MITIGATION OF FOULING WITH POPCORN COKE

摘要

How often is petroleum fouling mitigated by raising temperature? One case is if the fouling is caused by a polymerization reaction. Such carbonaceous solids are the result of molecular weight growth reactions of conjugated olefins in the oil that were formed by the thermal cracking process. An olefin is conjugated to another olefin when the double bond is one carbon away from a carbon connected to a different double bond or an aromatic. Those conjugated to aromatics are the greater fouling problem in oils formed by thermally cracking resids. A property of polymerization reactions is that they are greatest over a range of temperatures. At lower temperatures the reaction rate is too slow and at higher temperatures the polymerization bonds thermally crack faster than they are formed (ceiling temperature). Therefore, the recommended mitigation action (US Patent 6,210,560) is to minimize the residence time of the thermally cracked oil in this temperature range (particularly 500 - 580℉) of greatest polymerization rate. An analytical method to monitor conjugated olefins in thermally cracked oils will be described. In addition, a case study will be given when the coking of a fractionator downstream of a Flexicoker was mitigated by raising the bottom pool temperature.