- Renewable Energy
Choosing a biomass boiler
The choice of boiler depends on the type of fuel to be used. You must ensure that the fuel you have chosen and the equipment you are thinking about buying are compatible.
There are some boilers that have multi-fuel capability, but only operate within certain parameters.
Straw has a lower combustion temperature than wood and a tendency to produce clinker (lumps of solidified ash). For best results, a boiler with a water-cooled grate should be selected, but in some cases other designs can work well. Check the specification carefully with your supplier.
There is also a choice of ancillary components that help to reduce the daily maintenance requirements and save labour costs. These options include:
- Flue gas cyclones: These take the fly ash out of the flue gas and collect it into a container. They are relatively inexpensive and remove ash that would otherwise be emitted into the atmosphere. They also reduce the need for cleaning nearby areas, such as glasshouse roofs. In some circumstances, they may be a mandatory requirement. This depends on the local air quality / planning circumstances.
- Automatic fire tube cleaning: This maintains the boiler efficiency by automatically cleaning the fire tubes which exchange heat between the hot combustion gases and the boiler water. Regular cleaning removes the ash and soot deposits that can reduce efficiency. Different manufacturers use different cleaning methods. One example is the use of jets of high pressure air that are sent through the boiler tubes every five hours of operation.
- Automatic de-ashing: This process automatically removes the bottom ash from the combustion chamber into a bin, avoiding the need to shut the boiler down for manual cleaning.
Other equipment is dependent on specific site requirements, such as the type of fuel and volume required. The main additional items are fuel storage, reception and feed systems, heat stores, expansion vessels, fire protection and system control equipment.
- Biomass fuel stores need an agitation system to make sure that the fuel flows reliably into the fuel transfer system that feeds the boiler. For small stores holding up to approximately 50m3 of wood chip, a design incorporating a sweeping or rotary arm is common. Stores of this type are suitable for boilers up to 500 kilowatts (kW).
- Thereafter, a walking floor solution is commonly used. This design is capable of handling large volumes of fuel. Realistically, a large barn is required for fuel for storage and this should be designed so that deliveries can go into a store. Suitable clearance for tipping from the delivery vehicle should be provided.
- Because of its lower calorific density, straw burning requires additional space for a feed conveyor. This conveyor is usually long enough to hold one day’s worth of bales. A large storage area, lifting equipment such as a fork lift, and chopping or shredding equipment at the end of the conveyor are also needed.
All of the aspects of a project are interconnected. Ensure that you:
- Carefully research the performance of the boiler and other equipment you are thinking about purchasing. This is especially important for fuel specification parameters.
- Balance the cost of automation with any operational efficiency benefits and labour cost savings it can achieve.
- Take into account the space required for the installation you are considering.