About 2005 the DOE announced the $1.3 billion FutureGen project to design, build and operate a nearly emission-free coal-based electricity and hydrogen production plant.
About 700,000 tonnes of CO2 (some 60% of throughput) per year would then be separated by membrane technology and sequestered geologically. The hydrogen would have been burned in a 275 MWe generating plant and in fuel cells. Later FutureGen figures referred to 90% CO2 capture and 330 MWe gross, 240 MWe net generation.
If 700,000 tonnes is 60% of the total CO2 produced for maybe 330 MW-yr of energy, more than 1,360,000 tonnes is the total, and at a capture rate of 90% this still means, of the CO2 produced, over 136,000 tonnes escaping, and over 1,200,000 tonnes to be sequestered in some geological formation more stable than Virginia's. A Richter 5 earthquake could probably release it all.
In Sept, 2014 FutureGen 2.0 received the first-ever EPA permits for four class VI carbon dioxide sequestration wells in Morgan County, with plans to store 1.1 million metric tons per year for 20 years. Two exotic technologies are involved, oxy-combustion, and storage in underground saline aquifers.
So that's about 110,000 tonnes of CO2 per year released to the atmosphere by this "clean coal" process.
There are other ways of sequestering carbon dioxide, notably those used to help produce fossil hydrocarbon fuels,
-- which of course does not really help us to approach zero GHG emissions.
Actually restoring the forests, both equatorial and boreal, would help sequester CO2 as wood. Similar notions for the oceans have been proposed, but our knowledge of how to fertilise them without causing surface algal blooms and eutrophication is inadequate, IMHO.
Compare the present 25,000 tons of uranium oxide in the USA producing 100,000 MWe-yrs and 2500 tons of solid "nuclear waste" of which less than 100 tons is actual fission products. The rest could and should be consumed in fast neutron reactors, improving the efficiency of use of the fuel 100-fold, and of the "waste" products about 25 thousand times.*
*That's one 25th of the mass, times one thousandth of the lifetime, of the waste
-- assuming that the much larger stocks of "depleted" uranium are not being considered as "waste".
CCS, Carbon Capture and Sequestration, is a ridiculous idea, and does not even address the problem of the ravaged hillsides customary for the production of the coal to be "cleanly" used for power generation.
A fairly recent news item reveals that the Obama administration has had the sense to abandon the FutureGen project.