Process simulation and analysis of a five‐step copper–chlorine thermochemical water decomposition cycle for sustainable hydrogen production

A process model of a five‐step copper–chlorine (Cu–Cl) cycle is developed and simulated with the Aspen Plus simulation code. Energy and mass balances, stream flows and properties, heat exchanger duties, and shaft work are determined. The primary reactions of the five‐step Cu–Cl cycle are assessed in terms of varying operating and design parameters. A sensitivity analysis is performed to examine the effect of parameter variations on other variables, in part to assist optimization efforts. For each cycle step, reaction heat variations with such parameters as process temperature are described quantitatively. The energy efficiency of the five‐step Cu–Cl thermochemical cycle is found to be 44% on the basis of the lower heating value of hydrogen, and a parametric study of potential efficiency improvement measures is presented. Copyright © 2014 John Wiley & Sons, Ltd.     

Inoculum preparation of anaerobic mixed cultures by electric field for dark fermentative hydrogen production

The applicability of electric field as a pretreatment technique for inoculum preparation was confirmed in a previous study. In the present work, newly adopted electric pretreatment conditions were statistically optimized for the preparation of inoculum from anaerobic mixed cultures in dark fermentative H₂ production via response surface methodology with a Box–Behnken design. Pretreatment conditions of applied voltage, distance of electrode, and reaction time were chosen as independent variables, while H₂ yield was chosen as the response variable. Overall performance revealed that applied voltage and reaction time were slightly interdependent or significantly interactive influence on H₂ yield, and they were more influential compared with electrode distance on H₂ yield. In the confirmation test, H₂ yield of 1.42 mol H₂ per mol hexose_added was recorded, corresponding with 94.7% of the predicted response value, under applied voltage of 11 V, distance of electrode of 5 cm, and reaction time of 23 min. Although the H₂ yield under electric pretreatment was similar with the heat pretreated yield, the energy consumption efficiency was about 40‐fold lower. Therefore, it may be concluded that electric pretreatment is a potent alternate technique for inoculum preparation method in terms of energy consumption and easy applicability in the field with high effectiveness. Copyright © 2014 John Wiley & Sons, Ltd.     

Biogas from lignocellulosic feedstock: A review on the main pretreatments,inocula and operational variables involved in anaerobic reactor efficiency

Research focused on reusing lignocellulosic waste has been gaining ground, both for the purpose of obtaining energy from renewable sources, as well as for reducing feedstock costs and preventing environmental pollution. Despite being currently evaluated as a promising feedstock, large-scale application of lignocellulosic waste to obtain bioenergy is still scarce. One of the obstacles in terms of reusing it is its recalcitrant composition, often requiring pretreatment applications to break its fibers, increasing its bioavailability. In addition to the type of substrate, there are many operational parameters that may affect the process efficiency, including the type of reactor, temperature, pH, inoculum source, among others. Considering this, it is interesting to consider using statistical tools instead of “one-factor-at-a-time” methods for simultaneous optimization of these variables to increase the production of value-added compounds, such as Plackett-Burman screening design and Central Composite Rotational Design. In this context, this review aimed at compiling data regarding obtaining value-added compounds, focusing on bio-H₂ and bio-CH₄, from different lignocellulosic waste, such as sugarcane bagasse, citrus peel waste, coffee and cereal husks, brewer's spent grain, cocoa processing waste, sawdust, among others, considering the main operational parameters involved (temperature, pH, inoculum) and the type of pretreatment applied (physical, chemical and/or biological). The results described here may support future research on reusing residual lignocellulosic waste, in addition to elucidating the importance of different operational parameters to convert this waste into H₂ and/or CH₄.     

Methane tri-reforming over a Ni/β-SiC-based catalyst: Optimizing the feedstock composition

Tri-reforming of methane has proved to be a highly efficient process for obtaining synthesis gas suitable for use in the Fischer–Tropsch process and methanol synthesis. In this paper the influence of the feedstock composition on methane conversion, the H₂/CO molar ratio of the synthesis gas obtained by tri-reforming of methane and the heat released or supplied to the system with a Ni/β-SiC catalyst are all described. Firstly, a factorial plus central composite design of experiments was chosen in order to optimize the independent variables selected. Then, using the experimental data obtained, a quadratic model was built. It was observed that the effect of both water and oxygen volume flow on the H₂/CO molar ratio was positive while that of methane and carbon dioxide volume flow was negative. Finally, in order to obtain an energetic optimum inside the target region, the influence of the independent variables studied previously on the overall reaction heat was calculated.     

