Effects of fractal surface on rheological behavior and combustion kinetics of modified brown coal water slurries

The paper reports the effects of surface fractal structures on the rheological behavior and combustion kinetics of raw brown coal and three modified coal water slurries （CWSs）. The results show that the fractal structures and physicochemical properties of samples are dependent on various modification processes. The apparent viscosities of the coal water slurries increase with increasing surface fractal dimensions （D）, especially with decreasing shear rates. Fur- thermore, it has been proved that the ignition temperatures and apparent activation energies of modified CWSs are lower than that of raw coal water slurry. Compared with the traditional qualitative analysis of the effect of pore structures on CWSs properties, D can more efficiently indicate the quantificational effect of pore structures on the rheological behavior and combustion kinetics of CWSs.

Kinetic analysis and modeling of maize straw hydrochar combustion using a multi-Gaussian-distributed activation energy model

Combustion kinetics of the hydrochar was investigated using a multi-Gaussian-distributed activation energy model(DAEM)to ex-pand the knowledge on the combustion mechanisms.The results demonstrated that the kinetic parameters calculated by the multi-Gaussian-DAEM accurately represented the experimental conversion rate curves.Overall,the feedstock combustion could be divided into four stages:the decomposition of hemicellulose,cellulose,lignin,and char combustion.The hydrochar combustion could in turn be divided into three stages:the combustion of cellulose,lignin,and char.The mean activation energy ranges obtained for the cellulose,lignin,and char were 273.7-292.8,315.1-334.5,and 354.4-370 kJ/mol,respectively,with the standard deviations of 2.1-23.1,9.5-27.4,and 12.1-22.9 kJ/mol,re-spectively.The cellulose and lignin contents first increased and then decreased with increasing hydrothermal carbonization(HTC)temperature,while the mass fraction of char gradually increased.

Combustion characteristics and kinetics of anthracite with added chlorine

The combustion process of Yangquan anthracite（YQ） with the addition of 0.045wt%, 0.211wt%, 1.026wt%, and 2.982wt% chlorine was investigated using a thermogravimetric method from an ambient temperature to 1173 K in an air atmosphere. Results show that the YQ combustion characteristics are not significantly affected by an increase in chlorine content. Data acquired for combustion conversion are then further processed for kinetic analysis. Average apparent activation energies determined using the model-free method（specifically the KAS method） are 103.025, 110.250, 99.906, and 110.641 k J/mol, respectively, and the optimal kinetic model for describing the combustion process of chlorine-containing YQ is the nucleation kinetic model, as determined by the z（α） master plot method. The mechanism function of the nucleation kinetic model is then employed to estimate the pre-exponential factor, by making use of the compensation effect. The kinetic models to describe chlorine-containing YQ combustion are thus obtained through advanced determination of the optimal mechanism function, average apparent activation energy, and the pre-exponential factor.

Effect of binder addition on combustion characteristics of cotton straw pellets and kinetic analysis

In this study,the combustion characteristics and kinetics of cotton straw(CS)particles mixed with polyethylene(PE)film and coal gangue(CG)were investigated.The co-combustion characteristics of CS mixed with PE and CG at different heating rates were revealed by the thermogravimetric method and differential thermogravimetric method.The ignition temperature,burnout temperature,and maximum weight loss rate were measured,and the comprehensive combustion and flammability indexes were calculated.The results showed that the composite combustion characteristic index and flammability index increased with the increase in heating rate.The addition of PE and CG additives could effectively extend the combustion time.The Coats-Redfern(C-R)reaction model and N-order reaction model were used to evaluate the kinetic parameters of the blends.The results showed that 12.5%PE+12.5%CG particles had the lowest activation energy(Ea=103.73 kJ·mol^(-1))at the volatile combustion stage.The dynamics conform to the third-order dynamics model.In addition,the applicability of C-R model,Flynn-Wall-Ozawa(FWO)model,and Starink model in the calculation of activation energy was explored,and it was found that the FWO model is not suitable for the calculation of activation energy of biomass pellet combustion kinetics.This study provides a new method for the development and utilization of mixed fuel particles of cotton stalk and solid waste and expands the application prospect of biomass.

