Multi-level energy integration between units, plants and sites for natural gas industrial parks

Natural gas industrial parks are composed of raw natural gas refining plants, urea plants and power plants. The processes of natural gas refining and utilization in industrial parks are energy-intensive and involve complicated mass and energy networks. This study concentrates on heat and material stream integration for sustainable energy utilization in natural gas industrial parks. Energy integration of industrial parks is reviewed and a mixed integer non-linear programming framework is presented to minimize the total annual cost for the retrofitting of energy integration across plants in natural gas industrial parks. The mathematical framework combines the optimization models of energy-intensive processes, power plant operation and a new heat exchanger network design using some key variables. Total site analysis is proposed for a natural gas industrial park to obtain energy-intensive processes with energy saving potential and determine the process streams for energy integration across plants. The mathematical framework is then applied to the natural gas industrial park and can be solved using the deterministic global optimization solver in a reasonable solution time. The results demonstrate that the static investment payback period is less than two months and the total hot utility decreases by 30.5% through the energy retrofit of the entire natural gas industrial park.