Process and Chemical Engineering - Masters by Research Theses

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    Design and optimisation of a small, robust outdoor duckweed bioreactor for operation under ‘on-site’ farmyard conditions
    (University College Cork, 2024) O'Sullivan, Grace; Byrne, Edmond; Kavousi, Fatemeh; Department of Agriculture, Food and the Marine, Ireland
    Duckweed (Lemnaceae) is a small, aquatic plant that is ubiquitous across Ireland. It grows remarkably fast, with a doubling time of one to two days. Duckweed is typically found on slow moving water bodies, but it can grow on agricultural waste streams such as yard washings. Usefully, the plant removes excess nutrients (nitrogen and phosphorus) from wastewater to produce a high protein crop. Duckweed dry weight can contain up to 40% protein. Duckweed is currently being investigated for use in human nutrition, biofuel production, and the remediation of waste streams (Appenroth et al., 2017, Xu et al., 2012, Zhou et al., 2023). The rising need for sustainable agriculture systems magnifies the importance of a circular economy approach to farming. This project involves the design and optimisation of an outdoor duckweed growth system suitable for use on farms. It offers farmers a plausible solution to managing the large volumes of nutrient-rich wastewater produced on farms daily, whilst also generating high-value biomass. Hence, it can help provide a circular economy approach to sustainable agriculture. Currently, two main styles of growth systems are used in the production of duckweed: ponds and raceway systems. A literature survey (undertaken as part of this research) reveals that limited studies have been completed on the effect of system design on duckweed cultivation. The approach undertaken in this project involves a systematic analysis of fluid flow using Computational Fluid Dynamics (CFD) and tracer response experiments to inform the design of a system optimal for duckweed production. ANSYS Fluent is used to optimise the system geometry and interpret the effects of the geometry on nutrient distribution. Relative growth rate and nutrient uptake experiments were also employed to gain experiential knowledge and thus a holistic understanding of the impact of design on duckweed growth. From this study, it can be concluded that low levels of mixing within a cultivation system have a positive effect on both the relative growth rate of duckweed and its remediation ability. However, at higher flow rates the growth of duckweed is negatively impacted. The results also feature the design of a medium-scale outdoor duckweed cultivation system, informed by the literature review and experimental work. This work will inform stakeholders on the most suitable system for duckweed production in a farm setting. In addition to this, it will provide guidance on the style of system that is most suitable for large scale duckweed production sites worldwide.
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    Mixed signal compensation of sampling errors in ADCs due to noisy DPLL clock sources
    (University College Cork, 2021-06) Zheng, Hao; O'Hare, Daniel; O'Connell, Ivan
    This thesis clarifies a method to compensate for sampling errors in ADCs when a noisy digital phase locked-loop (DPLL). A time domain DPLL is built by MATLAB Simulink with a phase noise model. The phase noise is obtained from a measured oscillator. When DPLL achieve lock, the time-to-digital converter (TDC) provides an estimate of jitter which is used with an analog differentiator to provide an estimate of the ADC sampling error. This correction scheme has reduced the side band noise in the output signal and allows the ADC effective number of bits at high frequency to be improved from 2 bits to 6 bits. When slope and double slope ADCs with 6 bits of resolution are selected the scheme can be implemented consuming up to additional power consumption of 6.8mW.
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    Direct air capture (DAC): capturing CO2 from the air – design of a lab-scale PVSA system and the development of a carbon-based adsorbent material for atmospheric CO2 capture
    (University College Cork, 2020-05-06) Dineen, Cormac P.J.; Tsalaporta, Eleni; Flynn, Eoin
    Mankind faces huge economic, technological and societal challenges if we are to meet the climate targets set out in the Paris Climate Agreement of limiting global warming to 2°C and avoid the most devastating effects of climate change. Research carried out by the IPCC in 2018 on emissions mitigations pathways compatible with our climate targets shows that commercial-scale deployment of Carbon Dioxide Removal (CDR) technologies will be almost certainly be required if we are to limit warming to 2°C. This research focuses on Direct Air Capture (DAC), an emerging CDR technology designed to remove CO2 directly from the atmosphere using sorbent materials. Building on a rapidly expanding body of work, this research has two primary goals. Firstly, it aims to create a laboratory scale, Pressure Vacuum Swing Adsorption (PVSA) system, designed for the testing of the CO2 adsorption isotherms of new adsorbent materials. The second goal is the development and testing of a new adsorbent material for CO2 capture.Having reviewed the relevant literature, a dual-column PVSA system was designed to operate a Skarstrom cycle for atmospheric CO2 adsorption. The cycle was modified to include a vacuum pump, which provides further testing capabilities in the system. The designed system can assess adsorption-desorption isotherms at sub-atmospheric conditions of pressure, as well as atmospheric conditions of pressure. Following the build phase, the system was tested at a variety of different inlet pressures and it was found that the PVSA Skarstrom cycle operated successfully and as designed. A biopolymer adsorbent material was developed by expanding the surface area of a native Irish seaweed, Ascophyllum Nodosum. The adsorbent powder product was shown, using SEM and BET analysis, to have a vastly expanded surface area when compared with that of the initial biopolymer material. The adsorbent powder was then pelletized using different techniques, and the structural properties of the pellets, which are key performance parameters for PVSA systems, were analysed and described. On the basis of the work carried out in this research, and the current global GHG emissions profile, further opportunities for research exist, and are necessary, in the development of new adsorbent materials for atmospheric CO2 capture. As a result of this research, it is recommended that research be carried out in the development of new, carbon-based adsorbents, which exhibit good structural and chemical properties for CO2 adsorption but have not yet been widely analysed for suitability within DAC systems.