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Vikings, airships and ash: the history of Barlow Mound

10 January 2017

Sustainable business
Airship at Barlow Mound

Barlow Mound is a haven for wildlife. More than 100 different species call it home, including kingfishers, roe deer and falcons. It’s an area that looks like it’s never been touched by the industrialisation that surrounds it. The truth is very different.

Barlow mound is manmade. It was built in the 1970s using residue material from its neighbour Drax Power Station. It’s a success story of using what was then considered a waste material to create something natural and beautiful. But it has a long history before becoming what it is today and to explore that history is to track the outlook of the UK over the last millennium.

The military moves in

The area around Barlow and Drax was an important location for the very first Viking explorers who arrived here from the North Sea via the region’s Ouse and Aire rivers. But it wasn’t until 1086 that it received its first recorded mention, when it was listed as ‘Berlai-leag’ in the Domesday Book.

Translating to ‘a clearing where barley grew’, it was named by Anglo Saxon settlers, who established the region as a mix of farmland, fields and woodlands and it remained agricultural until the early twentieth century, when the country was plunged into war.

When the First World War began in 1914 and the need for new war machines arose, Sir W G Armstrong Whitworth & Co Ltd, a manufacturing company which had obtained the land in 1913 from the estate of Lord Londesborough, set up an airship factory on the site.

During its lifetime the factory constructed three airships, the 25r, R29 and R33, but when WWI ended and demand for airships sank, the factory shut down and the land passed to the Ministry of Defence (MOD).

During the Second World War the area became an important location in the country’s war efforts once again. The MOD set up an army ordnance and command supply depot manufacturing and storing items like mess tins and kerosene lamps. At one point the site also included a Prisoner of War camp.

By the 60s the UK’s needs for defence manufacturing had subsided. Instead, what it needed was more power. With the rich coal seams of the area and the existing rail network (the Hull-Barnsley line ran through), building a power station in the Barlow area was an obvious solution.

First-of-a-kind solution

In 1967 the land was bought by the Central Electric Generating Board (CEGB) which began the construction of Drax Power Station. One of the early challenges it faced was how to minimise the environmental impact to the surrounding countryside.

In particular, it needed a solution for the tonnes of ash that came from the burning of coal fuel, which included both pulverised fuel ash (PFA) and furnace bottom ash (FBA). The answer was a first-of-a-kind: build a mound using the materials.

Construction on Barlow Mound began in 1974. First the existing top soil was removed and preserved for later use, drains were added and then a layer of FBA was laid.

Next conditioned PFA was added and moulded to suit the original design, never reaching higher than 36 metres. At this height the mound would visually obscure the power station from the neighbouring houses.

The final step was to seal the mound with a polymer and then reintroduce the top soil before grass, trees and hedgerow were planted. The trees and plants had been carefully tested to ensure that their roots wouldn’t interfere with the ash and compromise the integrity of the structure.

Roe deer walking in grass field

An ecologically important area

As time has passed and Drax Power Station has produced more ash, the mound has developed and grown. More than 301 million m3 is stored in the current site – more than the capacity of three million double decker buses.

In addition to the 100 species living on the site, a tenant farmer works 20 fields and a swan rescue and wildlife hospital rehabilitates up to 2,000 birds a year. More recently, the Skylark Centre and Nature Reserve has now opened up the area to the public to explore walking trails and see the nature first-hand.

Barlow is an area that has changed consistently since 1086. From the North’s early beginnings as an agricultural hub and Anglo-Saxon settlement, to the necessity for large-scale power solutions and to the importance of preserving local ecology, Barlow is an area that has been characterised by the outlook of the country.

Like Drax Power Station, to which it is intrinsically linked, Barlow Mound is a part of the Northern Yorkshire landscape – literally and figuratively.

This train isn’t like any other in the UK

25 November 2016

Sustainable bioenergy
Man standing in front of train

For decades the sight was the same. Day after day, trains pulling open-top wagons filled with coal would arrive at Drax Power Station. Coal was the fuel on which the station ran, but as that changes and the world moves from the dirtiest of fossil fuels to renewables and other lower carbon technologies, so too do the make-up of Drax’s daily deliveries.

Now, more than half of Drax’s power is generated from compressed wood pellets instead of coal. The trains still arrive daily, but in addition to coal carriages, more are pulling state-of-the-art biomass wagons. They’re not only the first of a kind, they’re bigger than any others on UK railways.

Moving a modern fuel

Coal and biomass are fundamentally different. Whereas coal is a durable fuel that can be left open to the elements without concern, if compressed wood pellets are left in the rain they become unusable.

