Detonations in hydrocarbon fuel blends

A study of detonations in high-molecular weight hydrocarbon fuels of interest to pulse detonation engine applications was performed in a 280-mm diameter, 7.3-m long facility. Detonation pressure, wave speed, and cell width measurements were made in JP-10 mixtures and in mixtures representative of the decomposition products of JP-10.Experiments were performed in vapor-phase JP-10 mixtures at 353 K over a range of equivalence ratios (0.7 ≤ φ ≤ 1.4), nitrogen dilutions (fuel-oxygen to fuel-air), and initial pressures (20–130 kPa). The cell widths of the JP-10 mixtures are found to be similar to those of propane mixtures. A fuel blend representative of thermally decomposed JP-10 was studied at 295 K. This blend consisted of hydrogen, carbon monoxide, methane, acetylene, ethylene, and hexane with varying fractions of oxygen and nitrogen. The measured cell width of the fuel blend-air mixture is about half that of JP-10-air. The addition of components of the fuel blend (acetylene, ethylene, and methane) to JP-10 in air at 353 K was characterized.Nitrogen diluted mixtures of stoichiometric hexane-oxygen were studied and the cell widths for hexane-air and JP-10-air are found to be comparable. The addition of lower molecular weight fuels (hydrogen, acetylene, ethylene, and carbon monoxide) to hexane-air was investigated. The measured cell width decreases, indicating increased sensitivity to detonation, with increasing fraction of hydrogen, acetylene, and ethylene, in order of effectiveness. The addition of a small fraction of carbon monoxide produces a small decrease in the cell width, but addition of more than about 75% (by fuel mass) carbon monoxide results in a significant increase in cell width.Carbon monoxide is a principal intermediate product of hydrocarbon combustion yet there are relatively little cell width data available. Cell width measurements were made in carbon monoxide-air mixtures with the addition of hydrogen or hydrocarbons (acetylene, ethylene, and hexane). A linear relationship is found between the cell width and the reaction zone length when it is defined as the location of the peak in hydroxyl mole fraction.     

Model of accelerating coal dust flames

A model describing turbulent coal dust flame propagation and accelaration is based on the transient, macroscopic equations of change. The turbulent flame velocity was obtained from a simple correlative technique combining turbulence and chemical effects. Predictions indicate that a deflegrating coal dust flame can accelerate to high velocity and pressure, with increasing turbulence a major cause of the acceleration. A parametric study was conducted to identify key parameters in the model. The need for turbulent flame velocity data for particle-laden systems was identified and the effects of duct diameter, coal particle diameter, and various model parameters were described. The model is useful for describing relative effects of various parameters.     

Modelling of the process of coal dust combustion in a cyclone furnace

This study presents the concept of a cyclone furnace for coal dust oxy-fuel combustion and gasification.The results of numerical calculations for the combustion and gasification processes were also presented.     

煤的富氧气化特性研究

根据煤不同组分和不同反应阶段的特点,实施煤的热解、气化、燃烧分级转化,可以使煤气化技术简化,并有效解决煤中污染物的脱除问题。基于分级转化的思想,在小型流化床实验台上,采用枣庄烟煤为主要原料,研究了氧气浓度和空煤比对气化过程的影响,并与空气气化的结果进行对比分析,可为研究煤部分气化及半焦燃烧集成提供理论依据。     

An experimental study of coal dust ignition in wedge shaped hot plate configurations

Ignition behavior of bituminous coal dust deposited between two hot surfaces forming wedges of 60°, and 90° is experimentally studied. Three thermocouples placed along the symmetry plane of the wedge cross-section at various heights from the apex (lowermost, middle and top) are used to record the transient temperature data. Results show that ignition always occurs around the region surrounding the top thermocouple in the case of 60° wedge and both the top and the middle regions in the case of 90° wedge. The trends are explained by investigating three parameters affecting the ignition behavior, namely, the heat transfer from the hot plate to the coal dust, the subsequent chemical heat release, and the heat transfer between different regions within the coal dust. Furthermore, an experimental setup, similar to the standard ASTM E 2021 test, is used to determine the minimum ignition temperatures of coal layers of various thicknesses and to assess the ignition scenario in the wedge configuration using an effective length scale. Measured quantities such as minimum hot plate temperature that causes ignition and the ignition time, as well as the transient heat release rate and heat conducted between various zones, calculated based on the temperature data are used to quantify the three parameters and their effects on ignition behavior.     

