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a military history trip to hill 88 | mill valley, ca patch

a military history trip to hill 88 | mill valley, ca patch

Hill 88 in the Marin Headlands is the site of an old military radar control station for the former Nike missile base at Fort Cronkhite. The Nike missiles were positioned at batteries and bunkers throughout the Marin Headlands, most of which are still present. Many are dug into the hills forming tunnels and caves. A few are open to the public, but most are welded closed.

The path to Hill 88 follows an abandoned asphalt road that is now eroded, overgrown and has fallen into the sea in places. An adventure to the top feels a bit eerie and sometimes it is even hard to believe that you are still in the SF Bay Area and not some post cold war country that is now bankrupt. But all you need to do for a reality check is turn around and look out over the ocean or at the Golden Gate Bridge.

The Marin Headlands is a harsh place. The landscape is chaparral and grassland. Very few tress are found on the hills. Coyote bush, which is currently flowering dominates. Yellow Sticky Monkey Flower, red Paint Brush and blue Penny Royal are flowering between the shrubs and from the cracks in the old road. The ocean is just below and fog is more common than not, so the bushes get fog drip throughout the summer. Fall is official now and the foggy days will become less frequent and the little moisture it brings will soon be gone and the real dry season the coast will begin.

One of the highlight of this area are the numerous raptors that are present circling the hills. They congregate here because they don't like to cross the water at the golden gate. According to the Golden Gate Raptor Observatory,over the course of an average year it is possible to see up to 19 different species of hawk, kite, eagle, falcon, kestrel, osprey, vulture and harrier. Be sure to keep bring your binoculars and a good bird book.

We like to start this hike from Rodeo Beach where the Marin Mammal Center and Headlands Institute are located. Take the old road at the end of the main parking area and follow it up. The road becomes Coastal Trail about half way up. The old road is now closed in several places because the road as collapsed, so be sure to follow the signs for Coastal Trail. There are several bunkers allow the way and they are fun to explore and provide the best shade and a good place to rest. When you get close to the top you will see a chain link fence surround the top of a hill with some building. That's your destination. The view from the top is fantastic.

On the way back there are two paths. One is to double back half way and then take coastal trail to the Marine Mammal Center. The other way is to take Wolfback Ridge to Miwok trail and back along the lagoon to the parking area. We prefer to come back down on the coastal side. As you head up you are looking up and east mostly. Heading back you are looking out to sea and South - kind of like two hikes in one.

coal mill - an overview | sciencedirect topics

coal mill - an overview | sciencedirect topics

To control the quality of coal being sent to the burners located on the furnace walls. The word quality here means the temperature and fineness of the PF. The set temperature values are dependent on the percentage of volatile matter that exists in the main fuel. The controlled temperature is important for many reasons such as stability of ignition, better grindability of solid fuels, better floating ability of suspended PF particles, etc. However, a temperature more than 65 to 70 is not recommended for various reasons.

Operating data from a coal mill is used to compare the fault detection observer-based method and PCA/PLS models based approach. There are 13 process measurements available representing different temperature, mass flows, pressures, speed etc in the coal mill.

The measurement is not updated, if the variation is less than 1%. The variations of T(t) is in the major part of the operational time inside this interval. Therefore, it is not suitable to be chosen as the predictor variable. However, the variations can be extracted from the TPA(t), which is used to control the temperature of the mill. Therefore, the PLS model is developed with the temperature of the mill as the dependent variable. In addition 6 of the other variables are chosen as regressors since there is barely information in the remainder.

A static PCA model is first developed, which captures around 99% of variations with 5 PCs (see Fig.5), which indicates strong collinearity among regressors. As shown in Fig.6, both Q and T2 statistics (with 95% confidence level) of the static PCA model are noisy, which potentially lead to false alarms. A static PLS model with 2 LVs achieves the minimal PRESS (see Fig.7), which is applied to the test dataset. Fig.8 shows the comparison between process measurement and the static PLS model prediction, together with the 95% confidence level. The process gradually drifts away form the NOC model, which eventually moves beyond the threshold around the sample 150. Due to the noise involved in the prediction signal, the estimation moves in and out the threshold from 110 till 200, when it is clearly out of the confidence level. Both Figs.6 and 8 reveal that static PCA and PLS models may lead to false alarms due to the noisy estimation. In addition, process measurements are commonly auto-correlated, this behavior is expected since the coal mill runs dynamical. Thus, dynamic models are developed by including time lagged process measurements, to address the issue of auto-correlations and reduce the possibility of false alarms due the none modeled dynamics.

Including time lagged terms enhance the NOC model by including historical data. However, time lagged terms also introduce additional noise into the modeling data block. For example, including n+1 time lagged terms might lead to poorer validation performance than the model with n terms due to measurement noise. Therefore, PRESS is used to choose an appropriate number of time lagged terms for a dynamic PLS model.

