Rail loading of wood pellets at UK ports

Large-scale imports into the UK of wood pellets are primarily driven by those generators who have converted power station units to burn wood.

UK legislation requires the fuel to come from a sustainable source; sustainable generally means from ‘farmed or managed forests’ with an audited regime of re-planting and a harvesting cycle of 60 to 80 years.

To date, RWE, E.ON and more notably Drax have converted, or are in the process of converting, generating units to operate on biomass, predominantly wood pellets with Lynemouth Power looking like being the next to do so.

One of the quirks of the mathematics is that in round numbers 1m3/h of wood pellets will produce heat to raise enough steam to generate 1MWh of electricity.

A 500MW unit will consume approximately 500m3/h or 300tph (tonnes per hour) of pellets; operating for 8,000 hours 

per year, a unit will consume approximately 2.4mt (million tonnes) of wood pellets.

If all conversion plans come to fruition, a market for some 19.5mt per year of wood pellets will have been created. In reality, this is more likely to be 12mt to 13mt per year.

Currently tonnages imported into the UK are rising. Imported wood fuel in 2012 totalled 3.5mt, conservatively, by 2016 the demand looks like growing to four times this number.

To illustrate the logistical challenges using the lower figure of 12mtph (million tonnes per annum), this equates to the bulk carrying capacity of some 207 Panamax vessels a year delivering the fuel to UK ports for offloading, storage and forward shipment to the power stations. This means 7,500 train loads (or 400,000 lorry loads) per year from ports to power stations

Existing port infrastructure is geared up for these tonnages of coal, but biomass — and particularly wood pellets — pose their own set of unique challenges.

To comply with legislation, the pellet producers are prohibited from using any form of artificial binder. Pellets are formed at such a pressure that friction heating melts the lignin in the cell walls to form a natural binder. This bond is not particularly strong, so from the moment the pellet is formed it starts to degrade.

By the time pellets reach the UK up to 10% of the cargo may have reverted to sawdust. Pellets also swell and revert back to sawdust if they get wet.

Wood dust is not harmless and in the correct concentrations in air is explosive. The lower explosive limit (LEL) is generally agreed to be 30g of dust in a cubic metre of air.

Pellets can arrive in the UK ‘hot’ (generally up to 50°C); they are also prone to self-heating especially if they get wet prior to long term storage.

The risk of combustion is ever present, be it from self-heating or ‘sparked’ by an ignition source.

The material, being organic, is technically rotting all the time and steadily gives off carbon monoxide. In ship holds and in silo or shed storage systems, this leads to oxygen depletion in the atmosphere; over longer periods of time, the risk of methane off gassing increases.

The handling and storage challenges can therefore be summarized as:-

  • keep it dry
  • control fugitive dust emissions (EH40 – 5mg/m3 8hr TWA limit before PPE required);
  • design to comply with ATEX regulations;
  • monitor product temperature and moisture;
  • check for high CO and CH4 concentrations in enclosed spaces; and
  • be prepared for a fire (detection and suppression).



The driving design parameters are:

  • the time available to load the train;
  • the length of the train;
  • the number of rail cars making up the train; and v the percentage fill required.


The time available to load the train is often the starting point of the design; typically, this is specified as the total turnaround time of site (90 minutes is common).

To allow time for shunting, re-fuelling, driver change etc, Spencer settled on loading a train in better than one hour in order to guarantee the 90 minute turnaround.

The technology Spencer had in mind to perform the loading function was already in existence in the USA. Having a 40-year track record of loading bulk materials into rail wagons, particularly coal and iron ore, Spencer saw the potential in the Pebco® rail loading technology to load biomass trains quickly and efficiently.

The total length of the train is important. Biomass has a relatively low bulk density, typically 600 to 650kg/m3 so haulage volume takes precedence over haulage weight up to a maximum weight the locomotive can haul.

Nowadays, 30 wagon trains up to 600m long are being considered, coal trains are often less than 400m long.

In many cases, the existing site infrastructure is designed to suit coal train lengths it follows that most existing infrastructure usually requires extending.

Train length also directly influences the time to load; in-motion loading systems operate at a fixed speed, so the longer the train, the longer the time to load. 

The number of rail cars making up the train dictates the maximum load each train transports and the percentage fill (often 97% or better) is a function of train speed and the instantaneous fill rate.

By way of example: a 30-wagon 600m long train travelling at 0.5mph will take 46 minutes to pass a point on the track. During this time, each wagon should be loaded with better than 65 tonnes (108m3) of wood pellets.

Allowing for the gaps between the wagons when no material can be discharged, the calculated instantaneous loading rate to achieve the fill is in excess of 3,000tph (5,000m3/h). These material reclaim and conveying rates are achievable but at high cost. Spencer concluded that having a train load of material in a

silo above the loading point ready to discharge into the rail wagons would be the lower-risk, more cost-effective method of ensuring material was available at the point of loading when it was needed.

