Since some thermal equipment in a power plant may be exposed to some substances in the water to produce harmful components and cause corrosion of the equipment, the safe operation of the power plant has a direct relationship with the chemical water treatment system. The destruction of equipment by impurities in the water determines that the water in the power plant must be treated before it can be used. This treatment is the chemical water treatment system in the power plant.
1 Status of development of chemical water treatment technology in power plants
1.1 The three main methods used by power plants to obtain pure demineralized water:
(1) The traditional clarification, filtration + ion exchange method is adopted, and the process is as follows:
Raw water → flocculation clarification tank → multi-media filter → activated carbon filter → cation exchange bed → carbon dioxide removal fan → intermediate water tank → anion exchange bed → anion exchange bed → resin trap → unit water.
(2) The reverse osmosis + mixed bed water production method is adopted, and the process is as follows:
Raw water→flocculation clarification tank→multi-media filter→activated carbon filter→precision filter→security filter→high pressure pump→reverse osmosis device→intermediate water tank→mixed bed device→resin trap→demineralized water tank.
(3) Using pretreatment, reverse osmosis + EDI water production, the process is as follows:
Raw water → flocculation clarification tank → multi-media filter → activated carbon filter → ultrafiltration device → reverse osmosis device → reverse osmosis water tank → EDI device → microporous filter → demineralized water tank.
The above three water treatment methods are the main processes for obtaining pure demineralized water in power plants. Other water purification processes are mostly water production processes based on the above three water production methods.
1.2 Advantages and disadvantages of three water production methods:
(1) The advantages of using clarification, filtration and ion exchange are less initial investment, and the equipment occupies less place. The disadvantage is that the ion exchanger fails to require acid and alkali to regenerate to restore its exchange capacity, which requires a large amount of acid and alkali. . The waste liquid generated by the regeneration needs to be neutralized and discharged, and the later cost is high, which is easy to cause damage to the environment.
(2) The second type uses reverse osmosis + mixed bed. This water production process is a relatively economical method for chemically obtaining ultra-pure demineralized water. It only needs to regenerate the mixed bed, and the water quality after reverse osmosis semi-desalting treatment is better. Well, it alleviates the frequency of failure of the mixed bed. The amount of acid and alkali required for regeneration is reduced, and the damage to the environment is relatively small. The shortcoming is that the cost of reverse osmosis membrane is relatively high at the initial stage of investment, but the total comparison is relatively cost-effective. Most power plants are currently considering accepting this water production process.
(3) The third method of water production using pretreatment, reverse osmosis + EDI is also called full membrane water production. This method of water production can produce pure demineralized water without regeneration with acid or alkali, and will not cause damage to the environment. It is currently the chemical water production process of the power plant zui economy and zui environmental protection, but its shortcoming is that the initial investment of the equipment is too expensive compared to the previous two water production methods.
2 Power plant chemical water treatment measures
2.1 Treatment measures for make-up water
The power plant is responsible for production safety and efficiency in the supply of boiler feed water. At present, with the rapid development of science and technology, the concept of environmental protection and energy conservation in power plants is deeply rooted in people. In the past, traditional technologies such as ion exchange, clarification filtration or coagulation have been gradually abandoned. Nowadays, new fiber materials are widely used in filtration equipment. It not only removes colloids, microorganisms, and suspensions of some particles, but also has strong adsorption and interception ability in filtration, and has achieved quite good results. Membrane separation technology is adopted, and the current anti-seepage is dominant. Reverse osmosis technology can remove more than 90% of ions in water, such as organic matter in water and silicon with good removal rate. Due to the obvious advantages of membrane separation technology, a large amount of wastewater discharge due to the backward technology such as ion exchange or clarification filtration is saved in the treatment of boiler make-up water, and many problems in the past complicated operation and emission difficulties are also Improved. The new membrane separation technology not only meets environmental requirements. When the chlorine content in the water is relatively high, it can be treated with activated carbon or treated with a water reducing agent. The mixed bed still plays an important role in the desalination treatment. The mixed bed desalination technology is relatively mature and reliable, and the function of the mixed bed has other functions that cannot be replaced by salt removal. At present, the ultrafiltration, reverse osmosis device and electrodialysis desalination technology are effectively combined to form an efficient desalination process, which does not require acid or alkali regenerants, and can only be regenerated by H+ and OH- ionization of water. Thereby completing the regeneration and desalting of electrodialysis. This water production process will be the development direction of chemical water production in power plants.
2.2 Water treatment measures
The water treatment of power plant boilers is also a key factor to improve production efficiency. At present, in the treatment of boiler feed water, China adopts the methods of oxygen scavengers and deaerators, mainly using the volatility of ammonia and hydrazine. Neutral and combined treatments can be used when the water quality is stable. The use of hydrazine technology has certain advantages, but it also has certain limitations. For example, when the temperature of water is too low, the rate of oxygen removal is very slow, and if the temperature of decomposition is too high, it is very toxic. If you accidentally contaminate the worker's body, it will cause damage to the health of the workers in the gas-fired power plant. Therefore, some domestic power plants have begun to use the method of adding water to the boiler to treat the boiler feed water. The method is to create a redox atmosphere and achieve good results. Under low temperature conditions, a protective film can also be formed to prevent corrosion. . This method avoids the use of toxic drugs hydrazine, and the pH of the feed water is only controlled between 8.7 and 8.9, which saves the amount of ammonia used, prolongs the pickling cycle of the boiler, and effectively reduces the operating cost of the unit. The use of this method of operation requires the use of high purity feed water.
