During the operation of FV-1500B valve, serious internal leakage, wear, fluctuation and vibration of valve trim occurred.
1. Analysis of process parameters:
Medium: nitrogen; valve design pressure before valve is 6.1MPa, pressure after valve is 0.1MPa, full pressure difference is 6MPa. The nominal diameter of the process pipeline is 6" in front of the valve and 16" behind the valve. The maximum flow required by the process is 45250Nm3/h, the normal flow is 41250 Nm3/h, and the minimum flow is 31000 Nm3/h.
From the above process parameters, it can be found that the valve has special working conditions of large pressure difference, large flow rate and high flow rate.
2. Analysis of wear causes of valve trims:
Valve selection The nominal diameter of 4" is too small. The medium flow rate is fast with small valve diameter. A 14-inch CV234 noise reduction plate is installed after the original valve.
Control the pressure after the valve and before the plate to a maximum of 15.7bar, a normal 14.4bar, and a minimum of 10.86bar. Corresponding to the three working conditions, the flow rate of the valve outlet is 144m/s, which is converted into a nitrogen flow rate of Mach 0.4. Obviously, the flow rate has exceeded the safe flow rate of Mach 0.3.
The valve trim is designed as a cage-type single-seat valve, and the cage has the functions of throttling, noise reduction and guiding. However, the valve core has no bottom guide design, resulting in too large bottom gap between the valve cage and the valve core. After the valve is opened, the valve core is suspended and cannot play a guiding role.
To sum up, when the high-velocity medium flows through the valve core and the valve cage, it has a very large impact on the valve trims. When the high-velocity medium flows through the throttle surface of the valve core and the valve cage, the Good guidance to the spool leads to high-frequency vibration of the spool. During the vibration, the valve opens and closes, which causes the spool and the different parts of the cage to collide and rub against each other, causing the spool and the cage to wear out, and it is derived from the inside of the valve. leakage problem.
1. On the premise that the medium pressure and differential pressure are fixed, reduce the medium flow rate to reduce the impact of the high medium flow rate on the valve trim. Select the 16-inch noise reduction board KV320 after the valve to ensure that there is a pressure of 10bar between the back of the valve and the front of the board.
The valve needs to be 6"600lbs. The outlet flow rate of the valve is 75.9m/s, and the calculated Mach number is 0.21Ma. It is completely within the safe flow rate range, indicating that the 6-inch valve body is safe and reliable.
2. The valve trims are designed with pressure-balanced multi-stage decompression trims. There is a design of a balanced sealing ring between the valve core and the balance cylinder. The valve core design and the valve seat have a bottom guiding function to ensure that the balance type is opposite to the valve core. good orientation.
To sum up, for the FV-1500B high-pressure nitrogen vent valve, UTMOST adopts a pressure-balanced multi-stage drop valve trim structure, and the multi-stage pressure drop structure solves the problems of high pressure difference and loud noise. The added valve core of the pressure balance cylinder has a good bottom guide, and the top and bottom double guides ensure that the valve core does not vibrate when the high-pressure medium flows through the throttling surface. See calculation book for details.
3. The valve trim with porous structure rectifies the high-pressure medium. The medium no longer impacts one side of the valve core alone, but circulates evenly around the valve core, eliminating the impact force of the valve core by the medium.
4. The valve trim is designed to reduce the pressure in three stages, so that the pressure difference of each stage becomes smaller, which weakens the impact of the high-pressure medium on the throttle surface of the valve core.
5. Comprehensive degreasing treatment
UTMOST china valve supplier has advanced ultrasonic degreasing technology and a professional dust-free degreasing workshop of UTMOST Nitrogen Vent Valve for Coal Gasification Unit. The valve completes cleaning, degreasing, assembly, testing and other work in the dust-free degreasing workshop to ensure that the valve is free from external pollution after degreasing is completed. The oil content is required to be within 200mg/m2.