Study On Removal Of So₂from Claus Tail Gas By Adsorption And Elution Method

Oil is one of the world’s major primary energy, when manufacturinggasoline and diesel by hydrogenation, it produces large amounts of sulfurousgases which cause great harm to the ecological environment and human health.In order to recycle the sulfurous gases in petroleum processing, the Clausprocess comes into being and it is widely used since1960s. Nowdays Clausprocess has become one of the most important applied processes of sulfurrecovery so far. Under the effect of catalyst, Claus process fixes sulfurousgases in the form of sulfur element. However, the Claus reaction is areversible reaction; it is restricted by the chemical equilibrium. Even thoughwe adopt the four-stage Claus reaction converter, the Claus tail gases stillcontain a higher concentration of sulfurous compounds such as SO₂, CS₂andso on. The total sulfur recovery rate does not exceed97%and it is unable tomeet current national air pollutants emission standards.In order to minish the Claus tail gas’s pollution on the environment andimprove the sulfur recovery rate, varieties of tail gas treating technology aregenerally developed and applied in industry. The current mainstreamtechnology is the catalytic hydrogenation and the absorption process,including the traditional SCOT process, RAR process and the HCR process and so on. These processes take nickel, cobalt, molybdenum and palladium,rhodium, platinum family elements as hydrogenation catalyst, which turnClaus process tail gas such as S, SO₂, COS and CS₂in reduction or hydrolysisreaction into H₂S. H₂S that absorbed by MDEA solution is dumped intodesorption regeneration tower, and then H₂S is put it in the Claus furnace incirculation.The total tail gas recycle rate can exceed99%. Although thesetechnologies are mature and reliable, the investment in equipment, operatingcosts and energy consumption are huge and they have small market share.Many factories still discharge the tail gas after incineration which causesserious air pollution. To solve the Claus tail gas pollution problems, it isurgent to develop the Claus tail gas purification technology with highefficientcy and low cost.This thesis focuses on the high-water concentration in Claus tail gas,investigates the performance of various process parameters （including type ofactivated carbon, particle size, reaction temperature, water amount, fillers andso on） on the impact of activated carbon adsorption and removal of SO₂at situby washing regeneration process based on activated carbon drydesulfurization mechanism in the flue gases of stationary sources. This theisreveals the impact of reaction site and influence of different parameters onactivated carbon steady desulfurization rate, and recognizes the productdistributions in the eluent, drawing the following main conclusions:（1） Activated carbon has a low steady-state SO₂removal rate under the conditions of Claus tail gas（20-40℃,21%H₂O） which is only about10%. Themain product in the eluent of is H₂SO₄which generated in the activatedcarbon micropores can not be washed out, leading to a lower SO₂removal ratebut SO₂oxidation is not the determining factor.（2） Strengthening water and activated carbon contacting can significantlyimprove the steady-state SO₂removal rate, including condensing steam waterfeeding, improving the line speed of the water vapor, gas-liquidcountercurrent operation and so on.（3） The gas-liquid countercurrent can effectively enhance the mass transferand improve the dissolving capacity of SO₂which can increase the removalrate. When the countercurrent water increases, the steady-state SO₂removalrate is higher, and the proportion of SO₃²in the eluting product increases.Under the condition of5ml/min water flow, the effect of SO₂dissolutionexceeds the effect of SO₂oxidation, becoming the main reason fordesulfurization.（4） Filler plays a key role in water distribution. Through varieties of fillerscomparative experiments, we find that the quartz can significantly improvethe water vapor distribution and promote SO₂dissolved in water whichcontributes a high removal rate.