Crunching the emissions for CCS coal versus gas power plants

The NGOs say gas power plants are better than coal with carbon capture and storage, but one government source argues otherwise

Which is worse, four new gas-fired power stations or a bunch of coal-fired stations equipped for carbon capture and storage (CCS)? The NGOs say it's a no-brainer because the government is not insisting on 100% carbon capture from the outset, which may leave emissions higher than before. But Eco Soundings has been ­approached by a man in the Department of Energy and Climate Change who has crunched the numbers and begs to differ. His point is that if the energy companies go for pre-combustion CCS, then it looks better than gas. The argument is technical, but here it is in full:

The NGOs are saying that our coal policy may still leave emissions higher because of the 75% unabated coal given only 25% CCS required at the outset. But this ignores pre-combustion CCS, which is likely to be used for at least two of the four new plants. Pre-combustion as you know captures 90% of coal emissions from the outset, with no future retrofitting necessary. The effect of pre-combustion CCS means that our policy - even from the outset - will almost certanly lead to lower emissions than the only other realistic alternative of no coal at all (which is what the NGOs would have accepted) and four new gas plants instead. Here's why. First, let's give the emissions from different technologies: Unabated new (supercritical) coal: 750kg / MWh. New gas CCGT: 500kg / MWh = 66% of unabated coal. Pre-combustion CCS: 75kg / MWh = 10% of unabated coal (90% capture). Let's make this an index where unabated coal emissions = 100. Then gas = 66 and pre-combustion CCS = 10. Then imagine we had allowed 4 unabated coal-fired power stations. Then emissions would have been 400 on this index. If we had instead said no coal and had 4 new gas, emissions would have been 264 (4 x 66).

What will probably happen under our policy is 2 new coal with pre-combustion CCS and 2 with post-combustion CCS. The two with post-combustion will each have, at the outset, a minimum of 300MW CCS = 20-25% capture. Let's be conservative and call it 20%. That means their emissions will be 80 on our index. Two plants = 160. Now the two pre+combustion. Let's say they fit CCS to the whole plant. So their emissions = 10 on the index. Two plants = 20. So the total emissions from our CCS four plants = 180 (160 + 20). This is before any retrofit of post-combustion. So under our policy there will be around 40% lower emissions than under the all-gas alternative (160 against 264) - from the outset.

But what if the pre-combustion plants only instal CCS gasifiers on 50% of their total capacity? That would make them half coal and half gas. On their gas sides their emissions would be 66 on the index, so 33 for half a plant. On their coal sides emissions would be 10, so 5 for half a plant. So total emissions = 38. So for two plants = 76. So 76 for the two pre-combustion + 160 for the two post-combustion plants = 243.

That is still less than the 264 for four gas plants. Even before any retrofitting. QED.