In today’s episode of the Dust Safety Science podcast, Vincent Grosskopf, founder of Coal Mill Safety, talks about the changes in cement production moving from coal to alternative fuels, including hazards that need to be addressed.
“What is happening in the cement industry is that everybody is thinking and talking about decarbonization, and one of the possibilities the cement industry has in that field is to reduce the use of coal and that they can do,” Vincent explained. “There are all kinds of situations. There are all kinds of alternative fuels. Depending on where the cement plant is located, you will have to make a choice of the possibilities you have. And that means that the situation can end up in all kinds of ways. The replacement of coal in the fuel mix is going as far as roughly 70%. And, 70% of the coal can be replaced by alternative fuels of all kinds.”
What is Coal Typically Being Replaced With?
Vincent explained that one important fuel is sewage sludge. Dried sewage sludge, whether communal or industrial, can serve as a good fuel. Although its handling is not entirely easy, it can be stored in a silo and dosed effectively.
He mentioned that there are various natural products, such as nutshells—often referred to as “bomb pits” of walnuts—that can also be used. Materials like rubber tires or car tires, when cut, also form bulk material suitable for use. While not everyone cuts them, there are ways to introduce these materials into the kiln system to be burned as units.
Vincent noted that when rubber tires are ground, some people refer to the resulting material as carbon or carbon black. He mentioned that in African countries, the term “carbon black” is commonly used to describe ground rubber tires. However, Vincent cautioned that rubber tires contain sulfur and about 30% carbon black, which means they are not entirely harmless from a fire and explosion perspective.
How Should Equipment Be Reorganized to Handle These Alternative Fuels?
Vincent noted that nutshells, for example, can be programmed to be processed along with coal in the mill, which slightly alters the fire and explosion characteristics of the fuel. However, he admitted that he doesn’t have data on this and can’t provide much detail. Vincent also mentioned that other fuels are sent directly to the precalciner without any treatment or processing. One such example is rice husks, a product commonly used as an alternative fuel in Asia.
How Does Grinding Capacity Change With Using Different Fuels?
Vincent explained that when 70% of the coal is replaced, the grinding capacity can be reduced to 30%, which may render the mill inefficient. He noted that if the grinding capacity drops too low, the mill might become difficult to manage, potentially requiring interrupted grinding—grinding for one hour, then stopping, and repeating the process. Coal is typically viewed as something that should not be interrupted, but this is one of the challenges faced when reducing coal usage. Using less coal could also result in changes to the dosing system when replacing part of the fuel mix with alternative fuels.
Vincent also pointed out that alternative fuels can cause issues with the refractories in the kiln and other parts of the system. The chemical influences of these alternative fuels may negatively affect the refractories, requiring a change in their quality. He acknowledged that these challenges come with several problems, but emphasized that people will still pursue coal replacement despite these difficulties.
Vincent highlighted that many people working in the industry are often unaware of the very low level of protection they have against fire and explosions. He explained that in his extensive experience visiting cement plants worldwide, both large corporate-owned facilities and small family-owned operations, he has consistently found that the protection systems for coal grinding and handling are inadequate. He stressed that he has never encountered a system that is correctly protected against these risks.
Operators of these systems often cannot be blamed for this lack of awareness, as they may not realize the risks involved. When companies start using coal or co-grind materials with coal, there is little attention paid to understanding the potential explosion and fire hazards. Vincent observed that this lack of awareness is widespread, with people simply working with the systems they are given, without the necessary knowledge to evaluate whether those systems are safe or compliant with relevant standards.
Even large multinational companies, which one might expect to be particularly cautious about liability issues, often do not have properly protected systems. Vincent also criticized the effectiveness of ISO 9001 quality management certification in this context, explaining that while certifiers may recommend zoning within plants (such as designating areas as Zone 20, Zone 21, or Zone 22), they often fail to implement meaningful measures to ensure safety. According to Vincent, there is a lack of understanding about what needs to be done to make a system compliant with these zones.
He further explained that the standards themselves are often insufficient. For instance, he mentioned that the NFPA 85 standard in North America, which is intended for power generation and direct firing, is incorrectly claimed to be applicable to indirect firing and storage firing as well. Vincent argued that the information provided in NFPA 85 is of little value for ensuring plant safety.
