Study On Removal Of Sulfur Dioxide And Nitric Oxides By Activated Semi-coke

With the economy development, the problems of environment pollution, such as atmosphere pollution, have become more and more serious. Among the gaseous emission, SO₂ and NO_x (NO accounts for 90%) could lead to not only acid rain and photochemical smog, but also "green-house" effect. It is necessary to remove SO₂ and NO_x from the flue gas to protect environment and human being. However, how to eliminate SO₂ and NO_x of flue gas is still a tough task in the world wide, though some flue gas desulfurization technology has succeeded in industrial application. In this paper, the main work is focused on the research of NO_x removal.Selective catalytic reduction of NO_x with NH₃ (SCR) technique has been put into commercial application in the NO_x disposal, but it is restrained because of the well-known reasons such as storage and leakage of NH₃, costly equipment, strict operation conditions and formation of sulfate leading to pipe jam. Therefore, in order to find effective method of removal SO₂ and NO_x from flue gas, activated semi-coke has been successfully developed in substitution of activated carbon for removal of SO₂ and NO_x in the flue gas on the basis of the previous research. Semi-coke is derived from coal pyrolysis at low temperature(600-700℃). Due to the Incomplete decomposition process, plenty of hydrogen and oxygen containing functional groups were formed on the surface of semi-coke, as well as pore and surface structure, which provides favorable conditions for it to remove SO₂ and NO_x. The main work and results are followed as:The significance of the NO_x removal technology was discussed. The development and present situation of this technology for exhaust emission control was also summarized.In this paper, a series of activated semi-coke based catalysts were prepared from raw semi-coke from lignite by means of high pressure hydrothermal, high temperature heat treatment, HNO₃ oxidation and metal oxides loading. The results showed that high pressure hydrothermal could improve surface area and pore volume of the semi-coke; high temperature heat treatment could increase alkaline functional groups; HNO₃ oxidation could increase oxygen functional groups and acid functional groups, and then converted to alkaline functional group during high temperature heat treatment; metal oxides loading could provide more active sites. All of them was beneficial to the adsorption and oxidation of NO.The study of SO₂ removal by raw semi-coke and the activated semi-cokes were carried out in a fixed bed reactor with simulated flue gas. The research results show that the SO₂ removal efficiency and capacity for raw semi-coke were very low, but they were improved greatly by activated modification and metal oxides loading. When SO₂ conversion rate was 40%, the breakthrough time and capacity were 45min and 0.75gSO₂·(100gC)^-1 for raw semi-coke, 595min and 7.15gSO₂·(100gC)^-1 for V₃ and 786min and 8.41gSO₂·(100gC)^-1 for Fe₃.The influence of process conditions on NO removal for raw semi-coke and the activated semi-cokes were carried out in a fixed bed reactor with simulated flue gas. The research results show that high pressure hydrothermal, high temperature heat treatment and HNO₃ oxidation could improve the denitration efficiency remarkably, and among them, HNO₃ oxidation plus with high temperature heat treatment were the most effective modification methods, and the breakthrough time reached 680min.Then metal oxides loading (Fe₂O₃, MnO₂, V₂O₅, CuO) were studied. The research results show that all the metal oxides species had some good effects. Among them, FH₇₀₀CU₁ was better than the others with breakthrough time about 725min.FH₇₀₀CU₁ was choosed as catalyst to study the denitration efficiency. The research results show that the removal efficiency of NO increased as the increase of oxygen content, the decrease of steam content and inlet concentration. The optimum process conditions were: reaction temperature: 80℃; oxygen content: 5%; space velocity: 800h^-1 and no steam.Simultaneous removal of SO₂ and NO was studied and the inlet concentration ratio of SO₂ to NO was 0, 1, 3 and 5. The research results show that the removal efficiency of SO₂ remained 100%, while the removal efficiency of NO decreased significantly as the inlet concentration of SO₂ increased. It suggested that the existence of NO could promot the removal of SO₂, but the existence of SO₂ inhibited the removal of NO.This paper employed thermal desorption, water-washing regeneration and hydrous ammonia treatment regeneration to regenerate the deactivated catalyst. The research results show that the regenerated catalysts had lower removal efficiency of NO.With regeneration times increased, the removal efficiency of NO gradually decreased. Among those methods, water-washing regeneration was better than the other two, the removal efficiency of NO recovered to 45.9% after 3 regeneration times. It showed that the stability of catalyst was poor and more effective preparation and regeneration methods were needed.By use of surface area (BET),temperature programmed desorption (TPD) and scanning electron microscope(SEM) analysis technique, catalyst was evaluated and selected successfully.