The development of efficient non-noble metal catalysts for the hydrodeoxygenation (HDO) of lignin-derived phenolic compounds is critical for biomass valorisation. In this work, unsupported Fe-based nanocatalysts were systematically investigated to uncover the intrinsic active sites and eliminate support-induced complexities during the HDO of phenolic compounds. It was found that catalytic activity is positively correlated with the relative fraction of the metallic Fe0 phase. Among the catalysts evaluated, zero-valent nano-Fe (50 nm) exhibited the highest performance, achieving complete phenol conversion with a 97% cyclohexane yield at 300 degrees C and 4 MPa H2 after 20 h. Based on the characterisation results, this superior activity is not solely dependent on the geometric surface area, but is intrinsically driven by the synergy of an ultrathin surface passivation layer and a high density of exposed zero-valent iron (Fe0) defect sites. Furthermore, surface interactions were elucidated via density functional theory (DFT) calculations, revealing robust parallel adsorption and effective activation of the aromatic ring on the Fe (110) surface. Additionally, catalyst stability, phase evolution, and broad applicability for various lignin-derived substrates were systematically examined. These findings establish a fundamental baseline for the intrinsic activity of pure Fe nanoparticles, providing theoretical guidance for the rational design of support-free non-precious metal catalysts.
In this study, the coal feeding process from Garp Lignite Enterprise (GLE) in Kutahya, Turkey to the nearby Tuncbilek Power Plant (TPP) was evaluated from statistical process control point of view. During the examination of GLE-TPP coal feeding system, process stability and capability of the supplied coal were measured and analysed on the basis of calorific value (quality characteristic) of coal for the years of 2002 and 2003. Process stability was examined by taking the mean and range control charts into account for the two units of TPP. Process capability, on the other hand, was analysed by considering the capability indexes for the two units of TPP. As a result of the analyses, it was found that the operation of the system was unstable and incapable in 2002 and 2003, although some improvements were observed in 2003. This result indicates that the process was not controlled effectively. After the analysis, the reasons of the problem were also discussed and several suggestions were made.
In this study, a novel trigeneration system is proposed as an idea for future research based on the industrial waste heat recovery operated steam generator for process heat, and produces both power and refrigeration simultaneously with stack gases, using ammonia-water mixture as the working fluid. An extensive review of various energy and exergy based approach used in the analysis of different cogeneration and trigeneration cycles is reported. Energy and exergy efficiencies have been defined, and computational analysis is performed to investigate the effects of exhaust gas inlet temperature and gas composition on first law efficiency, electrical/thermal energy ratio and exergy efficiency of an industrial waste heat recovery based trigeneration system. The variation in specific heat with exhaust gas composition and temperature is accounted in the analysis for further discussion. The first law (energy) efficiency increases while electrical/thermal energy ratio and exergy efficiency decrease with increasing exhaust gas inlet temperature. Exergy efficiency significantly varies with gas composition and oxygen content of the exhaust gas. Approximating the exhaust gas as air and the air standard analysis leads to either underestimation or overestimation of proposed trigeneration cycle from the point of view of exergy analysis. The present analysis will provide a convenient and practical tool for engineers and researchers dealing with the energy efficiency improvements in a sustainable manner.
Turbulent flame speeds were measured over a range of pressures to 0.8 MPa using a jet flow apparatus fired with a synthetic mixture representing a mid-European natural gas. The equivalence ratio empty set was 0.9. The gas contained significant proportions of ballast gases and higher hydrocarbons. The method adopted was the 'flame angle' technique, using schlieren imaging to obtain the flame vertex angle from the peak density gradient. Image analysis techniques were developed to reduce interpretation errors and give an unbiased result. The data show higher flame speeds than those obtained with pure methane at elevated pressures, using similar methodology, and has an application in numerical modelling of combustors.
This work shows the influence of using different allocation approaches when modelling the inventory analysis in a soybean biodiesel life cycle assessment (LCA). Results obtained using mass, energy and economic based allocations are compared, focusing on the following aspects: normalised potential environmental impact (PEI) categories, total PEI and relative contributions to the total PEI from each life cycle stage and environmental impact category. Similar results are obtained either using economic and energy based allocations. However, different results are obtained when mass based allocation is used when compared with the other two. This study also illustrates that using different allocation approaches in biodiesel LCA may influence the final conclusions, especially in comparative assertions, emphasising the need to perform a sensitivity analysis in the LCA interpretation step.
