Author: admin

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.

 

How one company helped transform the biomass business

Sustainable bioenergy
Westfield terminal

If asked to picture Canada, its beautiful forests often spring to mind. In fact, 38% of the country is covered by them. Little wonder that Canada has one of the world’s biggest lumber industries. But all that lumber milling means a lot of sawdust.

It was in this sawdust, and the other ‘waste’ products the milling process creates, that one fledgling Canadian company spotted an opportunity.

Making the most of waste

Started by two brothers in the 1980s, Pinnacle originally made animal feed for farmers – compressed pellets of grass and grain.

Then, in the late Eighties, after hearing about wood pellet production in Scandinavia, and taking a look at all the sawmilling residues being burned up around them, they had an idea for a new direction.

At the time the Canadian government was looking to make the sawmilling industry a lot cleaner and more sustainable. “There was a lot of fibre around that needed to find a home,” explains Vaughan Bassett, a senior executive with the company.

Canada needed a way to put to good use materials that were previously just thrown away or even burnt out in the open, releasing greenhouse gas emissions, and wood pellets seemed like a natural fit. Even better, because there was so much waste fibre around at the time, Pinnacle was able to get its raw material for free and help to avoid the unnecessary emissions. All it had to do was pick it up and take it away.

Pinnacle Lavington grand opening

Finding a new business model

Making the transition from feed pellets to wood pellets involved a lot of trial and error.

“There was a lot of entrepreneurial spirit that went into this thing,” says Bassett. “It was untried, untested, unknown and there was no real market. It was just a couple of entrepreneurs trying stuff out.”

Initially, Pinnacle produced its wood pellets for local domestic markets – people looking to heat their homes, local businesses, and schools that used wood burners. This is a particularly convenient and efficient form of fuel for communities in off-the-grid, remote areas of Canada. But Pinnacle was keen to grow and make an even greater impact.

Rising demand for sustainability

By the early 2000s, some in the power generation industry were starting to rethink their long-term futures, looking to shift from fossil fuels like coal to cleaner alternatives in order to meet the challenges of sustainable energy production.

Central to Pinnacle’s business is a commitment to sustainability – something being based in Canada, where forest management is particularly advanced, makes possible. Being owned by the Crown, there are very tight controls over how Canadian forests are run – and how the trees are used.

“We’ve probably got the most sustainable wood fibre in the world. The numbers are just mad. Something like 95% of all the forests in Canada are ‘forest management certified’, which is unbelievable. Look at the next best country and it’s probably nearer 30%,” says Bassett, “It’s left us with an incredible asset that keeps growing every year. The industry never takes more wood than what grows.”

Indeed, carefully managed forestry is key to environmental sustainability. Fully-grown older trees don’t absorb as much CO2, so replacing them with younger, growing trees that do, can benefit the environment. Meanwhile, the waste product of sawmilling is converted into biomass, which produces further benefits by reducing reliance on fossil fuels.

Pinnacle and Drax: A sustainable partnership

Pinnacle first started supplying Drax with compressed wood pellets in 2009, marking a turning-point for the company. “Since 2011, our production has doubled,” says Bassett.

Pinnacle now contracts a fleet of ships and has its own dedicated port facility. Each vessel can transport 60,000 tonnes. Given that Drax uses around 16,000 tonnes a day with two of its three biomass units at full capacity, one shipment keeps a third of the huge power station in North Yorkshire going for nearly four days.

“Pinnacle now produces in the region of 1.5m tonnes of pellets a year, about half of which goes to Drax. So they’re a very important part of what we do,” says Bassett.

Read the Burns Lake and Houston pellet plant catchment area analysis here, part of a series of catchment area analyses around the forest biomass pellet plants supplying Drax Power Station with renewable fuel. Others in the series can be found here. 

Protecting the UK’s power from cyberattacks

Power generation

At the heart of all aspects of modern life is a common resource: electricity. We need it to power our homes and our devices, to do our jobs and increasingly with electric trains, trams and cars, to get from A to B. For that electricity to be generated we need power stations.

