Multi-scale Dynamic Simulation and Optimization for Cost-effective Industrial Emission Reductions

Flaring emissions during CPI (chemical process industry) plant startups, shutdowns, and upsets causes tremendous raw material and energy losses and also results in adverse environmental and social impacts. For instance, an ethylene plant with 1.2 billion pounds of ethylene production per year may flare five million pounds of ethylene during one typical startup, which generates 15.4 million pounds of CO2, 7.5 K lbs of NOX, 40 K lbs of CO, and 100 K lbs of highly reactive VOCs. Unfortunately, current practices in flare minimization almost exclusively depend on industrial experience and the “end-of-the-pipe” control strategies. For instance, the installation of flare gas recovery units (FGRU) can capture flare gas for recycle and reuse. Conceivably, it is less desirable since the “waste gas” is already generated. Meanwhile, the capital expenditure and operating cost of FGRU is considerable. Therefore, the key issue for existing CPI facilities to achieve significant emission reductions without large expenditures is to renovate current process designs and/or improve process operational strategies in a systematic way, so as to proactively and economically reduces emission sources instead of traditional “end-of-the-pipe” flare handling.

In this presentation, a systematic methodology on multi-scale dynamic simulation and optimization for cost-effective industrial emission reductions will be introduced. Since off-specification streams are inevitable during the plant turnaround operations, to significantly reduce flaring emission, they must be either recycled to the upstream process for online reuse, or stored somewhere temporarily for future reprocessing, when the plant manufacturing returns to stable operation. Thus, the off-spec products will be able to be reused instead of being flared. This presentation will address modeling and optimization for emission reduction under chemical plant start-up, shutdown, and upset conditions, as well as associated local air-quality impact studies. Both theoretical development and real plant test results could be presented.