a closed liquefaction cycle using a mixed refrigerant in a refrigerant circulation pipeline. This system is tailored to the cooling requirements of the coalbed methane. This invention contributes to achieving a cleaner liquefaction process.

[0022] Furthermore, the precooling system is a magnetic refrigeration system, which includes: a heated bed chamber; a cooled bed chamber, the heated bed chamber and the cooled bed chamber being circulated and connected; a second pump, the second pump being located between the outlet of the heated bed chamber and the inlet of the cooled bed chamber; and a fifth-stage intercooler, the fifth-stage intercooler being located between the second pump and the cooled bed chamber.

[0023] The precooling system is a magnetic refrigeration system that utilizes the magnetocaloric effect, where magnetic materials are alternately magnetized and demagnetized to transfer heat energy without the use of conventional refrigerants. Specifically, coalbed methane undergoes an initial precooling process in the magnetic refrigeration system, where a magnetic field is used instead of a traditional refrigerant to promote cooling. This process operates through adiabatic magnetization and demagnetization cycles, where magnetization increases the temperature of the magnetic material, while demagnetization lowers it. This alternating thermal effect, the magnetocaloric effect, absorbs and releases heat energy for effective cooling as the magnetic domains in the material rearrange. This approach enhances environmental sustainability because the process eliminates the need for chemical refrigerants.

[0024] Furthermore, the liquefaction unit also includes a liquid air energy storage system; wherein, the coalbed methane pipeline and the liquid air energy storage system exchange cold energy at the location of the first heat exchanger.

[0025] The coalbed methane liquefaction apparatus of the present invention further includes a third stage of liquefaction in the coalbed methane feed gas stream. In this third stage of liquefaction, the coalbed methane is liquefied by a liquid air energy storage system during its discharge phase, and a cold flame, which serves as liquid air storage, is used to enhance cooling efficiency.

[0026] It should be noted that in the three-stage liquefaction process, the mixed refrigerant in the refrigerant circulation line can be compressed to 3 bar in the first-stage compressor and then cooled to 40°C in an air-cooled intercooler. The mixed refrigerant is further compressed to 7.8 bar and then cooled back to 40°C. The mixed refrigerant is further compressed to 20.2 bar and then cooled to 40°C. The mixed refrigerant is finally compressed to 52 bar and then cooled to 98°C using liquid air. The high-pressure refrigerant stream is finally cooled to 40°C by an air cooler.

[0027] Furthermore, the liquid air energy storage system includes: a liquid air storage device connected to the first end of an air pipeline and used to output liquid air to a first heat exchanger; a combustion chamber and an air turbine connected sequentially to the end of the air pipeline; wherein the air pipeline extending from the liquid air storage device and connected to the combustion chamber and the air turbine passes through the first heat exchanger.

[0028] Furthermore, the liquid air energy storage system also includes a fourth heat exchanger; wherein air from the first heat exchanger first passes through the fourth heat exchanger and enters the combustion chamber and air turbine, then passes through the fourth heat exchanger again. This invention has an energy recovery mechanism that converts the thermal energy during the discharge phase of the liquid air energy storage system into electrical energy via the air turbine, thereby not only supporting the electricity demand of the liquefaction process but also potentially supplying surplus electricity to the outside. The hot air leaving the air turbine can be used to increase the temperature of the air entering the fourth heat exchanger.

[0029] Air is heated in the combustion chamber to 1300°C, then used to generate electricity in the air turbine, and finally rerouted to the fourth heat exchanger for heat self-recovery.

[0030] Furthermore, the liquefaction device also includes a third heat exchanger; wherein air from the first heat exchanger first passes through the third heat exchanger and then passes through the fourth heat exchanger for the first time, and refrigerant in the refrigerant circulation pipeline enters the first heat exchanger via the third heat exchanger.

[0031] In the third heat exchanger, the air is heated by the refrigerant's heat exchanger, reducing the external energy required for air expansion and cooling the refrigerant.

[0032] Furthermore, a fourth intercooler is provided between the third heat exchanger and the first heat exchanger.

