At best, coal mill safety is not well understood and, at worst, it is ignored. When it comes to coal mill systems, most cement plant operators just presume that the supplier of the equipment knows all of the standards and rules and is 100% capable of making a system that conforms to these and is therefore safe.
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GC: How would you characterize the state of coal mill system safety in the cement sector in 2019?
CMS: At best, coal mill safety is not well understood and, at worst, it is ignored. When it comes to coal mill systems, most cement plant operators just presume that the supplier of the equipment knows all of the standards and rules and is 100% capable of making a system that conforms to these and is therefore safe. However, this is not the case.
GC: Why is this not the case?
CMS: The suppliers’ designs have undergone relatively little development over time from a safety standpoint. They contain ‘legacy solutions.’ Even some of the best European suppliers lack the necessary expertise to really maximize coal mill safety in-house. There is no reason why an old design should be re-used just because it is convenient for the supplier and may be the most cost-effective solution for the user. There is too much at stake and the hidden costs, for example in excessive use of steel and concrete and poor maintenance access, quickly eat into the perceived economic advantages. Suppliers also say that a tailored solution will take longer. This is a major reason that old designs are repeated over and over again.
On top of this, suppliers are generally large companies that are not particularly dynamic, the designs take a lot of time and money to update and, frankly, there are more interesting projects to work on. Coal mill systems and their safety have taken a back seat for decades.
Of course, where there is not a focus on explosion protection, the supplier can create systems that are really dangerous. There are numerous suppliers all over the world, but particularly in Asia, that do not understand the safety principles and, some might say, don’t particularly want to.
So… the cement producer is stuck with what they can buy. Plus, they are in an even worse position than the supplier to know whether or not the system is safe or not.
GC: What are some of the common faults?
CMS: These include: Explosion pressure shock resistance and explosion isolation issues on the inlet side of mills; Incorrectly protected vertical roller mill reject discharges; Incorrectly designed mill-to-bag house riser duct configurations; Incorrectly protected main bag houses with their downstream equipment for conveying pulverized fuel; Incorrectly designed and protected pulverized fuel silos; Incorrectly designed/installed gas analyzer configurations and; Incorrectly configured emergency inerting systems. The methods and means of protection of raw coal stockpiles against fire are rarely organized and the designs of filters for the de-dusting of raw coal conveyor belt transition points are almost always wrong, from both fire and explosion protection points of view.
GC: Why have users not demanded improvement?
CMS: Producers do not have the expertise and very often don’t have the time to ask the right questions or put their finger on the design flaws. The fact that the designs are so old lulls users into thinking that they must be safe, creating the perception that there’s no need to act.
When things go wrong …
GC: What are some of the common ways that people get injured?
CMS: Many people are killed and maimed as a result of coal dust explosions but often you won’t hear about it. Even if you do hear about it, you won’t get any details, which makes analysis of wider trends really difficult. A very common incident is when people open the system in, for example, a baghouse, with the expectation of fighting a fire that’s inside. Oxygen enters the relatively oxygen-poor environment inside the system, there is a backdraft and anyone in the way is killed, or at least very badly burned.
GC: What data exists on the number of injuries and/or deaths caused by these systems?
CMS: There is pretty much no centralized data on this subject, which means we don’t really know how bad things actually are. What we do know is that in many places around the world there are fatalities and maimings with alarming regularity. Some might reach the local news but there are many more that don’t.
Even in developed markets, there are injuries and deaths as the result of explosions. They will be reported to local safety authorities but it’s very hard to get a picture of the scale of the situation beyond that.
GC: It’s not possible to say how much improving safety would reduce harm then, is it?
CMS: Even if there was a good set of data, I still think it would be hard to act on, especially in regions where safety is not a major concern. Perhaps a major association could collate the data, but there are many other jobs, monitoring environmental performance for example, that demand their attention. I am pessimistic that this situation will change soon.
GC: Do those with first-hand experience of coal explosions take them more seriously afterwards?
CMS: When things go wrong with coal grinding systems, consultants like CMS will get called. On day one after the explosion, the plant staff will be very concerned and ask, ‘What happened?, ‘How do we stop it happening again?’ and so on… By day three, the plant manager’s ‘downtime clock’ is ticking louder and louder and the onus returns to production. The plant then carries on, with many of the same flaws in place and a possible repeat of the incident on the cards.
