New Measures for Energy Saving and Environmental Protection——Discussion on Low Vacuum Heating of Small Condensing Turbine Generator Sets
It proves that the use of low-vacuum heating operation mode heating in small power plants is a new energy-saving and environmental protection measure that saves water and saves electricity and saves coal. It has high economic and environmental benefits.
1 Introduction As the current power supply is relatively moderate, the national energy policy has been adjusted, and a small-scale condensing steam turbine generator set with high energy consumption and high pollution has adopted a policy of closing deadlines. In order to obtain a living space, many small power plants in the vicinity of small cities are taking the road of cogeneration, and the small-scale power plant with a single-machine capacity of 6 MW or less in the coal system takes advantage of the convenient conditions near the mining area. The condensing unit is changed to a heating unit to supply heat to the mining area during the heating period. Compared with large and medium-sized power plants, these small pit-mouth power plants have large energy consumption and large pollution. However, compared with the scattered small-scale heating and heating boiler houses, they have great advantages in energy conservation and environmental protection. The more commonly used method is to change the condensing generator set to a low vacuum heating unit. The so-called low-vacuum heating is to reduce the steam exhausting degree of the steam turbine operation, and correspondingly increase the degree of steam turbine. The circulating cooling water after the temperature is increased is input into the heating system to replace the heating network circulating water of the heating system. The specific method is to reduce the steam exhausting degree of the steam turbine generator set from the 933 kPa exhaust steam pressure during normal power generation to 8 kPa exhaust steam pressure 403 required for heating, so that the steam in the condenser is exhausted during the heating period. The temperature is increased from 410 to 76. In accordance with this, the temperature of the circulating cooling water of the steam turbine is also increased from about 30 to about 65. After the temperature is raised, the condenser becomes a heat exchanger of the heating system, and the cooling process of the power generation process is performed. The water becomes the heat network circulating water of the heating system. The heat that was lost from the cooling tower to the atmosphere, that is, the heat source loss during power generation, enters the room through the indoor radiator to achieve the purpose of heating.
2 The thermal efficiency of small power plants under different operating conditions is below 121, and the boiler parameters are medium-temperature and medium-voltage power plants. In the following, the power generation of the 35-type condensing steam turbine generator set is 6MW; the inlet steam pressure is 3.43MPa; and the inlet steam temperature is taken as an example to analyze the operation of the small power plant. 2.1 Condensing power generation and its thermal efficiency The so-called small-scale power plant condensing power generation refers to the superheated steam produced by the boiler with a pressure of 3.43 MPa and a temperature of 435 C. The steam enthalpy of this state is 3304 to give people a condensing steam. The generator set expands the steam in the steam turbine to drive the generator to generate electricity. According to the Rankine cycle principle, the lower the steam pressure discharged by the turbine, the higher the steam work efficiency. To this end, the condensing generator set often reduces the exhaust pressure to 813, that is, the vacuum of 93.33 or less before discharging the condenser. Even if such a high vacuum is reached, the steam temperature has been reduced to 41.5, and the steam enthalpy is still 2576.7. The condensation heat is 2402.8, which accounts for the steam from the boiler. It is necessary to condense this part of the steam into water, so that the feed water pump can be used to deliver the boiler. When this part of the steam condenses into water, the condensation heat 2402.8 will be released in the condenser and taken away by the cooling water; because the temperature of the cooling water is only about 301, it cannot be utilized, and it has to be cooled by the cooling tower. Loss of water, coupled with boiler combustion losses and other heat losses, when the power consumption of small power plants is 72,1, the overall thermal efficiency of the power plant is around 17.
2.2 Extraction steam power generation and its thermal efficiency extraction steam power generation is to extract steam from the middle of the steam turbine and use it for thermal production. The heat carried by this part of the steam is mainly the heat of condensation. Released and utilized in the system. At this time, although some of the steam condensation heat is lost from the cooling tower, the overall thermal efficiency of the power plant is greatly improved. According to the data, Taiwan C6350.49 type, 6MW extraction steam turbine generator set, if the superheated steam of 0.49,250 is extracted every hour 20, the overall thermal efficiency of the power plant can be increased to 33 or more.
2.3 Low-vacuum heating and its thermal efficiency As mentioned above, low-vacuum heating is to increase the temperature of the circulating water, the heat loss from the cold source that should be lost to the atmosphere in the cooling tower, and send it to the room for heating and changing. Waste heat is a useful heat; in other words, low-vacuum heat recovery recovers the loss of cold source during power generation. If the pressure loss and heat loss of the main steam pipeline and the mechanical loss of the generator set are neglected, the relative loss of the cold source is extremely high. Small, it can be roughly considered that the heat that steam brings out from the boiler, partly used for power generation, and partly used for heat supply, is basically used effectively. Therefore, when low vacuum heating, the overall thermal efficiency of the power plant is almost close to the thermal efficiency of the boiler.
The boiling boiler of a small power plant that burns inferior coal and coal gangue has a thermal efficiency of about 7, and the overall thermal efficiency of the whole plant from condensing steam can exceed 60, which is about 4 times the overall efficiency of a pure condensing power plant. .
3 Energy-saving benefits of low-vacuum heating The raw materials of a pit-mouth power plant in northern Hebei Province are used to illustrate the energy-saving and environmental benefits of low-vacuum heating.
