- Email: [email protected]
Characterization of the woody cutting waste briquettes containing absorbed glycerol
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
Available online at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Characterization of the woody cutting waste briquettes containing absorbed glycerol Laurencas Raslavicius* Faculty of Mechanical Engineering and Mechatronics at Kaunas University of Technology, Ke˛stucio g. 27, 44312 Kaunas, Lithuania
article info
abstract
Article history:
The aim of the present work was to evaluate waste-to-energy technology for the utilization
Received 16 November 2010
of crude glycerol (84.5% purity) surplus, collected by the largest Lithuanian biodiesel plants.
Received in revised form
The research examined the use of glycerol and woody (timber) cutting waste (WCW) to
28 May 2012
produce fuel briquettes. Two ratios of glycerol mass share 10% and 20% per unit volume
Accepted 30 May 2012
were proposed as a partial substitute for WCW in briquette production process, thus
Available online 22 June 2012
solving glycerol utilization problems present in Lithuania. Proposed volumes of additive are in strong agreement with EN 14961-1. Affirmative proportions for interfusion of input
Keywords:
materials, durability rating of fuel briquettes, characterization of combustion regimes and
Crude glycerol
emission characteristics were assessed based on their composition. The optimum fuel
Fuel briquettes
properties were demonstrated by WCW briquettes containing maximum 10% glycerol mass
Durability
concentration. Combustion of such briquettes exposed low CO, SO2 and NOX emission
Woody cutting waste
levels, falling under requirements of LAND 43e2001. Further increase in glycerol share is
Biodiesel by-products
not recommendable, in the larger part due to the decrease in physical-mechanical properties, but not from emission constrains. ª 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
There are numerous waste-to-energy technologies, each with varying efficiencies and capabilities to digest complex waste streams [1]. After the energy crisis in the 1970s, considerable attention was focused on the development of alternate energy resources [2]. At present decade, there is a renewed interest in biofuels due to increasing concerns about energy security, environmental pollution [3e6], and problems connected with utilization of the industrial by-products of organic nature [7,8]. One such renewable fuel that is being widely commercialized is biodiesel. The biodiesel obtained via transesterification of vegetable oils or animal fats is an alternative to current fossil fuels [9,10]. Citing Fernando et al. [3], and Melero et al. [11], a large amount of glycerol as a by-product is generated in this process and new applications for this surplus need to be found.
1.1. Chemical principles of glycerol formation in biodiesel production process In a transesterification or alcoholysis reaction 1 mol of triglyceride reacts with 3 mol of alcohol to form 1 mol of glycerol and 3 mol of the respective fatty acid alkyl esters [12e15]. The process is a sequence of three reversible reactions, in which the triglyceride molecule is converted step by step into diglyceride, monoglyceride and glycerol [15,16]. In each step 1 mol of alcohol is consumed and 1 mol of ester is liberated. Usually, methanol is added in an excess over the stoichiometric amount in most commercial biodiesel production plants. Another advantage of methanolysis as compared to transesterification with higher alcohols is the fact that the two main products, glycerol and fatty acid methyl esters (FAME), are hardly miscible and thus form separate
* Permanent address: Savanoriu˛ pr. 370e4, 49362 Kaunas, Lithuania. Tel.: þ370 610 24254, þ370 37 718592; fax: þ370 37 718592. E-mail address: [email protected]. 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biombioe.2012.05.028
145
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
phases e an upper ester phase and a lower glycerol phase [16]. This process removes glycerol from the reaction mixture and enables high conversion. Citing Bacovsky et al. [16], Cernoch et al. [17] and Mittelbach and Remschmidt [13], ester yields can even be increased e while at the same time minimizing the excess amount of methanol e by conducting methanolysis in two or three steps. In this case only a portion of the total alcohol volume required is added in each step, and the glycerol phase produced is separated after each process stage [16].
1.2. Glycerol surplus subjected to biodiesel production in Lithuania According to the method used to produce the biodiesel fuel, glycerol (G) can be assigned to one of three categories based on its purity: raw glycerol (G 63.3%), crude (technical) glycerol (G w 80%) and glycerol of the highest purity (G > 99.8%) [18]. In the largest biodiesel production plants of Lithuania, methanol is evaporated from the glycerol fraction, and the free fatty acids are purified away by biodiesel washwaters, producing crude (technical) glycerol of w80% purity. In general, for every kilogramme of biodiesel produced, 0.09 kg of crude glycerol is liberated. Usually, crude glycerol is collected and purified up gas et al. [18] concluded that, the present situto 99.8%. Striu ation causes additional costs in energy and materials, and the demand for it is limited because of a large surplus in the market. Hereby, the new ways for effective utilization of crude glycerol must be founded. The Lithuania-wide potential of yearly glycerol yield was analysed using a resource-focused approach (see Table 1) to appreciate potentially available quota of glycerol, possibly been practiced as a partial substitute for woody cutting waste (WCW) in briquettes production.
1.3.
Pending issues and practical background
Currently, in EU-27 countries, an additive share to compound woody biomass intended for briquettes production is described by the following European norms: 1) EN 14961-3 (draft). The Normative establishes a maximum share of additive is 2% for non-industrial application.
2) EN 14961-1 gives a general classification of solid biofuels. In this case, the possibility of higher amounts of additives of pressing mass (up to 20%) is given. To sum it up, EN 14961-1 gives a real opportunity for a wider application of organic waste materials intended to be a partial substitute for densified biomass-to-industrial briquettes production and at the same time lay under the established requirements for solid biofuels. In many countries, industrial briquettes are acquiring an increasing importance [19]. Citing Szklo and Schaeffer [20], energy carriers for multi-fuel and multi-product strategies, where flexibility is a key target, allied to other co-benefits, especially those related to the increased use of renewable energy sources. The initial challenge of the present research activity was to mate the by-product (glycerol) cumulated by Lithuanian biodiesel plants and to prove that the stored waste can be effectively applied as an additive to industrial briquettes intended for industrial and institutional heating systems. The proposed type of solid biofuel was the result of the required thorough scientific analysis and high level of optimization with full consideration of the context within which it would be operating.
2.
Materials and methods
2.1. Organic input materials and specimens nomenclature Two organic input materials were selected for briquetting experiment: timber cutting waste and crude glycerol. Chemical composition of glycerol, applied for briquetting experiments after removal of methanol from glycerol phase, is presented in Table 2. Woody cutting waste for briquettes production was obtained at JSC Bionovus e the largest supplier of solid biofuels in Lithuania (member of Lithuanian biomass energy association LITBIOMA). An area harvested in the forest is located in Marijampole_ County LT-MR (WGS84: 54 330 3100 N, 23 200 5800 E; UTM: 34U 651922 6048214). WCW were collected from pure hardwood stands and mixed hardwood stands that had followed the cutting of 22e25 years old-field beech (Fagus grandifolia), oak (Quercus robur) and alder (Alnus glutinosa) as dominating tree species. The date of forest harvesting works
Table 1 e Biodiesel production in Lithuania (2004e2010) and cumulated amounts of crude glycerol. Year
2004 2005 2006 2007 2008 2009 2010
Biodiesel production, thousand tonnes
Constitutional part in total liquid fuel consumption, %
Crude glycerol (by-product), thousand tonnes
2.2 7.0 10.3 40.0 190.0 190.0 190.0
0.20 0.57 0.84 3.33 12.20 12.20 12.20
0.198 0.630 0.927 3.600 17.100 17.100 17.100
Table 2 e Experimentally settled chemical composition of crude glycerol. Composition Glycerol Water Methanol Phosphorus Potassium Rapeseed oil methyl ester (RME) Other contaminants
Crude (technical) glycerol 84.55% 6.82% 2.16% 0.15% 2.63% 0.37% 3.32%
3.60% 0.41% 0.34% 0.02% 0.15% 0.02% 0.23%
146
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
is December 7e18, 2009. Four bags of the randomly taken WCW were transported to the Department of Bioresources at Lithuanian University of Agriculture Institute of AgroEngineering. The moisture content of the WCW before briquetting was 38%e42%. The raw material was poured into a laboratory pneumatic drying system which automatically reduced the moisture content to 8% at 240 Ce290 C for 120 min. The size distribution of timber cuttings was found by sieve analysis. By limiting the largest mesh size to 5.0 mm, the mean particle length was found to be 3.0 mm. The calorific value of the timber cuttings was determined using a bomb calorimeter, and was found to be 16.7 MJ kg1. A pruned nomenclature G0, G10 and G20 means what percentage of the mass fraction of crude glycerol is actually in briquette, the rest is WCW.
