In addition to a nice selection of renewable fuels such as biogas and wind, the HBPW will also need to add capacity for generating base-load (always on, always available) power for our community in the months ahead. Here’s a look at the two main fuel options under consideration for base load generation:
Circulating Fluidized-Bed Combustion: Fluidized Bed Combustion (CFB) is a solid fuel combustion process by which fluidized beds suspend solid fuels on upward-facing jets of air during the combustion process. The result is a turbulent mixing of gas and solids. The tumbling action, which resembles a bubbling fluid, provides more effective chemical reactions and heat transfer.
CFB provides several advantages over standard coal-fired units, including:
• Reduced emissions: sulfur-absorbing chemicals, such as limestone or dolomite, are used during combustion to remove up to 95% of sulfur emissions from the air while simultaneously improving the unit’s generating efficiency. Additionally, fluidized beds operate at significantly lower temperatures than traditional units, well below the threshold at which nitrogen oxides begin to form—approximately 2,500 °F.
• Fuel flexibility: CFB allows the use of a variety of fuels, from coal and petroleum coke to renewable energy sources, such as biomass from our wastewater treatment plant. This would help us not only to provide cleaner, sustainable energy to our community, but to mitigate price hikes that may be caused by an interruption in the supply of any one fuel source.
Combined-Cycle Gas Turbine: Combined-Cycle Gas Turbine (CCGT) is a gaseous fuel combustion process that utilizes a combination of gas and steam turbines to generate electricity. Heat generated by the gas turbine is used to heat steam, which turns a second turbine, resulting in high efficiency electric generation.
Combined-Cycle Generation provides several advantages over conventional generating technologies, such as:
• High efficiency: CCGT generation can achieve upwards of 60% efficiency, nearly double the average peak efficiency of solid fuel generation, roughly 33%.
• Potential for combined heat/power, or cogeneration: Excess steam given off by CCGT generation can be used to provide district heating or further smaller scale electric generation to businesses throughout the community, as well as for public projects such as the downtown snowmelt system. Cogeneration further improves the efficiency of CCGT generation, making CCGT systems anywhere from 70-90% efficient.
The advantages don’t end there. We encourage you to look for additional information on each of these options. For starters, consider checking out:
• the Electric Power Research Institute at www.epri.com
• the Department of Energy at www.energy.gov
