Article pubs.acs.org/EF
Methods for Determination of Biomass Energy Pellet Quality Slavica Prvulovic,*,† Zorica Gluvakov,‡ Jasna Tolmac,† Dragiša Tolmac,† Marija Matic,† and Miladin Brkic‡ †
Technical Faculty “Mihajlo Pupin”, University of Novi Sad, 23000 Zrenjanin, Serbia Agricultural Faculty, University of Novi Sad, 21000 Novi Sad, Serbia
‡
ABSTRACT: This paper will give details of described methods for the laboratory on the examination of biomass energy pellets after they have been through the pressing and cooling process of pressed material. These methods are based on previous experiments collected through the literature. The fundamentals of these experiments are examinations of shape and dimensions, moisture content, bulk density, fine particle content, pellet attrition, ash content, and calorific value of energy pellets as they pass throughout the burning process. The examination results will contain a range of data that was gathered. It will contain evidence of physical characteristics of biomass energy pellets. A comparison of characteristics was performed on the basis of the existing literature and standards. After the comparison of the conducted examination, there will be an examination discussed with other sources or ideas formed by other international theorists. It was clear from the findings of the examination that parameters are acceptable, because the results were relatively similar. It is necessary to use the national standard for defining quality energy pellets and briquettes of biomass for the research. National standards regulate the methods for testing the quality of energy pellets and briquettes of biomass. small-scale combustion systems.12−14 Besides increasing the search for a renewable energy source, energy crops can provide a supplemental income for farmers and, at the same time, show the potential of restoring degraded lands, preventing soil erosion. The use of pellets as a fuel (made from sawdust and wood shavings) has been rapidly increasing throughout Europe. The pelleting process increases the specific density of biomass to more than 1000 kg m3.15−18 Pelleted biomass is low and uniform in moisture content. It can be handled and stored safely and cheaply using well-developed handling systems for grains.19−22 Forest and sawmill residues, agricultural crop, residues, and energy crop can be made into pellets. The pelleting process can upgrade the fuel characteristics and facilitate its use in several ways: (i) it reduces dust emission in the handling of the fuel; (ii) it improves the flow properties, which simplifies conveying and storage; (iii) it increases the bulk density, which eases storage and transportation; and (iv) it leads to a more stable, uniform product with more efficient combustion control. These advantages are likely to stimulate its use in small stoves and boilers, where its enhanced properties will outweigh its extra cost. In most of the European countries, there are no specific regulations concerning pellet energy quality. Biomass regulations are mostly used. Only a few countries have specific regulations.23 At the moment, only three countries have official standards for solid biofuels: Austria Ö NORM M 7135, Sweden SS 187120, and Germany DIN 51731 plus.24 Besides the previously mentioned countries, there is also an adopted European standard EN/TS 14961.
1. INTRODUCTION Biomass is a primary energy source and one of the most desirable renewable energy sources, because of its low level of carbon dioxide emissions and potential sustainability. This can be increased even more if the economic, environmental, and social impacts are properly managed.1−3 Biomass includes trees, agricultural and forest residues, human or animal waste, energy crops, organic fraction of municipal solid waste (MSW), food-processing wastes, sewage sludge, and leachate.4−6 With the continuous rise and fluctuations of fossil fuel prices and increasing environmental concerns regarding emissions produced through fossil fuel use, biomass can be considered an even more promising renewable energy source to meet a variety of energy needs and replace fossil fuels.3,7,8 Biomass is the fourth largest source of energy in the world, contributing about 35% of primary energy consumption in developing countries and 3% of primary energy consumption in industrialized countries. However, applications of biomass as an alternative fuel are limited because of the high transportation cost, storage difficulties, and reduced thermal efficiency during energy conversion. These results were of energy levels in the low density of biomass compared to traditional fossil fuels because of the high moisture content that commonly exceeds 50 wt % [wet basis (wb)]. Europe set a target of reaching 20% of renewable energies by 2020, and biomass can play an important role.9 However, the increasing need to make biomass from wood residues in the heating sector with sawmills, pulp, and paper resulted in the increase in the price of wood.10 As a result, the interest for alternative biomass fuels is growing rapidly, covering materials from wood residues of low quality, energy crops, and agricultural and forest residues.11 There are several benefits from expanding the spectrum of biomass raw materials used in © 2014 American Chemical Society