Two-stage thermophilic bio-hydrogen and methane production from lime-pretreated oil palm trunk by simultaneous saccharification and fermentation

A simultaneous saccharification and fermentation (SSF) process was applied for thermophilic bio-hydrogen production from lime-pretreated oil palm trunk (OPT) by Thermoanaerobacterium thermosaccharolyticum KKU19. The SSF hydrogen fermentation conditions were optimized to maximize hydrogen yield (HY). Based on Plackett-Burman design, substrate loading and initial pH had significant effects on HY. The substrate loading and initial pH were further optimized using response surface methodology with a central composite design. The optimum conditions were a substrate loading, enzyme loading, inoculum concentration, initial pH and temperature of 4.6%, 10 filter paper unit (FPU)/g-OPT, 10% (v/v), 6.3 and 50 °C, respectively, which yielded the highest HY of 60.22 mL H₂/g-OPT. Structural analysis showed that lime pretreatment and SSF decreased the crystallinity of OPT. Methane production was carried out following the hydrogen production to improve the energy yield from OPT. The results showed that methane production increased total energy yield from 0.65 to 11.79 kJ/g-OPT under the optimal conditions.     

Fermentative hydrogen production by conventionally and unconventionally heat pretreated seed cultures: A comparative assessment

In this study, the effects of pretreatment temperature and time during conventional and unconventional, microwave-assisted heat shock on the hydrogen producing capability of anaerobic seed sludge from soluble starch was focused. It was found that the different heat transfer techniques resulted in seed cultures with comparable hydrogen production potentials, with the highest obtainable values of approximately 0.9 L H₂/L-d. A comprehensive, statistical analysis revealed that both treatment temperature and time could be designated as significant process variables, however, in distinguishable extents for the two alternative methods. The results indicated that microwave-based sludge pretreatment needed remarkably shorter curing times (2 min) to eliminate H₂-consuming, methanogenic activity in comparison to the conventional heat shock method (30 min). It was also demonstrated that microwave irradiation increased the soluble organic matter content in the seed sludge.     

Optimization of key variables for the enhanced production of hydrogen by Ethanoligenens harbinense W1 using response surface methodology

The optimization of process conditions for the production of hydrogen by Ethanoligenens harbinense W1 was investigated using response surface methodology (RSM). Three parameters namely inoculum to substrate ratio, initial pH value and temperature were chosen as variables. The adequately high R² value (99.4%) indicated the statistical significance of the model. The optimum process conditions for hydrogen production rate were determined by analyzing the response surface three-dimension surface plot and contour plot and by solving the regression model equation with Design Expert software. The central composite design (CCD) was used to optimize the process conditions, which showed that an inoculum to substrate ratio of 14%, initial pH value of 4.32 and the experimental temperature of 34.97 °C were the best conditions. Under the optimized conditions, the maximum specific hydrogen production rate (SHPR) was 35.74 mL/g-CDW.h based on cell dry weight. The results were further verified by triplicate experiments. The batch reactors were operated under an optimized condition of the inoculum to substrate ratio of 14%, initial pH value of 4.3 and the experimental temperature of 35 °C. The maximum SHPR was estimated at 35.57 mL/g-CDW.h, which further verified the practicability of this optimum strategy.     

固态发酵产酶反应中体系传热传质行为分析

固态发酵是纤维素类生物质转化的有效途径,具有用水量少、容积产率高等优点。固态发酵生产纤维素酶一般是液态发酵酶产量的近3倍,可大幅降低酶的生产成本。在固态发酵过程,微生物在缺水环境中生长,发酵底物和接种物之间存在异质性,导致发酵热量分布不均匀、发酵过程氧气与中间产物不易扩散等问题。基于此,重点对固态发酵反应中体系传热传质方式及其影响因素进行了分析,并探讨其强化方法。根据传热方式,总结了发酵罐适用的导热微分方程及传热模拟方法,并分析气泡和颗粒基质中的传质过程及其限速步骤以及解决传质限速的途径。反应体系传热传质机理研究可促进固态发酵技术产业化应用进程。该研究可为有机废弃物固态发酵技术研究及应用提供一定的理论和技术支持。     

