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Compact hot gas clean-up system for particulate removal phase - 1

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Advanced power generation cycles from solid fuels can contribute significantly to future European energy security. This will require particle-free combustion / gasification product gases, at high temperatures, in order to achieve significant energy efficiency and environmental benefits. State-of-the-art hot gas particle clean-up technology is typically based on ceramic candle filters (rigid and soft) and, to a lesser extent, on smaller, one-piece honeycomb cross-flow filters. The technology is still relatively far from providing reliable and cost-effective particulate removal from hot gases. Major problem areas involves mechanical failure due to ash particle bridging, filter thermal stability and materials compatibility issues. Assembling many individual filter elements (candles) into one large filter unit, are to be viewed as a giant honeycomb. All one-piece honeycomb structures have the advantage of an extremely high mechanical strength. One-piece honeycomb structures are however rarely produced with diameters of more than 500mm. By enclosing many separate elements in a vessel or container, it becomes possible to obtain the same behavior as that of a one piece fabricated cross-flow honeycomb structure. It is expected that the unit described hereby can make more efficient use of the volume taken up by filtering systems using appropriate packaging technology. The weight reduction is important for any system where load transients are common, such as emergency and peak-power electrical plants. The objective of the project was then to develop a compact hot gas particulate clean-up system by integrating three specifically tailored, advanced high temperature ceramic materials (Silicon Carbide, high strength Cordierite and Aluminum Titanate) into a novel, and cost-effective filter design with the following objectives: 1. To overcome problems with current candle technology in terms of mechanical failure due to ash bridging, resulting in filter system breakdown and costly down-time and service. 2. To improve filter thermal stability and materials compatibility. 3. To increase the filter surface to volume ratio with simultaneous reduction of overall filter weight resulting in a very compact unit. 4. To provide high filtration efficiency - low pressure drop filter media at a lower manufacturing cost. Discussion: The design of tubes assembled into a giant honeycomb proved to be a feasible solution. This design alone is responsible for overcoming several problems from known ceramic filters for hot gas applications: -Ash bridging does not occur in the gap between the filter elements in cold conditions. -No thermal cracks over the unit structure cross section is possible. -Elimination of mechanical stress transferred to neighbouring elements. -Large scale manufacturing is made possible. -The filter surface is increased compared to other filters at same volume and the unit is therefore very compact. Furthermore, the design of the filter with floating support beams for the elements makes it possible to vary the size of the filters to customer demand, to a certain extent. One of the greater problems were to design an effective sealing of a honeycomb made from individual tubes, mainly due to the manufacturing tolerances of the ceramics, and the differences in the thermal expansion coefficient of the filter elements and the vessel. Corrosion maps has been evaluated for the three ceramics, focusing on the reactions in coal combustion and gasification environments. All three ceramics proved to posses the material specifications required to provide high filtration efficiency and a low pressure drop. The cold-flow test showed filtration efficiencies in the range of 99,90% for both SiC and Cordierite, and apparent permeability in the range of 2,76x10-12 m(2) for SiC. Furthermore, the test showed that both SiC and Cordierite have got the mechanical strength needed, making the filter less sensitive to load transients. Final conclusion: -A compact hot-gas filter with the desired specifications has been designed. -The three ceramic materials have been developed, tested, refined and evaluated. -A full-scale prototype has been constructed and cold flow tests have been carried out for two of the materials, and have proven that such a filter works under these conditions.

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