Study On Combustion Mechanism Of Micro-Pulverised Coal

Micro-pulverised coal combustion technology is a new combustion technology with low NOX. It is regarded as one of important technology reducing NOX emission in some countries. Combustion of micro-pulverised coal has not only the function of decreasing NOX emission, but also represents some combustion characteristics such as low ignition temperature, high burn-off rate, reduction or removal of settling and slag-off made of fly ash on heating surface in furnace. In China, study on this technology was just started. Experimental studies in industrial sector have been conducted, however, the study on combustion mechanism is not deep and intensive. In this article, based on the pyrolysis mechanism of micro-pulverised coal, the emission characteristics of Nitrogen and sulphide in process of pyrolysis, the combustion mechanism of micro-pulverised coal and the emission characteristics of pollutants in process of combustion, the catalysis and reduction mechanism of metal mineral to NO, the author studies systematically the combustion mechanism of micro-pulverised coal. The purpose of study is to provide valuable parameters for design and operation of furnace burning micro-pulverised coal and to provide theoretical basis for technical study on increasing combustion rate of coal and reducing emission of air pollutants.First, the author studies the pyrolysis characteristics of micro-pulverised coal by thermobalance, studies the effects on pyrolysis characteristics and pyrolysis dynamics characteristics of pulverised and micro-pulverised coal from different type, size of coal and temperature raise speed through the method of non-isothermal thermogravimetric analysis. Meanwhile, by using gas chromatography/mass spetrometer, the author studies the precipitation characteristics of nitrogen- and sulphide-containing compound in pyrolysis process of pulverised and micro-pulverised coal and analyses the influences on precipitation by the above-mentioned factors. This study is meaningful to understand in-depth the behaviour characteristics of pulverised and micro-pulverised coal before combustion. The result shows that micro-pulverisation change the precipitation characteristics of volatile content of coal and micro-pulverisation helps precipitation of volatile content; when the size is over 10μm, emission amount of nitrogen-containing gas has positive correlation with nitrogen amount contained in coal in process of pyrolysis; sulphide precipitation in process of coal pyrolysis is not completely controlled by total nitrogen amount, but controlled by form and content of sulphide in coal, by content of acidwashing minerals and alkali minerals, content of hydrogen and other exterior conditions.In order to understand further the characteristics of pulverised and micro-pulverised coal in process of combustion and the precipitation characteristics of pollutants, the author studies the ignition characteristics of pulverised and micro-pulverised coal by using thermal analysis scale, the maximum combustion speed rate and combustion characteristics, analyses the effects to ignition characteristics and general combustion characteristics by different size, temperature raise speed and oxygen concentration, studies the generation characteristics of SO2 and NOx which are main pollutants in coal air by gas chromatography/mass spetrometer, probe into effects to SO2 and NOx generation by different size, temperature raise speed and oxygen concentration and type of coal and find out the factor and mechanism controlling emission of pollution air. The study is meaningful to optimised operation of coal furnace.Mineral substance in coal is the important factor effecting combustion of pulverised and micro-pulverised coal. It is a hot study point at present as well. The author makes further study on this point, too. The main study method is to first de-ash pulverised and micro-pulverised coal, then add oxidate and hydroxide of Ca, Mg, Na, K, Al, Fe into deashed sample to study the influence to combustion characteristics of pulverised and micro-pulverised coal and precipitation characteristics of pollutants by corresponding mineral groups and to analyse possible reasons. The result shows that proper quantity of KOH and NaOH can improve the combustion characteristics of pulverised and micro-pulverised coal and reduce apparent activated energy. Three kinds of pulverised and micro-pulverised coal show 3-peak SO2 emission course in process of combustion, but SO2 emission course of deashed sample is double peak course. Temperature range for peak value occurring is not same neither. It is found that Na has strongest catalysis and reduction capacity relating to type of coal.NO catalysis and reduction is an important way of oxygen denitration. It has been studied by many researchers. However, catalysis and reduction of NO in combustion process in relatively complex, so far there is no any report on this study. The author uses quantum chemistry study and takes Mg5O5 of small-scaled MgO cluster model as objective to study the mechanism of catalysis reaction between coke NO and analyse NO decomposition approach. The study provides theoretical basis for de-NO technology in process of combustion. In the last part of article, the author studies the surface characteristics of raw coal and semicoke of pulverised and micro-pulverised coal. The surface fractional dimension number of sample of raw coals from Hegang, Tiefa and Zhungaer area is 2.3459, 2.2942 and 2.7267, respectively. The surface fractional dimension value of three coals is between 2 and 3. With reduction of particle size, specific area of pulverised coal increases and surface analysis dimension increases. That means with reduction of particle size of coal, the surface structure gets complex and analysis dimension gets high, therefore, it is helpful for combustion.