Research On Measurement Of Wet Coal Gas Flow Rate In Large Diameter Pipeline

The accurate measurement of wet coal gas flow rate in large diameter pipeline is an urgent and key issue to be solved in the steel industry,which directly affects the efficiency of green development,safe production and even energy regulation of iron and steel enterprises.Wet coal gas contains precipitated water and water vapor,which causes the change in its density.Meanwhile,the operational temperature and pressure of the wet coal gas constantly change with different time and different space.Thus,that is essentially a real gas-liquid two-phase flow in ultra-hostile environment,and is a worldwide problem in the field of metrology.Pitot tube flowmeter is widely used in the steel industry.However,there are still some limitations in simultaneous measurement of wet coal gas flow rate and liquid phase fraction for this type of flowmeter.Here,a combination scheme of a Pitot tube flowmeter and an inserted thermal sensor is put forward,considering that the heat transfer coefficient of water is much larger than the gas heat transfer coefficient.Theoretical analysis and experimental study are focused on the measurement characteristics of the thermal sensor for liquid phase fraction,and the major contents are as follows:Firstly,a local homogeneous flow model of the gas core is presented after analyzing the flow characteristic of wet coal gas in the large diameter pipeline.The Ishii model has been assured to be used by comparative research on the three empirical entrainment models in the gas core of wet coal gas flow,such as the Paleev model,the Pan model,the Ishii model.From this basis,the formula for the liquid phase fraction in gas core has been deduced,which provides a better method for metering the wet coal gas flow rate in large diameter pipeline.Secondly,a thermal flowrate detecting unit has been designed whose circuit accuracy has been analyzed and a thermal flowrate model of wet coal gas on basis of the factor of mass flowrate has been proposed.Thirdly,aiming at the problem of changeable thermal physical parameters in the gas core,the dynamic viscosity,thermal conductivity and Prandtl number of wet coal gas with temperature and pressure has been focused.Based on the method of dryness compensation,the influence of the composite-physical parameter,Pm_mix,on the thermal flowrate measurement model has been discussed deeply.A better physical formula with thePm_mix has been achieved and verified by this experimental tests according to the NIST.The full-scale error of the model of wet coal gas flow rate can be controlled less than 5%under the conditions of the three ranges of parameters,pressure,volume liquid fraction and the fluid flow rate,which are from 0.1MPa-0.5MPa,0.05%to 1.5%and from 1 to 12m/s respectively.