32 Air Monitoring - Biogas Focus
Biogas in Europe
The development of biogas production and monitoring has had many twists and turns since its early days in Germany, and is now driven by the economic considerations of each varying application and country. Government incentives and generation of revenue for renewable energy, local infrastructure and the characteristics of waste are now key factors in biogas production, monitoring and use.
Many monitoring solutions are available for the wide range of biogas applications around the world, whether it is a fi xed system installed to protect a CHP engine, or a portable analyser for spot checking gas levels throughout the AD process.
Europe lends itself to biogas production because of the commercial incentives and feedstocks available. Processing of small and large scale agricultural and food waste along with sewage and waste water allows for production of organic matter which readily breaks down to produce methane-rich biogas.
Waste water treatment
Anaerobic digestion (AD) of waste water and sewage has been common in many countries for years but increasing energy costs now drive effi ciency. In Turkey, at the $150m Antalya waste water plant, over 3,000,000m3
of waste water are treated daily, with the
biogas being used for a combined heat and power (CHP) engine. Similarly in the UK, at South West Water’s Countess Wear Sewage Treatment, the gases produced from two anaerobic digesters fuel four 165kW CHP engines, which generate electricity and heat.
Since CHP projects are so common across Europe where there may be a lack of infrastructure or funding for complete upgrading systems, a rapid change in gas quality has potential to damage or increase the maintenance of the CHP engine being powered by raw biogas, so it is essential that the process is monitored frequently and is accurate and reliable.
Often controlled circuits in PLC systems receive signals for engine shutdown before any potential damage is caused by a fast- changing gas mix. Gas thresholds and trigger alarms are set and the engine is automatically shut down, with gas often diverted to fl are. CHP systems are often totally dependent on gas analysis, with reliability and minimal downtime being essential.
Food and agricultural waste
Treatment of waste food and agricultural organic matter is a major source of raw biogas to energy throughout Europe, whether it is for CHP engines or biogas upgrading for use as a fuel or injection to grid. Many Eastern European projects have taken on processes which have been successful, with over 300 biogas upgrading facilities in Europe upgrading to grid or vehicle fuel. Most sites have either portable or fi xed biogas monitoring systems. At one AD plant in Austria, organic household and garden waste is sorted, crushed and then digested in an anaerobic digester to produce biogas. The digestate is then processed, separated and screened to produce high-quality compost. The biogas produced is a valuable commodity and is monitored by a fi xed biogas analyser to ensure the gas quality is correct for the CHP engines.
Author/Contact Details: Jessica Burniston,
Commercial Co-ordinator, Geotech
Email:
sales@geotech.co.uk Tel: +44 (0) 1926 338111
IET March / April 2014
www.envirotech-online.com
AD of agricultural waste, both small and large scale, is common across Europe. Many large agricultural processors install an AD plant to generate revenue and dispose of waste. This is usually from a single crop, such as potato in the UK. McCain Foods built a covered anaerobic treatment lagoon producing methane (CH4
) for burning from 77,000m3
starch. The lagoon’s cover keeps out oxygen (O2 collection of CH4
of waste water rich in potato ) and enables
for burning in the CHP engine to produce electricity. Monitoring the process with a fi xed biogas analyser South West Water’s Countess Wear Sewage Treatment
Waste water treatment plant in Turkey
enables McCain to ensure the protection of their CHP engine from dangerous hydrogen sulphide (H2
internal components.
The time taken for complete digestion to take place varies between feedstocks, as does the gas mix produced. Whilst the bulk gases of raw biogas are CH4 dioxide (CO2 and O2
, usually 50-60% and carbon ), usually 30-40%, two other critical gases are H2 .
Dealing with H2 H2
S
S is a challenge in biogas, as it readily forms sulphuric acid and causes extensive damage to the expensive engines used to generate electrical power by burning biogas. Whilst the boilers used to create heat for use on site may be more tolerant of H2
S,
the turbines that may be used to generate power on smaller sites have limits for H2
S content in biogas, and biogas that is purifi ed
for compressed natural gas (CNG) must normally contain no more than 50ppm of H2 H2
S.
S is a toxic and corrosive gas and monitoring levels can be as challenging as removing it. The portable equipment used to ‘spot check’ gas levels is only exposed to small amounts of the gas, so
S S) levels, which can corrode
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