Abstract
Abstract In this work, a gas containing CO2 and SO2 at the usual concentrations on the coal combustion flue gas reacted with calcium hydroxide to evaluate and quantify the influence of SO2 on the CO2 capture and vice versa. This influence was quantified with a continuous gas analyzer and by thermogravimetry (TG). Results show that the CO2 retained increases in general as its concentration does and decreases as the SO2 concentration increases. A similar behavior was found for the SO2 retention at different CO2 concentrations being more relevant the influence of the presence of SO2 on the CO2 capture than the opposite one. Results suggest that for a high CO2 capture, SO2 should be eliminated previously. With respect to the reaction process it was found that the desulfurization product clearly identified was CaSO3·½H2O; in the reaction between Ca(OH)2 and CO2, CaCO3 is mainly obtained, the complex CaO·CO2 being another possible product synthesized in low amount. Gas analyzer shows that SO2 and CO2 react simultaneously and that a part of the CaCO3 reacts with the SO2 and releases CO2. Sulfation values calculated by TG and from the gas analyzer are very similar but the amount of CO2 captured is not possible to know clearly by TG due to the synthesis and decomposition of CaCO3 during the process. The study of the evolution of the sorbent porosity in the process reveals that the presence of both acid gases produces a lower blockage of the pores than when only one gas is present probably due to the generation of new pores in the reaction of CaCO3 and SO2.
Highlights
Coal combustion is one of the energy sources for electricity generation
The flue gas generated from coal combustion power plant contains CO2 and SO2 at concentrations depending on the coal sulfur content, as well as NOx, H2O, O2 and N2
To calculate the calcium utilization in the reaction with CO2 by TG it must be considered that the CaCO3 present in the reacted sorbent is mainly due to the CaCO3 present in the commercial Ca(OH)2, the CaCO3 synthesized with the CO2 captured and the CaCO3 disappeared by reaction with SO2
Summary
Coal combustion is one of the energy sources for electricity generation. Coal produced about 18% of Spanish electricity and recently, as Spain depends on coal industry for employment, the government, according to the European Community, approved to maintain subsidies for domestic coal used to generate energy up to 2014 [1]. The influence of the presence of SO2 and CO2, at the usual concentrations in a coal combustion flue gas, on the co-capture of both gases by calcium hydroxide at low temperature is studied. The objectives were to know the reaction process and the products synthesized to explain the modification of the sorbent porosity and the influence of the presence of one gas on the capture of the other one, quantifying with two different techniques, this influence. All of this information will be used to predict the influence of the presence of SO2 on the cyclic CO2 capture by Ca(OH) at low temperature
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