Integrative studies on biomass gasification for energy and hydrogen production: From kinetic modelling and TEA and LCA to experimental investigation

Bioenergy production through biomass gasification technology plays a major role in the transition of the energy sector towards renewable and sustainable supplies. To achieve full-scale implementation of bioenergy technologies, reliable and comprehensive research, through modelling and experimental work, needs to be performed. In this context, gasification, which is the heart of the biomass conversion process, should be simulated accurately and optimised experimentally. Hence, the current study introduces a new improved kinetic model to simulate the gasification process within the downdraft gasifier using Aspen Plus and MATLAB. Compared to existing literature, a more realistic representation of the pyrolysis stage as a temperature-dependent sequential release of the non-condensable gases is employed. The predicted results are in very good agreement with the experimental data and therefore the model is utilised to predict the gasifier performance under different operating conditions.
The developed model is used to simulate a commercial scale 10 MWth two-stage downdraft gasifier for hydrogen production within the BECCS concept. In this study, the gasifier performance is optimised for hydrogen production in the cases of air-steam and oxygen-steam gasification. Additionally, the optimum steam-to-CO ratio (S/CO) for the high conversion of CO in the water gas shift reactors (WGSRs) is identified.
An extensive techno-economic and lifecycle assessment was conducted for different scenarios; (1): BECCS with grid electricity, (2): Bioenergy without CCS, (3): BECCS with onsite electricity generation. The estimated levelized costs of hydrogen (LCOH) for the three investigated scenarios are more than double the price of the typical fossil-based hydrogen. The analysis of global warming potential (GWP) has shown that the two BECCS scenarios are net negative emission approaches, whereas the scenario without CCS is a positive emitter, but still better than fossil-based hydrogen.
For experimental optimisation of the gasification process, a novel design of the gasifier reactor called the rising co-current gasifier was investigated. This design combines the advantages of fixed bed and fluidised bed reactors in terms of the efficiency and the quality of syngas. However, limited research has been conducted on such a design and therefore it lacks a full characterization of its capabilities and limitations. The current study presents a detailed analysis of the gasifier performance for syngas production and electricity generation using two different biomasses (wood pellets and miscanthus pellets) along with syngas and ash characterisation.