【作者】 夏敏；

【导师】 叶春松；

【作者基本信息】 武汉大学 ， 能源动力水质工程， 2018， 博士

【摘要】 燃煤电厂脱硫废水,具有成分复杂、水质水量不稳定等特点,是一种典型的高含盐废水。双极膜电渗析是一种新型的膜分离技术,可将盐溶液转化为相应的酸和碱,在废水处理与资源化领域具有广阔的应用前景。本文以预处理后脱硫废水为研究对象,探究了双极膜电渗析实现高盐废水资源化零排放的可行性,提出了进料-出料模式下产品酸和产品碱浓度的变化规律,揭示了产品碱浓度下降的机理,掌握了酸室中酸在阴离子交换膜中的迁移规律,提出了抑制产品碱浓度下降的解决方案,最后优化了酸浓度和碱能耗。研究的主要内容和主要结论归结如下:(1)建立了进料-出料运行模式下酸碱浓度变化趋势的数学模型。模型模拟结果表明,酸碱浓度均可达到平衡值,最终平衡浓度与电流密度和进出流速有关,电流密度越大或进出流速越小则酸碱平衡浓度越大,反之亦然。酸碱初始浓度和初始体积只影响平衡时间,与最终平衡浓度无关。通过Na2SO4和NaCl盐溶液验证试验表明,各过程参数对酸浓度的影响与模型模拟结果一致,但碱浓度在运行过程中增至最大值后呈下降趋势。通过研究盐室电导率、pH、钠氢浓度比和碱电流效率的变化可知,酸室酸泄漏是造成碱室碱浓度下降的主要原因。提高盐室钠氢浓度比,可消除酸泄漏对碱室碱浓度的影响。在NaCl和Na2SO4溶液中,将盐室钠氢浓度比分别提高至6和14以上,可使碱室碱浓度维持稳定。(2)通过测定HC1和H2SO4在阴离子交换膜中的浓度和扩散系数,结合Nemst-Planck方程和电中性原则,建立了酸在阴离子交换膜中迁移的数学模型。吸附试验结果表明,HC1和H2SO4在膜相中的浓度远大于Donnan模型计算值。热力学Gibbs自由能分别为-1.10 kJ.mol-1和-0.49 kJ.mol-1,表明酸在膜相中的吸附为自发进行过程,两者之间存在较强的亲和力。阴离子交换膜中凝胶相所占的比例远大于间隙相,其值高达96.6%,膜相中的酸基本集中在凝胶相中。扩散系数测定结果表明,Cl-和SO42-在膜相中的扩散系数均小于H+,两者之间的比值分别为0.22和0.46。数学模型计算结果表明,模型计算值与实际值具有较好的一致性,随着酸浓度的增加,模型计算值与实际值之间的差距将逐渐减小。(3)提出了两种控制盐室钠氢浓度比的措施,即调节盐室pH(调pH体系)和改变膜堆构型(四隔室体系),消除酸室酸泄漏对碱室碱浓度的影响。试验结果表明,在调pH体系中,控制盐室pH为2时,可使碱室碱浓度维持稳定。在四隔室体系中,控制盐2室初始盐浓度为1倍脱硫废水浓度即可满足要求。通过对比两体系酸碱电流效率和能耗可知,当维持碱浓度稳定时,两体系中酸碱生产的表观电流效率基本一致。四隔室体系中酸碱生产的表观能耗均大于调pH体系,但就碱生产的绝对能耗而言,四隔室体系更具优势,所需要的能耗约为调pH体系的88%。与此同时,采用四隔室体系可有效地缩短双极膜电渗析装置运行周期,提高生产效率。(4)通过响应曲面法中的Box-Behnken设计,选取初始盐浓度、电流密度、进出流速为主要过程参数,建立二次多项式模型优化双极膜电渗析过程中酸浓度和碱能耗。试验结果表明,当初始盐浓度为3倍脱硫废水浓度、电流密度为40.3 mA·cm-2、进出流速为10.8mL·min-1时,模型预测酸浓度为1.0mol·L-1,碱能耗为2.22kWh·kg-1NaOH。试验验证可得,酸浓度为0.99mol L-1,碱能耗为2.24 kWh·kg-1NaOH,实际值与理论预测值接近,说明该模型具有很高的准确度。经济性核算结果表明,双极膜电渗析过程总能耗成本和总固定成本分别为0.236$·kg-1NaOH和0.866 $ kg-1 NaOH。对运行后的离子膜进行SEM和FTIR分析可知,在酸碱生产过程中离子膜表面均未发现固体沉积和有机物吸附污染,表明双极膜电渗析技术适用于脱硫废水的资源化处理。更多还原

