Environmental Engineering Reference
In-Depth Information
Section 1
Introduction
In 1930, Bottoms [5.1] patented a technology to clean natural gas of its
impurity gasses — the amine scrubbing process, depicted in Figure 5.1.1.
Interestingly, although this technology is nearly a century old, the current
CCS version still looks very similar. As you can see,
the process consists of two parts: the absorber and the stripper . The
fl ue gas exhaust enters at the bottom of the absorber and rises through
the column, which is segmented into several tray decks. Each tray con-
sists of a fl at plate with holes and a weir to manage liquid solvent fl ow.
Liquid solvent enters at the top of the absorber and fl ows down the
plates in the opposite direction of the fl ue gas. The weir “holds up” just
enough solvent to ensure that the fl ue gas vapor bubbling up through the
holes in each plate allows the solvent to absorb CO 2 . As a result of
the falling solvent and rising fl ue gas passing through many such plates,
the exhaust at the top of the column will be signifi cantly CO 2 -depleted.
The solvent has a limited capacity to absorb CO 2 , so once it has
been in the absorber long enough to become completely saturated, it
needs to be moved from the bottom of the absorber to another device
where it is stripped of its CO 2 , and fi nally returned to the top of absorber
for a fresh round of absorption. The regeneration is done by the second
part of the process, in the stripper. The stripper looks and acts like the
opposite of an absorber. The CO 2 -rich solvent from the bottom of the
absorber is injected at the top of the stripper where it cascades through
plates with holes and weirs. Heat is added (in the form of steam) at the
bottom of the stripper so as to release CO 2 from the liquid solvent as well
as boil some solvent, thereby forming a gas phase that rises through the
stripper. At the top of the stripper a condenser returns the solvent, and
nearly pure CO 2 is ready for subsequent cooling, compression, and
transport for storage. With its CO 2 “stripped,” the hot liquid solvent is
transported from the bottom of the stripper and recycled back into the
top of the absorber. Due to the fact that the regenerated solvent is much
warmer, a heat exchanger (number 22 in Figure 5.1.1 ) is used to recover
some of the heat used for the regeneration process. The entire process
is a superb example of 20 th century chemical engineering — moving
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