Investigation of performance of fire‐tube boilers integrated with ion transport membrane for oxy‐fuel combustion

The performance of a carbon free fire‐tube boiler utilizing two‐pass oxygen transport reactors was numerically investigated. The influences of the oxygen transport reactors wall temperature on the reaction rate, oxygen permeation and heat flux were quantified. The performance of the reactors has been investigated at elevated temperature. It is observed that both heat transfer and combustion characteristics can be optimized at an elevated temperature of 1373 K. Increasing the mass fraction of methane in this reactor to 6% results in improvement of the heat transfer and combustion characteristics in the reactor. Further increase in CH₄% did not lead to any significant improvement. The fuel flow rate variation did not have any significant impact on the reactor performance. It is indicated that the membrane temperature has significant effect on the reaction rates and oxygen flux in the upstream region in particular. Copyright © 2016 John Wiley & Sons, Ltd.     

Fundamental study of heterogeneous KCl sulfation under oxy‐fuel combustion conditions

Under oxy‐fuel combustion condition, SO₂ in the flue gas would be accumulated by recirculation, which is conducive to the heterogeneous sulfation reaction of alkali metals. In the present study, experiments were conducted in a fixed bed to investigate the effects of operating parameters and mineral additives (SiO₂, CaO, and Fe₂O₃) on the heterogeneous sulfation of potassium chloride under oxy‐fuel combustion atmosphere. According to the results here, the heterogeneous sulfation reaction was a kinetically controlled process, with the activation energy of 93.6 kJ/mol. The reaction orders with respect to SO₂, O₂, and H₂O were determined as 1, 0.6 and 0 (H₂O involved in the reaction). While the reaction would be promoted obviously in the absence of H₂O. The rate law of heterogeneous sulfation of potassium chloride was derived based on the experimental data. Compared with air combustion, the heterogeneous sulfation rate was lower under oxy‐fuel combustion. All the mineral additives employed would affect the sulfation reaction. The sulfation reaction can be catalyzed by Fe₂O₃. While CaO would suppress the reaction by competing for SO₂ with KCl. The reaction between CaO and SO₂ could also be catalyzed by Fe₂O₃. Besides, SO₂ was more reactive towards CaO than KCl.     

Modeling of ion transport reactor for oxy‐fuel combustion

This paper aims at investigating the performance of a cylindrical ion transport reactor designed for oxy‐fuel combustion. The cylindrical reactor walls are made of dense, nonporous, mixed‐conducting ceramic membranes that only allow oxygen permeation from the outside air into the combustion chamber. The sweep gas (CO₂ and CH₄) enters the reactor from one side and mixes with the oxygen permeate, and the products are discharged from the other side. The process of oxygen permeation through the reactor walls is influenced by the flow condition and composition of air at the feed side (inlet air side) and the gas mixture at the permeate side (sweep gas side). The modeling of the flow process is based on the numerical solution of the conservation equations of mass, momentum, energy, and species in the axisymmetric flow domain. The membrane is modeled as a selective layer in which the oxygen permeation depends on the prevailing temperatures as well as the oxygen partial pressure at both sides of the membrane. The CFD calculations were carried out using fluent 12.1 (ANSYS, Inc., Canonsburg, PA, USA), whereas the mass transfer of oxygen through the membrane is modeled by a set of user defined functions. The model results were validated against previous experimental data, and the comparison showed a good agreement. The study focused on the effect of oxygen partial pressure and temperature on the resulting combustion zones inside the reactor for the two cases of co‐current and counter‐current flow regimes. The results indicated that the oxygen to fuel mass ratio increases as the percentage of CO₂ increases in the inflow sweep gas for both co‐current and counter‐current flows. The obtained sweep mixture ratio (CO₂/CH₄) of 24 is found within the stoichiometric limit over most of the reactor length in the co‐current configuration, whereas the sweep mixture ratio of 15.67 is found in the counter‐current configuration owing to the high O₂ permeation. Copyright © 2012 John Wiley & Sons, Ltd.     

