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Existence of impurities in the product gas hinders the application of the system which combines gasification with solid oxide fuel cell (SOFC). A new method is proposed to produce qualified syngas, which integrates the gasification unit with the supercritical water unit (SWU). The SWU contains supercritical water mixer, separator, reactor (SWR) and expander. To analyze performance of the proposed process from a systematic perspective, downstream operating units primarily including SOFC, burner, heat recovery steam generation and steam cycle are designed. Model for the whole system is developed by using Aspen Plus and a mathematical model for the SOFC. Sensitivity analysis regarding the fuel utilization factor ( U f ) and the mass ratio of tars to supercritical water (T/W) are conducted in terms of system electrical efficiency, SOFC electrical efficiency and cell voltage. Results show that combustible components in the obtained syngas mainly contain CH 4 , H 2 , and CO. Tars are completely decomposed and only slight amount of light hydrocarbons (except CH 4 ) are present. One SWR can undertake the functions of water gas shift, tar reforming and methane synthesis concurrently. The integrated process can offer a combustible components efficiency of 78.2%, and the system electrical efficiency is predicted to be 46.3%. U f has a significant influence on the SOFC electrical efficiency, while it has slight influence on system electrical efficiency. As the T/W rises from 1.6% to 2%, system electrical efficiency, SOFC electrical efficiency and cell voltage slightly increase. [ABSTRACT FROM AUTHOR]

Advanced technologies such as solid oxide fuel cells generally have a strict requirement on syngas quality especially the concentration of impurities. It is common to sacrifice economy and efficiency to achieve a qualified syngas by applying several cleaning and conditioning steps. The objective of this work is to propose a combined process by integrating the gasification unit with the supercritical water unit (SWU) to provide qualified syngas. The SWU includes supercritical water mixer, separator, supercritical water reactor (SWR) and expander. Detailed operating methods and appropriate equipment are presented. The whole process is modeled by using Aspen Plus to investigate effects of SWR inlet temperature, operating pressure, and mass ratio of tars to supercritical water (T/W) on the final product composition and on the outlet temperature of SWR. Results show that higher SWR inlet temperature facilitates achieving a higher H 2 and CO yield while lower inlet temperature assists in obtaining a higher H 2 /CO ratio. Lower SWR operating pressure benefits to achieve a higher H 2 and CO yield and a higher H 2 /CO ratio. Lower T/W benefits to have a higher H 2 yield and a lower CO yield, leading to a higher H 2 /CO. Tars could be completely decomposed at the given operating conditions in the proposed process. Higher inlet temperature, higher pressure and larger T/W lead to an increased SWR outlet temperature. Combustible components in the syngas mainly contains H 2 , CO, and CH 4 . [ABSTRACT FROM AUTHOR]

Abstract: In order to achieve the energy cascade utilization and improve the energy utilization efficiency of coal–water–slurry (CWS) gasification for hydrogen system, the heat integration scheme (HIS) between the water gas shift unit and the gasification unit is put forward. The effects of temperature change of CWS and oxygen on the gasification performance are investigated. Both the HIS and the non-heat integration scheme (NHIS) are analyzed by using gasification performance, energy conversion efficiency and exergy efficiency. The results show that the specific coal consumption and the specific oxygen consumption decrease by 2.7% and 6.5%, respectively, as the feedstock is preheated up to the temperature of 150 °C. The energy conversion efficiency of HIS and NHIS are nearly the same. The exergy efficiency of HIS (62.66%) is better than that of NHIS (62.02%). Therefore, the HIS is better than the NHIS by heat integration between the WGS unit and the gasification unit. [Copyright &y& Elsevier]

Abstract: The kinetic models were developed and applied for fermentative hydrogen production. They were used to describe the progress of a batch fermentative hydrogen production process, to investigate the effects of substrate concentration, inhibitor concentration, temperatures, pH, and dilution rates on the process of fermentative hydrogen production, and to establish the relationship among the substrate degradation rate, the hydrogen-producing bacteria growth rate and the product formation rate. This review showed that the modified Gompertz model was widely used to describe the progress of a batch fermentative hydrogen production process, while the Monod model was widely used to describe the effects of substrate concentration on the rates of substrate degradation, hydrogen-producing bacteria growth and hydrogen production. Arrhenius model was used a lot to describe the effects of temperature on fermentative hydrogen production, while modified Han–Levenspiel model was used to describe the effects of inhibitor concentration on fermentative hydrogen production. The Andrew model was used to describe the effects of H+ concentration on the specific hydrogen production rate, while the Luedeking–Piret model and its modified form were widely used to describe the relationship between the hydrogen-producing bacteria growth rate and the product formation rate. Finally, some suggestions for future work with these kinetic models were proposed. [Copyright &y& Elsevier]

