Tag: engineering

Is there such a thing as energy ‘terroir’?

16 April 2019

Power generation

‘Terroir’ comes from the French word ‘terre’, meaning land, earth or soil. In the French wine industry, it refers to the land from which grapes are grown. It is believed the terroir gives the grapes a unique quality specific to that particular growing site.

Terroir dictates the type of wine that comes from a region – it’s the reason we call one bottle a Bordeaux, and another a Côtes Du Rhone.

But could the idea of terroir hold relevance beyond just wine? What if we looked at electricity in the same way?

Certain environments are better placed to produce certain types of electricity.

These are some of the regions making the most of their unique location and landscape to produce electricity that makes sense for them.

La Rance tidal barrage

Brittany, France

Brittany boasts one third of mainland France’s coasts, and has long been a top destination for surfers, with waves as high as 7.6 metres in some places. With such tempestuous waters, it’s the perfect location for La Rance Tidal Power Station –the world’s first station of its kind. Opened in 1966, the site was chosen because it has the highest tidal range in France.

Tidal barrages like La Rance harness the potential energy in the difference in height between low and high tides.

The barrage creates an artificial reservoir to enable different water levels, which then drives turbines and generators to produce electricity.

While the station has been operating for close to 50 years, old tidal mills are still dotted around the Rance river, some dating back to the 15th century – proof that tidal power has deep roots in this region.

Xinjiang, China  

Whilst China may have some of the world’s most polluted cities, it is also the world’s biggest producer of renewable energy – including wind power. With one of the largest land masses on the planet, one in every three of the world’s wind turbines is in China, with the government installing one per hour in 2016.

In places like Xinjiang, China’s most westerly province, the windy weather used to be a nuisance, with overturned lorries and de-railed trains being a regular sight. This is caused by mountain ranges between Dabancheng and Ürümqi which form a natural wind tunnel, increasing the wind speed as air passes through. These days the region is harnessing this same wind to produce incredible amounts of electricity – with 27.8 terwatt hours (TWh) of electricity coming from the region in the first nine months of 2018.

Onshore wind farm in Xinjiang

Xinjiang local Wu Gang founded Goldwind to build China’s first windfarm here in the 1980s. Today it’s the world’s second largest turbine maker. The turbines work on a simple premise: wind turns the turbine blades which are connected to a rotor, causing it to spin. This in turn is connected to a generator, which takes the wind’s kinetic energy to produce electricity.

Hengill, Iceland

Iceland sits where the North American and Eurasian tectonic plates meet, meaning that magma rises close to the surface, bringing with it a lot of energy potential. One example of how the Icelandic people are harnessing this power is The Hellisheiði, the second largest geothermal power station in the world.

Here, high-pressure geothermal steam is extracted from 30 wells, ranging from 2,000 to 3,000 metres deep, and is used to turn turbines and generate electricity. This renewable plant has a capacity of 303 megawatts (MW) of electricity, which is used to power the capital city of Reykjavik.

The site was chosen due to its location in the Hengill volcanic area in the south of Iceland, one of the most active geothermal areas on the planet. Here, a giant magma chamber sits underground, with thousands of hot springs above. According to Iceland’s National Energy Authority, geothermal power from sites like this accounts for 25% of the country’s electricity production and 66% of primary energy usage.

But Icelanders aren’t only using the geothermal landscape for energy production – chefs here can cook food simply by burying it in the ground, producing delicacies like rúgbrauð, which translates as ‘hot spring bread’.

Ouarzazate, Morocco

From Iceland’s below-zero temperatures to Morocco, a popular holiday destination for sun-seekers, with 330 days of sunshine a year. Morocco lays claim to a chunk of the Sahara Desert, famously known as one of the hottest climates in the world. Where better, then, to situate the world’s largest solar thermal power plant?

Noor solar thermal plant

The Moroccan city of Ouarzazate, nicknamed the ‘door of the desert’ plays host to the huge Noor Complex, which is still under construction and is being implemented in four parts. The latest piece of the puzzle is Noor III, which was hooked up to Morocco’s electricity grid last year. Here, 7,400 mirrors reflect sun rays onto Noor III’s tower, the highest solar-thermal tower in the world, concentrating at the top of the building to create around 500ºC of heat. This heats up the molten salts inside the tower, which travel through a series of pipes, creating high pressure steam. This steam then moves a turbine to generate electricity.

