Experimental study of cake formation on heat treated and membrane coated needle felts in a pilot scale pulse jet bag filter using optical in-situ cake height measurement

Abstract

Pulse-jet bag filters are frequently employed for particle removal from off gases. Separated solids form a layer on the permeable filter media called filter cake. The cake is responsible for increasing pressure drop. Therefore, the cake has to be detached at a predefined upper pressure drop limit or at predefined time intervals. Thus the process is intrinsically semi-continuous. The cake formation and cake detachment are interdependent and may influence the performance of the filter. Therefore, understanding formation and detachment of filter cake is important. In this regard, the filter media is the key component in the system. Needle felts are the most commonly used media in bag filters. Cake formation studies with heat treated and membrane coated needle felts in pilot scale pulse jet bag filter were carried out. The data is processed according to the procedures that were published already [Powder Technology, Volume 173, Issue 2, 19 April 2007, Pages 93–106]. Pressure drop evolution, cake height distribution evolution, cake patches area distribution and their characterization using fractal analysis on different needle felts are presented here. It is observed that concavity of pressure drop curve for membrane coated needle felt is principally caused by presence of inhomogeneous cake area load whereas it is inherent for heat treated media. Presence of residual cake enhances the concavity of pressure drop at the start of filtration cycle. Patchy cleaning is observed only when jet pulse pressure is too low and unable to provide the necessary force to detach the cake. The border line is very sharp. Based on experiments with limestone dust and three types of needle felts, for the jet pulse pressure above 4 bar and filtration velocity below 50 mm/s, cake is detached completely except a thin residual layer (100–200 μm). Uniformity and smoothness of residual cake depends on the surface characteristics of the filter media. Cake height distribution of residual cake and newly formed cake during filtration prevails. The patch size analysis and fractal analysis reveal that residual cake grow in size (latterly) following regeneration initially on the base with edges smearing out, however, the cake heights are not leveled off. Fractal dimension of cake patches boundary falls in the range of 1–1.4 and depends on vertical position as well as time of filtration. Cake height measurements with Polyimide (PI) needle felts were hampered on account of its photosensitive nature.

The effect of operating conditions on resistance parameters of filter media and limestone dust cake for uniformly loaded needle felts in a pilot scale test facility at ambient conditions

“…Dust fraction settling in the filter and dust concentration relevant for filtration can be calculated because transient dust feed and dust collected in the filter are known. Besides an optical system is used to measure cake heights in-situ and intermittently [9,10] .…”

Exploring the Key Factors in Dusty Gas Filtration: Experimental and Modeling Studies

“…The pore blockage occurs in the initial stage, and then the particles deposit on the surface to form the cake layer. If the filtration is not terminated or cleaned, the total pressure drop will continue to rise. , …”

“…If the filtration is not terminated or cleaned, the total pressure drop will continue to rise. 49,50 4.6. Comparison of Different Parameters.…”

Study on the Filtration Performance of the Baghouse Filters for Ultra-Low Emission as a Function of Filter Pore Size and Fiber Diameter

“…They are used for the efficient removal of industrial dusts, especially fine particles [1,2,3]. The operation of a baghouse filter can be described as follows: when the airflow containing dust passes through the filter, the particles are captured and a dust cake is formed on the surface of the filter [4,5,6,7]. The formation of a dust cake on a conventional filter media has to go through three stages: depth filtration, transient filtration, and surface filtration [8,9].…”