Indirect energy input of agricultural machinery in bioenergy production

Sustainability of bioenergy products should be evaluated by means of an energy analysis that takes into account all relevant direct and indirect energy inputs. Direct energy input is viewed as the major energy consuming factor, and is quite easy to measure. Indirect energy input, however, has received relatively scant attention, so it is likely to be insufficiently analysed and possibly underestimated. This paper reviews the data available and suggests the type of research that would be needed to get a better understanding of the indirect energy input. The analysis addresses questions about the use of energy to produce and maintain agricultural machinery, the allocation of energy to different bioenergy products, and the real use and lifetime of machinery.     

Energy trade-offs between intensive biomass utilization, site productivity loss, and ameliorative treatments in loblolly pine plantations

Loblolly pine plantations are the most important source of forest products in the US and the slash remaining after conventional harvest represents a significant potential source of bioenergy. However, slash removal in intensive harvests might, under some circumstances, reduce site productivity by reducing soil organic matter and associated nutrients. Two complimentary studies in the Gulf Coastal Plain of the southeastern US were designed to test whether harvest intensity (level of biomass removal) could have a negative long-term impact on site productivity. Harvesting tree crowns in addition to the merchantable bole had a negative impact (18%) on pine biomass accumulation by age 7–10 years on 15 of 19 research blocks. Sites at risk of harvest-induced reductions in productivity were relatively unproductive prior to harvest and had low soil phosphorus (P) concentrations. Intensive harvesting, fertilization, and chemical control of non-crop vegetation were all energy efficient; the additional biomass energy gained through these practices was two-orders of magnitude greater than the energy needed to conduct the activities. Harvest of slash for bioenergy in the Gulf Coastal Plain of the southeastern US has the potential to reduce productivity on infertile soils, but fertilization has the potential to restore and even improve productivity on those sites in an energy-efficient way.     

Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production

Three annual plant species, maize, hemp and faba bean were tested for suitability as dedicated biomass crops in Boreal conditions. Biomass yields were 10-15 t ha^-1. The crops were analyzed for their composition and tested as raw materials for conversion to methane and to fermentable sugars. The methane yield was 379 ± 16 Ndm³ kg⁻¹ VS⁻¹ from maize, 387 ± 20 Ndm³ kg⁻¹ VS⁻¹ from faba bean and 239 ± 9 Ndm³ kg⁻¹ VS⁻¹ from hemp. Based on the yield per hectare, maize proved to be the most potential raw material source for methane production. Analogous to methane production, maize was the most productive raw material also in standard hydrolysis tests, with a conversion yield of about 80% of the theoretical sugars. Based on the amount of carbohydrates, the highest theoretical yield per hectare was obtained with hemp. However, considering all parameters, including the need for weeding and fertilizers, all three crops studied proved to be attractive options for cultivation in boreal conditions as well as being used as energy crops in boreal climate.     

Cost efficient utilisation of biomass in the German energy system in the context of energy and environmental policies

The possible uses of biomass for energy provision are manifold. Gaseous, liquid and solid bioenergy carriers can be alternatively converted into heat, power or transport fuel. The contribution of the different utilisation pathways to environmental political targets for greenhouse gas (GHG) emission reduction and energy political targets for the future share of renewable energy vary accordingly to their techno-economic characteristics. The aim of the presented study is to assess the different biomass options against the background of energy and environmental political targets based on a system analytical approach for the future German energy sector. The results show that heat generation and to a lower extent combined heat and power (CHP) production from solid biomass like wood and straw are the most cost effective ways to contribute to the emission reduction targets. The use of energy crops in fermentation biogas plants (maize) and for production of 1st generation transportation fuels, like biodiesel from rapeseed and ethanol from grain or sugar beet, are less favourable. Optimisation potentials lie in a switch to the production of 2nd generation biofuels and the enhanced use of either biomass residues or low production intensive energy crops.     

