Study On Compatibility Of Blending Heavy Oils

Colloidal stability of petroleum influences the reservoir, transporting and process of crude oils. During delayed coking process of residues, colloidal instability problem might occur, and cause fouling in the storage tanks and heat exchanger, coke formation on the wall of the furnace tubes and nozzles, or the undesirable product distribution which seriously affected the normal operation of oil refinery. Some residues might phase split during transportation, and lead to the difficulty of loading and unloading of the residues. To work out these problems, suitable methods for testing colloidal stability must be selected or set up.Firstly, four methods were characterized for testing colloidal stability. Results show that, mass fraction conductivity method is a simple, swift method. It can give an accurate result that fitted the properties of the residues in where it was used and can be used in a wide range. This method tells the differences of residues but do not tell whether the oil is stable or not, researches need to compare oil samples to get the result they want. HRS value method shows the result in an intuitive way, the result can be given in both qualitative and quantitative ways, however it can not be used in a wide range. Ultraviolet spectrophotometric method needs multi-steps to carry out one measurement. It might be complex, but the results with this method are accurate. In low dilution system asphaltene precipitation starting points have a linear relationship with their concentrations in toluene; while in high dilution system the relation is exponent. EP value method can not only tell the results in both qualitative and quantitative ways, but also foretells residues compatibility when they are blended with other oils through a parameter EPo/EPmin. Besides, the relationships of colloidal stability with residues components and their properties are examined. It is shown that the composition and the properties determine the stability of the residues. Asphaltenes with low H/C ratio and more polarity, higher aromaticity and condensation degree easily deposits from residues and ruined the stability of its colloidal system. Deposition of asphaltenes depends on asphaltene contents and also their dispersion conditions.Secondly, the stabilities of residues colloidal system were studies when they were mixed with other oils. Results show that when two oils both with low stabilities were blended their mixture oil has lower colloidal stability. And when residues with similar compatibility were mixed together, the colloidal stability of the mixture can be improved. During thermal reaction, residues colloidal stability became worse, but the situation can be delayed by being added suitable fraction oils, and the more, the better. Colloidal stability is not the only cause influencing the induction period of coke formation, other factors like carbon residue also play important role.Thirdly, addition of asphaltene deposition inhibitor is an effective way of improving residues stability. The determination of the colloidal stability of residues by mass fraction conductivity method was conducted in order to appraise the performance of several asphaltene deposition inhibitors. Results show that inhibitors with good compatibility with residues can improve colloidal stability of residue system, otherwise, it can accelerate asphaltene depositing rate from residues.