While he acknowledged that European standards are more applicable, Vincent pointed out that there is still no comprehensive standard that covers the entire scope of explosion and fire protection for coal grinding. Instead, there are various standards for specific aspects like explosion isolation, explosion venting, and explosion-resistant construction, but no single standard provides a complete guide on how a cement plant’s coal handling system should be designed to ensure safety. Vincent concluded by emphasizing that this lack of a clear, comprehensive standard is a real problem in the industry.
How Might We Go About Protecting These Systems?
Vincent explained that a direct system is relatively simple in its operation. It either blows or sucks coal directly to the boiler, and the connection between the mill and the boiler is a point where flame transitions can occur from the mill to the boiler.
However, he pointed out that this isn’t necessarily problematic. The real issue arises when the coal is collected from the coal grinding system and stored in a silo. This process requires the coal to pass through a filter, creating interconnected vessels where ignition can occur. An explosion ignited in one vessel can propagate through the duct system and impact the next enclosure, potentially increasing the severity of the explosion. This flame front transition can eventually reach the bag filter, leading to a situation where multiple interconnected components—such as the mill, separator, and bag filter—are affected. Vincent observed that the designs provided by suppliers often do not adequately address these risks.
He also mentioned that as more alternative fuels are introduced, there may be an increase in the number of storage silos and interconnected vessels, which raises the risk of explosions propagating from one vessel to another. Smouldering could also become a new issue, especially when different materials are mixed together, as their varying smoldering characteristics could lead to ignition.
While alternative fuels co-processed with coal could negatively influence the explosion and fire characteristics of the system, Vincent didn’t believe these effects were dramatic enough to warrant a complete rethink of explosion protection in the coal handling system. Instead, he stressed the importance of ensuring that the existing coal grinding system protection is properly addressed. When modifications are made to accommodate alternative fuels, it’s essential to use that opportunity to correct any deficiencies in the current system. In fact, correction of existing coal grinding system protection should be a priority whenever system modifications are undertaken.
Where Is The Industry Headed In This Regard?
Vincent advised that when it comes to changing systems for alternative fuels, extensive modifications might not be necessary. However, he cautioned that special care should be taken when purchasing a silo for alternative fuels. If the alternative fuel has an agricultural origin, there’s a risk that the cement plant might end up with a silo designed for agricultural use, supplied by a company typically serving the agricultural industry. While these silos may even come with some form of explosion protection, it is likely to be inadequate for the needs of a cement plant.
He pointed out that coal silos are fundamentally different from agricultural silos, and it’s the coal silo design that is needed for handling fuel. Agricultural silos typically have rupture panels, often located in the top section of the cylinder, where they are difficult to access and are not self-reclosing. Vincent explained that these non-self-reclosing explosion vents pose a significant risk because once they open, they allow wind and ambient oxygen to feed any fire that follows the explosion. This can worsen the situation by giving the fire access to more oxygen, making it more challenging to control.
Vincent also noted that if the system has an emergency inerting system using nitrogen or CO2, the inerting gas could be lost through these open vents, further compromising safety. He shared that he has encountered many silos designed for alternative fuels that were completely inadequate from a protection standpoint. Issues such as incorrect explosion pressure resistance, improper filter placement, and the creation of additional interconnected vessels all contribute to a system that is not safe for explosion protection.
Vincent stressed that it’s crucial to understand what you’re doing when dealing with these systems. Unfortunately, he observed that too many people lack the necessary knowledge and expertise to ensure that the systems are correctly designed and operated, which can lead to significant safety risks.
Conclusion
Vincent’s insights highlight a critical gap in the industry’s approach to integrating alternative fuels into existing systems. Handling these fuels, especially when they come from agricultural sources, demands more than just a superficial understanding of equipment and safety protocols. It’s about truly grasping the unique risks associated with each type of fuel and ensuring that the systems in place are robust enough to handle those risks.
The challenge lies not only in choosing the right equipment but in fostering a culture of continuous learning and vigilance. As the industry evolves, so too must our approach to safety. The goal should be to bridge the knowledge gap, ensuring that those responsible for these systems are equipped with the expertise needed to make informed decisions. Only then can we mitigate the inherent risks and confidently embrace the shift towards alternative fuels, knowing that our systems are not just compliant, but genuinely safe and resilient.
If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Vincent Grosskopf directly:
Website: https://coalmillsafety.com/
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
The resources mentioned in this episode are listed below.
Dust Safety Science
Combustible Dust Incident Database
Dust Safety Science Podcast
Questions from the Community
Companies
Coal Mill Safety
Download the episode
DSS281: Transition From Coal to Alternative Fuels in Cement Production With Vincent Grosskopf
