Korean J. Chem. Eng., 25(5), 1178-1183 (2008) SHORT COMMUNICATION 1178 † To whom correspondence should be addressed. E-mail: hjryu@kier.re.kr Development of novel two-interconnected fluidized bed system Ho-Jung Ryu* ,† , Young-Cheol Park*, Sung-Ho Jo*, and Moon-Hee Park** *Korea Institute of Energy Research, Daejeon 305-343, Korea **Hoseo University, Asan 336-795, Korea (Received 24 August 2007  accepted 4 March 2008) Abstract −Two-interconnected fluidized bed systems are widely used in various processes such as Fisher-Tropsch, hot gas desulfurization, CO 2 capture-regeneration with dry sorbent, chemical-looping combustion, sorption-enhanced steam methane reforming, chemical-looping hydrogen generation system, and so on. However, conventional two-in- terconnected fluidized bed systems are very complex, large, and difficult to operate because most of these systems re- quire a riser and/or pneumatic transport line for solid conveying and loopseals or seal-pots for gas sealing, recirculation of solids to the riser, and maintaining of pressure balance. To solve these problems, a novel two-interconnected fluidized bed system has been developed. This system has two bubbling beds, solid injection nozzles, solid conveying lines, and downcomers. In this study, the effects of operating variables on solid circulation rate and gas leakage between two beds have been investigated in a cold mode two-interconnected fluidized bed system. The solid circulation rate increased as the hole diameter on the injection nozzle, the diameter of the injection nozzle, the solid height above the holes, and the number of holes on the injection nozzle increased. The gas leakage between the beds was negligible. Moreover, long-term operation of continuous solid circulation up to 60 hours was performed to check the feasibility of stable op- eration. The pressure drop profiles in the system loop were maintained steadily and solid circulation was smooth and stable. Key words: Fluidized Bed, Gas Leakage, Long-term Operation, Solid Circulation Rate INTRODUCTION Two interconnected fluidized bed systems are widely used in var- ious processes to accomplish simultaneous dual reactions in one process such as Fisher-Tropsch, hot gas desulfurization, CO 2 cap- ture-regeneration with dry sorbent, chemical-looping combustion, sorption enhanced steam methane reforming, chemical-looping hy- drogen generation system, and so on. Most of these processes need two or more reactors and need non-mechanical valves for solid con- veying and gas sealing between two reactors such as loopseal, seal pot, J-valve, L-valve, U-valve, and so on [1]. Fig. 1 shows a con- ceptual diagram of conventional two interconnected circulating flu- idized bed systems [2-4]. Fig. 1(a) represents bubbling-bubbling- transport mode. This mode consists of two bubbling beds, one trans- port bed, two loopseals and three cyclones. Two bubbling beds are used as reactors for each reaction and the transport bed is used for solid conveying. This mode is usually applied when two reactions are slow and longer contact time between gas and solid is favor- able. However, this mode is difficult to operate because maintain- ing the pressure balance for three fluidized beds and loopseals is difficult, and a back flow of solid is the main problem. Indeed, this mode requires much solid inventory in loopseals and many gas in- jection ports, at least five. If one reaction rate is fast enough, the transport bed can be used for reaction and solid conveying, simul- taneously, as shown in Fig. 1(b). This mode consists of one bub- bling bed, one transport bed, two loopseals and two cyclones. One bubbling bed is used as reactor and the transport bed is used for reac- tion and solid conveying, simultaneously. In this mode it is also dif- ficult to maintain the pressure balance for two fluidized beds and loopseals (or other non-mechanical valves). The main disadvantages of bubbling-bubbling-transport and bubbling-transport mode are com- plexity and huge system volume. Actually, these two systems con- tain four or five vessels containing a gas-solid mixture (two or three fluidized beds and two loopseals), and therefore, many gas flows are required and the volume of systems is huge. To solve these problems, a two bubbling bed mode (Fig. 1(c)) has been proposed, which consists of two bubbling beds and two cyclones. Two bub- bling beds are used as reactors for each reaction and gases for each reaction are switched periodically. This mode is usually applied when two reactions are slow and longer contact time between gas and solid is favorable. However, there is pressure shock during gas switch- ing and this system requires purging to clean each bed before gas switching. Indeed, this mode is difficult to operate when two reac- tions take place at different temperatures. In this study, a novel two interconnected fluidized bed system has been developed. The compact two-bed system has two bub- bling beds, solid injection nozzles, solid conveying lines, and down- comers. With this system, the effects of operating variables on solid circulation rate and gas leakage between two beds have been in- vestigated and long-term operation of continuous solid circulation up to 60 hours has been performed to check the feasibility of stable operation. EXPERIMENTAL SECTION The solid circulation rate measurements, gas leakage tests, and long-term operation test were carried out in a two bubbling bed in- terconnected circulating fluidized bed system. A schematic of the system is shown in Fig. 2. The major components consist of ple-