If you’ll pardon the pun, activity is really heating up in the alternative fuel combustion market as a number of projects are commissioned this year. For Saxlund it’s a busy time and we are on schedule to deliver more than 13 alternative fuel handling solutions, supporting a variety of combustion and gasification projects in the UK alone. Most of these are now either waiting to be commissioned or already undergoing production trials.
Galliford Try Infrastructure, for example, appointed us back in 2016 to design and deliver the bulk fuel reception and handling technology for three waste wood gasification facilities in Barry, Boston and Hull, for the renewable energy company Biomass UK. All three projects are at an advanced stage, pending dry or wet commissioning, with project completion expected in the second half of 2017.
Other sites include the Tansterne Advanced Biomass Project in Hull for HRS Energy where the first of two fuel streams is already commissioned; fuel handling solutions for Bouygues Energies & Services at two waste-to-energy gasification plants, one at Hoddesdon in Hertfordshire and the second in Belfast; a fuel reception and delivery solution for a pioneering green gas generation plant at Marston Gate in Swindon for Go Gree Fuels; three projects with Babcock & Wilcox Vølund A/S, for biomass powerplants at Templeborough in Sheffield, Margam in South Wales and in Teesside; and a fuel handling solution for M+W Group the lead contractor for the Surrey County Council SUEZ operated Eco Park, at Charlton Lane in Shepperton.
Customers appointing Saxlund expect several things, but fundamentally they are looking for high availability, low maintenance solutions to ensure the plant achieves the projected output in terms of energy production, and in tandem with this the financial returns that shareholders are anticipating, without whom many of these projects would not be achievable.
Engineers who have worked with biomass and other alternative fuels will appreciate the challenges and will, no doubt, have experienced some of the issues that these fundamentally difficult fuels can present.
Mouldering and stagnated fuel heaps and constant recourse to air lances and the like to remove obstructions and restore flow have plagued many sites over the years, with constant stoppages and downtime. As an engineering design house, we frequently find ourselves troubleshooting systems that aren’t delivering, either where the original design has been defective in some way, or where the finances haven’t allowed a sufficiently robust solution in the first place.
Maintenance, or more particularly planned preventative maintenance, is another area that sometimes doesn’t receive enough upfront consideration. While it might be tempting to push machinery fractionally beyond its operating window, unplanned maintenance shutdowns due to breakdowns are likely to be costlier to rectify with consequences to downstream processes and supply chain deliveries.
Biomass and alternative fuels such as Refuse Derived Fuel (RDF), now on the increase in the UK, and Solid Recovered Fuel (SRF), share similar characteristics. They are typically non-free flowing, wet and liable to compact and will happily form bridges in silos and chutes. So the potential to disrupt downstream processes shouldn’t be underestimated.
Material characteristics can change too, delivery to delivery, and we frequently see over-optimistic expectations when it comes to feedstock quality and consistency. Even a reasonably consistent input material like waste wood can throw-up surprises. One in ten truckloads for example may be largely or completely composed of fine dust. Others may be black and compacted having been stored too long.
RDF with mixed organic residues can be even more challenging. These factors may be outside your control and will test the capabilities of installed handling systems if the design is defective, resulting in poor or erratic material flow, stagnant product and costly periods of outage.
Over the lifetime of a plant, twenty-five years or more, its quite conceivable that fuel specifications will change too, or that you need to switch to a different fuel, say from biomass to RDF. Planning for this at the design phase is also essential.
Returning to the fuel storage and handling projects in Barry, Boston and Hull for Galliford Try Infrastructure, future proofing the design specifically for this reason has been a key design focus from the outset.
Each site is similar with twin Saxlund Push Floor storage bunkers discharging waste wood into a conveying and screening system. This incorporates oversize material and ferrous metal removal and weighing systems before feeding fuel to twin gasifiers. At each site one of the Push Floors is designed to accept straightforward modifications to handle RDF, extending the operator’s fuel flexibly if supply pressures occur.
Each system will provide on-site storage for approximately 600m3 of waste wood and is designed to discharge some 100,000 tonnes of fuel per annum.
Good design is clearly essential if you want a fuel feed solution that works from day one and is also reliable. The temptation to select cheaper ‘equivalent’ solutions will be attractive if CAPEX expenditure can be reduced, but it makes no sense if the result is higher operational costs to resolve fuel feed issues, with expensive manual interventions and costly fixes.
Design direction to provide sufficient fuel storage, plus reclaim and conveying systems, will also be dictated by site constraints and available space, factors that are sometimes overlooked at the early stages of project development.
Permitted vehicle movements for example including delivery hours and weekend working will also determine storage requirements and truck reception systems, and there may be environmental factors at play, including noise, dust and water run-off to consider.
Whether you are processing fuel onsite or relying on shipments from third parties, fuel cleanliness will also be important with a requirement for oversize and undersize screening and metal removal. Weighing and sampling might also be required to monitor quality and deliver fuel at precise rates to the combustion process. Together with reception systems, storage systems and reclaim conveyors, these are elements that need to work together seamlessly, and for the life of the facility.
For Saxlund engineers key technologies for handling and storage revolve around activated surfaces and ‘first in, first out’ principles. This limits the opportunity for fuel to degrade and for most materials some form of Sliding-Frame or Push-Floor system is advisable. These make for dynamic rather than static storage and ensure that easily-compacted materials are kept on the move.
In general terms, a system design that favours vertical rather than inclined surfaces, broad rather than narrow channels and positive handling options such as screw-feeders and chain conveyors will minimise problems.
For most projects delivering the energy output required to make the plant viable will always be a major focus, but this shouldn’t ignore the fuel feed and handling aspects of a project. One is very much dependent on the other. Design features to overcome difficult fuel characteristics and to ensure full availability are clearly important.
Early engagement to allow a holistic approach is also beneficial and planning for changing fuel specifications, which may be outside your control, together with appropriate maintenance, must all be factored into the solution you choose. These are some of the reasons why clients select Saxlund International and with more than 60 years’ experience, we can ensure that bulk fuel handling solutions aren’t a weak link in your energy project too.