The predictive ability of the PLS model is improved with the inclusion of time lagged terms. The PRESS decreases from 1.645 to the minimal value of 1.142, which is obtained with a dynamic PLS of 3 LVs using 8 time lagged terms. The application of the dynamic PLS model to the test data reveals that the fault occurs in the process around sample 160. Fig.9 also shows a much smoother prediction such that the possibility of false alarms is significantly reduced. A dynamic PCA model is developed by the inclusion of 8 time lagged terms. The number of PCs is chosen as 2 through cross-validation, which explains 70.6% of process variations. The Q statistic of the dynamic PCA model is shown in Fig.10, the fault is detected around 160 samples, which is consistent with the dynamic PLS model.

The control loop for mill outlet temperature discussed here is mainly for TT boilers based on a CE design with bowl mill (refer to FigureVIII/5.1-2). A similar loop is valid for a ball-and-tube mill, which is discussed separately in the next section. In order to understand the loop in the figure, it is advisable to look at FigureVIII/5.0-1 and the associated PID figure (refer to FigureIII/9.2-4).

The outlet temperature of the coal mill is maintained at desired point so that the coal delivered from the mill is completely dry and achieves the desired temperature. Also, in case of high temperature at the mill outlet, cold air is blown in to reduce the risk of fire.

Normally, the entire requirement of PA flow necessary for a particular load at the mill is initially attempted through HAD so as to ensure complete drying of the coal (especially during rainy seasons) and to raise the mill temperature at a desired point. However, there may be times during hot dry summers when the mill outlet temperature shoots up. This is also never a desired situation because of fire hazard. In fact, to combat this fire hazard, arrangements for mill-inerting systems with inert gases (e.g.,N2 and CO2) need to be made (another purpose is to reduce air supply).

This is more important for ball-and-tube mills, especially when these are operated with one side only. Therefore, CAD comes into operation whenever there is need to bring down the mill temperature. Naturally when this damper operates (i.e., starts opening through process feedback), the hot air damper closes. Here also is a cross-operation of the two dampers but through process and not directly via the loop, so control loop disturbances are fewer than in the old days when cross-operations were implemented in the loop.

Mill outlet temperatures measured by redundant temperature elements and transmitters are put in an error generator. (Temperature element specialties were discussed earlier and so not repeated here.) The output of the error generator drives a PID controller. In general, since temperature is a sluggish parameter it is always advisable to use PID controllers for better results. To prevent controller saturation, controllers are put into service only when both the loops are in auto. The output of the controller through I/P converters normally drives pneumatic actuators meant for CAD.

As stated earlier, only when both HAD and CAD are in auto is the controller put into operation. Since FSSS operations depend on mill temperature conditions, with the help of the limit value monitor (LVM) necessary contacts statuses are shared with FSSS. The loop can be released to auto by an FSSS command. As a protection, both the full opening command and the >x% command for the mill CAD are issued from FSSS so sufficient cold air is circulated. If the auto release command from FSSS is missing or if HAD is in manual, it is necessary to inhibit auto operation so that the operator pay complete attention to the mill outlet temperature. That is the check back signal for FSSS from the loop for damper position.

How breakage energy and force are applied in the mill in order to achieve size reduction in an efficient and effective manner. This is a matter of design and performance of mills and the main subject of this section;

How the material being reduced in size behaves in terms of breakage characteristics such as strength and resulting broken size and shape. This relates to how the material responds to the application of breakage energy and force in terms of rate and orientation of application.

The analysis of individual mill design and operation is complex; so, for simplicity we will consider a typical mill layout for one mill type only. As VSMs have come to represent the bulk of the power station mill fleet, the explanation of mill operations will be based on this mill type. Figure13.2 illustrates the typical key components of a VSM.

In coal milling for power stations, a closed-loop process is used in which the rejects from the classifier are returned to the mill for regrinding. In VSMs, the re-circulation loop is within the mill, but some mill types would have an external loop. In fact, there are a number of re-circulation loops within a mill system. The situation is further complicated by the mill reject streams that reject undesirable material (tramp metal and non-coal bearing rock) from the mill. Generally, the following steps illustrate the path through a VSM:

Air entering through the Port Ring creates a fluidising zone in which heavy material (Mill Rejects) such as rock falls through the Port Ring into the Air Plenum below the Grinding Table and is ejected from the Mill through the Mill Reject System;

From the fluidising zone the ground coal is lifted up inside the Mill Body. Larger particles of coal reach a terminal velocity at which gravity will pull them back on to the Grinding Table for regrinding (Elutriation);

The fineness of the milling product and the capacity of the pulverizer are strictly connected. With increased fineness grows the overall circulation rate of coal in the mill, coal retention time and the flow resistance. As a result, the maximum mill capacity decreases and the rate of change of operational parameters of the furnace system deteriorates. In extreme cases, the performance of the boiler may be limited, and therefore improving the fineness of milling product must often include the modernization of the grinding system. The increase of the throughput of a pulverizer, which compensates the loss of capacity resulting from the increased fineness of coal dust, may be achieved through:

The analysis [45] proves that the maximum capacity of the ball-ring mill is obtained using 5 or 6 balls. Because earlier, as a rule, a greater number of balls was used, there is a possibility to increase the capacity by replacing the existing balls through a lower number of bigger balls. For example, in the EM-70 of FPM SA 9 balls of the diameter 530mm were replaced with 7 of 650mm. Such a modernized milling system can usually be set up on the existing gearbox. It should be noted that the costs associated with replacement of the classifier and the grinding elements are only slightly greater than the costs of the major repair of the mill. In the case where an existing mill has a grinding unit of the number of balls close to 6, the only way to increase performance is to increase the diameter of the balls, but this requires replacement of the mill body.