3.1 Reducing resource consumption The 6-thickness condensing steam generator set can recover the heat recovered in the heating season by the following formula = steam condensing capacity, vaporizing latent heat heating time 3.7, 1 steam turbine 1 Liao two-level steam extraction masterpiece 2394 condensed heat of steam, 24,146 local winter heating hours. The average calorific value of local coal is 1302 for 82700. If the boiler efficiency is calculated according to 69 provided by the sample, the coal consumption in each heating season can be calculated by the following formula, and the small heating boiler with evaporation less than 41 is sample. Although the indicated thermal efficiency is similar to that of the power plant boiler, when the local dispersed small boiler is actually running, it is difficult to achieve the thermal efficiency provided by the sample due to the technical grade of the boiler, etc., so the actual saved coal is much larger than the calculated value. many.
3.2 Water saving During low-pressure heating operation, the cooling water of the power generation cycle no longer enters the open cycle of the cooling tower, but enters the heating circulation system for closed circulation, which reduces the evaporation loss in the cooling tower. The loss is about 15 On the other hand, it also reduces the amount of water used in the operation of the decentralized boiler. The amount of water in the boiler is 41. The rated boiler water consumption is 4.5. The small boiler group with the heating capacity of the 6 units is at least 3 per hour. , 1 or more, each heating season can save more than 100,000 water.
3.3 Saving electricity When the low-pressure heating operation is running, the cooling circulating water pump stops running because the cooling circulating water enters the heating network circulation system, so that at least 400,000 electricity is saved in each heating season. In addition, each small boiler room stops running. The blower pump of the blower is also very impressive.
4 Environmental Benefits of Low Vacuum Heating 4.1 Reducing Waste Discharges As mentioned above, low vacuum heating can recover about 224 calories per heating season, which is equivalent to less consumption of raw coal 282931. According to the local raw coal containing rate of 42, The annual discharge of waste slag is more than 10,000. 1. The original actual situation is that before the implementation of centralized heating, the heating area is less than 120,000 m2, there are 6 small boiler rooms, and the total evaporation is 541. These six boiler houses form six large garbage spots in winter. Since the boiler room is located in the living office area, the slag is often not transported in time, often damaging the environment. Block traffic. If you encounter windy weather, the environment becomes even worse. After achieving low vacuum heating, these garbage dumps are naturally eliminated. The slag of the power plant can be used as a raw material for the manufacture of slag bricks and cement, turning waste into treasure, thus completely solving the problem of slag pollution in the place.
4.2 Reducing exhaust gas and dust emission After low vacuum heating, when the power supply of the power plant replaces the heating of the distributed furnace room, the boiler capacity is as follows. The height of the chimney is mostly below 20, and in the days when there is no wind, the chimney emerges. Black smoke could not drift away in time, causing the entire mine area to be covered in smoke. After the realization of low vacuum heating, the operation of the small boiler room was stopped, and naturally, the smoke pollution caused by the small boiler room was avoided. Each heating season can discharge less boiler flue gas 40010,13, reduce sulphur oxide emissions 1700 and reduce dust emissions 25001. Since the power plant dust removal equipment is relatively perfect, the chimneys, from this mine area, rarely see the smog.
4.3 Reducing Wastewater Discharge In the small boiler room, when there is decentralized heating, each boiler room has a set of water treatment equipment, which is recycled by salt. Due to the small equipment, the technical level of workers is uneven, the utilization rate of raw water in the water treatment process is low, the consumption of salt is large, and the environment is relatively polluted. With the shutdown of these small boiler houses, the pollution of this part of the wastewater was solved.
5There is a problem. 5.1 The water supply temperature is low, and the secondary heating is required. As mentioned above, when the low vacuum heat is supplied, the temperature of the circulating water of the hot network is the temperature of the cooling circulating water, and its level depends on the steam exhaust temperature of the steam turbine and the operation of the condenser. The situation, while most of the small power plants under low vacuum heating operation, the steam exhaust steam temperature is set below 76, so the temperature of the hot network circulating water is about 65, which can only meet the basic needs of heating, in the middle of the year. In the coldest months, the hot water circulating water must be heated twice. For the thermal power plant that originally had external heating, the original heating system can be used to heat the circulating water of the heating network; for the original pure condensing power plant, when implementing the low vacuum heating transformation, it is necessary to consider the secondary heating system at the same time.
5.2 The theory is based on the lack of blindness. For the condensing generators below 6 rivers, the original operating regulations stipulate that when the power generation of the condenser is reduced to 61.3, the steam pressure is reduced to 40. Measures, otherwise emergency stop. It is also noted that the temperature of the rear cylinder of the steam turbine should not exceed 70. The operation mode of the low vacuum heating is to operate under the abnormal state of the steam turbine. When the power plant is operating under low vacuum, the steam pressure of the turbine is maintained at 61.3. 40 spit, the rear cylinder temperature is around 76; of course, there is also a vacuum of 40 to 8 exhaust pressure 61.33, the rear cylinder temperature of 86 or so. In actual operation, there is also a case where the degree of vacuum is lower and the temperature of the rear cylinder is higher. In the end, the degree of vacuum control is more appropriate. Each unit is based on its own experience and there is not enough theoretical basis. In order to operate the turbine safely, each user unit should contact the original manufacturer. Through theoretical calculations, the minimum vacuum of each safe operation should be determined on the premise of ensuring the safety of the turbine to avoid major accidents.
In summary, the use of low-vacuum heating and heating in small power plants is a new energy-saving and environmental protection measure that saves water and saves electricity and saves coal. It has very good economic and environmental benefits.
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