Based on the fuel it burns, garbage incineration power plants are destined to produce unique pollutants in their flue gas. It is undeniable that there are certain heavy metals and dioxins in the flue gas of garbage incinerators that make some people shudder. Therefore, in the flue gas treatment process of garbage incineration, activated carbon injection technology must be added to the flue gas flow, and ensure that the activated carbon injection process can fully adsorb heavy metals and dioxins in the flue gas.

But what about activated carbon that adsorbs heavy metals and activated carbon? decide on what path to follow? This will require the bag filter we are going to introduce.

Bag filter?

Bag filter is a dry dust filtering device. It is suitable for capturing small, dry, and non fibrous dust. The filter bag is made of textile filter cloth or non-woven felt, and uses the filtering effect of fiber fabric to filter the dusty gas. When the dusty gas enters the bag filter, the large and heavy particles of dust settle down due to gravity and fall into the ash hopper. When the gas containing fine and small dust passes through the filter material, the dust is blocked and the gas is purified.

The original dust in the smoke generated in this way can be adsorbed by the cloth bag and then removed. At the same time, the activated carbon sprayed into the flue gas process in front of the bag to remove heavy metals and dioxins will also be adsorbed onto the bag with the flow of the flue gas, ensuring that these pollutants will not be discharged into the atmosphere or the ground.

That's why the GB18485-2001 Pollution Control Standard for Municipal Solid Waste Incineration explicitly requires all waste incineration power plants to install bag filters (usually made of PTFE fiber).

Working process of bag filter

When the new bag type dust removal device starts to operate, there is no dust on the new filter bag. As the filter bag is woven with fibers, its fiber diameter is generally 20-100 μ m; The diameter of needle punched felt fibers is mostly 20-100 μ m, and the distance between fibers is usually 10-30 μ m. After running for a few minutes, dust can easily bridge between the fibers and the surface, forming a thin (0.3-0.5) dust film on the surface of the filter bag. This layer of dust film is also called a primary dust layer or filter bed. The dust that continues to accumulate on top of the primary dust layer is called a secondary dust layer. (The pores of the dust film layer are much smaller than those of the filter material fibers, and the screening effect of these dust film pores during the filtration process even greatly exceeds that of the filter material fibers themselves. The dust removal efficiency of the plain weave fabric filter cloth itself is 85-90%, which is relatively low. However, after the dust film is established, a high dust removal efficiency of over 99.5% can be achieved. This type of filtration occurs in a certain depth between the dust layer and the filter material, so it is also called "deep filtration".)

When the cloth bag is made of multi-layer materials and the pores of the surface layer material are finer and more uniform than those of the inner layer base fabric material, this surface layer can act as the aforementioned dust layer, and the dust will be intercepted at the surface layer. Due to the smaller pore size of the surface layer compared to the base fabric, dust particles are basically not retained in the base fabric, and therefore cannot form dust cakes inside the filter material. As long as the surface dust is peeled off in a timely manner, the permeability of the filter material can be well maintained. At the beginning of use, the pressure loss of this filter material is higher than that of ordinary filter material, but after being put into operation, the pressure loss is not significant with the increase of usage time. However, the pressure loss of filter material using deep filtration method will increase with the extension of usage time. This type of filtration is called "surface filtration" because it occurs on the surface layer of the bag filter material

As the filtration continues, the dust accumulated on the outer wall of the bag will become thicker, and the corresponding smoke flow resistance will also increase. Excessive smoke flow resistance not only increases the electrical energy consumption of the induced draft fan, but also is not conducive to the operation of the boiler. At this time, it is necessary to remove some excess dust. Therefore, bag dust removal is equipped with a special air cleaning system. When the system detects that the smoke flow resistance reaches a certain value, compressed air is sprayed into the filter bag in a very short time (0.065-0.085 seconds) from the air source through the air bag, pulse valve, and nozzle on the blowing pipe. Compressed air expands rapidly inside the bag, causing high-frequency vibration and deformation of the filter bag. In addition, the reverse airflow causes the dust attached to the outside of the filter bag to fall off. (Bag spraying, usually set to start spraying after the pressure difference of the bag reaches a certain value, or set a reciprocating spraying in the program)

There is an ash hopper arranged at the bottom of the dust removal room, and the dust in the hopper is regularly or continuously discharged by a screw conveyor and a rigid impeller unloader, or sent out by pneumatic conveying. The ash is directly transported to a place (solidification room) for solidification, and then transported to a landfill for landfill, ensuring that there is no discharge of pollutants during incineration.