It has to be mentioned that the number of balls is increased during the mill operation. For example, the initial ten balls, after lowering the diameter below some value (due to wear), is complemented with the 11th additional ball.

If the existing pulverizer is equipped with 6 or 7 balls, increasing of its capacity is also possible by means of replacing the ball-ring system with the bowl and roller milling device. The milling costs per Mg of fuel in both systems are similar. However, with the same dimensions of the milling systems, the capacity of the roller system is about 15%20% higher. Another advantage is the shorter renovation time, which is about 714days for the ring-ball system, while for the roller mill, only 37days. In addition, hardfacing and re-profiling of grinding components are much easier for roller milling systems.

During the modernization of milling plant with compression mills, detailed analysis requires the selection of cross sections of nozzle-rings at the inlet of the drying agent to the mill, in order to minimize the amount of coal removed from the grinding chamber. The preferred solution is a rotating nozzle ring integrated with the bowl. This ring equalizes air distribution pattern at the periphery of the grinding chamber, which allows increasing the capacity of the grinding system without fear of excessive loss of fuel from the mill.

The rotational speed of the vertical spindle mill affects the operating conditions of the grinding unit. At high rotational speeds, the grinding unit operates at high flow of the material in the radial direction and low layers of the material under the grinding elements (balls, rollers). This causes the particles to be discharged without comminution and increases circulation in the mill. At the same time, the flow resistance and milling energy consumption (including erosive and abrasive wear) of the mill will increase.

If the rotational speed is too low, the material flow will decrease significantly. The thickness of the material layer under grinding elements will exceed the maximal height for which the particles are drawn under the grinding elements, causing excessive buildup of the material in front of the grinding elements. The material outflow from the bowl (or the bottom ring) is not supported by grinding elements movement, which results in higher flow resistance and uneven loading of the nozzle ring. These factors cause a significant decrease in mill efficiency.

Tests carried out for some industrial mills have proven that the change of grinding unit rotational speed strongly influences mill capacity. Therefore, by changing the gear ratio of the mill, both milling capacity and dynamic properties of the mill can be improved.

The fuel injector is designed to introduce the dispersed coal particles in a medium of air into the furnace. The mass ratio of air to coal is dependent on the coal mill manufacturer and usually ranges from 1.75 to 2.2 with a typical value of 2.0. An air to fuel mass ratio of 1.8 produces a primary stoichiometric ratio of approximately 0.16, or 16% of the air necessary for complete combustion of the coal. According to the previous discussion of NOx formation chemistry it is expected that lower NOx concentrations are achievable with lower primary gas/fuel ratios. The diameter of the coal transport line is constrained by the minimum velocity at which coal particles remain entrained in the carrier gas, or the coal layout velocity. This velocity is generally accepted to be 50 ft/s (Wall, 1987). The dimension of the fuel injector itself is selected by the burner manufacturer to provide the desired gas and particle velocity at the exit of the burner. The velocity here is anywhere from 50 to 115 ft/s and is chosen to provide the desired near flame aerodynamics impacting the mixing between the primary and secondary air. In many applications, there is an elbow, scroll or turning head in the coal pipe at the burner inlet. Such inlet devices result in roping, or an uneven distribution of coal within the fuel injector. Many manufacturers use components to redistribute the coal particles with an even density around the circumference of the fuel injector at its exit. A uniform distribution is typically desired to minimize NOx while maximizing combustion efficiency. The material of the fuel injector is chosen to be reliable under high temperatures and erosive conditions and is often a high grade of stainless steel. Another component of the fuel injector that is found on many commercial low NOx burners is a flame stabilizer. The function of this feature is to provide a stagnation zone at the fuel injector exit on the boundary between the primary and secondary air where small-scale mixing of coal and air occurs, providing ideal conditions for ignition and flame attachment.

