Simultaneous optimization of a heat integrated coal gasification process

• A novel model for profit optimization of gasification has been developed.
• The model simplifies the bi-level optimization problem into a single level problem.
• This model allows simultaneous optimization of all variables.

This study develops a novel mathematical model which simultaneously optimizes the key operating parameters of a heat integrated coal gasification process to achieve maximum economic profit. It has been proved that, at above 1400 K, the operating conditions that maximize the profit automatically lead to minimized Gibbs free energy of products. Thus, the complicated bi-level problem of profit optimization (CGE maximization and Gibbs free energy minimization) is simplified to a single level problem of profit maximization, and the model can be developed accordingly. The model consists of several constraints including the heat balance, elemental balances and feasible heat exchange. Optimum conditions for the maximum profit can be determined from the model using a generalized reduced gradients nonlinear solver. Case studies have been conducted to illustrate the effectiveness and efficiency of the profit optimization using this single level model. The results of the case studies also 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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