They’re a critical part of the UK’s infrastructure, and so for terrorists and foreign states that have much to gain from disrupting the country, electricity generators are an obvious target.

Drax Power Station is the UK’s largest, with the capability to generate enough electricity to power every home in the north of England. With this mantle comes a higher risk of security threats – notably cyberattacks. Protecting the plant from these attacks is not only essential for Drax’s business, but for the safety of the country.

The threat of cyberattacks

Cyberattacks exist in the digital space, but can have a very real and tangible effect on the physical world. Between 2007-10, a computer virus later called Stuxnet attacked the Iranian nuclear programme, damaging a number of the centrifuges – a key part of the nuclear manufacturing process. As a result, Iran was forced to decommission roughly 1,000 centrifuges.

In a separate attack, 35,000 computers belonging to the Saudi energy company Saudi Aramco were partially wiped and destroyed, disrupting Saudi Arabia’s ability to supply 10% of the world’s oil. Over the past few years the threat of malicious entities has only increased – an alleged nation state attack on Ukraine’s power grid in late December 2015 left thousands of homes without electricity.

Drax is not immune to similar attempts – every month, the security team investigates about 1,000 issues. On an average month, two of the 1,000 are judged to be serious enough to warrant further investigation.

This is where Darktrace comes in.

Identifying the threats 

Darktrace is an incredibly powerful system that identifies and deals with threats to Drax. It starts by getting to know you.

It learns every single device on the network, its speed of traffic, and the patterns of each user’s daily work behaviour. For example, if a user logs in to the work systems at 8pm but has never done so before, Darktrace will identify this behaviour and flag it as different from the norm.

Flagging each of these events depending on its assessed severity, it maps the devices into a graphic that looks like a galaxy of stars of different colours. Drax’s security team use this to see at a glance which devices need attention and action. 

The result is a view across the whole power station – both the corporate environment and our Industrial Control Systems. Those security experts can then see where there have been issues with password protection, software updates with errors, and where any breaches come from.

More importantly, they can see viruses infecting devices in real time. When the system thinks it might see one, there are three possible outcomes.

Ignore, Throttle, Kill

Once Darktrace identifies any abnormal activity that could be a threat, the system offers three options: ignore, throttle, or kill.

‘Ignore’ means allowing the system to continue as normal. This option would be used if the system flagged something as a threat which human investigation found was harmless.

The ‘throttle’ option is designed for a situation when a virus is affecting one part of the operation of one device, but shutting down the device entirely would disable a critical function. The ‘throttle’ option slows the affected part of the device down to a virtual standstill but allows the device to continue the rest of its operations while the system investigates.

‘Kill’ means removing the unit from the network immediately. If a machine behaves in a way that suggests it could be infected, it can be shut down almost immediately.

Every day, a live dashboard of variables is available to identify problems, investigate breaches, fix any infected devices and then rebuild those systems. It’s a daily schedule that not only ensures the power station can continue uninterrupted, but that the entire country can too.

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.

 

Better sustainability certification standards for healthier forests

Sustainable bioenergy
Mushrooms in a sustainably managed forest.

An increasing percentage of compressed wood pellets used at Drax Power Station are sourced from its own pellet plants in the southern US, but most biomass still comes from external suppliers.

In order to improve its sustainability systems, Drax has been encouraging suppliers to achieve Sustainable Biomass Program (SBP) certification. In the Baltics – a heavily forested region that has long been a source of renewable fuel – this rigorous auditing and certification process identified a new issue with certain types of raw material. The key to solving this problem was not just looking in the right places, but asking the right questions.

A surprising issue

In both Estonia and Latvia, around half the land is forested, so they’re countries in which wood has always played a huge part, not only for society but for the economy. And because it’s so important, it’s well protected by both governments.

“Latvia and Estonia have very strong forest legislation,” says Laura Craggs, Sustainability Compliance Manager at Drax. “You cannot harvest any site without the government giving you written permission.”

So, when it came to Laura’s attention that all forest product manufacturers and users in the region could be using wood from protected forestland called Woodland Key Habitats, it was a surprise.

