Power Plant Water Treatment Chemical Technology Development 2019
1. Three basic water production methods
1.1 Use traditional clarification, filtration + ion communication methods
The process is as follows: raw water – flocculation clarification tank – multi-media filter – activated carbon filter – cation communication bed – carbon dioxide fan – central water tank – anion communication bed – anion-cation communication bed – resin trap – unit water.
1.2 Select reverse osmosis + mixed bed water production method
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 equipment – central water tank – mixed bed equipment – resin trap – demineralized water tank.
1.3 Selection of pretreatment, reverse osmosis + EDI water production method
The process is as follows: raw water – flocculation clarification tank – multi-media filter – activated carbon filter – ultrafiltration equipment – reverse osmosis equipment – reverse osmosis water tank – EDI equipment – microporous filter – demineralized water tank.
The above three water treatment methods are the primary processes for desulfurization of power plants, and other water purification processes are mostly water production processes based on the above three water production methods.
Advantages and disadvantages of three water production methods
(l) The advantage of the first type of clarification filtration + ion communication is that the initial investment is small, and the equipment is relatively small. The disadvantage is that the ionizer fails to require acid and alkali to regenerate to recover its communication capacity, which requires a lot of consumption of acid and alkali.
The demand for waste liquid generated by regeneration is neutralized and discharged, and the cost is higher in the later stage, which is a simple damage to the environment.
(2) The second type uses reverse osmosis + mixed bed. This water-making 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, which alleviates the failure frequency of the mixed bed. The amount of acid and alkali used 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 large at the initial stage of capital contribution, but the total comparison is relatively cost-effective. Most power plant is now considering to undertake this water production process.
(3) The third method of water preparation using pretreatment, reverse osmosis + EDI is also called full membrane water production.
This method of water production does not require the regeneration of acid or alkali to produce demineralized water, which will not cause damage to the environment. It is the most economical and environmentally friendly chemical water production process in power plants. However, the disadvantage is that the initial funding of the equipment is too valuable compared to the previous two methods of water production.
2. Power plant water treatment chemicals method
2.1 Treatment method of make-up water
The power plant is responsible for production safety and power in the supply of boiler water. Now with the rapid development of science and technology, the concept of power plants on environmental protection and energy conservation is well known.
Previously backward technologies such as ion communication, clarification filtration or coagulation have gradually been abandoned.
New fiber materials are now widely used in filtration equipment. Not only the colloids, microorganisms, and suspensions of some particles are removed. In the filtration, it also has strong adsorption and interception, and has achieved quite good results.
Membrane separation technology was chosen, when reverse osmosis dominated. Reverse osmosis technology can remove more than 90% of ions in water, and has a good removal rate of organic matter and silicon in water.
Due to the significant advantages of membrane separation technology, many of the waste water discharges due to backward technologies such as ion communication or clarification filtration are saved in the treatment of boiler feed water. Many of the problems of previous messy and difficult emissions have also been improved.
The new membrane separation technology not only meets environmental requirements. When the chlorine content in the water is relatively high, activated carbon filtration or water quality recovery agent may be used for treatment.
The effect of the mixed bed in the desalination treatment still occupies an important position, and the mixed bed desalination technology is relatively mature. The function of the mixed bed has the effect that other demineralization cannot replace.
The useful distribution of ultrafiltration, reverse osmosis equipment and electrodialysis desalination technology now constitutes an efficient desalination process. No acid or alkali regenerant is required. The effect of regeneration can be ended only by H+ and OH- ionized by water, and then the regeneration and desalting of electrodialysis are terminated. This water production process will be the development direction of chemical water production in power plants.
2.2 Water treatment methods
The feed water treatment of power plant boilers is also a key factor in the advancement of production power. Nowadays, in the treatment of boiler feed water, China has adopted the methods of oxygen scavenger and deaerator. The primary treatment is the volatility of ammonia and hydrazine. Neutral and joint treatment methods can be applied when the water quality is stable.
The choice of hydrazine technology has certain advantages, but it has certain limitations. For example, when the temperature of the water is too low, the rate of removal of oxygen is very slow, and if the temperature of decomposition is too high, it is highly toxic.
