With the advancement of the industrial revolution, cars have become a standard feature of most families, which has led to an increasing demand for gasoline. In turn, the market has led major energy companies to build a large number of gas stations. However, while providing convenience, gas stations also cause certain pollution to the surrounding environment. For example, the volatilization and leakage of oil products will increase safety risks such as fire and explosion to varying degrees, and even increase the incidence of occupational diseases for gas station workers in the industry. Frequent accidents continue to remind the public. Under the strict constraints of the country's extensive publicity and environmental protection laws, people's awareness of safety and environment is increasing, and the introduction and application of vapor treatment process technology and equipment at gas stations is imminent.
1 vapor loss channels
There are many channels for vapor consumption in gas stations. Figure 1 is a schematic diagram of the process and consumption path of finished cars from the oil depot to the target vehicle tank. The amount of fuel volatilized in the process of unloading and refueling at the gas station alone reaches 2‰~3‰. According to the calculation of more than 177 million tons of refined crude oil in 2018, the loss of automobile fuel alone can reach 53,100 tons/year. According to the calculation of RMB 5,000/ton, the total loss value will reach RMB 265.5 million. Therefore, strengthening the research on vapor recovery technology in gas stations can create considerable economic value. Since the annual oil evaporation loss is very large, it not only causes harm to social security, but also increases the waste of management costs, thereby inhibiting the enthusiasm of the entire country's oil supervision work. First of all, since oil loss will have a great impact on the environment, oil smoke has also become the main "culprit" for the decline in air quality. At the same time, it will also have a great impact on human health, especially for some operators, it will greatly increase the probability of special diseases. Secondly, because oil leakage will also increase the probability of fire and explosion, the overall safety risk coefficient will increase, thus there is a considerable risk. Finally, due to the large amount of oil leakage, the overall density and efficiency of oil have decreased, and the oil efficiency has not met the technical indicators, thus restricting the entire national safety work. In addition, due to the waste of vapor, it may bring a great impact to the company, expand the company's economic losses, or form safety hazards, affecting the company's overall benefits and management benefits.
Since the automobile storage tanks at gas stations are mainly discharged from high altitudes through vent pipes, when the tank truck unloads oil into the gas tank, the vent cap will discharge some highly saturated automobile water vapor. The highly saturated gasoline water vapor accumulated on the upper part of the vent cap for a long time may cause a large explosion once any spark or static electricity appears. This is undoubtedly a time bomb for those automobile gas stations located in downtown areas [3]. Now some gas stations in downtown areas have also been equipped with air guns with gas return devices. Although the fuel evaporation pressure generated at the automobile refueling end is alleviated, the pumped back fuel cannot be collected and processed again, so most of it is discharged again after passing through the vent cap, resulting in the long-term accumulation of high-concentration organic wastewater vapor on the vent cap, which in turn aggravates the fire hazard risk of automobile gas stations. Therefore, vapor treatment can reduce safety hazards that may cause explosions, burns, etc., and can protect human life and property safety.
2 vapor recovery technology
Oil utilization refers to the process of collecting, storing and transporting oil generated during the loading and unloading process, storage and pumping of oil at oil storage depots and gas stations. The oil is first collected, stored and transported to the fire of the oil tank, then transported to the oil storage depot for concentration, and then converted from gas to liquid through corresponding processing procedures, and finally reprocessed into gasoline, thereby realizing the work flow of resource recycling [4]. At present, there are roughly four types of vapor processing technology in China: absorption method, absorption method, condensation method and membrane separation method [5].
2.1 Absorption method
Analysis of petroleum often requires hydrocarbon substances that can be decomposed into multiple components, and the solubility of such hydrocarbon substances under different types of direct adsorbents is also very different. Therefore, technicians should make full use of this characteristic of hydrocarbon substances to separate petroleum from gas. In the separation process, it is necessary to select a good direct adsorbent, because the quality of the direct adsorbent will have a great impact on the recovery effect, so usually the oil products with the same quality as the petroleum or lower quality oil products are selected. First, the direct adsorbent must be completely connected with the petroleum, so that the direct adsorbent can completely and directly adsorb the beneficial elements in the petroleum, and then the useless substances that cannot even be completely directly adsorbed will be released into the atmosphere. To improve the safety of the collection and treatment of petroleum, a flame arrester must be installed at the discharge port first, and the treatment of petroleum is completed through the process of collecting useful petroleum and discharging wastewater.
2.2 Adsorption method
Because the vapor in oil can be easily distinguished from air, it is possible to use adsorbents to separate oil from air. The process technology of oil recovery using absorption method is a digestion and absorption system composed of suction tower, vacuum pump, suction tower and other devices. First, the oil in Weihai Tashan Middle School is directly adsorbed to the surface of the adsorbent, and then desorbed using vacuum technology, and then the maximum vacuum is pumped for desorption, so that the desorbed oil is directly returned to the suction tower for liquefaction, and the vapor that cannot be directly adsorbed are directly released into the atmosphere through the discharge pipe, and then this process is used to use the oil, and then the oil products are recovered and used.
2.3 Condensation method
Because different components in oil produce saturated vapor pressure coefficients at different high temperatures, the condensation method can be used to separate oil from hot air. During the centrifugal process, the oil is cooled and condensed into liquid after reaching the supersaturated state, so that the oil and air are completely separated. Through this method, the oil can be cooled continuously in multiple stages, so that the vapor can be well separated and recovered, thereby improving efficiency.
2. 4 Membrane separation method
When using membrane separation method to treat vapor, qualified membranes must be selected. Petroleum contains hydrocarbon compounds, which have preferential permeability characteristics on certain macromolecular membranes. Then, high pressure is formed on the hydrocarbon substances, and the hydrocarbon substances are preferentially pushed out through pressure drive. Then, the stripped oil is recovered after sealing, and relevant measures are formulated to transport the oil to the oil tank, so that the oil can be used.
At present, these four vapor recovery technologies have their own advantages and disadvantages. According to the different vapor loss methods of specific gas stations, these methods can be effectively integrated and used to improve the efficiency of vapor recovery.