Certification step change

This issue was raised thanks to Drax’s efforts to improve sustainability standards. Drax has always maintained a rigorous vetting process for suppliers to ensure they operate with sustainable practices. But the creation of the Sustainable Biomass Program (SBP), a unique certification scheme for woody biomass used in industrial, large-scale energy production, has further improved this.

“SBP raises the bar slightly. It looks at each pellet plant and says ‘these are the standards to meet, show us how you meet them’,” says Craggs. While not a huge departure from the process Drax used previously, there was one added step in the SBP process that in Latvia proved crucial: stakeholder engagement.

The SBP has introduced regional risk assessments, which are conducted by appointed working bodies tasked with, amongst many other things, reaching out to relevant stakeholders in a country or region to assess whether there are any sustainability issues. In Latvia, it was this that brought up the possibility of Woodland Key Habitats being affected.

Identifying it as an issue, however, did not mean it was easy to investigate – in Latvia, Woodland Key Habitats aren’t mapped. Craggs explains: “You can’t avoid these areas if you don’t know where they are.”

Mapping the unknown

Latbio (the Latvian Bioenergy association), an environmental stakeholder group, were the first to respond to the issue raised by NGOs and commissioned a mapping programme to define where Woodland Key Habitats might be found. This mapping involved highlighting the potentially risky areas where Woodland Key Habitats could be, through identifying certain ages and species of forests.

“All roundwood entering a pellet plant is now being checked to ensure it’s not from a Woodland Key Habitat before being brought onto site,” says Craggs. “When you get a delivery of wood, there’s a specific code that comes with it telling you exactly where it came from. What Drax suppliers are now doing is, if the code is from a risky area, they’re rejecting it.”

As the mapping of the risky areas is, by nature, overly prudent, it is important to carry out further checks, as many of the forest areas highlighted as risky may not actually be Woodland Key Habitats. This mapping was followed up by teams of biologists who went to the potential at-risk areas and made more detailed studies, looking for indicators of a valuable biotope, like the presence of lichens, mosses or old growth trees. This work has now been developed into a checklist which harvesting companies can carry out prior to harvesting in these risky areas. If the checklist shows the area has many of the characteristics of a Woodland Key Habitat, the low value roundwood cannot be purchased by the pellet plant. The process has already had a huge effect in raising awareness and training in identifying Woodland Key Habitats.

With these standards in place, the SBP can roll out a more rigorous degree of woodland sustainability certification. The data is then published on their website for full public scrutiny – meaning anyone can check that biomass material is coming from sustainable sources.

Read the Estonia catchment area analysis here, and the Lativa analysis here. These form part of a series of catchment area analyses around the forest biomass pellet plants supplying Drax Power Station with renewable fuel. Others in the series can be found here. 

A solution for cheaper, cleaner power

Sustainable bioenergy
Senior couple checking their bills

Britain has some big energy targets ahead of it – namely an 80% reduction in carbon emissions by 2050 compared to 1990 figures. A renewable energy future is not an optimistic target, it is a necessary one.

But for this picture to also be a practical one it needs to be affordable. A study from NERA and Imperial College London, commissioned by Drax, suggests there are ways for renewable technology to be cheaper than it currently is.

In fact, in one scenario they looked at, there could be savings to the tune of £2.2 billion.

Incentivising decarbonisation

It’s a positive and necessary support mechanism. However, some renewable technologies, like compressed wood pellets, a form of biomass, are excluded from participating in upcoming the auctions scheduled between 2017-20. Why is this?

Missing the bigger picture

Currently, CfD support is based on how much a particular type of electricity costs combined with how much it takes to build and maintain the facility used to generate it. This figure is what’s called the ‘levelised cost of energy’ (LCOE). The spanner in the works comes in that not all costs are considered in making this judgement.

Powering a country requires more than just a power source. We need ancillary services like backup power to get the country back on the rails in the event of large-scale blackouts, and voltage control to ensure electronic devices continue to work and that power can move around the network. The costs associated with these services – system integration costs (SICs) – are excluded from the CfD equation.

