Julian Turner from IEP Technologies explains why an innovative approach to explosion supression is achieving impressive results.
It is well understood that the performance of an explosion suppression system is dependent upon the dust hazard (Kst - explosion rate of pressure rise; Plax - maximum explosion pressure) and the volume being protected.
What is less well understood is the relationship between the final Pred value (reduced explosion pressure due the suppression system) and the discharge characteristics of the suppression system including; the diameter and number of injection points; and the throw of the suppressant (how far the suppressant can be projected at the correct concentration).
IEP Technologies developed suppressors with 125mm and 75mm diameter valves during the 1980s to optimise the hardware to the volume protected. The 125mm valve is typically used with a 45 litre capacity cylinder, filled with suppressant and pressurised to 60 bar with nitrogen as a propellant. This suppressor is designed for vertical mounting on top of a vessel and can be used with a 90 degree elbow to project the suppressant horizontally as the application dictates.
The 125mm suppressor valve is designed for large volumes such as spray driers and silos where its discharge characteristics deliver low Pred values. This suppressor has been used very successfully on a number of tall elongated silos in the grain industry. These silos have a cylinder length of around 12m and a total volume of approximately 150m3. The silos are 0.3 bar strong and are nested together with limited space between the silos. Mounting suppressors on the side of these elongated vessels would require significant investment in access platforms, which would also be needed for servicing. Another issue with side mounted suppressors in this application is, what happens when the product inside the silo rises above one or more of the suppressors that may be mounted on the side of the silo? In the event of an explosion, these suppressors could discharge into a solid mass of product making them ineffective, leaving the possibility that the remaining suppressors cannot effectively suppress the explosion to below the vessel strength.
The correct technical solution is to mount all suppressors on top of the silo discharging the suppressant downwards. This allows relatively easy installation of the suppressors compared to side mounting especially with many applications having the top of the silos as a conventional floor. Installation and service access is made easier, minimising installation and service costs.
With the large 125mm valve, the first 27kg of suppressant is rapidly discharged in ~200msec, delivering a Pred value well below the 0.3 barg required, which would not be possible using the smaller 75mm suppressor valve. Due to the multi-modal particle size distribution of IEP’s suppressant, full concentration of suppressant is maintained at the furthest point of discharge, i.e., the silo cone, thereby taking account of all ignition source locations, product fill levels and ensuring a full explosion suppression solution to the silo.
This IEP Technologies explosion suppression system has been verified by independent Notified Body as part of the company's ATEX Compliance, resulting in full compliance when protecting volumes up to and including 1,000m3.