Sulfur in coal can affect power plant performance in several ways. Sulfur in the form of pyrite (FeS2) can lead to spontaneous combustion and contributes to the abrasion in coal mills; therefore, if a lower quality coal containing pyrite is used in place of the design coal it can lead to problems. As the overall sulfur concentration increases, so do the emissions of sulfur dioxide (SO2) and sulfur trioxide (SO3). While the majority of the sulfur is converted to SO2 (about 12% of the sulfur converts to SO3), the increase in SO3 emissions increases the flue gas dew point temperature, which in turn can lead to corrosion issues. Most countries have legislation restricting SO2 emissions and utilizing higher sulfur coals will require additional SO2 controls (Miller, 2010). In some cases, the use of low quality fuels may impair the desulfurization equipment because of a greater quantity of flue gas to be treated (Carpenter, 1998).

All power stations require at least one CW pump and one 50% electric boiler feed pump available and running to start up a unit. In addition, fossil plant requires either coal mills or oil pumps and draught plant, e.g., FD and ID fans, PA fans, etc. Gas-cooled nuclear plant requires gas circulators running on main motors or pony motors at approximately 15% speed, whereas water reactors require reactor coolant pumps. Both nuclear types require various supporting auxiliaries to be available during the run-up stages, the poor quality steam being dumped until the correct quality is achieved.

When steam of correct quality is being produced, the turbine-generator will be run up to speed with all the unit supporting auxiliaries being powered from the station transformers via the unit/station interconnectors.

The Amer 9 plant utilizes both direct and indirect co-firing configurations. The plant co-fires biomass pellets up to a maximum of 1200ktyr1, generating 27% by heat through two modified coal mills. Only wood-based fuel has been used since 2006, due to reduced subsidies for agricultural by-products.

For the indirect co-firing option, low-quality demolition wood is gasified in a CFB gasifier at atmospheric pressure and a temperature of approximately 850C. The raw fuel gas is cleaned extensively and combusted in a coal boiler via specially designed low-CV gas burners. An advantage of this concept is that there is no contamination of the fuel gas as it enters the coal-fired boiler. This allows a wide range of fuels to be co-fired within existing emission constraints while avoiding problems with ash quality. The challenge, as always, is working within the relatively stringent fuel constraints while avoiding the inevitable high investment costs [22]. Amer 8 also co-fires at high biomass feed levels but uses a standard hammer mill configuration.

Coastal power stations, due to their proximity to major urban areas, tend to be better managed in terms of production consistency and environmental standards. In China and India in particular, coastal power stations tend to mill coal more finely, use superior emissions to control technologies, and have a tendency to use higher-quality coal blends. The result is higher quality and greater consistency in fly ash chemical and physical properties, to the extent that the material is more desirable to local cement manufacturers and those in other domestic markets along the coast. This material is typically allocated in multiyear contracts.

Adding to this, coastal urban areas usually have high volume demand for construction materials. Coastal power stations are often fully contracted to supply cement-grade fly ash, as well as the run of station ash and bottom ash to serve this demand. This is particularly clear in China, where coastal cities such as Shanghai and Shenzhen have seen dramatic urban development over the last 20years. During this period, both cities have been net importers of fly ash, drawing from both inland and domestic coastal sources.

The cost of loading material onto vessels, whether in containers or bulk, is much lower at coastal power stations due to lower local land transport costs. As a result, coastal power stations have been logical first choices for exporters/importers, and many have already developed either domestic coastal markets for their ash or export markets.

long-lasting coal mill for efficient grinding | flsmidth

long-lasting coal mill for efficient grinding | flsmidth

Our ATOX Coal Mill is a compact vertical roller mill that can grind almost any type of raw coal. The coal mill utilises compression and shear force generated between the large rollers and the rotating table to crush and grind raw coal, removing the need for a separate piece of equipment for crushing. The coal mill can also grind petroleum coke and anthracite down to a fineness below 5% +90 micromillimeters (mm) when coupled with a variable speed mill motor.

As the feed material is added to the mill, the moisture evaporates almost immediately. A continuous gas stream from the nozzle carries the finer particles to the separator, where they will be assessed for the specified fineness. For safety reasons, the coal mill is designed with no external recirculation of materials. Material is prevented from spilling over the edge of the dam ring as both the dam ring height and grinding pressure are adjustable.

The ATOX Coal Mills efficient separator allows material that has reached the required fineness to leave the grinding mill and sends oversized material back for further grinding. The fineness is controlled by adjusting the rotor speed. The high efficiency of the separator is due to the rotor being equipped with an outer ring of louvre plates that are hardfaced for longevity.

The durable grinding mill can handle virtually any type of raw coal and has been designed to grind feed materials with varying moisture levels. The ATOX Coal Mill handles feed materials with less than one percent moisture and up to 25 percent moisture, where abrasiveness and stickiness is not an issue for grinding.

The materials used to produce the ATOX Coal Mills segmented wear surfaces are durable and therefore, last longer. The reversal of liner segment option maximises use of these hard surfaces, making sure every surface is exploited while helping to address uneven wear at the same time.

The separator, with the highest mill capacity, ensures high separation efficiency through having a low bypass to reject. An efficient separator leads to a number of benefits including low specific power consumption for the mill motor, low vibrations, energy savings due to minimal pressure loss, and optimised airflow.

