Practical considerations in energy efficient compressor set-point control strategies

Compressed air supply and demand strategies have received significant attention since integrated demand management was initiated by Eskom. Due to the expensive nature of this vastly utilised energy carrier, every increase in the efficiency of a system is needed. Usually controlling the compressed air demand resulted in a reduced need for supply, ultimately leading to energy savings. The majority of compressed air optimisation projects on deep level mines in South Africa utilise demand side management initiatives to control or reduce compressed air usage. However, reduction in usage through control, leak repairs and reduced demand often results in system pressure build up. Compressed air supply must also then be reduced accordingly using capacity controllers. The existing capacity control is typically upgraded to reduce compressor output capacity automatically. The problem encountered is that not all compressor controls are created equal, and they produce different results in terms of efficient supply reduction. Inefficient compressor control is frequently encountered in industry today. On average, compressors operate at 16% below their maximum efficient point due to inefficient surge and capacity controllers. In contrast to this, intelligent compressor control resulted in compressors operating within 9% of their maximum efficiency point. In this case study, financial savings of R 3-million per annum could be realised.