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 economic potential of wood pellet production from alternative,low-value wood sources in the southeast of the U.S.

The global demand for wood pellets used for energy purposes is growing. Therefore, increased amounts of wood pellets are produced from primary forestry products, such as pulp wood. The present analysis demonstrates that substantial amounts of alternative, low-value wood resources are available that could be processed into wood pellets. For three resources, test batches have been produced and tested to qualify for industrial pellet standards. These include: primary forestry residues from premerchantable thinning operations, secondary forestry residues from pole mills and post-consumer wood wastes from discarded wooden transport pallets. The total wood potential of these resources in the southeast of the U.S. (Florida, Georgia, North Carolina, South Carolina), was estimated to be 1.9 Tg y⁻¹ (dry) available at roadside (excluding transport cost) for 22 $ Mg⁻¹ (dry) increasing to over 5.1 Tg y⁻¹ at 33 $ Mg⁻¹ (dry). In theory, 4.1 Tg y⁻¹ pellets could be produced from the estimated potential. However, due to the geographically dispersed supply of these resources, the cost of feedstock supply at a pellet plant increases rapidly at larger plants. It is therefore not expected that the total potential can be processed into wood pellets at costs competitive with those of conventional wood pellets. The optimal size of a pellet plant was estimated at between 55 Gg y⁻¹ and 315 Gg y⁻¹ pellets depending on the location and feedstock supply assumptions. At these locations and plant sizes, pellets could be produced at competitive costs of between 82 $ Mg⁻¹ and 100 $ Mg⁻¹ pellets.     

Biogas production from catch crops: Increased yield by combined harvest of catch crops and straw and preservation by ensiling

The combination of catch crop cultivation with its use for biogas production would increase renewable energy production in the form of methane, without interfering with the production of food and fodder crops. The low biomass yield of catch crops has been shown as the main limiting factor for using these crops as co-substrate in biogas plants, since the profit obtained from the sale of methane barely compensates the harvest costs. Therefore, a new agricultural strategy to harvest catch crops together with the residual straw of the main crop was investigated, in order to increase the biomass and the methane yield per hectare. Seven catch crops harvested together with stubble from the previous main crop were evaluated. The effects of stubble height, harvest time and ensiling as a storage method for the different catch crops/straw blends were studied. Biomass yields as TS ranged between 3.2 and 3.6 t ha⁻¹ y⁻¹of which the catch crop constituted around 10% of the total biomass yield. Leaving the straw on the field until harvest of the catch crop in the autumn could benefit methane production from the straw both due to increased biomass yield and an increased organic matter bioavailability of the straw taking place on the field during the autumn months. Ensiling as a storage method could be feasible in terms of energy storage and guaranteeing the feedstock availability for the whole year. This new agricultural strategy may be a good alternative for economically feasible supply of catch crops and straw for biogas production.     

Technoeconomic analysis of jet fuel production from hydrolysis,decarboxylation, and reforming of camelina oil

The commercial production of jet fuel from camelina oil via hydrolysis, decarboxylation, and reforming was simulated. The refinery was modeled as being close to the farms for reduced camelina transport cost. A refinery with annual nameplate capacity of 76,000 cubic meters hydrocarbons was modeled. Assuming average camelina production conditions and oil extraction modeling from the literature, the cost of oil was 0.31 $ kg⁻¹. To accommodate one harvest per year, a refinery with 1 year oil storage capacity was designed, with the total refinery costing 283 million dollars in 2014 USD. Assuming co-products are sold at predicted values, the jet fuel break-even selling price was 0.80 $ kg⁻¹. The model presents baseline technoeconomic data that can be used for more comprehensive financial and risk modeling of camelina jet fuel production. Decarboxylation was compared to the commercially proven hydrotreating process. The model illustrated the importance of refinery location relative to farms and hydrogen production site.     

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.     

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%).     

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.     