If you accidentally contaminate the worker’s body, it will cause harm to the health of the workers in the gas-fired power plant. Therefore, some domestic power plants began to use the method of supplying water to oxygen to treat the boiler feed water. The method is to create an oxidizing environment and obtain better results. The maintenance film can also be formed under low temperature conditions, and then the corrosion can be prevented.
This method avoids the use of the toxic drug hydrazine, and the pH of the feed water is only controlled between 8.7 and 8.9. The amount of ammonia used is saved, the boiler pickling cycle is extended, and the working cost of the unit is reduced. The use of this working method requires the use of high purity true water supply.
2.3 Boiler furnace water treatment method
The boiler furnace water treatment technology has long used the in-furnace phosphate treatment technology. The lower boiler parameters in the past are the primary reason why this technology can be widely used.
There are often many calcium and magnesium ions in the boiler water. Under certain working conditions, the boiler is very simply fouled, and the phosphate is put into the boiler, so that the hardness and phosphate in the water are eliminated by the boiler. The use of phosphate treatment technology not only plays a better descaling effect, but also has a significant anti-corrosion effect.
However, as boiler parameters continue to advance, the “hidden” phenomenon of phosphate is becoming more and more severe, causing acid corrosion. Moreover, the boiler feed water system of the high-parameter unit has all used secondary demineralization, and the agglomeration system has precision processing equipment.
There is no hardness component in the bottom of the furnace water, and the primary effect of phosphate treatment is also changed from hardness removal to pH adjustment. Therefore, in recent years, low phosphate treatment and balanced phosphate treatment have been proposed.
The lower limit of the low phosphate treatment is controlled at 0.3-0.5 mg/L, and the upper limit is generally not more than 2-3 mg/L. The principle of balanced phosphate treatment is to reduce the phosphate content of the furnace water to the minimum concentration required to react with the hardness component. The furnace water has less than 1 mg / L of free NaOH to ensure that the pH of the furnace water is 9.0- Within the scope of 9.6.
2.4 Agglutination water treatment method
At present, most of the high-parameter units of 30 MW and above are equipped with agglutination water treatment equipment, and the first is equipped with iron remover + mixed bed, pre-filter + mixed bed, and agglomeration water regeneration system.
The agglutination water treatment system is mainly to purify the agglomerated water due to the metal corrosion of the unit work and the start and stop process and the leakage of the condenser into the water, to ensure the water vapor quality of the unit, shorten the start time of the unit, and extend the pickling interval of the thermal system to meet the part. The power plant has oxygenated water quality requirements.
2.5 Circulating water burying method
Circulating water is a major item of water consumption in power plants. The concentration ratio of the forward circulating cooling water system is a technical way to reduce circulating water consumption.
The concentration ratio of the circulating water treatment in the previous period is not more than 2.5. Now, the circulating water is used to participate in the organic scale inhibitor, the sterilization algaecide, and the etchant method. According to the water quality of the circulating water, the concentration ratio of the circulating water can be greatly advanced.
This is the key to strengthening the circulating water treatment technology. There is still a certain gap between the developed countries and the developed countries in terms of circulating water concentration ratio. Therefore, it is necessary to increase the intensity of research and then re-use the circulating water to reduce the environmental and water bodies. Secondary pollution.
2.6 Wastewater treatment method
The industrial wastewater of the power plant is mainly derived from the boiler pickling wastewater discharged from the reactor or at the time of initiation and the acid-base waste liquid of the 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 used to dispatch 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. The pool, after participating in the acid and alkali scheduling pH value, after all, qualified for reuse or discharge.
3. The gathering of water treatment chemicals control unit of power plant
The traditional process flow for water treatment chemicals in power plants has been in the form of imitation tray control. Following the advancement of technology, there are many power plants for the convenience of maintenance and processing, and many subsystems are brought together to form a trap system.
The PLC equipment is operated in harmony, so that the entire control flow of the water treatment chemicals is distributed. The processing is convenient, and it is also beneficial to the quick maintenance system.
According to the PLC equipment, all subsystems have the function of collecting data information and various technologies in modern data transmission to control all subsystems, thereby completing the separate operation and automation of monitoring and control.
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