Modeling advanced flash stripper for carbon dioxide capture using aqueous amines
The intensive energy use is the major obstacle to deployment of CO2 capture. Alternative stripper configurations is one of the most promising ways to reduce the energy consumption of CO2 regeneration and compression. The advanced flash stripper (AFS) proposed in this work provides the best energy performance among other alternatives.
A systematic irreversibility analysis was performed instead of examining all the possible alternatives. The overhead condenser and the cross exchanger were identified the major sources of lost work that causes process inefficiencies. The AFS reduces the reboiler duty by 16% and the total equivalent work by 11% compared to the simple stripper using aqueous piperazine. The AFS was demonstrated in a 0.2 MW equivalent pilot plant and showed over 25% of heat duty reduction compared to previous campaigns, achieving 2.1 GJ/tonne CO2 of heat duty and 32 kJ/mol CO2 of total equivalent work. The proposed bypass control strategy was successfully demonstrated and minimized the reboiler duty.
Approximate stripper models (ASM) were developed to generalize the effect of solvent properties on energy performance and guide solvent selections. High heat of absorption can increase partial pressure of CO2 at elevated temperature and has potential to reduce compression work and stripping steam heat. The optimum heat of absorption was quantified as 70–125 kJ/mol CO2 at various conditions, which is generally higher than existing amines with 60–80 kJ/mol. The energy performance of AFS is not sensitive to the heat of absorption. A techno-economic analysis with process optimization that minimizes the annualized regeneration cost was performed to demonstrate the profitability of the AFS. The AFS reduces the annualized regeneration cost by 13% and the major savings come from the reduction of the OPEX, which counts for over 70% of the regeneration cost. The compressor and the cross exchanger are the major components of the CAPEX. The optimum lean loading is around 0.22 mol CO2/mol alkalinity for PZ but is flat between 0.18 and 0.24 with less than 1% difference. The AFS was demonstrated as a flexible system that can be applied to a wide range of solvent properties and operating conditions while still maintaining remarkable energy performance. Further improvement of energy efficiency by process modifications is expected to be marginal. Increasing solvent capacity will give the most energy and cost reduction in the future.