The quantification of GHG from CTL using UCG are not well known and indeed further quantification will require measurements. However we can estimate the greenhouse gas emmissions with a degree of confidence based on our understanding of the efficiencies of the processes involved.
As a first approximation I expect UCG-GTL to have a similar well-to-wheel footprint as CTL from surface gasificaton. In that process, studies (see ref below) show that well-to-wheel (WTW) GHG are around 350 gCO2eq/km with a fair degree of uncertainty in the order +/- 50 gCO2eq/km. However GTL based on remote natural gas is about 180 gCO2eq/km or about half of the CTL figure. And bear in mind GTL is itself about 10-20% higher than WTW GHG emmissions from conventional diesel.
Now replacing surface coal gasification with UCG may lead to a reduction or increase in GHG. Reductions will come from no mining, less methane release due to mining and less energy for transport/grinding etc. However, the UCG gasification process itself is probably less efficient and produces more CO2 in the raw syngas, so more energy is required for oxygen and compression. There is less scope for tight heat integration in the UCG-CTL process. On balance I think these differences will be small overall when comparing with the large inherent difference between CTL and GTL due to the different feedstock.
So overall I expect the Linc process (and others) to have GHG on WTW basis of above 300 gCO2eq/km and I would imagine it will be much higher. This low figure I mention above is still aabout 70% higher than GTL from remote natural gas and more than 85% higher than from conventional diesel. So this process will not be GHG friendly no matter what.
The diesel of course is cleaner itself and the emmissions from use are less than conventional diesel. And there's less pollutants like sulfur. But the overall GHG will be much higher. Sorry but that's a fact.
ps: details of European studies I refer to can be found here: http://ies.jrc.ec.europa.eu/wtw.html
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