管输压力下实时记录式天然气发热量测定设备的开发

在管输压力下精确测定烃类组分发热量的一种方法及其样机已经开发成功,此设备的价格可允许目前采用间歇式取样的用户实现发热量的在线测定,在每分钟内多次测量、报告和记录体积基发热量。由于吸光池是在接近管道压力的条件下操作,因而管道中天然气的能量流量可以由单位体积基发热量与体积流率的乘积直接输出。利用分光光度计和标准硅CCD检测器在波长约900nm处进行测量,通过其吸收光谱测定天然气组成和发热量。与波长较长的红外吸收光谱相比,此区域内天然气各烃类组分的吸收光谱的线性关系更好。故对C1～C6组分和水分而言,谱图可以更精确地拟合为各组分(以单位体积中分子数量表示的)浓度。然后,将各组分的浓度加和即可得到天然气的体积基发热量。此外,诸如压缩因子、密度和相对密度等参数也可以由测定的体积组成求得。

Development of real time BTU measurement of natural gas at line pressure

A method and device have been developed which accurately measure the BTU con- tent of hydrocarbons at pipeline conditions. The cost of this device allows some users who cur- rently collect samples to have the advantages of on-line BTU measurement. The device meas- ures, reports, and logs the BTU value per unit volume several times per minute. As the absorp- tion cell is nearly isobaric with the pipeline, the energy flow through the pipeline can be compu- ted directly as the product of the BTU value per unit volume times volumetric flow rate. BTU and composition are measured via optical absorption spectroscopy in the vicinity of 900 nm using a spectrograph and a silicon array detector. In contrast to longer infrared wavelengths, the natu- ral gas absorption spectrum in this spectral region is a linear combination of the spectra of the component species. The observed spectrum can therefore be accurately fit to yield the concentration, in molecules per unit volume, of all C1 to C6 hydrocarbon components and water. The ener- gy content of the components is then summed to yield the BTU per unit volume. Additional information such as the compressibility, density, and relative density can also be obtained from the measured gas compositions.