Conclusions from 3 Years of Continuous Capture Plant Operation Without Exchange of the Amp/Pz-Based Solvent at Niederaussem – Insights into Solvent Degradation Management

Abstract

A many times heard mantra of solvent degradation management in amine-based post combustion capture is “keep the solvent clean” to minimize solvent consumption. It is assumed that the amine losses would decrease by the removal of metals, degradation products, and reactive trace components which are captured from the flue gas, like NO2 (as potentially driving components of the amine degradation besides dissolved O2). However, this theoretical hypothesis – based on results from laboratory experiments typically generated with fresh amines – disregards the complexity of the solvent matrix, interaction of potential metal catalysts with degradation products and oxidizing agents, and specific chemical requirements which must be fulfilled before a degradation mechanism can proceed. Degradation of the solvent CESAR1 (aqueous solution of 3.0 molar 2-amino-2-methylpropan-1-ol (AMP) and 1.5 molar piperazine (PZ)) is investigated in a unique long-time test campaign (testing time up to now 40 months; 24/7 operation) without replacement of the solvent inventory at the capture pilot plant at the lignite-fired power plant in Niederaussem. Three solvent management strategies with different effect mechanisms are investigated and evaluated: a) removal of only anionic compounds and trace elements (within 75 days solvent inventory treated two times) and anionic as well as cationic compounds and trace elements (114 days, inventory treated four times) from the solvent by ion exchange, b) adsorptive removal of trace elements from the solvent by active carbon in 35% of the operating time, and c) removal of >80% NO2 by flue gas pretreatment with thiosulfate/sulfite solution (dosing for 2,000 h). The results of the testing program clearly show that “ solvent cleanness” is not a well-defined parameter and that results from laboratory tests, tests without fully representative industrial flue gases, and short-term testing of monoethanolamine cannot be generalized for other solvents and industrial application. These results showcase that specific degradation management considering solvent, capture plant and flue gas quality is reasonable. Overshooting efforts for solvent management are contra-productive and produce unnecessary waste streams, efficiency losses and costs.

Keywords: AMP, piperazine, CESAR1, solvent management, solvent degradation, ion exchange, NO2 removal, pilot plant, demonstration