Read part one of Complying with New MACT Standards here.
Control, operation and monitoring
Once a plant has its new, converted or rebuilt dust collector, it is important to make sure operations are compliant day-in day-out. Unfortunately, there is no magic formula for compliance. The best designed dust collector, equipped with the most efficient filter bags, will not be enough. A plant will need to operate, control and monitor all of its systems more rigorously going forward. Earlier in the article, inlet design and velocity were mentioned. If air volume is increased to the dust collector, velocities through the system increase. There will be a point at which increasing the velocity will affect the bag life, cleaning efficiency and dust removal. It is essential to know the maximum air volume through the dust collector in order to maintain velocities below the danger zone.
An increase in air volume and production above design will mean greater dust loading to the dust collector. Greater grain loading means a shorter filter life due to the additional cleaning that the filter bags will need. Tracking the number of cleaning cycles of the filter bags in use is important and will show where a filter bag stands in its life cycle. Tracking cleaning cycles also helps to fine-tune cleaning differential set points and compressed air pressure. An increase in cleaning cycles should always be investigated. Usually, an increase will give an early warning of mechanical failure. These failures can be in the diaphragm, piston or solenoid valves. There are extremely reliable systems available that will alert staff to the exact valve that has failed, greatly reducing the time to determine the location of the failed diaphragm, piston or solenoid valves. However, most designs do not include an added safety factor.
An increase in cleaning could also mean that hoppers are being filled up due to a malfunction in the dust removal system. Reliable hopper level indicators and immediate corrective action are a must. A high dust level in one or more of the hoppers will increase the number of cleaning cycles and, if left uncorrected, will lead to filter bag failure from abrasion.
Almost all kiln dust collectors have opacity systems. Serious consideration should be given to the installation of a particulate continuous emissions monitor (CEM). A CEM unit gives quantifiable, real-time data on emissions levels. Based on the new low limits, the information from a CEM unit allows staff to react more quickly. Any increase above normal levels should always be investigated. Once again, there are reliable systems available that will pinpoint the failed bag, right down to the compartment and row. Manual troubleshooting takes much longer to locate the failed filter bag and increases the amount of dust contamination to the clean side of the dust collector. Even if the dust from the leaking filter bag is thoroughly cleaned from the tube sheet, a considerable portion of it will fall down into the filter bags. Each time the filter bags with dust contamination are cleaned, the dust will be stirred up and some will go out of the clean duct and into the stack. In some cases, this will be enough to put a plant over the compliance limit. Early detection and speedy replacement of failed filter bags will be paramount to staying compliant.
Charting filter bag failures is a good practice. If there are repeat locations, corrective action to eliminate the mode of failure will need to take place. If failures are not being charted, personnel will experience difficulty in identifying causes of failure and the plant will be at greater risk of repeat failures.
From an operational standpoint, sound start-up and shutdown procedures are essential. During start-up, only operate the number of compartments necessary to handle the volume the fan is moving. As a 300 °F inlet temperature or 6 in. differential pressure across the dust collector is reached, it is advised to start adding the remainder of the compartments one at a time. This will greatly minimise the time a compartment spends in the acid dew point. This is very important, especially if a stainless steel clean air plenum option was not incorporated in a plant’s design. When shutting the kiln down, it is recommended that the dust collector be manually cleaned for two cycles and that the hoppers and screws are completely cleared of all dust. If the dust collector will be shut down for a week or longer, all inlet and outlet dampers should be closed.
All personnel that come into contact with the kiln dust collector must be on the same page. Training on proper dust collector operation, dust collector control, monitoring capability, record keeping and corrective action will be extremely important for maintaining compliance. It is recommended that training be carried out quarterly. The training should include maintenance, production, automation, process and engineering, with a combination of learning in both a classroom setting and in the field. Testing is also advised to ensure desired levels of comprehension.
If a plant was to incorporate the tools and recommendations mentioned in this article, it should have a much better chance of meeting the new NESHAP standards with lower maintenance costs, lower energy costs and improved reliability. As a famous college football coach once said, “We all know perfection is not a possible reality, but striving for perfection is a good practice.”
Written by Andy Winston, CLARCOR Industrial Air. This is an abridged version of the full article, which appeared in the April 2014 issue of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/the-americas/28032014/complying_with_new_mact_standards_part_two_control_operation_and_training_948/