Boiler Combustion

Key Points

  • Combustion of bio-oil or bio-crude is in commercial application
  • Multiple companies/countries have commercial successes
  • Limited modifications are needed for existing petroleum fueled boilers to use bio-oil or bio-crude
  • Some applications co-fire with natural gas or fuel oil

Further Reading

  • PyNe 41: van de Beld on diesel engine firing of raw bio-oil.
  • PyNe 40:  Yelvington on bio-oil combustion.
  • PyNe 39:  Hermanns/Oasmaa/van de Beld on Residue2Heat.
  • PyNe 37:  Butcher on visiting Ensyn’s heating oil application; van de Beld/Meulenbroek on EMPYRO plant opening; Ensyn on Youngstown Thermal bio-oil heating.

Example Current Commercial Applications

Direct combustion of bio-oil or bio-crude oil is considered to be the easiest application for this specific fuel. Due to its differences from petroleum fuels, some modifications are required on the combustion system and operating conditions. Co-combustion with fossil fuels has been a simple way to introduce this fuel in the energy market. Yet most of the commercial applications use 100% pyrolysis oil combustion, using limited petroleum fuels as starters or pilot flame.  In addition to the current commercial links above, a few historical examples are shown below.

2012:  Replacing heavy fuel oil at Fortum’s district heating plant

Significant amounts of bio-oil have been combusted in Fortum Power and Heat’s 1.5 MW district heating plant in Masala, Finland since 2010. The bio-oil was produced at Metso’s pilot plant, and it was whole oil including extractive-rich top phase. No additives were used. The existing burner was replaced with a new bio-oil burner consisting of a modified mono block heavy fuel oil burner originally designed for high-pressure atomisation.

The modifications to the existing burner included, for example, burner head configuration. Also the piping, pumping and valve systems including pre-heating of the oil were specially designed for bio-oil. The total amount of bio-oil combusted is currently above 40 tons.

Two main topics for the tests were the overall functionality of the bio-oil receiving, storing, and pumping system and the function of the burner. Both topics were successfully addressed. The receiving system and oil tank were located outside the boiler building. The system worked well, despite the outside temperatures, which varied from -20 to +10°C during the test periods. As a result, good reliability and a satisfactory turn-down ratio of 1:3 were achieved. The unit has even been operated unmanned for one night. Flue gas emissions were close to those of heavy fuel oil. No odour emissions occurred.


Solantausta, Y., Oasmaa, A., Sipilä, K., Lindfors, C., Lehto, J., Autio, J., Jokela, P., Alin, J. & Heiskanen, J. 2012. Bio-oil production from biomass: Steps toward demonstration: ACS. Energy & Fuels, Vol. 26, No. 1, pp. 233-240.

Lehto, Jani; Oasmaa, Anja; Solantausta, Yrjö; Kytö, Matti; Chiaramonti, David. 2013. Fuel oil quality and combustion of fast pyrolysis bio-oils. Espoo, VTT. 79 p. VTT Technology; 87 ISBN 978-951-38-7929-7 (Soft back edition.); 978-951-38-7930-3 )

2011:  Combustion tests at Stork (Hengelo)

The combustion of pyrolysis oil made from pine wood was compared to a reference case of heavy fuel oil (HFO) in the 9 MWth Stork test boiler using a Stork Low NOx Double Register gas- and oil burner. A picture of the boiler is shown to the right. The pyrolysis oil was delivered by BTG BioLiquids.

For atomization of the liquid fuels, an optimized Y-jet steam-assisted atomizer was used. The pyrolysis oil was preheated to a temperature of 60°C in order to lower the viscosity and thereby enhance the atomization. The heavy fuel oil was preheated for the same reason to a temperature of 100°C.

Test results

Pyrolysis oil was successfully fired at 2.6 MWth while HFO was fired at a capacity of 4.7 MWth. The reason for the lower capacity on pyrolysis oil was the limited amount of available pyrolysis oil in combination with the minimum time required for reliable dust emission measurements.

The flame of the pyrolysis oil stabilized at a larger distance from the impeller than the HFO flame. This is most likely due to the water content of the pyrolysis oil in combination with the lower heating value. It was found that a small natural gas pilot flame of 0.6 MW is required for flame stabilization when firing pyrolysis oil. It is believed that this pilot flame can be reduced or even omitted when preheating the combustion air. Besides natural gas, a liquid fuel may also be used for the pilot flame.

The combustion of the pine oil was homogeneous and no abnormalities were visible. The combustion of the pine oil gave a significant lower NOx emission when comparing it to the HFO emission, which is due to the reduced flame temperature and low fuel nitrogen content. The measured emission levels for the combustion of pyrolysis oil and heavy fuel oil are shown in table below.

