7 must-have water treatments for power plants
Pure water equipment : http://euhowblog.com
With the continuous expansion of domestic thermal power units, the parameters and capacity of the units have been continuously improved, and the chemical water treatment of power plants has undergone profound changes. Chemical water treatment in power plants has undergone profound changes in technology selection methods, equipment layout, process flow, control monitoring, operation and maintenance, and production management.
1. boiler make-up water treatment
Conventional boiler make-up water pretreatment usually uses coagulation and filtration. Most of the domestic large thermal power plants' clarification treatment equipment are mechanically accelerated agitation clarification tanks, which have the advantages of fast response speed, convenient operation control, and large output. In recent years, frequency conversion technology has been continuously applied to coagulation treatment, which further improves the pretreatment effluent water quality and reduces manual operations. In terms of filter development, filtration technology using granular materials as filter material has experienced development stages such as slow filter, fast filter, multi-layer filter, and played a certain role in improving the pretreatment water quality. However, due to the limitations of granular materials, the effluent quality, pollution interception capacity, and filtration speed of filtration equipment are all greatly limited. At present, new filtering equipments that use fibrous materials instead of granular materials as filter sources continue to appear. Due to their small size, large surface area, and soft material characteristics, fibrous filtering materials have strong interface adsorption, interception, and water flow adjustment capabilities. Typical products include fiber ball filters, capsule squeeze fiber filters, and pressure plate fiber filters.
The development of reverse osmosis technology in boiler pre-salting water has become a bright spot. The biggest feature of reverse osmosis is that it is not affected by the change in the quality of the raw water. Reverse osmosis has a strong ability to remove organic matter and silicon. The removal rate of COD can reach 83%, which meets the strict requirements of large units for organic matter and silicon content. Reverse osmosis removes most of the ions in the water (usually about 90%), reducing the salt removal burden of the ion exchange system in the next process, thereby reducing the discharge of acid and alkali waste liquid and reducing the salt content of discharged wastewater , Improved economic and environmental benefits of the power plant.
In terms of boiler feed water desalination, mixed beds still play an irreplaceable role, and the development of mixed beds is mainly reflected in two aspects: environmental protection and energy saving. Packed-bed electrodialyzer (electrodesalination) CDI (EDI) is a fine desalting process combining electrodialysis and ion exchange desalination technology. Resin regeneration is completed by H + and OH- ionized by H2O, that is, under direct current The H + and OH- ionized in the field directly act as the regeneration agent of the resin, and no longer need to consume acid and alkali agents. At the same time, the device has a strong ability to remove weakly charged ions such as SO2 and CO2.
2.Boiler feed water treatment
Boiler feed water is currently more mature with volatile ammonia and hydrazine treatment, but it is more suitable for newly-built units. After the water quality is stable, it can be converted to neutral treatment and combined treatment. Oxygenation treatment has changed the traditional deaerator and deaerator treatment to create a redox atmosphere, and a protective film can be formed at a low temperature to suppress corrosion. This method can also reduce the corrosion output of the water supply system, reduce the amount of chemicals, extend the chemical cleaning interval, and reduce operating costs. The application of oxidizing water chemistry operation mode is relatively popular in Europe, and it is basically in the research and experimental stage in China. It must be emphasized that the oxidizing water chemical operation mode is only suitable for high-purity feed water, and attention should be paid to the compatibility of the system material with it.
