Cleaning of HGMF matrices

The successful application of high-gradient magnetic filtration to the processing of steelmaking waste gases will require an effective method of cleaning the matrix after use. Three cleaning methods have been tested on a laboratory scale, viz. mechanical rapping, blowing with compressed air jet and infrasonic cleaning. Dry basic oxygen furnace dust was used in the tests. All three methods were effective, with 95% removal or greater attainable. Sonic cleaning removed 93% within 20 seconds. In contrast, the air jet removed less than 90% in three minutes, although subsequent flow reversal improved the removal rate, suggesting the superiority of oscillatory flow. Rapping produced good removal provided that it was vigorous, removal being initially rapid when the matrix was fully loaded. As expected, infrasonic cleaning became increasingly effective as the peak velocity was increased. The peak oscillatory velocity attained was 7.9 m/s, which corresponded to a sound pressure level measurement of 125 dB. Even at such high levels, no silencing was necessary because of the sub-sonic frequency of 12 Hz. Infrasound permits in-situ cleaning with remote apparatus, requires minimal purge flow and can copy with heavy dust loadings.