OPTIMAL CONDITIONS FOR VALUATION OF WOOD WASTE BY BRIQUETTING

Transcription

1 8th International DAAAM Baltic Conference INDUSTRIAL ENGINEERING April 2012, Tallinn, Estonia OPTIMAL CONDITIONS FOR VALUATION OF WOOD WASTE BY BRIQUETTING Menind A.; Križan, P.; Šooš, Ľ.; Matúš, M.; & Kers, J. Abstract: In this paper some important processing parameters of wood waste briquetting are discussed. Firstly, the characteristics of input material (size of the milled product, humidity etc.) were analyzed and then different pre-treatment methods (shredding, disintegrator milling, drying) were used. Final briquette quality depends on basic material composition and optimal technological parameters. The most important parameters affecting the briquette quality are fraction size, pressing temperature, compacting pressure and material humidity. This final briquette quality was evaluated by measuring briquette density and mechanical strength according to known European Standards for solid high-grade biofuels. Key words: material moisture content, fraction size, disintegration, pressing temperature, compacting pressure, wood briquette 1. INTRODUCTION In the boiler plants of EU countries a wide range of various wood-based bio fuels are burned. Wood fuels can be divided into two major groups: non-refined wood fuels (traditional firewood, compressed forest residue, wood chips, sawdust) and refined wood fuels (briquettes, pellets, wood powder). Alternative fuels like biomass are making breakthrough in energy sector for production of green energy [ 1 ]. Fibre hemp and energy sunflower both have potential as raw material for biomass briquetting [ 2 ]. In previous studies the recycling technology for production of refuse derived fuel (RDF) was described [ 3 ]. Various types of wastes (wood, carton, paper, plastic and textile) were processed by two-shaft and single-shaft shredders to obtain the output product (1 2 mm), which was be suitable for briquetting process [ 4 ]. It was demonstrated that before briquetting of the waste pre-conditioning of the material would be necessary because lower moisture content improves strength and quality of the briquette [ 4 ]. Material composition has great influence on the final quality of produced briquettes (on the density and strength of the briquettes) [ 5 ]. Therefore it is strongly recommended to mix municipal waste with organic binder (paper, wood, sawdust) before briquetting [ 5 ]. The Slovak University of Technology in Bratislava has laboratory of disintegrating machines and briquetting equipment, which was used for briquetting of wood waste. Similar experiments were made in Research and Testing Laboratory of Materials Recycling of Tallinn University of Technology and briquetting laboratory of Institute of Technology in Estonian University of Life Sciences in Tartu. In this contribution several briquetting experiments with different type of wood waste from different sources were made. 2. EXPERIMENTAL STUDY 2.1 Material and process parameters to be studied Final briquette quality can be influenced by many parameters. Five of them are having 187

2 most significant effect to briquette properties. These parameters are material type, pressing temperature, compacting pressure, fraction largeness and material moisture content. Material type All the technological parameters of briquetting process are depending on material type. When wood sawdust is processed the following important physical parameters (temperature, pressure, moisture content, fraction size etc.) are having different values when straw, grass, rattan or wood crust briquettes are produced. Every type of material has its own specific nature as calorific value, ash content, humidity, chemical and trace elements content. Wood contains (see Table 1) lignin which helps to bind the saw dust particles together into the briquette. Lignin acts also as stabilizer of cellulose molecules in cell wall. The more lignin the material contains the more of it can be released to produce briquettes with higher quality. The higher concentration of lignin assures better briquette strength. Spruce Pine Beech Oak Component [%] [%] [%] [%] Cellulose Hemi cellulose Lignin Table 1. Approximate chemical composition of European wood Compacting pressure This is the most important factor influencing the compression strength of briquettes. The strength of briquettes increases with applying higher compacting pressure of briquettes. Briquettes manufactured by using higher compacting pressure are having fewer tendencies to absorb atmospheric humidity during the long term storage [ 6 ]. Pressing temperature This factor has significant effect on the quality and strength of briquettes. It determines the lignin excretion by cellular structures of wood. Lignin is released under certain pressing temperature, which has to be unconditionally reached to assure best briquette quality. Fraction size It affects compacting process of wood saw dust. For larger input fractions of wood need more energy for compacting. Despite of bigger compacting pressure the briquettes have lower homogeneity and compression strength [ 7 ]. Size reduction of wood scrap enables to produce briquettes with better quality. Decreasing the fraction size of wood saw dust increases the adhesion strength between the particles [ 8-9 ]. Fraction size has also very high influence on briquetting process. For the briquetting of coarser fraction the higher compacting power is needed and briquettes are having lower homogeneity and stability [ 3 ]. With increasing the fraction size, the binding forces inside the material are decreasing which results in faster decay by burning (briquette burns faster and that is a disadvantage). The enlargement of fraction size raises the compacting pressure and decreases briquette quality. Smaller fraction size is also an advantage in the drying process [ 5 ]. Material moisture content Is also important parameter which has great influence on lignin plasticisation process. Recent compressing technologies are enabling to compact material having relative moisture lower than 18% [ 10 ]. When the moisture content of the material is very high, the vaporization of surplus water tears the briquette into pieces. When the moisture content of the material is very low (less than 10%) then the higher pressures should be used to obtain briquettes with higher quality. This is expensive and uneconomic in the point of view of production technology [ 4 ]. 188