Long-lasting durability is extended to the separator where the inside of the reject cone and outlet top section are faced with Densit. The wear plates for the louvres are also hardfaced to maximise wear life.

The ATOX Coal Mills equipment is located at or above floor level for easy maintenance and cleaning. There are easy-access doors for inspection and maintenance of all of its parts, where roller replacement can occur while still inside the mill. For comprehensive maintenance, the large door is removable for crane access.

Our coal mill offers the flexibility of non-inert and inert operation, depending on the exploding potential of your coal type. The tailored layout considers your coal grinding needs, ensuring simple and optimised operation. For example, the availability of heat sources to dry raw coal helps determine the final layout.

Liner segments can be reversed so that the wear, which normally occurs on the outer edge, can be spread evenly, making use of the entire segment surface. The coal mills liner segments can also be repeatedly hardfaced for maximal longevity.

The heated rotary feed sluice ensures uniform flow of feed into the ATOX Coal Mill for optimum mill operation including minimising power consumption. It is the right solution for a sticky feed material as hot gas from the mill inlet is guided through the rotor, preventing the sticky

FLSmidth provides sustainable productivity to the global mining and cement industries. We deliver market-leading engineering, equipment and service solutions that enable our customers to improve performance, drive down costs and reduce environmental impact. Our operations span the globe and we are close to 10,200 employees, present in more than 60 countries. In 2020, FLSmidth generated revenue of DKK 16.4 billion. MissionZero is our sustainability ambition towards zero emissions in mining and cement by 2030.

boiler mill and coal pulverizer performance | ge steam power

boiler mill and coal pulverizer performance | ge steam power

Were a world leader in coal pulverizing and boiler mill operations for horizontal and vertical boiler millscommitted to high-efficiency performance, reduced maintenance costs, and longer time between outages.

YES.Our boiler mills and coal pulverizers span the globe and are built in a variety of sizes and capacities. We provide customized maintenance solutions regardless of original equipment manufacturer (OEM). We offer a full spectrum of high-quality solutions for eachin addition to our thousands of standardboiler mill partsand services. This is the Power of Yes.

In an ever-changing regulatory environment, flexibility and expertise are critical. With global fleet and project experience, we can integrate GE and other OEM boiler mill assets to enhance performance and reduce lifetime costsbut never at the expense of safety, reliability, or environmental compliance.

HCX2* ceramic inserted grinding elements significantly extend operating time between overhauls. Up to 3.5x life extension over high chrome and high chrome overlay. HCX2 lasts up to 2x longer than competitors ceramic. *Trademark of General Electric Company

GE Steam Power offers a broad portfolio of technologies and services predominantly for nuclear and coal power plants helping customers deliver reliable power as they transition to a lower carbon future.

coal mill safety

coal mill safety

Global Cement (GC): Please could you introduce your experience in the cement sector to date? Vincent Grosskopf (VG): I started working in the bulk handling arena in the early 1970s until 1992, when I joined Thorwesten. At that point Thorwesten Vent had begun to work with explosion vents, predominantly for its own coal silos. We were then approached by others, such as Polysius and FL Smidth, which wanted to licence vents for their own designs. Learning about the use of explosion vents in collaboration with such firms led to applications in coal grinding equipment, including bag filters. On the surface this appears to be quite simple but the situations are quite different. The inside of a silo is big and wide, which means the explosion front propogates relatively slowly. By contrast, inside the narrow ducts of a coal grinding and de-dusting system, explosions move much more rapidly and with greater pressure. At Thorwesten Vent we found solutions around these differences and other issues, gaining unrivalled experience in explosion venting.

GC: What led you to establish Coal Mill Safety? VG: I established Coal Mill Safety (CMS) as a consultancy after I retired in 2011. If a cement producer wants to install a new coal grinding system, they can commission CMS to look at the suppliers design and probe it from a safety angle. If it has an existing system, it can ask CMS how it can improve it.

GC: How would you characterise the state of coal mill system safety in the cement sector in 2019? VG: 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? VG: 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 maximise 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 particuarly in Asia, that do not understand the safety principles and, some might say, dont particularly want to.

Despite the use of oil and gas in many regions and the rapid rise of alternative fuels, coal remains the major cement production fuel. It must be safely handled when ground and fed into the kiln and, even though it is a difficult topic to broach, the onus to have the conversation is on the cement producer. (Picture: GlobalCementMagazin)

GC: What are some of the common faults? VG: 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 pulverised fuel; Incorrectly designed and protected pulverised fuel silos; Incorrectly designed/installed gas analyser configurations and; Incorrectly configured emergency inerting systems. The methods and means of protection of raw coal stockpiles against fire are rarely organised 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? VG: Producers do not have the expertise and very often dont 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 theres no need to act.

GC: What are some of the common ways that people get injured? VG: Many people are killed and maimed as a result of a coal dust explosions but often you wont hear about it. Even if you do hear about it, you wont 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 thats 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.

