Vacuum control method for distillation tower
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Sea friends, how is the vacuum level controlled in a distillation tower? The vacuum pump is a screw pump; the required vacuum level is -75 KPA, but the pump is capable of achieving a vacuum level close to absolute zero. How do I adjust the vacuum level? Should a control valve be placed in front of the vacuum pump, or should the exhaust gas be routed behind the vacuum pump and connected to the intake pipeline with a control valve there? Or in some other way? Primarily, what’s needed is the most stable control method; I would be grateful if experts could share their insights. Thank you! !
Your requirements can be met by controlling the amount of air entering the vacuum pump or by increasing the backflow at the inlet of the vacuum pump
The frequency converter changes the speed of the screw pump, thereby altering the backflow between its outlet and inlet.
The inlet air volume of the vacuum pump’s frequency conversion or regulation equipment can be adjusted
Theoretically, installing an inlet PV valve is more effective for pressure control, but the following factors need to be considered: 1. The gas volume in the main process can vary significantly under different operating conditions. Two PV valves are needed to handle it. 2. Once the process flow rate becomes very low, the opening degree of the PV and the flow rate passing through it become decoupled, and continuous pressure control turns into ON/OFF control. Alternatively, using a bypass PV for the pump is also a method (equivalent to adding nitrogen). For a more luxurious version, the pump is equipped with speed control, and the load can be set manually to match the flow rate.
A pressure stabilizing tank can be considered, with valves on the tank to regulate the vacuum level
Add an inverter or a return air control valve
1. A buffer tank is installed at the inlet of the vacuum pump to prevent unstable flow rates at that inlet. 2. Install return pipes for the vacuum pump’s outlet pipe and inlet pipe, controlled by manual gate valves. 3. A control valve is installed before the tee connecting the return pipe and the inlet pipe to finely adjust the air volume in the system, thereby stabilizing the system pressure.
The screw vacuum pump can regulate the vacuum level by means of variable frequency speed control
Adjust the vacuum pump using frequency conversion, or install automatic control valves on the tower to connect it to the atmosphere for regulation (in this approach, it is necessary to ensure that air can enter without causing any safety issues)
The exhaust gas from the condenser at the rear of the vacuum pump is led to the inlet pipe of the vacuum pump through a branch pipe. The amount of return gas is controlled by a control valve, and this control valve is interlocked with the pressure at the top of the distillation tower, thereby enabling stable control of the vacuum level in the distillation tower.