Vehicle-mounted screw natural gas compressor unit

Abstract

The utility model discloses a kind of vehicle-mounted screw natural gas compressor units, the unit includes compressor, motor, primary oil separator, secondary oil separator, tertiary oil separator, air-cooled condenser, air-cooled oil cooler, oil pump, outlet gas-liquid separator and inlet gas-liquid separator;The gas outlet of inlet gas-liquid separator is connected with the inlet of compressor;The outlet of compressor is sequentially connected to the inlet of air-cooled condenser by primary oil separator, secondary oil separator and tertiary oil separator;The outlet of air-cooled condenser is connected with the inlet of outlet gas-liquid separator;Motor is drivingly connected with compressor, to drive compressor operation;The oil outlet of primary oil separator, secondary oil separator and tertiary oil separator is all connected to the inlet of oil pump, the outlet of oil pump is connected to the inlet of air-cooled oil cooler, and the outlet of air-cooled oil cooler is connected with compressor.The natural gas compressor unit of the utility model not only can ensure mixed refrigerant liquefied natural gas, but also can be flexible and movable.

Description

Technical Field

[0001] This utility model belongs to the technical field of natural gas compressor units, specifically relating to a vehicle-mounted screw-type natural gas compressor unit. Background Technology

[0002] Natural gas is found in porous underground rock formations, including oilfield gas, gas field gas, coalbed methane, mud volcano gas, and biogenic gas, with a small amount also found in coal seams. It is mainly composed of methane (85%) and small amounts of ethane (9%), propane (3%), nitrogen (2%), and butane (1%), with slight variations depending on the gas's origin. It is primarily used as fuel and is also a raw material for manufacturing chemicals such as acetaldehyde, acetylene, ammonia, carbon black, ethanol, formaldehyde, hydrocarbon fuels, hydrogenated oils, methanol, nitric acid, syngas, and vinyl chloride. Natural gas is compressed into a liquid for storage and transportation. The calorific value of liquefied petroleum gas (LPG) is 11,000 kcal per kilogram, and with a specific gravity of 0.55, the calorific value of LPG is 25,200 kcal per cubic meter. The average lower heating value is 41.87 MJ / kg for petroleum, 38.97 MJ / kg for natural gas, and 20.93 MJ / kg for raw coal. The standard fuel coefficients for petroleum and natural gas are 1.4286 and 1.33, respectively.

[0003] In the entire LNG industry chain, natural gas liquefaction is the most capital- and technology-intensive and crucial link, accounting for approximately 30-40% of the total cost. Over the past thirty years, liquefied natural gas technology has developed rapidly as a new scientific and technological field worldwide. At the same time, countries around the world are striving to find and explore natural gas liquefaction technologies suitable for their own national conditions. Natural gas liquefaction technology is a highly technological and complex system engineering project, with its industrial chain consisting of a series of links including purification, liquefaction, storage, transportation, and receiving.

[0004] Natural gas liquefaction (LNG) units are generally classified into two categories based on their intended use: load-bearing LNG units and peak-shaving LNG units. Large, multi-bladed units that produce LNG for local use or external transportation are called load-bearing LNG units. LNG units used for peak load shaving, supplementing winter fuel supply, and emergency peak shaving are called peak-shaving LNG units. These units typically liquefy and store excess natural gas during off-peak periods and regasify it for use during peak periods or emergencies. These units have a smaller liquefaction capacity but a larger storage capacity. LNG units can also be classified into small, medium, and large-scale LNG units based on their production capacity. Small and medium-sized LNG units, characterized by their small size, skid-mountability, mobile transport, and ease of start-up and shutdown, are often used in small-capacity gas fields, offshore platforms, and peak-shaving stations, enabling the extraction of gas from dispersed gas fields. Vehicle-mounted screw compressor units are suitable for small and medium-sized units.

[0005] Depending on the refrigeration method, liquefaction processes are mainly divided into cascade liquefaction processes, mixed refrigerant liquefaction processes, and expansion refrigeration processes. Mixed refrigeration processes include SMR, C3-MR, DMR, and C3-MR+nitrogen processes; nitrogen expansion refrigeration processes include nitrogen expansion refrigeration and nitrogen and methane expansion refrigeration processes.

