Do we underestimate the impact of particles in coal-derived flue gas on amine-based CO_2 capture processes?

摘要

The effect of particulate matter on the amine-based capture process has, up till now, not been considered in much detail due to the relatively low concentration of particulate entering the capture plant. In this study we present results of leaching tests with 30 wt% MEA utilising real fly ash samples from a range of European coal-fired power plants. The effect of a number of parameters including CO_2 loading, temperature, pH, leaching time, solid/liquid ratio & organic heat stable salts have been investigated. These experiments show that the behaviour of the various compounds and elements is not uniform with different conditions. A strong correlation between reducing pH/increasing CO_2 loading and Fe, Cr & V levels is observed, but is not seen for other heavy metals. This impact of pH on metal solubility is striking and suggests that Fe, in particular, may be transported by the liquid system and stored as deposits in the stripper where increased pH reduces the solubility of Fe compounds. The presence of oxalate as a heat stable salt leads to the precipitation of calcium oxalate when calcium phosphate is leached out of the ash. This could result in deposits in areas such as the reboiler that may lead to plugging, reduced heat transfer efficiency and even corrosion issues. Solid/liquid ratio was also found to have some effect with lower solid/liquid ratios showing higher relative solubility for heavy metals. Temperature and leaching time were also investigated but only minor increases in metals content were observed by increasing either of these parameters. The results observed strongly suggest that the effects of particulate matter on the post-combustion capture process should not be ignored, particularly if levels are sufficient to lead to significant build up of ash in the solvent. Ash captured in the liquid has the potential to release significant amounts of Fe, Mg, Ca and (PO_4)~(3-) into the solvent with Fe levels, in particular, being a concern for the enhancement of solvent degradation processes.