Lau, Johnson Ho Kwong
(2025)
Biomass densification for minimal drying energy and optimised pellet quality.
EngD thesis, University of Nottingham.
Abstract
Biomass power generation has been gaining increasing importance globally in recent years to provide renewable energy and combat climate change. However, several constraints have limited the expansion of biomass power generation, and in particular, the use of alternative biomass feedstocks to wood. The major challenges of the industry include the high drying energy of biomass, the need for biomass densification and the variability in the properties of biomass. This thesis addresses several of the major challenges of the industry through the study of the properties of alternative biomass feedstocks, the development of a new novel low-energy biomass drying process, the in-depth investigation of biomass pelleting and pellet milling behaviour, and the use of Life Cycle Analysis (LCA) to study the environmental benefits of biomass power generation from a system perspective.
The results presented have provided new insights and addressed multiple gaps in knowledge in the existing literature. In addition, the new knowledge presented is valuable for the industry to improve the understanding of unconventional biomass feedstocks and industrial processes, and the new tools and methods developed can be used by industry to deliver substantial environmental and economic benefits.
The characterisation of several conventional and alternative biomass feedstocks was conducted. The characteristics of cardboard materials, including char morphology, burnout performance and particle shape change during combustion, were studied in detail and a new method of using thermogravimetric analysis to measure calcium carbonate content in cardboard was developed. In general, cardboard chars are more porous and thin-walled than eucalyptus chars, indicating a better char burnout performance. The challenges of using cardboard for power generation applications would include potential handling difficulties, a low calorific value and high ash content.
The feasibility of a new novel combined pasteurisation and natural drying process was established using a set of experiments with miscanthus and spent grains, which can dramatically decrease the drying energy of biomass. Biomass briquettes were pasteurised and monitored over a storge period of up to nine weeks. Substantial decrease of moisture content was achieved by natural drying, while optimised pasteurisation strategies can provide effective fungal growth suppression during the storage period. It was also found that microwave pasteurisation can achieve similar or better levels of fungal growth suppression with shorter processing times compared to conventional oven pasteurisation.
The pelleting and pellet milling behaviour of sugarcane straws was investigated and new parameters were developed to quantify the pelleting process. The influence of various factors on pelleting and pellet milling was investigated, including moisture content, particle size and harvest season. It was found that pelleting failure was more likely to occur at low moisture contents, at fine particle sizes, and with the dry season sample.
Lastly, an LCA study of a biomass power generation system using bagasse from the United States to generate power in the United Kingdom was conducted. It was found that for the system studied, the overall carbon footprint of the electricity generated is 81.6 g CO2/kWh. The main opportunities of reducing carbon emissions are the electricity use at the pellet plant and shipping between the origin port and the destination port. It was also concluded that substantial benefits in terms of global warming potential could be achieved by the system studied, particularly if carbon capture and storage is also integrated.
| Item Type: |
Thesis (University of Nottingham only)
(EngD)
|
| Supervisors: |
Williams, Orla
Lester, Edward
McKechnie, Jon |
| Keywords: |
Biomass power generation; Alternative biomass feedstocks; Biomass drying process; Pellets |
| Subjects: |
T Technology > TP Chemical technology |
| Faculties/Schools: |
UK Campuses > Faculty of Engineering |
| Item ID: |
80168 |
| Depositing User: |
Lau, Ho
|
| Date Deposited: |
31 Jul 2025 04:40 |
| Last Modified: |
31 Jul 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/80168 |
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