The main cause of boiler inefficiency is heat loss, and upgrading the controls is one of the most effective ways to recapture lost heat in an existing system. There are several control options available, depending upon a facility’s needs and goals. To increase boiler system efficiency and reduce costs, consider the following:
FACILITY REAPS THE BENEFITS OF A CONTROLS RETROFIT
A wastewater treatment plant in West Hill, Ontario, relies on five, 400-hp, Cleaver Brooks hot-water, firetube boilers to treat wastewater for a half a million area residents. The plant’s boiler controls were outdated and compromised the system’s efficiency. In addition, the two newest models (1998) had 30 ppm NOx reduction capabilities, but the plant’s three older boilers did not. The plant wanted to bring all of its boilers into compliance with CCME (Canadian Council of Ministers and the Environment) guidelines. After analyzing their options, plant management determined that upgrading the controls would meet both their efficiency and emissions goals.
Plant management contacted Kevin Kingston, sales and project manager for Johnson Paterson Inc., in Aurora, Ontario. Based upon the treatment plant’s needs and goals, Kingston recommended the following:
The conversion took place in three phases, beginning in June 2010. It was completed in January 2012. The wastewater treatment plant expects annual fuel savings of 12% to 15%.
There are several reasons for the anticipated double-digit fuel savings. First, the new boiler controls enable the plant to operate on digester gas more continuously, which also decreases the rate of natural gas consumption. The plant only uses natural gas as a backup fuel. Prior to the conversion, the older boiler control system was not able to provide proper boiler sequencing and controlled fire rates, so natural gas was tapped frequently.
In addition, the new Hawk master boiler lead lag sequencing control was interfaced with the boiler building SCADA system, providing operator interface with the individual boiler control panels and the master boiler lead lag sequencing control. The design engineer for the project wrote a strategy to control the main heating system’s circulating pumps based on the plant's heating loads. Summer heating loads require lower flow rates than the winter heating loads. The Cleaver-Brooks Hawk control systems are programmed to transmit a signal to the main remote processing unit (RPU). Depending on the number of boilers operating and the rate of firing, flow rates will increase or decrease to the main heating pumps, controlled by new VSDs, to match the heating loads.
Lastly, with 10:1 burner turndown, there is less cycling, and repeatability in the management of the fuel mixtures through the new parallel positioning controls. TB