Subscribe
Share
Share
Embed
In this episode we discuss the details that go into the system design of a dust collector that handles explosive dust.
Discover how clean air can affect the quality process for you and the workplace from world leading experts.
We find out how controlling air can bring benefits to production plants and facilities, the health of people who work there, and bringing greater efficiencies to your final product.
We're also joined by experts from Camfil, a world leader in the development and production of air filters and clean air solutions, on what they are doing to keep air clean and safe.
Andy Thomason 0:06
There are three things to keep in mind when designing an assistant is going to handle expose it does.
This subject is going to try to help you understand what the important items are to think about when you're trying to design a dust collection system that's going to handle explosive dust.
Jacob Stewart 0:37
Hello, and welcome to Let's talk clean air, where we find out more about how clean air can affect the quality process for you and the workplace. I'm your host Jacob Stewart. And in this episode, we're going to be discussing dust collection system design when handling explosive dust. With me today is camfil ABCs. Andy Thomason. So how are you doing today, Andy?
Andy Thomason 0:58
Jenkins, I'm fine. Thanks for the invite to help out on this podcast. For those of you that don't know me, I'm Andy Thomason, I'm the senior application specialist for camfil APC, my home office would be the Jonesboro Arkansas facility, where I'm part of the engineering and technical support team. My jobs range from supporting application reviews from our reps, dealers and end users and customers also have the responsibility for education to our customers and to our sales force. The last title that our responsibility that I have is to support r&d in their efforts to develop new product for our customers. Today, this subject is going to try to help you understand what the importance items are to think about when you're trying to design a dust collection system that's going to handle explosive dust. All
Jacob Stewart 2:08
right, awesome. Well, it's great to have you with us today, Andy. So if it's okay with you, we'll just go ahead and get right into the questions. So starting off, what are the most important things to keep in mind while designing a dust collection system for explosive dust,
Andy Thomason 2:25
there are three things to keep in mind when designing a system that's going to handle explosive dust. The first thing is to remember the dust explosion Paragon our Pentagon excuse me, the second is to use the best practices that are stated in the industrial ventilation manual. And the third is to abide by the National Fire Protection Agency or nspa standards that are applicable to your system, or to your Titan dust. Out of these three. The first we talked about was the dust explosion. Pentagon. Keep this in mind when I'm working with explosive dusts to remind me of the five things that are required, that would create a dust explosion. And those are the first side of the Pentagon is oxygen, we find oxygen available in a dust collection system because there's oxygen in the air we're using to motivate the dust and collected into the collector. The second side is confinement, you've got to have confinement of this dust in an enclosed area to create an explosion, and that would be considered the cavity of the collector or the body of the collector. Third side is dispersion of the dust itself, we would find the dispersion of the dust inside the collector during pulse cleaning. When there's a heavy cloud of dust present, and fourside is there's got to be an ignition source that can be created by some pieces of equipment that are creating mechanical movement, heat source static electricity, sparks or an open flame. And the last and the most important is let's call this where's the fuel or in other words, where's the explosive dusts present and your dust collection system. This second item to keep in mind when designing dust collection system that's handling exposure dust is to refer to the industrial ventilation manual which provides us a wealth of information on how to properly design the system so that the dust or in our case the fuel is captured and give aid into the collector. The manual provides us recommended capture velocities minimum conveying velocity These, her design and her geometries all for different types of dusts and applications. I utilize the manual for design procedures on how to size ducting systems. And by use of what we call the balanced by design method, which is required for us to use by the NFLPA 652 standards. This method helps us design ducting systems that will self balance by balanced by design method. This also helps us to achieve useful information that we can use to verify the system's performance once in the field, and also to create a pressure curve to evaluate fan selection to be used to motivate the air in the system. The third and last thing I try to keep in mind here are these NFA standards. There's four of them, that I tried to keep in mind that are the general ones that are used when designing a dust collection system with explosive dust. Those are enough pa 68 that covers explosion protection by delegation visiting in FPA 69 that covers explosion prevention systems, in FPA 652 that covers fundamentals of combustible dust. And in APA 654 that covers preventional provision of fires and dust explosions are manufacturing, processing and handling of conditional combustible dust particulate solids. These four cover a vast amount of information. And we'll probably have to create a new podcast just to help you cover the basics of those four. But keep in mind, there's many other NFLPA standards that should be reviewed when handling a collector that has combustible dust, but they more pertained to certain types of dust, or even certain types of operations within specific industries.
