Bag filters are used in many liquid filter applications, including bulk chemicals, food industry applications such as vegetable oils, coolants, cleaning fluids, paints, varnishes, waxes, and plasticizers. A bag filter may be simple, like a filter media bag connected to the end of a pipeline. If connected through an adapter, it may be more secure. For applications with higher pressure and larger volume, insert the bag into the shell and support it with a mesh basket.
Bag filters are used to clarify and filter fluids with relatively small particle loads to be removed. The particle suspension passes through and the particles settle in the bag. The filtration rate from inside to outside is approximately 100 m3/m2h. Therefore, bag filters are usually used together with auxiliary containers. Without the use of supports, the pressure drop at both ends of the filter must be lower. When using a bag filter, industry standards typically define the size of the bag filter.
The supporting container provides mechanical support for high productivity filters and prevents the filter material from elongating. The filter bag of a bag filter is usually made of needle punched non-woven fabric and used as a deep filter. The pore volume varies between 70-90%. Filter bags are usually sewn at the edges. By welding seams, bypass filtration can be avoided, but it is only possible to perform bypass filtration on polypropylene or polyester when the material used is thermoplastic.
Generally speaking, like basket filters, bag filters have the same purpose but higher filtration efficiency. They provide filtration for small solid particles with particle sizes ranging from 1-1200 µ m, flow rates between 1 and 1000m3/h, and low solid content. In operation, woven monofilament and multifilament fabrics, as well as bags in the form of needle punched or melt blown non-woven fibers, are equipped with top sealing devices to enable them to be positioned and sealed into suitable containers.
Considering the possibility of generating high pressure differentials across the entire bag, the usual approach is to provide some kind of support frame, which is a cage made of metal rods or a basket made of perforated metal or wire mesh (such as the support mesh basket shown in the picture above). The basket holds the bag in place and prevents it from breaking. When replacing the filter bag, you can also use a basket to lift a full bag.