2.2. Combustion device, gas analyser, and chemical analysis method An experimental combustion device was developed in order to study combustion process of glycerol contained WCW briquettes. The preferred embodiment of the apparatus is illustrated in Fig. 1. Fig. 1 shows a rectangular-shaped stoker equipped with air-cooled stationary sloping grate as well as air supply system (primary air and secondary air), which plays a very important role in the efficient and complete combustion of biomass. The installation incorporates a horizontal grate surface. For gratefiring, the overall excess air for most biomass fuels is normally set to 25% [21]. The split ratio of primary air to secondary air was set to be 80/20. Secondary air (advanced) supply system is one of the most important elements in the optimization of the gas combustion in the freeboard, for complete burnout and lower emissions, e.g., by forming local recirculation zones or rotating flows and by forming different local combustion environments (e.g., fuel-rich or oxygen-rich) [21]. Accordingly, an optimization of
the secondary air supply rates allowed us to retrofit the old combustion unit based on grate firing to describe the burning characteristics of newly derived type of biofuel. Fuel briquettes were delivered from the hopper to the stoker through the auger tube with a set periodicity. Each cycle consisted of the following distinct phases: working period (an auger was switched on) and pause period (an auger was switched off). Portions of the supplied fuel were adjusted by varying the durability of the working and pause periods. Combustion process was studied by alternating of the supplied air volume. The supply of combustion air (primary and secondary) was controlled via Rota Yokogawa rotameters, type RAKD. The rotameter was calibrated using FVA-Series air flow sensor FVA915-S120 and data logger ALMEMO-2290-8 equipped with AMR-Control software. Combustion temperature was measured via ultra high stability NiCroSil-NiSil (Type N) thermocouple and registered by ALMEMO-2290-8 with a 1 C accuracy. To evaluate the emission level of the combustion device operated in the previously established conditions, analyser of gases, model PCA-65 (CO; CO2; O2; SO2; NOx), manufactured by Bacharach Inc. was applied. The combustion products were also analysed for acroleine concentrations by GC (gas chromatograph) on CP Wax 52 CB capillary column (L ¼ 50 m, diameter ¼ 0.25 mm, film thickness ¼ 0.2 mm) in a HewlettePackard 5890 Series II gas chromatograph equipped with flame ionisation detector. Before the measurements, acroleine was absorbed from combustion products by SKC Sorbent Tube, XAD-2 (2Hydroxymethyl Piperidine). The chromatographic data were obtained by the H.P. Chemstation software. Acroleine samples were taken from the site in the grate stoker which is above the flue gas outlet. Ash content was established under the laboratory conditions, using a standardized procedure described by Sluiter et al. [22]. Methodology involved calculation of ashpercentage-rate as a relation between the ash weight of the
Fig. 1 e Experimental air-cooled stationary sloping grate stoker and briquettes supply system.
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
burnedeout specimen against the initial weight of the same specimen. An ash weight of the tested specimens was determined by weighting machine SA-120CE (accuracy: 0.2 mg).
2.3.
Briquettes production technology
A continuous automatic briquette press was developed for pressing glycerol absorbed WCW into briquettes (see Table 3). The main element of the pressing device consisted of a cylinder fitted with a sliding piston that exerted force upon a confined fluid, which, in turn, produced a clamping force (CF) upon a stationary baseplate. Glycerol was preheated until 40 Ce45 C and poured in various proportions over WCW to absorb the powdery mass. The specimens prepared for pressing contained glycerol mass share 10% and 20% per unit volume, respectively. To the baseline of the experiment, the control specimen consisted of straight WCW. The mass of a single specimen was 1.0 kg 0.072 kg. Various amounts of glycerol absorbed powdery mass dashed manually, thereafter closing the prepared specimens to the separate glass containers and placing them to the thermostatic cabinet (THSC) for 3 h to achieve the best possible soak-up characteristics of the interfused mass. Temperature in the THSC was set to 95 C 1 C. A clamping force was measured with the help of OBMG-160 manometer connected to the fluid hose of the hydraulic cylinder. Before the briquetting process, a pressing chamber was heated-up to 200 C 5 C by using an electric heater of 600 W capacity.
2.4.
Maximum glycerol insertion testing
A prepared mass for specimens production was stoked up to the matrix by piecemeal enclosure every time consolidating
Table 3 e Specification of the briquetting press. Technical data Press capacity Maximum clamping force Diameter of briquette Length of briquette Max. moisture content of cutting waste Manometer Diameter/Stroke of hydraulic cylinder Hydraulic gear pump
Hydraulic station Electric motor Dimensions (L H W) Weight
57 kg h1 1700 kg cm2 35 mm 70 mm 14% OBMG-160 220 mm/300 mm Sauer-Danfoss: Pressure (inlet) e 0.8 bar absolute recommended, Pressure (outlet) e 276 bar, Fluid viscosity e 10 mm2 sec1 (biodegradable fluid) HITECH (stationary; produced on request) BEVI (2D 180 L-4), 18.5 kW, n ¼ 1450 s1, 59.1 A, 230 V, 50 Hz 1800 mm 1900 mm 1800 mm 3000 kg
147
up it with a desktop laboratory press at CF¼80 N. After the matrix being well-stocked, a specimen was stressed by the hydraulic hoist at 50 kN, herewith monitoring a possible glycerol penetration through the interstice between the matrix walls and the piston. Standard laboratory safety precautions were observed when carrying out maximum glycerol insertion tests at process temperature of 200 C due to 2.16% methanol content in the chemical composition of glycerol (see Table 2). Personal protection for the safe handling of crude glycerol at elevated temperatures included adequate ventilation, wearing of safety glasses and chemical-resistant gloves coupled with evacuation of any unprotected personnel from laboratory premises.
2.5.
Physical and mechanical properties testing
The mean compressed density of the briquettes was determined immediately after removal from THSC as a ratio of measured weight over calculated volume. Measurement data for density calculations obtained via electronical weighting machine VLTK-500 (accuracy: 0.01 g) and vernier callipers (accuracy: 0.5 mm). To determine dimensional stability, the length of five representative briquettes from each production batch was measured under the stress effect of desktop laboratory press by embedding them between piston and stationary baseplate. The durability of the briquettes was determined with the aid of a durability tester, i.e., a dusttight 400 mm 305 mm 305 mm enclosed box rotating around diagonal axis. Test sample of five briquettes was tumbled for 3 min at rotational frequency n ¼ 13 min1. A percentage of a quantity of unshattered briquettes leftover in the box after the test trial against remaining ones, having a residual weight no less than 20% of their initial mass, was setted as the main strength criterion.
2.6.
Establishment of calorific value data
An isoperibolic temperature regulated oxygen bomb calorimeter (OBC: 230 VAC, 3 A, 50/60 Hz), manufactured by Fire Testing Technology Ltd, been applied to ascertain calorific value of glycerol purified by biodiesel washwaters.
3.
Results and discussion
3.1. Affirmative proportions for interfusion of input materials Samples of the G0, G10 and G20 briquettes produced are shown in Fig. 2. Briquettes produced using 100% woody cutting waste (G0) assumed a greyish brown colour, while those produced using different proportions of glycerol purified by biodiesel washwaters assumed different shades of darkly lit yellow colouration, depending on the quantity of crude glycerol included. As shown in Fig. 2, the average relaxed density (i.e., the density of briquette after removal from the press) of glycerol containing specimens ranged from 743 kg m3 13.6 kg m3
148
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
Fig. 2 e Specimens of WCW-G briquettes.
3.2.
Durability rating of fuel briquettes
The briquette durability (shatter-resistance (ShR) and stressresistance (StR)) rating test is intended to ascertain the ability of densified specimens to withstand the rigours of handling such that they keep their mass, shape, and integrity [23]. As shown in Fig. 3, the ShR of the different briquette composition ranged from 78.0% for G20 to 95.6% for G0 briquettes. Obtained durability rating values were comparatively high in collation with reported by Wamukonya and Jenkins [24] (46.5% and 88.4%, respectively) for sawdust briquettes having the comparable share of biomass (wheat straw) content. However, according to Richards [25], in the
120
1
0.97 kN
100
0.91 kN
95.6%
0.87 kN 86.7%
80
78.0%
0.9
0.8
60
0.7
40
0.6
20
0.5
0
0
10
20
0.4
G [%]
Fig. 3 e Briquette durability (shatter-resistance (ShR) and stress-resistance (StR)) versus glycerol share.
