(107a) Flare Minimization for an Ethylene Plant Shutdown Via Plant-Wide Dynamic Simulation

There is a great amount of raw materials sent to be flared during the ethylene plant start-up and shutdown, it generates much burned-off gases which including NOx, VOCs, CO, CO₂and so on. This not only increases operating cost, but also causes environment pollution which is highly concerned by local public and regulatory agency. Flare Minimization can reduce pollutant generation, save raw materials, and also lower the energy costs. The development of flare minimization strategy for an ethylene plant is quite crucial and beneficial for both plant and local environment.

In this paper, a dynamic simulation model has been built to study flare minimization opportunities of a front-end de-ethanizer ethylene plant shutdown operations. To minimize the shutdown flaring and smooth the plant shutdown operation, various operational improvements have been initiated and examined in this paper via the developed dynamic simulation model. For example, such an idea has been tested by dynamic simulation that shutting down all furnaces first and then recycling vapors from downstream columns to the CGC (Crack Gas Compressor) inlet to necessitate CGC running meanwhile enable flare source recovery. After that, there are much less hydrocarbons left in downstream vessels after CGC is shut down and before the nitrogen purge operation. Compared with the normal procedure, which is CGC shutdown first and then all the furnaces  shutdown, significant flare emissions have been saved.