Influence of sward maturity and pre-conditioning temperature on the energy production from grass silage through the integrated generation of solid fuel and biogas from biomass (IFBB): 2. Properties of energy carriers and energy yield

In order to determine influencing parameters on energy production of the IFBB process, herbage from a lowland hay meadow (Arrhenaterion) was sampled and ensiled at eight dates between 27 April and 21 June 2007. The silage from each date was processed in six IFBB treatments with and without hydrothermal conditioning at different temperatures. Methane yields and higher heating values were determined and an energy balance was calculated with whole-crop digestion (WCD) of the silage as reference system. Maximum net energy yields were 10.2 MWh ha⁻¹ for the IFBB treatment without hydrothermal conditioning and 9.0 MWh ha⁻¹ for the treatment with hydrothermal conditioning at 50 °C. WCD achieved a maximum net energy yield of 3.7 MWh ha⁻¹. Energy conversion efficiency ranged from 0.24 to 0.54 and was predicted with high accuracy by temperature of hydrothermal conditioning as well as concentration of neutral detergent fibre and dry matter in the silage (R² = 0.90).     

Influence of sward maturity and pre-conditioning temperature on the energy production from grass silage through the integrated generation of solid fuel and biogas from biomass (IFBB): 1. The fate of mineral compounds

The IFBB process, which separates biomass into a press fluid for biogas production and a press cake for combustion, is aimed at converting low-input high-diversity grasslands into energy, which is problematic with conventional conversion techniques. Herbage from a lowland hay meadow (Arrhenaterion) was sampled on eight dates between 24 April and 21 June 2007. Silage from each date was processed in six treatments without and with hydrothermal conditioning at different temperatures. The impact on mass flows of plant compounds and on elemental concentrations in the press cake was investigated. Elements detrimental for combustion were significantly reduced in the press cake compared to the silage. Mass flows and elemental concentrations in the press cake were strongly influenced by conditioning temperature as well as concentration of neutral detergent fiber and dry matter in the silage (R² from 0.70 to 0.99). Press cakes of late sampling dates were considered best suitable for combustion.     

The techno-economic potential of renewable energy through the anaerobic digestion of microalgae

The potential of microalgae as feedstock for methane production is evaluated from a process technical and economic point of view. Production of mixed culture algae in raceway ponds on non-agricultural sites, such as landfills, was identified as a preferred approach. The potential of straightforward bio-methanation, which includes pre-concentration of microalgae and utilization of a high rate anaerobic reactor was examined based on the premises of achievable up-concentration from 0.2-0.6 kg m(-3) to 20-60 kg dry matter (DM) m(-3) and an effective bio-methanation of the concentrate at a loading rate of 20 kg DM m(-3) d(-1). The costs of biomass available for bio-methanation under such conditions were calculated to be in the range of €86-€124 ton(-1) DM. The levelized cost of energy by means of the process line "algae biomass--biogas--total energy module" would be in the order of €0.170-0.087 kWh(-1), taking into account a carbon credit of about €30 ton(-1) CO2(eq).     

A direct fuel cell for the production of electricity from lignin

This report describes the use of an anthraquinone mediated fuel cell for the direct production of electrical energy from sulfonated lignin and Kraft Black Liquor. The cell produces the equivalent of 1 kWh for each 2-3 lb sulfonated lignin and 5-8 lb black liquor combustibles. In the case of the sulfonated lignin, chain session occurs during the oxidation process, reducing the molecular weight from ca. 2 x 10(4) to less than 1000 D.     

A Survey of Bioenergy Research in Forest Service Research and Development

Forest biomass represents 25–30 % of the annual biomass available in the USA for conversion into bio-based fuels, bio-based chemicals, and bioproducts in general. The USDA Forest Service Research and Development (R&D) has been focused on producing products from forest biomass since its inception in 1905, with direct combustion, solid sawn lumber, pulp and paper, ethanol as fuel, and silvichemicals all among the mission areas of product research and development. The renewed national interest in biomass conversion to fuels and chemicals is supportive of the most critical need of USDA Forest Service R&D, uses for small-diameter trees and other forest biomass that needs to be removed in the fuel mitigation–fire suppression and forest restoration work of the USDA Forest Service. This paper will summarize the recent USDA Forest Service research on direct combustion, fuel pellets, and conversion of forest biomass to ethanol, both as stand-alone biorefinery processes and as an addition to the traditional wood pulping process.     

