A dense phase carbon dioxide booster system

Abstract

This application belongs to the field of environmental protection equipment technology, and specifically relates to a dense-phase carbon dioxide pressurization system. While the development of CO2 pipeline transportation has saved costs, it has also brought new problems. CO2 transported via pipelines often reaches the injection station in a supercritical state, making it impossible to achieve pressurization using injection pumps. Therefore, there is an urgent need for a supercritical / dense-phase CO2 pressurization system for use in injection stations to meet production demands. This application provides a dense-phase carbon dioxide pressurization system, comprising an expander, a booster pump, and an ejector pump connected in sequence. The expander, back pressure valve, heat exchanger, and ejector pump are connected sequentially, with the heat exchanger connected to the booster pump. By combining the expander, booster pump, and ejector pump, and using the expander as the power source, zero-power-consumption dense-phase CO2 pressurization is achieved, saving a significant amount of electrical energy. The ejector pump recovers the low-pressure carbon dioxide after expansion, preventing CO2 from flowing into the atmosphere and contributing to the greenhouse effect.

Description

Technical Field

[0001] This application belongs to the field of environmental protection equipment technology, and in particular relates to a carbon dioxide dense phase pressurization system. Background Technology

[0002] Carbon capture, utilization, and storage (CCUS) is a key technology for addressing global climate change, with its emission reduction contribution projected to reach 600 million to 1.6 billion tons of CO2 by 2050. Currently, dozens of CCUS demonstration projects have been planned and built in China, among which CO2 enhanced oil recovery (EOR) is undoubtedly the best choice for utilization and storage. Pipeline transportation has become an indispensable part of this project. Currently, the global pipeline transportation pressure generally does not exceed 15 MPa, which is far lower than the pressure required for CO2 enhanced oil recovery. Therefore, CO2 is injected into the wellhead via a booster injection station at the pipeline end.

[0003] With the development of CCUS (Complex Combustion-Enhanced Oil Recovery) projects, CO2 pipeline transportation has become the main mode of transport. At the end of the pipeline, CO2 injection pumps are used to further pressurize and inject CO2 into the underground for oil displacement or storage. While pipeline transportation saves costs, it also brings new problems. At the pipeline end, the CO2 state is generally near its critical point, and both dense-phase liquid and supercritical states may coexist. Existing CO2 injection processes, generally as described in patent CN 107355680 A, use plunger pumps to pressurize and inject supercritical CO2 from the pipeline. When the pipeline flow is in a supercritical state, CO2 has a low density and viscosity similar to that of a gas. Especially in hot summer weather, the temperature at the pipeline end is high, and CO2 is mostly in a supercritical gaseous state. This poses a significant challenge to the CO2 injection pump. If a refrigeration unit is used to condense and cool the CO2 before it enters the pump, it will not only increase the power consumption of the injection system, but also increase the initial equipment investment and subsequent operation and maintenance costs. Injection stations are generally built near the wellhead, making power grid layout difficult; therefore, the power consumption of the injection system should be minimized. Therefore, there is an urgent need for a supercritical / dense phase CO2 booster system for use in injection stations to meet production requirements. Summary of the Invention

[0004] 1. Technical problems to be solved

[0005] In CCUS projects, CO2 pipeline transportation is the primary mode of transport. At the pipeline's end, CO2 injection pumps further pressurize and inject CO2 into underground oil displacement or storage. While pipeline transportation saves costs, it also introduces new problems. At the pipeline's end, CO2 is generally near its critical point, with both dense-phase liquid and supercritical states potentially coexisting. Especially during hot summer weather, the pipeline's end temperature is high, and CO2 is in a supercritical state. This poses a significant challenge to the CO2 injection pumps. Existing plunger pumps and centrifugal pumps cannot achieve the ideal pressure when pressurizing supercritical CO2, as supercritical CO2 easily causes cavitation, rendering the pumps inoperable. If a refrigeration system is used to cool the incoming CO2 before pumping, additional power consumption is required, increasing investment costs. To address these issues, this application provides a dense-phase CO2 pressurization system.

[0006] 2. Technical Solution

[0007] To achieve the above objectives, this application provides a carbon dioxide dense-phase pressurization system, comprising an expander, a booster pump, and an ejector pump connected in sequence. The expander, a back pressure valve, a heat exchanger, and the ejector pump are connected in sequence, and the heat exchanger is connected to the booster pump.

