Screening Low Ignition Energy Materials in Sensitive Industries

23.09.2024, Remscheid, Germany

Valentina Weber, RHEWUM GmbH

Dust explosions remain a serious threat in industries dealing with explosive low ignition energy materials, particularly in the defense sector. By investing in high-quality, static, and gas-tight screening machines, companies can significantly reduce the risk of dust explosions, ensuring both employee safety and the integrity of their production facilities.

In industries handling explosive materials, such as the production of black powder and ammonium nitrate, dust explosions present a significant hazard. Dust explosions are not limited to organic materials but can occur with any finely powdered combustible material that meets specific conditions, especially in high-risk industries.

Explosion Parameters

Dust explosions occur when three main conditions are met:

Critical Dust Concentration – Fine particles suspended in air, particularly below 0.4 mm (~40 mesh) in size, create an explosive atmosphere. For example, the explosion severity index (KSt) for fine materials can exceed 140 bar·m/s (1,400,000 psi·ft/s), classifying them as ST1, a moderately explosive category.
Oxygen – The presence of at least 9% oxygen is required for an explosion, making ambient air (21% oxygen) a particularly favorable environment for these reactions.
Ignition Source – Hot surfaces, sparks, and friction inside machinery can all serve as potential ignition sources.

In industries that produce or process explosives, these parameters are frequently met, making dust explosions a constant risk. In addition, the smaller the particle size, the more likely an explosion is to occur, with lower ignition temperatures and energy thresholds. For example, a dispersed dust can ignite at temperatures as low as 360°C (680°F), with a minimum ignition energy of just 10 MJ (9,478 BTU).

Role of Screening Machines in Explosive Environments

Screening machines play a critical role in the production of finely divided materials, whether organic or inorganic. Especially the vibration and motion involved in screening lead to friction and also increase the risk of dust dispersion, which can result in an explosive atmosphere within the machine itself. When handling sensitive materials like black powder, ammonium nitrate (AN) and calcium ammonium nitrate (CAN), these risks are magnified.

Proper containment and sealing of screening equipment are essential to prevent dust escape and external ignition sources from interacting with the explosive environment inside the machine. Gas-tight and static screening machines offer a reliable solution to this issue by maintaining an inert atmosphere, minimizing oxygen exposure, and preventing dust from dispersing into areas where ignition sources are present.

RHEWUM’s direct vibration transmission ensures only the screen vibrates while the housing stays static. This design reduces internal friction and wear, minimizing ignition risks. The static housing, combined with gas-tight, fixed flange connections, prevents dust escape and interaction with ignition sources, making it ideal for screening sensitive materials like black powder and ammonium nitrate.

Prevention and Avoidance

To prevent dust explosions, manufacturers must address both organizational and mechanical factors. Key prevention strategies include:

Dust containment: Screening machines should be completely sealed to prevent dust from escaping into the production environment.
Use of inert gases: Screening within an inert atmosphere (e.g., nitrogen or carbon dioxide) can significantly reduce the risk of an explosion by depriving the environment of oxygen.
Avoiding ignition sources: Ensuring that all moving parts are adequately shielded and that friction within the machine is minimized helps prevent the generation of sparks or hot surfaces.

Solutions for Screening Explosives with Global Impact

RHEWUM’s extensive experience in providing tailored screening solutions demonstrates the crucial role that these technologies play in preventing catastrophic explosions in high-risk environments.

Global Producer – One of the world's leading producers of fertilizers and explosives uses 134 RHEWUM screening machines, with 49 of them handling AN and CAN. These machines achieve high capacities, screening up to 560 tons per hour (617 STPH) or performing fine separations down to 0.8 mm (~20 mesh).

Germany – RHEWUM delivered 10 screening machines to a German supplier of key defense technologies. These machines are critical in screening sensitive materials under controlled conditions, preventing dust explosions and ensuring a high level of safety in the production of explosives.

France – A France-based company processes AN with multiple RHEWUM machines, ensuring precise and safe handling of this sensitive material.

South Africa – A chemical company producing nitrogen-based products uses five RHEWUM machines for processing CAN and AN, achieving a throughput of 160 tons per hour (176 STPH).

Australia – A company in Australia screens 110 tons per hour (121 STPH) of ammonium nitrate with RHEWUM machines, demonstrating the global reliance on advanced screening technology to ensure the safety of operations.