天然气流量计量标准装置的工艺流程优化

Process optimization of a natural gas fl ow measurement standard device

天然气计量标准工艺流程管件设备种类繁多、影响因素复杂,对计量标准装置计量性能的影响往往会在投产运行之后才逐渐显现,整改难度极大。因此,在建设初期科学优化流量计量标准装置的工艺流程,可有效提升其准确度。为此,提出了通过流体力学三维模拟仿真技术(FLUENT)优化高压大流量天然气计量标准装置工艺流程的方法。采用该方法可为天然气计量标准装置工作提供流态稳定的天然气介质,消除管道震动和噪音对计量标准装置计量性能的影响,进而提高天然气流量计量的准确度。同时,以管道弯头、整流器等典型工艺管件为例,通过建模和模拟计算,对不同工况条件下管道内流场进行分析,得出了流场分布规律。研究结果表明:①在检定工艺流程的标准支路与检定支路上游增加汇管,可减轻上游弯管对下游流态的影响;②在被检流量计及核查超声流量计上游10d处安装整流器,能够减小流态对计量结果的影响、提高计量标准装置的准确度。结论认为,该方法在国家石油天然气大流量计量站武汉分站工作级标准装置建设和工艺流程优化中得到了应用,经考核,工作级标准装置测量不确定度为0.29%(k=2),达到国内先进水平。

The pipe fittings and equipments in the natural gas measurement standard process are diverse and their influential factors are complicated. Their effects on the measurement performance of a measurement standard device will emerge gradually after they are put into operation, and the rectification is quite difficult. Therefore, the accuracy of the flow measurement standard device can be improved effectively by optimizing its process scientifically in its initial stage of construction. In this paper, it was proposed to optimize the process of a high-pressure large-capacity natural gas measurement standard device by using 3D simulation technology of fluid mechanics （FLU- ENT）. This method can offer a stable gas medium for the operation of this standard device and eliminate the effects of pipe vibration and noise on the measurement performance of the device, so as to improve the accuracy of natural gas flow measurement. In the meantime, the typical process pipe fittings （e.g. pipe elbows and rectifiers） were taken as examples to analyze the flow fields inside the pipes under different working conditions by means of modeling and simulation calculation. And accordingly the distribution laws of flow fields were figured out. It is indicated that the effect of upstream elbows on the downstream flow pattern can be reduced by adding manifolds at the standard branch of calibration process and the upstream of calibration branches; and that the effect of flow patterns on calculation results can be reduced and the accuracy of a measurement standard device can be improved by installing rectifiers at the position about 10 d （d refers to the diameter of a standard branch） distance to the upstream of a detected flowmeter and an ultrasonic reference flowmeter. This method is applied to the construction and process optimization of a working-level standard device at the Wuhan sub-station of the nation- al large-capacity oil and gas metering station. Based on check results, the measurement uncertainty of the working-level standard device is 0.29% （k = 2）, reaching the domestic advanced level.