Evaluation of oxygen as oxidant in coal fired open cycle MHD-steam power plants

This study compares the thermal efficiency and economics of using oxygen rather than air as the oxidant in large coal-fired MHD-steam energy conversion plants, using a computer model to calculate thermal efficiency. The systems compared are a coal-air system with a thermal input of 2000 MW_th and two coal-oxygen systems, one with an input of 2000 MW_th and one with 6600 MW_th. The paper describes the process; compares flame temperature, electrical conductivity, and specific enthalpy; and presents Mollier diagrams for the two systems. At an oxidant preheat temperature of 1644 K, the net thermal efficiency of the coal-oxygen system is 8 to 9 percentage points lower than that for the coal-air system, if the power required to produce the oxygen is taken into account; however, despite its lower thermal efficiency, the coal-oxygen system has a lower cost of electricity. At a preheat temperature of 1644 K, the cost advantage is small, but at temperatures below 1200 K, the cost advantage is significant.     

Chemical looping combustion of Victorian brown coal using NiO oxygen carrier

This study is part of a program assessing the suitability of chemical looping for direct combustion of Victorian brown coal. The performance of NiO as an oxygen carrier in presence of a dried Victorian brown coal was assessed during five alternating cycles of reduction and oxidation in a CO₂ environment using a TGA. The experiments indicate a 4.4-7.5% weight loss of the oxygen carrier per cycle. Preliminary SEM-EDX and FACTSAGE predictions also indicate weight loss, but not to the same extent. The percentage of combustion of coal achieved at the 5th cycle was approximately 67%. Cycle 2 showed maximum reactivity (during reduction) with a decreasing trend during the subsequent cycles. These initial experiments did not reveal much agglomeration between ash and NiO although longer duration experiments are required to explore this issue further.     

Numerical simulation of pulverized coal MILD-oxy combustion under different oxygen concentrations

As an emerging clean coal combustion technology, Moderate or Intense Low-Oxygen Dilution (MILD) combustion or oxy-fuel combustion, compared with traditional coal combustion, has many advantages. However, compared with MILD combustion and oxy-fuel combustion, MILD-oxy combustion is believed more attractive. In this work, MILD-oxy combustion characteristics with oxygen concentrations from 10% to 50% are studied numerically. The results show that within a certain range, increasing the oxygen concentration is in favor of MILD-oxy combustion performance close to that of MILD-air combustion. When the oxygen concentration is higher enough, the momentum reduced by the increase of oxygen concentration has a great influence on the furnace temperature. With the increase of oxygen concentration, the radiation heat transfer is enhanced and the convective heat transfer is weakened. The increase of oxygen concentration can promote the occurrence of char gasification reaction with CO₂. In addition, MILD-oxy combustion has a large impact on CO emission.     

Pressurized chemical-looping combustion of coal with an iron ore-based oxygen carrier