Development of life cycle inventories for electricity grid mixes in Japan

Since most industrial processes consume electricity, it is quite important to develop reliable inventory data for electricity. There is, however, a problem that only a few figures concerning emissions related to electricity have been reported. In this work, process models of power plants were developed for the Japanese situation which simulate the mass flows and estimate the missing figures of emissions dependent on technical parameters of the plants and fuels. In Japan, electricity is supplied to the various regions by 10 electric companies. Therefore, life cycle inventories for the electricity grid mixes of the 10 electric companies in 1997 were developed. The functional unit is 1 kWh of electricity distributed to electricity users in each region. The emission of CO₂, SO₂, NO_k, CH₄, CO, non-methane volatile organic compound (NMVOC), dust (all particulates) and heavy metals (Ni, V, As, Cd, Cr, Hg, Pb, Zn) from power stations as well as those from fuel production and transport were investigated. Other pollutants into air, emissions to water, solid wastes, radiation and radioactive emissions from atomic power stations were not included due to a limitation of the available data. Direct CO₂ emissions related to 1 kWh of electricity distributed by companies ranged from 0.21 to 1.0 kg/kWh (average value: 0.38 kg/kWh). Direct emissions of SO₂ and NO_x from power stations related to 1 kWh of electricity are 2.5* 10^-4 and 2.2* 10^-4 kg/kWh on the average, respectively. SO₂ emissions calculated in this work were somehow large compared with those reported by electric companies. Detailed information concerning total sulfur content in oil consumed in each oil-fired power station are required for an exact calculation of SO₂ emissions from oil-fired power stations. In addition, the ratio of sulfur that goes into slag in combustion must be investigated further. The average amounts of CO, CH₄, NMVOC and dust emissions were 5.0*10^-5, 8.2*10^-6, 1.8*10^-5 and 6.8 * 10^-6 kg/kWh, respectively. Heavy metal emissions from power stations were on the order of 10^-9 to 10^-8 kg/kWh. Detailed information concerning heavy metal content in oil and coals consumed in fossil fuel power stations are further required for an improved assessment of heavy metal emissions. Contribution of fuel production and transport to total CO₂ emission was relatively small. On the other hand, contributions of fuel production and transport to total SO₂ and NO_x emissions were relatively large. In the case of CO, NMVOC and dust, emissions in fuel production and transport were predominant to total emissions. Heavy metal emissions into air during production and transport of fuels were on the order of 10/^-8 to 10^-9 kg/kWh.     

Influence of enzyme loading and physical parameters on the enzymatic hydrolysis of steam-pretreated softwood

Softwood is an interesting raw material for the production of fuel ethanol as a result of its high content of hexoses, and it has attracted attention especially in the Northern hemisphere. However, the enzymatic hydrolysis of softwood is not sufficiently efficient for the complete conversion of cellulose to glucose. Since an improvement in the glucose yield is of great importance for the overall economy of the process, the influence of various parameters on the cellulose conversion of steam-pretreated spruce has been investigated. The addition of beta-glucosidase up to 50 IU g(-)(1) cellulose to the enzymatic hydrolysis process resulted in increased cellulose conversion at a cellulase loading up to 48 FPU g(-)(1) cellulose. Despite very high enzyme loading (120 FPU g(-)(1) cellulose) only about 50% of the cellulose in steam-pretreated spruce was converted to glucose when all of the material following pretreatment was used in the hydrolysis step. The influence of temperature, residence time, and pH were investigated for washed pretreated spruce at a dry matter (DM) content of 5% and a cellulase activity of 18.5 FPU g(-)(1) cellulose. The optimal temperature was found to be dependent on both residence time and pH, and the maximum degree of cellulose conversion, 69.2%, was obtained at 38 degrees C and pH 4.9 for a residence time of 144 h. However, when the substrate concentration was changed from 5% to 2% DM, the cellulose conversion increased to 79.7%. An increase from 5% to 10% DM resulted, however, in a similar degree of cellulose conversion, despite a significant increase in the glucose concentration from 23 g L(-)(1) to 45 g L(-)(1). The deactivation of beta-glucosidase increased with increasing residence time and was more pronounced with vigorous agitation.     

