Pure seawater desulfurization process uses the principle that the natural salinity of seawater and sulfate are harmless to the ocean. This new process is the only green process among more than 200 kinds of desulfurization processes in the world at present, which does not need any artificial raw materials and has no by-product emission, and the desulfurization efficiency is higher than 90%. Its equipment cost and operation cost are only one third of the traditional desulfurization process widely used in the world at present. ?
Pure seawater flue gas desulfurization is a computer software. This series of products adopts magnetostrictive technology as a new generation of high-precision liquid level sensor, which has the characteristics of stable performance, high reliability, long service life and convenient installation. The liquid level, interface and humidity of the medium can be measured continuously at the same time; Meet the industrial explosion-proof and anti-corrosion requirements; The average trouble-free working time is 23 years. It can be used with various measuring instruments, and is widely used in industrial measurement and control fields such as aerospace and petrochemical industry. ?
1. Process principle of seawater desulfurization?
Natural seawater contains a large number of soluble salts, mainly chloride and sulfate, and also contains a certain amount of soluble carbonate. Seawater is usually alkaline, and its natural alkalinity is 1.2-2.5 mmol/L, which makes seawater have natural acid-base buffering capacity and SO2 absorption capacity. Using this characteristic of seawater to wash and absorb SO2 in flue gas can achieve the purpose of purifying flue gas. ?
Seawater desulfurization processes can be divided into two categories according to whether other chemicals are added as absorbents: (l) represented by Flakt-Hydro process developed by ABB company in Norway, which uses pure seawater as absorbents without adding any chemicals. This technology has been widely used in industry. (2) Adding a certain amount of lime into seawater to adjust the alkalinity of absorption liquid, represented by Bechte Company of the United States. This technology has built a demonstration project in the United States, but it has not been popularized. The seawater desulfurization processes described below all refer to 1 level. The basic flow of pure seawater desulfurization process is shown in figure 1. ?
Seawater desulfurization process is mainly composed of flue gas system, seawater supply and discharge system, seawater recovery system, electrical system and control system. The main process is as follows: after the flue gas discharged from the boiler passes through the dust collector, it is sent to the hot side of the gas-gas heat exchanger by the booster fan of FGD system for cooling, and then it enters the absorption tower and is washed by part of seawater in the circulating cooling system. SO2 in the flue gas undergoes the following chemical reactions in seawater:
SO2+H2O→H2? SO3?
H2? SO3→H++HSO-3?
HSO three? →H++SO23-?
SO23-+ 1/2O2→SO24-?
H+ produced by the above reaction reacts with carbonate in seawater as follows:
CO23-+H+→HCO3-?
HCO3-+H+→H2CO3→CO2+H2?
The seawater after washing flue gas in absorption tower is acidic and contains more SO32-, so it cannot be directly discharged into seawater. The wastewater discharged from the absorption tower flows into the seawater treatment device and is mixed with seawater from the cooling circulation system, and a large amount of air is blown in by a blower to oxidize SO32- into SO42-; Discharge carbon dioxide from seawater. After the mixed treatment, the PH value and COD of seawater reach similar seawater quality standards and then discharged into the sea area. The purified flue gas is heated by GGH and then discharged into the atmosphere through the chimney. ?
2. Seawater Desulfurization Project for Unit 4 of Shenzhen West Power Plant?
2. 1 power plant overview?
Shenzhen West Power Plant is located at Mawan Port Wharf at the southwest end of Nantou Peninsula in Shenzhen. The unit of the first phase project (2×300MW) belongs to Mawan Electric Power Co., Ltd., and the second phase project (2? x? 300MW) unit belongs to Western Electric Power Co., Ltd., and Units 5 and 6 currently under construction also belong to Western Electric Power Co., Ltd., and the whole power plant occupies Mawan Port. Berth 9. 10. 1 1. The power plant is adjacent to Lingdingyang in the Pearl River Estuary to the west, and the plant area is basically formed by cutting mountains and filling the sea. Except the land along the mountain in the east, the rest are sea areas. What is the scale of power plant construction in western China? 4? x? 300MW, installation? Two imported domestic coal-fired units, Unit 3 was connected to the grid for power generation in September 1996, and Unit 4 was completed and put into operation in October 1997. Units 5 and 6 are under construction. The boiler adopts Hg- 1025/ 18.2-YM6 produced by Harbin Boiler Factory, and the dust collector adopts double-chamber four-field dust collector produced by Lanzhou Electric Power Repair Factory, with dust removal efficiency >? 99%。 Every two furnaces share 1? Sleeve chimney with a height of 2 10 m and an outlet diameter of 7 m has a reinforced concrete structure outside and a corrosion-resistant alloy steel inside. ?
2.2? What is the main design basis of FGD system?
2、2. 1? Burning coal?
