Acid gases, such as HCl and SO2, and dust particles emitted from fixed and mobile sources such as incinerators and diesel engines cause serious air pollution and the damages to process apparatus. To effectively reduce the acid gases and the dust particles, two treatment systems, dry and wet scrubbing systems, have been commonly used. The dry scrubbing systems are simple and no need of slurry treatment, but the conversion of sorbent and the removal efficiency of gas are low. While the wet scrubbing systems are complex and discharge liquid waste, give high removal efficiencies of gas and dust particles. For the proper design and the optimum operation of the systems, it is very important to understand the mechanism of gas absorption and dust separation, and the characteristics of the sorbents in the systems. Although some researches on these systems have been reported and mathematical models have been developed to describe the mechanism of gas absorption and dust separation, it has still not yet been clear enough.
The propose of this study is to evaluate the performance and analyze the mechanism of gas absorption in a dry system, to evaluate the performance and analyze the mechanism of gas absorption and dust separation in a wet system, and to discuss the advantages and the disadvantages of dry and wet systems.
In this section, A bag filter reactor was used to absorb SO2 using Ca(OH)2 sorbent as a dry system. The experimental apparatus has been described in detail in Mariana, et al. (2003, 2004a) as shown in Figure 1. SO2 and N2 were mixed using a gas mixer (MS-202, Stec Inc., Japan). The gases at a flow rate of 2 liter/min passed through an electric furnace were heated up to various temperatures, and then reacted with solid sorbents in a glass thimble filter (Advantex 86R, Tokyo Roshi Co. Ltd., Japan). The amount of solid sorbents was 1 g which adhered uniformly to the inner surface of the glass thimble through the use of a compressor. The glass thimble diameter was 2.2 cm, and the filtration area was 51.83 cm2. The relative humidity of the gas phase was regulated using a micro feeder (JP-V Furue Science Co. Japan) by assuming that all of the water was vaporized.
Figure 1 Experimental apparatus of a bag filter reactor.
The humidity was the ratio between the volume of water vapor and the total gas volume. The outlet concentration of SO2 was continuously measured with an SOx analyzer (EIR500S Yanaco Co., Japan). The conversion of Ca(OH)2 was calculated based on the loss of SO2 in the gas stream at the exit of the reactor. The water in the outlet gas was absorbed using a CaCl2 absorber to measure the SO2 outlet concentration. The sorbent used in this research was 72.8% - Ca(OH)2, with an ignition loss of 24.22% (Yoshizawa Lime Industry Co. Japan), had a specific surface area, SBET, of 12.6 m2/g, a density of 2.24 g/cm3, an initial porosity of particle , εpo, of 0.05, and a mean particle...