混氢天然气对流量计安装条件的适应性分析

Adaptability analysis of hydrogen-mixed natural gas to flowmeter installation conditions

目的 将氢气混入天然气中后会改变流体的性质和流动状态,从而影响流量计的计量准确度,采用ANSYS Fluent模拟弯头后混氢天然气的速度分布,分析现行的孔板流量计和超声流量计安装条件标准是否适用于混氢天然气管道。方法 模拟单90°弯头和双90°弯头后混氢天然气的速度场,分析现行标准中规定的流量计安装位置是否能使混氢天然气速度达到对称分布,从而说明是否需要延长现行标准中规定的弯头后流量计安装位置前直管段长度。结果 (1)在单90°弯头后44D和50D截面处,掺氢量(摩尔分数,下同)为10%~30%时,气体流速未恢复到对称速度分布;(2)在双90°弯头后44D截面和50D截面处,掺氢量为10%时,气体流速已恢复到对称速度分布,掺氢量为20%~30%时的流速未恢复到对称速度分布;(3)在双90°弯头后30D截面处,掺氢量为10%时的流速未恢复到对称速度分布。结论 (1)对于混氢天然气,应适当延长现行标准中规定的单弯头后流量计前直管段长度;(2)当掺氢量达到20%~30%时,应适当延长双弯头后流量计前直管段长度;(3)当掺氢量达到10%且孔板孔径比减小时,应适当延长孔板流量计前直管段长度。

Objective Mixing hydrogen into natural gas will change the properties and flow state of the fluid,thus affecting the metering accuracy of the flowmeter.ANSYS Fluent was used to simulate the velocity distribution of hydrogen-mixed natural gas after bending pipe,and analyze that whether the existing installation conditions of orifice flowmeter and ultrasonic flowmeter are suitable for hydrogen-mixed natural gas pipeline.Methods Simulating the velocity field of hydrogen-mixed natural gas after single 90°bending pipe and double 90°bending pipe,and comparing the velocity distribution of hydrogen-mixed natural gas with different hydrogen content on the pipeline center line and some sections after the bending pipe to analyze whether the installation position of the flowmeter specified in the current standard achieves symmetrical velocity distribution for hydrogen-mixed natural gas,and to determine whether the length of the front straight pipe section of the installation position of the elbow back flowmeter stipulated in the current standard needs to be extended.Results(1)At the 44 D and 50 D sections after a single 90°bending pipe,the H 2 molar fraction with 10%-30%H 2 did not return to the symmetrical velocity distribution;(2)At the 44 D section and 50 D section after the double 90°bending pipe,the flow velocity with 10%H 2 has returned to the symmetrical velocity distribution,while the flow velocity with 20%-30%H 2 has not returned to the symmetrical velocity distribution;(3)At the 30 D section after the double 90°bending pipe,the velocity with 10%H 2 did not return to the symmetrical velocity distribution.Conclusions(1)For hydrogen-mixed natural gas,the length of the straight front section of the single bending pipe rear flowmeter stipulated in the current standard should be appropriately extended;(2)For 20%-30%H 2,the length of the straight pipe section in front of the flowmeter after the double bending pipe should be appropriately extended;(3)When the orifice aperture ratio decreases,the length of the straight pipe section in front of the orifice flowmeter with 10%H 2 should be appropriately extended.