A compressor capable of pressurizing and injecting dense phase carbon dioxide

Abstract

A compressor capable of pressurizing and injecting dense-phase carbon dioxide belongs to the field of carbon capture, utilization, and storage. Dense-phase carbon dioxide is input into a compressor skid through a pipeline. A first shut-off valve is provided on the inlet pipeline of the compressor skid, which is sequentially connected to a second control valve, an emergency shut-off valve SDV1 and a small flow regulating valve PV1 connected in parallel, a heater, an air intake separator, an air intake buffer tank, a compressor, an exhaust buffer tank, a temperature control valve TV2, an air cooler, an exhaust separator, a back-pressure valve PV3, and an emergency shut-off valve SDV2. The gas is finally fed to a gas injection system. The pipe-side inlet and outlet of the heat exchanger are connected to the left and right ends of the second control valve via a pipeline, and the shell-side inlet and outlet of the heat exchanger are connected to the left and right ends of the temperature control valve TV2 via a pipeline. The inlet pipeline is provided with a temperature control valve TV1, and the left end of the air cooler is connected to the right end of the heater via a bypass valve BPV and a reflux regulating valve PV2 connected in parallel. The present invention reduces project engineering costs and energy consumption, and improves the economic benefits of CCUS-EOR projects.

Description

Technical Field

[0001] This invention belongs to the field of carbon capture, utilization, and storage technology, specifically to a compressor capable of pressurizing dense-phase carbon dioxide for injection. This technology is applicable to the field of pressurized injection of carbon dioxide into underground oil recovery after long-distance supercritical CO2 pipeline transportation. This process utilizes a compressor to increase the pressure of CO2 transported via supercritical CO2 pipelines even after it enters the dense phase. Background Art

[0002] CCUS (Carbon Capture, Utilization and Storage) is a carbon capture, utilization and storage technology. CCUS technology can store carbon dioxide emitted during the production process, or purify it and put it into a new production process for recycling. Among them, carbon dioxide recovery and storage (CCUS-EOR) has become the main carbon utilization and storage method at present. It can improve the crude oil recovery rate while storing carbon dioxide. The additional crude oil produced makes carbon sequestration have better economic benefits. It is the only large-scale utilization and storage technology that can achieve near-zero carbon dioxide emissions from fossil energy output at this stage.

[0003] After carbon dioxide is captured at the carbon source, it is often far from the injection site. Pipeline transportation, due to its high transport capacity and long distances, is the most economical method for carbon transportation. Pipeline transportation of carbon dioxide includes gaseous, liquid, and supercritical phases. Supercritical phase transportation is generally used for high-volume, long-distance pipelines. High-pressure carbon dioxide injection methods include liquid, supercritical, and dense phase injection. When carbon dioxide is transported to the injection point via a supercritical pipeline and then injected supercritically, the following problems arise: Due to its low critical temperature during long-distance pipeline transportation, the supercritical phase of carbon dioxide gradually transforms into a dense phase as the temperature decreases. At the end of the pipeline, to avoid significant changes in physical properties due to phase differences that could affect the normal operation of the compressor, the carbon dioxide is generally required to be transported away from the supercritical point before entering the supercritical compressor. This requires the dense phase carbon dioxide to be reheated to a supercritical state before it can be pressurized by the compressor. To address these issues, a solution is typically to use high-power electric heaters or furnaces to heat the dense phase carbon dioxide to bring it to a supercritical state. However, this method suffers from high energy consumption and excessive operating costs. Summary of the Invention