In short, traditional hoppers, the large open-top train wagons used to transport coal, aren’t big enough, nor do they provide enough protection, for transporting biomass.

To deliver roughly 20,000 tonnes of wood pellets to the power station every day it would need an entirely new railway wagon. For this Drax turned to Lloyd’s Register Rail (now Ricardo Rail) and WH Davis.

DRATECH19_Train_crane_In_line_dp7ney

Putting a lid on it

One of the first things to solve was the open top. The team designed a pneumatically operated roof for each wagon that could open and close on demand – providing easy access for loading, but suitable protection for the pellets when in transit.

A similar system on each wagon’s base was introduced to make unloading just as simple. A typical hopper design includes a wide roof that narrows into a shoot at its base for releasing fuel. The Drax wagons are different.

When they arrive at the power station, automated flaps on their underside open in stages as they pass through the biomass unloading area. This releases pellets into a sorter that delivers them into storage, ready to be used for generation. With this system in place, each train can unload in under 40 minutes.

The big problem: space

A more significant hurdle to overcome was the question of space. The obvious answer was to make the wagons bigger, but UK railways have some of the most restrictive dimensions in the world thanks to its bridges and tunnels – some of which were constructed in Victorian times.

So to get a similar efficiency out of the compressed wood pellet loads as previously obtained with coal, the wagons needed to be bigger – not in physical size, but in volume.

The team looked to the normally unused space at the ends of traditional wagons to house the braking and control equipment cubicle, while the pipework was designed to run inside the wagon’s siding, creating more inside storage space.

The result is a wagon with 116m3 capacity, almost a 30% increase in volume compared to the coal wagons. They are not only the first ever bespoke biomass wagons, they’re also the largest on UK railways.

DRATECH19_Train_Journey_In_Line_dgx81z

Bigger wagons, better economy

The impact of these wagons is felt beyond just the railway lines. WH Davis is the UK’s last independent freight wagon manufacturer and relationships like this are not only good for Drax, but positively impact the wider UK economy.

A joint study by Oxford Economics for Drax calculated that in the East Midlands, where WH Davis is headquartered, Drax supports 1,100 jobs through its supply chain and the resulting economic activity. In total, the report found Drax had added £60.3 million to the local economy through indirect and induced means. Nationwide, in 2015 that impact extended to a total of £1.24 billion in contribution to the UK GDP and more than 14,000 jobs.

There’s potential for this impact to be even greater. Roughly 14 trains arrive every day at the power station from ports in Liverpool, Tyne, Immingham and Hull, delivering up to 20,000 tonnes every day to fuel the three of Drax’s six generating units that run on wood pellets. But if all six are upgraded it will mean more biomass, more deliveries and more trains.

The railways have always been a part of the power station, and in the foreseeable future it’s likely they always will be.

If you’re afraid of heights, don’t do this job

27 October 2016

Power generation
Reparing the colling tower at Drax Power Station

Be they for nuclear, coal, or biomass power, cooling towers and their colossal, tapering silhouettes are the most iconic element of the architecture of energy. Drax has 12 of them.

But a structure of that size poses a considerable maintenance challenge. For the first time since Drax’s six towers were constructed between 1967 and 1974, one of them was in need of repair.

Ladder up a Drax cooling tower

What could possibly go wrong?

No matter how well you build something, things can go wrong after more than five decades of continuous operation. Each tower is made from concrete that varies in thickness from seven inches in the middle to around 15 inches at the top and bottom. Over time, even a structure this solid can begin to weaken.

Cooling towers are reinforced with steel bars embedded within their concrete which can rust and expand, causing the concrete around it to crack – a process called spalling. Water vapour, which passes through the towers on an almost constant basis, can also migrate into poorly compacted concrete inside the tower and cause further cracks.

Before the Drax team could set about repairing the towers, they needed to know where these cracks were. Inspecting a structure that tall needed an innovative solution. It needed drones.

Surveying the damage

Drones were used to make a comprehensive, photographic record of the towers that could be inspected for signs of damage. The drones also helped produce a 3D model of the structure to visualise the tower’s defects. It was the first-of-a-kind for the company.

The drone survey found that on tower 3B there were a number of cracked concrete patches on the towers that needed repairing and maintenance was scheduled to coincide with Drax’s 2016 outages – periods during the summer months when electricity demand is lower and parts of the power station undergo routine repair work.

The next challenge was how to carry out these repairs on a structure taller than the Statue of Liberty.

A 3D model of a Drax cooling tower

To inspect the cooling tower, Drax created a 3D model with the help of CyberHawk.

