Brief analysis of zero discharge process of desulf

Brief analysis of zero discharge process of desulfurization wastewater from coal-fired power plants

the harmful substances in desulfurization wastewater do great harm to the environment and water pollution, so we should pay attention to the treatment of desulfurization wastewater. At present, zero emission process technology is widely adopted, and good results have been achieved

I

overview of zero discharge of wastewater from coal-fired power plants

zero discharge does not mean that water is not discharged, but that harmful substances are not discharged into the natural environment through water bodies. The water resources used in power plant production are eventually discharged into the environment in the form of steam, or retained in the internal water circulation system of the power plant, which greatly improves the utilization rate of water resources and avoids the pollution of the natural environment by polluted water bodies, Ensure water safety for residents. From the perspective of sustainable development, the current and future water resources will always be in a relatively scarce state, and zero discharge of sewage is the inevitable trend of industrial development. The requirement of zero discharge on water treatment technology is very high, which requires high technical investment, so its capital investment and strict management and supervision system are essential

with the rapid development of China's economy and electricity, the availability of water resources in areas with more coal but water shortage in northern China has decreased year after year, and the sewage charges and total sewage volume are rising. Even in the south, which is relatively rich in water resources, with the deterioration of the environment and the improvement of environmental protection awareness, the voice of zero discharge of wastewater is also rising. It is a very complex system engineering to realize zero discharge of wastewater from power plants. China's thermal power plants have been committed to the research and improvement of water-saving methods for many years, but the past research purpose was only to ensure the safe operation of power plants, and did not rise to the height of environmental protection and water saving. The consideration of water conservation is relatively few, which leads to the fact that power plants in China pay little attention to the development of low water consumption technology, and always think of using water first, then treating wastewater and discharging. Nowadays, the shortage of water resources is becoming increasingly prominent, especially in northern China. Water resources have become an important issue in the development of China's power industry. Make it difficult to identify the yield point

II

water quality characteristics and influencing factors of desulfurization wastewater

water quality characteristics of desulfurization wastewater:

the composition and concentration of desulfurization wastewater have a great impact on the operation and management of the treatment system, and are key factors affecting the selection of treatment equipment, corrosion, etc. Desulfurization wastewater generally has the following characteristics:

(1) strong corrosivity

the strong corrosivity of desulfurization wastewater is due to the fact that the wastewater contains more acidic substances, which will not only pollute the environment where the enterprise has only three production lines, but also corrode the mechanical equipment of coal-fired power plants, causing the equipment of coal-fired power plants to be particularly vulnerable to damage

(2) high salt content

the salt content of desulfurization wastewater changes according to the operating conditions of desulfurization facilities. Generally, desulfurization wastewater will contain tens of thousands of mg/L of salt

(3) high hardness, easy to scale

desulfurization wastewater is enriched with high calcium and magnesium ions, and calcium sulfate is in a supersaturated state. In this case, desulfurization wastewater is very easy to scale, which will cause serious damage to desulfurization equipment

three

zero emission technology of desulfurization wastewater

technology class I: strong evaporation process

(1) flue evaporation process

flue evaporation process is a process based on spray drying technology. The basic principle of spray drying technology is to spray the solution into the drying tower with an atomizer, contact with high-temperature gas in the form of droplets, and dry the droplets in a short time. The biggest feature is that the surface area of evaporation and drying is very large. As long as these dispersed particles with large surface area come into contact with high-temperature gas, strong heat exchange will occur, and most of the water will be evaporated quickly to form solid products with less water content, so the drying speed is very fast

flue evaporation process of desulfurization wastewater refers to setting atomizing nozzles in the flue between the air preheater and the dust collector at the tail of the boiler, and pumping desulfurization wastewater to the atomizing nozzles for atomization. Due to the high temperature of the flue gas after passing through the air preheater, the atomized droplets evaporate in the flue under the action of high-temperature flue gas and are discharged with the flue gas, while the impurities in the wastewater enter the dust removal system and are trapped and discharged with the ash, So as to achieve the goal of zero discharge of desulfurization wastewater

(2) evaporative concentration crystallization process

evaporative concentration crystallization process is to concentrate desulfurization wastewater by using evaporator. The product water is reused, and the concentrated water can be converted into solid salt for disposal through crystallization and drying processes. This kind of technology has wide applicability to wastewater quality, units and coal types, and has a wide application prospect

the commonly used pretreatment method of desulfurization wastewater in China's coal-fired power plants is neutralization coagulation sedimentation, which is mainly aimed at removing heavy metal ions and suspended solids in the wastewater. The waste water enters the neutralization tank from the regulating tank, adding hydrated lime to adjust the pH, so that the precipitation generated by heavy metal ions is removed, and then flows into the flocculation tank, adding flocculants. The particles in the waste water flocculate to form large flocs, and finally settle down in the clarifier. The primary coagulation sedimentation process has a serious scaling tendency. In order to eliminate the scaling phenomenon, Na2CO3 softening and re clarification process is subsequently added, which is a two-stage clarification and full softening treatment process. This process can maximally remove ca2+, mg2+, so42-, f- and other scaling factors in the water and ensure the incoming water quality of the subsequent process

