https://doi.org/10.1016/j.egypro.2017.03.1289
“The final absorber configurations evaluated for the case study conditions outlined in Section 4.3 are summarized in
Table 3 (90% CO2 capture) and Table 4 (99% CO2 capture).”
“The selection of absorber configurations for each case provides insight into the impact of process conditions on
absorber configuration and intercooling requirements. For the 2×3 hybrid designs at 90% removal, the lower loading
of 0.20 mol CO2/mol alkalinity requires a 2×3+1 while a lean loading of 0.27 mol CO2/mol alkalinity can operate with
a simple 2×3 configuration. This appears counterintuitive as the leaner condition should have larger driving forces.
However, the intrinsically lower L/G at the loading of 0.20 means the design does not perform as well in terms of
cooling the gas (to replace the DCC). The reduced performance in the hybrid section requires a countercurrent bed to reach the removal specification. This highlights one potential advantage of the recycle design: the recycle rate can be
varied without changing the equipment configuration, and can address process condition specific issues.
In all cases, the 1×3+1 hybrid is a feasible design, and the tables highlight a major advantage of the configuration.
The 1×3+1 has only two discrete packing sections and has eliminated the DCC. The recycle design requires a minimum
of 3 sections to replace the DCC and perform the intercooling function. Frailie indicated that the costs of support
equipment (distributors, packing supports, etc.) required when breaking packed columns into multiple sections can be
significant [6].
Finally the 99% removal cases indicate the importance of advanced intercooling concepts to achieve deeper CO2
removal. The recycle intercooling design cannot achieve 99% removal at the solvent rates (1.3*LMIN, ISOTHERMAL) while
replacing the direct contact cooler. The limited driving forces in the column at the higher removals mean that back –
mixing the solvent at the ends of the column is undesirable. Therefore, recycling solvent at the rich end of the column
to cool the flue gas prevents the double recycle design from achieving 99% removal. In addition, the inherently low
L/G at the lean loading required to achieve 99% removal reduces the effectiveness of the intercooling section. A higher
solvent feed rate or recycle rate might address the issue, but would come at the expense of energy performance and
additional capital costs (larger equipment). Similarly, the 1×3+1 design is not capable of achieving 99% removal as
the additional row of hybrid contacting (2×3+1) is required to more closely approximate countercurrent contacting
and to offset the diminished performance in the bottom beds with a low L/G contacting the hot flue gas.
The results for the cases in Table 3 and Table 4 are summarized in terms of packing requirement in Table 5.”
“In all cases, where the advanced intercooling design is feasible it reduces the packing requirement compared to the
baseline configuration and eliminates the DCC. The 2×3 configurations provide the largest packing reductions, and
are feasible at all conditions in the case study. For the 90% removal cases, where the 1×3 design is feasible, the
configuration reduces packing compared to the baseline configuration, but is outperformed by the advanced design.
This must be weighed against the reduced complexity and costs of the 1×3+1 design. Finally, for the 99% removal
case, the 2×3+1 design provides a reduction in packing compared to the recycle design and eliminates the DCC,
making it a potentially appealing option since an advanced intercooling approach is required at these conditions.”