The development of agro-residue densified fuel in China based on energetics analysis
Introduction
China is an agricultural country and the yield of agro-residues in 2007 reached about 700 million tones (NBSC, 2008). Due to their tremendous amount, agro-residues play an important role in biomass resource in China. Currently, these agro-residue resources have four utilization routes: as industrial material, as fertilizer directly returned to the field, as livestock feeding, and as fuel. The relative proportion of agro-residues used as livestock feeding is also finally returned to the field. The utilization pathway not only increases production for animal husbandry, but also maintains soil organic matter. Compared with other pathways, utilization as fuel is the most important one with about 50% of total utilization amount, followed by livestock feeding (about 30%), fertilizer (about 15%), and paper making industry (about 5%) (Han et al., 2003). The utilization amount of agro-residues only accounted for about 65% of total yearly output and the remaining agro-residues were discarded as waste (Xiang, 2005). If including the existing fuel utilization, the amount of available agro-residues for developing fuel industry is over 60% of the total yearly output. This indicates that developing fuel industry from agro-residues in China has a strong feedstock support.
Densification is one of the many important technologies converting agro-residues into fuel (Zeng et al., 2007). Densification technology has many advantages. Firstly, it can improve the characteristics of agro-residues for collection, transportation and storage. Secondly, densification technology increases energy density, resulting in higher energy efficiency during combustion. Some researchers investigated energy difference of loose and densified biomass (Wilen et al., 1987). The results showed that energy density of densified biomass was fivefold higher than that of loose biomass. Finally, densified fuel has widely used pathways, such as serving residential, commercial and industrial applications.
For investigating the development feasibility of agro-residue densified fuel in China, the energetical property and energy potential of main agro-residues in China were firstly analyzed and then the development of agro-residue densified fuel in every region was evaluated based on energetics analysis. The result of this study can be used to optimize area layout for developing agro-residue densified fuel in China.
Section snippets
Physicochemical properties of main agro-residues in China
Unlike conventional energy feedstock, agro-residues have complex physicochemical properties that complicate the processing and combustion of agro-residue densified fuel (Werther et al., 2000). The main physicochemical properties of interest can be characterized by proximate and elemental analyses. For proximate analysis, moisture content (MC), volatile matter (VM), fixed carbon (FC), and ash content (AC) in agro-residues are determined as weight percent, and calorific value (CV) is determined
Energy potential of agro-residues in China
Energy potential was estimated by the production and heating value of agro-residues. The model for estimating energy potential was written as follows:where ni is the ratio of the i-th agro-residue available for densified fuel and it was set to 0.675 according to the present utilization of agro-residues in China (Han et al., 2003, Xiang, 2005), PCi is the amount of the i-th crop product (tonne/year), RCRi is residue to crop ratio, ηi is the coefficient equal to tonne of
Energetics analysis of densified fuel from agro-residues
The primary energy embodied per unit of useful energy is an important index of energetics analysis of fuel. It can be used to evaluate energetical viability of fuel. Recently, Purohit and colleagues (Purohit et al., 2006) proposed a model to calculate the primary energy embodied per unit of useful energy (PPEI) as follows:where PEIP, PEIT and PEIU are energy consumption for producing fuel (MJ/t), energy consumption for transporting fuel from producing to end-use point (MJ/t),
Conclusions
Agro-residue is one of the important biomass resources in China. The energetical property and energy potential of main agro-residues in China were firstly analyzed and then the development of agro-residue densified fuel in every region was evaluated based on energetics analysis. The results show that main agro-residues in China are good feedstocks as densified fuel and they constitute enormous energy potential for developing densified fuel. However, the situation of every region should be
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