Factors to be considered in the selection of dust collector

1. Air volume (Q)

The treatment air volume refers to the volume of gas that the dust removal equipment can purify per unit time. The unit is cubic meter (m3/h) or standard cubic meter (Nm3/h) per hour. Is one of the most important factors in the design of bag filter.

According to the air volume design or selection of bag type dust collector, generally can not make the dust collector run in excess of the specified air volume, otherwise, the filter bag is easy to plug, shorten the life, pressure loss is greatly increased, dust removal efficiency is also reduced; But also can not choose the air volume is too large, otherwise increase equipment investment and cover an area. The reasonable choice of treatment air volume is often based on process conditions and experience.

2, the use of temperature

For bag filter, its use 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 a large number of glass fiber filter material selection, its maximum use temperature can reach 280℃, for higher than this temperature of the gas must take cooling measures, for lower than the dew point temperature of the gas must take temperature measures. For bag dust collector, the relationship between service temperature and dust removal efficiency is not obvious, which is different from that of electric dust collector. For electric dust collector, the change of temperature will affect dust specific resistance and other influences on dust removal efficiency.

3. Dust concentration in the entrance

The inlet dust concentration, which is determined by the process at the dust point, is the next most important factor in the design or selection of a bag filter after the air volume. In terms of g/m3 or g/Nm3.

For bag filter, the dust concentration at the inlet will directly affect the following factors:

(1) Pressure loss and ash cleaning cycle. As the inlet concentration increases, the ash accumulation rate on the same filtration area increases, and the pressure loss increases, resulting in the need to increase the number of ash removal.

The filter bag and box wear. In the case of strong abrasive property of dust, the amount of wear can be considered as proportional to the concentration of dust.

(3) There is no need to collect dust in advance. Pre-dust collection is to add a level of dust removal equipment before the entrance of the dust collector, also known as the pre-stage dust removal.

(4) Ash discharge capacity of ash discharge device. The ash discharging capacity of the ash discharging device should be based on the dust that can be discharged completely, and the dust quantity is equal to the dust concentration at the entrance multiplied by the air volume.

(5)Operation mode. Bag type dust collector is divided into positive pressure and negative pressure operation mode. In order to reduce fan wear, positive pressure operation mode should not be adopted in case of large inlet concentration.

4. Dust concentration at the outlet

The outlet dust concentration refers to the discharge concentration of the dust collector, which is expressed in the same way as the inlet dust concentration. The size of the outlet dust concentration should be subject to the local environmental protection requirements or the requirements of users. The discharge concentration of bag dust collector can generally be less than 50mg/Nm3.

5. Pressure loss

The pressure loss of bag-type dust removal 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.

The pressure loss of filter material. Related to the properties of the filter material (such as porosity, etc.).

⑶ Pressure loss of dust layer accumulated on the filter material.

6. Operating pressure

The operating pressure of bag dust collector is determined according to the static pressure value and installation position of the device and fan before and after the dust collector, and it is also the design pressure value of bag dust collector.

7, filtration speed

Filter speed is an important factor in the design and selection of bag filter. It is defined as the speed of the filter gas through the filter material, or the ratio of the air volume through the filter material to the area of the filter material. The units are expressed in m/min.

When the filter area of bag filter is determined, the size of its air volume depends on the selection of filtration speed, and the formula is:

Q = v * s * 60 (m3 / h)

Where, Q is the air volume treated

V-filter wind speed (m/min)

S -- Total filtration area (m2)

Note: Filtration area (m2)= air volume (m3/h)/(filtration speed (m/min)x60)

The filter speed of bag filter is divided into wool filter speed and net filter speed. The so-called wool filter speed refers to the treated air volume divided by the total filter area of bag filter, while the net filter speed refers to the treated air volume divided by the net filter area of bag filter.

In order to improve the cleaning effect and the ability of continuous work, the bag filter is divided into several chambers (or areas) in the design, and each chamber has a main air valve to control the chamber in the filtering state or stop filtering state (online or offline state). When a room for cleaning or maintenance, it is necessary to make the main air valve closed and in the shutdown state (offline state), at this time the air volume is completely burdened by other rooms, the total filtration area of other rooms is called the net filtration area. In other words, the net filtration area is equal to the total filtration area minus the number of cleaning rooms and maintenance rooms that must be maintained in operation.

8. Length to diameter ratio of filter bag

The length-diameter ratio of the filter bag refers to the ratio of the length and diameter of the filter bag. The length-diameter ratio of the filter bag is stipulated as follows:

Reverse blow type - 30 ~ 40

Mechanical shaking type -- 15 ~ 35

Pulse type -- 18 to 23