Research On The Gas Flow Measurement In Large Diameter Pipeline With Tracer Gas Technique

Large diameter pipeline transportation of gases is widely used in theindustrial field of metallurgy, petrochemical and energy and the municipalengineering. But the gases generally fail to get effective purification treatment in theprocess of conveying due to the cost of production. The impurity and corrosivematerials of gases are accumulated easily in the pipeline inwall and the surface ofcomponents, influencing the accuracy of measurement. Measuring the large diameterpipeline gas flow with tracer gas method is an effective solution. This paper reports afurther investigation on the measurement of the large diameter pipeline gas flow withtracer gas method via the combination of numerical simulations and experiments.1.Experimental verification of measuring gas flow with tracer method ina standard gas flow set with pipeline of300mm diameter. Results show.1)Inthe straight pipe the tracer gas and the air mixes unevenly but mixes quiteuniformly in the90degree elbow bend.2)The bias of tracer gas concentrationat sampling points by five-points injection/sampling method are smaller thanone-point injection/sampling method.3)There is a good correlation betweenthe gas flow rates measured by using tracer gas technique and turbineflowmeter, which the relative errors are the range of-2.15¹.69%when thetracer gas injection points on the upstream at bend with the distance of7¹3D（D is the internal diameter of pipe）, and the sampling points on thedownstream at bend with the distance of10¹4D.4)The relative errors areincreased from-1.85¹.18%to-4.47⁴.65%when the release of the tracer gasflow from the1L/min increased2L/min.5)The90degree elbow is replaced bythe60degree elbow （the injecting point is upstream of the bend duct7D，thes ampling point is downstream of the bending duct14D），the relative errorsare increased from-1.84¹.18%to1.73³.9%.2.Numerical simulation on the mixing properties of tracer gas and gasstream in the pipeline. On condition of full development pipe flow, theNumerical simulation was performed in the duct of300mm diameter with theFLUENT software, using CO as tracer gas and air as gas stream. The resultsshow，1) In the straight the relative errors is larger of the maximumconcentration, minimum concentration and average concentration for thetracer gas in the sample section.2)In the90degree elbow bend the tracer gas and the air mixes quite uniformly. The average concentration and the relativeerror of the theory of the concentration is small in the sample section. MixingEffect gets better as the pipe bending heavier but changes no more whenexceeding a certain distance.3)The secondary flow enhances tracer gas dispersion,which help to tracer gas and air mixing uniformity.4)When sampling the tracergas; the error of sampling axially is smaller than radically.The greater thebending angle（0⁹0°）, the better the mixing uniformity.3.Analysis on experimental error and uncertainty. Results show that therelative error of this experiment, measuring large diameter flow with tracermethod, is3.8%. The uncertainty of indication errors are U_95rel1.0%andV_eff50, in condition that the flow is452.54m³/h of the Turbine flow meter.