Fig. 13 Outline of P value measuring method

Fig. 14 Example of estimation of blending stability of C oil

(2) Evaluation of stability during the storage for a long time of cracked heavy oil When the directly desulfurized heavy oil degraded in stability or the visbreaker heavy oil is stored in a tank, the sludge is generated. According to the study by Nomura et al ⁵⁾, the storage stability shows the scale effect of the container, and the sludge generation is decreased the more when the ratio (V/S) of the volume (V) of the storage container to the surface area (S) of the oil level is increased the more. In order to prove this finding, the test for storage for a long time was carried out for the directly desulfurized bottom. The test was carried out using two kinds of containers, i.e., the storage container of the beaker size (0.05 m in diameter x 0.05 m in height) and the storage container of small tank size (2.3 m in diameter x 2.7 m in height). Fig. 15 shows the plotted relationship between the oil height (the ratio of the oil quantity to the surface area) and the days required for generating the dry sludge of the specified quantity (0.05 mass.%). When these are logarithmically expressed, it is shown that the straight relationship is obtained at the specified temperature. By using the relationship in Fig. 15, it is possible to roughly predict the sludge generation (equivalent to 150 days for the tank of 10m in oil height) of a large tank from the result of the accelerated degradation test of the beaker size tank (0.05% in sludge with 75℃ x 5 days.

　

Fig. 15 Estimation of stoarage stability of direct desulfurized heavy oil

　

4.2.2 Evaluation of thermal stability

The result of the measurement of the pyrolysis in air by the panel coking test and the TG-DTA is shown. Though the coking quantity of C oil is rapidly increased from the temperature close to 250℃, the difference in the coking quantity can be recognized by the sample (Fig. 16). The oxidation degradation start can be measured by DSC (Differential Scanning Calorimeter) or TG-DTA (Fig. 17).

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