Light oil recovery

For internal floating roof storage tanks, when the concentration of oil and gas is between 10,000 and 50,000 mg/m3, it is generally necessary to first establish a nitrogen seal, with the pressure of this nitrogen seal being between 500 and 600 Pa； Next, flame arresters and single-vent valves are installed. After connecting the single-vent valves of each storage tank through pipes to facilitate the flow of oil and gas, recovery is carried out. There are three methods available for recovering light oil: 1) Recovery using absorption technology: This technique relies on the principle that similar substances dissolve in each other; a low-volatility or non-volatile absorbent is used to come into direct contact with the waste gas, thereby transferring VOCs into the absorbent solution and achieving the separation and purification of pollutants. Based on the mechanism, absorption processes can be divided into physical absorption and chemical absorption. The efficiency of absorption depends mainly on the properties of the absorbent and the structural characteristics of the absorption device. An absorbent should possess properties such as high solubility, no corrosivity to equipment, low volatility, non-toxicity, chemical stability, low cost, and easy availability. It is usually a liquid substance, primarily a mixture of liquid petroleum products, surfactants, and water. Absorption devices mainly include spray towers, packed towers, various types of washers, bubble towers, and sieve plate towers. If you have storage tanks for heavy oils such as diesel, which have a low saturated vapor pressure, in your tank area, you can use these heavy oils for absorption ； 2) Use of membrane separation technology: This technology takes advantage of the different rates at which various gas molecules dissolve and diffuse through polymer membranes, thereby achieving separation under certain pressures. The partial pressure difference between the gases on either side of the membrane is the driving force for membrane separation, which can be achieved by compressing the incoming gas or using a vacuum pump on the side where permeation occurs. Therefore, the membrane separation process is often integrated with condensation or compression processes. The key to membrane separation lies in the selection of membrane materials; currently, silicone rubber membranes and hollow fiber membranes are commonly used. The common membrane separation processes for treating VOC waste gases include vapor permeation, gas membrane separation, and membrane contactors. Compared with traditional condensation, adsorption, and absorption methods, it offers advantages such as a simple process, high recovery rates, low energy consumption, and no secondary pollution, making it a separation method with great application prospects. This method is suitable for the separation and recovery of medium to high concentrations of VOCs. 3) Adsorption method: This technique makes use of solid adsorbents with a large specific surface area to capture organic volatiles in exhaust gases, thereby separating light oil from the gas. Once the adsorbent becomes saturated, water vapor or hot air is used as a desorbing agent to remove the light oil from the surface of the adsorbent and recover it. Adsorption is one of the mainstream technologies for treating VOCs in industry today, with key elements including adsorbents, adsorption equipment and processes, regeneration media, and post-treatment processes. The efficiency of adsorbents in capturing VOCs depends not only on the properties of the adsorbent itself but also on the type, concentration, and properties of the VOCs, as well as the temperature and pressure of the adsorption system. Generally, an adsorbent’s ability to absorb VOCs increases as the molecular weight of the gas increases; gases at lower pressures are more easily absorbed than those at higher pressures.