Sources like wind and solar, being intermittent, can’t offer most of these on-demand ancillary services but we still need them to play a part in the UK’s energy supply. Biomass facilities can provide a number of these itself, meaning it actually has a negative SIC cost.

However, in the current pricing system – ignoring these associated costs – biomass is considered more expensive than onshore wind and solar. With the high SIC costs for wind and solar included, biomass is in fact the cheapest option.

Finding the right mix

This is not to say that solar and wind are not an integral part of a more renewable future. A truly flexible low carbon, high voltage electricity grid should be a mix of elements. Current rules do not look at the full picture, and are ruling out important alternatives, but there are possible solutions. One could be unifying the markets.

There are four markets that feed into the UK’s electricity supply and there’s little transparency or cohesion between them. This leads to inefficiencies.

Jens Price Wolf, Regulations and Market Director at Drax, explains: “Solar is the cheapest renewable, diesel is the cheapest option in the capacity market and gas will be the cheapest for energy production.”

By considering each market as separate you end up buying the cheapest solution for that individual purpose rather than considering its performance across all. This misses out solutions that can benefit the whole system.

“Biomass might be the second cheapest option in each field,” says Wolf. “So supporting investment to upgrade existing coal power stations with biomass technology satisfies multiple needs and leads to it being ultimately cheaper than the old mix.”

A single market approach that treats all technologies and generation methods in the same way could lead to significant cost savings, and those savings could be passed on to bill payers in households and businesses.

While this could be a longer-term solution, there are ways short-term actions that can make a difference. If the government were to include biomass in the mix for the next round of CfD auctions it could bring about savings of over £2 billion over the next 15 years, or a £85 saving per household over the same period. And, it would do this while ensuring the grid remains adaptable without sacrificing emissions targets.

Black start: the most important back up plan you’ve never heard of

Power generation

Movies where major cities are razed to the ground or overrun by zombies are good fun when watched safe in the knowledge that such disasters are never likely to happen in the UK.

But how prepared would Britain’s infrastructure be if faced with a real disaster? If, for example, something were to happen that caused the national electricity grid to shut down? What would happen next?

Of course, the chance of this ever happening is remote in the extreme. Nonetheless, Britain has had a contingency plan in place for decades.

Britain’s ultimate power back up

First things first – if the whole of the network, including the power stations supplying the national high voltage electricity distribution network (the grid), loses power, you would need to restart those individual power stations before they can get the grid powered up again.

The challenge? Normally, all power stations need electrical supply to start up. But with a total electricity blackout, there’s no electricity to restart the system.

That’s why the reboot procedure is called ‘Black Start’ – and it’s one the most important, yet little-known back up plans in the UK.

The good news? There has never been a blackout so widespread that Drax has been asked to do a Black Start.

drax_black_start_v6_high

Preparing for the unlikely

But that’s not to say that such a procedure may never be needed.

In October 1987, there was a regional Black Start in the wake of the powerful hurricane that hit the south of the country. The storm damage left Kent and Sussex disconnected from the National Grid – but thanks to Black Start contingency plans, most people barely noticed. Kingsnorth Power Station restored power to the area and it ran independently, cut off from the rest of the Grid, until repairs enabled it to be connected up again.

A total, nationwide grid blackout may be unlikely, but that doesn’t mean it’s not prepared for. Tests happen regularly to assess how long it would take to restart an individual generation unit at a major power station, bring it up to capacity, and make sure that any Black Start would run smoothly.

The most recent test took place at Drax in July 2011, with representatives from the National Grid witnessing the procedure. To simulate blackout conditions, three of the generating units were disconnected from the grid. In that test, it took 83 minutes to return one unit back to service.

A simple plan

Not all power stations can do a Black Start – some simply do not have control ability to be the starting point of a system reboot. But modern coal, gas and biomass power plants are able to restart rapidly on demand. This is why Drax – first operational in the 1970s – is modern and responsive enough to be a key part of today’s Black Start planning.

The way it works is actually relatively simple: using smaller power sources to start ever bigger ones, scaling up and up until the entire country is powered up again.

