Development & Instrumentation of Atmospheric Drop Tube Furnace for the Gasification of Solid Hydrocarbon

Abstract

This thesis tackles material overconsumption and ineffective waste management by promoting a shift to a circular economy. It highlights the escalating issue of municipal solid waste in the Middle East/North Africa (MENA) region and the urgent need for effective waste treatment and energy recovery solutions. The study notes a potential rise in global material extraction from 92B tonnes in 2018 to 177B tonnes by 2050 without intervention. Focusing on waste-to-energy technologies, particularly gasification, the research explores converting waste into syngas for power generation using olive pomace, sewage sludge, and electronic waste, including printed circuit boards. Through detailed material characterization, equilibrium, comprehensive experimental analyses and an effort to conduct high-fidelity numerical modelling, the thesis provides insights into the opportunities and challenges of transforming solid waste into energy, setting the stage for future advancements in sustainable waste management.

This thesis outlines a comprehensive methodology for studying gasification processes applied to various solid waste feedstocks, including olive pomace, sewage sludge, and PCBs. The initial steps involve de-moisturizing and sizing the feedstocks, followed by detailed characterizations using both traditional (proximate, ultimate, calorific values) and analytical (Fourier transform infrared spectroscopy (FT-IR), x-ray diffraction (XRD), and scanning electron microscopy (SEM)) methods. This approach aims to deeply understand the properties of each feedstock. The study also assesses operational parameters such as mass flow rate (MFR), power rating, and storage time to evaluate the gasification process's efficiency and practicality. Olive pomace shows particular promise, with a high calorific value of 23.48 MJ/kg and a low ash content of 5.75%, in contrast to the lower values and higher ash contents found in sewage sludge and PCBs.

Operational analysis reveals that larger particle sizes (200 µm) and increased rotational speeds (1000 rpm) optimize MFR values, with olive pomace achieving 7.691 g/min, outperforming other feedstocks. Optimal power ratings are identified as 3.01 kW for olive pomace, 4.01 kW for sewage sludge, and 5.19 kW for PCBs. Smaller particles (80 µm) result in longer storage times, indicating the nuanced interplay of factors in the gasification process. Further, the thesis incorporates low fidelity equilibrium modelling techniques, such as response surface methodology (RSM) and gasification equilibrium modelling, to predict gasification products and cold gas efficiency (CGE) under various conditions. These models help identify the optimal operating temperatures and pressures, showing an ideal gasifier temperature of 1,272.15°C, a pressure of 31.68 bar, and an oxidizer mole ratio of 0.986, resulting in a CGE of 64.02%. Equilibrium modelling specifies the best conditions for gasifying olive pomace as 1,200°C, 30 bars, and 1.014 moles (ER = 1.05), achieving a CGE of 64.13%. Sensitivity analyses explore the impact of various reactions and conditions on syngas production efficiency, highlighting how char formation can significantly reduce CGE to 18.58%. This detailed investigation into the gasification process provides valuable insights into optimizing gasification efficiency and understanding the complex chemical dynamics involved.

Experimental investigation is performed in a custom-built drop tube reactor (DTR), measuring temperature profiles and syngas composition during reactive and non-reactive experiments. It confirms the model's temperature distribution, with non-reactive temperatures reaching 1,200 K at 0.4 m and reactive temperatures around 1,050 K at 0.6 m. Analysis shows dynamic changes in gas composition along the gasification pathway, with minimal H2 concentrations (maximum 0.07%) indicating limited secondary reactions. The SEM analysis of olive pomace particles shows significant morphological changes that impact gasification efficiency based on the porosity, surface area, temperature gradient, and residence time.

Additionally, the study attempts to conducts an in-depth high fidelity numerical analysis using ANSYS Fluent to evaluate the gasification process, particularly focusing on moisture release, devolatilization, and char formation within a DTR. It aims to capture the complexities of particle conversion and syngas generation, emphasizing temperature profiles and gas species distribution. For non-reactive cases, it achieves a maximum temperature of 1,350 K at 1.1 meters with an optimal heat flux of 15 kW/m². During reactive operations, the peak temperature reaches 1,213 K at 1.1 meters. The model estimates a cold gas efficiency (CGE) of 28% and identifies discrepancies in CO and H2 concentrations (47.06% and 1.23%, respectively) compared to equilibrium predictions (60.30% and 36.40%). This suggests an overestimation in CO2 and H2O generation (13.18% and 32.11%, respectively), emphasizing the need for further understanding of the numerical model and optimization of the parameters.

This comprehensive study of gasification technology provides insights into the transformation of solid waste into syngas, underscoring its potential for sustainable energy recovery and waste management. By combining material characterization, modelling, and experimental investigation, the thesis lays a foundation for future advancements in gasification technology, aiming for more sustainable and efficient waste management practices.

Date of Award	13 May 2024
Original language	American English
Supervisor	Isam Janajreh (Supervisor)