Experimental Study On The Removal Of NO_x/SO₂/Hg⁰ In Oxy-Fuel Combustion Flue Gas By Compression Process

Oxy-fuel combustion flue gas contains not only high level of CO₂（85%or more）,but also high concentrations of gaseous pollutants,such as SO₂,NO_x,Hg⁰ and so on.The purification of flue gas is crucial to the compression,liquefaction,transportation,utilization（such as EOR）and storage of CO₂.It has a unique advantage to remove SO₂,NO_x and Hg⁰ from flue gas by CO₂-rich flue gas compression and liquefaction process,and it is a kind of highly competitive flue gas purification technology of oxy-fuel combustion.In this paper,the experimental study on the removal of gaseous pollutants（SO₂,NO_x and Hg⁰）in the process of flue gas compression was carried out,and it has a strong theoretical significance and engineering application value,which can provide a theoretical basis for the design and development of oxy-fuel combustion flue gas purification technology with high efficiency and economic removal capacity.First of all,an experiment bench was made to study the simultaneous removal of NO_x and SO₂ under high pressure,the removal of NO_x and SO₂ at different pressures in the dry/wet N₂ atmosphere and the simulated oxy-fuel combustion flue gas were studied.Then ion chromatography detection was used to analyze the product of flue gas purification,and the possible reaction mechanism at wet condition was also proposed.Study found that the simultaneous removal of NO_x and SO₂ can be realized under the condition of wet N₂-rich atmosphere.The elevated pressure could promoted the NO_x and SO₂ partly converted into nitric acid and sulfuric acid,while the other part was converted into nitrite and sulfurous acid.The system pressure and initial NO concentration had a positive influence on the the removal rate of NO.The presence of SO₂ inhibited the removal of NO_x,whereas the presence of NO contributed to the removal of SO₂.Subsequently,the removal of Hg⁰ under high pressure was studied in this paper.The removal of Hg⁰ under different pressures and the effects of NO_x and SO₂ in flue gas on the removal of Hg⁰ were studied.It found that NO₂ is the main factor of mercury removal,and it can react with Hg⁰ in high pressure,the higher the pressure,the better the removal effect of Hg⁰.SO₂ itself can not react with Hg⁰,but it will affect the reaction of NO₂ and Hg⁰.It is shown that SO₂ is beneficial to the removal of Hg⁰ under low pressure,but the experimental rules just opposite under high pressure.Under the condition of CO₂-rich atmosphere,the removal rules of Hg⁰ was similar to that under N₂-rich atmosphere.The removal rate of Hg⁰was not significant between two different atmospheres under the middle and low pressure stage,but in the high pressure stage,the CO₂-rich atmosphere was less than that of the N₂-rich atmosphere.Finally,this paper studied the simultaneous removal of three kinds of gaseous pollutants（NO_x,SO₂,Hg⁰）from oxy-fuel combustion flue gas under high pressure,and the mercury removal data were compared with the experimental data of single mercury removal,the effect of water on the removal of Hg⁰ was also analyzed.The study results shows that the removal of three kinds of gaseous pollutants can be realized in the process of the oxy-fuel combustion flue gas compression and liquefaction,the higher the pressure,the better the removal effect of pollutants.When the pressure was increased to 2 Mpa,the removal rate of Hg⁰ was up to 90.24%,the removal rate of NO_x was as high as more than90%,and SO₂ was completely removed,thus the feasibility of simultaneous remove three kinds of gasous pollutants in the process of oxy-fuel compression flue gas compression was verified.The presence of vaporous water at high pressure was beneficial to the removal of Hg⁰.