Jacob Stewart 7:19
So with the dust explosion, Pentagon, the industrial ventilation manual and the nspa standards like these all sound like really helpful things for designing your collector, where would somebody go to access this information?
Andy Thomason 7:36
The dust explosion, Pentagon is probably so that you can find a picture of to help you understand somewhere on the website, or even at nsba. There's also a website for NFLPA that lists the standards for public review to help you understand the third for the industrial ventilation manual that something that you can purchase through the AC gi J. They they publish this book, I think it's about 120 $140. And I think they're all the way up to edition number 29. For our customer base and our sales force, we offer a very short course at the plant and jonesborough on industrial ventilation, and these in FPA standards. I think we're just waiting for COVID to relax situation so we can start the process of starting training back and these certain subjects, we love the opportunity to have our customers come to the plant jonesborough and see our facility how we work and to learn our culture.
Jacob Stewart 8:50
Absolutely. So for the next question, what design characteristics are necessary for capturing fugitive dust into your dust collection system?
Andy Thomason 9:00
This is a good question, there's two things that you really need is you need to determine the correct capture velocity. And you need to create and design the proper hood geometry. These two factors are derived from your basic or knowledge or your knowledge that you need to gather about dust, your knowledge about the process, the understanding of the environment around the process, and how it influences the dust and also knowing the dispersion pattern of the fugitive dust that the process is generating.
Jacob Stewart 9:38
Right. It could you explain a little bit more about the importance of capture velocity.
Andy Thomason 9:44
Sure. It's it's actually the crux or the main foundation of what you got to get right in the beginning when designing the dust collection system. expecially when it's the dust collection system, that's handling An explosive duster. In this case, let's keep the mindset of that it's a fuel. The capture velocity is in this fundamental, by definition is the where you have to create an airflow across the point of dust generation so that it wants to change any momentum that that dust has to reach a momentum and change its momentum to move towards and accelerate into the opening of your hood, whether it's a an enclosure, whether it's a containment booth, or whether it's just a plain hood, or even a closed captured hood, you've got to motivate this dust into the hood so that you can collect it, low capture velocities will leave dust are this of course in our discussion, the fuel won't capture it all this dust is gonna end up remaining in the workspace or even loadable dust How have the ability to migrate even other parts of the plant by being carried with air currents that are present in the plant. By definition, you could also think of the capture velocity as being of lossy, that's great enough to overcome the dust dispersion momentums buoyancy and external influences many people that tried to at the beginning of design experience, they mistakenly forget to add influences or increase capture velocities to overcome external influences. And also to compensate for the respect to where the hood is located with respect to where the dust is being generated. hoods, especially close capture hoods, are very sensitive to their location via where the dust is being generated, you might design for that hood to be a certain distance from the dust being generated. And if that hood has moved away, the efficiency of that hood or the capture velocity from that hood vase distance drastically decreases. So you have to be very careful to make sure that whatever you decide or whatever design distance you use in calculating your velocity pressure required at some distance away from the hood, you need to make sure that the hoods not gonna move from that position. The other mistake that designers will make is that not recognizing that there might be some external air currents around the hood that are going to disturb that velocity pattern that's trying to pull that dust or make that dust change its mind or or marry a momentum of a of that dust movement into the hood, like a man cooler fan, or even a air conditioning event could be blowing the dust or changing the momentum of the dust.
Jacob Stewart 13:14
And another term that you mentioned was balanced by design. Could you explain a little bit more about what that means?
