I. Background Analysis

This client is a factory engaged in the production and processing of auto parts. The factory is equipped with 12 machining equipment units, and a GA160W air compressor has been installed for these machines. The surface of the machined parts contains a large amount of aluminum chips and coolant mixed oil, so they need to be spray-cleaned with hot water and chemical cleaning agents. For this purpose, the factory has also installed a hot water boiler with a maximum power of 500 kW for the parts cleaning line.

As we know, 100% of the electrical energy consumed by the air compressor is dissipated in the following forms:

  • 75% of the electrical energy is converted into heat stored in the hot oil and removed by the oil cooler
  • 10% of the electrical energy is converted into heat contained in the compressed air and removed by the air cooler
  • 10% of the electrical energy is converted into heat lost through radiation and uncontrollable internal compression losses
  • 5% of the electrical energy is lost as motor heat

It can be seen from the above that for the GA type oil-injected screw compressor, approximately 75% of the energy is consumed in the hot oil circuit. The heat recovery unit is designed to recover most of the above heat in the form of hot or warm water without any negative impact on the compressor performance, with a recovery rate of 65%~75% of the actual input shaft power.

II. Energy Recovery Analysis and Calculation

The actual working pressure of the GA160 air compressor currently used by your company is 6.5 bar. According to the standard data of Atlas Copco, the actual input shaft power is approximately 160 kW.

The recoverable energy calculated at 70% is: 160 x 70% = 112 kW

Based on full-load operation of a single air compressor, the daily recoverable energy (24 hours) is: 112 x 24 = 2688 kWh

Converted to heat energy: 2688 x 3600/4.2 = 2304000 kcal

Considering a 15% heat loss in the external hot water pipelines, the effective daily heat energy available from one GA160 (24-hour full load) is approximately: H1 = 2304000 x 85% = 1958400 kcal

With a return water temperature of 65 C, the system can continuously produce water with a 10 C temperature rise (up to 75 C) at a rate of about: 1958400/1000/10 C/24 = 8.16 tons/hour

Daily gas cost savings: approximately 1,185 RMB/day