Low-temperature oil gas recovery refrigerating unit

Abstract

The invention discloses a low-temperature oil gas recovery refrigerating unit, which belongs to the technical field of oil gas recovery and comprises a precooling compressor, a cryogenic compressor, a condenser, an oil separator, a gas-liquid separator, a heat regenerator, an expansion tank, a drying filter, an electromagnetic valve, a sensor and a controller. The precooling system and the cryogenic system share a condenser, and the cryogenic system forms an auto-cascade refrigeration cycle through multi-stage separation and heat regeneration. The controller is connected with the compressor, the electromagnetic valve and the sensor through wires. By arranging the expansion tank and the matched electromagnetic valve branch, the expansion tank is automatically adjusted to be on and off according to the exhaust pressure in the initial starting stage, high-pressure gas storage and low-pressure gas supply are achieved, and high-pressure impact caused by starting of the compressor is effectively avoided; meanwhile, a temperature sensor is used for monitoring the cryogenic temperature, an oil gas inlet valve is controlled in an interlocking mode, and oil gas is introduced after the set low temperature is reached. The problems of unstable system starting and initial oil gas escape are solved, and therefore the safe reliability and the oil gas recovery efficiency of a unit are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil and gas recovery, in particular to a low-temperature oil and gas recovery refrigeration unit. BACKGROUND

[0002] In the process of petroleum chemical industry, pharmaceutical manufacturing and oil storage and transportation, a large amount of volatile organic oil gas will be produced. This not only causes waste of resources, but also causes serious pollution to the atmospheric environment, and even exists a safety hazard. Therefore, efficient oil and gas recovery technology has become an inevitable requirement for the development of the industry.

[0003] In the current oil and gas recovery process, the condensation method is widely used due to its simple process flow, high purity of recovered components, good safety and other advantages. In particular, based on the self-lifting refrigeration cycle of non-azeotropic mixed working medium, a single compressor can realize a deep cooling temperature of-80°C or even lower, which is the core technology to realize deep condensation recovery of oil gas.

[0004] However, the existing self-lifting low-temperature oil and gas recovery unit still has the following significant technical pain points in actual operation:

[0005] The exhaust pressure is too high at the initial start-up, causing unstable system operation: The self-lifting refrigeration system uses a non-azeotropic mixed working medium composed of high, medium and low boiling point components. In the long-term shutdown or static state of the system, the low boiling point components (such as R14, R23, etc.) in the mixed working medium completely fill the pipeline in gaseous form. When the system is restarted, since the high boiling point components have not completely liquefied to form an effective condensation and throttling cycle, the compressor sucks in a large amount of low boiling point gas, causing the compressor exhaust pressure to rise sharply. This "high pressure at start-up" phenomenon often triggers the high pressure protection switch of the compressor, causing shutdown, and even damaging the compressor valve, which seriously limits the reliability and start-up success rate of the equipment.

[0006] The coupling degree of the pre-cooling and deep cooling systems is low, and there is a lack of air inlet protection logic: The traditional oil and gas recovery device usually designs the pre-cooling section (used to remove water and heavy component oil) and the deep cooling section (used to condense light components) independently, and often equips them with independent condensers and heat dissipation systems, resulting in large equipment size, complex pipeline and high manufacturing cost. In addition, the existing control logic is relatively simple, and oil gas is often introduced into the system as soon as it is started, or only controlled by time. If oil gas is introduced into the system before the deep cooling space reaches the designed low temperature, the light components in the oil gas cannot be effectively condensed and will directly penetrate the system and be discharged, causing substandard recovery.

[0007] Therefore, based on the above problems, we propose a low-temperature oil and gas recovery refrigeration unit that can automatically adjust the start-up pressure, has a compact structure and intelligent air inlet control logic. SUMMARY

[0008] The technical problem solved by the present application is to provide a low-temperature oil gas recovery refrigeration unit, which is provided with an expansion buffer tank, so that the suction amount of the compressor can be controlled according to the exhaust pressure in the initial start-up period, thereby avoiding the phenomenon of high start-up pressure; and the unit is provided with an automatic defrosting system, which periodically defrosts to improve the operation efficiency of the system, thereby meeting the needs of users for long-term stable operation of the equipment and high-precision oil gas recovery.

