Research On The Alkali-saving Process Of Ammonia Removal By Distilling In The Treatment Of Coking Remaining Ammonia Wastewater

The coking industry,which discharges millions of tons of wastewater each year,of which the main part is remaining ammonia wastewater,is a major industry in China which causes severe pollution.Due to the large water volume,high ammonia nitrogen concentration,and complex composition,the remaining ammonia wastewater cannot be directly subjected to biochemical treatment.At present,the coking industry generally adopts the ammonia distillation process to pretreat the remaining ammonia wastewater before biochemical treatment,but the current ammonia distillation process has the problem of high cost.This article analyzes the ammonia distillation process,and proposes alkali-saving process for the problem of large consumption of alkali,which provides reference and guidance for the cost reduction and the optimization of effluent water quality of the ammonia distillation process.Through batch ammonia distillation experiment,the characteristics of the traditional ammonia distillation process of remaining ammonia wastewater were studied.Experiments showed that with the progress of traditional distillation,the p H of the liquid phase increased first and then decreased,and the larger the amount of alkali added,the higher the initial p H and the lower the amplitude of the p H rise.This phenomenon provided theoretical basis of alkali saving for the two-stage ammonia distillation.In the ammonia distillation without alkali,a turning point showed where the rate of ammonia vaporization changed significantly,and the two-stage alkali-saving process of ammonia distillation with alkali addition at the turning point was determined through experiments.The study of the two-stage ammonia distillation process showed that the ammonia distillation process with the addition of alkali after partial separation of free ammonia and acidic substances from the liquid phase saved the amount of alkali added and improved the outlet wastewater quality,indicating the feasibility of the two-stage ammonia distillation process on the existing ammonia distillation tower.Through gas-liquid balance experimental research,theoretical calculation and Aspen Plus simulation,the internal mass transfer characteristics of the existing ammonia distillation tower were studied.Setting the board near the turning point as the alkali-adding board,the feasibility of using the alkali-saving process in the original ammonia distillation tower to achieve the same or better outlet water quality was discussed.A study on the liquid phase concentration of the tray at the bottom of the ammonia distillation tower found that the existing ammonia distillation tower using the two-stage alkali-saving process of ammonia distillation still meets the effluent requirements.Through the adaptability study of tower load changes,it was found that the ammonia distillation tower adapts to the change of ammonia nitrogen concentration in the influent.Based on the experimental results and simulation calculation,the economics of the two-stage ammonia distillation process were analyzed and discussed,indicating that the application of the alkali-saving process can bring cost savings to the coking industry.Through the study in this article,the advantages of the two-stage ammonia-saving process and its applicability in the original ammonia tower were showed,which provided a useful reference for the implementation of the two-stage ammonia-saving process.