2.3 Condensation method
The condensation method utilizes the difference in vapor pressure of hydrocarbons at different temperatures to cool down the hydrocarbon vapor in the oil and gas to a supersaturated state and condense it into a liquid state, thereby realizing the recovery of oil and gas. The condensation method has a simple process principle, high recovery efficiency, high safety and high automation level. However, this method requires a large initial investment and relatively high refrigeration energy consumption, and often requires at least two condensers to switch between operations.
According to different implementation methods, it can be divided into two categories: (1) Direct contact method. As the name suggests, it is a direct contact between the cooled gas and the coolant or refrigerant for heat exchange, thereby achieving condensation. This method is usually carried out in a spray tower, contact tower or ejector, and the coolant is directly sprayed into the oil-containing gas, and the heat is removed by direct contact to condense the oil and gas. The advantages of the direct contact method are high heat transfer efficiency, the ability to quickly reduce the gas temperature, and the effective recovery of oil and gas. However, due to the direct contact between the coolant and the oil-containing gas, the condensate may be contaminated to a certain extent, and further treatment is required before it can be recycled. (2) Indirect contact method. This technology uses cooling walls and other devices to separate the exhaust gas from the coolant, avoiding direct contact between the two. The main devices used are shell and tube condensers, sprinkler condensers, and spiral plate condensers. The advantage of the indirect contact method is that the condensate is pure and can be directly recycled without additional processing steps. However, since it adopts indirect heat transfer logic, it has high requirements for low-temperature environment, and needs to reach -70 ~ -80℃ to ensure the improvement of recovery rate.
2.4 Membrane separation method
The membrane separation method is based on the difference in the permeation rate of oil and gas components and air through polymer membranes. Through the "filtration" effect of membrane components, oil and gas are separated from air, thereby recovering oil and gas resources, as shown in Figure 1. The core of membrane separation is high-performance gas separation membrane components. These membrane components are usually composed of composite structures. The surface layer is a dense silicone rubber layer, which is responsible for the separation function; the middle layer and the bottom layer are made of loose materials to enhance the mechanical strength of the membrane. When the oil-containing gas passes through the membrane component under the pressure difference on both sides of the membrane, the oil and gas components preferentially pass through the membrane due to their higher permeation rate, while the air is selectively intercepted. In this way, the oil and gas enriched flow out from one end of the membrane component, and the purified air with oil and gas removed from the other end. The membrane separation method has the characteristics of advanced technology and relatively simple process. Its emission concentration is low and the recovery efficiency is high, which can effectively reduce the pollution of oil and gas volatilization to the environment. In addition, the membrane separation method also has a high level of automation, which is easy to operate and maintain. However, the high-performance gas separation membrane is expensive and has not yet been domestically produced, resulting in a large investment in equipment. Moreover, the membrane has a limited service life and needs to be replaced regularly. The membrane separation method also has relatively high requirements for gas flow and pressure stability, and the operating conditions are relatively harsh.
3 Application process of oil and gas recovery technology in oil and gas storage and transportation
3.1 Oil unloading link
During the oil unloading process, oil and gas are usually stored in a negative pressure environment, and the emission is relatively concentrated. In order to effectively recover these oil and gas, the oil unloading facilities need to be optimized. For example, when using train tanks for oil and gas transportation, it should be ensured that the tanks have good sealing performance to reduce the volatilization of oil and gas during transportation. At the same time, during the oil unloading process, vacuum pumps and other devices can be used to extract the oil and gas in the tank and process them through the oil and gas recovery system. This process usually includes steps such as oil and gas collection, compression, condensation or adsorption, and finally the recovered oil and gas are re-injected into the oil storage facilities.
3.2 Oil storage link
During the storage of oil and natural gas, due to the influence of external factors such as environment and temperature, oil and gas are prone to volatilization and loss. In order to reduce this loss, it is necessary to strengthen the sealing performance of the oil storage system to prevent oil and gas leakage. In addition, oil and gas recovery devices can also be used to recover the oil and gas in the oil storage tank. These devices usually include components such as adsorption towers and condensers, which can efficiently separate the oil and gas in the oil storage tank and treat them. During the treatment process, the appropriate recovery method can be selected according to the composition and concentration of the oil and gas, such as condensation, adsorption or membrane separation. 3.3 Oil receiving and sending link When receiving and sending oil, the liquid level in the oil storage tank will change due to the injection and extraction of oil products, resulting in pressure fluctuations in the tank, which in turn causes the volatilization of oil and gas. In order to control the oil and gas loss in this process, oil and gas recovery technology can be used. Specifically, oil and gas recovery devices such as oil and gas separators and compressors can be installed on the oil receiving and sending pipelines. When oil is injected into the oil storage tank, the oil and gas generated will be captured by the separator and sent to the compressor for compression; when the oil is extracted from the oil storage tank, the pressure in the tank decreases. At this time, the air intake valve of the recovery device can be opened to inhale the air outside the tank and mix it with the remaining oil and gas in the tank and then send it to the compressor for treatment. In this way, the oil and gas in the oil delivery process can be effectively recovered.
4 Conclusion
In summary, the effectiveness of the rational use of oil and gas recovery technology in oil and gas storage and transportation is mainly reflected in two aspects: resource conservation and environmental protection. By efficiently recovering volatile oil and gas, this technology greatly reduces the waste of oil and gas resources and improves the efficiency of resource utilization. At the same time, oil and gas recovery effectively reduces the emission of volatile organic compounds in the atmosphere, improves air quality, and reduces environmental pollution pressure. In addition, the application of oil and gas recovery technology has also promoted the green development of the oil and gas storage and transportation industry, and enhanced the environmental protection image and social responsibility of enterprises.
In general, the application of oil and gas recovery technology in the field of oil and gas storage and transportation has not only achieved a win-win situation in economic and ecological benefits, but also made important contributions to promoting the sustainable development of the energy industry.