Effect of varying fuel types on oxy‐combustion performance

In search for clean energy solutions in a global warming era, oxy‐fuel combustion systems are promising. In the study, combustion products are calculated, and exergy analysis is done using the proposed multifeature equilibrium combustion model. And the results obtained for oxy‐combustion of different fuels at various oxygen fractions are given in comparison with conventional combustion. For validation, the model results are compared with popular combustion calculation tools, GASEQ and CEA. Effect of oxygen content on oxy‐combustion exergy analysis is calculated, also considering changes in equivalence ratio and combustion chamber inlet temperature. Moreover, indicating parameters for combustion performance, temperature ratio, chemical exergy, physical exergy, total specific exergy, and exergy destruction are utilized in the calculations elaborately. Changes in combustion product mole fractions are explained for rich and lean combustion regions. And also, specific exergy results are presented. In terms of exergy destruction, oxy‐combustion is more advantageous than conventional combustion. It has been shown that exergy destruction in combustion process with conventional air is approximately 1.5 times higher compared with 21% oxy‐combustion, both at different equivalence ratios and at different combustion chamber inlet temperatures. Nowadays, environment‐friendly, clean energy production systems are growing in numbers. In this concept, exergetic analyses of combustion for different fuels and greener natural gas, compared with diesel, gasoline, and methanol, are given in comparison. Considering four fuel types, advantageous and disadvantageous cases are presented for oxy‐combustion at different oxygen fractions and conventional combustion. As a result, diesel fuel is more advantageous than the other three fuel types, in terms of temperature ratio and exergy. Natural gas combustion appears to be disadvantageous in terms of specific exergy and temperature ratio, but it is the most advantageous in terms of exergy destruction. Consequently, distinctive comparison is done for oxy‐combustion and conventional combustion, determining positive and negative effects for different fuels.     

A review of recent developments in carbon capture utilizing oxy‐fuel combustion in conventional and ion transport membrane systems

Fossil fuels provide a significant fraction of the global energy resources, and this is likely to remain so for several decades. Carbon dioxide (CO₂) emissions have been correlated with climate change, and carbon capture is essential to enable the continuing use of fossil fuels while reducing the emissions of CO₂ into the atmosphere thereby mitigating global climate changes. Among the proposed methods of CO₂ capture, oxyfuel combustion technology provides a promising option, which is applicable to power generation systems. This technology is based on combustion with pure oxygen (O₂) instead of air, resulting in flue gas that consists mainly of CO₂ and water (H₂O), that latter can be separated easily via condensation, while removing other contaminants leaving pure CO₂ for storage. However, fuel combustion in pure O₂ results in intolerably high combustion temperatures. In order to provide the dilution effect of the absent nitrogen (N₂) and to moderate the furnace/combustor temperatures, part of the flue gas is recycled back into the combustion chamber. An efficient source of O₂ is required to make oxy‐combustion a competitive CO₂ capture technology. Conventional O₂ production utilizing the cryogenic distillation process is energetically expensive. Ceramic membranes made from mixed ion‐electronic conducting oxides have received increasing attention because of their potential to mitigate the cost of O₂ production, thus helping to promote these clean energy technologies. Some effort has also been expended in using these membranes to improve the performance of the O₂ separation processes by combining air separation and high‐temperature oxidation into a single chamber. This paper provides a review of the performance of combustors utilizing oxy‐fuel combustion process, materials utilized in ion‐transport membranes and the integration of such reactors in power cycles. The review is focused on carbon capture potential, developments of oxyfuel applications and O₂ separation and combustion in membrane reactors. The recent developments in oxyfuel power cycles are discussed focusing on the main concepts of manipulating exergy flows within each cycle and the reported thermal efficiencies. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental study on combustion of torrefied palm kernel shell (PKS) in oxy‐fuel environment

Oxy‐combustion of biomass can be a major candidate to achieve negative emission of CO₂ from a pulverized fuel (pf)‐firing power generation plants. Understanding combustion behavior of biomass fuels in oxy‐firing conditions is a key for design of oxy‐combustion retrofit of pulverized fuel power plant. This study aims to investigate a lab‐scale combustion behavior of torrefied palm kernel shell (PKS) in oxy‐combustion environments in comparison with the reference bituminous coal. A 20 kW_th‐scale, down‐firing furnace was used to conduct the experiments using both air (conventional) and O₂/CO₂ (30 vol% for O₂) as an oxidant. A bituminous coal (Sebuku coal) was also combusted in both air‐ and oxy‐firing condition with the same conditions of oxidizers and thermal heat inputs. Distributions of gas temperature, unburned carbon, and NO_x concentration were measured through sampling of gases and particles along axial directions. Moreover, the concentrations of SO_x and HCl were measured at the exit of the furnace. Experimental results showed that burnout rate was enhanced during oxy‐fuel combustion. The unburnt carbon in the flue gas was reduced considerably (~75%) during combustion of torrefied PKS in oxy‐fuel environment as compared with air‐firing condition. In addition, NO emission was reduced by 16.5% during combustion of PKS in oxy‐fuel environment as compared with air‐firing condition.     

