- About pre-coating
Pre-coating or pre-coating is a dry, chemically inert, non-toxic, and easy-to-use powder that can be used to wrap or adjust the filter bag in a bag filter to increase filtration efficiency and effectiveness. Think of it as forming a uniform, three-dimensional, porous auxiliary or reinforcing agent in the bag filter.
The pre-coating has a naturally balanced particle size distribution that promotes air flow and improves collection efficiency, thereby reducing pressure differentials and reducing energy costs. The use of pre-coating can also increase the service life of the filter bag and protect the filter bag from clogging. Since the pre-coating layer has a high melting point, it can also suppress harmful sparks when used as a control layer.
In summary, the main advantages of using pre-coating in bag dust collectors include:
- Enhance the service life and performance of the filter bag;
- Protect the filter bag from clogging;
- Increase air flow;
- Reduce the pressure difference;
- Help improve dust collection efficiency;
- Prevent the appearance of destructive sparks;
- Will absorb harmful moisture, oil and hydrocarbons;
⑧ Reduce operation and maintenance costs.
- The rule of thumb for pre-coating coverage
① Pre-coated materials
For many years, lime and fly ash have been used to pre-treat filter bags. Lime is an alkaline substance that will condense in a humid environment, causing filter clogging and increasing pressure differential. In addition, lime is composed of particles with very similar shapes and sizes, thus forming a dense filter cake, which will result in higher air flow resistance.
Because the bulk density of lime is heavier than our pre-coating, it can only cover 3 square feet of cloth per pound, so it takes a lot of work to complete.
The bulk density of fly ash is also heavier than our pre-coating and is also an abrasive. Depending on the type of fly ash purchased, it can range from extremely acidic to highly alkaline. Fly ash is extremely heavy and may even fall off the filter bag filter under pressure. This means that most of the “paint” will end up in the hopper instead of on the filter bag.
Compared with pre-coating, fly ash can only cover 4 square feet of cloth per pound, which has little economic advantage.
② Common formulas and usage examples of pulse spray bag filter pre-coating
Precoat material weight / filter bag area = 0.0421 lbs / sqft