"I announce that the first tank of concrete in the coal-electricity integration project of Yuneng Yanghuopan has started pouring!" On September 19, with the order of Zhang Yi, member of the Party Committee and deputy general manager of Yuneng Group, the first tank of concrete for the main workshop foundation of the world's first natural ventilation direct air cooling unit (2×660MW) began to be poured, completing the milestone plan one day ahead of schedule, marking the official start of the main project.
Zhang, member of the Party Committee and deputy general manager of Yuneng Group, chief auditor, heads of relevant departments, and more than 200 heads of Northwest Electric Power Design Institute, Harbin Electric Power Group Corporation, Northwest Electric Power Construction Supervision Co., Ltd., North China Electric Power Design Institute, Henan Erjian Group Co., Ltd., Zhejiang Erjian Group Co., Ltd. and Yanghuopan Coal Mine attended the pouring ceremony.
Before the groundbreaking ceremony, Yang Qian, Chairman and General Manager of Yanghuopan Coal and Electricity Company, introduced the general situation of the project and the construction process to the invited guests. At the ceremony, Yang Qian delivered a warm speech. He said that the Yuneng Yanghuopan coal-electricity integrated power plant project is a key project in Shaanxi Province, and the start of the project is of great significance to the transformation and upgrading of Yuneng Group, high-quality development and the comprehensive construction of a world-class high-end energy and heavy chemical industry base in Yulin. He stressed that in the process of project construction, the construction unit, EPC general contractor and all participating units should pay close attention to the four goals of project safety, quality, progress and integrity, constantly clarify their responsibilities, strengthen the concept of service cooperation, and plan the great cause of project construction. At the same time, we will continue to integrate the superior resources of the industry, form a strong team effort, work with one heart and one mind, and strive to promote project construction with high quality and efficiency. EPC general contractor Northwest Electric Power Design Institute, supervision company Northwest Electric Power Construction Engineering Supervision Company, bid section A of main workshop of Henan Erjian Group Co., Ltd. and bid section B of cooling tower of Zhejiang Erjian Group Co., Ltd. made statements successively.
The air cooling system of power plant can be divided into direct air cooling system and indirect air cooling system. Indirect air cooling system refers to indirect air cooling system of hybrid condenser (Heller indirect air cooling system) and indirect air cooling system of surface condenser (Harmon indirect air cooling system).
Direct air cooling system-it uses mechanical ventilation to condense the steam turbine exhaust directly in the finned tube air-cooled condenser, which generally consists of large-diameter exhaust pipe, air-cooled condenser, axial cooling fan and condensate pump;
Indirect air cooling system, also known as Harmon system, consists of surface condenser, air cooling radiator, circulating water pump, air cooling tower of nitrogen charging protection system, circulating water replenishment system and radiator cleaning system. The system is basically similar to the conventional wet cooling system, except that the air cooling tower replaces the wet cooling tower, the closed circulating cooling water system replaces the open circulating cooling water system, and the circulating water uses demineralized water.
A, mechanical ventilation direct air cooling system (ACC)
This kind of system, also known as ACC system, means that the exhaust steam of steam turbine condenses directly with air, and the air exchanges heat with steam. The process flow is that the exhaust steam of the steam turbine passes through the coarse exhaust pipe to the outdoor air-cooled condenser, and the axial-flow cooling fan makes the air flow through the outer surface of the cooler to condense the exhaust steam into water, and the condensed water is pumped back to the boiler.
The advantages are:
(1) does not need intermediate media such as cooling water, and the initial temperature difference is large.
⑵ Less equipment, simple system, small floor space and flexible system adjustment.
Its disadvantages are:
(1) The vacuum system is huge, and it is difficult to find the leakage point when the system leaks, which may easily lead to the dissolved oxygen of deaerator and condensate exceeding the standard.
⑵ Forced ventilation will increase the consumption of auxiliary power.
(3) The noise of large-diameter axial flow fan is about 85 decibels, which is very large.
(4) It is greatly influenced by environmental wind.
Second, the surface indirect air cooling system
The process flow of indirect air cooling system of surface condenser is as follows: circulating water enters the water side of surface condenser, and the steam turbine exhaust on the steam side of condenser is cooled by surface heat exchange. The heated circulating water is sent to the air cooling tower by circulating water pump, and the surface heat exchange with air is carried out by air cooling radiator, and then it returns to the condenser to cool the steam turbine exhaust after air cooling, forming a closed cycle.
