Thermogravimetric determination of the influence of water vapour in the FGD in-duct injection at low temperatures

The practical procedure to design and optimise the FGD in-duct injection pr ocesses at low temperatures requires the application of the kinetic rate eq uation of the reaction SO2-Ca(OH)(2) in the mass balances of gas and solid phases corresponding to the ductwork, the sorbent utilization ability being an important parameter in the kinetic description. The objective of the st udy was focused on the behaviour of Ca(OH)(2) working under different level s of the process variables, temperature, relative humidity and water vapour content in the gas stream, in order to evaluate their influence on the sor bent utilization in the desulfurization reaction. The experimental data wer e obtained in an integral fixed bed reactor, monitoring continuously the SO 2 content in the exit gas stream until the breakthrough curve was completed . The solid product was analysed by a thermogravimetric technique to calcul ate the final sorbent utilization. From the TG analysis, the contributions of the sulfation and carbonation reactions were established in terms of sol id conversion: X-S, mol of SO2 mol of reacted sorbent and X-C, mol of CO(2) mol of reacted sorbent, and X, total sorbent utilization considering the am ounts of both calcium sulfate and calcium carbonate in the reaction product . A detailed planning of experiments was followed: three different temperat ure levels were investigated: 54, 60, 70 degrees C, while the range of rela tive humidity was varied between 40 and 95%. The composition of the gas pha se was kept constant (4000 ppmvSO(2), 12% CO2, 5% O-2, N-2 balance) as well as the amount of sorbent introduced in the reactor. The experimental data obtained were evaluated and the statistical significance of the effects of relative humidity, temperature and their interactions, was tested through a n ANOVA table. From the sorption results, it was seen that there was a slig htly negative influence of the reaction temperature while the relative humi dity dependence was stronger at higher levels due to the sulfation reaction , with X-S values increasing from 0.05 to 0.50 when the relative humidity i ncreased from 40% to 95%. The contribution of the carbonation reaction to t he solid utilization was not affected significantly by the relative humidit y or temperature. The carbonation fraction of reacted solid, X-C, reached v alues of around 0.20 in the whole experimental range. (C) 2000 Society of C hemical Industry.