Değişik sorbentler yardımıyla baca gazlarından kükürt dioksit'in giderilmesi

Abstract

Sulphation experiments were performed under bag-filter conditions, at constant temperature (338 K) and in a gaseous mixture consisting of 5 % O2, 10 % C02, 85 % N2 with the 55 % relative humidity and conducted in two different systems; 1) In a fixed bed reactor and 2) In a thermogravimetric analysis system. Ca(OH)2 conversions and total sulphur dioxide sorption capacities of the activated sorbents were determined. It was observed that the sulphation results obtained from fixed bed reactor and thermogravimetric analysis systems are compatible with each other. The measured Ca(OH)2 conversions of the activated sorbents ranged from 17.96 % to 96.05 %. The chemical composition of the sorbents has minor importance in sulphation, whereas wide variations in the sulphation properties of sorbent can be related to the differences in their physical properties. An ampirical relation between Ca(OH)2 conversion or sulphur dioxide sorption capacities and physical properties of sorbents were found. The unreacted shrinking core model was used to modeling sulphation reactions which were performed in a thermogravimetric analysis system in the gaseous atmosphere with three different relative humidity. According to this model, for spherical particles, the analytical relationship between conversion and reaction time depends upon the rate controlling step. A comparison between the experimentally determined conversion-time data and the theoretical values calculated by using the equations of this model were made. The experimental results were found to be correlated successfully by this model. The effect of sulphation conditions on the overall reaction rates of activated sorbents was also investigated. Calculated initial rate constants values (ks) and ultimate Ca(OH)2 conversions increased with increasing relative humidity of sulphation atmosphere. XX The deliquescent inorganic salts (NaCl, KCI, LiCl, CaCl2, BaCl2, Na2S04, NaS03, Ca(N03)2, NaN03, NaN02, Na2S203; NaBr, etc.) are also used to increase the Ca(OH)2 reactivity. These deliquescent substances improve the Ca(OH)2 reactivity by absorbing a great amount of water on the sorbent surface. As mentioned earlier, the relative humidity and the amount of water adsorbed on the surface of sorbent have strong effect on sulphur dioxide capture. Sulphation reactions that take place in these processes for different sorbents are given below: Ca(OH)2 + S02 > CaS03. Vz H20 + V% H20 (5) 2 CaOSi02 3/2 H20 + 2 S02 > 2 CaS03. Vi H20 + 2 Si02 + H20 (6) Ca(OH)2. Salt + S02 > CaS03. Vi H20 + Salt + '/2 H20 (7) In this study, reactivation of Ca(OH)2 with fly ash and silica fume samples was activated by hydrating them at different conditions. Also, the sulphation properties of activated sorbents were investigated. For this purpose, fly ash samples collected from five different coal-fired power plants and three fluidized bed systems in Turkey were used. The effect of hydration conditions such as temperature, pressure, time and fly ash/Ca(OH)2 weight ratio on the physical properties of activated sorbents were determined. A statistical design technique was applied by using of two-level factorial design matrix to interprate experimental results. The physical properties, which involve pore volume (cc/cc), surface area (m /g) and average pore radius (urn) of the activated sorbents prepared under different conditions were determined using a mercury porosimeter (AUTOSCAN-33). It was found that the physical properties of sorbents were strongly effected by the hydration conditions and chemical composition of puzzolan material. The ampirical equations derived from the experimental data by regression analysis clearly showed that; the surface area values of activated sorbents increased with increasing hydration time and temperature. In addition, it was determined that the hydration at a pressure higher than atmospheric pressure caused a reduction in sorbent preparation time and the ratio of fly ash to Ca(OH)2. The activated sorbents were characterized by using their thermal decomposition TG curves and X-ray diffraction patterns. X-ray diffraction patterns indicated that calcium silicate hydrates and calcium aluminum silicate hydrates were the principal Ca-containing species formed during the hydrothermal reaction between Ca(OH)2 and fly ash or silica fume. Fly ash samples were also activated by hydration at different conditions without mixing them with Ca(OH)2. Experimental results showed that fly ashes with high CaO content can be used as S02 sorbent after activation. XIX Sulphation experiments were performed under bag-filter conditions, at constant temperature (338 K) and in a gaseous mixture consisting of 5 % O2, 10 % C02, 85 % N2 with the 55 % relative humidity and conducted in two different systems; 1) In a fixed bed reactor and 2) In a thermogravimetric analysis system. Ca(OH)2 conversions and total sulphur dioxide sorption capacities of the activated sorbents were determined. It was observed that the sulphation results obtained from fixed bed reactor and thermogravimetric analysis systems are compatible with each other. The measured Ca(OH)2 conversions of the activated sorbents ranged from 17.96 % to 96.05 %. The chemical composition of the sorbents has minor importance in sulphation, whereas wide variations in the sulphation properties of sorbent can be related to the differences in their physical properties. An ampirical relation