Engineering at an altitude

Drax tower 3B is nearly 115 metres tall, enough to fit in the Statue of Liberty or St Paul’s Cathedral with room to spare.

How do you go about repairing a structure like this? The answer: Steeplejacks. Steeplejacks were called so because, originally, they were the people used for scaling the side of church steeples to make repairs. But a cooling tower presents a distinctly different structure that can’t necessarily be climbed up from the bottom. To scale it and make the repairs, a different approach was needed.

Drax reached out to specialist steeplejack contractors Zenith Structural Access, who build devices that allow the scaling of industrial-scale structures.

Zenith’s solution was to fix a metal frame to the top of the tower, which then lowers a walkway suspended by strong metal cables down its side. From a perch suspended from the top of tower 3B, workmen were deployed to make the repairs – more than 100 metres above ground.

Suspended in their cradles, the teams sealed the surface of each crack and then injected resin to fix the cracks in the concrete shell. Where the concrete had spalled, new specialist repair mortars were applied.

Repairs on Drax Tower 3B

Regular repairs

With the identified defects on the tower fully repaired, attention can now move on to others on site. Routine inspections using drones and binoculars have been planned to take place every three years. These will monitor the condition of all the towers and allow for future maintenance to be planned in advance.

Two more towers are already scheduled for repair in 2017’s outages. Once again, it’ll be case for engineering work at elevation.

How do you build a dome bigger than the Albert Hall?

6 October 2016

Sustainable bioenergy
Drax dome being raised.

For decades the most iconic sight at Drax Power Station has been its large grey cooling towers, but that’s changing. Today the most striking image on the Selby skyline is four white domes, each larger in volume than the Royal Albert Hall.

These are Drax’s biomass storage domes, standing 50 metres high and holding 300,000 tonnes of compressed wood pellets between them – enough to power Leeds, Manchester, Sheffield and Liverpool for more than 12 days.

They’re an integral part of Drax’s ongoing transition from coal to renewable biomass electricity generation. But while biomass is a far cleaner source of energy than coal – reducing carbon emissions by more than 80% – it comes with its own challenges. A key one is storage. That’s where the domes come in.

The need for a new storage space

Storing coal is a relatively simple task. With some management by heavy vehicles to reduce the occurrence of air pockets, coal can quite happily sit outside in the rain and still work efficiently as fuel. Compressed wood pellets are different. If a wood pellet gets wet it can degrade and become unusable. The main reason to compress wood into high density pellets in the first place is to take its moisture content down, saving weight for transportation and increasing its efficiency as a fuel for power station boilers.

More than that, because the biomass pellets are made from wood – a living and breathing organic material – they have to be stored in sensitively calibrated environments to keep them in a safe and usable state. Each storage dome had to be carefully designed, engineered and constructed to ensure it was fit to maintain this environment.

Construction began back in 2013 and required a Drax engineering team working closely with Idaho-based Dome Technology and York’s Shepherd Construction. At more than 50 metres tall, they’re the largest of their kind in the world – a new approach to construction had to be considered.

There were three key steps involved in the build:

Blowing up a giant balloon

The first stage is to prepare the foundation which takes the form of a massive concrete circular ring beam. A giant PVC airform dome is laid out over the ring beam and inflated using fans that are about the size of a Doctor Who telephone box, to form the outside of the dome.

Insulating the inside

With the dome still air-inflated, a thin 15mm layer of polyurethane foam is sprayed to the inside, serving to both insulate the structure and provide purchase for the first layers of steel reinforcements.

Completing the shell

Once the first steel reinforcing grid is attached to the polyurethane, the concrete spraying process begins. The dome wall is built up to a thickness of up to 350mm by adding further layers of steel reinforcement grid and reinforced concrete.

An engineer at Drax spraying the inside of a biomass storage dome.

Under pressure

The challenge the team now face following construction is maintaining a safe atmosphere inside the domes. The pellets are stored inside the domes in vast quantities and weight, which collectively create high amounts of pressure. As the pressure builds up the pellets release oxygen, which can cause a build-up of heat, and potentially an explosion.

But by addressing the cause of the increase in heat – the oxygen – the team found they could limit the danger potential. The solution was a specially-designed system that releases nitrogen into the dome. The gas forms non-flammable compounds with the oxygen, which keeps the inside of the dome stable.

The Drax cooling towers are still visible in and around Selby. And while they’re still an essential part of the power station, emitting steam (not smoke) used in the generating process, they’re no longer its most iconic image. The four storage domes sitting beside them more closely represent the future of Drax: a renewable one built on biomass technology.

Drax biomass storage domes

Now that the domes have been built, find out how their atmosphere is controlled.