Andy Thomason 13:23
Yeah, balanced by design is a method of calculating the duck static pressure losses. And it uses duck frictional factors or losses and also accounts for all the dynamic losses in terms of loss to pressure. Some people will call the balance by design they also call it a blast velocity pressure method of calculating duck losses and system static pressures by using this method that is designer the owner can evaluate the ducts branches, static pressure loss, and adjust the design configuration of that branch to balance the static pressure at each junction point. Also, by theory, what happens is that where two air streams come together, you've got to have the same static pressure. If you don't, those two branches one branch will increase in their volume or decrease in air volume until there is an equal static pressure where there's two air to air streams come together and in the past are old school calculations would be that people would just kind of use an equivalent loss method or foot method loss for sizing ducting, put it in the field and then do fine balancing of the branches to get the flow that they need by adding manual dampers or sly gates that take it open and close to create a fault pressure So that the static pressures would meet at the junction point and the flows can be adjusted to match the performance that they need and the detriment to that old type design is that one those manual dampers Could someone could come up after they've been set and change their position to better one process, but yet negate the amount of air needed for another process or at another branch. Sometimes you they found that these would vibrate loose and change their positions which would mess up your capture velocity and your momentum convey velocity also in some of rays of explosive dusty founded over a period of time, those dampers would actually wear which would also change the set static pressure that they were trying to achieve by balancing with a manual damper nsba actually recommends that you do not wherever possible use balancing dampers to adjust your flows. This bounce by design procedure allows you to design ducting, so that these blast gates are not are balancing dampers are not needed.
Jacob Stewart 16:22
Could you explain more about the importance of hood geometry?
Andy Thomason 16:27
Sure, hood geometry needs to be considered so that the blot velocity profiles is being projected around the area of where you're generating the dust or where the process is generating the dust. That profile you're wanting to be at the capture velocity required that you are designing for. A lot of people don't realize that there is a profile velocity profile created by different hood geometries. And it's not intuitive because of course, the air you can't see it. If your processes smoky, you might be able to see a smoke pattern, or they're being accelerated and gathered by the hood. But conceptually, it's a it's a difficult thing to realize. So the industrial ventilation manual has come up with many different practical geometries, and a good explanation of what those projective velocity profiles will look like as you change those hood geometries. For the audience. Here's a practical example of hood. Let's say that's collecting welding smoke, if you had a piece of material that you're welding, and let's say it's 12 inches long, and it's placed, let's say 12 inches from the face of the hood opening, you'd actually need to create a hood, that projects of velocity profile that has the capture of lossy, that's going to be something wider than that 12 inch piece of material, and actually can project that needed velocity profile at a distance of more than 12 inches away from the hood face. That way, you can ensure that that profile as you weld from one side of that 12 inch piece of metal to the other side, that any smoke being generated is going to be captured with in that velocity projected profile. Some additional ways to explain the importance of hood geometry would be here. Here's another example that might help you the listener, imagine what we're talking about. If you had a, let's say you had a hood opening that was short and high, but long in length or in other words, maybe you heard that had an opening to create an aspect ratio of height the width of something of less than 0.20 ratio, that type hood or that configuration hood would project velocity profile that is only present for a short vertical height, but would be present over along with a along the length of the hood. Another way to think about that profile might be to imagine a flattened elliptical shape of the velocity profile in front of the hood. Consequently, a hood that's nearly square and it's opening in an order the words the opening is tall is the opening would be wide, would project the velocity profile that's just as wide as it is tall or maybe You can think of it is a Hemi spherical shape. Again, using the wrong hood geometry, we'd leave the dust or the fuel and undesired locations. So it's very important to get not only the correct velocity profile, but also to make sure that that velocity profile is being developed by the correct hood geometry.
Jacob Stewart 20:25
Right. For our next question, can you explain what the minimum conveying velocities are for the different types of dust?
