• Biofuels
•  

Use of liquid biofuels in domestic heating - effects on boiler performance

The potential use of biofuel as a heating oil has been extensively researched in the UK by OFTEC, BSRIA and burner manufacturers.

Trials that have been carried out show that the efficiency and flue gas emissions are not adversely affected by use of the various blends of biofuel. Liquid biofuel include rape-seed oil, vegetable and waste cooking oils which are blended with kerosene or diesel. Typical blends commercially available for the UKs heating industry include B30, B50, B100 (100% pure biofuel).

For domestic heating applications, B30 is generally used. For commercial heating applications, B50 and B100 is employed. In all applications the burners must be matched to the fuel specification. Because of the viscosity of the biofuel, burning the fuel is beyond the capability of normal oil burners. When liquid biofuel is specified as a fuel source, it must conform to the requirements of EN 14213 and be sourced from a reputable supplier.

Field trails carried out recently by OFTEC over an 18 month period on a blend B30 (30% Fatty Acid Methyl Esters (FAME) manufactured from waste cooking oil and 70% kerosene) showed that carbon emissions were reduced by 28% when compared to conventional kerosene. It has been estimated that the use of this renewable fuel could save up to 2 million tonnes of CO2 per annum up to 2020.

Effects of different fuel mixtures on boiler operation

When designing and specifying liquid biofuel boilers it is particularly important to obtain data such as flow rate, pressure loss data for different pipes sizes when using a particular grade of biofuel, winter ambient conditions, fuel temperature and burner type. All these parameters can affect thermal performance and emissions of boilers.

The following testing and investigations can provide this valuable data:

• Efficiency testing of boilers using any concentration of liquid biofuel in order to determine the change in efficiency and emissions performance.
• Investigation of the use of biofuels in domestic and commercial oil fired boilers to measure the calorific value of the fuel, including measurement of NOx, CO2, CO and unburnt hydrocarbons. The test would normally be carried out at the conditions given under the Boiler Efficiency Directive (BED) unless otherwise specified by the client. The results are compared with the base line results obtain for kerosene or diesel as appropriate to determine the change in efficiency and emissions performance.
• Testing the effects of severe ambient conditions on the combustion performance of biofuels can be conducted where the temperature of the liquid-biofuel and the temperature of the combustion air to the burner can be held as low as - 10 degrees C. The effect on the thermal performance and emissions of a matched boiler/burner combination can then be investigated.
• Other tests on biofuels include determination of the pressure drop per meter for given flow rates and pipe diameters over a range of temperatures. As the viscosity of the liquid biofuel is temperature dependent, this also affects the flow rate to the burner and ultimately the performance of the boiler. Pressure loss data for different pipes sizes when using a particular grade of biofuel is particularly important when designing the fuel supply system from the biofuel storage tank to the boiler.
• BSRIA works closely with manufacturers and suppliers of liquid bio-fuels, in particular on forensic type investigations of the use of biofuels on the degradation of the components within the burner and other ancillary components within the fuel delivery system such as rubber seals, fire valves and oil nozzles. Tests are generally conducted with the boiler operating under a cycle that closely matches that of a boiler under typical operating conditions in the field. In the absence of a harmonised BSI or European test standard, BSRIA would write its own test method in collaboration with the client to ensure that the project objectives are met. All test work is audited under BSRIA's QA system in accordance with BSEN ISO/IEC 17025 "General requirements for the competence of testing and calibration laboratories" to ensure compliance with the test standard and client requirements.

Contact BSRIA Test & Certification

Telephone: +44 (0)1344 465600
Email; test@bsria.co.uk