| In the process of delayed coking, high foam layer often forms in coke drum, which imposes great threat on the safe and stable operations of the coking unit. And effective measures of controlling the foaming during delayed coking is necessary. In order to develop high-efficiency defoamers to decrease foaming in delayed cokers, the foaming tendency of different viscous oils were studied by the self-designed heavy oil coking foaming performance evaluation apparatus, as well as the mechanism of foam layer formation. First of all, the foaming performance of different viscous oils under non-reaction and thermal reaction conditions were tested by the evaluation apparatus. And then, the preliminary foaming mechanism was proposed via the exploration of the effect of some factors such as the viscous oil constitution and the surface tension to the foaming performance of simulating oils. On this basis, the foam layer obtained from thermal simulating experiment was characterized and the fundamental cause of foam in the coking drum was further studied. Furthermore, the defoaming mechanism was explored and high efficient defoamers, which were able to suppress foaming of heavy oils under coking conditions effectively, were developed by the method of formulating and modifying. The results are as follows:There was an obvious correlation between the foaming height of simulating oils and asphaltene content of feedstocks, while resins only affected the foaming performance of simulating oils in collaboration with asphaltenes. Results of further study showed that resins and asphaltenes must be the main factors affecting the viscosity, surface properties and interfacial rheological properties of simulating oils. The foaming performance evaluation result from thermal simulation was consistent with that from cold simulation, which indicated that the viscous oil with strong foaming nature usually showed strong foamability during coking process. And with reaction temperature increasing, the highest foaming height of viscous oil decreased, which accorded with the operation experience from delayed coking process. And the analysis of the thermal simulating foam layers showed that the components responsible for foaming during delayed coking were polycyclic aromatic asphaltene aggregates with high viscosity condensed from resins and asphaltenes. Furthermore, resins and asphaltenes with higher degree of condensation and more heteroatom compounds tended to have a higher foaming height during delayed coking.Under cold simulating experiment, the defoming effect of defoamers was achieved by affecting the surface properties of simulating oil. And the property changes of simulating oils with defoamers showed that the defoming effect of defoamers conformed to the bridging-stretching mechanism.The high efficient defoamers selected through formulating and modifying were(viscosity reducer 2# + silicone B + polyether E) and(viscosity reducer 2# + silicone B + polyether E), which were able to lower the average foaming height in thermal simulation effectively. |
