Assessment of the energetic and mechanical properties of pellets produced from agricultural biomass

This paper presents an assessment of the energetic and mechanical properties of pellets produced from agricultural biomass. For the production of pellets the following raw materials were used: wheat straw, rape straw, and maize straw. Additionally, the mixtures of wheat-rape straw, wheat-maize straw, and rape-maize straw (each accounting for 50% of the mass) were applied. The studied resources were ground with the use of a universal shredder driven by a 7.5 kW electric engine. A pelleting machine fitted with a fixed flat matrix with two driven thickening rolls was used to produce the pellets. Analyses of the moisture and calorific value of resources as well as the bulk density and mechanical strength of pellets were performed according to biding standards. The moisture of resources ranged from 16.5% to 18.5% for rape and maize straw, respectively. The average calorific value fluctuated between 15.3 MJ kg⁻¹ for a mixture of wheat and rape straw to 16.2 MJ kg⁻¹ for maize straw. The bulk density and mechanical strength of pellets depended on the type of resources used. The lowest bulk density was recorded for wheat straw pellets (386–420 kg m⁻³), and the highest (561–572 kg m⁻³) for maize straw pellets. The lowest mechanical strength of pellets was noted for rape (95.4–96.8%), whereas the highest was for pellets made from a wheat and maize straw mixture (96.8–98.9%).     

Physical properties of rice husk and bran briquettes under low pressure densification for rural applications

Agriculture generates large amount of by-products that could be used to produce energy and reduce the amount of fuelwood required to meet the daily cooking needs, especially in developing countries. Rice is a major crop grown in West Africa and rice husk is a by-product of the milling process. The goal of this study was to develop a low cost system to produce biomass briquettes from rice husks in the context of a rural village. A manual press generating a pressure of 4.2 MPa was developed and used. The influence of the briquette formulation (type of binder, binder content, water addition, and bran content) was studied. The binders investigated were cassava wastewater, rice dust, and okra stem gum. The physical properties (density, moisture content, calorific value, durability, and compressive strength) were tested to identify the briquettes with the highest quality, i.e. greatest physical integrity. The briquettes made with rice dust had the highest durability (91.9%) and compressive strength (2.54 kN), while the briquettes made with cassava starch wastewater had the greatest density (441.18 kg m⁻³). Water added to the rice husk before densification positively influenced the briquette quality while bran seemed to mostly increase the density, but not necessarily the briquette quality. The briquette formulation did not significantly influence the calorific value. With a higher heating value of 16.08 MJ kg⁻¹ dry basis, rice husk briquettes represent an interesting alternative to fuelwood.     

Recycling phosphorus by fast pyrolysis of pig manure: Concentration and extraction of phosphorus combined with formation of value-added pyrolysis products

In order to recycle phosphorus from the livestock chain back to the land, fast pyrolysis of concentrated pig manure at different temperatures (400 °C, 500 °C, 600 °C), was undertaken to concentrate the phosphorus in the char fraction for recovery. Results show that 92%–97% of the phosphorus present in the pyrolysis feedstock ends up in the char fraction, while 60%–75% of that can be directly leached as ortho-phosphate, and 90% as total phosphorus. After char combustion, 100% of the phosphorus present can be leached as ortho-phosphate from the ash. Yields, heating values, and properties of the pyrolysis products have been analyzed. Expressed per tonne of fresh pig manure, the char phosphorus value is estimated at 0.81 € t⁻¹–0.86 € t⁻¹, energy application value at 2.4 € t⁻¹–3.6 € t⁻¹ (liquid organic phase) and 0.5 € t⁻¹–0.7 € t⁻¹ (char), and the fertilizer value of the aqueous phase at 0.10 € t⁻¹–0.18 € t⁻¹. Including costs for energy requirement, solid–liquid separation, and drying, pyrolysis costs are estimated around 0.4 € t⁻¹–4.4 € t⁻¹ for pig manure. It is concluded that pyrolysis costs compare positively with pig manure transportation costs of 0.06 € t⁻¹ km⁻¹, while it also offsets phosphorus extraction from the rapidly depleting phosphate rock.     