As train lengths have got longer and wagon capacities have increased, so silo volumes have increased from 2,000m3 (atTyne) to 3,000m3 (at Hull).

To control the fill rate of an individual rail wagon, the Spencer/ Pebco® system employs a ‘flood loading’ philosophy.

Flood loading is achieved when the instantaneous loading rate is so large that the material floods into the receiving rail car, backs up and chokes the discharge chute.

Once the chute is choked, material can only flow from the chute at a rate dictated by the movement of the train under the chute. Providing the choke is maintained, then control of the loading operation is straightforward.

In simple terms, on detection of the front of a rail car, the chute is lowered to the loading height and the discharge gate opened.

An instantaneous flow rate of 10,000m3/h ensures that the choked state is achieved in approximately eight seconds (during which time the rail car has moved 1.8m).

The balance of the rail car is filled as it moves under the chute presenting a void into which material floods into to maintain the choke.

The end of the car is detected and the discharge gate closed allowing sufficient time for the material in the chute (the in-flight material) to fill the back of the car without over-spilling the back and the chute retracted until the next rail car presents.

The control system monitors train speed, wagon position and, in the case of biomass wagons, verifies the top doors of the wagon are open before allowing loading to proceed.

Whilst in this instance wagons are volumetrically loaded, an independent track weighing system completes the loading system providing tare and gross weight information for each axel of each wagon to an accuracy approved by trading standards.


Designed and built by The Spencer Group in 12 months from date of order, commissioned and taken-over 2 months later.

The scope included:

  • 2km of rail track, 600m of road way and piled foundations; v two road vehicle tipping facilities supplied by Samson
  • Engineering (300tph each);
  • one chain conveyor supplied by Tramco (600tph);
  • one troughed belt conveyor supplied by Spencer (600tph);
  • one overband magnet supplied by Master Magnets;
  • 3,000m3 silo complete with explosion relief designed and supplied by Spencer;
  • one Spencer/Pebco® rail loading system including PLC and hydraulic system;
  • site-wide vacuum cleaning supplied by BVC, and site-wide reverse jet filters at material transfers and at the rail loading point supplied by Heaton Green Ltd.
  • design details included double skinned buildings to minimize dust ledges;  
  • a full Spencer Group EC&I package


Performance achieved


  • better than an average weight of 65 tonnes per wagon loaded; trains loaded in 40 minutes;
  • fugitive dust emissions — 0.6mg/m3 (8 hr time weighted average); and
  • all design mechanical handling rates.


Other applications

Any relatively free flowing bulk material, including: v coal;

  • limestone;
  • iron ore;
  • gypsum;
  • fertilizer;and 
  • grain.


CDM Systems meets the challenge — an end to inefficient feedstock handling 

A small power producer had a contract to supply a nearby malting facility with its electricity and heating needs. The plant produced approximately 20 Megawatts of power. Any excess was sold to the area utility grid. The power producer struggled to fulfill its obligations at times due to unexpected downtime of conveyors and poor material distribution.

The material flow issues began at the truck receiving system

to the storage facility. The power producer received a mixture of woodchips, hulls, and hog fuel by truck which was unloaded into a pit hopper either by truck dumper or live bottom trailer. The conveyor under the hopper was expected to meter the material, elevate material out of the pit, and transfer it to a bucket elevator; however due to shortcomings with the original layout and plant design, the result was a pit, hopper and conveyor which was less than desirable. The inaccurate layout created an instantaneous load on the conveyor which caused excessive stress on the drive, chain and housing of the conveyor. In addition, the short horizontal section and a steep +60° incline made the loads on the chain flights excessive.This created premature wear, damage and unexpected downtime.

The inefficient unloading process added labour costs, maintenance cost, and production costs while creating unexpected downtime and reduced output.

The power producer needed a better way to move feedstock from unload and storage to the boiler. The goals of a redesigned material handling system were a reduction of equipment, streamlined material flow, built in redundancy, and improved safety and reliability. CDM, a major designer and manufacturer of drag chain conveyors, was contracted to supply two en-masse drag chain conveyors with a capacity of 60,000 lbs/hr per conveyor. The two conveyors allowed the facility to have built in redundancy and ensure a continuous supply of fuel to the boilers.

The new conveyors would be designed in an L-Path configuration. This design allowed for a short horizontal section, ±20 ft., and relatively long incline section, ±120 ft., at roughly a 40° incline to provide 80’ of lift. This enhanced layout and design, along with proper selection of a chain and flight assembly, would allow the power producer to effectively unload and evenly distribute the feedstock. The exclusive dropped forged case hardened chain resists wear and provides a long service life, even in harsh service environments.

