天然氣發電廠氣渦輪機組燃料流量計線上校正可行性評估-以複循環發電廠氣渦輪機組為例

「失之毫釐，差之千里」為量測誤差所造成計量偏差下了最好的註解。本文舉例國內常用的幾種天然氣流量計並說明運作原理與差異，並列出各國流量研究機構相繼發佈的各種天然氣計量相關標準做為本次天然氣計量評估作業的參考基礎。本次研究的電廠所使用是差壓式天然氣流量計，量測的是機組天然氣體積流量。評估作業包含廠區天然氣流量系統查驗、機組天然氣流量計各項元件檢驗等工作，對於機組天然氣流量計設備，則參考美國儀錶協會(Instrument Society of America,簡稱ISA)所提出的校正概念進行校正評估，將機組流量計作為待測件，進行比對校正。因拆卸機組流量計送至國內實驗室進行校正有實務上的困難與安全考量，故而採取科氏力 (Coriolis)質量流量計做為線上標準件與機組流量計串聯於同一管線上進行線上實流比對校正，運用質量流量不受管路環境影響的特性，取用電廠計量站氣相層析儀(Gas Chromatography Analyzer，簡稱GC)之天然氣成份資料，使用美國氣體協會(American Gas Association，簡稱AGA) AGA 8標準計算天然氣密度，將標準件的質量流量轉換成參考體積流量，但因目前電廠運轉因素致標準件尚無法安裝於機組管路上，故採機組實際運轉資訊做為分析基礎，藉由待測件內部的雷諾數與釋放係數(Reynold Number vs Discharge Coefficient，簡稱Re vs Cd )對應參數表與AGA 3計算功能，模擬出待測件逐次疊待修正的計算結果，達成待測件的器差修正的校正目標。

關鍵字

體積流量；質量流量；天然氣密度； AGA 3 ； AGA 8

並列摘要

As an idiom, “a miss is as good as a mile”, it is the best description for how tiny errors lead to extreme inaccuracy of measurement. This study lists various kinds of gas flowmeters commonly used in Taiwan, explains their mechanisms, enumerates their differences, and introduces the standards of measurement issued by institutes in different countries as references to gas flow measurement. The power plant in our study uses a differential pressure flowmeter, which measures volumetric flow. The operating procedures included the inspection of the natural gas flow system in the power plant and each component of the gas flowmeter in the generator set. Calibration of the flow meter, in which the flowmeter shall be used as the test piece, was performed based on the methods proposed by the Instrument Society of America (ISA). Because of the difficulties and safety concerns of disassembling the flowmeter and sending to other domestic laboratories for calibration, the Coriolis force mass flowmeter was used as a standard meter and was connected in series to the flow meter in the generator set to measure the true flow. With the fact that mass flowmeters have characteristic of not being affected by the environment of pipelines, the data of the component of natural gas was collected by the Gas Chromatography (GC) in the power plant, the density of natural gas was calculated based on the standard of American Gas Association (AGA) 8, and the mass flow of the standard meter was converted into the referred volume flow. However, since the power plant was in operation and the standard meter cannot be installed on the pipeline. The data of actual operations was collected instead for analysis in this study. Through the internal Reynold Number vs Discharge Coefficient (Re vs Cd) table, and AGA 3 calculation function, the gradual corrected results of test meter can be simulated in order to reach the correction target.