Capturing CO2 from ambient air - David Keith

When the author toured the caustic recovery plant at a paper mill (the management of the mill asked that it
not be identified), a process engineer there explained that heat recovery from the slaking reaction would be
difficult because of scaling issues – any heat-exchange equipment with small openings and lots of surface
area would be prone to clogging by mineral build-up. On the other hand, he says, heat recovery from the
calciner flue gas would be possible but has not been implemented at the mill, which has limitations of
space, capital, and no sense of scarcity of energy (the mill generates much of its own heat from burning
lignin in the pulping process). Thus we do not assume recovery of the slaking energy but do use the
calciner steam to run the amine recovery boiler in our example system. In contrast, Zeman assumes that
heat from the slaking reaction (Reaction 4 in Table 2.1) can be recovered for pre-drying the CaCO3 mud,
and so does not include energy for dewatering. We would not argue that this is unrealistic, only that the
practicality is uncertain. Baciocchi et al. take the most conservative stance, assuming no recovery of low
grade heat at all.
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