HEALTH & SAFETY THE CO . PILOT
REMBE
Explosion prevention in new spheres
The topic of “ explosion safety ” is omnipresent for plant operators and OEM ´ s when it comes to handling or transporting combustible dusts . Despite the widespread assumption that an increased risk of explosion only exists for gases , enormous forces can also be released by explosive dust- / air mixtures .
To help minimise the risk of explosions when handing combustible dusts , it is important to understand the requirements for an explosion and the respective dust safety characteristics , which are described below . The following picture shows the fire triangle and the explosion pentagon which must be taken into account .
The following conditions must exist for an explosion to occur within a production facility or machine :
If any one of the afore mentioned prerequisites is eliminated , explosion prevention has intrinsically been practised . However , if this is not possible at all times and in all operating states , explosion hazards will still be present . In this case , it is necessary to divide any potentially explosive atmospheres into zones and systematically apply safety measures .
Drying processes in particular are used in many industries to produce material , for easier storage , more efficient transport and a longer shelf life . However , the combination of moisture extraction and high temperatures creates an increased risk of both , fires and explosions .
If fires and / or explosions occur in drying plants , which are usually very large , the situation is not only extremely dangerous for the machines and the business , but especially for the employees on site .
Operators of spray dryers must combat a particular type of ignition source – namely smouldering nests that can lead to spontaneous combustion if the material undergoes excessive caking . Caking occurs due to sub-optimal drying of the material and its initially high moisture content . The caked material is then insulated against the surrounding air by a build-up of moist material . The high temperatures ensure that the caked material is continuously heated until a biological reaction takes place involving protein , carbohydrate and water – known as the Maillard reaction . The Maillard reaction generates additional heat that cannot be dissipated due to the insulating layer of caked material . This process continues to accelerate until spontaneous combustion finally occurs .
Caking of this kind can build up both on the nozzles and the inner wall of the spray dryers . If the nozzle malfunctions , droplets may fall down into the fluid bed and cause further clumping . If a smouldering nest is able to form , this can ignite the explosive atmosphere inside the dryer or the downstream machinery .
HOW CAN SUCH CONDITIONS , WHICH ARE FREQUENTLY ENCOUNTERED IN PRACTICE , BE PREVENTED ?
Everything starts with the human factor , i . e . properly trained personnel for the respective processes . Optimal process control is also required to avoid caking . But without precise and reliable information / measurements , this is virtually impossible , even for specialists . Nowadays , humidity and one of the by-products of spontaneous combustion at early stages – carbon monoxide ( CO ) – are used as indicators to ensure a smooth and thus safe process . However , the fact that combined measurement systems cannot clearly distinguish between these two indicators is problematic and can result in inaccurate measurements .
The REMBE CO . Pilot makes exactly this symbiosis possible !
Via a permanent comparison of recorded data with a database of stored reference gases that serve as “ fingerprints ” of the selected gases , it is possible to perform a one-time check in real time and thus permanently verify the measurement accuracy . At the same time , the realtime fingerprint analysis eliminates the cross-sensitivity to other gases in the measurement spectrum that is common in commercial gas analysers .
To ensure a reliable measurement of the operating status , samples are sucked in from all of the dryer ’ s relevant supply and exhaust air ducts under very high vacuum . REMBE calculates the delta CO value on the basis of the absolute values measured at the individual measuring points . This value is the mathematical difference between the CO content of the extract air and the CO content of the supply air . Thus , only events that actually occur in the respective process are detected . External factors that may disturb the process can thus be ignored .
A proprietary evaluation algorithm ( RFA REMBE Flow Algorithm ) enables the measured supply and exhaust air values to be compared in real time . As a result , the REMBE CO . Pilot is the first system on the market that makes it possible to adjust the individual alarm limits and gas run times for the individual measuring points in the dryer ’ s various air throughputs without any delays . The ratios of the different supply air channels and the flexible operating hours are balanced via the software and calculated accordingly in the PLC .
Thus , if an increased carbon monoxide concentration is detected due to spontaneous combustion during the process , countermeasures can be initiated immediately .
BUT WHAT DOES THIS MEAN IN DETAIL ?
This special sampling process eliminates the need for costly and error-prone gas treatment , thus ensuring that the CO . Pilot is less susceptible to faults and requires less maintenance . Furthermore , this measurement method can make recurring calibrations unnecessary . Due to the precise measurement technology and the reproducible results , false alarms and downtimes can also be avoided . And in combination with moisture measurements , the entire drying process can be optimally controlled , significantly increasing the energy efficiency of the system .
For further information , please visit www . rembe . com
84 PECM Issue 60