GC: Where is coal mill safety the best in the world?
CMS: This is not a question that can be answered geographically. There is no ‘best’ or ‘worst’ country at the moment, even when you look at litigious markets like Europe and the US. I’d even go so far as to say that there isn’t one completely safe cement sector coal mill system, anywhere in the world.
There may be some marginal improvements coming in Germany, where some inspections are now finally taking place, after ATEX Directives were transposed into national law. In Egypt, the ATEX Directives will have to be complied with by all coal-using industries very soon. This will be a start, but without the benefit of 50 years of experience that, for example, we have in the coal-using industries in Germany, the safety level in Egypt is bound to be relatively low for some time to come. There is no correlation between a plant’s safety and age.
GC: How would you improve the situation?
CMS: Everyone in this industry needs to start taking this issue more seriously. The industry needs to understand that there is no standard approach and that every plant is a one-off. Generalizing the use of a novel design means there are no teething problems, but they soon come. Instead, the industry needs to understand the hazards and construct every plant and system safely and specifically to the site’s requirements. Risk assessments must be done at all levels. It is not possible to make a safety system foolproof because the plant has to work and for this, a certain level of ‘risk’ must be accepted. However, the hazards can and must be controlled and minimized. Regular check-ups, testing and maintenance must be organized to fit in with production requirements.
A further hazard that must be addressed is that of new risks being created by the introduction of advanced sensors and the new data-based business models. What happens if a hacker enters and manipulates a cement company’s sensor data and control system? What if your IT guy has malicious intent? A further issue is that, with the increasing automation and controls, many plants are becoming ‘unmanned.’ This presents new safety challenges of its own. On the upside, safety technology is developing at such a rate that there are novel ways to design the plant and operating methods that mean the hazards are greatly reduced.
GC: How much safer is the industry now than in previous decades?
CMS: I don’t know the safety figures in most detail. However, I do believe that the huge volumes of material moved and processed by these plants combined with a generally worse understanding of the inherent hazards and the increasing use of alternatives such as RDFs have created a much more risky situation. The levels of supervision have decreased and new suppliers are less familiar with the hazards. If that is not matched with increased regulation and enforcement then we’re in trouble. The industry has many more plants than it used to. Perhaps there are now 3500 cement plants and 3500 raw coal grinding systems around the world. All of these plants are exposed to fire and explosion hazards. However, this is not a one-size-fits-all challenge. Coal dust explosions have happened in all of these.
GC: How much risk does a cement plant have of blowing up?
CMS: By far the most risk is carried by coal grinding. There are countless units worldwide. Fire and explosion protection of these coal grinding systems is challenging due to the high quantity of coal processed and the number of fire and explosion incidents per kiln in the 1990s was almost exactly twice that of the previous decade.
For example, very few people have had the experience of using the most modern flame arresters and despite this, the industry has not been very successful in reaching a consensus about whether the devices work. They need to be correctly tested and proven with valid methods to international standards. I’ve been a plant manager and I’ve had to decide what maintenance is done when and where. I fully understand that this is not simple. Although the cement plants I have worked in have improved and have been very safe, I do know of one situation where a steel plant’s waste fuel tank exploded, but this plant has its own set of particular hazards.
GC: How would the safety level of the cement sector compare with other industries?
CMS: I don’t have enough data to say. What I do know is that while all plants have numerous safety hazards, all sites are different and, while not one of them is completely safe, some are much worse than others.
GC: Finally, in your view, does the cement industry do enough to train its personnel in safety?
CMS: It’s a mixed bag. Some companies do it very well. Safety is very often compromised and not made a priority. We hear a lot about this and we hear a lot of calls for more action and generally very little follows. Safety can often be very low down in the budget order and to the disadvantage of new developments. It’s just another sad fact in this story.
How to get your coal grinding system correctly protected? You will be surprised about what has gone wrong with fire and explosion protection of your system(s). Be sure about that! Evaluation of a coal grinding system’s fire and explosion protection, including the raw coal storage and the fine coal silo storage normally can be done in one day, mostly without having to stop coal grinding.
The evaluation will be done by way of touring the plant, making photos and having interviews with the people responsible for the operation. This will result in a comprehensive illustrated report and complete recommendations with explanations for necessary corrections. Ask for a free-of-charge offer indicating your airport.
