Understanding the basics of Dust Suppression using Sprinklers. Fugitive and inhalable dust suppression is not only a nuisance but most importantly it poses great danger to human health hence legislative protocols should be followed in order to maintain the level of dust within acceptable and allowable limits. The need to effectively reduce dust is embodied in all the different solutions which vary from one dust suppression method to the other. Mechanical engineering has also had its fair share of contribution and still evolves in the participation in coming up with effective dust suppression methods through dust suppression sprinklers. The first exposure to sprinklers for most is either through irrigation or garden lawns which in most cases the common denominator is water. However we will focus on use of sprinklers in dust suppression in mining. The context of our discussion ventures into understanding what dust suppression sprinklers are utilized for. The mechanisms applicable to dust suppression and finally rounding our article with the synergy between Global Road Technology products and dust suppression sprinklers.
Understanding the hardware
Dust suppression sprinklers consist of components that satisfy different functional properties when it comes to applications in mining dust suppression. In the interest of understanding the structure to function relationship we will highlight comparisons between a mining dust suppression rain gun sprinkler vs high volume dust suppression rain gun designed for mining applications. The comparison of the former vs the latter will be given for the following properties below:
- Water input : 2” Female BSP vs 2.5” Flanged
- Working pressure : Both 44 – 100 psi
- Water flow : 250 – 967 l/min vs 683 -1800 l/min
- Shooting radius : 27 – 47 m vs 38 – 55 m
- Free Nozzles : 12, 14, 16, 18, 20, 22 vs 26, 28, 30, 32 mm and both 24 mm
- Body angle : Both 430
- Weight : 9 kg vs 13 kg
The practical implications of the properties mentioned above come into effect in different scenarios. For instance, air turbulence created by the machine water sprays results in dust clouds at the cutting face to expand and back up against the weaker airflow on the side opposite the ventilation duct. This phenomenon of rollback can lead to contamination of incoming air breathed by mine workers. The air turbulence that causes rollback can be reduced by lowering the spray water pressure and aligning spray nozzles so that they are confined only to spray on the broken coal. As a rule of thumb studies have shown that it is best to wet the material fully during the breakage process as this is when the most mechanical mixing is bound to happen. Timing is important because uniformity in wetting is best obtained on utilization of more nozzles at lower flow rates taking into consideration that they are aimed at broken material instead of just spraying into the air and wetting adjacent surfaces. It should also be acknowledged that every situation is the same rather the circumstances dictate the effective use of spray nozzles depending on the mining conditions, the type and nature of dust to be suppressed amongst many other factors to be taking into account. In addition the variety of free nozzle ranges is important as nozzles with very small orifices tend to be susceptible to clogging which serves to say well informed nozzle selection can enhance their application for dust suppression.
Dynamic and stationary dust control
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The mechanisms of application for dust suppression sprinklers vary from wetting to airborne capture. Dust suppression effectiveness relies heavily on sufficient wetting mechanisms which relies on understanding that bulk of the dust particles remain attached to the surface of the disintegrated material. Imperative is to have a fine balance between the need for dust suppression and the possible deterioration in calorific value for the material subjected to dust suppression. A very good example is the use of water for coal dust suppression, its use creates material handling challenges and compromises on product quality because of the differences in surface chemistry which might tempt one to use more water because of the need to wet the material enough and uniformly which comes at the expense of calorific value and can even create further airborne dust in the process. Airborne capture on the other hand really depend on mining conditions as dust clouds are unconfined hence the moving droplets from the dust suppression sprinklers exert drag on the adjacent air, therefore sprays tend to move the air which results in air entrapment spreads the cloud instead of capturing making capture by the spray less efficient. Air entrapment also can cause airflow to bounce back from the coal face to the operator raising the dust level this amongst the water curtain effect which is based on the premise that dust particles passing across a barrier row of spray will always be captured which unfortunately is never the case.
Not having the foggiest…
Perhaps then understanding what nozzles work best for which scenario would be a good starting point in improving efficiency of dust suppression sprinklers. Before we get into that, it has been found that matching the particle size of the dust to be suppressed also improves the dust suppression efficacy. Reduction in droplet size through atomization or fog sprays offer improved dust capture in addition to the economical use of dust suppressants but in general the downside always comes with the correlation between smaller nozzles and susceptibility to clogging. Amongst many other reasons smaller droplets tend to evaporate quickly which releases captured dust along with dissolution components in the dust suppressant. Targeted nozzle selection shows that atomized sprays are the most efficient although hollow-cone sprays are second to them with their opted selection based on larger orifices which make them less likely to clog in practical mining applications. Flat fan sprays are effective in narrow rectangular spaces as less water is lost by spraying against an adjacent surface. Efficiency per unit use of water is vastly improved using high pressure sprays although the downside is that they entrain large volumes of air, leading to more dispersal of dust than is actually captured.
Partnering good hardware with the right chemistry
Although water has been the most predominant dust suppressant, the wetting and airborne capture is greatly compromised especially in cases where the surface chemistry mirrors that of water. In this case even the most effective atomization can have minimal effect. The missing discipline in these application is industrial chemistry. As an example, Global Road Technology offers GRT Activate UG which improves efficiency of existing dust suppression sprinkler systems whilst enabling adaptability for other dust suppression areas such as dust conveyor systems and transit from pit to port. Given its ability to make water work (independent testing shows 12 times greater dust sequestration of Activate treated water than water alone) the return on investment when using GRT Activate UG is use of less water in the process of effective and targeted dust suppression.
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