Tag: technology

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.

 

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.

 

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.

Inside the dome

Sustainable bioenergy

There are four storage domes at Drax Power Station and each of them can hold 80,000 tonnes of compressed wood pellets. It’s these biomass pellets, a sustainable fuel, that Drax is being upgraded to run on and produce renewable electricity.

Wood pellets are an incredible fuel that can match coal for efficiency – the challenge is you just need more of them as the density and calorific value of coal is greater. However, storing such large quantities in a confined space presents risks that have to be managed, 24/7.

Atmospheric control

The crucial difficulty with storing the pellets is their chemical volatility. Wood, which the pellets are made from, emit carbon monoxide (CO). In a confined space such as the storage dome, this CO can build up and – due to CO’s extreme flammability – require the entire internal atmosphere to be regulated by a set of highly sophisticated engineering solutions.

As long as materials are emitting more heat into the atmosphere than they are storing in themselves, there is no risk of combustion. A single wood pellet in a fuel store poses no fire risk. Nor does a small pile. But when thousands upon thousands are piled together, the pressure builds up and causes the pellets to heat up.

Gradually, the rate of temperature increase speeds up, and before you know the flashpoint threshold has been crossed and there’s potential for danger.

However, remove or limit the oxygen supply in the silo and purge the CO that’s emitted from the pellets, and the risk of a thermal event is substantially reduced. The challenge for the engineers at Drax constructing the domes was finding a way to manage temperatures within the dome.

Neutral nitrogen

To do this they created a system to automatically inject nitrogen into the storage dome. While nitrogen isn’t a truly inert gas, it is much less reactive than CO and oxygen.  With this pumped into the dome’s atmosphere it is a much safer environment.

To get a steady supply of nitrogen, regular air from our atmosphere – which is 78% nitrogen – is passed through a molecular filter, which removes the larger oxygen molecules. The gas collected at the other end is 96% nitrogen.

This nitrogen-rich air is then injected from underneath the dome and continually distributed around it. Not only is this a fire prevention method, but also a firefighting one that can be pumped in larger quantities in the event of combustion. Separate to the above measures which are there to manage fuel temperatures, the dome is also fitted with a carbon dioxide (CO2) injection system and water deluge system which are there as fire extinguishing precautions.

The big ear inside the dome

The next problem facing the designers was how to accurately monitor the quantity of compressed wood pellets inside the dome. To achieve this, each dome is fitted with a sonar system – which sounds a bit like a chirping bird – that provides continuous feedback on how full the dome is.

The sonar monitoring system provides level, profile and volume information which is translated into a 3D image of the stored biomass. This method of volumunetric measurement allows the operators to view and monitor in ‘real time’ the effects of their actions when filling and unloading domes, so they can target specific areas particularly when unloading and for fuel accounting purposes.

Other tools and tricks

Five thermocouple arrays measure the pile temperature and provide feedback in real time to the operators to allow them to assess the status of the dome and effectively plan material filling and reclaim. Gas monitors measure the levels of CO and CO2 as well as O2 depletion within the head space of the dome.

A dome breather vent (a two way acting valve, which as its name suggests, allows the dome to breathe) is fitted to the top of the dome and acts as a vacuum breaker maintaining a relatively even pressure allowing air in during unloading and releasing head space gasses during nitrogen inserting.

The final piece of the atmospheric control puzzle is regulating pressure. At the top of each dome is a controllable aperture called a slide gate which is closed unless the dome is being filled to allow material to enter. A dome aspiration system is installed here to filter and remove displaced air from within the head space during filling, but also allow a route for CO and other offgassing products to escape.

All the hidden systems within these four huge white domes allow the operator to effectively control their atmospheric conditions and crucially to store massive amounts of potentially volatile biomass safely on site.

Find out more about these giant storage domes – read the story about how they were constructed. 

The single biggest transformation of our century

Sustainable bioenergy

At the turn of the millennium, Drax was facing a serious issue. Demand for electricity was high and increasing, but so was the desire for sources of power that were less harmful to the environment than coal, at that time Drax’s fuel.

To continue to meet demand in a cleaner and more sustainable way, an alternative approach was needed. Drax had a legacy in this field – in 1988, it was the first coal-fired power station to install flue-gas desulphurisation technology, which removes 90% of coal’s harmful sulphur dioxide (SO2) emissions.

In the two decades that followed, however, the sustainability conversation moved beyond how to make coal cleaner. Instead, the focus was finding a truly viable alternative fuel.

Finding a new fuel

In those early days, the idea of converting a fully coal-fired station to another fuel seemed outlandish to say the least.

“We made a lot of people’s heads hurt with this project,” says Drax Strategic Projects Engineering Manager Jason Shipstone. “No one had the answers. It was a bit like going for a walk but not knowing where you’re going.” Back then it was all about experimentation.

Jim Price, Alternative Fuel manager at the time, explains: “Initially, we found a few distressed cargos of wood pellets and sunflower husks that someone had ordered but didn’t want. We mixed that with coal at very low concentration.”

Price and his team found they could use the plant-based fuel alongside coal at low percentages without it detrimentally affecting the boilers. It was a long way from being a new business model, but it was a start. They spent the next year working with willow wood, a subsidized energy crop that proved difficult to turn into a fuel that could be used efficiently to power a boiler.

