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Performance Evaluation of Potassium Catalyst Recovery Process in the K2CO3-Catalyzed Steam Gasification System
- Author(s)
- YUAN XIANGZHOU
- Advisor
- 김형택
- Department
- 일반대학원 에너지시스템학과
- Publisher
- The Graduate School, Ajou University
- Publication Year
- 2016-08
- Language
- eng
- Alternative Abstract
- In this study, the catalyst recovery process (CRP) was investigated utilizing different operating conditions and washing methods. Two different gasified residues, generated through a catalytic steam gasification process (CSGP) in fixed and fluidized bed reactors, were collected and utilized as CRP samples. Firstly, when conducting the CSGP with K2CO3 as a catalyst, H2-rich syngas was obtained under a gasification temperature of 800 °C and catalyst loading amount of 10 wt % (saturation capacity). Based on X-ray diffraction (XRD) analysis results, the potassium compounds in the gasified residues mainly existed in three forms (KAlSiO4, KHCO3, and K2SO4). KAlSiO4 is an insoluble potassium compound, KHCO3 can be transformed from K2CO3 in the presence of H2O and CO2, and K2SO4 is steadily formed through oxidation of K2S when the gasified residue is held without discharging air treatment. Secondly, after conducting lab- and bench-scale CRPs, the following optimal operating parameters were elucidated: pressure of 20 bar, reaction time of 1 h, reaction temperature of 150 °C, water-to-residue (wt %) ratio of 10/1, and three washes using the No.1 combined washing method. Under these parameters the catalyst recovery efficiency (ηK) reached 87.62 %. Based on CRP experiments in the lab-scale reactor, a scaled-up bench reactor was designed and equipped with fast heating and cooling systems, which can accurately control reaction time, and mesh wire was set at the bottom of the reactor, in order to conveniently and readily separate the recovered catalyst from the reactor. Thirdly, Brunauer-Emmett-Teller (BET) analysis shows that the combined washing method can effectively and adequately enlarge surface area, total pore volume, and average pore size, thereby increasing the area in contact with the CRP washing solution, which increases ηK. Fourthly, the recovered catalyst was loaded with raw coal and CSGP was undertaken in order to verify its catalytic activity. Not only were the trends of carbon conversion (XC) similar at each gasification temperature, but there was also no obvious difference in volume percentage of gases produced. When adopting the random pore model (RPM), both reaction rate constant (kRPM) and activation energy (Ea) remained similar whether using fresh K2CO3 or recovered catalyst. Therefore, it can be concluded that the recovered catalyst has the same catalytic activity as fresh K2CO3. Fifthly, a new and advanced system was conceptually designed, including CSGP, CRP, and carbon capture, utilization and storage (CCUS), which will play a significant role in energy utilization in the next few decades. On one hand, the K2CO3 CSGP can produce H2-rich syngas, and the CO2 produced can be captured and used in CRP as a washing atmosphere; on the other hand, the K2CO3 catalyst, utilized in CSGP, can be recovered in CRP and recycled in CSGP to lower the catalyst investment and eliminate the pollution caused by alkali metals in gasified residues.
- Fulltext
- Appears in Collections:
- Graduate School of Ajou University > Department of Energy Systems > 4. Theses(Ph.D)
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