Abstract: A fractional factorial design was carried out to investigate the effects of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures in batch tests and then the experimental data of substrate degradation efficiency, hydrogen yield and average hydrogen production rate were described by a neural network, based on which the simultaneous optimization of the three responses was performed by the method of desirability function. The analysis showed that the neural network could successfully describe the effects of temperature, initial pH and glucose concentration on the substrate degradation efficiency, hydrogen yield and average hydrogen production rate of this study. The maximum substrate degradation efficiency of 95.3%, hydrogen yield of 305.3mL/g glucose and average hydrogen production rate of 23.9mL/h were all obtained at the optimal temperature of 39.0°C, initial pH of 7.0 and glucose concentration of 24.6g/L identified by the method of desirability function based on a neural network. In sum, the method of desirability function based on a neural network was a useful tool to optimize several responses for fermentative hydrogen production processes simultaneously. [Copyright &y& Elsevier]

Abstract: This review summarized several main factors influencing fermentative hydrogen production. The reviewed factors included inoculum, substrate, reactor type, nitrogen, phosphate, metal ion, temperature and pH. In this review, the effect of each factor on fermentative hydrogen production and the advance in the research of the effect were briefly introduced and discussed, followed by some suggestions for the future work of fermentative hydrogen production. This review showed that there usually existed some disagreements on the optimal condition of a given factor for fermentative hydrogen production, thus more researches in this respect are recommended. Furthermore, most of the studies on fermentative hydrogen production were conducted in batch mode using glucose and sucrose as substrate, thus more studies on fermentative hydrogen production in continuous mode using organic wastes as substrate are recommended. [Copyright &y& Elsevier]

Abstract: A central composite design was carried out to investigate the effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures in batch test. The modeling abilities of the response surface methodology model and neural network model, as well as the optimizing abilities of response surface methodology and the genetic algorithm based on a neural network model were compared. The results showed that the root mean square error and the standard error of prediction for the neural network model were much smaller than those for the response surface methodology model, indicting that the neural network model had a much higher modeling ability than the response surface methodology model. The maximum hydrogen yield of 289.8mL/g glucose identified by response surface methodology was a little lower than that of 360.5mL/g glucose identified by the genetic algorithm based on a neural network model, indicating that the genetic algorithm based on a neural network model had a much higher optimizing ability than the response surface methodology. Thus, the genetic algorithm based on a neural network model is a better optimization method than response surface methodology and is recommended to be used during the optimization of fermentative hydrogen production process. [Copyright &y& Elsevier]

Abstract: This review summarized the experimental design methods used to investigate the effects of various factors on fermentative hydrogen production processes, including one-factor-at-a-time design, full factorial design, Taguchi design, Plackett–Burman design, central composite design and Box–Behnken design. Each design method was briefly introduced, followed by the introduction of its analysis. In addition, the advantages and disadvantages of each design method were briefly discussed. Moreover, the application of each design method to the study of fermentative hydrogen production was analyzed and discussed. Based on the discussion in this review, an experimental design strategy for optimizing fermentative hydrogen production processes was proposed. In the end, the software packages that can carry out the above mentioned factorial design and analysis were briefly introduced. [Copyright &y& Elsevier]

Abstract: The inhibitory effect of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production by mixed cultures was investigated in batch tests using glucose as substrate. The experimental results showed that, at 35°C and initial pH 7.0, during the fermentative hydrogen production, the substrate degradation efficiency, hydrogen production potential, hydrogen yield and hydrogen production rate all trended to decrease with increasing added ethanol, acetic acid, propionic acid and butyric acid concentration from 0 to 300mmol/L. The inhibitory effect of added ethanol on fermentative hydrogen production was smaller than those of added acetic acid, propionic acid and butyric acid. The modified Han–Levenspiel model could describe the inhibitory effects of added ethanol, acetic acid, propionic acid and butyric acid on fermentative hydrogen production rate in this study successfully. The modified Logistic model could describe the progress of cumulative hydrogen production. [Copyright &y& Elsevier]