Received: December 4, 2013 Revised: February 5, 2014 Published: February 5, 2014 2013
dx.doi.org/10.1021/ef402361k | Energy Fuels 2014, 28, 2013−2018
Energy & Fuels
Article
Table 1. New European Standards for Energy Pellet ENplus parameter
unit
diameter length bulk density calorific value moisture fine particles
mm mm kg/m3 MJ/kg mass % mass %
mechanical durability ash content ash melting behavior chlorine sulfur nitrogen copper chrome arsenic cadmium silver plumbum nickel zinc mercury
mass % mass % °C mass % mass % mass % mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg
ENplus A1
ENplus A2
ENplus A3
6−8 (±1) 6−8 (±1) 6−8 (±1) 3.15 ≤ L ≤ 40; maximum, 45 (1%) 3.15 ≤ L ≤ 40; maximum, 45 (1%) 3.15 ≤ L ≤ 40; maximum, 45 (1%) ≥600 ≥600 ≥600 ≥16.5 ≥16.5 ≥16.0 ≤10 ≤10 ≤10 the amount of fine dust must be ≤1%, counting the amount of dust in the packing pellets or end customer, if it performs bulk transport; the amount of fine dust may be an agreement between the manufacturer and the customer ≥97.5 ≥97.5 ≥96.5 ≤0.7 ≤1.5 ≤3.0 ≥1200 ≥1100 ≥1100 ≤0.02 ≤0.03 ≤0.03 ≤0.05 ≤0.05 ≤0.05 ≤0.3 ≤0.5 ≤1.0 ≤10 ≤10 ≤10 ≤10 ≤10 ≤10 ≤1 ≤1 ≤1 ≤0.5 ≤0.5 ≤0.5 ≤0.1 ≤0.1 ≤0.1 ≤10 ≤10 ≤10 ≤10 ≤10 ≤10 ≤100 ≤100 ≤100 ≤0.05 ≤0.05 ≤0.05
The European Committee for Standardization25 (CEN) under Committee TC 335 has published 27 specifications for solid fuels from 2003 to 2006.26 These technical specifications are amended and adopted as European standards (EN) 2010. When EN standards become valid, the national standards have to be changed to match these new standards. The new European standards for energy pellets ENplus A1, A2, and A3 are shown in Table 1.27 These standards resulted from the standard EN 14961. Conditions defined with these standards must be complied to make the energy pellets of standard quality, which can later be placed on the market and used. Quality standardization and its method of production along with the delivery are extremely important for the successful creation of energy pellets. It is possible to check quality standards using methods for examining defined parameters of energy pellets. The aim of this work is to examine the results of the laboratory examination of quality of energy pellets produced after biomass pressing and cooling.
analysis for accurate conclusions. Checking of methods for analysis of energy pellet quality was carried out in the Laboratory for Thermodynamic and Processed Technique of the Department for Agricultural Techniques, Faculty of Agriculture in Novi Sad. 2.1. Method for Shape and Dimension Determination in Energy Pellets. Determination of the shape of biomass energy pellets was decided visually. The dimension of energy pellets is the diameter and length. The necessary equipment used for deciding the dimension of the energy pellet is Vernier Fowler calipers (mobile-type measurer). The average sample is measured by Vernier Fowler calipers. After that, the average value of the dimension (diameter and length) of energy pellets is calculated. 2.2. Method for Measuring the Moisture Content Determination in Energy Pellets. The moisture content in biomass pellets is the “loss” of mass that a chipped pallet mass loses during 2 h of the drying process at a temperature of 105 °C. The moisture content determination in pellets was carried out according to the standard SRS E.B8.012. Necessary equipment for moisture content determination in the pellet is an analytical scale with an accuracy of ±0.1 g, a laboratory mill (for crunching a pellet), metal drying pots, an electric dryer with the possibility of temperature regulation, adjusted at 105 °C, and an eksikator. The sample with a weight of 20 g was taken as the average sample for the moisture content determination of the pellets and powder. The grounded pellets were immediately placed in measured pots, and its mass was measured before it absorbed any amount of moist from the surrounding air. The moisture content of energy pellets is calculated on the basis of the mass ratio to obtain the mass percentage according to the formula