Assessment of black liquor gasification in supercritical water

Supercritical water gasification of black liquor (waste pulping chemicals) has been examined. The aim was to evaluate the feasibility of using this technique to convert such bio-based waste to value added fuel products, as well as recovery of pulping materials. Supercritical gasification may improve overall process efficiency by eliminating the energy intensive evaporation step necessary in conventional process and product gas obtained at high pressure may be ready for utilization without any compression requirement. Appropriate operating parameters, including pressure, temperature, feed concentration, and reaction time, which would yield the highest conversion and energy efficiency were determined. Reaction was performed in a quartz capillary heated in a fluidized bed reactor. Results indicated that pressure between 220 and 400 atm has insignificant influence on the gas products and extent of carbon conversion. Increasing temperature and residence time between 375-650 degrees C and 5-120 s resulted in greater gas production, overall carbon conversion, and energy efficiency. Maximum conversion to H(2), CO, CH(4), and C(2)H(X) was achieved at the highest temperature and longest residence time tested showing an overall carbon conversion of 84.8%, gas energy content of 9.4 MJ/m(3) and energy conversion ratio of 1.2. Though higher carbon conversion and energy conversion ratio were obtained with more dilute liquor, energy content was lower than for those with higher solid contents. Due to anticipated complex design and high initial investment cost of this operation, further studies on overall feasibility should be carried out in order to identify the optimum operating window for this novel process.     

Preparation and Evaluation of Hybrid Composites of Chemical Fuel and Multi-walled Carbon Nanotubes in the Study of Thermopower Waves

When a chemical fuel at a certain position in a hybrid composite of the fuel and a micro/nanostructured material is ignited, chemical combustion occurs along the interface between the fuel and core materials. Simultaneously, dynamic changes in thermal and chemical potentials across the micro/nanostructured materials result in concomitant electrical energy generation induced by charge transfer in the form of a high-output voltage pulse. We demonstrate the entire procedure of a thermopower wave experiment, from synthesis to evaluation. Thermal chemical vapor deposition and the wet impregnation process are respectively employed for the synthesis of a multi-walled carbon nanotube array and a hybrid composite of picric acid/sodium azide/multi-walled carbon nanotubes. The prepared hybrid composites are used to fabricate a thermopower wave generator with connecting electrodes. The combustion of the hybrid composite is initiated by laser heating or Joule-heating, and the corresponding combustion propagation, direct electrical energy generation, and real-time temperature changes are measured using a high-speed microscopy system, an oscilloscope, and an optical pyrometer, respectively. Furthermore, the crucial strategies to be adopted in the synthesis of hybrid composite and initiation of their combustion that enhance the overall thermopower wave energy transfer are proposed.     

Energy production from biomass (Part 2): Conversion technologies

The use of biomass to provide energy has been fundamental to the development of civilisation. In recent times pressures on the global environment have led to calls for an increased use of renewable energy sources, in lieu of fossil fuels. Biomass is one potential source of renewable energy and the conversion of plant material into a suitable form of energy, usually electricity or as a fuel for an internal combustion engine, can be achieved using a number of different routes, each with specific pros and cons. A brief review of the main conversion processes is presented, with specific regard to the production of a fuel suitable for spark ignition gas engines.     

