Cement, Energy and Environment

--- - t his design. The refiltering of already cleaned particles, by contrast, is seen as a disadvantage. However, this disadvantage only becomes significant with very fine dispersed and non- agglomerating particles. Jet pulse filters in online mode are therefore both the first choice for auxiliary filters with bag lengths up to 6 m and for process filters with dust that has normal agglomeration characteristics. This is why numerous process filters from lntensiv-Filter are successfully deployed in clinker cooler dedusting and in the product separation of rotary kiln and raw meal mills exhaust gas with bag lengths of up to 8m. Features of modern jet-pulse bag filters in the offli ne mode In the offli ne design, individual filter modules are put into an almost flow-free state during cleaning. Today the raw gas flow in the filter areas to be cleaned is interrupted mainly by means of pneumatically controlled flaps on the clean gas side. This so-called semi-offline design is entirely suited to produce an almost flow-free state in the area of the filter bags, separated by the gas flow in such a way. This offers the advantage that a refiltering of already cleaned particles is effectively eliminated. Thus, particularly in the case of finely dispersed and poorly agglomerating dust, the complete sedimentation in the dust collection hopper is guaranteed and the average dust load of the filter bags is reduced to the procedural minimum. The energy efficiency of the bag filter operation, which according to amounts constitutes by far the largest proportion of energy consumption due to the flow resistance of the filter cake, can be significantly lowered by using the offline mode. [1]. Also, the application of energy required to reliably remove the filter cake from the filter bag is considerably less than in the online mode, since the flow energy of the filtration flow does not have to be surmounted. In practice, storage pressures in the compressed air tank of only 0.1 - 0.3 Mpa are necessary, which considerably lowers the compressed air consumption and also contributes to a reduction in the LCC. To minimize the pressure fluctuations, the clean gas flaps are favourably connected overlapping so that one filter chambers respectively is in the cleaning process. This practically eliminates cyclical fluctuations in the operating filter area. lntensiv-Filter already supplied this design as a semi– offline filter at the start of the 1990s and has at its disposal numerous references in almost all fields of industry. In the cement process, offline process filters are often fitted with glass fibre bags with a laminated ePTFE membrane filter medium. Owing to the low cleaning pressures, the mechanical stress in the filter bags is clearly reduced so that today a four year service life can be achieved with t his filter media qual ity, too. The semi-offline design in connection with ePTFE membrane/glass fibre bags is excellently suited as a retrofit solution for electrostatic precipitators. [2] Here, the head modules of the bag filter are installed with clean gas flaps and a clean gas channel after the cover of the electrostatic precipitator housing has been removed . Figure 1 shows an electrostatic precipitator retrofit to a bag filter installation in semi– offline mode. It should go unmentioned that reverse air filters are also designed in an offline version. In combination with e.g. horizontally arranged flat filter bags, the cleaning can be carried out by using moveable flushing carriers which also close the outlets of the respective neighbouring bag rows so that a flow status equal to a semi-offline filter applies. In the following, however, only bag filters cleaned by pressure surge are taken into account. (electrostatic precipitator retrofit, Deuna Zement!Germany) 47