Study on combustion characteristics of two sizes pulverized coal in O2/CO2 atmosphere

The main purpose of this study was to examine the effect of particle size on blending methods for pulverized coals, using a thermo-gravimetric analyzer (TGA) and an entrained drop tube reactor (EDTR). The experiment was performed with three particle sizes (small: 45–75 μm, medium: 75–90 μm, large: 150–180 μm) and two blending methods (bunker-blend and furnace-blend). The TGA results show that high rank coal (Trafigura), containing lower volatile matter, was more difficult to ignite than low rank coal (Berau). Also, faster ignition and higher reactivity were observed because of increase in the surface area with decreasing particle size. The EDTR results show that first, during bunker-blend, as the particle size decreased, the amount of carbon in ash (CIA) reduced. Moreover, the highest point of CIA shifted to a low blending ratio (LBR 50%) because a highly oxygen-deficient environment was rapidly created. In contrast, as the blending ratio of low rank coal increased, NO x emissions gradually increased at all conditions because of the fuel bonding N content in the coal, and the NO x reduction efficiency of a fine particle is larger than that of a coarse one. Second, during furnace-blend, CIA and NO x gradually decreased by approximately 33–52% (small sizes) and 9–27% (medium sizes) as the length of the tube increases. However, for the large sizes of coal, the amount of CIA and NO x increased because of the adverse effects of the greater particle size. The CO and O2 results among flue gases supported these phenomena. Thus, these results suggest that using fine particles in furnace-blend can effectively reduce CIA and NO x emissions.

Section: = S R R T T / Max Mean I 2 Bsupporting

confidence: 91%

Impact of Pulverized Coal Particle Sizes on Combustibility and NO_x Emission in Different Blending Methods

Lee

Shagdarsuren²,

Jeon³

2019

“…It has been known that the ignition and combustion characteristics of coal particles are strongly influenced by their sizes. , For smaller coal particles, especially for superfine ones with particle diameter d p < 20 μm, the particle temperature rise is faster and the ignition delay time is shorter. − Compared to coarse coal particles, fine coal particles have the advantages of high burning rate, high combustion efficiency, and low NOx formation. However, fine coal particles are more energy consumption to produce and their storage is also a concern.…”

Section: Introductionmentioning

confidence: 99%

Effects of Particle Size Distribution and Oxygen Concentration on the Propagation Behavior of Pulverized Coal Flames in O₂/CO₂ Atmospheres

Xue

et al. 2017

Self Cite

The ignition and flame propagation behavior of pulverized coal particles in an O 2 /CO 2 atmosphere was studied in a long quartz tube reactor. The effects of mixing ratio of fine (mean diameter 16 μm) and coarse (mean diameter 82 μm) coal particles and oxygen concentration on the ignition characteristics, flame front distance, and flame propagation velocity were investigated by capturing the flame ignition and propagation using a high-speed video camera. The experimental results show that the particle size distribution has a strong influence on the ignition and flame structure of coal particles. Smaller coal particles result in earlier ignition, a smoother flame front, longer flame, and faster flame propagation velocity. Mixing of smaller coal particles with larger ones shortens the ignition delay and enhances the propagation velocity of the flame front. For different coal particle size distributions, the variation of flame propagation velocity with time in general displays an "M"-shaped curve. The curve of flame propagation velocity vs time is single-peaked at 40% oxygen concentration for both coarse and fine particles with mean diameters of 82 and 16 μm, respectively. The effect of oxygen concentration on the flame propagation becomes stronger as the percentage of fine particles increases. The effect of fine coal particles on the volatile release rate of coarse particles was analyzed by numerical simulation. The results show that increasing the ratio of fine coal particles shortens the time for volatile matter release from the coarse coal particles and increases the coarse particle temperature.

“…The specific size fraction significantly influences the combustion and emission characteristics . For the NO x emission characteristics with coal particle sizes, many studies ,− have been carried out to find the relationship between particle size and NO produced. However, very little experimental data has been accumulated regarding the effect of particle size of char on NO conversion after the volatile combustion, which will influence final NO x emission.…”

Section: Introductionmentioning

confidence: 99%

Effect of Char Particle Size on NO Release during Coal Char Combustion

Sun

Ismail

et al. 2017

In this study, the effect of particle size on the release of NO during the char combustion under particle packed-layer conditions was investigated at combustion temperatures of 900–1400 °C. The results show that, after pyrolysis, the small size char favored more pores and specific surface area. No significant variations of the intrinsic reactivity of O2 and NO with char particle size were measured. By increasing char particle size, more NO conversion from nitrogen in char (char-N) was found regardless of the combustion temperature and bulk oxygen concentration. This can be explained as follows. By increasing char particle size, less O2 penetrated into the pores and then more NO formed which was attributed to a less accessible pore surface area and a decreased NO reduction time. The effects of reaction temperature and bulk oxygen concentration were also discussed. A quantified description using a first-order reaction model shows that the char particle size will finally influence the accessible pore surface area and depth of O2 diffusion, which will directly determine the char-N/NO conversion. The evolution of nitrogen functionality with particle size and burnoff were also presented to demonstrate migration tendency of the char-N. The larger ratio of O/C in smaller size particle as determined using XPS (X-ray photoelectron spectroscopy) further confirmed higher pore diffusion. In addition, nitrogen was found to be preferentially retained in the char when carbon is oxidized.