StR [kN]
process development stages, it is suggested that the tests should relate to the briquette material, rather than the briquette as an entity. Appreciating the fact, that glycerol insertion to the sawdust or cutting waste was not examined in a broad-brush content, these would allow inter-laboratory inferences of briquette formulations. The definitive durability rating (see Fig. 3) for twocomponent solid biofuel was observed in briquettes produced with 90% woody cutting waste (G10). As it was expected, the G0 briquettes were found to have better overall handling characteristics. It stands to reason, therefore, that the WCW briquettes, that had 8% moisture content and the highest density also had the highest ShR (95.6%) as well as StR (0.97 kN) rating. Agreeably, the indication of durability rating for G20 briquettes (ShR ¼ 78.0%; StR ¼ 0.87 kN) fell by the wayside in search of key composition. Notwithstanding this fact and citing Chin and Siddiqui [26], fuel briquettes of different biomass materials required different optimum conditions of fabrication and generally showed a promising potential for further development.
ShR [%]
to 798 kg m3 15.3 kg m3, while the average density of G0 briquettes balanced in the range of 861 kg m3 24 kg m3. According to experimental results, G20 specimen revealed in 1.16 times lesser density than G0 (see Fig. 2). It was established that 20% of glycerol containing briquettes compressed in a closed cylinder had a tendency to expand as the pressure was released. Fig. 2 shows that G20 briquettes were significantly deformed and lost their cylindrical shape. Also an expansion was observed, which took place in longitudinal direction, i.e., direction in which the load was applied. The shape structure of G10 and G0 was not observed to change. During the briquetting experiment, the CF ranged from 73 MPa 3.6 MPa for G20 to 92 MPa 5.1 MPa for G0, respectively. A disparity in values of clamping force for materials of different consistence is attributed to the excellent lubricating properties of glycerol. A better performance of press device is explained by the decrease of friction force between the walls of the presschamber. However, a briquetting process of the interfused mass (CF ¼ 73 MPa) having 20% glycerol mass concentration indicated some troubles due to observed glycerol penetration through the interstice between the matrix walls and the piston. The production process was restricted by glycerol viscosity drop due to the process temperature (200 C).
The fuel burnt as it fell down from the auger tube under gravity. After ignition, a reaction front propagated against the direction of the primary air. The heat, generated in the reaction front, was transported against the primary air flow and dried and devolatilized the briquettes. This allowed the reaction front to propagate. The gases released from biomass conversion on the grate and a small amount of entrained fuel particles continued to combust in the freeboard, in which the secondary air supply played a significant role in the mixing, burnout, and emissions [21]. The O2 concentration in the gas dropped quickly in a space of 11 min at t ¼ 2.5 min from ambient level (20.9%) to a 5% (see Fig. 4). This was followed by a sharp increase in CO and CO2 to 20.5% and over 17,000 mg m3 respectively. The level of CO2 was mostly above 7600 mg m3e6900 mg m3 for 60 min from t ¼ 25 min to t ¼ 85 min (01:25:00). As the rate of mass loss of the briquettes gradually decreased, CO concentration declined steadily from 10% to about 2% in that period of time. O2 concentration began to rise at t ¼ 14 min marking a participation of excess air. Participation of the sulphur dioxide in the flue gases was inconsiderable and varied within range of the margin of error. A combustion temperature ranges of fuel briquettes as a function of specific volume of air (SVA) at the supply condition were presented in Fig. 5. In order to burn G0, G10 and G20 briquettes effectively the fuel had to be supplied into a 900 Ce1000 C temperature environment (see Fig. 5). The experimental data showed that briquettes consisting only of pressed WCW (G0) had a decidedly lower combustion temperature (Tcomb) than briquettes with 10% and 20% of glycerol content. The highest combustion temperature (985 C) was observed while burning of the G20 specimens at SVA ¼ 4 m3 kg1. An observed tendency, when the marked improving in SVA at the supply condition caused the decrease in Tcomb values is explained by stoker cooling effect provided by excess air. The best combustion characteristics were demonstrated by G10 at SVA ¼ 3e6 m3 kg1, taking into consideration an optimum glycerol share (see Chapter 3.1). Appreciating the formation mechanism of nitrogen oxides for two organic constituents, a major source of the NO formed
Fig. 4 e Combustion process characteristics for G10 briquettes.
Tcomb [oC]
3.3. Characterization of combustion regimes and emission characteristics
1300
200 G20
1250 1200
180
G10
160
NOX [mg m-3]
149
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
G0
1150
140
1100 G20
1050
G10 G0
1000 950 900 850
100 80
G20 G10
G20 G10 G0
G0 2
120
4
6 SVA [m3 kg-1]
8
10
60 40
Fig. 5 e Comparison of the dependence of Tcomb and NOX emissions on the SVA at the supply condition and glycerol share.
in combustion process could be explained by oxidation of atmospheric N2, i.e. thermal NO [9]. Li and Thompson [27] concluded, that for the simplified models describing the relationships between NOX emissions and combustion device operational parameters, it is reasonable to accept the precondition, that excess air is always provided in the combustor to ensure complete combustion. In this case, the contribution of prompt NO to total nitrogen oxide emissions is negligible. Nitrogen oxide emission values were obtained by alternating of the supplied air volume. Fig. 5 shows the measured increase in effluent NOX concentrations with increasing crude glycerol share and for the combustion tests performed for this study. The distribution of NOX is relatively low for investigated types of fuel briquettes and falls under requirements of LAND 43-2001 [28], limiting nitrogen oxides content in exhaust gases to 650 mg m3 while burning any solid biomass. It is likely that the share of crude glycerol extends the reaction zone allowing for greater mixing of fuel and combustion air, so that a greater percentage of fuel nitrogen is released [29] in comparison with G0. This explanation is substantiated by the observation that the G20 briquettes demonstrated in 8%e12% higher NOX emission level (160 mg m3e189 mg m3) than the G10 (148 mg m3e168 mg m3), for the same excess air (3 m3 kg1e5 m3 kg1). Further increase in SVA rates (starting from 4 m3 kg1 and ending with 10 m3 kg1) caused an overall decrease in NOx emission level for all three types of briquettes (G0, G10 and G20). This tendency was influenced by cooling effect (i.e. decreased combustion temperature) in the stoker. Since the burning of glycerol contained woody cuttings briquettes is a relatively new trend in biomass application for heat production, not much has been done to characterize hazardous compounds emitting from the combustion of glycerol. There has been a long-standing fear that combustion of glycerol releases toxic acrolein gas unless carried out at a sufficiently high temperature. Moreover, scholars in the field have theorized that complete and clean combustion of glycerol requires a burning temperature in excess of 1000 C and a relatively long mean residence time in the combustion chamber. The chromatographic analysis curves for the
150
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
samples were compared to the calibration curves as described gas [31]. When the chromatographic peaks in detail by Striu are examined, it was observed that they are very insignificant and are difficult to differentiate from the noise distribution around a base curve shape. On this understanding, from the pure WCW-G specimen combustion analysis it was concluded that acroleine decomposes in full at 900 Ce1000 C temperature environment and it was not detected by the used method. In summary, the results of the experiment show that safe, clean, and efficient combustion of a WCW-G briquettes is possible with an air-cooled stationary sloping grate stokers of the proposed modification and primary/secondary air ratio. Otherwise, effective combustion of glycerol also requires combination with another fuel source, such as sawdust, cuttings, etc [30]. Boham et al. [32] concluded, that in some cases primary carbonyl (acroleine) emissions from glycerol combustion in the described above temperature range may be comparable to those from other conventional fossil fuels. It is in strong agreement with the results obtained by other researchers who had a goal to understand and improve the combustion characteristics of crude glycerol at temperature range of 800 Ce1000 C [18,30e32].
3.4. Calorific value, origin of the ash content and its alternation Calorific value of investigated biomass briquettes was affected by the ash content (see Fig. 6). The higher the ashes content of the raw material, the lower the calorific value, because ash is a material that does not generate energy [33]. If we look into briquette’s calorific value, it can be seen that the higher ash content of G0 (1.45%) and G10 (0.9%) briquettes produced the lower calorific value (16.7 MJ kg1 and 17.1 MJ kg1) in comparison to G20 (17.5 MJ kg1). Pure WCW briquettes resulted in the lowest calorific value (16.7 MJ kg1) because they had the highest ash content of 1.45%. Ash from WCW comes from the minerals presented in the structure of trees in addition to any soil contamination. Properties of wood waste ash depend on a variety of factors including type of tree, part of the tree (bark or wood), type of
soil, climate, combination with other fuel sources, and conditions of combustion. To sum it up, the powdery mass of timber cuttings, interfused with glycerol in proportion G10 and G20 shows a markable decrease in measured ash content. Notwithstanding this fact, only 10% of glycerol share in WCW briquetting process was possible under proposed technology, because G20 briquettes were not uniform in density, nor had good structural strength. Thus, combustion characteristics for G0 and G20 briquettes were investigated on the purpose of a supporting approach e to study the tendencies for many variable parameters, hereby obtaining comparative data for G10 analysis-subjected research trial.
