空气和高压天然气实流标定涡轮流量计的差异性

Differential flow calibration of turbine flowmeters for air and high pressure natural gas

随着天然气供求量的高速增长,国家级天然气实流检定站的产能无法满足城市管网和地区输配气干线上中、高压天然气流量计的周期性检定的需求,大量涉及贸易结算的涡轮流量计只能被送至法定计量检定机构在常压空气下标定,对于其检定结论和校准数据是否适用则存在着争议。为此,分别在常压(0.1 MPa)空气流量标准装置和德国国家高压(2.5 MPa和5 MPa)天然气流量标准装置上对32台涡轮流量计进行了实流标定,引入涡轮流量计扩展校准模型,并基于雷诺数对误差作了对比分析。研究结果表明:①常压和高压下的误差线分别位于两个不同的流动特征区域,不具有可比性;②在分界流量以上区域,涡轮流量计的误差仅随雷诺数而变化;③在各段压力工况中,存在着误差接近的雷诺数重叠区;④工况压力增加,所对应的误差数据可以被认为是对涡轮流量计准确度性能的连续延拓;⑤不同的工作介质对涡轮流量计的性能没有明显的影响。结论认为,常压空气下的标定数据不能用于0.4 MPa以上工况流量计的检定和校准,在压力限制条件下使用空气标定高压天然气流量计是一种可行的方案。

With the rapid growth of natural gas supply and demand,the capacity of national natural gas flow measurement stations is incapable of meeting the periodic verification demands of medium-and high-pressure natural gas flowmeters installed in urban pipeline networks and local transmission and distribution lines,and a great number of turbine flowmeters involved in trade settlement have to be sent to statutory metrological verification institutions for calibration in atmospheric air,so the applicability of verification conclusions and calibration data is still controversial.To deal with this situation,this paper carried out actual flow calibration on 32 turbine flowmeters by using the flow calibration facility of atmospheric air(0.1 MPa)and the Germany national flow calibration facility of high-pressure natural gas(2.5 MPa and 5 MPa)respectively.Then,an extended calibration model for turbine flowmeters was introduced,and the errors were comparatively analyzed on the basis of Reynolds number.And the following research results were obtained.First,error lines under atmospheric pressure and high pressure are situated in different flow characteristic regions,so the calibration curves for atmospheric pressure and high pressure are not comparable.Second,the errors of turbine flowmeters in the range above the transition flow rate are only dependant on the Reynolds number.Third,under the working condition of each pressure interval,there are Reynolds number overlapping sections with similar errors.Fourth,with the increase of the working pressure,the corresponding errors can be considered as a continuous extension of turbine flowmeter's accuracy performance.Fifth,the effect of working medium on the performance of turbine flowmeters is not obvious.It is concluded that the calibration data in atmospheric air is not applicable to the verification and calibration of the flow meter for the working pressure above 0.4 MPa.It is feasible to make use of air to calibrate high-pressure natural gas flowmeters under restricted pressure conditions.