Experimental Investigation On The Combustion Characteristics Of Semi-cokes In Low Oxygen Concentration

In this thesis, experimental analyses are used to investigate combustion performance of semi-cokes with different coal rank, semi-coke of shale and lean coal. The experiment wanted to provide theoretical basis on combustion application. By using hesigewula lignite, naomaohu long flame coal, shenmu bituminous coal were chosed as raw materials, and liushuhe shale and jixi lean coal were used as the contrast.Combustion experiments on semi-cokes and lean coal were carried out in thermogravimetric analyzer and obtain their combustion TG and DTG curve. The effects of heating speed, oxygen content and activating reaction on the combustion characteristics of semi-cokes and lean coal were investigated. Kinetic parameter of different conditions was gained by dynamic equation.The results show that:(1).With the increase of heating rate, TG and DTG curves move to high temperature, the combustion characteristic temperature and combustion characteristic index increase. With the increase of coal rank, the ignition temperature of semi-cokes increased and ignition performance becomes poor. Through the calculation of C-R dynamic equation, the activation energy and pre-exponential factor reduced with the increase of heating rate. Therefore, semi-cokes and lean coal are much easier to burn. At the same time, it was revealed by DAEM dynamic equation that activation energy of five samples reduced with the increase of conversion rate. Combustion reactions required more energy at the beginning of the reaction, as the reaction progressed, the required energy decreased. (2). The samples with two different particle sizes(<0.2mm and<0.05mm) have been used to study the effects of low oxygen concentration on combustion characteristics. When the oxygen content reduced from 21% to 8%, the burning curve of two different particle sizes is similar. TG and DTG curves of all samples move to the higher temperature zone, and with lower the density of oxygen, the higher combustion characteristic temperature and the lower combustion characteristic index is, in addition, maximum mass loss reduces. The appearances show that the reducing of oxygen content has a disadvantageous to the combustion of semi-cokes and lean coal. When the size of samples reduced, the combustion characteristic temperature reduced. It shows that reducing the size of samples can improve the characteristic of ignition and burnout. (3). Compared with raw semi-cokes, the specific surface area of activated semi-cokes increased. Combustion TG and DTG curves move to high temperature. Because of the content of combustible matter reduced after the activating reaction, the burning weight loss of activated semi-cokes and lean coal reduced obviously. Meanwhile the combustion characteristic temperature increased; combustion characteristic index diminished; combustion rate reduced; activation energy E increased. Therefore, combustion performance of activated semi-cokes and lean coal become poor.