Comparison of quality and production cost of briquettes made from agricultural and forest origin biomass

This paper presents the quality and cost of small-scale production of briquettes, made from agricultural and forest biomass in north-eastern Poland. The experiment involved production of eight types of briquettes. The highest net calorific value was determined for briquettes made from pine sawdust (18,144 MJ t⁻¹). The value measured for briquettes made from perennial energy plants was over 1500 MJ t⁻¹ lower, and for those made from straw 2000 MJ t⁻¹ lower than for sawdust briquettes. The sawdust briquettes left significantly the lowest amount of ash (0.40% of dry mass). The significantly highest content of hydrogen, sulphur and nitrogen was found in briquettes containing the highest portion of rapeseed oilcake. The quality of briquettes varied and only some of them met the requirements of DIN 51731. Briquettes made from pine sawdust were of the highest quality. The briquette production cost ranged from 66.55 € t⁻¹ to 137.87 € t⁻¹ for rape straw briquettes and for those made from a mixture of rape straw and rapeseed oilcake (50:50), respectively. In general, briquette production was profitable, except for the briquettes made from a straw and rapeseed oilcake mixture.     

Assessment of different feedstocks in South Tyrol (Northern Italy): Energy potential and suitability for domestic pellet boilers

The present study aims to quantify the main biomass resources in South Tyrol (Northern Italy) and estimate the potential contribution for the energy sector. Moreover, four representative feedstocks have been tested in a domestic pellet boiler under standard conditions in order to assess its performance and pollutant emissions.The unexploited biomass potential for energy conversion applications, expressed as dry weight, has been estimated to be 135 000 t y⁻¹ from forest, 14 950 t y⁻¹ for apple pruning residues and 12 000 t y⁻¹ from the industrial sector. The scenario of utilizing the unexploited local biomass resources – in energy systems such as the ones deployed in South Tyrol – would contribute with an annual bioenergy production contribution of 130–270 TJ of electricity and 1700–2100 TJ of heat. Finally, the tested feedstocks can be used in domestic boilers, however, some modifications are required when using agricultural residues.     

Techno-economic assessment of pellets produced from steam pretreated biomass feedstock

Minimum production cost and optimum plant size are determined for pellet plants for three types of biomass feedstock – forest residue, agricultural residue, and energy crops. The life cycle cost from harvesting to the delivery of the pellets to the co-firing facility is evaluated. The cost varies from 95 to 105 $ t⁻¹ for regular pellets and 146–156 $ t⁻¹ for steam pretreated pellets. The difference in the cost of producing regular and steam pretreated pellets per unit energy is in the range of 2–3 $ GJ⁻¹. The economic optimum plant size (i.e., the size at which pellet production cost is minimum) is found to be 190 kt for regular pellet production and 250 kt for steam pretreated pellet. Sensitivity and uncertainty analyses were carried out to identify sensitivity parameters and effects of model error.     

Marginal cost of delivering switchgrass feedstock and producing cellulosic ethanol at multiple biorefineries

Limited information is available regarding the change in cost to deliver dedicated energy crop feedstock as the quantity of required feedstock increases. The objective is to determine the marginal cost to produce and deliver switchgrass feedstock to biorefineries. A mathematical programming model that includes 77 production regions (Oklahoma counties), monthly feedstock requirements, integer activities for harvest machines and integer activities for each of 16 potential biorefinery locations was constructed. The model was initially solved for a single biorefinery. The number of plants was incremented by one and the model resolved until nearly 10% of the cropland and improved pasture land was converted to switchgrass. The estimated cost to deliver 1.0 Mg of feedstock to a single 189 dam³ y⁻¹ capacity biorefinery is 55 $. The cost to deliver feedstock increases as additional biorefineries are constructed and the cost for the ninth biorefinery of 87 $ Mg⁻¹ is 58% greater than the cost to deliver to the first biorefinery. The cost difference is primarily due to differences in transportation cost. Initial cellulosic biorefineries will have an opportunity for establishing a feedstock cost advantage by carefully selecting land for conversion to switchgrass and by negotiating long term leases.     

