During the operation of the unit, the high-temperature pneumatic ball valve is mainly used on the residual oil pipeline between the heater outlet and the coke tower and the overhead oil and steam pipeline. The residual oil pipeline is the pipeline with the highest temperature in the whole coking unit and the most prone to coking. Its temperature is between 500~505 ℃, which is also the coking temperature of residual oil. Due to the characteristics of the internal structure of the high-temperature pneumatic ball valve, part of the residual oil will enter the cavity between the valve body and the ball body and the internal and external steam cavities of the bellows. Although there is steam injection at these two places, due to the location of steam injection (the steam injection location of the valve chamber is at the upper part of the valve) and the factors of steam injection volume (the steam temperature and its injection volume have an impact on the refining process), the residue is often deposited at the location far from the steam injection inlet, and then gradually forms hard coke. The residual oil coming in later will continue to accumulate and coke on the original coke block along the cavity wall. The coking in the valve body is mainly concentrated between the bottom of the ball and the valve body. The coking in this part will cause the ball position to be lifted by the coke block, causing local contact between the sealing surface of the ball and the sealing surface of the valve seat, resulting in internal leakage of the valve, and even more serious will cause the valve to fail to close. What is more serious is that a hard coke layer is formed outside the sphere, covering the whole sphere, and the valve action fails.

4、 At present, the super large air separation units are mostly used in the chemical industry. Many large-scale coal chemical industries are built in remote areas such as Inner Mongolia. At this time, the impact of the environment on the valves should also be considered. For example, the harsh low temperature environment requires the selection of valve accessories (including positioners, solenoid valves, etc.) suitable for this environment.