Structural features of high temperature butterfly valves

1. no blow off stuffing box. The purging device is installed as a spare part only. The purging device is connected with a continuous nitrogen or steam source. The pressure of the gas source is adjusted to 0.035-0.07 MPa higher than the working pressure inside the valve. When the packing seal is worn inside or outside, the purging medium will leak to the inside or atmosphere of the valve. There is no flow indicator in the pipe of the purging device during normal operation of the non-purging packing box. Once the flow meter indicates that the purging gas enters the system, it indicates that leakage is occurring.

When the leakage leaks to the outside, the fastening bolt of the packing box is tightened; when the leakage leaks to the inside, the middle packing seal can be strengthened by injecting the sealing grease, and the sealing sleeve can be pushed outward, and the main packing seal can be compressed to the middle to reduce or eliminate the leakage. When the flow indicator indicates no flow, it means that the leak has stopped.

Locate the ring at the bottom of the outer seal by the ring bolt (or limit pin) so that when the outer packing seal is tightened, other packing seals are tightened. If the retaining ring contacts to the end, only the outer packing seals will be tightened; when the packing cap is fully in, the retaining ring contacts to the bottom. When the retaining ring contacts the bottom part, the outer packing seal needs to be replaced. In order to replace the outer packing seals, the intermediate packing seals must be strengthened first, and the sealing effect is assumed by the intermediate packing seals. Closing the purging weather, the outer packing seal can be removed and replaced during operation.

2. stem purging. The high temperature butterfly valve is provided with a purging hole at the shaft sleeve position, which can be purged by nitrogen or steam according to different requirements, and the pressure of feed gas is kept appropriately higher than that of flue gas in the pipeline. Continuous purging ensures the cooling of the valve body seal and prevents catalyst particles from entering the packing box in the flue gas, affecting the sealing effect as well as the wear and sticking of the valve stem.

The purging flow should be designed according to the requirements of the manufacturer of high temperature butterfly valves. Compressed air (industrial air) is not recommended for purging. Oxygen components in compressed air can easily oxidize metal materials at high temperatures. In an incomplete regenerative catalytic cracking unit, CO components in high temperature flue gas may produce secondary combustion when contacting O2 of compressed air, which may damage metal equipment. Therefore, it should be decided to avoid using compressed air to purge the high temperature butterfly valve for the equipment using the incomplete regenerative catalytic cracking process.

Development direction of high temperature butterfly valve

With the development of FCC energy recovery technology and the increase of FCC unit capacity, the performance of matching butterfly valve is required to be improved. It is required that the valve has large caliber, large output torque, high reliability and high control sensitivity, so as to ensure the safe, stable and long-term operation of the device and recover as much energy as possible. High temperature butterfly valves abroad are developed early and have many varieties. However, China started late, after trial-production, improvement and other continuous development, domestic manufacturers of high-temperature butterfly valves, they manufacture high-temperature butterfly valves performance indicators have reached a higher level. High-temperature butterfly valves designed at home and abroad are mainly driven by pneumatic and electro-hydraulic forms. At present, the direction of development is electro-hydraulic high-temperature butterfly valves. Pneumatic high-temperature butterfly valves are gradually withdrawing from the use of the field, currently in use is very few.

At present, most of the high-temperature butterfly valves designed and manufactured in China are still stepped seal structures. In recent years, aiming at several serious damage accidents caused by unit overspeed in succession, some improvements and improvements have been made in the structure of valve body to improve the response speed of high temperature butterfly valve at the inlet of flue gas turbine, cut off quickly and ensure the reliability of long-term operation.

A hardfacing carbide wear-resistant bushing is added between the valve stem and the butterfly plate hub to protect the valve stem from erosion by high-speed air flow.

B. The high-temperature silicified graphite sliding bearing is used instead of the supporting shaft at both ends of the valve stem to overcome the disadvantage that the original rolling bearing is easily blocked by high temperature or rust.