The power producer had a tight capital budget and short window to get the conveyors installed; the malting company was running six days/week and could not afford a loss of power or a blackout. CDM worked with the manufacturer to re-use some of the existing conveyor components that still met safety and performance specifications. CDM also instructed the power producer’s maintenance crew on how to properly install and maintain the conveyors. These ancillary project management offerings by CDM not only saved the power producer on up- front capital costs, but also saved on long-term maintenance and provided optimum conveyor performance.

The CDM en-masse drag chain conveyors have been operating for years without downtime. The fuel handling system redesign enabled the power producer to reduce unloading time of the trucks and minimize maintenance and downtime. This facility has improved safety, reliability, and feedstock flow, while removing countless pieces of equipment from operation.


For more than 40 years, CDM Systems has provided high-quality en-masse conveyors and conveying systems that offer guaranteed quality, dependability, and operational efficiency. CDM Systems

uses its material handling experience and industry knowledge to solve the most difficult bulk transportation challenges. Its conveying systems are specifically designed for reliable 24/7 operation in aggressive and high-temperature applications. Whether unloading trucks, railcars, or vessels, or moving commodities within a process facility, CDM Systems provides the technical support and the right equipment designed specifically for its customers’ needs. 

Siwertell breaks new ground with first UK multi fuel unloader delivery  

Following an order placed in March 2013, Siwertell, part of Cargotec, has delivered, installed and commissioned two Siwertell ship unloaders at ABP’s (Associated British Ports) port of Immingham, UK.

Manufactured and assembled in Italy, the type ST790-D screw type unloaders are equipped with slewable gantry tail conveyors. They will be used to discharge wood pellets and coal to supply the Drax power station. Both types of fuel will be unloaded at a rate of 1,200tph (tonnes per hour).

The customer, ABP, chose the Siwertell unloaders after observing a similar Siwertell unit in operation at Mersey Docks in Liverpool, as well as reviewing a number of machines on the market and paying visits to various facilities across Europe.

“Our customer was impressed by the conveyor’s continuous high capacity, dust-free function and simple operation, even in wind speeds of up to 25m/s,” says Lars-Eric Lundgren, Siwertell’s Regional Sales Manager for Europe. “One of ABP’s main stipulations was that the level of cargo degradation should not exceed accepted limits. We were able to offer firm assurances on this matter, supported by numerous successful tests carried 

out by independent surveyors, along with testimonials from satisfied customers.”

This is the first Siwertell unloader delivery to the UK for combined coal/biomass handling. It may well be the first of many similar orders as the government seeks to reduce the level of coal used in UK power plants. “Pressure is building on UK companies to source more of their energy from renewable, low- carbon sources, and we anticipate a much greater demand for biomass used in combination with coal,” said Lundgren.

“Biomass in bulk handling has the potential for fire and explosion, so companies will be seeking to minimize those risks when selecting machinery to handle this mix of fuels. To ensure safe multi-fuel handling, Siwertell unloaders incorporate safety systems that were originally developed for sulphur handling. Furthermore, the economic benefits of investing in an unloader that can handle both coal and biomass without adjustment should not be underestimated.”

In 2012, Drax announced plans to convert three of its six generating units to burn biomass. The first unit was converted in April 2013 and the second in October 2014. 

Planet-friendly power with help from Geometrica storage solutions  

When waste becomes a power source, planet earth has a greener and more promising future, writes Melanie Saxton, Geometrica. Geometrica is pleased to play a part in the overall picture as a dome provider for waste-to-energy facilities.

The biomass sector is continuously evolving. According to Francisco Castano, president of Geometrica, “Design, vision, environmental impact are all elements necessary to develop modern waste management facilities that also recover energy and supply electricity to communities.” Biomass is ideally processed, stored and distributed beneath long spans of thoughtfully designed waste management infrastructure. The barrier-free interior of a Geometrica dome — or Freedome® — allows for the free flow of traffic, equipment, assorted waste and personnel.

Interestingly, a ‘clean’ initiative may blossom anywhere in the world, as exemplified by two iconic domes. The Marchwood facility in the UK is a prime example of biomass processing and 

storage, while the Domestic Solid Waste Management Center (DSWMC) is the first of it’s kind in Qatar to service the national grid.


The Marchwood ‘Silver Dome’ is a stunning shoreside icon designed by renowned French Architect Jeanrobert Mazaud in consultation with local residents and councils. It seems to hover like a spaceship, with fanciful skirting wrapped around the exterior. At 110m wide with chimneys measuring 65m tall, it is one of the most beautiful — yet practical — applications for the processing of waste to energy.

