Experimental Study On The Effects Of Ca-based Absorbent's Physical Properties On Removal Of NO₂ And SO₂

Simultaneous removal technology of NOx/SO₂ by Ca-based absorbent at low temperature, which comes from the semi-dry desulphurization process, is paid some attention by scientists because of its low water consumption, cheap absorbent, simple scrubbing system and easy disposal of by-products, etc. However, now it is still in the fundamental research stage due to its low NOx removal efficiency and low calcium utilization. The thesis studies the effect of preparation conditions for hydrothermal reaction of Ca(OH)₂ with fly ash on the physical properties of Ca-based absorbent, and investigates the NO₂/SO₂ removal efficiency by the newly hydrated Ca-based absorbent in a fixed-bed reactor and its reaction mechanism.In the process of hydro-preparation, hydration temperature,hydration time,ratio of fly ash to Ca(OH)₂,ratio of solid to liquid and dry temperature will have strong influence on the specific surface area(Sg) and porosity structure of the Ca-based absorbent. The experimental results show the high specific area and good porosity structure of the absorbent can be achieved under the condition of higher hydration temperature,longer hydration time,appropriate ratio of fly ash to Ca(OH)2, ratio of solid to liquid and lower dry temperature. It is found in the simultaneous removal experiments of NO₂/SO₂ that the Ca-based absorbent with higher specific area Sg and rich porosity structure will have the better capture activity in general.Furthermore, it is observed in the research that the specific area Sg and the pH value over the absorbent are two crucial factors affecting the NOx removal efficiency, especially having a close dependance to release of NO in the initial period of denitrification process. The larger Sg and higher pH value can enhance the simultaneous removal of NO₂/SO₂ and reduce the release of NO in the initial denitration period. However, the method to increase the pH value of Ca-based absorbent by addition of NaOH in the solution reduces the removal efficiency of SO₂/NO₂ in total and especially of NO₂ due to the decrease of specific area and change of porosity structure. On the contrary, the addtion of solid NaOH into the Ca-based absorbent hydrated by fly ash and Ca(OH)2 can enhance the removal effect of SO₂/NO₂.Reaction temperature plays an important role in the exclusive removal of NO₂. Under the constant relative humidity the denitrification efficiency will decrease at first and then increase with reaction temperature rise.