Carbon capture conditions

In recent years, the efficiency of electricity plants that operate with pulverized coal has improved steadily from about 35% to close to 40%, since it has been possible to raise the temperature and pressure of the steam, consequent upon the development of new alloys for turbine blades. The latest state-of-the-art, coal-fired plant, which uses supercritical pressure steam conditions, has an efficiency as high as 46%. Some new coal stations of this type are equipped with carbon capture, while others are being built capture ready (/.c., with appropriate land and other facilities for the required technology to be installed later). The reason for the latter option is that carbon dioxide capture adds to the capital and operating costs and will not lightly be undertaken until demanded by legislation or the economics become favourable. 

For the ZEPP system presented in Fig. 2.7 the allowable installed costs for the capture plant have been estimated to be in between 80 and 120M for a 1.4GWthermai input natural gas combined cycle (NGCC) plant. To meet the cost targets, an ITM based ZEPP power plant should have an electric efficiency of at least 52%. Capture ratios (carbon captured/carbon fed to the process) of 100% result in plant efficiencies lower than 50%. Capture ratios of the order of 85% are accompanied with plant efficiencies of about 52%. The allowable installed costs window is satisfied when the oxygen flux is at least 20 ml/cm min and the costs of the ITM tubes should be less than 1,500 /m. This clearly sets the targets for materials and turbine development in order for the system to be economically viable within the capture cost boundary conditions. 

Lozinska, M.M., Mangano, E., Mowat, J.P.S., Shepherd, A.M., Howe, R.F., Thompson, S.P., Parker, J.E., Brandani, S., Wright, P.A. Understanding carbon dioxide adsorption on univalent cation forms of the flexible zeolite rho at conditions relevant to carbon capture from flue gases. J. Am. Chem. Soc. 134, 17628-17642 (2012)... 

The chemical stability of the K-Mg70 sorbent material was shown for more than 1500 cycles of adsorption and desorption at the envisaged industrial operating conditions. In Figure 6.7, the CO2 level in the product gas is plotted for the first 1400 cycles. The low slip of CO2 in the product gas confirmed that carbon capture levels of well above 95% can be realised with the SEWGS technology. In additional experiments, the chemical stability was demonstrated for more than 4000 cycles. 

The composition and physical condition of flue gases present a challenging environment in which the adsorbents will need to operate. Water and oxygen will always be present in the flue gases, irrespective of the fuel combusted. As their removal prior to the capture process will involve a significant energy penalty, any solid sorbent for carbon capture will have to meet the performance requirements and be stable in the presence of these components. This leads to one key difference between amine solvent systems and solid adsorbent systems where water poses little problem in what is already an aqueous system. 

Ouyang, LB. New Correlations for Predicting the Density and Viscosity of Supercritical Carbon Dioxide under Conditions Expected in Carbon Capture and Sequestration Operations, The Open Petroleum Engineering Journal, Vol. 4 (2011), pp 13 - 21... 

Similarly to any separation problem, the definition of the system boundary conditions is an essential prerequisite before simulations are performed. In the case of post-combustion carbon capture, the boundary conditions will correspond to the flue gas composition at the inlet, and the target purity specifications for pipeline transport at the outlet (Figure 2.1). 

Figure 2.1 Schematic representation of the different steps included in the carbon capture and storage chain, showing the inlet and outlet boundary conditions of the capture step.

Second, what will be the energy requirement of the process when the previous conditions are fulfilled The energy challenge, one of the most stringent selection criteria of carbon capture processes has to be stressed here. 

An ipso attack on the fluorine carbon position of 4-fIuorophenol at -40 °C affords 4-fluoro-4-nitrocyclohexa-2 5-dienone in addtion to 2-nitrophenol The cyclodienone slowly isomenzes to the 2-nitrophenol Although ipso nitration on 4-fluorophenyl acetate furnishes the same cyclodienone the major by-product is 4 fluoro-2,6-dinitrophenol [25] Under similar conditions, 4-fluoroanisole pnmar ily yields the 2-nitro isomer and 6% of the cyclodienone The isolated 2 nitro isomer IS postulated to form by attack of the nitromum ion ipso to the fluorine with concomitant capture of the incipient carbocation by acetic acid Loss of the elements of methyl acetate follows The nitrodienone, being the keto tautomer of the nitrophenol, aromatizes to the isolated product [26] (equation 20) Intramolecular capture of the intermediate carbocation occurs in nitration of 2-(4-fluorophenoxy)-2-methyIpropanoic acid at low temperature to give the spiro products 3 3-di-methyl-8 fluoro 8 nitro-1,4 dioxaspiro[4 5]deca 6,9 dien 2 one and the 10-nitro isomer [2d] (equation 21)... 

A mixture of exo- and endo-isomers of 5-methylbicylo[2.2.1]hept-2-ene is hydrogenated with the aid of five equivalents of triethylsilane and 13.1 equivalents of trifluoroacetic acid to produce a 45% yield of < <7o-2-methylbicylo[2.2.1] heptane (Eq. 71). The same product is formed in 37% yield after only five minutes. The remainder of the reaction products is a mixture of three isomeric secondary exo-methylbicylo[2.2.1]heptyl trifluoroacetates that remains inert to the reaction conditions. Use of triethylsilane-l-d gives the endo-2-methylbicylo-[2.2.1]heptane product with an exo-deuterium at the tertiary carbon position shared with the methyl group. This result reflects the nature of the internal carbocation rearrangements that precede capture by the silane.230... 

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