Research On Full Range Feed-water Control In 1000MW Ultra Supercritical Unit

In the 21 st century,our country adjusted the structure of electric power industry.The new thermal power generating units has entered the ultra(ultra)critical parameters,1000 MW,and large unit stage.At present,ultra supercritical unit has been widely used in many countries,and it has become a mature and reliable power generation technology in the world.Feedwater system is an important subsystem in the control system of the thermal power generating units,especially in the ultra supercritical units,the control system is more complicated and difficult.This paper mainly focus on full range feedwater control of 1000 MW ultra supercritical unit.Ultra supercritical units use the one-through boiler,compared with the natural circulation boiler,the boiler is no steam drum,replaced by a built-in steam separator.In the unit start-up and different load operation,the function of the built-in type steam separator is also different.During the boiler start-up and low load operation,the steam separator is in the wet state,and the dynamic characteristics of the boiler are similar to that of the boiler.The change of feedwater flow mainly affects the level of the separator.During normal operation of the boiler,the steam separator is in dry state,without water,and just as a steam passage.At this time,the outlet temperature of the steam separator is used as the intermediate point temperature,which is controlled by the feed flow rate and boiler load instruction.At present,the switch from the start to the normal operation of the ultra supercritical units in China need manual operation,which can not realize the full automatic control of the feedwater in the real sense.This is the difficulty of the global feedwater control of ultra supercritical unit.At the same time,the typical PID control scheme is adopted in the domestic ultra supercritical units.Compared with foreign similar units,the control effect is not ideal,and the quality of control is needed to improved.Based on the 1000 MW ultra supercritical unit feedwater system and its start-up process,the structure of the water-steam cycle,the feedwater of the starting and normal operation of the boiler and the existing feedwater control scheme are analyzed and studied in this paper.In the view of the characteristics of the feedwtaer system of ultra supercritical units,combining with more mature fuzzy control theory in the current.The existing feedwater control scheme of ultra supercritical units is improved,and the control scheme is designed by using the fuzzycontroller.According to the operation rule of the ultra supercritical units and the control experience of the operation personnel for many years,design the control scheme of the steam separator wet and dry state switching.And the control scheme of full range feedwater is designed according to the operating state control scheme.