Venturi-cascading is a technique to control pollutant emissions from diffusion flames by modifying air infusion and fuel-air mixing rates through changing the flow dynamics in the combustion zone with a set of venturis surrounding the flame. A propane jet diffusion flame at a burner-exit Reynolds number of 5100 was examined with a set of venturis of specific sizes and spacing arrangement. The venturi-cascading technique resulted in a decrease of 33 percent in NO emission index along with a 24-percent decrease in soot emission from the flame, compared to the baseline condition (same flame without venturis). In order to understand the mechanism behind these results, laser-induced fluorescence (LIF) spectroscopy was employed to study the concentration field of the radicals (OH, CH, and CN) in the baseline and venturi-cascaded flames. The LIF measurements, in the near-burner region of the venturi-cascaded flame, indicated an average decrease of 18, 24 and 12 percent in the concentrations of OH, CH, and CN radicals, respectively, from their baseline values. However, in the midflame region, a 40-percent average increase in OH from its baseline value was observed. In this region, CH or CN radicals were not detected. The OH radical concentration in the downstream locations was mostly affected by soot rather than by temperature.
An effort is made here to develop a systematic design method for fluidised bed gasifiers. Three design approaches are considered: equilibrium approach, residence time approach and kinetic model approach. The equilibrium approach, which only predicts the gas composition, has two models: simple stoichiometric model and more comprehensive model. The latter gives better prediction of maximum achievable gas yield for a given set of feedstock and operating conditions. The residence time approach is primarily based on experimentally derived char gasification time and provides a good option for sizing of a gasifier, especially for carbonaceous fuels. The kinetic model, which is generally used for simulation of an existing gasifier, has been used here for the design considering the rate of reactions and effect of geometry and bed hydrodynamics on the gasifier performance. Because of its complexity, the kinetic model is most difficult to implement for initial design of a gasifier. More than three design approaches have been used to theoretically design a gasifier. Design results are compared with those predicted and obtained from experiments.
Melon seeds containing similar to 30% oil are wasted after the fruit is consumed. The chemical and physical properties of melon seed oil are very similar to vegetable oils used as biodiesel fuel. There are no studies regarding the use of melon seed oil or its esters as fuel in literature. In this study, oil was extracted from waste melon seeds and transformed to melon seed oil methyl ester (MSOME) by transesterification process. This fuel is used in a four stroke single cylinder direct injection diesel engine, and its effects on performance and emissions were investigated for various engine speeds at full load. In addition, diesel fuel no. 2 and soy bean oil methyl ester (SOME) is used as fuel under the same operating conditions for comparison purposes. According to the experiment results, specific fuel consumption is found to be more in both biodiesel fuels compared to diesel fuel, and the engine torque is 1-6% lower with MSOME and 3-5% with SOME compared to diesel fuel. Exhaust gas temperature is lower with MSOME and SOME than with diesel fuel. Furthermore, it is found that CO and HC emissions and smoke density are generally lower in both biodiesel fuels. However, NOx emission is slightly higher for SOME and MSOME than that for diesel fuel.
Characteristics of direct injection (DI) combustion, direct injection-homogeneous charge compression ignition (DI-HCCI) combustion and HCCI combustion in an engine fuelled with dimethyl ether are investigated. The combustion stabilities of three combustion modes are compared, and the effects of premixed ratio, speed and load on them are given. The analysis shows that the maximum values of pressure, heat release rate, pressure rise rate and acceleration of DI combustion are lower than those of HCCI combustion and their phases are retarded. The combustion duration of DI combustion is shorter than that of HCCI combustion. In DI-HCCI combustion, with increasing premixed ratio, the maximum values of pressure, pressure rise rate and acceleration increase, and their phases advance respectively, and the combustion duration shortens evidently. The coefficient of variation (COV) of maximum pressure of DI combustion is much larger than that of HCCI combustion at 1100 and 1500 rev min(-1). In DI-HCCI combustion, the COV first decreases with increasing premixed ratio, and then changes little at 1100 rev min(-1). The COV with large premixed ratio was lower in comparison to that with small premixed ratio at various Loads. At 1500 rev min(-1), premixed ratio has few effects on COV, no matter with large or small premixed ratio; COV is maintained at a relatively small value at various Loads. The pressure fluctuation results are consistent with those of the COV analysis.
