Just before Christmas of the past year, the EPA announced with a certain amount of political pomp and circumstance, that the new Mercury and Air Toxin Standards MATS for fossil fuel users. The standard is based on the top 12 percent of coal power plants which will put about 10 percent of older coal plants out of business and require the remaining plants to retrofit to meet the standard or switch to another fuel likely natural gas. 25megaWatts is the minimum size plant that the standards apply. A possibly unintended consequence, it that the standards may very well have an equal or strong impact on cleaning up the renewable energy sector, biomass in particular.
Coal got its toxins from the biomass that became coal of millions of years. Depending on the growing conditions, renewable biomass can contain a significant, at least with respect to MATS, amount of toxins. The range of Mercury content varies and I have not seen a complete study of biomass Mercury content, but 0.026 micrograms per gram, the average for dried peach leaves, is a fair estimate for biomass grown in the marsh or swampy location typical of timber products. Timber products tend to promote swampy conditions, which is an important factor in maintaining water shed efficiency.
Of course, the Mercury content in coal is not listed in micrograms per gram, that would be too simple, coal is listed in grams per ton, short ton in the United States. There are 907184.7 grams per short ton and average quality coal contains about 0.1 grams per short ton. That converts to 0.11 micrograms of Mercury to gram of coal versus 0.026 for dried peach leaves. So the Mercury in peach leaves is much less than the Mercury is coal right?
Well, so is the energy content. Coal has 28 Mj/kg while peach leaves, which I would estimate to be about the same as switch grass or wood products, has about 5Mj/kg wet. It takes energy to dry stuff and if you use enough you can convert that switch grass or wood to charcoal or biopellets for a wood stove. If you adjust the Mercury content of the peach leaves to allow for the energy difference, Peaches leaves would produce 0.146 micrograms of Mercury per equivalent coal gram of energy. That by the way does not include the differing amount of energy required to dry to biomass for use as a fuel.
This would tend to reinforce my suggestion of Coal/Biomass co-generation as a responsible use of existing resources and the reduction of the massive mountains of waste buried all across our great nation.
I am sure though, that there must be a warm and fuzzy reason to regulate this crazy idea into oblivion.
