Articles & Case Studies


Posted: Tuesday 4th March 2014

The commissioning of a new cost-saving micro-biological desulphurisation system at the Cory Waste Management site in Weston-super-Mare is the result of a successful collaboration between UNIFLARE, the Warwickshire based environmental technology specialists and ALLISON ENGINEERING.

Uniflare’s expertise in designing, manufacturing and installing landfill and waste gas control treatment and utilisation equipment, combined with Allison Engineering’s range of innovative gas analysers, has enabled Cory Waste Management to protect its combined, heat and power (CHP) plant at minimal installation and operational cost.

As part of the overall Uniflare gas train package the desulphurisation system at the Cory site features the Allison Engineering AWITEBiogas analyser which is supplied with its own air compressor and uses a combination of PID and Fuzzy Logic control to automate the injection of small quantities of air (0.5 to 1%) into the gas stream within the digester. The oxygen converts the Hydrogen Sulphide (H2S) to elemental sulphur and water, a process which is completely automatic and does not require any operator input and so eliminates additional operational and maintenance costs.

The H2S concentration in the biogas produced from Anaerobic Digestion (AD) can be up to 2,000 to 3,000ppm and when the biogas is burnt in the CHP plant to produce electricity the H2S breaks down to produce a weak sulphuric acid that can cause corrosion within the engine which can lead to increased maintenance costs and downtime. For this reason many engine manufacturers stipulate a maximum H2S concentration in their warranty statements.

One of the most common ways of reducing the H2S concentration is to inject Iron Chloride into the digester slurry / feed substrate which converts the H2S to Iron Sulphide particles

Whilst this is very effective it requires additional process control functions with dedicated pumps and storage vessels and the associated on-going operational costs.

James Hladkij, the AD Technician at the Cory Waste Management site in Weston-super-Mare said, “We need to protect our CHP plant operations and maintaining H2S concentration levels to less than 300ppm is essential part of this process. He continued, “The Uniflare system has enabled us to achieve levels of less than 100ppm and at minimal operational cost”.

From small agricultural sites to larger industrial AD plants, accurate and dependable online gas composition analysis is an essential part of this process and the Awite range provides a wide choice of options. The range comprises the Awi-Eco, a low cost, compact discontinuous analyser which provides 50 CH4 and CO2 measurements per day, with 4-20mA output and USB connection. For more sophisticated monitoring and analysis requirements the Awi-Flex provides continuous measurement for CH4, CO2, H2S, O2 and H2. This system provides up to 5 measuring points; Ethernet, Profibus, Modbus and USB connection. Most importantly, it can also be used to take flow, temperature and pressure inputs and undertake automated desulphurisation control.

All Awite analysers utilise a rugged, touch screen industrial interface which allows easy access to recorded data, sensor parameters and system diagnostics. This ensures that all information is instantly available, remotely.

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