孔板流量計量表測量天然氣誤差與解決方案

發(fā)布：2018-12-18 | 點擊：人次

摘要：孔板流量計量表測量天然氣誤差與解決方案資訊由優(yōu)秀的流量計、流量儀生產(chǎn)報價廠家為您提供。一、孔板流量計測量天然氣誤差原因上下游直管段長度不夠，氣流得不到充分發(fā)展，將使計量結果造成較大誤差。計量標準規(guī)定的zui短直管段長度，在現(xiàn)場實際中一般很難得到滿足。更多的流量計廠家選型號價格報價歡迎您來電咨詢，下面是孔板流量計量表測量天然氣誤差與解決方案文章詳情。

一、孔板流量計測量天然氣誤差原因

上下游直管段長度不夠，氣流得不到充分發(fā)展，將使計量結果造成較大誤差。計量標準規(guī)定的zui短直管段長度，在現(xiàn)場實際中一般很難得到滿足，特別是由于輸氣工藝等原因，計量裝置的上游往往都存在彎頭。如果是單彎頭或平面雙彎頭將使計量結果偏高;對于多個彎頭，將使計量結果偏低。

二、解決措施

應該在節(jié)流裝置之前加裝整流器，避免旋轉流、渦流對計量的影響。

天然氣的氣質(zhì)和氣流條件

1、產(chǎn)生誤差的原因

GB/T21446-2008《用標準孔板流量計測量天然氣流量》標準中規(guī)定，通過孔板的天然氣是經(jīng)凈化處理后的天然氣，氣流的流動應是保持亞音速的、穩(wěn)定的或僅隨時間緩慢變化的。氣流是均勻單相的牛頓流體。若氣體含有質(zhì)量分數(shù)不超過2%的固體或液體微粒，且成均勻分散狀態(tài)，也可以認為是均勻單相的牛頓流體。氣流流經(jīng)孔板以前，其流束應與管道軸線平行，氣流流動應為充分發(fā)展紊流且無旋渦，管道橫截面所有點上的旋渦角小于2°即認為無旋渦。

通過計量調(diào)查發(fā)現(xiàn)，目前在油田天然氣計量中約50%的計量點其氣流條件具有以下兩個特點。

（1）氣體流量不穩(wěn)定，并隨時間周期性地大幅度變化，屬脈動流體。產(chǎn)生脈動源的原因[2]：①往復式壓縮機、發(fā)動機和葉片式增壓機;②調(diào)壓閥猛開關或者閥芯松動和磨損;③大量水或油的冷凝物在管線中不規(guī)則運動。

（2）氣質(zhì)中含水量大，并夾帶原油及微量顆粒雜質(zhì)，氣流流經(jīng)節(jié)流裝置時產(chǎn)生凝析液。氣質(zhì)、氣流條件達不到GB/T21446-2008《用標準孔板流量計測量天然氣流量》標準中規(guī)定的要求，必將產(chǎn)生計量附加誤差。為了獲得準確的計量值，必須抑制氣流的脈動及消除氣質(zhì)中的水分和雜質(zhì)。

2、解決措施

進入流量計的氣體必須先通過氣液分離器、過濾器。

（1）把測量管裝在對消除脈動來說較為有利的位置，例如裝在調(diào)壓閥的入口或遠離脈動源處。

（2）為了減少脈動幅度，可在脈動源和測量管之間的管線上加裝一個容器，或者設計專門的脈動衰減器。把節(jié)流閥或限流器裝在脈動源和測量管之間是減少脈動的zui有效方法，但是這種方法壓力下降過大，除非條件許可，否則不宜采用。

（3）在差壓仍然保持較高的操作前提下，可用較小的測量管，而孔板開孔直徑基本不變。

（4）在流量計前、后取壓管出口處分別加裝一個具有一定容積的氣液分離器，使進入流量計的差、靜壓信號達到先氣液分離及緩沖后再進入計量裝置。

（5）導壓管路上的上、下游導壓閥應選用大通徑的球型閥。

（6）為了防止導壓管的凍堵，必須對導壓管路進行保溫，并增加加熱補償保溫措施。

（7）對于因下游波動源而引起計量點氣流脈動的情況，可通過調(diào)整流量計下游側閥門的閥位（關小），使計量點氣流脈動幅度減小。試驗證明，采用關小計量管下游閥的方法來控制氣流的脈動，效果是十分明顯的，此方法在實際使用時，必須在確保安全生產(chǎn)的情況下進行。