Relationship between proximate analysis parameters and combustion behaviour of high ash Indian coal

This work presents the analysis of combustion characteristics of high ash Indian coal(28%-40%)collected from different mines of Singaurali coalfield,India.All the coal samples were characterized by proximate and gross calorific value analysis.Combustion performance of the coals were characterised using thermo-gravimetric analysis to identify the burning profile of individual coals.Various combustion kinetic parameters such as ignition temperature,peak temperature and burnout temperature,ignition index and burnout index,combustion performance index plus rate and intensity index of combustion process,activation energy were determined to analyse the combustion behaviour of coal.Further all these combustion properties were compared with the volatile matter,ash,fixed carbon and fuel ratio of each coal.Theoretical analysis shows that with increase in ash content,combustion performance initially increases and later descends.Further,coal with(25±1.75)%volatile matter,20%-35%ash and fuel ratio 1.4-1.5 were found to be optimum for coal combustion.

Combustion of Sewage Sludge as Alternative Fuel for Cement Industry

The combustion of sewage sludge and coal was studied by thermogravimetric analysis.Both differential scanning calorimetric analysis and derivative thermogravimetric profiles showed differences between combustion of sewage sludge and coal,and non-isothermal kinetics analysis method was applied to evaluate the combustion process.Based on Coats-Redfern integral method,some reaction models were tested,the mechanism and kinetics of the combustion reaction were discussed.The results show that the combustion of sewage sludge is mainly in the low temperature stage,meanwhile the ignition temperature and Arrhenius activation energy are lower than that of coal.The combustion of sewage sludge has the advantage over coal in some aspects,thus sewage sludge can partly replace coal used as cement industry fuel.

Effect of plasma on combustion characteristics of boron

As it is very difficult to release boron energy completely, kinetic mechanism of boron is not clear, which leads to the lack of theoretical guidance for studying how to accelerate boron combustion. A new semi-empirical boron combustion model is built on the King combustion model, which contains a chemical reaction path; two new methods of plasma-assisted boron combustion based on kinetic and thermal effects respectively are built on the ZDPLASKIN zero-dimensional plasma model. A plasma-supporting system is constructed based on the planar flame, discharge characteristics and the spectral characteristics of plasma and boron combustion are analyzed. The results show that discharge power does not change the sorts of excited-particles, but which can change the concentration of excited-particles. Under this experimental condition,plasma kinetic effect will become the strongest at the discharge power of 40 W; when the discharge power is less than 40 W,plasma mainly has kinetic effect, otherwise plasma has thermal effect. Numerical simulation result based on plasma kinetic effect is consistent with the experimental result at the discharge power of 40 W, and boron ignition delay time is shortened by 53.8% at the discharge power of 40 W, which indicates that plasma accelerates boron combustion has reaction kinetic paths, while the ability to accelerate boron combustion based on thermal effect is limited.

Effect of Oxygen-Rich Combustion on Flame Propagation of Syngas in a Half-Open Pipe at Elevated Temperatures

The investigation of syngas flame propagation has great benefits for the effective use of gas turbines.This essay sets out to study the flame propagation of premixed oxygen-rich combustion(oxygen enrichment coefficient in volumeΩ:0.21,0.27,0.32,0.37)of syngas(H_(2):CO=2:8)in half-closed rectangular ducts at elevated temperatures(T:300 K,400 K,500 K)and evaluate the effects of initial temperature and oxygen enrichment coefficient on the LBV from sensitivity analysis and kinetic analysis.This paper presents the effect of the expansion effect on laminar burning velocity for the first time,and separates the effect of the expansion effect on laminar burning velocity by a new method.Research shows that as the initial temperature goes up,the faster the exponential growth phase of the flame front velocity,the slower the slow growth phase.The smaller and earlier the maximum flame front velocity arrives,the slower the average flame speed is.As the oxygen enrichment coefficient goes up,the peak value of the flame front velocity gradually decreases.Oxygen-rich combustion and increasing initial temperature inhibit flame propagation in a half-open tube,but promote laminar burning velocity,which increases the key chemical bond and adiabatic flame temperature.The net reaction rate shows that oxygen-rich combustion mainly promotes the combustion reaction of H_(2)(R2).However,increasing the initial temperature mainly promoted the oxidation of CO(R29).Analysis of the reaction path showed that oxygen-rich combustion and increased initial temperature promoted the reaction of H_(2)and CO with key chemical bonds,increased OH concentration,and inhibited OH cracking reaction.