The indirect air cooling system with surface condenser is different from Heller's indirect air cooling system. The cooling water and steam turbine exhaust are not mixed, and the surface heat exchange can meet the requirements of large-capacity units for boiler feed water quality. The system is basically the same as the conventional wet cooling system, but the differences are that air cooling tower is used instead of wet cooling tower, stainless steel condenser is used instead of copper tube condenser, softened water is used instead of circulating water, and closed circulating cooling water system is used instead of open circulating cooling water system.
Its advantages are:
(1) Less equipment and simpler system.
⑵ The cooling water system and condensate water system are separated, and the water quality is treated according to their own standards. The cooling system adopts softened water and runs in a closed way, which basically eliminates the scaling and blockage in the condenser tube bundle and greatly improves the heat exchange efficiency.
(3) The circulating water system is in a closed state, and the circulating water pump has low lift, low power consumption and low auxiliary power.
(4) The cooling water runs completely in a closed loop, and basically does not produce water loss. Theoretically, the water consumption of the system is zero.
Its disadvantages are:
(1) cooling water must be exchanged twice, and the heat transfer effect is poor.
(2) It covers a large area. The bottom diameter of air cooling tower 143m, the outer edge diameter of radiator 15 1m, the tower height 165m, the outlet diameter of air cooling tower 92m and the throat diameter of air cooling tower 90m.
(3) The initial investment is larger than that of direct air cooling, even similar to that of boiler, mainly because of radiator. Cost of indirect cooling air-cooled radiator: ~85 yuan /m2 The total area of finned tubes of air-cooled radiator is 1803400 m2.
3. Comparison of environmental meteorological conditions between direct air cooling unit and indirect air cooling unit:
Direct air cooling: the change of air temperature will directly affect the back pressure of direct air cooling unit. When the temperature is high in summer, the back pressure of steam turbine increases, which seriously affects the safe operation of the unit. At present, the domestic direct air-cooled units are operated in summer, and the safe operation of the units is ensured by reducing the output and maintaining a relatively low back pressure.
1, the direct air cooling system is extremely sensitive to the influence of wind direction, wind speed and upstream buildings and structures on air circulation, especially under high temperature conditions, the back pressure of the steam turbine is already high, and the back pressure of the steam turbine suddenly increases due to heat reflux and poor heat dissipation caused by unfavorable wind direction, and the output of the steam turbine decreases. Under high temperature conditions, serious thermal reflux and poor heat dissipation are likely to make the back pressure of steam turbine exceed the back pressure protection limit and trip and stop. Under the strong convective weather conditions in summer, there have been many turbine trip accidents in China.
2. When the wind speed exceeds 3.0m/s, the direct air-cooling system will have a certain impact on the heat dissipation effect of the air-cooling system, especially when the wind speed reaches 5.0 ~ 6.0/s, different wind directions will form heat reflux to the air-cooling system, even reduce the fan efficiency, leading to the increase of the back pressure of the steam turbine, which will seriously affect the safe operation of the power plant.
3. When the power plant is running, the hot air discharged by the cold air through the radiator rises in a feather shape. When the strong wind blows from the back of the furnace to the platform radiator, and the wind speed exceeds 8m/s, the plume is destroyed and the hot air flows back. The updraft of hot air is dropped below the steel platform by the wind pressure behind the furnace, and such hot air is sucked by the fan in the form of hot air recirculation. Even the fans in the outermost row rotate in the opposite direction.
4. The elevation of the plant site and the atmospheric pressure of the plant site directly affect the mass flow of the direct air-cooled heat transfer medium and the shaft power of the direct air-cooled condenser axial fan. The solar radiation heat on sunny days will affect the heat transfer of direct air-cooled condenser.
Indirect air cooling: air temperature is still the main factor affecting the back pressure of indirect air cooling units. However, because the heat transfer medium in the air-cooled radiator and condenser of the air-cooled tower is water, the relative heat transfer coefficient is high, and the back pressure of the turbine in the indirect air-cooled system is lower than that in the direct air-cooled system. If the same type of steam turbine is used, its safety in summer operation is relatively high.
