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Beating the blast

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World Cement,

Berthold Bussieweke, Thorwesten Vent, walks through constructional explosion protection in grinding and storage plants processing coal, alternative fuels, and other explosive media.

Every week, various media outlets publish reports on fires and explosions in pellet, sawdust, and coal storage facilities, as well at their corresponding grinding plants. Whenever a dusty atmosphere is generated and there is sufficient oxygen content, together with an ignition source, the preconditions for an explosion are met.

In order to limit the consequences of an explosion to a manageable degree, reliable constructional explosion protection methods – by means of explosion venting – are required.

State-of-the-art constructional explosion protection e.g. in grinding systems as well as in alternative fuel processing and storage systems is nowadays regulated by international rules and directives.

However, as the grinding system is only a part of a very large equipment scope, less attention is paid to this issue during the overall decision-making process. Non-standard design in terms of constructional explosion protection systems leads to negative consequences such as serious, or even fatal, injuries to workers.

Over recent years, several severe explosions in grinding systems, as well as in the alternative fuel processing industry, have emphasised the necessity for properly-working constructional explosion protection. Therefore, the corresponding rules and directives should be implemented in any installation right from the beginning. European ATEX directives are helpful but their correct implementation is not that easy. ATEX compliance is enabled through the installation of such technology but this largely has to be organised by the operator of the systems themselves.

European ATEX directives are divided into:

  • Directive 1999/92 EG – relevant for operators covering the aspects of risk assessment, zoning, as well as technical and organisational measures pursuant to the primary target: the protection of workers in potentially hazardous areas.
  • Directive 2014/34/EC – relevant for manufacturers of explosion protection devices, covering the requirements of autonomous protection systems, components, as well as safety and control equipment. The significance of this directive is emphasised by the common requirements for equipment and protective systems. The part which is related to constructional explosion protection is as follows: “Should an explosion occur possibly endangering persons directly or indirectly (or for that matter domestic animals or property), such an explosion is to be halted immediately and/or the range of explosion flames and explosion pressures are to be limited to a sufficient level of safety”.
  • Only ATEX-approved explosion venting devices assure proper functionality, as well as a properly determined venting area.

EN European/US American Standards:

  • These standards are of great significance for grinding systems in terms of explosion-resistant equipment (EN 14460), dust explosion venting protective systems (EN 14491), and explosion isolation systems (EN 15089).
  • Corresponding American Standards issued by the National Fire Protection Association (NFPA) are covered, mainly referring to NFPA 68, as well as NFPA 69.

Another decisive factor in implementing effective constructional explosion protection, is generated as a result of varying coal properties in terms of the highly volatile fuels to be ground. Fuels of a VM content between 35 – 45% are not a rarity. These are designated as high-risk fuels. The fact that high VM coals have the strong tendency to create smouldering fires (even in the coal yard), reflects a potential explosion risk in the coal grinding system. At this point, it must be emphasised that even the milling of pet coke creates an explosive atmosphere and may lead to an explosion.

In this context the explosivity of alternative fuels needs to be highlighted. The risks associated with the handling and processing of alternative fuels are often underestimated or even neglected. The reduction of carbon dioxide in terms of replacing fossil fuels with alternative fuels is one step in the right direction, but requires a strict consideration of reliable constructional explosion protection, based on valid rules and regulations.

For example, safe handling and storage of solid biofuel pellets in commercial and industrial applications for capacities greater than 100 t is nowadays well-regulated by DIN EN ISO 20024. Surely, this is just the beginning of new regulations in this regard, and will be followed by more of its kind.

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