2.3 Treatment measures for boiler water
The boiler furnace water treatment technology has long used the in-furnace phosphate treatment technology. The lower boiler parameters are the main reason why the technology can be widely used for a long time. There are often a large amount of calcium and magnesium ions in the boiler water. Under working conditions, the boiler is very easy to scale, and the phosphate is put into the boiler, so that the hardness of the water and the phosphate phosphate scale are eliminated or eliminated by the boiler. The phosphate treatment technology not only plays a good role. Descaling effect, while anti-corrosion effect is also very obvious. However, as the boiler parameters continue to increase, the "hidden" phenomenon of phosphate becomes more and more serious, thereby causing acid corrosion. Moreover, the boiler feed water system of the high-parameter unit has all adopted secondary demineralization, and the condensate system is provided with a finishing treatment device. There is basically no hardness component in the furnace water, and the main effect of the phosphate treatment is also from the removal of the hardness to the adjustment of the pH value. Therefore, in recent years, low phosphate treatment and balanced phosphate treatment have been proposed. The lower limit of low phosphate treatment is controlled at 0.3 to 0.5 mg/L, and the upper limit is generally not more than 2 to 3 mg/L. The basic principle of balanced phosphate treatment is to reduce the phosphate content of the furnace water to only enough hardness.
The low concentration of zui required for the component reaction, while allowing less than 1 mg/L of free NaOH in the furnace water to ensure that the pH of the furnace water is in the range of 9.0 to 9.6.
2.4 Condensate treatment measures
At present, DC boilers, most of the high-parameter units of 300 MW and above are equipped with condensate treatment equipment, mainly equipped with iron remover + mixed bed, pre-filter + mixed bed, condensate regeneration system. The condensate treatment system is mainly used to purify the condensed water. The metal corrosion of the unit during operation and start-stop process and the leakage of the condenser into the water to ensure the water vapor quality of the unit, shorten the start-up time of the unit, and prolong the pickling interval of the thermal system. The power plant has oxygenated water quality requirements.
2.5 Circulating water treatment measures
Circulating water is a major item of water consumption in power plants. Increasing the concentration ratio of circulating cooling water system is a technical way to reduce the loss of circulating water. The concentration ratio of early circulating water treatment is not more than 2.5. Now, the organic scale inhibitor, bactericidal algaecide and corrosion inhibitor are added by circulating water. The comprehensive treatment process of circulating water can greatly increase the concentration ratio of circulating water. This is the focus of strengthening circulating water treatment technology. There is still a certain gap between China and developed countries in terms of circulating water concentration ratio. Therefore, research should be strengthened to improve the recycling efficiency of circulating water and reduce the environmental and water bodies. Secondary pollution.
2.6 Wastewater treatment measures
The industrial wastewater of power plants mainly comes from boiler pickling wastewater discharged from unit accidents or start-up, and acid-base waste liquid from boiler feed water treatment system. The waste liquids are respectively transported to the wastewater storage tank, stirred evenly by compressed air, acid or alkali is added to adjust the pH value of the waste liquid, mixed with the coagulant, and then clarified by entering the slanting plate clarifier, and the effluent is filtered through the filter to enter the neutralization. After the pool is added with acid and alkali to adjust the pH value, the zui is finally used for recycling or discharge.
3 Centralization of chemical water treatment control unit of power plant
The traditional process for chemical water treatment in power plants has previously adopted a mode of analog disk control. With the advancement of technology, there are many power plants at present for the purpose of facilitating maintenance and management. Many subsystems are brought together to form a trap system, which is coordinated with PLC equipment to make the entire control flow of chemical water treatment more concentrated. The management is convenient and also facilitates the quick maintenance system. It is possible to control all subsystems according to the PLC device's function of collecting data information for all subsystems and various technologies for modern data transmission, thereby achieving separate operation and automatic monitoring and control.
4 Conclusion
With the continuous advancement of the social economy, power plants play an important role in the development of society. Therefore, only the rational application of chemical water treatment systems to effectively ensure the quality of water can improve the water treatment efficiency of power plants and ensure the realization of power plants. Economic benefits. Chemical water treatment is the key to improving the power generation efficiency of power plants. It plays an extremely important role in ensuring the stability of thermal equipment operation. It is an important process to avoid scale or salt accumulation in the process of water circulation. The purpose of analyzing and researching chemical water treatment technology in power plants is to improve the efficiency of water treatment, reduce the production cost of power plants, and improve economic and social benefits.
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