(57e) Thermal Cracking Studies by Design of the Pilot Plant

Thermal cracking of hydrocarbons from ethane up to gasoil is one of the most important processes for production of olefins, the basic feedstock for the petrochemical industry. The key to successful process control in the manufacture of ethylene, is temperature control of thermal cracking furnaces. This paper studies a computerized thermal cracking pilot plant and its capabilities for experimental activities. A computer program was developed for the monitoring and control purposes. The effect of temperature on ethylene yield is investigated by simulation and experimental studies. The results show good agreement between. Comparison of these results with industrial data, show that, they have the same trends. Coil Outlet Temperature (COT) is an important parameter affecting yield of ethylene production and therefore it should be controlled. Since furnaces are the first step in the production process, disturbances that occur due to the furnace operation will effect the entire process. COT is controlled by measuring the cracked gas temperature in the coil outlet and manipulating the heat input to the furnace. This loop is one of the most important loops in the control of thermal cracking furnaces. Fluctuations on COT is caused by the coke deposited on the COT measuring thermocouple. Furnace temperature tracks the furnace set point. Increasing the oscillation at higher set points, are due to nonlinear plant dynamic and using constant controller tunings. Based on the kinetic model a computer program for simulating the plant is developed. The software program is used to investigate the effects of temperature on the product yields. Simulation results indicate that increasing COT, increases the ethylene yield. Simulation results was tested experimentally by the pilot. Comparison of simulation, experimental and industrial results show, those have the same trends. The discrepancies between industrial and simulation results refer to the reactor configuration and the discrepancies between simulation and experimental results are due to the nonlinear and unknown furnace dynamic model, and some measurement errors in experiments.