[0008] Another embodiment provided in this application is that the expander is a liquid expander.

[0009] Another embodiment provided in this application is as follows: the booster pump is coaxially connected to the expander, the expander serves as the power source for the booster pump, and the ejector pump recovers the low-pressure carbon dioxide after expansion.

[0010] Another embodiment provided in this application is that the booster pump, the second flow control valve and the ejector pump are connected in sequence.

[0011] Another embodiment provided in this application is as follows: the expander is connected to the transport pipeline through a first flow control valve, and the transport pipeline is connected to the heat exchanger.

[0012] 3. Beneficial effects

[0013] Compared with the prior art, the advantages of the carbon dioxide dense phase pressurization system provided in this application are as follows:

[0014] The carbon dioxide dense-phase pressurization system provided in this application offers a solution to the problem of pressurizing CO2 pipeline flow near the critical point within the injection station.

[0015] The carbon dioxide dense phase pressurization system provided in this application combines components such as an expander, a booster pump, and an ejector pump to achieve zero-power-consumption CO2 dense phase pressurization, saving a significant amount of electrical energy.

[0016] The carbon dioxide dense phase pressurization system provided in this application utilizes only the pressure energy of the fluid and requires no additional power input. Compared with the traditional dense phase pressurization process, although it increases the initial equipment investment cost, it eliminates the need for subsequent operating power costs. As the operating time increases, the cost is lower than that of traditional equipment.

[0017] The carbon dioxide dense phase booster system provided in this application avoids the cavitation phenomenon that occurs when traditional CO2 dense phase pumps draw supercritical CO2, improves pumping efficiency, and thus enhances production benefits.

[0018] The carbon dioxide dense-phase pressurization system provided in this application, with its ejector pump connected in series, prevents the venting of a large amount of CO2 gas flow, thus avoiding the exacerbation of greenhouse gas effects. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the carbon dioxide dense phase pressurization system of this application.

[0020] Figure 2 This refers to the state changes of carbon dioxide in various components of the system in the embodiments of this application. Detailed Implementation

[0021] In the following, specific embodiments of this application will be described in detail with reference to the accompanying drawings. Based on these detailed descriptions, those skilled in the art will be able to clearly understand and implement this application. Without departing from the principles of this application, features from various embodiments can be combined to obtain new implementations, or certain features from some embodiments can be substituted to obtain other preferred implementations.

[0022] See Figures 1-2 This application provides a carbon dioxide dense phase pressurization system, including an expander 3, a booster pump 2 and an ejector pump 7 connected in sequence. The expander 3, a back pressure valve 4, a heat exchanger 5 and the ejector pump 7 are connected in sequence, and the heat exchanger 5 is connected to the booster pump 2.

[0023] The flow rate and outlet pressure of the expander 3 are controlled by the first flow control valve 1 and the back pressure valve 4.

[0024] After the CO2 transported by pipeline enters the CO2 injection station, a branch pipeline is constructed to divert a portion of the CO2 flow into expander 3 to perform work. The flow rate of expander 3 is regulated by the first flow control valve 1 before the inlet, while the outlet pressure is controlled by the back pressure valve 4 after the outlet of expander 3. During the operation of the expander, the pressure and temperature of the CO2 branch flow decrease, transforming it into a gas-liquid mixed cold CO2 flow. Subsequently, the cold CO2 flow enters the heat exchanger 5, where it exchanges heat with the mainstream CO2 in the pipeline. The cold CO2 flow absorbs heat, changing from a gas-liquid state to pure gaseous CO2, forming a CO2 gas flow that flows to the secondary inlet of the ejector pump. After heat exchange, the temperature of the mainstream CO2 in the pipeline decreases, becoming a dense liquid state. It then enters booster pump 2, which pressurizes it to a state higher than the injection pressure. Booster pump 2 is coaxially connected to expander 3, and the work done by expansion drives booster pump 2. The pressurized high-pressure CO2 flow enters the ejector pump 7. The flow rate of the dense phase CO2 entering the ejector pump 7 is regulated by the second flow control valve 6 before the ejector pump 7, thereby controlling the speed. Through the mutual conversion of pressure energy and kinetic energy, the CO2 gas flow is drawn into the pump for mixing and pressurization to obtain a CO2 flow that meets the injection pressure.

