Process Control of Ice Plant System- Precise Full Range Bidirectional Automatic Control of Expansion Valve with Unidirectional Pulses

The parameters which are influencing the efficiency of Ice plant refrigeration process control system are torque (motor pulley size) of the induction motor, ammonia gas pressure, opening of expansion valve, salt solution density, atmospheric temperature etc. Presently, the ice plant system is equipped with manually controlled expansion valve. The thermo-dynamic property of ammonia gas is continuously changing during one complete cycle of water to ice block formation. Under this situation, the expansion valve delivers ammonia gas and partially ammonia liquid in to the cooling coil. The ammonia liquid does not contribute to the heat transfer between water and ammonia liquid and hence goes as a waste and reduces the efficiency of the system. The proposal is for automatic adjustment of expansion valve. using Delta-sigma modulator (DSM) based control circuit. The proposed control circuit provides precise full range bidirectional automatic control of expansion valve with unidirectional pulses. The proposed control circuit ensures that the refrigerant ammonia circulates in the cooling coil in gas form only. The expansion valve is controlled by a stepper motor which in turn controlled by the proposed control circuit. The proposed technique reduces the ice formation time and power consumption.