Biomass equations for hybrid larch growing on farmland

Johansson, T. 2011. Biomass equations for hybrid larch growing on farmland.Data were collected from 20 stands of hybrid larch (Larix x eurolepis) growing on abandoned farmland in southern and central Sweden (Lat. 55–60° N.). The mean stand age was 19 years (range 18–23). The mean number of stems per hectare was 1150 (range 364–2374) and the mean breast height diameter (over bark) was 15.6 cm (6.8–24.2). Soil types in the stands were light and medium clay and tills (sandy-silty and light clay).Mean dry weight above stump level (20 cm) for a hybrid larch tree in this study was 117 kg (range 36–245) and the standing dry weight for hybrid larch stands was 120 t ha⁻¹ (42–350). Mean annual increment (MAI) for the tree was 6.09 kg y⁻¹ (1.89–13.61) corresponding to production of 90–120 t ha⁻¹ after 15–20 years growth and a stem number of 1000–1500, if the stand is mainly used for biomass. Alternatively, for pulp wood and timber production a rotation period of 30–40 years can be used, with thinnings being exploited for biomass.     

Spatial assessment of the bioenergy potential of forest residues in the western province of Spain, Caceres

The present work is mainly devoted to provide a rigorous analysis on the quantification, the mapping and the management of the bioenergy potential of forest residues from the most representative forestry species of the west-central region of Spain (Cáceres).An appropriate methodological approach for the estimate of potential biomass and potential bioenergy as well as the use of GIS for data process are both crucial for the design of thermal plants and for the accurate estimate of biomass collection and transportation costs, according to the scale economy of the plant.The total forest residues in the province of Cáceres are estimated as 463 000 t y⁻¹. The availability of such major biomass potential for energy production is strongly conditioned to the inherent difficulties during the extraction process. This way, an energy potential of 139 000 toe y⁻¹ would be achieved if the above-mentioned biomass collection rate is assumed.The method to optimise the search for suitable locations for thermal plants as well as for biomass extraction/collection areas, based on the combined use of GIS and spatial analysis techniques, is also described.     

Rice straw as a lignocellulosic resource: collection,processing, transportation,and environmental aspects

As open-field burning of rice straw is being phased out in California, rice growers and government agencies are looking for new rice straw uses. The amount of rice straw that may be available as a feedstock ranges from 1.0 to 1.4 million t yr⁻¹. Irrespective of its actual use as a source of raw material for liquid fuel, fiber, or power generation, a study of issues dealing with its harvest is needed. This paper reviews possible harvesting systems and provides an analysis of operating parameters such as straw moisture, density, storage, and optimal number of transport units. A case study of rice straw production in the Sacramento Valley was conducted, which illustrates that 550 t d⁻¹ of straw can be accessed at an estimated net delivered cost of about US $20/t (dry), which is generally considered attractive for an ethanol feedstock. Gainfully utilizing this residue can ease the disposal problem facing agricultural operations in the State. Furthermore, the potential environmental benefits of diverting rice straw from open-field burning will be to significantly reduce criteria air pollutants such as VOC, SO_x, NO_x, and PM10, and also silica emissions, which are not specifically monitored but can be a health hazard.     

