It is proved that the use of small-scale power plants to operate under low-vacuum heating mode is a new energy saving and environmental protection measure that saves water, saves electricity, and saves coal. It has high economic and environmental benefits.
1 Foreword Due to the relative ease of power supply, the national energy policy has been adjusted, and the policy of closing the steam turbine generator sets with relatively high energy consumption and high pollution for a limited period of time has been adopted. In order to obtain a living space, many small power plants in the vicinity of small cities have taken the road of cogeneration, and the small coal-fired power plant with a single coal storage capacity of 6MW or less has taken advantage of the convenience conditions near the mining area. The condensing unit will be changed to a heating unit and will provide heat for the mining area during the heating period. These small pit power plants are also more energy-intensive than large- and medium-sized power plants, but they have greater advantages in terms of energy conservation and environmental protection than decentralized small-scale heating boiler houses. The more commonly used method is to change the condensing generator unit to a low-vacuum heating unit. The so-called low-vacuum heating is to reduce the degree of exhaust steam vacuum turbine operation, the corresponding increase in steam turbine, will increase the temperature after the cooling water input heating system to replace the heating system of the heating network of circulating water. The specific method is to reduce the exhaust vacuum degree of the turbine generator unit from the 933 kPa exhaust pressure at normal power generation to 8 kPa to 613 exhaust pressure 403 required for heating during the heating period, so that the condenser exhausts steam. The temperature increased from 410 to 76. In response to this, the temperature of the circulating cooling water of the steam turbine also increased from approximately 30 to approximately 65, and the temperature-increasing condenser was changed to a heat exchanger of the heating system, and the circulating cooling of the power generation process was performed. The water becomes the heat network circulating water of the heating system. The heat originally lost from the cooling tower to the atmosphere is the loss of the cold source during the power generation, and it enters the room through the radiator of the room to achieve the purpose of heating.
2 The thermal efficiency of small-scale power plants under different operating conditions is 121 or less, and the boiler parameters are medium-temperature and medium-voltage power plants. The following takes the 35MW condensing turbine unit generating power 6MW; steam inlet pressure 3.43MPa; intake steam temperature as an example to analyze the operation of small power plants. 2.1 Condensing power generation and its thermal efficiency The so-called condensing power generation of small-scale power plants means that the pressure produced by the boiler is 3.43 MPa and the superheated steam at a temperature of 435C is used. In this state, the steam enthalpy is 3304 to give people condensation. The generator set allows the steam to expand work in the steam turbine and drive the generator to generate electricity. According to the Rankine cycle principle, the lower the exhaust steam pressure discharged by the steam turbine, the higher the steam work efficiency. For this reason, condensing generators often reduce the exhaust pressure to 813, which is less than 93.33 degrees of vacuum, to discharge the condenser. Even if such a high degree of vacuum is reached, the temperature of the steam has been reduced to 41.5, and the steam enthalpy is still 2576.7. Condensation heat is 2402.8, which accounts for the steam condensing from the boiler and must condense this part of steam into water before it can be used to send water to a boiler. When this part of steam condenses into water, the heat of condensation 2402.8 is released to the condenser and taken away by the cooling water. Since the temperature of the cooling water is only around 301, it cannot be used, but has to be cooled by the cooling tower and it will circulate. Loss of water, coupled with boiler combustion losses and other heat losses, when the small-scale power plant power consumption of coal is 72,1, then the overall thermal efficiency of power plants are around 17.
2.2 Extraction steam power generation and its thermal efficiency Extraction steam power generation is to extract the steam at the pressure and temperature from the middle of the steam turbine and use it for heat production. The heat carried by this steam extracted is mainly the heat of condensation in the heat. Released and utilized in the system. At this time, although the heat of condensation of some steam is still lost from the cooling tower, the overall thermal efficiency of the power plant is still greatly improved. According to the introduction of the data, Taiwan C6350.49 type, 6MW extraction steam turbine generator sets, if the extraction of superheated steam of 0.49,250 per hour, the overall thermal efficiency of the power plant can be increased to more than 33.
2.3 Low-Vacuum Heat Supply and Its Thermal Efficiency As mentioned above, low-vacuum heating is to increase the temperature and circulate water, and the heat lost from the cold source that should have been lost to the atmosphere in the cooling tower is sent to the interior for heating. Waste heat is a useful heat; in other words, low-vacuum heat recovery recovers the loss of cold source during power generation, if the neglect of the main steam pipeline pressure loss and heat loss and the loss of mechanical losses of the generator set part of the relative cold loss ratio Small, it can be roughly assumed that the heat that steam brings out of the boiler is partly used to generate electricity, and part of it is used for heating, and it is basically used effectively. Therefore, when the low-vacuum heating is provided, the overall thermal efficiency of the power plant has almost reached the thermal efficiency of the boiler.
The thermal efficiency of a boiling boiler for a small-scale power plant that burns low-quality coal and coal gangue is about 7, and the overall thermal efficiency of the whole plant 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-pit 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 Taiwan 6 condensing condensing generator sets, the amount of heat recovered in a heating season can be calculated using the following formula = steam turbine condensing volume, vaporization latent heat heating time 3.7,1 steam turbine 1 Liaoliang two steam extraction volume masterpiece ; 2394 The lack of steam condensation heat 24,146 local winter heating hours. The average low calorific value of the local coal is 1302 for 82700. For example, the boiler efficiency is calculated according to the 69 provided by the sample. Then, for each heating season, the approximate amount of coal used can be calculated by the following formula, and the small heating boiler with an evaporation of less than 41 can be sampled. Although the indicated thermal efficiency is similar to that of the power plant boiler, the actual operation of the local small boiler is difficult to achieve the thermal efficiency provided by the sample because of the level of fuel technology of the boiler maker. Therefore, the actual amount of coal saved is far greater than the calculated value. many.