Minimization of entropy generation in flat heat pipe

A thermodynamic model of flat heat pipe is developed based on the laws of thermodynamics. Major reasons for entropy generation, which is considered as a significant parameter on heat pipe performance, are temperature difference between hot and cold reservoirs, frictional losses in the flow of working fluid, and vapor temperature and pressure drop along heat pipe. The objective of the present work is to minimize the entropy generation in a flat heat pipe. The physical situation is formulated as a non-linear programming problem with non-linear objective function and constraints. Using available software, the optimum values of selected design variables are arrived. The effect of heat load, adiabatic length, etc. on the optimum design variables and corresponding entropy generation are studied.     

Numerical simulation and multiobjective optimization of a microchannel heat sink with arc-shaped grooves and ribs

ABSTRACT

In order to obtain the optimal structure size of a microchannel heat sink (MCHS) with arc-shaped grooves and ribs according to the actual demand, multiple parameters that influence the performance of the microchannel are analyzed by combining the multi-objective evolutionary algorithm (MOEA) with computational fluid dynamics (CFD). The design variables include the relative groove height, relative rib height and relative rib width, and the two objective functions are to minimize the total thermal resistance and pumping power in constant volume flow rate. The influences of the design variables on the two objective functions are analyzed by CFD firstly. The results show that each design variable has a different impact on the two functions. The competitive relationship between the two objective functions is depicted in plots of the Pareto front obtained by MOEA. Pareto sensitivity analysis is carried out to find that the relative rib height has the most significant impact on the two objective functions.     

Effects of various pretreatment methods of anaerobic mixed microflora on biohydrogen production and the fermentation pathway of glucose

The influence of different pretreatment methods on anaerobic mixed inoculum was evaluated for selectively enriching the hydrogen (H₂) producing mixed culture using glucose as the substrate. The efficiency of H₂ yield and the glucose fermentation pathway were found to be dependent on the type of pretreatment procedure adopted on the parent inoculum. The H₂ yield could be increased by appropriate pretreatment methods including the use of heat, alkaline or acidic conditions. Heat pretreatment of the inoculum for 30 min at 80 °C increased the H₂ yield to 53.20% more than the control.When the inoculum was heat-pretreated at 80 °C and 90 °C, the glucose degraded via ethanol (HEt) and butric acid (HBu) fermentation pathways. The degradation pathways shifted to HEt and propionate (HPr) types as the heat pretreatment temperature increased to 100 °C. When the inoculum was alkali- or acid-pretreated, the fermentation pathway shifted from glucose to a combination of the HPr and HBu types. This trend became obvious as the acidity increased. As the fermentation pathway shift from the HEt type to the HPr and HBu types, the H₂ yield decreased.     

Optimizing thermomechanical pretreatment conditions to enhance enzymatic hydrolysis of wheat straw by response surface methodology

Wheat straw was pretreated with a thermomechanical process developed in our laboratory to improve the enzymatic hydrolysis extent of potentially fermentable sugars. This process involves subjecting the lignocellulosic biomass for a short time to saturated steam pressure, followed by an instantaneous decompression to vacuum at 5 kPa. Increasing of the heat induced by saturated steam result in intensive vapour formation in the capillary porous structure of the plant material and the subsequent release of the pressure to vacuum allows fixing the expanded structure. Response surface methodology (RSM) based on central composite design was used to optimize three independent variables of the pretreatment process: processing pressure (300-700 kPa), initial moisture contents of wheat straw (10-40%) and processing time (3-62 min). The process was optimised for hydrolysis yield and initial hydrolysis rate obtained by enzymatic hydrolysis on the pretreated solids by Celluclast (1.5 L). The analysis of variance (ANOVA) revealed that, among the process variables, processing pressure and processing time have the most significant effect on the hydrolysis yield and on initial rate of hydrolysis whereas initial moisture content observed significantly lower effect on the two responses. The predicted hydrolysis yield and in a lesser extent the predicted initial rate of hydrolysis agreed satisfactorily with the experimental values with R² of 96% and 86% respectively.     

