Fundamental Kinetic Studies of CO2 and Steam Gasification

Gasification is the thermochemical conversion of a carbon-based fuel into a combustible product gas (syngas) using a gasifying agent, such as steam, carbon dioxide (CO2) or a combination of both. The application of this technology is limited, due to its slow reaction rate, making kinetics determination one of the most active research topics in this field. Different kinetic models have been proposed in the literature for the study of coal and biomass gasification, based on assumptions about their reaction mechanisms. Consequently, a thorough understanding of gasification mechanisms and the validity of these accepted assumptions is necessary to align theoretical studies and industrial results. A maximum rate is typically observed when the experimental gasification rates are plotted against conversion. The scientific community considers this to be an inherent part of the reaction mechanism, associated specifically with char surface changes. It is proven here that the stated maximum rate is a consequence of the reaction gas concentration development. Moreover, the increase in time for which the sample is held in an inert atmosphere reduces the char mesopore area, thereby reducing the char reactivity. As a result of the non-existence of a maximum gasification rate associated with changes in the char surface, kinetic modeling can be simplified. The active char surface area (based on its carbon content) and the amount of catalyst (related to the char alkali content) are the most important variables affecting char reactivity. A new semi-empirical equation correlating these two variables has been developed to estimate gasification rate constants of raw coal and their mixtures for a broad range of ash contents. The selection of a kinetic model mathematically affects the estimation of the kinetic parameters, i.e. activation energy and frequency factor. Therefore, a validation tool for kinetic models is the comparison of their kinetic parameters with those estimated independent of a kinetic model. A new theoretical approach to estimate kinetic parameters independent of a kinetic model for batch experiments has been derived and evaluated for coal gasification. The method can be extended to any chemical reaction and is, therefore, a contribution to chemical reaction engineering fundamentals. The assumption of no mass transfer limitations has been studied at temperatures lower than 900°C. It has been proven that steam gasification rates from most literature reports are limited by interparticle diffusion. A new experimental gasification procedure with negligible mass transfer limitations that do not induce a maximum rate has been developed, providing an alternative for more accurate kinetic studies.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Discipline thesis:degree_discipline

Chemical and Petroleum Engineering

Grantor dc:publisher.institution

Graduate Studies

Year dc:date.issued

2015

Author dc:creator

• Gomez Quevedo, Ramon Arturo

Advisor dc:contributor.advisor

• Mahinpey, Nader

• Engineering--Chemical

Statement dc:rights

• University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.

Language dc:language.iso

eng

DOI

http://dx.doi.org/10.11575/PRISM/26248

OAI identifier oai:identifier

oai:ucalgary.scholaris.ca:11023/2227