How To Choose Suitable Filter Bags ?

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  • jenny at
  • March 30, 2017

Factors for Filter Bags

1,Inlet gas/fume temperature 

Dusty gas temperature is the important factor in bags' chosen.Usually, <= 120 ℃ dusty gas is called normal temperature , >= 120 ℃ dusty gas called high temperature, so the bag can be divided into two categories, namely the bag of below 120 ℃ at room temperature and higher than 120 ℃ high temperature cloth bag.Therefore, we should choose the appropriate filter bags according to the dusty gas temperature , also some people called medium temperature gas which is between the 120 ℃ ~ 200 ℃ , but the filter bag is usually chosen high temperature type. 

2, Gas humidity 

Dusty gases can be divided into three forms in humidity: relative humidity below 30% for dry gas;Relative humidity was 30% ~ 80% for general condition;Relative humidity above 80% for the high wet gas.For high wet gas, and are in a state of high temperature, especially SO3 is contained in dusty gas, gas cooling can produce condensation phenomenon.It's not only can make the bag surface fouling and plugging, but corrode the bag.

Therefore for choice for the wet gas bag should pay attention to the points: (1) the wet gas make the dust captured by filter bags wetting and binding, especially water imbibition, deliquescence and wet dust will cause cloth paste bag, therefore should choose nylon with smooth surface such as glass fiber, long fiber, which is easily dust cleaning. And surface treatment can be done waterproof or laminating process. (2) the presence of high temperature and high humidity will affect the cloth wet resistance, especially for polyamide, polyester, and amide hydrolysis stability material should avoid as far as possible;(3) for wet gas, round type filter bag is suitable, as far as possible do not use complicated shape, very compact flat and rhombus bag;(4)dusty gas inlet temperature should be higher than the dewpoint temperature of 10 ~ 30 ℃. 

3. The chemical nature of the gas 

In a variety of furnace flue gas and chemical waste, they often contain acid, alkali, oxidants, organic solvents and other chemica composition, and often cross affected by temperature, humidity and other factors. This selection should be considered when choose the bag. Polyester filter bag at room temperature has good mechanical properties and acid and alkali resistance, but it is very sensitive to water, gas, prone to hydrolysis to decline the using strength sharply. So, polyester filter bag in dry gas, the long-term operating temperature should be less than 120 ℃, but in high moisture flue gas, its long-term operating temperature can only be reduced to 60 ~ 100 ℃; Nomex filter bag has good temperature, Chemical, but in high moisture flue gas, the temperature will be reduced from 240 ℃ to 150 ℃. PPS filter bag with high temperature and acid and alkali resistance can maintain a good performance in coal-fired flue gas filtering, but the poor antioxidant capacity; P84 bag can make up for its deficiencies, but the hydrolysis stability is not ideal. As the "filter king" PTFE filter bag with the best chemical resistance, but more expensive. 

So in the selection of dust bag we must have comprehensive consideration based on the chemical composition of dust-laden gas and main factors.

filter bag