Studies on Coal Ignition and Combustion Characteristics

2017 ◽  
Author(s):  
Xue Chen ◽  
MingYan Gu ◽  
XianHui He ◽  
Dan Yan ◽  
Jimin Wang ◽  
...  
Keyword(s):  
Oxygen Concentration ◽  
Coal Particle ◽  
Gas Flow ◽  
Ignition Time ◽  
Particle Diameter ◽  
Combustion Characteristics ◽  
Gas Temperature ◽  
Flow Temperature ◽  
Particle Ignition ◽  
Coal Particles

A 2-D numerical model of flow, heat transfer, and combustion of coal particles in a laminar gas flow at O2/CO2 atmosphere was developed based on the Eulerian-Lagrangian methodology. The gas-phase combustion was modeled using the GRI-Mech 3.0. The motion of coal particles was simulated using a trajectory model. The model was employed to study the coal ignition time, temperature and mass changes. The effects of particle diameter, the flow temperature and oxygen concentration on the ignition time and the combustion characteristics of coal particles were also investigated. The results obtained show that smaller size particle experiences a shorter ignition time with a higher coal temperature. A higher gas temperature leads to a shorter coal particle ignition time; increasing the flow temperature the difference in the ignition time of different sized coal particles decreases. The coal particle ignition time is decreased when the oxygen concentration is increased.

Study on Coal Particle Combustion Characteristics and NO Emission in a Hot Laminar Gas Flow

2017 ◽  
Author(s):  
MingYan Gu ◽  
Dawei Yan ◽  
XianHui He ◽  
Dan Yan ◽  
FengShan Liu ◽  
...  
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Coal Particle ◽  
Gas Flow ◽  
Combustion Process ◽  
Mass Ratio ◽  
Gas Temperature ◽  
Uniform Size ◽  
Coal Particles

The combustion and NO formation characteristics of coal particles of different size distributions in a laminar gas flow were investigated by numerical simulation. The variation of coal particle size distribution was obtained by changing the mass ratio of small-sized coal to large-sized coal. The gas-phase combustion was modeled using GRI-Mech 3.0. The particle motion was simulated using a trajectory model. The results show that the coal particle size distribution has a significant impact on combustion process and NO distribution. Coal particles of uniform size at either 105 or 75 μm results in a higher NO concentration than coal consisting of both the large and the small particles. The smaller-sized coal particles experience a rapid volatile release, a higher maximum gas temperature, and a higher maximum NO concentration. Increasing the mass ratio of the smaller-sized coal particles changes the gas temperature and the averaged NO distribution and lowers the maximum NO concentration.

Combustion Characteristics of Ultrafine Coal Particles-Light Diesel Oil Mixtures in a Cylindrical Horizontal Furnace

2020 ◽  
Vol 143 (7) ◽  
Author(s):  
ELSaeed Saad ELSihy ◽  
M. M. Salama ◽  
M. A. Shahein ◽  
H. A. Moneib ◽  
M. K. Abd EL-Rahman
Keyword(s):  
Flame Temperature ◽  
Fuel Mixture ◽  
Combustion Characteristics ◽  
Slight Reduction ◽  
Percentage Increase ◽  
Gas Temperature ◽  
Flame Zone ◽  
Constant Input ◽  
Coal Particles ◽  
Loading Ratio

Abstract This work presents an experimental study that aims at investigating the effect of the loading ratio of coal in a coal-diesel fuel mixture on the combustion characteristics and exhaust emissions. Sub-bituminous coal from the El-Maghara coal mine is utilized. It is washed, dried, and grounded to particle sizing of ≤ 30 μm. The experiments are conducted inside a horizontal, segmented water-cooled cylindrical furnace fitted with a coaxial burner having a central air-assisted atomizer for oil-coal mixture admittance. All experiments are executed at constant input heat of 350 kW and air-to-fuel ratio of 15:1 while varying the percentage (mass basis: 5% and 10%) of coal in the fuel mixture. The measurements within the flame zone include mean gas temperatures, dry volumetric analyses of species (CO2, NOx, and O2) concentrations, and the accumulative heat transfer to the cooling jacket along the combustor. All measurements are compared regarding the pure oil flame. The results indicate that increasing the coal-loading ratio up to 5 wt% leads to a progressive increase in the accumulated heat transferred and the combustor overall efficiency from 40% to 58% within a percentage increase around 45%. In addition, there is a slight reduction in mean gas temperature within the flame zone when compared with the pure oil flame. The reduced flame temperature due to increasing the coal-loading ratio caused a decline in the volumetric concentrations of NOx from 100 ppm to 20 ppm as expected.