Molten salts are used at Noor III because they can operate at high temperatures and store heat effectively, so that the site can continue to produce energy for up to 7.5 hours when there’s no sun. Once up and running, the plant will generate enough energy to power 120,000 homes with no atmospheric emissions of carbon dioxide (CO2). Along with the other projects at the Noor Complex, Noor III is helping Morocco to achieve its goal of obtaining 42% of its power from renewable sources by 2020.

Ben Cruachan, Scotland

The sun rays that shine on the Noor Complex are few and far between in the Highlands, but there are mountains a-plenty – Ben Cruachan being one of them. Ben Cruachan is the highest point in the Argyll and Bute area of Scotland and is right next to the picturesque Loch Awe. This provides the backdrop for the world’s first high head reversible pumped-storage hydro scheme, built by British engineer Edward McColl over 50 years ago.

Cruachan Power Station’s reservoir and Loch Awe, viewed from the top of Ben Cruachan

With the help of a 4,000-strong army of workers nicknamed the Tunnel Tigers, McColl turned the slopes of Ben Cruachan into a geological battery which Great Britain still relies on today.

It works by using excess electricity on the national grid to pump water from Loch Awe at the foot of the mountain up to the Cruachan Reservoir 300 metres above. During times of heightened demand – like when everyone puts the kettle on during a Coronation Street ad break or when the wind speed suddenly drops around breakfast time – this water is released back down the mountain to turn the turbines that live inside the hollowed mountain.

In this way, Cruachan Power Station can meet the nation’s energy needs within seconds, whereas gas or nuclear stations would take many tens of minutes or hours to reach such capacity.

While Ben Cruachan lends itself perfectly to this pumped-storage hydro facility, it is only one of four such sites in the UK. The challenge in installing more is that there are only a few sites which are mountainous with suitably large bodies of water nearby – things that are inherently necessary for pumped-storage hydroelectricity.

The growing importance of ‘terroir’

All of these places embrace the land around them to produce energy in inventive ways, and as levels of decarbonisation grow around the world, there are an increasing number of places using what’s available close to home for energy solutions.

Take Barbados, a country that has traditionally relied on imported fossil fuels for 96% of its electricity. But with short driving distances and 220 days of pure sunlight every year, the government has seen the potential for electric vehicles run by solar power. With modular solar carports now a regular sight in Barbados, the island has become one of the world’s top users of EVs – preserving the picturesque landscape and reducing its dependence on imported petrol.

Solar panels above an office car park in Barbados

Meanwhile Palau, a small Pacific island nation, is building the world’s largest microgrid, consisting of 35 MW of solar panels and 45 MWh of energy storage. For a nation threatened by rising sea levels, making use of its geographic features allows it to work towards its 70% renewable energy target by 2050 and reduce its reliance on imports.

As more countries continue to move away from fossil fuels, taking advantage of their unique ‘terroir’ will increasingly enable them to produce electricity that works with their landscape.

The inside of a cooling tower looks like no place on earth

29 November 2018

Power generation

The silhouette of cooling towers on the horizon is one of the most recognisable symbols of electricity generation around the world. But inside these massive structures is an environment unlike any other.

When cooling towers are in operation, torrents of warm water cascade down to a huge pond at its base, the air cooling it as it falls. Plumes of water vapour rise through the structure and into the air.

But when shut down – for maintenance, for example – the inside of a cooling tower is a very different place. The vast emptiness of the space can be eerily silent. Even the smallest noise echoes around its concrete shell.

Standing at over 114 metres high, each of Drax’s 12 cooling towers are 86 metres in diameter at their base, 53 metres at their summit, and could comfortably fit the Statue of Liberty inside. Everything about them is huge, but they are not the unsophisticated masses of concrete they appear from afar.

“Look at a cooling tower and you might think it’s a substantial, thick structure. It’s not,” explains Nick Smith, a civil engineer at Drax. “It’s basically like an egg shell. It is the shape that gives it its strength.” For the majority of their height, a typical cooling tower is between just 178 and 180 mm – or 7 inches – thick.

It’s a testament to the original design and construction that they require such limited maintenance more than half a century after plans were first drawn up. Especially considering they are in daily use.

What does a cooling tower do?

Water is an essential part of thermal electricity generation. It is turned into high-pressure steam in the extreme temperatures of a boiler before being used to spin turbines and generate electricity. Water within the boiler is ‘de-mineralised’ and purified to prevent damage to the turbine blades and infrastructure.

