Optimal fan speed and compression ratio of an air-condensed vapor-compression ammonia recycling system

• Thermodynamic model for the ammonia recycling system was developed.
• Cost function was given to determine the optimal control variables.
• A solution scheme was proposed to solve the cost function.
• The matching of ammonia mass flow rate and air flow rate are optimized.

In the technology of liquid ammonia modification, the ammonia is recycled by compression and condensation. To minimize the energy-consumption of ammonia recycling system, compression ratio and fan speed are optimized. Thermodynamic models for the compressor and evaporative condenser are developed respectively. Mathematical equations are given to determine the optimal compression ratio and the corresponding fan speed ratio. To solve the equations, a numerical algorithm is proposed. By controlling the fan speed, the matching of ammonia mass flow rate and air flow rate can be optimized, which brings about the minimal energy-consumption. When the wet-bulb temperature is 22 °C, the system energy-consumption could be saved by 10.8–12.9% under optimal compression ratio and fan speed.