[0006] The mixed refrigerant liquefaction process uses a mixture of multiple components as the refrigerant, replacing the single-component multiple refrigerants used in cascade refrigeration cycles. The mixed refrigerant refrigeration cycle uses a mixture of five or more refrigerants, including C1-C5 hydrocarbons and N2, as the circulating refrigerant. However, theoretically, the composition ratio of the mixed refrigerant must be determined based on the composition, pressure level, and process flow of the feedstock (natural gas). Therefore, strict requirements are placed on the refrigerant ratio and the composition of the natural gas, and these cannot be easily changed after preparation. Even if this can be achieved, it is difficult to perfectly match the cooling capacity required for the entire liquefaction process (from room temperature to -162°C) with the cooling capacity provided by the refrigerant; generally, only a partial approximation of the cooling curve is possible. Therefore, the efficiency of the mixed refrigerant cycle is lower than that of the stepped cycle process with nine temperature gradient levels. This method is currently the most widely used natural gas liquefaction process in the world. Its principle involves supplying cooling in two stages: the high-temperature stage uses propane compression refrigeration to pre-cool the feedstock natural gas to -40°C at three temperature levels; the low-temperature stage employs two heat exchange methods: a high-pressure mixed refrigerant exchanges heat with the higher-temperature feedstock gas, and a low-pressure mixed refrigerant exchanges heat with the lower-temperature feedstock gas, thereby maximizing efficiency. However, due to process limitations, its energy consumption is significantly higher, approximately 15% higher than that of a cascaded liquefaction process, and its configuration is more complex, requiring more difficult data calculations. Nevertheless, the overall process is simpler than a cascaded process, using fewer pieces of equipment, and its cost is 20% lower than that of a cascaded liquefaction process. Utility Model Content

[0007] This utility model is proposed to address the above-mentioned shortcomings, and aims to provide a vehicle-mounted screw-type natural gas compressor unit that not only ensures the mixing of refrigerant and liquefaction of natural gas, but is also flexible and mobile.

[0008] To achieve the above objectives, this utility model provides a vehicle-mounted screw-type natural gas compressor unit, including a compressor, a motor, a primary oil separator, a secondary oil separator, a tertiary oil separator, an air-cooled condenser, an air-cooled oil cooler, an oil pump, an outlet gas-liquid separator, and an inlet gas-liquid separator;

[0009] The gas outlet of the inlet gas-liquid separator is connected to the inlet of the compressor; the outlet of the compressor is connected to the inlet of the air-cooled condenser in sequence through the first-stage oil separator, the second-stage oil separator, and the third-stage oil separator; the outlet of the air-cooled condenser is connected to the inlet of the outlet gas-liquid separator; the motor is connected to the compressor to drive the compressor to operate;

[0010] The oil outlets of the primary oil separator, secondary oil separator, and tertiary oil separator are all connected to the inlet of the oil pump. The outlet of the oil pump is connected to the inlet of the air-cooled oil cooler, and the outlet of the air-cooled oil cooler is connected to the compressor.

[0011] Furthermore, the compressor, motor, primary oil separator, secondary oil separator, tertiary oil separator, air-cooled condenser, air-cooled oil cooler, oil pump, outlet gas-liquid separator, and inlet gas-liquid separator are all mounted on a common base.

[0012] Furthermore, the common base is securely locked to the vehicle chassis via a locking structure.

[0013] Furthermore, an inverted U-shaped elbow is provided at the inlet of the air-cooled oil cooler to form an oil seal.

[0014] Furthermore, the fan of the air-cooled condenser is detachably mounted below the air-cooled condenser.

[0015] Furthermore, the bottom of the primary oil separator, the secondary oil separator, and the tertiary oil separator are all provided with oil collection outlets, which are connected to the inlet of the oil pump through pipelines; the outlet of the oil pump is connected to the inlet of the air-cooled oil cooler through pipelines, and the outlet of the air-cooled oil cooler is connected back to the compressor through pipelines.