Once it leaves the turbine, the steam is cooled to pure water again in the condenser so it can be reused in the boiler. To do this the steam is passed over pipes containing cold water from the cooling towers, which cools and condenses the steam while also heating up the cold water to roughly 40 degrees Celsius, the temperature it is at when it enters the cooling tower.

Inside the towers the warm water is poured over what’s known as the cooling tower pack, a series of stacks of corrugated plastic that sit roughly 30 metres up the tower. The heat and the tower’s height create a natural draught. This pulls air in from the cavities at the base of the tower – called the throat – which cools the water to around 20°C as it cascades down the stack into a pond below. It is then returned to the condenser where the cooling cycle starts all over again.

Only around 2% of the water escapes through the top of the cooling towers as water vapour – which is what can be seen exiting the top of the towers – with a further 1% returned to the River Ouse to control water levels. These small losses are replenished with water taken from the Ouse. It highlights the genius of the towers’ design that their shape alone can cool water so efficiently on an industrial scale with minimal environmental impact. 

A lasting design

A cooling tower’s iconic shape is known as a hyperboloid, referring to its inward curve. This makes them very stable, but to make them strong enough to last as long as they have, Drax’s cooling towers have the added assistance of reinforced concrete.

“Concrete is very strong in compression, but it has hardly any tensile strength,” says Smith. “Therefore our cooling towers have both vertical and horizontal hoop reinforcement to take any tensile forces generated. It is the concrete and steel working together that gives the reinforced concrete its strength.”

The level of design and engineering of Drax’s cooling towers are all the more impressive considering their age. “The construction of our first tower was completed in 1970 and designed in the mid 1960s,” says Smith, pointing out, “they were designed at a time where there wasn’t huge computing processing power, so they would likely have been designed by hand.”

“They were constructed to a very high degree of accuracy even when a lot of the equipment used would have been manual,” he adds.

Designing and building a cooling tower today, he adds, would require significant computing power and sophisticated setting-out equipment to ensure the accuracy of the construction. However, the underlying principles of the towers’ shape and how well they have continued to perform since their construction would give little reason to deviate from the current design.

In fact, that consistent performance means that even as the nature of generating electricity develops to include new fuels and technologies, cooling towers remain an integral part of the process. Drax’s Repower project– which could see the conversion of the plant’s remaining coal units to gas and the installation of a giant battery facility – is a significant step forward in the evolution of power generation, yet the design and purpose of the cooling towers would remain the same.

The structures that will shape the landscape of the future of electricity generation may include wind turbines, biomass domes and solar panels. But the enduring functionality of natural draught concrete cooling towers means they will still play a role in producing the country’s electricity – even as generation diversifies.

Watch Inside a cooling tower

How turbines came to power the world

5 September 2018

Power generation

Charles Algernon Parsons knew he was onto something in 1884. The young engineer had joined a ship engineering firm and developed a steam turbine engine, which he immediately saw had a bigger potential than powering boats.

He connected it to a dynamo, turning it into a generator capable of producing up to 7.5 kilowatts (kW) of power, and in the process kickstarted an electrical and mechanical revolution that would reshape how electricity was produced and how the world worked.

Today turbine-based generation is the dominant method for electricity production throughout the world and even now – almost a century and a half later – Parsons’ turbine concept remains largely unchanged, even if the world around it has.

Steam dreams

Throughout the 20th and into the current century, electricity generation has depended on steam power. Be it in a coal, nuclear or biomass power plant, heating water into highly pressurised steam is at the core of production.

Greek mathematician and inventor Hero of Alexandria is cited as building the first ever steam engine of sorts with his aeolipile, which used steam to spin a hollow metal sphere. But it wasn’t until the 18th century, when English ironmonger Thomas Newcomen designed an – albeit inefficient – engine to pump water out of flooded mines, that steam became a credible power in industry.

Scottish engineer James Watt, from whose name the unit of energy comes from, built on these humble beginnings and turned steam into the power behind the industrial revolution around 1764 when he added an condensing chamber to Newcomen’s original design.

It was the combination of this engine with Thomas Edison’s electrical generator late in the 19th century that first made large-scale electricity production from steam a reality.

The turbine takes over

Steam engines and steam power was not a new concept when Parson began his explorations in the space. In fact, nor were steam turbines. Others had explored ways to use stream’s velocity to spin blades rather than using its pressure to pump pistons, in turn allowing rotors to spin at much greater speeds while requiring less raw fuel.

