Deposits of unconventional fuels—both crude oil and natural gas—occur in geological environments with very low energy. The exploitation of these low-energy deposits/reservoirs will require...
A new future for small coal-fired plants.
of crop waste really represent the most important rate-limiting factors.
Fortunately, there is an emerging solution to many of the dilemmas posed by crop waste as a power-generation fuel—biocoal. Biocoal is a fuel produced from biomass whose physical and chemical properties have been changed so it looks and acts to a large degree like coal. It’s important to note that biocoal, as the term is being used here, isn’t simply densified biomass. Instead it’s a plug-and-play coal substitute.
Biocoal is produced from biomass with a combination of chemical and physical processing. Chemical processing is used primarily to remove impurities, while physical processing is used primarily to increase energy density. Crop-waste biocoal is simply coal made from crop waste.
Biocoal has physical and chemical properties that are much closer to coal than raw biomass, and can often be used in existing coal boilers with minimal or no modifications. It typically has a heat content (gross calorific value) of 3,500 to 4,500 kcal/kg (or 6,000 to 7,000 Btu/lb), similar to low grade coal.
Biocoal has only recently and partially emerged from the research stage, and the path to commercial biocoal production hasn’t been smooth. There have been numerous false starts and dead ends, but momentum now appears to be building—despite difficult economic conditions and uncertain environmental regulation. RWE, a major European utility, and Topell, a clean energy technology company, recently announced plans to build the world’s first biocoal plant, a 60,000 tons-per-year facility located in the Netherlands. And Global Bio-coal Energy reportedly is working to develop a 120,000 tons-per-year biocoal facility in Vancouver, Canada. Both of these plants are expected to rely primarily on wood waste, although their processes might be appropriate for a broader range of feedstocks including crop waste.
In the United States and elsewhere, considerable progress has been made specifically in crop-waste biocoal. In terms of R&D, extensive research is happening at organizations such as the Energy and Environmental Research Center in North Dakota. On the commercial side, startups and established firms are moving the technology past the R&D stage. For example, Xcel Energy funded extensive work by Bepex, a Minnesota chemical and physical processing firm, on the design of a commercial facility to produce biocoal from corn stover.
While cost estimates are difficult to obtain and remain uncertain, the incremental delivered cost of finished biocoal over raw biomass ranges from as little as $50/ton or $3/MMBtu to as much as $75/ton or $5/MMBtu. These figures likely will be reduced by as much as 50 percent over the next several years as the technology and infrastructure improves.
Given projected availability and price, biocoal could be catalyst for bridging the gap between the crop-waste biomass supply and the small-coal unit demand.
Economic and Environmental Benefits
The potential economic and environmental benefits of biocoal are best illustrated through a concrete example. This example is built on data obtained from public sources, including available reports on the Charter Street and Capitol generating units in Wisconsin. However, the example is illustrative and the analysis isn’t intended to represent any specific unit.