JP4371959B2 - Heating deaerator for boiler - Google Patents

Description

  The present invention relates to a boiler degassing apparatus that heats and pressurizes boiler water and removes dissolved oxygen in the boiler water by flashing under reduced pressure.

  If the water supplied to the boiler contains dissolved oxygen, it causes corrosion in the boiler, so deaerated water from which dissolved oxygen has been removed is supplied. As a degassing device for removing dissolved oxygen, a flash type degassing device as described in JP-A-11-337209 has also been known. The flash type deaerator is configured to take out deaerated water by heating and pressurizing boiler water, flushing the boiler water by a pressure drop, and separating and discharging dissolved oxygen. The boiler water can be heated by installing a deaeration heat exchanger in the exhaust gas passage through which the high-temperature exhaust gas passes, and feeding the boiler water into the deaeration heat exchanger.

In the case of Japanese Patent Application Laid-Open No. 11-337209, most of the condensate discharged from the steam turbine is heated to a high temperature with exhaust gas, and then the pressure is reduced with a pressure reducing valve to deaerate and supply to the deaerator. At this time, it is described to cool and condense the vapor in the deaerator by injecting the remaining condensate (minimum amount) into the deaerator without heating. Further, examples of the temperature after heating are 120 ° C. to 150 ° C., and examples of the pressure upstream and downstream of the pressure reducing valve are 9.9 × 10 ³ hpa (0.99 MPa), 3.5 × 10 ³ hpa (0 .35 MPa).

  When boiler water is heated using the heat of exhaust gas, if the amount of heat absorption in the deaeration heat exchanger is increased to increase the boiler water temperature at the inlet of the deaeration unit, heat exchange for deaeration There is a problem that the cost of the vessel and the pressure loss on the exhaust gas side increase. Further, when the boiler water pressure at the inlet of the deaeration unit increases, there is a problem that the cost of the pump, the reliability of the piping, and the electricity cost increase.

JP-A-11-337209

  The problem to be solved by the present invention is to provide a heating and deaeration device for a boiler that can prevent the increase in cost and can effectively deaerate.

  The invention described in claim 1 includes a degassing heat exchanger for heating boiler water, a depressurizing unit for generating flash steam by depressurizing the heated and pressurized boiler water, and boiler water degassed by flash steam generation. A degassing water tank to be stored and a water supply tank for collecting boiler water before being sent to the degassing heat exchanger are provided, water is passed from the water supply tank to the degassing heat exchanger, and heated by the degassing heat exchanger. In the boiler degassing device that removes dissolved oxygen from the boiler water by flushing the degassed boiler water, a part of the degassed water is removed by connecting the degas water tank and the water supply tank with a communication pipe. It is designed to return from the water tank to the water supply tank, and from the water supply tank to the deaeration heat exchanger is continuously supplied with water that is 1.1 to 2 times the rated output of the boiler. Deaerate While continuing to recirculate from the water tank to the water supply tank, the water temperature of the boiler water at the inlet of the pressure reducing section is 103 ° C. to 115 ° C., the water pressure is 0.03 MPaG to 0.4 MPaG, and the pressure in the deaerated water tank is atmospheric pressure. It is characterized by being adjusted.

  According to a second aspect of the present invention, in the boiler degassing apparatus, a flash steam channel for discharging flash steam is connected to the deaerated water tank, and the boiler water is disposed in the middle of the flash steam channel. A heat recovery heat exchanger for exchanging heat with the heat exchanger is provided.

  According to a third aspect of the present invention, in the boiler degassing apparatus, the steam valve for shutting off the steam supply to the steam use location side in the middle of the steam supply pipe for sending the steam generated in the boiler to the steam use location side When the water temperature or water pressure at the inlet of the pressure reducing unit is lower than a predetermined range, the steam supply to the steam use location side is stopped until the steam pressure in the boiler reaches the predetermined pressure. .

  According to a fourth aspect of the present invention, in the boiler degassing apparatus, a path for supplying boiler water (a path from a raw water path for supplying water to a water supply tank to a deaerated water tank including a water supply tank and a deaerated water tank) A heater for heating the boiler water is provided in the middle, and when the water temperature or water pressure at the inlet of the pressure reducing unit is lower than a predetermined range, the boiler water is used by combining the heating with the heater. It is characterized by promoting deaeration.