4.
Conclusions
Crude glycerol generated in biodiesel plants is a suitable material to be a partial substitute for woody cutting waste (in definite mass proportions of 10:90) in the briquette production. This stock does not have a character typical for byproduct waste with supererogatory negative impact on environment and financial management of its producer. Therefore its consequent energy processing does not require drying or disintegration, that is to say e energy consuming technological operations usually applied for treatment of other materials. Proposed briquettes comply with EN 14961-1 and LAND 43-2001 requirements thus being relevant fuel for industrial and institutional heating systems.
Acknowledgements The exploratory works were performed at the Lithuanian University of Agriculture Institute of Agro-Engineering (now Aleksandras Stulginskis University) and funded as scheduled research activity. Combustion tests were performed at Leibniz Institute for Agricultural Engineering Potsdam-Bornim. Author is grateful to G. Burneika, a person, who shared his ideas with me and gave me his time and comments.
references
Fig. 6 e Comparison of the dependence of calorific value and ash content on the glycerol share.
[1] Valdes JJ, Warner JB. Tactical garbage to energy refinery (TGER). In: Singh OV, Harvey SP, editors. Sustainable biotechnology. Sources of renewable energy. Dordrecht: Springer; 2010. p. 83e103. [2] Bridgwatera AV, Double JM. Production costs of liquid fuels from biomass. Fuel 1991;70(10):1209e24. [3] Fernando S, Adhikari S, Kota K, Bandi R. Glycerol based automotive fuels from future biorefineries. Fuel 2007; 86(17e18):2806e9. ius L, Narbutas L, Slan iauskas A, Dz iugys A, [4] Raslavic c The districts of Lithuania with low heat demand Bazaras Z. density: a chance for the integration of straw biomass. Renew Sust Energy Rev 2012;16(5):3259e69. Ecological assessment and ius L, Bazaras Z. [5] Raslavic economic feasibility to utilize first generation biofuels in cogeneration output cycle e the case of Lithuania. Energy 2010;35(9):3666e73.
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
[6] Demirbas A. Biodiesel production from vegetable oils by supercritical methanol. J Sci Ind Res India 2005;64(11):858e65. [7] Haas MJ, McAloon AJ, Yee WC, Foglia TA. A process model to estimate biodiesel production costs. Bioresour Technol 2006; 97(4):671e8. [8] Valliyappan T, Bakhshi NN, Dalai AK. Pyrolysis of glycerol for the production of hydrogen or syngas. Bioresour Technol 2008;99(10):4476e83. Variations in oxygenated blend ius L, Bazaras Z. [9] Raslavic composition to meet energy and combustion characteristics very similar to the diesel fuel. Fuel Process Technol 2010; 91(9):1049e54. Prediction of multiecomponent ius L, Bazaras Z. [10] Raslavic effects on ignition delay of oxygenated diesel fuel blends. Indian J Eng Mater S 2010;17(4):243e50. [11] Molero JA, Vicente G, Morales G, Paniagua M, Bustmante J. Oxygenated compounds derived from glycerol for biodiesel formulation: Influence on EN 14214 quality parameters. Fuel 2010;89(8):2011e8. [12] Ramos MJ, Fernandez CM, Casas A, Rodriguez L, Perez A. Influence of fatty acid composition of raw materials on biodiesel properties. Bioresour Technol 2009;100(1):261e8. [13] Mittelbach M, Remschmidt C, editors. Biodiesel. The comprehensive handbook. 1st ed. Vienna: Boersedruck Ges.m.b.H; 2004. [14] Mittelbach M, Trathnigg B. Kinetics of alkaline-catalyzed methanolysis of sunflower oil. Fett Wiss Technol 1990;92(4): 145e8. [15] Soetaert W, Vandamme EJ, editors. Biofuels. 1st ed. Chichester: John Wiley & Sons Ltd; 2009. [16] Bacovsky D, Ko¨rbitz W, Mittelbach M, Wo¨rgetter M. Biodiesel production technologies and European providers. Report to IEA Bioenergy Task 39, Biofuels, T39-B6. Available from: http://www.task39.org; 2007. p. 104. [17] Cernoch M, Hajek M, Skopal F. Ethanolysis of rapeseed oil e distribution of ethyl esters, glycerides and glycerol between ester and glycerol phases. Bioresour Technol 2010;101(7): 2071e5. iauskas A, Makarevic iene_ V, Gumbyte_ M, gas N, Slan [18] Striu c Janulis P. Processing of the glycerol fraction from biodiesel production plants to provide new fuels for heat generation. Power Eng (Energetika) 2008;54(3):5e12. [19] Hood AH. Biomass briquetting in Sudan: a feasibility study [Internet]. United States Agency for International Development (USAID). Available at: http://www.fuelnetwork. org/index.php?option¼com_docman&task¼doc_ download&gid¼297; August 2010. p. 95 [cited 2010 May 14]. [20] Szklo A, Schaeffer R. Alternative energy sources or integrated alternative energy systems? Oil as a modern lance of peleus for the energy transition. Energy 2006;31(14):2513e22. [21] Yin C, Rosendahl LA, Kær SK. Grate-firing of biomass for heat and power production. Prog Energy Combust 2008;34(6):725e54.
151
[22] Sluiter A, Hames B, Ruiz R, Scarlata C, Sluiter J, Templeton D. Determination of ash in biomass, laboratory analytical procedure (LAP). Golden (CO): National Renewable Energy Laboratory; 2008 Jan. Report No.: NREL/TP-510e42622. Contract No.: DE-AC36-99-GO10337. Sponsored by the U.S. Department of Energy. [23] Al-Widyan MI, Al-Jalil HF, Abu-Zreig MM, Abu-Hamdeh NH. Physical durability and stability of olive cake briquettes. Can Biosyst Eng [Internet] 2002;44(3):41e5. Available from: http:// www.bioeng.ca/publications/cbe-journal? sobi2Task¼sobi2Details&catid¼37&sobi2Id¼953 [cited 2010 Jan 8]. [24] Wamukonya L, Jenkins B. Durability and relaxation of sawdust and wheatestraw briquettes as possible fuels for Kenya. Biomass Bioenergy 1995;8(3):175e9. [25] Richards SR. Physical testing of fuel briquettes. Fuel Process Technol 1990;25(2):89e100. [26] Chin OC, Siddiqui KM. Characteristics of some biomass briquettes prepared under modest die pressures. Biomass Bioenergy 2000;18(3):223e8. [27] Li N, Thompson S. A simplified nonelinear model of NOX emissions in a power station boiler. In: Proceeding of the UKACC International Conference on Control (Selected papers); 1996 Sep 2e5; University of Exeter, UK. London. [28] LAND 43-2001. Standards for fuel burning equipment (amdt. _ Zinios 2004). Official Gazette Valstybes 2004, No.: 37e1210. [Internet] [updated Mar 2004; cited 2010 Feb 12]. Available from: http://www.valstybes-zinios.lt/vpp3/lt/. [29] Rostam-Abadi M, Khan L, DeBarr JA, Smoot LD, Germane GJ, Eatough CN. Combustion properties of coalechar blends: NOX emission characteristics. Prep Pap - Am Chem Soc Div Fuel Chem 1996;41:1132e7. [30] Roberts WL, Metzger B, Turner TL, inventors; North Carolina State University, assignee. Process for combustion of high viscosity low heating value liquid fuels. United States patent US 20080305445. 2008-12-11. gas N. Analysis of acroleine production during glycerol [31] Striu combustion. COST action CM901: Detailed chemical kinetic models for cleaner combustion: Proceedings of the 1st Annual Meeting on European Cooperation in Science and Technology; 2010 Sep 15e17; Nancy, France. Nancy: The E´cole Nationale Supe´rieure des Industries Chimiques (ENSIC); 2010. Available from: http://www.ensic.inpl-nancy. fr/cost/fileadmin/utilisateurs/COST_ Documents/20100128MC/20100915-Meeting/WG2/7_R010_Striugas_WG2.pdf [32] Bohon MD, Metzger BA, Linak WP, King CJ, Roberts WL. Glycerol combustion and emissions. P Combust Inst 2011; 33(2):2717e24. [33] El Bassam N, Maegaard P, editors. Integrated renewable energy for rural communities: planning guidelines, technologies and applications. 1st ed. Amsterdam: Elsevier Science; 2004.
