TreeHugger poured over the coal-to-natural gas-to-liquid fuel technology literature. Indeed, by some estimates it would seem "cost effective" to make liquid hydrocarbon fuel from US coal. And it would certainly reduce foreign oil dependency (as opposed to fossil fuel dependency). But clean and purty it ain't.
In the interest of brevity, and begging forgiveness of any engineers reading this, we present, below, a simplified list of steps through which coal might generally be made into liquid fuel. Note: this hypothetical list does not reflect on any specific patented, or trademarked coal conversion process, either pro or con.
*Sort, crush, grade and clean it, disposing of the stone and washings, if any.
*Ship to conversion operation.
*Leach coal with strong acid solution if needed, to remove heavy metals and sulfer.
*Treat the acid wash water prior to disposal, producing a heavy metal bearing sludge.
*Generate methane (natural gas) from the coal's carbon content, borrowing hydrogen from water (steam) inside the coal gasification process step.
*Synthesize the "coal gas" (methane) into liquid hydrocarbon fuel (this is the Fisher-Tropfsch process step).
*Manage, according to regulations of the governmental entitites where the process is deployed, aqueous waste, waste steam, fly ash, carbon monoxide, carbon dioxide, coal tar, "char", various sulfer compounds or elemental sulfer, and so on.
*Deliver liquid hydrocarbon fuel to refinery.
*Refine and distribute liquid fuel products.
*Continue to liberally consume hydrocarbon fuels in overpowered cars, SUV's and Mega-Trucks, once freed from the price increases that otherwise would be caused by worsening oil shortages.
The US probably will need to convert coal to liquid fuels. Come to think of it, it's bound to happen in this century (we're fond of the long view). But, setting expectations to a negligible environmental burden is wrong. Every process has its inputs and outputs. And while we're still in reality mode, a 40-year supply won't help our grand children much will it?
Efficiency is where the game needs to start.