Hydrogen production from (cane-molasses) stillage by citrobacter freundii and its use in improving methanogenesis

Citrobacter freundii is a facultatively anaerobic fermentative organism capable of H₂ production from sugars and lactate. A locally isolated strain of C. freundii was shown to be capable of H₂ production on an equimolar basis (i.e. 1:1.2 mol/mol) from glucose. It was also found capable of H₂ production from cane-molasses stillage (having BOD₅ of 54 kg m⁻³) at a rate of 1.2 m³ (m³waste) ¹ day⁻¹. This was tested on various scales, ranging from 0.06 to 100 1 and was found to be consistent over these variations in scale. Simultaneously, the BOD₅ value was reduced at a rate of 5.4 kg (m³waste)⁻¹ day⁻¹.

One of the uses of the evolved H₂ was as feed for an anaerobic digestor containing (untreated) cane-molasses stillage as substrate. With this arrangement, the methanogenesis was enhanced by way of increased production of methane (i.e. rise in volumetric methane content of the evolved gas), while added H₂ vanished totally from the digestor. The question of whether microbially produced H₂ can be used more profitably in microbial utilization of H₂ for energy production is considered in detail.     

Environmental assessment and extended exergy analysis of a “zero CO2 emission”, high-efficiency steam power plant

Aim of this paper is to analyze the performance of an innovative high-efficiency steam power plant by means of two “life cycle approach” methodologies, the life cycle assessment (LCA) and the “extended exergy analysis” (EEA).

The plant object of the analysis is a hydrogen-fed steam power plant in which the H₂ is produced by a “zero CO₂ emission” coal gasification process (the ZECOTECH^© cycle). The CO₂ capture system is a standard humid-CaO absorbing process and produces CaCO₃ as a by-product, which is then regenerated to CaO releasing the CO₂ for a downstream mineral sequestration process.

The steam power plant is based on an innovative combined-cycle process: the hydrogen is used as a fuel to produce high-temperature, medium-pressure steam that powers the steam turbine in the topping section, whose exhaust is used in a heat recovery boiler to feed a traditional steam power plant.

The environmental performance of the ZECOTECH^© cycle is assessed by comparison with four different processes: power plant fed by H₂ from natural gas steam reforming, two conventional coal- and natural gas power plants and a wind power plant.     

Solar cooling in Madrid: Energetic efficiencies

In this paper, a clear day is defined as one generating a thermal load, and its daily level of solar energy, H_gIT, is higher than the daily threshold energy imposed by the process, H_min. In Madrid, for the air-conditioning of indoor spaces, H_min varies from about 24 MJ m⁻² day⁻¹ in June to about 18 MJ m⁻² day⁻¹ in September. Using the representative input data of a clear day in Madrid and applying the Hottel-Willier, Duffie, Beckman and Klein model, taking into account the heat capacity effects and the variable regime, a theoretical simulation of a lithium bromide absorption cooling system was performed to obtain a daily collector efficiency of about 22%, a daily COP of the cooling machine of about 55% and a daily efficiency of the solar energy-cooling conversion of about 12%.     

Thermodynamic evaluation of water splitting by a cation-excessive (Ni, Mn) ferrite

