Study On The Difference Of Air And Natural Gas Flow Measurement Gas Flowmeters

At present,there are two ways to test the gas flow meter with the real flow in China:First,test with natural gas as a medium under the positive pressure,the other is the use of air as a medium under normal pressure.Different test methods in the field measurement process will produce differences,this difference will inevitably affect the outcome of trade handover measurement.In order to study the source of the differences,we need to conduct a study of the differences.In this paper,we choose the most widely used flowmeter in china,such as turbine flowmeter,roots flowmeter and precession vortex flowmeter as the experimental object,and conduct performance tests and differential studies in the air flow standard device of Chongqing gas mine and Chuanzhong oil&gas mine and the natural gas flow standard device of Chengdu sub station of Southwest Oil and gas field.The performance test includes repeatability tests,stability tests,indication error tests,and determines the experimental samples for differential studies.The differential study shows:(1)Chongqing Gas Mine and the Chuanzhong Oil and Gas Mine,upper hydrocarbon siltstones mineral critical flow venturi nozzle standard device and chengdu substation secondary standard device differences between the results of the verification flow meter,turbine flowmeter,roots flowmeter difference is small,the precession big difference on turbine flowmeter,and shows that the type of meter produced by different differences in different size,because of the defferent structure of the flowmeter;(2)with air as medium verification instrument coefficient of flow meter is greater than the gas as medium for verification of the instrument coefficient of flow meter,even to air as medium test of flowmeter,the measured flow smaller than the actual flow;(3)with natural gas as medium of experiment,the stress change of the vortex precession flowmeter had a greater influence on the performance curve,had a little effects on the rest of the flowmeter performance curve,impact test results shows that gas pressure,but it is not a major factor in the production of difference;The influence of natural gas temperature on turbine flowmeter and swirl vortex flowmeter is relatively large,which has little influence on the rotz flowmeter,indicating that the natural gas temperature will produce certain difference to the test result;(4)the gas composition changes brought about by the calibration instrument K maximum 0.23%,coefficient of deviation on the flowmeter calibration instrument coefficient is small,the influence of gas composition is not a major factor in the production of difference;(5)with air as medium of experiments,the air temperature for(turbine flowmeter and vortex precession flowmeter,smaller influence on roots flowmeter,shows that the air temperature is different makes a difference in test results.The influence of air pressure on the vortex flowmeter of DN50 is relatively large,which has little effect on other flowmeter,indicating that the pressure change has little effect on the detection result.Testing flowmeter types,therefore,will be on air flow and gas solid test gas flowmeter have great difference,but its not a different medium test meter the principal causes of differences,but medium temperature,followed by the test medium pressure,gas composition changes.