J. Seville et al Gas flow △Pr Figure 3. Pressure distribution in medium and cake during reverse flow. is entirely uniform across the filter surface and this may be why 'patchy cleaning is observed, i. e cake is almost completely removed in some retained in others. Space does not permit discussion of the consequences of patchy cleaning for filter operation, save to note that when the filtration flow is restored after incomplete cleaning, the local gas velocity in the cleaned areas may initially be many times greater than its average or overall face velocity [13] 3 CURRENT RESEARCH Figure 4 summarizes the research issues which have been of most concern to both academic and industrial workers For the academic, the major difficulty in obtaining a full understanding of filter operation is that both filtration and cake detachment steps depend on both the fluid mechanics of the gas flow and the particle mechanics of cake formation and cake detachment (Table 2). These issues are discussed further below For the industrial user, reassurance that the ceramic filter will provide long-term stable operation is the first essential. Stephen [15]su Does the filter have sufficient mechanical strength and erosion resistance to withstand its operating environment? How can a minimal and stable operating pressure drop be achieved over the filter
662 J. Seville et al. Figure 3. Pressure distribution in medium and cake during reverse ow. is entirely uniform across the lter surface and this may be why ‘patchy cleaning’ is observed, i.e. cake is almost completely removed in some areas and completely retained in others. Space does not permit discussion of the consequences of patchy cleaning for lter operation, save to note that when the ltration ow is restored after incomplete cleaning, the local gas velocity in the cleaned areas may initially be many times greater than its average or overall face velocity [13]. 3. CURRENT RESEARCH Figure 4 summarizes the research issues which have been of most concern to both academic and industrial workers. For the academic, the major difculty in obtaining a full understanding of lter operation is that both ltration and cake detachment steps depend on both the uid mechanics of the gas ow and the particle mechanics of cake formation and cake detachment (Table 2). These issues are discussed further below. For the industrial user, reassurance that the ceramic lter will provide long-term stable operation is the rst essential. Stephen [15] summarizes the issues: ² Does the lter have sufcient mechanical strength and erosion resistance to withstand its operating environment? ² How can a minimal and stable operating pressure drop be achieved over the lter life span?
Gas cleaning at high temperatures cake formation Filtration mechanical prop chemical resistance Cake detachment geometry fracture mechani novel geometries filter surface modification <Combinations of cyclone filter (Combinations of physical chemical separators Figure 4. Research issues in the development of ceramic filters for hot gases [141 Table 2 Academic issues in ceramic filter research [141 Fluid mechanics Particle mechanics Filtration flow field distribution cake formation Cleaning pulse propagation cake detachment What is the effect of the challenging dust, in relation to the operating temperature. on the operating pressure drop? Is the filter medium suitable in relation to the particle size distribution of the challenging dust and system operating conditions? How can the energy requirement for cleaning be minimized? What are the optimum layout and geometry of the filter vessel? Industrially, these issues are being investigated through the use of pilot plants and advanced power generation demonstration plants, e. g. the 71 Mw(th) PFBC demonstration plant at Wakamatsu, Japan and the 15 MW(e)hybrid demonstration plants in Wilsonville, USA. Additionally, controlled pilot-scale investigations have been conducted. However, the majority of industrial knowledge(for both power and non-power generation applications) is gained from plant operating experience rather than a prior fundamental understanding of the principles involved. At present, the most pressing issue in industrial applications concerns the mechanical strength and chemical resistance of the filter medium in relation to its operating environment
Gas cleaning at high temperatures 663 Figure 4. Research issues in the development of ceramic lters for hot gases [14]. Table 2. Academic issues in ceramic lter research [14] Fluid mechanics Particle mechanics Filtration ow eld distribution cake formation Cleaning pulse propagation cake detachment ² What is the effect of the challenging dust, in relation to the operating temperature, on the operating pressure drop? ² Is the lter medium suitable in relation to the particle size distribution of the challenging dust and system operating conditions? ² How can the energy requirement for cleaning be minimized? ² What are the optimum layout and geometry of the lter vessel? Industrially, these issues are being investigated through the use of pilot plants and advanced power generation demonstration plants, e.g. the 71 MW(th) PFBC demonstration plant at Wakamatsu, Japan and the 15 MW(e) ‘hybrid’ demonstration plants in Wilsonville, USA. Additionally, controlled pilot-scale investigations have been conducted. However, the majority of industrial knowledge (for both power and non-power generation applications) is gained from plant operating experience rather than a prior fundamental understanding of the principles involved. At present, the most pressing issue in industrial applications concerns the mechanical strength and chemical resistance of the lter medium in relation to its operating environment.