Combustion Behavior Of Coal Research Articles

Inhibiting effect of CO2 on the oxidative combustion thermodynamics of coal.

A thermal analysis experiment was conducted in O2/N2/CO2 and O2/N2 atmospheres (O2 concentrations were 21, 14, 8, and CO2 concentrations were 0, 39, 46, 52) to investigate the thermal behavior of coal oxidation and combustion. Results demonstrated that an elevated CO2 concentration or decreased O2 concentration had a delaying effect on the thermogravimetric analysis and differential scanning calorimetry (DSC) curves; moreover, the characteristic temperatures were substantially augmented. When the O2 concentration was 21 vol%, the total heat released by coals A (highly volatile bituminous coal) and B (anthracite coal) decreased by 5.8% and 4.1%, respectively, after CO2 addition. The comprehensive combustion performance index was also lowered. The DSC curve can be divided into two exothermic peaks, and the ratio of the peak 1 to peak 2 areas decreased with the addition of CO2, which indicated that CO2 inhibited the oxidation of the active functional groups of coal structures. Apparent activation energy in O2/CO2/N2 was less than that in O2/N2.

Effect of weathering on physico-chemical properties and combustion behavior of an Indian thermal coal

An open air stockpile of conical shape was formed with 3.5 m base diameter and 5 m height using 500 tons of − 200 mm size ROM thermal coal on a concrete floor. Coal sample from the stockpile were collected at 30 days interval for analysis of various chemical properties like; proximate analysis, ultimate analysis, gross calorific value (GCV) and various combustion related properties such as ignition temperature, peak temperature, burnout temperature, maximum combustion rate, ignition index, burnout index, combustion performance index and combustion rate intensity index. Experimental results show that, due to weathering of coal fixed carbon decreased from 35.6% to 19.9%, elemental carbon (C) decreased from 46.6% to 28.6%, hydrogen (H) decreased from 3.3% to 2.9% and GCV decreased by up to 55% of original value during 330 days of storage of coal in an open atmosphere. Ash content of coal increased form 29.2% to 46.6% due to loss of combustibles. Sulfur (S) of coal was found to get increased from 0.33% to 1.08% during storage. The activation energy of coal combustion increased from 22 kJ/mol to 54 kJ/mol. Variation in combustion parameters signifies that weathering has significant negative impact on coal combustion properties as coal become difficult to ignite.

Effects of momentum ratio and velocity difference on combustion performance in lignite-fired pulverized boiler

To study the effects of momentum ratio and velocity difference between primary and secondary air flow on boiler performance, simulation work was conducted on a lignite-fired boiler within a three dimension computational fluid dynamics model. Within the model, 8 cases were simulated where momentum ratio and velocity difference vary among cases. The distributions of combustion temperature, radiative heat flux, gas species concentration and residual particles’ concentration were analyzed. Results show that momentum ratio of primary and secondary air flow significantly determines coal combustion behavior and boiler performance, and a reasonably small momentum ratio is beneficial for boiler performance. The velocity difference between primary and secondary air also affects coal combustion performance, and a relatively large velocity difference is favorable in boiler operation. These findings reveal the effects of momentum ratio and velocity difference on boiler performance, and can be helpful in guiding the actual operation of lignite-fired boiler to avoid the unfavorable boiler performance degradation.

Combustion behaviors and kinetics analysis of coal, biomass and plastic

In this paper, thermal analysis method (TGA) was adopted to describe the combustion behavior of bituminous coal(GC), anthracite(LC), biomass(PS) and plastic(PVC).The structure characteristics of these samples were carried out using Raman spectroscope followed by peak deconvolution and data analysis. The kinetic parameters and combustion reaction mechanism were obtained by fitting experimental data with the random nucleation nuclei growth model (RNGM) and volume model (VM) in order to find out the kinetics characteristics responsible for the combustion of the samples. The results indicate that significant difference between combustion process of these samples are mainly attributed to their differences structures, the combustion reactivity of PS is better than GC duo to the catalysis of alkali matter in biomass ash. RNGM model is better than VM model for simulating the combustion process, and TRNGM model plays a good performance in depicting the combustion process of PVC with three reaction stages.