What made Parsons’ design so important was its ability to keep rotational speeds moderate while also extracting as much kinetic energy from steam jets as possible.

He explained in a 1911 Rede Lecture that this was done by “splitting up the fall in pressure of the steam into small fractional expansions over a large number of turbines in series,” which ensured there was no one place the velocity of the blades was too great.

The design’s strength was also apparent at scale. In 1900 his company (which was eventually acquired by Siemens) was building turbine-generator units capable of producing 1,000 kW of electricity. By 1912, however, the company was installing a 25,000 kW unit for the City of Chicago. Parsons would live to see units reach 50,000 kW and become the primary source of electricity generation around the world.

Turbines in the modern grid

The world is a vastly different place to the one in which Parson designed his turbine, yet the fundamentals of his concept have changed very little. The results of what they achieve and the scales at which they work, however, have increased significantly.

Today the turbines that make up Drax’s six generating units are each capable of producing more than 600 MW (or 6,000,000 kW) of electricity with the shape, materials and arrangement of blades carefully designed to maximise efficiency.

And while that first design was purely with steam in mind, turbine technology has advanced beyond dependency on a single power source, and has been developed to accommodate for the shift towards lower-carbon power sources.

One such example is gas turbines, which work by sucking in air through a compressor, which is then heated by burning natural gas, in turn spinning a turbine as it expands. These can jump into action much faster than other turbines as they don’t require any steam to be created to power them.

Renewable sources, such as hydro and wind power, also depend on spinning turbines to generate electricity. Where these differ from gas or steam-powered turbines is that rather than being encased in metal and blasted with gases, wind and hydro turbines’ blades are exposed, so flowing air or water can spin them, powering a generator in turn.

Turbine technology helped bring access to electricity around the world, but the ingenuity and flexibility of the design means it is now serving to adapt electricity production for the post-coal age.

Does electricity have a smell?

20 July 2018

Electrification

Freshly baked bread, newly cut grass, sizzling bacon. Many of the world’s most evocative smells often need electricity to make them, but does electricity itself have a smell?

The short answer is no. An electric current itself doesn’t have an odour. But in instances when electricity becomes visible or audible it also creates a distinctive smell.

“The smell electricity emits is the contents of the gasses created when electricity conducts through air,” says Drax Lead Engineer Gary Preece. “In an instance of a failure on a switch board, for example, and there’s a flash of electricity, gasses are created from the charged air including ozone.”

It’s the same ozone gas that makes up the lower layer of the earth’s atmosphere and is often described as having a clean, chlorine-like, but burnt, smell. While it can sometimes be dangerous, ozone is also a very useful gas.

What is ozone?

Ozone’s scientific name is trioxide as it is made up of three oxygen molecules. While the normal oxygen we breathe is O2, ozone is O3 and is created by electricity in a similar way to how it forms naturally in the atmosphere.

There are large amounts of oxygen and nitrogen floating around in the atmosphere protecting life on earth from the sun’s intense UV radiation. These rays are so powerful they can ionise the oxygen, ripping it apart into two individual molecules. However, these lonely molecules are highly reactive and will sometimes collide and bond with nearby O2 to create ozone.

An electric current at a high voltage – given the right conditions – will conduct through the air, ionising oxygen in its wake and creating ozone, just as the sun’s UV rays do. When electricity behaves like this it’s known as a corona discharge, which makes a crackling sound and creates a visible plasma.

The most common time people may come into contact with a whiff of ozone is when a storm is approaching. Lighting is essentially a massive plasma that creates ozone as it conducts through the air, with the smell often arriving before the storm hits. It highlights quite how pungent ozone is considering humans can smell it in concentrations as low as 10 parts per billion in ordinary air. 

The concerns and capabilities of ozone

While ozone protects the planet when it’s in the atmosphere, it can be dangerous at ground level where it can also form through naturally occurring gases reacting with air pollution sources. High exposure to ozone at ground level can lead to lung, throat and breathing problems. However, because it also has a damaging effect on bacteria, ozone can be very useful in the medical field, and electricity is being used to deliberately create it.

In fact, ozone has been experimented with in medicine for more than a century, with its ability to attack and kill bacteria making it useful as a disinfectant. During the First World War it was used to treat wounds and prevent them becoming inflamed and was also found to aid blood flow.

