三冲量在制氢装置锅炉汽包液位控制中的应用

Application of Three-element System in Controlling Boiler Drum Water Level for Hydrogen Plants

锦西石化公司5×104m3/h(标准状态)制氢装置有一台转化气锅炉和一台废热锅炉,共用一个汽包,汽包液位采用三冲量调节控制系统。锅炉汽包水位越高,汽水分离的空间越小。水位过高会严重影响汽水分离效果,造成蒸汽带水影响过热段运行;水位过低会造成锅炉水循环的破坏,影响锅炉运行,容易使水全部汽化烧坏锅炉甚至爆炸。汽包液位波动还会影响汽包连续排污系统,最终使蒸汽品质恶化。为了克服给水压力扰动的现象,将给水流量和蒸汽流量信号都引入汽包液位调节系统,汽包液位是被控变量,是主冲量信号,蒸汽流量和给水流量是辅助冲量信号。工业应用结果表明,汽包液位控制在50%~60%,优于工艺卡指标;过热蒸汽的Na+含量和Si O2含量均达到工艺指标,使余热锅炉系统的稳定性和可靠性得到提高,取得了较好的效果。

PetroChina Jinxi Petrochemical Company＇s 5x104m3/h （under standard state） hydrogen production plant is equipped with a reforming gas boiler and a waste heat boiler and shares a steam drum with other units.A three-element regulating system is used for steam drum liquid level control.The higher the water level of the steam drum is,the smaller room there is for steam and water separation.An excessively high water level will severely affect the effect of steam and water separation ,resulting in entrainment of water in steam, in turn compromising the operation of the superheat section.An excessively low water level will damage the water circulating system of the boilers,affecting the normal operation of boilers.In that case ,all water may be vaporized,resulting in burn-out or even explosion of the boilers.A fluctuation in the liquid level of the steam drum will also affect the continuous sewage drainage system of the steam drum,eventually worsening the quality of steam.In order to overcome the pressure disturbance in water supply,a steam drum liquid level regul^ing system will be introduced for both water and steam flow signals.The liquid level of the steam drum is a manipulated variable and the main element signal.Steam flow and supplied water flow are auxiliary element signals.Industrial applications show that a liquid level of steam drum at 50%-60% is better than the specifications of the operation card.Both Na＋ content and SiO2 content of superheated steam meet process specifications.As a result,both the stability and reliability of the residual heat boiler system have improved.