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Show formation and clogging are readily resulted from using limestone as absorbent. Therefore, packing tower is out of the scope of this study. (2) 802 gas analyzer: Beckman Model 880 Non-dispersive Infrared Analyzer. (3) Absorbent limestone: Produced at I-Lan, Taiwan; composition: CaO 51.05%, MgO 0.83%, 8i02 5.86%, and Al203 0.059%; particle size 100% < 27nm. (4) Flue gas: Air (heated to 130 0C ); NG ( controlled at 130 0C ); coal (controlled at 130 °C ). Compositional ~alysis is shown in Table 4. 2. Methods: In order to effectively control 802 removal efficiency and render FGD system to reach optimum operation condition, it is essential to study factors influencing 802 removal efficiency. Generally, pH value in reaction tank, Ca/8 or Mg/8 mole ratio, flux ratio of circulating slurry to flue gas (UG ratio ), 802 concentration, flow rate of flue gas (i.e., turndown ratio) and others are important factors influencing 802 removal efficiency; among which, variation of pH value is in relation to Cat8.or Mg/8 ratio so that it is not an independent variable. Commercial FGD systems often use pH to control feeding amount of absorbent. However, we choose 802 concentration, Ca/8 or Mg/8 ratio, I.JG ratio and turndown ratio as major influential factors. Furthermore, in order to obtain meaningful informations, we adopt partial factorial design as our experiment design method [7] to examine factors influencing 802 removal efficiency. Before performing tests on influencing factors, air was heated to 130 °C and injected 802 to make artificial flue gas with 1000ppm 802 for carrying out primary test on 802 removal efficiency. A 802 gas analyzer was used to analyze 802 concentration input and output the absorber to calculate 802 removal efficiency, and further coupled with stoichiometry ratio to estimate utilization of absorbent. Based on this, experimental testing conditions of partial factorial design were thus determined ( Table 5). Then, flue gas produced by natural gas injected with various amount of 802 was used in 9 groups of experimental tests. Their results was subject to statistical analyzing process so as to obtain degree of influence of various factors on 802 removal efficiency of this system. 3. Results: (1) Table 6 lists results of tests under same conditions by using air, natural gas and coal combustion flue gases as samples, which indicate that flue gases with different composition have little effect on 802 removal efficiency.The 802 removal efficiency includes 10% efficiency by prescrubber so that it can be lighter than Cat8 ratio. (2) Results from 9 groups of partial factorial design experiments performed on spray and sieve tray towers and variance analysis data were listed in Table 7 and 8. These results suggested that, in spray tower, UG ratio affects 802 removal efficiency the most, 802 concentration is the next, while Cat8 ratio and Turndown ratio (Tr) have relatively neglible effect. In sieve tray tow~r, the most influential factor is 802, lJG 5 |