Energy self-sufficient production of bioethanol from a mixture of hemp straw and triticale seeds: Life-cycle analysis

Industrial hemp shows exceptional potential for cellulosic ethanol production, especially regarding yields per hectare, costs and environmental impact. Additionally, co-products, such as high-value food-grade oil, increase the value of this plant. In this work, hemp straw was steam-exploded for 45 min at 155 °C and hydrolysed with a cellulase/xylanase mixture. Up to 0.79 g g⁻¹ of cellulose was degraded and subsequent simultaneous-saccharification-and-fermentation with added triticale grist resulted in >0.90 g g⁻¹ fermentation of cellulose. Hemp straw is very suitable, as it contains 0.63 g g⁻¹ of cellulose and only 0.142 g g⁻¹ of hemicellulose.A 2000 m³ a⁻¹ ethanol biorefinery requires a land use of 3 km² each for hemp and for triticale. A total of 2630 kg ethanol and 150 kg hemp oil can be gained from 1 ha. Slurry and triticale straw serve as raw material for the biogas fermenter or as animal feed. Biogas supplies thermal and electric energy in combined heat and power. Ethanol will remain at 0.66 € dm⁻³ based on market prices. In addition, data have been calculated for market prices plus and minus 30% market prices (0.51–0.81 € dm⁻³). Carbon dioxide (CO₂) abatement for ethanol achieves 121 g MJ⁻¹ CO_2eq for a combined ethanol/biogas plant. The CO₂ abatement costs vary from 38 € to 262 € t⁻¹ CO_2eq.     

Bioenergetic potential of agricultural soils in Slovakia

Knowledge of the energy potential of an agricultural soil and the potential production of biomass, together with economic parameters, can help pinpoint more effective sites for growing plants for traditional purposes and for fuel production. There is approximately 10 206 PJ of potential energy accumulated in Slovakia's agricultural soils. The lowest utilisation was found in the Cambisols soil type (0.7–1.8%) and the highest in Regosols (3.1–7.0%). The bioenergy production potential of agricultural soils in Slovakia was determined for chosen soil parameters according to the production of the plants grown. With regard to energy, the most productive are soils of the Chernozem type (25.1 MJ m⁻²) and Mollic Fluvisols (22.5 MJ m⁻²). Gleysols, Histosols, Solonetz and Leptosols (3.0–5.0 MJ m⁻²) produce the lowest bioenergy levels. The highest energy production precondition (22.2 MJ m⁻²) occurs in soils in the very warm, very dry lowland climatic region. According to the granularity, the most energy (14.0–15.0 MJ m⁻²) is produced by deep clayey soils (18.0 MJ m⁻²) in a slope to 3° (18.3 MJ m⁻²) that are not or sporadically gravelly (19.2 MJ m⁻²). The highest energy yields can be expected from the biomass of plants grown in arable land (approximately 11.0 MJ m⁻²). Regarding the efficiency of economic and financial inputs, plants growing in Chernozem, Mollic Fluvisols, Fluvisols and Haplic Luvisols soil types in very warm, very dry, lowlands to warm, very dry, basin-like, continental climatic regions appear to be profitable in slopes to 7°, with no or only a sporadic gravel content.     

Quality,productivity, energy and costs of woodchip produced by Cedrus deodara plantations: A case study in Italy

The main tree species planted for woodchips production for energy use are: poplar (Populus spp.), willow (Salix spp.), black locust (Robinia pseudoacacia L.) and eucalyptus (Eucalyptus spp.). Nevertheless, in the course of the years, other tree species were planted (i.e. Pinus strobus L.; Pauwlonia spp …). The scope of this study is the evaluation of energy and economic advantages, and quality of woodchip produced by a Cedrus deodara plantation situated in Italy.The plantation had a surface of 1.2 ha and trees were 14 years old.An amount of 363 t of fresh comminuted wood (about 300 t ha⁻¹) was produced by the plantation considered. A total time of 39.5 h (about 5 days) was required to transform all trees in woodchip. The moisture content of woodchip produced was 52%, while the average Low Heating Value (HHV) was 8.51 MJ kg⁻¹. In this study, economic (production cost = 93 € t⁻¹ DM) and energetic (output/input ratio = 74) evaluations of woodchip produced by Cedrus deodara plantations were positives. Nevertheless, the results obtained in this experimentation are close to the climate conditions and soil characteristics of Northwestern Italy.     