[0004] In order to solve the above-mentioned problems, the present invention proposes: a compressor that can pressurize and inject dense-phase carbon dioxide, the dense-phase carbon dioxide is input into the compressor skid group through a pipeline, and a first shut-off valve is arranged on the inlet pipeline of the compressor skid group, which is connected in sequence to the second control valve, the emergency shut-off valve SDV1 and the small flow regulating valve PV1 connected in parallel, the heater, the air intake separator, the air intake buffer tank, the compressor, the exhaust buffer tank, the temperature control valve TV2, the air cooler, the exhaust separator, the back pressure valve PV3 and the emergency shut-off valve SDV2, and finally transported to the gas injection system, the pipe-side inlet and outlet of the heat exchanger are connected to the left and right ends of the second control valve through a pipeline, and the shell-side inlet and outlet of the heat exchanger are connected to the left and right ends of the temperature control valve TV2 through a pipeline, the temperature control valve TV1 is arranged on the inlet pipeline, and the left end of the air cooler is connected to the right end of the heater through the bypass valve BPV and the reflux regulating valve PV2 connected in parallel.

[0005] Furthermore, the compressor inlet stream and outlet stream enter the tube side and shell side of the heat exchanger respectively, and the compressor outlet hot stream first enters the heat exchanger to heat the inlet cold stream before going to the air cooler.

[0006] Furthermore, the compressor inlet flow is 8MPa, 20℃, and the outlet pressure is 20MPa. When the compressor is compressed in the first stage, the outlet temperature is about 115℃. After setting the inlet and outlet heat exchangers, the inlet flow temperature can be increased to 40℃ to ensure that the compressor inlet temperature requirements are met.

[0007] Furthermore, when the compressor adopts multi-stage compression, it enters the next stage of compression without inter-stage cooling to ensure the temperature of the medium at the outlet of the last stage. If the temperature of the medium entering the next stage exceeds the maximum temperature allowed by the specification, it can enter the cooler to be cooled to the maximum temperature allowed before entering the next stage.

[0008] Furthermore, when the compressor outlet pressure is low and the compression heat is insufficient to heat the inlet stream temperature to above 40°C, a heater or heating furnace is set after the heat exchanger as a supplement.

[0009] Furthermore, a compressor startup low-flow heater is provided in the compressor skid assembly for heating the inlet flow stream when the compressor is started. The heater is only used when the compressor is started and can be deactivated after the compressor is operating normally.

[0010] Furthermore, the low-temperature startup process of the supercritical compressor is as follows:

[0011] ① Compressor reflux status: compressor reflux regulating valve PV2 is fully open, bypass valve BPV is open, temperature control valve TV1 is open, and other control valves are closed;

[0012] ② Low-flow heating intake warm-up: Open the first shut-off valve, second control valve, low-flow electric heater and low-flow regulating valve PV1 at the inlet to heat the inlet stream to 80°C, charge the compressor system to 0.3-0.4 MPaG, close PV1, and warm up the compressor unit and inlet and outlet heat exchangers;

[0013] ③Start the machine at the minimum flow rate to increase the system temperature: Start the main motor, and the speed reaches the minimum allowable speed when the compressor is under low load. Gradually open PV1 and slowly inject air into the system. At the same time, close the bypass return valve BPV, gradually reduce the return regulating valve PV2, slowly increase the compressor outlet pressure, monitor the fluid temperature in the system, and when it rises to 45°C, gradually reduce the heater power to keep the temperature at the front end of the compressor in the system at 45-50°C. When the pressure in the compressor unit system rises to 8MPaG, open SDV1, and close PV1 and the second control valve at the inlet.

[0014] Furthermore, the following is further included: ④ A back pressure valve PV3 is provided at the compressor outlet. When the compressor downstream pressure does not reach the set gas injection pressure, or the compressor outlet pressure does not reach the pressure to ensure sufficient compression heat in a short period of time, the minimum back pressure of the compressor is set to ensure compression heat: SDV2 is opened, the back pressure valve is set to the minimum outlet pressure to ensure that the inlet stream can be heated to 40°C, and the reflux regulating valve PV2 is gradually reduced to fully closed. When the pressure in front of the back pressure valve rises to the set pressure, the heater is completely turned off;

[0015] ⑤ When the pressure behind the monitored back pressure valve PV3 reaches the set pressure, fully open the back pressure valve PV3 and adjust the main motor speed to increase it to the full load operating speed of the compressor.

