Silo Safety

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Book on silo safety
  Your guide to protecting tanker-filledsilos from over-pressurisation  Contents 3Background to silo safety guidelines 4Prepare for peak airflow4Silo filters – the first line of defence 5Pressure ReliefValves (PRVs) – the last line of defence 5Implications of the new guidelines for PRVs6Choosing an effective PRV 7Auto shut-off – your early warning system 7Choosing an auto shut-off system 8Making sense of maintenance guidelines 9Ground-level testing – a solution to work at height restrictions 10Summary: Safeguarding your silos against over-pressurisation  Background to silo safety guidelines Silos that are filled directly from a pressurised tanker need to incorporate suitablemechanisms to allow displaced air within the silo to escape during filling. If thesemechanisms are insufficient for the pressures created within the silo, or if theequipment is poorly maintained and becomes inefficient, dangerously high pressurescan build up within the silo.This can lead to a catastrophic blow out, damaging plantand equipment, dispersing possibly toxic silo contents over a wide area andendangering the lives of employees.It was just such an incident that led to the publication by the Health and SafetyExecutive (HSE) of new Guidance to prevent over-pressurisation of storage silosduring the delivery of powder in the cement, concrete and quarrying industries. Defrahas published its own guidance notes on Blending, Packing, Loading and Unloading andUse of Bulk Cement, which covers requirements for environmental protection, as itsobjective. However, both documents provide similar recommendations on how toprevent dangerous and environmentally damaging over-pressurisation during silo filling.To simplify this extensive guidance, the British Cement Association (BCA) put out itsown straightforward guide to help plant managers make sense of the newrecommendations.The BCA’s Customer Site Safety Brochure takes the user through astep-by-step assessment of their plant.The BCA uses these completed assessments todetermine whether it is safe to continue tanker deliveries to a plant, or whetherfurther safety systems need to be implemented.While all of this guidance is targeted at the cement industry, the safetyrecommendations set out apply equally to any storage plant that receives bulk deliveries of powdered material from pressurised tankers.In this report, we bring together all of the guidance and recommendations into asingle, easy-to-understand guide to safeguarding your plant against silo over-pressurisation.At the same time, we highlight the implications of the HSE and Defraguidance for silo safety equipment. 3Return to index  Prepare for peak airflow One of the major changes to existing assumptions outlined in the HSE document wasthe need to specify silo safety equipment to cope with a peak airflow from the silo of 13,000m³/hour.The previous assumption had been that peak airflow caused by over-pressurisation during tanker filling could only reach around 2,000m³/hour. To test the new assumption, Portasilo built its own test rig and modelled a variety of over-pressurisation incidents.The company found that it was possible to reach a peak airflow from the silos of almost 13,000m³/hour as a result of over-pressurisation.Thenext step was to investigate the ability of existing safety equipment to cope with thisincreased airflow and, where necessary, redesign it. Silo filters – the first line of defence All silos that receive pressurised tanker deliveries must be fitted with a filter in theroof.This allows displaced air from within the silo to escape to the atmosphere. Portasilo tests found that filter sizes and specifications did not need to be changed inresponse to the new peak airflow assumptions in the HSE guidelines. If properly sizedand maintained, existing filters could already cope with an airflow of 13,000m³/hourand it was our assumed minimum filter velocity that had changed not the requirementfor more filter area.However, regular filter maintenance is essential to sustain the required levels of performance. Silo filters incorporate filter bags to prevent dust escaping into theatmosphere. These bags must be regularly cleaned to prevent clogging which couldinhibit the free outflow of air from the silo.A number of automated filter cleaning mechanisms are available, but the most efficientand effective are reverse jet-cleaned filters.These systems use jets of air to blow thedust from inside the filter bags. It’s also important that the air supply to the filter isclean and dry. Moist air can quickly exacerbate the clogging of filter bags, particularlywith particulate powder silos. 4Return to index


Jul 23, 2017


Jul 23, 2017
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