3.2 Saving water When the low-vacuum heating operation is in progress, the power generation circulating cooling water no longer enters the open cycle of the cooling tower, but enters the heating circulation system for closed circulation, reducing the evaporation loss in the cooling tower, and the loss is about 15%. On the other hand, it also reduces the amount of water used in the operation of decentralized boilers. The rated water consumption of the fast-installed boilers with a capacity of 41 evacuations is 4.5 small boilers that are compatible with the heating capacity of the 6 units. This water consumption is at least 3 per hour. 1 or more, each heating season can save a total of more than 100,000 water.
3.3 Saving electricity When running with low-vacuum heating, the cooling circulating water enters the heating network circulation system and the cooling circulating water pump stops running. This saves at least 400,000 electricity per heating season. Plus, each small boiler room stops running. The blower draught fan pumps are also quite considerable.
4 Environmental benefits of low-vacuum heating 4.1 Reducing emissions of waste As mentioned above, low-heating heat can recover about 224 calories per heating season, which is equivalent to less consumption of raw coal 282,931. Each year, less than 10,000 waste slags can be discharged. 1. The actual situation in the local area was that before the implementation of centralized heating, the heating area was less than 120,000 m2. There were 6 small boiler rooms and 541 total evaporations. The six boiler houses form six large garbage sites in the winter. Because the boiler room is within the living and working area, slag often cannot be shipped outside in time, often destroying the environment. Block traffic. If you encounter windy weather, the environment will become even worse. After the realization of low-vacuum heating, these dumps naturally disappeared. The slag of the power plant can become the raw material for the manufacture of slag bricks and cement, turning waste into treasure, which completely solves the problem of slag contamination in the area.
4.2 Reducing exhaust gas and dust emission When the low-vacuum heating is achieved, when the power plant heating replaces the decentralized furnace room heating, the boiler capacity is below the Tuenqi. The chimney height is generally below 20, and the chimney will emerge in the days without wind. Smoky smoke can not drift away in time, causing the entire mining area to be shrouded in smoke. After the realization of low-vacuum heat supply, the operation of the small boiler room was stopped, and smoke pollution caused by the small boiler room was naturally avoided. Each heating season can be less emissions of boiler flue gas 40010,13, reduce sulfur oxide emissions 1700 reduce dust emissions 25001. Because the power plant dust removal equipment is more complete, the chimney, from the mine rarely see the kind of smoky scene.
4.3 Reducing Effluent Emissions In the case of distributed heat supply in small boiler rooms, each boiler house has a water treatment facility that uses salt for regeneration. Due to the small equipment, the technical level of workers is uneven, the utilization of raw water in the water treatment process is low, and the consumption of salt is large, causing relatively large pollution to the environment. With the suspension of the operation of these small boiler rooms, the pollution of this part of the wastewater was subsequently solved.
5. Presence 5.1 Water Supply Temperature is Low and Subheating is Required As mentioned above, when low vacuum heating is performed, the temperature of the circulating water of the heating network is the temperature of the circulating cooling water, and its level depends on the exhaust temperature of the turbine and the operation of the condenser. The situation, while most of the small-scale power plants operating under low-vacuum heating, the steam turbine exhaust temperature is generally less than 76, so the heat network circulating water temperature is also the most about 65, can only meet the basic needs of heating, to the middle of the year In the coldest months, the heating network circulating water must be heated again. For the original thermal power plant with external heating, the original heating system can be used to sub-heat the circulating water of the heating network; for the original pure condensing power plant, when the low-vacuum heating reconstruction is realized, the secondary heating system needs to be considered at the same time.
5.2 The theoretical basis is insufficient, with blindness For the condensate generators below 6 rivers, the original operating rules stipulate that when the normal power generation, when the condenser vacuum is reduced to 61.3 to set the exhaust pressure 40, it is necessary to take corresponding reasons. Measures, otherwise emergency stop. It is also noted that the temperature of the rear cylinder of the steam turbine should not exceed 70. The low vacuum heating operation mode is operated in the abnormal state of the steam turbine. When the general power plant operates in the low vacuum heat supply, the steam turbine vacuum level is maintained at 61.3 exhaust pressure. 40 spit, the rear cylinder temperature is about 76; of course, there are also the vacuum is maintained at 40 set 8 exhaust pressure 61.33, rear cylinder temperature is about 86. The actual operation also has a lower vacuum and a higher rear cylinder temperature. In the end, the degree of vacuum control is more appropriate, and all units are based on their own experience and there is no sufficient theoretical basis. For the safe operation of steam turbines, all use units should contact the original manufacturer to calculate the minimum vacuum for their safe operation on the premise of ensuring the safety of the steam turbine in order to avoid major accidents.
In summary, the use of small-scale power plants for low-vacuum heating and heating is a new energy saving and environmental protection measure that saves water, saves electricity, and saves coal. It has very good economic and environmental benefits.
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