Improved Air Compressor Controls Help Church-Dwight Slash Energy Consumption
BY CHRIS KANOFF, ROCKY MOUNTAIN POWERFebruary 28, 2013
As much as 40 percent of electricity to power air compressors in some industrial plants is wasted through inefficient compressor controls, according to an Office of Energy Efficiency and Renewable Energy report. Utilities and other energy efficiency organizations can help companies save energy and money by sharing best practices and by offering technical services to identify and quantify energy efficiency upgrades, as well as incentives to help reduce the payback for upgrades.
An example is the Green River, Wyo., plant of Church & Dwight, the manufacturer of Arm & Hammer Baking Soda, powdered laundry detergent and cat litter. Compressed air supports production, including the transport of raw materials and finished products at the plant. The Green River facility has three compressor rooms. Each room contains two compressors that feed into air dryers and receivers and feed the common air delivery system (see Figure 1). Standard practice at the plant was to run more compressors than needed to ensure an adequate peak air supply to the plant. Even when the laundry detergent line was shut down three days a week, its compressed air lines remained pressurized because of processes that required static pressure. A sufficient number of compressors were run to meet the peak demand required by the dense phase transport process. Compressors were turned on manually and used variable displacement and inlet modulation for part-load control. As demand decreased on each compressor, variable displacement decreased the power to about 70 percent at 50 percent flow. As demand decreased further, the inlet would begin to modulate, further reducing flow and power until the discharge pressure eventually reached the unload set point. Once reached, the compressor would unload, but instead of allowing the oil sump to fully blow down, the compressor would recirculate air, keeping power at about 62 percent all the way down to zero air delivery. Because of the excessive number of compressors that were running, many of the them were at that less than 50 percent position-effectively flatlined. Compressor power was fairly constant independent of demand. Church & Dwight was not aware of the delivery of each compressor because there was no gauge or flow meter to indicate actual load. As a result, the plant was consuming more than twice the energy needed for an optimal system. Beside the electrical compressors, the plant ran a diesel, engine-driven compressor full time to ensure enough air was available. Tuning a complex system such as this to improve efficiency is more difficult with the control inputs' being made at the compressor rather than via a central control system. Because of control inefficiencies, it also is typical for the plant to run the system at a higher pressure than necessary to meet production needs. These factors combined to waste as much as the aforementioned 50 percent of the energy used to provide compressed air.