The beauty of biomass

As power generators look to biomass as a vital ‘green’ ingredient, for co-firing with coal or firing on its own, many ports see potential big business on the horizon.

Logically, ports that have traditionally been part of the supply chain serving coal-fired power stations would be expected to take up the opportunities. But therein lies a problem, or several problems – including dust, risk of fire and/or explosion, and the need for significant areas of covered storage and specialised handling systems.

“It isn’t just a matter of using the same assumptions as when handling coal, and just using the same equipment and processes for biomass,” says Yannick Tilley, international sales and business development manager at the Geldof Metaalconstructie, the Belgian supplier of components and solutions for storage and handling of bulks.

“Biomass is a material that requires particularly careful attention. There are numerous examples out there of people not treating biomass, and especially wood pellets, with the necessary safety precautions in mind – and they can find themselves facing explosion or fire. And even if you have the most far advanced handling system on the quay, it is still important to check the material coming in. We have heard stories of ships coming in with the biomass already smouldering.”

Too many people mistakenly assume that biomass is ‘just another bulk’ and that somehow it will seamlessly follow coal from quay to power station, says Mr Tilley.

However, the differences are significant. When handling coal, dust problems can be resolved by using water sprinklers. Wood pellets, when handled, create a lot of dust – and there is already a certain percentage of dust within the material, which can potentially cause an explosion. But wood pellets must be kept dry, because if moisture levels get too high, they can disintegrate or the moisture will speed up the biological activity within the pellets which could lead to combustion.

“That has an impact, because the belt and transport systems must be covered – and that affects the design and price of the system.”

Another key factor is quantity.

“People forget that wood pellets are a lighter, more voluminous product,” says Robert van Muiden, general manager of Van Uden Bulk Logistics in Rotterdam.

“In the same ship, you might carry 50,000 tonnes of coal – but only 30,000 tonnes of wood pellets. In the same warehouse, where you normally might fit 10,000 tonnes of coal, maybe you will fit 6-7,000 tonnes of wood pellets.

“All the terminals are saying millions of tonnes of wood pellets are coming. There were 1.2m tonnes through Rotterdam last year – which sounds impressive, but is a flea bite compared with coal.”

And then there is the comparative calorific value; the calculations show that for every tonne of wood pellets versus coal, the biomass option is twice as expensive and offers half the caloric value, points out one industry expert.

In the rush to be green, he says, politicians have focused on subsidies for power stations but no one has thought about the investments required in ports or trains. Coal wagons are open; wood pellets must be carried in enclosed wagons.

Robert van Muiden says: “A supply chain includes all the costs from origin to end user. People should be aware that logistics costs can kill a project, or make it.”

Wood pellets are a clean, renewable, carbon-neutral biomass fuel, says Andrew Moffat, chief executive of the Port of Tyne.

The Tyne has led the way in the handling of wood pellets, with throughput last year of nearly 1m tonnes. This was all for the Drax power station, served by rail from the quay; the port is also in talks with other generators about potential biomass imports.

“It’s important to recognise that handling biomass isn’t like handling coal just because it is going down the same supply chain to the same end user,” says Mr Moffat. “Wood pellets are basically softwood sawdust compressed using steam. I would say there are a lot of similarities with grain. For example, there is a high moisture content – the cargo can heat up and combust, if left alone, and that is one of the challenges.”

And while combustion in coal can be dealt with by raking out the stack outside and using water sprinklers, clearly that’s not an option for pellets. They would disintegrate and become unusable. Stock rotation is important: “You have to make sure you are moving stock around and aerating it, so you don’t get heat spots and potential combustion.

“Another issue is dust. When you handle the wood pellets, you get degradation of quality, leading to further dust.”

The Port of Tyne describes its first year of handling wood pellets as “both challenging and fruitful”. It invested an initial £20m in a dredging project and the construction of a biomass handling, storage and transportation facility which it believes is the most advanced of its kind in Europe, added another £1m to make some short-term modifications, and in January this year installed two new specialist hoppers, total cost £2.2m. These are equipped with extractor fans to remove dust and return it to the cargo.

The wood pellets are unloaded on the quayside using traditional grabs, operating behind a forced air curtain to keep the dust contained. The cargo is fed through the hoppers, transported to the shed and subsequently moved by covered conveyor to a silo for automatic top-loading of trains as required.

“You could cut corners and go for a least-cost solution but if you are not careful you will get environmental issues, whether that is dust or potentially storing for too long and risking fire,” says Mr Moffat. “We are a key element of the supply chain and believe that you need to invest properly, as we have done. We handled nearly 1m tonnes last year. The potential is huge.”

Geldof has provided biomass handling solutions for logistics and utility customers throughout Europe – among recent projects, the company delivered a wood pellet handling installation for the Electrabel Gelderland power plant in the Netherlands, where barges are unloaded pneumatically at 500 tonnes/hour via a mobile unit that eliminates dust emissions. The complete circuit, from quay to boiler, uses closed conveyor belts, silos, hammer mill and buildings kept under slight pressure to avoid the escape of wood dust.

Yannick Tilley says people tend to talk about biomass as one type of cargo, when the variety is considerable in both quality and handling requirements.

“One of the biggest misconceptions is that wood pellets, wood chips and waste-wood (often processed from demolition sites) can be treated in the same way.”

It is logical that ports want to maximise flexibility and storage, he says. “And of course people on the power side also want maximum flexibility; they have no idea what long-term or medium-term contract they can secure for their supplies, and they want to keep their options open.”

But the materials are very different in their physical properties, he emphasises. Wood pellets tend to be free-flowing and need to be kept dry. Wood chips are less sensitive to moisture and do not have the same dust-related problems. But they tend to stick together, which potentially gives a lot of problems with transport. And because waste-wood often comes from old furniture and fittings, residues of paint and other coatings can be an environmental issue.

“If you just mix it all up and try to come up with a one solution fits all type of installation, it becomes very technically very hard,” says Mr Tilley.