Composition of control valve in gas purification unit

Modern technology attaches importance to innovation and progress in industry and common equipment. For example, the modern use of physical methods to separate the oxygen in the air, and the equipment to obtain nitrogen, nitrogen generators are mainly divided into three types, namely, cryogenic air separation, molecular sieve air separation (PSA) and membrane air separation. The control valve is a very common terminal control element of the air separation equipment, such as the guide vane of the compressor and the nozzle of the expander.

The control valve is composed of valve body, valve trim, actuator supplying valve driving force and valve accessories. Typical valve accessories are composed of electric valve positioner, solenoid valve, limit switch and filter pressure reducing valve. In order to control the care time of the valve, some accessories such as booster, damper and quick discharge valve need to be added.

Gas purification unit

The control signal output from the control surface of the nitrogen generator is input to the electric valve positioner, which converts 4~20mA signals into gas signals to actively adjust the stroke of the actuator. Through the feedback system, the stroke and signal are changed proportionally, and then the correct positioning of the valve is completed.

In the accessories of the control valve, the general electric valve positioner is mainly used to complete the continuous dispatching of the valve, and the solenoid valve can complete the full opening or full closing of the valve when the safety interlock is required. The accessories are different according to the control requirements of the control system for the valve. The connection between control requirements and DCS control signals and accessories (electric valve positioner, solenoid valve) of the valve is generally clarified in three situations.

Here, it is necessary to clarify that the valves of nitrogen generator can be divided into two types according to the function of the whole machine: gas on and gas off (gas off). Air opening means that the opening increases with the increase of signal pressure. When there is no air signal, the valve is fully closed; With the increase of gas signal pressure, the valve will gradually close, when there is no gas signal.

There is also a corresponding to the above situation that the equipment is in the full-open mode. The operation mode has changed to a certain extent. The actuator can be divided into positive action and reaction according to the direction of the displacement of the push rod. The signal pressure increases and the push rod moves downward is positive; On the contrary, it is called reaction. The direct stroke single-seat air-opening valve selects the reaction actuator, and the air-closing valve selects the positive actuator.