Low sulfur

high paraffin content and low aromaticity are the characteristics of some Chinese crudes. The vacuum gas oil obtained from these crudes have similar properties and therefore excellent cracking performance is to be expected. The pyrolysis kinetics and product yield pattern of the vacuum gas oil have been studied in a bench scale unit having about 2 kg/h hydrocarbon throughput capacity

where the temperature and pressure are profile controlled. Based on the data from experiments on bench scale unit

pilot plant and commercial pyrolysis furnace

parameters of the reaction rate constant equation for vacuum gas oil cracking have been determined

and the curves and equations correlating the feedstock properties and operating conditions against main products yields have also been expressed. A semi-commercial pilot plant of about 100 kg/h hydrocarbon throughput capacity

is used to confirm the products yield pattern and study the process technology

particularly to observe the coking tendency of the pyrolysis coil and the operating performance of the transfer line exchanger quenching device. It is found that at medium severity

with steam to oil ratio 0.75-1.00

residence time 0.4-0.5 sec.

hydrocarbon partial pressure 0.8 kg/cm2

the main products yields are as follows

ethylene 22.5-23.0%

propylene 16.0-17.5%

butadiene 4.7-5.2%

heavy fuel oil 10-12%. The yields are similar to those obtained from the Middle East atmospheric gas oil cracking. Thus it is proved that the Chinese vacuum gas oil is a competitive feedstock for the manufacture of lower olefins in tubular pyrolysis furnace.