[0016] Furthermore, the primary oil separator is equipped with a vortex separation component, a grid separation component, and a filter element separation component; the secondary oil separator and the tertiary oil separator are both equipped with grids and filter elements for separating the lubricating oil in the compressed gas step by step.

[0017] Furthermore, the inlet of the inlet gas-liquid separator is located in its middle part and the outlet is located at its top, so that the natural gas entering the inlet gas-liquid separator is discharged from the top into the compressor after being separated by gravity from bottom to top; the inlet of the outlet gas-liquid separator is located in its middle part and the outlet of the outlet gas-liquid separator is located at its top.

[0018] Furthermore, both the air-cooled condenser and the air-cooled oil cooler are positioned above the unit, with space reserved below them for air circulation.

[0019] Furthermore, the vehicle-mounted screw-type natural gas compressor unit also includes a control cabinet, which is used to control the operation of various components of the compressor unit.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] Firstly, the vehicle-mounted screw-type natural gas compressor unit of this invention is entirely placed on a flatbed truck, making the transportation and lifting of the entire unit much more convenient than other stationary units. Furthermore, due to fewer lifting operations, the unit can be made longer without deformation. The common base is connected to the truck bed via locking mechanisms, ensuring the stability of the compressor unit during transportation. The truck cab can be detached from the truck bed, giving the compressor unit four operating and maintenance surfaces. The compressor unit needs to be selected as large as possible while remaining within the appropriate vehicle dimensions to meet the requirements of various operating conditions.

[0022] Secondly, the oil cooler and condenser of this utility model are air-cooled to meet various user needs. The oil cooler and condenser must be installed at a high position with an open bottom to ensure unobstructed airflow. Considering shutdown requirements, the inlet and outlet of the air-cooled oil cooler are designed with an inverted U-shape to minimize oil backflow into the oil separator during shutdown. Due to the unit's mobility, users do not need to prefabricate the plant on-site; the plant can be redesigned after the operating conditions stabilize. This unit can meet the urgent usage needs of most regions in China.

[0023] Thirdly, this utility model's unit forms a complete natural gas compression, oil separation, cooling, and gas-liquid separation process. It can complete the entire chain of natural gas processing from low pressure to high pressure and then to condensation in one go under vehicle operating conditions, without the need for on-site separate equipment. A closed-loop oil circulation circuit maintains stable compressor lubricating oil temperature and oil content, meeting the stringent requirements for low oil content in mixed refrigerant liquefied natural gas processes and avoiding the risk of oil buildup in the cold box. The rigid drive between the motor and compressor results in a compact structure, reducing vibration and centering maintenance, and improving unit reliability and portability.

[0024] Fourth, all key components of this unit are pre-assembled and aligned on the same common base, making it a complete set upon delivery. It can be hoisted onto a vehicle or placed on the ground as a whole, shortening the on-site installation and commissioning cycle and avoiding equipment misalignment, oil pipe stress, and frame deformation caused by multiple hoisting operations. This achieves "commissioning upon arrival," facilitating later overall maintenance or replacement and reducing operation and maintenance costs. The common base and the vehicle platform are rigidly locked together by latches, ensuring that the unit will not shift or loosen due to vibration under high-speed transportation or harsh road conditions, ensuring safety. The latches can be quickly opened and closed, separating the vehicle head from the carrying platform, increasing the on-site operating area and improving maintenance convenience.

[0025] Fifth, the unit of this utility model uses a three-stage gradient separation process—vortex, grid, and filter element—to progressively improve oil mist collection efficiency, reducing the oil content in the final stage to meet requirements and creating conditions for subsequent cold box processes. Standardized components allow for quick filter element replacement, shortening downtime.