Electricity plays an important role in almost everything we interact with on a daily basis, affecting all our senses, even smell.

The night shift

21 June 2018

Power generation
Draw power station at night

Things are different at night. As darkness falls the familiar sights and sounds that make up daily life retreat, creating a strange yet familiar world. There’s less activity, but that doesn’t mean there is no activity.

While Great Britain sleeps, phones charge and fridges hum. Electricity is a 24-hour need, and so the stations generating it must be 24-hour operations. But the life of a power station by night is very different to that by day.

“Walking around the power station at night can almost feel like the Mary Celeste,” says Simon Acaster, Drax Power Station’s Generation Manager. “There may be as few as 50 to 60 people on site, which isn’t a lot when you consider the size of the plant and compare it to the day, when there are some 650 people around.”

Drax Power Station by day is a hive of activity. Alongside generation there are maintenance, engineering, trading and contract support. At night, this is all stripped back.

“Work is focused on the core production issues: looking after the asset and maintaining power generation output to meet our contract position, keeping the teams safe and making sure we stay environmentally compliant,” says Mark Rhodes, Shift Manager at Drax.

“It’s a quieter place,” he adds.

Keeping power flowing

The nightshift at Drax Power Station

Typically, teams at Drax swap over at 8pm and 8am on a cycle of day and night shifts. During the summer months, when one or more of the station’s six, 600+ megawatt (MW) units can be on outage and maintenance is carried out across the station, work often continues around the clock right through the night.

But during a period of normal operation, the night workforce is reduced to basic operations and maintenance teams, material handling teams receiving biomass deliveries – which continue through the night – and security staff.

Demand for electricity typically falls overnight, so Drax shuts down unneeded generation units around 10pm. As morning approaches teams prep them to restart in time for when people wake up and turn on kettles.

“Even when we shut the units down, the turbine is still turning throughout the night,” says Acaster. “All the hydraulic pumps and lube oil systems are still functioning. A lot of plant is in service even when the units are shut down.”

This means there’s still the potential, as during the day, for something to need maintenance or attention at any moment requiring the teams to jump into action.

“We aim to sort any short-term issues through the night,” says Rhodes. “But for any technical issues that can wait, we tackle them when the day team returns and we’re fully staffed. At night it’s more about safely managing the asset.”

The hardest part of a running the power station overnight, however, is not a technical one, it’s a human one.

“There’s no doubt about it, working nights is tiring,” says Acaster. “The biggest challenge is keeping everybody focused and aware of what’s happening.”

He continues: “Unit controllers regularly talk to their plant operators, checking in every hour so we know they’re safe. Supervisors need to be out on plant engaging and talking to employees, checking on what they’re doing and keeping them active and alert.”

The shifting of the night shift

The decarbonisation of Great Britain’s electricity system has changed the way Drax operates during the day, and the same is true of the night.

“Historically, we had six units and they would be baseload, generating 645 MW each,” says Rhodes. “They would operate continuously day and night.” But with the demand profile changing, lower power prices, and other methods of generation coming onto the system, that model is changing.

“Overnight is normally the time of least demand and when the price of power becomes most depressed,” Rhodes continues. “So we take units off and prepare them for the morning, returning when there is value.”

Regularly shutting down and starting the units takes a tougher toll on the equipment than running them continuously, which increases the need for maintenance teams on night shifts. There’s also a need for teams to be on standby to ramp up or down generation.

The increased volatility of the country’s power network, brought on in part by increasing levels of intermittent renewables, means National Grid can often ask Drax to increase or decrease generation at short notice to provide balancing services like inertia, frequency response or reserve power.

“Our units can come down to 300 MW and stay at that level,” says Acaster. “Across three units that gives National Grid 900 MW of spare capacity that can be turned up. It’s like a sleeping giant awaiting start up at any time.”

But unlike other sleeping giants this one is never truly at rest. The demands of the network keep it, and the men and women operating it, humming through the night, 24-hours a day. The power station at night is a quieter place, but it is never a silent one.

People strategy

21 March 2018

Sustainable business

Our people strategy: One Drax

Following extensive consultation with employees, we developed our people strategy to 2020 – One Drax. It has been designed to address the key issues that were raised by employees in our 2016 employee survey, such as the need for clearer learning and development programmes and more effective internal communications. The strategy focuses on valuing our people, driving business performance and developing talent to deliver our strategic and operational objectives.