2. MATERIALS AND METHODS Energy pellets made from raw materials were used during this evaluation process. Raw materials used in the production process of the final product (pellets) were straw, fir sawdust, beech sawdust, and mixed biomass. On the basis of the raw materials used, five different kinds of pellets were produced: straw pellets, fir pellets, beech pellets, 87.5% beech and 12.5% fir pellets, and 50% fir, 30% beech, and 20% straw pellets.28 Sampling of energy pellets for analysis of biological and thermal properties was aided by the production plants of companies who are interested in pellet production. The way of deciding is determined by the manual for wheat sampling UP.05.3.002. Energy pellet samples of 3 kg were placed in sealed bags and stored in a refrigerator until analysis. Working methods were designed for the collection of data analysis of energy pellet quality based on previous standards and regulations. What was also considered was the building of necessary equipment and laboratory checking for the most important methods for pellet
ω=
(m1 − m2) × 100 m1
where ω is the moisture content (%), m1 is the mass before drying (g), and m2 is the mass after drying (g). For every moisture content reading, it is necessary to do at least three measurements at the same time. The difference between these measurements must not be more than 0.2% (absolute value). The moisture content is shown as an average result of measuring, to two decimals. 2014
dx.doi.org/10.1021/ef402361k | Energy Fuels 2014, 28, 2013−2018
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Table 2. Test Results of the Form, Properties, and Dimensions of Biomass Energy Pellets species material
origin of material
structure of materials
form
average length (mm)
diameter (mm)
87.5% beech and 12.5% fir wheat straw 50% fir, 30% beech, and 20% wheat straw fir beech
sawdust straw sawdust sawdust sawdust
crushed crushed crushed crushed crushed
cylindrical cylindrical cylindrical cylindrical cylindrical
21.0 21.0 23.7 14.5 14.9
6 6 6 6 6
Table 3. Test Results of the Bulk Density, Unit Weight, Porosity, Fine Particles, and Obliteration of Biomass Energy Pellets species material
bulk density (kg/dm3)
unit weight (kg/dm3)
porosity (%)
fine particles below 3.15 mm (%)
obliteration (%)
87.5% beech and 12.5% fir wheat straw 50% fir, 30% beech, and 20% wheat straw fir beech
0.554 0.734 0.573 0.735 0.655
1.271 1.350 1.500 1.292 1.300
50 53 66 50 54
0.22 0.05 0.45 1.74 3.07
0.55 0.19 1.39 2.03 3.75
2.3. Method for Bulk Mass Determination in Energy Pellets. Bulk mass (bulk density) is a parameter that is easy to determine and is the mass and total volume of the energy pellet ratio, according to Mohsenin29 and Singh and Goswami.30 The bulk mass of a pellet is calculated according to the formula m ρn = V
the combustion (20 g), and then we measure the mass of the cooled mixture of coke and ash, to find the percentage of a mixture of coke and ash in the total sample of pellets. From the total weight of a mixture of coke and ash, we took 1 g of sample for annealing. After annealing, the measured mass of cooled ash and the calculation of the ash percentage in 1 g of sample mixture of coke and ash is determined. After that, we determined the mass of ash in the total weight of a mixture of coke and ash. Finally, on the basis of the mass of ash in the total weight of the mixture of coke and ash, we determined the percentage of ash in the total mass of the sample pellet of 20 g. 2.7. Method for Determination of the Calorific Value of Energy Pellets. The upper calorific value of pellets is determined calorimetrically by EN ISO 1716. The mass of dry milled or whole sample of 1 g was measured on the analytical scale and placed in a small bowl. The small vessel with the sample was placed in the upper part (cover) of the “bomb”, where the electrodes were connected with a wire. After that, the “bomb” was closed and filled with oxygen under a pressure up to 30 bar. The device causes the process of complete combustion of the sample. A certain amount of heating energy was released by combustion of the sample, which was noted, and was transferred to the computer record. For each determination of the ash content, at least three measurements should be performed and then calculated for the average thermal value of the energy pellets rounded to two decimals. The lower calorific value of pellets was obtained from the formula