Integra South West (Marchwood) processes 165,000 tonnes of non-recyclable waste and supplies up to 16MW of electricity to the national grid. This energy recovery dome helps supply electricity to more than 22,600 homes in the United Kingdom community of Southampton, Hampshire, which also plays host to the two great ocean liners, the Queen Elizabeth 2 and the Queen Mary. Importantly, the dome under which it operates is Waste Incinerator Directive (WID) compliant and contains particulates — one of the eight substances for which the British government

has established an air quality standard as part of its national Air Quality Strategy.

The facility comprises 100km of cables — enough to wrap Wembley Stadium 100 times. Approximately one million hours were spent on site during construction, largely devoted to the following:


  • 150,000 hours spent building the envelope;
  • 150,000 hours on assembling the boilers and piping; v 70,000 hours on cabling and electrical installation; 
  • 400,000 hours on structural work and finishing;
  • 40,000 hours on process erection; and
  • 100,000 hours on project management.


The veolia.co.uk website shares a Marchwood installation video, demonstrating the tremendous installation effort. Overall, 700 tonnes of structural steelwork (the weight of 100 double decker buses) support the operations. Of this, the Geometrica dome, using galvanized structural tubing joined with high-strength aluminium hubs, weighs less than 300 tonnes. The original concept, if built with conventional hot-rolled steel, called for more than 1,000 tonnes of superstructure. In addition, 15,000m3 of concrete was involved (the weight of approximately 36,000 cars). A total of 12,000m2 of aluminium cladding covers the dome, and this installation was the first time that a waste-to-energy dome of such immense proportion was built directly over the process equipment inside.

The facility is a leading example of environmental practice and quality handling of biomass, and won the 2009 Best Designed Project Award by Partnerships Bulletin (formerly Public:Private Awards). But the real prize is that nearby families are now warmed by newly generated power as an industrial jewel graces Southampton water. 


Word of mouth brought Geometrica another waste-to-energy challenge. Marchwood Silver Dome contractors, who had worked side by side with Geometrica, shared news of a project in the Middle East — the Qatar Domestic Solid Waste Management Center (DSWMC). The challenge was to find a firm that could accommodate the developer’s distinct architectural vision. Because Geometrica designs some of the world’s largest free span domes, Freedome technology became an ideal solution.

The plans included installation of state-of-the-art systems for separation and recovery of resources and energy from waste, including sorting, mechanical and organic recycling, and waste-to- energy composting. The goal was to have these processes work together in synergy, complementing and feeding off one another to support increased energy and material recovery from households, commercial establishments and the construction industry. The side benefit included a surplus of multiple dozens of megawatts to the national grid.

Early in the construction process, Keppels Seghers, a Singaporean engineering firm, was contracted to design, build and operate the DSWMC’s Green Waste Storage Composting Plant. They sought a roof structure which processes yard and garden waste, tree cuttings, as well as food and kitchen products such as expired vegetables or peels. The material is subsequently shredded, screened and stored inside the Green Waste Storage facility. Grab-cranes then feed
the material into anaerobic digesters which further break down the waste and produce biogas, which is eventually translated into a form of
power generation.

The waste material is broken down through biochemical conversions, much like it is broken down in nature. To house the green waste breakdown process, Keppels Seghers required a structure that could span the large, open space of the building without internal support columns to interrupt the flow of materials and waste. Initially,Keppels Seghers designed the structure as a large steel framed roof with trusses. However, after considering the advantages of the Geometrica system, Keppels Segher opted for a Freedome.

“We were already aware of Geometrica’s systems,” said Geoffrey Piggott, the Keppels Seghers director of the Qatar facility. “But they visited us, and gave us an impressive proposal that was aesthetically attractive, cost competitive and had schedule advantages to us, as well.”

rectangular in shape and sits on a concrete perimeter that varies in elevation. The dome is almost 20 metres tall above its support wall, is clad in with 3,384 panels of painted steel, and covers 1,923m2 of area required to house the Green Waste storage and its various sorting and shredding machinery. According to the Qatar Green Building Council Solid Waste Interest Group, the DSWMC is the largest composting plant in the world, and Geometrica’s unique structural system of offered the ideal cover.

Today, the facility treats and processes domestic solid waste for the whole of Qatar, recycling select materials and using organic waste and biomass to generate various forms of energy. More than 95% of the waste is reclaimed or converted into energy, with less than 5% of the materials entering the facility diverted to a landfill. The facility is capable of treating up to 2,300 tonnes of domestic solid waste per day, and incinerates approximately 1,000 tonnes of other waste.


Geometrica designs and prefabricates domes that may be single- layer, double-layer vierendeel, double-layer truss, or ribbed. Lighter or heaver structural density may be achieved by varying the section of the tubes, or the length of the members. Regardless of geography, terrain, weather conditions or corrosive factors, Geometrica can design a waste management dome that helps improve the carbon footprint of any facility.