Study On The Law Of Oil Spill Weathering Transportation And Distribution In Low-Temperature River

With the development of petrochemicals industry along the Songhua River and crude oil transportation as well as the laying of oil pipes through the river, potamic oil spill accidents have already become a threat to the security of the entironment and water drinking of inhabitants. It is an important measure to establish the forecast and lash-up treatment system to emergent oil spill accidents for reducing the harm to environment and economic loss. Although many researchers have done some study on the oil weathering and spreading, the oil spills in low-temperature rives still have their own characteristics such as the fast oil spreading due to the high flow velocity, and the contaminative area would be lager; the influence on oil spreading from the interaction between oil and banks; the great difficulty in the tracing and counteraction to the oil spill due to he ice cover on the river in winter. Therefore, this paper developed the study on the oil weathering, spreading and drifting on the low-temperature river in order to provide the guidance on the prediction of polluted area and counteraction to an emergent oil spill.On the base of exhaustive analysis about the applied conditions and predictive effects of the prevalent mathematic models on the oil weathering and spreading, this paper improved the most condign model with considering the characteristics of potamic oil spills. And the parameters in the models were determined via the experimental simulation tests. It was the fist time to establish the oil weathering, spreading and drifting models in the low-temperature river. And they were used to predict the oil evaporation, dissolving, the changing process of oil qualities, oil spreading, remnant oil on the water surface and the oil adsorption on river banks in different seasons and the interaction between oil and ice cover.It can be concluded that the evaporation process is mainly controlled by the moving of volatile component from main body to the surface of liquid at low-temperature condition from the academic analyses about the evaporation mechanism of mixed liquid. The liquid resistance would become larger as the temperature gets lower, and the slick where the volatile component exists would be thinner, and the evaporation amount is smaller. Therefore, the environmental temperature is an important factor for the oil evaporation. An attenuation coefficient e^-k/Δθ related to the temperature was added to the Fingas'model. It was the first time to establish the evaporation model for the high-viscosity or semiliquid oil at the temperature close to the solidifying point. It was found that the improved model should be adopted when the temperature difference between environmental temperature and solidifying point was smaller than 10℃via the shallow pan evaporation test. The resistance coefficients of 0# diesel oil and Daqing crude oil were 1.07 and 2.64, respectively. The slick area exposed to the air A_f played an important role on the oil evaporation in river with ice cover. In this condition, an attenuation coefficient (A_f h_oe^-k/Δθ)/V was added to Fingas'model to simulate the oil evaporation, and these model were all validated via the shallow pan evaporation tests.It was the fist time to study the oil sorption on sand, clay and rubble type river banks via the flume tests. They all accorded with the second order kinetics equation and the Langmuir isotherm equation. The sorption mechanism of porous granule banks such as sand and clay is the synthetical action of physical sorption, conglutination, active ion sorption and capillarity sorption. Besides, the holes among the cumulated granules provide the huge"oil storage space". And the oil sorption on the rubble bank mainly depends on the viscous force.The sorption amount of oil on sand and clay banks would increase at fist and then decrease as the wave height increasing. The amount reached the maximal value while the wave height is at the range of 30⁶0 mm. The oil sorption amount on rubble bank would decrease as the wave height increasing. And the sorption amounts for these there kinds of banks all decreased as the bank gradient (θ) increases. Whenθrises from 5°to 30°, the amplitude reduction of the rubble bank is the largest, are 63.4% and 73.3% in high and low hydraulic conditions, respectively. We also compared the oil sorption amount among the inboard, outboard and straight banks. And results are: sorption amount of outboard bank > sorption amount of straight bank > sorption amount of inboard bank. It was the fist time to establish the oil sorption calculated mode for river banks. It was also the fist time to discuss the sorption behave of floating oil on the ice cover. The results sh_owed that sorption velocity was very high, and the time of adsorption was less than 15 min and it accorded with the second order kinetics equation. The saturated adsorption amount was 0.0008 ml/cm² and 0.00117 ml/cm² in high and low hydraulic conditions, respectively. And it accorded with the Langmuir-Freundlich isotherm equation.The transportation of oil on moving water is the combination of isotonic flow due to the daggle action of the current and the mechanical spreading on the calm water due to the asymmetry in the oil slick thickness. The velocity profile across the vertical section within the slick with dimensionless pressure gradient p* being the parameter was also given. The first half part before the slick center was down-pressure flow and the other part behind the slick center was called against-pressure flow. As the slick was spreading, the absolute value of dp/dx decreased gradually. The dispersion dimension was added into the Fay's model to establish the oil spreading-dispersion model for the early stage. The dispersion coefficient K_x was determined via the circulating flume test. With the increasing of flow velocity, K_x increased from 4.34 cm²/s to 20.08 cm²/s in the open wager and increased from 2.80 cm²/s to 5.64 cm²/s under ice. The effect of wave height and temperature on K_x was also investigated. The improved model was validated by using the experimental results, on the base of which a new two-phase oil spill model made up of improved Fay's model and oil particle theory was put forward.Emergent oil spills of 10 t were pretended to occur at upriver reach of Harbin in Songhua River. The oil sorption mode and the two-phase oil spill model in this paper were used to simulate oil spreading and space-time distribution for 48 h during the high water period, average water period, low water period and icebound period, respectively. The rudimental oil amount on the water was predicted. The study showed that the oil sorption amount on banks during low water period was the largest: 2.45%, 1.39%, 1.03% and 0.61% for 10 t, 50 t, 100 t and 200 t, respectively. The sorption amount on the ice cover was small: 0.39%, 0.23%, 0.16% and 0.084%. The rudimental oil on water surface during the icebound period was as more as 9.5 t. And the rudimental oil amount during the high water with SE wind was the smallest, less than 2.2 t. The flow velocity, wind field and width of river would affect the length of oil slick. The oil spreading in waters near islands and anabranch collection was also simulated.