evaporative crystallization. There are two main types of evaporation technology: multi effect evaporation technology (MED) and mechanical vapor recompression Technology (MVR). Multi effect evaporation technology (MED) refers to that several evaporators are connected in series, and the secondary steam produced by the former evaporator is used as the heating source of the latter evaporator, so that the steam heat energy can be used for many times, so as to improve the utilization rate of heat energy. The majority of users of mechanical steam can choose according to their own conditions in the process of selection. Recompression Technology (MVR) is to send the secondary steam from the evaporator into the heating chamber of the evaporator after adiabatic compression by the compressor. The temperature of the secondary steam rises after compression, condenses in the heating chamber to release heat, so that the material liquid absorbs heat, boils and vaporizes, and then produces secondary steam, which enters the compressor after separation, and goes back and forth, The steam is fully utilized and the thermal efficiency is improved

(3) salt concentration process

salt concentration process is an advanced treatment process, which can separate distilled water and highly concentrated salt solution by-products from desulfurization wastewater treated by conventional system

first, the desulfurization wastewater is preheated, the air is removed through the degasser, and then heated again and fed to the salt solution concentrator. The slurry is distributed to a layer of film on the inner wall of the titanium alloy pipe. When the slurry film flows down the pipe, the water will evaporate. The generated steam reaches the steam compressor through the demister, and its saturation temperature is raised above the boiling point of the recycled salt solution. The compressed steam can be condensed into distilled water for reuse. In addition, part of the recovered salt is treated by the cyclone, and part is transferred to the finished product tank and transported to the market

technology class II: strong evaporation process

because the "zero discharge" of desulfurization wastewater requires a high degree of water salt separation, multiple reverse osmosis filtration process is usually used. The reverse osmosis process needs to be pretreated first

the pretreatment process of reverse osmosis is mainly membrane filtration, supplemented by sterilization process and sedimentation process. The purpose is to remove suspended solids and microorganisms in the water, so that the treated water quality can initially meet the influent requirements of reverse osmosis. The main process usually adopts a two-stage reverse osmosis system. Since the influent of the second stage system is the concentrated water of the first stage system, it needs special chemicals to treat it to ensure that the influent parameters of the second stage system meet the requirements. At the same time, before it enters the second stage system, professional scale inhibitor and regulator can be added according to its water quality to ensure the stable operation of the system. The product water enters the reuse pool, and a small amount of concentrated water in the system can be used to flush the slag, realizing zero discharge of the water treatment system

IV

brief analysis of typical cases of MVR evaporative crystallization technology application

the desulfurization wastewater advanced treatment project of Guodian Hanchuan Power Plant Phase III expansion project is the first desulfurization wastewater zero discharge project of one million units in China. Hewlett Packard covallis factory, the EPC of Guodian Beijing langxinming Environmental Protection Technology Co., Ltd. Nanjing Branch, is responsible for the supply of complete sets of equipment and technical services for the desulfurization wastewater advanced treatment (evaporative crystallization) project

the difficulties faced by the project lie in the large fluctuation of water quality, high salt content and complex water quality, which are the test of process design ability and overall technical strength. In view of the high energy consumption of multi effect evaporator operation, the general contractor Guodian Lang Xinming Nanjing Branch decided to adopt MVR evaporative crystallization technology. Based on the introduction of internationally renowned brand Weiting technology and product equipment, united high tech has adopted design and system integration optimization, The best MVR evaporative crystallization process scheme is designed for this project

the desulfurization wastewater of Hanchuan project enters the MVR evaporative crystallization system after pretreatment, softening, salt separation, concentration and reduction. The solute in this part of concentrated brine is mainly sodium chloride, and the amount of concentrated brine is about 8t/h. The evaporated crystalline salt is automatically packaged after fluidized bed drying. The final product is bagged sodium chloride with purity higher than 97.5%, which meets the secondary standard of refined industrial salt specified in the gb/t industrial salt standard

the project adopts DCS control system to monitor the process operation status in real time, collect process parameters and automatically form spreadsheets. The operators can track and manage the process operation data at any time, so as to comprehensively improve the automatic control level and improve the labor intensity and operation environment of operators. The implementation of the project can save 280000 tons of water for enterprises every year and reduce the production of about 7000 tons of solid waste

mvr evaporative crystallization system is the best solution for zero emission of desulfurization wastewater.

desulfurization wastewater has the characteristics of high salinity, high suspended solids, high hardness and high corrosivity. The difficulty of zero emission treatment lies in the resource treatment of end solid salt. If the separated crystalline salt is not properly treated, it will still return to the environment after encountering water and cause secondary pollution. The desulfurization wastewater MVR evaporative crystallization technology provided by Hezhong high tech can be effectively combined with the salt separation process. Under the condition of meeting the zero discharge of wastewater, the solid waste is finally converted into refined secondary industrial salt. Compared with traditional technology, MVR evaporative crystallization system is more energy-saving and environmental friendly, and saves more than 60% of the operating cost compared with traditional multi effect evaporator