| Volatile organic compounds(VOCs),one of the main components of air pollutants,not only do harm to human health,but also cause a series of environmental problems,including haze.Organic waste gas emissions from industrial processes are one of the main sources of VOCs in the atmosphere.Therefore,the degradation methods for the removal of VOCs have become the hot point in the field of air pollution control in China.In recent years,photocatalytic degradation of VOCs has been extensively studied due to its simple operation and mild reaction conditions.However,the single photocatalytic method for VOCs treatment is limited in practical application because of its low degradation efficiency and inadequate degradation of VOCs.In this paper,in order to realize high efficient degradation of low concentration organic waste gases with high airflow,the effects of process conditions and parameters on the VUV photocatalytic degradation method for VOCs were investigated.Furthermore,the VOCs degradation performances of three combined photocatalytic methods were investigated.Finally,a plasma,hydrogen peroxide and photocatalysis combined process was developed and the equipment of this combined photocatalytic method was prepared.And the experimental study of industrial scale pilot equipment was progressed and completed.For the ultraviolet photocatalytic method of VOCs,the effects of light source type,reaction residence time,catalyst-loading amount,initial concentration of pollutants and relative humidity on the VOCs degradation performance were investigated in terms of the removal efficiency of VOCs,mineralization rate and ozone escape concentration in tail gas.Then,the optimum process parameters were selected:185+254 nm dual-band ultraviolet light,6 s residence time,70%relative humidity and 1.5:40 catalyst/carrier mass ratio.Under the selected process parameters,the removal efficiency of toluene was achieved 59.0%with initial concentration of 80 ppm.In order to improve the degradation performance of VUV photocatalytic method,methods such as non-thermal plasma,transition metal modified photocatalyst and ultrasonic atomized hydrogen peroxide were combined with VUV photocatalytic method,and the VOCs degradation performances of these combined VUV photocatalytic method were observed.The toluene degradation efficiency of the non-thermal plasma process was mainly controled by the input voltage of the power supply.The non-thermal plasma process realized a stable performance for ozone generation and toluene degradation at 130 V input voltage.The toluene removal efficiency of plasma combined VUV photocatalytic process reached 87.8%and the degradation performance of mixed VOCsreached 89.6%.Also the toluene removal efficiencies were investigated whilst MnOx and FeOx modified composite photocatalysts were used in this plasma combined VUV photocatalytic process.Among the tested photocatalysts,MnOx doped photocatalyst showed the best degradation performance.The removal efficiency of toluene reached 96.7%,and the concentration of ozone in tail gas decreased by 87.6%.with the introduction of ultrasonic atomized hydrogen peroxide,the generation of hydroxyl radical was reinforced.The removal efficiency and mineralization rate of mixed organic waste gas reached 94.4%and 69.3%respectively.Based on the above research,a combined process of non-thermal plasma,gas-phase hydrogen peroxide oxidation and VUV phocatalytic oxidation was developed,and an industrial scale pilot plant with a maximum gasflow of 1000 m3/h was designed and built.The comprehensive degradation performance of the pilot plant was systematically investigated under simulated conditions.The input voltage and pulse discharge frequency of power supply will affect the degradation performance of VOCs by plasma module.The highest removal rate of toluene by non-thermal plasma was 42.3%.The removal efficiency of toluene reached 77.4%at 1000 m3/h airflow in plasma combined VUV photocatalytic process.The use of 1%Mn-doped composite catalyst could consume 72.7%of the ozone in the exhaust gas,and the toluene removal efficiency could be increased to 89.6%at 1000m3/h airflow.With the introduction of ultrasonic atomized hydrogen peroxide,the removal efficiency of the simulated mixed organic waste gas containing four characteristic pollutants reached 97.0%. |
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