Chemical properties and combustion behavior of constituent relative density fraction of a thermal coal

ABSTRACTThis work presents the experimental results showing the impact of relative density of coal on its properties and combustion behavior. Coal of different mean relative densities (RDm) in the range of 1.375 to 2.0 was prepared through sink–float method of coal beneficiation from the crushed run of mine (ROM) coal. All the RDm fractions were characterized for proximate analysis (PA), ultimate analysis (UA), and gross calorific value (GCV). Combustion behaviors of different coals were carried out by thermogravimetric analysis in the oxygen atmosphere. Important combustion characteristic temperatures like ignition temperature (), peak temperature (), burnout temperature (), and maximum combustion rate () were evaluated from differential thermogravimetric (DTG) data. Further different combustion parameters like ignition index (), burnout index (), combustion performance index (S), combustion rate intensity index (), and activation energy (AE) were evaluated to access the effects of RDm on combustion behavior of coal. Experimental results showed that, with increase in RDm, from 1.375 to 2.0, ash increased from 12.2% to 62.1%, GCV decreased from 8,254 to 3,084 kcal/kg, increased from 357 to 421ºC, increased from 459 to 488ºC, varied from 543 to 553ºC, and decreased from 6.735 to 4.831 wt%/minute. With increase in RDm from 1.375 to 2.0, decreased from 5.8 wt%/minute4, decreased from 9.8 to 4.1 wt%/mintute4, and S decreased from 11.3 × 10−8 to 4.0 × 10−8 wt %2/minute2C3 signifies difficulty in combustion process which was further confirmed by an increase in AE from 92.7 to 173.5 kJ/mole. Overall, experimental and theoretical analysis briefs that coal having lower RDm have better combustion properties compared to higher density coals.

Effects of silicoaluminate oxide and coal blending on combustion behaviors and kinetics of zhundong coal under oxy-fuel condition

Oxy-fuel combustion of high-alkali coal is beneficial for near-zero emission of pollutants in power plants and has the potential for extensive, efficient, and safe utilization of Zhundong coal in future. The present work was performed on oxy-fuel combustion of Zhundong coal, while the effects of silicoaluminate oxide and coal blending on oxy-fuel combustion characteristics and kinetics of high-alkali coal were further studied using thermogravimetric analysis. The thermogravimetric curves of Zhundong coals present two obvious stages but the contrastive coals are different. The increase in oxygen content weakens the impact of coal property on oxy-fuel combustion behavior of high-alkali coal. The addition of Al2O3 and kaolin results in a slight decline of the peak combustion rate, while the influences of SiO2 and diatomite additives are negligible. The additive fraction of silicoaluminate oxide gives rise to a non-monotonic impact on combustion characteristics of Zhundong coal. The interaction effect within blended coal could cause a reduction in reaction rate during the intense combustion stage, while its influence on kinetics is intensified during the later stage of oxy-fuel combustion. The impact extent of silicoaluminate oxide and coal blending on oxy-fuel combustion kinetics of high-alkali coal is highly associated with additive species and individual coals.

Characterization on Ignition and Volatile Combustion of Dispersed Coal Particle Streams: In Situ Diagnostics and Transient Modeling

In this paper, applying OH-PLIF diagnostics, we explored the ignition and volatile combustion of dispersed coal particle streams in a Hencken flat-flame burner. The effects of ambient temperature and oxygen mole fraction on coal combustion behaviors have been systematically examined. First, different coal combustion stages and ignition modes (i.e., heterogeneous ignition, homogeneous ignition, and hetero-homogeneous joint ignition) in different ambiences are characterized by the OH profiles within the coal flame domain, with ignition delay time and volatile combustion time being quantitatively determined. Then, an improved transient model, integrating the gas-phase flame-sheet reaction model and the chemical percolation devolatilization (CPD) model, is established to reveal the underlying physicochemical mechanisms during the early stage of coal combustion. This transient model well captures the effects of ambiences on both the characteristic ignition delay time and volatile combustion time. Finally, base...

Combustion behavior of KOH desulphurized coals assessed by TGA-DTG

ABSTRACTThis work presents the results obtained from the experimental study on the effects of KOH treatment and its combustion behavior of high sulfur Indian coal. Coal was treated with 5–20% KOH (v/v) concentration for 6–24 h reaction time to identify the effects of KOH treatment on coal properties. Experimental results showed that upto 36.79% of total sulfur can be removed from coal with 20% KOH concentration and 24 h contact time at atmospheric condition. However, gross calorific value of coal decreased from 6800 to 6084 kcal/kg due to removal of combustibles from coal. Combustion characteristics of treated coal were assessed by Thermo-gravimetric analysis/ Differential thermo-gravimetric (TGA/DTG analysis). Further various combustion kinetic parameters like ignition temperature, peak temperature, burnout temperature, activation energy (E), and pre-exponential factor (A) are estimated. Experimental results show that the ignition temperature of coal decreased from 321°C to 252°C, peak temperature decreased from 459°C to 409°C due to changes in the coal matrix after desulfurization. The activation energy of coal calculated decreased from 79 to 45 kJ/mol due to desulfurization using 20% KOH concentration and 24 h reaction time.

