Hamilton's Wastewater Treatment Plant Cogeneration Facility

摘要

This paper describes a project which captures a waste product's (sludge) energy value (biogas) by combining it with a valuable natural resource (natural gas) in recycled, redundant assets (the gas engines) using another by-product (waste heat) to provide a win-win-win energy efficient and sustainable embedded cogeneration plant. The paper commences by outlining the USD27 million secondary treatment upgrade of the Pukete Wastewater Treatment Plant in Hamilton. The upgraded site would require more electricity, more heat for the new high temperature digesters, generate more biogas and need more standby power in the event of a mains power outage. The circumstances which led the owner, Hamilton City, to come to an agreement with its energy supplier On Energy (previously Natural Gas Corporation) and the network provider (WEL Energy) for an embedded generation project are outlined. The availability of two second hand 920 kW gas engines led to the innovative use of a blender valve and controller to continuously mix low pressure, low calorific value biogas with high pressure, high calorific value natural gas into a standard spark ignition gas engine. Waste heat from the gas engines is used to heat and digest the sludge from the treatment plant. The site heat loop was modelled to ensure that it was sufficiently responsive to meet all the varying requirements of sewage throughput, biogas production, electricity site use and export. The electrical connections and control enable the cogeneration plant to use all the biogas, heat the digesters, supply the plant load and (by using natural gas) export electricity into the local network when the electricity market price is right. The cogeneration plant can also operate in an isolated mode when the network fails to ensure that the essential treatment plant equipment remains operational and effluent quality is maintained. The paper concludes with the recipe for a successful project through the co-operation of the various parties.