THESIS
2015
xii, 81 pages : illustrations (some color) ; 30 cm
Abstract
Power generation used around 40% of primary energy with coal as the major contribution, which
causes not only severe environmental pollutions but also increases the threat of global warming.
As a result, utilizing coal gasification technology which has many environmental benefits in
electricity generation has attracted increasing attention worldwide. However, most gasification
studies focus on optimizing cold gas efficiency (CGE) by sensitivity analysis or control variant
method and ignore how the integration of sensible heat would affect the power generation.
In this study, a novel mathematical model which simultaneously optimizes the key operating
parameters of a heat integrated coal gasification process to achieve maximum economic profit is
developed. Based on the equilibrium...[
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Power generation used around 40% of primary energy with coal as the major contribution, which
causes not only severe environmental pollutions but also increases the threat of global warming.
As a result, utilizing coal gasification technology which has many environmental benefits in
electricity generation has attracted increasing attention worldwide. However, most gasification
studies focus on optimizing cold gas efficiency (CGE) by sensitivity analysis or control variant
method and ignore how the integration of sensible heat would affect the power generation.
In this study, a novel mathematical model which simultaneously optimizes the key operating
parameters of a heat integrated coal gasification process to achieve maximum economic profit is
developed. Based on the equilibrium modelling work, it is found that, at above 1400 K, the
operating conditions that maximize the profit automatically lead to minimized Gibbs free energy
of products. Thus, the complicated multi-objective problem of profit optimization (profit
maximization and Gibbs free energy minimization) is directly simplified to a single objective
problem of profit maximization, and the model can be developed accordingly. Further, how the
integration of sensible heat would influence the overall performance is taken into account. One
way of handling such heat integration problem is to use pinch analysis method to ensure the
feasibility of heat exchange and maximum heat recovery. To achieve simultaneous optimization,
a set of constraints and piecewise functions are developed to handle the variable temperatures,
flow rates as well as the phase change of process streams. Case studies have been conducted to
illustrate the effectiveness and robustness of the profit optimization using the developed models.
The results indicates that by assigning part of the sensible heat to preheat the reactants, the profit
can be increased by 40% compared with that of using sensible heat for HP steam production
indifferently.
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