Flexible Funding 2022: Dr Nejat Rahmanian, University of Bristol

Evaluation of properties of biomass wood pellets in power generation

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Key facts about this Flexible Funding research project

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Institution: University of Bristol
Department: Faculty of Engineering and Informatics
Start date: 1 December 2022
Principal investigator: Dr Nejat Rahmanian
Amount awarded by UKCCSRC: £9,974

Why is this research needed?

Biomass is the UK’s second-biggest source of renewable electricity. The UK government’s Net Zero Strategy aims to achieve net-zero carbon emissions by 2050 and this relies heavily on bioenergy with carbon capture and storage (BECCS). To achieve this aim, the UK continues to progress with world-leading BECCS projects; for example, Drax, the largest power plant in the UK, has converted four out of its six boilers from coal to biomass burning, with plans to fully discard coal combustion in the near future. With an anticipated increase in biomass combustion, the co-generation of biomass combustion products (BCP) presents significant social, economic and environmental concerns. Owing to their unique characteristics, BCP have demonstrated as the current state-of-art for applications in post-combustion CO2 capture.

The wood pellet has been recognized as a sustainable source to replace traditional coal, thanks to its lower CO2, SOx, NOx and ash content than the coal and torrefied wood pellets. The safe and effective storage, transportation and processing of biomass (wood) pellets are then highly important for the design and operation of BECCS plants and requires a good understanding of the physical, chemical and mechanical properties of the pellets.

This project addresses research needs in CCS which were demonstrated by the UKCCSRC ‘what are our research needs’ workshops. This project, directly and indirectly, impacts both CCS and CCU, as it stands upstream of both CCS and CCU processes.

What is this research investigating?

Biomass is the biggest source of renewable energy consumed in the UK [1]. This project aims to determine the impact of physical and mechanical properties of biomass wood pellets on the liberated energy and gas emissions, mainly CO2, in the power sector. The motive for this project has been initiated as the current state-of-the-art for use of wood pellets is the cofiring and co-generation of biomass combustion products (BCP). The safe and effective storage, transportation and processing of wood pellets is therefore highly important for the power sector. The integrity of the quality of pellets during handling is key in ensuring that pellets do not degrade physically in the chain of manufacturing until feeding into a pulverized fuel burner. This reduces transport costs and minimises the risk of fires and dust explosions.

There are available studies into the chemical characterisation of biomass [2], especially for the residential sector. However, there are few studies available in the literature that focuses on the physical and mechanical properties of commercially produced biomass wood pellets used in the power sector. There are also no robust and similar standards for BECSS applications to those used for well-established fossil fuel power plants while there are some guidelines under development for residential uses.

This project aims to conduct a systematic study on the characterisation of biomass wood pellets used as the feedstock in power plants in the UK such as the Drax power station. The study will include:
1. Searching for available experimental data on the characterisation of both physical and chemical properties of pellets
2. Explore experimental techniques including durability, quasi-static and dynamic impact tests for strength characterization of the pellets
3. Quantify the rate of energy release and gas emission such as CO2 from at least ten different wood pellets sources used in the UK
4. Find a potential correlation between both liberated energy and CO2 emission with the pellet properties.

In this project, at least ten commercially produced wood pellets used in power sectors in the UK will be fully characterized for their physical and mechanical properties such as strength, structure, density, porosity, size distribution, and mechanical durability. The chemical characterization using elemental analysis and flue gas (Sox, Nox, and CO2) composition and ash contents will also be conducted. The influence of these properties on the liberated energy and CO2 release will be fully accessed using the Design of Experiments (DoE) approach.

References:
[1] Office for National Statistics,
www.ons.gov.uk/economy/environmentalaccounts/articles/aburningissuebiomassisthebiggestsourceofrenewableenergycon
sumedintheuk/2019-08-30 accessed on 1 May 2022
[2] Vassileva, S.V., Baxter, D., Andersen, L.K., Vassileva, C.G., 2010, An overview of the chemical composition of biomass,
Fuel, 89, 913-933.

What does the research hope to achieve?

The outcome of this project as a seed fund is used later to pave the way for the standardization of feedstock properties of wood pellets in power plants by adapting a British Standard and applying for a major grant application.

The proposed project is also expected to later gain monetary income from consultancy services. The research findings will be disseminated via publication of journal papers in Chemical Engineering & Research Design, and presentation at a UKCCSRC conference in 2023/24.

The successful implementation of the project will result in reducing the risk of using biomass wood pellets for BECCS application, by identifying the physical and mechanical properties which led to the formation of dust and potential fire and explosion.

Research outputs

This research is ongoing. Outputs will be shared below as they become available.

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Blog post - February 2024