Tag: engineering

This train isn’t like any other in the UK

25 November 2016

Sustainable bioenergy
Man standing in front of train

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

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

Moving a modern fuel

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

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

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

DRATECH19_Train_crane_In_line_dp7ney

Putting a lid on it

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

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

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

The big problem: space

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

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

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

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

DRATECH19_Train_Journey_In_Line_dgx81z

Bigger wagons, better economy

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

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

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

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

What does an Instrument Craftsperson do?

10 November 2016

Power generation
Instrument Craftperson in action

How do you go about fixing a turbine that, on a normal day, spins 3,000 times every minute? The first port of call is to call in someone like Alice Gill, an Instrument Craftsperson at Drax Power Station. 

What does an Instrument Craftperson do?

What I do is maintain and repair the equipment that links the outside power plant and the control room – equipment that tracks temperature, levels or positioning that then informs our operators in the control room what’s happening on the plant.

Things like an oxygen analyser. It’s a probe that sits in the boiler and monitors the oxygen level so the operator can ensure the correct ratio of fuel to air is going into the boiler to reach optimum combustion.

I might be called on to do calibration checks on that sensor to ensure that it’s working properly. Or I might be asked to completely remove it and then to repair it.

How did you come to be doing this job?

I’m not the sort of person who likes to sit down at a desk all day – I’m more of a hands on sort of person. My dad was always working and fixing things in the garage at home and I liked being in there with him.

When I was at school I decided I didn’t want to go to university so started applying for apprenticeships and looking into engineering opportunities. Drax was one of those schemes and was the one I most wanted to be selected for – luckily enough I was offered a place.

The apprenticeship was four years and there are loads of training courses and so much to learn, including hands on experience and working in the plant.

I remember first arriving to the power station and not really believing the scale of the place. You think, ‘How am I ever going to find my way around?’, but you soon get used to it and it becomes the norm.

In September I became a full Instrument Craftsperson so now I can really get stuck in.

Alice Gill at Drax Power Station

“I’m not the sort of person who likes to sit down at a desk all day – I’m more of a hands on sort of person.”

What sort of challenges do you face?

Over the summer I’ve been doing a lot of work on the turbines. It’s a big job as they’re one of the most important elements driving the plant and generating the power. During outages the whole thing gets overhauled and given a full health check.

The turbine team needs to get into machinery, which is densely constructed and put together, so it’s my job to go in and carefully remove instrumentation so they can access it. When they’re done, I have to go back in, refit everything and check it’s all working again.

How do you do that?

When you’re removing the instruments it’s a bit more of a ‘just get it off’ approach – you just make sure you get it off safely without damaging it.

Then when we’re refitting it, we’re out there with our multimeters making sure we’re setting different probes at the right voltages and that everything is calibrated correctly.

There’s a screen in our workshop we use to watch the activity of the turbine so we can see the speed of the turbine creeping up as they switch it back on. It’s always a big moment. You know things are going to be alright because you’ve done everything, but there are still some nervous people in the room. The turbines are spinning at 3,000RPM so you really need it all to be working properly.

Is there anything that could wrong on an average day?

One of the biggest things that could go wrong in my area is the potential to trip an entire generating unit. It might be that you over-pressurise something or you accidentally trigger a switch that then sets off a daisy chain of events that ends up in a unit tripping. Tripping is where the unit turns off which basically leads to a total shutdown in electricity generation from one sixth of Drax Power Station.

There’s something called the 660 club – at full load the units are operating at 660 MW so if you trip one you enter into this infamous club. There are a few guys in the 660 club but thankfully I haven’t joined! When operating at full load of 660 MW, our units supply the National Grid with around 645 MW– enough to power an entire city.

What do you do outside of work?

I’ve got a horse called Red – I’ve had him for seven years but I’ve been riding since I was eight. It’s quite different to working with things that do exactly what you tell them. When you get on the horse he just does what he wants – he’s got a mind of his own. It’s a big change!

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

27 October 2016

Power generation
Reparing the colling tower at Drax Power Station

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

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

Ladder up a Drax cooling tower

What could possibly go wrong?

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

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

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

Surveying the damage

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

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

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

A 3D model of a Drax cooling tower

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

Engineering at an altitude

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

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

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

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

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

Repairs on Drax Tower 3B

Regular repairs

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

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

Summer in the station

6 October 2016

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.

 

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.