IGNITION CONDITIONS OF A SINGLE BORON PARTICLE IN HOT GAS FLOW

2020 ◽  
Author(s):  
G. V. Ermolaev ◽  
◽  
A. V. Zaitsev ◽  
Keyword(s):  
Oxygen Concentration ◽  
Gas Flow ◽  
Flame Temperature ◽  
Combustion Process ◽  
Experimental Studies ◽  
Gas Temperature ◽  
Hot Gas ◽  
Combustion Models ◽  
Boron Particle ◽  
Boron Particles

The basic experimental studies on boron combustion are done with the same general scheme of the experiment. Boron particles are injected into flat-flame burner products with the help of the transporting jet of cold nitrogen. Boron particle combustion process is registered with a number of optical methods. It is proposed that boron particle is injected into the main hot gas flow instantly, combustion takes place at the flame temperature and predefined oxygen concentration, and the influence of the transporting cold nitrogen jet is ignored. Recent combustion models are based mostly on this type of experiments and characterized with high complexity and low prediction level. In our study, we reconstruct the particle injection conditions for several basic experimental papers. It is shown that in all experimental setups, ignition, combustion, and even total particle burnout take place in the wake of the cold nitrogen jet. This zone is characterized with a much lower gas temperature and oxygen concentration than the main flat burner flow. The total temperature decrease can be about several hundred degrees, oxygen concentration can be 30%-50% lower than that used in the previous analysis of the experimental results. The temperatures of ignition and transition to the second stage of combustion are found with the help of the test particle trajectory and temperature tracking. It is shown that analysis of the influence of boron particles injection on gas temperature and oxygen concentration is mandatory for the development of future combustion models.

Numerical Study of Conduction and Convection Between Immersed Object and Gas Fluidized Bed

Volume 1 ◽  
2004 ◽  
Author(s):  
W. M. Gao ◽  
L. X. Kong ◽  
P. D. Hodgson ◽  
B. Wang
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Solid Phase ◽  
Numerical Study ◽  
Particle Diameter ◽  
Conductive Heat ◽  
Gas Temperature ◽  
Transfer Coefficients ◽  
Immersed Surfaces ◽  
Particle Layer

To analyze the heat transfer mechanism between fluidised beds and surfaces of an immersed object, the heat transfer and gas flow was numerically simulated for different particle systems based on a double particle-layer and porous medium model. It is fund that the conductive heat transfer occurs in the stifling regions between particle and the immersed surface, which have different temperature. The diameter of the circular conduction region, dc, is a function of particle diameter, dp, and can be given by dc/dp = 0.245dp−0.3. In other areas, the heat transfer between the dense gas-solid phase and the immersed object surface is dominated by convection from the moving gas in the tunnel formed by the first-layer particles and the immersed surfaces. The average dimensionless gas velocity, εmfU/Umf, in the tunnel is a constant of about 4.6. The virtual gas temperature at the free stream conditions can be given by the surface temperature of the first-layer particles. The heat transfer coefficient on the conductive region is about 6∼10 times of that on the convection region. The Nusselt numbers for calculating the instantaneous conductive and convective heat-transfer coefficients were theoretically analysed respectively.

Studies on Combustion Characteristics of Two Interacting Coal Particles at Different Separation Distance

2017 ◽  
Author(s):  
XianHui He ◽  
MingYan Gu ◽  
DaWei Yan ◽  
Xue Chen ◽  
Dan Yan ◽  
...  
Keyword(s):  
Temperature Rise ◽  
Ignition Time ◽  
Particle Interaction ◽  
Particle Separation ◽  
Separation Distance ◽  
Combustion Characteristics ◽  
Char Combustion ◽  
Coal Particles ◽  
Char Burnout ◽  
Combustion Processes

To understand the interactions of coal particles on devolatilization, volatile burning, and char combustion, the combustion characteristics of two interacting equal-sized coal particles placed in the upstream and downstream configuration in a hot laminar flow are numerically investigated. A two-dimensional mathematical model was developed based on the wall surface reaction theory in the commercial software FLUENT. The numerical results show that the particle interaction has different effects on the coal ignition time and combustion characteristics of the upstream and downstream particles. The upstream coal particle undergoes a faster temperature rise, earlier coal devolatilization, and faster char burnout than the downstream one. With increasing the particle separation distance within a certain range, the temperature rise, coal devolatilization, and char combustion processes are further enhanced and weakened for the upstream particle and the downstream particle, respectively. There exists a critical particle separation distance beyond which the combustion processes of the two particles are similar to those of a single particle.

