Evaluation of fluid dynamics in a hot and a cold system of interconnecting fluidised beds
Conference contribution, 2009
Interconnecting fluidized beds is a well known principle, applied in circulating fluidized bed (CFB) boilers (combustor-external cooler). The two reactors are connected by fluidised loop-seals which allow the material to circulate while the gases are kept separate (figure 1). This technique is as well the foundation for more recent developments such as, indirect gasification (IG) and chemical looping combustion (CLC) [1-3]. The insistence of a nitrogen free atmosphere during operation in IG and CLC, compared to CFB-boilers, puts elevated demands on tightness in loop-seals and the knowledge of fluid dynamics. A cold reactor system of interconnecting fluidised beds is built to study fluid dynamics of an equally sized hot reactor system. The hot reactor system is coupled to the raw gas line in Chalmers biomass Gasifier system , where the main emphasis of research is to study gas solid interactions. This hot reactor system will be taken into operation during autumn 2009. The perspex cold reactor system has been in operation during the summer 2009 with both air and helium as fluidising media. Helium is used as a complement to air, as the density and viscosity has better agreement with the gases in the hot system. Since helium is a much more expensive gas than pressurised air several experiments are performed to find a correlation between these. The research of the cold reactor system is focused on mapping pressure profiles in the system and solid rate circulation as a function of fluidisation velocity (u0). The study shows that the Solid rate circulation can be sufficiently controlled with both u0 in the inferior loop-seal and u0 in the riser. It is also shown that experiments performed with air and helium can give sufficient agreement. Furthermore, the pressure signals are shown to give vital information regarding solid rate circulation and fluidisation regimes in the riser.
Dual fluidised bed