We launched the five aspects of the strategy: my career, my performance, our behaviours, our reward, my recognition. In 2018, we will focus on all of these aspects and, in particular, our reward, my recognition and my career.

Behavioural framework

We have developed a number of HR programmes in line with our people strategy. The foundation of this is a new behavioural framework that identifies positive behaviours reflecting our Company values: honest, energised, achieving, together. The behaviours are integrated into all areas of our people management processes at Drax Group. The HR team consulted with one in five employees across the business, including senior leaders and union representatives, to develop the framework.

In 2018 we will further embed the behavioural framework and our Company values into our culture by developing an online tool for employees to evaluate how they demonstrate the behaviours.

Developing our people / apprenticeships

At Drax Power, we have a proud history of apprenticeships, with the majority remaining to work at Drax and progressing through the Company.

Mick Moore joined Drax on 7 September 1976 as a craft apprentice.

On completion of his apprenticeship, Mick continued to further his education and completed an HNC in Electrical & Electronic Engineering. After a 10-year break he resumed his further education, graduating from Humberside & Lincolnshire University with a degree in Electronics & Control Engineering, achieving Chartered Engineering status with the Institute of Electrical Engineers in 1999.

Having worked at Drax for 41 years, Mick’s career has included roles such as Instrument Mechanic, various engineering grades from Assistant Engineer to Process Control Engineer & Maintenance Section Head. Mick is now the Electrical, Control & Instrumentation Engineering Section Head for Drax Power and is currently responsible for a team of 51 people.

 

The wooden buildings of the future

22 January 2018

Sustainable bioenergy
Wooden building with blue sky background

When we think of modern cities and the buildings within them, we often think of the materials they’re constructed from – we think of the concrete jungle.

Since the 19th century, steel, glass and concrete enabled the building of bigger and more elaborate buildings in rapidly-growing cities, and those materials quickly came to define the structures themselves. But today that could be changing.

New technologies and building techniques mean wood, a material humans have used in construction for millennia, is making a comeback and reducing the carbon footprint of our buildings too.

Return of the treehouse

Civilisation has been building structures from wood for longer than you may realise.

Horyu-ji Temple in Nara, Japan

The 32-metre tall Pagoda of Horyu-Ji temple in Japan, was built using wood felled in 594 and still stands today. The Sakyumuni Pagoda of Fogong Temple in China is nearly twice as tall with a height of 67 metres. It was built in 1056.

Today, wood is once again finding favour.

The 30-metre tall Wood Innovation and Design Centre of the University of British Columbia (UNBC) in Canada was completed in October 2014 and is among the first of this new generation of wooden buildings. And they’re only getting bigger.

This year, the completion of the 84-metre, 24-storey HoHo Tower in Vienna will make it the tallest wooden building in the world. But this will be far surpassed if plans for the Oakwood Tower in London are approved. Designed by a private architecture firm and researchers from the University of Cambridge, the proposed building will be 300-metres tall if construction goes ahead, making it London’s second tallest structure after The Shard. And it would be made of wood.

Falling back in love with wood

Wood construction fell out of favour in the 19th century when materials like steel and concrete, became more readily available. But new developments in timber manufacturing are changing this.

Researchers in Graz, Austria, discovered that by gluing strips of wood with their grains at right angles to each other the relative weakness of each piece of wood is compensated. The result is a wood product known as cross-laminated timber (CLT), which is tougher than steel for its weight but is much lighter and can be machined into extremely precise shapes. Think of it as the plywood of the future, allowing construction workers to build bigger, quicker and lighter.

Glued laminated timber, commonly known as glulam, is another technology technique enabling greater use of wood in more complex construction. Manufactured by bonding high-strength timbers with waterproof adhesives, glulam can also be shaped into curves and arches, pushing wood’s usage beyond straight planks and beam.

These dense timbers don’t ignite easily either. They are designed to act more like logs than kindling, and feature an outer layer that is purposefully designed to char when exposed to flame, which in turn insulates the inner wood.

Susceptibility to mould, insect and water damage is indeed a concern of anyone building with wood, but as the centuries-old Pagodas in Japan and China demonstrate, care for wood properly and there’s no real limit to how long you can make it last.

So, wood is sturdy. But so is steel – why change?

Green giant

Construction with concrete and steel produces an enormous carbon footprint. Concrete production on its own accounts for 5% of all our carbon emissions. But building with wood can change that. UNBC’s Innovation and Design centre saved 400 tonnes of carbon by using wood instead of concrete and steel.

