A reboiler duty of 89.0 Million Btu/Hr (22.4 Million kcal/hr) of heat is added each of two CO2 Strippers to thermally strip the
CO2 from the rich MDEA solution using process gas and steam reboilers, 105-C and 111-C, located at the bottom of each
CO2 Stripper column.

Steam and CO2 vapor with trace inerts which are dissolved in the MDEA solution exit the top of the CO2 Stripper columns and
combine, further passing through the 110-CA/CB Condensers, feeding into 103-F Reflux Condensate Separator. The CO2
Product stream exits the 103-F Reflux Condensate drum containing 3556.6 LbMoles/Hr (1613.2 KgMoles/Hr) of CO2 at a dry
gas purity of 99.42 mole percent CO2. The residual inerts are primarily Hydrogen and Nitrogen. Lean, stripped MDEA solution
passes from the stripper columns through the lean/rich MDEA solution exchanger, being cooled from 256 Deg F (124 Deg C)
at the base of the CO2 Stripper columns to 207 Deg F (97.2 Deg C) flowing to the Lean Solvent Cooler (108-C). The lean
solution then combines with Reflux Condensate and makeup water before being further cooled by the Lean Solution Cooler,
108-C to 115 Deg F (46.1 Deg C), and then returned to the CO2 Absorber using the 107-J MDEA solution pump. The lean
solution loading is 0.024 mole CO2 per mole of total amine (Pz plus MDEA). The sieve trays in the CO2 Absorber are
calculated with Design II as operating at 74% flood at the top tray and 94% flood at the bottom tray. The sieve trays in the
Stripper columns are calculated as operating at 59% flood at the top tray and 89% flood at the bottom tray. These operating
tray loadings have been proven to be acceptable. Simulations of other MDEA CO2 Removal Systems with calculated tray
loadings have not resulted in any columns flooding, up to near 100% percent predicted percent of flood. (The correlations are
rather conservative)

In Figure 2 (Example 1) the Base Case, the CO2 Removal System operates at an efficiency of 50,050 Btu/LbMole (27800
Kcal/KgMole) of CO2 removed. These operating conditions and the operating efficiency is typical of many MDEA based
systems. Although quite typical, this CO2 Removal System energy use can be further improved by optimization with Design II
or other simulator software, and this as has been demonstrated in plants. A strong advantage of optimization with software, is
the engineer can develop optimal plant efficiency or capacity conditions in the office, and see the risks and opportunities,
before making tedious, slow optimization steps in the plant.

As shown in Figure 3, Example 2 illustrates how Design II process simulation software can be used to optimize the CO2
Removal System process efficiency and energy use. In the Base Case previously described, the lean solution had a
composition (CO2 Free basis) given as 4.4 Wt% Pz, 35.7 Wt% MDEA, balance Water. In simulator process optimizing, the
composition of the lean solution is changed to be 5 Wt% Pz, 35 Wt% MDEA, balance Water. The circulation of the lean
solution is progressively decreased. This permits reduction in the Stripper reboiler duty. By systematic tuning, the lean solution
flow and reboiler duty are gradually reduced until the lean solution loading is equal to or just below 0.025 mole CO2/mole total
amine.
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