Tag: wood pellets

This is how you unload a wood chip truck

30 June 2017

Sustainable bioenergy
Truck raising and lowering

A truck arrives at an industrial facility deep in the expanding forestland of the south-eastern USA. It passes through a set of gates, over a massive scale, then onto a metal platform.

The driver steps out and pushes a button on a nearby console. Slowly, the platform beneath the truck tilts and rises. As it does, the truck’s cargo empties into a large container behind it. Two minutes later it’s empty.

This is how you unload a wood fuel truck at Drax Biomass’ compressed wood pellet plants in Louisiana and Mississippi.

What is a tipper?

“Some people call them truck dumpers, but it depends on who you talk to,” says Jim Stemple, Senior Director of Procurement at Drax Biomass. “We just call it the tipper.” Regardless of what it’s called, what the tipper does is easy to explain: it lifts trucks and uses the power of gravity to empty them quickly and efficiently.

The sight of a truck being lifted into the air might be a rare one across the Atlantic, however at industrial facilities in the United States it’s more common. “Tippers are used to unload trucks carrying cargo such as corn, grain, and gravel,” Stemple explains. “Basically anything that can be unloaded just by tipping.”

Both of Drax Biomass’ two operational pellet facilities (a third is currently idle while being upgraded) use tippers to unload the daily deliveries of bark – known in the forestry industry as hog fuel, which is used to heat the plants’ wood chip dryers – sawdust and raw wood chips, which are used to make the compressed wood pellets.

close-up of truck raising and lowering

How does it work?

The tipper uses hydraulic pistons to lift the truck platform at one end while the truck itself rests against a reinforced barrier at the other. To ensure safety, each vehicle must be reinforced at the very end (where the load is emptying from) so they can hold the weight of the truck above it as it tips.

Each tipper can lift up to 60 tonnes and can accommodate vehicles over 50 feet long. Once tipped far enough (each platform tips to a roughly 60-degree angle), the renewable fuel begins to unload and a diverter guides it to one of two places depending on what it will be used for.

“One way takes it to the chip and sawdust piles – which then goes through the pelleting process of the hammer mills, the dryer and the pellet mill,” says Stemple. “The other way takes it to the fuel pile, which goes to the furnace.”

The furnace heats the dryer which ensures wood chips have a moisture level between 11.5% and 12% before they go through the pelleting process.

“If everything goes right you can tip four to five trucks an hour,” says Stemple. From full and tipping to empty and exiting takes only a few minutes before the trucks are on the road to pick up another load.

Efficiency benefits

Using the power of gravity to unload a truck might seem a rudimentary approach, but it’s also an efficient one. Firstly, there’s the speed it allows. Multiple trucks can arrive and unload every hour. And because cargo is delivered straight into the system, there’s no time lost between unloading the wood from truck to container to system.

Secondly, for the truck owners, the benefits are they don’t need to carry out costly hydraulic maintenance on their trucks. Instead, it’s just the tipper – one piece of equipment – which is maintained to keep operations on track.

However, there is one thing drivers need to be wary of: what they leave in their driver cabins. Open coffee cups, food containers – anything not firmly secured – all quickly become potential hazards once the tipper comes into play.

“I guess leaving something like that in the cab only happens once,” Stemple says. “The first time a trucker has to clean out a mess from his cab is probably the last time.”

Forests, sustainability and biomass – the expert’s view

Matthew Rivers, Director of Corporate Affairs, Drax, Group Special Advisor

6 October 2016

Opinion

It was a forestry catastrophe that first inspired Matthew Rivers’ interest in forests.

Dutch Elm trees, an iconic part of the UK landscape for over 250 years were becoming infected with a fatal and fast-spreading disease. The race was on to save them.

A schoolboy in North London at the time, Rivers joined the after curricular school team tasked with saving its trees – first by injecting them with insecticide, and when that didn’t work, by felling and replanting them. It was an early foundation in how forests work and the challenges of keeping them healthy.

Decades later, Rivers is Director of Corporate Affairs at Drax. It’s a role he finds himself in following a career as a forester, helping to manage forestry businesses, and supporting the setting up of wood product manufacturing plants.

His own estimation of his working life is a humble one, however. “I think I’m probably a failed farmer,” he says.

“A forester always plants in hope.”

Rivers studied forestry at university in Scotland before taking up jobs in the forestry industry across the UK, Uruguay and Finland. Working in this industry, he says, is one that requires patience.

“In the UK we’re talking about 30- or 40-year growth cycles. The trees I planted at the start of my career are only just coming to maturity now,” he explains.

But more than the long investment of time, being a forester relies on faith. “A forester always plants in hope,” he says. When a forester plants a tree, he or she most commonly does not know who the end customer will be.