[0033] Furthermore, the refrigerant circulation line is equipped with a first Joule-Thomson valve, as well as multiple alternating multistage compressors and intercoolers.

[0034] Furthermore, the liquefaction unit also includes a second heat exchanger; wherein the coalbed methane pipeline between the first heat exchanger and the storage tank passes through the second heat exchanger, and the air pipeline between the liquid air storage device and the first heat exchanger passes through the second heat exchanger.

[0035] Furthermore, a second Joule-Thomson valve is provided between the second heat exchanger and the storage tank, and a first pump is provided between the liquid air storage device and the second heat exchanger.

[0036] Beneficial effects

[0037] The coalbed methane (CBM) liquefaction process integrating a liquid air energy storage system and a moving magnetic refrigerator, as described in this invention, has the following main advantages:

[0038] 1. The active magnetic refrigeration system utilizes the magnetocaloric effect for cooling, making it more energy-efficient than traditional gas compression refrigeration systems. Combined with the energy storage capacity of a liquid air energy storage system, this integration can significantly reduce energy consumption during the liquefaction process.

[0039] 2. By improving the energy efficiency of the liquefaction process, overall operating costs are reduced. Furthermore, liquid air energy storage systems can utilize off-peak electricity prices for energy storage, further reducing costs.

[0040] 3. Active magnetic refrigeration systems are an environmentally friendly technology because they do not rely on refrigerants that emit greenhouse gases. This contributes to cleaner liquefaction processes, aligning with global sustainability goals.

[0041] 4. Improved precooling efficiency from active magnetic chillers may increase the liquefaction rate of coalbed methane, making the process faster and more efficient, thereby increasing productivity;

[0042] 5. Liquid air energy storage systems offer a way to store and recover potentially wasted energy, allowing for better overall energy management and utilization;

[0043] 6. The modular nature of active magnetic chillers and liquid air energy storage systems allows for scalability, making the liquefaction process more adaptable to operations of different scales and sizes;

[0044] 7. Integration with liquid air energy storage offers the potential to co-generate electricity, providing an additional source of revenue or electricity for the liquefaction process itself;

[0045] 8. The system also features an innovative heat recovery mechanism, in which the airflow generated by the air turbine is redirected back to the heat exchanger to recover heat. This process utilizes the heat generated by the expanded air, improving the overall heat transfer efficiency within the heat exchanger.

[0046] In summary, these advantages demonstrate that the present invention can make the liquefaction of coalbed methane (CBM) more efficient, economical, and environmentally friendly. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of a coalbed methane liquefaction device based on a single mixed refrigerant (SMR) in the prior art;

[0048] Figure 2 This is a schematic diagram of the coalbed methane liquefaction device of the present invention. Detailed Implementation

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, a detailed description of specific embodiments of the present invention will be provided below.

[0050] Figure 1 This is a schematic diagram of a coalbed methane liquefaction system based on a single mixed refrigerant in existing technology. In existing technologies, the single mixed refrigerant coalbed methane liquefaction solution is used to cool the gas to the low temperature required for liquefaction. For example... Figure 1 As shown, in the prior art, the process of liquefying coalbed methane using a single mixed refrigerant typically includes the following steps:

[0051] First, the raw coalbed methane needs to be pretreated to remove water vapor, carbon dioxide, and other contaminants that may freeze during the liquefaction process;

[0052] Subsequently, the pretreated coalbed methane needs to be cooled in stages using a closed-loop refrigeration system with a single mixed refrigerant. This mixed refrigerant is typically a mixture of nitrogen (N2), methane (C1), ethane (C2), and propane (C3), chosen because their thermodynamic properties match the cooling curve of the coalbed methane during heat exchange. The aforementioned mixed refrigerant is then... Figure 1 Arrow 1 in the diagram is compressed by multiple compressors (K1, K2, K3, K4) to reach the discharge pressure; these compressors are assisted by four interstage coolers (E1, E2, E3, E4); after each compression stage, the temperature is reduced to a fixed value of 40°C by the interstage coolers; the cooling medium in the interstage coolers is air, and its initial temperature depends entirely on the environmental conditions.

