Experimental Studies On Combustion Characteristics Of A Petroleum Coke

Petroleum coke is the main byproduct of the oil refining industry, with an increasing amount in China and worldwide. Though with high sulfur and low volatile content, petroleum coke is regarded as a potential alternative fuel for the pulverized coal fired boilers since it contains little ash, and possesses high heating value. Thus, it is of significance to understand the combustion characteristics of a petroleum coke for the boiler design and operation.Experimental studies on the combustion characteristics of a specific petroleum coke was first conducted on the thermogravimetry analyzer (TGA) under various heating rates, sample masses, and sample sizes. Based on the TGA measurements, the kinetic parameters, combustion indexes of the coke were calculated and with different methods proposed in the literatures. The ignition temperature of the petroleum coke is rather high due to its low volatile content. However, due to the high heating value, it shows intensive burning behavior after ignition. Therefore, the kinetic control region, of which temperature is lower than 900K, is rather short. In order to measure the kinetic parameters more accurately, it is suggested that low heating rate should be selected to last the duration of kinetic control region for the TGA measurement.Because of the low heating rate and low terminated temperature, the combustion of the solid particles in the TGA system is quite different from that in the boiler furnace. Therefore, a drop tube furnace (DTF) was designed and established in the levorotary. The furnace is of 42mm I.D., with an effective heating zone of 0.5m in length. The maximum temperature is 2000K, electrically heated with the graphite heating elements. Much effort has been paid to tune up the DTF system. With the DTF, a series experiments under high temperatures were conducted, including the sample preparation, the pyrolysis and combustion process of the petroleum coke.With the samples prepared in the high temperature DTF, porous structures of the petroleum coke and JX anthracite were studied by using nitrogen absorption method. The distributions of specific surface area and pore volume with pore diameter were derived by using BET and BJH methods. It was found that the porestructure was less developed for the petroleum coke comparing at the anthracite coal. However, the variation of the porous structure with pyrolysis temperature for both fuels was similar. The pores accounting for major specific surface area and pore volume are those ones in micro-size. Furthermore, with the increasing pyrolysis temperature, the specific area and pore volume increase firstly but then decrease when pyrolysis temperature exceeds a certain value. It was suggested that the melting of internal ash during high temperature pyrolysis is the main cause for such a phenomenon, and the turning point is related to the melting point of the char. The porous structure was also studied with samples prepared in high temperature oven. Fractal analysis was also conducted on the porous structure of the petroleum coke, and it was found the dimension factor is close to 3 when the pyrolysis process lasts 1 hour long.Some primary experiments were also conducted on the pyrolysis and combustion processes of the petroleum coke and other low volatile content coals. The flue gases were sampled and then analyzed online with FTIR system. Some primary results were obtained. In addition, the limitation of the DTF in combustion process study was discussed and some comments were given for the further improvement of the system.