| Summary: | 碩士 === 中原大學 === 化學工程研究所 === 97 === Abstract
Production of hydrogen chloride (HCl) in an incineration or combustion process, such as municipal solid waste (MSW) incinerator and RDF boiler shows an appearance of the apparatus being corroded. Due to the strong oxidation of HCl, the apparatus of an incinerator, combustor or boiler cannot avoid the corrosion by HCl. An experiment of removing HCl in high temperature was designed for the purpose to become more familiar with the process of removing HCl in situ furnace at high temperature. Ca-Based sorbents are commonly used in an incineration process to remove acid gases from flue gas such as HCl and sulfur dioxide (SO2). The purpose of this present study is to investigate the initial reaction behaviors of calcium oxide (CaO) and HCl. The experiments were carried out in a bench scale fixed-bed reactor and the experimental data were analyzed by unreacted shrinking-core model to calculate the reaction rate constants at each temperature. The tested reaction temperatures were operated in a range of 600-800℃ in this study. The average sorbent diameters were 163, 385 and 545 μm, respectively. Breakthrough curve is an important index in fixed bed reactor. The utilization of sorbent and width of mass transfer zone can be understood from the breakthrough curve. By the results of this experiment, there was the most utilization and narrowest mass transfer zone before breakthrough time at 650℃.
Scanning electron microscope (SEM) analyses showed that the rare-limiting step for the reaction altered with the extent of solid conversion in sequence at temperature exceeding 600℃: chemical reaction control, and simultaneous chemical reaction and product layer diffusion control for a long period of time. The experimental results were analyzed by using the unreacted shrinking core model. At high temperature, the product layer is loose and porous. The reaction rate does not only relate to temperature, it is also affected by the type and structure of sorbent and bed porosity. The activation energy of the CaO and HCl surface reaction are 6.84, 5.00 and 4.37 (kJ/mol) for 163,385 and 545μm sorbents was obtained from the analysis of the reaction rate constants in Arrhenius' law in this present. Combining the data of this present and previously, the reaction between CaO and HCl is a two steps mechanism in series. The controlling mechanism step is that CaO reacts with HCl to produce the mediate, calcium hydrochloride (CaClOH), at high temperature (>=650℃); on the other hand, CaClOH reacts with HCl to produce CaCl2 at low temperature (<650℃).
The experimental result show that the conversion of CaO to CaCl2 increases with bed high. The effect of CaCO3 removing HCl is the same between CaO and HCl at high temperature. The calcination of CaCO3 took place under high temperature condition simultaneously with the reaction of CaCO3 and HCl. The activation energy of the CaCO3 and HCl surface reaction is 21.32 kJ/mol.
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