Autohydrolysis Pretreatment of Mixed Softwood to Produce Value Prior to Combustion

Autohydrolysis is a hot water pretreatment to extract soluble components from wood that can be used prior to converting the woody residuals into paper, wood products, fuel, or other goods. In this study, mixed softwood chips were autohydrolyzed in hot water at 150, 160, 170, and 180 °C for 1 and 2 h residence times. The objective was to understand the tradeoff between the extraction of fermentable sugar and the residual solid total energy of combustion quantitatively. This process strategy will be referred to as “value prior to combustion”. High-performance liquid chromatography was used to determine chemical compositions (sugars and byproducts such as acetic acid, furfural, and hydroxymethylfurfural) of the extracted liquid and residuals; a bomb calorimeter was used to measure the heating value of original wood and solid residue. As the autohydrolysis temperature increased, material balances of the system indicated higher volatile byproducts loss. More hemicelluloses were solubilized by the hot water extraction process at higher temperatures and longer residence times, and a greater degree of sugar degradation was also observed. The maximum sugar yield was determined to occur at conditions of 170 °C for 2 h, during which 13 g of sugar was recovered from the extract out of 100 g of oven-dried wood. The heating value of the solid residues after extraction was greater than the original wood. The total energy content of the solid residual after extraction ranged from 85 to 98 % of the original energy content of the feed with higher temperatures reducing the total energy content.     

Techno-economic evaluation of producing ethanol from softwood: comparison of SSF and SHF and identification of bottlenecks

The aim of the study was to evaluate, from a technical and economic standpoint, the enzymatic processes involved in the production of fuel ethanol from softwood. Two base case configurations, one based on simultaneous saccharification and fermentation (SSF) and one based on separate hydrolysis and fermentation (SHF), were evaluated and compared. The process conditions selected were based mainly on laboratory data, and the processes were simulated by use of Aspen plus. The capital costs were estimated using the Icarus Process Evaluator. The ethanol production costs for the SSF and SHF base cases were 4.81 and 5.32 SEK/L or 0.57 and 0.63 USD/L (1 USD = 8.5SEK), respectively. The main reason for SSF being lower was that the capital cost was lower and the overall ethanol yield was higher. A major drawback of the SSF process is the problem with recirculation of yeast following the SSF step. Major economic improvements in both SSF and SHF could be achieved by increasing the income from the solid fuel coproduct. This is done by lowering the energy consumption in the process through running the enzymatic hydrolysis or the SSF step at a higher substrate concentration and by recycling the process streams. Running SSF with use of 8% rather than 5% nonsoluble solid material would result in a 19% decrease in production cost. If after distillation 60% of the stillage stream was recycled back to the SSF step, the production cost would be reduced by 14%. The cumulative effect of these various improvements was found to result in a production cost of 3.58 SEK/L (0.42 USD/L) for the SSF process.     

Production of Electrical Energy from Carbohydrates using a Transition Metal-Catalysed Liquid Alkaline Fuel Cell

Biomass may be converted to energy by enzymatic hydrolysis to monomer components and fermentative conversion of those products to ethanol for use as fuel. Both glucose and xylose in aqueous solution were directly converted to electrical energy using a liquid alkaline fuel cell (AFC) at room temperature. Hydrolysis products derived from the action of cellulase and amylase on cellulose and starch, respectively, were also used as fuels in the AFC system. We suggest that this approach may provide a more direct means of accessing some of the energy available from biomass.Revisions received 27 September 2004     

Highly Efficient Materials Assembly Via Electrophoretic Deposition for Electrochemical Energy Conversion and Storage Devices

Featuring pronounced controllability, versatility, and scalability, electrophoretic deposition (EPD) has been proposed as an efficient method for film assembly and electrode/solid electrolyte fabrication in various energy storage/conversion devices including rechargeable batteries, supercapacitors, and fuel cells. High‐quality electrodes and solid electrolytes have been prepared through EPD and exhibit advantageous performances in comparison with those realized with traditional methods. Recent advances in the application of EPD materials in electrochemical energy storage and conversion devices are summarized. In particular, the parameters that influence the efficiency of an EPD process from colloidal preparation to deposition are evaluated with the aim to provide insightful guidance for realizing high‐performance electrochemical energy conversion materials and devices.     

