Introduction to Geological Sequestration - Introduction to Carbon Capture and Sequestration - page 355

Section 1
Introduction

We have discussed ways to capture CO 2 from fl ue gasses using absorption,
adsorption, and membrane processes. In this chapter and the following two
chapters, we address the question of what to do with the CO 2 we have
captured. Let us start by recalling two questions we raised in the introduc-
tion. It is not by accident that these are the questions most frequently posed
to anyone working in carbon capture and sequestration research:

• Why don't we put the fl ue gas directly into selected geological forma-

tions? Capturing carbon is very expensive! Could the cost of carbon
capture be avoided by injecting all fl ue gas directly into the
subsurface?

• Is it safe to store CO 2 in geological formations? Will giant bubbles of

CO 2 not become a threat to our environment?

Transporting CO 2 over large distances and injecting it into geological
formations is something we know how to do. We have carried out these
processes for around 40 years for the purpose of enhancing oil recovery
through injection of CO 2 into oil fi elds with declining primary productivity.
This process is known as CO 2 - enhanced oil recovery or CO 2 -EOR. While
the quantities of CO 2 transported and injected are considerable for the
individual oil fi elds involved, the amounts are small when compared to the
scale one would need to signifi cantly affect global CO 2 emissions. So, we
will need to fi nd alternative geological formations once we have saturated
all current oil and gas fi elds that would benefi t from CO 2 injections.

The scale of CCS

Let us start by recalling some results from the fi rst chapters. In CCS, we are
dealing with very large numbers. For example, our medium size 500 MW
coal-fi red power plant emits about 400 m 3 /s of fl ue gas containing about
12% of CO 2 (volume). This gives us each year about 2.6 million tonnes of
CO 2 . If we assume a lifetime of 50 years, we have to sequester 140 million
tonnes of CO 2 coming from 6.3 x 10 11 m 3 of fl ue gas at each power plant.