Air filter filter bag selection considerations

- Jan 01, 2019-

Air filter filter bag selection considerations

1. Filter bag treatment air volume

Filter bag treatment air volume refers to the volume of gas that can be purified by the dust removal equipment in unit time. The units are cubic metres per hour (m3/h) or standard cubic metres per hour (Nm3/h). Treating air volume is one of the most important considerations in the design of bag filter.

When using the filter bag, do not exceed the specified air flow, otherwise, it is easy to block the filter bag, shorten the service life, the pressure loss greatly increased, dust removal efficiency should be reduced; But also cannot choose the air volume is too big, otherwise increase equipment investment and floor space. Reasonable selection of treatment air volume is often based on process conditions and experience to determine.

2. Dust concentration at the inlet of the filter bag

That is, inlet dust concentration, which is determined by the process of dust point, in the design or selection of bag filter, it is next to the treatment of air volume is another important factor. Expressed as g/m3 or g/Nm3.

For a bag filter, the concentration of dust in the inlet will directly affect the following factors

(1) pressure loss and ash removal cycle. With the increase of inlet concentration, the ash accumulation rate on the same filter area is fast, and the pressure loss increases accordingly. As a result, the number of ash removal times has to be increased.

(2) wear of liquid filter bags and boxes. In the case of highly abrasive dust, the wear amount can be considered as proportional to the dust concentration.

(3) whether it is necessary to collect dust in advance. Pre-dust collection is in front of the entrance of the dust collector to add a dust removal equipment, also known as the former dust removal.

(4) ash removal capacity of the ash removal device. The ash removal capacity of the ash removal device shall be based on the ability to discharge all the collected dust, and the dust volume shall be equal to the concentration of dust at the inlet multiplied by the treatment air volume.

(5) operation mode. Bag filter is divided into positive pressure and negative pressure operation mode, in order to reduce the fan wear, the inlet concentration is large should not be used positive pressure operation mode.

3. Dust concentration at the outlet of the filter bag

The dust concentration at the outlet refers to the emission concentration of the dust collector, which is expressed in the same way as the dust concentration at the inlet. The size of the dust concentration at the outlet shall be subject to the local environmental protection requirements or the requirements of users

4. Use temperature of filter bag

For a bag filter, its operating temperature depends on two factors, the first is the maximum bearing temperature of the filter material, the second is the gas temperature must be above the dew point temperature. At present, due to the large selection of glass fiber filter material, its maximum temperature can reach 280℃, gas above this temperature must be taken cooling measures, gas below the dew point temperature must be taken to improve the temperature measures. For bag precipitators, the relationship between temperature and dust removal efficiency is not obvious, which is different from electric dust removal. For electric precipitators, the change of temperature will affect the specific resistance of dust and affect the dust removal efficiency

5. Operating pressure of bag filter

The operating pressure of the bag precipitator is determined by the static pressure of the device and fan before and after the precipitator as well as its installation position

6. Pressure loss of bag dust removal

The pressure loss of bag dedusting refers to the pressure drop, or resistance, of the gas from the inlet to the outlet of the dust collector. The pressure loss of bag dusting depends on the following three factors:

(1) pressure loss of equipment structure.

(2) pressure loss of filter material. Relating to the properties of the filter material (e.g., porosity, etc.).

(3) pressure loss of dust layer accumulated on filter material.