Ilona Šimoníková discusses alternative fuels and their utilisation regarding fire and explosion protection.
One huge current trend throughout all industries emphasises ecology and waste utilisation. For this reason, waste gasification technology along with the ability to process it into pellets, briquettes (and their subsequent usage) are two key areas being developed.
Just like with any fuel, it’s crucial to understand the fire and technical characteristics of these alternative fuels. Given that the combustion of solid alternative fuels is often conducted in existing technologies such as coal and wood chips, several essential parameters must be assessed and determined from a fire and explosion perspective to ascertain whether the fuel can be used in the technology as is or requires modifications before it can be implemented.
First and foremost, it’s necessary to possess fire and technical characteristics of both existing and new fuels. Without this knowledge, clear conclusions cannot be drawn. The following text outlines certain parameters that require focus and details how a parameter change influences practice.
A significant parameter is the lower explosive limit (LEL). Based on this, spaces are classified into zones – Zones 22, 21 and 20. If the new fuel has a considerably low lower explosive limit, space classification might shift, e.g., from Zone 22 to Zone 21.
The ignition temperature of suspended/deposited dust is crucial to assess whether hot surfaces that might occur in the technology could serve as an ignition source. If the new fuel significantly lowers these temperatures, existing installed equipment might not comply, necessitating replacement with new equipment that aligns with those temperatures.
KST is crucial
Another crucial parameter is the Kst constant and the associated explosivity class St. These two parameters are closely linked. The Kst value is used for explosion protection design, e.g., calculating areas for explosion venting devices. Individual protective elements are certified for explosivity classes St1, St2, and St3. A system designed for St 2 cannot be used for a higher class like St3; however, it can be used for a lower class like St1.
Maximum explosion pressure is another parameter used for vent area calculations, and knowing its value is essential. The higher its value, the larger vent areas must be installed on the equipment.
If the fire and technical characteristics of the new fuel exhibit more favourable values than the existing fuel, this new fuel can be safely used with existing technologies. However, introducing a new fuel raises several critical questions:
Is there something that can be done to prevent zone tightening (installation of exhaust or increasing the performance of the existing system)?; Are devices currently installed in the newly classified zone appropriately designed, meeting the requirements for maximum surface temperature?; When reevaluating zones, what potential ignition sources may emerge, such as in assumed or exceptional malfunctions?
This leads to the related topic of whether ignition sources can be excluded or not, necessitating the installation of explosion protection.
All parameters of the new fuel, risk analysis and technical measures to ensure operational safety must be evaluated in the most important document addressing this issue: the Explosion Protection Document (EPD).
Ilona Šimoníková is Head of Risk Analysis department at VVUÚ.
