Modeling and Experimental Studies of SO₂ Effects on CO₂ Capture with Chilled Ammonia Solvent

Abstract

Combustion of fossil fuel produces air emissions including carbon dioxide, nitric oxide, and sulfur dioxide, which cause severe environment problems, in particular, global warming and environmental pollution. The discharge of the power plant is the primary source of carbon dioxide emission. For CO₂ capture from existing plants, the post-combustion carbon capture is the most widely used technology because of the lower cost to retrofit the plant. Chilled ammonia has been reported as an absorbent in post-combustion carbon capture, which shows low energy cost and high efficiency. Although carbon dioxide is usually captured after desulfurization and denitrification of the flue gas, such processes can hardly remove the entire sulfur dioxide. Sulfur dioxide is known to have a negative effect on carbon dioxide capture. In this study, the effect of sulfur dioxide on carbon dioxide mass transfer was investigated. Chilled ammonium water was used as absorbent. The experimental data confirms the negative effects of sulfur dioxide on carbon dioxide capture using chilled ammonia. The mass transfer of carbon dioxide decreased with increasing concentration of sulfur dioxide in the gas phase. Numerical modeling of mass transfer of carbon dioxide in the presence of sulfur dioxide was developed and validated experimentally to better understand the effect of sulfur dioxide on carbon dioxide absorption by aqueous ammonia. In this work, an assumed reaction plane was introduced to explain the sulfur dioxide effect on carbon dioxide mass transfer into aqueous ammonia. For easiness of using the model to estimate the effect of sulfur dioxide, a general equation was also developed by fitting the numerical solutions. The concentration of carbon dioxide reacted with aqueous ammonia is lower than the equilibrium concentration of carbon dioxide in the gas-liquid interface. The main outcome was the quantification of the concentration of carbon dioxide in the reaction plane (Cᵣ ) as a function of partial pressure of SO₂ in the gas phase (S₀) and equilibrium concentration of carbon dioxide in the liquid surface (C₀) with various aqueous ammonia concentration (C(NH₃) )); this relationship is as follows: Cᵣ = (1+(-2.92744+1.75(1-exp(-C(NH₃)/0.6213) )) S₀×10⁻⁴+1.2525×10⁻⁸ S₀² ) C₀