Application Research On Electrolysis-Electrocoagulation Coupled Hardness Removal System In Circulating Cooling Water

The circulating cooling water system usually employs water as the cooling medium and is widely used in industrial production industries,such as steel,petroleum,metallurgy,and power generation.During the process of water circulation,the continuous evaporation of water in the system leads to the continuous increase of salt content in the system,which easily causes scaling on the surface of the heat exchanger,shortens the service life of the equipment,and endangers the safe and stable operation of the system.The chemical agent method causes secondary pollution,while the traditional electrochemical hardness removal technology is limited by the surface area of the cathode,resulting in low hard removal efficiency and high overall energy consumption.Therefore,it is particularly important for the stable operation of the system to develop a green and efficient new electrochemical hardness removal technology system for circulating cooling water.In this study,a non-diaphragm electrolysis-electrocoagulation coupling process was developed for the softening of circulating cooling water.The non-diaphragm electrolytic cell uses a titanium filter element coated with a catalyst as the anode,which is characterized in that the H⁺produced by electrolysis can be extracted from the anode diffusion layer,and the acid-base separation is realized in the single-chamber electrolytic system without a diaphragm.10 m M Na₂SO₄ synthetic solution was used as the simulated solution for the investigation of the acid-base separation performance of the electrolytic cell.Under the electrolytic cell current density of 10m A cm^-2,the total flow rate of the process water was 100 m L min^-1,and the extraction flow rate of the acid solution was 15m L min^-1,it can achieve p H of 11.73 in alkaline solution and 77.35%current efficiency,and 1.91 in acid solution and 31.23%in current efficiency.The alkaline solution separated by the non-diaphragm electrolysis cell flows into the electrocoagulation cell,so the scale crystallization and sedimentation process occurs on the extensive floc surface in the electrocoagulation cell instead of being limited to the cathode surface,which provides a basis for the long-term stable operation of electrochemical water softening technology.The demineralized water,after flocculation and precipitation,was mixed with acid solution from the anode boundary layer to further reduce residual alkalinity and minimize scaling risks.Under the conditions of an electrolytic cell current density of 10 m A cm^-2,total water flow rate of 100 m L min^-1,acid solution extraction flow rate of 15 m L min^-1,and iron-based electrocoagulation current density of 6 m A cm^-2,the effluent water achieved a reduction in total hardness from 500 mg L^-1Ca CO₃ in the raw water to 190mg L^-1 Ca CO₃,with a hardness precipitation rate of 84.62 g h^-1 m^-2 and an energy consumption of only 3.59 k Wh kg^-1 Ca CO₃.Analysis of the precipitate using SEM and XRD confirmed the presence of aragonite as the main crystal form of calcium carbonate,along with a small amount of calcite.In addition,the study found that the presence of scale inhibition can significantly inhibit the removal efficiency of hardness ion crystals in electrolytic alkaline effluent,and the inhibitory effect is enhanced with the increase of the concentration of scale inhibition.The coupling electrocoagulation process showed better hardness removal efficiency,mainly because the flocs produced by electrocoagulation removed organic phosphonic acid scale inhibitors in water through adsorption,effectively eliminating the scale inhibition effect of scale inhibitors.Under the same current density,the inhibition effect of electrocoagulation using iron-based materials to eliminate scale inhibitors is much higher than that of electrocoagulation using aluminum-based materials.In the process of iron-based electrocoagulation,when the current density is 14 m A cm^-2,the residual hardness in water decreases by 220 mg L^-1,the scale inhibition rate is only 13.84%,and the concentration of total phosphorus in water is reduced from the initial 3.13 mg L^-1 to0.43 mg L^-1.XRD and SEM analysis of the iron-based electrocoagulation deposits confirmed the presence of aragonite as the crystal form of calcium carbonate,possibly resulting from the combined effect of scale inhibitors and iron ions.The mapping diagram shows that there is P element in the sediment,and the existence of P element proves that the organic phosphine scale inhibitor in water can be removed by floc adsorption generated by electrocoagulation.In conclusion,a coupled electrolysis-electrocoagulation process was developed to achieve efficient softening of circulating cooling water.The electrolytic cell without a diaphragm realizes the acid-base separation in the single-chamber electrolytic system.The coupled electrocoagulation process provides broad crystal precipitation sites for the removal of hardness ions,which not only removes the organic phosphine scale inhibitors by adsorption,but also eliminates the inhibitory effect of scale inhibitors on traditional electrochemical softening.It provides novel insights and technical guidance for the treatment of circulating cooling water.