[0026] Sixth, the gas-liquid separator structure of this utility model is arranged with the inlet in the middle and the outlet at the top to form a stable upward flow, realizing the gravity stratification of natural gas and condensate, with high separation efficiency and low pressure drop, improving system safety and downstream storage tank quality. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the main structure of the vehicle-mounted natural gas compressor unit of this utility model;

[0028] Figure 2 This is a top view of the vehicle-mounted natural gas compressor unit of this utility model;

[0029] Figure 3 This is a schematic diagram of the working principle of the vehicle-mounted natural gas compressor unit of this utility model;

[0030] In the diagram: 1. Compressor; 2. Motor; 3. Primary oil separator; 4. Secondary oil separator; 5. Tertiary oil separator; 6. Air-cooled condenser; 7. Air-cooled oil cooler; 8. Oil pump; 9. Outlet gas-liquid separator; 10. Inlet gas-liquid separator; 11. Control cabinet; 12. Common base. Detailed Implementation

[0031] The following examples illustrate the implementation of this utility model in detail, but they do not constitute a limitation on this utility model and are merely illustrative. Furthermore, explaining the advantages of this utility model will make it clearer and easier to understand.

[0032] This utility model discloses a vehicle-mounted screw-type natural gas compressor unit, comprising a compressor 1, a motor 2, a primary oil separator 3, a secondary oil separator 4, a tertiary oil separator 5, an air-cooled condenser 6, an air-cooled oil cooler 7, an oil pump 8, an outlet gas-liquid separator 9 and an inlet gas-liquid separator 10, a control cabinet 11, and a common base 12. The gas outlet of the inlet gas-liquid separator 10 is connected to the inlet of the compressor 1. The outlet of the compressor 1 is connected to the inlet of the air-cooled condenser 6 in sequence through the primary oil separator 3, the secondary oil separator 4, and the tertiary oil separator 5. The outlet of the air-cooled condenser 6 is connected to the inlet of the outlet gas-liquid separator 9. The motor 2 is driven by the compressor 1 to drive the compressor 1. The oil outlets of the primary oil separator 3, the secondary oil separator 4, and the tertiary oil separator 5 are all connected to the inlet of the oil pump 8. The outlet of the oil pump 8 is connected to the inlet of the air-cooled oil cooler 7. The outlet of the air-cooled oil cooler 7 is connected to the compressor 1. Compressor 1, motor 2, primary oil separator 3, secondary oil separator 4, tertiary oil separator 5, air-cooled condenser 6, air-cooled oil cooler 7, oil pump 8, outlet gas-liquid separator 9, and inlet gas-liquid separator 10 are all mounted on a common base 12. The common base is securely locked to the vehicle chassis by a locking mechanism.

[0033] In the above technical solution, an inverted U-shaped elbow is provided at the inlet of the air-cooled oil cooler 7 to form an oil seal. The fan of the air-cooled condenser 6 is detachably installed below the air-cooled condenser 6. Both the air-cooled condenser 6 and the air-cooled oil cooler 7 are arranged above the unit, with space reserved below them for air circulation.

[0034] In the above technical solution, the bottom of the first-stage oil separator 3, the second-stage oil separator 4 and the third-stage oil separator 5 are all provided with oil collection outlets. The oil collection outlets are connected to the inlet of the oil pump 8 through pipelines. The outlet of the oil pump 8 is connected to the inlet of the air-cooled oil cooler 7 through pipelines. The outlet of the air-cooled oil cooler 7 is connected back to the compressor 1 through pipelines.

[0035] In the above technical solution, the first-stage oil separator 3 is equipped with a vortex separation component, a grid separation component, and a filter element separation component; the second-stage oil separator 4 and the third-stage oil separator 5 are both equipped with grids and filter elements, which are used to separate the lubricating oil in the compressed gas step by step.

[0036] In the above technical solution, the inlet of the inlet gas-liquid separator 10 is located in the middle and the outlet is located at the top, so that the natural gas entering the inlet gas-liquid separator 10 is discharged from the top into the compressor 1 after being separated by gravity from bottom to top; the inlet of the outlet gas-liquid separator 9 is located in the middle and the outlet of the outlet gas-liquid separator 9 is located at the top.