Competition between biomass and food production in the presence of energy policies: a partial equilibrium analysis

Bioenergy has several advantages over fossil fuels. For example, it delivers energy at low net CO₂ emission levels and contributes to sustaining future energy supplies. The concern, however, is that an increase in biomass plantations will reduce the land available for agricultural production. The aim of this study is to investigate the effect of taxing conventional electricity production or carbon use in combination with subsidizing biomass or bioelectricity production on the production of biomass and agricultural commodities and on the share of bioelectricity in total electricity production. We develop a partial equilibrium model to illustrate some of the potential impacts of these policies on greenhouse gas emissions, land reallocation and food and electricity prices. As a case study, we use data for Poland, which has a large potential for biomass production. Results show that combining a conventional electricity tax of 10% with a 25% subsidy on bioelectricity production increases the share of bioelectricity to 7.5%. Under this policy regime, biomass as well as agricultural production increase. A carbon tax that gives equal net tax yields, has better environmental results, however, at higher welfare costs and resulting in 1% to 4% reduction of agricultural production.     

Biomass production and soil nutrients in organic and inorganic fertilized willow biomass production systems

The use of organic waste materials as nutrient sources for willow biomass production is an attractive means to decrease fertilization costs, increase biomass production and reduce greenhouse gas emissions associated with the system. In this study, changes in soil nutrients and biomass production of two willow varieties (Salix miyabeana–SX64 and Salix purpurea–9882-34) in organic and synthetic fertilized systems were compared at three locations in Northeastern U.S.A: Middlebury VT (MID), Delhi NY (DEL) and Fredonia NY (FRE). A 150 and 200 kg available N ha⁻¹ of urea as commercial fertilizer (CF), biosolid compost (BC) and digested dairy manure (DM) and a control (CT0) treatments were applied in June 2008 to the willow which was re-sprouting after coppice. There was no significant difference (p > 0.05) in biomass production among the fertilization treatments at any of the three sites and for either of the varieties. First rotation biomass production of 9882-34 ranged from 9.0 to 11.6 Mg ha⁻¹ yr⁻¹ at DEL, 3.4–8.8 Mg ha⁻¹ yr⁻¹ at MID and 3.5–7.7 Mg ha⁻¹ yr⁻¹ at FRE. For SX64, biomass production ranged from 13.2 to 19.0 Mg ha⁻¹ yr⁻¹ at DEL, 9.0–15.0 Mg ha⁻¹ yr⁻¹ at Mid and 5.5–9.3 Mg ha⁻¹ yr⁻¹ at FRE. SX64 deployed small numbers of large stems and produced more biomass than 9882-34 which deployed large numbers of small stems. Application of BC significantly increased soil N and P levels at MID in both 2008 and 2009 (p < 0.05). At DEL, BC and DM treatments increased soil N, Ca, Mg and OM levels in both 2008 and 2009 (p < 0.05). The fertilization treatments had no significant effect on any soil nutrients at FRE. This study indicates that willow biomass can be produced without fertilizer additions in the first rotation across this range of sites due to the nutrient status of these sites and high internal nutrient cycling in these systems.     

The influence of organic and inorganic fertiliser application rates on UK biomass crop sustainability

Bioenergy and energy crops are an important part of the UK’s renewable energy strategy to reach its greenhouse gas reduction target of 80% by 2050. Ensuring the sustainability of biomass feedstocks requires a greater understanding of all aspects of energy crop production, their ecological impacts and yields. This work compares the life-cycle environmental impact of natural gas and biomass from two energy crop systems grown under typical UK agronomic practice. As reported in previous studies the energy crops provide significant reductions in global warming potential (GWP) compared to natural gas. Compared to no fertiliser application, applying inorganic fertiliser increases the GWP by 2% and applying sewage sludge increases the GWP by a lesser extent. In terms of an equivalent GWP savings per unit area of land, the emissions associated with fertiliser production and application can be offset by a yield increase of <0.2 t/ha. However, very large increases in eutrophication and acidification levels are incurred compared to the natural gas reference case when applying either fertiliser. For sewage sludge the impact of varying the allocation factor between the function of wastewater treatment and that of crop growth is also illustrated.     