[0053] Furthermore, the compressed refrigerant passes through Figure 1 Arrow 9 indicates that the coalbed methane is being fed into the main liquefied natural gas cryogenic heat exchanger CHX-1, via which... Figure 1Arrow 12 indicates that the gas is being fed into the low-temperature heat exchanger CHX-1, where the two fluids co-condense; CHX-1 is a key component of the gas liquefaction plant; the coalbed methane is subsequently cooled in CHX-1; along... Figure 1 Arrow 10 indicates that the refrigerant flowing out has the highest pressure and is throttled by the Joule-Thomson valve VLV-1. The lower-pressure refrigerant then... Figure 1 Arrow 11 indicates the entry point into the low-temperature heat exchanger CHX-1. Because the refrigerant and coalbed methane exchange heat through the low-temperature heat exchanger CHX-1, from... Figure 1 The temperature of the coalbed methane exiting via arrow 13 drops to a cryogenic value of -155°C. The refrigerant entering the cryogenic heat exchanger CHX-1 via arrow 11 continues to participate in the cycle. The mixture of liquid and vaporized methane is then guided to a separator, where the liquid coalbed methane is collected at the bottom, and the remaining vapor is typically recovered to the system. The refrigerant mixture in the single-mixed refrigerant process is specifically designed for the properties of the coalbed methane feed gas, aiming to achieve high efficiency and optimal heat exchange. The single-mixed refrigerant process is widely used due to its relative simplicity, flexibility, and adaptability to different production capacities. However, this process is also energy-intensive, prompting the need for the development of more advanced cryogenic technologies. This invention aims to overcome the shortcomings of poor energy efficiency and high cost in the existing single-mixed refrigerant liquefaction process by proposing a coalbed methane liquefaction device integrating liquid air energy storage and active magnetic refrigeration technology, with the goal of reducing dependence on refrigerants with high global warming potential, lowering the cost of coalbed methane liquefaction, and improving its energy-saving effect.

[0054] Specifically, the principle of liquid air energy storage technology is to utilize inexpensive off-peak electricity to absorb air from the environment, cool it into a liquid, and store it in a low-temperature storage tank. During peak electricity demand, the liquid air is released from the tank, pressurized, and heated to drive equipment such as steam turbines to generate electricity, thus achieving peak-load utilization of off-peak electricity. Active magnetic refrigeration is a refrigeration method that utilizes the magnetocaloric effect. The magnetic core of active magnetic refrigeration is located inside a magnet, and the heat exchange fluid can travel through the magnet. Utilizing the magnetocaloric effect of the material, a larger cooling capacity can be achieved across a wider magnetic circulation temperature range. This invention utilizes liquid air energy storage and active magnetic refrigeration technology to provide an energy-saving and cost-effective coalbed methane liquefaction device. This method, by integrating with a liquid air energy storage system and an active magnetic refrigeration machine, can promote the co-production of electricity and provide effective cooling and heating during the pre-cooling stage of coalbed methane liquefaction. Specifically, the liquid air energy storage system stores energy in the form of liquid air, and in its discharge mode, it can provide cooling and heating during the coalbed methane liquefaction stage, thereby improving overall energy efficiency. During the discharge phase of liquid air energy storage, electricity is also generated through an air turbine, which can be used as the input power for the compressor during the coalbed methane liquefaction process.

[0055] The following reference Figure 2 The coalbed methane liquefaction apparatus of the present invention will be described in detail. It should be noted that the simulation operation assumes the use of 100% pure methane in order to make a rigorous comparison with conventional processes. Figure 2 The demonstration showcases a coalbed methane liquefaction process involving liquid air energy storage and an active magnetic chiller, where various processes and equipment work together to effectively liquefy coalbed methane.

