In today’s episode of the Dust Safety Science podcast, we’re talking to Joseph Finn, Process Ventilation Engineer at Finn Equipment Sales, about how to develop a dust control project in coal handling processes.
Joe has established a successful career specializing in process ventilation, dust collection, and dust control projects. Over the years, he has become an esteemed member of the combustible dust safety community. Our interactions with Joe have been frequent and ongoing since the inception of the incident database, Helpdesk, and Dust Safety Professionals. Whenever we require insights in the field of coal dust handling systems, Joe is always willing to share his expertise and offer his valuable opinions.
We recently encountered an incident at a cement plant involving coal dust combustion, specifically in the processing and handling areas. After seeking Joe’s insight, we realized that a comprehensive discussion was needed, so today we’re going to talk about the various operations involved in coal handling processes. We will also explore the process of evaluating dust control measures for such sites: specifically, Joe will guide us through a nine-step procedure and highlight common mistakes, providing effective strategies to address them.
Coal Handling- an Overview
Regarding coal handling, the utilization of coal encompasses various aspects. Firstly, it originates from mining operations, both surface and underground. The transportation of coal involves multiple methods such as rail, river barging, and truck handling. The ultimate destinations for coal are the operation points, which may pertain to different areas of coal application. While coal’s applications in chemistry, chemicals, and plastics may not be widely known, its primary uses lie in power generation and steel production through the conversion of coal into coke, which is used in blast furnaces.
With mining operations, coal handling involves processes such as screening and crushing, primarily conducted at surface operations and occasionally underground crushing. At coal power plants, the coal is received, often via rail, and unloaded using a rotary dumper or a bottom dumping rail system. It is then transported via conveyors to a stockpile located underneath a reclaim tunnel. From there, the coal is conveyed and transported as needed. It is usually directed to a crusher building or a crushing operation within the power plant.
Subsequently, the crushed coal is fed into bunkers or silos situated above the boilers in the power plant. From these bunkers, it may be transferred to a pulverizer crusher before being blown into the boilers. The pulverized coal is finely ground and burns like a gas in the boiler, facilitating highly efficient energy transfer for steam production. This overview provides a brief understanding of the coal handling operations involved.
Joe explained that there is a wide range of coal types, varying from high BTU coal to low-grade lignite. Notably, anthracite coal is rich in bituminous content, while Powder River Basin (PRB) coal from Wyoming falls under the sub-bituminous category. PRB coal is highly friable, making it extremely combustible, yet it boasts low sulfur content. Consequently, due to regulatory emissions requirements, many coal power plants have shifted to utilizing PRB coal from the Wyoming Basin.
This coal type presents unique challenges and necessitates special considerations due to its combustibility, friability, and susceptibility to self-combustion. Consequently, dust control becomes even more crucial in such situations, leading to significant work and expertise in this area.
Dust Control in Coal Handling
In general coal handling operations, multiple strategies are employed for dust control. These include exhaust ventilation control, suppression misting systems, and the utilization of specific chemical formulations. Additionally, various control methods are employed in areas such as roadways where dust control is a concern.
Over the past two decades, Joe has primarily been involved in wet dust extraction. This entails designing and providing control solutions for handling and transferring coal, including crushing, screening, loading onto conveyor belts, and other related processes.
Nine-Point Strategy for Dust Control in Coal Handling
Joe explained that the process begins by gaining a comprehensive understanding of the existing situation. While his perspective will focus on examining an established operation rather than a newly designed plant, the mental process remains the same.
Step One- Identifying Dust Generation Areas
The initial step involves identifying each source of dust emissions and determining the appropriate control approach for each source. For instance, this could involve using hoods to evacuate dust from conveyors, ventilating silos, or utilizing canopy hoods in processes involving vapors, fumes, or smoke. The assessment of each source point entails understanding how dust is generated, identifying the necessary capture hood design, and considering any service access requirements. With coal dust, it is also important to determine whether a dry system or a wet dust collector would be more effective.