Beneficial effects of biochar application to contaminated soils on the bioavailability of Cd,Pb and Zn and the biomass production of rapeseed (Brassica napus L.)

Phytoremediation of soils contaminated by heavy metals was tested by liming (CaCO₃) or adding biochar (1%, 5% and 10%, mass fraction) and by growing rapeseed (Brassica napus L.), a common bioenergy crop. Bioavailable metal concentrations (0.01 mol L⁻¹ CaCl₂ extraction) decreased with increasing concentrations of biochar amendment. The reduction reached 71%, 87% and 92% for Cd, Zn and Pb respectively in the presence of 10% biochar. Twelve weeks after sowing, all plants cultivated on the untreated soil and on the soil amended by biochar at 1% had died, while the plants grew normally on the soil that had the other treatments. Compared to liming, treatment with 10% biochar proved equally efficient in reducing metal concentrations in shoots but the biomass production tripled as a result of the soil fertility improvement. Thus, in addition to C sequestration, the incorporation of biochar into metal-contaminated soils could make it possible to cultivate bioenergy crops without encroaching on agricultural lands. Although additional investigations are needed, we suggest that the harvested biomass might in turn be used as feedstock for pyrolysis to produce both bioenergy and new biochar, which could contribute further to the reduction of CO₂ emission.     

Evaluation the potential economic impacts of Taiwanese biomass energy production

The Taiwanese rice paddy land set-aside program diverts a substantial land area. Given today’s high energy prices and interests in energy security, that set-aside area could be converted to produce bioenergy feedstocks. This study evaluates the economic and environmental impacts of such a policy change using a Taiwanese agricultural sector model. The results show that such a strategy provides increased farm revenue, increased rural employment, increased energy sufficiency and reduced greenhouse gas emissions but also increased government expenditures. These outcomes indicate that the agricultural sector could play a positive role by producing renewable energy.     

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.     

Giant cane (Arundo donax L.) for biogas production: The effect of two ensilage methods on biomass characteristics and biogas potential

Arundo donax L. is a perennial plant that can substitute for traditional energy crops to produce biogas, reducing costs because of its high biogas yield per Ha cultivated and low agronomic and energetic inputs. Nevertheless, Arundo donax biomass needs to be ensiled to be preserved and used. Because no full-scale data exist about A. donax ensilage and the effect of this process on potential biogas production, in this work two different ensiling techniques, i.e. trench and silo-bag ensiling, were performed at full scale, and the processes studied for 200 days. Results obtained indicated that A. donax could be successful ensiled by using the two approaches. Ensilage proceeded by fermentation of organic acids already present in the biomass, i.e. malic and oxalic acids that were degraded, giving volatile fatty acid accumulation. This was different from corn ensiling characterized by starch fermentation to lactic acids. Biological processes determined a loss of the potential biomethane production, namely −20.1% and −7.6% for trench and silo-bag, respectively. Taking into consideration biomethane yield per Ha and ensilage losses, potential biomethane losses of 5000 Nm³ CH₄ Ha⁻¹ for trench silage and of 2000 Nm³ CH₄ Ha⁻¹ for silo bag, were estimated, respectively. Nevertheless, taking into consideration the higher biomass and biomethane yields Ha⁻¹ in comparison with the other energy crops, A. donax still remained more efficient and cheaper than traditional energy crops in producing biogas.     

