高溫 雰圍氣用 스테인리스 스틸 필터의 製造 및 集塵 特性에 관한 硏究
(A) Study on fabrications and dust collecting properties of stainless steel filter for high temperature atmosphere
고온분위기용 스테인리스스틸필터제조 스테인리스스틸필터집진 금속재료공학;
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The fail safety filter element have an very important function of assistant filter mounted in a filter unit to prevent particle leak when parts of the main elements(ceramic candle type filter) are broken. The filter element should easily to meet the sealing purpose and should have high permeability to save the mounting space. And, hot gas cleaning with ceramic or metal filter elements have been thought to be the most effective and prominent method to remove particles at high temperature in advanced power generation processes such as integrated gasification combined cycle(IGCC) and industrial processes. This study focuses on the preparation of the high permeability metal filter element, that can be prepared effectively by using large size powder as filter material. However, on the basis of several trials, we found that there was a limit to the extent to which particle size would be increased, because with large particles, the contact area between particles would be reduced, and thus the filter element would be weakened. The filter elements were fabricated by using the cold isotropic press (CIP) method and the filler metal method. The permeability was effectively controlled by the following factors: material size(54 - 840㎛), CIP pressure from 1.2×10^8 to 2.0×10^8Pa, and sintering temperature(1100 - 1250℃). The high porous metal element of 9.2×10^-11㎡, permeability was prepared in optimal conditions using 420?840㎛ metal powder, fabricated at CIP pressure of 1.7×10^8Pa, and sintered at 1200℃ for 1-2 hours. The pressure drop across this element was six times less than that of the commercial ceramic filter element used in the main filter element. The metal filter with a higher permeability of 2.76×10^-10㎡ was also prepared by filler metal method by using 420 - 840㎛ metal powder. In this study, the maximum allowable particle size was 420 - 840㎛, when a CIP pressure of 1.2×10^8 - 2.0×10^8Pa was applied. Stronger mould material is required to replace teflon in order to apply high CIP pressure. We experienced another problem when separating from the mould: when high CIP pressure was applied, the filter element tended to penetrate into the flexible mould. The filter element fabricated by powders of 420-840㎛ size, reveals a pressure drop of about 300Pa at the face velocity of 0.1m/s. The filter element of 2.0㎜ thickness with a permeability of 9.2×10^-11㎡ was prepared by CIP method in the optimum conditions of CIP pressure (1.7×10^8Pa) and sintering temperature of 1250℃ by using a 420 - 840㎛ powder size. The O-ring strength of porous metal was 1.78×10^6Pa, which is reasonable to maintain the dust collecting system while keeping the pressure loss under 1.0×10^4Pa. The filter element showed a very low pressure drop under 300Pa at a face velocity of 0.10㎧, which means that the length of the fail safe filter element can be reduced to a fifth part more than the main filter element length while keeping the same pressure drop. A filter element of especially high permeability (2.76×10^-10㎡) was prepared by the binding method using 540 - 840㎛ powder size. The sulphidation reaction tests of Fe-based alloys and Ni-based alloys have been analyzed by the gas-solid reaction kinetics. The alloy specimens were SUS 310L, SUS 316L, Inconel 600, and Hastelloy X. All the specimens were tested periodically every 8 hours during 48 hours in the isothermal temperature from 500℃ to 700℃ with various gas conditions: H₂S in N₂(dry), N₂(H₂O saturation), CO₂(dry) and CO₂(H₂O saturation). Corrosion products on the surface were identified by X-ray diffraction and scanning electron microscopy. As the results, Fe-based high chrome alloy(SUS310L) and Ni-based high Chrome alloy(Hastelloy X) showed good corrosion resistance up to 600℃ and 1.7% H₂S condition. The corrosion rate was greatly increased with H₂S gas concentration. SUS310L is the best corrosion resistance alloy among these alloys tested in coal gas condition. The corrosion rate was greatly increased with increasing H₂S gas concentration in the range of 0.3-4.99%H₂S, that is, from 6㎎/d㎡?day to 314㎎/d㎡?day for SUS316L, and from 5㎎/d㎡?day to 336 ㎎/d㎡?day for Hastelloy X. The reaction orders for H₂S concentration were about 1.48 to 1.91%. The main corrosion products on the surface was indicated as (Fe, Ni)sulphides.
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