SMART BUILDINGS & CONTROLS
Protect your investment – why gas analysis is crucial to anaerobic digestion performance
With anaerobic digestion (AD) plants increasing across the UK, much is being made of AD’s ability to provide a source of renewable energy and an alternative source of income for operators. However, Dean Kavanagh, Managing Director at QED Environmental Systems Ltd, says that the best ROI from AD can only be achieved by implementing a robust gas monitoring and measuring system
T
here are now more than 650 operational 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 lead to a reduction in maintenance and protecting 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 the desulphurization process. With CH4 monitoring, 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 O2 monitoring, any increase can cause sudden and serious damage to CHP engines that can be caused by 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, 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 optimize 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 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 help to maximise the efficiency of the process, which
20 BUILDING SERVICES & ENVIRONMENTAL ENGINEER FEBRUARY 2023
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. Gas analysis equipment with IoT functionality 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.
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