The world’s freshwater resources are limited, the water shortage problem in coastal cities and island areas is more serious, and the supply of fresh water is increasingly tight, and the use of inexhaustible seawater as industrial water has been a general trend and imperative. Coastal nuclear power plants use seawater resources instead of fresh water as circulating system cooling water, which can not only save fresh water resources, but also protect the environment and maintain ecological balance. Seawater generally contains more suspended matter, colloids, organic matter, microorganisms (such as algae) and shells, turbidity and chroma is large, there is a circulating water system biological breeding and blocking problems, taking into account the economic, safe and stable operation of the entire system, the key is to solve the problem of seawater corrosion and biological fouling.
There are usually two methods for anti-microbial fouling treatment of circulating cooling water: the first method is to make sodium hypochlorite by electrolysis of seawater, and to treat sodium hypochlorite of circulating cooling water, which has high investment cost, but low operating cost and no pollution to the environment; The second method is to add liquid chlorine, which has low investment cost, but high operating cost, toxic and environmental pollution.
In order to reduce environmental pollution, sodium hypochlorite is prepared by electrolytic seawater for chlorination of circulating cooling water. The concentration of chloride ions in natural seawater at the site of nuclear power plant should meet the requirement of seawater electrolysis for chlorine production, and it is suitable to use seawater electrolysis for sodium hypochlorite extraction.
Working principle: Since NaCl in seawater exists in an ionic state, under the action of electric field, Cl is produced on the anode surface, HCl is produced on the cathode surface, and NaOH is produced in a secondary chemical reaction to generate NaClO in solution. The electrochemical reaction equation is as follows:
Anode 2Cl–—2e→Cl2
Cathode 2Na++2H2O+2e→H2↑+2NaOH
Because the cathode and anode of the electrolyzer have no ionic membrane, it is a film-free electrolysis, Cl2 and OH- chemically react in solution to form ClO– :
Cl2+2NaOH→NaCl+NaClO+H2O
Total reaction formula: NaCl+H2O→NaClO+H2↑ (electrolysis)
Electrolytic seawater NaClO generator makes use of natural seawater and adopts electrolysis process to produce highly active NaClO solution on site, effectively killing microorganisms, Marine organisms, algae and bacteria in the water body, and preventing clog of circulating water pipeline and condenser system.
The NaCIO system consists of electrolysis system, pickling system and cooling system.
Each set of electrolytic NaClO production unit includes sea water pump, self-cleaning filter (the size of particles allowed to pass is not more than 05mm) electrolytic cell set, transformer, rectifier.
Due to the presence of calcium and magnesium ions in seawater, these ions will form calcium and magnesium ions in the cathode precipitate, affecting the electrolysis effect and increasing energy consumption, so the electrode needs regular pickling. The pickling system provides 10% dilute hydrochloric acid solution for the pickling of the electrolytic cell group, and the dilute hydrochloric acid solution circulates between the electrolytic cell and the pickling tank through the pickling pump. After the pickling is finished, the waste acid is discharged to the outdoor wastewater neutralization pool, and the neutralization is up to the standard. The main equipment of pickling system includes acid storage tank, alkali storage tank, acid discharge pump, alkali discharge pump, pickling tank, pickling pump, acid mist absorber, carbon dioxide absorber, neutralizing pump, etc.
The rectifier provides power input to the generator, and generates a lot of heat in the process of electrolyzing seawater. In order to ensure its normal use, the rectifier needs to be cooled, and the rectifier cooling is water-cooled. The main equipment of the cooling system is the cooling water tank, the cooling water pump, the cooling water pipeline pump, and the plate heat exchanger.
After the seawater is boosted by the sea pump, it enters the self-cleaning filter, removes the large particulate matter in the seawater, and enters the electrolytic cell group. The transformer rectifier converts alternating current into low-voltage direct current and supplies it to the electrolytic cell group. The seawater flowing through the electrolytic cell group is electrolyzed by direct current to produce NaClO solution and hydrogen into the outdoor NaCIO storage tank. At the same time, a trace amount of chlorine gas is produced.
The structure of the electrolytic cell mainly has two kinds of tube electrolytic cell and plate electrolytic cell. In recent years, the domestic large-scale electrolytic seawater chlorine system mostly uses plate electrolyzer. Plate electrolytic cell has the advantages of small size, compact structure, easy installation and maintenance, simple commissioning and operation, low maintenance cost, long electrode life, but low current efficiency, low voltage resistance and electrode polarization. BLUEWAV electrolytic seawater electrolyzer is divided into three types: CTE (Concentric Tubular Electrolysis cell), PPE (Parallel Plates Electrolysis cell), MESH (Mesh Plates Electrolysis cell), in the past, CTE was commonly used, and now the most PPE type of electrolyzer is used. For the process of chlorine production by electrolytic seawater, reasonable selection of electrolytic cell and electrode materials is the key to design. Compared with the tube electrolytic cell, the plate electrolytic cell is generally better, with outstanding process characteristics, modular design, high automation level, compact equipment, easy maintenance, and more widely used. Compared with plate anode, plate mesh anode can increase the seawater turbulence, improve the current efficiency, and have a larger active area, which can increase the chlorine production of single tank.
In the process of production and storage of electrolytic seawater chlorine system, hydrogen will be discharged from the cathode, which can prevent the occurrence of danger. At present, there are two kinds of hydrogen removal methods commonly used: intermediate hydrogen removal and sodium hypochlorite storage tank hydrogen removal. Intermediate dehydrogenation means that each electrolytic cell is equipped with an intermediate dehydrogenator, and a hydrogen exhaust pipeline is designed to release hydrogen in the electrolyte timely and effectively, reduce the negative impact of the gas extraction effect, and improve the current efficiency. The second hydrogen discharge method is the hydrogen removal of sodium hypochlorite storage tank, which is designed in two ways: ① The storage tank adopts natural hydrogen discharge design, without hydrogen exhaust fan. Hydrogen gas is naturally diluted and discharged into the atmosphere through air at the top of the sodium hypochlorite storage tank, and the natural hydrogen discharge scheme is economically feasible, but certain safety protection measures must be taken in the electrolytic room and the sodium hypochlorite storage tank area to prevent explosion. ② The storage tank is equipped with a blower, and the air volume of the blower should be able to dilute the hydrogen concentration of the generating device under rated operating conditions by less than 1%. The generating device should have a spare blower. When the operating blower fails and stops, the spare blower should be able to automatically start and run. The sodium hypochlorite storage tank is located outdoors.
BLUEWAV electrolytic seawater sodium hypochlorite generator can be widely used in seawater desalination, power plants, nuclear power plants, oil industry anticorrosive and other aspects, has a number of export project trading experience, can provide you with localized technical support, modular integrated design, plug and play, easy installation, welcome to buy!
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