CO2 capture by Condensed Rotational Separation

Condensed Rotational Separation (CRS) technology is a patented method to upgrade gas mixtures. A novel application is thecapture of CO2 from coal-combustion fired power stations: Condensed Contaminant Centrifugal Separation in Coal Combustion(C5sep). CRS involves partial condensation of a gas mixture: a gas mixture is brought into the vapor-liquid region bycombination of a temperature and pressure change. The liquid phase mainly contains molecules of species with the lowest partialvapor pressure. The vapor phase mainly contains molecules of species with the highest partial vapor pressure. The liquid phase isformed as a mist of micron-sized droplets as a result of mostly heterogeneous condensation. The mixture is fed to a RotationalParticle Separator (RPS). The RPS is capable of removing micron-sized droplets from a gas stream with a separation efficiencyof over 99%, and is an innovative development of the Eindhoven University of Technology in the Netherlands.To separate CO2 from pre-cleaned flue gas, i.e. flue gas that mainly consists of CO2 and N2 and is disposed of water, sulfuroxides and other particulates, the flue gas must be brought to a pressure and temperature where partial condensation occurs. Theflue gas is divided over a N2 rich vapor phase and a CO2 rich liquid phase. The concentrations of CO2 and N2 in the vapor andliquid phase are dependent on separation conditions (p,T). Separation conditions are optimized to separate a maximum amount ofCO2 from the flue gas. It is found that the amount of CO2 in the liquid phase increases at lower temperatures and for higher CO2concentrations in the flue gas feed. A CO2 feed concentration of at least 40% is required to reach reasonable separationefficiency. Depending on separation conditions, 80 to 95% of the CO2 can be captured, resulting in a reduced exhaust flow with aCO2 concentration of about 14%. The vapor-liquid phase region of N2/CO2 mixtures concerns moderate to high pressures (5150 bar) and temperatures between 20and -60o C. Power plants usually emit their flue gas at atmospheric pressure and slightly above ambient temperature.Compression and cooling of the flue gas is therefore necessary to facilitate the separation. The energy cost involved solely withcompression and cooling decreases the power plant overall efficiency with roughly 15%. Smart engineering of the installationinvolving compression, cooling, heating and expansion is required in order to minimize the penalty in plant efficiency.Irreversible losses in the process are investigated to find the minimum in energy consumption. A simple base case is energeticallyevaluated for different separation conditions and different CO2 concentrations in the feed to judge the feasibility of C5sep. It isfound that the energy cost of the cooling, compression and expansion decreases with increasing CO2 concentration in the feed. Conventional power plants widely use air for combustion of coal. This results in a CO2 concentration of 15 to 21% in the fluegas. Upgrading the CO2 concentration (i.e. CO2 enrichment) in the flue gas is a must for C5sep. The energy costs of pre- and postcombustionCO2 enrichment are investigated. Pre-combustion CO2 enrichment is realized by (partially) Oxygen Enriched CoalCombustion (OECC). The oxygen enriched combustion air is supplied by conventional cryogenic air separation, or otherwise byoxygen enrichment membranes. Post-combustion CO2 enrichment is realized by nitrogen separating membranes. The energycosts of CO2 enrichment are rising with the concentration of CO2 in the feed.This primary study on the concept of C5sep shows promising results in energy costs and separation capacity. The implementationof heat integration is expected to cut down the energy costs below that of modern carbon capturing techniques. Future work onC5sep is planned on CO2 enrichment, optimization of the separation efficiency and energy consumption, and experimentalverification of the separation part of the C5sep concept