Experimental study of a single char particle combustion characteristics in a fluidized bed under O2/H2O condition

This work studies the single coal particle combustion process in an O2/CO2 atmosphere based on spectral diagnostics technology in a visual drop tube furnace (VDTF). The chemiluminescence characteristics of OH*, CH*, Na*, and K* in single coal particles at two reaction stages and different oxygen fractions (X i,O2 ) are investigated. The results show that both flame temperature and alkali metal spectral intensity increase first and then decrease, and the trend of temperature variation is consistent with that of alkali metal spectral intensity. Meanwhile, with X i,O2 increases, Na* and K* peak intensities are enhanced because of the improvement in the oxygen flow rate. In the volatile reaction stage, the coal particle shows a typical envelope flame with high soot generation and luminosity. As the reaction time increases from 10 to 30 ms, the flame size increases and the flame temperature increases from 1550 to 1950 K. The spectroscopic results corresponding to the volatile reaction stage show that, as X i,O2 increases from 30 to 50, the OH* and CH* intensity peaks increase linearly. Moreover, the intensities of the Na* and K* peaks increase by approximately 50.2 and 89.2%, respectively. During the volatile–char reaction stage, the coal particle exhibits a brighter luminous characteristic. As the reaction time increases from 40 to 70 ms, the flame size reduces and the flame temperature decreases from 1900 to 1700 K. The spectroscopic results corresponding to the volatile–char reaction stage indicate that, with the increase in X i,O2 , the positions of the OH* and CH* peaks change little and the intensities of the Na* and K* peaks increase by 21.3 and 75.1%, respectively. Our results prove that the flame temperature and alkali metal atomic emission spectroscopy exhibit the same trends as a function of the reaction time, and the alkali metal atomic emission spectroscopy can be used to characterize the flame temperature.

Section: Resultsmentioning

confidence: 99%

Analysis of the Single Coal Particle Combustion Process under O₂/CO₂ Atmosphere Based on Spectral Diagnostics Technology: Combination of Spectroscopic Characteristics and Flame Temperature

Xie

Wei

et al. 2022

“…Besides, the gasification effect on char combustion weakens with decreasing temperature. In our previous work, 25,27,28 we have found that the proportion of gasification increases along with temperature, while the CO 2 concentration, fluidization number, and particle size have little effect on the gasification reaction fraction.…”

Section: Introductionmentioning

confidence: 81%

Gasification Decoupling during Pressurized Oxy-Coal Combustion by the Isotope Tracer Method

Hong

Duan

et al. 2022

Self Cite

As one of the crucial means of CO 2 emission reduction in coal-fired power plants, oxy-fuel combustion has attracted widespread attention for years. Since oxy-fuel combustion and air combustion vary considerably in the gaseous environment, the gasification reaction has proved to be non-negligible. Exploring the promotion and competition mechanism between oxidation and gasification reactions will help regulate the combustion characteristics of char through pressure and atmosphere. Thence, it is critical to explore the influence of the gasification reaction on oxy-fuel combustion and decouple the contribution ratio of the gasification reaction. The experiments under different conditions are performed on a laboratory-scale pressurized fixed bed in the research. The C atom in CO 2 gas is labeled with 5.95% 13 C; thus, the contribution ratio of the gasification and oxidation reactions can be decoupled by tracking the 13 C atom abundance in CO 2 and CO. The results are apparent: the pressure, temperature, and oxygen concentration increase, the combustion process is promoted, the combustion rate increases significantly, and the burnout time (t 80 ) decreases. In addition, the problem of the low combustion rate under oxy-fuel combustion can be solved by increasing the O 2 concentration. The decoupling results indicate that the contribution ratio of the gasification reaction increases with increasing pressure and temperature. As the CO 2 partial pressure increases, the gasification reaction is promoted. With the increase of temperature, the gasification reaction growth rate is faster than the oxidation reaction. In contrast, the contribution rate shows a decreasing trend due to the increased O 2 concentration promoting the oxidation reaction.

“…10 The high concentration of steam significantly affects the chemical structure and combustion reactivity. 11,12 CO 2 and H 2 O change the char structure by improving its aromatization and increasing the O-containing reactive groups, which changes the reactivity. 13,14 The chemical structure of pulverized coal changes continuously during combustion as a result of thermal effects at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…More disordered carbon is formed during the pyrolysis of coal in CO 2 than in N 2 , and new O-containing reactive groups are generated . The high concentration of steam significantly affects the chemical structure and combustion reactivity. , CO 2 and H 2 O change the char structure by improving its aromatization and increasing the O-containing reactive groups, which changes the reactivity. , The chemical structure of pulverized coal changes continuously during combustion as a result of thermal effects at high temperatures. The study of the carbon crystal structure of char in different atmospheres is useful to understand the evolution of carbon during combustion and, hence, the combustion mechanism of pulverized coal.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of CO₂ and H₂O Action on Char in Oxy-fuel Combustion with Wet Flue Gas Recirculation

Feng

Sun

et al. 2023

The mechanism of the combined action of the C–CO2 and C–H2O reactions has yet to be clarified in the study of oxy-fuel combustion with wet flue gas recirculation (WFGR). The ultrahigh temperature (1573 K) and atmosphere of an industrial boiler are simulated in the flat flame burner reaction system (FFB-RS). The measurement of surface reactive groups and combustion reactivity of char uses Fourier transform infrared spectroscopy (FTIR) and a microfluidized bed reaction analyzer (MFBRA). The results show that char combustion reactivity has an excellent positive correlation with an O-containing reactive group. Above a 35% H2O concentration, its physical properties dominate, while below 35%, its chemical properties play a significant role. When the ratio of H2O/CO2 is close to 1, there is a synergistic relationship between the C–CO2 and C–H2O reactions, which did not occupy the same active sites, promoting the formation of O-containing reactive groups (33.83%) and alkyl complexes (19.6%) with a combustion reaction rate of 0.225%/s.