Comparative net energy ratio analysis of pellet produced from steam pretreated biomass from agricultural residues and energy crops

A process model was developed to determine the net energy ratio (NER) for the production of pellets from steam pretreated agricultural residue (wheat straw) and energy crops (i.e., switchgrass in this case). The NER is a ratio of the net energy output to the total net energy input from non-renewable energy sources into a system. Scenarios were developed to measure the effects of temperature and level of steam pretreatment on the NER of steam pretreated wheat straw and switchgrass pellets. The NERs for the base case at 6 kg h⁻¹ are 1.76 and 1.37 for steam-pretreated wheat straw and switchgrass-based pellets, respectively. The reason behind the difference is that more energy is required to dry switchgrass pellets than wheat straw pellets. The sensitivity analysis for the model shows that the optimum temperature for steam pretreatment is 160 °C with 50% pretreatment (i.e. 50 % steam treated material is blended with the raw biomass and then pelletised). The uncertainty results for NER for steam pretreated wheat straw and switch grass pellets are 1.62 ± 0.10 and 1.42 ± 0.11, respectively.     

Comparative techno-economic analysis of biohydrogen production via bio-oil gasification and bio-oil reforming

This paper evaluates the economic feasibility of biohydrogen production via two bio-oil processing pathways: bio-oil gasification and bio-oil reforming. Both pathways employ fast pyrolysis to produce bio-oil from biomass stock. The two pathways are modeled using Aspen Plus^® for a 2000 t d⁻¹ facility. Equipment sizing and cost calculations are based on Aspen Economic Evaluation® software. Biohydrogen production capacity at the facility is 147 t d⁻¹ for the bio-oil gasification pathway and 160 t d⁻¹ for the bio-oil reforming pathway. The biomass-to-fuel energy efficiencies are 47% and 84% for the bio-oil gasification and bio-oil reforming pathways, respectively. Total capital investment (TCI) is 435 million dollars for the bio-oil gasification pathway and is 333 million dollars for the bio-oil reforming pathway. Internal rates of return (IRR) are 8.4% and 18.6% for facilities employing the bio-oil gasification and bio-oil reforming pathways, respectively. Sensitivity analysis demonstrates that biohydrogen price, biohydrogen yield, fixed capital investment (FCI), bio-oil yield, and biomass cost have the greatest impacts on facility IRR. Monte-Carlo analysis shows that bio-oil reforming is more economically attractive than bio-oil gasification for biohydrogen production.     

Lignocellulosic ethanol production employing immobilized Saccharomyces cerevisiae in packed bed reactor

Most of ethanol production processes are limited by lower ethanol production rate and recyclability problem of ethanologenic organism. In the present study, immobilized co-fermenting Saccharomyces cerevisiae GSE1618 was employed for ethanol fermentation using rice straw enzymatic hydrolysate in a packed bed reactor (PBR). The immobilization of S. cerevisiae was performed by entrapment in Ca-alginate for optimization of ethanol production by varying alginic acid concentration, bead size, glucose concentration, temperature and hardening time. Remarkably, extra hardened beads (EHB) immobilized with S. cerevisiae could be used up to repeated 40 fermentation batches. In continuous PBR, maximum 81.82 g L⁻¹ ethanol was obtained with 29.95 g L⁻¹ h⁻¹ productivity with initial glucose concentration of 180 g L⁻¹ in feed at dilution rate of 0.37 h⁻¹. However, maximum ethanol concentration of 40.33 g L⁻¹ (99% yield) with 24.61 g L⁻¹ h⁻¹ productivity was attained at 0.61 h⁻¹ dilution rate in fermentation of un-detoxified rice straw enzymatic hydrolysate (REH). At commercial scale, EHB has great potential for continuous ethanol production with high productivity using lignocellulosic hydrolysate in PBR.     

Industrial sugar beets to biofuel: Field to fuel production system and cost estimates