Andy Thomason 20:33
Yes, that's a very important design feature. The last of the three and important design features one and review was our capture velocity you got to get that right. The second is the her geometry. And the third is this minimum conveying velocity based on what type of dust that you're handling. This is true, whether it's exposure and non explosive dust, all dust have their own aerodynamic characteristic or and therefore require different airspeed to keep them in suspension. So that they can be conveyed from the point of generation into the hood through the ducting and into the collector. Some people refer to this individual error dynamic characteristic of a dust particle as being their Stokes equivalent, which is another subject that we could have a podcast about, because the subject so deep industrial ventilation manual gives us groupings of different types of dusts with examples to help us derive it, I'm going to call it just a starting point of where we should design for a minimum conveying velocity, I highly recommend that you try to consult with someone that has experience in handling the same dust that's being created by the same process that you have just so you can confirm this mental convey and glossy and find proof of it there's not a very strong detailed information about what true minimum conveying velocities need to be only generality since there's always some exception the even what the industrial ventilation manual might give you the value that they may give you. A good example of that would be let's say that you might look at the industrial ventilation manual and see what kind of minimum conveying velocity you need for say welding welding. Suppose normally to design welling spoke you would need a middle conveying velocity to be created the adopting of about 2500 feet per minute, but if that welding operation, if they're welding on material that's been soaked in oil to prevent the material from rusting, or maybe the welder is spraying a anti weld splatter material on the well before our material before you weld it, as the welding process happens those oils in a weld splatter will vaporize or, and mix with welding dust and actually build up and create a sticky dust that will build up on the interior of your ducting that you're using the Kobe the dust and because of that, you might have to increase your duct mineral quervain velocity to something around maybe 3800 to 4000 feet per minute. So you need to make sure that you review your process and not just depend on the generalities that the industrial ventilation might give you. Not designing your system to meet this minnow conveying velocity is it gonna allow the dust or again in our scenario, the fuel the buildup on the inside of the dark ducting system or lay in the bottom of the ducting system. And this is going to be dis detrimental, especially when handling an explosive dusts because now we're spreading the fuel or we've distributed fuel or dust in locations in the ducting system. Well, we're not expecting it to be and we haven't provided any for vet protection in case of an incident with that dust being located and the ducting
Jacob Stewart 24:43
and do you have any advice for those who are about to purchase their own dust collector for combustible dust?
Andy Thomason 24:50
That's a great question. I'll try to answer that question without being prejudiced to the type collectors that we sell But I would recommend that the owner or the purchaser, find a manufacturer that has good quality, and can produce a collector that provides a low cost of ownership ship or operation with the collector, something you can do is have the manufacturers supply you with a copy of their ancy ASHRAE 199 test. The results of that test give you some insight about the collectors performance and how it performs under different process conditions. Its energy consumption, and also provide a photometric admissions statement. Those test results are valuable tools, all those things, and helping you decide and determine what collector is going to be the best offering for you. And also select a collector based on size or let's call it air to media ratio, based off the performance requirements that best match the demands of your process. And do this selection in keeping in mind of what's going to offer the most convenient filter lifecycle that meets your requirement in production. That sounds like a mouthful, but you have to keep in mind that you can purchase a collector that's very small that will do the job or you can collect our purchase collector that has more media in it that will do the same job and the size of those collectors and the amount of filter material that you have in them or air cloth ratio is going to greatly determine what kind of life you have on your filter material. It's important when you're selecting the collector for especially for combustible dust is that you understand and you can control the the pressure drop across the collector media and control that and that's expecially important when sizing your collector for handling combustible dust. also choose a collector configuration that's going to enable dust to flow off the filters and into some kind of removal device at the bottom of the hopper the collector, you want to ensure that the dust or our discussion, the fuel that enters the collector doesn't have the chance to remain inside the collector. The collected configuration should also compliment the required explosion protection devices that we need in handling the combustible dust. The last thing I would recommend is that you purchase from a collective manufacturer that has the good understanding of what these NFLPA standards are we've talked about and also understands the practices that are stated in the industrial ventilation manual.