3 2.2 Mechanical parameters of briquettes Briquettes must be consistent or otherwise cracks, scratches could appear and fine elements would separate and that is/would be not acceptable. Briquettes with higher density have longer burning time. Standard Ő-Norm M 7135 defines briquette density value for group HP (wood briquettes) and for group RP (crust briquettes) more than 1,12 kg/dm3 (g/cm3), and for other briquettes this value must be more than 1 kg/dm3 (g/cm3). Standard DIN defines interval of briquettes density values from 1 to 1.4 g/cm 3. Standard DIN (additional standard DIN 51731) also describes testing method for briquette density. The density of the briquette is calculated by formula (1) as: m N N, (1) VN where VN is the briquette volume and m N is briquette weight [ 7 ]. The compression strength of briquettes in cylindrical shape is determined by cleft failure [ 7-8 ]. 3. RESULTS AND DISCUSSION 3.1 Technological tests with briquettes The briquettes were made from various particle size of milled wood saw dust materials. For samples manufacturing the briquetting press developed in Slovak University of Technology in Bratislava was used. In Fig. 1 manufactured briquettes from different fractions of pinewood sawdust are presented. By manufacturing briquettes from smaller fraction size of wood particles the visible quality of briquettes was improved. Then, several tests to estimate the influence of compacting pressure to briquette quality were performed. The results are presented in the Fig. 2. Briquettes from the same type of material (wood sawdust) with same fraction size with same moisture content were experimentally manufactured at same pressing temperature by changing only one parameter - compacting pressure. As it follows from Fig. 2 the briquettes manufactured at lower pressures fall to pieces. Briquettes produced at higher pressures are consistent and compact Evaluation of the physical parameters in briquetting process The influence of two important parameters - pressing temperature and compacting pressure to the density of briquettes was determined in following experiments. Four different types of wooden raw materials were used for briquetting. Two samples were from the group of softwoods (pine and spruce) and two samples from the group of hardwoods (beech and oak). Pressing temperature was changed from 85ºC to 115ºC. The compacting pressure was changed from 61 MPa to 191 MPa. In the briquetting experiments the size of sawdust particle was ~2 mm. All raw materials were dried to achieve same material moisture content 10%. In the experiments the research was focused on determining the differences between various materials behavior throughout the compacting process according to the final briquette density. From previous and subsequent results it is clear how important parameter is the type of material to be used in the compacting process briquetting. Among the other significant quantifiable parameter that are also important, the pressing temperature and material moisture content, which have the greatest influence. Pressing temperature is not a direct parameter of the pressed material but significantly influences some material properties, changing and influencing also the material structure and chemical composition during the compacting process. As it follows from the Figs 3-6 Briquettes from materials with higher lignin and cellulose contents softwoods (pine, 189

4 Briquettes from Briquettes from Briquettes from Briquettes from Briquettes from pine wood with pine wood with pine wood with pine wood with pine wood with fraction size fraction size fraction size fraction size fraction size > 4 mm < 4 mm < 2 mm < 1 mm < 0.5 mm spruce) have evidently higher density than pressure for pressing briquette with same Figure 1. Pressed briquettes from different fraction size of pine wood briquettes from hardwoods (oak, beech). As it can be seen on curves represented in Figs 3-6 briquettes density is increasing with increase of pressing temperature and compacting pressure. By lower temperatures we need higher compacting quality, and vice versa. To use higher compacting temperature is better than higher pressure from lignin plasticization point of view. 31 MPa 63 MPa 159 MPa 191 MPa 254 MPa Figure 2. The effect of the compacting pressure to briquette quality Fig. 3 Dependence of briquettes density (kg/dm 3 ) from pine sawdust from compacting pressure (MPA) by various pressing temperatures (w r =10%; L=2mm). 190 Fig. 4 Dependence of briquettes density (kg/dm 3 ) from spruce sawdust from compacting pressure (MPA) by various pressing temperatures (w r =10%; L=2mm).

