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Miscanthus: a sustainable alternative to wood fuel

Posted by FairEnergy . on 15 April 2013 at 9:27 am

Concerns that we will eventually run out of biomass wood fuel have been refuted by the Forestry Commission which says it that the wood fuel industry will be sustainable for many years yet.

It estimates that the woodfuel industry could generate £1 billion and support more than 15,000 jobs in the UK. It could also improve the management of English woodlands, around half of which are currently under-managed, as trees in dense woods are thinned to produce the fuel. Opening up the forests will also benefit wildlife. 

According to Forestry Commission chairwoman Pam Warhurst: "about half of the woodland in England is under-managed. This means there is a great deal of wood, at least two million tonnes a year, that could be used for woodfuel and it is just sitting there as woodlands slowly suffer. 

"This could supply enough energy to heat the equivalent of 800 hospitals or 3,000 schools and save 1.5 million tonnes of CO2 a year, roughly the emissions from three million barrels of crude oil."

With this in mind, heating our homes, businesses and social buildings looks perfectly sustainable with biomass (wood fuel).  But there is an alternative. And that alternative is energy crops.

So what are energy crops?

Energy crops are a form of fuel which can be frequently replenished, providing us with a completely sustainable biomass fuel source. At Fair Energy, we regularly receive enquiries about a popular energy crop known as Miscanthus.  Here are some key facts about this rhizome crop:

• Miscanthus is one of the most productive and environmentally friendly means of producing biomass.  It is a true Energy Crop with a 1:33 energy return per ha compared with Oil Seed Rape at 1:4.

• Miscanthus is naturally harvested dry circa 15% annually, therefore producing a higher CV than fuels containing 30% moisture or more.  Growers growing their own fuel on their own land can produce fuel at £0.0625/kwh which includes crop establishment cost, annual harvest and inflation, before the additional benefit of any government-backed RHI payment.

• Miscanthus produces double the yield of woodland and is harvested annually, whilst completing the carbon cycle neutrally.

• DEFRA has said that the UK could grow up to 3.63 million hectares of Energy crop without impinging on food production.

• The oldest Miscanthus crops in the UK are 29 years old and still producing high biomass yields.

Some biomass boiler manufacturers guarantee their systems to burn Miscanthus, so if you are looking to invest in a system and wish to consider Miscanthus as a fuel, this is something you should be checking before you make your purchase as not all systems are suitable.  

The technical stuff

When burning Miscanthus, the burn chamber of the boiler can exceed the temperature achieved when burning regular wood chips.  This is due to the fuel being significantly dryer than wood chip (approximately 40%).  The boiler is therefore not using energy to draw moisture out of the fuel as it combusts, so temperatures can easily exceed 1,000°c.  

The more advanced systems on the market can easily deal with this by factory-fitting a kit which re-circulates exhaust gases during combustion to safely restrict the combustion process to below 1,000°c.  If dry fuel is burnt without this precaution, a process named ‘clinkering’ can form during which molten ash creates volcanic type rocks, which then stick to internal parts of the boiler with damaging effect.

So what does this all mean?

By making your boiler selection wisely, you can future proof your system and ensure a sustainable energy supply.  And if you are someone that has their doubts about wood fuel past 2020, you can opt for an energy crop friendly boiler and you will open many more doors to fuel suppliers in the future.

Picture: Fred Thomson, technical surveyor at Fair Energy

With thanks to Mike Cooper of Miscanthus Nurseries (for factual information).

About the author: Fred Thomson is a technical surveyor and John Fursdon is a senior technical sales consultant at Fair Energy

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

2 comments - read them below or add one

Deepi

DeepiComment left on: 12 May 2014 at 8:31 am

Biomass briquettes are the best sustainable alternative to wood and ohter fossil fuels which is made from briquetting machine or briquette plant. 

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Paul C

Paul CComment left on: 29 April 2013 at 10:42 pm

Interesting article but I am still confused over the conflicting opinions of the major manufacturers.

Obviously Miscanthus is not suitable for many applications due to the additional storage space required over wood chip or pellet.

I note that your ETA boilers have a factory fitted kit to reduce 'clinkering', however as you point out continuity of performance over the lifetime of the boiler is critical to ensure fuel savings and RHI income. 

HDG state that their boilers will run on Miscanthus but will no longer support boilers burning miscanthus as potential premature failure could adversly affect their reputation as a quality manufacturer.

The give the following reasons-

• The increased amount of dust when handling miscanthus fuel

• Practice has shown that the ash content is at least 4 times  higher than with wood chips

• Increased requirement for cleaning the combustion chamber, grate and heat exchanger

• Miscanthus is prone to bridging in the hopper area and may cause fuel starvation issues and excessive wear to the rotary sluice

• Reduced combustion temperature will result in a power loss expected to be at least 25%;

• Significant risk of corrosion due to the ingredients sulphur and chlorine

• The boiler is not type tested for such fuels and as such has no EN testing approval for heat output or emission levels.

My major concern would be premature failure of your boiler outside of the warranty period as a result of burning miscanthus.

Would you please be kind enough to offer your comments on the above points and also how you would deal with a failure outside of warranty that could be attributed to the burning of miscanthus?

Thank you

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