[0009] To solve the above technical problems, the present application adopts the following technical scheme: wherein the precooling system comprises a precooling compressor (1-1), a condenser (2), a capillary tube (8-1), a dry filter (5-1), a precooling heat exchanger (12), a liquid storage tank (7), and a precooling space (14); the deep cooling system comprises a deep cooling compressor (1-2), a condenser (2), an oil separator (3), gas-liquid separators (4-1, 4-2), dry filters (5-2, 5-3, 5-4), heat recovery devices (6-1, 6-2, 6-3), capillary tubes (8-2, 8-3, 8-4), one-way valves (9-1, 9-2), an expansion tank (10), first, second, third, fourth, fifth, and sixth electromagnetic valves (11-1, 11-2, 11-3, 11-4, 11-5, 11-6), a deep cooling heat exchanger (13), a pressure sensor (16), and a temperature sensor (17); the exhaust outlets of the precooling compressor (1-1) and the deep cooling compressor (1-2) are connected to the input end of the condenser (2); the deep cooling compressor (1-2), the oil separator (3), the condenser (2), the heat recovery device (6-1), the gas-liquid separator (4-1), the heat recovery device (6-2), the gas-liquid separator (4-2), the heat recovery device (6-3), the dry filter (5-4), the capillary tube (8-4), and the deep cooling heat exchanger (13) are sequentially connected to form a self-lifting refrigeration cycle; the precooling compressor (1-1), the condenser (2), the liquid storage tank (7), the dry filter (5-1), the capillary tube (8-1), and the precooling heat exchanger (12) are sequentially connected; the first electromagnetic valve (11-1) is located between the deep cooling compressor (1-2) and the expansion tank (10); the second electromagnetic valve (11-2) is connected in parallel with the one-way valve (9-1) and is located between the expansion tank (10) and the condenser (2); the fourth electromagnetic valve (11-4) is arranged between the oil tank (19) and the precooling space (14); the fifth electromagnetic valve (11-5) is arranged between the deep cooling space (15) and the oil tank (19); and one end of the sixth electromagnetic valve (11-6) is connected to the deep cooling space (15), and the other end is connected to the atmosphere.

[0010] Compared with the prior art, the present application has the following beneficial effects:

[0011] This invention introduces a pressure regulating branch consisting of an expansion tank and a solenoid valve, which effectively solves the problem of high pressure impact during the startup of a non-azeotropic working fluid system. Through the strategy of "high pressure gas storage and low pressure gas replenishment", it ensures that the compressor operates within a safe range.

[0012] This invention employs a temperature-interlocked air intake mechanism, which eliminates the oil and gas escape phenomenon caused by insufficient temperature in the early stage of start-up, and significantly improves the oil and gas recovery rate and emission compliance rate.

[0013] This invention simplifies the system structure, reduces the equipment footprint, and lowers manufacturing costs by sharing a condenser between the precooling and cryogenic systems. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of a low-temperature oil and gas recovery refrigeration unit.

[0015] Figure 2 This is a logic flowchart of the expansion tank pressure stabilization control and air intake interlock control;

[0016] Figure 3 This is a flowchart of the start-stop control logic for oil and gas pipelines;

[0017] In the diagram: 1-1, Precooling compressor; 1-2, Cryogenic compressor; 2, Condenser; 3, Oil separator; 4-1, 4-2, Gas-liquid separator; 5-1, 5-2, 5-3, 5-4, Dryer filter; 6-1, 6-2, 6-3, Regenerator; 7, Liquid receiver; 8-1, 8-2, 8-3, 8-4, Capillary tube; 9-1, 9-2, Check valve; 10, Expansion tank; 11-1, 11-2, 11-3, 11-4, 11-5, 11-6, Solenoid valve; 12, Precooling heat exchanger; 13, Cryogenic heat exchanger; 14, Precooling space; 15, Cryogenic space; 16, Pressure sensor; 17, Temperature sensor; 18, Controller; 19, Oil tank. Detailed Implementation

[0018] The principles and system of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are descriptive and not limiting, and are not intended to limit the scope of protection of the present invention.

