Effectiveness of Absorber Intercooling for CO2 Absorption from Natural Gas Fired Flue Gases Using Monoethanolamine Solvent

Chemical absorption using aqueous amine is one of the most feasible options for post-combustion CO2 capture. One of the main challenges of this technology is its high energy requirements. Absorber intercooling was considered as a viable method to offer benefits in terms of solvent absorption capacity and mass transfer efficiency in CO2 absorption processes. However, the effectiveness of absorber intercooling on overall energy requirements depends on other factors such as lean loading and liquid to gas ratio. This study evaluates the benefits of using two different configurations of absorber intercooling, i.e. “in-and-out” and “recycled” intercooling when using 30 wt% aqueous monoethanolamine (MEA) to capture 90% CO2 from a natural gas fired turbine with 4 mol% CO2. The Lean CO2 loading was varied from 0.15 to 0.42 (mol CO2/mol MEA) to determine the lean loading at which the application of intercooling is most significant. Absorber intercooling provides the most benefit at lean loading from 0.30 to 0.34. The use of in-and-out and recycle intercooling at 0.34 lean loading, provided 15.6 and 15.8% reduction in the total equivalent work associated with 32.0% and 36.6% reduction in required packing area when using 1.2 times the minimum liquid flow rate. At lean loading greater than 0.34, the benefit of absorber intercooling is a trade-off between reduction of solvent flow rate and total energy requirement and the drawback of greater packing area in the absorber. The greatest saving in total equivalent work, 17%, was observed at the 0.36 lean loading associated with nearly 60% more packing area when using 1.2 times the minimum solvent flow rate. At very low lean loading and very high lean loading absorber intercooling does not offer significant benefit.