Study On Concentration Distribution Of Paroxysmal Pollutants With Local Ventilation System

In industrial production process of adding steel slag to the converter, pouring materials by slag car and coke oven working etc., there are always polluted sources which release pollutants discontinuously, i.e. the paroxysmal pollution sources. Due to the intermittent release of polluted source, the concentration field is unsteady and pollutants production is uncertain. Therefore, it is difficult to control the pollutants in practice. In this paper, the unsteady concentration field by this kind polluted source with local ventilation system was studied with nitrous oxide(N2O) as a tracer gas by Fluent.First of all, the simulation method validation of steady flow was done through the error analysis of temperature field in the experiment and simulation based on the experiment done by our research group. On the above basis, the validation of unsteady simulation method was realized by error analysis on pollutants concentration of the exhaust system(including local and general ventilation system). Secondly, the initial flow field, the concentration variation in exhaust system and typical space points(including nose and mouth breathing height when the staff sits quietly and stands, the aerial work height) were analyzed in the unsteady process(including emitting stabilization stage and attenuation stage). Variation of transient capture efficiency for local exhaust system was studied in emitting stabilization stage. The fitting equation of pollutants concentration in exhaust system was established in the attenuation stage.Finally, the influence on the concentration variation was researched about the intensity of polluted source(including pollutants concentration and air velocity) and the localexhaust air rate.The following main conclusions were obtained in this paper:(1) The concentration in exhaust system keeps increasing first, then tends to be stable with time in emitting stabilization stage. The moment at which the curve of concentration in general ventilation system reaches stable is later than that for local exhaust ventilation system. The concentration in exhaust system attenuates with negative exponent in attenuation stage.(2) In the unsteady process, the curve of concentration in exhaust system remains almost unchanged when one of factors varies including the pollutants concentration and air velocity of polluted source, the local exhaust air rate. Analysis results show that the concentration of tracer gas should not be too large when nitrous oxide(N2O) is adopted to study capture characteristic of the exhaust hood. The larger air velocity of polluted source, more quickly the curve of concentration in emitting stabilization stage changes, the more obvious the curve varies in the early attenuation stage, and the greater pollutants concentration is at the same moment. By contrast, air velocity of polluted source has little effect on pollutants concentration variation of general ventilation system. Pollutants concentration of exhaust system decreases with the increase of exhaust air rate at some moment. The larger the exhaust air rate is, the earlier the moment is at which the curve of pollutants concentration reaches stable in emitting stabilization stage, the more smooth the curve changes in attenuation stage.(3) In emitting stabilization stage, the larger air velocity of polluted source, the greater pollutants concentration in typical space points is at some moment. And pollutants concentration in typical space points decreases with the increase of exhaust air rate at the same moment. The curve of concentration in typical space points remains unchanged first, then decreases in attenuation stage.