基于对偶模型的超低含液率湿气双参数测量方法

Dual-Parameter Measurement Method for Ultra-Low Liquid Volume Fraction Wet Gas Based on Dual-Model

长期以来我国低渗透气田井口计量广泛使用着旋进漩涡流量计.当旋进漩涡流量计用于湿气计量时,漩涡进动频率通常会产生偏差,从而影响气相流量的计量.研究采用了节流比为0.64、叶片数为6、叶片升角为60°的旋进漩涡流量计,提出了一种旋进漩涡流量计湿气测量方法.通过在旋进漩涡流量计两端并联差压变送器,测量出流量计两端的压降,结合频率与压降信号进行湿气特性研究.研究发现,当体积含液率小于0.50%时,漩涡进动频率会随着含液率的增大而降低,实际计算出的气相流量偏低,产生“虚低”现象,而流量计两端的压降随含液率的增大而增大,产生“虚高”现象;当体积含液率大于0.50%时,由于液相流量过大,破坏了漩涡的进动信号,导致旋进漩涡流量计的测量结果失真.研究使用量纲分析法给出影响频率信号、压降信号的无量纲相似准数,以空气-水为介质进行实流实验,分析了不同压力、不同气相表观流速下,漩涡进动频率和流量计两端压降随体积含液率的变化关系.在旋进漩涡流量计的单相计量原理基础上,通过增加幂指数形式的无量纲湿气修正项的方法,建立了频率和压降参数的对偶模型.实验结果表明,在置信概率为95%时,气相体积流量的相对误差为0.797%,液相体积流量的相对误差为23.2%,体积含液率的绝对误差为0.028%.

The swirlmeter has been widely used in low-permeability gas field wellhead metering in China.However,the precession frequency deviates when the swirlmeter is used for wet gas measurement,which affects the gas-phase flow rate.Thus,a new method of flow rate measurement using the swirlmeter was proposed in this study.The flow-meter includes a throttle ratio of 0.64,6 blades,and a blade lift angle at 60 degrees.Both ends of the swirlmeter were connected with a differential pressure transmitter in parallel.Frequency signals that reveal a pressure loss are captured to describe the characteristic of wet gas.The research shows that when liquid volume fraction(LVF)is<0.50%,the precession frequency decreases as the LVF increases as the actual calculated gas-phase flow rate is low,which results in an“under reading”phenomenon.In addition,the pressure loss increases as the LVF increases,which results in an“over reading”phenomenon.The liquid-phase flow rate becomes larger when the LVF is>0.50%,which destroys the precession frequency signal of the vortex and results in damages.A dimensional analysis method was used in this study to give the nondimensional similarity criterion that affects the frequency signal and the pressure loss signal.The actual flow experiment is carried out with air-water as the medium,and the relationship between the precession frequency and the pressure loss at both ends of the swirlmeter with the change of liquid volume fraction under different pressures and different superficial gas velocity is analyzed.Based on the single-phase meas-urement principle of the swirlmeter,this paper adds a dimensionless wet gas correction term in the form of a power exponent,and establishes a dual-model of the frequency and pressure loss of the swirlmeter.The experimental results show that when the confidence probability is 95%,the relative error of the gas volume flow rate is 0.797%,the rela-tive error of the liquid volume flow rate is 23.2%,and the absolute error of the LVF is 0.028%.