Study On New Methods And Processes Of SO₂ Removal With Fe(â…¢) /Cast Iron Scraps

Traditional methods employing lime and limestone for gas desulfurization are facing many problems, including producing a large amount of calcium sulfate and huge financial burdens. The process of SO₂ absorption with Fe(III) solution is a fundamental research, in which S(IV) can be catalyzed oxidation to S(VI), and the valuable product can be obtained with the sulfuric acid. The typical process was the Chiyoda which had high consumed-energy and byproduct of calcium sulfate. In order to solve those problems, the desulfurization of Fe(III) solution need to be improved. On the other hand, there lacked of reports of related kinetic data in those processes. Based on the above consideration, in this study, the systematic research was conducted on SO₂ absorption with the Fe(III) solution. Cast iron scraps were used as packing for SO₂ enhancement absorption with Fe(III) solution, which was helpful for invariability of pH and iron sulfate could be obtained; Also, the magnetic field was used for SO₂ enhanced absorption in cast iron scraps system. At last, nano-hematite was prepared with the Fe₂(SO₄)₃-Urea homogeneous system for the further uilitization of byproducts. Then a a green desulfurization processes is formed.1. The systematic research was conducted on SO₂ absorption with different concentration Fe(III) solution (0.001-0.12M), including: pH, [Fe(III)], gas-liquid ratio and the inlet concentration of SO₂. The optimization parameters was (kLa=0.0025s-1): pH≥2.0, [Fe(III)]≥0.05M, T=40℃, the ration of liquid/gas kept at 10L/m3.The distribution of Fe(III) and S(IV) species was calculated, which can be used for explain of the influence of SO₂ absorption efficiency with different [Fe(III)]. According to the kinetic equation r=k[FeOH2+][HSO3-], the reaction of Fe(III)-S(IV) can be considered as a second order, and the SO₂ absorption was controlled by gas film and liquid film.According to the two-film model and gas-liquid transfer theory, the enhancement factor for macro-kinetics can be calculated in different experimental conditions, which can be use for reactor design and verification of kinetic equation.It can be deduced that the lower rate of reaction of Fe(III)-S(IV) and enhancement factors was obtained when pH was kept below 2.0. In order to keep higher desulfurization efficiency, higher engery consumed was need. Then the enhanced way shoud be used for desulfurization with Fe(III) solution for the economic consideration.2. The packing of cast iron scraps was used for SO₂ absorption cooperating with Fe(III) in our research. Single factor experiments including pH, electrolyte, inlet concentration of SO₂, temperature, and height of packing, and spraying solution circularly used were conducted. It can be found that, SO₂ absorption can be effectively enhanced by corrosion processes of cast iron scraps, S(IV) can be oxidation by Fe(III) in solution, and a certain valuable iron sulfate can be obtained as byproducts. The corrosion rate was restrained by deposited corrosion product. Also, [Fe(III)] and the dissolved oxygen in solution were gradually decreased and SO₂ absorption was restrained. The SO₂ absorption and corrosion processes include: as SO₂ enters the solution, a series of electrochemical reactions occur; hydrous ferrous oxides are easily oxidized to ferric hydroxides; some of them are dissolved by proton, while others are transformed to insoluble ferrous/ferric hydroxylsulfate and hydroxylsulfite. Then pH was kept constant and the Fe(III)-S(IV) happened. As the deposited rusts were cumlative, the SO₂ absorption was inhibited. 3. DC magnetic field was used for SO₂ absorption in packing reactor of cast iron scraps, the results showed: The compacted phenonmenon was decreased dramatically. The low concentration SO₂ (700ppm < Cso2in < 1350ppm) can be effectively enhanced by DC magnetic field; With the higher intensity magnetic field, the SO₂ removal efficiency was gradually enhanced and the effect was not obvious when the intensity of magnetic field was more than 20mT; more than 50℃, SO₂ absorption was controlled by physical absorption. SO₂ absorption was enhanced by corrosion processes, and the corrosion processes can be changed by magnetic field. It can be thought that two kinds of magnetic field force (MHD and FGF) exist in electrochemical corrosion processes, and they can cause a transport of all ions because of the difference in the magnetic susceptibility in the solution at the cast iron scraps surface with oriental direction, then the deposited rusts turned to be looser and corrosion rate was increased.4. At last, spherical nano-hematite was prepared by homogeneous hydrolysis of Fe₂(SO₄)₃-Urea system for the uilitization of byroducts. The influence factors for the shape and size of hematite were studies, including: reaction time, [Fe(III)], [Urea], hydrolysis temperature, the calcined temperature. In the condition of Urea/Fe=1.7,T=95℃,[Fe(III)]=0.125M, t= 8h, the pH can be controlled below 5, the deposited ration of Fe(III) is above 85%, and with the thermal treatment in the condition of 800℃, the uniform spherical hematite with the size of 50nm is obtained. The hydrolysis and thermal treatment include the subsequent way: a number of ferric sulfate complex species and its basic complexes were formed at first; then ammonium–hydronium jarosite were the main products with a small amount of ferrihydrite; By the thermal treatment at 200-800℃, the poor crystalline products were gradually transformed to spherical crystalline of nano-hematite.