Drax’s auxiliary generating units consist of three gas turbines which can be started from batteries. These would in turn generate enough power to restart one or two main generating units. The restarted generating units would be used as the backbone of an ‘island network’ – a network operating independently of the national grid – that would be grown by adding pockets of supply. The generating units would match the speed and frequency to create normal grid conditions and to restore supplies fast locally. Finally the affected area’s ‘island networks’ would be hooked up to each other so electricity can be distributed around the country with the reliability and stability we have become accustomed to.

Staying prepared

When the electricity market was privatised, there was a risk that such nationwide plans as Black Start could have fallen apart. To prevent this, formal contracts were put in place to continue to restart from scratch if necessary. Drax recently renewed its contract.

This makes Black Start – and Drax – as important as ever. If a disaster scenario ever struck for real, the most important back up plan you’d never heard of (until now) will swing into action.

This short story is adapted from a series on the lesser-known electricity markets within the areas of balancing services, system support services and ancillary services. Read more about system inertia, frequency response, reactive power and reserve power. View a summary at The great balancing act: what it takes to keep the power grid stable and find out what lies ahead by reading Balancing for the renewable future and Maintaining electricity grid stability during rapid decarbonisation.

This is how you make a biomass wood pellet

Sustainable bioenergy
Compressed wood pellets

Wood has been used as fuel for tens of thousands of years, but this wood – a compressed wood pellet – is different. It’s the size of a child’s crayon and weighs next to nothing, but when combined with many more it is a smart solution to generating cleaner electricity compared to coal.

Wood pellets like these are being used at Drax Power Station to generate electricity and power cities. Not only are they renewable and sustainable, but because they are compressed, dried and made from incredibly fine wood fibres, they’re also a very efficient fuel for power stations.

This is how a compressed wood pellet is made at the Drax Biomass Amite BioEnergy Pellet Plant in Mississippi.

The wood arrives to the yard

Wood arrives at the plant via truck and is sent to one of four places: the wood storage yard, the wood circle (where wood is primed for processing), the piles of sawdust and woodchip, or straight into processing.

Bark is removed and kept for fuel

Logs are fed into a debarker machine, which beats the logs together inside a large drum to remove the bark. The bark is put aside and used to fuel the woodchip dryer, used later in the process.

Thinned wood stems become small chips

The logs – low-value fibre from sustainably managed working forests – need to be cut down into even smaller pieces so they can then be shredded into the fine material needed for creating pellets. Inside the wood chipper multiple blades spin and cut the logs into chips roughly 10mm long and 3mm thick. The resulting chips are fed into the woodchip pile, ready for screening.

Chips are screened for quality and waste is removed

Chipped down wood can include waste elements like sand, remaining bark or stones that can affect pellet production. The chips are passed through a screener that removes the waste, leaving only ideal sized wood chips.

The biggest hairdryer you’ve ever seen

The wood chips need to have a moisture level of between 11.5% and 12% before they go into the pelleting process. Anything other than this and the quality of the resulting pellets could be compromised. The chips enter a large drum, which is blasted with hot air generated in a heater powered by bark collected from the debarker. The chips are moved through the drum by a large fan, ready for the hammer mill.

Wood pellet Hammer Mill

Small woodchips become even smaller woodchips

Inside the hammer mill there’s a spinning shaft mounted with a series of hammers. The wood chips are fed into the top of the drum and the spinning hammers chip and shred them down into a fine powdery substance that is used to create the pellets.

Putting the chips under pressure – a lot of pressure

The shredded woodchip powder is fed into the pellet mill. Inside, a rotating arm presses the powdered wood fibre through a grate featuring a number of small holes. The intense pressure heats up the wood fibre and helps it bind together as it passes through the holes in a metal ring dye, forming the compressed wood pellets.

Resting and cooling down

Fresh pellets from the mill are damp and hot, and need to rest and cool before transporting off site. They’re moved to large storage silos kept at low temperatures so the pellets can cool and harden, ready for shipping.

One of the biggest domes you’ve ever seen

This is the final stage before shipping. Specially designed and constructed storage domes are used to store the wood pellets after they are transported to the Mississippi River, Louisiana and before they make their way across the Atlantic to the UK.