Capturing CO2 from ambient air - David Keith

The market price of high-calcium quicklime should reflect the industrial cost of calcination, inclusive
of operation and capital recovery. One major adjustment is needed, however, because this price will
include the cost of the raw material – crushed limestone. This is not needed in the air capture system,
aside from a small amount of make-up lime, since the material is reused. Miller (2003) reports that the
average price of this product in the United States is 78 $/t-CO2 (converted to CO2 terms). Subtracting the
average price of crushed limestone sold for lime manufacturing of 12 $/t-CO2 (Tepordei, 2002), this gives
65 $/t-CO2.
4.2 Cost of example system
In Section 2.3, we described an example air capture system making maximum use of existing, well-known
industrial components, but costs for a contactor were not available. From Chapter 3, we now have a
detailed cost analysis of one type of contactor. The analysis, unfortunately, gives a very large range of
costs for spray-based contactors, some of which are very high. However, Chapter 3 also makes the case
that there is no fundamental limitation to a low-cost contactor and that many engineering parameters have
a large effect on the cost. No type of extremely costly contactor would be built. Considering that designers
of an air capture system would select parameters to yield the lowest-cost contactor, we argue that one of the
middle-assumption scenarios can serve as a reasonable upper bound on contactor cost. The “optimized”
cost is also considered. We take the mid-level cost as 70 $/t-CO2, reflecting both the middle-assumptions
no-coalescence scenario and the high-coalescence scenario with favorable assumptions. The optimized
cost is 20 $/t-CO2.
Now that we have costs for the contactor, we can complete a total system estimate. Two systems are
considered: the base system, and an improved system. The base system is just as described in Chapter
2: a spray tower, a conventional caustic recovery system, and an amine capture system. It is fired with
gas, either natural, coal-derived, or bio-derived. We assume a price of thermal energy, ptherm, of 6 $/GJ.
Upstream carbon emissions from gas production are ignored. The CO2 from fuel combustion is captured
in the amine plant along with the calcined CO2. In many ways this is a highly suboptimal system, but,
as discussed in Chapter 2, it is the most valid way to make use of available cost estimates and industrial
experience.
In the improved system we calculate the effects of moving to several more efficient components. The
energy requirements for caustic recovery are matched to the results from Baciocchi et al. (2006) for the
case of advanced dewatering technology. Additionally, an oxyfuel capture scheme is employed instead of
amines, and the optimized contactor scenario is used. We don’t have a strictly valid way of estimating
capital costs for this new scheme. We will leave them the same as for the base case except for addition
of capital and operating costs for an oxygen separation unit. Parameters for the unit are taken from
Singh et al. (2003).
of industrial calcination) is to construct a system which captures the energy from Reaction 3 for heat or useful work, something
which cannot be accomplished in quicklime manufacturing. This appears quite possible, but the captured energy would likely
be used for several purposes which aren’t part of quicklime manufacturing: solvent regeneration (or oxygen production in an
oxyfuel system), dewatering and drying of CaCO3 mud, and electricity for pumps and fans.
52