LNG接收站海水泵及高压泵变频节能探究

Energy saving analysis on variable-frequency seawater pump and high-pressure pump in LNG terminal

关键词:  LNG接收站  海水泵  开架式气化器  能耗过剩  高压泵  变频节能 

Key words:  LNG terminal  seawater pump  open rack vaporizer  excess energy comsumption  high-pressure pump  frequency energy-saving

摘要:

国内LNG接收站通常采用一台海水泵额定流量运转为一台开架式气化器(ORV)提供海水的模式气化LNG,非冬季运行,由于海水温度较高、外输天然气流量较小,ORV所需海水流量小于海水泵额定流量。所以,此运行模式普遍存在能耗过剩。同时,由于外输天然气压力调节范围较大,而高压泵只能提供其额定出口压力。因此,当外输天然气压力较小时,高压泵出口压力过剩,导致能耗过剩。为了解决海水泵、高压泵能耗过剩问题,开展了对其变频节能的探究。首先,分析了海水泵、高压泵变频的必要性；然后,以海水泵为例,以其特性曲线为基础,计算了海水泵工频出口压力及电机功率,再运用二分法及泵相似理论计算了海水泵变频电机功率；之后对海水泵及高压泵工频计算进行了误差分析,最大相对误差为3.5%；最后,通过能耗对比发现:海水泵采用变频,每年可节省电能39.41%；高压泵采用变频,每年可节省电能47.39%；采用海水泵、高压泵变频,接收站每年可节省经济成本约426万元。 

Abstract:

Domestic LNG terminals usually use the model that a seawater pump with rated flow operation provides seawater for a single open rack vaporizer (ORV) to gasify LNG. Due to higher seawater temperature and lower natural gas flow of external input, the required seawater flow of ORV is less than the rated flow of seawater pump during non-winter operation. Therefore, this operation model is associated with excess energy consumption. Meanwhile, since the pressure range of natural gas pressure of external input is wide and the high-pressure pump can only provide the rated outlet pressure, so the outlet pressure of the high-pressure pump will be excessive when the pressure of natural gas of external input is lower, and resulting in excess energy. In order to solve the excess energy consumption problem of seawater pump and high-pressure pump, this paper started to explore its frequency energy-saving. Firstly, necessity of seawater pump and high-pressure pump frequency was analyzed. Secondly, in seawater pump, for example, outlet pressure and motor power of power frequency was calculated based on its characteristic curve. Then motor power of variable frequency was determined with the dichotomy and the similarity theory of pump. Thirdly, error analysis of power frequency was made on the seawater pump and high-pressure pump, showing the maximum relative error is 3.5%. Finally, through the comparison of the energy consumption, the seawater pump with variable frequency could save energy by 39.41% per annum, while the high-pressure pump with variable frequency could save energy by 47.39% per annum. Furthermore, economic cost of approximate 4.26 million yuan in LNG Terminal could be saved with variable frequency seawater pump and high-pressure pump per annum.