Thermal Behavior of Coal Used in Rotary Kiln and Its Combustion Intensification

Pyrolysis and combustion behaviors of three coals (A, B, and C coals) were investigated and their combustion kinetics were calculated by the Freeman–Carroll method to obtain quantitative insight into their combustion behaviors. Moreover, the effects of coal size, air flow, oxygen content, and heating rate on coal combustion behaviors were analyzed. Results showed that the three coals have a similar trend of pyrolysis that occurs at about 670 K and this process continuously proceeds along with their combustion. Combustion characteristics and kinetic parameters can be applied to analyze coal combustion behaviors. Three coals having combustion characteristics of suitable ignition temperature (745–761 K), DTGmax (14.20–15.72%/min), and burnout time (7.45–8.10 min) were analyzed in a rotary kiln. Combustion kinetic parameters provide quantitative insights into coal combustion behavior. The suitable particle size for coal combustion in a kiln is that the content of less than 74 μm is 60% to 80%. Low activation energy and reaction order make coal, especially C coal, have a simple combustion mechanism, great reactivity, be easily ignited, and a low peak temperature in the combustion state. Oxygen-enrichment and high heating rates enhance coal combustion, increasing combustion intensity and peak value, thus shortening burnout time.

Combustion Behavior of Coals in Rotary Kiln and Their Interaction on Co-combustion

In order to clearly reveal coal combustion behaviors and quantitatively evaluate using coal in a rotary kiln, combustion behaviors of four coals (C13, C23, C32, and C6 coals) and their blended coals were investigated. Meanwhile, their interactions and combustion kinetics were analyzed. The results showed that C13 and C23 coals having combustion characteristics of high heating value, suitable ignition temperature, burnout time and kinetic parameters (Eα and n) conform to the requirement of a rotary kiln. The partial substitution of C23 coal for C13 coal in the production is feasible, while the replacement of C32 and C6 coals for C13 coal will affect coal combustion and result in production fluctuation because C32 and C6 coals have an effect on C13 coal combustion. The blended coals have the similar characteristics of proximate analysis and heating value contrasting to C13 coal, but they show different combustion behaviors that cannot be calculated in an additive manner. Their combustion behaviors show mult...

Determination of the Self-Heating Temperature of Coal by Means of TGA Analysis

In this study, the self-heating tendency of Tavsanli (Turkey) coal was investigated by the apparatus of thermal analysis. TG-DTG and DSC-DDSC plots obtained at air atmosphere from 25 to 800 °C were used to determine the self-heating temperature (Tsh) and the combustion behavior of coal. The self-heating temperature changes versus the particle sizes of coal and heating rates were examined . Also, kinetic parameters of the main combustion region were obtained in the temperature range of 25 to 800 °C at different heating rates (1, 2.5, 5, and 10 °C min–1) under nonisothermal heating conditions at air atmosphere. The activation energy, pre-exponential factor, and reaction mechanism were calculated by using KAS, FWO, Coats–Redfern, and Master-Plot methods. It was understood that the oxidation process of coal was controlled by the first order [F1: −ln (1 – α)] mechanism.

Prediction of Pulverized Coal Combustion Behavior around Tuyere by Using LES and Extended CPD Model

Prediction of Pulverized Coal Combustion Behavior around Tuyere by Using LES and Extended CPD Model

Effects of Fuel Properties on Ignition Characteristics of Parallel-Bias Pulverized-Coal Jets

To further understand the bias combustion behavior of new coal used for horizontal bias combustion and obtain its characteristic parameters, combustion experiments were conducted in a 250-kW pilot-scale bias combustion simulator; multiple research measurements of flame spectra, combustion temperatures, and burnout rates of residual solids were used. Bituminous coal from Australia, sub-bituminous coal from Indonesia, and a blend of these coals were tested. The effects of the raw-coal equivalent moisture (RCEM), pulverized-coal fineness (PCF), and coal type on the ignition characteristics of parallel-bias pulverized-coal jets in a reducing atmosphere were investigated. The results indicate that, with decreasing RCEM and PCF, the standoff distance gradually decreased, the flame stability gradually increased, the burnout rate gradually increased, and the ignition characteristics gradually improved. The RCEM had negative effects on ignition in the early stage but positive effects during subsequent combustion. ...

Gas emissions from blends of bituminous coal and biomass chars under different pyrolysis conditions

ABSTRACTIn this work, thermal behavior and gas emission characteristics of coal, different kinds of biomass chars, and their blends were evaluated by using the thermogravimetric analyzer coupled with a mass spectroscope. The chars were prepared from wheat straw at 300°C and 500°C under N2 and CO2 atmosphere, respectively. The results show that the pyrolysis temperature has a greater effect on the combustion characteristics of biomass char than the pyrolysis atmosphere. NOx emissions were reduced effectively with the addition of biomass chars. The study also reveals that there is an obvious improvement in the combustion behavior of coal when blended with biomass chars.

