NO Emissions from Oxidizer-Staged Combustion of Superfine Pulverized Coal in the O₂/CO₂ Atmosphere

Abstract

The CO 2 control technologies have been studied extensively in recent years, among which the oxy-fuel combustion shows a vast number of advantages to be explored commercially in the near future. However, unexpected problems, such as bad combustion characteristics and serious slagging and depositing issues, show up with the replacement of N 2 by CO 2 . These inherent disadvantages in normal O 2 /CO 2 combustion can be restrained via combining the superfine pulverized coal and oxy-fuel combustion technology. The axial NO emission characteristics of this new technology were focused here. The effects of the oxidizer staging were also studied in detail. Results indicate that the axial NO emissions of the unstaged O 2 /CO 2 combustion basically showed "M" type of distributions along the furnace. The "M" type can be divided into the main homogeneous and heterogeneous reaction zones. The oxidizer-staged O 2 /CO 2 combustion can mitigate NO emissions effectively. Coals with smaller particle sizes and higher volatiles are more advantageous for eliminating NO in the staged O 2 /CO 2 combustion technology. The superfine pulverized coal used with certain low NO combustion technologies shows significant superiority in both combustion performance and NO abatement.

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

“…The mean diameters of the fine and coarse particles are 16 and 82 μm. Hereafter, the fine and coarse coal particles are named as D 16 and D 82 , respectively. Experiments were conducted for five coal particle samples, which were prepared by mixing D 82 and D 16 coal particles according to the following five mass ratios of 1:0, 7:3, 5:5, 3:7, and 0:1.…”

“…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.…”

“…Increasing the proportion of small sized particles, i.e., D16 ,o r the oxygen concentration can enhance the coal ignition characteristics and improve the flame front distance.4.3. Effects of Coal Particle Size Distribution on the Flame Propagation Velocity.To quantify the influence of particle size distribution on the combustion characteristics of pulverized coal, the variation of the flame front propagation velocity of the five coal samples with time was analyzed.…”

Pyrolysis of superfine pulverized coal. Part 3. Mechanisms of nitrogen-containing species formation

“…Therefore, these experimental data provide the support for the new technique we proposed, i.e., combining superfine pulverized coal with de-NO x combustion methods such as fuel reburning and air staging. The technique benefits both the combustion performance and NO x abatement [30,33]. However, the increase of NH 3 for smaller particles is not accompanied by a corresponding decrease in HCN formation.…”

Chemical Properties of Superfine Pulverized Coal Particles. 3. Nuclear Magnetic Resonance Analysis of Carbon Structural Features

“…Therefore, the R&D (research and development) of clean coal technologies have attracted increasing attention on the more efficient and cleaner usage of coal . The novel superfine pulverized coal combustion technology shows plenty of advantages for flame stability, combustion efficiency, fusion characteristics, and alleviation of NO x /SO 2 /CO 2 emissions, etc. − Thus, a complementary description of the representative molecular models plays a paramount role in better understanding its utilization processes such as chemical/physical adsorption, swelling, coking, pyrolysis, gasification, liquefaction, and combustion . The influence of particle size on coal’s physical and chemical properties should be emphasized.…”