Investigation Of Combination Of Dry And Wet Vacuum Pumps Frequency Conversion Control Extraction System For Tuebines

The extraction system of a condensing steam turbine needs to establish vacuum quickly while the unit starts up and maintain reasonable vacuum degree during operation.Improper vacuum pump configuration results in an increase in start-up time,the pressure in the condenser and the power consumption of the pump set.At present,the water ring vacuum pumps are widely used in power plants.Although its pumping capacity and working efficiency have been improved compared with steam-jets and ejectors used in the past,they are sensitive to the water temperature and the suction compression ratio is relatively fixed.This article aims to study and develop a new type of extraction system that reduces the sensitivity to water temperature,takes start-up and normal operating conditions into account and aims to enhance the controllability of the extraction system and reduce power consumption.The main research content and conclusion are as follows:Based on the operating characteristics of the condenser,the changes of pumping compression ratio of the typical unit in different seasons are calculated.Through the analysis of the adaptability throughout the year and problems of water ring pumps,it is concluded that the small overcooling degree of the water ring pump working fluid leads to a decrease in the volumetric efficiency of the vacuum pump and a rise in condenser pressure.Furthermore,the requirement of variable compression ratio and flexible operation is made for the condenser extraction equipment.A design scheme of a combination of dry and wet vacuum pumps frequency conversion control extraction system is also put forward.Based on the working principle of roots vacuum pump and water ring vacuum pump,a design scheme of the new extraction system for condenser with roots vacuum pump as a pre-pump,an intermediate water-spray cooler and a frequency conversion control water ring vacuum pump as the main pump is proposed.A mathematical model is established for the roots vacuum pump,the water-spray cooler and the water ring pump.The operating characteristics of the roots vacuum pump and the water ring pump under different working conditions are simulated and calculated.Based on the mathematical model established,for the combination of dry and wet vacuum pumps hybrid frequency conversion control extraction system,the effect of different compression ratio combination of dry and wet vacuum pumps and different water injection dosages on the pumping capacity,working fluid temperature and power consumption under different operating conditions throughout the year is calculated and analyzed,based on which the optimum operating parameters of the dry and wet vacuum pumps are obtained.The selection and parameter design of the combination of dry and wet vacuum pumps frequency conversion control extraction system are conductedBased on the LabVIEW software platform,a dynamic mathematical model is established for the combination of dry and wet vacuum pumps frequency conversion control extraction system for a 600 MW steam turbine,and a simulation study is conducted for air pumping while startup and variable frequency pumping while normal operation.