Concentrated Piperazine: A Case Study of Advanced Amine Scrubbing
Gary T. Rochelle
Department of Chemical Engineering
The University of Texas at Austin
Wednesday, March 3, 2010 - 10:00 am
Ben Bandy Conference Center
UK Center for Applied Energy Research
CO2 capture by concentrated piperazine with a 2-stage flash regeneration has all the desirable properties of an advanced system for amine scrubbing. Piperazine can be used with reasonable viscosity at 40 wt% (8 m) and offers a reversible CO2 capacity of 0.8 mole/kg amine+water, compared to 0.4 for 30 wt% MEA or 1.2 for concentrated hindered amines. It provides a rate of CO2 absorption as fast as any known amine solvent that is twice as fast as 7 m MEA. Piperazine has a moderately high heat of absorption (70 kJ/mole) that combines with exceptional thermal stability to provide excellent energy performance with temperature swing regeneration at 150OC and 7 to 15 bar. With careful integration into an existing coal-fired power plant the energy requirement should approach 0.2 MWH/tonne CO2 removed . This system will include an intercooled absorber to maximize reversibility and solvent regeneration will be simplified by a two-stage flash heated at 150oC. The CO2 will be compressed to 150 bar in a multistage intercooled compressor. Steam will be extracted from at variable working pressure before the existing low pressure turbines.
Secondary environmental impacts and costs of solvent makeup will be minimized. Even in the presence of dissolved CO2, piperazine is stable up 150oC. Oxidation of piperazine is slow and will be further reduced by a proprietary oxidation inhibitor. Its amine volatility at lean conditions is less than 20 ppm and emissions will be reduced by effective water wash to 1 ppm or lower as required to eliminate any significant effects on atmospheric air pollution. Reclaiming by sulfate crystallization and advanced thermal distillation will remove sulfate, flyash, and other impurities from the flue gas and limestone slurry scrubbing. Piperazine is available as a commercial amine that has been heavily used in acid gas treating and can be intentionally produced in new plants by the hydrodimerization of monoethanolamine.