Improved bio-energy yields via sequential ethanol fermentation and biogas digestion of steam exploded oat straw

Using standard laboratory equipment, thermochemically pretreated oat straw was enzymatically saccharified and fermented to ethanol, and after removal of ethanol the remaining material was subjected to biogas digestion. A detailed mass balance calculation shows that, for steam explosion pretreatment, this combined ethanol fermentation and biogas digestion converts 85-87% of the higher heating value (HHV) of holocellulose (cellulose and hemicellulose) in the oat straw into biofuel energy. The energy (HHV) yield of the produced ethanol and methane was 9.5-9.8 MJ/(kg dry oat straw), which is 28-34% higher than direct biogas digestion that yielded 7.3-7.4 MJ/(kg dry oat straw). The rate of biogas formation from the fermentation residues was also higher than from the corresponding pretreated but unfermented oat straw, indicating that the biogas digestion could be terminated after only 24 days. This suggests that the ethanol process acts as an additional pretreatment for the biogas process.     

Application of life cycle inventory analysis to fuel tank system design

Life Cycle Assessment is becoming an important tool for guiding environmental design improvements in the automotive industry. This paper reports the life cycle inventory profiles for two fuel tank systems based on a collaborative effort between the National Pollution Prevention Center at the University of Michigan, General Motors Research and Development, and the National Risk Management Research Laboratory of the U.S. Environmental Protection Agency. Two 31 gallon functionally equivalent fuel tank systems used on a 1996 light duty vehicle were investigated: a multi-layer HDPE tank with a steel shield and PVC coated steel straps, and a steel tank with a HDPE shield and painted steel straps. Overall, the HDPE fuel tank system is environmentally preferable to the steel tank system based on the set of inventory results presented in this investigation. The Life Cycle Inventory analysis indicated lower energy burdens for the HDPE tank system and comparable solid waste burdens for both systems. The total life cycle energy consumption for the steel and HDPE tank systems were 4.9 GJ and 3.6 GJ per tank, respectively. The energy consumption and most of the air pollutants inventoried occurred as a consequence of the use phase. The solid wastes were generated primatily during the material production phase for the steel tank (13 kg) and during the end-of-life management phase for the HDPE tank (14 kg). This study also highlights data analysis and modeling challenges, including manufacturing and use phase allocation methods.     

Food and processing residues in California: resource assessment and potential for power generation

The California agricultural industry produces more than 350 commodities with a combined yearly value in excess of $28 billion. The processing of many of these crops results in the production of residue streams, and the food processing industry faces increasing regulatory pressure to reduce environmental impacts and provide for sustainable management and use. Surveys of food and other processing and waste management sectors combined with published state data yield a total resource in excess of 4 million metric tons of dry matter, with nearly half of this likely to be available for utilization. About two-thirds of the available resource is produced as high-moisture residues that could support 134 MWe of power generation by anaerobic digestion and other conversion techniques. The other third is generated as low-moisture materials, many of which are already employed as fuel in direct combustion biomass power plants. The cost of energy conversion remains high for biochemical systems, with tipping or disposal fees of the order of $30-50Mg(-1) required to align power costs with current market prices. Identifying ways to reduce capital and operating costs of energy conversion, extending operating seasons to increase capacity factors through centralizing facilities, combining resource streams, and monetizing environmental benefits remain important goals for restructuring food and processing waste management in the state.     

