Wind and solar power are clean and free but they only work part of the time. When the sun goes down and the wind dies, coal is still the workhorse for generating baseload power. But coal is killing us by warming the planet, acidifying our lakes and oceans and sprinkling mercury over the landscape. Geothermal can do part of the job but it will take decades to drill enough wells.
One quick fix that is finally catching on is converting existing coal plants to biomass. Fuel and maintenance costs are actually reduced and expensive pollution control upgrades can often be avoided because biomass contains very little sulphur or mercury. Often the biomass can be grown locally, providing good local jobs and keeping the ratepayers dollars in the community. Biomass burning is carbon neutral because the CO2 emitted by one crop is taken back by the next.
But wait! The U.S. burns a billion tons of coal per year. Since biomass is less energy dense than coal it would take 1.6 billion tons of biomass per year to replace all that coal. According to a DOE study, we can grow about 1.3 on exising available land.
Not quite enough. But there is a way: Efficiency! Existing coal power plants are only about 33% efficient. That means that 67% of the coal’s energy is simply thrown away, often simply heating up a nearby river!
A DOE study estimated the U.S. biomass growing capacity as 1.3 billion tons/yr.
We can get quick reductions in pollution and global warming by simply repowering existing coal power plants. However, a better long-term approach is to start building much more efficient, small-scale power plants where the waste heat can be put to immediate use. Combined Heat and Power (CHP) plants can achieve efficiencies of up to 90% by using the waste heat from electrical generation to produce hot water, heating and air conditioning. Office buildings, hotels, industrial parks and shopping centers are already proving the practicality of CHP.
Efficient, small-scale electrical generation is already possible using fuel cells and microturbines. Systems as small as 300 kW can generate electrical power at 47% efficiency and then deliver the remaining 338 kW for heating applications. Most systems today are powered by natural gas, but biomass can be gasified to produce carbon-neutral syngas, which burns just like natural gas. Small plants can run unattended because internet-connected remote control consoles at the manufacturer can be monitored by experts.
Biomass gasifiers aren’t fussy about what they burn. Even plants that look very different to us are chemically very similar and all produce about 7000 Btu-per-pound when dry. This means that monoculture is not necessary and complimentary mixtures of plants can be grown as feedstock. Marginal land can be used by growing specially-selected crops. Agave, for example, grows happily in semi-desert and produces four times the yield of corn.
Biomass has a tarnished reputation because early attempts to use it were so inefficient. When you ferment ethanol from corn, you get only 330 gallons of ethanol per acre. If you burn 1/7 of an acre of corn you will get the same amount of heat as burning 330 gallons of ethanol. To make matters worse, the ethanol will be burned in a car engine that is only about 25% efficient. Elecric car motors are 90% efficient, so an electric car charged by a 90% efficient biomass CHP plant can go about 22 times as far on an acre of corn as one burning fermented ethanol!
New generation ethanol plants actually use a gasifier to make syngas, which is then transformed into ethanol by catalysts or enzymes. Coskata has a process that makes 100 gallons/dry ton of biomass. A big improvement, but still no match for the efficiency of an electric car. Making ethanol by fermentation also uses lots of energy cooking, fermenting and drying the ethanol. Gasifiers need no external energy once they are started. Gasifiers are also very convenient for converting coal power plants because the syngas can be piped to burners inside the coal-fired boiler. The gasifier can be built in any convenient place leaving the coal burning boiler intact for fuel flexibility.
Gasifiers aren’t fussy about what they are fed. In fact old automobile tires and municipal waste work just fine. In fact, the trash left over after recyclables are diverted works just fine. There are already 90 Waste-to-Energy (WTE) plants in operation in the U.S. This connection between biomass and trash burning turns out to be most unfortunate because an amazingly negative activist movement has grown up to fight against incinerators.
Paul Connett, who also crusades against fluoridation, took up the cause of incinerators, back in the 1980’s. At that time incinerators were a serious source of dioxins and mercury. Now, the incinerators are 1000 times cleaner but the fight continues. By quoting “facts” from studies done before the cleanup, it is still possible to scare well meaning people into marching down to city hall to block permits. Your backyard barbeque produces seven times more dioxins than are allowed at the stack of a modern incinerator.
Unfortunately, the panic about incinerators has spread across the blogsphere and well meaning but misinformed volunteers have blocked permits for far to many well-conceived biomass power plants and WTE facilities. Every time the activists shoot down a project the environment suffers as people are forced to bury the waste or burn it in a backyard barrel. By stopping clean power generation the activists also perpetuate our dependence on dirty coal power plants!
The internet is a wonderful thing, but bad ideas can spread like wildfire. Just like the global warming denial sites, Zero waste sites sound very convincing. The problem is we can’t economically recycle everything. “Zero waste” sounds good just like “clean coal” does, but both are impractical. We must provide a clean, safe way to detoxify the trash that remains after recycling. Plasma gasifiers leave only 0.2% ash residue and generate significant green power in the bargain. If we run short of trash they can happily run on biomass too.
source: http://www.renewableenergyworld.com/rea/news/article/2009/06/can-biomass-replace-coal?cmpid=WNL-Thursday-June25-2009
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