Production of xylose and glucose from rapeseed straw in subcritical water – Use of Doehlert design for optimizing the reaction conditions

The hydrothermal depolymerization of the hemicellulosic and cellulosic fractions of rapeseed straw was carried out in a batch reactor in subcritical water. The experimental design methodology (Doehlert matrix) was used to model the hydrothermal process and to optimize operational parameters reaction temperature and holding time for highest yields of saccharides: xylose and glucose, obtained in experimental series 1 and 2, respectively. In good agreement with experimental results, the model predicts an optimal yield of xylose (60.4 g kg⁻¹ ± 2.1 g kg⁻¹) at a temperature and a holding time of about 203 °C and 13 min. The optimal yield of glucose (180.7 g kg⁻¹ ± 2.8 g kg⁻¹) required higher temperatures but shorter times and was obtained at a temperature 255 °C and a holding time of 9 min. A further increase of both reaction parameters would lead to the undesirable transformation of the saccharides: their dehydration, retro-aldol condensation, isomerization and tautomerization. The obtained results confirm that the hydrothermal treatment of rapeseed straw in optimal reaction conditions might be an alternative route for the production of xylose and glucose.     

Energy characterisation of herbaceous biomasses irrigated with marginal waters

The paper reports the results of a research program aiming to evaluate the agronomic, and energy sustainability of the biomass production by perennial non-food herbaceous crops irrigated with different kinds of marginal waters. In four different sites (Bologna, Padova, Reggio Calabria, and Catania) the same four species (Arundo, Typha, Phragmites, and Lythrum), usually tested without irrigation, were planted and monitored during 2008–2010. The results show that a planting density of 10 m⁻² is necessary to obtain a maximum dry yield levels already from the second year of transplanting. The maximum productivity was obtained with Arundo (close to 100 Mg ha⁻¹ y⁻¹ in Bologna and 86 Mg ha⁻¹ y⁻¹ in Padova, 50–60 Mg ha⁻¹ y⁻¹ in the southern locations). Lythrum productivity ranged from 5.2 to 9.2 Mg ha⁻¹ y⁻¹ in all the RUs, with the exception of Reggio Calabria. Typha (around 10 Mg ha⁻¹ y⁻¹ at the third year) and Phragmites (5–8 Mg ha⁻¹ y⁻¹) gave significant production only in the northern locations. The HHVs were close to 15.5 MJ kg⁻¹ for Phragmites (except for Catania and Reggio Calabria with 20.0 MJ kg⁻¹) 18.0 MJ kg⁻¹ for the Arundo (except for Catania with 20.0 MJ kg⁻¹), 18.5 MJ kg⁻¹ for the Typha and Lythrum (except for Catania with 20.0 MJ kg⁻¹).     

Operational short rotation woody crop plantations: Manual or mechanised harvesting?

Harvesting is the most expensive, but the least investigated process in the cultivation of short rotation woody crops (SRWC). To get a better idea of the harvesting process (in terms of its performance, productivity, cost, soil compaction, cutting height and quality as well as biomass losses), we closely monitored the second harvest of a SRWC culture in Flanders (Belgium). We compared our results to the harvests of other, small European parcels. The trees at our site were harvested with both a manual and a mechanised (Stemster harvester) cut-and-store system, while the cut-and-chip system was analysed from an extensive literature survey. The production cost (to the edge of the field) at our site reached 426 (manual) and 94 (mechanised) € t⁻¹, while the average values found in the literature are respectively 104 and 78 € t⁻¹, versus 17 € t⁻¹ for the cut-and-chip harvesting system. The productivity at our site reached 14 (manual) and 22 (mechanised) oven-dry tonnes per scheduled machine hour, while the average values found in the literature are respectively 15 and 23 t h⁻¹. Based on the good performance (ha h⁻¹) and productivity (t h⁻¹) of the cut-and-chip system as well as its lower costs, this harvesting system is recommended for operational SRWC.     

