# Co-Firing of Fast Pyrolysis Bio-Oil and Heavy Fuel Oil in a 300-kW\({}_{\text{th}}\) Furnace
## 1 Introduction  
Bio-oil, a renewable liquid product produced via the fast pyrolysis process, has a lower sulfur and nitrogen content compared with that in fossil fuels. Fast pyrolysis of biomass thermally cracks solid biopolymers to generate a bio-oil, which can be used as a fuel directly or can be upgraded to form a higher-energy-content transportable liquid for power, heating, or the generation of electricity [1; 2; 3; 4]. The decoupling nature of the plant is the most significant advantage of biomass pyrolysis liquid bio-oils [5]. The use of pyrolysis bio-oil has spread around the world. Bio-oil derived from pyrolysis processes has great potential to replace conventional fossil fuels (such as diesel, heavy fuel oil, and natural gas) for on-site power generation and heating, as well as to be a fuel source for medium- or large-scale combustion systems such as furnaces, boilers, and turbines [6]. There are two methods for the pyrolysis process, namely slow and fast pyrolysis [7]. The heating rate, the maximum reaction temperature, and the residence time (biomass heating time) are the main parameters controlled in the pyrolysis process. Heating rates for slow pyrolysis are typically below 100 \({}^{\circ}\)C/min, whereas those for fast pyrolysis can exceed 500 \({}^{\circ}\)C/min. The reaction temperature for slow pyrolysis is about 300 \({}^{\circ}\)C, and that for fast pyrolysis is around 500 \({}^{\circ}\)C. The residence time for slow pyrolysis is several minutes or even hours, while that for fast pyrolysis is short (less than two seconds). This difference in the residence time leads to substantial differences in pyrolysis product distributions; slow pyrolysis generates primarily bio-gas (syngas), while fast pyrolysis produces primarily bio-oil [8]. Biochar, as the by-product of biomass pyrolysis, is the second highest yield product for both slow andfast pyrolysis systems. On a weight basis of the biomass feedstock, typical biochar yield is in a range between 15% and 40%. It is not suitable for upgrading condensable liquids from slow pyrolysis to transportation fuels [8]. Nevertheless, fast pyrolysis is an advanced process, and has gained great interest in recent years due to the high yield (about 70%) of raw bio-oil that can be directly produced from biomass [9; 10]. [PERSON] et al. [6] investigated the spray combustion characteristics of bio-oil that was fast pyrolyzed from rice husk. After attaining steady state combustion, the temperature in the center of the combustion chamber was found to exceed 1400 \({}^{\circ}\)C. The CO concentration dropped, with an increase in the equivalence ratio, indicating that complete combustion was improved under operating conditions with higher oxygen concentrations. Meanwhile, the NOx concentration was slightly increased at a higher equivalence ratio due to the higher temperature and the increased O\({}_{2}\) concentration. Furthermore, the measured SO\(x\) concentration was very low (smaller than 30 ppm), since bio-oils contain insignificant amounts of sulfur. Fast pyrolysis bioliquids have good potential for the replacement of conventional fuel oils such as heavy fuel oil and diesel. Using fast pyrolysis liquids (bio-oils) as fuel offers many advantages, including a clearly positive CO\({}_{2}\) balance, high-energy density, and a possibility of utilization in both small-scale power generation systems and large power stations [3; 11]. As an alternative fuel, bio-oil can be co-fired in fuel oil, natural gas, or coal plants. In addition to the advantages of higher overall efficiencies and lower investment costs in comparison with 100% biomass fired in existing power plants, co-firing bio-oil with conventional fossil fuels has several environmental benefits, such as reduced emissions of CO\({}_{2}\), NOx, and SO\(x\)[3; 12]. Moreover, bio-oil can be utilized as either a start-up or back-up fuel for industrial facilities [13]. Biofuels as a renewable green energy can be used alone or blended with common fossil fuels as alternative fuels in diesel engines, furnaces, and boilers.