Abstract: The effect of temperature, initial pH and glucose concentration on fermentative hydrogen production by mixed cultures was investigated in batch tests, and the optimization of fermentative hydrogen production process was conducted by response surface methodology with a central composite design. Experimental results showed that temperatures, initial pH and glucose concentrations had impact on fermentative hydrogen production individually and interactively. The maximum hydrogen yield of 289.8mL/g glucose was estimated at the temperature of 38.6°C, the initial pH of 7.2 and the glucose concentration of 23.9g/L. The maximum hydrogen production rate of 28.2mL/h was estimated at the temperature of 37.8°C, the initial pH of 7.2 and the glucose concentration of 27.6g/L. The maximum substrate degradation efficiency of 96.9% was estimated at the temperature of 39.3°C, the initial pH of 7.0 and the glucose concentration of 26.8g/L. Response surface methodology was a better method to optimize the fermentative hydrogen production process. Modified logistic model could describe the progress of cumulative hydrogen production in the batch tests of this study successfully. [Copyright &y& Elsevier]

Abstract: Effect of temperatures ranging from 20°C to 55°C on fermentative hydrogen production by mixed cultures was investigated in batch tests. The experimental results showed that, at initial pH 7.0, during the fermentative hydrogen production using glucose as substrate, the substrate degradation efficiency and hydrogen production potential increased with increasing temperatures from 20°C to 40°C. The maximal substrate degradation efficiency was 98.1%, the maximal hydrogen production potential was 269.9mL, the maximal hydrogen yield was 275.1mL/g glucose and the shortest lag time was 7.0h. The temperature for fermentative hydrogen production by mixed cultures was optimized to be 40°C. The expanded Ratkowsky models could be used to describe the effect of temperatures on the hydrogen production potential, maximum hydrogen production rate and the lag time during fermentative hydrogen production. [Copyright &y& Elsevier]

Abstract: The pretreatment of digested sludge by five methods (by acid, base, heat-shock, aeration and chloroform, respectively) was conducted in batch tests to evaluate and compare their suitability in the enrichment of hydrogen-producing bacteria. The experimental results showed that, at 35°C and initial pH 7.0, the hydrogen yields of the pretreated digested sludge were higher in comparison with the control test during the fermentative hydrogen production using glucose as the substrate. In all tests, for fermentative hydrogen production from glucose, the digested sludge pretreated by heat-shock could obtain the maximal hydrogen production potential, maximum hydrogen production rate, hydrogen yield, substrate degradation efficiency and biomass concentration, which were 215.4mL, 120.4mL/h, 221.5mL/g glucose, 97.2% and 2739mg/L, respectively. The final pH values in the liquid after fermentative hydrogen production in all tests were between 3.4 and 4.1. Heat-shock is an easy and practical pretreatment method for enriching hydrogen-producing bacteria from digested sludge. [Copyright &y& Elsevier]

Abstract: The effect of the concentrations ranging from 0 to 1500mg/L on the fermentative hydrogen production from glucose was investigated in batch tests by mixed cultures at 35°C and initial pH 7.0. The experimental results showed that in certain concentration range, was able to enhance the hydrogen production rate, the cumulative hydrogen quantity, and the hydrogen yield by the mixed cultures. The maximum cumulative hydrogen quantity of 302.3mL and the maximum hydrogen yield of 311.2mL/g glucose were obtained at the concentration of 300 and 350mg/L, respectively. The major soluble metabolites produced by the mixed cultures were ethanol, acetic acid, and butyric acid, with little or no propionic acid. The glucose degradation efficiency had the trend to decrease with increasing concentrations from 0 to 1500mg/L, but when the concentrations were lower than 350mg/L, the glucose degradation efficiency was between 96.25 and 98.78%, which is relatively high and kept unchanged with increasing concentrations. In certain concentration range, was able to enhance the biomass production yield. When the concentrations were between 100 and 750mg/L, there was a high biomass production yield plateau ranging from 259.2 to 334.2mg/g glucose. The final pH value had the trend to decrease with increasing concentrations from 0 to 1000mg/L, and the lowest final pH value was about 4.3 at the concentration of 1000mg/L. [Copyright &y& Elsevier]