Available online at www.sciencedirect.com
http://www.elsevier.com/locate/biombioe
Characterization of the woody cutting waste briquettes containing absorbed glycerol Laurencas Raslavicius* Faculty of Mechanical Engineering and Mechatronics at Kaunas University of Technology, Ke˛stucio g. 27, 44312 Kaunas, Lithuania
article info
abstract
Article history:
The aim of the present work was to evaluate waste-to-energy technology for the utilization
Received 16 November 2010
of crude glycerol (84.5% purity) surplus, collected by the largest Lithuanian biodiesel plants.
Received in revised form
The research examined the use of glycerol and woody (timber) cutting waste (WCW) to
28 May 2012
produce fuel briquettes. Two ratios of glycerol mass share 10% and 20% per unit volume
Accepted 30 May 2012
were proposed as a partial substitute for WCW in briquette production process, thus
Available online 22 June 2012
solving glycerol utilization problems present in Lithuania. Proposed volumes of additive are in strong agreement with EN 14961-1. Affirmative proportions for interfusion of input
Keywords:
materials, durability rating of fuel briquettes, characterization of combustion regimes and
Crude glycerol
emission characteristics were assessed based on their composition. The optimum fuel
Fuel briquettes
properties were demonstrated by WCW briquettes containing maximum 10% glycerol mass
Durability
concentration. Combustion of such briquettes exposed low CO, SO2 and NOX emission
Woody cutting waste
levels, falling under requirements of LAND 43e2001. Further increase in glycerol share is
Biodiesel by-products
not recommendable, in the larger part due to the decrease in physical-mechanical properties, but not from emission constrains. ª 2012 Elsevier Ltd. All rights reserved.
1.
Introduction
There are numerous waste-to-energy technologies, each with varying efficiencies and capabilities to digest complex waste streams [1]. After the energy crisis in the 1970s, considerable attention was focused on the development of alternate energy resources [2]. At present decade, there is a renewed interest in biofuels due to increasing concerns about energy security, environmental pollution [3e6], and problems connected with utilization of the industrial by-products of organic nature [7,8]. One such renewable fuel that is being widely commercialized is biodiesel. The biodiesel obtained via transesterification of vegetable oils or animal fats is an alternative to current fossil fuels [9,10]. Citing Fernando et al. [3], and Melero et al. [11], a large amount of glycerol as a by-product is generated in this process and new applications for this surplus need to be found.
1.1. Chemical principles of glycerol formation in biodiesel production process In a transesterification or alcoholysis reaction 1 mol of triglyceride reacts with 3 mol of alcohol to form 1 mol of glycerol and 3 mol of the respective fatty acid alkyl esters [12e15]. The process is a sequence of three reversible reactions, in which the triglyceride molecule is converted step by step into diglyceride, monoglyceride and glycerol [15,16]. In each step 1 mol of alcohol is consumed and 1 mol of ester is liberated. Usually, methanol is added in an excess over the stoichiometric amount in most commercial biodiesel production plants. Another advantage of methanolysis as compared to transesterification with higher alcohols is the fact that the two main products, glycerol and fatty acid methyl esters (FAME), are hardly miscible and thus form separate
* Permanent address: Savanoriu˛ pr. 370e4, 49362 Kaunas, Lithuania. Tel.: þ370 610 24254, þ370 37 718592; fax: þ370 37 718592. E-mail address: [email protected]. 0961-9534/$ e see front matter ª 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biombioe.2012.05.028
145
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
phases e an upper ester phase and a lower glycerol phase [16]. This process removes glycerol from the reaction mixture and enables high conversion. Citing Bacovsky et al. [16], Cernoch et al. [17] and Mittelbach and Remschmidt [13], ester yields can even be increased e while at the same time minimizing the excess amount of methanol e by conducting methanolysis in two or three steps. In this case only a portion of the total alcohol volume required is added in each step, and the glycerol phase produced is separated after each process stage [16].
1.2. Glycerol surplus subjected to biodiesel production in Lithuania According to the method used to produce the biodiesel fuel, glycerol (G) can be assigned to one of three categories based on its purity: raw glycerol (G 63.3%), crude (technical) glycerol (G w 80%) and glycerol of the highest purity (G > 99.8%) [18]. In the largest biodiesel production plants of Lithuania, methanol is evaporated from the glycerol fraction, and the free fatty acids are purified away by biodiesel washwaters, producing crude (technical) glycerol of w80% purity. In general, for every kilogramme of biodiesel produced, 0.09 kg of crude glycerol is liberated. Usually, crude glycerol is collected and purified up gas et al. [18] concluded that, the present situto 99.8%. Striu ation causes additional costs in energy and materials, and the demand for it is limited because of a large surplus in the market. Hereby, the new ways for effective utilization of crude glycerol must be founded. The Lithuania-wide potential of yearly glycerol yield was analysed using a resource-focused approach (see Table 1) to appreciate potentially available quota of glycerol, possibly been practiced as a partial substitute for woody cutting waste (WCW) in briquettes production.
1.3.
Pending issues and practical background
Currently, in EU-27 countries, an additive share to compound woody biomass intended for briquettes production is described by the following European norms: 1) EN 14961-3 (draft). The Normative establishes a maximum share of additive is 2% for non-industrial application.
2) EN 14961-1 gives a general classification of solid biofuels. In this case, the possibility of higher amounts of additives of pressing mass (up to 20%) is given. To sum it up, EN 14961-1 gives a real opportunity for a wider application of organic waste materials intended to be a partial substitute for densified biomass-to-industrial briquettes production and at the same time lay under the established requirements for solid biofuels. In many countries, industrial briquettes are acquiring an increasing importance [19]. Citing Szklo and Schaeffer [20], energy carriers for multi-fuel and multi-product strategies, where flexibility is a key target, allied to other co-benefits, especially those related to the increased use of renewable energy sources. The initial challenge of the present research activity was to mate the by-product (glycerol) cumulated by Lithuanian biodiesel plants and to prove that the stored waste can be effectively applied as an additive to industrial briquettes intended for industrial and institutional heating systems. The proposed type of solid biofuel was the result of the required thorough scientific analysis and high level of optimization with full consideration of the context within which it would be operating.
2.
Materials and methods
2.1. Organic input materials and specimens nomenclature Two organic input materials were selected for briquetting experiment: timber cutting waste and crude glycerol. Chemical composition of glycerol, applied for briquetting experiments after removal of methanol from glycerol phase, is presented in Table 2. Woody cutting waste for briquettes production was obtained at JSC Bionovus e the largest supplier of solid biofuels in Lithuania (member of Lithuanian biomass energy association LITBIOMA). An area harvested in the forest is located in Marijampole_ County LT-MR (WGS84: 54 330 3100 N, 23 200 5800 E; UTM: 34U 651922 6048214). WCW were collected from pure hardwood stands and mixed hardwood stands that had followed the cutting of 22e25 years old-field beech (Fagus grandifolia), oak (Quercus robur) and alder (Alnus glutinosa) as dominating tree species. The date of forest harvesting works
Table 1 e Biodiesel production in Lithuania (2004e2010) and cumulated amounts of crude glycerol. Year
2004 2005 2006 2007 2008 2009 2010
Biodiesel production, thousand tonnes
Constitutional part in total liquid fuel consumption, %
Crude glycerol (by-product), thousand tonnes
2.2 7.0 10.3 40.0 190.0 190.0 190.0
0.20 0.57 0.84 3.33 12.20 12.20 12.20
0.198 0.630 0.927 3.600 17.100 17.100 17.100
Table 2 e Experimentally settled chemical composition of crude glycerol. Composition Glycerol Water Methanol Phosphorus Potassium Rapeseed oil methyl ester (RME) Other contaminants
Crude (technical) glycerol 84.55% 6.82% 2.16% 0.15% 2.63% 0.37% 3.32%
3.60% 0.41% 0.34% 0.02% 0.15% 0.02% 0.23%
146
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
is December 7e18, 2009. Four bags of the randomly taken WCW were transported to the Department of Bioresources at Lithuanian University of Agriculture Institute of AgroEngineering. The moisture content of the WCW before briquetting was 38%e42%. The raw material was poured into a laboratory pneumatic drying system which automatically reduced the moisture content to 8% at 240 Ce290 C for 120 min. The size distribution of timber cuttings was found by sieve analysis. By limiting the largest mesh size to 5.0 mm, the mean particle length was found to be 3.0 mm. The calorific value of the timber cuttings was determined using a bomb calorimeter, and was found to be 16.7 MJ kg1. A pruned nomenclature G0, G10 and G20 means what percentage of the mass fraction of crude glycerol is actually in briquette, the rest is WCW.
