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ATEX EQUIPMENT
CUTTING EXPLOSION RISKS IN BIOGAS PRODUCTION
contaminant gases. It is produced when organic matter is digested down by micro- organisms through a process of anaerobic digestion. Biogas can be combusted to produce energy, either through burning in boilers or recycling through a combined heat and power system.
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The first UK biogas plant was built in 2011, and the number of plants has grown steadily to 109 operating today. China has by far the largest number of biogas plants, with an estimated 50 million households using biogas fuel generated by small scale home or village plants.
Because it is produced from animal and human waste and crop and food waste, biogas is a seen as a renewable energy source. With fossil fuels increasingly seen as an unacceptable option if we are to reduce greenhouse gas emissions, biogas has emerged as a real alternative. In the UK in 2018, energy production from biogas amounted to 2,809 metric kilotons of oil equivalent, the second highest energy production among all 28 EU nations. The water industry is taking the potential seriously – the European Biogas Association int latest report estimates that 142TWh of biogas per year can be captured from wastewater produce by industries such as biodiesel, pulp and paper beer and meat and dairy.
ESTIMATING THE RISKS
Certain conditions make biogas, in combination with air, an explosive mixture. The risk can occur from a number of causes, including a gas leak, welding operations and blocked or frozen pipes or the creation of an explosive atmosphere.
An explosive atmosphere is generated when several conditions are met - the main ones are the presence of a gas such as methane, an
ne of the most interesting options for an alternative to hydrocarbon fuels is biogas, a mixture of methane, carbon dioxide and traces of other
With energy and its availability being very much in the news, people are increasingly looking at alternatives to the more traditional sources of hydrocarbon fuels. David Bowers, product manager ABB Measurement & Analytics, explores the opportunities and risks of the rapid expansion of biogas generation in the UK
oxidant such as oxygen form the air, a confined space and the concentration of the combustible gas in its explosive range. For example, for a biogas consisting of 60 per cent methane and 40 per cent carbon dioxide, the range of biogas concentrations necessary to reach the explosive range is between 8.5 and 20.7. Risks of explosion are defined by the ATEX Directives. Among the terms is an effective ignition source, defined as an event which, in combination with sufficient oxygen and fuel, can cause an explosion.
Effective ignition sources can include: lightning strikes; open flames; sparks generated by mechanical impacts or friction; electrical sparks or electrostatic discharges; high surface temperatures; radiation; or the heating effects of compressed gases such as air. To control the risks, the ATEX Directive covers explosions from flammable gas and vapours and combustible dusts and fibres. It does this by categorising risk through the definition of several zones. For gas, vapours and mists, these zones are:
Zone 0 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is present continuously or for long periods or frequently.
Zone 1 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally.
Zone 2 – A place in which an explosive atmosphere consisting of a mixture with air of dangerous substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only.
Biogas plants pose specific risks that have been assessed by the Institut National de l’Environnement Industriel et des Risques (INERIS). These are outlined in the table on the facing page.
INSTRUMENTS FOR ATEX
Accurate assessment of biogas production is essential for both production and billing purposes. It also enables the efficiency of the anaerobic digestion process itself to be calculated. For optimum efficiency, it is important to get the right balance between too much and too little biomass - adding excessive biomass may inactivate
30 MAY/JUNE 2023 | INDUSTRIAL COMPLIANCE
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