Improvement Of Phenols And Ammonia Recovery Process For The Treatment Of Coal Gasification Wastewater

Coal gasification wastewater(CGW)is generated from the gas washing,condensation and fractionation processes.These effluents are characterized by hard biodegradation,complex components and high concentration of pollutants,in which ammonia and phenols are considered as priority pollutants.Phenols and ammonia recovery process consisting of the sour water stripper,extraction and the solvent recovery system is applied to removing these pollutants.A suitable thermodynamic model is established on the analysis and simplification of CGW.Therefore,the operating conditions of conventional phenols and ammonia recovery process are determined by steady state simulation.And dynamic simulation is performed to investigate the transient response on the influent fluctuations in case of accidents.Two control schemes are proposed and compared.The structure which the top temperature of column is controlled by manipulating the flow rate of sour gas shows better control performance.The system is running stable and easy to operate.In order to further achieve the purpose of energy saving,an improved phenols and ammonia recovery process that the sour water stripper and the solvent recovery system are thermal integrated is proposed based on the conventional wastewater treatment process.Therein,the ammonia-rich gas drawn from the middle of sour water stripper,as a heat source,is exchanged with the reboiler of the solvent distillation column and the solvent stripper.The results show that the operating costs are about 34% less than that of the conventional process,and the total annual costs can be decreased by about 30.8% under the same design requirements of product purity.Besides,the extractant has a great influence on the performance and economy of the phenols recovery process.In this paper,mesityl oxide,as a novel extractant,is found with high phenols removal efficiency through quantum chemical calculations.To confirm that,the removal performance with three different solvents(diisopropyl ether(DIPE),methyl isobutyl ketone(MIBK)and mesityl oxide)are investigated and compared via multi-stage counter-current extraction experiments.Both theoretical and experimental results identified that the performance using mesityl oxide as solvent is better than that using DIPE and MIBK.The total phenols concentration can be reduced from more than 5000 mg/L to less than 250 mg/L.The thermodynamic databases are significant for mechanism models of units.Subsequently,experimental LLE data for mesityl oxide-phenols-water system were measured and correlated with the NRTL activity coefficient model,and the corresponding binary interaction parameters were regressed.Eventually,phenols recovery process using mesityl oxide as solvent is developed and conceptual designed.Both two improved phenols and ammonia recovery processes are proven to be effective and economical processes with good application prospects.