Chemical-looping combustion (CLC) is a new combustion technology with inherent separation of CO₂. Most of the previous investigations on CLC of solid fuels were conducted under atmospheric pressure. A pressurized CLC combined cycle (PCLC-CC) system is proposed as a promising coal combustion technology with potential higher system efficiency, higher fuel conversion, and lower cost for CO₂ sequestration. In this study pressurized CLC of coal with Companhia Valedo Rio Doce (CVRD) iron ore was investigated in a laboratory fixed bed reactor. CVRD iron ore particles were exposed alternately to reduction by 0.4 g of Chinese Xuzhou bituminous coal gasified with 87.2% steam/N₂ mixture and oxidation with 5% O₂ in N₂ at 970 °C. The operating pressure was varied between 0.1 MPa and 0.6 MPa. First, control experiments of steam coal gasification over quartz sand were performed. H₂ and CO₂ are the major components of the gasification products, and the operating pressure influences the gas composition. Higher concentrations of CO₂ and lower fractions of CO, CH₄, and H₂ during the reduction process with CVRD iron ore was achieved under higher pressures. The effects of pressure on the coal gasification rate in the presence of the oxygen carrier were different for pyrolysis and char gasification. The pressurized condition suppresses the initial coal pyrolysis process while it also enhances coal char gasification and reduction with iron ore in steam, and thus improves the overall reaction rate of CLC. The oxidation rates and variation of oxygen carrier conversion are higher at elevated pressures reflecting higher reduction level in the previous reduction period. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analyses show that particles become porous after experiments but maintain structure and size after several cycles. Agglomeration was not observed in this study. An EDX analysis demonstrates that there is very little coal ash deposited on the oxygen carrier particles but no appreciable crystalline phases change as verified by X-ray diffraction (XRD) analysis. Overall, the limited pressurized CLC experiments carried out in the present work suggest that PCLC of coal is promising and further investigations are necessary.     

Interaction between bimetallic composite oxygen carriers and coal and its contribution to coal direct chemical looping gasification

Coal direct chemical looping gasification (CDCLG) to produce synthesis gas was investigated with Fe-based bimetallic composite oxygen carriers (Fe–M oxides, M = Ba, Ca, Cu, Ni and Co). Thermogravimetric-mass spectrum analysis and fixed-bed tests indicated that reaction between coal and Fe-based composite oxygen carriers via direct contact could not be negligible in the CDCLG process. The contribution of the reaction between the two solid particles to the carbon conversion was estimated. Furthermore, the yields of synthesis gas production were also conducted to evaluate performance for the prepared samples. Of the five investigated Fe-based bimetallic composite oxygen carriers (OCs), Fe–Ni oxides/Al₂O₃ presented high reactivity with coal and high selectivity for synthesis gas during coal-OC steam gasification, which made it attractive for the CDCLG process. By comparing with the main phases of the Fe-based OCs after cycling and the raw samples before test, it could be observed that there were no significant changes in material phases. Combined with the SEM images of the Fe-based OCs samples, we can conclude that the prepared OCs showed a good heat-resistant property, which was beneficial for keeping a stable performance in the CDCLG experiment.     

Measured effects of light intensity and catalyst concentration on photocatalytic hydrogen and oxygen production with zinc sulfide suspensions

In this paper, an experimental study is performed for hydrogen and oxygen production by new photo-catalytic and electro-catalytic water splitting systems. An effective method for hydrogen production by solar energy without consumption of additional reactants is a hybrid system which combines photo-chemical and electro-catalytic reactions. Experiments are performed in batch and dual cell quasi-steady operation with different light intensities and zinc sulfide photo-catalyst concentrations. The photo-reactor in batch operation achieves 6 mL h⁻¹ of hydrogen production with 3% w/v of catalyst. The hydrogen production rate corresponds to a quantum efficiency of 75% as measured through illumination of zinc sulfide suspensions in a dual cell reactor.     

Experiments on chemical looping combustion of coal with a NiO based oxygen carrier

