Bay View Waste Water Treatment Plant
Since the early 1950s, the plant had used the digester gas to power the engine-driven aeration blowers. This equipment had survived well beyond its useful life, and was being replaced with modern blowers driven by 1500 HP electric motors. With that background, the backup power project was developed to provide six new Caterpillar generators: (1) 3516, 2 MW Diesel, (3) 3520, 2 MW Natural Gas, and (2) 3520, 1200 RPM, Digester/Natural Gas. These new generators, along with one existing 1650 kW diesel generator are connected to a new lineup of Russelectric Generator Control Switchgear. Heat recovered from the two digester gas generators is used to heat the digesters.
JDRM Engineering services included designing several modes of operation available to the plant. Typically one or both of the digester gas units (depending on the amount of gas available) will run continuously in parallel with the Utility to utilize the digester gas. If there is a Utility outage, all of the generators start and come on line to backup the plant. For improved reliability during a power outage, the digester gas generators will switch over to natural gas. If the power outage is going to be long term situation, the plant can shut down excess generators. Typically four generators are kept on line. If the plant load is stable, both diesels can be shut down, and the plant backup power is fueled entirely by natural gas. If plant demands require starting up a large load, such as an aeration blower, one of the diesel generators is first brought back on line.
In a peak shaving mode, all of the generators are capable of being run in parallel with the Utility. Peak shaving is accomplished in a “base load” mode or an “import set point” mode. In the base load mode, the generators are set to produce a fixed amount of kW and the remainder of the plant load is supplied by the Utility. In the import set point mode, the amount of plant load supplied by the Utility is fixed and the rest is made up by the generators.
Cooling for the generators is provided by a fully redundant cooling tower system. Engineering design encompassed three towers and each included two cells. Only two towers are required for the six generators. The pumping system is also fully redundant, with two sets of pumps.
The overall design process was approximately thirteen months.
Schematic Design Phase (Preliminary Design Documents) 4 months
Design Development Phase (Design Documents 60% complete) 5 months
Construction Documents Phase (Ready for Bidding) 4 months
Halfway through the Design Development Phase, pre-purchase bid documents were issued for the generators and switchgear, as those pieces of equipment required a long lead time.