Water-splitting potential by cation-excessive (Ni, Mn) Ferrite, Ni_{0.5(1 + )}Fe_{1.99(1 + )}O₄ was evaluated using the standard Gibbs free energy change (ΔG°) for the cation-excessive ferrite formation in different O₂ partial pressures. The cation-excessive degree ranged from 0.026 to 0.16 in pO₂ values of 7.9 × 10⁻⁷ to 1.0 × 10⁻¹. From the relation between value of (Ni, Mn) ferrite and oxygen partial pressure, equilibrium constant K(th) was determined. Furthermore ΔH°s for O₂ releasing and water-splitting reactions with cation-excessive (Ni, Mn) ferrite were evaluated from the van't Hoff plot and compared with that for magnetite-wüstite system; where ΔH°s were assumed to be the same values for both (Ni, Mn) ferrite and magnetite-wüstite system: +300 kJ for O₂ releasing and −35 −63 kJ for water-splitting. ΔG°s evaluated for water-splitting with cation-excessive (Ni, Mn) ferrite and wüstite were −38 kJ and −35 kJ, respectively, at 298K. It suggests that water splitting with cation-excessive (Ni, Mn) ferrite proceed easily compared with that with wüstite. ΔS°s for water-splitting are −0.93 kJ K⁻¹ for the former and −0.83 kJ K⁻¹ for the latter. H₂ generation rates by reaction with H₂O for (Ni, Mn) ferrite were studied at temperatures of 573 K-1073 K. It reached the maximum at 1000 K while it proceeds preferentially below 830 K from thermodynamics.     

Seasonal dynamics of nutrient accumulation and partitioning in the perennial C4-grasses Miscanthus × giganteus and Spartina cynosuroides

Seasonal variation in the accumulation and partitioning of nitrogen, phosphorus and potassium was determined in both the above-ground and below-ground dry matter of the potential energy crops Miscanthus × giganteus and Spartina cynosuroides. It is desirable from both economic and environmental perspectives that such crops should exhibit a high nutrient use efficiency and minimal nutrient losses to the environment. The N, P and K concentrations in the above-ground dry matter, at final harvest, were 5.0, 0.6 and 12.0 mg g⁻¹ respectively in M. × giganteus and 3.0, 0.4 and 1.0 mg g⁻¹ in S. cynosuroides. Both species exhibited the high N-use efficiency expected of C₄ plants. Nitrate leaching was negligible. At the end of the growing season, nutrients were translocated to the rhizomes and, in the case of M. × giganteus, recycled to the soil in shed leaves. Consequently the nutrient content of the crop offtake was low. It was calculated that the N, P and K requirements of a M. × giganteus crop producing an above-ground harvest of 1.5 kg m⁻² dry matter would be 9.2, 1.3 and 20.4 g m⁻² respectively. The corresponding nutrient requirements for S. cynosuroides would be 7.5, 1.7 and 8.8 g m⁻². Except for the K requirement of M. × giganteus, the N, P and K demands of both species were less than those of typical graminaceous crops, including maize.     

Kinetic study on fermentation from CO2 and H2 using the acclimated-methanogen in batch culture

Methane was produced from H₂ and CO₂ using the acclimated-mixed methanogens in a 3.71 fermentor in batch culture at pH 7.2 and 37°C. The Fermentation kinetics parameter for the growth of methanogens, overall mass transfer coefficient of the reactor, and the conversion rate of H₂ and CO₂ to CH₄ by the acclimated-mixed culture were determined using the technique of Vega et al. The maximum specific growth rate (μ_max) and H₂ specific consumption rate (q_max) were found to be 0.064(h⁻¹) and 104.8 (mmol h⁻¹ g⁻¹) respectively. Monod saturation constants for growth (Kp) and for inhibition (K′p) were found to be 3.54 (kPa) and 0.57 (kPa), respectively. These findings indicate that without very low dissolved H₂ levels, the fermentations are carried out under μ_max, and the specific uptake rate (q) was almost not affected at any dissolved H₂ level in the range studied. The yield of CH₄ (Yp/s) was calculated to be 0.245 (mol CH₄ mol⁻¹ H₂), which is near the stoichiometric value of 0.25. DH₂ was also measured using the Teflon tubing method and was in good agreement with those estimated by kinetic calculations.     

