Handling air volume (Q)
The treatment air volume refers to the volume of the gas that can be purified by the dust removal equipment per unit time. The unit is cubic meters per hour (m3/h) or cubic meters per hour (Nm3/h). It is one of the most important factors in the design of bag filter.
When designing or selecting a bag filter according to the air volume, it is generally impossible to operate the dust collector in excess of the specified air volume. Otherwise, the filter bag is easily blocked, the life is shortened, the pressure loss is greatly increased, and the dust removal efficiency is also reduced; The air volume is selected too large, otherwise the equipment investment and floor space will be increased. Reasonable choices to handle air volume are often determined based on process conditions and experience.
Operating temperature
For baghouses, the temperature at which they are used depends on two factors, the first being the highest temperature with which the filter material is subjected, and the second being that the gas temperature must be above the dew point temperature. At present, due to the large selection of glass fiber filter materials, the maximum use temperature can reach 280 ° C, for the gas above this temperature must take cooling measures, for the gas below the dew point temperature must take warming measures. For the bag filter, the relationship between the use temperature and the dust removal efficiency is not obvious. This is different from the electric dust removal. For the electrostatic precipitator, the temperature change affects the specific resistance of the dust and the like.
Inlet dust concentration
That is, the inlet dust concentration, which is determined by the dusting point process, is another important factor after the design or selection of the bag filter. Expressed in g/m3 or g/Nm3.
For bag filters, the dust concentration at the inlet will directly affect the following factors:
(1) Pressure loss and cleaning cycle. As the inlet concentration increases, the ash deposition rate on the same filtration area is fast, and the pressure loss increases, with the result that the number of cleaning operations has to be increased.
(2) Wear of the filter bag and the case. In the case where the dust is highly abrasive, the amount of wear can be considered to be proportional to the dust concentration.
(3) Whether pre-collection is necessary. Pre-collection is to add a level of dust removal equipment before the entrance of the dust collector, also known as pre-stage dust removal.
(4) The ash discharge capacity of the ash discharge device. The ash discharge capacity of the ash discharge device shall be based on the ability to discharge all the collected dust, and the amount of dust is equal to the inlet dust concentration multiplied by the treated air volume.
(5) Mode of operation. The bag type dust collector is divided into two types of operation modes: positive pressure and negative pressure. In order to reduce the wear of the fan, it is not suitable to use the positive pressure operation mode when the inlet concentration is large.
Export dust concentration
The concentration of dust in the outlet refers to the concentration of the dust collector. The method is the same as the dust concentration of the inlet. The concentration of the dust in the outlet should be determined by local environmental protection requirements or the requirements of the user. The discharge concentration of the bag filter can generally reach 50mg/ Below Nm3.
Pressure loss
The pressure loss of bag dust removal refers to the pressure drop, or resistance, of gas from the inlet to the outlet of the dust collector. The pressure loss of bag dust removal depends on the following three factors:
(1) Pressure loss of equipment structure.
(2) Pressure loss of the filter material. Related to the nature of the filter material (such as porosity, etc.).
(3) Pressure loss of the dust layer accumulated on the filter material.
Operating pressure
The operating pressure of the bag filter is determined according to the static pressure value of the device and the fan before and after the precipitator and its installation position, and is also the design withstand voltage value of the bag filter.
Filter speed
Filtration speed is an important factor in the design and selection of bag filters. It is defined as the rate at which the filtered gas passes through the filter, or the ratio of the amount of air passing through the filter to the area of the filter. The unit is expressed in m/min.
The filter area of the bag filter is determined, then the size of the treated air volume depends on the selection of the filtration speed.
The formula is: Q = v × s × 60 (m3/h)
Where: Q — handle air volume
v — filtered wind speed (m/min)
s — total filtration area (m2)
Note: Filter area (m2) = treatment air volume (m3 / h) / (filtration speed (m / min) x 60)
The filter speed of the bag filter is divided into the gross filter speed and the net filter speed. The so-called hair filter speed refers to the treatment air volume divided by the total filter area of the bag filter, and the net filter speed refers to the process air volume divided by the bag filter net filtration area.
In order to improve the cleaning effect and the ability to work continuously, the bag filter is divided into several chambers (or zones) in the design, and each chamber has a main air valve to control whether the chamber is in a filtered state or a filter-stop state (online or Offline status). When a chamber is cleaned or repaired, it is necessary to close the main air valve and stop it (offline state). At this time, the processing air volume is completely borne by other chambers, and the total filtration area of other chambers is called the net filtration area. That is, the net filtration area is equal to the total filtration area minus the sum of the number of cleaning chambers and the number of maintenance rooms that must be maintained during operation.
Length to diameter ratio of filter bag
The aspect ratio of the filter bag refers to the ratio of the length to the diameter of the filter bag. The aspect ratio of the filter bag is as follows:
Anti-blowing type – 30 ~ 40
Mechanical rocking type – 15 ~ 35
Pulse type – 18 ~ 23