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Filter Drag: Cost of Filtration

Cost associated with Baghouse operation can be classified into 3 categories:

  1. Filter Bag Replacement cost

  2. ID fan Power Cost

  3. compressed air cost or RA fan cost

With exception of some premium product manufacturing, ID fan power cost contribute the most in overall baghouse operational Cost. It may go further higher if captive power plant is not installed.

The resistance of the filter media while filtering out dust particles is called “Filter Drag”. The higher the resistance of the filter media, the higher will be the pressure drop and higher will be the Fan energy cost.

In short, this is what we pay to accomplish the job of filtering the dust from the gas. Therefore, it is important to check the operating filter drag.

It can be misleading to compare DP from one bag house to another since DP is affected by multiple factors including airflow, filter bag performance, bag house design and bag house condition. Once a bag house is installed, the operator can not impact, bag house design, air leaks or other mechanical losses in any major way. The operator can adjust airflow. Filter bags can impact the DP at any given airflow, and therefore have the greatest impact on performance. Normalizing DP data for airflow and making filter bag comparisons in the same bag house can reveal real differences in the performance of different filter bag materials.

This will take in to account bag house to baghouse variation in gas flow rate, bag size, no. of bags per compartment and no. of compartments. In Short baghouse operating at different air to cloth ratio can be compared.

This is the resistance of the filter media and the dust cake. One should track the filter drag for the bags over the entire life of the bag to check the variation in the membrane performance over time. As the membrane wears and tears over time, the filter drag will increase.

Higher filter drag will lead to :

  1. Higher pressure drop and increased power consumption

  2. Lower airflow

  3. Lower production rate (if the Fan limit is reached)

  4. More frequent cleaning and therefore shorter bag life

Thus, the bag performance must be tracked in the field over the entire useful bag life.

Units : mmwg/m/min

Filter Drag is the measure of resistance offered filter bag under the operating condition.

Regular check on filter drag is the basic health parameters for bag filter operation and should be carried out every six months.

Fan energy is influenced by the amount of pressure required to push air through filter bags. Fan power consumption is directly proportional to the differential pressure across the baghouse as expressed in below equation. (considering air density constant).

Higher the Filter Drag, higher will be the Pressure Drop across the bag filler, if a low drag filter bag can offer 20 mm wg lower pressure drop then for a typical reverse air bag power saving of Rs 1,637 per bag per year is possible.

Filter bags with lower filter drag (lower pressure drop) also provide longer baglife due to reduced mechanical wear and tear.

To know more about baghouse operation cost refer (TCO) article, To calculate ROI/ Payback analysis please article.(payback)

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