Specialized varieties of sugar beets (Beta vulgaris L.) may be an eligible feedstock for advanced biofuel designation under the USA Energy Independence and Security Act of 2007. These non-food industrial beets could double ethanol production per hectare compared to alternative feedstocks. A mixed-integer mathematical programming model was constructed to determine the breakeven price of ethanol produced from industrial beets, and to determine the optimal size and biorefinery location. The model, based on limited field data, evaluates Southern Plains beet production in a 3-year crop rotation, and beet harvest, transportation, and processing. The optimal strategy depends critically on several assumptions including a just-in-time harvest and delivery system that remains to be tested in field trials. Based on a wet beet to ethanol conversion rate of 110 dm³ Mg⁻¹ and capital cost of 128 M$ for a 152 dam³ y⁻¹ biorefinery, the estimated breakeven ethanol price was 507 $ m⁻³. The average breakeven production cost of corn (Zea mays L.) grain ethanol ranged from 430 to 552 $ m⁻³ based on average net corn feedstock cost of 254 and 396 $ m⁻³ in 2014 and 2013, respectively. The estimated net beet ethanol delivered cost of 207 $ m⁻³ was lower than the average net corn feedstock cost of 254–396$ m⁻³ in 2013 and 2014. If for a mature industry, the cost to process beets was equal to the cost to process corn, the beet breakeven ethanol price would be $387 m^-3 (587 $ m⁻³ gasoline equivalent).     

Microbial changes during the on-farm storage of canola (oilseed rape) straw bales and pellets

The effect of on-farm storage on microbial growth on baled and pelletised Brassica napus (oilseed rape/canola) straw was investigated. Canola straw collected in 2008 and 2009 was stored baled in an open shed for 3, 4, 7, 10 and 20 months in 2008 and for 1 and 3 months in 2009. Pellets were produced from straw stored for 3, 7, and 10 months in 2008 and straw stored for 3 months in 2009, and stored for up to 48 weeks.The moisture content (MC), water activity (a_w), bacterial and fungal colony-forming units (CFU), and carbon-to-nitrogen ratio (C:N) of canola straw bales and pellets were measured during storage. In addition, temporal environmental conditions (ambient temperature and relative humidity) and bale temperature were monitored. The moisture content showed a tendency to stabilise during storage, with an equilibrium moisture content of approximately 155 g kg⁻¹ total weight for straw bales and 110 g kg⁻¹ total weight for straw pellets. Consequently, the water activity of canola straw bales remained below 0.8 and that of pellets below 0.66 during storage, providing an explanation for relatively low microbial growth. The number of bacterial and fungal CFU present in the straw bales and pellets followed the trend of ambient relative humidity and no correlation was found with the C:N ratio of the biomass. Canola straw pellets were considered a superior combustion fuel to straw bales due to lower moisture content and less microbial deterioration during storage.     

Reed canarygrass (Phalaris arundinacea) outperforms Miscanthus or willow on marginal soils,brownfield and non-agricultural sites for local,sustainable energy crop production

Growing biomass on non-agricultural land could potentially deliver renewable energy services without displacing land from food production, avoiding the social and environmental conflicts associated with bioenergy. A variety of derelict underutilized and neglected land types are possible candidates, sharing a number of challenges for agronomy, including contaminants in soils, potential uptake and dispersion through energy use. Most previous field trials have grown woody biomass species during phytoremediation. Five one-hectare brownfield sites in NE England, were each amended with c.500 t ha⁻¹ of green-waste compost, planted with short-rotation coppice willow, Miscanthus, reed canarygrass and switchgrass,¹ and then harvested for 3–5 years.Critical issues for the economic and environmental viability of energy production on brownfield land were investigated: The yields achieved on non-agricultural land; the potential for fuel contamination; the suitability for use and potential markets for any biomass produced. RCG appears best suited to the challenging soil conditions found on non-agricultural land, outperforming other species in ease of establishment, cost, time to maturity, yield and contamination levels. Invasive spreading and low melting ash compositions were not observed. Annual yields of 4–7 odt ha⁻¹ from the second growth season were found consistently across a range of previously-developed, capped or former landfill sites, with a gross annual energy yield of 97 GJ ha⁻¹ at contamination levels acceptable for domestic pellets. The analogy with marginal agricultural land suggests that this species and approach could help boost biomass production while avoiding the natural capital “nexus” related to global food-fuel-land-water limits.