In September 2015, the new National Emissions Standards for Hazardous Air Pollutants (NESHAP) for the cement industry will be enforced. The new particulate standards are 0.07 lb/t of clinker based on manual stack testing and 0.02 lb/t of clinker for new or reconstructed sources based on manual stack testing. If a plant’s kiln falls under this limit, plans have most likely been put in motion to meet the standards. In most cases, plans to comply with the new NESHAP regulations will include new equipment, rebuilding or converting existing equipment or spit polishing existing equipment. Emissions compliance strategies should cover the following areas:
- Filter media.
- Control, operation and monitoring: necessary operational changes, changes in maintenance practices.
- Monitoring for assured compliance.
When preparing for the new standards, it is recommended to research designs that are currently performing well in the industry. In addition to checking previous and current performance of plant operation, the following components should also be evaluated:
- Inlet design: first and foremost, the duct from the kiln to the duct collector should have a straight duct run with a minimum length of eight diameters entering the dust collector. The velocity of the gas stream into the individual compartments is also another area that must be addressed. Computational Fluid Dynamics (CFD) is a useful tool for analysing this. Using CFD in the design process helps ensure that the equipment supplier’s design will function.
- Filter cleaning system and controls: a programmable logic controller (PLC) package that controls the entire dust collector, in place of one controller for each compartment, is recommended. If properly designed, it is not necessary or advantageous to use nozzles or injectors on the blowpipes. In this case, a simplistic approach is best.
- Dust evacuation system: it is essential that any collected dust can be moved and evacuated. The hoppers must have low dust levels at all times.
- Filter bag and cage design: too many designs presently on the market require numerous parts that can be improperly installed, creating leaks. Simplicity is recommended – a bag that snaps into the tube sheet and a one-piece cage is ideal.
- Online and offline ease of maintenance: a plant must be able to perform online maintenance. Plant personnel must be able to change out failed bags, as even the best filter bags in the best dust collectors are subject to failure. Clean side contamination must be keep to a minimum.
Woven fibreglass laminated with expanded PTFE membrane has been the most efficient and long lasting filter media used in the market to date. A well-manufactured fibreglass with a quality PTFE membrane, which is properly laminated, is the best available technology. There are differences from one filter bag company to another and it is important to research and look for a supplier that controls the production process from membrane manufacturing to lamination to finished filter bags. The advantage of a filter bag company such as this is a high quality end product, in addition to better customer service.
Read part two of Complying with New MACT Standards here.
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_one_plant_design_and_performance_947/