Experimental trials to make wheat straw pellets with wood residue and binders

Crude glycerol, bentonite, lignosulfonate, and softwood residue (wood residue) were investigated in this study as binders for biomass fuel pellets for thermochemical conversion to enhance pellet quality for transportation and storage. The mass fraction of water of the wheat straw and the wood residue used for pelleting were 0.0676 and 0.0949, respectively. Wheat straw with crude glycerol, bentonite, lignosulfonate, wood residue, and pretreated wood residue with crude glycerol were compressed in a single pelleting unit at a temperature of 95 °C. The specific energy consumption, density, dimensional stability, tensile strength, calorific value, ash content, and chemical composition of the pellets made were determined. Results showed that the specific energy consumption for wheat straw pelletization significantly decreased with the addition of lignosulfonate, bentonite, wood residue, and pretreated wood residue with crude glycerol. With the addition of binders chosen in this study, the tensile strength of wheat straw pellets was improved with values ranging from 1.13 to 1.63 MPa. There was a significant increase in the higher heating value (17.98 MJ kg⁻¹ to 18.77 MJ kg⁻¹) when crude glycerol, wood residue, and pretreated wood residue were used as binders. The addition of both pretreated and non-pretreated wood residue significantly decreased the ash content of wheat straw pellets.     

Evaluation the efficacy of extrusion pretreatment via enzymatic digestibility and simultaneous saccharification & fermentation with rapeseed straw

The efficacy of extrusion pretreatment was evaluated by enzymatic hydrolysis and simultaneous saccharification and fermentation (SSF) with straw of rapeseed, Brassica napus, an agricultural residue. An acceptable pretreatment result was obtained at a barrel temperature of 165 °C, acid concentration of 20 g L⁻¹, liquid feeding rate of 13.4 cm³ min⁻¹, solid feeding rate of 1.0 g min⁻¹, screw rotation speed of 6.3 rad s⁻¹, and residence time of 10.2 min, with a yield of xmg, representing the sum of the corresponding hydrolyzed sugars; xylose, mannose and galactose, of 794.3 g kg⁻¹ and a glucose release of 21.0 g kg⁻¹. These were calculated to be 963.0 g kg⁻¹ and 910.3 g kg⁻¹ based on cellulose and hemicellulose recoveries,respectively. The highest enzymatic digestibility of 781.0 g kg⁻¹was higher than that obtained from the batch pretreatment with dilute acid by 1.4-fold. The SSF process afforded an ethanol concentration of 16.0 g L⁻¹, corresponding to an ethanol yield of 790 g kg⁻¹ based on the total available cellulose in the pretreated rapeseed straw.     

Grinding energy and physical properties of chopped and hammer-milled barley,wheat, oat,and canola straws

In the present study, specific energy for grinding and physical properties of wheat, canola, oat and barley straw grinds were investigated. The initial moisture content of the straw was about 0.13–0.15 (fraction total mass basis). Particle size reduction experiments were conducted in two stages: (1) a chopper without a screen, and (2) a hammer mill using three screen sizes (19.05, 25.4, and 31.75 mm). The lowest grinding energy (1.96 and 2.91 kWh t⁻¹) was recorded for canola straw using a chopper and hammer mill with 19.05-mm screen size, whereas the highest (3.15 and 8.05 kWh t⁻¹) was recorded for barley and oat straws. The physical properties (geometric mean particle diameter, bulk, tapped and particle density, and porosity) of the chopped and hammer-milled wheat, barley, canola, and oat straw grinds measured were in the range of 0.98–4.22 mm, 36–80 kg m⁻³, 49–119 kg m⁻³, 600–1220 kg m⁻³, and 0.9–0.96, respectively. The average mean particle diameter was highest for the chopped wheat straw (4.22-mm) and lowest for the canola grind (0.98-mm). The canola grinds produced using the hammer mill (19.05-mm screen size) had the highest bulk and tapped density of about 80 and 119 kg m⁻³; whereas, the wheat and oat grinds had the lowest of about 58 and 88–90 kg m⁻³. The results indicate that the bulk and tapped densities are inversely proportional to the particle size of the grinds. The flow properties of the grinds calculated are better for chopped straws compared to hammer milled using smaller screen size (19.05 mm).     

