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Design and Experimental Study of a Sabatier Reactor for Conversion of CO2 and Biogas into Renewable Natural Gas

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Zhuang_Yichen.pdf (9.39 MB)

Date

2022-05-04

Authors

Zhuang, Yichen

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University of Waterloo

Abstract

Biogas is a product of anaerobic fermentation which is rich in CO2. Upgrade of biogas is commercially achieved by separating CO2 and impurities to improve its quality. As an alternative, the CO2 contained in biogas can be directly converted into CH4 via the thermocatalytic Sabatier reaction without separation, using H2 generated by water electrolysis (utilizing renewable or surplus, low carbon footprint electricity). One of the major elements of this technology is the configuration of the Sabatier reactor. For industrial applications, it is beneficial to eliminate the energy-intensive CO2 separation step, converting biogas to RNG directly. This study aimed to demonstrate the feasibility of converting CO2 and anaerobic fermentation streams (such as biogas and landfill gas) into renewable natural gas (RNG) in an autonomous Sabatier reactor. The highly exothermic nature of the Sabatier reaction brings challenges to the design and operation of Sabatier reactors, especially the issues of thermal management. A completely autothermal operation of the N2-cooled, stainless-steel reactor, using a Ni/Al2O3 catalyst has been demonstrated. The effects of feed temperature, space velocity and cooling rate were investigated using three prototypes with different sizes and configurations. The maximum CO2 conversion of 93.5%, with 100% selectivity to CH4 generation, was achieved in a 10″-length reactor, over 120 h of a continuous, stable operation with a pure CO2 feed (at 2,400 L/(kg h), without any reactor heating or feed preheating. The same reactor also delivered 91% CO2 conversion with 100% CH4 selectivity using a synthetic biogas feed (without H2S and VOCs) for 100 hours of stable operation. Experimental data, including outlet concentrations and temperature distribution, were collected using an automated system and carefully analyzed. Kinetic parameters in a Sabatier-RWGS model were estimated and the final prototype reactor was modeled in COMSOL. A critical analysis of the collected data is presented, and future perspectives are discussed.

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Keywords

Sabatier reactor, Renewable Natural Gas, CO2 methanation

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URI

http://hdl.handle.net/10012/18225

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Chemical Engineering