If you take a bunch of dead trees and grasses and shrubs and bury them underground and wait a couple of hundred million years, you get coal: a highly concentrated energy source which has the unfortunate side effect of releasing a very large proportion of carbon dioxide into the atmosphere. But what if you simply took those same trees and shrubs and burned them directly without waiting all that time? You would get biomass, a much less concentrated, but also less harmful source of fuel.
Biomass is less harmful because the carbon it releases into the air had only just been pulled out of the atmosphere during the life of the plants that are burned. This carbon would be released (along with some additional methane) anyway, were the plants left to decompose naturally. Biomass is bulky, but if you have a plentiful source of it and a means to transport it, it can be a very practical alternative to fossil fuels.
The University of Wisconsin’s Madison campus, home to roughly 42,000 students, has made the decision to convert its coal-powered Charter Street Heating and Cooling Steam Plant to run on biomass.
The steam will be used for both heating and cooling, as well as for producing electricity in a process known as cogeneration where high pressure steam is first run through turbines to generate power before being passed through steam pipes for heating in winter or through a lower pressure turbine to run a chiller in summer. The steam plant has both 9MW and 20MW steam turbines, which can be switched in and out depending on the load and the steam available at any given time.
Nationally, biomass produces roughly 11,000MW of electricity, making it the second largest source of renewable energy, after wind. Biomass combustion produces some NOx emission as well as particulates and a small amount of CO2, but since much of the feedstock is diverted from landfills, this can lead to an overall reduction of methane. There are two types of biomass power plants currently employed: biomass gasification, where the methane is collected and burned, and direct combustion, where the organic material is burned as is.
The Madison plant uses direct combustion and will be equipped with state of the art emission controls. Plant operators plan to use an estimated 225,000 tons of biomass, which could be switchgrass, corn or soybean byproducts as well as forestry waste material, collected locally in southern Wisconsin. They are working with the Wisconsin Department of Agriculture, Trade & Consumer Protection to develop the supply chain and plan to work in cooperation with local farmers who might qualify for federal incentives to grow fuel feedstock on marginal land, which can also help with runoff mitigation to reduce flooding and loss of topsoil.
Researcher Heather MacLean of the University of Toronto recently completed a new Biomass Life-Cycle Analysis, which shows that “biomass utilization in coal generating stations should be considered for its potential to cost-effectively mitigate” greenhouse gas emissions. This study was part of the Ontario government’s plan to phase out coal entirely by 2014. It includes the option of mixing biomass with coal as a more modest approach to emission reductions.
Going even farther back, in 2006 a 50MW coal boiler in Portsmouth, NH was converted to run on wood chips using fluidized bed technology.
Back in Wisconsin, the biomass conversion plant is facing scrutiny by some lawmakers who are concerned about its estimated $250 million price tag at a time when the state is running a $2 billion deficit. They wonder if there aren’t some lower cost alternatives such as natural gas that should be pursued instead. But when you consider the fact that Wisconsin spends close to $20 billion annually on coal that comes from out of state, the fact that all of that could be replaced locally has to have a positive effect on the local economy. “When you get off of coal, you create local jobs,” said David Jenkins, director of commercialization and market development with the state Office of Energy Independence. “That’s never been more important in my lifetime than it is right now.”
John Harrod, Director of Madison’s Physical Plant, says that public support for the project has been strong, but he’s heard the arguments from all quarters. “In the end, we’re just looking for a sustainable source of fuel that we can use to heat our campus for years to come.” This is the kind of gift to the future that is a hallmark of sustainable thinking.