| With the large-scale water injection in the oilfield,the water content of the produced crude oil increases,and the amount of oil-water mixture treated by the sewage recycling station increases sharply.The oil-water mixture is mainly separated from the oil-water through the gravity sewage settling tank in the sewage station,and the separated sewage oil is collected by the oil collecting tank.Due to the high viscosity and poor fluidity of the sewage oil,a heating coil is required to heat it for recovery.For a long time,there is no very accurate or ideal calculation formula and method for the design of the heat tracing coil in the sewage settling tank,which leads to the possibility that the oil cannot be collected when the external ambient temperature is low.And after the heat tracing coil is put into production for a period of time,it will be damaged,deformed,corroded,perforated and leaked to different degrees due to factors such as heat exchange medium,dirty oil and external force,which will lead to the decline of the water quality of the sewage station.Therefore,based on the heat transfer theory,this paper establishes a thermal analysis model of the sewage settling tank and the heat tracing coil,and determines the temperature change of the sewage oil in the sewage settling tank through the analysis of factors such as the inlet velocity and inlet temperature of the heat tracing coil.,and analyze the influence of changing the above factors on the structural stress state and fatigue life of the heating coil,determine the operating parameters of the heating coil under high heat transfer and low stress,and carry out heat transfer efficiency and structural calculations,which can be implemented on site Change the fixing method of the heating coil under certain conditions,thereby improving the operating life of the heating coil.The specific research work carried out is as follows:(1)Analysis of the heat transfer characteristics and structural strength of the heat tracing coil of the sewage settling tank.A thermal coupling finite element model for the analysis of the temperature field in the liquid level lifting process of the sewage settling tank and the oil collection process was established,and the following conclusions were drawn through calculation: The oil collection tank was obtained during the analysis of the temperature field in the sewage settling tank during the liquid level lifting process.The bottom temperature reaches a maximum value of 332.3K at 0°,a minimum temperature of 318.7K at 210°,and the temperature gradually decreases with the increase of the height from the sump.In the process of oil recovery,the temperature field in the sewage settling tank is analyzed,and the temperature range of the bottom of the oil tank is 317.6K～330.7K;secondly,the structure V coupling model of the heat tracing coil is established.According to the fixing method of the heat tracing coil in the sewage settling tank And the load,the stress state and boundary conditions of the heating coil are determined,and the following conclusions are obtained:The heating coil reaches the maximum stress value at the connection between the fifth coil and the outlet manifold,and the value is 431 MPa.The strength check results of each coil coil meet the strength requirements.The fatigue life analysis of the maximum stress point of the heat tracing coil shows that the number of fatigue life is 18900 times.(2)Analysis of the influence of the heat transfer characteristics of the sewage settling tank heat tracing coil.By calculating the operating parameters of the sewage settling tank,the external environment and other factors.The results show that when the inlet temperature increases from 52℃ to 62℃,the temperature at the lower end of the oil collecting tank increases by 5.89℃～9.1℃.After changing the inlet flow rate of the heat tracing coil,the temperature of the fifth and sixth coils increased significantly.When the ambient temperature rises from-24°C to 24°C,the temperature at the low end of the oil collecting tank increases by 0.6°C to 5.1°C.After increasing the thickness of the insulation layer,the temperature of the slop oil at the 180° position of the sedimentation tank increased by 10.7℃～23.7℃.After changing the pipe diameter,the temperature at the bottom of the oil collecting tank increased by 5℃～6.7℃.(3)Analysis of the influence of the structural stress and fatigue life of the heat tracing coil of the sewage settlement tank.After the strength analysis and fatigue life calculation of the operating parameters of the sewage settling tank,the external environment and other factors,the following conclusions are obtained: after reducing the inlet temperature of the heating coil,the maximum stress value of the heating coil will decrease,and the number of fatigue life will decrease.increased.After increasing the inlet flow rate,the maximum stress value of the heat tracing coil changed little,and the corresponding fatigue life times were18830 times and 18960 times when the inlet flow rate was 3m/s and 2m/s,respectively.After the external ambient temperature increased from 0℃ to 24℃,the stress value of the heat tracing coil increased slightly,and the number of fatigue life decreased from 19180 times to19040 times.After adding the insulation layer,the maximum stress value of the heating coil decreases,and the number of fatigue life is 19,200 times compared with 18,900 times without the insulation layer.After changing the pipe diameter,the maximum stress of the heat tracing coil increases.After the fatigue calculation,the fatigue life times of the pipe diameters of60 mm and 89 mm are 18850 times and 18480 times,respectively.(4)Structural improvement of the heat tracing coil for sewage settling tank based on high heat transfer and low stress.According to the optimized operating parameters and the structure size of the heat tracing coil,the heat transfer efficiency analysis of the improved heat tracing coil shows that the temperature of the dirty oil at the tank wall increases significantly after the optimization,and the temperature of the lower end of the oil collecting tank also increases.0.5℃～6.5℃.At the same time,according to the improved parameters,the improvement analysis of the low stress of the heating coil is carried out.By changing the fixing method,it is obtained: the stress of the heating coil is reduced from 435.7MPa to311.9MPa,and the number of fatigue life is increased from 18990 times to 34550 times.This paper calculates the operating parameters of the sewage settling tank and other factors,and analyzes the heat transfer efficiency,structural stress state and fatigue life of the heating coil.Flow rate,inlet temperature and increase the insulation layer of the sewage settling tank,under the premise of meeting the production requirements,limit the circumferential rotation of the fourth and fifth heat tracing coils,the above methods can effectively increase the oil collection efficiency of the sewage settling tank and Increase the service life of the heat tracing coil. |
