Coal Chemical Industry Wastewater Regeneration Treatment And The Water Network Integrated Optimization

With the rapid development of economy,the consumption of water during industrial production increases significantly in recent years.As a water-intensive industry,coal chemical industry has attracted great attention.It is imperative to improve the water recycle use ratio in coal chemical industry,owing to the shortage of freshwater and increase in cost,as well as strict discharge standard and environment friendly requirements.In this paper,the water system of a typical coal chemical industry factory was analyzed,and a noval three-phase internal-circulating heterogeneous Fenton system was established to guarantee the application of water network integration.Water pinch point and mathematical programming methods were employed for water network design and optimization.Moreover,response surface methodology（RSM）was used for sensitivity analysis of effective process changes in water network.The water system of a typical coal chemical industry factory was analyzed.Based on the data analysis,the water balance was investigated.The units those with high potential for water saving were selected.Circulating water station,desalted water station,and gasification workshop were denoted as sinks.Circulating water station,desalted water station,gasification workshop and rectifying workshop were denoted as water sources.Water quality tests conjoined with correlation and principal component analysis suggested that chemical oxygen demand（COD）,NH₄⁺-N,and calcium hardness were the key components of water system optimization.To ensure the feasibility of water system optimization,copper and iron modified Ti O₂-Al₂O₃（Cu-Fe/Ti O₂-Al₂O₃）based heterogeneous Fenton system was established.SEM,XPS and BET analysis results show that the catalysts are mesoporous materials with larger specific surface area and total pore volume.The metallic oxides are distributed equably on the surface.And the main components of the synthesized catalyst are Fe OOH,Fe₂O₃,Cu O,and Cu₂O.The developed heterogeneous Fenton process exhibited high efficiency,stable and flexibility for quinoline and secondary effluent of coal chemical wastewater treatment.The presence of Cu-Fe/Ti O₂-Al₂O₃ catalyst expanded the Fenton reaction p H,and heterogeneous catalytic hydrogen peroxide decomposition to form hydroxyl radicals was the main mechanism.Using heterogeneous Fenton as advanced treatment technology could be convenient for water system transformation and reducing the investment cost without changing the original water treatment system.Water pinch point method was used to preliminary optimize the water network.COD,NH₄⁺-N,and calcium hardness were selected as the target pollutants,and water pinch point of directly reuse system was calculated by the concentration interval calculation table.The obtained minimum fresh water flow was 174.9,171.5,and 186.5 t/h,respectively,corresponding to save fresh water46.65%,47.71%,and 43.14%,respectively.Under the guidance of the nearest neighbor algorithm（NNA）,the water network was designed based on the conservation of flow and mass.Mathematical programming method was employed to deep optimize the water network.The single pollutant direct reuse system model was calculated via the superstructure mathematical model.The water network structure was compared,and the was further optimized.The reuse rate of wastewater could be further increased by adding the regeneration unit after the direct reuse reaches the reuse limit.In single pollutant regeneration recycling system,according to the reclaimed water quality could be guaranteed by the wastewater regeneration technology,the objective pollutants concentrations in the effluent of regeneration unit were determined,and the water network was optimized.Results suggested that addition of regeneration unit greatly reduced the fresh water demand.When the COD,NH₄⁺-N,and calcium hardness were selected as the target pollutants,the minimum fresh water flow were 90.8,15.0,and 30.4 t/h,respectively.The regeneration water flows were 205.2,313.0,and 267.6 t/h,respectively.Central composite design（CCD）based on RSM was applied to for sensitivity analysis of effective process changes in water network.Fresh water and regeneration water were selected as response values.Limited inlet COD concentration of cooling plant,desalted water station and gasification units,and effluent COD concentration of regeneration unit were taken as dependent variables.Results suggest that quadratic model could best relate the dependant and independent variables,and the related quadratic fitting equations were obtained.Based on the response surface analysis of each dependent variables effects on the response value,unreliable results could be ruled out in the optimization process,and the reliability of the model could be ensured.Meanwhile,the heterogeneous photo-Fenton system was employed as regeneration water treatment unit to ensure the stability recycled water quality.The influence of regeneration water quality on water network changes was examined,and the implementation of water-saving technology was evaluated from the perspective of water network design.Water network optimization that investigated in this paper can promote the availability of wastewater,and reduce fresh water consumption and wastewater discharge.Meanwhile,an efficient and stable wastewater regeneration technology was also developed.Water network optimization conjoined with regeneration water treatment technology can guarantee the feasibility of water system optimization.Therefore,the results of this work can be used to solve the bottleneck problem of the coal chemical wastewater recycle use,and has the theoretical significance as well as the bright application prospect.