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Title: Enhanced instrumentation, control and process optimisation for biomass gasification
Author: Kamble, Prashant Ram
ISNI:       0000 0004 9356 0487
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2020
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The world is faced with critical challenges to reduce its dependency on fossil fuels due to anthropomorphic CO2 emissions, which are resulting in climate change. Renewable energy provides a crucial role in reducing these emissions whilst providing sustainable energy; energy conversion of biomass forms a valuable part of a renewable energy portfolio, with capability for baseload provision, and gas and electricity production. The UK government set targets to provide energy from a renewable sources; 12% of its heat, 30% electricity and 10% of its transportation fuels from renewable resources by 2020 (MacNeil et al. 2016). Gasification is a common method used for thermal decompositions of biomass which mainly produces carbon monoxide and hydrogen which can be further used to produce heat, electricity or platform chemicals. Biomass gasification presents challenges in limitation of control systems, feedstock variability and tar production which can reduce the performance, durability of the gasifier and downstream syngas utilisation. From the literature review on biomass gasification systems, the conclusion is that well-established instrumentational control systems and strategies are not developed and applied. However, large scale gasifiers use expensive systems and will benefit from reduced cost and simple platforms. Low cost, open-source and highly robust control systems are needed for biomass gasification. Moreover, an experimental investigation is required to find optimal conditions of biomass gasification for a variety of feedstocks. Up to date, no one has reported biomass gasification control using Arduino based control systems and real-time tar detection techniques by using a PMT (Photomultiplier Tube) with different control strategies. Previously, some techniques (only temperature and pressure) have been developed by Arduino control systems for biomass gasification (All-Energy Lab, California, USA) which were not robust and have a lot of limitations. The focus of this research is centred on developing instrumentation and control systems for a novel downdraft gasifier and thermochemically processing various Miscanthus feedstocks. The current work seeks to establish robust instrumentation and control systems to improve the performance of an in-house, downdraft gasifier and seeks to identify control strategies to allow operation on the minimum tar production point with an open-source protocol. The major outcome of this research is to investigate the impact of feedstock variety on gasification performance and identify preferred Miscanthus varieties to grow at scale with optimised gasification and to allow real-time monitoring and automated optimisation of the gasification process using feedback control systems with tar detection system in a gaseous phase Five genotypes of Miscanthus feedstock were provided by Terravesta, four of these were bred in 2014 at IBERS, University of Aberystwyth. These samples are different from each other in growth habits, stem density, height, maturation time and harvest moisture content. The elemental compositions results were provided by IBERS, University of Aberystwyth which shows each Miscanthus samples varied with their genetic properties. A small-scale throated downdraft gasifier (~3.4 kW) and test rig were designed and manufactured at the University of Glasgow and built to easily assess the gasification performance under different conditions e.g. feedstock variety and with different instrumentation and control strategies. The gasification test rig allowed the testing of downstream tar detection systems, downstream gas cleaning processes and control on the output quality of the producer gas. The gasifier was operated in batch mode and to improve repeatability, the throat, grate and assembly were cleaned after each experiment. The Arduino platform was used as the core of the instrumentation and control system and integrated with opensource PLX-DAQ and Telemetry for the Graphical User Interface (GUI). Different versions of an automated instrumentation and Gasifier Control Unit (GCU) Rev 1.0, 2.0 and 3.0 were developed and installed, tested and validated. These allowed measurement of gasification process parameters: temperature, humidity, tar concentration, pressure, mass flow and liquid flow (water) and controlling the airflow. The design and development of the algorithms for the automated control systems for optimised gasification performance is discussed and includes time-based, PI-based and airflow-based control strategies. Various feedstock varieties of Miscanthus genotypes MxG, OPM12, OPM52, OPM53, OPM54 were gasified under the same equivalence ratio (ER 0.30) with various control systems and their strategies. The experimental performance found that the system achieved average gasification temperature of 600°C (for 50 mins) which produced more liquid (biocrude - moisture, bio-oil, tar, other chemical components) and producer gases with an PI-based control strategy for GCU (Rev 3.0). The experimental gasification parameters studied were carbon conversion efficiency, gas yield, cold gas efficiency and gas heating values. In this research found that, the average value for carbon conversion efficiency, cold gas efficiency, heating values and gas yield were 92%, 82%, 20 MJ/m3 and 0.83 m3/kg (biomass), respectively. Overall, GCU (Rev 3.0) system was set at 3 sec delay response time and 115000 bits per seconds (bps) baud rate. This whole system worked automatically to control the inlet airflow rate (E R) of the gasifier. It is a low cost and robust instrumentation and control system which provided accurate data on a real-time basis with an opensource protocol. Also, the output data is recorded using the telemetry (Java) based data acquisition system which is beneficial to avoid the high cost software (like: MATLAB, LabVIEW and SCADA). The reported performance parameters for the hybrid Miscanthus in the present study were comparable GCUs (Rev 1.0, 2.0 and 3.0) and improvement of their limitations to various control strategies with their GCUs systems and comparable to those from conventional Miscanthus pellet gasification in downdraft gasifiers. Also, chemical analysis of the by-products, biocrude and char, are reported along with the technical specification comparison of the GCUs systems. Overall. the Gasifier Control Unit (GCU) system is low cost with an open-source protocol, allowing other developers to benefit and expand the core of this research.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TJ Mechanical engineering and machinery ; TK Electrical engineering. Electronics Nuclear engineering ; TP Chemical technology