City of Missoula Cogeneration System Upgrades
Helping Reduce Carbon Emissions
Morrison-Maierle was contracted to provide the preselection of the cogeneration system, electrical and mechanical design, bidding, and construction oversight for the installation of a cogeneration system for the City of Missoula Wastewater Treatment Plant (WWTP). The main goal for the installation of a cogeneration system was to use all the biogas produced by the facility to create electricity and heat for the plant and remove the need to flare the biogas during portions of the year when heat is not needed.
The team selected a system with respect to efficiency, ease of operation, maintenance, and overall effectiveness to find a solution that best fits the needs of the city’s staff who operate the CHP system. It also meets the requirements as lined out in the city’s conservation and climate action plan.
Services & Highlights
Pre-selection of the cogeneration system
Electrical and mechanical design
Coordination with supplier’s design team and subcontractor for controls design and programming
Helps city meet its carbon emission reduction goals
Produces 100% of the plant’s electrical usage during an average winter day
Producing over 24% of the plant’s electrical usage
Starting with a Study
The City of Missoula hired Morrison-Maierle to study adding cogeneration equipment to the WWTP. A cogeneration system would generate electricity and useful thermal energy for the plant from the biogas that is produced as part of the solids stabilization process at the plant. As a result of this initial study, the city contracted Morrison-Maierle to design and provide construction administration for the installation of a new cogeneration system.
Cogeneration systems are facilities that use a fuel source to generate electrical power while simultaneously providing thermal energy for process or heating loads. These systems are commonly referred to as combined heat and power (CHP) systems. The system they selected is a gas-fired, reciprocating engine style. A preselection process was performed to select a specific unit that the electrical and mechanical design would be based upon. This process entailed providing the production amount and quality of the biogas that would be used as a fuel supply to the unit. From that information, the supplier sized a unit that would consume the current biogas production plus allow for higher levels of gas consumption as the population base increases in the community and the biogas generated by the plant increases.
The CHP System
The unit installed at the WWTP is 220kW rated which is de-rated to 190kW due to the altitude at the site. Additional gas filtration and dehumidification were added as part of the manufacturer’s supplied system. A natural gas blending system was also added to the system to even out the fluctuations of the biogas production at the plant.
The electrical output of the cogeneration system is connected to the larger of the two utility services at the plant and the unit’s heat output is connected through a glycol/water loop and heat exchanger to the WWTP hot water heating loop that currently supplies the building and process heat for the plant. The current electrical output of the unit is 150kW with a 10% natural gas mixture. The current heat output is 754.5 MBH, which is available for use by the plant processes and building heating.
At the current operational levels, the cogeneration system is producing more than 24% of the WWTP’s electricity and heat required on an average winter day in Missoula.