試驗證明通過上述方法能有效地抑制氣流的脈動、消除氣質(zhì)中的水分及雜質(zhì)，減少流量計的計量附加誤差。

英文版本：

A, orifice plate flow meter in measuring gas error

The upstream and downstream straight pipe length is not enough, the airflow is not fully developed, will make a larger error caused by measurement results. Measurement standard shortest straight pipe length, in the field in general difficult to meet, especially due to gas transmission process, the upstream metering devices often have elbow. If you are single or double elbow bend plane will make the measurement result is high; for more than one elbow, will enable the measurement results.

Two, measures

Should be installed before the rectifier in the throttling device, avoid the influence of rotating flow, vortex on the measurement.

The temperament of gas and air condition

Reason 1, error

Regulation of GB/T21446-2008 "by flowmeter measurement of natural gas flow standard" standard orifice plate, the plate of natural gas is purified natural gas, the flow is subsonic, maintain stable or only slowly varying with time. The airflow is Newton homogeneous single-phase fluid. If the gas containing solid or liquid particles concentration of not more than 2%, and the dispersed state, can also be considered as a homogeneous single-phase Newton fluid. Before the gas flows through the orifice plate, the beam should be parallel with the pipe axis, air flow should be fully developed turbulent flow and vortex vortex free, all points on the tube cross section angle less than 2 degrees that no vortex.

The survey found, about 50% measurement points in Oilfield Metering of natural gas in the air condition has the following two characteristics.

（1） gas flow instability, and with time periodically changes greatly, belonging to pulsating fluid. [2] causes of pulsating source: ① reciprocating compressor, engine and the blade type supercharging machine; the pressure regulating valve with switch or spool loosening and wear; condensate and large amounts of water or oil in the pipeline in irregular motion.

（2） temperament big water content, and some oil and trace impurities, the condensate gas flows through the throttle device. Temperament, air conditions are not up to the GB/T21446-2008 "requirements for flow meter measurement of natural gas flow standard orifice plate" in the standard of measurement, will bring additional error. In order to obtain the exact value of measurement, pulse must restrain the flow and eliminate the temperament in the water and impurities.

2, measures

Gas enters the flowmeter must first through the gas-liquid separator, filter.

（1） the measuring tube is arranged in the elimination of pulsating relatively advantageous position, for example, installed in the entrance pressure regulating valve or away from the pulsating source.

（2） in order to reduce the fluctuation amplitude, a container may be fitted between the pulsating source and the measuring tube lines, or special design pulsation attenuator. The throttle valve or a current limiter is arranged between the pulse source and the measuring tube is the most effective way to reduce the fluctuation of pressure drop, but this method is too large, if conditions permit, or should not be used.

（3） in the differential pressure remains high operation premise, the measuring tube can be smaller, and the hole diameter ratio unchanged.

（4） the pressure at the outlet with a certain volume of gas-liquid separator in front of flowmeter, after entering the flowmeter, differential pressure signal, achieve again into the metering device to gas-liquid separation and buffer.

（5） tube on the downstream pressure guide valve, should choose the type of large diameter ball valve.

（6） in order to prevent the pressure guide tube blockage, must be on the tube for thermal insulation, heat preservation measures and increase the heating compensation.

（7） for the downstream source of fluctuation caused by gas pulsation measurement points, can be adjusted through the flowmeter downstream side of the valve the valve position （Guan Xiao）, the measurement point of the flow pulsation amplitude decreased. Test shows that, by using the method of closing small pulsating metering tube downstream valve to control the flow, the effect is very obvious, this method in actual use, must be carried out to ensure safety in production situation.

Tests show that the pulse, through the above method can effectively suppress the airflow to eliminate moisture and impurities in the reduction of temperament, additional error flowmeter measurement.

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孔板流量計量表測量天然氣誤差與解決方案