Energy Fuels 2010, 24, 5228–5234 Published on Web 08/31/2010
: DOI:10.1021/ef100823b
Increasing the Calorific Value of Rye Straw Pellets with Biogenous and Fossil Fuel Additives Satyanarayana Narra,*,† Yonggui Tao,† Claudia Glaser,† Hans-J€ org Gusovius,‡ and Peter Ay† †
Chair of Mineral Processing, Processing of Biogenous Resources, Brandenburg University of Technology Cottbus, Germany, and ‡ Department of Post Harvest Technology, Leibniz Institute for Agricultural Engineering Potsdam-Bornim, Germany Received June 29, 2010. Revised Manuscript Received August 10, 2010
Pelletizing biomass, especially straw and stalky materials, require a product-specific size reduction and liberation. This paper characterizes the cereal straw rye and specifies the necessities for production of energy pellets. The product-specific size reduction was achieved with the help of an impact mill. Further, the moisture content and the particle size distribution play an important role in the pelletization process and also with respect to the energy characteristics. Rye straw pellets have a lower heating value of 17.2 MJ/kg. The objective of this work is to increase the heating value from 17.2 MJ/kg to a value in between 18 and 18.5 MJ/kg. The pellets are prepared with increasing water contents and with the biogenous and fossil additives. The biogenous and fossil additives are chosen such that they ensure the necessary binding and simultaneously increase the heating value. Besides the heating value, the main pellet quality parameters such as mechanical stability, abrasion resistance, and combustion technical characteristics have been tested € according to the existing norms (DIN51731, ONORM-M7135, DINplus, Agroþ, and Agro). The particle size characteristics indicate an ideal distribution of the particles for the combustion in furnaces. The durability and mechanical stability of the pellets were in acceptance with the existing norms. Particle size characteristics, abrasion values, and strength characteristics showed a good correlation and displayed optimal combustion characteristics.
future depletion of fossil fuel resources increasing the fuel utilization prices.5 Co-firing of these fuels (biomass and fossil fuels) is already utilized to mitigate CO2 emissions in an economically feasible way. The use of such biomass residues in combination with the fossil fuels as energy source is considered as a solution in reducing global warming risks. This research work uses the principle of cofiring biomass and fossil fuels as a background and prepares densified biomass pellets blended with biogenous and fossil fuels as additives (biomass-mix-pellets BMP). BMPs promise a great potential in enlarging the use of biomass for energy. There has recently been an increased intereast in the production of BMPs by the project developers, pellets producers, and energy producers. The biogenous and fossil fuel additives are primarily selected such that they enhance the heating value of rye straw from 17.2 MJ/kg to a heating value between 18 and 18.5 MJ/kg. The densification of biomass and biomass with additives is generally carried out either with high pressure compaction or with the combination of medium pressure compaction and a heating device. The densified biomass conveys mechanical interlocking between the fibres under high pressure compaction.6 During the high temperature compaction, the lignin softens and forms a fine layer on the solid particle.7 This layer of lignin contributes to improved bonding of particles. There are several advantages of densified fuel pellets compared to
Introduction The use of biomass is a promising and attractive form of energy conversion. The environmental benefits such as reduction in greenhouse gas emissions make biomass fuels more eco-compatible compared to fossil fuels. Biomass is becoming an increasingly important energy source for the future as it is a readily available renewable energy source that reduces carbon dioxide emissions.1 Biomass is essentially composed of cellulose (40-45%), hemicellulose (20-30%), lignin (20-30%), and extractives (2-5%).2 Biomass pellets are densified biomass particles formed into cylindrical pellets, which are employed in many industries to form a more durable substance and to enhance the material characteristics, such as (i) to facilitate storage, transport, and handling; (ii) to combine a number of substances (binders and additives); and (iii) to recycle/reclaim materials.3 The primary reason for pelletization is to increase the bulk and energy densities of the material. Pellets of various agricultural residues can be used for energy production in a broad range from private household appliances to full scale power plants.4 The application of biomass residues in power generation has become more attractive in recent years as a consequence of concerns in the reduction of greenhouse gases and also due to *To whom correspondence should be addressed. E-mail: narra@ tu-cottbus.de. (1) Petrou, E. C.; Pappis, C. P. Energy Fuels 2009, 23, 1055–1066. (2) Dhepe, L. P.; Fukuoka, A. ChemSusChem 2008, 1 (12), 969–975. (3) Finney, K. N.; Sharifi, V. N.; Swithenbank, J. Energy Fuels 2009, 23, 3195–3202. (4) Obernberger, I. Thek, G. Herstellung und energetische Nutzung von Pellets. Produktionsprozess, Eigenschaften, Feuerungstechnik, € Okologie und Wirtschaftlichkeit. Schriftenreihe Thermische Biomasse, Institut f€ ur Prozesstechnik, Technische Universit€ at Graz 2009, Band 5. r 2010 American Chemical Society
(5) Nola, Di. G.; De Jong, W.; Spliethoff, H. Fuel Process. Technol. 2010, 91, 103–115. (6) Grover, P. D.; Mishra, S. K. Biomass Briquetting: Technology and Practices, Regional wood energy development program in Asia GCP/ RAS/154/NET, Field document No. 46; Food and Agriculture Organization of the United Nations: Bankok, Thailand, 1996. (7) Gilbert, P.; Ryu, C.; Sharifi, V.; Swithenbank, J. Fuel 2009, 88, 1491–1497.
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Energy Fuels 2010, 24, 5228–5234
: DOI:10.1021/ef100823b
Narra et al.
€ Table 1. Standard Quality Values of the Wood Pellets As Specified in DIN 51 731, ONORM M 7135, DINplus, and for Agricultural Pellets Agroþ and Agro from France norms for pellets diameter length abrasion heating value water content ash content density additives S N Cl
DIN 51 731 4-10 mm e50 mm 17.5-19.5 MJ/kg e12% 540 kg/m3 not allowed