The design coal is northern Shanxi bituminous coal, with sulfur content? 0.63%。 Upon arrival, the coal is mixed coal, and the sulfur content is 0.75 ℅. Under the working condition of steam turbine T-ECR, the actual coal consumption of boiler is114.4t/h; When the boiler B-MCR works, the actual coal consumption of the boiler is 126.9 t/h?
2.2.2? Smoking?
The design value of FGD system for flue gas treatment is the boiler flue gas quantity under T-ECR condition, that is? 165438+ 10000 m3/h, FGD system according to the boiler? B-MCR design. The design value of flue gas temperature at the entrance of FGD system is 123℃. What is the range of flue gas temperature? 104- 145℃。 ?
2、2、3? Seawater?
The circulating cooling water of the condenser of Unit 4 is used as desulfurization absorption liquid. The design value of seawater flow is 12t/s, and the seawater temperature at the condenser outlet is 27-40℃. Seawater salinity? 2.3%。 ?
2、3? Western power plant seawater FGD system?
Seawater of Unit 4 in Western Power Plant? The FGD process flow is shown in Figure 2. The process consists of flue gas system, absorption system, seawater supply and drainage system and recovery system, and electrical and monitoring system. ?
2.3. 1 flue gas system?
The flue gas treated by FGD system is led out from the contact flue at the outlet of induced draft fan of Unit 4, and the system is equipped with inlet and outlet baffle doors and bypass flue baffle doors. During the normal operation of FGD system, the bypass damper door is closed, and all flue gas is discharged from the chimney after passing through the desulfurization system. When the FGD system stops running, the bypass flue is opened, the baffle doors of the flue at the entrance and exit of the FGD system are closed, and the flue gas directly enters the chimney for discharge. The flue gas in FGD system enters GGH after being cooled by booster fan, and then enters the absorption tower. After the purified flue gas is heated by GGH, it is discharged into the atmosphere from the chimney. ?
2.3、2? SO2 absorption system?
The absorption tower of FGD system is a packed tower with reinforced concrete structure. Flue gas is introduced from the lower part of the absorption tower, flows upward through the absorption zone, fully reacts with seawater injected into the absorption tower on the surface of the packing, and the purified flue gas is discharged from the tower body after water droplets are removed by the top demister. The seawater after washing flue gas is collected at the bottom of the tower and discharged into the seawater recovery system by gravity. ?
2.3.3 Seawater water supply and drainage system?
The seawater used for circulating water in the western power plant is a once-through unit water supply system. The cooling water is taken from Lingdingyang Fan Shi Waterway, and the deep seawater is taken from No.2 intake for the use of Unit 4. The water source of FGD system is directly taken from siphon well at the condenser outlet of Unit 4. Part of seawater enters the suction tank and is sent to the absorption tower by the booster pump to wash the flue gas. The seawater discharged from the absorption tower flows into the aeration tank, where it meets the seawater siphoned out and directly discharged into the aeration tank, and is fully mixed and aerated. The treated seawater enters the sea through the drainage ditch of Unit 4. ?
Seawater recovery system?
The main structure of seawater recovery system is aeration tank. The acidic seawater discharged from the absorption tower is fully mixed with the alkaline seawater discharged from the condenser in the explosion tank. At the same time, an appropriate amount of compressed air is blown into the tank through the aeration system, so that sulfite in seawater is converted into stable and harmless sulfate, and CO2 is released at the same time, so that the seawater quality reaches the same seawater quality standard and then discharged into the sea. ?
2.3.5? Electrical?
What is the power supply voltage of FGD system? 6kV and? 380V and 6kV power supplies are used for motors of 200kw or more, and 380V power supplies are used for motors of less than 200kW. ?
2.3.6? Instrument and control?
The instrument control system of FGD system has the following main functions: (1) data acquisition function. Continuously collect and process important measuring point signals reflecting the operation status of FGD system, such as? SO2, O2 concentration and flue gas temperature at the inlet and outlet of FGD system. PH value, chemical oxygen demand, water temperature, etc. At the discharge port of aeration tank. (2) Control function. The pressure difference before and after the flue gas baffle is controlled in closed loop, and other equipment is controlled in sequence. (3) Equipped with various necessary on-site monitoring instruments for flue gas and seawater. ?
2.4? What is the operation status of seawater FGD system?
With the support of Shenzhen Energy Group Corporation and relevant functional departments of governments at all levels, Shenzhen Energy Environmental Protection Engineering Company, which undertook the construction of seawater desulfurization project for Unit 4 of Western Power Plant, successfully passed the 72-hour continuous operation and handed over production on March 8 after more than two years of intense construction by the participating units. 1999 At the end of June and the beginning of July, the performance of seawater flue gas desulfurization system was tested by both Chinese and foreign parties, and the seawater flue gas desulfurization device was monitored on site by China Environmental Monitoring Center before acceptance. The test results show that the desulfurization system runs stably, the equipment is in good condition, and the main performance indexes meet the national review requirements, reaching or exceeding the design value. ?