[0025] Considering that the CO2 flowing from the pipeline is generally in a supercritical state or a dense liquid state, the expander 3 is preferably a liquid expander.

[0026] Expander 3 not only provides driving force for booster pump 2, but also supplies cooling medium to the incoming CO2 flow, ensuring that the CO2 entering the pump is in a dense liquid state. Ejector pump 7 recovers the cooling medium CO2, preventing it from entering the atmosphere and increasing the greenhouse effect. Specific Implementation

[0028] Combination Figure 2 The state changes of CO2 in various components of this application are described in detail, along with the technical process of this application. For example... Figure 2 The state of CO2 flowing from the pipeline is shown at point a, with a pressure of 10 MPa and a temperature of 40℃. Assuming the proportion of CO2 flowing into expander 3 through the branch pipeline is x, this portion of CO2 enters expander 3 and performs work. The state of the expansion outlet is shown at point b. The output work of expander 3 is calculated using the following formula: W expander =q m2 (h se,out -h e,in )η e (1)

[0029] W expander The power output of the expander is expressed in kW; q m2 To divert the flow rate to the expander, q m2 =x*q m ,kg / s;h se,out It is the specific enthalpy of the outlet of the expander after isentropic expansion, in kJ / kg; he,in The specific enthalpy at the expander inlet is expressed in kJ / kg; the specific enthalpy is calculated using the software REFPROP, η. e For the expander efficiency, we take a value of 80% in this example.

[0030] The expanded CO2 exists in a gas-liquid two-phase state and is then introduced into heat exchanger 5 to exchange heat with the mainstream CO2 in the pipeline. The absorbed heat causes the gas-liquid CO2 to become gaseous, as shown in state c. After gaining cooling, the mainstream in the pipeline reaches state d, with a pressure of 10 MPa and a temperature of 10 °C. The CO2 then enters booster pump 2 in this state, where it is pressurized to 30 MPa, reaching state e. The power consumption of booster pump 2 is shown in the following formula:

[0031] W pump =q m1 (p p,out -p p,in ) / (ρη p (2)

[0032] W pump Power consumption of the booster pump, kW; q m1 For mainstream CO2 traffic, q m1 = (1-x)*q m ,kg / s;p p,in ,p p,out These represent the pump inlet and outlet pressures, in MPa; ρ is the density, in kg / m³. 3 η p For the booster pump efficiency, a value of 80% is used in this example.

[0033] Expander 3 serves as the power source for booster pump 2, and has W... expander =W pump Based on this relationship, the flow split ratio x = 60%, meaning that by utilizing 60% of the pipeline flow to expand and do work, the pressurization of the remaining 40% of the pipeline flow can be achieved. In current ejector pump technology, high-pressure liquid ejection of low-pressure gas is very easy because the liquid density is much higher than the gas density, and the working fluid pressure is much higher than the low-pressure gas pressure. State point fi represents the change of CO2 within the ejector pump 7, where high-pressure liquid CO2 ( Figure 2 State point e) rapidly expands to state point f through the ejector pump nozzle, attracting low-pressure gas CO2 into ejector pump 7 for thermo-mass mixing to state h, and then CO2 reaches state i in the diffusion section. Thus, CO2 pressurization is completed.

[0034] Although this application has been described above with reference to specific embodiments, those skilled in the art will understand that many modifications can be made to the configurations and details disclosed in this application within the principles and scope of the disclosure. The scope of protection of this application is determined by the appended claims, and the claims are intended to cover all modifications included in the literal meaning or scope of equivalents of the technical features in the claims.

Claims

1. A carbon dioxide dense-phase pressurization system, characterized in that: It includes an expander, a booster pump, and an ejector pump connected in sequence. The expander, a back pressure valve, a heat exchanger, and the ejector pump are connected in sequence, and the heat exchanger is connected to the booster pump. The booster pump is coaxially connected to the expander, the expander serves as the power source for the booster pump, and the ejector pump recovers the low-pressure carbon dioxide after expansion. The expander is connected to the transport pipeline via a first flow control valve, and the transport pipeline is connected to the heat exchanger.

2. The carbon dioxide dense-phase pressurization system as described in claim 1, characterized in that: The expander is a liquid expander.

3. The carbon dioxide dense-phase pressurization system as described in claim 2, characterized in that: The booster pump, the second flow control valve, and the ejector pump are connected in sequence.

Images