A coal grinding system with a mill-to-bag house riser duct (marked with red line) that is very long. Through it, unmitigated flame front propagation could reach a velocity too high for the installed protection to effectively protect the bag house. This is a typical situation and it needs to be corrected.

GC: What data exists on the number of injuries and/or deaths caused by these systems? VG: There is pretty much no centralised data on this subject, which means we dont 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 dont.

Even in developed markets, there are injuries and deaths as the result of explosions. They will be reported to local safety authorities but its very hard to get a picture of the scale of the situation beyond that.

GC: Its not possible to say how much improving safety would reduce harm then, is it? VG: 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? VG: 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 managers 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? VG: 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. Id even go so far as to say that there isnt 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 very interesting process to observe.

A cyclone of an indirect firing coal mill system that hardly could have been laid out worse. The cyclone has been installed inside a building, which disallows protection by means of explosion venting. Equipping it with explosion vents has been aborted, as evidenced by the blind covers that have been installed in place of explosion vents. The explosion pressure shock resistance will be very low, if present at all. Flame front propagation would run into the cyclone completely unmitigated, since no explosion de-coupling upstream of the cyclones dirty inlet is installed. The configuration shown here is disastrous, since disintegration of the cyclone could cause a dust cloud inside the building, which, if ignited, could blow up the building itself.

GC: Can a coal mill system actually ever be safe? VG: Absolutely! If you combine all of the knowledge available to properly design and engineer your system, operate it correctly and maintain it, there is no reason why the system cannot be completely safe. This is why it is such a shame that the reality is so far from the situation we could have. If an explosion were to happen in such a system, there would be no loss of life, no injury and no major system damage.

GC: What can be done to improve the situation? VG: It starts with the cement plant operator asking the right questions during the design phase. To do that they may need the help of a consultant like CMS. Whoever is asking the questions, they need to have the power to actually demand changes to the design. Otherwise there is no point. Once, a major European cement multinational asked me to help negotiate the purchase of a coal system from a Chinese supplier. However, I was not given authority by the purchaser in that situation and the result of my efforts were negligable. The cement producer needs to understand that being the customer means they should be knowledgeable enough to not accidentally get the somewhat flawed 40 year old design the supplier wants to sell! You also need to operate the system safely and know how it needs to be used. It needs to be maintained properly too. Otherwise the system will become unsafe within three or four years. Even if the plant staff are really on the ball there will still be a place for experts. I was once at a plant in the Philippines where an explosion had occurred during the night before I visited. The plant staff were poring over their computers and control systems to try and find out about the incident. They could, for example, work out where the temperature rose too far and where there was too much oxygen in the system, but, looking at the damage quickly proved that their efforts to understand the effects of the explosion and why their protection had failed went nowhere. 45 years experience allows you to understand that part, without computers.

GC: Does it surprise you that after 45 years, an expert such as yourself is still needed at the plant? VG: No, Im not surprised. Plant staff in the cement industry need to focus on producing cement. Fire and explosion protection for coal grinding is a highly specialised field. You cannot expect that plant staff recognise flaws in the system that has been put in front of them, normally with no or very little input from their end.

GC: Will there be a brain drain in this area as consultants like yourself leave the field? VG: Thats a risk, yes. I just have to pass on as much information as I can in the remaining time that I can have in the sector.

GC: Are attitudes gradually changing? VG: Overall, no. Nothing is really changing at this point. Some producers are making sporadic efforts to understand this area and improve, but such large companies move so slowly. Many suppliers are listening to Thorwesten Vent, which is good. However, Thorwesten Vent can only influence certain aspects of fire and explosion protection of coal grinding systems, not everything.

GC: Could the standards be improved? VG: The standards and codes are very complicated and difficult to follow. They are always referred to but not understood. In some cases the standards leave a lot of room for interpretation. So, you see, you cannot even blame the engineers for misinterpreting the situation they are doing their best! The information from ATEX or the EN codes tell you all kinds of interesting information but they are not, and cannot, be exhaustive in terms of engineering solutions. You wont find answers to all the workarounds you need, most probably because it hasnt been needed before. There may be warnings at best. Ive already mentioned flame front propagation through a duct. That is something that the standards speak of, but they dont say how to deal with it.

GC: Is that because those writing the standards also dont know? VG: Its not that this is unknowable, but there are no standards with a focus on indirect firing coal grinding systems, which typically have some special conditions. NFPA 85, in spite of its pro-forma applicability to the indirect firing coal grinding systems of the cement industry, in reality only covers direct firing for the power generation industry, almost completely neglecting the elements that would form the basis of correct fire and explosion protection of indirect firing grinding systems.