Experimental and numerical analysis of oxy‐fuel combustion in a porous plate reactor

The present work focuses on studying experimentally and numerically the oxy‐fuel combustion characteristics inside a porous plate reactor towards the application of oxy‐combustion carbon capture technology. Initially, non‐reactive flow experiments are performed to analyze the permeation rate of oxygen in order to obtain the desired stoichiometric ratios. A numerical model is developed for non‐reactive and reactive flow cases. The model is validated against the presently recorded experimental data for the non‐reacting flow cases, and it is validated against the available literature data for oxy‐fuel combustion for the reacting flow cases. A modified two‐step oxy‐combustion reaction kinetics model for methane is implemented in the present model. Simulations are performed over wide range of operating oxidizer ratios (O₂/CO₂ ratio), from OR = 0.2 to OR = 0.4, and over wide range of equivalence ratios, from φ = 0.7 to φ = 1.0. The flame length was decreased as a result of the increase of the oxidizer ratio. Effects of CO₂ recirculation amount on the oxy‐combustion flame stability are examined. A reduction in combustion temperature and increase in flame fluctuations are encountered while increasing CO₂ concentration inside the reactor. At high equivalence ratio, the combustion temperature and flame stability are improved. At low equivalence ratio, the flame length is increased, and the flame was moved towards the reactor center line. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermogravimetric and composition analysis of Jordanian oil shale

Jordan occupies the eighth place in oil shale reserve in the world. Prospective efforts are directed toward the production of fuel from shale. Analysis of oil shale samples will help in planning for energy strategies. Oil shale samples were collected from Wadi Ash Shallala at Yarmouk Basin. X-ray fluorescence spectrometer and X-ray diffraction showed that calcite is the dominant mineral. Other minerals such as; Kaolinite, quartz, and Fluorapatite, were detected. Thermogravimetric analysis revealed that mass loss is due to organic matter decomposition at 350–550°C and carbonate and silicate decomposition at 650–850°C. Fourier transform infrared analysis revealed the main organic groups.     

Characteristic evaluation of a CO2‐capturing repowering system based on oxy‐fuel combustion and exergetic flow analyses for improving efficiency

A CO₂‐capturing H₂O turbine power generation system based on oxy‐fuel combustion method is proposed to decrease CO₂ emission from an existing thermal power generation system (TPGS) by utilizing steam produced in the TPGS. A high efficient combined cycle power generation system (CCPS) with reheat cycle is adopted as an example of existing TPGSs into which the proposed system is retrofitted. First, power generation characteristics of the proposed CO₂‐capturing system, which requires no modification of the CCPS itself, are estimated. It is shown through simulation study that the proposed system can reduce 26.8% of CO₂ emission with an efficiency decrease by 1.20% and an increase power output by 23.2%, compared with the original CCPS. Second, in order to improve power generation characteristics and CO₂ reduction effect of the proposed system, modifications of the proposed system are investigated based on exergetic flow analyses, and revised systems are proposed based on the obtained results. Finally, it is shown that a revised proposed system, which has the same turbine inlet temperature as the CCPS, can increase power output by 33.6%, and reduce 32.5% of CO₂ emission with exergetic efficiency decrease by 1.58%, compared with the original CCPS. Copyright © 2010 John Wiley & Sons, Ltd.     

Dust explosion of oil shale and olive cake solid fuels: a comparison study

This paper investigates the inhibition of oil shale and olive cake dust explosions when they are used as an alternative source of fuel. Special emphasis was given to the effect of particle size of the same material on the maximum permissible oxygen concentration to prevent dust explosion for different concentrations using nitrogen as the diluent gas. It was found that olive cake is ignited more easily than oil shale all over the range of particle sizes and dust concentration. Tests on different particle sizes were carried out, and it was found that the maximum permissible oxygen concentration for a given dust concentration increases with increasing the particle size for both oil shale and olive cake. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of coal characteristics to performance of a highly efficient thermal power generation system based on pressurized oxy‐fuel combustion

