The strategically placed coastal ports have, for very many years, played a key role in both the export and import of huge volumes of fossil fuels used to keep the lights switched on and the wheels of commerce turning across Europe.
Millions of tonnes of fossil fuels — specifically coal — have, for generations, passed through these gateways, destined to fuel large industries including the fleet of coal-fired power stations. For decades these facilities have formed the core of power generation across northern Europe at a time when the priority was simply to generate power, no matter what the environmental cost. In the drive to improve energy efficiency and reduce the carbon footprint of the energy generating industry, large-scale investments have been made, or are in the process of planning, to convert many existing coal power stations to co-firing units, consuming a more sustainable fuel diet which includes large volumes of biomass and wood pellets.
Drax Power, located near Selby in the UK, is a leader in the move away from fossil fuels. It has invested heavily in new combustion technology and the associated storage and handling facilities, which will not only store 450,000m3 of wood and agri pellets, but will also have an annual appetite of 7.5mt (million tonnes) of biomass sourced mainly from the US and Canada.
This surge in demand has meant not only must the power stations make significant investments, but also the port facilities such as Immingham, Liverpool, Port of Tyne and Teesport. At these sites large ships are unloaded and their cargo temporarily stored in a variety of covered silos and buildings before onward transfer via rail or road transport to the power stations.
Immingham Renewable Fuel Terminal (IRFT) is one such facility, located at the UK’s Port of Immingham and owned by Associated British Ports (ABP). In March 2013, ABP signed a 15-year contract with Drax Power, a deal which has enabled ABP to invest £100 million (€119.6 million) in its Humber terminals at Hull, Goole and Immingham, with the largest proportion of that investment — £60 million — being made in
the Port of Immingham. Graham Construction was awarded an 18-month contract to undertake the design and construction of the Immingham terminal, with a target completion date in October 2014. VibraFloor is discussing phase 2 of the project with the client, with a view to agreeing terms very shortly.
The Port of Immingham is the UK’s largest handler of dry bulk cargo and has always been an energy port since it opened just over 100 years ago. The new biomass terminal will be an 11.5-acre fully automated bulk handling facility constructed adjacent to the existing coal terminal.
Unlike coal, wood-pellets need to be stored carefully and kept protected from the weather. They are also dusty and must be handled correctly in order to control emissions and either manage or eliminate fire, explosion and health risks, as the biomass can be approximately 1,000 times more combustible than coal.
Operations at the facility will run 24/7 for 365 days per year, with the first phase capable of handling around 3mt per year, storing 100,000 tonnes in four new concrete silos with a total capacity of 168,000m3.
The port has risen to the challenge of handling such large volumes of wood pellets by providing two continuous ship unloaders capable of handling 2,500 tonnes per hour to offload the ships. A total of 1.2km of covered conveyors will be installed to transfer the wood pellets, controlling the dust and isolating the hydroscopic pellets from the elements and harsh salt-laden atmosphere of an east coast UK port.
Once the wood pellets are stored in the silos, Immingham will face the same issues and risks of spontaneous combustion as a result of degradation and long-term residence. The Drax project addressed this problem by utilizing VibraFloor as the bulk reclaiming system.
Unlike other alternative reclaiming technologies,VibraFloor requires no routine maintenance, it has no major wearing or rotating parts, achieves 100% clearance of the stored product without generating dust or degrading the pellets and operates using very little energy.
The system works by creating a wave in the flexible surface plate of each module, instigated by a low power centrifugal vibrating motor. This undermines and collapses the leading edge of cohesive and free flowing material through a low pressure zone, creating a progressive avalanche of the stored material. The collapsed material is gently swept away by the wave action (much as the effects of erosion on coastal cliffs), constantly undermining any obstruction or bridged material held in the store.
And Drax and Immingham are not alone in adopting the Vibrafloor concept.Tilbury (before the project was cancelled) and other portside and power generation projects which are currently proliferating across Europe, each with similar ambitions to operate fully automated wood pellet and biomass storage facilities, have also included the system within their projects, handling both cohesive and free flowing materials.
From the outside, the Immingham project appeared to have many similarities with the larger and more advanced Drax facility, however the detail within has made it a very different project. Drax sits at the receiving end of the supply chain where the pellets will ultimately be ground to a fine powder and injected as a dust cloud into the combustors. Immingham on the other hand is located in the middle of the supply chain as a transfer facility, where gentle handling of the product from ship to railcar, to avoid pellet degradation and dust generation, is of major importance as penalties are included within the contract for any degradation incurred.
Drax opted to build four larger (63m diameter) concrete dome storage vessels with twin conveyor tunnels and a ‘W’ profile silo floor covered with VibraFloor reclaiming modules. They were designed to feed the 16 outlets positioned above the twin reclaiming conveyor tunnels, at an average rate of 2,600tph (tonnes per hour) per conveyor.
At IRFT, a different concept is being used, with more traditional slip formed concrete silos (36.5m diameter) constructed with a conical ‘O’ profile silo floor, feeding a single central outlet per silo. Both arrangements have their own advantages and disadvantages, although Graham Construction decided that discharging the silos via a single central outlet at an average rate of 2,000tph made controlling the flow easier and simpler to manage.
On a project of the size and complexity of Immingham, which was to be completed within a tight construction programme, security, safety and risk are at the forefront of everybody’s minds. The project was designed to provide a safe and reliable system that will empty ships and refill eight trains per day destined for Drax, at a rate of 1,600tph. This obligation is not only for the 15-year term of the current contract, but also to provide a good return on investment over the 30 year design life of the project.
The substitution of sustainable biomass for fossil fuels is broadly acknowledged as a positive step. However, technical and safety issues associated with the combustion and storage of biomass still remain. Not the least of which is the risk of fire within a storage vessel as a result of hot particles or spontaneous combustion.
In common with many similar projects, Graham Construction has introduced a series of measures to detect or mitigate problems as swiftly as possible. One of the most effective measures is to introduce pressurized nitrogen to a wood pellet silo as a flame retardant. The distribution of nitrogen across the base of a silo to allow percolation through the product had been problematic. At IRFT, nitrogen is pumped in to the silo via pressurized pipes and valves located beneath perforated duct covers which lie between each segment of the silo floor, ensuring an even distribution of gas.
Projects such as the IRFT are, by their very nature, complex and risky. By including VibraFloor within the project, at least one of the key elements has been made simpler safer and more efficient.