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.
majority of crop wastes are concentrated in the Great Lakes and Upper Midwest region—the same region with a majority of small coal units, as shown in Figure 3. This suggests a natural and remarkable match between the crop-waste supply and the small coal unit demand. For example, Iowa has an estimated 1,200 MW of small coal units, and an estimated 24 million tons of annual crop waste, enough to supply perhaps 2,000 MW of baseload generation. Minnesota has an estimated 1,000 MW of small coal units and an estimated 14 million tons of annual crop waste, enough to supply that same 1,000 MW of baseload generation. Ohio has an estimated 1,100 MW of small coal units and an estimated 5 million tons of annual crop waste, enough to supply perhaps 400 MW in baseload generation. The list goes on. On a state-by-state basis, there appears to be a reasonable match between the amount of small coal-unit capacity and the amount of available crop waste.
Of course, while transportation costs are a major issue, there’s little reason that all crop waste must be used within the state where it is generated. Taking a regional perspective, in the NERC ECAR, MAIN and MAPP regions, which overlap quite closely with this Upper Midwest and Great Lakes region, there’s an estimated 130 million tons of available crop waste at $5/MMBtu. 5 This is enough to supply roughly 10,000 MW in baseload generation. The bottom line is that there appears to be sufficient crop waste biomass to fuel most if not all of the small coal units in this region.
However, while crop waste contains the necessary Btus of energy, the physical and chemical nature of raw biomass makes this apparent match far from perfect.
On the physical front, raw crop waste isn’t dense, and is therefore difficult and expensive to collect, transport and store. Crop waste is typically one-quarter to one-fifth as dense as coal. Crop waste also has relatively low calorific value, perhaps one-half to one-third that of coal. All told, crop waste produces perhaps one-tenth the energy of coal on a volume basis, and this hinders the potential for using crop-waste fuel in power plants. In addition to the volume issue, crop waste is relatively difficult to use as a boiler fuel. It isn’t uniform in size and doesn’t crumble or pulverize easily, making it unfit for many existing boilers.
On the chemical front, crop waste is highly variable in composition. This is a difficulty in itself since many existing boilers are designed for a narrow range of fuel specifications. To make matters worse, crop waste often has high levels of impurities that create combustion problems. The biggest issue is typically the presence of alkali metals that cause boiler fouling.
There are also a variety of non-technical factors that impede the use of crop waste for power generation, such as the difficulty in aggregating supplies from multiple parties and the absence of large, established vendors. But these non-technical factors could likely be overcome with suitable infrastructure and technology development. The physical and chemical properties