GC: Would you advocate that a cement group standardise its coal mill safety solutions? VG: Yes. It would be good to issue a group guideline covering both design specifications/requirements and best practices. Compliance needs to be part of each plants quality management, with strong monitoring by the groups management. However, such an approach has become more difficult in the past decade or so, with the closures and downsizings of some groups technical centres. Lafarge, Holcim, HeidelbergCement and others used to have several of their own technical centres that would have some degree of in-house know-how and responsibilities, which certainly improved situations in the group. They would look at selected new and existing situations, but were not able to support, let alone control the safety of all the systems of their large groups. Now the big groups have closed or downsized several of their technical centres and delegated responsibilities to their plants management, where the necessary know-how will definitely be insufficient.

An awkwardly designed and installed explosion vent on a pulverised coal silo. The silo has been installed in a building, which disallows explosion venting without special measures that control the blasts exit from the building. These are not present. The explosion vent is of a design that will not reclose, due to design faults that will cause its hinged lid to deform and not to fall back after the explosion, leaving it open to ingress of O2 and uncontrolled losses of inerting medium that will make firefighting impossible. Explosion pressure shock resistance of the silo and the explosion vent are lacking. The explosion effects will affect the silos in-feed drop chutes. When venting, the blast will hit the concrete ceiling, which is far too close to prevent the flame bodys dangerous deflection, spread and expansion into the building.

GC: What kinds of producers are most proactive in coal mill safety? VG: The multinationals are starting to move in the right direction on paper, but its really slow. They dont help themselves with constant personnel changes. I have been in a situation where Ive been training say 8-10 individuals across a group. Everything goes well and then, six months later, I try to reconnect with them to see their progress. The problem is, theyre almost certainly in a different role by then! Theyve most likely forgotten everything they ever knew about coal mill safety and probably didnt transfer knowledge to the next person in their old role.

GC: What is the one easiest thing to do to improve an existing system with poor safety? VG: Sometimes the best solution is to rip it out and start again. That way you have a clean slate and can avoid so many of the common mistakes. When thats not possible, there is no easy win. Its all hard work! All situations are different in any case.

GC: It seems that your final answer sums up the whole issue VG: Indeed. Improving coal mill safety in the cement sector is a continuous and varied challenge. I hope that by highlighting some of the most common problems and failings in these pages in terms of systems, attitudes and regulations I can make others aware of how they can influence this area for the better. This will help the suppliers, cement producers and, most importantly, the men and women that risk their lives working with these unsafe systems.

in discussion - vincent grosskopf, coal mill safety

in discussion - vincent grosskopf, coal mill safety

Despite the use of oil and gas in many regions and the rapid rise of alternative fuels, coal remains the major cement production fuel.Vincent Grosskopf, founder of Coal Mill Safety (CMS).A coal grinding system with a mill-to-bag house riser duct (marked with red line) that is very long. Through it, unmitigated flame front propagation could reach a velocity too high for the installed protection to effectively protect the bag house. This is a typical situation and it needs to be corrected.A cyclone of an indirect firing coal mill system that hardly could have been laid out worse. The cyclone has been installed inside a building, which disallows protection by means of explosion venting. Equipping it with explosion vents has been aborted, as evidenced by the blind covers that have been installed in place of explosion vents. The explosion pressure shock resistance will be very low, if present at all.An awkwardly designed and installed explosion vent on a pulverised coal silo. The silo has been installed in a building, which disallows explosion venting without special measures that control the blasts exit from the building. These are not present. The explosion vent is of a design that will not reclose, due to design faults that will cause its hinged lid to deform and not to fall back after the explosion, leaving it open to ingress of O2 and uncontrolled losses of inerting medium that will make firefighting impossible. Explosion pressure shock resistance of the silo and the explosion vent are lacking. The explosion effects will affect the silos in-feed drop chutes. When venting, the blast will hit the concrete ceiling, which is far too close to prevent the flame bodys dangerous deflection, spread and expansion into the building.

Vincent Grosskopf has more than 45 years of experience in bulk material handling, particularly regarding the safety of coal grinding systems. As the founder of Coal Mill Safety, he acts as a consultant to those seeking to design and build safe greenfield coal grinding systems or improve existing installations. However, since such systems are often an afterthought within the cement sector, theres a lot of work to be done...

Vincent Grosskopf (VG): I started working in the bulk handling arena in the early 1970s until 1992, when I joined Thorwesten. At that point Thorwesten Vent had begun to work with explosion vents, predominantly for its own coal silos. We were then approached by others, such as Polysius and FLSmidth, which wanted to licence vents for their own designs. Learning about the use of explosion vents in collaboration with such firms led to applications in coal grinding equipment, including bag filters.

On the surface this appears to be quite simple but the situations are quite different. The inside of a silo is big and wide, which means the explosion front propogates relatively slowly. By contrast, inside the narrow ducts of a coal grinding and de-dusting system, explosions move much more rapidly and with greater pressure. At Thorwesten Vent we found solutions around these differences and other issues, gaining unrivalled experience in explosion venting.

VG: I established Coal Mill Safety (CMS) as a consultancy after I retired in 2011. If a cement producer wants to install a new coal grinding system, they can commission CMS to look at the suppliers design and probe it from a safety angle. If it has an existing system, it can ask CMS how it can improve it.

