A comparative TEA of a two-step process using chemical solvents for producing an ultra-sweet natural gas

Abstract

A comprehensive Techno-Economic Analysis (TEA) was performed to evaluate the economic feasibility of a novel two-step process (TSP) developed in Aspen Plus V12.1 to desulfurize and decarbonize a raw natural gas containing (2 mol% H₂S and 5 mol% CO₂) into an ultra-sweet natural gas containing (1.72 ppmv H₂S and 4.19 ppmv CO₂). The raw natural gas flow rate used in the TSP was 117.74 kg/s at 60 °C and 50 bar. The TSP combines an H₂S desulfurization step using potassium carbonate (K₂CO₃) and a CO₂ capture step using 3 different chemical solvents, monoethanolamine (MEA), sodium glycinate (SGS), and potassium glycinate (PGS). Both steps employ fixed-bed absorbers packed with Mellapak 250Y structured packing.

The hydraulics and mass transfer characteristics for the TSP were calculated, indicating normal operation with higher gas-side (k_G) than liquid-side (k_L) mass transfer coefficients. The TEA of TSP indicated that PGS had the most promising economic feasibility among the 3 solvents as it exhibited the lowest Levelized Cost of CO₂ capture (LCOC) of $47.54/ton.CO₂ at a Capital Expenditure (CAPEX) of $24.98 million, and an Operating Expenditure (OPEX) of $12.20 million/year. Also, the TSP could produce one MMSCF of ultra-sweet natural gas at a total cost of $339.55.