Progress and Application of Water Treatment Chemical Technology in Power Plants

Introduction

With the continuous expansion of the domestic thermal power units, the parameters of the unit and the capacity of continuous improvement, power plant Water Treatment Chemical has undergone profound changes. Water Treatment Chemical in power plant in the selection of technology, equipment layout, process, control, monitoring, operation and maintenance, production management and other aspects of a profound change occurred.

1. Boiler make-up water treatment

Traditional boiler make-up water pretreatment usually adopts coagulation and filtration treatment. Domestic large thermal power plant to clarify the processing equipment for the mechanical acceleration mixing clarifier, its advantages are: fast response, easy operation and control, to contribute. In recent years, frequency conversion technology continues to be applied to the coagulation process, to further improve the pretreatment of water quality, reducing the manual operation. In the development of filter, granular material filter technology has gone through a slow filter, fast filter, multi-filter media filter stage of development, improve the pretreatment water quality has played a role. However, due to the limitations of granular materials, so that the water quality of filtration equipment, sewage interception capacity and filtration rate are subject to greater restrictions. At present, the fiber material instead of granular materials as a filter source of new filtration equipment continue to appear, fiber filter material due to small size, large surface area and soft material characteristics, with a strong interface adsorption, interception and water flow adjustment. Representative of the products are fiber ball filter, capsule squeeze fiber filter, pressure plate fiber filter.

In the boiler feed water pre-desalting technology, reverse osmosis technology (referred to as RO) development has become a bright spot. Reverse osmosis is the biggest feature is not subject to the impact of changes in raw water quality, reverse osmosis has a strong addition to organic matter and in addition to silicon capacity, COD removal rate of up to 83%, to meet the large units of organics and silicon content of the stringent requirements. Reverse osmosis removes most of the ions in the water (typically around 90%), reduces the burden of acid-base and alkali-containing waste, and reduces the salt content of the waste water by reducing the burden of the ion exchange system in the next process , Improve the power plant economic and environmental benefits.

Mixed bed is still playing an irreplaceable role in the treatment of boiler feed water desalination, while the development of mixed bed itself is mainly reflected in two aspects: environmental protection and energy conservation. Packed bed electrodialysis (electric desalting) CDI (EDI) is a combination of electrodialysis and ion exchange desalination technology combined fine desalination process, resin regeneration is by the H2O ionization of H + and OH- to complete, that is, in the DC The ionized H + and OH- directly act as regenerating agents for the resin, eliminating the need for acid and alkali agents. At the same time, the device on the weak ions, such as SO2, CO2 removal capacity is also strong.

2. Boiler feed water treatment

Boiler feed water is currently used ammonia and hydrazine volatile treatment is more mature, but it is more suitable for the new unit, to be stable after the water quality can be converted to neutral treatment and joint treatment. Oxygen treatment changed the traditional deaerator, oxygen scavenger treatment, the creation of redox atmosphere, in the low temperature state can generate protective film, inhibit corrosion. This method can also reduce the water supply system corrosion yield, reduce the amount of drugs, extend the chemical cleaning interval, reduce operating costs. The application of oxidative water chemistry is more popular in Europe, and the domestic is basically in the research stage. It must be emphasized that the oxidation of the water chemical run only for high purity water, and should pay attention to the system material with compatibility.

3. boiler water treatment

Phosphate treatment furnace technology has been more than 70 years of history, and now around the world, 65% of the boiler drum boiler water treatment of phosphate. Because of the low boiler parameters and the backward water treatment technology, a large amount of calcium and magnesium ions are often present in the boiler water. To prevent boiler scaling, a large amount of phosphate has to be added to the boiler to remove the hardness in the boiler water. Of the pH value is very high, alkaline corrosion problem is particularly prominent. In such circumstances, the coordination of phosphate treatment came into being, and achieved a certain degree of anti-corrosion effect. However, with the continuous improvement of boiler parameters, phosphate "hidden" more and more serious, the resulting acidic corrosion is also increasing. On the other hand, high-parameter units of the boiler make-up water system has been fully used two-stage desalination, condensate system with fine processing device. In this way, there is almost no hardness in the furnace water, phosphate treatment from the main role in addition to the hardness of the pH value to adjust corrosion. Therefore, the past 10 years, people also proposed low phosphate treatment and balanced phosphate treatment. The lower limit of low phosphate treatment is controlled at 0.3 ~ 0.5 mg / L, the upper limit is generally not more than 2 ~ 3 mg / L. The basic principle of the equilibrium phosphate treatment is to reduce the phosphate content of the boiler water to the minimum concentration required to react with the hardness component while allowing the free NaOH to be less than 1 mg / L in the furnace to ensure that the boiler water pH In the range of 9.0 to 9.6.

4. Condensate treatment

At present, most of the 300 MW and above high-parameter units are equipped with condensate polishing device, and to import the main products of its regeneration system is a high tower separation device and cone separation device. But the real long-term ammoniation can run the fine processing device is not much, only Xiamen Songyu Power Plant and a few, Songyu Power Plant mixed bed cycle of 100 days or more, the cycle of water up to 500,000 t or more. From the environmental and economic point of view, to achieve the amination of the future operation of the fine processing system will be the direction of development. In addition, the investment in equipment, equipment layout and process optimization, should be considered as much as possible to use the original plant of the common system, such as reducing resin regeneration fan and mixed bed recirculation pump, as far as possible the program control device And the regeneration unit is installed on the boiler make-up water side, so as to realize the centralized management.

On the other hand, the powder resin (POWDEX) fine processing system with the dual function of filtration and desalination has been gradually applied, such as Fuzhou Huaneng II, Nantong Huaneng II and other power plants. However, due to the higher price of powder resin, mainly dependent on imports, making the fine powder resin processing equipment to promote the use of a certain limit.

5. Recycling water buried

The use of closed-cycle cooling of thermal power plants, cooling water recycling and water quality stabilization technology development is the focus of water treatment work. Developed countries, recycling water concentration ratio has reached 6 to 8 times the majority of domestic power plant circulating water concentration rate of 2 to 3 times, the domestic thermal power plants should improve the efficiency of recycling water and reuse efforts. In order to avoid the secondary pollution of phosphorus water treatment chemicals to the environment water, high-efficient scale inhibitor and dispersant of low phosphorus and non-phosphorus formula, multi-copolymer water treatment chemicals are gradually applied. The use of open-discharge cooling of thermal power plants, especially in seawater as cooling water in coastal power plants, cooling water is generally treated with chlorination, the common device is the United States CaptialControl company's products. However, some plants use electrolytic seawater to produce sodium hypochlorite as a biocide. Such as Zhangzhou after the stone power plant, Beilun port power plants.

6. Wastewater treatment

At present, the domestic large-scale industrial wastewater treatment plant layout of the basic application of Baosteel power plant wastewater treatment mode, that is, centralized collection of wastewater, step-by-step approach. Generally used to blast aeration oxidation, pH adjustment, coagulation clarification, sludge concentration treatment process. However, the disadvantage of this approach is the complexity of the water quality and a wide range of changes in the treatment of large water, and affect the comprehensive utilization of waste water recycling. In recent years, two-phase solid-liquid separation technology has been gradually applied, the technology uses a dosing coagulation, in a combination of facilities to complete flocculation, sedimentation, clarification, scraping scum and sludge concentration process, the water Sediment, suspended solids, algae suspended matter and oil are separated in the same facility. The treatment technology to improve the water quality, reduce processing costs, expanding the scope of reuse.