"A negative-carbon corn ethanol plant?"
I am not the biggest fan of corn ethanol. But I am the biggest fan of cogeneration, also known as combined heat and power, CHP (well, maybe the second biggest fan). It is probably the single most overlooked strategy for sharply cutting greenhouse gas emissions while reducing overall energy costs.
Important caveat: Impact of Combined Heat and Power on Energy Use and Carbon Emissions in the Dry Mill Ethanol Process does NOT examine the energy consumed (or emissions generated) from growing and harvesting the corn or from transporting the corn or ethanol. Still, with CHP, corn ethanol can actually generate significant CO2 reductions compared to gasoline.
If Congress is serious about promoting ethanol in a manner that actually reduces GHGs, they should require all new ethanol plants to cogenerate.
[UPDATE: Link to EPA study is fixed!]