[0019] A low-temperature oil and gas recovery refrigeration unit is characterized by comprising a precooling compressor (1-1), a cryogenic compressor (1-2), a condenser (2), an expansion tank (10), and various heat exchange and separation components.

[0020] In the precooling cycle, the high-temperature refrigerant output by the precooling compressor (1-1) enters the condenser (2) for condensation. The condensed liquid refrigerant enters the storage tank (7), and after being throttled by the dryer filter (5-1) and capillary tube (8-1), it enters the precooling heat exchanger (12) for evaporative cooling, thereby reducing the temperature of the precooling space (14) and precooling the oil and gas.

[0021] In the cryogenic cycle, the working fluid output from the cryogenic compressor (1-2) passes through the oil separator (3) and condenser (2) before entering the liquid storage tank (7). The mixed working fluid enters the first-stage regenerator (6-1), and the liquid working fluid is throttled through the dryer filter (5-2) and capillary tube (8-2). This process involves multi-stage separation (4-1, 4-2) and the regenerator (6-2). Finally, the low-temperature working fluid passes through the dryer filter (5-4), capillary tube (8-4), and one-way valve (9-2) before entering the cryogenic heat exchanger (13) for evaporation.

[0022] As an example, the system includes three core control modes:

[0023] Regulated start-up mode:

[0024] When the system is shut down and stationary, the expansion tank (10) is filled with gaseous working fluid, and the first solenoid valve (11-1) is in the normally open state, connecting the expansion tank (10) to the low-pressure side of the system to balance the system pressure. When the unit starts, the controller collects the discharge pressure data of the cryogenic compressor (1-2) fed back by the pressure sensor (16) in real time. If the discharge pressure is detected to be higher than the set upper limit of the safety value, the controller immediately controls the first solenoid valve (11-1) to close. At this time, the expansion tank (10) is isolated, cutting off the supply of gas to the low-pressure side, thereby reducing the suction density and discharge pressure of the compressor and preventing the compressor from tripping due to high pressure or damaging the valve plate. When the discharge pressure drops and is lower than the set lower limit of the safety value, the controller controls the first solenoid valve (11-1) to reopen. At this time, the working fluid in the expansion tank (10) participates in the circulation again to maintain the required refrigeration flow and cryogenic capacity of the system. Through the above dynamic adjustment of "high-pressure isolation and gas storage, low-pressure release and gas replenishment", the compressor can achieve a smooth soft start.

[0025] Frost mode:

[0026] The controller has a built-in timing logic that automatically accumulates the effective operating time of the cryogenic compressor (1-2). When the accumulated time exceeds the set defrosting cycle threshold, the system determines that defrosting is required and automatically enters the defrosting program; the controller outputs a signal to open the third solenoid valve (11-3). At this time, high-temperature and high-pressure gaseous refrigerant is bypassed and injected into the cryogenic heat exchanger (13) to melt the attached frost layer using hot gas; during the defrosting process, the temperature sensor (17) continuously monitors the temperature of the cryogenic space. When the monitored temperature reaches 5°C, the controller closes the third solenoid valve (11-3), stops the hot gas bypass, and the unit automatically returns to normal cooling mode.

[0027] Intake air temperature interlock control mode:

[0028] When the unit is first started or during the cooling process, if the cryogenic temperature detected by the temperature sensor (17) is higher than the set low temperature upper limit, the controller will forcibly lock the fourth solenoid valve (11-4) and the fifth solenoid valve (11-5) in the closed state. At this time, the oil and gas are in the oil tank to prevent the direct discharge of uncondensed oil and gas; only when the temperature detected by the temperature sensor (17) reaches or falls below the set low temperature lower limit will the controller issue an instruction to open the fourth solenoid valve (11-4) and the fifth solenoid valve (11-5) at the same time. At this time, the oil and gas mixture from the oil tank (19) enters the precooling space (14) for preliminary condensation under the action of pressure difference, and then enters the cryogenic space (15) for deep condensation to ensure that the oil and gas components are fully liquefied and recovered.