[0016] The beneficial effects of the present invention are:

[0017] (1) As the injection pressure of CCUS-EOR projects in various oil fields is generally high, and the compression process of the gas injection compressor generates a large amount of compression heat, the compression heat of the gas injection compressor is fully utilized to save the energy consumption of heating the dense phase carbon dioxide to a supercritical state through an electric heater or a heating furnace and then sending it to the compressor for pressurization;

[0018] (2) The inlet and outlet streams of the gas injection compressor are the same stream, the heat exchange process is simple, and under a constant gas injection pressure, the compression heat required for heat exchange is stable and guaranteed;

[0019] (3) Using the compression heat of the gas injection compressor to heat the inlet stream can also greatly reduce the load of the compressor outlet cooler and save cooler energy consumption;

[0020] (4) Currently, carbon dioxide high-pressure injection compressors do not allow dense-phase carbon dioxide to directly enter the compressor for pressurization. It must be heated to a supercritical state in advance before entering the compressor. After adopting the present invention, it can be achieved under specific working conditions that dense-phase carbon dioxide directly enters the compressor skid for pressurization and injection.

[0021] (5) The present invention can save the investment in electric heaters or heating furnaces required to directly heat dense phase carbon dioxide to a supercritical state, thereby reducing project engineering costs. At the same time, the energy savings can significantly reduce the annual operating costs of the project and improve the economic benefits of the CCUS-EOR project. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The figure is a schematic diagram of the compressor flow for pressurizing and injecting dense phase carbon dioxide according to the present invention. DETAILED DESCRIPTION

[0023] In order to make the technical means and objectives of the present invention easier to understand, the present invention is further described below in conjunction with specific embodiments. A compressor capable of pressurizing and injecting dense phase carbon dioxide is described. Figure 1 As shown, dense-phase carbon dioxide is input into the compressor skid through a pipeline. A first shut-off valve is provided on the inlet pipeline of the compressor skid, which is sequentially connected to the second control valve, the emergency shut-off valve SDV1 and the small flow regulating valve PV1 connected in parallel, the heater, the air intake separator, the air intake buffer tank, the compressor, the exhaust buffer tank, the temperature control valve TV2, the air cooler, the exhaust separator, the back pressure valve PV3 and the emergency shut-off valve SDV2, and finally transported to the gas injection system. The pipe-side inlet and outlet of the heat exchanger are connected to the left and right ends of the second control valve through a pipeline, and the shell-side inlet and outlet of the heat exchanger are connected to the left and right ends of the temperature control valve TV2 through a pipeline (the temperature control valve TV1 is provided on the inlet pipeline). The left end of the air cooler is connected to the right end of the heater through the bypass valve BPV and the reflux regulating valve PV2 connected in parallel.

[0024] (1) A shell and tube heat exchanger is installed in the compressor skid. The inlet and outlet streams of the compressor enter the tube side and shell side of the heat exchanger respectively. The hot stream at the outlet of the compressor enters the heat exchanger to heat the inlet cold stream before going to the air cooler. Generally, the pressure of carbon dioxide in a supercritical state piped to the terminal gas injection station is greater than the supercritical pressure (generally ≥8MPa), and the temperature drops to about 20℃. According to the statistics of gas injection pressure in carbon dioxide flooding blocks currently carried out in China, the general wellhead reinjection pressure is about 20MPa. Therefore, a large amount of compression heat is generated during the compressor compression process. Taking the inlet stream of 8MPa, 20℃, and outlet pressure of 20MPa as an example, the outlet temperature of the compressor during the first stage of compression is about 115℃. After installing the inlet and outlet heat exchangers, the inlet stream temperature can be increased to 40℃ to ensure that the compressor inlet temperature requirement is met.

