Industrial Utility Efficiency    

Compressor Controls

It was early summer, the air compressors were above the production floor on a mezzanine, and temperatures were heating up both outdoors and indoors. The compressed air system was comprised of three 500-horsepower centrifugal air compressors, and one 350-horsepower variable speed drive oil-free rotary screw air compressor.
The U.S. Department of Energy estimates that air compressors use as much as 10% of all electricity generated in the United States. Further, the DOE calculates that as much as 50% of this energy is wasted. Compressed air leaks alone account for 25-30% of compressed air use.
The objective of a compressed air management system is to improve the Key Performance Indicator (KPI) of “Energy Intensity” as it relates to compressed air. This translates into improving the ratio between the volume of product shipped and the net electricity (kWh) consumed by the compressed air system. How many thousand bottles, per compressed air kWh consumed, were shipped this month?
Production processes get their energy from the air stored at higher pressure in the piping distribution system. The air compressors simply replenish the air that is consumed. It is an important distinction to make. The energy input in compressing the air is supplied to the connecting pipes for delivery to the various demands throughout the facility.
Pneumatic air cylinders play a major role in allowing a modern sawmill to produce at the high-speed production rates required. Stable air pressure is critical to allow the air cylinders to respond in a timely manner and avoid any production delays.
Recently, this major pulp & paper mill made compressed air optimization a mill-wide priority. At the request of the utility company providing energy to the mill, Compression Energy Services performed a comprehensive energy analysis that outlined the following four energy efficiency measures (EEM’s) for the mill to consider.
“First there are the old conventions. The majority of compressor houses still employ fixed speed compressors and a cascaded pressure switch control system. This arrangement will be familiar to many, but it is outdated and inefficient, and needs to be changed. There is a comfort factor with familiar technology, which is exacerbated by constant time pressure due to other day-today responsibilities and a lack of information and good advice on what can be achieved.”  
A Tier 1 automotive plant was spending $364,259 annually on electricity to operate their compressed air system. This figure was expected to increase as electric rates were forecasted to rise from their current average of 7.16 cents per kWh. Our firm, Air Power USA, conducted a full supply and demand-side compressed air system assessment. The set of projects recommended by the assessment, would reduce these energy costs by $218,670 or 60%.
“Compressed air systems with multiple compressors operating to supply demand requirements present unique challenges in compressed air system control schemes.”
This pharmaceutical plant spends $265,100 annually on energy to operate the compressed air system at their facility. This figure will increase as electric rates are projected to be raised from their current average of 7.7 cents /kWh. The set of projects identified in the compressed air system assessment could reduce these energy costs by $139,300 per year (52%).
The $mart Sequencer® is an air compressor control system designed to reduce a plant’s energy costs by continuously monitoring system demand and automatically selecting the most energy efficient combination of available air compressors.