Housekeeping plays a vital role in minimizing dust accumulation. Joe has encountered instances where dust levels were alarmingly high, reaching up to ankle level in coal plants. Therefore, ensuring effective housekeeping measures is critical. This may involve the use of blowing fans and long reach vacuum tools.
Step Two- Identifying the Control That Needs to be Captured
The second step involves determining the control volume required for capturing the dust. Let’s consider the scenario where exhaust ventilation is being employed. Imagine dust rising from a conveyor and entering a load chute, descending through a tower, and ultimately being loaded onto a conveyor belt leading to a coal silo room or bunker. At each of these dust sources, it is essential to establish the necessary volume of air.
Three key considerations come into play: displaced air, induced air, and in-draft air, taking into account factors like temperature and wind conditions. To calculate the required volume, Joe begins by assessing the displaced air, which occurs as air from or moving into the area pushes out existing air. The volume of the bulk material can be factored in when determining the displaced air.
Next is the induced air, which refers to the air pulled along by a conveyor. While it may constitute a minor portion, a long drop chute could introduce a more significant amount of induced air.
The third consideration is in-draft air. Suppose there is an enclosure, such as a head box at a conveyor or a skirt box at the bottom discharge. In such cases, overcoming the displaced and induced air necessitates adding additional air volume to create an in-draft. This involves determining the appropriate containment air velocities to ensure that air remains within the control enclosure, being pulled in, contained, and controlled.
Once the control volumes at the various source points have been determined, one can proceed to the next step.
Step Three- Develop Layout Drawings
The third step involves creating drawings of the area, including the facility layout and necessary equipment. This entails locating the hoods and incorporating plan views, elevation views, section views, and utilizing helpful resources like photos. Recently, Joe has begun utilizing laser scanning for 3D modeling. It serves as a valuable tool for accurate measurements, replacing more traditional methods utilized in the past.
Step Four- Figure Out the Ductwork
Once the drawings and layouts are in place, the subsequent steps unfold concurrently, considering the interdependencies. It is essential to factor in the location of the dust collector, as it impacts the overall layout. Simultaneously, one proceeds with drawing the hood locations and plan views while also determining the optimal placement of the ductwork. The process involves a comprehensive overview, considering both the big picture and individual steps simultaneously.
Step Five- Create Line Sketches
For Joe, these drawings often take the form of field sketches, where he designs the system on-site in a rough manner. These field sketches are detailed enough to facilitate the creation of engineering drawings. Subsequently, he uses this information to determine the appropriate diameters for the ductwork at each source point. For example, if there is a required airflow of 3000 CFM (cubic feet per minute), he must ascertain the desired velocity at the exhaust hood inlet. In scenarios like a conveyor skirt box, it is crucial to avoid pulling product, so there is a guideline to keep the velocity at the hood inlet below 500 feet per minute. On the other hand, for hoods with a nozzle design, a velocity of 2500 feet per minute may be desired.
Step Six- Use Information to Size the Equipment
Step six involves the intricacies of duct sizing, encompassing factors such as duct lengths, velocities, and more. This analysis enables one to determine the static pressure within the ductwork, assess the overall duct losses in the system, and calculate the total static loss. These calculations are crucial for appropriately sizing the dust collector and exhaust fan, as well as determining the required equipment differential pressure. If a baghouse or cartridge collector is being utilized, their sizing is also determined at this stage.
Joe noted that in his experience with wet dust extractors, which feature an integral fan, you base their rating on the inlet losses in the ductwork and any exhaust losses. As a result, there is no need to incorporate a loss factor specifically for the equipment. However, if a dry collector or a venturi scrubber is employed, all these factors must be taken into account and factored in during the sizing process.
Step Seven- Determine the Dust Control Equipment
Moving on to step seven, one focuses on determining the appropriate dust control equipment. This step is crucial because the purpose of dust control is not only to contain the dust within the plant but also to effectively remove it through an air filtration device. The chosen equipment must meet specific performance requirements, including filtration efficiency, while consistently maintaining the required air volume to ensure adequate transport velocity.
