A biomass boiler is classed as a solid fuel appliance and as such produces a waste product, apart from flue emissions, this waste is ash. Ash production is around 3% for wood chips at 30% moisture content and much lower for pellets at around 1%.
Ash is a highly insulative material and due to the nature of the passage of exhaust gases through the boiler and the combustion process, coats steel surfaces in contact with it very easily. If ash is coating a particular area of the heat transfer section in a biomass boiler, then heat dissipation is greatly reduced. If the heat transferred has been reduced then more fuel is required to be burnt to get the same amount of energy from the boiler.
In order to maintain the thermal efficiency of a boiler, it is important that it is cleaned regularly.
Different manufacturers give different recommendations. Typically there should be a minimum of one main service a year. Two services would be more effective and these do not necessarily need to be 6 months apart. It is more appropriate to service the plant proportionally with the actual operational hours of the boiler.
Large biomass boilers have a greater number of safety systems, motors, fans, cleaning components etc. and these items generally have a quarterly servicing regime.
Over and above the main services the boiler should be cleaned, lubricated and visually inspected on a regular basis.
There are a variety of signals which may mean that your boiler needs servicing. The boiler may have a few or all of these indicators:
• Excessive visual levels of unburnt fuel within the ash deposit chamber
• Excessive visual levels of soot within the combustion chamber
• Excessive levels of clinker within the combustion chamber (clinker is solidified ash which has been taken past its melting point and allowed to cool)
• Excessive black smoke production during combustion
• Large yellow, wispy flames within the combustion chamber
• Excessive flue gas temperatures at exit point of boiler (indicates heat exchanger lining is coated with ash/debris and is acting as insulator, preventing correct heat exchange of flue gasses to water jacket)
• Adverse fluctuations in the O2 content of the flue gasses causing incomplete/inefficient combustion
• An engineer’s analysis of the flue gases may show incorrect combustion reflected in adverse readings of CO, CO2, NOx, SO2 and the CO-CO2 ratio results.
This depends on the level of boiler cleaning automation, customer servicing ability and fuel type and quality. Typically, the efficiency could be improved with servicing by between 7% and 15%, depending on the condition of the boiler.
The most important thing is continue to monitor fuel quality and consumption. The higher the quality of the fuel, the more efficiently the boiler operates. Burning the fuel at maximum efficiency results in less maintenance and cleaning. This leads to reduced maintenance and running costs and ensures the boiler maximises its operational lifetime.
Apart from emptying the ash box regularly and keeping the boiler free from obstructions and general dirt the modern biomass boilers are pretty much self monitoring. ETA’s Web based monitoring system makes keeping an eye on your boiler a breeze.
Having a well serviced and maintained biomass boiler plant and associated wet heat distribution system will maximise RHI income. It makes sense to get a biomass boiler serviced to be able to budget effectively.
Summer service
A visit during the summer period when the boiler will need to be switched off 24 hours prior to the visit. Work includes:
• Internals within the heat exchanger are thoroughly inspected and cleaned. All airway ports, primary and secondary are cleared of carbon build up.
• Boiler and bunker feed screws are examined and cleaned where necessary.
• Geared motor units, seals and bearings checked and greased where necessary.
• Inspection of anti-burn back protection/safety equipment.
• Inspection of automatic ignition system.
• Electrical inspection of boiler connections and control panel.
Upon completion a service report will be issued and notification of any remedial work required.
Winter service
A visit during the winter period, carried out whilst the boiler is operating. Work includes:
• General inspection of the boiler
• General inspection of associated feeding equipment
•A flue gas analysis to report on the efficiency of the boiler during working conditions.
Upon completion a service report will be issued with data attached and notification of any remedial work required.