When does a fabric filter achieve its best efficiency?

A fabric filter typically achieves its best efficiency when the layer of dust is building up. This is due to the concept of "cake filtration," where a thin cake or layer of dust forms on the surface of the filter fabric. Initially, when the filter is new or is first put into service, the dust particles are collected on the fabric, and the fabric itself is cleaner, leading to lower efficiency as the pores are more open.

As the dust cake builds up, it fills the gaps between the filter fibers, creating a finer barrier that enhances filtration. The growing dust layer traps additional particles, which increases the overall filtration efficiency. It’s important to note that while there is an optimum level of dust buildup for efficiency, too much dust can eventually lead to increased pressure drop across the filter, which can affect performance negatively.

In contrast, a thin dust layer does not maximize efficiency because it is not yet able to trap more particles effectively. When the filter is new, the efficiency is generally lower due to the lack of a full dust cake. High pressure conditions might help in some cases, but they do not directly correlate with optimal efficiency due to the potential for increased wear or breakthrough of particulates. Therefore, the most efficient operation of a fabric filter occurs when