MSU Extension

The utility-scale production of electricity has relied on coal as a feedstock for many years. Michigan uses coal to produce about 54 percent of the electricity used in the state. But many regulators are placing considerable pressure on coal-powered facilities because of concerns about emissions. The demanding regulatory environment, mandates for renewable energy and deteriorating public opinion of feedstocks that cause greenhouse gas emissions have many utilities evaluating alternative feedstocks, including woody biomass, crop residue and dedicated energy crops.

Just as the historical generation of electricity has relied on several feedstocks – coal, natural gas, nuclear and hydro – the future scenario will likely include multiple feedstocks as well. Natural gas is in ample supply and therefore low in cost, and it is lower in emissions than coal. Though it is also a fossil fuel, it serves as a transition to renewable energy sources needed for sustainable electric power. We already see some of these new generation sources, such as the wind turbines that extend above the horizon in several areas around Michigan. Solar panels are also contributing to the renewable energy profile. Each energy source has its advantages and disadvantages. Wind and solar technology both utilize an undeniably renewable source of energy -- the wind and the sun. The challenge to these is the fact that they are intermittent -- they rely on air movement and the sun shining -- and may not always align with power demand. This contrasts with historical generation, which is considered baseload -- this means that the electrical output is always available and can be dispatched to match varying customer demand. The variability in output from day to day and even within one day makes it difficult for power companies to keep adjusting output from conventional feedstocks (coal and natural gas) to meet the current demand.

If a significant portion of our baseload generation is to be switched away from burning coal, then how will the baseload electricity be provided? Some experts say that using the existing infrastructure for baseload electricity should be a primary goal to extend the investment in electric power generation capacity. Where existing boilers and furnaces are feedstock-flexible, the switch to an alternative feedstock is relatively simple. But where boilers and furnaces are designed specifically to burn coal, such as pulverized coal systems, alternative feedstock options are more limited.

Alternative feedstock options can be evaluated by looking around us and using what is available and abundant. It is no surprise that plant biomass can be burned and is a good source of energy. Our ancestors burned wood and other plants for various uses. So why not use plant biomass in place of coal? It can be used instead of coal in feedstock-flexible boilers and furnaces but not so well when feedstocks must be pulverized. A promising plant biomass processing technology called torrefaction could change this.

Torrefaction is a biomass processing option that involves heating raw biomass to temperatures ranging from 250 to 300 degrees Celsius (480 to 570 degrees Fahrenheit) with low or no oxygen to produce a charcoal-like fuel. Torrefaction is driven by the combustion of volatile gases that are released from the heated biomass and subsequently recovered and recycled to fuel the process. The reduction of volatiles and moisture reduces the mass of the plant material by 30 percent while consuming only 10 percent of the original energy content. The torrefied product is characterized by higher energy density, improved storability and less costly shipping after pelletization, and it can be pulverized like coal.

Torrefied biomass is a renewable fuel that is high in energy density, low in moisture content, resistant to moisture absorption and readily mixable with coal at conventional pulverized-fuel-fired boilers at power plants. Furthermore, these qualities benefit existing power facilities by minimizing the amount of new capital investment required of power producers to utilize biomass – the cost of a torrefaction facility is much less than that of a new power plant.

Michigan State University is one of several institutions researching torrefaction and the utilization of torrefied biomass along with bioenergy plantations on non-cropland. The T.B. Simon Power Plant at MSU is adopting transitional practices including increased use of plant biomass. The research and lessons learned in this process will be valuable to utilities and consumers across a wide area and will be widely disseminated with help from Michigan State University Extension.

According to Michigan State University Extension, Michigan is home to 19 million acres of forestland and 10 million acres of farmland that can supply feedstocks to the alternative energy industry. This local supply can replace a substantial portion of fossil feedstocks such as coal and natural gas that are now imported into Michigan.

Mark Seamon is a MSU Extension bioeconomy innovation counselor. He can be reached at seamonm@msu.edu.