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Appropriate scales and technologies for energy recovery by thermal processing of waste in the urban environment

Yassin, L; (2008) Appropriate scales and technologies for energy recovery by thermal processing of waste in the urban environment. Doctoral thesis , UCL (University College London). Green open access

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Abstract

In the developed world, 75% of the population live in urban areas, a figure projected to rise to nearly 83% by 2030, while in the developing world, the rate of urbanisation is even faster. One of the most important environmental problems associated with urbanisation is the amount of waste that is generated at a rate that outstrips the ability of the natural environment to assimilate it and authorities to manage it. Therefore, if we are to deliver a more sustainable economy, we must do more with less by making better use of resources. The recovery of energy from waste or EfW is an important component of an integrated waste management strategy, as it reduces our reliance on landfill. It is also a low carbon, low cost fuel, which by displacing fossil fuels can help the UK Government in meeting its energy policy and emission targets. Furthermore, EfW can contribute to energy security through diversification of supply it is projected that EfW may supply up 17% of the total UK electricity consumption by 2020. The main objectives of this work are to investigate the appropriate scales and technologies for the production of energy from waste in the urban environment. The suitability and effectiveness of fluidized bed combustion and gasification processes have been studied, together with gas clean-up systems. The most appropriate scales for each of these approaches in relation to system efficiencies and costs were evaluated, so that a sound judgement can be made as to which processes should be used in the urban context. Within this framework, a comprehensive assessment of fluidized bed reactor types and operational process conditions has been presented. Current and future status of these technologies was discussed, as well as the non-technical barriers hampering their development. The assessment concluded with a review of the different emissions and residues generated from the thermal treatment processes, their management, practices and costs. Mass and energy balances of traditional moving-grate combustion plants and key issues regarding the treatment of the output gas stream have been investigated during a five- month placement programme at Germana & Partners Consulting Engineers in Rome (Italy). The aim of the study was to gain an in-depth understanding of design methodologies and engineering principles applied in the detailed design of real industrial energy recovery plants. The study led to the development of a consistent approach for the technical and economic evaluation of more advanced technologies, namely fluidized bed combustion and gasification systems. Two different scale scenarios of 50,000 tpa and 100,000 tpa plant capacities were considered for the generation of electric power using a steam turbine for the combustion process and gas engine & combined cycle gas turbine (CCGT) for the gasification process. Mass and energy balances of the processes were performed and the cost effectiveness of the different waste treatment options was assessed using a discounted cash flow (DCF) analysis, which includes current market-based mechanisms, such as eligibility for Renewables Obligation Certificates (ROCs). A sensitivity analysis was carried out to evaluate the effects of changing system variables on the economic performances of the different waste treatment options. Seventeen system variables have been chosen and the effects of a 10% change in these variables on the levelised costs and gate fees were examined. These variables include waste calorific value, gasifier efficiency, prime mover electrical generation efficiency, as well as electricity and ROC prices and biodegradable fraction of the waste. As part of this study, the techno-economic performances of traditional moving-grate combustions systems was reported and compared against the different fluidized bed systems co-located with Mechanical Biological Treatment (MBT) facilities. The work was subsequently extended to analyse the technical and cost effectiveness of the simultaneous generation of heat and power from EfW fluidized bed combustion and gasification systems, using the same scale scenarios of 50,000 tpa and 100,000 tpa. The study focused on the additional capital and operating costs involved in incorporating combined heat and power (CHP) into EfW facilities. The projected revenues from heat sales and eligibility for ROCs were also evaluated for a range of market penetration levels. Furthermore, the environmental benefits associated with EfW with CHP facilities were assessed and the CO2 savings achieved from displacing fossil fuels in the separate generation of heat and power were also determined.

Type: Thesis (Doctoral)
Title: Appropriate scales and technologies for energy recovery by thermal processing of waste in the urban environment
Identifier: PQ ETD:593490
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
URI: https://discovery.ucl.ac.uk/id/eprint/1446161
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