[0037] In the overall process, natural gas enters the inlet gas-liquid separator 10, and then is compressed by the compressor 1 to form a high-temperature and high-pressure gas. Most of the lubricating oil is separated by the first-stage oil separator 3, and the remaining lubricating oil is separated by the second-stage oil separator 4 and the third-stage oil separator 5. The oil is pressurized by the oil pump 8 and then enters the air-cooled oil cooler 7 to lower the oil temperature before returning to the compressor 1. After being separated in the third-stage oil separator 5, the natural gas enters the air-cooled condenser 6 for cooling. After being cooled to the specified temperature, it enters the outlet gas-liquid separator 9 to separate the condensed liquid, and then goes to the user's storage tank.

[0038] In this embodiment, a suitable vehicle is first required as the carrier. Since the mixed refrigerant requires a cold box in the later stages of the process, the oil content of the mixed refrigerant is typically required to be below 0.1 ppm. Without using an oil-free compressor, a four-stage oil separator is usually needed. Furthermore, to meet most operating conditions, the compressor head needs to be selected as large as possible, meaning the unit's length typically needs to be around ten to twelve meters. On another front, to meet road safety requirements, the overall width of the vehicle needs to be around three to four meters, thus determining the overall width of the unit to be approximately 12 meters × 4 meters × 3.4 meters.

[0039] Based on this, the following components need to be arranged: compressor, motor, control cabinet, primary oil separator, secondary oil separator, tertiary oil separator, oil cooler, oil pump, condenser, and gas-liquid separator. These devices are placed on a common base for transporting the entire unit. Due to the uncertainties of the project site, water-cooled and evaporative types are typically not used for the condenser and oil cooler; air-cooled types are more common. Therefore, the number of devices arranged below the air duct should be minimized. Furthermore, since air-cooled systems have a smaller oil storage capacity and are generally higher than the equipment's oil level, an inverted U-shaped bend needs to be installed at the air-cooling inlet to seal the oil inside the oil cooler, ensuring that oil does not flow back to the lower oil level (e.g., the primary oil separator) after shutdown, thus preventing the compressor head from being without oil for an extended period during startup. The common base needs to be designed with a structure that can be securely locked by the vehicle base, for example, with extended locking latches, to ensure the stability of the unit during transport. The vehicle head itself can be detached from the transport section, allowing operation in all four directions and increasing the unit's operability. The air-cooled fan can be detached and placed below the air-cooling unit, which reduces the transport height and transportation costs during transportation. It can then be reinstalled when in use.

[0040] Natural gas enters from the middle of the inlet gas-liquid separator 10. After undergoing gravity separation from bottom to top, it exits the gas-liquid separator from the top and enters the compressor 1. Powered by the motor 2, the compressor compresses the natural gas into a high-temperature, high-pressure gas, which then enters the first-stage oil separator 3 from the bottom. Inside, it undergoes three steps of separation: vortex separation, grid separation, and filter element separation, before entering the bottom of the second-stage oil separator 4 from the top. After grid separation and filter element separation in the second-stage oil separator, it enters the bottom of the third-stage oil separator 5 from the top. After grid separation and filter element separation in the third-stage oil separator, it enters the air-cooled condenser 6 from the top. The air-cooled condenser is generally placed in a space at the bottom where air flows out. After condensation in the air-cooled condenser, the gas enters the outlet gas-liquid separator 9 from the middle. After gravity separation from bottom to top in the gas-liquid separator, the gas exits from the top and is connected to the user's storage tank. On the other hand, the oil filtered from the bottom of the first-stage oil separator 3, second-stage oil separator 4, and third-stage oil separator 5 is pressurized by the oil pump 8 and enters the air-cooled oil cooler at the top. After condensation, the oil is pressurized back to the compressor.

[0041] This utility model places the entire unit on a flatbed truck, making transportation and lifting much more convenient than other fixed units. Due to fewer lifting operations, the unit can be made longer without deformation. The common base is connected to the truck bed via a locking mechanism, ensuring the stability of the compressor unit during transport. The truck head can be separated from the truck bed, providing four operating and maintenance surfaces for the compressor unit. The compressor unit needs to be selected as large as possible within the vehicle's dimensions (12m × 4m × 3.4m) to meet the needs of various operating conditions. Air-cooled oil coolers and condensers are used to accommodate diverse user requirements. The oil coolers and condensers must be positioned high, with the bottom left unobstructed to ensure unobstructed airflow. Considering shutdown requirements, the inlet and outlet of the air-cooled oil cooler must be designed with an inverted U-shape to minimize oil backflow into the oil separator during shutdown.

