Introduction to Carbon Capture - Introduction to Carbon Capture and Sequestration - page 156

required to compress the CO 2 contributes signifi cantly to the costs of
carbon capture. If we assume ideal gas behavior, we can compute the
energy for the compression using:

p

Transport

transport

∫

W = p dV = n RT ln ,

comp cap

p

Capture

capture

where n cap is the amount of gas we need to compress, p transport and p capture
are the pressures at which we transport and capture the gas, respectively.
However, CO 2 does not behave like an ideal gas at these conditions,
so we need a more accurate equation of state, such as from the real gas
properties of the NIST database REFPROP [4.7] for fl uid properties.
Using these numbers, one gets a minimum energy requirement of 218 kJ/
kg CO 2 [4.4].

Section 3
Parasitic energy

As we have seen in the previous sections, the energy associated with a CCS
process is parsed into two components: the energy required to separate the
CO 2 from the fl ue gas, and the energy required to compress the CO 2 for
transport and storage. While minimizing the total of these two energies is a
design goal, different capture processes may distribute the energy demands
differently between separation and compression. To best compare different
processes, then, engineers use the concept of parasitic energy .
We can easily formulate an equation for parasitic energy by recog-
nizing that carbon capture consumes two forms of energy from the
power plant: electricity directly from the generators, and heat in the form
of the steam that derives from fuel combustion. For example, compres-
sors that deliver 150 bar CO 2 for transport and storage will likely be
powered directly by power plant electricity. The capture process itself