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Biomass fuels and supply

Posted by Gordon Traill on 9 March 2009 at 10:10 am

Biomass fuels encompass a wide variety of products but, not surprisingly, most come from wood.

Clean wood is a wonderful fuel, producing up to 5.5kWh per kg dry matter (dm). Wood pellets produce slightly less, at 4.7 to 5kWh per kg. Most suppliers guarantee moisture content to be less than 10 per cent (often 8 per cent in real life) and 4.7kWh per kg (again this is often nearer 5kWh per kg). The lower levels are stated as varieties of timber vary slightly.

The difference in energy values of softwood and hardwood is also small, with softwood usually having a slightly higher value. Because hardwood is denser, hence heavier, it is often assumed it has more energy, but per kg this is not the case (tonne of feathers, tonne of lead!). Wood also has one of the lowest ash contents of any biomass fuel, as little as 0.5 per cent.

Modern biomass heating systems can burn wood pellets, chip or logs at efficiency levels of up at 95 per cent, which is at least comparable to the best fossil fuel boilers.

So which fuel is most appropriate? And are there concerns about supply?

Obviously the least processed, and hence the most readily available fuel is logs. Woodland produces in the region of seven tonnes of wood dry matter per hectare per year, and normal forestry management ensures a ready supply of suitable fuel. Logs are available in almost all areas of the UK, and of course many people have access to their own. The cost per kWh is likely to be half that of oil, if the logs are purchased.

Wood chip is only slightly more expensive than logs and the boilers which burn chip can be fully automated. The problems associated with wood chip are the cost of the boiler and the space that the chip storage requires. As wood chip is simply logs which have been chipped by a fuel grade chipper (chip quality is very important and arboreal chippers such as used by tree surgeons do not produce consistent length chip), supplies are readily available. Wood chip is the best solution where the heat demand is high and storage space is not a problem.

Wood pellets have been used throughout Europe for many years, with millions of tonnes produced and sold per year. Most is produced from waste sawdust, a by-product of sawmills. This sawdust is then dried and pelleted to produce wood pellet fuel.

Previously most wood pellets were imported, some from Northern Ireland where there is a plant producing over 50,000 tonnes per year, or Austria and Germany. Recently many small to medium plants have opened in the UK, with a great deal more coming on stream in the next couple of years. Wood pellets cost almost as much as oil at current prices, however after the ‘credit crunch’, as fossil fuel prices rise and with increases in supply, the differential will increase.

Wood pellet boilers are the closest in terms of convenience to fossil fuel, being physically smaller and requiring less storage space for fuel, as per cubic metre pellets contain 3 times the energy of chip. Pellet boilers are cheaper than chip boilers and more appropriate for average size dwellings, or where storage space is an issue.

So the choice between log, chip or pellet? We at TRECO supply all three system, all have advantages and disadvantages. Sometimes biomass is not the appropriate technology and we would recommend an efficient conventional boiler, perhaps supplemented by PV and or solar thermal panels, but alas that’s not for me to talk about!

More information about Biomass Boilers on YouGen.

Find a Biomass Boiler installer

Need help with any Jargon?

About the author: Gordon Traill is a founder director of TRECO

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

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Comments

6 comments - read them below or add one

Deepi

DeepiComment left on: 26 December 2015 at 4:53 am

Biomass fuel is the best source to use without creating any type of pollution in the atmosphere. This type of bio fuel can produce through briquetting machine which is manufactured by briquetting machine manufacturers. If anyone want to purchase briquette making machine than please do conact us.

Our website is www.briquettingpressmachine.com

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Caitlin Moran

Caitlin MoranComment left on: 21 October 2014 at 3:46 pm

Hi @Graham Marshall

 As a rough guide

1 tonne of wood pellets  = 1.6 cubic metres 

1 tonne of wood chips  = 4 cubic metres

With wood chips you will have to look at chip size, density of wood and the mosture content.

We can't really answer your second question, it is best to find out what size the manufacturer recommends.

Caitlin -YouGen Team

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Graham Marshall

Graham MarshallComment left on: 18 October 2014 at 5:07 am

The going rate for wood pellets around here is £240 per ton and wood chip £100. You say that pellets contain 3 times the energy of wood chip per cubic metre but how do they compare per ton?

I am ofered wood chip which varied in size from one to four inches. Is there a significant possibility that larger chips will clog the auger leading to fuel starvation in an automated system?

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Golden Coals

Golden CoalsComment left on: 24 November 2011 at 9:24 am

Hello...I can tell you that wood briquettes (Golden Coals) produce 3,629 Kcal/ Kg versus 3,509 Kcal/ Kg for seasoned woodlogs(Ash).  Golden coals wood briquettes are approx 0.7% ash and 8% moisture content which improves on-costs (flue health etc) of burning Golden Coals over seasoned logs with a moisture content of circa 45%.

The efficiency of an open fire is very difficut to assess as there are many factors to consider in terms of draught coming through a room which can depend on windows, door fitting, number of doors etc whereas with a multifuel stove or log burner, the burning environment is controlled.  I guess some of the stove manufacturers will have stats of individual products however the efficiency is incredibly higher than an open fire.

If you wish to try some Golden Coals to sample the eco-friendly high heat-output then please contact us at www.goldencoals.com

Thanks

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Cathy Debenham

Cathy DebenhamComment left on: 27 March 2009 at 11:43 am

Ball park figures for efficiency are as follows: Open fire: 10-20 per cent efficient - so most of the heat goes up the chimney, and it also creates draughts that may cancel out the little heat coming into the room. Log burning stove: these vary considerably from 30 to 70 per cent efficiency. Pellet stove: 80-95 per cent efficiency. I hope that's useful. Cathy

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MGH Trading Ltd

MGH Trading LtdComment left on: 26 March 2009 at 9:02 pm

Gordon. That is an interesting article. You say that biomass heating systems can be as much as 95% efficient. Do you happen to know a ball park figure for the efficiency of an open fire burning logs, and a standard living room wood burning stove?

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