利用管式炉平台研究了两种低阶煤的热破碎特性。实验结果发现，粒径为1.0 mm ~ 5.0 mm的褐煤、烟煤在600°C ~ 800°C温度下均发生了一定程度的破碎。低阶煤的热破碎程度与煤阶、粒径大小及温度等因素有关。在研究范围内，煤阶越低、原煤颗粒越大、温度越高，原煤发生的热破碎越剧烈。
|其他摘要||Coal plays a very important role in the national economic and social development of China. The present situation that consumption of coal occupies a dominant position in energy consumption can not be fundamentally changed in the next few decades. With the gradual reduction of high-rank coal and the increasing demand for energy, the use of low-rank coal is gradually put on the agenda. How to cost-effectively utilize low-rank coal resources is very important.
"Demonstration of key technologies for clean and efficient utilization of low-rank coal”, sponsored by strategic priority research program of the Chinese Academy of Sciences, proposed the route that "Firstly extract oil and gas resources in the existing coal by efficient pyrolysis technology, then the surplus char can be used for combustion or conversion to liquid fuels and chemicals via gasification". Clean and efficient combustion of char/coal” is one of the important researches in this technical route. Circulating fluidized bed combustion technology is one of the most successfully commercialized combustion technologies for coal or char. When the low-rank coal and char are used in the technology of circulating fluidized bed combustion, fragmentation characteristics of particles will influence the material density distribution in the bed, which should be solved for the design and operation of circulating fluidized bed. In addition, the studies of oxy-fuel combustion and oxy-enriched combustion reaction characteristics for low-rank coal char can provide basic data for the fluidized bed combustion technology of low-rank coal char, and thus lay the foundation for engineering amplification. In this paper, the characteristics of low-rank coal’ thermal fragmentation and oxy-fuel combustion reactivity of low-rank coal chars were studied. Shenmu lignite and Shenmu bituminous coal, two kinds of typical Chinese low-rank coal, were selected as the experimental samples to study the thermal fragmentation characteristics. Then different kinds of low-rank coal chars were prepared at different pyrolysis temperatures to explore their oxy-fuel combustion characteristics. The effects of different atmospheres (CO2, N2 and Ar) and different oxygen concentrations on the combustion characteristics were studied in detail, and kinetic analysis of the combustion profiles of the coal chars with different oxygen concentration was also performed.
The thermal fragmentation of two kinds of low-rank coals were conducted using a tube furnace platform. Experimental results showed that fragmentation occurred among lignite and bituminous coal for their particle size from 1.0 mm to 5.0 mm at a pyrolysis temperature from 600 °C to 800 °C. Thermal fragmentation of low-rank coals was exacerbated by the decreasing of coal rank, increasing of coal particle size and the increasing of temperature within the present investigation conditions.
Oxy-fuel combustion characteristics of the low-rank coal chars obtained under different pyrolysis temperatures were studied with different atmospheres and different oxygen concentrations using thermal-gravimetric analyzer. The results showed that the TG curve of chars shifted to high temperature zone with increasing the preparation temperature of char, and both ignition temperature and burnout temperature increased accordingly. This means that higher preparation temperature of char does not favor the combustion reaction. Oxy-fuel combustion characteristics of chars were also different by changing atmospheres. And the differences of density and thermal diffusivity among CO2, Ar and N2 may be the reason. When the oxygen concentration was greater than 40%, gaps among TG curves of char combustion under three different atmospheres became very small, and the values of characteristic temperature were almost at the same level. With a higher oxygen concentration, the oxidation rate increases drastically and plays a dominant role, and the difference of the gas’s physical property has hardly influence on the char combustion characteristics. Thus, when the oxygen concentration is greater than 40%, three different atmospheres studied can be treated as one kind of atmosphere for char combustion. Char combustion characteristic analysis under different oxygen concentrations showed that ignition temperatures and burnout temperatures were reduced with increasing oxygen concentration. The kinetic analysis showed that the oxy-fuel combustion reaction of the chars conformed to D6 model of solid phase reaction mechanism function, and then the apparent activation energy E and the pre-exponential factor A were calculated based on the D6 model. Furthermore, it was found that kinetic compensation effect presented between the char combustion reaction under different oxygen concentrations. So the judge of reaction reactivity for char combustion just by activation energy is unreasonable.|
沈国栋. 低阶煤热破碎特性及其半焦富氧燃烧反应特性研究[D]. 北京. 中国科学院大学,2016.