[0025] (2) If the compressor adopts multi-stage compression, it should enter the next stage of compression without inter-stage cooling to ensure the temperature of the medium at the outlet of the last stage. If the temperature of the medium entering the next stage exceeds the maximum temperature allowed by the specification or the manufacturer, it can enter the cooler to cool to the maximum temperature allowed before entering the next stage.

[0026] (3) If the compressor outlet pressure is low and the compression heat is insufficient to heat the inlet stream temperature to above 40°C, an electric heater or heating furnace can be installed after the heat exchanger as a supplement.

[0027] (4) A compressor startup low-flow electric heater is installed in the compressor skid to heat the inlet stream when the compressor is started. This electric heater is only used when the compressor is started and can be deactivated after the compressor is operating normally. The power calculation of this electric heater is based on the ability to heat the stream to 80°C at the minimum flow rate allowed when the compressor is started.

[0028] The low-temperature startup process of a supercritical compressor is as follows:

[0029] ① Compressor reflux status: compressor reflux regulating valve PV2 is fully open, bypass valve BPV is open, temperature control valve TV1 is open, and other control valves are closed;

[0030] ② Low-flow heating intake warm-up: Open the first shut-off valve, second control valve, low-flow electric heater and low-flow regulating valve PV1 at the inlet to heat the inlet stream to 80°C, charge the compressor system to 0.3-0.4 MPaG, close PV1, and warm up the compressor unit and inlet and outlet heat exchangers;

[0031] ③Start the machine at the minimum flow rate to increase the system temperature: Start the main motor and make the speed reach the minimum allowable speed when the compressor is under low load. Gradually open PV1 and slowly inject gas into the system. At the same time, close the bypass return valve BPV, gradually reduce the return flow regulating valve PV2, slowly increase the compressor outlet pressure, monitor the fluid temperature in the system, and when it rises to 45°C, gradually reduce the heater power to keep the temperature at the front end of the compressor in the system at 45-50°C. When the pressure in the compressor unit system rises to 8MPaG, open SDV01 and close PV1 and the second control valve at the inlet;

[0032] ④ Set a back pressure valve PV3 at the compressor outlet. When the compressor downstream pressure does not reach the set gas injection pressure, or the compressor outlet pressure does not reach the pressure to ensure sufficient compression heat in a short period of time, set the compressor minimum back pressure to ensure compression heat: open SDV2, set the back pressure valve pressure to the minimum outlet pressure that can ensure the inlet flow is heated to 40°C, gradually reduce the reflux regulating valve PV2 to fully closed, and completely turn off the heater when the pressure in front of the back pressure valve rises to the set pressure;

[0033] ⑤ When the pressure behind the monitored back pressure valve PV3 reaches the set pressure, fully open the back pressure valve PV3 and adjust the main motor speed to increase it to the full load operating speed of the compressor.

[0034] To address the problem that when carbon dioxide is transported through supercritical pipelines and its phase changes to dense phase, it cannot directly enter the downstream supercritical compressor for pressurization. Conventional solutions such as using electric heaters or heating furnaces to directly heat the dense phase carbon dioxide to a supercritical state consume too much energy and have too high operating costs. Therefore, a compressor that can pressurize and inject dense phase carbon dioxide has been developed to achieve the goal of simplifying the process and saving energy.

