Experimental Study Of High-alkali Coal On Combustion Characteristic

Xinjiang will become an important construction base of the powerand energy with its high reserves of coal resources. However, severe ashdeposit and even fouling and slagging problems have occurred whenburning Zhundong coal because of its high content of alkalis, which is abarrier of exploiting Zhundong coal on a large scale.Therefore,it’snecessary to make some researches on the combustion characteristics andash behavior of Zhundong coal, in order to provide some theoretical anddata support for the boiler that can be suitable for burning Zhundong coal.In this dissertation, the combustion characteristics and ash behavior arestudied by using a hot stage microscope attaching a camera as well as ahigh-temperature electrical furnace on the scale of laboratory. The resultsare listed as follows:Zhundong coal has a good combustion characteristic on account ofits typical coal properties, such as high content of volatiles, low contentof ash and high content of alkalis. On the air condition, the ignition temperature is300℃and the average volume changing rate is1.28，which is higher than the other four kinds of coals.On the oxygencondition, the ignition temperature is298℃,which is lower than the otherfour kinds of coals. According to the ash behavior experiment, ofZhundong coal ash is770℃and at the same time, the initial meltingcapacity is24％.In order to improve the discriminant accuracy, we usethe comprehensive slagging index which involves the effects of ST、silicon ratio an alkali/acid ratio to evaluate the slagging tendency. Thecomprehensive slagging index of Zhundong coal is7.01, which is muchhigher than that of the other four kinds of coal ashes. With the increase ofthe ashing temperature, the Zhundong coal ash slagging tendencydeclines, the initial melting temperature has increased from700℃to770℃,the initial melting capacity has decreased from38％to24％,andthe comprehensive slagging index has decreased from7.35to7.01.During the experiment of the wettability and corrosion of Zhundongcoal on the surface of different materials, we found that at the sametemperature, the contact angle and interface tension between the ash andaustenite steel are lower than those between the ash and Ni-coating steelmaterial, and the work of adhesion of the former is higher than that of thelatter. What’s more,the corrosion of ash on the austenite steel is moreserious than that on the Ni-coating steel material. This phenomenon canindicate that the ash deposit and slagging may be controlled by nickel plated treatment on the surface of heat-exchange tubes.