The hidden cost of poor quality fuel

Part 2

3 minute read

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Further to yesterday’s post about the hidden cost of poor quality wood fuel, today’s article looks at the use of grain and miscanthus as fuel in biomass boilers and offers some guidance on what constitutes good quality fuel for use in Guntamatic Powerchip, Biocom or Powercorn biomass boilers.

How to get the best out of grain (oats, wheat, barley)

Grain can be an economical and convenient fuel for use in biomass boilers. All types of 'pourable' grain such as oats, wheat and barley (all which have a low nitrogen content) can be used in Guntamatic’s Powerchip, Biocom and Powercorn biomass boilers.

Grain must not be used in our biomass boilers with a residual moisture content of more than 13%. Otherwise, energy that would be used to generate heat is used to burn off water, which reduces the boiler’s performance and gives less heat for the same amount of fuel and the same cost.
 As the fusion point of grain ash (which is the point of clinker formation, where the fuel forms lumps which can reduce the boiler’s performance) is around 700°C, compared to wood ash at 1,200°C.

The moving, self-cleaning step grate in the Guntamatic Biocom, Powercorn and Powerchip biomass boiler helps keep fuel moving and prevents clinker from causing problems within the boiler and reducing its performance.

It is also advisable to add approx. 0.3–0.5% by weight of slaked lime (calcium hydroxide Ca(OH)2) to the fuel before use in boilers with ratings up to 50kW and 0.5–0.8% for boilers with ratings over 50kW. That increases the calcium content of the fuel, thereby raising the ash fusion point and reducing the amount of clinker that can form in the first place.

The calorific values of grain can vary slightly, with barley giving 4.3-4.4kWh per kg and wheat giving 4.5-4.6kWh per kg. Grain is a slightly denser fuel than miscanthus, so will require less space to store for the same amount of heat.

Miscanthus

Miscanthus,(or 'elephant grass') is a perennial grass originating from Asia. It is becoming popular as an energy crop as it can easily and quickly grow on poor quality land, with no need for fertilisers or very much intervention, making its cultivation relatively simple and straightforward.

The crop offers a limited yield in the first year of cultivation and harvesting usually takes place in the 2nd or 3rd year. Crops can reach three to four metres in height and have a lifecycle of up to 20 years.  The dried straw from the plant’s stems is harvested annually from the 3rd year of cultivation using a combine harvester and then chopped. The crop should have a maximum moisture content of 20% when used in our biomass boilers.

Miscanthus can be used as biomass fuel in pelleted or chopped for in Guntamatic Powerchip, Powercorn and Biocom biomass boilers. These boilers, when set up for miscanthus, are supplied with a special stainless steel firebox liner in order for the biomass boiler to cope with the acidic nature of this fuel.

Miscanthus has to be stored dry, with sufficient ventilation and must not have a moisture content above 15%. It should also conform to the W20 fuel quality standard for air dried chopped or pelleted miscanthus or W30 for fuel which is suitable for storage and drying.

Miscanthus has a calorific value of 3.6–4kWh per kg and a weight of 70-90kg per M3. With a slightly denser make-up, miscanthus will need slightly more space than grain to store enough fuel to generate the same amount of heat.

The fusion point of miscanthus ash (which is the point of clinker formation, where the fuel forms lumps which can reduce the boiler’s performance) is around 900°C,  compared to wood ash at 1,200°C. The moving, self-cleaning step grate in the Guntamatic Biocom, Powercorn and Powerchip helps keep fuel moving and prevents clinker from causing problems within the boiler and reducing the boiler’s performance.

In addition, it is advisable to add approx. 0.3–0.5% by weight of slaked lime (calcium hydroxide Ca(OH)2) to the fuel before use for boilers with ratings up to 50kW and 0.5–0.8% for boilers with ratings over 50kW. This increases the calcium content of the fuel, thereby raising the ash fusion point.

We do hope the information above is useful, but please do contact the team if you have any questions.

Do you have a biomass or low carbon project?

Speak to our biomass team today

01884 250 790

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