Given that the fluid within the tubes of some industrial heat exchangers is under a state of fully developed laminar flow with a constant Nu number, increasing the surface area for heat transfer will significantly increase the flow resistance. In this paper, we filled metal porous medium with high thermal conductivity, high porosity and high filling radius in the central area of fully developed laminar flow within the tube, and established corresponding numerical models for fluid flow and heat transfer. Numerical simulation results indicate that after filling the tube with metal porous medium, the temperature profiles within the porous medium area are very uniform, and the temperature difference between the tube wall and the fluid decreases significantly which correspondingly results in a notable increase of Nu number; meanwhile, the characteristic of flow field redistribution occurs within the enhanced tube, but the total flow resistance composed of the Darcy resistance and inertial resistance of the porous medium area and the shear stress caused by velocity gradient and fluid viscosity of the non-porous medium area near the wall increase; correspondingly, the performance evaluation criteria (PEC) value is thus applied to evaluate the effect of the heat tranfer enhancement method. For a tube of 9 mm in radius, the PEC values are all above 1 when the filling radius of the metal porous medium is larger than 7 mm.
The objective of this study is to develop a pattern recognition based artificial neural network (ANN) for energy auditing and inefficiency diagnostics of the most influential design elements in buildings. The influential design elements examined include: envelope insulation, glazing insulation, glazing size, infiltration, economiser, building direction and orientation, and daylighting control. For generating the data bank needed for training the ANN, several buildings with different floor areas and known inefficiencies are simulated and their energy performance patterns, in terms of monthly energy demand and consumption, are determined. Monthly energy performance data including energy demand and consumption information for one year as well as building floor area are input. The developed ANN is validated and it is found that the expert auditing tool developed is effective for diagnosing the inefficient design elements. The application of the developed algorithm for real buildings and actual data is recommended for future work.
A simple analysis is made on the air flow through a solar chimney power generation system and a thermodynamic cycle of the system including the environment is established. Later, mathematical models for the ideal and actual cycle efficiencies are also established. The research results show that the ideal cycle efficiency and actual efficiency of standard Brayton cycle corresponding to medium scale solar chimney power generation system are 1.33 and 0.3% respectively, while the same parameters for large scale solar chimney power generation systems are 3.33 and 0.9% respectively. The results can give a theoretical guidance to the commercial application of solar chimney power generation systems in China.
The performance of an air standard Otto cycle is analyzed using finite-time thermodynamics. In the model, the linear relation between the specific heat ratio of the working fluid and its temperature, the friction loss computed from the empirical correlation, the internal irreversibility described using the compression and expansion efficiencies, and the heat transfer loss is considered. The relations between the power output and the compression ratio, between the power output and the thermal efficiency are derived by detailed numerical examples. The results show that the maximum power output, the working range of the cycle, the optimal compression ratio corresponding to maximum power output, the optimal power output corresponding to maximum thermal efficiency and the optimal thermal efficiency corresponding to maximum power output decrease with the increase of the value of the specific heat ratio. The results also show that if the compression ratio is less than a certain value, the power output increases with increasing engine speed, while if the compression ratio exceeds a certain value, the power output first increases and then starts to decrease with increasing engine speed. With further increase in the compression ratio, the increase in engine speed results in decreasing the power output. The results are of importance to provide good guidance for the performance evaluation and improvement of practical Otto engines.
