Process Cooling Of Engine/Generator Sets With Reuse Water

By Dr. Marcus N. Allhands, PE, Vice President of Business Development, Orival, Inc.

Located along the banks of one of the largest tributaries to the Mississippi River, this 100 MGD (million gallons per day) wastewater treatment plant (WWTP) has a large demand for service water with low suspended solids. Nearly 3 MGD of water are needed for various on-site services but perhaps none as important as cooling large V-12 internal combustion engine/generator sets. These engines run off of methane gas produced on-site from the anaerobic sludge digestion process. The cooling process passes water one time through the engine blocks and then discharges the water back to the head of the WWTP. Therefore, this cooling water must be free of organic and inorganic particles that could interfere with heat transfer at the engine wall/water interface. The power produced by these engines can supply nearly all the electricity needed to run the entire wastewater treatment plant. However, if the engines overheat, safety controls shut down the engines and stop electricity production until the cooling problem can be solved. This immediately switches all power necessary to run the myriad of motors on pumps, aeration blowers, sludge presses and automated treatment equipment to purchased electricity. If this cooling process was to use potable water, as in many other facilities, the cost of this cooling water would nearly offset the savings of on-site power generation. An automatic self-cleaning screen filtration system provided by Orival, Inc. was installed recently using effluent from the wastewater treatment process for this non-potable cooling requirement saving enough potable water each day to supply an additional 500 homes in the area.