Microwave assisted Pre-treatment of lignocellulosic residues for better performance as solid fuels in fluidised bed technologies

Project Description

Exploitation of alternative fuels (lignocellulosic biomass waste) in energy production offers the advantages of: resource efficiency and improved waste management, increased renewables in power production and reduced dependence on imported energy. Advanced thermal processes like gasification, in combination with exploitation of lignocellulosic (woody) waste can lower the carbon footprint of the energy production sector.

When forest or agricultural residues (e.g. cereal straws) are fed raw or mixed with other fuels into fluidised bed gasifiers (FBGs), operational problems like ash fusion and bed agglomeration appear. This is a result of the undesirable interactions of some of the ash constituents (alkali and alkaline earth metals) of woody waste with silica sand, which is the most common bed material of FBGs. Under the operating temperatures of wood gasifiers (> 850oC) eutectic mixtures are created, the bed agglomerates and can even cause shut down of the energy production units.

To ensure efficient operation of FBGs fed on woody waste, this kind of feedstock needs to be pre-treated in order to remove those problematic elements and ensure long term operation without disturbance. The problem of how to optimise the physicochemical properties of such new types of solid biofuel can be solved by integrating traditional pre-treatment techniques (leaching) with novel chemical engineering concepts (microwave extraction). With support from Energy Works (Hull) Ltd, this multicultural and interdisciplinary team of researchers from the UK and EU, will develop a novel microwave pre-treatment technique as a solution to the bed agglomeration problem when wood waste is to be processed or co-processed in FBGs.

The proposed pre-treatment process emerges from the integration of a traditional and already proven successful pre- treatment method (leaching) with a novel one (microwave extraction). It aims not only to optimize the specifications of the solid biofuel, but also to address the challenges facing future development of a practical and affordable pre-treatment system.

By in short term co-feeding and in the long term by running efficiently with woody waste, this new process will allow the conventional energy production sector to meet its sustainability criteria. Development of the microwave enhanced leaching process of woody waste with ionic liquids like water is the primary target. This will enable stabilization of the woody waste properties and optimize operational behaviour in FBG energy production technologies. In this way also an underestimated biomass 'waste' source of the UK will be upgraded to a highly desirable solid biofuel.

The key element of the novel process is the integration of the microwave irradiation with the traditional leaching pre-treatment of such waste. Water leaching has been proven efficient in removal of the alkali and alkaline earth metals and sulphur elements from woody waste. It is however time-consuming and resource intensive (solvents). Microwave extraction techniques on the other hand have been proven to reduce extraction time, use less solvent, or even none for high moisture materials. Thus integration of both techniques can lead to improvement in waste pre-treatment for solid biofuel production.

The new pre-treatment technique is still not well understood in terms of microwave mechanisms and requires fundamental studies to allow scaling-up for commercialization. The present proposed project will develop a new generation of leading UK academic researchers focusing on a multi-disciplinary problem-solving approach and with a powerful commitment to train our future engineers accordingly.

It will also complement the recent 22 Conference of Parties (COP22) Marrakesh agreement to put forward the practice of COP21 Paris decisions for large scale energy production via less CO2 emitting technologies like woody waste gasification.