Because of its fuel flexibility and high efficiency, pressurized oxy‐fuel combustion has recently emerged as a promising approach for efficient carbon capture and storage. One of the important options to design the pressurized oxy‐combustion is to determine method of coal (or other solid fuels) feeding: dry feeding or wet (coal slurry) feeding as well as grade of coals. The main aim of this research is to investigate effects of coal characteristics including wet or dry feeding on the performance of thermal power plant based on the pressurized oxy‐combustion with CO₂ capture versus atmospheric oxy‐combustion. A commercial process simulation tool (gCCS: the general carbon capture and storage) was used to simulate and analyze an advanced ultra‐supercritical(A‐USC) coal power plant under pressurized and atmospheric oxy‐fuel conditions. The design concept is based on using pure oxygen as an oxidant in a pressurized system to maximize the heat recovery through process integration and to reduce the efficiency penalty because of compression and purification units. The results indicate that the pressurized case efficiency at 30 bars was greater than the atmospheric oxy‐fuel combustion (base line case) by 6.02% when using lignite coal firing. Similarly, efficiency improvements in the case of subbituminous and bituminous coals were around 3% and 2.61%, respectively. The purity of CO₂ increased from 53.4% to 94% after compression and purification. In addition, the study observed the effects of coal‐water slurry using bituminous coal under atmospheric conditions, determining that the net plant efficiency decreased by 3.7% when the water content in the slurry increased from 11.12% to 54%. Copyright © 2016 John Wiley & Sons, Ltd.     

我国燃料油供需状况分析及替代燃料的研究趋势

介绍了我国燃料油市场的供需现状及其形成原因,预测了燃料油市场未来走向。对替代燃料研究的发展趋势进行了简要分析,介绍了国内现有的替代燃料研究以及不同研究项目的特点、利弊。     

Preparation,characterization, engine combustion and emission characteristics of rapeseed oil based hybrid fuels

In this study, hybrid fuels consisting of rapeseed oil/diesel blend, 1% aqueous ethanol and a surfactant (oleic acid/1-butanol mixture) were prepared and tested as a fuel in a direct injection (DI) diesel engine. The main fuel properties such as the density, viscosity and lower heating value (LHV) of these fuels were measured, and the engine performance, combustion and exhaust emissions were investigated and compared with that of diesel fuel. The experimental results showed that the viscosity and density of the hybrid fuels were decreased and close to that of diesel fuel with the increase of ethanol volume fraction up to 30%. The start of combustion was later than that of diesel fuel and the peak cylinder pressure, peak pressure rise rate and peak heat release rate were higher than those of diesel fuel. The brake specific fuel consumption (BSFC) of hybrid fuels was increased with the volume fraction of ethanol and higher than that of diesel. The brake specific energy consumption (BSEC) was almost identical for all test fuels. The smoke emissions were lower than those for diesel fuel at high engine loads, the NO_x emissions were almost similar to those of diesel fuel, but CO and HC emissions were higher, especially at low engine loads.     

A review on the operating conditions of producing bio‐oil from hydrothermal liquefaction of biomass

Hydrothermal liquefaction (HTL) is a promising technology that involves converting biomass into a liquid energy carrier called bio‐oil in sub/supercritical water. The unique physico‐chemical properties of bio‐oil, particularly its remarkably high energy density, renewability, and sustainability, can address current global environmental challenges and energy crisis. This review assesses the influence of operating parameters, including biomass type, reaction temperature, holding time, biomass/H₂O ratio, heating rate, pressure, and atmosphere, and catalysis, on the yield and quality of bio‐oil. The existing problems in HTL are also analyzed, and its further development is explored. Copyright © 2016 John Wiley & Sons, Ltd.     

Bio‐oil,solid and gaseous biofuels from biomass pyrolysis processes—An overview

As the global demand for energy rapidly increases and fossil fuels will be soon exhausted, bio‐energy has become one of the key options for shorter and medium term substitution for fossil fuels and the mitigation of greenhouse gas emissions. Biomass currently supplies 14% of the world's energy needs. Biomass pyrolysis has a long history and substantial future potential—driven by increased interest in renewable energy. This article presents the state‐of‐the‐art of biomass pyrolysis systems, which have been—or are expected to be—commercialized. Performance levels, technological status, market penetration of new technologies and the costs of modern forms of biomass energy are discussed. Advanced methods have been developed in the last two decades for the direct thermal conversion of biomass to liquid fuels, charcoals and various chemicals in higher yields than those obtained by traditional pyrolysis processes. The most important reactor configurations are fluidized beds, rotating cones, vacuum and ablative pyrolysis reactors. Fluidized beds and rotating cones are easier for scaling and possibly more cost effective. Slow pyrolysis is being used for the production of charcoal, which can also be gasified to obtain hydrogen‐rich gas. The short residence time pyrolysis of biomass (flash pyrolysis), at moderate temperatures, is being used to obtain a high yield of liquid products (up to 70% wt), particularly interesting as energetic vectors. Bio‐oil can substitute for fuel oil—or diesel fuel—in many static applications including boilers, furnaces, engines and turbines for electricity generation. While commercial biocrudes can easily substitute for heavy fuel oils, it is necessary to improve the quality in order to consider biocrudes as a replacement for light fuel oils. For transportation fuels, high severity chemical/catalytic processes are needed. An attractive future transportation fuel can be hydrogen, produced by steam reforming of the whole oil, or its carbohydrate‐derived fraction. Pyrolysis gas—containing significant amount of carbon dioxide, along with methane—might be used as a fuel for industrial combustion. Presently, heat applications are most economically competitive, followed by combined heat and power applications; electric applications are generally not competitive. Copyright © 2011 John Wiley & Sons, Ltd.     

