Absorber Intercooling Configurations using Aqueous Piperazine for Capture from Sources with 4 to 27% CO2

Abstract

A systematic evaluation of the solvent capacity and mass transfer benefits of absorber intercooling was conducted for CO2 capture with 8 m piperazine (PZ) for three different flue gas sources: NGCC (4.1% CO2), coal-fired boiler (14.7% CO2), and steel blast furnace (27.4% CO2). The study identified the best intercooling strategy as a function of operating conditions (lean loading, liquid to gas ratio (L/G)). For all applications, operation at low lean loadings did not require intercooling to avoid temperature-related capacity or mass transfer penalties. In a broad intermediate loading range, simple in-and-out intercooling provided large solvent capacity benefits (measured as minimum solvent rate, LMIN) compared to a column without intercooling. LMIN was reduced by 71%, 53%, and 42% for NGCC, coal, and steel, respectively. Finally, the coal and steel applications had a large L/G range at higher loadings where intercooling was once again unnecessary. An enhanced intercooling design for NGCC could yield up to 62% reduction in packing and 46% reduction in solvent capacity at specific conditions (benefits for coal and steel were much lower). A recycle intercooling design for NGCC was introduced to reduce overall column temperatures and enhance mass transfer. For the case evaluated with recycle intercooling, the new design achieved significant packing reductions (>50%) compared to a simple intercooling design and approximated the performance of an isothermal column.