The Effect of Forced Convection on Mass and Heat Transfer During Single Coal Particle Combustion

2019 ◽  
Author(s):  
Lele Feng ◽  
Yang Zhang ◽  
Yuxin Wu ◽  
Kailong Xu ◽  
Hai Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Oxygen Concentration ◽  
Turbulent Mixing ◽  
Coal Combustion ◽  
Coal Particle ◽  
Flame Temperature ◽  
Particle Diameter ◽  
Particle Combustion ◽  
Mass And Heat Transfer

Abstract MILD coal combustion is one of promising technologies for clean coal utilization due to uniform heat flux and low NOx emission, while the effect of turbulent mixing on single coal particle combustion under high temperature and low oxygen concentration remains to be studied for micron level particles. In this paper, a 1-D transient coal combustion model was applied to describe mass and heat transfer around a single particle, and the effect of forced convection was modeled to represent turbulent mixing according to similarity analysis. Based on that, effect of particle Reynolds number (Rep) on single coal particle combustion was investigated at various temperature (Ta), oxygen concentration (xO2) and particle diameter (d0). As Rep increases, ignition time (ti) decreases quickly at first and then decreases slowly. ti of larger particle is more sensitive to Rep. As Rep increases, flame temperature (Tf) for 40 μm coal particle decreases, while Tf for 80 μm coal particle barely changes, and that for 160 μm coal particle increases a little. The recommended d0 for MILD coal combustion is smaller than 80 μm. As xO2 decreases from 21% to 5%, ti apparently increases and Tf decreases. ti at lower Ta is more sensitive to Rep. Tf decreases with increasing Rep when Ta < 1200 K. But it appears the opposite trend at Ta = 1600 K. The recommended Ta for MILD coal combustion is lower than 1400 K, while it cannot be too low considering the burnout of char particle.

Formation of Deposits From Heavy Fuel Oil Ash in an Accelerated Deposition Facility at Temperatures Up to 1206°C

2017 ◽  
Author(s):  
Robert G. Laycock ◽  
Thomas H. Fletcher
Keyword(s):  
Gas Turbines ◽  
Gas Flow ◽  
Particle Diameter ◽  
Capture Efficiency ◽  
Fuel Oil ◽  
Nickel Base Superalloy ◽  
Gas Temperature ◽  
Heavy Fuel Oil ◽  
Hot Gas ◽  
Exhaust Stream

Some industrial gas turbines are currently being fired directly using heavy fuel oil, which contains a small percentage of inorganic material that can lead to fouling and corrosion of turbine components. Deposits of heavy fuel oil ash were created in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University under gas turbine-related conditions. Ash was produced by burning heavy fuel oil in a downward-fired combustor and collecting the ash from the exhaust stream. The mass mean ash particle diameter from these tests was 33 microns. This ash was then introduced into the TADF and entrained in a hot gas flow that varied from 1088 to 1206°C. The gas and particle velocity was accelerated to over 200 m/s in these tests. This particle-laden hot gas stream then impinged on a nickel base superalloy metal coupon approximately 3 cm in diameter, and an ash deposit formed on the coupon. Sulfur dioxide was introduced to the system to achieve 1.1 mol% SO2 in the exhaust stream in order to simulate SO2 levels in turbines currently burning heavy fuel oil. The ash deposits were collected, and the capture efficiency, surface roughness, and deposit composition were measured. The deposits were then washed with deionized water, dried, and underwent the same analysis. It was found that, as the gas temperature increased, there was no effect on capture efficiency and the post-wash roughness of the samples decreased. Washing aided in the removal of sulfur, magnesium, potassium, and calcium.

Study on Factors Influencing Pulverized Coal Ignition Time

2012 ◽  
Vol 614-615 ◽  
pp. 120-125
Author(s):  
Xiang Gou ◽  
Jin Xiang Wu ◽  
Lian Sheng Liu ◽  
En Yu Wang ◽  
Jun Hu Zhou ◽  
...  
Keyword(s):  
Coal Particle ◽  
Ignition Time ◽  
Flame Temperature ◽  
Particle Diameter ◽  
Pulverized Coal ◽  
Dominant Factor ◽  
Ignition Process ◽  
Heat Absorption ◽  
Convection Heat ◽  
Radiation Heat

Pulverized coal ignition time is one of crucial parameters in coal ignition process. Based on a general heat absorption equation without chemical reaction, this study was focused on some crucial factors which influence pulverized coal ignition time to theoretically explain the mechanism of heat absorption of pulverized coal. The influences of recirculated flue gas (RFG) temperature, flame temperature, primary air temperature, and coal particle diameter on ignition time were discussed. The importance of radiation heat and convection heat was analyzed. The results show that the higher temperatures of RFG, flame, and primary air can lead to the shorter ignition time respectively. The increase of the coal particle diameter greatly increases the ignition time, and as the diameter goes up, the amount of the ignition delay becomes greater. For high accuracy of ignition time calculation, both radiation heat and convection heat should be taken into account. When flame temperature is very high and RFG temperature is very low, radiation is the dominant factor, otherwise convection is more crucial.

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