Biogas Desulphurisation System Reduces Costs at Waste Management Site

The commissioning of a new cost-saving microbiological desulphurisation system at the Cory Waste
Management site in Weston-super-Mare is the result of a successful collaboration between Uniflare (UK), the Warwickshire based environmental technology specialists and Allison Engineering – both ADBA members.

Uniflare’s expertise in designing, manufacturing and installing landfill and waste gas control treatment
and use 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 AWITE Biogas 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 (HS) 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 HS concentration in biogas from anaerobic digestion (AD) can be up to 2,000 to 3,000 ppm. When the biogas is burnt in a CHP plant to generate electricity the H S breaks down, producing a weak sulphuric acid that can cause corrosion within the engine, leading to increased maintenance costs and downtime. For this reason many engine manufacturers stipulate a maximum H S concentration in their warranties.

One of the most common ways of reducing the H S concentration is to inject iron chloride into the digester slurry or feed substrate, converting the H S into iron sulphide particles. Whilst this is very effective it requires additional process control functions with dedicated pumps and storage vessels and therefore has 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 H S concentration levels to less than 300 ppm is essential part of this process. The Uniflare system has enabled us to achieve levels of less than 100 ppm and at minimal operational cost."

From small agricultural sites to larger industrial AD plants, accurate and dependable online as 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 CH and CO measurements per day, with 4-20 mA output and USB connection. For more sophisticated monitoring and analysis requirements the Awi-Flex provides continuous measurement for CH , CO , H S, O and H . This system provides up to five 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 use 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.