[0056] The magnetic refrigeration working mechanism of this invention will be described first. See [link to relevant documentation]. Figure 2 At the upper left end, the liquefaction process of this invention uses coalbed methane (CBM) as the main input. The CBM first enters the fifth heat exchanger CHX-5 for pre-cooling, and the circulation of the fifth heat exchanger CHX-5 and the magnetic refrigeration system 100 achieves a potential synergistic effect. The magnetic refrigeration system 100 utilizes the magnetocaloric effect, specifically an active magnetic refrigerator (AMR), which includes a heated bed chamber 110 and a cooled bed chamber 120. The heated bed chamber 110 and the cooled bed chamber 120 are connected by a circulation pipeline. A second pump 2 and a fifth interstage cooler E5 are provided between the outlet end of the heated bed chamber 110 and the inlet end of the cooled bed chamber 120. The aforementioned fifth heat exchanger CHX-5 is provided between the inlet end of the heated bed chamber 110 and the outlet end of the cooled bed chamber 120. In this invention, refrigeration can be achieved without the need for conventional refrigerants by using the heated bed chamber 110 and the cooled bed chamber 120. The magnetic refrigeration system 100 of this invention is an active magnetic refrigeration system. Its operation cycle begins with adiabatic magnetization, heating the magnetic bed. Subsequently, a working fluid (air in this document), driven by a second pump 2, moves from the colder portion of the regenerator to the hotter portion, causing the magnetic material to cool. The system then performs adiabatic demagnetization, lowering the temperature of the magnetic material. Upon completion of the cycle, the working fluid moves from the heated end back to the cold end, thereby heating the magnetic bed. The cooler working fluid provides cooling for the pre-cooling section of the incoming coalbed methane (CBM) via a fifth heat exchanger CHX-5.

[0057] The working mechanism of the liquid air energy storage system of the present invention will then be described. It is worth noting that the complete liquid air energy storage system includes two main stages in operation: charging and discharging. Air is liquefied during the charging stage and vaporized during the discharging stage. In this process, the present invention only considers the discharging end of the liquid air energy storage, where the liquid air is vaporized to generate electricity to meet the energy requirements of the liquefaction unit.

[0058] See Figure 2At the lower end, liquid air enters the liquid air storage device 210 via arrow 18, and is then sent to the first pump 1 via arrow 19 to increase its pressure. This liquid air enters the second heat exchanger CHX-2 via arrow 20, cooling the partially liquefied coalbed methane (CBM) in the intake section. It then flows through the first heat exchanger CHX-1, which serves as the main heat exchanger, where the liquid air exchanges most of its cooling energy with the refrigerant and CBM, thus significantly reducing its temperature at arrow 22. To increase the air temperature and pre-cool the refrigerant, the air passes through the third heat exchanger CHX-3, specifically a shell-and-tube heat exchanger. This utilizes the refrigerant arrow 8 for heating, reducing the power consumption of the external heat source; and uses the air arrow 22 for cooling the refrigerant arrow 8. Therefore, the liquid air (-194°C) reaches arrow 23 (89°C). This invention requires no external energy source, reducing energy intensity. Subsequently, the airflow 23 passes through the fourth heat exchanger CHX-4. Subsequently, airflow 24 passes through combustion chamber 220 to increase the air temperature. Airflow 25 generates electricity via air turbine 230. Airflow 26 returns to the fourth heat exchanger CHX-4 for heat self-recovery, that is, utilizing the heat from the expanded airflow 26 after air turbine 230 for combustion. In this way, the heat transfer efficiency between the working fluids in the fourth heat exchanger CHX-4 is improved.

[0059] Table 1 Feeding conditions and composition of coalbed methane and liquid air

[0060]

[0061]

[0062] The following will combine Figure 2 The specific operating process of the liquefaction apparatus of the present invention is described below. Coalbed methane (CBM) enters the liquefaction apparatus under specified conditions, for example, a pressure of 4 bar and a temperature of 30°C. The feed conditions and composition of the CBM and liquid air are provided in Table 1.