A chemical looping combustion process for coal using interconnected fluidized beds with inherent separation of CO₂ is proposed in this paper. The configuration comprises a high velocity fluidized bed as an air reactor, a cyclone, and a spout-fluid bed as a fuel reactor. The high velocity fluidized bed is directly connected to the spout-fluid bed through the cyclone. Gas composition of both fuel reactor and air reactor, carbon content of fly ash in the fuel reactor, carbon conversion efficiency and CO₂ capture efficiency were investigated experimentally. The results showed that coal gasification was the main factor which controlled the contents of CO and CH₄ concentrations in the flue gas of the fuel reactor, carbon conversion efficiency in the process of chemical looping combustion of coal with NiO-based oxygen carrier in the interconnected fluidized beds. Carbon conversion efficiency reached only 92.8% even when the fuel reactor temperature was high up to 970 °C. There was an inherent carbon loss in the process of chemical looping combustion of coal in the interconnected fluidized beds. The inherent carbon loss was due to an easy elutriation of fine char particles from the freeboard of the spout-fluid bed, which was inevitable in this kind of fluidized bed reactor. Further improvement of carbon conversion efficiency could be achieved by means of a circulation of fine particles elutriation into the spout-fluid bed or the high velocity fluidized bed. CO₂ capture efficiency reached to its equilibrium of 80% at the fuel reactor temperature of 960 °C. The inherent loss of CO₂ capture efficiency was due to bypassing of gases from the fuel reactor to the air reactor, and the product of residual char burnt with air in the air reactor. Further experiments should be performed for a relatively long-time period to investigate the effects of ash and sulfur in coal on the reactivity of nickel-based oxygen carrier in the continuous CLC reactor.     

An experimental study on ignition of single coal particles at low oxygen concentrations

An experimental study on the ignition of single coal particles at low oxygen concentrations (X_{{\mathrm{O}}_2}<21%) was conducted using a tube furnace. The surface temperature (T_s) and the center temperature (T_c) of the coal particles were obtained from the images taken by an infrared camera and thermocouples respectively. The ignition processes were recorded by a high-speed camera at different X_{{\mathrm{O}}_2} values and furnace temperatures T_w. Compared with literature experimental data obtained at a high X_{{\mathrm{O}}_2} value, the ignition delay time t_i decreases more rapidly as X_{{\mathrm{O}}_2} increases at the low X_{{\mathrm{O}}_2} region. The responses of T_s and T_c to the variation of X_{{\mathrm{O}}_2} are different: T_s decreases while T_c remains nearly constant with increasing X_{{\mathrm{O}}_2} at a low X_{{\mathrm{O}}_2} value. In addition, t_i is less sensitive to T_w while the ignition temperature T_i is more sensitive to T_w at a low X_{{\mathrm{O}}_2} value than in air. Observations of the position of flame front evolution illustrate that the ignition of a coal particle may change from a homogeneous mode to a heterogeneous or combined ignition mode as X_{{\mathrm{O}}_2} decreases. At a low X_{{\mathrm{O}}_2} value, buoyancy plays a more significant role in sweeping away the released volatiles during the ignition process.     

Effects of oxygen concentration on the macroscopic characteristic indexes of high-temperature oxidation of coal

To explore the macroscopic characteristic indexes for oxidation of coal under high-temperature conditions, an XKGW-1-type high-temperature-programmed heating experimental system was constructed. Tests on high-temperature oxidation of coal under high-temperature conditions at five oxygen concentrations of 21, 17, 13, 8, and 3 vol% were independently conducted. Laws of variation in high-temperature oxidation of coal indices, such as the coal temperature, gas ratios, rate of oxygen consumption, and exothermic strength from indoor temperature to 500 °C, were investigated at those oxygen concentrations. The results showed that the variation tendencies of characteristic indices for high-temperature oxidation of coal at different oxygen concentrations were extremely intricate. At the five oxygen concentrations, the rate of oxygen consumption increased rapidly with an increase in coal temperature and eventually remained at a higher range. The rate of oxygen consumption increased with temperature with an approximate exponential trend at the five oxygen concentrations tested. For the same coal temperature, the rate of oxygen consumption decreased with the oxygen concentration. The variation tendencies of the CO and CO₂ production rates were similar, both increased rapidly with an increase in coal temperature in the early stages and reached a maximum at a coal temperature of 380 °C. They decreased slightly with an increase in coal temperature at first and increased promptly thereafter. The concentrations of CH₄, C₂H₄, and C₂H₆ first increased with an increase in the coal temperature and markedly decreased after the maximal value. The temperatures for the extreme points were 480, 410, and 420 °C for CH₄, C₂H₄, and C₂H₆, respectively. The trends of the macroscopic characteristic indexes throughout the process of high-temperature oxidation of coal in a certain temperature range at various oxygen concentrations can be used for temperature prediction and fire prevention during coal mining.     