Screening design of nutritional and physicochemical parameters on bio-hydrogen and volatile fatty acids production from Citrus Peel Waste in batch reactors

Different nutritional and physicochemical conditions to obtain H₂ from Citrus Peel Waste (CPW) were evaluated. For this, a screening design was carried out using Plackett and Burman design, in order to verify the main significant conditions of this process. The variables studied were pH (5.5–8.5), temperature (30–44 °C), autochthonous inoculum (0.75–2.25 gTVS.L^?1), allochthonous inoculum (1–3 gTVS.L^?1) and substrate (5–15 g.L^?1), headspace (40–60%) and nutritional medium components, such as yeast extract (0–1 g.L^?1), CaCO₃, NaCl and peptone (0–5 g.L^?1). The most significant operational variables were pH (8.5), allochthonous inoculum (3 gTVS.L^?1) and substrate concentration (15 g CPW.L^?1), conditions that favored the highest H₂ (13.29 mmol.L^?1) and acetic acid productions (1340 mg.L^?1). Escherichia (34.5%) and Clostridium (29.93%) were the main genera identified under these conditions.     

Ultrasound-assisted extraction of oil from Moringa oleifera Lam. seed using various solvents

The present research analyzes the extraction of oil from Moringa oleifera Lam. seed using ultrasound-assisted extraction (UAE) technique under different operating conditions such as temperature, solvent type, and time. Three factors with three levels Box-Behnken response surface design was employed to optimize and investigate the effect of process variables on the response (oil yield). The independent variables showed significant effect on the extraction process. Interactive effects of the extraction process variables were analyzed by Pareto analysis of variance (ANOVA), and second-order polynomial model was used to plot the 3D response surface plot. Optimum extraction conditions for the maximizing the extraction yield of oil (59%) was found to be: temperature of 35°C, solvent type of 2, and time of 20 min. FT-IR was used to analysis the oil. From the results, it can be concluded that the UAE is the effective technique to extract the oil from Moringa oleifera Lam. seed.     

Fermentative hydrogen production from lipid-extracted microalgal biomass residues

The conversion of lipid-extracted microalgal biomass residues (LMBRs) into hydrogen plays the dual role in renewable energy production and sustainable development of microalgal biodiesel industry. An anaerobic fermentation process to covert LMBRs into hydrogen was investigated in this work. Using batch experiments, the effects of pretreatment of inoculum (by acid, base, heat, and chloroform, respectively), initial pH (5.0–7.0), inoculum concentrations at 0.59–2.94 g VSS/l (volatile suspended solids, VSS) and substrate concentrations at 4.5–45 g VS/l (volatile solids, VS) were investigated, respectively. The results showed that the most effective hydrogen production was obtained from fermentation of LMBRs with a concentration of 36 g VS/l at the initial pH 6.0–6.5 using the heat-treated anaerobic digested sludge as inoculum. Acetate, propionate and butyrate were the main fermentation byproducts in the conversion of LMBRs into hydrogen.     

Hydrogenase activity monitoring in the fermentative hydrogen production using heat pretreated sludge: A useful approach to evaluate bacterial communities performance

The conversion of organic compounds into H₂ has received increasing attention. Enrichment of inocula by heat pretreatment eliminates non-spore forming hydrogen consuming microorganisms and promotes spore germination in genus Clostridium, which is known as one of the key hydrogen producers. Useful information about metabolic pathway is provided by some intermediate metabolites, such as: acetic, propionic, butyric and formic acids. The increase of acetic/butyric acids ratio indicates H₂ production in heat pretreated inoculum when compared to untreated inoculum in the same cultivation conditions. The effect of heat pretreatment on inocula and consequently on the performance of bacterial communities responsible for H₂ production was monitored through the measurement of the level of hydrogenase gene expression, as well as through the content and distribution of volatile fatty acids. The acetic acid type fermentation was followed by the microorganisms presented in untreated and heat pretreated sludge. The medium containing untreated sludge presented a ratio of acetic/butyric acid of approximately 4, the same parameter was 7 when heat pretreated sludge was employed. The level of hydrogenase gene expression tripled when heat pretreated inoculum was used, indicating a higher production of H₂.     