Then in 2005, after building a prototype plant and finding a way to pulverise the willow into a fine powder – called wood flour – and combine it with coal dust, the team hit its first key milestone. It was able to power a Drax boiler.

“That was the Eureka moment,” says Price.

“No one had the answers. It was a bit like going for a walk but not knowing where you’re going.”

A change in attitude

The response to the success was immediate. Senior management support for the project had been in place from the beginning, but now there was a change across the whole company. “People started to think maybe it can be done,” says Price.

Work continued on the project and – after more experiments – Drax eventually settled on compressed wood pellets. This form of biomass ultimately required investment in four vast storage domes that between them store 80,000 tonnes of pellets.

Then there was the issue of supply and delivery. Materials were sourced from the US, shipped to the UK, then freighted to the plant in specially designed covered train wagons, each carrying up to 7,600 tonnes.

“Everything else had to carry on as normal. This had to be seamless. We had to work the same as Drax has always worked – reliable and available,” says Shipstone.

Jason Shipstone, Drax Strategic Projects Manager, played an instrumental role in upgrading Drax.

Jason Shipstone, Drax Strategic Projects Manager, played an instrumental role in upgrading Drax.

The final hurdle

In 2009 the team overcame one of the final challenges, and successfully adapted the boilers to combust the new fuel, proving that co-firing (the process of using two fuels powering one boiler – in this case wood pellets and coal) could work. It was enough to show there was a future in wood pellets and it could work at scale.

Although nothing was fully built yet, but Dorothy Thompson, CEO of Drax, was convinced. Shipstone remembers the conversation after Thompson signed the contract to begin the transition in earnest. “’So we can do 10%. What does it take to get to 50%?’ she asked,” recalls Shipstone. His response? No problem. “It was the right answer,” he says.

Toward a coal-free future

Fast forward to 2016, and Drax is Europe’s largest decarbonisation project – reducing emissions by at least 80% of the 12 million tonnes of carbon dioxide that the three, now converted, former coal generation units would have released per year. Although only half of Drax’s six units have been upgraded from coal to use compressed wood pellets, 65% of the electricity generated at the power station is the result of a renewable, rather than a fossil fuel. Its three biomass units produce enough electricity to power the equivalent of four million homes – or more than half of all residential properties in northern England.

Given the challenges the world faces regarding the future of energy production, decisive action is required if we’re to meet carbon reduction targets. In the UK the government has voiced ambitions of phasing out coal by 2025. Drax has aims of doing it quicker. Thompson has spoken of plans that see all coal units taken off the Drax system by 2020, if not before.

The story of energy since the dawn of the Industrial Revolution has been one of fossil fuels. This simply has to change. By finding a way to ease the transition away from coal, Drax is helping to write the next chapter.

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.

How to plug the electricity gap

Andy Koss, CEO Generation until April 2020

26 January 2016

Opinion

By 2025, the UK will face a 40-55 per cent gap between electricity supply and demand, according to a report from the Institute of Mechanical Engineers. The government has disputed IMechE’s projection but its own forecasting suggests that UK electricity demand will be 19% higher in 2035 vs. 2015.

The alleged 2025 gap will be caused by the closure of coal-fired power stations to meet targets for carbon reduction. According to the IMechE, current plans to plug the gap by building new gas-fired capacity are unrealistic. (It would require a staggering 30 new power stations to be planned and built from scratch within the next 10 years.)

At Drax, we have already developed a solution. We can do it quickly, cheaply and safely. In fact, it would drastically reduce the time and money involved in building all of those 30 new gas power stations from scratch.

We’ve already adapted three of our coal-fired generating units to use high-density pellets made from compressed low-grade wood. And we’re using world-beating technology developed by our own engineers here in the UK to do it.

In all, around four or five per cent of the UK’s entire electricity needs every single day of the year are already being met thanks to our unique biomass technology at Drax. It’s an approach that could be adopted elsewhere in the country, providing a huge contribution to plugging the electricity gap.

Our high-density compressed wood pellets are the only non-fossil fuel that can bring about these changes in the time we have left.

Given the right support, within two or three years, we could convert the remaining three units at Drax power station to run on biomass wood pellets.

With all six units converted, plus Lynemouth power station – which already has that future secured – and one or two other, smaller biomass power stations, around 10 per cent of the UK’s electricity could be generated using this technology well before 2025 – long before new gas-fired capacity could come on stream.

The costs involved would be dramatically lower too. We invested around £650 million to convert three generating units, develop a supply chain and build new storage at Drax. It is estimated that the equivalent in new combined cycle gas turbine power stations would cost more as it would be new rather than repurposed infrastructure.

Energy hierarchy

The IMechE has developed an energy hierarchy, listing five sustainability-related priorities against which to judge any future energy strategy. The two that focus on energy generation are a perfect fit in terms of coal-to-biomass conversions at Drax and Lynemouth.

“Priority 3 – utilisation of renewable, sustainable resources”

High density compressed wood pellets are made from low-grade wood sourced according to the highest levels of forestry conservation.

“Priority 5 – utilisation of conventional resources as we do now”

Using world-leading engineering skills and avoiding the need to build brand new power stations, our coal units can be converted without the need for new National Grid connections.

Many of our European neighbours such as Sweden and Germany already use a far higher proportion of biomass to meet their energy needs. Catching up with the European average is the simplest, quickest and most affordable way to avoid a shortfall between supply and demand predicted by 2015.