Research On The Application Of Rotating Packed Bed To Decarbonization And Alkalinity Reduction Of Coal Chemical Wastewater

A large amount of coal chemical wastewater will be produced in the industrial production process.The wastewater generally contains a large amount of carbon-containing components such as CO32-,HCO3-and dissolved CO2,so it cannot be directly discharged or applied to the subsequent chemical production process due to the high carbon content and total alkalinity.It is thus necessary to find suitable and efficient treatment methods.At present,there are many mature treatment methods in coal chemical wastewater treatment processes,and the gas-stripping method has good effect for decarbonization and alkalinity reduction.The gas-stripping method generally uses air and other gases to treat carbon-containing wastewater.Because the partial pressure of CO2 in the air is less than the partial pressure of CO2 in the gas phase in equilibrium with the solubility of CO2 in water,according to Henry's law,the dissolved CO2 in the water will continue to escape,so as to achieve the purpose of reducing the carbon content.The gas-stripping method is simple in principle and easy to operate,but generally requires a longer processing time.High-gravity technology is an efficient chemical treatment technology that is mainly carried on a Rotation Packed Bed(RPB).In recent years,it has mature applications in wastewater and waste gas treatment as it can greatly strengthen the reaction process and improve treatment efficiency.Therefore,this research uses RPB combined with gas-stripping method to strengthen the alkalinity reduction process and improve the treatment effect.This study is targeting the simulated wastewater and three actual coal chemical wastewater.The effects of experimental conditions on decarbonation and alkalinity reduction were discussed,and the gas-stripping model was established.The specific research results are as follows:(1)The simulated wastewater was prepared with anhydrous sodium carbonate and treated by gas-stripping in an RPB.It is found that the RPB can effectively improve the gas-stripping efficiency,but after the speed reaches a certain level,the effect is no longer significantly improved.As the gas-liquid ratio and temperature increase,the treatment effect is on the rise,and as the pH increases,the experimental effect continues to decrease.In the gas-stripping process,the effect of using nitrogen is better than that of using air,but the cost will increase accordingly.In the cyclic treatment,the decarbonization effect will increase with the increase of the treatment time.Therefore,comprehensive consideration of treatment effect and cost factors,the rotation speed of 400-600 rpm,gas-liquid ratio of about 5:1,pH of 5.00-5.50,room temperature can be selected as the process conditions to achieve the processing target.(2)Three types of wastewater produced in the actual coal chemical production process were treated in the RPB stripping process.As for the influence each condition on the decarbonization and alkalinity reduction of the wastewater,the research results obtained by using the actual wastewater are basically consistent with those of the simulated wastewater.It is found that with the increase of the RPB speed,the gas-stripping effect increased first,then stabilized and no longer changed significantly.With the continuous increase of temperature and gas-liquid ratio,the decarbonization percentage also continues to increase.A lower pH is favorable for decarbonation.Under suitable conditions,the total alkalinity of concentrated brine and mine water can be reduced from about 200 mg/L to less than 80 mg/L,and the alkalinity reduction percentage of concentrated water after secondary concentration can reach more than 70%.(3)According to the reasonable hypothesis,the gas-stripping model was established,and the expressions of gas-stripping efficiency and total mass transfer coefficient were deduced.Then the effect of different factors on the total mass transfer coefficient was calculated.From the point of mass transfer,it is proved that the gas-stripping effect is positively correlated with the rotational speed of RPB,gas-liquid ratio and temperature.