A Pulse Jet Dust Collecting Baghouse Is Ideal
A pulse-jet baghouse is ideal for controlling dust in many bulk solids processing plants. Bag house parts and services In the baghouse, rows of bag filters are suspended from a tubesheet and cleaned at intervals by pulses of compressed air that are directed down into each filter. The pulsing action dislodges the dust on the filter, causing the particles to fall into the baghouse's hopper for collection and recycling to the process or disposal. Most baghouses have one of two filter-cleaning control systems: a pulse-on-demand system that pulses the filters based on a preset baghouse pressure-drop reading, or a continuous-pulse system that activates the pulses at a timed interval. For some tough applications, however, these systems aren’t enough to keep the baghouse operating at peak levels.
Look for the obvious. Check the structural support members for signs of fatigue and excessive corrosion. Be certain that all fasteners are in place and tightly secured, especially on the ladder and access platform. Replace any missing bolts, clean and reweld any cross bracing or gussets that may have cracked welds. Look closely at the filter's external walls for corrosion or signs of bowing. Clean and repaint where necessary. Repair any holes that may have developed in the dust collector walls or hoppers.
49. Auxiliary Equipment Aside from the baghouse itself, a thorough inspection of any system will include a check of all miscellaneous complimentary equipment. Some of these items may include the exhaust fan, rotary airlock valve, screw conveyor, inlet and/or outlet dampers, etc. It is very important that any ancillary equipment be added to the inspection log.
Ductwork Another important component in a ventilation system is the ductwork. If the particulate does not have an opportunity to reach the baghouse, the dust collector will not be able to perform its function. Standard practices suggest a minimum airstream velocity within any duct of 3,500 fpm, and between 4,000 and 4,500 fpm for heavier dusts, such as sand. Should the dust travel at lower than adequate velocities, it will tend to settle and accumulate in the ducts and choke the system. This restriction of flow will increase the pressure drop in the system as well as the energy required to induce the air to move. The result will be reduced ventilation air at the pick-up points. Periodically inspect the entire length of the duct work for dust accumulation.
Start-up procedures Proper start-up procedures will help extend the life of new filter media in a dust collector. What is generally accepted as "start-up" procedures is the process designed to intentionally develop a dust cake on the bags. This is referred to as seasoning, or conditioning, the filter media.
Seasoning of a collector's filter bags is one of the most important procedures that a company can perform. In a fabric filter dust collector, the filter media is used to support a dust cake. A dust cake is the porous layer of collected particulate that develops during the conditioning period of new collector bags and following each cleaning cycle. The process can be accelerated in many installations by introducing a precoat material, such as agricultural lime, into the system. Commercial precoats also are available.
Following installation of the filter bags and inspection of the related auxiliary equipment, the exhaust fan can be started. However, it is extremely important that the new filter bags are not exposed to the full volume (ACFM) of the fan.
First, close the fan damper (or inlet dampers) to one-half open until the monitoring gauge reads about 50% to 65% of the manufacturer's recommended maximum flange-to-flange differential drop. At roughly 75% of the manufacturer's recommended differential pressure, the cleaning system can be initiated. Normal operation and periodic cleaning will bring the pressure drop to a calculable and historically stable level.
Depending on the application, development of this differential pressure may take a number of hours or even days. This is necessary to ensure that the new filter media is exposed to low filtering velocities of dust-laden air. Reducing the volume decreases the airstream's velocity (air-to-cloth ratio), thus protecting the virgin bags from a high velocity impingement of dust. Should the bags be exposed to the fan's full volume, fine particles may embed themselves into the inner fibers of the bags and begin blinding condition. This also can damage the fibers of the media, reducing the life of the bags.
With this information as a guide, a maintenance program can be developed for any dust collection system. However, this is not offered as an all-inclusive list. Each piece of equipment and application is different, and each has its own unique components and features. Those unique characteristics should be accounted for in the maintenance program.