VG: 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.

VG: 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 maximise 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 particuarly in Asia, that do not understand the safety principles and, some might say, dont particularly want to.

CG: 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 pulverised fuel; Incorrectly designed and protected pulverised fuel silos; Incorrectly designed/installed gas analyser configurations and; Incorrectly configured emergency inerting systems. The methods and means of protection of raw coal stockpiles against fire are rarely organised 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.

VG: Producers do not have the expertise and very often dont 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 theres no need to act.

VG: Many people are killed and maimed as a result of a coal dust explosions but often you wont hear about it. Even if you do hear about it, you wont 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 thats 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.

VG: There is pretty much no centralised data on this subject, which means we dont 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 dont.

Even in developed markets, there are injuries and deaths as the result of explosions. They will be reported to local safety authorities but its very hard to get a picture of the scale of the situation beyond that.

VG: 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.

VG: 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 managers 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.

VG: 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. Id even go so far as to say that there isnt 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 very interesting process to observe.

VG: Absolutely! If you combine all of the knowledge available to properly design and engineer your system, operate it correctly and maintain it, there is no reason why the system cannot be completely safe. This is why it is such a shame that the reality is so far from the situation we could have. If an explosion were to happen in such a system, there would be no loss of life, no injury and no major system damage.

Once, a major European cement multinational asked me to help negotiate the purchase of a coal system from a Chinese supplier. However, I was not given authority by the purchaser in that situation and the result of my efforts were negligable. The cement producer needs to understand that being the customer means they should be knowledgeable enough to not accidentally get the somewhat flawed 40 year old design the supplier wants to sell!

Even if the plant staff are really on the ball there will still be a place for experts. I was once at a plant in the Philippines where an explosion had occurred during the night before I visited. The plant staff were poring over their computers and control systems to try and find out about the incident. They could, for example, work out where the temperature rose too far and where there was too much oxygen in the system, but, looking at the damage quickly proved that their efforts to understand the effects of the explosion and why their protection had failed went nowhere. 45 years experience allows you to understand that part, without computers.

VG: No, Im not surprised. Plant staff in the cement industry need to focus on producing cement. Fire and explosion protection for coal grinding is a highly specialised field. You cannot expect that plant staff recognise flaws in the system that has been put in front of them, normally with no or very little input from their end.

VG: Overall, no. Nothing is really changing at this point. Some producers are making sporadic efforts to understand this area and improve, but such large companies move so slowly. Many suppliers are listening to Thorwesten Vent, which is good. However, Thorwesten Vent can only influence certain aspects of fire and explosion protection of coal grinding systems, not everything.

VG: The standards and codes are very complicated and difficult to follow. They are always referred to but not understood. In some cases the standards leave a lot of room for interpretation. So, you see, you cannot even blame the engineers for misinterpreting the situation - they are doing their best!

The information from ATEX or the EN codes tell you all kinds of interesting information but they are not, and cannot, be exhaustive in terms of engineering solutions. You wont find answers to all the workarounds you need, most probably because it hasnt been needed before. There may be warnings at best.

VG: Its not that this is unknowable, but there are no standards with a focus on indirect firing coal grinding systems, which typically have some special conditions. NFPA 85, in spite of its pro-forma applicability to the indirect firing coal grinding systems of the cement industry, in reality only covers direct firing for the power generation industry, almost completely neglecting the elements that would form the basis of correct fire and explosion protection of indirect firing grinding systems.

VG: Yes. It would be good to issue a group guideline covering both design specifications/requirements and best practices. Compliance needs to be part of each plants quality management, with strong monitoring by the groups management. However, such an approach has become more difficult in the past decade or so, with the closures and downsizings of some groups technical centres. Lafarge, Holcim, HeidelbergCement and others used to have several of their own technical centres that would have some degree of in-house know-how and responsibilities, which certainly improved situations in the group. They would look at selected new and existing situations, but were not able to support, let alone control the safety of all the systems of their large groups.

VG: The multinationals are starting to move in the right direction on paper, but its really slow. They dont help themselves with constant personnel changes. I have been in a situation where Ive been training say 8 - 10 individuals across a group. Everything goes well and then, six months later, I try to reconnect with them to see their progress. The problem is, theyre almost certainly in a different role by then! Theyve most likely forgotten everything they ever knew about coal mill safety and probably didnt transfer knowledge to the next person in their old role.

VG: Sometimes the best solution is to rip it out and start again. That way you have a clean slate and can avoid so many of the common mistakes. When thats not possible, there is no easy win. Its all hard work! All situations are different in any case.

VG: Indeed. Improving coal mill safety in the cement sector is a continuous and varied challenge. I hope that by highlighting some of the most common problems and failings in these pages - in terms of systems, attitudes and regulations - I can make others aware of how they can influence this area for the better. This will help the suppliers, cement producers and, most importantly, the men and women that risk their lives working with these unsafe systems.

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