Biomass and biomass water use efficiency in oilseed crop (Brassica juncea L.) under semi-arid microenvironments

Biomass production in arid and semi-arid regions requires a special attention owing to spatiotemporal scarcity of irrigation water wherein improved water use efficiency (WUE) of the crop is targeted. Under field conditions, the crop undergoes dynamic changes in near ground or within-canopy microenvironments. This changed microclimatic condition may have an impact on phenological response of the oilseed crop which in turn would affect biomass productivity, economic seed yield and water use efficiency of the crop. Henceforth, quantification of biomass production and its WUE of oilseed Brassica crop is essentially required owing to have better understanding of the crop water requirement under the era of climate change. Following a 2 years field experiment, it was revealed that the changes in leaf area index were explained by about 68–74%. The best fit polynomial third order regression analysis indicated >93% prediction in biomass production as a function of time factor. Improved biomass partitioning into economic sinks was also observed. Small scale change in near ground microenvironment may reduce the prediction of biomass variability to the extent of 3%. The mean ET variations were observed as 2.4, 1.5 and 3.2 mm day⁻¹ during the critical phenological stages. Mean seed yield, biomass WUE and seed yield WUE ranged between 2.71 and 2.87 Mg ha⁻¹, 11.4 and 13.1 g m⁻² mm⁻¹ and 19.3 and 22.9 kg ha⁻¹ mm⁻¹ respectively. Variations in both biomass and seed yield water use efficiencies due to small scale change in near ground microclimates were revealed.     

Monitoring of methanogen density using near-infrared spectroscopy

In order to improve anaerobic digester productivity, raising the microbial mass in the reactor and the prediction of changes in the biomass is required. In this study the possibilities for using near-infrared spectroscopy (NIR) to monitor methanogen density in a biogas process was examined. Methane production from H₂ and CO₂ was carried out with acclimated-methanogens with fed-batch substrate gas (H₂/CO₂, 80:20 v/v) at pH 7 and 37°C. The cells of the methanogens were washed and dried, and then original NIR spectra for predicting methanogen density were recorded. The specified absorption spectra were collected and examined. As a result, absorption spectrum peaks were found to be predominantly based on alpha proteins and lipids mainly from the cytoplasm and cell membranes of the methanogens. Furthermore, NIR was used to monitor the methane fermentation system using acetic acid as substrate. The responses from NIR analysis were correlated to methanogen density of fermentation broth by partial least-squares regressions. The correlation coefficient (R), model standard error of calibration (SEC) and standard error of prediction (SEP) of the test calibration for methanogen density were 0.99, 0.14 gl⁻¹ and 0.55 gl⁻¹, respectively. For volatile fatty acids (acetic acid) R, SEC and SEP were 0.99, 0.36 gl⁻¹ and 0.63 gl⁻¹, respectively. The results indicated that within the range of the density of methanogens and the concentration of acetic acid used in this study, it was possible to monitor the important variables of methanogen density and acetate concentration simultaneously in pure substrate-fed anaerobic digesters.     

Electrochemistry of poly(vinylferrocene) modified electrodes in aqueous acidic media

A cyclic voltammetric study of the electrochemistry and chemical stability of the poly(vinylferrocene) (PVFc) redox couple, coated on a gold substrate, in aqueous solutions of H₂SO₄, HClO₄ and HCl was carried out. It was found that the anodic peak potential (E_pa) did not depend on the acid concentration in the range (1.0 × 10⁻² to 1.0 × 10⁻⁷ mol L⁻¹). However, the E_pa values shifted linearly to less positive potentials when investigated in more concentrated acid solutions in the range 1–5 mol L⁻¹. The slope of the E_pa versus acid concentration graph was found to be in the order H₂SO₄ > HCl > HClO₄. In this regard PVFc behaved very similar to 1,1′-bis(11-mercaptoundecyl)ferrocene (Fc(C₁₁SH)₂) except for its chemical stability. In H₂SO₄ media the PVFc was found to be much less stable than 1,1′-Fc(C₁₁SH)₂. The dependence of E_pa on acid concentration could be used to monitor state of charge of lead-acid batteries. However, for this application Fc(C₁₁SH)₂ would be a better choice because of its superior chemical stability.     