[0063] Table 2 Operating conditions of coalbed methane liquefaction unit

[0064] Parameter Refrigerant flow rate (kg / s) — [N2] 0.92 [C2] 0.70 0.70 [C2] 0.41 [C3] 2.77 Total mixed refrigerant (kg / s) 4.80 Refrigerant suction pressure (bar) 1.18 Refrigerant discharge pressure (bar) 52.0 Refrigerant subcooling (°C) -163.7 Compression capacity (kW) 1603 Total power consumption (kW) 2520 Electricity generated with air turbine (kW) 905

[0065] Then, the coalbed methane (CBM) is pre-cooled by an active magnetic refrigeration system 100. This system utilizes a magnetic field to achieve refrigeration without conventional refrigerants through a series of adiabatic magnetization and demagnetization processes, thereby raising and lowering the temperature of the magnetic bed. In some embodiments of the invention, a single mixed refrigerant technology can be used to convert the CBM into a liquid state. The refrigerant consists of nitrogen, methane, ethane, and propane, and is input along arrow 1. The operating conditions of the CBM liquefaction device of the present invention are provided in Table 2.

[0066] A single refrigerant mixture contains up to four components: nitrogen (N2), methane (C1), ethane (C2), and propane (C3). The second refrigerant is air, which contains up to two components: nitrogen (N2) and oxygen (O2).

[0067] The mixed refrigerant passes through a multi-stage compressor (K1, K2, K3, K4) and an intercooler (E1, E2, E3, E4). After multi-stage compression and cooling, the mixed refrigerant enters the third heat exchanger CHX-3 via arrow 8 (maximum discharge pressure 52.0 bar, temperature 104.0 °C), and then passes through the first heat exchanger CHX-1 via arrow 9 to obtain maximum cooling capacity from liquid air, thereby reducing the temperature of the refrigerant flow along arrow 11 to a low temperature of -144 °C.

[0068] Utilizing the Joule-Thomson effect, the mixed refrigerant is delivered to the first heat exchanger CHX-1 via the first Joule-Thomson valve VLV-1 and arrow 12 (-164°C). Therefore, the first heat exchanger CHX-1 receives more cooling energy to liquefy coalbed methane (CBM). Due to this self-recovery cooling operation of arrow 12, the refrigerant's power consumption is further reduced to achieve maximum synergistic effect. Thus, the refrigerant temperature returns to its initial temperature of 37°C along arrow 12 and circulates in arrow 13. This system can generate liquid CBM at a low temperature of -159°C and a mass flow rate of 1.0 kg / s. Furthermore, 905 kW of electricity can be generated from the discharge end of the liquid air energy storage system, reducing the power consumption of external heat sources. The electricity generated by the liquid air energy storage can be used for compressors in the CBM plant. Liquid air from arrow 19 is sent to the first pump 1 to increase its pressure to 25.0 bar. This liquid air passes through the second heat exchanger CHX-2, which partially liquefied coalbed methane (CBM) entering via arrow 15, to achieve subcooling. It then passes through the first heat exchanger CHX-1, where the liquid air exchanges most of its cooling energy with the refrigerant and CBM, thereby lowering the temperature at arrow 22 to 36°C. To raise the air temperature and pre-cool the refrigerant, the air passes through a shell-and-tube third heat exchanger CHX-3. Thus, the heating energy of the refrigerant at arrow 8 can be utilized, reducing the power consumption of the external heat source for air expansion, and the cooling energy of the refrigerant at arrow 8 can be achieved through the cooling energy of the airflow at arrow 22. Therefore, the liquid air (-194°C) reaches the position at arrow 23 (89°C) without an external heat source, thus reducing the energy intensity. Subsequently, the airflow from arrow 24 is heated in combustion chamber 220, raising its temperature to 1300°C. This heated air, via arrow 25, generates electricity through air turbine 230. After electricity is generated, air is re-transported to the first heat exchanger CHX-1 via arrow 26 for heat recovery. This means that the heat energy of the airflow retained in arrow 26 after the air turbine 230 expands is effectively collected, thereby improving the heat transfer efficiency in the fourth heat exchanger CHX-4. The coalbed methane (CBM) entering the second heat exchanger CHX-2 via arrow 15, after leaving CHX-2, enters the second Joule-Thomson valve VLV-2 via arrow 16, and then enters the storage tank 130.