【Abstract】 Desulfurization wastewater from thermal power plant was the high salinity wastewater,which had the characteristic of complicated composition and instability of water quantity and quality.Bipolar membrane electrodialysis(BMED)had been considered as one of the most effective next-generation membrane separation technologies.It could be used to generate the acid and base by means of the corresponding saline ions.Therefore,BMED hold a great promise in the practical application of environmental protection and resource reclamation.In this paper,we primarily investigated the feasibility of BMED for treating the pretreated desulfurization wastewater.Evolution of acid and base concentration under feeding-bleeding(FB)mode,mechanism of base concentration reduction,acids transfer through anion exchange membrane(AEM),stabilization of base concentration and optimization of acid concentration and base energy consumption were emphasically proposed and discussed.The primary research contents and conclusions were summarized as follows:(1)Variation trend of acid and base concentration under the FB mode was simulated by establishing a mathematical model.Simulation results indicated that acid and base concentration could ultimately reach the stable state with its concentrations positively and negatively related to current density and feeding-bleeding rate,respectively.Besides,either initial volume or initial concentration could not influence the final equilibrium value except for equilibrium time.In order to investigate the reliability of this model,Na2SO4 and NaCl solutions were selected for real verification in BMED operation.Experimental results showed that acid concentration change was highly consistent with the simulation results.However,the evolution of base concentration increased first and then declined after reaching the maximum.Through the investigation of conductivity,pH,Na/H concentration ratio and base current efficiency,it could demonstrate the acid leakage from acid compartment was the main reason resulting in the decrease of base concentration.Therefore,controlling the suitable Na/H concentration ratio could efficiently eliminate the effect of acid leakage from acid compartment on base concentration.In the case of NaCl and Na2SO4 solutions,the critical Na/H concentration ratio for holding the base concentration stabilization was 14 and 6,respectively.(2)A mathematical model was established to describe the acid leakage process on AEM through determination of HCl and H2SO4 concentration and diffusion coefficient on AEM and combining Nernst-Planck equation and electric neutrality principle.The adsorption results suggested the acid adsorption on AEM were much higher than that calculated from Donnan mode,the Gibbs free energy of-1.10 kJ·mol-1 for HCl and-0.49 kJ·mol-1 for H2SO4 indicated acids adsorption on the AEM were spontaneous process and both the acids and AEM showed high affinity.It could be found the volume proportion of gel phase was far outweigh interstitial phase,which accounted for 96.6%of AEM,implying the acid in AEM was mostly concentrated in the gel phase.According to analysis of the diffusion coefficient,it could be found the diffusion coefficients of both Cl-and SO42-were lower than H+and the ratio of Cl-(SO42-)and H+ were 0.22(0.46).Through the mathematical model calculation,the results indicated the model value was in a good agreement with experimental value,and with the increase of acid concentration the differences of which would decrease gradually.(3)Two systems for elimination of acid leakage on the influence of base concentration were proposed through controlling the Na/H concentration ratio,i.e.pH adjustment in the three compartment configuration(System 1)and addition of extra AEM forming four compartment configuration(System 2).For System 1,the experimental results showed when the pH in the salt compartment was around to 2.0,the base concentration could keep stability.With regard to System 2,the objective could be easily achieved with the salt 2 concentration set to the initial value without any concentration.Compared to apparent current efficiency(CEapp)from both Systems,it could be found there were no obvious differences in CEapp for acid and base production.Nevertheless,as for energy consumption(EC),the apparent energy consumption(ECapp)for acid and base production from System 2 was always higher than from that of System 1.Whereas,System 2 presented a certain superiority for absolute energy consumption(ECabs)of base production,the required ECabs value was about 88%of the System 1.On the other hand,in comparison to System 1,System 2 could further shorten the operation time,increasing production efficiency.(4)The response surface methodology(RSM)using Box-Behnken design was employed to establish the quadratic polynomial model to optimize acid concentration(AC)and base EC.According to analysis applying Design Expert software,the optimized operating parameters were obtained which values were initial salt concentration ×3,current density 40.3 mA·cm-2 and feeding-bleeding rate 10.8 ML·min-1.Verification test under this condition showed experimental value of 0.99 mol·L-1 for AC and 2.24 kWh·kg-1 NaOH for base EC had nearly no significant difference with the predicted value of 1.0 mol·L-1 for AC and 2.22 kWh kg-1 NaOH for base EC,proving the quadratic polynomial model possessed high accuracy for prediction of AC and base EC.By evaluating the economic of BMED process,it was concluded the total energy cost and total fixed cost were 0.236 $ kg-1 NaOH and 0.866 $·kg-1 NaOH,respectively.With the characterization of ion membranes by means of SEM and FTIR techniques,it could be confirmed there was no membrane fouling discovered throughout the BMED running.更多还原