Supply chain optimization of residual forestry biomass for bioenergy production: The case study of Portugal

Within a large set of renewable energies being explored to tackle energy sourcing problems, bioenergy can represent an attractive solution if effectively managed. The supply chain design supported by mathematical programming can be used as a decision support tool to the successful bioenergy production systems establishment. This strategic decision problem is addressed in this paper where we intent to study the design of the residual forestry biomass to bioelectricity production in the Portuguese context. In order to contribute to attain better solutions a mixed integer linear programming (MILP) model is developed and applied in order to optimize the design and planning of the bioenergy supply chain. While minimizing the total supply chain cost the production energy facilities capacity and location are defined. The model also includes the optimal selection of biomass amounts and sources, the transportation modes selection, and links that must be established for biomass transportation and products delivers to markets. Results illustrate the positive contribution of the mathematical programming approach to achieve viable economic solutions. Sensitivity analysis on the most uncertain parameters was performed: biomass availability, transportation costs, fixed operating costs and investment costs.     

Current status and prospects of biomass resources for energy production in Lithuania

Basic biomass sources in Lithuania are comprised of wood, straw, biofuel and biogas. The current status and the problems from using biomass for energy production in Lithuania are analyzed. The possibility of utilizing wood waste, firewood, straw and biogas for energy is evaluated. Forest comprises about 2.05 Mha or 31.3% of Lithuanian land area. About 4.3 million m³ solid volume of wood per year can be used for fuel (843 ktoe). Wood as fuel is used directly or in processed form (briquettes, pellets and chips).Agriculture produces approximately 1.5–2.0 million tons of straw each year for animal feed, litter and olericulture. Around 30–40% (130 ktoe) could be used as fuel for energy production. Boiler houses for combusting the straw have increased and now comprise about 7 MW. Straw is also used for heating private houses.Sources for biogas production include sludge from water cleaning equipment, animal manure and organic waste in food processing companies. Total volume of operating bioreactors comprises about 24 000 m³, and annual production of biogas is 6.3 million m³ per year (3.4 ktoe). By year 2010 the total volume of bioreactors will increase to 35 000 m³ and about 50 000 m³ by 2040.In Lithuania biodiesel and bioethanol are mainly used in blending with conventional fuel. Following the requirements of the European Union (EU), 2% of total consumed fuel per year is to be produced in 2005. By 2010 biofuel should comprise not less than 5.75% of all fuel existing in the market.     

Optimization-based planning of a biomass to hydrogen (B2H2) system using dedicated energy crops and waste biomass

The utilization of biomass for hydrogen production is one of the promising options for a sustainable energy system. In this paper, we develop a new optimization-based approach for design and analysis of the B2H2 system including production, storage, and distribution using dedicated energy crops as well as various resources of waste biomass. To achieve this goal, we first develop an optimization model using mixed-integer linear programming technique that includes practical variables and constraints for decision-making about the usage of dedicated energy crops. We then conduct a case study of the B2H2 system for the road transportation sector of future Korea. As a result, we identify an optimal system configuration that includes the utilized biomass types, occupied land sizes, the number and location of facilities, and the biomass and hydrogen flows between regions. We also analyze the cost distributions and the sensitivity of the main cost drivers on the total annual cost (TAC). The results reveal that the proposed B2H2 system is economically competitive with some of the other renewable-based hydrogen supply systems (wind and solar) in Korea.     

Energy analysis of the system of two-stage anaerobic processing of liquid organic waste with production of hydrogen- and methane-containing biogases

