Prevent Everything from Coal Dust to Sugar Dust Explosions
Pneumatic conveying offers solutions that remove critical elements of the combustible dust explosion pentagon, helping ensure your facility can prevent combustible dust explosions and meet NFPA 654 standards.
|Removal of any leg of the combustible dust pentagon can prevent an explosion.|
1. How do combustible dust explosions happen?
There are five elements that are needed to fuel a combustible dust explosion. They are:
- Fuel to burn – combustible dust
- Ignition source – heat, spark, etc.
- Oxygen in the environment
- Confinement of the dust cloud – which supports that concentration of the dust dispersion
- Dispersion of combustible dust particles – to the right concentration in the air
The first three elements are needed to ignite a fire. The last two elements can turn that fire into an explosion. If any one of the five sides of the combustible dust explosion pentagon are removed or suppressed, an explosion can be avoided.
2. How can I avoid providing the fuel for a dust explosion?
Obviously, dust from processing your materials is the fuel for a combustible dust explosion. Even some materials that would not normally be considered a risk in their unaltered state, can produce dust that become combustible. The particle size is important (generally less than 40 mesh), as is the accumulation of those particles. It can be very difficult to eliminate dust altogether. But there are ways to minimize the fuel source.
Dense phase pressure or vacuum pneumatic conveying can work with minimal product breakage – which means your system will produce less dust. High pressure, low volume air conveys the material at low velocity, for a more gentle, less abrasive convey process. This controlled conveying reduces the production of dust.
Accumulation of dust in any area can also provide a fuel source for fire and explosion. So it is important that your convey process does not allow product to drop out of the flow and collect at any point along the convey line. Nol-Tec’s Air Assist technology adds motive air into the convey line at those points that might be prone to dust collection. This additional energy keeps any dust moving along the line and into an appropriate dust collection point.
3. Are there ways to avoid ignition sources in my process?
Ignition sources can be anything from sparks produced by an out-of-alignment system component to an overheating bearing or belt. System pressures, temperatures, and blockages can all become the source of an ignition. It can be difficult to visually monitor your entire system, to find these areas of potential ignition.
With pneumatic conveying, there is a minimum of moving parts that come in contact with your materials or with other equipment. Without friction between components, pneumatics can reduce sparking and heat sources. Also, Nol-Tec’s expert electrical engineers can design and incorporate the automated controls and monitoring devices needed to optimize your process safety. Our controls can integrate with your entire system. With precision controls, you can monitor your system to stop potential equipment problems before they can develop into an ignition source.
4. Isn’t oxygen in the system always going to be a problem?
It is difficult to imagine any way to keep oxygen out of any process. We are surrounded by it! However, you don’t need to eliminate oxygen completely. You just need to make sure the concentrations of oxygen and combustible dust are controlled so that the point of explosive interaction is not reached. This oxygen concentration level varies greatly, depending on the explosive agent in question, but it is typically less than 15% 02.
Gas inerting in pneumatic conveying is an alternative approach to conveying with oxygen. By using inert gases (for example, nitrogen) as the conveying air, rather than oxygen, we can remove the explosion threat for the vast majority of compounds. Gas inerting can help you avoid costly explosion mitigation and suppression modifications to your system, if you are already using pneumatic conveying. Nol-Tec and Air Products & Chemicals have partnered on research for a system that would, in fact, prevent combustible dust explosions. They have co-authored a paper in the March 2015 issue of Chemical Engineering. Further details on this research and its practicality for conveying combustible dust materials can be found here.
5. How do I avoid the concentration needed for an explosion of dispersed dust particles?
Combustible dust needs to be in specific concentrations in the atmosphere in order to be an explosion hazard. The National Fire Prevention Association (NFPA) has done deep research on combustible materials and has developed specific formulas for the calculation of these concentrations. Each powder/dust and each system needs to be reviewed individually to understand how to avoid the concentration of dispersed dust in your particular circumstance.
Nol-Tec’s expert design team does just that. We work directly with you and your staff to ensure we design pneumatic conveying systems that move your materials effectively and keep your plant safe. Our custom-designed electrical controls and monitoring systems will meet your individual needs for safety and system monitoring.
6. Is all containment of dust hazardous?
One of the elements of the combustible dust explosion pentagon is containment of the dust cloud. In this simplified presentation of risks, it can certainly seem as if any containment of the dust from your materials is hazardous.
However, there are proper dust containment and collection methodologies that will allow you to keep your material dust controlled. Pneumatic conveying, with the variety of solutions presented in previous questions, allows you to contain dust safely, collect and pull it from the system effectively, and keep your combustion risks to a minimum. Containment is only a concern if all other elements of the pentagon are present. With a Nol-Tec pneumatic conveying system, we can tame the combustible dust explosion pentagon, while partnering with you for handling success.
7. Which dusts are most combustible?
Under the right circumstances, nearly any type of dust can be combustible. However, some dusts are more combustible than others. Examples of combustible dusts include:
- Sugar Dust
- Coal Dust
- Aluminum Dust
- Saw Dust
- Graphite Dust
- Corn Dust
- Titanium Dust
- Paper Dust
8. What caused the Imperial Sugar dust explosion?
In February, 2008, the Imperial Sugar refinery in Savannah, Georgia, experienced a massive sugar dust explosion after a large amount of combustible dust gathered in the packaging building. A spark was likely generated by equipment that was overheating due to the large build-up of dust along the conveyor belt line.The explosion killed 14 workers and injured 38 others. The Imperial Sugar dust explosion was one of the high-profile accidents that lead OSHA to enforce stricter standards for explosion mitigation. You can learn more details about this explosion at the U.S. Chemical Safety Board site.