Effect of compressive load and particle size on compression characteristics of selected varieties of wheat straw grinds

In this study, the effect of compressive load and particle size on compression characteristics of four varieties (Strongfield, Blackbird, DT773 and DT818) of wheat straw grown at two different fields was investigated. Particle size, bulk and particle densities of all wheat straw samples were determined after grinding. Ground wheat straw samples were densified in a cylindrical die at 90 °C using an Instron testing machine. The wheat straw samples with 9% moisture content were compressed at five levels of compressive pressures (31.6, 63.2, 94.7, 126.4 and 138.9 MPa) and two levels of particle sizes (1.6 and 3.2 mm). Dimensions and mass of all compressed samples were measured to calculate the pellet density. The specific energy required to compress and eject the pellets was calculated from force-displacement data. Applied compressive force and particle size significantly affected the pellet density of wheat straw samples. The pellet density was in the range of 699–1064 kg m⁻³ increasing with pressure and particle size. The total specific energy required for compression and ejection of pellets varied from 4.35 to 33.64 MJ t⁻¹ that increased with compressive load and particle size. Higher compressive forces and particle size increased the durability of pellets to more than 95%. Blackbird variety was the most compressible of the four varieties of wheat straw.     

Efficiency of a compactor in wood chip volume reduction

The baling of freshly harvested wood chips was tested in an Orkel MP2000, a baling machine extensively used in agriculture and industry to densify residues. Wood chips from two different feedstocks: poplar (Populus x euroamericana) and black locust (Robinia pseudoacacia). Baling effected a volume reduction of 43% with respect to the loose bulk density of the piled chips. Each bale has an average mass of 638 kg, and the time consumption to produce one bale was typically 98 s – 122 s. Productivity then varied from 19.8 t h⁻¹ and 21.7 t h⁻¹ of the fresh (green) wood chips. Diesel fuel consumption ranged from 1.4 L t⁻¹ to 1.5 L t⁻¹ of fresh chip weight and represented about 12% of the production cost. The packaging cost is approximately 23 € t⁻¹ of fresh chips equivalent to a bale cost of 15 €. Comminuted wood pressed into bales could provide a valid solution in the use of conventional agricultural and forestry machines. In fact, the handling and transportation of bales can be performed by means of equipment normally used in other agro-forestry activities (front loaders of tractors). In addition, pressed woodchips in packaged bales with waterproof sheets also guarantees a useful storage technique with significant storage surface reduction relative to loose wood chips.     

Potential for rice straw ethanol production in the Mekong Delta,Vietnam

This study is to evaluate the potential for development of a cellulosic ethanol facility in Vietnam. Rice straw is abundant in Vietnam and highly concentrated in the Mekong Delta, where about 26 Mt year⁻¹ of rice straw has been yearly produced. To minimize the overall production cost (PC) of ethanol from rice straw, it is crucial to choose the optimal facility size. The delivered cost of rice straw varied from 20.5 to 65.4 $ dry t⁻¹ depending on transportation distance. The Mekong Delta has much lower rice straw prices compared with other regions in Vietnam because of high density and quantity of rice straw supply. Thus, this region has been considered as the most suitable location for deploying ethanol production in Vietnam. The optimal plant size of ethanol production in the region was estimated up to 200 ML year⁻¹. The improvement in solid concentration of material in the hydrothermal pre-treatment step and using residues for power generation could substantially reduce the PC in Vietnam, where energy costs account for the second largest contribution to the PC, following only enzyme costs. The potential for building larger ethanol plants with low rice straw costs can reduce ethanol production costs in Vietnam. The current estimated production cost for an optimal plant size of 200 ML year⁻¹ was 1.19 $ L⁻¹. For the future scenario, considering improvements in pre-treatment, enzyme hydrolysis steps, specific enzyme activity, and applying residues for energy generation, the ethanol production cost could reduce to 0.45 $ L⁻¹ for a plant size of 200 ML year⁻¹ in Vietnam. These data indicated that the cost-competitiveness of ethanol production could be realized in Vietnam with future improvements in production technologies.     

