"Emissions increase when a filter bag bursts, so it is desirable for the fabric filter to be equipped with a control system that identifies burst bags and other malfunctions quickly."
Dr. Ahsen Hussain
Regional Sales Manager at FLSmidth
Best practices in selecting efficient air pollution control solutions.
With environmental regulations becoming ever-more stringent, the demands on air pollution control (APC) equipment become even heavier. Continuous, trouble-free operations are the goal of all cement plant owners. But if the APC equipment fails, owners may face shutdowns and loss of production.
Unforeseen shutdowns can be the result of insufficient process knowledge and lack of understanding of individual plant requirements. Moreover, increased dust emission due to low-quality or inadequately designed APC equipment not only impacts the environmental footprint, but can also cause extensive wear on other equipment, such as filter fans, which increases overall maintenance and operational costs.
Strict legislation drives market requirements
Cement producers are under increasing legislative pressure to reduce dust emissions, which highlights the need for high-quality APC equipment. In addition to installing new equipment, the options available are likely to involve rebuilding, retrofitting, converting or replacing existing equipment.
Today, therefore, APC manufacturers need to be able to offer cement producers a full range of technology and service solutions that meet, and even exceed environmental regulations. Overall, this involves designing, building and installing standard or custom APC solutions. At a technology level, this demands specialist knowledge of fabric filters, electrostatic precipitators, hybrid solutions, gas suspension absorbers, gas conditioning towers and heat exchangers.
“With the increasing focus on reducing emissions, it becomes even more important that plants today carefully consider three areas”, says Dr. Ahsen Hussain, Regional Sales Manager at FLSmidth. Ahsen Hussain has helped deliver feasible APC solutions to cement plants around the world for more than ten years. “First, the supplier must have a very high degree of process knowledge and experience as well as technological leadership. This means being at the forefront of developing new technologies to optimise APC equipment and solutions”.
“Second, the solution needs to ensure the best possible fit to the specific need and existing equipment of the plant while matching the client’s expectations of low initial cost. And third, the design and quality should enable long equipment lifetimes and low operational costs”, says Ahsen Hussain.
What’s behind an effective APC solution?
A number of specific technologies boost the performance and efficiency of APC solutions. Fabric filters, in particular, are crucial to APC solutions as they are proving to be particularly effective in minimising dust emissions to very low levels. Ever-decreasing maximum emission levels and a growing use of alternative fuels are significant market factors driving the use of fabric filters. A well-designed fabric filter can help minimise operational costs. The filters should thus be able to operate continuously over long periods of time with minimum attention. An example of an effective fabric filter design is FLSmidth’s FabriClean®, which is suitable for different ranges and applications.
Footprint versus bag length (cloth area of both is 8620 m2)
FLSmidth star-shaped cages (black = ring/wires; blue = bag). This is an example of a cage design that eliminates contact between the horizontal cage ring and the bag.
This means the bag is only in contact with the vertical wires, which prevents any mechanical wear at the ring and wire crossing points.
It’s all in the bag
Bag length influences the dimension, footprint and weight of the fabric filters. A longer bag allows for a smaller footprint, more efficient use of materials and has fewer parts to maintain.
Longer bag life
The gas distribution system is an important feature of fabric filters for kiln, cooler and bypass applications as it extends the life of the filter bag. Ahsen Hussain explains how:
“An effective gas distribution channel reduces the problem of re-entrainment (when pulsed downward flowing dust is re-entrained due to opposite flowing contaminated gas), resulting in a significant decrease in the amount of pulse air required to clean the bags. This reduces power consumption and extends bag life leading to lower operational and maintenance cost. Likewise, controlling gas distribution around the bags can minimise turbulence and prevent wear caused by bag-to-bag friction. Prematurely worn bags lead to increased maintenance and, eventually, shutdowns.”
Minimum bag-to-cage contact
Bag cage design also plays an important role as contact between the cage and the bag should be minimised. Ahsen Hussain elaborates, “It only takes a single bursting bag to increase emission levels, and it only takes a few bursting bags to not only increase emissions to an unacceptable level, but also risk triggering unforeseen shutdowns. To reduce the chances of this, it is desirable to choose an intelligent cage design and high quality bags as well as to ensure excellent bag-to-cage match.” (see image on top of the page).
Optimising maintenance procedures
The continuous operations of kilns and clinker coolers mean that some filters are expected to be in use 24/7. In these cases, online maintenance is necessary to help prevent unforeseen shutdowns. Online maintenance can be effectively carried out by isolating individual compartments with inlet/outlet dampers. This creates safe working conditions for maintenance staff in the isolated compartments, while ensuring the remaining fabric filter can continue to operate.
“Depending on the process, inlet gas temperatures acceptable for the installed bags are obtained with either a gas conditioning tower or heat exchanger or by bleeding fresh air through dampers. In all cases, it is essential that fresh air dampers are installed to protect against high temperature upset conditions that may otherwise damage the bags and ultimately cause shutdowns”, explains Ahsen Hussain.
He also emphasises the need for control systems as an important part of maintenance procedures:
“Emissions increase when a filter bag bursts, so it is desirable for the fabric filter to be equipped with a control system that identifies burst bags and other malfunctions quickly.”
Know-how and quality make all the difference
Technology alone will not prevent unforeseen shutdowns; the right know-how is vital to ensure the equipment is suitably designed for a specific need or process. For example, the design must take into account the characteristics of the particular pollutant.
Some processes may involve corrosive, abrasive, sticky, explosive or otherwise hazardous materials, and special attention needs to be taken in selecting the filter material type and thickness, lining, gas velocities and stack materials. It also impacts on the design of the ducting, hopper and dust removal system.
Together with know-how, quality principles are an integral part of all processes within APC solutions. It is therefore essential that an APC supplier and the equipment is governed by an effective quality management system, such as ISO 9001. This ensures that the required international quality control and assurance standards are met.
Dedicated to delivering efficiency and quality
Preventing unforeseen shutdowns has become a key issue for cement plant owners, and some of the potential causes for shutdowns can be eliminated with robust, reliable APC technology and solutions designed for a plant’s specific needs. FLSmidth has an unrivalled track record in delivering quality solutions that meet and even exceed the plants’ needs for efficiency as well as fulfilling legislative restrictions.
About the Author
Ahsen.Hussain@flsmidth.comMore Content by Ahsen Hussain