Original Paper Study on gravity flow of granules in beds supported by louver–sublouver system J. Smid a , S.S. Hsiau b,c, * , S.A. Tsai b , C.C. Tzeng a , Y.P. Chyou a a Institute of Nuclear Energy Research, Atomic Energy Council, ROC, No. 1000, Wunhua Road, Longtan Township, Taoyuan County 32546, Taiwan, ROC b Department of Mechanical Engineering, National Central University, No. 300, Jungda Road, Chung-Li City, Taoyuan County 32001, Taiwan, ROC c Graduate Institute of Energy Engineering, National Central University, No. 300, Jungda Road, Chung-Li City, Taoyuan County 32001, Taiwan, ROC article info Article history: Received 22 December 2007 Received in revised form 28 March 2008 Accepted 12 April 2008 Keywords: Moving granular bed Louvered walls Sublouvers Gas filtration High-temperature gas cleanup abstract The moving granular bed filter has been developed for high-temperature gas cleanup. The existence of stagnant zone is an important problem to be solved since the dust particulates and fly ash coming with flue gas may plug the system and the filtration efficiency decreases remarkably. We proposed the idea of placing sublouvers into the convergent channel between louvers. The idea has been demonstrated the possibility to diminish the stagnant zones. This paper tries to study the influence of vertical shift of the sublouver position on the flow pattern. A quasi two-dimensional cross-flow moving granular bed, with systems of louvers and sublouvers, was used as the experimental facility. We used the silica sands as filter granules discharged from an upper hopper and circulated to the bed. An image pro- cessing system was used to record the granular flow for analyzing the flow patterns and velocity fields of filter granules. In this study, the optimum design of louver–sublouver moving bed has been demon- strated to almost completely eliminate the stagnant zones. Besides the quasi two-dimensional cross-flow moving bed tests, we also tested a three-dimensional moving bed using the optimum design of louver–sublouver. The results were also very satisfactory. Ó 2008 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved. 1. Introduction The price of crude oil continually increases due to limited re- sources. Burning of fossil fuel in electricity generation, industry, agriculture and transportation causes serious greenhouse effect resulting in global warming. Precautionary and prompt action be- come necessary. Based on combustion and gasification of coal or biomass, the power generation systems of integrated gasification combined cycle (IGCC) and advanced pressurized fluidized bed combustion (PFBC), are important to be developed. For these power systems, the gasified gases with very high-temperature, above 1260 °C, enter gas turbines to generate power. Therefore the flue gas needs to be cleaned and desulfurized in high-temper- ature environment. Granular moving bed filters and adsorbers for hot gas cleanup continue to be developed as a key component of current IGCC and PFBC power generation systems [1]. In order to protect downstream heat exchanger and gas turbine components from fouling and erosion while cleaning the gas stream to meet environmental emission requirements, it is very critical for the power system to perform effective particulate removal. Several conventional gas cleanup technologies could be employed for IGCC applications, but they may cause higher costs and lower efficiency. On the other hand, the hot gas filtration is necessary for an ad- vanced PFBC system since cold gas cleanup is not a practical option [2,3]. The good performance of hot gas cleanup is really essential for the higher power generation efficiencies resulting from reten- tion and utilization of the sensible heat in the flue gases. Due to the limitations of the developed technologies, however, current IGCC systems remove particulates by condensing or quenching the raw fuel gas with water (wet scrubbing). Present PFBC designs employ cyclone (inertial) separators upstream of the gas turbine, in conjunction with an electrostatic precipitator (ESP) and fabric filter downstream of the gas turbine. The high efficiency could not be accomplished without a mature development of hot gas cleanup technology. By passing a contaminated gas through a bed of granular mate- rial such as sand or granular adsorbent, granular bed is possible to be employed to remove the gas-entrained particulates and chemi- cal impurities [4]. In the case of filtration, the gas-entrained partic- ulates are collected on the upstream surface of and within the granular bed. However the fixed-bed suffers from a major disad- vantage because the gas flow must be stopped for cleaning from time to time. It is less effective in removing small particulates to employ the fluidized bed technology although it is continuous in operation. Furthermore, it requires a substantially uniform flow of gas. Any sudden surge of gas going through the fluidized bed can result in not only the previously contained particulates passing 0921-8831/$ - see front matter Ó 2008 The Society of Powder Technology Japan. Published by Elsevier BV and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2008.04.002 * Corresponding author. Address: Department of Mechanical Engineering, National Central University, No. 300, Jungda Road, Chung-Li City, Taoyuan County 32001, Taiwan, ROC. Tel.: +886 3 426 7341; fax: +886 3 425 4501. E-mail address: sshsiau@cc.ncu.edu.tw (S.S. Hsiau). Advanced Powder Technology 20 (2009) 127–138 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt