Article pubs.acs.org/EF
Biomass-Based Pyrolytic Polygeneration System for Bamboo Industry Waste: Evolution of the Char Structure and the Pyrolysis Mechanism Haiping Yang,† Baojun Huan,‡ Yingquan Chen,*,† Ying Gao,† Jian Li,† and Hanping Chen† †
State Key Laboratory of Coal Combustion School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan 430074, China ‡ Xuji Croup Corporation, Xuchang Henan 461000, PR China S Supporting Information *
ABSTRACT: Biomass-based pyrolytic polygeneration system can commercialize all products (liquids, gases, and solids) generated during pyrolysis, while fast pyrolysis, gasification and carbonization, can only singly commercialize liquids, gases, and solids, respectively. To determine the optimum operational parameters for biomass pyrolytic polygeneration while using bamboo waste as the feedstock, the product characteristics were investigated over a temperature range of 250 to 950 °C. Meanwhile, details of the evolution of the char structure were analyzed to reveal the pyrolysis mechanism. Results showed that to increase the yield of char, the operational temperature should be at 350 °C; however, at this temperature, no inner pores were formed and a low quality char product was produced. Thus, the optimum operating temperature recommended for biomass pyrolytic polygeneration of bamboo waste was set to 550 °C. At the optimum temperature, the surface area of the char was 200 m2/g, the calorific value of gas was 14 MJ/m3, and the concentration of phenols in liquid reached the maximum level. A pyrolysis mechanism based on the evolution of the char structure was proposed. First, the ordered organic macrostructure in raw biomass was converted to a network-like structure consisting of a “3D network of benzene rings” during the “initial decomposition stage (550°C)”. The results of this study are expected to be beneficial for the comprehensive utilization of bamboo waste and provide new insight into the pyrolysis mechanism.
1. INTRODUCTION Bamboo is an important cash crop in the mountainous areas of Asia, especially in China, which is the biggest supplier of bamboo products.1−3 The annual value of China’s bamboo industry output is $14.5 billion according to data from the last 10 years, and an ambitious development objective has been set to increase the total value of output to $48 billion by 2020, as detailed in the China Bamboo Industry Development Plan that was formulated in 2013.1 However, this rapid development of the bamboo industry has been accompanied by a dramatic increase in bamboo industrial waste.4,5 Converting bamboo waste to bamboo charcoal in charcoal kilns is now a popular way to handle the waste in the mountainous bamboo planting areas because charcoal kilns are easily built and are simple to operate.6,7 According to the China Bamboo Industry Development Plan of 2013, bamboo charcoal output in China will amount to approximately 220 000 tons in 2020.1 This growth could pose serious environmental risks if the byproducts generated from charcoal kilns are discharged directly into the environment;8 these byproducts include gaseous products, such as CH4 and CO2, which contribute to global warming, and liquid products, such as acids, phenols, ketones, and others with complex organic compositions that can contaminant groundwater and harm ecosystems. Hence, diverting some of the bamboo waste destined for charcoal kilns to other environmentally friendly processes would be desirable. © 2016 American Chemical Society
Biomass pyrolytic polygeneration technology can convert bamboo waste to valuable char, liquid products, and gas products with near zero release of environmental pollutants. This system can commercialize all products (liquids, gases, and solids) generated during pyrolysis while other pyrolysis technology typically commercialize a single product, therefore the commercial pyrolysis factories based on polygeneration had a good performance in terms of economic costs9 and feedstock adaptability,10 and they are associated with low initial investment costs and good flexibility. Hence, commercial pyrolysis factories may represent a viable approach to meet the needs for technological advancement in the bamboo waste processing industry in mountainous planting areas. Bamboo, which is a type of plant in the Poaceae grass family, possesses some properties similar to woody biomass, such as its lower ash content (500 °C) was different with the chars at low temperature (
