Pocket and Candle Filters

In the dry filtration processes that use pads or panels to capture dust, the filter surface is basically flat - one side of the filter sheet in a pad filter, or the upstream surface of a pleated medium panel. The group of filter types to be described next capture the dust inside or on the outer surface of a generally bag-shaped element, of circular or elongated oval cross-section. These three types - the filter bag, the filter pocket and the filter candle - are very important components of the dust collection equipment spectrum, but bags are also used in liquid clarification. 

Filter bags for liquids are effective in removing particulate contaminants in the processing of a wide variety of materials. Bag filtration is a pressure-driven operation, wherein the product to be filtered is forced through the filter unit. Such a unit would normally consist of the filter housing, a retaining basket and the filter bag. 

Generally speaking, liquid bag filters are used for the same purpose, but for a finer degree of filtration than that for which the strainers of Section 3B would be used. They provide filtration systems for small solid particles of particle size in the 1-1200 micrometre range, with flow rates between 1 and 1000 m /hr and for low sohd concentrations. 

Several bags can be housed in one vessel, supported from the same tube plate, and operated in parallel. This arrangement (very common in the bag houses used for gas filtration) is akin to a candle filter, and is described later in this section. 

One of the most common sights in a power station or processing plant is the large chamber filled with an array of filter bags, known in some industries as a baghouse, and in others as a fabric filter. These are used on large exhaust gas streams, mainly to prevent pollution from dust residues, but quite often for the recovery of valuable solids from the exhaust. 

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A. Introduction 3B. Strainers 3C. Screens 3D. Nutsche filters 3E. Tipping pan and table filters 3F. Rotary drum filters 3G. Rotary disc filters 3H. Horizontal belt filters Centrifugal filters Pad and panel filters 3K. Bag, pocket and candle filters 3L. Cartridge filters... 

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