Water & Wastewater Treatment

28 | OCTOBER 2015 | WWT | www.wwtonline.co.uk In the know Getting to grips with… biogas CHP systems solution that is able to remove 95% of the siloxane, water droplets and particles above one micron wide from the gas fuel. It uses a filter that has a media life of around five years and can be regenerated very cheaply. Ultimately, however, there is no one-size-fits-all solution out there and making the most out of biogas electricity generation is a continual balancing act. The best approach is always to look for professional advice from a supplier with relevant experience and a proven track record in specifying and maintaining generators. What else is there to consider when planning a CHP system? It is extremely important to work out and understand the lifecycle cost. The cheapest CHP system that you uncover during the procurement process may not necessarily work out to be the most cost-effective to run over an extended period of time. Finally, make sure you purchase an operations and maintenance service contract at the same time as the installation – this should give a solid guarantee of the system's performance. About the author: Richard Russett is General Manager - Engineering at Finning, which is the sole supplier of Caterpillar equipment in the UK and Ireland and a major supplier of power solutions. produce a precise cost comparison demonstrating the potential savings to be made from each CHP system. It can also be useful to look into which renewable payments you can apply for – visit the Renewable Energy Association website at www.r-e-a.net for more information. How difficult is it to install a CHP system? The full system involves a substantial amount of equipment, so installing one on a working site can involve considerable disruption. However, when it comes to installing one of its own systems Finning has worked to reduce much of the impact by taking a modular approach to the process where much of the engineering and design work is completed off-site, cutting both the time on site and impact on operations. What are the challenges involved with running CHP with biogas? Although there are many benefits to using biogas as a fuel source, biogas can contain contaminants. The exact concentrations of these will vary from site to site, but one of the most common – and most troubling – is sulphur, mainly found as hydrogen sulphide. When it combines with water this gas creates acid that attacks the metals contained in the generator. Many systems that deal with wastewater will also have to deal with high levels of organic silicon, known as siloxane in its gaseous form, the vast majority of which comes from toiletries such as shampoo and skin creams. While these siloxane compounds are inert at room temperatures, they start to react when put through the combustion process and form silicon dioxide and similar compounds. These materials build up in the combustion chamber, causing abrasive wear and hard deposit issues that can reduce equipment lifespan. How significant a problem are these contaminants? There are a number of engineering and design decisions that can help to cut down on the damage caused by contaminants. Changing the metallurgy of certain engine components to reduce their vulnerability to acid can lessen the impact of hydrogen sulphide. It's also possible to increase the coolant temperature so that surfaces don't fall below 100°C, preventing any condensation forming on them. Activated carbon filters also offer a way to remove low levels of inorganic pollutants such as siloxenes before the gas enters the combustion chamber, but this comes with high operating costs. Injecting the engine with a fine water vapour is a comparatively cheap method for preventing deposits building up, though unless the gas being burned is low in acids this can cause problems of its own. Finning has been able to engineer an alternative coalescing gas filtration

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