[0035] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed in the present invention, who makes equivalent replacements or changes based on the technical solutions and concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A compressor capable of pressurizing and injecting dense phase carbon dioxide, characterized in that: Dense-phase carbon dioxide is input into the compressor skid through a pipeline. A first shut-off valve is provided on the inlet pipeline of the compressor skid, which is sequentially connected to the second control valve, the emergency shut-off valve SDV1 and the small flow regulating valve PV1 connected in parallel, the heater, the air intake separator, the air intake buffer tank, the compressor, the exhaust buffer tank, the temperature control valve TV2, the air cooler, the exhaust separator, the back pressure valve PV3 and the emergency shut-off valve SDV2, and finally transported to the gas injection system. The pipe-side inlet and outlet of the heat exchanger are connected to the left and right ends of the second control valve through a pipeline, and the shell-side inlet and outlet of the heat exchanger are connected to the left and right ends of the temperature control valve TV2 through a pipeline. The temperature control valve TV1 is provided on the inlet pipeline, and the left end of the air cooler is connected to the right end of the heater through the bypass valve BPV and the reflux regulating valve PV2 connected in parallel; The low-temperature startup process of a supercritical compressor is as follows: ① Compressor reflux status: compressor reflux regulating valve PV2 is fully open, bypass valve BPV is open, temperature control valve TV1 is open, and other control valves are closed; ② Low-flow heating intake warm-up: Open the first shut-off valve, second control valve, low-flow electric heater and low-flow regulating valve PV1 at the inlet to heat the inlet stream to 80°C, charge the compressor system to 0.3-0.4 MPaG, close PV1, and warm up the compressor unit and inlet and outlet heat exchangers; ③Start the machine at the minimum flow rate to increase the system temperature: Start the main motor and reach the minimum speed allowed when the compressor is under low load. Gradually open PV1 and slowly inject air into the system. At the same time, close the bypass return valve BPV, gradually reduce the return flow regulating valve PV2, slowly increase the compressor outlet pressure, monitor the fluid temperature in the system, and when it rises to 45°C, gradually reduce the heater power to keep the temperature at the front end of the compressor in the system at 45-50°C. When the pressure in the compressor unit system rises to 8MPaG, open SDV1 and close PV1 and the second control valve at the inlet; ④ Set a back pressure valve PV3 at the compressor outlet. When the compressor downstream pressure does not reach the set gas injection pressure, or the compressor outlet pressure does not reach the pressure to ensure sufficient compression heat in a short period of time, set the compressor minimum back pressure to ensure compression heat: open SDV2, set the back pressure valve pressure to the minimum outlet pressure that can ensure the inlet flow is heated to 40°C, gradually reduce the reflux regulating valve PV2 to fully closed, and completely turn off the heater when the pressure in front of the back pressure valve rises to the set pressure; ⑤ When the pressure behind the monitored back pressure valve PV3 reaches the set pressure, fully open the back pressure valve PV3 and adjust the main motor speed to increase it to the full load operating speed of the compressor.

2. The compressor capable of pressurizing and injecting dense phase carbon dioxide according to claim 1, characterized in that: The compressor inlet stream and outlet stream enter the tube side and shell side of the heat exchanger respectively. The compressor outlet hot stream enters the heat exchanger to heat the inlet cold stream before going to the air cooler.

3. The compressor capable of pressurizing and injecting dense phase carbon dioxide according to claim 2, characterized in that: The compressor inlet stream is 8MPa, 20℃, and the outlet pressure is 20MPa. When the compressor is in the first stage of compression, the outlet temperature is about 115℃. After installing the inlet and outlet heat exchangers, the inlet stream temperature can be increased to 40℃ to ensure that the compressor inlet temperature requirements are met.

4. The compressor capable of pressurizing and injecting dense phase carbon dioxide according to claim 1, characterized in that: When the compressor adopts multi-stage compression, it enters the next stage of compression without inter-stage cooling to ensure the temperature of the medium at the outlet of the last stage. If the temperature of the medium entering the next stage exceeds the maximum temperature allowed by the specification, it can enter the cooler to be cooled to the maximum temperature allowed before entering the next stage.

5. The compressor capable of pressurizing and injecting dense phase carbon dioxide according to claim 1, characterized in that: When the compressor outlet pressure is low and the compression heat is not enough to heat the inlet stream temperature to above 40°C, a heater or heating furnace is installed after the heat exchanger as a supplement.

6. The compressor capable of pressurizing and injecting dense phase carbon dioxide according to claim 1, characterized in that: A compressor startup low-flow heater is installed in the compressor skid to heat the inlet flow when the compressor is started. The heater is only used when the compressor is started and can be stopped after the compressor is running normally.

Images