| As a mainstream industrial dust removal and purification equipment,pulse-jet dust cleaning collector has been widely used in metallurgy,power plant,tunnel,mine,tobacco,pharmaceutical and other fields.In the dust collector operation,in order to maintain the efficient and stable retention of dust in the filtration process to ensure the operational efficiency of the dust collector,the dust particles accumulated on the filter material are often removed by pulse injection in the dust cleaning process.The difference of pulse injection parameters will cause the change of pulse air flow field,which will affect the sidewall static pressure distribution on the filter element and the final cleaning effect.Most of the existing researches on pulse injection analyze the sidewall pressure distribution by means of experiment or simulation,and use single and multiplei ndexes such as the peak pressure,the average value of the peak pressure,the uniformity of the pressure distribution,the cleaning amount and the residual pressure drop to judge the cleaning effect.In this paper,the formation law of sidewall pressure distribution under different pulse injection conditions and the problem of non-uniform decision criteria when a single index is used to judge the occurrence of nonsimultaneous direction are studied.Firstly,the pulse injetcion flow field of tubular nozzle and the calculation method of sidewall static pressure were constructed,and verified by experiments.Then,the comparison experimental of the sidewall static pressure distribution of filter caridge under different nozzle types was carried out,the comprehensive evaluation method of the dust cleaning effect was proposed.Finally,the industrial application experiment of continuous operation of filtration-dust cleaning was carried out to verify the reliability of the comprehensive evaluation method.The main research contents and achievements are as follows:(1)Based on the restricted jet theory,the dynamic characteristics of the pulse injection flow field were studied.The physical models of pulse-jet dust cleaning of tubular nozzle with three different sizes were established,and the dynamic change of pulse injection flow field was simulated under different injecton pressure.The results showed that the pulse injection flow field of tubular nozzle with different sizes is similar.The main axis velocity of the injection flow is proportional to the injetction pressure.There is a relatively stable pressure stage when the air flow is fully diffused and expanded.This stage paly a major role in dust cleaning.According to the characteristics of its flow field,it is divided into the shock wave oscillation attenuation section,the front restricted jet section,the top restricted jet section,middle restricted jet section and the end wake section.The first two sections are located within the injetction distance,which accounting for 57.2% and 42.8% respectively,and the last three sections are located inside the filter element,which accounting for 33.2%,42.9% and 23.9%of the filter element length respectively.(2)Combined with the permeability characteristics of the filter element,the sidewall static pressure calculation method under the tubular nozzle pulse injection was proposed.According to the characteristics of the flow field,and considering the influence of the filter element on the basis of the theoretical formula of the circular section jet,fitting the theoretical formulas of the dimensionless central axis velocity and the average velocity of cross section in the filter element by the dimensionless analysis method.By combining the unit permeability of the filter element and Darcy’s law,the theoretical calculation formula of the sidewall pressure at each point of the filter element is fitted.The maximum error between the numerical simulation results and the calculated value of the formula is less than 9%.The experimental platform is set up for experimental verification,and the maximum error between the calculated value of the formula and the experimental result is less than 20%.(3)The static pressure dynamic measurement platform was built.With the filter cartridge as the research object,the sidewall static pressure distribution characteristics were tested and compared under different working conditions when the tubular nozzle and the upper opening diffuser nozzle was installed.The results showed that,compared with the tubular nozzle,the sidewall static pressure of the upper measuring point increases,the lower measuring point decreases,and the uniformity is obviously improved when using the upper opening diffuser nozzle.Compared with the optimal working conditions of the two nozzle types,under the injection pressure of 0.3 MPa ～ 0.6MPa,when using the upper opening diffuser nozzle,the static pressure increase range of the upper measuring point is 1.15 ～1.70 times,the static pressure decrease range of the lower measuring point is 43.42%～46.43%,and the nonuniformity coefficient is reduced from 0.73～0.94 to 0.15～0.45,which is more conducive to improving the phenomenon of upper cleaning failure and lower excessive cleaning.At the same time,it was found that the best injection distance exists when the tubular nozzle is used,but not all conditions are suitable for installing the upper opening diffuser.(4)Aiming at the problem that a single evaluation method can not accurately reflect the cleaning effect when it has non-homogeneity,a comprehensive evaluation method of filter cartridge cleaning effect was established.According to the theory of entropy method,the weight of sidewall pressure was determined based on the principle that the minimum static pressure of sidewall has the most important influence on dust cleaning,and the integrated pressure was used as the comprehensive evaluation index of dust cleaning effect.By evaluating the static pressure distribution results of the tubular nozzle and the upper opening diffuser,it was found that when the injection distance is less than 150 mm,the integrated pressure could be increased by installing the upper opening diffuser.When the injection distance is greater than 150 mm,the installation height of the upper opening diffuser should be greater than 90 mm,otherwise the integrated pressure will be reduced.At the same time,the evaluation index was applied to the annular-slit nozzle and the cone structure installed in the filter cartridge,and the results are found to be consistent with the literature research results.(5)A visual application platform for dust-cleaning with powder was built to verify the reliability of the evaluation index of dust-cleaning effect based on integrated pressure.The continuous operation characteristics of filtration and cleaning were monitored by high speed camera and differential pressure meter,and the dynamic characteristics of cleaning were analyzed.The results showed that there was an exponential relationship between dust removal quality and residual pressure drop under experimental conditions.When the tube nozzle was used,the dust in the lower part of the filter cartridge would splash and spread seriously in the process of falling off due to excessive sidewall pressure.When the upper opening diffuser nozzle was installed,the dust is stripped along the length direction of the filter cartridge,and the phenomenon of dust splashing is not.When the injection distance is 200 mm and the installation height of the upper opening diffuser is 120 mm,the total dust removal amount of filtration and cleaning for 8 consecutive runs reached 11010 g,which is the maximum dust removal amount in all test results of all experimental conditions,which is consistent with the integrated pressure evaluation results.There were the best injection distance and diffuser installation height in pulse injetcion. |
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