Softening And Micro-alkalizing Prevent Recirculating Cooling Water System From Scaling, Corrosion And Microbial Reproduction Coordinately

The recirculating cooling water system is the biggest water consumer in industrial field, in which the normal problem is scaling, corrosion and microbial reproduction as well as drainage pollution and water resource waste. Accordingly, the paper proposes recirculating cooling water softening and micro-alkalizing through removing contamination and adjusting water quality, which can prevent scaling, corrosion and microorganism pollution without any chemicals coordinately. In the same time, it succeeds to save water resource and decrease drainage.After a series of model calculation and experiment, the main achievements are listed:1. A method and a process of ion-exchange softening and micro-alkalizing has been proposedThe thermodynamic balance of the three system-Fe, Cu and Zn in carbonate slution has been calculated, and the corrosion contraling experiment of carbon steel and brass has been carried out, the result tells that:when the total alkalinity of the sodium carbonate solution is adjusted to 6-10mmol/L(pH=9.2-9.5), the A3 carbon steel and the brass is coated well by oxide film, of which the corrosion speed is controlled under the Chinese national standard in anti-corrosion of the recirculating cooling system. In the same time, the property test of RHCO3 resin has been carried out. The change merchanism and the equilibrium constant between HCO3- and CO32- in the resin have been researched, and the operation and regeneration process parameters have been optimized.Based on the test, a method of ion-exchange softening and micro-alkalizing, which was suitable to small-sized recirculating cooling water system (such as central air conditioning system), has been proposed, and the process for two different systems has been designed:for the recirculating cooling system without copper, the makeup water treating used the series connection process between RNa resin and RHCO3 resin. And for that containing copper is the parallel connection of between the two series connection, one conclude RNa resin and ROH resin, and the other conclude weak acidic resin, RH strong acerbic resin and weak anionic resin. In the same time, the economic characteric of the process has beed researched, the results tells that:it can save 35～44% operational fee than the process of adding chemicals.2. A method and a process of nanofiltration combining with anion-exchange softening and micro-alkalizing has been proposedFor the large-scale recirculating cooling system (such as the cooling recirculating cooling system in thermal power plant), the paper propose that softening and micro-alkalizing by removing all the hardness and a part of monovolant ions in water with nanofiltration and then change the anion into HCO3 with RHCO3 resin. The process experiment of series connecting between NF90 membrane and RHCO3 resin has been carried out, the results tell that:when the nanofiltraion membrane-NF90 is series connected with RHCO3 anionic resin, the process can remove much monovalent ion (about 80%), and can soften as well as alkalize the water. The product water quality will fill the makeup water quality requirement of softening and micro-alkalizing system.3. The stability of softening and micro-alkalizing system and the "three preventing effects" has been studiedThe model calculation of the CO2 mass transfer from the adjusted water to the air and the simulating test has been carried out, the result tells that:when flushed by weak acidic makeup water in running, the micro-alkalized system will recover in 1-2 hours and kept balance with the CO2 in the air. The increasing of the flow rate and the system alkality will help increasing resistance capacity and keeping water quality and quantity stable.Then, the "three preventing effects" of the adjusted water has been studied, the kinetic experiment results of coating on brass surface tell that:there will need 24 hours to create an integrated film on the brass surface. The oxide film is much dense and cover the surface to prevent the brass corrosion; the preventing microorganism effect tests results tell that:the population of the microorganism will decrease 68% after removing nitrogen and phosphorus by softening and micro-alkalizing process, and the population of aerobic heterotrophic bacteria will decrease 33% and there is no scaling after softening.The fesxibility of the recirculating cooling water softening and micro-alkalizing method is confirmed by the experimental results. Based on the two innovative points, we have appled for two invention patents. We hope that a new pratical technique will be exploited to treat with the recirculating cooling water.