| As a great commercial potential CO2capture technology, O2/CO2combustion recently gained extensive attention. Since a large number of exhaust gas circulation, H2O concentration in O2/CO2combustion is obviously higher that in conventional air combustion, even up to40%in the system adopting wet exhaust gas circulation. The high H2O concentration inevitably affects the combustion, studying the combustion and gasification of pulverized coal in O2/CO2/H2O atmosphere is help to deeper reveal the complex mechanism of pulverized coal combustion and transformation in real oxyfuel atmosphere, and it is of great scientific significance to the industrial application of oxyfuel technology.This thesis firstly studied the effects of28kinds of typical coal rank on O2/CO2combustion characteristics using TG-DTG method. It was found that pulverized coal with high internal water, high volatiles matter, and low fixed carbon and low ash content presents higher reactivity. High fixed carbon content of the coal is easy to improve combustion by increasing O2concentration. The effect of increase in O2concentration can significantly improve the combustion of coal with high C, low O/C and low H/C. Coal with a high fuel ratio or a high degree of graphitization presents greater need of increasing O2concentration to improve combustion. In this paper, the effect of particle size on the pulverized coal combustion in an O2/CO2atmosphere was also studied. The effect of particle size on the combustion of pulverized coal under O2/CO2atmosphere is greater than that at O2/N2atmosphere. And the higher content of volatile matter in the coal, the more affected. Compared to the O2/N2atmosphere, the combustion characteristic of pulverized coal changed with the particle size under O2/CO2atmosphere shows greater fluctuation. And the fluctuation of coal on a small particle size becomes greater with the content of volatile matter increase.For H2O concentration in real oxy-fuel combustion atmospheres is vary high, this study studies the effect of high H2O on pulverized coal combustion behaviour in O2/CO2 atmosphere. The ignition temperature, burnout temperature and comprehensive reactivity of three types of Chinese coal at different H2O and O2concentrations in O2/CO2/H2O atmosphere were investigated. The effect of particle size, sample weight, gas flow rate and heating rate on the pulverized coal combustion was also studied under high-H2O-concentration oxy-fuel atmosphere. The results showed that the presence of H2O strongly affects the combustion characteristics of coal and coal char in O2/CO2atmosphere, leading to a greater ignition delay, faster burnout and higher comprehensive reactivity. These changes are more obvious for brown coal. Under O2/CO2/H2O atmosphere, H2O can improve the diffiisivity and heat capacity of the combustion atmosphere, which is one of the reason to improve the pulverized coal combustion.At last, gasification caused by high H2O, CO2concentration in O2/CO2/H2O atmosphere is the focus of this study. For in-depth discussion the effect of C-H2O and C-CO2reaction on pulverized coal devolatilization and char structure, the pyrolyses and gasification of kinds of coal under H2O, CO2atmosphere was studied. With the horizontal tube furnace and drop tube furnace, flue gas properties of pulverized coal in O2/CO2/H2O atomosphere under gas evolution and rapid reaction were studied. The proportion of combustion and gasification with kinds of pulverized coal under different H2O concentrations and various temperatures were calculated. The result has shown that the abundant porosity of char structure under H2O atmosphere greatly affected the gasification of the high rank coal. Under the O2/CO2/H2O atmosphere, competition exsit between C-CO2and C-H2O reaction. Increase in H2O concentration can weak C-CO2gasification and enhance C-H2O gasification. With the increase of coal rank, the gasification reaction in the coal combustion process was gradually weakened. Effect of temperature on coal combustion was directly affected by the test condition. Gasification proportion was low in a fixed bed of gas evolution at a low temperature and low in a drop tube furnace of fast reaction at a high temperature. |
PDF Full Text Request