Can cavitation occur when using a centrifugal pump to draw liquefied gas? What if it happens? How to solve it?

Due to the development of China’s petroleum industry, the transportation and filling of liquefied petroleum gas are now very common. There are also increasingly more situations in which liquefied petroleum gas pumps are used for transporting such gas. However, the most troublesome aspect of operating such pumps is the problem of pump cavitation. Of course, there are many reasons for cavitation to occur in LPG pumps. For us operators, the most common cause is the vaporization of LPG in hot weather, which often leads to such phenomena!

Air blockage, the occurrence of cavitation, and preventive measures 　　　1. The occurrence of air blockage 　　　Liquefied petroleum gas has a low viscosity; when the ambient temperature or pipeline pressure changes, it easily vaporizes and exists in both gas and liquid phases. After vaporization, it accumulates and gets trapped at certain points within the pipeline, usually forming an air pocket at the highest point of the pipeline. As the ambient temperature rises or the residual pressure inside the pipeline decreases, the expansion of the gas phase space may lead to gas blockage or even flow interruption. 　　 　　2. Formation of cavitation 　　　At a certain temperature, liquid liquefied petroleum gas begins to vaporize when the pressure at the pump inlet drops below the saturated vapor pressure of that liquid at that temperature; bubbles are formed as a result. When these bubbles enter areas of higher pressure along with the liquid flow, they burst, and the surrounding liquid quickly fills in the voids left by those bubbles, creating hydraulic shock. This process of bubble formation, growth, and bursting is known as cavitation. 　　 　　3. Hazards of air resistance and cavitation: ① Possible interruption of flow; ② Generation of abnormal noise and intense vibrations; ③ Decline in pump performance; ④ Corrosion and damage to the flow-related components generally do not occur. However, when cavitation occurs, a very thin lubricating film cannot be formed between the rotating blades and the inner sleeve (oil-free lubrication), resulting in the blades softening or melting due to mechanical friction. Precautionary measures: ① Improve the flow conditions in the inlet pipeline, ensuring it is as short as possible with few elbows, and connected to the pump body at a slightly downward horizontal angle. ②When the inlet pipe is larger than the pump connection pipe, an eccentric reducer with a length four times the pipe diameter should be used for transition. ③If the inlet pipeline is long, insulation material can be used to wrap the pipeline for thermal insulation. ④Use a compressor to pressurize the storage tank to ensure sufficient static head in the inlet pipe. ⑤Before starting the pump, open the relief valve to release air; if abnormal noises occur during operation, stop the pump immediately to release air. ⑥The installation height of the pump should satisfy Hь≥102×10³/ρ(∑∆P＋∆h)＋u²/2g (see page 68 of the Code for Design of Urban Gas Supply GB50028-93 for details)

We have two types of devices for transporting fluids; one is called a pump, which is used to transport liquids； Another type is called a compressor, which is responsible for transporting gases. The medium pumped by the pump must not contain a gas phase, and the medium pumped by the compressor must not contain a liquid phase; their roles are clearly defined. Liquefied gas must enter the pump in a gaseous state; that is, the pressure of the medium at the inlet to the impeller must be greater than its saturated vapor pressure at that temperature, otherwise cavitation will occur. Liquefied gas is prone to phase changes when pressure and temperature change, and therefore is susceptible to cavitation. The prevention methods are: reducing the medium temperature to lower its saturated vapor pressure or increasing the inlet pressure of the medium.

The people upstairs have all said very good things. For such operating conditions, I think there are only two factors: cooling and pressurization.

The people upstairs have all said very good things. For such operating conditions, I think there are only two factors: cooling and pressurization.