Measured emissions

Oil Heat Total [MW] Heat Oil [%] Oil flow [kg/h] O2 [vol% dry] CO [ppm vol] NOx [mg/m03@3%O2] Dust [mg/m03@3%O2]
Heavy Fuel Oil (HFO) 4.7 100 411 4.0 <5 550 30
Pine Oil 2.6 76 606 3.0 <50 133 13-20


9th European Conference on Industrial Furnaces and Boilers (INFUB-9), Estoril, Portugal, 26-29 April 2011.

25. Deutscher Flammentag 2011, Karlsruhe, Germany, 14- 15 September 2011.

Experience with firing pyrolysis oil on an industrial scale, Maarten Rinket, Ardy Toussaint, PyNe newsletter No. 31, pp 3-4.

2003:  Fortum’s field tests to replace light fuel oil using a modified burner

In 2003, Fortum (formerly Neste Oil) successfully performed field tests with their pyrolysis product Forestera in a 400 kWthheating fuel boiler. Their aim was to replace light fuel oil in heating. Field tests were performed in order to verify critical components and to determine the required fuel quality.

The burner was provided by Oilon Oy of Finland, which was the result of their joint development work during the period 2000-2002. In the field tests more than 12m3 of Forestera bio-oil was combusted, in over 1500 cycles. The combustion system was fully automated and operated under the control of a thermostat. One of the more important findings of the work was the necessity to reduce solids to < 0.1 wt%, and to ensure that inorganics in the form of ash and sand left over from the feedstock are present in concentrations of < 0.03 wt%. The conclusion of these tests was that emissions could be reduced to acceptable levels, provided that a fuel of sufficient quality is used, and that flame characteristics are modified using a modified burner. It was also found that the combustion system is more complex and costly than for conventional heating fuels. This would require a lower-cost pyrolysis bio-oil to compensate for the higher installation costs to get customers to be willing to test this option.


Martin, P. & Gust, S. 2003. Development of combustors for pyrolysis bio-oils. In: Pyrolysis and Gasification of Biomass and Waste. Bridgwater, A.V. (Ed.) CPL Press, Vol. 1. Pp. 187-190.

Kytö, M., Martin, P. & Gust, S. 2003. Development of combustors for pyrolysis liquids. In: Pyrolysis and Gasification of Biomass and Waste, Strasbourg, France, September 30 – October 1, 2002. Bridgwater, A. (Ed.). CPL Press: Newbury, UK. Pp. 187-190.

Lehto, Jani; Oasmaa, Anja; Solantausta, Yrjö; Kytö, Matti; Chiaramonti, David. 2013. Fuel oil quality and combustion of fast pyrolysis bio-oils. Espoo, VTT. 79 p. VTT Technology; 87 ISBN 978-951-38-7929-7 (Soft back edition); 978-951-38-7930-3 (URL: )

2002:  Co-firing pyrolysis oil and natural gas at Electrabel (Harculo)

The Electrabel power plant in Harculo (the Netherlands) is a combined cycle type which solely uses natural gas as fuel. The power station consists of a turbine and a boiler which is coupled to a steam cycle. In 2003, pyrolysis has been co-fired in the boiler replacing part of the natural gas.

In the test campaign, 15 tonnes of pyrolysis-oil have successfully been co-fired and 25 MWhr of green electricity was produced. Pyrolysis oil was fed at a rate of 1,900 kg/h corresponding to 8 MWth. During the combustion campaign, the power station control system maintained a constant power output of 251 MWe and the resulting reduction of the natural gas flow also corresponded to 8 MWth. During pyrolysis oil co-firing an increase of 3 ppm in NOx emission was observed due to the nitrogen in fuel.


Bio-oil as a coal substitute in a 600 MWe Power Station, BM Wagenaar, RH Venderbosch, W Prins, F Penninks, 12th European Conference and Technology Exhibition on Biomass for Energy, Industry and Climate Protection, 17-21 June 2002, Amsterdam, the Netherlands.

2001:  Oilon pyrolysis oil combustion tests in an industrial boiler

The combustion properties of various pyrolysis oils derived from biomass have been studied at Oilon’s R&D Centre in Lahti, Finland. Oilon is the biggest burner manufacturer in Finland and is interested in boiler applications in the burner size class of 350 kW – 45 MW. The dimensions, operating parameters and characteristics of pyrolysis oils were tested and compared, and emissions were measured for each test.

The most important parameters for pyrolysis oil combustion are viscosity, water and particulates content, amount of methanol addition, bio-oil raw material and bio-oil age. Concerning equipment modifications and adjustments, the following factors improved combustion and flame:

  • Strong swirl;
  • Intense symmetrical flame;
  • Pressure air atomization (compared to steam);
  • Increase of air coefficient and combustion power;
  • Suitable atomization viscosity (about 15 – 20 cSt).