2.2. Combustion device, gas analyser, and chemical analysis method An experimental combustion device was developed in order to study combustion process of glycerol contained WCW briquettes. The preferred embodiment of the apparatus is illustrated in Fig. 1. Fig. 1 shows a rectangular-shaped stoker equipped with air-cooled stationary sloping grate as well as air supply system (primary air and secondary air), which plays a very important role in the efficient and complete combustion of biomass. The installation incorporates a horizontal grate surface. For gratefiring, the overall excess air for most biomass fuels is normally set to 25% [21]. The split ratio of primary air to secondary air was set to be 80/20. Secondary air (advanced) supply system is one of the most important elements in the optimization of the gas combustion in the freeboard, for complete burnout and lower emissions, e.g., by forming local recirculation zones or rotating flows and by forming different local combustion environments (e.g., fuel-rich or oxygen-rich) [21]. Accordingly, an optimization of
the secondary air supply rates allowed us to retrofit the old combustion unit based on grate firing to describe the burning characteristics of newly derived type of biofuel. Fuel briquettes were delivered from the hopper to the stoker through the auger tube with a set periodicity. Each cycle consisted of the following distinct phases: working period (an auger was switched on) and pause period (an auger was switched off). Portions of the supplied fuel were adjusted by varying the durability of the working and pause periods. Combustion process was studied by alternating of the supplied air volume. The supply of combustion air (primary and secondary) was controlled via Rota Yokogawa rotameters, type RAKD. The rotameter was calibrated using FVA-Series air flow sensor FVA915-S120 and data logger ALMEMO-2290-8 equipped with AMR-Control software. Combustion temperature was measured via ultra high stability NiCroSil-NiSil (Type N) thermocouple and registered by ALMEMO-2290-8 with a 1 C accuracy. To evaluate the emission level of the combustion device operated in the previously established conditions, analyser of gases, model PCA-65 (CO; CO2; O2; SO2; NOx), manufactured by Bacharach Inc. was applied. The combustion products were also analysed for acroleine concentrations by GC (gas chromatograph) on CP Wax 52 CB capillary column (L ¼ 50 m, diameter ¼ 0.25 mm, film thickness ¼ 0.2 mm) in a HewlettePackard 5890 Series II gas chromatograph equipped with flame ionisation detector. Before the measurements, acroleine was absorbed from combustion products by SKC Sorbent Tube, XAD-2 (2Hydroxymethyl Piperidine). The chromatographic data were obtained by the H.P. Chemstation software. Acroleine samples were taken from the site in the grate stoker which is above the flue gas outlet. Ash content was established under the laboratory conditions, using a standardized procedure described by Sluiter et al. [22]. Methodology involved calculation of ashpercentage-rate as a relation between the ash weight of the
Fig. 1 e Experimental air-cooled stationary sloping grate stoker and briquettes supply system.
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
burnedeout specimen against the initial weight of the same specimen. An ash weight of the tested specimens was determined by weighting machine SA-120CE (accuracy: 0.2 mg).
2.3.
Briquettes production technology
A continuous automatic briquette press was developed for pressing glycerol absorbed WCW into briquettes (see Table 3). The main element of the pressing device consisted of a cylinder fitted with a sliding piston that exerted force upon a confined fluid, which, in turn, produced a clamping force (CF) upon a stationary baseplate. Glycerol was preheated until 40 Ce45 C and poured in various proportions over WCW to absorb the powdery mass. The specimens prepared for pressing contained glycerol mass share 10% and 20% per unit volume, respectively. To the baseline of the experiment, the control specimen consisted of straight WCW. The mass of a single specimen was 1.0 kg 0.072 kg. Various amounts of glycerol absorbed powdery mass dashed manually, thereafter closing the prepared specimens to the separate glass containers and placing them to the thermostatic cabinet (THSC) for 3 h to achieve the best possible soak-up characteristics of the interfused mass. Temperature in the THSC was set to 95 C 1 C. A clamping force was measured with the help of OBMG-160 manometer connected to the fluid hose of the hydraulic cylinder. Before the briquetting process, a pressing chamber was heated-up to 200 C 5 C by using an electric heater of 600 W capacity.
2.4.
Maximum glycerol insertion testing
A prepared mass for specimens production was stoked up to the matrix by piecemeal enclosure every time consolidating
Table 3 e Specification of the briquetting press. Technical data Press capacity Maximum clamping force Diameter of briquette Length of briquette Max. moisture content of cutting waste Manometer Diameter/Stroke of hydraulic cylinder Hydraulic gear pump
Hydraulic station Electric motor Dimensions (L H W) Weight
57 kg h1 1700 kg cm2 35 mm 70 mm 14% OBMG-160 220 mm/300 mm Sauer-Danfoss: Pressure (inlet) e 0.8 bar absolute recommended, Pressure (outlet) e 276 bar, Fluid viscosity e 10 mm2 sec1 (biodegradable fluid) HITECH (stationary; produced on request) BEVI (2D 180 L-4), 18.5 kW, n ¼ 1450 s1, 59.1 A, 230 V, 50 Hz 1800 mm 1900 mm 1800 mm 3000 kg
147
up it with a desktop laboratory press at CF¼80 N. After the matrix being well-stocked, a specimen was stressed by the hydraulic hoist at 50 kN, herewith monitoring a possible glycerol penetration through the interstice between the matrix walls and the piston. Standard laboratory safety precautions were observed when carrying out maximum glycerol insertion tests at process temperature of 200 C due to 2.16% methanol content in the chemical composition of glycerol (see Table 2). Personal protection for the safe handling of crude glycerol at elevated temperatures included adequate ventilation, wearing of safety glasses and chemical-resistant gloves coupled with evacuation of any unprotected personnel from laboratory premises.
2.5.
Physical and mechanical properties testing
The mean compressed density of the briquettes was determined immediately after removal from THSC as a ratio of measured weight over calculated volume. Measurement data for density calculations obtained via electronical weighting machine VLTK-500 (accuracy: 0.01 g) and vernier callipers (accuracy: 0.5 mm). To determine dimensional stability, the length of five representative briquettes from each production batch was measured under the stress effect of desktop laboratory press by embedding them between piston and stationary baseplate. The durability of the briquettes was determined with the aid of a durability tester, i.e., a dusttight 400 mm 305 mm 305 mm enclosed box rotating around diagonal axis. Test sample of five briquettes was tumbled for 3 min at rotational frequency n ¼ 13 min1. A percentage of a quantity of unshattered briquettes leftover in the box after the test trial against remaining ones, having a residual weight no less than 20% of their initial mass, was setted as the main strength criterion.
2.6.
Establishment of calorific value data
An isoperibolic temperature regulated oxygen bomb calorimeter (OBC: 230 VAC, 3 A, 50/60 Hz), manufactured by Fire Testing Technology Ltd, been applied to ascertain calorific value of glycerol purified by biodiesel washwaters.
3.
Results and discussion
3.1. Affirmative proportions for interfusion of input materials Samples of the G0, G10 and G20 briquettes produced are shown in Fig. 2. Briquettes produced using 100% woody cutting waste (G0) assumed a greyish brown colour, while those produced using different proportions of glycerol purified by biodiesel washwaters assumed different shades of darkly lit yellow colouration, depending on the quantity of crude glycerol included. As shown in Fig. 2, the average relaxed density (i.e., the density of briquette after removal from the press) of glycerol containing specimens ranged from 743 kg m3 13.6 kg m3
148
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
Fig. 2 e Specimens of WCW-G briquettes.
3.2.
Durability rating of fuel briquettes
The briquette durability (shatter-resistance (ShR) and stressresistance (StR)) rating test is intended to ascertain the ability of densified specimens to withstand the rigours of handling such that they keep their mass, shape, and integrity [23]. As shown in Fig. 3, the ShR of the different briquette composition ranged from 78.0% for G20 to 95.6% for G0 briquettes. Obtained durability rating values were comparatively high in collation with reported by Wamukonya and Jenkins [24] (46.5% and 88.4%, respectively) for sawdust briquettes having the comparable share of biomass (wheat straw) content. However, according to Richards [25], in the
120
1
0.97 kN
100
0.91 kN
95.6%
0.87 kN 86.7%
80
78.0%
0.9
0.8
60
0.7
40
0.6
20
0.5
0
0
10
20
0.4
G [%]
Fig. 3 e Briquette durability (shatter-resistance (ShR) and stress-resistance (StR)) versus glycerol share.