Experimental methods of estimating heat transfer in circulating fluidized bed boilers

Four different experimental methods have been used for the estimation of the bed-to-membrane wall heat transfer in a 12 MW_th circulating fluidized bed boiler. The methods are compared for a case of normal operating conditions and the measured heat transfer coefficients are presented. In the central part of the combustion chamber where most of the cooling surface is located, the cross-sectional average suspension density normally varies in the range of 10–20 kg m⁻³ and the heat transfer coefficient is around 130 W m⁻² K⁻¹ with a scatter of ±15% due to the different methods. The methods are critically analyzed and the heat transfer data are compared with relevant literature data.     

Analysis of solar chemical processes for hydrogen production from water splitting thermochemical cycles

This paper presents a process analysis of ZnO/Zn, Fe₃O₄/FeO and Fe₂O₃/Fe₃O₄ thermochemical cycles as potential high efficiency, large scale and environmentally attractive routes to produce hydrogen by concentrated solar energy. Mass and energy balances allowed estimation of the efficiency of solar thermal energy to hydrogen conversion for current process data, accounting for chemical conversion limitations. Then, the process was optimized by taking into account possible improvements in chemical conversion and heat recoveries. Coupling of the thermochemical process with a solar tower plant providing concentrated solar energy was considered to scale up the system. An economic assessment gave a hydrogen production cost of 7.98$ kg⁻¹ and 14.75$ kg⁻¹ of H₂ for, respectively a 55 MW_th and 11 MW_th solar tower plant operating 40 years.     

Quality of gas produced from wheat straw in a dual-distributor type fluidized bed gasifier

A 400 kW, dual distributor type fluidized bed gasifier was used to investigate the production rate and composition of the gas produced from wheat straw at various equivalence ratios (0.17, 0.20, 0.25, 0.35) and fluidization velocities (0.28, 0.33 and 0.37 m s⁻). The results showed that the equivalence ratio was the major parameter affecting the gas composition. The equivalence ratio of 0.25 appeared to be the optimum with respect to the quality of the gas. The mole fractions of the combustible components reached their maximum values at this equivalence ratio. A typical gas composition at the equivalence ratio of 0.25 was 7% H₂, 7% hydrocarbons (CH₄, C₂H₂, C₂/H₄ and C₂H₆), 14% C0₂, 22% CO and 50% N₂. The higher heating value of the produced gas (6.3–7.3 MJ Nm⁻³) obtained at this equivalence ratio appeared to be higher than most values reported in the literature for several types of biomass fuels.     

Kinetics of the NCO radical reacting with atoms and selected molecules

Rate constants for the reaction of isocyanate radicals (NCO) in its electronic ground state ( ²Π) with oxygen atoms were determined at 2.5 Torr total pressure in the temperature range 302–757 K. Excimer laser photolysis (ELP) of chlorine isocyanate (ClNCO) produced NCO radicals detected by laser-induced fluorescence (LIF). The reaction NCO + O exhibits a negative temperature dependence, described by the two-parameter equation: k_NCO+O(T) = (4.3_−2.2^+3.2) × 10⁻⁸ × T^{−1.14_−0.12+0.08} cm³ molecule⁻¹ s⁻¹. Measurements at 298 K and total pressures of 2.5 and 9.9 Torr, respectively, indicated a slight pressure dependence. For the reaction of NCO radicals with hydrogen atoms, the rate constant k_NCO+H = (2.2 ± 1.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹was obtained at 298 K and a total pressure of 2.6 Torr for the first time by a direct measurement. From a single measurement k = (3.8 ± 1.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ was determined at 548 K and 2.4 Torr total pressure. In addition, rate constants for the reactions of NCO radicals with molecular oxygen (O₂), carbon dioxide (CO₂), molecular hydrogen (H₂), and carbon monoxide (CO), which is a dissociation product of CO₂ in a microwave discharge, were measured at two different temperatures. At room temperature these reactions were slow and at the detection limit of the ELP/LIF technique. However, at elevated temperatures at least the rate constants of the reactions NCO + O₂ and NCO + H₂ become significantly larger and, therefore, should be taken into account, when modeling combustion processes under certain conditions.     

