The global demand for energy and chemical production is drastically increasing due to the rapid increase in the world population and industrialization. Intensive reliance on fossil fuels poses environmental challenges related to energy security, climate change and increased greenhouse gas emissions. The increase in world population and the improvement in living standards also lead to the increased demand for the automobile sector. This in turn results in excessive production of waste tyres leading to another environmental concern. Gasification of biomass and waste tyre provides a viable pathway with the potential to tackle the concerns of energy supply security and waste management. This thesis aims to kinetically analyse the thermal decomposition of biomass and waste tyre and to investigate the syngas production from gasification of biomass and waste tyre through process modelling and simulation.
Understanding the decomposition of biomass and waste tyre in terms of thermal behaviour and the underlying kinetics is important to evaluate the existence of synergetic interaction and optimise their uses. The experimental data acquired through thermogravimetric analysis (i.e. TGA) of pine bark, waste tyre and their blends are used to evaluate the behaviour of the samples during thermal decomposition and to calculate the kinetics data. The main findings are as follows: (i) The increase in the heating rate shifted the differential thermogravimetric (i.e. DTG) curves to higher temperatures and resulted in the variation in the difference in weight loss thus the extent of positive synergetic interaction, (ii) Based on various kinetic analysis approaches adopted in this thesis, the use of pine bark and waste tyre with a mass ratio of 1:3 showed maximum synergetic interaction in which the activation energy decreased by 13.95-17.21% compared to a single waste tyre, (iii) The reaction mechanisms describing the thermal decomposition of pine bark, waste tyre and their blended samples are a combined effect of nucleation, growth and diffusion which are estimated using the Sestak Berggren model. The differences in the chemical structures and composition of the pine bark and waste tyre account for the different thermal and kinetic behaviours observed.
CO2 gasification of biomass and waste tyre was conducted through process modelling and simulation using ASPEN Plus® to utilise CO2. After the successful validation of the developed model, the effect of gasification temperature, CO2-to-feed ratio and feed flow rate was analysed. Gasification temperature and feed flow rate had a positive effect on H2 and CO production in which the temperature had a predominant effect on CO2 conversion to CO. The maximum total concentration of H2 and CO with the highest fraction of H2 compared to CO was found to be 62.97 vol% at a temperature, CO2-to-feed ratio and feed flow rate of 1173 K, 0.20 and 0.045 kg/hr. Under the same conditions, the highest H2/CO ratio and LHV with values of 1.56 and 17.75 MJ/Nm3 were obtained. Comparing the pine bark and waste tyre blended samples, pine bark and waste tyre with a mass ratio of 1:3 resulted in syngas with slightly better H2/CO ratio and LHV than other blended samples.
Since the use of steam has a positive effect on H2 production, co-gasification of biomass and the waste tyre was analysed using steam and steam/CO2 mixture as gasifying agents using ASPEN Plus®. The increase in temperature showed a positive effect on the H2 content of the syngas in both steam and steam/CO2 gasification. The maximum H2 content was reported at a temperature of 1223 and 1273 K for steam and steam/CO2 gasification respectively. The highest H2/CO ratio was reported at a temperature of 1173 and 1048 K with values of 4.76 and 3.79 for steam and steam/CO2 gasification respectively. During steam gasification, a negligible effect on syngas composition was reported at steam-to-feed ratio higher than 2.90 which was not the case in steam/CO2 gasification. Therefore, the H2/CO ratio peaked at an average steam-to-feed ratio of 3.22 with values ranging between 2.32 and 4.80 for all the samples. Feed flow rate and gasification temperature of 0.20 kg/hr and 1173 K, respectively, resulted in syngas with LHV of 13.96-17.74 MJ/Nm3 in steam gasification and 10.34-13.01 MJ/Nm3 in steam/CO2 gasification. In comparison to CO2 gasification, steam/CO2 gasification produced syngas with a total H2 and CO content three times higher than CO2 gasification whereas H2/CO ratio was higher by a minimum of 1.7 times in case of WT1PB0 at a temperature, feed flow rate and CO2-to-steam mass ratio of 1173 K, 0.045 kg/hr and 0.5:0.5.
The findings of the current research could provide a comprehensive understanding of the co-gasification of biomass and waste tyre under different operating conditions prior to considering experimental and/or large-scale implementation of such technology. In addition, they aid in diversifying waste disposal options with the potential to mitigate CO2 emissions.