[0042] Due to the unit's mobility, users do not need to prefabricate the factory on-site; the factory can be redesigned after the operating conditions stabilize. This unit can meet the urgent needs of most regions in China. This utility model's unit is mobile and flexible compared to conventional hybrid refrigeration and compressor units. It can achieve high production capacity and quick returns in the early stages of a project. Furthermore, its adaptable location allows for reuse in multiple projects, reducing user operating costs to some extent.

[0043] The above are merely specific embodiments of this utility model. It should be noted that any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this utility model should be included within the protection scope of this utility model. Any other aspects not described in detail are prior art.

Claims

1. A vehicle-mounted screw-type natural gas compressor unit, characterized in that: It includes a compressor (1), a motor (2), a primary oil separator (3), a secondary oil separator (4), a tertiary oil separator (5), an air-cooled condenser (6), an air-cooled oil cooler (7), an oil pump (8), an outlet gas-liquid separator (9), and an inlet gas-liquid separator (10). The gas outlet of the inlet gas-liquid separator (10) is connected to the inlet of the compressor (1); the outlet of the compressor (1) is connected to the inlet of the air-cooled condenser (6) in sequence through the first-stage oil separator (3), the second-stage oil separator (4) and the third-stage oil separator (5); the outlet of the air-cooled condenser (6) is connected to the inlet of the outlet gas-liquid separator (9); the motor (2) is connected to the compressor (1) to drive the compressor (1) to operate; The oil outlets of the primary oil separator (3), the secondary oil separator (4) and the tertiary oil separator (5) are all connected to the inlet of the oil pump (8), the outlet of the oil pump (8) is connected to the inlet of the air-cooled oil cooler (7), and the outlet of the air-cooled oil cooler (7) is connected to the compressor (1).

2. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, characterized in that: The compressor (1), motor (2), primary oil separator (3), secondary oil separator (4), tertiary oil separator (5), air-cooled condenser (6), air-cooled oil cooler (7), oil pump (8), outlet gas-liquid separator (9) and inlet gas-liquid separator (10) are all mounted on a common base (12).

3. The vehicle-mounted screw-type natural gas compressor unit according to claim 2, characterized in that: The common base (12) is securely locked to the vehicle chassis by a locking structure.

4. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The air-cooled oil cooler (7) is provided with an inverted U-shaped elbow to form an oil seal at the inlet.

5. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The fan of the air-cooled condenser (6) is detachably mounted below the air-cooled condenser (6).

6. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The bottom of the first-stage oil separator (3), the second-stage oil separator (4) and the third-stage oil separator (5) are all provided with oil collection outlets. The oil collection outlets are connected to the inlet of the oil pump (8) through pipelines. The outlet of the oil pump (8) is connected to the inlet of the air-cooled oil cooler (7) through pipelines. The outlet of the air-cooled oil cooler (7) is connected back to the compressor (1) through pipelines.

7. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The first-stage oil separator (3) is equipped with a vortex separation component, a grid separation component and a filter element separation component; the second-stage oil separator (4) and the third-stage oil separator (5) are both equipped with a grid and a filter element.

8. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The inlet of the inlet gas-liquid separator (10) is located in the middle and the outlet is located at the top, so that the natural gas entering the inlet gas-liquid separator (10) is discharged from the top into the compressor (1) after being separated by gravity from bottom to top; the inlet of the outlet gas-liquid separator (9) is located in the middle and the outlet of the outlet gas-liquid separator (9) is located at the top.

9. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: The air-cooled condenser (6) and the air-cooled oil cooler (7) are both located above the unit, with space reserved below them for air circulation.

10. The vehicle-mounted screw-type natural gas compressor unit according to claim 1, 2, or 3, characterized in that: It also includes a control cabinet (11) for controlling the operation of the various components of the compressor unit.

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