Biomass boiler stacks

ImageThe photo above shows the boiler stacks at Gundersen Health System’s central plant in La Crosse, Wisconsin. This photo was taken on a cold day in March, 2013, as the new biomass boiler was starting operation. Hospitals require steam to heat buildings, sterilize surgical instruments, remove moisture for air-conditioning systems, and for laundry services, and cafeteria services. Even on the hottest summer days, a large boiler is necessary to support these important processes. In fact, roughly 60% of the energy Gundersen Health System consumes is heat and roughly 40% is electricity.

The three stacks on the left are for the existing natural gas boilers which are over 40 years old and nearing the end of their duty life. The new biomass boiler will be the workhorse for the campus in the future. Natural gas is a clean burning fuel but it is not a renewable resource, emits fossil fuel carbon dioxide, and prices can fluctuate significantly in short periods of time. The stack on the right is for the new biomass boiler which uses woody biomass fuels. Both fuels can be combusted cleanly and the biomass boiler utilizes high temperatures, automated burner controls, an economizer, a cyclonic separator, and an electrostatic precipitator to minimize emissions and capture fine particulates. The biomass fuel specification is also very stringent and eliminates any chemicals or heavy metals from the fuel source … only utilizing pure, organic wood fuels.

The white plumes that you can see from the top of the two stacks is water vapor from the hot gas hitting the cold outside air. The stack temperature on the new biomass boiler is roughly 280 degrees Fahrenheit. The temperature in the firebox approaches 1,000 degrees Fahrenheit, which gives you an idea of the efficiency of the system. Most of the heat is utilized for its purpose in steam production with only a small amount escaping to the atmosphere. In warmer months, these plumes are not visible. The high temperatures and emission systems used on the biomass boiler do not leave a wood smoke odor, which is a common misconception of biomass systems. Gundersen’s staff and the Wisconsin Department of Natural Resources regularly test boiler emissions to ensure that they are maintained at a healthy level and that they comply with air permit codes. The wood resource is a renewable supply of clean fuel, abundant in the upper Midwest region where Gundersen Health System is located.

 

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