Biomass boilers burn “biomass”. In theory this could be burning anything that has been recently living, probably plant matter, in a boiler.
We often get questions like:
“can your boiler burn logs and pellets at the same time?”
“Can we burn any sort of wood in your boiler?”
“is it possible to use Miscanthus in your boiler?”
This article is intended to help you in your path towards choosing a biomass fuel that works for your situation and matching it to the sort of boiler that you may want to use.
We are happy to answer questions. Please contact us using the form on the side of the page.
Part 1 – different burning materials
It is possible to burn almost anything. However if you have ever tried to burn plastic then you know that the fumes that are given off are toxic and the gas leaves a residue that is difficult to shift. Therefore when choosing burning materials you can only use materials that will burn cleanly without leaving a difficult to clean residue.
As well as burning cleanly you also do not want to have too much ash left over to clean out of the boiler. Therefore some possible burning materials that leave behind clinker or partially burnt materials and again give you extra work to do.
Different burning materials burn best in different conditions. It is therefore likely that you need different amounts of air to burn each material. Your boiler has been tested for specific burning materials and probably commissioned for one. Unless there are specific claims by the boiler, then it is unlikely that it can burn more than one material at a time.
If you are interested in grants then the biomass materials that you consider need to be approved ie burning them is more beneficial to the environment than burning fossil fuels.
This means that the boilers have to be engineered to only burn “biomass” rather than a fossil fuel. Biomass in the real world is any living matter, but in the world of the RHI it means an accredited boiler where the boiler has been tested to work efficiently with a given fuel. Biomass in the domestic and small business market therefore means:
- Logs – seasoned to at least 20% moisture for good burning and possibly less depending on the boiler
- Pellets – dried to 10-12% moisture and made from virgin sawdust
- Wood Chip – dried to 15% moisture
- There are other fuels that are discussed, but less readily available e.g. cherry stones, pine kernels, olive stones etc which can burn in a small number of boilers
Part 2 Examples of different biomass boilers
Log Burning Boilers
Multifuel Biomass Boilers
Wood pellet boilers
Wood pellet boilers come in lots of shapes and sizes. Most installations are wood pellets. The wood pellet is automated and therefore easier to use. Log boilers can be cheaper but require more space and suit businesses and organisations that can feed a boiler. This could be a farmer who is near to the boiler most days. For those that have to travel to work you want your boiler to provide heat automatically and this may be when you are not there.
Wood pellet boilers use a hopper to deliver pellets to a burning chamber. On domestic models boilers such as the Musa by MCZ or the LP14 by Extraflame have an internal hopper that you would need to fill by hand several times a week during winter. You would probably buy your pellets in bags.
The above diagram shows how the pellets are fed from the hopper (behind) into the burner unit on the LP14. It is a very similar process with all Italian made boilers.
The Pell burner unit mentioned earlier can be fitted onto a WBS boiler or comes as part of a Pelleburn boiler.
Here the pellets are fed from a 500l hopper into the top of the burner and then an internal screw pushes the pellets into the end of the burner where air is applied and an efficient flame results.
The pelleburn can burn up to 94% efficient. This is due to the technology used towards dedicating the burning purely on pellets.
If you have a larger system or do not want to buy bags of pellets, you can get a lorry to blow the pellets into a pellet store. The advantage of this is that you have the extra cost of the pellet store, however you may be able to get a discount on the buying price of the pellets.
Blowing pellets into a pellet store can be very effective for the home owner as they can leave the pellet system working. We find that there is an even split between those people who are quite happy loading their own pellets and those that want to have a pellet store.
If you want a pellet store then you need to consider how to feed the pellets from the store to the boiler. If you can locate the store near to the boiler then you can use another auger to feed in the pellets. Augers are reasonably cost effective and start at close to £1000 for a 3 or 4 meter auger.
If you need to locate your store further away from the pellet boiler then you will have to use a vacuum system. This involves more technology and more pipe. It will push up the cost of your installation by up to £2-5000 depending on the options you go for.
The storage units themselves are designed for either inside or outside. Inside units are a little cheaper, and outside units do not need a special store.
Part 3 Buying biomass fuel
Wood, whether it is wood pellets, wood chip or logs can be a complex subject and off putting to a potential purchaser. The industry recommends only good fuel because you will either get boiler problems or you will need to clean your boiler more frequently. Part of the problem is that a beautifully packed carton of logs from a petrol station can be very expensive.
Look for good wood pellets
Wood pellets need to be approved. You can look for signs such as
Use a local distributor and work with them
Transporting wood pellets is expensive. Getting 1 tonne to your door at your convenience can be very expensive. Distributors work hard to deliver pellets in a system and therefore letting them know in advance what your needs are can bring your costs down.
Do shop around. There are often deals to be done. For instance you may get your 10th tonne free if you are a bulk user.
Logs need some care
Logs can also come from sustainably managed sources, however the difficulty is the moisture of the logs. If you buy them wet or dry or by tonne or volume, you want to know that the wood will work well in your boiler. For instance dry willow will burn very quickly and it is not very energy dense. Ash contains a lot more energy.
You will find that a local supplier is best as logs are heavy and cost a lot to transport.
If you are using your own logs then you will also need to consider how you are going to dry them.
Even dry logs need good storage. If left in the open seasoned timber will still absorb moisture.
When you first get a log boiler then there will be a learning process as you adjust both the cost of the wood that you buy with how well it burns.
Wood Chips also need care
All of the above information is quite general. We are happy to have a conversation about your specific thoughts. Please contact us using 01225 580 401