The Use of Particulate Emission Monitors to Support Arrestment Plant Operation and Upkeep

The operation of filtration type arrestment plant can be optimised by the effective use of Particulate Emission Monitors (eg Filter Leak Monitors and Filter Performance Monitors). Particulate Emission Monitors are installed throughout the broad spectrum of industrial processes to satisfy regulations (IPPC, Part B Guidance Notes, WID and LCPD) for emission limit enforcement. In addition, where processes are controlled with arrestment

plant, these instruments also serve to provide feedback on the operation and performance of the arrestment plant itself. Specifically after filtration plant (bag-filter type), appropriate instruments may be used to reduce

running costs and minimise emissions.

Bagfilters and cartridge filters, as their names imply, use bags or cartridges of various media types to filter out particulate from the exhaust stream. Filter bags are typically provided in various dimensions and are fitted over ametal cylindrical cage. Hanging vertically in rows within the arrestment plant, filtration occurs when air passes through the outside of the bags into the middle of the cylinder and then up into the clean air plenum. Particulate is collected on the outside of the bag where it may forma “cake”, which provides evenmore efficient filtration. Periodically the “cake” must be removed from the bag so that the pressure drop across the bags does not obstruct the air flow through the filter media.

In most current filter plant, cake removal or cleaning of the filter media is carried out using a reverse jet pulse of air applied to the top of the cylinder which inflates the media. On inflation, the particulate “cake” is cracked, the filter material’s pores are opened and the particulate falls to the bottom of the filter plant hopper where it is collected. After the air pulse is removed, the filter media recovers to its original shape and resumes filtration. During the cleaning process there is a small discharge of particulate, which shall be referred to as a ‘pulse’, when the particulate in the filter (in addition to the “cake”) has been dislodged. The cleaning mechanism in such filtration plant typically occurs sequentially within a defined time period (e.g. 30 seconds) between the cleaning of each row.