Devolatilization Characteristics of Coal Particles Heated with CO₂ Laser Controlled by Double Shutters. 1. An Experimental Investigation

Abstract

A CO 2 laser controlled well by specially designed double shutters was used to heat uniformly dispersed coal particles in nitrogen. The temperatures of the coal particles were measured using a highly accurate multiplepoint, two-color temperature measurement system. The average performance and characteristics of three kinds of coals with different volatile content were carefully investigated at various experimental conditions. The conclusions are as follows: (1) the proximate volatile matter content, particle size, and laser intensity are the three most important factors in the devolatilization process of coal particles under the laser heating condition;(2) the devolatilization processes can be separated into two parts by the proximate volatile matter contents of three coals, which suggests that two devolatilization schemes exist in each coal; (3) the effect of laser intensities on the devolatilization processes indicates that the devolatilization process cannot be well-characterized by only laser intensity; (4) the existence of cross points in the curves of weight loss and particle temperatures among the samples with different sizes are one of the important features of laser heating, which is distinctively different from other heating methods; (5) the variation in V/V 0 values of all three kinds of coals with particle temperatures exponentially depends on coal particle temperatures, and can be expressed as V/V 0 ) 9.0 × 10 -4 exp(5.3 × 10 -3 T p ) with R 2 ) 0.8833; (6) the change in V/V 0 of W coal with different particle sizes is highly dependent on particle temperatures and can be expressed as V/V 0 ) 1.3 × 10 -3 exp(5.2 × 10 -3 T p ) with R 2 ) 0.9169; (7) a comprehensive expression, which includes volatile matter content, in situ energy density per surface area of coal particle, final particle temperature, and in situ particle properties, such as swelling, shrinking, emissivity, etc., should be further investigated.

Devolatilization Characteristics of Coal Particles Heated with a CO2Laser Controlled by Double Shutters: A Simulation Investigation†

“…As discussed in our earlier paper, the devolatilization rate is dependent on the volatile matter content, particle size, particle temperature, laser intensity, and heating rate. If a model that includes these parameters can be established, the predictions for the devolatilization process of coal particles under laser heating conditions will become possible.…”

“…They indicated that using measured temperature histories was more reliable than using predicted average bulk temperatures for kinetics calculation. Gao et al published their results on the devolatilization characteristics of coal particles heated with a CO 2 laser, in which they investigated the group features rather than a single particle to avoid the potential problems caused by heterogeneities of coal particles and supplied reliable data which could be used for temperature and kinetics calculations under laser heating conditions. More recently, Biagini et al studied the specific heat, size, and shape distribution, and density variation of low- and high-volatile-matter coal particles after devolatilization with CO 2 laser in an electrodynamic balance (EDB).…”

“…In this model, the well-known classical two-competing reaction mechanism proposed by Kobayashi et al was used; the proximate volatile matter content, coal particle size, laser intensity, and in situ energy density per surface area of coal particles were incorporated. The kinetics data for the devolatilization were obtained by analyzing the experimental data . The major reason for this interest in obtaining a better understanding of the pyrolysis, gasification, and combustion of coal lies in the increasing concern for the environmental impact of large-scale gasification and combustion processes.…”

“…The major reason for this interest in obtaining a better understanding of the pyrolysis, gasification, and combustion of coal lies in the increasing concern for the environmental impact of large-scale gasification and combustion processes. Another reason for this work is to solve some problems that remain from our early work …”

“…Another general model, the so-called FG-DVC model, belongs to a depolymerization model, in which there are some difficulties in obtaining optimum adjustable parameters. Considering the simplicity and practicality of the model for application, a relatively simple two-competing-reaction scheme proposed by Kobayashi et al was used to establish an empirical model under laser heating conditions and the model parameters were obtained by fitting our experimental data …”