Three Dimensional Numerical Simulation Research Of Warm Water Discharge In Offshore Platform

As a kind of renewable energy,wind energy is inexhaustible and inexhaustible,and will not cause major pollution in the process of mining and use.Our country has abundant wind energy resources and a superior geographical location.The rational mining and utilization of wind energy resources is of great significance to solving future energy depletion and environmental pollution problems.In recent years,our country’s offshore wind energy has been reasonably developed and utilized.For offshore wind farms,the electric energy is generally collected to the offshore converter station first,and then transmitted to the land converter station through flexible DC transmission.In the process of working at the offershore inverter station,the unit is generally cooled by in-situ water extraction,and then the warm water is discharged into the ocean.The unreasonable discharge of warm water into the marine environment not only brings about the increase of temperature in local areas of the marine environment,which leads to thermal pollution,but also affects the growth of marine life to a certain extent,posing a threat to the survival of animals and plants in the ocean.Therefore,it is crucial to study the effects of different influencing factors on the ocean temperature field,and it has important guiding significance for the design of the warm water discharge system of offshore platforms.Based on the summary of domestic and foreign research on the impact of cooling water discharge on the marine environment,a three-dimensional model of cooling water discharge from an offshore platform is established.The computational fluid dynamics method with standard k-? turbulence model in Fluent is used to discuss the influence of the environmental velocity,the warm water discharge speed,the diameter of the drainage pipe,the drainage temperature,the drainage angle,and the dual-port discharge on the temperature field.The change law of the temperature rise envelope area with the velocity ratio under the action of different parameters is summarized.The important conclusions of this research are as follows:(1)For the vertical single-port(drainage angle of 90°)discharge model,different working conditions is simulated when the ambient flow rate is constant.Studies show that with the increase of the warm water discharge speed,the temperature rise envelope area shows a trend of “first decrease and then increase”,that is,there is an optimal drainage speed(called the “inflection point speed”),which minimizes the impact of warm water on the environment(corresponding to the “minimum area”);the temperature rise envelope area increases with the increase of the drainage pipe diameter;with the increase of the warm water discharge temperature,the “inflection point speed” increases,and the temperature rise envelope area increases with a greater range of change.For the working condition simulated in this paper with a temperature difference of 9℃,the velocity ratio corresponding to the "minimum area" is around 6 and 7.(2)For the vertical single-port discharge model,the working conditions under different parameters is simulated when the discharge speed of warm water is constant.The research results show that the temperature rise envelope area increases with the increase of the drainage pipe diameter,and the range of changes is large;with the increase of the warm water discharge temperature,the “minimum area” increases and the velocity ratio corresponding to the “minimum area” continues to increase.(3)The warm water discharge angle has a relatively large influence on the temperature rise envelope area.As the warm water discharge angle increases,the “minimum area” keeps decreasing and the velocity ratio corresponding to the “minimum area” keeps increasing.Under the working conditions where the velocity ratio changes in the range of 3-10,when the discharge angle is 75°,60° and 45°,the temperature rise envelope area presents a "first decrease and then increase" trend with the increase of the velocity ratio;when the discharge angle is 30°,the temperature rise envelope area increases continuously with the velocity ratio.(4)For the vertical double-port discharge model,the influence range of warm water discharge is explored by changing the pipe spacing,and the comparison found that: when the pipe spacing is small,the first drain will have a strong superimposition effect on the temperature rise of the second drain;with the increase of pipe spacing,the influence of the first outlet on the second outlet will continue to weaken.For the simulation conditions in this paper,the superimposition effect disappeared under the action of high velocity ratio when the pipe spacing is 2m.