Primary Study On Catalytic Cracking Of CGO Mixing With High Acid Number Crude Oil

The study is directed to provide a fluid catalytic cracking process for treating coke gas oils (CGO) containing high levels of nitrogen which has a deleterious effect on cracking catalysts with acidic crude oil (ACO) including high total acid number (TAN) compounds contributing to corrosion and fouling of refinery equipment. The object is to provide such a process without the necessity of first treating the feedstock to remove substantially of nitrogen-containing and acidic constituents. The research work is mainly consisted of three parts.Firstly, the trends of TAN and basic nitrogen contents (BNC) were investigated under different mass mixing ratios blending CGO with acidic crudes in order to obtain the optimal mass mixing ratio. The results showed that TAN of mixtures gradually increased while BNC gradually reduced as the ratios increased. It was interesting that absolute difference of TAN between calculated and measured values was increased and then decreased which was the same conclusion for BNC while the ratios increased. The absolute difference value reached a peak at the ratio of 1:2. This experimental phenomenon showed that the rule of acid-base neutralization happened when CGO mixed to ACO. Coexistence of TAN and BNC in the mixtuers showed that neutralization only partially taken place in the role of acid-base.Secondly, further work was completed with the pilot fluid catalytic cracking unit. The variation of product distribution and hydrocarbon group analysis of gasoline were studied when mixtures of high-acid crudes and CGO under different ratios of CGO to ACO. The yield of LPG slight decreased as the ratios increased, while the yield of dry gas firstly increased and then decreased which was the same trend to the yields of gasoline and diesel. Meanwhile, coke yield gradually increased. The yield of light oils (gasoline yield plus diesel yield) plateaued at the ratio of 1:2 which was the same value to TAN and BNC experiments mentioned above. The yield of light olefins showed a first rise and then a falling trend and the maximum yield was occurred when the mixed ratio of CGO to ACO was 1:2. Furthermore, the selectivity of light olefins was reduced as the ratios increased. As to the group composition of gasoline, paraffin contents first increased and then reduced while the cycloalkane contents remained basically unchanged. Aromatic contents had a significantly increased while Olefins had a dramatically decreased.Finally, primary study on operating conditions was carried out using the pilot fluid catalytic cracking unit to explore the effects on product distribution, low-carbon olefins yield and their selectivity under the best mixing ratio 1:2. Operating conditions in the experiments were reaction temperature, C/O (the weight ratio of catalyst to oil), residence time and W/O (the weight ratio of water to oil). The experimental results indicated that the optimum reaction temperature was 510°C, and the best catalyst to oil ratio was 8. The optimal residence time was about 1.7s while the suitable water to oil ratio was 20%.