[0029] This invention effectively solves the problem of difficult start-up of self-cascade units and ensures high efficiency and safety of oil and gas recovery. It is suitable for gas stations, chemical plants and other occasions with high requirements for environmental protection and equipment stability.

[0030] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A sub-cooled oil and gas recovery chiller unit characterized by: The application relates to a refrigeration system, which comprises a precooling system and a deep cooling system, wherein the precooling system comprises a precooling compressor (1-1), a condenser (2), a capillary tube (8-1), a dry filter (5-1), a precooling heat exchanger (12), a liquid storage tank (7) and a precooling space (14); the deep cooling system comprises a deep cooling compressor (1-2), the condenser (2), an oil separator (3), gas-liquid separators (4-1 and 4-2), dry filters (5-2, 5-3 and 5-4), heat regenerators (6-1, 6-2 and 6-3), capillary tubes (8-2, 8-3 and 8-4), one-way valves (9-1 and 9-2), an expansion tank (10), first, second, third and fourth electromagnetic valves (11-1, 11-2, 11-3 and 11-4), a fifth electromagnetic valve (11-5), a sixth electromagnetic valve (11-6), a deep cooling heat exchanger (13), a pressure sensor (16) and a temperature sensor (17); the exhaust outlets of the precooling compressor (1-1) and the deep cooling compressor (1-2) are connected with the input end of the condenser (2); the deep cooling compressor (1-2), the oil separator (3), the condenser (2), the heat regenerator (6-1), the gas-liquid separator (4-1), the heat regenerator (6-2), the gas-liquid separator (4-2), the heat regenerator (6-3), the dry filter (5-4), the capillary tube (8-4) and the deep cooling heat exchanger (13) are sequentially connected to form a self-recovery refrigeration cycle; the precooling compressor (1-1), the condenser (2), the liquid storage tank (7), the dry filter (5-1), the capillary tube (8-1) and the precooling heat exchanger (12) are sequentially connected; the first electromagnetic valve (11-1) is located between the deep cooling compressor (1-2) and the expansion tank (10); the second electromagnetic valve (11-2) is connected in parallel with the one-way valve (9-1) and is located between the expansion tank (10) and the condenser (2); the fourth electromagnetic valve (11-4) is arranged between an oil tank (19) and the precooling space (14); the fifth electromagnetic valve (11-5) is arranged between a deep cooling space (15) and the oil tank (19); one end of the sixth electromagnetic valve (11-6) is connected with the deep cooling space (15) and the other end is communicated with the atmosphere.

2. The low-temperature oil and gas recovery chiller unit according to claim 1, characterized in that: The first electromagnetic valve (11-1) is always open; the refrigeration unit has a safe starting mode: when the pressure sensor (16) monitors that the exhaust pressure of the deep cooling compressor (1-2) is higher than the upper limit of the set safety value, the first electromagnetic valve (11-1) is closed; when the exhaust pressure is lower than the lower limit of the set safety value, the first electromagnetic valve (11-1) is opened.

3. The low-temperature oil and gas recovery chiller unit according to claim 1, characterized in that: When the temperature sensor (17) monitors that the temperature is higher than the upper limit of the set low temperature, the fourth electromagnetic valve (11-4) and the fifth electromagnetic valve (11-5) remain in the closed state; when the temperature sensor (17) monitors that the temperature reaches or is lower than the lower limit of the set low temperature, the fourth electromagnetic valve (11-4) and the fifth electromagnetic valve (11-5) are opened, and the oil gas enters the precooling space (14) and the deep cooling space (15) in sequence.

4. The low-temperature oil and gas recovery chiller unit of claim 1, wherein: The refrigerating unit has an automatic defrosting mode: the controller (15) accumulates the operation time of the cryogenic compressor (1-2), when the operation time of the cryogenic compressor (1-2) is higher than a set value, the third electromagnetic valve (11-3) is opened to start defrosting; when the temperature measured by the temperature sensor (17) reaches 5-10 DEG C, the third electromagnetic valve (11-3) is closed to stop defrosting.

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