As a very important energy source in modern industrial production and daily life, the safety and environmental protection of vapour in the storage and transportation process have attracted much attention. In the process of vapour storage and transportation, due to its strong volatility, it often causes waste of resources and environmental pollution. Therefore, the application of vapour recovery technology is particularly important. With the enhancement of environmental awareness and the continuous advancement of technology, vapour recovery technology has become an indispensable part of the field of vapour storage and transportation. Through a variety of technical means such as adsorption, condensation, absorption and membrane separation, vapour recovery technology can effectively convert volatile vapour into usable resources while reducing environmental pollution. This article will deeply analyze the specific application and effects of these technologies, in order to provide a reference for the sustainable development of the vapour storage and transportation industry.
1 Causes and hazards of vapour loss
1.1 Causes
In the process of vapour storage and transportation, the loss of vapour is an issue that cannot be ignored, and its causes are diverse and complex.
(1) Small breathing loss is a common phenomenon in vapour storage and transportation. It is mainly caused by the diurnal changes in the temperature of the gas space and the vapour concentration in the oil storage tank. During the day, as the atmospheric temperature rises and the intensity of solar radiation increases, the temperature of the gas space and the oil surface in the tank rises, and the pressure in the gas space increases. When the pressure reaches the control value of the breathing valve, the oil vapor will be discharged out of the tank through the breathing valve, causing loss. At night, as the temperature drops, the pressure of the gas space decreases, and the breathing valve will inhale air, reducing the vapour concentration in the gas space, thereby accelerating the evaporation of the oil product and forming new losses. (2) Large breathing loss often occurs during the oil receiving and sending operations of the oil storage tank. When the oil tank receives oil, the oil level rises, the vapour between the oil surface and the tank top are compressed, and the pressure continues to rise. When it reaches the control pressure of the breathing valve, the vapour will be discharged out of the tank. When dispensing oil, as the oil level drops, the gas space pressure decreases, and the breathing valve will inhale air, which will also cause the vapour concentration in the tank to decrease and accelerate the evaporation of the oil. This loss caused by the rise and fall of the oil level in the oil tank is called the large breathing loss.
(3) The viscosity of vapour and the temperature of the storage tank are also important factors affecting the loss of vapour. During the storage and transportation of vapour, if the temperature of the storage tank is not properly controlled, it will cause the viscosity of the oil to change, thereby affecting the fluidity and volatility of the oil and increasing the loss of vapour. At the same time, if the vapour in the storage tank has a large viscosity, it will intensify molecular friction and increase the adhesion of vapour, which will cause adhesion in the storage tank and cause a large amount of loss.
1.2 Hazards
On the one hand, the volatilization and escape of vapour during storage and transportation will affect the quality of the surrounding environment to a certain extent. vapour contain a variety of harmful components, such as volatile organic compounds such as benzene, toluene, and xylene. These substances accumulate in the air, which will not only reduce air quality, but also form photochemical smog, aggravate the haze phenomenon, and pose a serious threat to people's health. Long-term exposure to this environment may cause people to have health problems such as respiratory diseases and nervous system damage, and even increase the risk of cancer. On the other hand, vapour loss also brings serious safety hazards. After vapour escape, a flammable mixed gas will be formed in the air. Once it encounters open flames or high temperatures, it is very easy to cause fires and explosions, which will not only damage vapour storage and transportation facilities and cause huge economic losses, but also threaten the lives of operators. Especially in densely populated areas of vapour storage and transportation, once a fire or explosion occurs, the consequences will be disastrous, which may trigger a chain reaction and pose a major threat to the safety of the entire area.
2 Application of vapour recovery technology in vapour storage and transportation
2.1 Absorption method
The absorption method uses a specific liquid absorbent to absorb hydrocarbon components in vapour into the absorbent through countercurrent contact with vapour to form a rich liquid. Then, the vapour in the rich liquid are separated through a desorption process, thereby realizing the recovery of vapour. The absorption method is relatively simple to operate and can effectively recover vapour resources and reduce environmental pollution.
At present, the more common absorption methods are mainly normal temperature and pressure absorption method and normal pressure cooling absorption method: (1) Normal temperature and pressure absorption method is a method of removing vapour by contacting the exhaust gas with the absorbent at normal temperature and pressure. This method makes full use of the natural conditions of the environment and reduces the operating cost. At the same time, due to its simple operation and low equipment requirements, it is suitable for treating a large amount of vapour in exhaust gas. At present, the normal temperature and pressure absorption method has been widely used, and the recovery rate of some recovery devices can even reach 95%, and the application effect is very ideal. (2) Normal pressure cooling
The absorption method is to use refrigeration equipment to cool the absorbent to a low temperature on the basis of normal temperature and pressure, and then send it to the absorption tower to spray the mixed vapour.
Since the absorbent temperature is low, the light component absorption gas stripping operation can be omitted, and the recovery effect is better. However, this method requires complex refrigeration system equipment, and also has special requirements for the equipment of the absorption device, so the cost and operating expenses are relatively high.
2.2 Adsorption method
The adsorption method mainly relies on the strong adsorption capacity of solid adsorbents for hydrocarbon components in vapour. It usually uses activated carbon as the basic material for treatment and separation. vapour are separated from the gas phase through physical or chemical action to achieve resource recycling. The adsorption method vapour recovery system usually includes key components such as adsorption tower, regeneration tower, cooler, heater and control system. In the adsorption stage, vapour enter the adsorption tower through a closed pipeline and fully contact with the adsorbent. The hydrocarbon components are adsorbed on the surface of the adsorbent, and the purified gas is discharged from the system. As the adsorbent gradually becomes saturated, the system enters the regeneration stage. The adsorbed hydrocarbon components are desorbed from the adsorbent by heating, reducing pressure or flushing, and collected and recovered. The regenerated adsorbent restores its adsorption capacity and can be put back into the next round of adsorption process.
The advantages of the adsorption method are high processing efficiency and high recovery rate, and it can adapt to the treatment needs of vapour with different concentrations and flow rates. Especially for low-concentration vapour emissions, the adsorption method has demonstrated excellent treatment capabilities. In addition, the adsorption vapour recovery system is also easy to operate and maintain, and the application of automated control technology further improves the stability and reliability of the system. However, the adsorption method also faces some challenges, such as the selection and regeneration efficiency of adsorbents, system energy consumption, and equipment investment costs. Different adsorbents have different adsorption properties for hydrocarbon components, and suitable adsorbents need to be selected according to the vapour composition and recovery goals. At the same time, energy consumption during the regeneration process is also a key factor affecting the economy of the system. Although the initial investment in the adsorption vapour recovery system is high, in the long run, its resource recovery and environmental protection benefits are significant, which helps to reduce corporate operating costs and improve the environmental image.