StR [kN]
process development stages, it is suggested that the tests should relate to the briquette material, rather than the briquette as an entity. Appreciating the fact, that glycerol insertion to the sawdust or cutting waste was not examined in a broad-brush content, these would allow inter-laboratory inferences of briquette formulations. The definitive durability rating (see Fig. 3) for twocomponent solid biofuel was observed in briquettes produced with 90% woody cutting waste (G10). As it was expected, the G0 briquettes were found to have better overall handling characteristics. It stands to reason, therefore, that the WCW briquettes, that had 8% moisture content and the highest density also had the highest ShR (95.6%) as well as StR (0.97 kN) rating. Agreeably, the indication of durability rating for G20 briquettes (ShR ¼ 78.0%; StR ¼ 0.87 kN) fell by the wayside in search of key composition. Notwithstanding this fact and citing Chin and Siddiqui [26], fuel briquettes of different biomass materials required different optimum conditions of fabrication and generally showed a promising potential for further development.
ShR [%]
to 798 kg m3 15.3 kg m3, while the average density of G0 briquettes balanced in the range of 861 kg m3 24 kg m3. According to experimental results, G20 specimen revealed in 1.16 times lesser density than G0 (see Fig. 2). It was established that 20% of glycerol containing briquettes compressed in a closed cylinder had a tendency to expand as the pressure was released. Fig. 2 shows that G20 briquettes were significantly deformed and lost their cylindrical shape. Also an expansion was observed, which took place in longitudinal direction, i.e., direction in which the load was applied. The shape structure of G10 and G0 was not observed to change. During the briquetting experiment, the CF ranged from 73 MPa 3.6 MPa for G20 to 92 MPa 5.1 MPa for G0, respectively. A disparity in values of clamping force for materials of different consistence is attributed to the excellent lubricating properties of glycerol. A better performance of press device is explained by the decrease of friction force between the walls of the presschamber. However, a briquetting process of the interfused mass (CF ¼ 73 MPa) having 20% glycerol mass concentration indicated some troubles due to observed glycerol penetration through the interstice between the matrix walls and the piston. The production process was restricted by glycerol viscosity drop due to the process temperature (200 C).
The fuel burnt as it fell down from the auger tube under gravity. After ignition, a reaction front propagated against the direction of the primary air. The heat, generated in the reaction front, was transported against the primary air flow and dried and devolatilized the briquettes. This allowed the reaction front to propagate. The gases released from biomass conversion on the grate and a small amount of entrained fuel particles continued to combust in the freeboard, in which the secondary air supply played a significant role in the mixing, burnout, and emissions [21]. The O2 concentration in the gas dropped quickly in a space of 11 min at t ¼ 2.5 min from ambient level (20.9%) to a 5% (see Fig. 4). This was followed by a sharp increase in CO and CO2 to 20.5% and over 17,000 mg m3 respectively. The level of CO2 was mostly above 7600 mg m3e6900 mg m3 for 60 min from t ¼ 25 min to t ¼ 85 min (01:25:00). As the rate of mass loss of the briquettes gradually decreased, CO concentration declined steadily from 10% to about 2% in that period of time. O2 concentration began to rise at t ¼ 14 min marking a participation of excess air. Participation of the sulphur dioxide in the flue gases was inconsiderable and varied within range of the margin of error. A combustion temperature ranges of fuel briquettes as a function of specific volume of air (SVA) at the supply condition were presented in Fig. 5. In order to burn G0, G10 and G20 briquettes effectively the fuel had to be supplied into a 900 Ce1000 C temperature environment (see Fig. 5). The experimental data showed that briquettes consisting only of pressed WCW (G0) had a decidedly lower combustion temperature (Tcomb) than briquettes with 10% and 20% of glycerol content. The highest combustion temperature (985 C) was observed while burning of the G20 specimens at SVA ¼ 4 m3 kg1. An observed tendency, when the marked improving in SVA at the supply condition caused the decrease in Tcomb values is explained by stoker cooling effect provided by excess air. The best combustion characteristics were demonstrated by G10 at SVA ¼ 3e6 m3 kg1, taking into consideration an optimum glycerol share (see Chapter 3.1). Appreciating the formation mechanism of nitrogen oxides for two organic constituents, a major source of the NO formed
Fig. 4 e Combustion process characteristics for G10 briquettes.
Tcomb [oC]
3.3. Characterization of combustion regimes and emission characteristics
1300
200 G20
1250 1200
180
G10
160
NOX [mg m-3]
149
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
G0
1150
140
1100 G20
1050
G10 G0
1000 950 900 850
100 80
G20 G10
G20 G10 G0
G0 2
120
4
6 SVA [m3 kg-1]
8
10
60 40
Fig. 5 e Comparison of the dependence of Tcomb and NOX emissions on the SVA at the supply condition and glycerol share.
in combustion process could be explained by oxidation of atmospheric N2, i.e. thermal NO [9]. Li and Thompson [27] concluded, that for the simplified models describing the relationships between NOX emissions and combustion device operational parameters, it is reasonable to accept the precondition, that excess air is always provided in the combustor to ensure complete combustion. In this case, the contribution of prompt NO to total nitrogen oxide emissions is negligible. Nitrogen oxide emission values were obtained by alternating of the supplied air volume. Fig. 5 shows the measured increase in effluent NOX concentrations with increasing crude glycerol share and for the combustion tests performed for this study. The distribution of NOX is relatively low for investigated types of fuel briquettes and falls under requirements of LAND 43-2001 [28], limiting nitrogen oxides content in exhaust gases to 650 mg m3 while burning any solid biomass. It is likely that the share of crude glycerol extends the reaction zone allowing for greater mixing of fuel and combustion air, so that a greater percentage of fuel nitrogen is released [29] in comparison with G0. This explanation is substantiated by the observation that the G20 briquettes demonstrated in 8%e12% higher NOX emission level (160 mg m3e189 mg m3) than the G10 (148 mg m3e168 mg m3), for the same excess air (3 m3 kg1e5 m3 kg1). Further increase in SVA rates (starting from 4 m3 kg1 and ending with 10 m3 kg1) caused an overall decrease in NOx emission level for all three types of briquettes (G0, G10 and G20). This tendency was influenced by cooling effect (i.e. decreased combustion temperature) in the stoker. Since the burning of glycerol contained woody cuttings briquettes is a relatively new trend in biomass application for heat production, not much has been done to characterize hazardous compounds emitting from the combustion of glycerol. There has been a long-standing fear that combustion of glycerol releases toxic acrolein gas unless carried out at a sufficiently high temperature. Moreover, scholars in the field have theorized that complete and clean combustion of glycerol requires a burning temperature in excess of 1000 C and a relatively long mean residence time in the combustion chamber. The chromatographic analysis curves for the
150
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
samples were compared to the calibration curves as described gas [31]. When the chromatographic peaks in detail by Striu are examined, it was observed that they are very insignificant and are difficult to differentiate from the noise distribution around a base curve shape. On this understanding, from the pure WCW-G specimen combustion analysis it was concluded that acroleine decomposes in full at 900 Ce1000 C temperature environment and it was not detected by the used method. In summary, the results of the experiment show that safe, clean, and efficient combustion of a WCW-G briquettes is possible with an air-cooled stationary sloping grate stokers of the proposed modification and primary/secondary air ratio. Otherwise, effective combustion of glycerol also requires combination with another fuel source, such as sawdust, cuttings, etc [30]. Boham et al. [32] concluded, that in some cases primary carbonyl (acroleine) emissions from glycerol combustion in the described above temperature range may be comparable to those from other conventional fossil fuels. It is in strong agreement with the results obtained by other researchers who had a goal to understand and improve the combustion characteristics of crude glycerol at temperature range of 800 Ce1000 C [18,30e32].
3.4. Calorific value, origin of the ash content and its alternation Calorific value of investigated biomass briquettes was affected by the ash content (see Fig. 6). The higher the ashes content of the raw material, the lower the calorific value, because ash is a material that does not generate energy [33]. If we look into briquette’s calorific value, it can be seen that the higher ash content of G0 (1.45%) and G10 (0.9%) briquettes produced the lower calorific value (16.7 MJ kg1 and 17.1 MJ kg1) in comparison to G20 (17.5 MJ kg1). Pure WCW briquettes resulted in the lowest calorific value (16.7 MJ kg1) because they had the highest ash content of 1.45%. Ash from WCW comes from the minerals presented in the structure of trees in addition to any soil contamination. Properties of wood waste ash depend on a variety of factors including type of tree, part of the tree (bark or wood), type of
soil, climate, combination with other fuel sources, and conditions of combustion. To sum it up, the powdery mass of timber cuttings, interfused with glycerol in proportion G10 and G20 shows a markable decrease in measured ash content. Notwithstanding this fact, only 10% of glycerol share in WCW briquetting process was possible under proposed technology, because G20 briquettes were not uniform in density, nor had good structural strength. Thus, combustion characteristics for G0 and G20 briquettes were investigated on the purpose of a supporting approach e to study the tendencies for many variable parameters, hereby obtaining comparative data for G10 analysis-subjected research trial.