In recent years, public attention has been increasingly attracted to solving two inextricably linked problems - preventing the depletion of natural resources and protecting the environment from anthropogenic pollution. The annual consumption of livestock waste for biogas production is about 240 thousand m³ per year, which is 0.17% of the total manure produced at Russian agricultural enterprises. At present, the actual use of organic waste potentially suitable for biogas production is 2–3 orders of magnitude lower than the existing potential for organic waste. Currently, hydrogen energy is gaining immense popularity in the world due to the problem of depletion of non-renewable energy sources - hydrocarbons, and environmental pollution caused by their increasing consumption. Of particular interest is the dark process of producing hydrogen-containing biogas in the processing of organic waste under anaerobic conditions, which allows you to take advantage of both energy production and solving the problem of organic waste disposal. An energy analysis of a two-stage anaerobic liquid organic waste processing system with the production of hydrogen- and methane-containing biogases based on experimental data obtained in a laboratory plant with increased volume reactors was performed. The energy efficiency of the system is in the range of 1.91–2.74. Maximum energy efficiency was observed with a hydraulic retention time of 2.5 days in a dark fermentation reactor. The cost of electricity to produce 1 m³ of hydrogen was 1.093 kW·h with a hydraulic retention time of 2.5 days in the dark fermentation reactor. When the hydraulic retention time in the dark fermentation reactor was 1 day, the specific (in ratio to the processing rate of organic waste) energy costs to produce of 1 m³ of hydrogen were minimal in the considered hrt range, and amounted to 26 (W/m³ of hydrogen)/(m³ of waste/day). Thus, the system of two-stage anaerobic processing of liquid organic waste to produce hydrogen and methane-containing biogases is an energy-efficient way to both produce hydrogen and process organic waste.     

Life cycle assessment of different bioenergy production systems including perennial and annual crops

Energy crops are expected to greatly develop in a very short-term bringing to significant social and environmental benefits. Nevertheless, a significant number of studies report from very positive to negative environmental implications from growing and processing energy crops, thus great uncertainty still remains on this argument. The present study focused on the cradle-to-grave impact assessments of alternative scenarios including annual and perennial energy crops for electricity/heat or first and second generation transport fuels, giving special emphasis to agricultural practices which are frequently surprisingly neglected in Life Cycle Assessment studies despite a not secondary relevance on final outcomes. The results show that cradle-to-farm gate impacts, i.e. including the upstream processes, may account for up to 95% of total impacts, with dominant effects on marine water ecotoxicity. Therefore, by increasing the sustainability of crop management through minimizing agronomic inputs, or with a complementary use of crop resides, can be expected to significantly improve the overall sustainability of bioenergy chains, as well as the competitiveness against fossil counterparts. Once again, perennial crops resulted in substantially higher environmental benefits than annual crops. It is shown that significant amount of emitted CO₂ can be avoided through converting arable lands into perennial grasslands. Besides, due to lack of certain data, soil carbon storage was not included in the calculations, while N₂O emission was considered as omitted variable bias (1% of N-fertilization). Therefore, especially for perennial grasses, CO₂ savings were reasonably higher that those estimated in the present study. For first generation biodiesel, sunflower showed a lower energy-based impacts than rapeseed, while wheat should be preferred over maize for first generation bioethanol given its lower land-based impacts. For second generation biofuels and thermo-chemical energy, switchgrass provided the highest environmental benefits. With regard to bioenergy systems, first generation biodiesel was less impacting than first generation bioethanol; bioelectricity was less impacting than first generation biofuels and second generation bioethanol by thermo-chemical hydrolysis, but highly impacting than Biomass-to-Liquid biodiesel and second generation bioethanol through enzymatic hydrolysis.     

Effect of fertilization on the biomass production of coppiced mixed birch and willow stands on a cut-away peatland

