We’ve seen a rise in problems related to the use of poor quality wood chip and wood pellet fuel in our biomass boilers. Although Treco does not supply wood fuel, we know lots of people that do and thought that we would write a feature to highlight the issue and to offer some tips and guidance. Part 1 relates to wood chips and wood pellets.
The benefits of good quality wood chips and wood pellets
Fuel cost caving of up to 80%
When the correct grade and quality of wood fuel is used in Treco’s biomass boilers, fuel cost savings of up to 80% versus fossil fuels has seen our clients save a lot of money by moving from oil or LPG to biomass.
The best performance from your biomass boiler
In addition, when the correct grade and quality of wood fuel is used the performance of the boiler is maximised, enabling peak efficiencies of up to 96% to be achieved and the most heat for your money to be delivered from your biomass boiler
Sustainable and renewable
Unlike our supplies of oil, LPG and mains gas, quality assured biomass fuel is sustainable and renewable so offer futures fuel security in the face of dwindling reserves of fossil fuels.
CO₂ saving of up to 98%
Biomass fuel per se also offer a CO₂ reduction of up to 98% versus electricity and 96% versus oil and LPG. So, for those simply wishing to reduce their carbon footprint, biomass offers an easy way to do so.
Planning, Code for Sustainable Homes, Building Regulations and the RHI
With such significant CO₂ savings and such low emissions from the Guntamatic Powerchip, BMK, Biostar and Biocom biomass boilers, there are a range of benefits to those involved in new build. These range from ease of planning, to compliance with the new maximum emission levels soon to be introduced (summer 2013) in the Building Regulations to gaining advantages in Code for Sustainable Homes Developments. See our overview of how biomass offers advantages in Code for Sustainable Developments here.
The new emission levels to be applied in the Building Regulations will be a maximum of 30g/GJ particulate matter and 150g/GJ nitrogen oxides and this will also be a requirement for all new applications for inclusion in the Renewable Heat Incentive (RHI).
Peace of mind and an easy life
Good quality wood fuel, combined with a robust, efficient and automated fuel delivery system to the biomass boiler, will ensure ease of use and will make switching to biomass from fossil fuels straightforward for the user. Done correctly and with the right biomass boiler system should involve no more effort by the user than will oil or LPG, but can require more effort if done badly.
Problems with poor quality fuel
However, the use of poor quality fuel is one of the most common issues that can result in Treco’s biomass customer support being called out to investigate faults on site. The most common issues that poor quality wood fuel can cause include the following, although the list is not exhaustive;
Reduced boiler performance; burning off water which means a higher unit cost to generate the same amount of heat.
Contaminated fuel increasing your carbon footprint, particularly if you are located in a UK Smoke Control Area.
Fly ash can be generated which is hot and can cause flammable materials to catch fire or injury to persons.
Poorly constructed and maintained fuel stores containing stones or areas where moisture/ rainwater can enter and reduce the quality of the fuel or require more time to reduce moisture below acceptable levels.
The characteristics of good quality fuel
The characteristics of good quality biomass fuel vary, depending on the type of fuel but a general rule is that the fuel should be free from contaminants, metals or any other pollutants and not be 'wet' or have excessive moisture content. Great care must be taken when planning to use wood waste to ensure it does not feature nails, glues or other contaminants. For this blog, we have focused on logs, wood chips and wood pellets.
Logs
For use in the Guntamatic BMK, logs should not be burned until they have been adequately seasoned so they have moisture content below 20%. It is ideal to have no nails, barbed wire or contaminants such as tanalised coatings or preservatives as this will add to the boiler’s emissions, as opposed to delivering the high up to 98% CO2 savings that biomass can offer compared to fossil fuels.
Hard woods will take longer to season (roughly 2 years) than soft woods (1-1.5 years) and the ideal size for use in the BMK log boiler is 500m in length and 12-15cm thick. Coarse wood chips (above G30) can be used in the Guntamatic BMK, but it is important to always cover each load of coarse wood chips with a layer of logs and to always refill with a layer of logs before a layer of coarse wood chips.
Wood chips
The Guntamatic Powerchip, which also burns wood pellets, grain and chopped or pelleted miscanthus, is designed for burning G30 wood chips, with an average wood chip size of 3mm and a maximum moisture content of 30%. It is not advisable to burn wood chips with a significant percentage of water as energy that could otherwise be used to generate heat is used to burn off the water in the fuel.Wood chips then generally fall into 2 categories – bought in or contract chipped on site.
Bought in wood chips
If buying in wood chips, care must be taken to select a supplier who can give you assurances of quality, such as being approved by HETAS against the Woodsure or ENplus fuel quality standards.
A good starting point is to view the Carbon Trust and Biomass Suppliers' List (BSL). Their interactive map enables you to zoom in and locate suppliers in your area and filter by both fuel type and either Accreditation by ENplus or Woodsure. We like it so much we have included it on the Treco website.
It is also important to visually inspect any delivery of wood chips to ensure that it does not contain nails, barbed wire, animal carcases or other contaminants that may reduce the performance of your boiler. A moisture meter can also be a great way of establishing if your wood chips have the ideal below 30% moisture content.
Contract chipped on site
If you have your own supply of wood fuel, the largest savings of up to 80% versus fossil fuels can be made, with prices of £50 per tonne being achievable. However, there are a range of considerations relating to quality. Firstly, the wood fuel needs to be seasoned so that moisture levels are below 30%. The time taken to season the wood fuel can be between 1-2 years, with hardwoods taking longer to season than softwoods. Once the logs are seasoned and dry enough to burn efficiently, a large number of our clients are making use of the contract chipping service that a number of local suppliers offer. However, it is very important to ensure that the chipping machine that the supplier uses enables fuel quality chips to be made, which conform the G30 fuel standard.
Whether you buy in or chip your own wood fuel, further consideration needs to be given to fuel storage. The fuel store needs to be regularly swept (just before refill) in order to ensure there are no stones or other foreign objects that may reduce the boiler’s performance. Additionally, the fuel store needs to be set up so that water cannot enter and there is sufficient ventilation to allow your wood fuel to breathe. There are other considerations, so do take a look at our fuel delivery systems, which give a range of other tips and bits of advice.
Wood pellets
They should be dry, clean, mechanically robust and to the appropriate fuel grade standard, with no additives or binding agents. Wood pellets are generally made from sawdust, with their structural integrity achieved by compression at the pellet processing plant. Treco’s biomass boilers require 6mm diameter wood pellets to the EN14961 fuel standard and with a maximum moisture content of 10%. We recommend only using quality assured suppliers, to get the most heat for your money.
For use in the Guntamatic Biocom, the ideal characteristics of wood pellets should be 5-30mm in length and 5-6mm in diameter, with a water content of 8-10% and ash content of 0.5%. This gives a bulk weight of 650kg/m³ and 4.9kWh per kg.
Wood pellets should also be mechanically robust, with to avoid disintegration, with a hard and shiny surface, to enable them to easily flow through the boiler’s fuel delivery system. If the wood pellets are not, they may turn into dust, which will not work well in the boiler.
As a general rule, wood pellets should be stored in absolutely dry storerooms, with adequate ventilation and the appropriate levels of fire protection. There are other considerations, so do take a look at our fuel delivery systems, which give a range of other tips and bits of advice.
We will be blogging other tips and advice regarding wood fuel supply over the coming months, so do watch this space!