On top of that, building with wood ‘freezes’ the carbon captured by the trees as they grow. When trees die naturally in the forest they decompose and release the carbon they have absorbed during growth back in the atmosphere. But wood felled and used to construct a building has captured that carbon for as long as it stands in place. A city of wooden buildings could be a considerable carbon sink.

This can have further ripple effects. The more timber is required for construction, the more it increases the market for wood and the responsibly-managed forests that material comes from. And the more forests that are planted, and managed with proper governance, the more carbon is absorbed from the atmosphere.

According to research from Yale university, a worldwide switch to timber construction would, on its own, cut the building industry’s carbon emissions by 31%.

Granted, that will be a difficult task. But if even a fraction of that can be achieved, it could mean a future of timber buildings and greener cities.

How do you keep a 1.2 tonne steel ball in prime condition?

18 January 2018

Power generation

There are 600 giant balls at Drax Power Station. Each one weighs 1.2 tonnes – roughly the same as a saloon car – and is designed for one simple, but very specific, purpose: to pulverise.

Every day thousands of tonnes of biomass and coal are delivered to the power station to fuel its generators. But before this fuel can be combusted, it must be ground into a powder in pulverising mills so it burns quicker and more efficiently. It’s the giant balls that do the grinding.

And although these balls may be incredibly durable, the constant smashing, crushing and pulverising they go through on a daily basis can take its toll. Maintaining the 600 balls across the power station’s 60 mills is a vital part of keeping the plant running as effectively as possible.

Surviving the pulveriser

Each of the six generating units at Drax (three biomass and three coal) has up to 10 mills that feed it fuel, all of which operate at extreme conditions. Inside each one, 10 metal balls rotate 37 times a minute at roughly 3 mph, exerting 80 tonnes of pressure, crushing all fuel in its path.

Air is then blasted in at 190 degrees Celsius to dry the crushed fuel and blow it into the boiler at a rate of 40 tonnes per hour. To survive these extremities, the balls must be tough.

Drax works with a local foundry in Scunthorpe, Lincolnshire to manufacture them. First, they are cast as hollow orbs of nickel steel or chrome iron and then smoothed to within one millimetre of being perfectly spherical.

After 8,000 hours of use, engineers check how rapidly they’re wearing down by measuring their thickness using ultrasound equipment and, if deemed to be too thin (which usually occurs after about 50,000 hours of use), replace them.

For this, they must first remove the top of the mill – including the grinding top ring – and then individually lift out and replace each massive ball. Those that are removed are typically shipped back to Scunthorpe to be recycled.

Transforming for a decarbonised future

When Drax Power Station was first built in the 1970s, the mills were designed to only crush coal, but since it was upgraded to run primarily on biomass, in the form of sustainable wood pellets, they have been adapted to work with the new fuel.

For the most part, this requires only minor changes – the primary difference is that coal is harder to fully pulverise. Coal typically does not get entirely ground down in the first cycle, so a classifier is needed in the mill to separate the heavier particles and recirculate them for further grinding.

The process of switching one mill from biomass to coal takes about seven days and nights. This work was carried out on Unit 4’s mills ahead of this winter, following biomass trials in the spring and summer of 2017. Now that the decision has been made to permanently upgrade that fourth power generation unit, converting one of its 10 mills from coal to biomass later in 2018 will take about twice as long.

Using the same essential equipment and process for both fuels helps to quicken the pace of decarbonisation at Drax Power Station as the UK moves to end the production of unabated coal-fired electricity by 2025. Come seven years from now, one thing will remain consistent at the huge site near Selby, North Yorkshire: the giant pulveriser mills will continue their tireless, heavy-duty work.

Refurbishing a 300-tonne generator core within the heart of a power station

6 December 2017

Power generation
Electricity generator

At the centre of Drax Power Station, in a corner of the cavernous turbine hall, is a white box. The inside of this box is spotlessly clean. Not only are its white walls free of dirt, they are free of even dust. But there is one outlier inside this sterile environment: a 300-tonne chunk of industrial equipment.

This equipment is a generator core – the central component for converting the mechanical energy to electrical power.

Electricity generator core

The core is driven by the steam turbine. Ninety tonnes of generator rotor spinning at 3,000 rpm with just millimetres of clearance from the core produce 660 megawatts (MW) of electricity. That’s enough – 645 MW when exported from Drax into the National Grid – to power a city the size of Sheffield.