between Ca(OH)2 conversion or sulphur dioxide sorption capacities and physical properties of sorbents were found. The unreacted shrinking core model was used to modeling sulphation reactions which were performed in a thermogravimetric analysis system in the gaseous atmosphere with three different relative humidity. According to this model, for spherical particles, the analytical relationship between conversion and reaction time depends upon the rate controlling step. A comparison between the experimentally determined conversion-time data and the theoretical values calculated by using the equations of this model were made. The experimental results were found to be correlated successfully by this model. The effect of sulphation conditions on the overall reaction rates of activated sorbents was also investigated. Calculated initial rate constants values (ks) and ultimate Ca(OH)2 conversions increased with increasing relative humidity of sulphation atmosphere. XX The deliquescent inorganic salts (NaCl, KCI, LiCl, CaCl2, BaCl2, Na2S04, NaS03, Ca(N03)2, NaN03, NaN02, Na2S203; NaBr, etc.) are also used to increase the Ca(OH)2 reactivity. These deliquescent substances improve the Ca(OH)2 reactivity by absorbing a great amount of water on the sorbent surface. As mentioned earlier, the relative humidity and the amount of water adsorbed on the surface of sorbent have strong effect on sulphur dioxide capture. Sulphation reactions that take place in these processes for different sorbents are given below: Ca(OH)2 + S02 > CaS03. Vz H20 + V% H20 (5) 2 CaOSi02 3/2 H20 + 2 S02 > 2 CaS03. Vi H20 + 2 Si02 + H20 (6) Ca(OH)2. Salt + S02 > CaS03. Vi H20 + Salt + '/2 H20 (7) In this study, reactivation of Ca(OH)2 with fly ash and silica fume samples was activated by hydrating them at different conditions. Also, the sulphation properties of activated sorbents were investigated. For this purpose, fly ash samples collected from five different coal-fired power plants and three fluidized bed systems in Turkey were used. The effect of hydration conditions such as temperature, pressure, time and fly ash/Ca(OH)2 weight ratio on the physical properties of activated sorbents were determined. A statistical design technique was applied by using of two-level factorial design matrix to interprate experimental results. The physical properties, which involve pore volume (cc/cc), surface area (m /g) and average pore radius (urn) of the activated sorbents prepared under different conditions were determined using a mercury porosimeter (AUTOSCAN-33). It was found that the physical properties of sorbents were strongly effected by the hydration conditions and chemical composition of puzzolan material. The ampirical equations derived from the experimental data by regression analysis clearly showed that; the surface area values of activated sorbents increased with increasing hydration time and temperature. In addition, it was determined that the hydration at a pressure higher than atmospheric pressure caused a reduction in sorbent preparation time and the ratio of fly ash to Ca(OH)2. The activated sorbents were characterized by using their thermal decomposition TG curves and X-ray diffraction patterns. X-ray diffraction patterns indicated that calcium silicate hydrates and calcium aluminum silicate hydrates were the principal Ca-containing species formed during the hydrothermal reaction between Ca(OH)2 and fly ash or silica fume. Fly ash samples were also activated by hydration at different conditions without mixing them with Ca(OH)2. Experimental results showed that fly ashes with high CaO content can be used as S02 sorbent after activation. XIX Sulphation experiments were performed under bag-filter conditions, at constant temperature (338 K) and in a gaseous mixture consisting of 5 % O2, 10 % C02, 85 % N2 with the 55 % relative humidity and conducted in two different systems; 1) In a fixed bed reactor and 2) In a thermogravimetric analysis system. Ca(OH)2 conversions and total sulphur dioxide sorption capacities of the activated sorbents were determined. It was observed that the sulphation results obtained from fixed bed reactor and thermogravimetric analysis systems are compatible with each other. The measured Ca(OH)2 conversions of the activated sorbents ranged from 17.96 % to 96.05 %. The chemical composition of the sorbents has minor importance in sulphation, whereas wide variations in the sulphation properties of sorbent can be related to the differences in their physical properties. An ampirical relation between Ca(OH)2 conversion or sulphur dioxide sorption capacities and physical properties of sorbents were found. The unreacted shrinking core model was used to modeling sulphation reactions which were performed in a thermogravimetric analysis system in the gaseous atmosphere with three different relative humidity. According to this model, for spherical particles, the analytical relationship between conversion and reaction time depends upon the rate controlling step. A comparison between the experimentally determined conversion-time data and the theoretical values calculated by using the equations of this model were made. The experimental results were found to be correlated successfully by this model. The effect of sulphation conditions on the overall reaction rates of activated sorbents was also investigated. Calculated initial rate constants values (ks) and ultimate Ca(OH)2 conversions increased with increasing relative humidity of sulphation atmosphere.