So when the call came from Drax for a forestry expert to help guide the company through an important transformation – upgrading the power station from coal to biomass – the challenge was one he was ready to take.

“Drax already had ambitions of converting three boilers to run on biomass. That would mean consuming tonnes of compressed wood pellets,” he says. The business needed a supply, and Rivers was drafted in to set this up.

As part of the supply solution, and Chaired by Rivers, Drax set up Drax Biomass, a pellet manufacturing business in the USA that makes and supplies compressed wood pellets to Drax Power Station.

Setting up its own manufacturing plant not only means Drax needs to rely on fewer external suppliers, but also that it can use the learnings about the technologies, the economics and the sourcing of the process to continually hone its supply chain.

To operate responsibly and receive governmental support, Drax has to be sustainable, and this is particularly important when it comes to where and how it sources its fuel. This comes with its own challenges.

No universal definition of sustainability

“To my understanding, there is no universal definition of sustainability,” says Rivers. So how do you proof your business for an unclear entity?

“At its heart, sustainability is about not doing anything today that would prejudice doing the same thing for the next generation or generations to come.”

A responsibly managed forest is one that is as healthy, productive, diverse and useful in 100 or 500 years’ time as it is today. They key to this, is to think of forests as a whole.

Rivers explains: “Think about a single tree – you fell it and use it to heat your home over one winter. But it’s going to take perhaps 30 years for that tree to grow back,” he says. “What do you do for the next 30 years?”

“In a sustainably managed forest you have all different ages of tree represented – one thirtieth devoted to each age- and, when you use an older tree to warm you in winter, you plant a replacement. That way, for every year you’ll have trees reaching maturity ready to provide your power.” It’s a cycle that, if managed responsibly, keeps delivering a useful resource as well as maintaining the health of the forest.

Rivers continues: “Sustainability is the very nature of what a forester does; because if we don’t take care of our forests, and ensure we have a crop to harvest year after year, we lose our livelihood.”

forests_trees_growing_for_winter_heating_smh4nj

Becoming a private forester

Two decades ago, Rivers completed a loop he started decades ago amidst the Dutch Elm crisis and became a forest owner himself. In Scotland, he bought, and now manages, his own private forest.

“We’ve had kids’ birthday parties, we’ve dug out a pond, we harvest chanterelles in the autumn – there’s a millennium capsule buried somewhere,” he says.

It’s not only a family heirloom. It’s a place for him to exercise a passion – maintaining and managing a responsible and healthy forest.

 

This is how you make a biomass wood pellet

Sustainable bioenergy
Compressed wood pellets

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

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

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

The wood arrives to the yard

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

Bark is removed and kept for fuel

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

Thinned wood stems become small chips

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

Chips are screened for quality and waste is removed

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

The biggest hairdryer you’ve ever seen

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

Wood pellet Hammer Mill

Small woodchips become even smaller woodchips

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

Putting the chips under pressure – a lot of pressure

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

Resting and cooling down

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

One of the biggest domes you’ve ever seen

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

Inside the dome

Sustainable bioenergy

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

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

Atmospheric control

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

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

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

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

Neutral nitrogen

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

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

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

The big ear inside the dome

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

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

Other tools and tricks

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

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

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

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

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

The single biggest transformation of our century

Sustainable bioenergy

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

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

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

Finding a new fuel

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

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

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

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

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

“That was the Eureka moment,” says Price.

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

A change in attitude

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

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

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

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

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

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

The final hurdle

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

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

Toward a coal-free future

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

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

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

The biggest balls of electricity generation

Power generation

When making a cup of tea, it’s unlikely you consider the industrial equipment kicked into action the moment you switch on your kettle. And of all of the activity going on behind the scenes, it’s even more unlikely you think about a 1.2-tonne steel ball.

But without a number of 1.2-tonne balls and the electricity they help generate, your kettle would be nothing more than a fancy jug.

How do giant balls help to generate power?

The answer lies in the way fuels like coal and compressed wood pellets are used to power boilers and generate electricity. Drax started its life as a coal power station, but today it is in the process of upgrading to run on biomass. Progress has already been made – three of the station’s six units already run on compressed wood pellets, Drax’s biomass fuel, generating around 20% of the UK’s renewable electricity.

To generate enough power to supply 8% of the UK’s demand – as Drax does – a lot of fuel is needed. Hundreds of thousands of wood pellets are delivered to Drax every day, arriving on custom-built trains travelling from the Ports of Tyne, Hull, Immingham and Liverpool.

The pellets pass through a system of conveyor belts until they arrive at one of four massive conical storage domes, located on site in Yorkshire. Before the wood pellets can be converted into fuel, they need to be crushed: this is where the balls come into play.

