Tag: power station

Summer in the station

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.


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

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.


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

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.

The power industry in 2016: Where are we now?

Britain is in the middle of a transition. While at one point it was the centre of the global coal industry, it’s now pushing further towards renewable resources. But 2016 has been a tumultuous year marked by political changes that have sent shock waves through the whole country. The energy industry is no exception – but that is not to suggest it’s on shaky ground.

Here we look at some of the year’s major events and how they’ve affected the energy landscape.

Leaving Europe

Britain’s vote to leave the EU could have a major impact on the domestic energy landscape. Europe has played a central role in setting emissions targets for power stations, promoting renewable technologies and trading carbon. The UK also benefits from being in the Single Energy Market, where energy market rules and regulations are harmonised across a number of European countries. A post-Brexit resolution to these issues is likely to remain uncertain for some time.

As Drax CEO Dorothy Thompson told a conference in Florida in late September:

“It will take a number of years for the UK to actually exit the EU, and we think politicians on all sides will push for an orderly departure.”

Implementing the Paris Agreement

Following last year’s Paris Agreement on Climate Change, the UK Government demonstrated its commitment to being a world leader in clean energy by setting its Fifth Carbon Budget. The Budget, initially proposed by the independent advisory body the Committee on Climate Change, sets a cap on the UK’s greenhouse gas emissions for the period 2028-2032. The cap is ambitious and would require the UK to reduce its emissions to a level 57% lower than they were in 1990. The Government is working on a new Emissions Reductions Plan that will map out how it intends to meet this goal and accelerate decarbonisation in the power, heat, transport and agricultural sectors.

Political change

The reshuffle following Theresa May’s election as Conservative Leader and therefore Prime Minister also marked the end of the Department of Energy and Climate Change (DECC), previously responsible for overseeing the country’s energy policy and its transition towards greener, more renewable energy sources. While the decision raised concerns in some quarters over the Government’s commitment to decarbonisation, placing energy policy at the heart of a modern industrial strategy under the new Department for Business, Energy and Industrial Strategy could reap dividends in the long-term.

Green light for Hinkley Point

Perhaps the single most highly scrutinised energy issue of the year, and an indirect fallout of the summer’s political drama, was the Government delaying its approval of the planned Hinkley Point C nuclear power station.

The project backed by EDF and Chinese investors was, when first announced by the French government-controlled energy company in 2007, due to be generating electricity by the festive period just a decade later.

Jumping ahead to 2016 and having been approved by Theresa May two months’ later than the industry anticipated, expectations are that the development is unlikely to cook its first Christmas turkey until 25th December 2025 – at the very earliest. This raises serious questions over what will fill the gap left by aging nuclear power stations that are due to close over the next few years. This said, delays to Hinkley Point C present an opportunity for alternative energy sources such as offshore wind, solar and compressed wood pellets to make their case to work together as smart, affordable solutions that could be in place well ahead of 2025.

Whole system costs

The research and thinking around the issue of whole system costs continued to grow. A series of reports from NERA Consulting and Imperial College London showed that intermittent technologies such as wind and solar make managing the national energy grid more expensive in the absence of flexible, dispatchable technologies like biomass. It is only when these hidden costs are taken into consideration that we can truly understand the affordability of different energy technologies.

Recognising the importance of this issue to good policy making, the Government has commissioned its own research on whole system costs, which is due to be published later this year.

Coal closure

2016 saw some important landmarks in Great Britain’s history as a coal-using nation. A 12-hour stretch in May this year was the first time since 1882 – the year GB’s first coal-fired power station went online – that the country was powered for more than half a day completely by other fuels.

Plans outlined last year by then Energy Secretary Amber Rudd had aimed to ban unabated coal power stations by 2025. This year has already seen coal-fired casualties. Full or partial closures of five major coal burning power plants in Great Britain have taken place in 2016: Ferrybridge, Longannet, Rugeley, Fiddler’s Ferry (some units of SSE’s north west coal station will remain active until next year) and Eggborough (re-opened in late September for the winter 2016/17). By the end of 2016, the equivalent of between two and three Hinkley Cs (8 GW) will have come off the system.

While Rudd’s plans still stand, delays to Hinkley Point C and a lack of new flexible power stations being built in Great Britain means that the Government will need to think carefully about how to get coal off the grid in an orderly fashion to avoid a capacity crunch in the early 2020s.

Ancillary = essential; Capacity crunched

Despite the strides made by renewables over the course of the year and the recent boon to the nuclear sector’s future, GB power infrastructure badly needs flexible fuels. The ability to generate more power – or less – in mere seconds when the country demands it is becoming increasingly important with the growth of wind and solar power.

As more offshore wind arrays are constructed and solar farms and roofs proliferate, there are an increasing number of gaps in our electricity supply being filled by power sources that can be dialled up and down when the wind doesn’t blow and the sun doesn’t shine. While Drax and two planned power projects in the North East of England (Lynemouth and MGT Teeside) are turning to a coal-to-biomass conversion and a new build biomass combined heat and power plant to meet these needs, the Government continues to look for ways to encourage companies to build new gas power stations as well as emerging battery storage technologies. A critical route to incentivising these technologies is the not-very-aptly-named ancillary services market. It involves the high voltage electricity system operator in Great Britain, the National Grid, buying services to ensure the lights stay on, the increasingly electric transport sector keeps running and our high-tech world of work stays online.

Energy future

So far there have been some very big changes over the course of the year. However the energy ecosystem in Great Britain should be robust and flexible enough that the transition from coal to low carbon and renewable technologies in the future should be a secure and affordable one. This will require a mix of smart solutions. A key enabling technology will be coal-to-biomass upgrades that can run as both baseload and flexible generators.

The single biggest transformation of our century

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

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.