This investigation deals with the biomass production of coppiced mixed birch and willow stands growing on a peat cut-away area at Aitoneva, Kihniö (62°12′N, 23°18′E), Finland. The 16-year-old stands were harvested and left to coppice for 14 years, fertilization experiment (control, PK and wood ash fertilization) with three replications was established after the clear cutting. The mother stands before clear cutting (11,000 stems per hectare on average) were dominated by silver birch (69% of the stem number). After clear cutting the number of stems rose 7-fold to 75 500 stems ha⁻¹. Now the stands were dominated by Betula pubescens with 46% out of the total stem number, the share of B. pendula being only 25% and with Salix spp 29%. At the age of 14 years self-thinning had decreased the stem number to 12,800 stems ha⁻¹. The leafless biomass production of the coppiced stands on the control plots was lower than that of the seed originated mother stands had been during the previous rotation. However, with fertilization the 14-year-old coppiced stands reached the same total production as the 16-year-old mother stands had reached. The foliar phosphorus concentrations showed a severe phosphorus deficiency on the controls. Fertilization increased biomass of the stands considerably. After 14 growing seasons the above-ground leafless dry-mass of the fertilized stands was 61.8 (PK-fertilization) and 61.4 t ha⁻¹ (Ash) and that of the control stands 37.6 t ha⁻¹. A single PK fertilizer application had increased the standing biomass by 24 t ha⁻¹ (64%). Even though fertilization increased biomass production it did not increase nutrient concentrations of wood and bark, but rather decreased them. Fertilization decreased the nitrogen concentrations of leafless above-ground biomass.     

Bioenergy in Australia: An improved approach for estimating spatial availability of biomass resources in the agricultural production zones

Bioenergy production from crops and agricultural residues has a greenhouse gas mitigation potential. However, there is considerable debate about the size of this potential. This is partly due to difficulties in estimating the feedstock resource base accurately and with good spatial resolution. Here we provide two techniques for spatially estimating crop-based bioenergy feedstocks in Australia using regional agricultural statistics and national land use maps. The approach accommodates temporal variability by estimating ranges of feedstock availability and the shifting nature of zones of the highest spatial concentration of feedstocks. The techniques are applicable to biomass production from forestry, agricultural residues or oilseeds, all of which have been proposed as biofuel feedstocks.     

Profitability of short-rotation biomass production on downy birch stands on cut-away peatlands in northern Finland

The economic feasibility of short-rotation energy biomass production was evaluated from measurements on six naturally afforested 15–26-year-old downy birch-dominated (Betula pubescens Ehr.) stands in a former peat-production area in northern Finland. In the financial analysis, afforestation by natural or broadcast seeding was assumed, and the stands were regenerated by coppicing after the first, second, and third rotations. With respect to the first rotation, the sales revenues from whole-tree fuel chips covered their production costs in five cases out of six when a 21 EUR MWh⁻¹ price for energy on delivery was assumed. The bare land value (BLV) was positive even with a five per cent discount rate in five cases, reaching a maximum of 995 EUR ha⁻¹. With an interest rate of three per cent, for example, the break-even stumpage price for energy wood (assessed as the net present value of the first generation equal to 0) fluctuated between approx. 1 and 7 EUR per cubic metre, implying an economic surplus to be reached without subsidies in these cases. The unit price of energy (when bare land value equals 0) for the majority of the stands was well below the assumed price level, indicating noteworthy long-term financial incentives associated with the production.     

Combustion characteristics of solid waste biomass,oil shale,and coal

In this study, a developed two-dimensional mathematical model was used to represent the physical model of the combustion process of olive cake and date seed, and solve the governing equations using finite-volume method. The simulation was performed using ANSYS/Fluent software in order to estimate maximum temperature, heating values and pollutants concentrations. The obtained results were compared with experimental results, and corresponding values of oil shale and coal. The experimental work of direct burning of olive cake and date seeds was performed using an existing circulated fluidized bed (CFB) unit.

It was found that the adiabatic flame temperatures were 1380 K and 839 K for olive cake and date seed, and 2260 K and 1080 K for coal and oil shale, respectively. The experimental results showed that the maximum temperatures were 1126 K and 723 K for olive cake and date seed, respectively. The lower heating values were 19,500 kJ/kg and 16,400 kJ/kg for olive cake and date seed, and 29,000 kJ/kg and 7000 kJ/kg for coal and oil shale, respectively.

Thus, biomass such as date seed and olive cake may be used as an alternative fuel in electrical power plants in olive- or date-producing countries, which may save 40% of fuel cost.