Discussion on the Application of V-port Ball Valves Replacing Double-seated Control Valves Under High Temperature, High Pressure Differential and Large Load Fluctuation Conditions

Compared with double-seated control valves, V-port ball valves have the advantages of wide adjustment range, high pressure differential resistance, and good high-temperature resistance, eliminating potential safety hazards.

Keywords: ball valve, temperature and pressure reduction system

1 Overview

Anyang Chemical Industry Group Co., Ltd. has an annual output of 240,000 tons of synthetic ammonia, 430,000 tons of urea, 60,000 tons of refined methanol, 50,000 tons of methylamine, DMF, etc. It has new and old systems.The old system is equipped with a set of temperature and pressure reduction equipment, in which steam from the boiler outlet is sent to the subsequent process after temperature and pressure reduction.The process load of this system varies greatly. The upstream pressure of the control valve is 2.5–3.8 MPa, the downstream pressure is 0.2–0.4 MPa, and the steam flow rate is 5–30 t/h.

The main reasons for the large process load variation are as follows:

① Startup and shutdown of the steam turbine.When the steam turbine is in operation, its extraction steam is directly sent to the downstream of the valve, and the control valve needs to reduce its opening; otherwise, the opening should be increased.

② Supply and cutoff of 3.8 MPa steam from the new system.When 3.8 MPa steam is supplied, the control valve needs to reduce its opening; otherwise, the opening should be increased.

2 Existing Problems

The key component in this control system is the control valve, which regulates the downstream system pressure by controlling its opening.Originally, double-seated control valves were used. The control system operated stably when there was no 3.8 MPa steam.However, after adding 3.8 MPa steam together with the startup and shutdown of the steam turbine, the original control valves could no longer meet the application requirements, as shown below:

① Large internal leakage and poor tightness, resulting in the control valve operating at small opening and poor regulation characteristics.

② Severe vibration and high noise of the valve body.

③ High fluid velocity inside the valve caused long-term erosion of the valve plug. The valve stem vibrated violently up and down, leading to fracture at the connection between the valve stem and the valve plug, which directly disabled steam passing through the control valve.

3 Application of V-port Ball Valves

To thoroughly solve the above problems, we analyzed the process conditions and characteristics of various control valves, and finally decided to replace the original double-seated control valves with V-port ball valves.

Double-seated control valves are unsuitable for the above conditions due to complex flow paths, large flow resistance, and small adjustment range. The up-and-down movement of the valve stem results in poor stability of the valve plug and severe vibration.

V-port ball valves have significant advantages over linear-stroke valves due to their structural design.The valve plug of a V-port ball valve adopts an eccentric structure. The plug does not contact the seat except at the closed position, reducing wear. Once opened, the plug disengages from the seat, lowering the operating torque.Meanwhile, the unique V-notch on the plug ensures excellent regulation performance at small openings, solving the problem of poor performance of linear-stroke valves at small openings.

V-port ball valves have a simple, straight-through flow path with low flow resistance and wide adjustment range. As a flow-open valve, its pressure recovery coefficient is higher than that of double-seated valves, making it more suitable for cavitation conditions.

The plug and stem of a V-port ball valve adopt rotary motion instead of linear motion, enabling it to withstand a much higher pressure differential (2.5–10 times that of linear-stroke valves).For high-temperature applications, V-port ball valves adopt a rigid-flexible elastic hard seal to solve the problem of seizure and jamming caused by thermal expansion at high temperatures. High-temperature wear-resistant packing is also used to ensure reliable sealing of the valve stem at high temperatures.

4 Operation Performance

After more than one year of operation, it has been proven that V-port ball valves feature fast regulation response, wide flow control range, almost no vibration, significantly reduced noise, and eliminated hidden dangers in the system.