Flow Field Performance Optimization Of Low Pressure Cylinder In High Back Pressure Heating Turbine

Combine heat and power generation is a system that can produce both heat and electricity at the same times.It can provide heat for the users while generating electricity.It is considered as an effective solution to improve energy efficiency.Traditional heating methods usually extract steam with high parameters from medium pressure cylinders of steam turbines to heat water,so as to provide heat to users.However,due to the high extraction parameters of the steam in medium pressure cylinder,the loss of cold source is increased.In recent years,in order to make full use of exhaust heat and expand the heating capacity of the unit,high back pressure heating technology has been widely recognized.For wet-cooled units,the exhaust steam temperature of steam turbines is low.If it is directly used to heat water,it can not satisfied the heating demand in winter.The exhaust steam parameters of steam turbine can be better improved by using high back pressure heating method,so that the water can be heated to a higher temperature.In order to satisfy the high back pressure operation in winter,double rotor exchange technology is usually adopted.In the non-heating period,the low pressure cylinder rotor with more stages is used to satisfy the higher power generation,and in the heating period,the rotor with fewer stages is used to satisfy the high back pressure heating.For reducing the large amount of work in the process of double rotor interchange,the rotor of low pressure cylinder is improved.The rotor is not replaced from non-heating period to heating period,only the last two stages are removed on the basis of the original rotor during heating period,and the diaphragm of turbine is also removed.The increase of exhaust steam parameters during heating period and the change of the low pressure cylinder structure lead to the flow field inside the low pressure cylinder has great change.Due to the increase of exhaust parameters and large space after blades removing,vortex will be formed in the space after blades removing,resulting in large energy loss and affecting the efficiency of low pressure cylinder.This dissertation mainly studied the change of flow field in low pressure cylinder before and after high back pressure heating.According to the distribution of the flow field in the low pressure cylinder,the structure of the low pressure cylinder is optimized to optimize the distribution of the flow field in the low pressure cylinder.Low pressure cylinder of 300MW turbine unit is selected as research object.Solidworks is used to build solid model according to actual model and design diversion ring for it.NUMECA is used to do numerical analysis.According to the distribution characteristics of the flow field in the last stage of the low pressure cylinder,the diversion ring of the low pressure cylinder of the steam turbine is designed,and the flow field in the last stage of the low pressure cylinder before and after adding the diversion ring is analyzed numerically.Comparing the numerical simulated results of low pressure cylinder flow field to which adding different diversion ring.Optimal plan will be obtained after analyzing vortex distribution,static pressure recover coefficient and total pressure loss coefficient in flow field under different heating conditions.The results showed when the starting position of the guide ring at the fifth stage blade,the radius of the inner ring is 1600 mm and the width of the outlet is 300 mm,the optimization effect of the flow field in the low pressure cylinder is the best.Adding appropriate diversion ring bringing about vortex effectively reduced,and leading to a sharp increase of 7.84%in efficiency of low pressure cylinder and 62.65%in statistic pressure recover efficient,it also contributing to apparently decrease of 94.74%in total pressure loss efficient.All the results indicated that aerodynamic performance of low pressure cylinder has obvious promotion.At the same times,the optimization schemes of different diversion rings under different working conditions are simulated and analyzed to verify the adaptability of the optimal diversion ring under different working conditions.When under high back pressure heating condition,structure of low pressure cylinder changed,the research will provide important theory evidence for optimization of low pressure cylinder flow field.