3. Boiler furnace water treatment
Furnace phosphate treatment technology has a history of more than 70 years, and now 65% of drum boilers worldwide use furnace water phosphate treatment. Because the previous boiler parameters were low and the water treatment process was backward, a large amount of calcium and magnesium ions often appeared in the boiler water. In order to prevent boiler scaling, a large amount of phosphate had to be added to the boiler to remove the hardness of the boiler water. In this way, the boiler water The pH value is very high, and the alkaline corrosion problem is particularly prominent. Under such circumstances, coordinated phosphate treatment emerged at the historic moment, and achieved a certain preservative effect. However, with the continuous improvement of boiler parameters, the "hidden" phenomenon of phosphates becomes more and more serious, and the acid corrosion caused by them is also increasing. On the other hand, the boiler make-up water systems of high-parameter units have all adopted secondary desalination, and the condensate system is equipped with a precision treatment device. In this way, there is almost no hardness component in the furnace water, and the main role of phosphate treatment is to switch from removing hardness to adjusting the pH value to prevent corrosion. Therefore, in the past 10 years, low phosphate treatment and balanced phosphate treatment have been proposed. The lower limit of low phosphate treatment is controlled to 0.3 to 0.5 mg / L, and the upper limit is generally not to exceed 2 to 3 mg / L. The basic principle of balanced phosphate treatment is to reduce the phosphate content of the boiler water to the minimum concentration required to react with the hardness components, and allow free NaOH less than 1 mg / L in the boiler water to ensure the pH of the boiler water. It is in the range of 9.0 to 9.6.
4. Condensate treatment
At present, most of the high-parameter units with a capacity of 300 MW and above are equipped with condensate fine treatment devices and are mainly imported. The mainstream products of their regeneration systems are high tower separation devices and cone bottom separation devices. However, there are not many precise treatment devices that can realize long-term ammoniation operation. There are only a few such as Xiamen Songyu Power Plant. The operating cycle of the mixed bed of Songyu Power Plant is more than 100 days, and the periodic water production capacity is more than 500,000 tons. From the perspective of environmental protection and economy, the realization of ammoniation operation will be the development direction of fine processing systems in the future. In addition, in terms of equipment investment, equipment layout, and process optimization, consideration should be given to using as much of the existing public systems of the power plant as possible, such as reducing the fan for resin regeneration and recirculating pumps in the mixed bed. And regeneration devices are installed on the boiler make-up water side to facilitate centralized management.
On the other hand, the powder resin (POWDEX) fine processing system with dual functions of filtration and desalination has also been gradually applied, such as Fuzhou Huaneng Phase II and Nantong Huaneng Phase II power plants. However, due to the high price of powder resin, which mainly depends on imports, the promotion and application of powder resin fine processing equipment has been limited.
5. Buried in circulating water
Thermal power plants adopting closed cycle cooling, the recycling of cooling water and the development of water quality stabilization technologies are the focus of water treatment. In developed countries, the circulating water concentration ratio has reached 6 to 8 times. Domestic thermal power plants should work hard to improve the recycling water recycling efficiency. In order to avoid secondary pollution of environmental water bodies by phosphorus-based water treatment chemicals , low-phosphorus and non-phosphorus-based formulas of high-efficiency scale inhibitor dispersant and multi-copolymer water treatment agents are gradually applied. Thermal power plants that use open-discharge cooling, especially coastal power plants that use seawater as cooling water, are generally treated with chlorination. The common device is the product of CaptialControl in the United States. However, some power plants use electrolytic seawater to produce sodium hypochlorite as a biocide. Such as Zhangzhou Houshi Power Plant and Beilun Port Power Plant.
6. Wastewater treatment
At present, the layout of domestic large-scale power plant industrial wastewater treatment basically applies the wastewater treatment model of Baosteel Power Plant, that is, the centralized collection of wastewater and the step-by-step treatment method. Generally, the processes are mainly blast aeration oxidation, pH adjustment, coagulation and clarification, and sludge concentration treatment. However, the disadvantage of this treatment method is that it is difficult to treat incoming water with complex water quality and a wide range of changes, and it affects the comprehensive recycling of wastewater. In recent years, the two-phase flow solid-liquid separation technology has been gradually applied. This technology uses one-time dosing and coagulation to complete flocculation, sedimentation, clarification, scum scraping, and sludge concentration in a combined facility. Sediment, suspended solids, algae suspended matter and oil are separated in the same facility. The treatment technology improves the quality of the effluent water, reduces the treatment cost, and expands the scope of reuse.
7. Physical water treatment
The process of using physical scale inhibition, filter material decontamination, and filter material removal of COD has been used in many foreign power plants and chemical plants, and has achieved good economic benefits and environmental protection with minimal application of pesticides. Such as SSP physical scale inhibition, KL decontamination, CC removal of COD has been used in Malta Thermal Power Plant and Unilever Chemical Plant in Germany.