(590e) Packing Economy Analysis for Post-Combustion CO2 Capture

Packing
Economy Analysis for post-combustion CO₂ capture

by Chao Wang^1,2, Micah Perry², Frank
Seibert², Gary T. Rochelle¹

¹Department of Chemical Engineering, The University of
Texas at Austin

²Separations Research Program, The University of Texas
at Austin

Austin, TX 78712

Packing is widely
used in post-combustion CO₂ capture because of its low pressure
drop, good mass transfer efficiency, and ease of installation. In the post combustion CO₂ capture process, absorber and
stripper costs can be divided into two parts: the capital costs and the
operation costs. Economy analysis of these costs has been done by changing the
operating gas velocity, liquid flow rate, column diameter, packed height,
packing type( including the total area and the corrugation angle) to find the
optimum costs.

Capital costs include the one-time
investment of building the column, packing costs and auxiliaries such as pump
and blower costs. The column and packing costs are determined by the diameter
of the column, the packed height, as well as the packing type. The blower
purchased costs is determined by the maximum gas flow rate and pressure drop
while the pump purchased costs is determined by the maximum liquid flow rate. Operation
costs include the running costs and the maintenance costs. The running costs
are related to the work of the blower and pump while the maintenance costs are
estimated.

The column is operated with 7m MEA at 40°æ with a capacity of
approximately 1 mol CO₂/kg solvent. The required Number of Transfer
Unit (NTU) is calculated based on 90% removal of CO₂ with an inlet
CO₂ concentration of 12mol%. The Height of Transfer Unit (HTU) is
calculated by equation HTU=u_G/K_OGa_eRT. The
effective area is calculated from modified Tsai's area model:

The overall mass transfer coefficient K_OG
is calculated from the gas film mass transfer coefficient k_G, liquid
film mass transfer coefficient k_L, and the mass transfer coefficient
related to the chemical reactions by this equation:

The chemical reaction constant can be
obtained from reports; k_G and k_L values for different
packings are from mass transfer models developed from this work based on
measured values. Thus, the packed height can be calculated.

For this case, the column is operated with
a fixed ratio of gas and liquid flow rate (L/V). The column diameter is
calculated by the operating gas velocity (u_G). Therefore, the
variables can be reduced to two: the gas velocity and the packing type. Eight
structured packings with different total area and corrugation angle are chosen
to run case by case. An Excel program including all the required information to
calculate the total costs is build. The SOLVE function is utilized to optimized
the total costs by varying gas velocity throughout the operating range.

For data analysis, the equipment costs are
converted to total fixed plant costs by a multiplication factor of 4 based on
the Chilton method. The total fixed plant costs is then converted to annualized
costs with the assumption of a 1-year start-up time, a 2-year construction
time, and a 10-year project life. Finally, the overall costs are described as
the costs per tonne CO₂ by dividing the annualized costs and the annual
CO₂ output of the plant.

Results of economy analysis for each
packing are shown. For each case, the optimized gas velocity, column diameter,
packed height, and the minimized costs per tonne CO₂ are listed in
tables. The figure of overall costs varying with operating gas velocity is
shown. Figure 1 shows the case for packing MP250Y, running in a pilot plant
with an annual output of 250MW. Comparison of minimum costs between different
packings is made to find the optimized packing total area and corrugation
angle.

Figure
1. Economy analysis for MP250Y in a 250MW pilot plant