where ρn is the bulk mass (kg/m3), m is the sample mass (kg), and V is the total volume of the sample (m3). 2.4. Method for Determination of Fine Particles in Energy Pellets. Fine particles of energy pellets (sample) are particles (impurity) smaller than 3.15 mm, as well as dust in the sample.28 The necessary equipment for determination of fine particles are an analytical scale, a measuring pot, and a sieve with a dimension of 3.15 mm (in our case, it was 3.25 mm, because we did not have the standard sieve). For every determination of fine particles, it is necessary to do at least three measurements. Pellet attrition is the average result of measurements of fine particles. 2.5. Method for Determination of Energy Pellet Attrition. Resistance of energy pellets to attrition (wear) is determined in a rotational container according to ASAE standard 269.2.31 The device was constructed in a workshop of the Department for Agricultural Techniques, Faculty of Agriculture in Novi Sad. Samples of 1 kg with a deviation of ±20 g were taken for attrition determination, placed in a box with dimensions of 300 × 300 × 450 mm, closed, and spun at the speed of 13 times/min for 3 min. When the standard box stopped turning, the sample was sifted and the calculation of the fine particle percentage was performed. The difference minus the percentage of fine particles is the pellet resistance. 2.6. Method for Determination of the Ash Content in Energy Pellets. The ash content of the sample is the mass of energy pellets remaining after complete combustion of the sample at a temperature of 575 ± 25 °C, expressed as a percentage, according to SRS H.N8.136. The necessary equipment for working out the ash content are a platinum, quartz, or porcelain pot, cup, or bowl, an electric furnace with a temperature control at 575 ± 25 °C, a catcher for the pot, cup, or saucer, a laboratory chopper, and analytical laboratory scales. From the average sample used for the determination of the ash, a 20 g sample was taken and chopped very fine. Fragmented pieces of appropriate size were immediately put into a pan and carefully burned at the open flame to full carbonization (carbonization of the sample). After a complete combustion of the sample, a mixture of ash and coke was obtained. The weight of 1 g of combusted sample was taken from the bowl and put into a cup. The cup was placed in a kiln, which was gradually heated. Annealing was performed at 575 ± 25 °C for the next 3 h. During the annealing process, the coke is completely burnt. The ash content in the energy pellets is calculated in the following order: first, we measure the mass of a sample of crushed pellets before
hg = hd + 2500(9h + w) where hg is the upper calorific value (kJ/kg), hd is the lower calorific value (kJ/kg), h is the amount of water after hydrogen combustion (kg), and w is the moisture content in relative units (′).
3. RESULTS AND DISCUSSION The basic results of the described tests were obtained by laboratory research into the determination of the shape, size, moisture content, bulk mass, content of fine particles, attrition, thermal values, and strength of energy pellets. The tests of physical and mechanical properties and thermal energy pellets from fir, beech, and mixtures of wheat straw biomass (fir and beech and fir, beech, and straw) were conducted. Tables 2−4 show the results of tests of biomass energy pellets. The origin of the pellet material is straw or sawdust, with the material structure segmented (chopped to 3−5 mm). Examined energy pellets were cylinder shape. The diameter of the pellets, 6 mm, was the same. The average length of the energy pellet samples was different (from 14.5 to 23.7 mm; Table 2). On the basis of these data, it can be concluded that the pellets of fir and beech have the same length, that a mixture of beech and fir also 2015
dx.doi.org/10.1021/ef402361k | Energy Fuels 2014, 28, 2013−2018
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density than from literature sources. The bulk density in biomass energy pellets is defined by EN plus standard (≥600 kg/m3), which coincides with the statement above, and in comparison to the values of the apparent density for all tested pellets, it was in the range acquired from literature sources. The bulk density is not defined in the DIN standard. The bulk density of all analyzed pellets is within the regulated performance standards EN 14961-1 (from ≥550 to ≥700 kg/ m3 and over 700 kg/m3). The content of fine particles and attrition are directly corresponding to the level of resistance of biofuels to pressures or damage during handling or transportation, but these parameters are not defined in standard DIN or EN standards plus and even in available literature. The EN 14961-1 standard content of fine particles (
