String-wound filters

Smaller particles can be removed by cartridge filters, which can be rated for various particle sizes down to 10 pm. These are typically candle filters whose filter elements are bobbins of nylon or similar string wound onto a former. When clogged, they must be replaced. 

Disposable cartridge filters should be made of synthetic, non-degradable materials such as nylon or polypropylene. Their construction can be spun-bonded or melt-blown, string-wound, and pleated. These are described below. 

String-wound These cartridge filters consist of a string of polypropylene (or cotton, nylon, jute, polyester, and so forth) wound around a central core. String-wound cartridge filters rely on Van der Walls forces to capture small particles. These filters suffer from the potential to unload particles at higher pressure drops. Additionally, a slower flow rate is recommended for these filters, about 2 -3 gpm per 10-inch equivalent. 

String-Wound, and Melt-Blown Cartridge Filters ... 

Upon start-up of new cartridge filters, the initial effluent should be sent to drain. This is necessary to prevent fouling of the RO membranes with materials used in the manufacture of the cartridge filter media. For example, lubricants and emulsifiers are used in the manufacture of the strings used in string-wound cartridge filters. These materials can coat the RO membranes and foul them. In the case of polypropylene depth filters, phthalates are used in their manufacture. As little as 50 ppb of phthalate will irreversibly foul an RO membrane. ... 

Amine filter elements that have been washed with surfactants or contaminated with oils during manufacture (e.g., string wound cartridge filters made with virgin cotton, but containing cottonseed fragments). 

String-wound cotton cartridge filters are probably the most common filter used for amine solution filtration since they have lowest replacement cost. However, string-wound cotton cartridge filter changeouts may require considerable operating labor when these filters are... 

Wash bottle This may consist of a 500 ml flat-bottomed flask, and the stopper carrying the two tubes should be preferably of rubber (cf. Fig. 11.1%). It is recommended that the wash bottle be kept ready for use filled with hot water as it is usual to wash precipitates with hot water this runs through the filter paper rapidly and has a greater solvent power than cold water, so that less is required for efficient washing. Asbestos string or cloth should be wound round the neck of the flask in order to protect the hand. 

String discharge drum filter (Figure 50.14a), endless strings are wound over the filter medium to lift off and remove the filter cake. The strings normally pass from the drum over a discharge roll where, because of the small radius of the roll, they make a sharp turn and dislodge the cake. 

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