Study On Measurement System Of Blast Furnace Gas Dust Concentration In High Precision

At present, more than ninety percent of the blast furnace gas (BFG) is used forrecycling by wet process in China. After the purification, the dust concentration isgenerally low. In addition BFG is flammable and explosive which contains high contentpoisonous gas, for example CO, etc. These factors lead to a lot of difficulties in openingand sealing of sampling mouth. Based on the above characteristics, the measurementdevice of dust content in BFG is significantly different from other flue gas.During the existing dust content measurement devices, the precision of sensormeasurement is high, but its disadvantages are zero drift and complex calibration.Although operation of the filter cartridge isokinetic sampling device is very easy, themeasurement cost is too high and the measurement precision is not high for lowconcentration dust. Therefore, we need to develop a suitable measurement device for lowconcentration dust of BFG, in order to solve the above problems.Based on the mechanism of fiber filtration, first of all, the filtration efficiencyformula of forces on the dust during filtering process was obtained. Then, the reasons foradopting constant speed sampling theory in measurement process were analyzed. Inaddition, the mechanism and the error caused by non uniform sampling were alsodescribed in detail, which has provided theoretical basis for test study.Through the experimental research on the dust concentration measurement, theinfluence of filter membrane thickness, fiber diameter, particle size of dust and samplingtime on the measurement results has been tested. The results show that the impact of thefilter membrane thickness is not important on the measurement results. Within a certainrange, the dust collection efficiency of the device is inversely proportional to the glassfibre diameter, but proportional to the average particle size of dust. Moreover, researchshows this device has high collection efficiency for dust particles sized about10micron,with the best sampling time of5minutes. Under the same experiment conditions, throughthe repeatability test between the filtration membrane and filter cartridge isokineticsampling device, as well as the uncertainty theory calculation of filtration membraneisokinetic sampling device, it can be seen that the repeatability of filtration membrane isokinetic sampling device is better than the two others for its uncertainty was only0.73mg/m~3.The experimental researches show that this dust concentration measurement devicehas obvious advantages through the comparison among the three kinds of devices indifferent aspects. The device using glass fibre filter film as the dust filter material, not onlycan quickly and accurately measure gas of low concentration dust content with low cost,but also can be applied widely, due to its simple operation, and good repeatability,whichmake it suitable for industrial field measurement.