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Recent Development of Biomass Fast Pyrolysis Technology and Biooil Upgrading: An Overview Nurul Suhada Ab Rasid1,a and Mohammad Asadullah2,b 1,2
Faculty of Chemical Engineering, Universiti Teknologi MARA, 40450 Shah Alam, Selangor, Malaysia b
E-mail:
[email protected]
Keywords: renewable energy, biomass, fast pyrolysis, bio-oil upgrading
Abstract. The increasing demand of energy has led to the development of renewable energy in order to mitigate the dependency of fossil fuels. Fast pyrolysis of biomass is one of the most anticipated renewable energy technologies since it has a huge potential to become the efficient, environmentally sustainable, and cost effective technology for energy. Fast pyrolysis process produces liquid bio-oil as a main product, along with solid char and combustible gas. Bio-oil can be utilized for heat and power generation as well as it can be used as a feedstock for pure chemicals production. Over the last decades, numerous researches have been conducted in order to develop the process in terms of reactor design and process optimization in order to achieve the high yield of liquid with high organics and less water content. The aim of this review is to provide the state-ofthe-art on fast pyrolysis of biomass with some suggestions presented on upgrading the bio-oil. Based on the recent reactor configurations, current status of biomass fast pyrolysis in commercial scale around the world, the fuel and chemical characteristic of bio-oil compared to the conventional fossil fuels, and the potential application of bio-oil in the future, some recommendations are proposed. Introduction Nowadays, fuel for energy is essential for our modern civilization. The current consumption of primary energy is consumed to be around 495 EJ/year and is expected to be double in the near future. Most of the energy demand is currently satisfied by fossil fuels. However the fossil fuel resources is depleting and causes green house gas emission, thus it needs to be replaced with renewable and sustainable energy. Biomass is one of the renewable sources of energy which can be converted to produce energy in the form of electricity, heat and steam. In addition, it is renewable, sustainable, abundantly available, and cheap. Fast pyrolysis of biomass is one of the anticipated renewable energy technologies that have received a lot of attention since it can convert the lignicellulosic biomass into combustible liquid bio-oil. The bio-oil produced has a great potential to be used as a substitute of the conventional fossil fuels in the transportation and industrial sectors. Besides, the bio-oil has also advantages in the view of its product handling, storage and transportation for its further utilization process. The University of Waterloo (Canada) has established the fast pyrolysis principle in 1980, which was then further developed by many researches and developments made by various research groups and companies. A lot of research has been done in order to improve the reactor and plant design, physical and chemical characterization of bio-oil, upgrading and utilization methods of biooils [7]. Besides, the optimum operating conditions have been studied using different methodologies in order to improve the production yield and the product quality of the bio-oil. Although fast pyrolysis process has received significant progress it is yet to be commercialized. This is because the bio-oil quality is still not up to the application level in the energy and chemical sectors due to its poor properties and characteristics [12]. However, with recent development made by various researches in improving the production and standard quality of bio-oil for specific application, private companies has shown their interest recently to make
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significant investment for this opportunity. In order to develop affordable applications of bio-oil, the construction of larger biomass pyrolysis plant has been made which has capability to produce bio-oil at lower cost. The aim of this paper is to provide the recent development on the fast pyrolysis of biomass which includes the recent update on fast pyrolysis reactors development, current status of the fast pyrolysis process in commercial scale, upgrading bio-oil technologies development and summarize the problem and potential solution in making the fast pyrolysis process in the mass production for renewable energy. This review also compares the properties of bio-oil with conventional fossil fuels in order to seek the future potential of bio-oil to be the substitutes in producing the heat, power, chemical and transportation fuels. Fast pyrolysis of biomass Fast pyrolysis is a thermal decomposition of the biomass into gas, liquid and solid in the absence of oxidizing agent for complete combustion. The main product of fast pyrolysis process is bio-oil (liquid) while combustible gas and solid charcoal are the byproducts. In fast pyrolysis process, large molecules of cellulose, lignin and hemicellulose are broken down into smaller molecules of gas, liquid and solid at high temperature. The yield of the product of this process depends on the biomass properties, the type of process and conditions, and also the efficiency of the method of the product collection. Factors to be considered for Fast Pyrolysis Process. The reactors are the heart of the fast pyrolysis technologies which control the cost of the plant, the energy efficiency, and most importantly, the production the yield and quality of the product. Table 1 shows several reactor configurations used in both demonstration and commercial scales [12]. Since the beginning of the fast pyrolysis technology in 1980s, the modification and development for several reactor configurations are still proposing. The optimum operating parameters are continuously studied in order to maximize the yield of bio-oil and increase the product quality in terms of its physical and chemical characteristics. The reactors need very fast heat transfer in order to ensure the rapid heating in biomass particle at low temperature and very low residence time to minimize the secondary reaction. Table 1. Reactor types for fast pyrolysis of biomass with product distribution Typical product biomass Heat distribution (wt%) Operating particle transfer temperature size coefficient Reactor Tar Char Gas (oC) (mm) (W/m2 K) Bubbling Fluidize Bed 75 15 10 480