4.
Conclusions
Crude glycerol generated in biodiesel plants is a suitable material to be a partial substitute for woody cutting waste (in definite mass proportions of 10:90) in the briquette production. This stock does not have a character typical for byproduct waste with supererogatory negative impact on environment and financial management of its producer. Therefore its consequent energy processing does not require drying or disintegration, that is to say e energy consuming technological operations usually applied for treatment of other materials. Proposed briquettes comply with EN 14961-1 and LAND 43-2001 requirements thus being relevant fuel for industrial and institutional heating systems.
Acknowledgements The exploratory works were performed at the Lithuanian University of Agriculture Institute of Agro-Engineering (now Aleksandras Stulginskis University) and funded as scheduled research activity. Combustion tests were performed at Leibniz Institute for Agricultural Engineering Potsdam-Bornim. Author is grateful to G. Burneika, a person, who shared his ideas with me and gave me his time and comments.
references
Fig. 6 e Comparison of the dependence of calorific value and ash content on the glycerol share.
[1] Valdes JJ, Warner JB. Tactical garbage to energy refinery (TGER). In: Singh OV, Harvey SP, editors. Sustainable biotechnology. Sources of renewable energy. Dordrecht: Springer; 2010. p. 83e103. [2] Bridgwatera AV, Double JM. Production costs of liquid fuels from biomass. Fuel 1991;70(10):1209e24. [3] Fernando S, Adhikari S, Kota K, Bandi R. Glycerol based automotive fuels from future biorefineries. Fuel 2007; 86(17e18):2806e9. ius L, Narbutas L, Slan iauskas A, Dz iugys A, [4] Raslavic c The districts of Lithuania with low heat demand Bazaras Z. density: a chance for the integration of straw biomass. Renew Sust Energy Rev 2012;16(5):3259e69. Ecological assessment and ius L, Bazaras Z. [5] Raslavic economic feasibility to utilize first generation biofuels in cogeneration output cycle e the case of Lithuania. Energy 2010;35(9):3666e73.
b i o m a s s a n d b i o e n e r g y 4 5 ( 2 0 1 2 ) 1 4 4 e1 5 1
[6] Demirbas A. Biodiesel production from vegetable oils by supercritical methanol. J Sci Ind Res India 2005;64(11):858e65. [7] Haas MJ, McAloon AJ, Yee WC, Foglia TA. A process model to estimate biodiesel production costs. Bioresour Technol 2006; 97(4):671e8. [8] Valliyappan T, Bakhshi NN, Dalai AK. Pyrolysis of glycerol for the production of hydrogen or syngas. Bioresour Technol 2008;99(10):4476e83. Variations in oxygenated blend ius L, Bazaras Z. [9] Raslavic composition to meet energy and combustion characteristics very similar to the diesel fuel. Fuel Process Technol 2010; 91(9):1049e54. Prediction of multiecomponent ius L, Bazaras Z. [10] Raslavic effects on ignition delay of oxygenated diesel fuel blends. Indian J Eng Mater S 2010;17(4):243e50. [11] Molero JA, Vicente G, Morales G, Paniagua M, Bustmante J. Oxygenated compounds derived from glycerol for biodiesel formulation: Influence on EN 14214 quality parameters. Fuel 2010;89(8):2011e8. [12] Ramos MJ, Fernandez CM, Casas A, Rodriguez L, Perez A. Influence of fatty acid composition of raw materials on biodiesel properties. Bioresour Technol 2009;100(1):261e8. [13] Mittelbach M, Remschmidt C, editors. Biodiesel. The comprehensive handbook. 1st ed. Vienna: Boersedruck Ges.m.b.H; 2004. [14] Mittelbach M, Trathnigg B. Kinetics of alkaline-catalyzed methanolysis of sunflower oil. Fett Wiss Technol 1990;92(4): 145e8. [15] Soetaert W, Vandamme EJ, editors. Biofuels. 1st ed. Chichester: John Wiley & Sons Ltd; 2009. [16] Bacovsky D, Ko¨rbitz W, Mittelbach M, Wo¨rgetter M. Biodiesel production technologies and European providers. Report to IEA Bioenergy Task 39, Biofuels, T39-B6. Available from: http://www.task39.org; 2007. p. 104. [17] Cernoch M, Hajek M, Skopal F. Ethanolysis of rapeseed oil e distribution of ethyl esters, glycerides and glycerol between ester and glycerol phases. Bioresour Technol 2010;101(7): 2071e5. iauskas A, Makarevic iene_ V, Gumbyte_ M, gas N, Slan [18] Striu c Janulis P. Processing of the glycerol fraction from biodiesel production plants to provide new fuels for heat generation. Power Eng (Energetika) 2008;54(3):5e12. [19] Hood AH. Biomass briquetting in Sudan: a feasibility study [Internet]. United States Agency for International Development (USAID). Available at: http://www.fuelnetwork. org/index.php?option¼com_docman&task¼doc_ download&gid¼297; August 2010. p. 95 [cited 2010 May 14]. [20] Szklo A, Schaeffer R. Alternative energy sources or integrated alternative energy systems? Oil as a modern lance of peleus for the energy transition. Energy 2006;31(14):2513e22. [21] Yin C, Rosendahl LA, Kær SK. Grate-firing of biomass for heat and power production. Prog Energy Combust 2008;34(6):725e54.
151
[22] Sluiter A, Hames B, Ruiz R, Scarlata C, Sluiter J, Templeton D. Determination of ash in biomass, laboratory analytical procedure (LAP). Golden (CO): National Renewable Energy Laboratory; 2008 Jan. Report No.: NREL/TP-510e42622. Contract No.: DE-AC36-99-GO10337. Sponsored by the U.S. Department of Energy. [23] Al-Widyan MI, Al-Jalil HF, Abu-Zreig MM, Abu-Hamdeh NH. Physical durability and stability of olive cake briquettes. Can Biosyst Eng [Internet] 2002;44(3):41e5. Available from: http:// www.bioeng.ca/publications/cbe-journal? sobi2Task¼sobi2Details&catid¼37&sobi2Id¼953 [cited 2010 Jan 8]. [24] Wamukonya L, Jenkins B. Durability and relaxation of sawdust and wheatestraw briquettes as possible fuels for Kenya. Biomass Bioenergy 1995;8(3):175e9. [25] Richards SR. Physical testing of fuel briquettes. Fuel Process Technol 1990;25(2):89e100. [26] Chin OC, Siddiqui KM. Characteristics of some biomass briquettes prepared under modest die pressures. Biomass Bioenergy 2000;18(3):223e8. [27] Li N, Thompson S. A simplified nonelinear model of NOX emissions in a power station boiler. In: Proceeding of the UKACC International Conference on Control (Selected papers); 1996 Sep 2e5; University of Exeter, UK. London. [28] LAND 43-2001. Standards for fuel burning equipment (amdt. _ Zinios 2004). Official Gazette Valstybes 2004, No.: 37e1210. [Internet] [updated Mar 2004; cited 2010 Feb 12]. Available from: http://www.valstybes-zinios.lt/vpp3/lt/. [29] Rostam-Abadi M, Khan L, DeBarr JA, Smoot LD, Germane GJ, Eatough CN. Combustion properties of coalechar blends: NOX emission characteristics. Prep Pap - Am Chem Soc Div Fuel Chem 1996;41:1132e7. [30] Roberts WL, Metzger B, Turner TL, inventors; North Carolina State University, assignee. Process for combustion of high viscosity low heating value liquid fuels. United States patent US 20080305445. 2008-12-11. gas N. Analysis of acroleine production during glycerol [31] Striu combustion. COST action CM901: Detailed chemical kinetic models for cleaner combustion: Proceedings of the 1st Annual Meeting on European Cooperation in Science and Technology; 2010 Sep 15e17; Nancy, France. Nancy: The E´cole Nationale Supe´rieure des Industries Chimiques (ENSIC); 2010. Available from: http://www.ensic.inpl-nancy. fr/cost/fileadmin/utilisateurs/COST_ Documents/20100128MC/20100915-Meeting/WG2/7_R010_Striugas_WG2.pdf [32] Bohon MD, Metzger BA, Linak WP, King CJ, Roberts WL. Glycerol combustion and emissions. P Combust Inst 2011; 33(2):2717e24. [33] El Bassam N, Maegaard P, editors. Integrated renewable energy for rural communities: planning guidelines, technologies and applications. 1st ed. Amsterdam: Elsevier Science; 2004.