Damage limitation

Paul Boughton

Explosion prevention through better detection. By Roger Bours

To avoid equipment damage, production interruptions and risks for personnel, industries working with combustible dusts need to assure that the required level of safety of the process is achieved at all times. The standard requirements for the industry, underpinned by legislative framework such as ATEX, are that the conditions where such (dust) explosions can exist must be prevented and measures taken to reduce the consequences when they should occur.

Smouldering is generally recognised as one of the most common ignition sources of fires and dust explosions in industrial processes. Unfortunately it is also one of the most difficult to prevent by either controlling process conditions or by making modifications to the equipment.

Smouldering dust will typically generate traces of carbon monoxide (CO), carbon dioxide (CO2) and water (H2O) in values depending on the chemical composition of the combustible dust and of the temperature the dust is exposed to. With CO2 and water being freely available in nature and CO being rarely present, the timely detection of CO provides a unique and reliable early warning signal for smouldering conditions within processes in the food, power generation, chemical and pharmaceutical industries. Equipment/processes to be protected in high value industries (such as dairy products, coffee, flavourings, colourings, spices, cacao, sugar, etc.) are mills (spray and flash) driers, cutters, cyclones, silos, etc. to avoid risks for investments and loss of production/market share due to unplanned interruption of production.

Early warning

A suitably designed warning system will detect and signal smouldering at an early stage, allowing for suitable corrective actions before damage to the process equipment can occur. The alarm signals can be used to trigger safety systems, such as operator intervention, process shutdown or water injection therefore reducing the risk for dust explosions to result.

The Fike WarnEx system typically consists of multiple sampling and detection units (SDUs) strategically located on process air inlet and outlet. CO gas, created by smouldering, will be detected by the WarnEx SDU placed on the main air outlet of the process. Where a risk exists for nuisance CO entering the system from the outside, additional SDUs are placed on the air inlet pipe(s). This arrangement allows for the determination of differential value CO, therefore eliminating the effects of externally produced CO.

The WarnEx Control Unit processes the signals from the SDUs and alerts the process operators and safety systems in case smouldering material is present.

This innovative detection concept provides a variety of features and benefits to its users. It is a stable and reliable system, designed and tested in industrial environments, based on proven CO-sensor technology. It features self-monitoring sensor technology with built in self-calibration mode, designed for industrial applications resulting in low cost of ownership. It represent reliable stray CO-nuisance elimination. Its SIL2-certified architecture provides the highest reliability level. The system is also easy to install, to use and maintain.

Other key features include: fast response times, multiple sensors, short sampling lines; event analysis through data logging and visual trending; and simple integration with an automatic fire suppression system.

WarnEx is a ‘smouldering detection system’, a safety system that can detect smouldering (which precedes a dust explosion) in a machine or installation. As the smouldering is identified in its earliest stages, corrective actions can be taken to ensure a potential explosion is avoided. WarnEx uses sophisticated electro-chemical detection technology and a centralised system architecture that allows it to manage multiple sensors.

Fike’s WarnEx is designed for use in production environments where processes result in combustible solids from animal feeds, as well as sugars and flour, powders from milk, paint, metal and chemicals and dusts from materials such as wood, paper and textiles.

For more information, visit www.engineerlive.com/ede

Roger Bours is with Fike

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