The improvement of hog fuel by removing fines,using a trommel screen

The study tested the use of a trommel screen originally designed for compost materials to reject oversize particles from hog fuel, processed from several sources and by two different comminution devices. The experiment consisted in screening material previously comminuted by a convertible crusher, designed to use both hammers and knives. Three different feedstock types were used, and namely: discarded pallets, logs and branches from park maintenance. Each feedstock type came in two different qualities, depending on the tool used for comminution, i.e. hammers or knives. Trommel screen productivity varied between 4.2 t h⁻¹, and 5.2 t h⁻¹ of oven dry material. Screening hog fuel derived from pallets was 30% and 40% less productive than screening fuel derived from logs and branches, respectively. Screening cost varied from 16.2 € t⁻¹ dry material in the case of branches, to 19.9 € t⁻¹ oven dry material for pallets. Screening allowed an increase of fuel quality only when applied to pallet-derived hog fuel.     

Comparison of energy inputs in glasshouse double crop (fall and summer crops) tomato production

The study examines energy use patterns and the relationship between energy inputs and yield for double crop (fall and summer) glasshouse tomato production in Antalya province, where is one of the most important greenhouse centres in Turkey. The data of the study was retrieved from 37 fall and 25 summer glasshouse tomato producers via face to face survey in 2007. The research findings revealed energy use values for inputs such as manure, electricity, chemical fertilizer and fuel. While the average yield per hectare is 25025.4 kg for enterprises involved in tomato production in fall, it is 22392.9 kg for summer production. The overall energy consumption is higher in fall production with 81362.2 MJ ha^?1 in comparison to summer production 63023.2 MJ ha^?1. In addition, the specific energy requirement is 3521.2 MJ t^?1 and 2814.4 MJ t^?1 for fall and summer production in order and the energy efficiency was found out to be 0.31 kg MJ^?1 and 0.36 kg MJ^?1 respectively. Finally, the energy relationship was tested using the production relationship. The findings indicated that direct energy sources are effective in tomato yield for both of the two seasons. More clearly, the most significant energy input was electrical energy for summer production and a combination of electrical energy, human power and machinery for fall production. Yet, excess and unconscious use of chemical ingredients in glasshouse tomato production was confirmed as energy derived from chemical drugs leaded a declination in the yield for fall season. Therefore, the paper revealed energy relationship for double crop glasshouse tomato production in Antalya, being a reference for similar production methodologies.     

Investigating the energy use of vegetable market waste by briquetting

The present paper reports a study conducted at Sardar Patel Renewable Energy Research Institute, aiming at transforming vegetable market waste (VMW) into an energy-briquette. The raw green vegetable market waste gave about 15–20% dry matter after open sun drying. The dried mass of the VMW was converted into a pulverized form and subsequently into briquettes without using any external binding agent. Although the lignin contents of the VMW were low (3.23–5.51%) as compared to other lingo-cellulosic biomass, good quality briquettes were produced without using any binding agent. The bulk densities of briquettes were almost 10–15 times higher than the material in dry loose form. The calorific value of four different types of VMW used in this study ranged 10.26–13.70 MJ kg⁻¹ of dry matter.     

Evaluation of sorghum hybrids for biomass production in central Italy

Two field experiments were carried out in 2005 and 2006 in central Italy in order to evaluate the biomass production and quality in eight sorghum hybrids, to define their biomass partitioning among leaves, panicles and stems and to identify which were the most adapted at early harvest. Sorghum showed a high potential in terms of biomass production in central Italy, with biomass dry yield of 25 t ha⁻¹ in average, adopting low input in terms of irrigation and fertilization. The most productive hybrids were H133 (26.3 t ha⁻¹) and H952 (25.9 t ha⁻¹) among the biomass hybrids and SS506 (27.3 t ha⁻¹) among the forage hybrids. The trends of dry weight and moisture content of biomass during the different hybrids growth cycles allowed to estimate the biomass production of each hybrids, hypothesizing an early harvest at 20 August with in-field drying of biomass. Early harvest reduced dry weight of biomass from 4.6% to 21.7%, depending of hybrids; SS506 and H128 showed to be the most adapted at early harvest. HHV and LHV of biomass showed average values higher in biomass hybrids (18.4 and 17.5 MJ kg⁻¹ d.m.) than in forage hybrids (17.7 and 16.8 MJ kg⁻¹ d.m.); while, ash content average values were lower in biomass hybrids (6.8% d.m.) than in forage hybrids (7.7% d.m.). The highest values of leaves + panicles partitioning in the forage hybrids increased ash content, reducing the quality of their biomass for thermal utilization; the biomass hybrids should be therefore preferable.