The pulveriser

The wood pellets used at Drax are compressed and dried wood that is formed into small capsules the size of a child’s crayon. But, like with coal, to get the best results in the power station’s huge boilers, the material needs to be turned into a very fine powder in pulverising mills. When very fine, the fuel burns as efficiently and as quickly as a gas.

Inside each mill are 10 giant steel balls that grind down either the wood pellets or coal. Each ball is three quarters of a metre in size, made of hollow cast steel alloy and weighs roughly 1.2 tonnes – equivalent in weight to British-made Jaguar XE mid-sized saloon car or an entire football team.

And to make sure that each one is up to the task of extreme pulverisation, they need to be hard. Each one is heat treated during manufacture to make sure they’re up robust enough to consistently crush raw fuel.

The benefit of this durability is that they can readily pulverise fuel to feed Drax boilers, to power kettles across the country – a big responsibility for a big ball.

How does Europe use biomass?

Sustainable bioenergy
Family on summer Senja coast (Norway, polar day)

At the heart of Norse folklore is a figure called Yggdrasil that connects its nine worlds and gods. It’s an immensely important and holy icon, but it is not a god itself – it is an ash tree.

That the central figure of mythical Scandinavian cosmology should be something as humble as a tree is no surprise, Scandinavia is a heavily forested region. Sweden, the largest country in the area, is more than 68% forest. Wood is an inherent part of life there. For thousands of years it’s been used as a resource and a fuel, and today is no different.

Throughout much of Europe the same is true. But, while historically wood was used only for cooking, heating and light, today its use as a form of energy also includes generating electricity and heat when formed into compressed wood pellets.

Europe and wood pellets

Nearly 22 million tonnes (Mt) of wood pellets were used in the European Union in 2015, making the region the leading wood pellet consumer in the world. It is also the world’s leading producer, creating roughly half of the world’s global output – largely from European trees.

A report from the Standing Forestry Committee, set up to represent the forestry industries in EU countries, found that just 4% of the woody biomass used in the EU was imported.

Of the 22Mt used across Europe, 10.5Mt was used for heating, while 11.5Mt was used for industrial uses like fueling power plants. But in the UK, the level of wood used for fuel falls some way behind EU averages. Thanks in large part to Drax and its transition from coal to renewable wood pellet-powered electricity generation, that’s changing, but the UK still has a way to go to catch the continental average.

Where is the UK falling behind and how is wood being used to power the rest of the continent? Here, we look at some of the largest consumers and producers of biomass in Europe and how it’s being used.

Sweden

Sweden is the third highest consumer of wood as a source of energy in Europe, trailing only Finland and Latvia in its use. A key use of biomass in Sweden is powering district heating systems. In a district heating system, rather than each building or home having its own boiler, whole areas of cities are heated through a single central plant distributing heat to buildings. These plants can be powered by a variety of fuels, but many run on wood pellets or distribute the waste heat captured at power plants.

rax_europe_biomass_sweden

Germany

In 1713, an accountant and mining administrator, Hans Carl von Carlowitz, published what is considered the first ever book to look in depth at forestry management, effectively kickstarting the modern idea of sustainable forestry. In the 300 years that have passed, Germany has embraced the cultivation of wood and has made wood and biomass a fixed part of its energy makeup.

More recently, the Renewable Energy Heating Act and Market Incentive Programme was passed in 2009, which requires new building owners to provide a percentage of their heat from renewable sources, including wood-fired boilers. The aim is to increase the country’s share of renewable heat to 14% by 2020.

Europe, Biomass, Germany

Finland

Nearly three quarters of Finland is forestland, making it one of the most forested countries in the world, let alone Europe. As a result, wood plays a large part in Finnish culture. Stora Enso, one of the world’s leading paper and packaging manufacturers is Finnish and more than 20% of the country’s exports are from wood and wood products. Coupled with a strong focus generating much of its energy from renewables, energy derived from wood and products made from wood is high.

drax_europe_biomass_finland

United Kingdom

In 2013, less than 10% of all energy used in the UK was generated from wood and wood products. This places it some way behind countries like Germany and Sweden, in part owing to a lack of infrastructure for providing heating derived from wood and wood biomass.

This could change if the government continues to back technologies equally in initiatives like the Renewable Heat Incentive (RHI). Available to homeowners, landlords and commercial customers, RHI provides incentives for installing generators of renewable heat such as wood pellet boilers.

To reach climate goals, the then Department of Energy and Climate Change noted that both biomass-driven electricity generation and heating should continue to increase in the UK. And with the upgrade of Drax and Lynemouth power stations from coal to compressed wood pellets, there are positive signs the UK can catch up to the European biomass average. In doing so, renewable biomass electricity generation can also help increase wind and solar power generation in the UK, and help create a more sustainable energy future.

drax_europe_biomass_united_kingdom