5 The results our hypothesis that compacting pressure, which may seem to be a parameter having the biggest effect on the Therefore it is very important to know the optimal parameter values which influence final briquette quality for various types of materials. 5. REFERENCES Fig. 5 Dependence of briquettes density (kg/dm 3 ) from oak sawdust from compacting pressure (MPA) by various pressing temperatures (w r =10%; L=2mm). Fig. 6 Dependence of briquettes density (kg/dm 3 ) from beech sawdust from compacting pressure (MPA) by various pressing temperatures (w r =10%; L=2mm). Therefore it is recommended for designing of wood briquetting and compacting machines to include heating section into machine construction. 4. CONCLUSION The main aim of the experiment was to detect and identify the effect rate of monitored parameters on the final briquettes quality evaluated by briquettes density. By the individual steps it was demonstrated that the most significant effect on briquettes quality has pressing temperature and then material moisture and mutual interaction of these two parameters. 1. Paist, A., Kask U, Kask L, et al., Potential of biomass fuels to substitute for oil shale in energy balance in Estonian energy sector, Proceedings of Estonian Academy of Science Engineering, 22, 1, (2005), pp Alaru, M., Kukk, L., Olt, J., Menind, A., Lauka, R., Vollmer, E., Astover, A., Lignin content and briquette quality of different fibre hemp plant types and energy sunflower, Field Crops Research, 124, (2011), pp Kers, J.; Križan, P.; Letko, M.; Šooš, L.; Kask, Ü. & Gregor, A. Mechanical recycling of compounded polymeric waste and evaluation of briquetting parameters, In Proceedings of the 7th international conference of DAAAM Baltic Industrial Engineering 22-24th April (2010), Tallinn University of Technology Press, pp Kers, J., Kulu, P., Aruniit, A., Laurmaa, V., Križan, P., Šooš, L., and Kask, Ü., Determination of physical, mechanical and burning characteristics of polymeric waste material briquettes, Proceedings of Estonian Academy of Science Engineering, 16, 4, (2010), pp Križan, P., Matúš, M., Šooš, L., Kers, J., Peetsalu, P., Kask, Ü., Menind, A. Briquetting of municipal wastes by different technologies for quality and properties evaluation. (2011), Agronomy Research, 19, pp Križan, P., Šooš L., Matúš, M., Svátek, M., Vukelić, D., Evaluation of measured data from research of parameters impact on final briquettes density, Journal of Applied Mathematics, 3, 3, (2010), pp

6 7. Grover, P.D., Mishra S.K., Biomass Briquetting:Technology and Practices; Food and Agriculture Organization of the United Nations; Bangkok, April Rizki, M., Tamai, Y., Koda, K., Kojima, Y. and Terazawa, M., Wood Density Variations of Tropical Wood Species: Implications to the Physical Properties of Sawdust as Substrate for Mushroom Cultivation in Wood Research Journal; Journal of Indonesian Wood Research Society, 1, 1, Nielsen, N.P.K., Gardnerb, D.J.1, Fuel, C.F., Effect of extractives and storage on the pelletizing process of sawdust; Publisher: Elsevier Ltd, Volume 89, Issue 1, January 2010, pp W. E. Hillis and A. N. Rozsa, High temperature and chemical effects on wood stability; Wood Science and Technology,Volume 19, Number 1, pp ADDITIONAL DATA ABOUT AUTHORS Slovak Republic, tel.: M. Matúš, MSc. PhD Student Institute of Manufacturing Systems, Environmental Technology and Quality Management, Slovak University of Technology in Bratislava, Nám. Slobody 17, Bratislava, Slovak Republic, tel.: , milos.matus@stuba.sk Jaan Kers, PhD. Professor Chair of Woodworking Department of Polymer Materials Tallinn University of Technology Teaduspargi 5, 12618, Tallinn, Estonia Phone: Fax: jaan.kers@ttu.ee Andres Menind, MSc. PhD student Institute of Technology, Estonian University of Life Sciences, Estonia, Kreuzwaldi 56, Tartu, Estonia Phone: andres.menind@emu.ee P. Križan, PhD. Head of the Institute of Manufacturing Systems, Environmental Technology and Quality Management, Slovak University of Technology in Bratislava, Nám. Slobody 17, Bratislava, Slovak Republic, tel.: , peter.krizan@stuba.sk L. Šooš, PhD. Dean of Faculty of Mechanics Slovak University of Technology in Bratislava, Nám. Slobody 17, Bratislava, 192