Abstract
This paper describes the application of process integration and optimization to the conceptual design of an integrated chemical complex with natural gas and locally sourced minerals as the main raw materials.
Different processes are available for converting natural gas to synthesis gas, with different ratios of hydrogen to carbon monoxide content. The economies of scale make it worth investigating a central synthesis gas plant supplying different downstream processes, matching their different demands for hydrogen or carbon monoxide. The study aims to select appropriate combinations of process type and production scale, and optimize the exchange of materials and energy.
The methodology applied is to construct a spreadsheet model containing the different processes and material and energy exchanges estimated mainly from literature sources. The relationships between the key process variables are described in the spreadsheet, and linearized (piecewise if necessary). The optimization of the selection of process alternatives, and values of the variables is then made using mixed- integer linear programming (reMIND and CPLEX) and the results returned to the spreadsheet model. The process is then repeated with sensitivity analyses on key variables. The objective function is defined to maximize the profit while taking account of carbon dioxide emission tax scenarios.
The initial phase of the project has identified potential capital cost savings from integrating different syngas-utilizing processes with a common syngas plant. Sensitivity of the optimized result to variations in raw material costs is presented. Development of the model for process design alone is probably not justified, however the model also can be applied to the identification of optimal responses to unplanned stops of individual processes. This can be used to make a fair and transparent system for apportioning the benefits (and cost/penalties) arising from process integration of separate processes. This is viewed as important in the motivation of separate companies to cooperation.