 

Summer in the station

Power generation
Biomass domes

Bees buzz and heat haze fizzes on the tarmac. It’s summer, and since the days are warm and long, demand for electricity sinks as lights are left off and life is lived outdoors.

Electricity demand is lower, so the assumption would be that activity at the UK’s power stations is minimal. The reality however, is far different.

Instead, the fall in demand is an opportunity to perform crucial maintenance work – to upgrade and extend the life of power stations across the world.

In many ways, summer in the station is the busiest time of the year.

Slowing the beating heart of the country

To get up close and personal with the equipment and carry out major repairs, large sections of the power station need to come offline – this is a procedure called an outage. At Drax Power Station there are six units, which together supply around 7-8% of the UK’s supply. Taking one offline is a big project, but a necessary one.

“Many years ago we use to do a mixture of major and minor outages but we have reconfigured the outage cycle, so all we do now are major outages. Now, we run a schedule where each unit has an outage every four years,” says Andrew Squires, Outage Manager at Drax.

This year each of our six units have come offline – five outages have already been completed and one is set to be back in service at the beginning of November. With two of these being major outages and the other four taken off the system for essential high pressure (HP) Turbine module repair works.

To ensure this all operates smoothly, planning starts early. The process starts a minimum of a year in advance, during which time scoping, planning, parts and materials are ordered for the outage. It’s a necessary advance, given the challenging timescales, projects and numbers of people that are needed to carry out the work required.

Calling in the helping hands

Drax drafts in engineering contractors in large numbers to carry out the huge scale of work required to shut down and maintain units at the power station. 2016 was a particularly busy year – at peak points 3,500 people were on site carrying out the work. “It’s a number we’ve never seen previously,” Squires says.

Main projects delivered during the outage timescale in 2016 include changing the Generator Stator core, Generator Transformer, Oil Burner system and HP Turbine module. The Main Steam pipework replacement being the largest of all, this pipework runs from the Boiler to the Turbine and is the first time this had been done in the lifetime of the plant. Now complete, this is set to last the life of the station.

Engineering work happening at Drax Power Station

Industry pioneers

Drax uses compressed wood pellets in three of its six units and this pioneering step brings implications for how they’re maintained. In the industry it’s a whole new challenge for which Drax engineers are still writing the rulebook. “We’re understanding the engineering implications of using biomass in our boilers, and developing strategies for maintenance,” says Squires.

As Europe’s largest decarbonisation project, maintaining and consistently learning comes with the territory. It’s just another challenge for the team to tackle during summer in the station and beyond.

 

The biggest balls of electricity generation

Power generation

When making a cup of tea, it’s unlikely you consider the industrial equipment kicked into action the moment you switch on your kettle. And of all of the activity going on behind the scenes, it’s even more unlikely you think about a 1.2-tonne steel ball.

But without a number of 1.2-tonne balls and the electricity they help generate, your kettle would be nothing more than a fancy jug.

How do giant balls help to generate power?

The answer lies in the way fuels like coal and compressed wood pellets are used to power boilers and generate electricity. Drax started its life as a coal power station, but today it is in the process of upgrading to run on biomass. Progress has already been made – three of the station’s six units already run on compressed wood pellets, Drax’s biomass fuel, generating around 20% of the UK’s renewable electricity.

To generate enough power to supply 8% of the UK’s demand – as Drax does – a lot of fuel is needed. Hundreds of thousands of wood pellets are delivered to Drax every day, arriving on custom-built trains travelling from the Ports of Tyne, Hull, Immingham and Liverpool.

The pellets pass through a system of conveyor belts until they arrive at one of four massive conical storage domes, located on site in Yorkshire. Before the wood pellets can be converted into fuel, they need to be crushed: this is where the balls come into play.

The pulveriser

The wood pellets used at Drax are compressed and dried wood that is formed into small capsules the size of a child’s crayon. But, like with coal, to get the best results in the power station’s huge boilers, the material needs to be turned into a very fine powder in pulverising mills. When very fine, the fuel burns as efficiently and as quickly as a gas.

Inside each mill are 10 giant steel balls that grind down either the wood pellets or coal. Each ball is three quarters of a metre in size, made of hollow cast steel alloy and weighs roughly 1.2 tonnes – equivalent in weight to British-made Jaguar XE mid-sized saloon car or an entire football team.

And to make sure that each one is up to the task of extreme pulverisation, they need to be hard. Each one is heat treated during manufacture to make sure they’re up robust enough to consistently crush raw fuel.

The benefit of this durability is that they can readily pulverise fuel to feed Drax boilers, to power kettles across the country – a big responsibility for a big ball.