Maintaining velocity within the ductwork is considered one of the most critical factors in the design process. Other factors such as external considerations, service requirements, and maintenance costs are also taken into account.
A large part of this involvement entails understanding how the plant operates. During this step, Joe evaluates the type of equipment suitable for the specific application. This could be a cartridge collector, a baghouse collector, or even a wet system, as previously mentioned. It is also important to determine the destination of the captured dust. Will it be dropped back onto a conveyor belt?
Step Eight- Location and Size of the Dust Control Equipment
Step eight addresses the placement and size considerations for the dust control equipment. This entails determining the optimal location within the plant and assessing the spatial requirements. In the case of a baghouse, which tends to be sizable, adequate space must be allocated. On the other hand, with the wet dust collector systems Joe has been working with, they can often be situated inside the plant itself.
However, if the equipment is intended to handle combustible dust, certain precautions must be taken. Notably, a wet dust collector can be placed inside the plant, but for dry equipment, it is generally necessary for it to be located outside. Under carefully controlled conditions, the dry equipment may incorporate explosion venting outside the facility.
Safety considerations play a vital role in the decision-making process, particularly concerning explosion venting. It is essential to assess the feasibility and safety implications associated with implementing explosion venting measures. This involves evaluating the potential risks and ensuring proper safety protocols are in place.
Step Nine- Put All the Drawings Together
The final step encompasses integrating all the components into a cohesive system, which involves creating detailed drawings in both 3D and 2D formats. These drawings serve as a foundation for fabrication and installation processes.
Throughout this design phase, it is crucial to remain mindful of potential interference points. Identifying obstacles, such as electrical conduits and equipment, is essential for effective system integration.
Specific considerations can also arise depending on the chosen dust control method. For dry systems, the design must account for the provision of compressed air, while for wet systems, a water supply is necessary. Determining the source of water and establishing the appropriate infrastructure becomes significant. Furthermore, it is essential to plan for the management of dirty water effluent, ensuring that proper disposal or treatment measures are in place.
By addressing these aspects in the final step, the system can be successfully implemented, incorporating all necessary components while accounting for potential challenges and logistical requirements.
What is Wet Dust Collection in Coal Handling?
Essentially, a wet dust collector serves as an air filtration device, employing various concepts such as water bath scrubbers and venturi scrubbers. However, it’s important to note that air scrubbers designed for odour control are not suitable for capturing dust, as they contain components specifically used to capture fumes. There are also oil mist collectors that utilize a wet approach.
In the wet dust extraction system Joe has worked with, the initial capture occurs at the impeller of the fan. The air is moistened at the fan’s inlet, sometimes with the aid of a pre-separation stage, especially when dealing with fibrous dust in coal handling. This pre-separation stage helps remove a significant amount of particulate matter. The wet dust extractor incorporates scrubbing around the impeller and progresses through a bifurcated venturi stage, which efficiently captures coal dust at a high efficiency rate of around 99%.
Conclusion
The nine-step process shared by Joe offers a comprehensive framework for evaluating, designing, and implementing dust control systems. The emphasis on wet dust extraction, its advantages, and the considerations for equipment placement and sizing added depth to the conversation. Through a deeper understanding of dust control fundamentals and challenges, listeners will be able to promote safety and efficiency within the coal handling industry.
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Joseph Finn directly:
Website: https://finnequipmentsales.com/
LinkedIn: https://www.linkedin.com/in/joseph-finn-433b66/
Email: [email protected]
If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.
Resources mentioned
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Dust Safety Academy
Dust Safety Professionals
Dust Safety Share
Companies
Incidents
Explosion at Pakistan Coal-Powered Plant Injures at Least Five People
Previous Episodes
DSS110: Alternatives to Dust Collection in Coal Burning Applications with Blake Nelson
DSS055: Coal Mill Safety In Cement Production Industries With Vincent Grosskopf
DSS210: Incident Update – 2021 Coal Dust Explosion in Baltimore, Maryland
DSS215: Incident Update – 2021 Coal Dust Explosion in Baltimore, Maryland (Revisited)
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