Preparation and electrochemical properties of double-metal nitrides containing lithium

A study is reported of the preparation, chemical composition, and crystal structure of binary compounds of Li₃N with other nitrides, i.e., Mg₃N₂, AlN, BN, and Si₃N₄. Most of the crystal structures are related to an antifluorite system. Except for LiMgN, the compounds are pure lithium ion conductors. A new compound, Li₈SiN₄, has the highest lithium ion conductivity (viz., 1 × 10⁻³ S m⁻¹ at 298 K) of the double-metal nitrides investigated.     

生物质气化工艺废水特征及预处理实验研究

对生物质气化中试现场产生的废水进行了水质及水量特征分析,针对生物质气化工艺废水固体颗粒含量高、有机物浓度高、难生化降解、废水增量少的特点,采取减压蒸馏及芬顿氧化对生物质气化废水进行预处理。实验结果表明,在85 ~ 90℃、真空度 -0.07 ~ -0.095 MPa减压蒸馏条件下,废水COD、NH₄-N脱除率分别为74.38%、94.46%;在Fe²⁺-H₂O₂体系中,考察了H₂O₂与废水质量比、H₂O₂与Fe²⁺摩尔比、反应时间、H₂O₂浓度对COD、NH₄-N、TOC、TN等的影响,当H₂O₂与废水质量比为8.40%时,可将减压蒸馏蒸出液COD从2.05 × 10⁴ mg/L降至4.11 × 10³ mg/L,NH₄⁺-N从143 mg/L降至11.1 mg/L。     

High temperature rate coefficient for the reaction of O(P) with H2 obtained by the resonance absorption of O and H atoms

The reaction of O(³P) with H₂ has been studied behind reflected shock waves in the temperature range of 1713–3532K at total pressures of about 1.4–2.0 bar by Atomic Resonance Absorption Spectroscopy using mixtures of N₂O and H₂ highly diluted in Ar. The O atoms were generated by the fast thermal decomposition of N₂O and the reaction with H₂ was followed by monitoring the time dependent O and H atom concentrations in the postshock reaction zone. For the experimental conditions chosen, the measured O and H atom concentrations were primarily sensitive to the well-known N₂O dissociation and to the studied reaction and hence its rate coefficient could be deduced. The measured rate coefficient data are fitted by the least-squares method to obtain the following three parameter expression: K₄=3.72×10⁶(T/K)^2.17exp(−4080K/T)cm³ mol⁻¹8⁻, which is in excellent agreement with the recent ab initio calculations for the rate coefficient of this reaction in the overlapping temperature range. The present result is also compared to the experimental results reported by earlier investigators.     

Miscanthus sinensis ‘giganteus’ production on several sites in Austria

In Austria it is planned to use Miscanthus sinensis ‘Giganteus’ as a renewable energy source. The influence of site, age of crop and time of harvest on yield, water content, nitrogen content and quality was investigated. In the first year the yield was 0.7 to 2 t dry matter ha⁻¹, in the second year 7.9 to 15.5 t ha⁻¹ and in the third year 17.4 to 24.5 t ha⁻¹. In February of the first year the water content was 40 to 50%, in the second year 34 to 49% and in the third year 24 to 38%. Sufficient precipitation (about 800 mm) in mild climates is required for high yields. On sites with more rain the water content of the plants was higher. Water and nitrogen content decreased significantly during the six week period from January to the end of February. In February of the first year the nitrogen content was 7.8 to 16.6 g kg⁻¹ dry matter, in the second year 3.7 to 6.2 g kg⁻¹ and in the third year 2.6 to 7.5 g kg⁻¹. The calorific value was as high as that of firewood (18 to 19 MJ kg⁻¹ ). The ash content exceeded firewood but was lower than that of straw. By the third year of cultivation 60 to 150 kg N ha⁻¹, 100 to 200 kg K20 ha⁻¹, 10 to 35 kg P₂ O₅ ha⁻¹, 10 to 25 kg MgO ha⁻¹ and 20 to 35 kg CaO ha⁻¹ had to be taken up by the harvest at the end of February.     