Influences of different diluents on ignition delay of syngas at gas turbine conditions：A numerical study

Ignition delay of syngas is an important factor that affects stable operation of combustor and adding diluents to syngas can reduce NO_x emission.This paper used H_2O,CO_2 and N_2 as diluents and calculated ignition delay of syngas in temperature range of 900-1400 K and at pressures of 10 and 30 atm respectively.In high temperature range,comparing with N_2 dilution,adding H_2O and CO_2 can significantly inhibit autoignition of syngas because they have higher collision efficiencies in reaction H + O_2(+ M) = HO_2(+ M).As for low temperature conditions,adding H_2O can increase reactivity of syngas,especially under high pressure,because of its high collision efficiency in reaction H_2O_2(+ M) = 2OH(+ M).Comparing with different dilution rates shows that for syngas and operating conditions in this paper,adding N_2 mainly influences temperature rising process of syngas combustion,thus inhibiting reactivity of syngas.In addition,this paper calculated ignition delay of syngas at different equivalence ratios(φ= 0.5,1.0).Higher equivalence ratio(φ≤1) means that less air(especially N_2) needs to be heated,thus promoting ignition of syngas,

Thermogravimetric kinetic analysis of Nannochloropsis oculata combustion in air atmosphere

The thermal behavior of Nannochloropsis oculata combustion in air atmosphere were investigated by performing experiments on STA PT1600 Thermal Analyzer at heating rates of 10℃/min, 40℃/min and 70℃/min and range of temperatures from room tempera- ture to 1200℃. The kinetic parameters were evaluated by using Kissinger and Ozawa methods. The result showed that Nannochloropsis oculata combustion occurred in five stages. Started with initial devolatilization, the main thermal decomposition and combustion process, transition stage, the combustion of char and the last stage was the slow burning reaction of residual char. In line with increasing heating rate, the mass loss rate increased as well, but it delayed the thermal decomposition processes toward higher temperatures. The average activation energy at the main thermal decomposition stage and the stage of char combustion were approximately 251 kJ/mol and 178 kJ/mol, respectively.

Combustion characteristics of tannery sludge and volatilization of heavy metals in combustion

Incineration is considered one of the most readily available techniques for sewage sludge disposal, including tannery sludge, which often contains significant amounts of volatile heavy metals. The combustion characteristics and kinetic analysis of tannery sludge were investigated using thermogravimetric analysis (TGA) at a heating rate of 30 °C/min in 50–950 °C. In addition to confirming that tannery sludge has a high content of volatile material and ash, it was further discovered that almost all the zinc (Zn) in tannery sludge is volatilized at 900 °C. The degree of volatilization for heavy metals at 900 °C followed the order of Zn>Cd>Cu>Mn>Pb>Cr. Moreover, the volatilization of these heavy metals increased with temperature. It is thus concluded that, to avoid heavy metal volatization during incineration disposal, 800 °C is a reasonable incineration temperature.

Kinetics of Ignition of n-Pentane in a Shock-Tube

The combustion kinetics of n-pentane was fully investigated for the first time. Ignition delay times ofn-C5H12 and Oxygen diluted in Argon mixtures were measured over a wide range of compositions, pressures and temperatures. The 240 shocks were statistically correlated and this correlation was comparedto two known kinetic schemes, those of Warnatz and of Westbrook. The schemes needed correctionswhich are discussed here.