滤槽除尘器在静电除尘器改造中的应用

介绍了滤槽除尘器的结构，材料及除尘原理，滤槽除尘器在不同工况下的除法效率，附加脱硫率，阻力和排放浓度等参数的测试结果，利用滤槽除尘器时的改造方案，运行中应注意的问题及实验机的运行情况。     

Co-combustion of low rank coal/waste biomass blends using dry air or oxygen

Biomass species such as the rice husk and the olive milling residue, and a low quality Turkish coal, Soma Denis lignite, were burned in a thermal analyzer under pure oxygen and dry air up to 900 °C, and differential thermal analysis (DTA) and derivative thermogravimetric (DTG) analysis profiles were obtained. Co-combustion experiments of lignite/biomass blends containing 5–20 wt% of biomass were also performed. The effects of the oxidizer type and the blending ratio of biomass were evaluated considering some thermal reactivity indicators such as the maximum burning rate and its temperature, the maximum heat flow temperature, and the burnout levels. FTIR (Fourier transform infrared) spectroscopy and SEM (scanning electron microscopy) were used to characterize the samples, and the variations in the combustion characteristics of the samples were interpreted based on the differences in the intrinsic properties of the samples.     

Comparison of CuO and NiO as oxygen carrier in chemical looping combustion of a Victorian brown coal

Chemical looping combustion (CLC) is a novel process where an oxygen carrier, preferably oxides of metal, is used to transfer oxygen from the combustion air to the fuel. The outlet gas from the process reactor consists of CO₂ and H₂O, and concentrated stream of CO₂ is obtained for sequestration when water vapour is condensed. Chemical looping has been widely studied for combustion of natural gas; however its application to solid fuels, such as coal, is being studied relatively recently; no work has been done using Victorian brown coal which represents a very large resource, over 500 years at current consumption rate. In this study we carried out an experimental investigation pertaining to CLC of a Victorian brown coal from Loy Yang mine using NiO and CuO as oxygen carrier. The experiments were conducted using a thermogravimetric analyser (TGA) under CO₂ gasification environment with NiO and CuO. The reduction and re-oxidation of NiO in five repeated cycle operations were performed at 950 °C. However, the same cyclic operation for CuO was performed at 800 °C, as it was observed that at 950 °C CuO could not be re-oxidized to its original state due to sintering, which significantly altered the morphology. The extent of coal combustion and re-oxidation of metal oxides resulted in a 4.4-7.5% weight loss of NiO per cycle. No such weight loss was observed in case of CuO at 800 °C. The high reactivity of CuO was observed as compared to NiO during cyclic operation. The percentage of combustion at the end of the 5th cycle with CuO was 96% as compared to 67% with NiO. Fresh oxide particles and solid residues are characterized using SEM to understand surface morphological changes due to combustion. The energy dispersive X-rays (EDX) helped to get surface elemental information, albeit qualitative, of fresh and used metal oxide particles. The current study, for the first time, has generated practical information on the temperature range, approximate time, and percent combustion that can be achieved while using NiO and CuO as oxygen carriers during CLC with Loy Yang brown coal. Based on these results the ongoing work includes long duration experiments with Loy Yang and other Victorian brown coals.     

