Ads by Google
Natural gas is measured with standard orifice, which still occupies more than 95% at natural gas measurement at present. According to the requirements of Article 4.2.3 in SY/T6143-1996 Measurement Method of Natural Gas Flow with Standard Orifice: before gas flows through orifice, the flow bundle must be parallel to tube axis without rotation. To eliminate rotational flow of flow mediums in the process tube in front of orifice caused by various process equipment (such as header, valve, etc), the minimum length of straight tube in front of orifice has been stipulated in Article 5.1.3 of this Standard. But However, according to the research results at home and abroad show that, even the length of straight tube in front of orifice approaches to 100D (D indicates the inside diameter of meter tube), it is still difficult to eliminate the instability of rotational flow completely, which seriously affects the measuring precision that the flow measured by the orifice is less than the actual flow, making the economic benefits of gas seller be harmed severely. At present, the measure of equipping rectifier in front of standard orifice has been broadly used aboard to eliminate the instability of rotational flow, and positive effects are created. According to the relevant test results from API, AGA and China: adding tube bundle rectifier in front of orifice 12D can reduce the length of straight tube in front of orifice from former 40 – 100D to about 18D, and also keep the relative stability of flow state, then the measuring precision is greatly improved.
The newly issued ISO5167, AGA N03 Report and Measurement of Natural Gas Flow by means of Standard Orifice Plates Meter (SY/T6143) of China make great changes to the installation of upstream tube of orifice on the basis of the updated test data, including: no installation of tube bundle rectifier, installation of 19 tube bundle rectifier installation and Zanker plate rectifier installation. As to flow chokes in any form, installation of 19 tube bundle rectifier at 13D+0.25D in front of orifice or Zanker plate rectifier at the distance equal to or greater than 7.5D in front of orifice can shorten the straight tube from 30D-145D to 17D or 30D.Only if the installation requirements in the new standards are followed accordingly, the flow medium can be distributed fully at the desired speed before it flows in the flow meter, thus, flow is correctly measured.
Tube Bundle Rectifier