The generator is a serious piece of industrial machinery. And despite the pristine conditions, this white box is the site of serious engineering.

A process normally done by large-scale manufacturers in dedicated factories, ‘rewinding’ a generator core – as the process is called – is a major operation.

No other UK facility is capable of doing this complex job. So it’s here, in a white box, in the middle of an operational power station in North Yorkshire, that a team of engineers is undertaking work that will secure the generator’s use for decades. This is the Drax rewinding facility.

Turbine structure

How a generator works

A generator consists of two main components, a spinning rotor and a stationary stator. The rotor, which is directly connected to the main turbine and spins 50 times every second, sits inside the stator. Both the stator and the rotor contain a large number of copper coils known as windings. These windings are what carry the electrical current.

The rotor acts like a very strong electromagnet, which, when a voltage is applied, produces a strong magnetic field. Because the rotor sits inside the stator, this magnetic field intersects the copper windings of the stator and induces a voltage in these windings, allowing current to flow.  This voltage is then brought out of the stator and passed through a step-up transformer, where it is increased to a level suitable for transmission through the National Grid.

The stator core is made from many elements with hundreds of thousands of laminations, 84 water-cooled insulated copper bars, each 11 metres long and weighing 200kg forming the windings, various insulating materials, blocks, packing, wedges and condition monitoring equipment.

Generator stators can operate for decades without fault.

DIY at Drax

In 2016, a team of engineers at Drax embarked on a project to construct a facility to rewind the stator on site. This required cross-company collaborative working to design and construct this huge purpose built facility.

Contamination can cause operational problems, so the team built a sterile, white room within the turbine hall – one of just two places within the power station with foundations strong enough to support the incredible 450 tonnes required for the rewind facility. Designed to hold the stator core and the conductor bars, air is forced out of the room to limit the possibility of contamination to the core during the rewind.

“When the unit is in service it becomes magnetic, so any metallic particles left in the space will be attracted to the core,” explains Drax electrical engineer Thomas Walker. “Once magnetised, any metal particles could be drawn in, burrowing into the insulation and core lamination.”

This is the kind of event that an electricity generator wants to avoid – but when it happens, be prepared to fix it.

Roll with it

When Drax’s stators were manufactured in the 1980s, completing their construction relied on manual handling techniques. Modern day facilities, however, rotate the core to minimise human contact.

It took just six months for a partnership involving Drax, Siemens and ENSER to manufacture what could be the largest stator rollers in the world and within that time, ship them from the US to North Yorkshire.

With the rollers installed, the next step was to move in the core. Two of the turbine hall’s cranes, each capable of lifting 150 tonnes, were combined to lift it, hoisting the core onto the mechanical ‘roller’ within the rewind facility.

Once in place, the roller rotates the core, allowing for the copper conductor bars to be safely removed and inserted. Despite this mechanical help, the removing and replacing of each one is still at its heart a human job.

“We still need 10 men to physically move the conductor bars with lifting aids, which makes it not an easy process,” says Walker. Using this method, the bars weighing 200kg each can be safely and precisely fitted into the core.

Electricity turbine generator at Drax

Opting for in-house

Rewinding a stator is a complex process. However, when the time, logistics and costs of shipping the core to Siemens – the German-based manufacturers – was factored in, the decision to do the work at Drax Power Station was an easy one.

“A 300-tonne core is not easy to transport and the Highways Agency do not like things like that on the roads. They’d want us to use waterways” says Drax lead engineer Mark Rowbottom. “Logistically it just wasn’t worth it. It’s too much money to move and ship that weight to Germany. So, we looked at what we could do onsite.”

More than just an economical and logistical decision and with the UK’s diminishing manufacturing facilities, Drax is now equipped to support generator rewinds for many years to come. Building and operating the rewind facility was a project that leveraged the engineering abilities of Drax employees. They are increasingly doing engineering traditionally outsourced to equipment manufacturers.

“The experience we have gained and the close working relationship we have established with Siemens enables us to support the generator for the remaining life of the station,” says Rowbottom.

“To see the core in that many pieces and stripped down to this level is very rare,” says Walker, who began working at the plant as an apprentice. Of the 84 conductor bars, half have been fitted, and the team is scheduled to complete the stator rewind in early 2018. “I never thought I’d do anything like this but am proud to say that I’ve done it.”