Jacob Stewart 28:16
Right So in addition to that, do you have any advice for selecting a fan for your dust collector,
Andy Thomason 28:23
I do select in a fan best suited for a dust collection system. When handling explosive dust is very important because the fan is not smart enough to provide you a constant flow. It is a centrifugal device or some people term it is a slipstream device that only knows to operate in a position on its performance curve where the system that you've designed dictates it to or where say the pressure drop across the system and your filters dictate it to operate. bands are probably the most misunderstood component and dust collection systems they they always get blamed for bad performance of dust collection system when almost 90% of the time the problem is due to incorrect system calculations or installation or someone not truly understanding this selecting a dust collection dust collector that's with filters that's going to provide a predictable performance of pressure drop fans, you got to keep in mind that fans are only capable of providing an operating performance point that's dictated by the system resistance to a given flow. The owner or the selector of the fan should always select a fan There's going to be capable of providing the required flow under all possible system pressure changes, the system curve will change its positions, and therefore change the position on the fan performance curve at the collectors filters built in pressure and lose differential pressure. When dust builds up on the filters, the designer is got to conduct a critical review of the fan and the SR curve that's developed to ensure design airflow will be maintained, the system design is based on required airflow at each pickup point to maintain that capture velocity that we've talked about, and also establish a minimum conveying velocity and the ducting. Without these things, we're not going to collect the dust or motivate the dust into our hoods. And we're not going to be able to convey the dust from the hoods through the ducting into a collector. Selecting a fan that creates an airflow lower than the system volume that you've designed for when challenged by the increase filter pressure drop is going to result in the fuel being spread throughout the system. It'll be fuel left, where you expected it to be collected at the hood face or in the process. And it's also going to leave dust in the ducting where you weren't expecting it to be and you haven't provided any protection for explosion.
Jacob Stewart 31:47
Okay, and moving on to our last question, just as kind of a summary of what we've talked about. Could you summarize some of the important design goals when designing a dust collection system that's meant to handle explosive dusts?
Andy Thomason 32:02
Always at the end of the design? I give myself a ton of a personal review and I would suggest you do too. Is it yes yourself the following questions and make sure that by answering yes to these questions, it's going to help you make sure that your your design is in compliance with the needs of the dust collection system that's going to handle an explosive dust. The first question is, will the capture velocity that I'm using motivate the dust into the hood? The second would be with the hood geometry that I've selected project a velocity profile to cover the total area of where the dust is being generated. Third would be will the design dot velocity keep the dust from collecting within the ducting system that relates back to our minimum conveying velocity? And fourth question would be have I used the principles of design as outlined in the industrial ventilation manual In other words, the do's and don'ts of how to configure and how to build and design your ducting system. Five Do I have controls and instrumentation available in my system to help me monitor and control the collectors performance. It's important to know what the collector is doing and how it's performing. Because you want to make sure that it's performing within the criteria that you've designed is selected your fan. Last question is also related to the previous one is, will the selection or the fan that I've selected? Is it going to be operating in a stable performance over the complete range or save changes that my system is going to see towards static pressure? Jacob I appreciate the time that you've given me it's important for us it can feel a PC to take every opportunity we can to help educate our customers and to establish a relationship. We're proud of the product that we make. We're proud of how we try to keep up with industry standards of the NFLPA in industrial ventilation practices. I am just one of many that we have on staff that are available to try to help you in your selection and design of a dust collection system and or one that's going to be handling explosive dusts. So thanks for your time. Yeah, absolutely.
Jacob Stewart 34:57
Thank you so much for for agreeing to do this. Randy, I feel like we we all learned a lot from this. So if you'd like to find out more about this and other topics, simply follow the links in the show notes, which you'll find in the description of this podcast. They include links, contact details, and anything else you might need to get more information. This podcast was produced by cam Phil, the world leader in the production and development of air filters and clean air solutions. You could find out more at Camp build calm. Be sure to join us for our next episode, and be sure to subscribe to get notifications for future episodes. Until then, I'm your host, Jacob Stewart and this has been let's talk plein air. Thank you for listening.