[0069] The liquefaction process of this invention has been successfully simulated in the simulation software Aspen HYSYS v14, which uses the thermodynamic model REFPROP and Peng-Robinson to estimate and predict the physical properties of the fluid. In the simulation, specific energy consumption (SEC) is defined as the net work done per unit mass of liquid coalbed methane (CBM), and is considered as the objective function, while the minimum internal proximity temperature in the cryogenic heat exchanger is considered as a constraint for effective heat transfer. Through rigorous simulation and corresponding analysis, the specific energy consumption of this invention reaches 0.7 kWh / kgL of CBM, which is far lower than the energy consumption of current commercial and industrial units. In addition, this invention also generates 905 kW of electricity, the input power of which is also included in the aforementioned specific energy consumption of 0.7 kWh / kgL of CBM. These results demonstrate that this invention is more competitive than traditional single-mixed refrigerant CBM liquefaction processes.

[0070] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A coalbed methane liquefaction device, characterized in that, The liquefaction device includes: Precooling system; A coalbed methane pipeline (300) is provided at the end of which a storage tank (130) for storing liquefied coalbed methane is provided. A refrigerant circulation line (200) is provided with a circulating refrigerant; The first heat exchanger (CHX-1) is where the coalbed methane pipeline (300) and the refrigerant circulation pipeline (200) exchange cold energy. The fifth heat exchanger (CHX-5) is located on the coalbed methane pipeline (300) and before the first heat exchanger (CHX-1); The coalbed methane pipeline (300) and the precooling system exchange cold energy at the location of the fifth heat exchanger (CHX-5); The liquefaction apparatus further includes: Liquid air energy storage system; The coalbed methane pipeline (300) and the liquid air energy storage system exchange cold energy at the location of the first heat exchanger (CHX-1); The liquid air energy storage system includes: A liquid air storage device (210) is connected to the beginning of an air pipeline and is used to output liquid air to the first heat exchanger (CHX-1). A combustion chamber (220) and an air turbine (230) are connected in sequence to the end of the air duct; The air duct extending from the liquid air storage device (210) and connecting to the combustion chamber (220) and the air turbine (230) passes through the first heat exchanger (CHX-1). Fourth heat exchanger (CHX-4); Air from the first heat exchanger (CHX-1) first passes through the fourth heat exchanger (CHX-4) and enters the combustion chamber (220) and the air turbine (230), and then passes through the fourth heat exchanger (CHX-4) again.

2. The liquefaction apparatus according to claim 1, characterized in that, The precooling system is a magnetic refrigeration system (100), which includes: Heated bed chamber (110); The cold bed chamber (120) is connected to the hot bed chamber (110) in a circulating manner; The second pump (2) is located between the outlet of the heated bed chamber (110) and the inlet of the cooled bed chamber (120); The fifth-stage intercooler (E5) is located between the second pump (2) and the cooling bed chamber (120).

3. The liquefaction apparatus according to claim 1, characterized in that, The liquefaction apparatus further includes: Third heat exchanger (CHX-3); Air from the first heat exchanger (CHX-1) first passes through the third heat exchanger (CHX-3), and then passes through the fourth heat exchanger (CHX-4) for the first time. The refrigerant in the refrigerant circulation pipeline (200) enters the first heat exchanger (CHX-1) via the third heat exchanger (CHX-3).

4. The liquefaction apparatus according to claim 3, characterized in that, A fourth intercooler (E4) is provided between the third heat exchanger (CHX-3) and the first heat exchanger (CHX-1).

5. The liquefaction apparatus according to claim 3, characterized in that, The refrigerant circulation line (200) is equipped with a first Joule-Thomson valve (VLV-1), as well as multiple alternating multistage compressors and intercoolers.

6. The liquefaction apparatus according to claim 1, characterized in that, The liquefaction apparatus further includes: Second heat exchanger (CHX-2); The coalbed methane pipeline (300) between the first heat exchanger (CHX-1) and the storage tank (130) passes through the second heat exchanger (CHX-2), and the air pipeline between the liquid air storage device (210) and the first heat exchanger (CHX-1) passes through the second heat exchanger (CHX-2).

7. The liquefaction apparatus according to claim 6, characterized in that, A second Joule-Thomson valve (VLV-2) is provided between the second heat exchanger (CHX-2) and the storage tank (130), and a first pump (1) is provided between the liquid air storage device (210) and the second heat exchanger (CHX-2).

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