Development of a BB-2590/U rechargeable lithium-ion battery

PolyStor has teamed with Hawker Eternacell (US) to develop a BB-2590/U rechargeable lithium-ion battery under contract with the US Army CECOM (Ft. Monmouth, NJ, USA). The concept involves using commercially available ICR-18650 cylindrical lithium-ion cells. The individual cells have a high specific energy of 135 Wh kg⁻¹ and an energy density of 335 Wh dm⁻³. Electronic circuitry was developed to provide pack protection, charge equalization and battery management (fuel gauging). PolyStor's rechargeable BB-2590/U battery provides 4.5 Ah at 28 V nominal or 9.0 Ah at 14 V nominal, translating into 108 Wh kg⁻¹ and 150 Wh dm⁻³. The key developments are discussed in this paper.     

Production of hydrogen via methane reforming using atmospheric pressure microwave plasma

In this paper, results of hydrogen production via methane reforming in the atmospheric pressure microwave plasma are presented. A waveguide-based nozzleless cylinder-type microwave plasma source (MPS) was used to convert methane into hydrogen. Important advantages of the presented waveguide-based nozzleless cylinder-type MPS are: stable operation in various gases (including air) at high flow rates, no need for a cooling system, and impedance matching. The plasma generation was stabilized by an additional swirled nitrogen flow (50 or 100 l min⁻¹). The methane flow rate was up to 175 l min⁻¹. The absorbed microwave power could be changed from 3000 to 5000 W. The hydrogen production rate and the corresponding energy efficiency in the presented methane reforming by the waveguide-based nozzleless cylinder-type MPS were up to 255 g[H₂] h⁻¹ and 85 g[H₂] kWh⁻¹, respectively. These parameters are better than those typical of the conventional methods of hydrogen production (steam reforming of methane and water electrolysis).     

Comparative economic analysis of perennial, annual, and intercrops for biomass production

Herbaceous crops may be an important source of renewable energy. Production costs can be more competitive by increasing yields so that overhead costs are applied to more biomass. Most previous economic studies of energy crops have concentrated on the production of switchgrass (Panicum virgatum L.). This study analyzes the biomass yield and economic potential of several high-yielding annual and perennial crops on prime and marginal, sloping land. Crops evaluated were reed canarygrass (Phalaris arundinacea L.) harvested twice per year; switchgrass and big bluestem (Andropogon gerardii Vitman var. gerardii); alfalfa (Medicago sativa L.); and sweet sorghum, forage sorghum [both Sorghum bicolor (L.) Moench], and maize (Zea mays L.). The intercropping of the two sorghum species into reed canarygrass and alfalfa was also analyzed. All crops but alfalfa were fertilized with 0, 70, 140, or 280 kgNha⁻¹, with economic analysis performed assuming 140 kgNha⁻¹. Sorghums were most productive, with more than 16 t of dry matter ha⁻¹. Switchgrass was the highest-yielding perennial crop. Costs per ton of biomass produced were lowest for sorghum, somewhat higher for switchgrass, higher still for big bluestem, and highest for alfalfa and reed canarygrass. Yields per ton for intercropped species were higher than for perennial species but lower than for monocrop sorghum. Costs per ton for intercropped species were less than for either alfalfa or reed canarygrass, but were higher than costs per ton of monocrop sorghum. Although the sorghums had the highest yields, high potential for erosion on sloping soils may preclude their use on these soils.