Cylindrical tank level control

Three vertical cylindrical tanka (10 feet high, 10 feet diameter) are used in a process. Two tanks are process tanks and are level controlled by manipulating outflows using proportional-only level controllers (PB 100). Level transmitter Spans are 10 feet. Control valves are linear, 50 percent open at the normal liquid rate of 1000 gpm, air-to-open, constant pressure drop. These two process tanks are 50 percent full at the normal liquid rale of 1000 gpm. 

The liquid flow rate from a vertical cylindrical tank, 10 feet in diameter, is flow-controlled. The liquid flow into the tank is manipulated to control liquid level in the tank. The control valve on the inQow stream has linear installed characteristics and can pass 1000 gpm when wide open. The level transmitter has a span of 6 feet of liquid. A proportional controller is uaed with a gain of 2. Liquid density is constant. 

The process sketched in Fig. 1.6 consists of two vertical cylindrical tanks with a level controller on each tank. The feed stream to the first tank comes from an upstream unit. The liquid level in each of the tanks is controlled by manipulating the flow rate of liquid pumped from the corresponding tank. The level signal from the level transmitter on each tank is sent to a level controller. The output signal from each controller goes to a control valve that sets the outflow rate. 

The liquid level h, ) in a tank is held by a PI controller that changes the flow rate F(,) out of the tank. The flow rate into the tank Fo(,) and the level setpoint are disturbances. The vertical cylindrical tank is 10 ft in cross-sectional area. The transfer function of the feedback controller plus the control valve is... 

Another level control situation where a nonlinear element might be introduced into the loop is the case of level control of a cylindrical tank lying on its side, shown in... 

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