The extreme working temperature differences of combined thermoelectric devices, i.e. thermoelectric generator driven thermoelectric refrigerator or heat pump, are analysed using non-equilibrium thermodynamics. The extreme working temperature differences versus the ratio of numbers of thermoelectric elements, i.e. the ratio of the number of thermoelectric elements of the generator to the total number of thermoelectric elements of the combined devices, of the two models are obtained. The effects of the hot junction temperature of the generator on the extreme working temperature differences are analysed. The results show that, if a thermoelectric generator works under a condition of 150 K temperature difference, similar to 60 K temperature difference for cooling or 200 K temperature difference for heating could be reached. The coefficient of performance can reach to 0.08-0.15 which is considerable for application in a wide scale for specific purposes. For a fixed ratio of numbers of thermoelectric elements, there is a fixed extreme working temperature difference, the larger working temperature difference, the smaller cooling (heating) load and coefficient of performance. The results obtained herein may provide guidelines for the design and application of practical combined thermoelectric devices.
A model for an irreversible four-heat-source absorption refrigerator with continuous flow, which considers the irreversibilities resulting from thermal resistance and internal dissipations of the working fluid, is established. In this model, an absorption refrigerator is treated as a combined cycle system of an irreversible Carnot heat engine driving an irreversible Carnot refrigerator. Two parameters I-he and I-r are introduced to characterise the internal irreversibilities of the heat engine and refrigerator in the equivalent cycle system respectively. Under a given total heat conductance of the heat exchangers, the optimal relation between the cooling rate and coefficient of performance is derived, and the conditions for the optimal design of the system are determined. Then, this relation is used to deduce some new performance bounds. Moreover, the effects of the internal irreversibility parameters I-he and I-r on the optimal performance of the system are also investigated. The results obtained here are important for the optimal design and performance improvement of a real absorption refrigerator.
Exponential temperature change in non-isothermal kinetics has been discussed. A new empirical formula for the temperature integral integral(T)(0)(e(-RT)/T)dT has been presented, which has the form integral(T)(0)(e(-E/RT)/T)dT = (RT/E) [E-0.547781RT)/(E+3.45861RT)](0.249418) e(-E/RT). A comparison of the proposed approximation has been made with the approximation proposed by Gorbachev (V. M. Gorbachev: J. Therm. Anal., 1977, 11, 125-128). The results have shown that the new approximation is more accurate than the Gorbachev approximation and deviates by < 0.0035% for x(E/RT) as low as five. An analysis of the relative error involved in the activation energy obtained from the integral methods has been performed, and the validity of the integral method has been examined with some theoretical data.
In this study, an experimental research on the combustion and emission characteristics of a spark ignition engine fuelled with a blended gas was performed at different engine load operations. The blended gas, which was composed by the compressed natural gas and nitrogen, was lower heating value gas. In the experiments, the parameters of combustion characteristics were analysed under 0-35% nitrogen volume fraction in the blends. The results show that the maximum cylinder pressure, the maximum rate of pressure rise and the maximum rate of heat release decrease with increasing nitrogen fraction. The flame development duration and the main combustion duration increase with the higher level of the nitrogen fraction. Meanwhile, the HC, CO emission increase and the NO(x) decreases remarkably with the increase in the nitrogen volume fraction.
Combustion of biomass and municipal solid wastes is playing an increasingly important role in modern society as one of the alternative energy sources reducing global CO2 emission and minimizing land contamination. The combustion of these fuels, especially municipal solid waste is subject to high moisture variations, which could jeopardize the plant performance. In this paper, both the experimental results and details of mathematical simulation for the combustion of biomass and simulated wastes in a stationary bench-top rig are presented. Stable combustion was achieved for all moisture contents except the highest level tested (47%) where the flame extinguished 20 min after ignition. It was found that drier fuels undergo two distinctive combustion stages and the burning rate was inversely proportional to the moisture content. Wetter fuels had a thinner flame front and the combustion stoichiometry shifts from sub-stoichiometric (fuel rich) to super-stoichiometric (fuel lean) as the moisture content increases. Results show that 30% moisture in fuel produced the lowest flame-front temperature while 40% moisture in fuel resulted in the highest flame-front temperature. Flame extinction at high moisture level is related to the amount of combustible material above the moisture evaporation layer and it was found that the minimum combustible mass above the evaporation zone was 1.25 kg m(-2) for sustained burning under the conditions investigated.
