Digester Gas Energy Recovery - Deciding Between Driving Blowers or Making Electricity

摘要

The Rivanna Water and Sewer Authority operates the 57 ML/d (15 mgd) Moores Creek WWTPin Charlottesville, Virginia. Residuals from the treatment plant are thickened and stabilized viaanaerobic digestion prior to dewatering. The facility had relied on gas engine-driven aerationblowers equipped with a waste heat recovery system to provide hot water for digester andbuilding heating. The engine-driven blowers routinely utilized supplemental natural gas toproduce sufficient hot water for digester heating, resulting in excessive aeration. The existingaeration blowers were replaced with motor-driven high-speed direct-drive centrifugal blowers,and a combined heat and power (CHP) system for electrical power generation from digester gaswas installed during a recent facility improvements project. Heat recovered from the CHPsystem is used for digester heating with supplemental heating provided by a new hot waterboiler. The energy efficiency improvements at the Moores Creek WWTP provide substantialsavings in purchased natural gas and electrical power while providing an economically andenvironmentally sustainable alternative energy product (digester gas). The energy improvementsalso enhance nutrient removal performance by eliminating digester heating’s dependency onoperation of the aeration blowers.