Term of Award

Spring 2023

Degree Name

Master of Science, Mechanical Engineering

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Mechanical Engineering

Committee Chair

Prakash Bhoi

Committee Member 1

David Calamas

Committee Member 2

Sevki Cesmeci

Abstract

This research explores the potential of mitigating CO2 emissions from fossil fuel consumption and providing an alternative renewable source of energy by gasifying biochar with carbon dioxide (CO2) and steam (H2O). The utilization of captured carbon dioxide and wastewater in industrial sectors is considered to further contribute to the advancements in energy-efficient and low-emission technological solutions. This research evaluated the performance and kinetic parameters of biochar gasification through CO2 and H2O gasification using a stainless-steel fixed bed reactor. The operating parameters including biochar mass, reactor temperature, and inlet flow rate were varied. Biochar bed sizes of ~35 g, ~52 g, and ~70 g was used for both gasification processes. The CO2 gasification process involved reactor temperatures ranging from 900°C to 1000°C, with inlet CO2 flow rates of 5 L/min to 7 L/min. H2O gasification process was conducted at reactor temperatures between 800°C to 1000°C, with inlet flow rates of 3 mL/min and 5 mL/min. The study aimed to identify the optimum operating conditions for biochar gasification and improve understanding of the process kinetics. Prior to the gasification process, the biochar was crushed and sized using a 2.0 mm sieve to achieve biochar particle size of 1-2 mm. A NOVA gas analyzer was employed to analyze the outlet gaseous compounds, while the volumetric reaction model (VRM) was used to evaluate the kinetic parameters. Results showed that higher temperatures favored CO and H2 production in both CO2 and H2O gasification processes. A reactor temperature of 950°C, CO2 inlet flow rate of 5 L/min, and biochar bed size of ~52 g resulted in 100% CO2 conversion and maximum CO production. The activation energy for CO2 gasification at 5 L/min flow rate was 136.3 kJ/mol. The study also evaluated various performance parameters, including gas yield, syngas composition, and H2/CO ratio for the H2O gasification process. An increase in temperature and inlet flow rate resulted in increased H2 molar yield, but a decrease in H2/CO molar ratio. The highest H2/CO molar ratio of 5.45 was achieved at a reactor temperature of 800°C, biochar bed size of ~52 g, and inlet flow rate of 5 mL/min. The lowest molar ratio of 1.29 was obtained at 1000°C with ~70 g of biochar and flow rate of 3 mL/min. The activation energy for H2O gasification was found to be in the range of 107.5 kJ/mol to 119.1 kJ/mol. The study suggests that implementing both gasification processes in conjunction could achieve the optimal H2/CO ratio of 2 for Fischer Tropsch (FT) synthesis processes.

Research Data and Supplementary Material

No

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