Abstract
Thermogravimetric combustion characteristics of ginkgo leaves (GK), pine needles (PN), corn straw (CS), aspen leaves (AS), and white poplar leaves (WP) were studied. Results showed that the combustion of selected samples consisted of at least two weight loss stages. Besides, characteristic temperatures lagged towards high temperature zones under high heating rate, which was considered as the effect of insufficient transfer of heat. The combustion of volatile compounds and char from PN and CS was isolated under high heating rate and consequently the exothermic rate around 300 °C was intensified and the exothermic rate over 400 °C was decreased, while the maximum heat release rates of GK, AS, and WP were transferred into high temperature zones with the increasing of heating rate. The average activation energy of PN and CS was high though their combustion completed at a lower temperature, which was possibly due to the low average energy of molecules in samples in low temperature environment. The aromaticity, degree of condensation, CH2/CH3, and structure parameters of oxygen-containing functional groups were calculated according to the peak areas derived from the convolution of FTIR spectra. These parameters explained the discrepancy in both reactivity and exothermic behaviors of biomass samples during combustion.
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Kinetic Analysis on Non-isothermal Combustion of Several Urban Biomass Fuels
Ying Wang, Zhi-jun He,* Qing-hai Pang,* Ji-hui Liu, Jun-hong Zhang, and Wen-long Zhan
Thermogravimetric combustion characteristics of ginkgo leaves (GK), pine needles (PN), corn straw (CS), aspen leaves (AS), and white poplar leaves (WP) were studied. Results showed that the combustion of selected samples consisted of at least two weight loss stages. Besides, characteristic temperatures lagged towards high temperature zones under high heating rate, which was considered as the effect of insufficient transfer of heat. The combustion of volatile compounds and char from PN and CS was isolated under high heating rate and consequently the exothermic rate around 300 °C was intensified and the exothermic rate over 400 °C was decreased, while the maximum heat release rates of GK, AS, and WP were transferred into high temperature zones with the increasing of heating rate. The average activation energy of PN and CS was high though their combustion completed at a lower temperature, which was possibly due to the low average energy of molecules in samples in low temperature environment. The aromaticity, degree of condensation, CH2/CH3, and structure parameters of oxygen-containing functional groups were calculated according to the peak areas derived from the convolution of FTIR spectra. These parameters explained the discrepancy in both reactivity and exothermic behaviors of biomass samples during combustion.
Keywords: Thermogravimetric analysis; Biomass; Kinetics of combustion; Heating rate
Contact information: Research Institute of Mass Energy Optimization and New Technology of Metallurgy, University of Science and Technology Liaoning, Anshan, Liaoning, China;
* Corresponding authors: hzhj2002@126.com; edikitty@126.com
INTRODUCTION
The increasing industrial depletion of fossil fuels and deterioration of the human resident environment in China has been attracting attention due to the enormous Chinese industrial capacity (Hoel 1996). Annually, a huge amount of coal and petroleum are being consumed at an industrial scale, and consequently a large quantity of particulate matter and greenhouse gases are being generated. As a result, many major cities have been frequently suffering from the phenomenon of fog and haze, which is considered to be closely related to the particulate matter produced by the wide application of coal-based and petrolic fossil fuels during industrial production and manufacture (Zhang et al. 2015). In order to maintain the contribution of industrial development on the Chinese economy, policies have been issued to mediate the contradiction between industrial expansion and human ecological environment. Therefore, it becomes urgent for Chinese researchers to explore new energy sources to realize the “green development” of Chinese industry.
Biomass energy is a widely distributed, carbon neutral, environmentally friendly energy source, and hence it has received increasing attention from all over the world (Caputo et al. 2005; Zeng et al. 2007; Abbasi and Abbasi 2010; Qin et al. 2017). China, as an agricultural country with vast yield and territory, generates a huge amount of by-products from agricultural production and green plants. Although the chronic oxidation and spontaneous combustion of these biomasses will both increase the emission of CO2 and the possibility of conflagration in wild areas, these by-products are still not well collected and utilized in China at present. On the contrary, if above biomasses can be well collected and classified as an energy source for industrial application, not only the discharge of greenhouse gases will be partly decreased but also the possibility for natural disasters will be reduced. Thus, the development of by-products from agriculture and plants as a sustainable energy resource is conducive to reduce the dependence of industry on fossil fuels (Zhou and Wu 2005; Ying and Jiang 2007).
Many studies have evaluated the application possibility of biomass in different industrial links. Combustion behavior of agricultural residues such as miscanthus, poplar wood, and rice husk was studied by Mustafa et al. (2013) with thermogravimetric analysis. The results indicated that the reactivity of biomass can be attributed to the formation of volatile compounds, while the energy releases from biomass fuels during combustion is related to the proportion of fixed carbon. Emre et al. (2012) analyzed the co-combustion behavior of biomass fuels and oil shale blends and found that the addition of biomass lowers the ignition temperature and facilitates the combustion property of oil shale in blends. The addition of biomass will increase the proportion of volatile in blends and stabilize the ignition and combustion of blends; consequently, a superior combustion of blends is achieved with 10% or 20% addition of biomass into oil shale. Mustafa et al. (2017) investigated the combustion characteristics of main components of lignocellulose, cellulose, hemicellulose and lignin in biomass (hazelnut shell) and noticed that the average activation energy of these compounds in biomass varies between 83.8 and 191.7 kJ·mol-1 for both OFW and KAS methods. Kandasamy et al. (2017) studied the combustion of poplar wood, hazelnut shell, and wheat bran and revealed that the reactivity of biomass is related to the content of light volatile, while the quantity of heat releases during the combustion is determined by the content of fixed carbon in biomass.
The overall aim of this research was to investigate the combustion behavior of by-products from common urban plants and acquire the reaction mechanism of various components at different stages of combustion, which is critical for the further application of these biomass fuels in industrial or civil scale. Hence, non-isothermal thermogravimetric combustion experiments on by-products from five common urban plants under low heating rates were conducted in this research in order to separate the independent combustion peaks from conversion rate curves and kinetic studies were also carried out with Flynn-Wall-Ozawa (FWO) method. As a result, the combustion sequence of components in biomass samples was determined, while the activation energy values of samples at different conversion rates were also calculated. Meanwhile, Fourier transform infrared spectroscopy (FTIR) was also introduced to analyze the functional group structures of selected samples and explain the difference in reactivity of these biomasses during combustion. Eventually, the feasibility and reaction condition of various biomasses for industrial application can be analyzed based on above results.
EXPERMENTAL
Materials and Preparation
Biomass samples of ginkgo leaves (GK), pine needles (PN), corn straw (CS), aspen leaves (AS), and white poplar leaves (WP) were collected in autumn from urban areas of Anshan city, which is located in the northeastern part of China. The original morphology of selected biomass samples are shown in Fig. 1. All biomass samples were dried at a temperature of 100 ± 5 °C for 8 h, then crushed and sieved to a particle sized below 0.074mm.
