Kinetic Study On Co-Gasification Of Petroleum Coke And Biomass

The big current issues in the world energy consumption are mainly rapid depletion of fossil fuels and environmental problems caused by the utilizations of the fossil fuels, such as direct coal combustion. Gasification is a clean, efficient, promising technology and an attractive option to produce high quality fuel gases from coal, petroleum coke (PC), biomass, etc. Extensive studies on gasification of biomass, coal or PC have been performed by many researchers. However, there is an apparent knowledge gap in understanding the co-gasification process of PC and biomass, such as Sudanese PC and sugar cane bagasse (SCB) which have quite low sulphur content and are abundant in Sudan. In addition, the previous research work on the Sudanese SCB gasification does not provide an understandable relationship between pyrolysis conditions, char structure and char reactivity. This remains a unexplored area of research. Therefore the main contribution of this research is gaining a fundamental understanding on gasification of PC and SCB, and co-gasification of their blends in CO2or H2O.This thesis presents research on the non-isothermal gasification of PC and SCB, and co-gasification of their blends by using a thermogravimetric analyser (TGA). The gas products during CO2non-catalytic gasification were identified online by fourier transform infrared spectroscopy (FTIR) connected to the TGA. The behaviour, effects of catalyst (iron chloride, FeCl3) and H2O concentration, synergistic effects between PC and SCB during gasification in CO2or H2O were investigated. In addition, the characteristics (physical and chemical properties) of SCB chars as a function of pyrolysis temperature were studied by applying Brunauer-Emmett-Teller (BET) surface area and FTIR. Finally, the homogeneous model (HM), chemical first order reaction (O1) and shrinking core model (SCM) or phase boundary controlled reaction (R2and R3), based on Arrhenius’s equation through Coats-Redfern approximation were used to describe the reaction mechanism and estimate the kinetic parameters of the gasification processes. While, Vyazovkin method based on the Coats-Redfern approximation and Flynn-Wall-Ozawa method based on the Doyle’s approximation were used for SCB chars gasification. The main results can be categorised into several parts:Firstly, the CO2gasification of the PC took place in only one stage (char gasification stage) at temperatures higher than800℃and700℃for non-catalytic and catalytic gasification, respectively. During steam gasification with H2O concentration of25and50%PC is presented in two stages, which were pyrolysis stage at lower than500℃and char gasification stage at higher than700℃. If the H2O concentration was75%, the PC is presented in only char gasification stage. On the other hand, the gasification of SCB chars took place almost completely in one stage process at temperature higher than600℃. The main released gases are CO and CO2obtained at higher temperature (>700℃), and CH4, HCOOH, C6H5OH and CH3COOH obtained at lower temperature (<500℃).Secondly, the addition of7wt%FeCl3to PC leads to improve the reactivity of PC from1.39%/min up to2.19%/min and decrease the activation energy from218.12kJ/mol to170.32kJ/mol. On the other hand, the addition5wt%FeCl3for char gasification of SCB and blend leads to improve their reactivities from1.70%/min to3.45%/min and from1.25%/min to1.63%/min, and decrease their activation energies from134.87kJ/mol to120.42kJ/mol and from138.70kJ/mol to114.90kJ/mol, respectively.Thirdly, significant synergistic effects existed in both reaction stages of the blend gasification, especially for the gasification with the PC content higher than75%. As well as, the effects is more significant for the catalytic gasification.Fourthly, as pyrolysis temperature increased, the atomic ratios of H/C and O/C decreased continuously from1.55and0.74in pure SCB to0.29and0.22for the char prepared at900℃. The SCB char reactivity is directly proportional to gasification heating rate. The hydroxyl, aliphatic C-H, carbonyl and olefinic C=C groups were lost at pyrolysis temperatures higher than800℃.Fifthly, the H2O co-gasification behaviour and kinetic parameters were significantly affected by increasing the H2O concentration, PC content and FeCl3loading. The activation energy increases by36.44%when the H2O concentration increases from25to75%, which are achieved by the model R2. Similarly, the results of fuel blend effects show that the activation energy increases by77.16%when the PC content increases from0to100%. Finally, it was found that the boundary controlled reaction R2was the most suitable model to describe the thermal behaviour and predict the reaction mechanism of CO2(non-catalytic and catalytic) and H2O gasification of PC, SCB and their blends. The Vyazovkin and Flynn-Wall-Ozawa methods were effective for predicting the reaction mechanism of H2O gasification of SCB chars.