How to choose a suitable bag filter

There are many kinds of bag filters, and its selection calculation is particularly important. Improper selection, if the equipment is too large, will cause unnecessary traffic costs; Equipment selection will affect production and it is difficult to meet the requirements of environmental protection.

There are many calculation methods for type selection. Generally speaking, the basic process parameters of flue gas should be known before calculation, such as the flow rate, properties and concentration of dust-containing gas, as well as the dispersibility, wettability and viscosity of dust. Knowing these parameters, we can choose the type and model of equipment by calculating the filtering wind speed, filtering area, filter material and equipment resistance.

1, processing capacity calculation

When calculating the treatment gas of the bag filter, it is first required to calculate the gas quantity under the working condition, that is, the actual gas quantity passing through the bag filter, and also consider the air leakage quantity of the bag filter itself. These data should be determined according to the actual operation experience or test data of existing factories. If the necessary data is lacking, it can be calculated according to the amount of gas produced in the production process and the amount of air mixed in the gas collector (about 20% ~ 40%).

It should be noted that if the amount of gas produced in the production process is the amount of gas in the working state, it needs to be converted into the amount of gas in the standard state when selecting and comparing.

2. Selection of filtering wind speed of bag filter

The filtering wind speed depends on the nature of dusty gas, the type of fabric and the nature of dust, and is generally selected according to the recommended data of bag filter samples and the actual experience of users. The filtration wind speed of most back-blowing bag filters is between 0.6 ~ 13/m, that of pulse bag filters is about 1.2 ~ 2m/s, and that of glass fiber bag filters is about 0.5 ~ 0.8m/s. The filtration wind speed listed in the following table can be used for reference.

Dust types fall off by themselves by cleaning, or are formed by condensation and chemical reaction of gas discharged from cement kiln, activated carbon, carbon black in cement, silicon dioxide (silica), sublimation of aluminum and zinc, and other gas solutions by artificial vibration, mechanical vibration and back-blowing pulse bag filter. 0.25 ~ 0.40.3 ~ 0.50.33 ~ 0.600.8 ~1.2 sublimation of iron and ferroalloy, foundry dust, alumina, cement discharged from cement mill, carbonizer changhua, lime, corundum, plastic, iron oxide, coke powder and pulverized coal 0.28 ~ 0. 0.30-500.50-1.00.6-1.21.5-3.0 fly ash, ceramic production dust, carbon black (secondary processing), pigment, kaolin, limestone, mine dust, bauxite and cement (from cooler).

3. Determination of filtration area

(1) The total filtering area is calculated as follows according to the total air flow through the bag filter and the predetermined filtering speed:

After calculating the total filtration area, the overall scale and size of the bag filter can be determined.

(2) The area of a single filter bag is the area of a single circular filter bag.

In the process of processing the filter bag, because the filter bag should be fixed on the flower board or short pipe, and some of them should be hung on the bag cover, the two ends of the filter bag need double-layer sewing or even multi-layer sewing: this part of the double-layer sewing has no filtering function because of the increased resistance, and some filter bags need to be fixed in the middle, and there is no filtering function.

In large and medium-sized back-blowing bag dust collectors, the filter bag has a length of 10m and a diameter of 0.292m, and its nominal filtration area is 0.0292×10 = 925m; = 925m If the unfiltered area is subtracted from 0.75m, the net filtering area is 8.25-0.75 = 7.5m. It can be seen that the useless filtering area of the filter bag accounts for 5% ~ 10% of the filter bag area, so the net filtering area should be indicated in the instructions of large and medium-sized dust collectors. However, in the existing dust collector samples, the filtration area mostly refers to the nominal filtration area, which should be paid attention to in design and selection.

(3) After calculating the total filtering area and the area of a single dust bag, the number of filter bags can be calculated. If the number of filter bags in each filter bag room is determined, the number of rooms in the whole dust collector can be calculated. Although the number of rooms is determined according to the needs in the design or selection of dust collector, considering the convenience of site layout and maintenance, the number of disassembling machine rooms with more than 6 rooms is often set to double rows. Each chamber of a dust collector with less than 5 chambers is designated as a single row.

4, bag filter resistance calculation

The resistance of the bag filter consists of three parts: (a) the resistance of the main structure of the equipment refers to the resistance of gas from the population of the bag filter to the outlet of the bag filter; (b) The resistance of filter bag refers to the resistance of filter material when filtering dust, which is about 50 ~150 Pa; (c) The resistance of dust layer on the surface of filter bag is about j ~ 10 times that of clean filter cloth. If the resistance of the filter bag and the dust layer attached to its surface is called filtration resistance, the filtration resistance can be calculated as follows:

In addition, the filtration resistance can also be obtained by calculating the amount of filtered dust. The dust filtering capacity can be calculated by the following formula: the structural resistance of bag filter increases with the increase of filtering wind speed, and the resistance of various bag filters with different sizes and types is different, so it is difficult to calculate it by an expression. Generally, when the filtration wind speed is 0.5 ~ 3 m/h, the body resistance is generally between 50 ~ 50~500Pa. However, when considering the resistance of the body structure, we should also consider certain reserves.

If you think the above methods are complicated and troublesome, you can also consult us directly, and our engineers will provide you with a one-stop dust treatment scheme.