大型海藻发酵生产甲烷技术研究

大型海藻发酵生产甲烷属生物质能,是一种碳中性的清洁能源,是重要的海洋生物碳汇。不同种类的藻类发酵产甲烷的潜力是不一样的,其中巨藻含有丰富的甲烷成分,但其自然资源量有限,而人工养殖依然是一个难题,如何持续不断地提供原材料是巨藻生物质能源开发中亟待解决的问题。海藻发酵产甲烷是多种微生物联合作用的结果,从整体上可划分为产甲烷菌群和不产甲烷菌群,它们相互依赖又相互制约,产甲烷菌利用不产甲烷菌的代谢产物H2、CO2等最终合成甲烷。海藻发酵过程的微生物要求具有一定的耐盐性,大体可以利用沼气发酵微生物经过定向培养和筛选而获得。多数人支持将沼气发酵过程分为水解液化、酸化和甲烷化三个阶段的理论,而甲烷形成途径包括菌种间H2的转移和由乙酸产生甲烷。甲烷发酵的影响因素包括原料的预处理、原料的成分和颗粒大小以及接种物、发酵温度、发酵料液pH值、接种率及接种物中对发酵菌活性有影响的物质等,甲烷产率最大化的最主要前提是反应条件要达到最优化。我国在海藻大规模养殖方面具有先天的自然条件及技术和人力优势,为海藻生物质能源开发提供了巨大的潜力,但在技术上还有待突破,特别是在接种物培养、甲烷产率控制等一些特定环节上还需加强研究。     

A quasi-3D analysis of the thermal performance of a flat heat pipe

The thermal performance of a flat heat pipe thermal spreader has been described by a quasi-3D mathematical model and numerically modeled. An explicit finite volume method with under-relaxation was used for computations in the vapor phase. This was combined with a relatively small time step for the analysis. The physical problem consisted of an evaporator surface that was transiently heated non-uniformly for a short period of time and the heat source then removed. Then the system was cooled by natural convection and radiative heat transfer at the condenser region. The transient temperature distributions at the front and back of the heat spreader were obtained for different times during the transient period. The velocity distribution in the vapor core was also obtained. Due to the effect of phase change at the evaporator and condenser sides, a significant amount of energy is found to be absorbed and partially released during the transient heating and cooling processes. The numerical results indicate that advection and the high thermal diffusivity of the vapor phase accelerate the propagation of the temperature distribution in the vapor core, making it uniform during this process. The condenser temperature distribution was almost uniform at the end of the transient heating process. The transient temperature distribution on a solid aluminum plate was compared with the flat heat pipe results and indicated that the flat heat pipe successfully spread the heat uniformly at the condenser side of the structure.     

超声波促进污泥厌氧消化的研究

介绍了超声波的作用机理，指出在污泥厌氧消化过程中，污泥水解是限速步骤，在厌氧消化前，对污泥进行超声波破解预处理，促使细胞壁破裂，细胞内含物溶出，可以加速污泥的水解过程，从而达到缩短消化时间，减少消化池容积，提高沼气产量的目的。     

Numerical simulation of the magnetic field and Joule heating effects on force convection flow through parallel-plate microchannel in the presence of viscous dissipation effect

The effects of Joule heating, Hartman, Brinkman, and Reynolds numbers on the flow pattern and thermal characteristics of force convection flow through a parallel-plate microchannel are investigated in various nanoparticles volume fraction. Water–Al₂O₃ is considered as the working nanofluid while taking viscous dissipation effect (VDE) into account. The mid-section of the microchannel is heated with a constant uniform heat flux and influenced by a magnetic field with a uniform strength. The effective thermal conductivity and viscosity of nanofluid are calculated through a new correlation in which the influence of Brownian motion is considered. A control volume finite different scheme, along with the SIMPLE algorithm, is adopted to conduct the numerical analyses and solve the discrete equations. Contour plots of streamlines and isotherms are presented to graphically display the impact of the investigated variables. Furthermore, the values of the Nusselt number for the minimum temperature and maximum velocity are calculated and presented through figures. The results show that all of the Brinkman, Joule, nanofluid concentration, and Hartmann numbers have decreasing effect on the heat transfer. The conclusion is supported by the fact that all the aforementioned factors increase the temperature throughout the flow field. The higher the flow field temperature, the lower the heat transfer from the wall. Higher Brinkman number leads to the friction intensification between flow layers due to considering VDE. It can be said about the Joule heating that, since this term has an inverse relation with the squared velocity, increase in Joule number is followed by a reduction of heat transfer from the walls. Also, an increase in the nanofluid concentration increases the temperature throughout the microchannel leading to heat transfer deterioration.