Control scheme for the tower top condenser in the gas separation unit
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Control scheme for the top condensers in the gas separation unit: The control schemes for the top condensers of the propane tower and the propylene distillation tower in the gas separation unit employ thermal bypass control; there is also another approach known as the bottleneck control method. Please discuss the advantages and disadvantages of these two control schemes
There are generally two approaches to controlling the pressure at the top of a condenser: 1. The approach of controlling the refrigerant flow rate, which is commonly used in condensers where phase changes occur in the shell side. 2. The approach of controlling the gas-phase stream to bypass the condenser, which is often used in condensers that utilize circulating water as a refrigerant (or some other inexpensive refrigerant). Typically, the design capacity of a condenser is set with a margin of safety. If the first approach is adopted and circulating water is used, it will be necessary to throttle the flow rate of this water significantly during the initial operation phase; however, too low a flow rate of circulating water is detrimental to the heat exchanger, as it accelerates scaling. For materials with a relatively simple composition at the tower top, the first approach yields slightly poorer stability control compared to the second approach.
Could you provide a detailed explanation of the PID process for the tower top condenser control scheme?
1. The control tower pressing method that restricts progress is rarely seen in current designs. Because it affects the equilibrium of the distillation column, resulting in poor control stability. 2. For the propane column, if propylene is used as the refrigerant, the column pressure can be controlled by regulating the refrigerant liquid level; additionally, an exhaust line at the top of the reflux drum is used to jointly control the column pressure. If circulating water is used as the coolant, thermal bypass is employed for control. In propylene towers, circulating water is generally used as the coolant; heat bypass is employed to control the tower pressure, with a discharge line at the top of the reflux tank used in combination for control.