Research On Influencing Factors Of Water-cooled Wall Temperature Of Ultra-supercritical Boiler

The contradiction between the increasing domestic demand for electricity and the increasingly serious environmental pollution problem has caused domestic power plants to gradually popularize the more efficient and energy-saving ultra-supercritical generating units.Compared with conventional generator sets,ultra-supercritical units have higher steam pressure and temperature,so the working environment of the internal water-cooled wall pipes is extremely harsh.If the temperature distribution of the water-cooled wall is uneven or the temperature rises substantially,there is a risk of a tube burst accident.Aiming at temperature distribution problem on water-cooled wall of the ultra-supercritical power plants,the water-cooled wall of an ultra-supercritical boiler is taken as the research object,and mathematical modeling method is used to calculate the parameters such as the thermal load on the water-cooled wall of the boiler and the temperature of the working medium in the water-cooled wall.Finally,the temperature distributionof water-cooled wall is obtained.And the influence of thermal deviation,flow deviation and water-cooled wall size on wall temperature distribution of water-cooled wall are compared.First,the average wall heat load of the water-cooled wall in the boiler furnace is calculated.In the calculation process,the mathematical idea of zero-dimensional modeling is used to simplify the interior space of the furnace into a whole,focusing on the heat value entering and exiting the furnace.The total heat absorption of the water-cooled wall inside the furnace can be obtained by calculating the difference between these two values.By combining with the heating area calculation of the cold wall in the furnace,the average heat load of the water cooled wall can be obtained.In the actual operation of the boiler,due to factors such as the existence of a combustion center in the flame,there is a certain degree of non-uniformity in the heating of the wall of the water-cooled wall.Therefore,the calculated average heat load of the water-cooled wall needs to be corrected.After the wall heat loadunevenness coefficient is corrected,the distribution of the wall-surface heat load of the water-cooled wall in the furnace can be obtained.Secondly,one-dimensional mathematical modeling is used to determine the state of the working fluid in the tube of water-cooled wall,including the pressure and temperature of the working fluid.In the modeling process,the water-cooled wall pipeline is divided into several small sections,and each small section is considered as a whole for calculation.Synthesize the state of working fluid in each small tube to determine the state distribution of working fluid in water-cooled wall.It also compares the changes of working fluid temperature in water-cooled wall tubes with different flow deviations under different loads.According to the comparison results,it can be found that when the forward flow deviation reaches 15%,the temperature of the working medium in the tube rises and then drops under various loads,which affects the overall economics of the boiler.Therefore,it is recommended that the actual forward flow deviation be controlled within 13%.Finally,according to the above calculation results,combined with the calculation of the heat transfer coefficient between the inner surface of the water-cooled wall tube and the working medium,the temperature distribution of the wall surface of the water-cooled wall is finally obtained.In the calculation process,the heat transfer coefficients of the inner surface of the water-cooled wall tube and the working medium are obtained according to the obtained working medium state,and then the heat load distribution of the water-cooled wall and the temperature distribution of the working medium in the water-cooled wall are combined to obtain the temperature distribution of water-cooled wall.And the change of wall temperature distribution of water-cooled wall in different flow deviations under different loads are compared.It can be seen from the comparison results that when the negative flow deviation reaches 10%,the wall temperature of the water-cooled wall will rise sharply.At the same time,the effects of water-cooled wall sizes and structures on the wall temperature distribution of water-cooled walls were compared.It was found that when the ratio of the width and thickness of the film-type water-cooled wall fins was about 0.9,the temperature difference between the fin end and the fin root is the smallest.It is better to make the width is as small as possible after guarantee the strength.In order to observe theworking conditions of water-cooled wall pipelines more intuitively,the paper uses the results of the above-mentioned calculations and comparisons combined with the theory of thermal profit analysis to solve the thermal stress distribution of water-walled pipelines.The above conclusions are further verified from the perspective of deformation and stress.The analysis of the factors affecting the temperature of the water-cooled wall can better help the power plant staff grasp the temperature distribution of the water-cooled wall,and then better prevent the occurrence of the abnormal temperature of the water-cooled wall,so that the ultra-supercritical boiler can run more safely and effectively.