Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/763461
16 WET NEWS JANUARY 2017 The financial and green credentials of wastewater AD are clear, which is why CHP engines need to be kept in tip-top condition, says CooperOstlund's Johan Ostlund. Maintaining AD performance INSIGHT Renewable energy A naerobic digestion (AD) is the process through which we harness biogas produced by the natural rotting of organic matter (which, when applied to the wastewater industry, is human waste). CHP engines combust this biogas to generate heat and renewable energy. This energy can then be used to power your own facilities, neighbouring sites or sold to the national grid. Wastewater is particularly attractive as an energy source as its organic matter is fertile and contains almost ten times the energy needed to treat it. During the processing of wastewater, the UK generates more than two million tonnes of sludge every year. AD not only creates energy from the sludge but it also reduces the solids content by up to 30%, which reduces the energy costs involved in its transportation. Water and wastewater AD facilities can rapidly translate into substantial savings with a typical payback of 12-18 months, whist also being environmentally friendly. The financial and green credentials of wastewater AD are clear but there are also numerous problems when working with human waste as an energy source. The first problem you face is feedstock quality. In other sectors where AD is successful, the quality of feedstock can be much more controlled. Animal by-products, wood chippings, commercial kitchen cuttings CHP engines should be working at full capacity 24/7 tend to be fairly consistent. Feedstock from human waste is less so. The time of year, day of the week and geography of the source all create significant variables. For example, waste produced over Christmas is obviously richer and therefore generates a greater volume of methane gas. The same is true aŠer a weekend's drinking and merriment, as the makeup of alcohol is perfect for combustion. Drainage Other factors that effect the quality of output include the rain (not a problem if your site is in California, but one that is hard to avoid if it is in Glasgow). Rain dilutes feedstock, resulting in less combustible gas. You are also at the mercy of what people decide to put down the drain. For example, if an abattoir empties blood into the drainage system, the quality and consistency of feedstock can be altered. Now, despite what Wizzard states, it can't be Christmas every day and we cannot stop the rain, so how do we address the fundamental problems these issues raise? The quality of the feedstock itself cannot be easily altered; it is not like adding extra flour to a cake to make it rise. But, you can counterbalance its impacts in the calibration and maintenance of your CHP engine. This should be working at full capability, 365 days a year, 24 hours a day (ensuring a continuous output of renewable energy and maximising return on investment). If it is not, there is a fundamental issue that needs addressing. At CooperOstlund, we have seen poorly calibrated and installed engines running at less than 50% performance as a result of control unit calibration, air/methane ratio entering the carburettor, timing patterns and fluid choice. Poor advice from the outset, combined with a rushed installation to save labour costs, will oŠen result in poor engine performance. However, even when operating 24 hours a day, this workload inevitably takes its toll on the performance of any CHP engine. Poorly maintained engines can see efficiencies fall by as much as 20%. Indeed, a well-managed 500kW engine could be generating an additional £35,000 in revenues every year. Hence, CHP maintenance is not a 'nice to have' option – it could be the difference between profit and loss. The decision you make on oil and lubricants is important as this is a variable you can control to counter poor gas quality. Broadly speaking, the better your oil, the longer your unit can run, as you are counter- balancing sub-standard fuel with oil in the combustion process. An additional benefit of good quality oil is that it requires less drainage. The same is true of using high quality fluids and lubricants – again quality speaks volumes. Our team has arrived at jobs where engines have been leŠ to seize due to low fluid and lubrication levels, where incorrect calibration of the carburettor has seen engines operating to less than 30% efficiency. Balance Like running a car, spark plugs are integral to a system. A single misfiring cylinder, leŠ overnight, can result in a snapped crankshaŠ and serious downtime. Regular cleaning and maintenance of spark plugs and the ignition system are key to preventing misfiring. • Well-maintained engines can generate efficiency savings