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ANAEROBIC DIGESTION
GAS ANALYSIS IS CRUCIAL TO AD
Dean Kavanagh, Managing Director at QED Environmental Systems, says that the best ROI from AD can only be achieved by implementing a robust gas monitoring and measuring system
a source of renewable energy and an alternative source of income for operators. However, it’s important to recognise that gas analysis is crucial to AD performance. There are now more than 650 operational
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AD facilities in the UK with many more in the early stages of development. According to the NNFCC, the UK produces over 100 million tonnes of organic material that is suitable for treatment by AD, either from agricultural by- products like manure and slurry, through to food waste and sewage sludge. There truly is money to be made from waste. However, with an AD system costing
anywhere between £750,000 and £1,000,000 to put in place, the initial investment is steep. It is therefore hugely important that plants monitor their output, not only to ensure maximum efficiency but also in order to maximise AD plant uptime. Why is measurement important and so
often overlooked? One of the most common gases to be produced by an AD plant is hydrogen sulphide or H2S, which is poisonous, corrosive and highly flammable. For example, regularly monitoring H2S can reduce the frequency of costly Biogas engine oil changes – as H2S is known to contaminate engine oil – and therefore reduce maintenance and protect the initial investment. Gas measurement data is a key part of the
digester efficiency picture. CH4, CO2 and O2 gases can first be monitored in the digester stage and H2S and other gas levels can be checked before and after desulphurisation. With CH4monitoring, specifically the volume
of biogas and methane concentration, the amount of energy and efficiency of biogas conversion can be calculated. Correct CH4 concentrations are vital in protecting a CHP engine. With O2monitoring, any increase can cause sudden and serious damage to CHP engines
ith anaerobic digestion (AD) plants increasing across the UK, much is being made of AD’s ability to provide
downtime and process optimisation. With AD systems running 24/7 and offering excellent ROI, it is vital that downtime is minimised and plant upsets are avoided. The benefits of process optimisation can
often be overlooked, but the importance of gas analysis equipment is more than just an ‘added extra’. Rather, it is essential in improving the quality of the biogas produced, protecting against plant damage, making plants safe and, crucially, ensuring optimal yield. Measuring varying levels of CH4 and H2S can
from a leak of air into the system. H2S monitoring offers insight into CHP engine
performance with continuous monitoring highlighting trends in engine performance enabling the adjustment of feedstock. So, what are the benefits of integrating gas
analysis data into the operations of your anaerobic digestion system? Firstly, reliable, accurate and consistent
monitoring of CH4, CO2, O2, H2S levels allows for fine tuning of the digester, used in anaerobic digestion, which is a 24/7 process. The continuous monitoring and the identification of trends in both gas composition and engine performance enable the adjustment of feedstock to optimise performance. Secondly, process instability can affect the
efficiency of biogas production. Stability can be ensured if gas levels are monitored, understood and reacted to quickly. What’s more, integration of gas analysis
data into plant control systems can provide a quick reaction to significant events, such as allowing the use of SCADA controls to pause/ cease processes and flag for investigation. The other big gains are reduction in
56 DECEMBER 2022/JANUARY 2023 | PROCESS & CONTROL
help to maximise the efficiency of the process, which is even more important when different/varied feedstock is being used. Gas analysis is an essential part of maintaining and improving the gas quality and yield in AD plants as high O2 levels can indicate leaks, fractures or fissures in the process infrastructure. Similarly, blockages can be identified through accurate gas flow measurement. It is also important to remember that
operators are dealing with varying types of gas when running an AD system and that safety must always be a priority. As such, any gas analysis equipment must have proper ATEX or IECEx accreditation. One final point to consider is that, in an era of internet connectivity, gas analysis equipment can form a key pillar of a system’s IoT or remote connectivity capability. This can play a crucial role in reducing downtime and service costs. In conclusion, gas monitoring is vital in
ensuring AD operators get the most from investment, by protecting their systems from damage, ensuring maximum uptime and delivering maximum yield with optimal digester performance.
QED Environmental Systems
www.qedenv.com
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