An Experimental Study of Carbon Dioxide Desorption from a Calcium Oxide Based

Synthetic Sorbent Using Zonal Radio-Frequency HeatingE Pradhan Dr J Fernandez Prof E Rebrov ndash epradhanwarwickacuk JFernandezwarwickacuk ERebrovwarwickacuk

Department of Engineering University of Warwick Coventry CV4 7AL

Ove

rvie

w Hydrogen (H2) is seen by many as a promising future energy carrier As part of a larger study into the production of H2 fuel cells the main aim of this project is to test the efficiency of two different samples of Calcium Oxide (CaO) in adsorbing Carbon Dioxide (CO2) using a zonal heating method which in theory should result in major energy savings due to reduced heat losses to the environment

Fuel

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The set up is shown in figures 1 and 2 CO2 and Nitrogen (N2) flow through the gas inlet and into a mass spectrometer A copper coil is placed around the reactor and is heated using a RF generator With the intentions of carrying out these same processes at much larger scales industrial temperatures (650degC - 850degC) are used The research consists of twenty cycles worth of data Each cycle had two steps adsorptioncarbonation and desorptioncalcination where the reversible reaction stated by equation 4 takes place at approximately 650degC and 850degC respectively measured using an infrared camera Regenerating the sorbent (desorptioncalcination step) results in releasing CO2 suitable for storage

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Equations (1) ndash (3) Steam reforming reversible reactions for methaneCO2 can be removed from the equations stated above by using a sorbent (a material used to absorb or adsorb liquids or gases) Sorption enhancement enables lower reaction temperatures while maintaining the conversion To enhance the reaction the CO2 produced should be removed

CH4 + H2O hArr CO+3H2 CO + H2O hArr CO2 + H2 CH4 + 2H2OhArr CO2 +4H2

ΔH = 2062 kJ mol1113088-1 (1)ΔH = -421 kJ mol1113088-1 (2)ΔH = 165 kJ mol1113088-1 (3)

Figure 3 Experimental setup of reactor

Figure 4 Expected concentration of CO2 outlet in the mass spectrometer for a given CaO sample for one cycle of the experiment The table shows how the CO2 signal measured by the mass spectrometer changes with respect to the other variables in the experiment

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Equations (4) The carbonationcalcination (or adsorptiondesorption) equilibrium reaction CaO has been investigated thoroughly as a suitable sorbent for SER processes and is believed to be thermodynamically the best candidate among metal oxides for CO2 capture in zero emission power generation systems This experiment tests two different samples of CaO powder

CO2 + CaO hArr CaCO3 ΔHabs = -170 kJ mol1113088-1 (4)

Figure 1 Fuel cells are devices that convert chemical energy from a fuel into electricity through a chemical reaction of positively charged H2 ions with oxygen (O2) Fuel cells can eliminate pollution caused by burning fossil fuels for hydrogen fuelled fuel cells the only by-product at point of use is water

0 2 4 6 8 10 12 14 16 18 200

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Adsorption Cycle SummariesSample 1Sample 2

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0 2 4 6 8 10 12 14 16 18 200

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Desorption Cycle Summaries

Sample 1Sample 2

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Rates of adsorption and desorption used to calculate the capacities (in mass ie the percentage mass of CO2 adsorbed per given percentage mass of CaO) to calculate which of the two samples is more efficient as a sorbent Referring to graphs 1 and 2 sample 1 initially has a higher capacity However the greater degradation of said capacity over twenty cycles in comparison to sample 2 leads to the idea that it has the lower capacity evident from adsorption cycle 15 onwards Recorded temperature data proved the effectiveness of RF heating Temperatures of 850degC were reached in a matter of five minutes with only 170A supplied much faster than conventional methods of heating

Graphs 1 (above) amp 2 (below)

Figure 2 RF heating setup with RF generator connected to copper coil via heating workhead The use of dielectric materials (electrical insulators that can be polarized by an applied electric field) means heat is dissipated instead of conducted through the material enabling zonal heating This also allows much higher heating ratesRa

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• Slide 1