See table 1 for operation and design data. See Table 2 and Table 3 for the design values and measured values of performance guarantee of seawater desulfurization system. ?
3? What is the role and application prospect of the demonstration project of western power plants?
3. 1? What are the characteristics of seawater desulfurization process?
See Table 4 for the main performance comparison between seawater desulfurization process and wet limestone-gypsum process, rotary spray desulfurization process, calcium injection in furnace and humidification activation desulfurization process. ?
As can be seen from Table 4, the seawater desulfurization process has the following characteristics:
(1) Natural seawater is used as the absorbent, and no other chemicals are added, thus eliminating the preparation system of absorbent.
Unified and simple process. ?
(2) The absorption system will not cause scaling, blockage and other operational problems, and the system availability rate is high.
(3) The seawater of the washing flue gas is discharged into the sea after being treated to meet the requirements of environmental protection, and no desulfurization ash is generated, so there is no need to set up ash removal facilities. ?
(4) High desulfurization efficiency and obvious environmental benefits. ?
(5) The investment and operation costs are lower, generally lower than that of wet limestone-gypsum process 1/3.
3.2? Demonstration function of seawater desulfurization project in western power plant?
With the promulgation and implementation of atmospheric environmental protection laws and regulations, China's restrictions on SO2 emission are becoming more and more strict. In the acid rain control area and? In areas with serious sulfur dioxide pollution, it is an urgent task to control sulfur dioxide emission and reduce the harm of acid rain by using flue gas desulfurization technology. However, the high investment and operation cost of desulfurization project has always been an important problem that hinders the development and application of desulfurization technology in China. Over the years, the State Economic and Trade Commission, the State Power Company and the State Environmental Protection Administration have been committed to developing desulfurization technologies with low investment, low operating costs and reliable operation, which are suitable for China's national conditions. The characteristics of seawater desulfurization technology meet the above requirements, and it is a desulfurization process suitable for China. ?
China has a long coastline, developed economy in coastal areas, rapid industrial development, dense population and strict environmental protection requirements. There are many new construction, reconstruction and expansion projects in coastal thermal power plants, and seawater desulfurization technology has a broad application market in China. ?
In September, the State Environmental Protection Administration presided over the "Summary Seminar on Acceptance of Seawater Desulfurization Demonstration Project of Shenzhen Western Power Plant", 1999. State power company attending the meeting. China National Environmental Monitoring Center, Guangdong Provincial Environmental Protection Bureau, Shenzhen Environmental Protection Bureau and other relevant units have conducted extensive and in-depth discussions on whether the seawater desulfurization process can be further promoted and localized in the coastal areas of China. The meeting held that the performance index of seawater desulfurization system in Shenzhen West Power Plant reached or exceeded the design value, which met the national requirements for project review and environmental protection standards. The monitoring results of SO2 concentration on the surface of aeration tank by China National Environmental Monitoring Center show that there is no SO2 overflow during aeration, which will not adversely affect the surrounding environment. ?
According to the requirements of the State Power Company and the State Environmental Protection Administration, the tracking, monitoring and research projects on the influence of desulfurization process drainage on the water quality, marine life and seabed sediments in the nearby waters were carried out at the same time of project construction. Since 1997, the Chinese Academy of Water Resources and Hydropower Research and Nanhai Institute of Chinese Academy of Sciences have conducted background detection in the waters near the power plant outlet before and after commissioning. In the same period, Shenneng Group Company tested the water quality of desulfurization system. On June 5, 2000 and June 6, 2000, a stage summary report meeting was held under the auspices of the State Environmental Protection Administration. Through the analysis of the test results, the leaders and experts at the meeting agreed that the drainage of seawater desulfurization process has no adverse effects on seawater quality and marine life, and can be popularized and applied as a relatively desulfurization process in coastal power plants with conditions. On September 30, 2000, the State Environmental Protection Administration issued the meeting minutes to all relevant units in China in document 2000/200 1. 200011.After five years of marine tracking and monitoring, all the contents required by the outline have been completed, and the State Environmental Protection Administration is organizing the preparation of the general report. The above monitoring and research work provides a powerful scientific basis for the popularization and application of seawater desulfurization technology in thermal power plants in coastal areas of China. ?
In a word, the seawater desulfurization process uses the natural alkalinity of seawater for desulfurization, without adding any chemical reagent, with simple system, reliable operation, high desulfurization efficiency, low investment and operation cost, and easy to realize domestic equipment matching. The demonstration project of seawater desulfurization in Shenzhen West Power Plant and related experimental research, as well as the ongoing domestic construction project of seawater desulfurization in the continuation project of Units 5 and 6, will lay a foundation and accumulate experience for the popularization and application of seawater desulfurization technology in China and the domestic design, equipment matching and construction.