页岩气压裂返排液电渗析脱盐处理技术研究

Research on electrodialysis desalination technology for shale gas fracturing flowback fluid

页岩气压裂返排液具有高盐、高COD的污染特征,其TDS约为3.2×10^(4)~4.0×10^(4) mg/L。采用GC-MS对压裂返排液进行分析,结果表明,其有机污染物包括烷烃、环烷烃、醇类、卤代烃,以及少量酮类、酚类、酯类等。烷烃是页岩气压裂压返液的主要污染成分。采用电渗析技术对页岩气压裂返排液进行处理,研究操作电压、极水质量分数等因素对脱盐率、电导率及COD去除率的影响。实验结果表明,电渗析处理过程中,随着操作电压的增加(5~20 V范围内),压裂返排液的脱盐率和COD去除率随之升高;电压为20 V时,TDS和COD的去除率分别达到99.94%、79.99%。在不同操作电压下,前40 min脱盐速率较快,60 min后脱盐速率降低,随后趋于平缓。极水质量分数为0.5%~0.75%时,压裂返排液的脱盐率、COD去除率随极水质量分数的增加而提高。此后进一步提高极水质量分数,TDS和COD的去除率均有所降低。电渗析过程中离子价态对各离子的去除率有一定影响。阴离子SO_(4)^(2-)、Cl^(-)的去除率分别为99.3%、96.6%;不同阳离子之间的去除率相差不大,Ca^(2+)、Mg^(2+)、Na+和K+的去除率分别达到99.8%、99.7%、96.9%、99.3%。

The shale gas fracturing flowback fluid has the characteristics of high salt and high COD,and its TDS is about 3.2×10^(4)-4.0×10^(4) mg/L.GC-MS was used to analyze the fracturing flowback fluid,and the results showed that its organic pollutants included alkanes,cycloalkanes,alcohols,halogenated hydrocarbons,and a small number of ketones,phenols,and esters.Alkanes were the main components of shale gas fracturing flowback fluids.Electrodialysis technology was used to treat shale gas fracturing flowback fluid,and the effects of operating voltage,mass fraction of electrode water and other factors on desalination rate,conductivity and COD removal rate were investigated.The experimental results showed that desalination rate and COD removal rate of the fracturing flowback fluid increased with the increase of operating voltage(in the range of 5-20 V)during the electrodialysis treatment.The removal rates of TDS and COD reached 99.94%and 79.99%,respectively,when the voltage was 20 V.Under different operating voltages,the desalination rate was faster in the first 40 minutes,and then decreased after 60 minutes and leveled off.The desalination rate and COD removal rate of the fracturing flowback fluid increased with the increase of electrode water mass fraction when the electrode water mass fraction was 0.5%-0.75%.The removal rate of TDS and COD decreased when the mass fraction of electrode water was further increased.In electrodialysis process,ion valence had an effect on the removal rate of ion.The removal rates of anions SO_(4)^(2-) and Cl^(-)were 99.3%and 96.6%,respectively.The differences in the removal rates of different cations were not significant,with Ca^(2+),Mg^(2+),Na+and K+reaching 99.8%,99.7%,96.9%and 99.3%,respectively.