Thermal Decomposition Characteristics of Miscanthus and Ulva during Pyrolysis

Abstract

Global warming, caused by the excessive release of greenhouse gases due to the use of fossil fuels, is the main reason why a switch to renewable energy sources is becoming a necessity. A renewable energy source with a high potential to contribute to the energy needs worldwide is biomass. Biomass can be used for the production of electricity and heat or for the production of chemicals for a wide range of applications.

The overall challenge for the thermal conversion of biomass is the development of robust and efficient technologies to process biomass with a high conversion efficiency into a useful and clean product. Biomass pyrolysis has great potential to convert a wide range of biomass species into various products.

In this project, the decomposition characteristics of two high-potential biomass feedstocks, Miscanthus and Ulva, were investigated. The grass species Miscanthus has been in the spotlight as a potential biomass feedstock due to its rapid growth, high biomass yield potential and high calorific value. There is a growing interest in the seaweed species Ulva as a potential biomass feedstock due to its rapid growth and due to the fact its use may lead to a reduction of ecological problems (Ulva is a major sea pollutant).

Decomposition characteristics of Miscanthus and Ulva at slow heating rates were investigated with a thermogravimetric analyser. Proximate analysis results and mass loss rate graphs were obtained. The shapes (peaks) of the mass loss rate graphs were linked to the different biomass components present in Miscanthus and Ulva.

For the decomposition at fast heating rates pyrolysis experiments were carried out in a Pyroprobe reactor. The solid, liquid and gaseous product yields were analysed for different final pyrolysis temperatures. The compositions of the gas fractions were analysed using a micro gas chromatograph. The influences of pyrolysis temperature and biomass feedstock composition on the product yields and compositions were linked to different pyrolysis mechanisms

In order to determine the role of different biomass components in the pyrolysis process, the decomposition of the biomass feedstocks and pyrolysis kinetics are further investigated by modelling the mass loss rates of Miscanthus and Ulva during slow pyrolysis obtained from thermogravimetric analysis. For this purpose, the independent parallel reaction (IPR) model was used.

The experimental and modelling results obtained in this study for Miscanthus and Ulva help characterising the two biomass species. Based on the decomposition rates, product yields and gas compositions, a better understanding of the pyrolysis reaction mechanisms of the different constituents of Miscanthus and Ulva is gathered. This is a contribution to the knowledge required to optimise thermal conversion processes for different biomass species.