Compared with direct air cooling system, indirect air cooling system has less sensitivity and influence on environmental meteorological conditions. Because the indirect air cooling system generally adopts natural ventilation cooling tower, the wind direction and speed of ambient air will also have an impact on the cooling tower, but it is also obviously smaller than the direct air cooling system, and there is no hot air reflux. The elevation and atmospheric pressure of the plant site have little influence on indirect air cooling, but have influence on the area of air cooling radiator and the diameter and height of cooling tower. Radiant heat basically does not affect the heat transfer of indirect air-cooled radiator.
Four, direct air cooling unit and indirect air cooling unit water consumption and water consumption rate, feed water pump steam turbine supporting equipment, equipment power consumption, noise impact analysis, annual coal consumption, operation and maintenance of the pros and cons of comparison:
Direct air cooling
1. Wet cooling systems such as mechanical ventilation cooling tower, auxiliary engine cooling water pump and auxiliary engine cooling water pipe are used for the exhaust steam of steam-driven feed water pump of direct air cooling unit, and the water consumption per million kilowatts is about 0.141m3/s/s. 。
2. Wet cooling systems such as mechanical ventilation cooling tower, auxiliary engine cooling water pump and auxiliary engine cooling water pipe should be used for exhaust steam of feed water pump turbine of direct air cooling unit, which will increase investment cost. Due to mechanical forced ventilation, the auxiliary power consumption is slightly higher than that of indirect cooling system.
3. The noise of the large-diameter axial fan of the direct air cooling unit is about 85 dB, which may exceed the standard in some areas of the power plant boundary, but this can be solved by adopting a series of noise prevention measures such as ordinary low-noise low-speed fans and setting up virtual factory boundaries. But the investment has increased even more.
4. Comparing the direct cooling and indirect cooling of the same type of 600MW units in China, the coal consumption of direct air cooling is 3 ~ 5g higher than that of indirect air cooling, and the coal consumption of the same type of 300MW units is1.5 ~ 25,000 tons higher than that of indirect air cooling, and the annual coal consumption can be 5.25 ~ 8.75 million yuan more (the power generation utilization hours are calculated as 5,000 hours, and the coal price is calculated as 350.
5. The direct air cooling system is simple, with few equipment and uncomplicated control system, so the operation adjustment is relatively simple. The counter-current condenser and fan are used to adjust the air volume, and the air-cooled condenser tube is an oval tube with a large diameter, which is not easy to accumulate water, which is conducive to preventing equipment accidents caused by freezing in winter.
6. The direct cooling system has a huge vacuum pumping system, many large axial fans and heavy maintenance workload.
7. The operation and maintenance cost is high, but the initial investment of direct air cooling is low.
Indirect air cooling;
1. The indirect air cooling system can adopt the steam-driven feed water pump scheme, which drives the exhaust steam of the turbine of the feed water pump to directly enter the condenser, and the water consumption per million kilowatts is about 0.125m3/s.gw. Compared with the direct air cooling system, the indirect air cooling system saves about 15% of water and saves operating costs.
2. The exhaust steam of the feed water pump turbine of the indirect air cooling system is connected to the air cooling system of the main engine without additional equipment.
3. Indirect air cooling system has low noise and can generally meet the requirements of environmental protection.
4. Because the back pressure of indirect cooling system is lower than that of direct air cooling system, the coal consumption per kilowatt hour is lower, and the annual power generation benefit of indirect cooling system is higher than that of direct air cooling system.
5. Due to the addition of the intermediate cooling link, the surface condensation indirect cooling system is complicated and complicated to operate. However, the amount of equipment maintenance is small, the maintenance is convenient and the operation and maintenance cost is low. 6. The initial investment of surface indirect air cooling is large, which is 725 1 10,000 yuan more than that of direct air cooling.
Verb (abbreviation of verb) conclusion and suggestion
At present, we are not only concerned about the economy of air cooling system design optimization, but also about the safety of air cooling system. The so-called safety mainly includes two aspects: one is whether the high temperature in summer can ensure the full play of the design assessment points, and the other is the safe operation of the unit under strong wind conditions. According to the above analysis, both direct air cooling system and surface indirect air cooling system are technically feasible, and surface indirect air cooling system has certain advantages in economy. Although the investment of surface indirect air-cooling system is generally higher than that of direct air-cooling system, the coal consumption per unit kw.h is lower than that of direct air-cooling system because of the low back pressure, and the surface indirect air-cooling system has certain advantages in economy, and its advantages will increase with the increase of on-grid electricity price. Therefore, it is suggested to adopt the surface indirect cooling scheme.