PERFORMANCE EVALUATION AND FOULING MITIGATION IN A GASOLINE FRACTIONATOR

摘要

The Gasoline Fractionator (Gas Frac) at NOVA Chemicals Corunna Ethylene facility has a history of fouling since coming on-stream in 1977. Fouling of the packed bed affects separation efficiency of the column, and therefore influences raw pyrolysis gasoline (RPG) quality. Fouling also reduces overall run length, imposes added cleaning costs during turn-around (T/A), and impacts the overall efficiency of the unit. Moreover, it is well known that fouled equipment exhibits a high risk of developing process fires due to the high reactivity and combustibility of fouling deposits. Mitigating Gas Frac fouling is key to extending the Corunna Olefins Unit operating time between full maintenance turnarounds. This research effort was initiated to better understand current tower performance and to experimentally establish the role of process parameters on the fouling rate. To accomplish this, current performance of the tower was evaluated by simulation. Simulation results convey the importance of good initial liquid distribution in a large diameter tower. Improper liquid distribution is a primary cause of poor separation efficiency and can potentially compound the fouling problem. In a second phase, fouling reactions were replicated in a lab scale unit to identify fouling precursors and to understand the fouling mechanism. The effects of temperature and metallurgy on fouling rate were determined. The experimental study revealed that fouling rate has an Arrhenius type dependence on temperature, with negligible polymer formation below a fouling threshold temperature. The fouling propensity of various metallurgies showed that stainless steel alloys can reduce the amount of fouling by up to forty percent compared to carbon steel. Based on the data collected, a new stainless steel distributor and stainless steel packing for the top bed were installed during the 2005 turnaround.