Iron ore as oxygen carrier improved with potassium for chemical looping combustion of anthracite coal

Chemical looping combustion (CLC) is an innovative combustion technology with inherent separation of CO₂ without energy penalty. When solid fuel is applied in CLC, the gasification of solid fuel is the rate-limiting process for in situ gasification of coal and reduction of oxygen carrier. The K₂CO₃-decorated iron ore after calcinations was used as oxygen carrier in CLC of anthracite coal, and potassium ferrites were formed during the calcinations process. The experiments were performed in a laboratory fluidized bed reactor with steam as a gasification medium. Effects of reaction temperature, K₂CO₃ loading in iron ore and cycle on the gas concentration, carbon conversion, gasification rate and yields of carbonaceous gases were investigated. The carbon gasification was accelerated during the fast reaction stage between 860 °C and 920 °C, and the water–gas shift reaction was significantly enhanced in a wider temperature range of 800 °C to 920 °C. With the K₂CO₃ loading in iron ore increasing from 0% to 20% at 920 °C, the carbon conversion was accelerated in the fast reaction stage, and the fast reaction stage became shorter. The yield of CO₂ reached a maximum of 94.4% and the yield of CO reached a minimum of 3.4% when use the iron ore loaded with 6% K₂CO₃. SEM analysis showed that the K₂CO₃-decorating in iron ore would cause a sintering on the particle surface of oxygen carrier, and the K₂CO₃ loading in iron ore should not be too high. Cycle experiments indicate that the K₂CO₃-decorated iron ore has a relative stable catalytic effect in the CLC process.     

Conversion of brown coal in supercritical water without and with addition of oxygen at continuous supply of coal-water slurry

A study of conversion of organic matter of brown coal in supercritical water (SCW) at 30 MPa, 400−760 °C and continuous supply of coal-water slurry (CWS) into a tubular reactor is presented. It was found that 48−63% (depending on the SCW temperature) of coal organic matter (COM) is ejected from CWS coal particles as liquid and gaseous products when they move through the reactor. We termed this stage of SCW conversion as dynamic conversion (DC) of coal. It turns out that the particles which underwent the DC stage did not aggregate in the reactor during static conversion (SC) within a coal layer due to continuous pumping through this layer. The experimental data on the composition of DC and SC products, degree of coal conversion, and the data on the degree of combustion of carbon in the presence of oxygen are given.     

Characterization of chemical looping combustion of coal in a 1 kWth reactor with a nickel-based oxygen carrier

Chemical looping combustion is a novel technology that can be used to meet the demand on energy production without CO₂ emission. To improve CO₂ capture efficiency in the process of chemical looping combustion of coal, a prototype configuration for chemical looping combustion of coal is made in this study. It comprises a fast fluidized bed as an air reactor, a cyclone, a spout-fluid bed as a fuel reactor and a loop-seal. The loop-seal connects the spout-fluid bed with the fast fluidized bed and is fluidized by steam to prevent the contamination of the flue gas between the two reactors. The performance of chemical looping combustion of coal is experimentally investigated with a NiO/Al₂O₃ oxygen carrier in a 1 kW_th prototype. The experimental results show that the configuration can minimize the amount of residual char entering into the air reactor from the fuel reactor with the external circulation of oxygen carrier particles giving up to 95% of CO₂ capture efficiency at a fuel reactor temperature of 985 °C. The effect of the fuel reactor temperature on the release of gaseous products of sulfur species in the air and fuel reactors is carried out. The fraction of gaseous sulfur product released in the fuel reactor increases with the fuel reactor temperature, whereas the one in the air reactor decreases correspondingly. The high fuel reactor temperature results in more SO₂ formation, and H₂S abatement in the fuel reactor. The increase of SO₂ in the fuel reactor accelerates the reaction of SO₂ with CO to form COS, and COS concentration in the fuel reactor exit gas increases with the fuel reactor temperature. The SO₂ in the air reactor exit gas is composed of the product of sulfur in residual char burnt with air and that of nickel sulfide oxidization with air in the air reactor. Due to the evident decrease of residual char in the fuel reactor with increasing fuel reactor temperature, it results in the decrease of residual char entering the air reactor from the fuel reactor, and the decrease of SO₂ from sulfur in the residual char burnt with air in the air reactor.