Energy and Electricity - Introduction to Carbon Capture and Sequestration - page 23

energy; if we have this energy, why not convert it directly to electricity
instead of using it to upgrade CO 2 into a fuel to be burned for making
electricity? There is considerable scientific interest in “CO 2 to fuels”
research, particularly if one imagines capturing existing atmospheric CO 2
and converting it back to fuel. Again, we will say more about this topic in
our chapter on future sequestration directions.
Section 4
Making electricity
In the previous section we stated that electric power generation is
responsible for the bulk of stationary CO 2 emissions. Figure 1.4.1 illus-
trates the relative importance of the various energy sources for making
electricity. This is a complex figure that reveals a great deal of informa-
tion. For example, it reveals the paucity of renewable energy sources
for electricity production. We can hope that in the future this share will
increase significantly, but as the starting point is so low, ramping up the
efforts such that its share is comparable to, say, natural gas, will be a
major challenge. What is important in the present context is the preva-
lence of coal (and natural gas) in our current electricity production.
So let us now focus on coal and natural gas for the production of
electricity. In Chapter 4 we will demonstrate that it is much more expen-
sive to capture CO 2 at very low concentrations, and therefore it is more
cost-effective to capture carbon from flue gas streams with higher CO 2
concentrations. Table 1.4.1 compares the CO 2 concentrations in the flue
gasses from coal and natural gas power plants to the CO 2 concentration
in air. The comparison of coal and natural gas is interesting. In natural
gas the hydrogen-to-carbon ratio is much higher (natural gas is largely
CH 4 ), hence the burning of natural gas generates relatively more water
than CO 2 . This suggests that one can decrease the CO 2 emissions by a
factor of two simply by changing from coal-fired power plants to natural
gas-fired power plants. Indeed, making this change is one of the wedges
in the scheme by Pacala and Socolow [1.4]. Currently (as of 2012) this is