Improved quality of liquefied petroleum gas via non-stirred blending

Abstract

Liquefied Petroleum Gas (LPG) which contains more than 0.1% mole of butadiene is classified as a carcinogen and mutagen and regulatory have set the limit of butadiene to be below 0.5 % mole in LPG mixture. LPG suppliers in Malaysia are facing problem since butadiene level from one port exceeded 0.5 % mole. By blending of LPG from other ports might produce LPG products which satisfy the regulatory limit. The study focused on homogeneous blending time in a 17.28 m3 tank without artificial mechanical equipment through simulation modelling by Fluent 6.2.16 with two sources of LPG which were Ports A and B. The results showed that as the volume of LPG with butadiene increased, the butadiene level in mixed LPG also increased. The mass fraction between Ports A and B was below than 93% and 7% produced mixed LPG product within the regulatory limit. The blending time is approximately 3.98 hours to achieve homogeneous product mixture with a constant flow rate of 0.52 kg/s. Numerical modelling reveals that the effect of liquid-liquid diffusion by Wilke-Chang correlation does not significantly affect the blending time for homogeneous mixture. In fact the required blending time is shorter compared to blending time estimated by numerical modeling.