Compressed Air Energy Management Through Artificial Demand Control
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Compressed air is used widely across Industry and is often considered the ‘fourth utility’ after electricity, gas and water at many facilities. It is substantive to process requirements, for operating pneumatic tools and equipment, and to meet instrumentation needs. Almost every industrial plant, from a small machine shop to an integrated iron and steel plant, has some requirement for compressed air. Often, the compressor uses more electricity than any other type of equipment. The perception is that air is free but, taking into consideration electricity costs, it is actually one of the most expensive sources of energy.

Fluctuating compressed air supply is a major issue faced in various industries due to the varying rate of demand and supply along with the inability to cater to useful storage. These fluctuations in air pressure lead to increased consumption of energy, interruptions in production schedules; inconsistent equipment performance and variable product quality which further give rise to artificial demand in the process sections.

The Forbes Marshall Master Air Controller (MAC) is an energy saving control system that actively helps control the balance across the demand and supply sides. It introduces a differential pressure between the receiver and itself and thus creates a useful high-pressure storage. This helps in isolating the compressors from the demand surges. Peaks in demand are handled by the MAC, rather than being directed towards the compressors.

This allows compressors to run for longer on no-load. As a result, mass of air is reduced and a high and compressor load cycles are reduced. This decrease in compressor load cycles is directly proportional to the decrease in energy consumed by the compressors. Thus, due to the MAC compressors are protected from artificial demand and have to cater only to base demand, resulting in savings on compressed air energy consumption.

Let’s look at a case, A compressor with a motor rating of 480 kWh operates at a free aid delivery or FAD capacity of 2000 SCFM delivered at 7 bar g pressure. It has a receiver tank which is sized at a capacity of 10 m3 that acts as a buffer for any sudden surge in demands from the end user. The total power consumption, considering 8400 operating hours yearly, amounts to 38,40,000 kWh. After a survey of the site, it was discovered that base demand of the plant was 5.9 bar g and the pressure being delivered was in an excess of 1.1 bar. With the Forbes Marshall MAC, the pressure requirement was reduced from 7 bar g to 5.9 bar g, while considering a leakage of 20%. The observed savings in flow ~ 12% with a reduction of 4,40,840 kWh in total power consumption.