Coal Combustion Behavior in New Ironmaking Process of Top Gas Recycling Oxygen Blast Furnace

The top gas recycling oxygen blast furnace (TGR-OBF) is a new ironmaking process which can significantly reduce the coke ratio and emissions of carbon dioxide. To better understand the coal combustion characteristics in the TGR-OBF, a three dimensional model was developed to simulate the lance–blowpipe–tuyere–raceway of a TGR-OBF. The combustion characteristics of pulverized coal in TGR-OBF were investigated. Furthermore, the effects of oxygen concentration and temperature were also analyzed. The simulation results show that the coal burnout increased by 16.23% compared to that of the TBF. The oxygen content has an obvious effect on the burnout. At 70% oxygen content, the coal burnout is only 21.64%, with a decrease of 50.14% compared to that of TBF. Moreover, the effect of oxygen temperature is also very obvious.

Investigation on Coal Slagging Characteristics and Combustion Behaviour in Furnace

This paper describes an investigation of coal characteristics and slagging potential using coal slagging assessment tool such as numerical slagging indices. Historical data on coal use according to type and shipment in power plant was use for the analysis. It is found that higher content of silica oxide results in higher softening temperature and the monomers modifiers can alter the softening temperature. Calculation also reveals encouraging conditions that could possibly prevent the slagging potential inside the furnace.

Air and oxy-fuel combustion kinetics of low rank lignites

The air and oxy-fuel combustion processes of two low-grade lignite coals were investigated by thermogravimetric analysis (TGA) method. Coals were provided from two different coal mines in the Aegean region of Turkey. Oxy-fuel combustion experiments were carried out with three different gas mixtures of 21% O2–79% CO2; 40% O2–60% CO2 and 50% O2–50% CO2 at 950 °C and heating rates of 10 °C/min, 20 °C/min and 40 °C/min. The kinetics of the oxy-fuel combustion of coals were studied by using four different methods namely, Coats-Redfern (model-fitting method), Friedman (FR), Flynn–Wall–Ozawa's (FWO) and Kissinger–Akahira–Sunose's (KAS) methods. The apparent activation energies of combustion process calculated by FWO method are slightly but systematically higher than that calculated by the KAS and FR methods for the oxy-fuel atmospheres. Combustion behavior of both coals in the oxy-fuel combustion environment could vary significantly, likely due to their characteristics such ash and volatile matter contents.

No.1-1 流動層を用いた石炭のOxy-Fuel 燃焼挙動の解明

No.1-1 流動層を用いた石炭のOxy-Fuel 燃焼挙動の解明

Large eddy simulation of a semi-industrial scale coal furnace using non-adiabatic three-stream flamelet/progress variable model

To describe the combustion process in the burners with complicated configuration used in the industrial applications, a non-adiabatic three-stream flamelet/progress variable (FPV) model for simulating pulverized coal combustion (PCC) is proposed in the context of large eddy simulation (LES). A conserved scalar associated with oxidizer split is introduced to characterize mixing of different oxidizer streams while the manifold of enthalpy defect is incorporated to account for heat losses. As a first step towards real industrial applications, the present model is evaluated by simulating a semi-industrial swirl-stabilized pulverized coal flame. Qualitative analyses are first carried out to explore the details of the coal combustion behaviors in this complicated configuration burner. We find that the coal particle reaction is closely related to the distribution of the oxidizer split. In addition, the results show that the reaction in the swirl induced internal recirculation zone is mainly generated by homogeneous combustion while the heterogeneous reaction dominates in the downstream region. Quantitative comparisons among the present model, the eddy break up model and the experiments are also conducted. The results from the flamelet model agree well with the experimental data and outperform those from the eddy break up model. However, discrepancies still exist in species concentrations at certain area, which may be further improved by high-fidelity devolatilization model in the future study.

Effect of Oxygen-Coal Lance Configurations on Coal Combustion Behavior

The extent of coal combustion within the tuyere and raceway region is one key factor affecting the maximum pulverized coal injection (PCI) rate. Coal burnout strongly depends on the availability of oxygen. In this paper, a three-dimensional model is developed to simulate the lance–blowpipe–tuyere-raceway of a blast furnace. This model aims to describe the coal flow and combustion behaviors along the coal plume under different local oxygen enrichment ways. Room-temperature oxygen has two effects on coal combustion. On one hand, the cooling effect of oxygen delays the coal combustion. On the other hand, the oxygen content around the coal particles significantly increases, benefiting coal combustion. Therefore, aiming at different local oxygen enrichment ways, three different lance configurations, including a single coaxial oxygen-coal lance, a double oxygen-coal lance, and an oxygen-coal double lance, are designed. Under the single coaxial oxygen-coal lance, the burnout has the maximum increase of 4.05%. Under the double oxygen-coal lance, the burnout has the maximum increase of 12.51%. Under the oxygen-coal double lance, the burnout has the maximum increase of 12.84%. Therefore, the effect of different local oxygen enrichment ways should not be neglected.