Off-gas processing device

Purpose: To remove volatile ruthenium in off-gases at high efficiency. Constitution: In a pre-processing tower, off-gases are at first washed by a scrubber thereby removing most of impurity ingredients such as NOx having strong affinity with scrubbing water to increase the relative ratio of volatile ruthenium relative to the impurity ingredients in the off-gases. Then, the off-gases are once cooled to condensate to about 20 deg C by a cooler and mist components are removed by a demister and, further, heated by a heater to 70 - 80 deg C to reduce the water concentration in the off-gases to less than about 4 %. Since most of noxious materials to silica gel such NOx or water content are eliminated by way of the adsorption tower after applying such a pre-treatment, adsorption can be conducted in the adsorption tower mainly for volatile ruthenium. (Seki, T.)