An investigation of thermal behaviour of biomass and coal during co‐combustion using thermogravimetric analysis (TGA)

The thermal behaviour and kinetic analysis of biomass (cypress wood chips and macadamia nut shells) and Australian bituminous coal during combustion were studies using the thermogravimetric technique with four different heating rates under an air atmosphere. Each type of biomass was blended with coal at mass ratios (biomass:coal) of 95:5, 90:10, 85:15 and 80:20 to investigate the effect of coal as a supplementary fuel on thermal behaviour during the combustion process. Combustion of the individual samples and the blends took place in three steps comprising dehydration, devolatilisation and char oxidation. During co‐combustion, the thermal decomposition behaviour of the blends followed that of the weighted average of the individual samples in the blends. In kinetic analysis, thermal decomposition of biomass and coal appeared to take place independently, and thus, the activation energy of the blends can be calculated from that of the two components. No evidence for any significant synergetic effects or thermal interaction was found between either type of biomass and the coal during co‐combustion based on the lack of deviation from expected behaviour of the blends. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative assessment of a biogas run dual fuel diesel engine with rice bran oil methyl ester,pongamia oil methyl ester and palm oil methyl ester as pilot fuels

The present study tries to explore the potential of three different types of biodiesel viz. Rice bran oil methyl ester (RBME), Pongamia oil methyl ester (PME) and Palm oil methyl ester (POME) as pilot fuels for a biogas run dual fuel diesel engine designed for power generation. The results indicated that under dual fuel mode, RBME-biogas produced a maximum brake thermal efficiency of 19.97% in comparison to 18.4% and 17.4% respectively for PME-biogas and POME-biogas at 100% load. The emission study divulged that under dual fuel mode, on an average, there was an increase of CO emission by 25.74% and 32.58% for PME-biogas and POME-biogas, respectively in comparison to RBME-biogas. Furthermore, on an average, the HC emissions for PME-biogas and POME-biogas increased by 11.73% and 16.27%, respectively in comparison to RBME-biogas. On the other hand, on an average, there was a decrease in NO_X emission by 5.8% and 14%, respectively for PME-biogas and POME-biogas respectively in comparison to RBME-biogas.     

Bio‐oil production from rapid pyrolysis of cottonseed cake: product yields and compositions

Fixed‐bed fast pyrolysis experiments have been conducted on a sample of cottonseed cake to determine the effects of pyrolysis temperature, heating rate and sweep gas flow rate on pyrolysis yields and chemical compositions of the product oil. The liquid products and the subfractions of pentane soluble part were characterized by elemental analysis, FT‐IR spectroscopy, ¹H‐NMR spectroscopy and pentane subfraction was analysed by gas chromatography. The maximum oil yield of 34.8% was obtained at final temperature of 550°C with a heating rate of 700°C min^?1 and nitrogen flow rate of 100 cm³ min^?1. Chromatographic and spectroscopic studies on bio‐oil have shown that the oils obtained from cottonseed cake can be used as a renewable fuel and chemical feedstock. Copyright © 2005 John Wiley & Sons, Ltd.     

A comprehensive study on performance,emission and combustion behavior of a compression ignition engine fuelled with WCO (waste cooking oil) emulsion as fuel

This work aims at evaluating the performance, emission and combustion of a diesel engine fuelled with WCO (waste cooking oil obtained from palm oil) and its emulsion as fuel. A single cylinder water-cooled diesel engine was used. Base data was generated with diesel and neat WCO as fuels. Subsequently, WCO oil was converted into its emulsion and tested. Neat WCO resulted in higher smoke, hydrocarbon and carbon monoxide emissions as compared to neat diesel. Significant reduction in all emission was achieved with the WCO emulsion. Cylinder peak pressure and maximum rate of pressure rise were found to be higher with WCO emulsion as compared to neat WCO mainly at high power outputs. Ignition delay was found as higher with neat WCO and its emulsion. It is concluded that WCO emulsion can be used in diesel engines without any modifications in the engine with superior performance and reduced emissions at high power outputs.     

Design and simulation of a novel bipolar plate based on lung‐shaped bio‐inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung‐shaped bipolar plate was modeled. Simulations in this research showed that the lung‐shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung‐shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.