Biomass Handling at the Port
In February 2014, following a 10-month programme of works, Hull, UK-based engineering company Spencer Group handed over the new biomass handling facilities at the Port of Hull to port operators Associated British Ports (ABP).
It is the first project to be completed as part of a £100 million (€131 million) investment in biomass handling operations at the Humber Ports. Along with a similar but larger development at Immingham, the Hull facility will enable the delivery of millions of tonnes of sustainable biomass to Drax Power Station, which it requires to become predominantly biomass-fuelled generator.
The biomass pellets are imported by sea from Europe, mainly Portugal and Latvia, and transferred from ship to warehouse before being delivered by truck to the new biomass handling facility close to Hedon Road in Hull. From here the pellets are tipped into ground reception hoppers which transfer the material onto an enclosed 250m long conveyor to the top of the 50m high silo tower. This silo can store up to 1,800 tonnes of wood pellets.
The final 30 miles from Hull to Drax requires sophisticated technology that has been specially developed by Spencer Group for the project.
New Approach to Loading
Coal is transported to power stations in open-topped train wagons, which are often loaded manually rather than using an automatic system. This can result in uneven loading or heaps of material protruding above the top wagon. Biomass pellets, on the other hand, must be kept dry as they decompose quickly if exposed to the weather.
To address this, Drax developed its own patented railway cars with doors on the top to keep the rain out and the pellets inside. These biomass railway cars demand a totally new approach to loading compared with open topped coal wagons: if they are overfilled or the load is not level, the doors on the top of the wagon are unable to close. This triggers a safety mechanism on the train that prevents the brakes from being released and the whole process grind to a halt.
To overcome these issues, and other inherent differences between coal and biomass, several modifications to the loading system had to be made:
- – To ensure that the biomass stayed dry, the loading facility had to be fully enclosed, with space for three rail wagons undercover at any one time – one with its doors opening, one being loaded, and one with its doors closing.
- – The loading chutes were adapted from coal loading chutes produced bu US firm Pebco. Spencer became sole agents for the Pebco chute in Europe and adapted the design to better cope with biomass. Due to the free-flowing properties of biomass, a smaller chute proved to be more controllable. The high flowrate of the biomass out of the chute was also found to act like a plunger, compressing the aire beneath the material flow and displacing it away from the loading point. This displaced air conditioning fugitive dust, therefore requiring the careful design of extraction systems that enclose the wagon being loaded and vent the chute as well.
- – Due to the tight tolerances when it comes to fill accuracy and profile, the loading of the wagons is fully automatic and carried out whilst the train is moving at 0.5mph. This movement, coupled with the specially adapted chutes, means each 25-wagon train can be loaded to between 90-95% by volume with a level surface in just 45 minutes.
- – As the wagon fills, the weight of the biomass causes it to sink on its suspension. The loading chute has to follow this drop in height to ensure that the wagon does not overfill. A combination of laser photocells and radar sensors are used to monitor the position and height of each wagon during loading in order to achieve the required fill profile.
As well as being susceptible to the weather, biomass is also much dustier than coal. Controlling the dust emissions is important for two reasons. Firstly, the dust created by biomass wood pellets is highly combustible so fall under ATEX and DSEAR regulations. Secondly, there are risks associated with human inhalation which fall under environmental health regulations.
As well as designing the loading system to limit the amount of dust created in the first place, Spencer Group also developed containment strategies to minimise the amount of dust released to the atmosphere. These include chute seals and the creation of areas of negative pressure within the loading facility that extract fugitive dust emissions from the area.
The dust-laden air is filtered using a fan assisted, reverse jet cleaned bag filter. The clean air is released to the atmosphere whilst the filtered dust is blown back into the loading silo. HSE guidance advises the workplace exposure limit (WEL) for hard and soft wood dust should be less than 5mg/m³ calculated over an eight hour time weighted average period. The system put in place by Spencer Group have resulted in measurements of less than 1mg/m³ of dust in the atmosphere in all areas of the facility.
‘The Humber Ports are becoming a major gateway for biomass shipments into the UK and a strategic asset driving the growth of green energy industries along the estuary,’ says Gary Thronton, Spencer Groups chief operating officer. ‘The facility we have constructed at the Port of Hull is both a showcase for Spencer Group’s multi-disciplinary engineering capability and a beacon for the Humber’s growing reputation as the UK’s renewables region.’
Biomass by numbers
- – The silo at the new biomass handling facility can store 1,800 tonnes of biomass pellets.
- – It takes 65 – 70 truckloads of biomass pellets to fill the silo
- – It takes 3 hours to load the silo, at a rate of 600 tonnes per hour
- – The facility can accommodate up to 4 trains a say heading for Drax Power Station.
- – There are 25 wagons on each train.
- – Each rail wagon carries a minimum of 60 tonnes of biomass.
- – 0.5 miles an hour is the speed that the train continues to travel during loading.
- – 5,450m³ is the instantaneous loading rate of the biomass into rail wagons (at this rate you could fill the equivalent of an Olympic size swimming pool in around half and hour).
- – 100 jobs have been created during the construction of these new terminals, with additional 100 jobs created once all the facilities become fully operational.