Analysis Of Safety Characteristics Of Low Pressure Last Stage Of Heating Unit In Full Working Condition

With the development of new energy,the demand for heating units to participate in deep peaking has become more and more urgent,and it is significant to ensure the operational safety under small volume flow conditions during peaking operation in the full load range of heating units.The current analysis of the flow in the cylinder under small volume flow conditions does not take into account the effect of changes in the thermal system operation mode on the unit peaking operation boundary in the actual full range of operating conditions.This paper couples one-dimensional thermal system simulation to numerically analyze the steam flow characteristics,temperature and steam humidity changes in the low-pressure cylinder at the end of the heating unit under three small-volume flow conditions,such as pumping for heating,low-pressure cylinder cutting for heating,and deep peaking during the non-heating period,in order to identify The abnormal conditions affecting the safety of the unit under the three operating conditions,determine the safety boundary of deep peaking of the unit,and provide theoretical support for the peaking operation of the heating unit at full load range,the results show that:when the unit is operating at peak,the low-pressure cylinder steam flow is the main cause of flow deterioration and blast over-temperature.As the steam flow rate decreases,the flow deterioration and blower overtemperature intensifies,further leading to changes in steam humidity,increased blade vibration and local overtemperature problems,and in the blower overtemperature at the end of the dynamic blade there is serious reflux,put into the temperature reduction back into the spray water to lead to water corrosion of the blade out of the steam side.Pumping steam heating process because most of the steam is pumped out of the use of low-pressure cylinder flow deterioration and other problems in the three operating conditions in the most serious.In contrast,when cutting the cylinder heating steam into the low-pressure cylinder through the reduction of temperature and pressure,the volume flow increases the temperature decreases,so that the low-pressure cylinder only need to retain less cooling steam,thereby increasing the heat supply and improving peak performance,but less cooling flow will lead to relatively rapid flow deterioration when the flow rate changes.Compared with the general pure condensing unit,the final stage blades of the heating unit are optimized for small flow rates,and the flow deterioration during deep peaking is improved but still exists at lower loads.In the process of pumping steam for heating,the flow deterioration occurs during the whole operation process when the pumping capacity increases from 450 t/h to 600 t/h.The pumping capacity increases to 580 t/h and the final stage dynamic blade enters the blast condition,and the pumping capacity increases to 600 t/h,and the temperature of the final stage dynamic blade and the exhaust temperature exceed 100℃.When the unit was running in the 120-20 t/h cooling steam flow range with cylinder cutting,the abnormal working condition mainly appeared in the 60-20 t/h flow range.Cooling flow rate from 60.1 t/h down to 40.3 t/h in the process,the final stage flow deterioration and rapid development into the blast condition.At the same time,after the flow rate drops to 50 t/h,the through-flow portion of the steam no longer condenses.When the flow rate decreases to 30.4 t/h,the temperature of the dynamic lobe of the final stage exceeds 100℃.When the unit is in peak operation during the non-heating period,abnormal operating conditions mainly occur within the range of 10-30%THA load,the load drops to 30%THA,the low-pressure through-flow flow deterioration;the load drops to 20%THA end-stage dynamic lobe into the blast condition;the load drops to 10%THA end-stage dynamic lobe local temperature exceeds 100℃.When the heating unit is in peak operation,the low-pressure cylinder is in small volume flow condition for a long time,and the problems of flow deterioration and blowing at the end stage are more serious.Insufficient steam flow,steam deflection impact blade is the main reason for flow deterioration,when the flow deterioration is further aggravated at the end stage into the blast condition,the blade will also compress the steam will lead to blade local and discharge steam over the safety threshold,so when the flow deterioration occurs should strengthen the unit vibration and low-pressure through-flow temperature monitoring,at the same time,because the blast over temperature at the end stage there is steam reflux,put into the temperature reduction spray water will erode the blade Out of the steam side.In addition to the blade optimization,atomization temperature reduction spray water,but also by controlling the low-pressure cylinder into the steam flow,to avoid abnormal working conditions to reduce the impact.When pumping steam for heating,the pumping volume is controlled in the range of 450-580 t/h,with auxiliary peaking such as heat storage tanks.Heating load or peak demand further increase,can cut cylinder operation,will be controlled in the cooling flow 120-20 t/h,which cooling flow down to 60 t/h after the rapid reduction to 40 t/h below,in order to avoid the rapid development of vortex intensified blade chatter,reduce condensation droplets on the blade erosion,but the inlet steam flow can not be lower than 30.4 t/h for a long time,in order to prevent blade over temperature and detemperature spray water erosion blade.Non-heating period blade optimization after the turbine can run at a lower load,can be peaking operation range control in the 100-20%THA between to reduce the impact of abnormal conditions,this time should also strengthen the monitoring of other equipment low load operating stability.