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Study of combustion performance of a number of liquid pyrolysis products at the semi-industrial scale

Objective

To evaluate two pyrolitic biomass oils for :

- combustion performance, heat transfer characteristics and pollutant emissions;
- to optimize burner and atomizer design and to generate design guide-lines;
- to set up a standard test procedure for non standard liquid fuel;
- to compare performance with a standard heavy fuel oil.
The International Flame Research Foundation (IFRF) performed a series of semiindustrial scale combustion tests ondifferent pyrolitic biomass oils and compared the combustion performance with a standard heavy fuel oil.

The 2 pyrolitic biomass oils studied had widely differing characteristics. The first pyrolitic oil (PB1) had a viscosity below 10 mm{2}s{-1} (at 70 C), a high water content and contained a small amount of particulates, below 2% weight for weight. The lower calorific heating value (LCV) of this oil was approximately 20 MJ/kg and the fuel nitrogen content was around 1% weight for weight. The second pyrolitic oil (PB2) had extremely high viscosity, up to above 500 mm{2}s{-1} (at 70 C), lower water content and high particulate concentration, up to 25% weight for weight. The fuel bound nitrogen content was around 0.9% weight for weight and a LCV of around 26 MJ/kg.
The heavy fuel oil (HFO) was of similar composition and characteristics for both experimental phases with a viscosity 70 to 20 mm{2}s{-1} at 80 to 120 C, LCV of 40 MJ/kg and fuel bound nitrogen content of 0.4% weight for weight.

Combustion of pyrolitic biomass oils was possible but results in high nitrous oxide and particulate emissions. In general the combustion performance was less than the performance of heavy fuel oil under similar burner and furnace conditions.
In general, the 2 biomass oils tested behaved with similar trends as heavy fuel oil with respect to burner and furnace operation such as excess air, swirl and thermal input variations.
Handling and storage of pyrolitic biomass oils is a substantial problem and clearly requires improvement with respect to storage, homogenization, heating and pumping of the oils.
A variety of recent EC funded research programmes have evaluated various technologies for converting waste or excess biomass into industrial fuels.

Complementary to this work, the International Flame Research Foundation (IFRF), also funded by the EC, performed a series of semi-industrial scale combustion tests on different pyrolitic biomass oils and compared the combustion performance with standard heavy fuel oil (HFO) with respect to fuel handling, heat transfer and pollutant emissions (NOx, smoke).

The experimental campaign was carried out in two phases at the end of 1989 and the beginning of 1990. In total 165 different flames (0,5-2,2 MW) were studied ; 65 for pyrolytic oil 1,20 for pyrolytic oil 2 and 80 for HFO.

The experiments were executed on IFRF Furnace No 2. The furnace is water cooled and has internal dimensions of 4,4 x 1,2 x 1,2 m. The furnace was equipped with specific refractory lining to simulate the thermal boundary conditions of a small industrial boiler or process heater. The experimental burner was a flexible, generic, externally air staged burner which allowed for variations in swirl number, combustion air velocities, atomizer design and staging ratio for low NOx performance.

The two pyrolysis oils studied had widely differing characteristics. Oil 1 had low viscosity (10 mm2/s-70 C), a high water content, low particulate concentrations and heating value of 20 MJ/kg. Oil 2 had extremely high viscosity (500 mm2/s-70 C), lower water content, high particulate concentration and heating value of 26 MJ/kg. The heavy fuel oil was of standard characteristics with a viscosity 70-20 mm2/s at 80-120 and heating value of 40 MJ/kg. Furthermore, the inhomogeneous character and the low boiling point of these biofuels make proper fuel handling of extreme importance.

Flue gas emissions (NOx, CO, CO2, O2, smoke) and fuel heat extraction profiles were monitored for all the flames. Furthermore, analysis on the PB Oils was performed with respect to composition, PAH, particle size distribution and flue gas particles for Oil 1 and HFO for high and low NOx flames. Finally suggestions are made for future research and applicable possibilities with respect to fuel handling, improved combustion performance and reduced pollutant emissions.

Coordinator

INTERNATIONAL FLAME RESEARCH FOUNDATION
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Netherlands