Hospital Patient‐Care and Outside‐the‐Hospital Energy Profiles for Hemodialysis Services

Studies investigated the patient‐care (in‐hospital) and outside‐the‐hospital energy consumptions for delivering the hemodialysis (HD) service. A life cycle inventory methodology was used for this patient‐based analysis for two hospitals located in Wichita, Kansas. It was found that, for both hospitals, the actual HD machines consumed approximately 3.5 kilowatt‐hours (kWh) of electrical energy per HD, only 8% to 16% of the total energy used for delivering the HD service (in hospital). This increases to 9.6 to 28.9 kWh of hospital billable energy for the whole system of HD machine, auxiliaries, and dialysis water treatment. Converting these hospital direct electrical energy values to natural resource energy (nre) then adding the cradle‐to‐gate natural resource energy for the manufacturing and supply chain of all the HD consumables, the total is 78 to 149 kWh nre/HD. The nre measures all the direct fuel burned to generate energy and is thus directly related to emissions to the air, water, and land and is a direct secondary impact on public health from HD. The ratio of outside‐the‐hospital energy to direct hospital HD electrical energy consumption is 4:1 to 7:1, so a broader base exists for improvement than just the hospital.     

Assessment of Mass Flows and Fuel Quality During Mechanical Dehydration of Silages Using Near Infrared Reflectance Spectroscopy

This study was implemented to evaluate the potential of near-infrared reflectance spectroscopy (NIRS) technology to estimate chemical composition of dried press cake samples characterised by a wide range of parent materials. A total of 210 samples, derived from two studies on production of solid fuels from agricultural crops by application of the IFBB technology (Integrated production of solid fuels and biogas from biomass), were analysed to determine their chemical composition. A Foss XDS-spectrometer was used to obtain near-infrared spectra (400–2,500 nm). Prediction equations, developed for chemical components, showed that NIRS technology could predict N, inorganic ash (ash), crude fiber (CF), ether extract (EE) and nitrogen free extracts (NFE) accurately (RSQ_cal and SECV of 0.93 and 0.04 % DM, 0.89 and 0.48 % DM, 0.93 and 1.67 % DM, 0.87 and 0.28 % DM and 0.93 and 1.72 % DM, respectively). Mineral components could also be predicted with a moderate degree of accuracy using NIRS technology (RSQ_cal and SECV of 0.85 and 0.10 % DM (K), 0.77 and 0.01 % DM (P) and 0.84 and 0.02 % DM (Cl), respectively), whereas calibration of gross energy (GE) did not succeed. Subsequent, external validation confirmed these results. Regression of mass flows with measured and NIRS-predicted values showed accurate results (RSQ 0.72–0.99) and promise an accelerated quality management in working biogas plants.     

The influence of biomass temperature on biostabilization-biodrying of municipal solid waste

A laboratory study was carried out to obtain data on the influence of biomass temperature on biostabilization-biodrying of municipal solid waste (initial moisture content of 410 g kg wet weight (w.w.)(-1)). Three trials were carried out at three different biomass temperatures, obtained by airflow rate control (A = 70 degrees C, B = 60 degrees C and C = 45 degrees C). Biodegradation and biodrying were inversely correlated: fast biodrying produced low biological stability and vice versa. The product obtained from process A was characterized by the highest degradation coefficient (166 g kg TS0(-1); TS0(-1) = initial total solid content) and lowest water loss (409 g kg W0(-1); W0 = initial water content). Due to the high reduction of easily degradable volatile solid content and preservation of water, process A produced the highest biological stability (dynamic respiration index, DRI = 141 mg O2 kg VS(-1); VS = volatile solids) but the lowest energy content (EC = 10,351 kJ kg w.w.(-1)). Conversely, process C which showed the highest water elimination (667 g kg W0(-1)), and lowest degradation rate (18 g kg TS0(-1)) was optimal for refuse-derived fuel (RDF) production having the highest energy content (EC = 14,056 kJ kg w.w.(-1)). Nevertheless, the low biological stability reached, due to preservation of degradable volatile solids, at the end of the process (DRI = 1055 mg O2 kg VS(-1)), indicated that the RDF should be used immediately, without storage. Trial B showed substantial agreement between low moisture content (losses of 665 g kg W0(-1)), high energy content (EC = 13,558 kJ kg w.w.(-1)) and good biological stability (DRI = 166 mg O2 kg VS(-1)), so that, in this case, the product could be used immediately for RDF or stored with minimum pollutant impact (odors, leaches and biogas production).