At the optimum adjustments of this combustion system, the mean combustion results and emission values of typical pyrolysis oils were as follows:

O2 NOX CO Hydrocarbons Soot Particles
3.5 vol% 88 mg/MJ 4.6 mg/MJ 0.1 mg/MJ 2.4 Bac. 86mg/MJ


Oasmaa, A., Kytö, M. & Sipilä, K. 2001a. pyrolysis liquid combustion tests in an industrial boiler. In: Progress in Thermochemical Biomass Conversion; Bridgwater, A. (Ed.). Blackwell Science: Oxford, UK. Vol. 2. Pp. 1468-1481.

Lehto, Jani; Oasmaa, Anja; Solantausta, Yrjö; Kytö, Matti; Chiaramonti, David. 2013. Fuel oil quality and combustion of fast pyrolysis bio-oils. Espoo, VTT. 79 p. VTT Technology; 87 ISBN 978-951-38-7929-7 (Soft back edition); 978-951-38-7930-3 (URL: )

1999:  Bio-oil combustion for district heat in Stockholm, Sweden

The first encouraging large-scale bio-oil utilization tests published were carried out at Årsta District Heating Plant in Sweden. It is used as a peak load and stand-by plant within the net. Årsta District Heating Plant is equipped with four hot water boilers and one boiler producing steam for soot blowers. The plant is operating from October until the middle of May. The 9 MW boiler was originally designed for heavy fossil fuel, but it was later adapted to different bio-oils. The boiler has forced circulation with a temperature regulated at 160°C and no flue gas cleaning equipment. The burner is a rotating cup burner manufactured by Petrokraft AB. Fuel is added inside a rotating cone (5000 rpm), and the rotation together with the primary air added outside the cone, atomises the fuel. When using different fuels, it helps to mix them.

Fuels were produced in the Fortum’s pilot-scale production plant in Porvoo, Finland, during the autumn of 2003, shipped to Stockholm in September 2003 and stored for 8 months in 1m3 plastic containers. Before testing, fuel was pumped from the containers into a storage tank. It was necessary to co-fire the pyrolysis oil with a support fuel. In this test, fatty acid was used, but it could also have been tall pitch oil or heavy oil (heating value 45 MJ/kg). Pyrolysis oil was handled in a separate test unit – an airtight, stainless, 10m3 tank with a stirring device. The bio-oil was led from the tank to a loop-rotor pump with controlled rpm and on to a 400 micrometer filter, a pre-heater and through a mass flow meter. The boiler was started up with 100% support fuel. After a while, fast pyrolysis bio-oil was added. During the test, burning bio-oil was mixed with a decreasing amount of fatty acid. When the combustion began to be unstable, the flame started to pulsate and the CO-level to increase. The amount of pyrolysis oil (PO) was then reduced until stable conditions appeared again. Over the two days, the boiler was operating with bio-oil for approximately six hours, and the total consumption of PO was about 4m3.


Hägerstedt, L.-E. & Jakobsson, A. 1999. Biofuel oil for power plants and boilers. Final report: Handling, storage and transport of biofuel oil. Stockholm: Birka Teknik och Miljö AB. European Commission (EC) Contract JOR3-CT95-0025.

Hallgren, B. 1996. Test report of Metlab Miljö AB. Skelleftehamn: Metlab Miljö AB. Reg. no. ALL1668, 1996 02 0809. 17 p.

Solantausta, Y. 2004.

Lehto, Jani; Oasmaa, Anja; Solantausta, Yrjö; Kytö, Matti; Chiaramonti, David. 2013. Fuel oil quality and combustion of fast pyrolysis bio-oils. Espoo, VTT. 79 p. VTT Technology; 87 ISBN 978-951-38-7929-7 (Soft back edition); 978-951-38-7930-3 (URL: )

1997:  Bio-oil co-firing by Ensyn and Canmet

Bio-oil produced by Red Arrow Products Company by the RTPTM process was co-fired in a coal station at the Manitowoc public utilities power station, Wisconsin, in a 20 MWe low-sulphur Kentucky coal-fired stocker boiler. A total of 370 h of operation have been accumulated, feeding 5% of thermal input by pyrolysis oil, corresponding to 1 MWe power output. The plant was operated without significant problems after cost-effective modification of the boiler to allow for co-firing. No adverse effects were observed on emission levels (sulphur emissions were reduced by 5%), maintenance programs or ash handling.

Industrial ovens are also potential users of bio-oil. At least short duration lime kiln tests have been carried out, although results have not been published. Canmet has studied the use of pyrolysis oils in drying kilns. Pyrolysis oils performed well in a hot furnace (approx. 500°C). At ambient temperatures start-up with 50% natural gas was necessary in order to sustain ignition. An addition of 10-20% natural gas improved emissions and stabilized the flame. A CLM nozzle with external mix air assist atomiser worked well, but improved nozzles to achieve a “cold” start are required.


Sturzl R. 1997 The commercial co-firing of RTP bio-oil at the Manitowoc Public Utilities power generation station. Available at

Preto, F., Wong, J., Zhang, F., Coyle, I., Bethune, S. & Allard, R.-P. 2012. Pyrolysis Oil Combustion at CanmetENERGY.