  By implementing the present invention, the following effects can be obtained. Since the water temperature at the inlet of the pressure reducing unit is optimized, it is possible to prevent an increase in the cost of the deaeration heat exchanger and the pressure loss on the exhaust gas side. Since the water pressure at the inlet of the pressure reducing unit is optimized, the cost of the deaeration pump and the increase in the electricity bill can be prevented, and the reliability against water leakage from the piping and the like is increased. Since the decompression section outlet is substantially at atmospheric pressure and the inside of the deaeration water tank is at atmospheric pressure, the deaeration water tank does not have to be pressure-resistant and hermetically sealed. Temperature and pressure can be reduced.

  The continuous water supply from the water supply tank to the deaeration heat exchanger and the flow rate of continuous water supply are increased from the boiler's rated water supply to 1.1 to 2 times, so the amount of heat recovered from the exhaust gas is larger. Become. The deaeration water tank and the water supply tank are connected by a communication pipe, and the deaeration water tank is circulated by the difference between the flow rate of continuous hot water supply from the deaeration water tank to the water supply tank and the rated water supply amount of the boiler. So you can preheat the water in the water tank. Thereby, even when the temperature of the water supply tank and the water supply is low, the water temperature at the inlet of the pressure reducing unit can be more reliably and quickly set to a predetermined value. The supply water is supplied substantially from the deaeration water tank that stores deaerated water, and the boiler does not contain the high concentration of dissolved oxygen in the feed water before deaeration, so the dissolved oxygen concentration of the water supplied to the boiler There is no rise.

  In addition, the boiler water cannot be sufficiently heated at the time of start-up, the period during which deaeration is insufficient can be shortened, and the supply of water having a high dissolved oxygen concentration can be minimized.

  In order to prevent corrosion of each part of the boiler for a long period of time, it is preferable to set the corrosion rate of each part of the boiler to about 10 mdd level or less. In this case, in order not to exceed this corrosion rate due to the dissolved oxygen concentration in the boiler water, it is known that the average dissolved oxygen concentration in the boiler water is preferably about 0.3 mg / L or less. .

  The pressure in the deaerated water tank is atmospheric pressure. For example, a flash steam channel for discharging flash steam is connected to the deaerated water tank, and a pressure control valve for adjusting the pressure in the deaerated water tank is provided in the middle of the flash steam channel. Adjust the pressure inside the water tank to atmospheric pressure. However, the pressure control valve may be omitted. In addition, it is a preferable example that a heat recovery heat exchanger is provided in the middle of the flash steam flow path and the heat of the water vapor generated by the flash is used for preheating the feed water.

  The heat exchanger for deaeration is designed so that the inlet temperature of the decompression section is 103 ° C to 115 ° C. If it is less than 103 degreeC, deaeration is insufficient and dissolved oxygen concentration becomes high and the objective of corrosion prevention cannot be achieved. If it exceeds 115 ° C, the cost of the heat exchanger for deaeration and the pressure loss on the exhaust gas side become excessive. More preferably, it is 105 ° C or higher. In this case, even if an unsteady state such as a decrease in exhaust gas temperature or a decrease in exhaust gas amount occurs during operation, the dissolved oxygen concentration can be stably maintained at a necessary level. More preferably, it is 110 degrees C or less. In this case, the cost of the heat exchanger for deaeration and the pressure loss on the exhaust gas side can be further reduced.

  As a control of the pressure reducing part inlet temperature, it is a preferable method to use a flow rate adjusting valve (pressure reducing valve) in the pressure reducing part and control the flow rate by a signal of the inlet temperature of the pressure reducing part. In addition, a throttle may be separately provided on the downstream side of the flow rate adjustment valve as the pressure reducing unit. Further, the pressure reducing unit may be configured only by the throttle without using the flow rate adjusting valve for controlling the pressure reducing unit inlet temperature. It is also possible to use the discharge nozzle in the deaerated water tank as a throttle and use it as a decompression unit.

  There may be a plurality of flash nozzles for discharging boiler water into the deaerated water tank. A nozzle having a small nozzle diameter and a large number is preferable because dissolved oxygen is easily released into the atmosphere.

  The pressure reducing part is designed so that the water pressure at the inlet of the pressure reducing part is 0.03 MPaG to 0.4 MPaG. If the water pressure is less than 0.03 MPaG, degassing is insufficient and the dissolved oxygen concentration increases, increasing the risk of not achieving the purpose of preventing corrosion. If the water pressure exceeds 0.4 MPaG, the cost and electricity cost of the deaeration pump will increase. There is also a problem from the viewpoint of reliability against water leakage from pipes and the like. More preferably, 0.05 MPaG to 0.3 MPaG. Even if an unsteady state such as a decrease in exhaust gas temperature or a decrease in the amount of exhaust gas occurs during operation, the dissolved oxygen concentration can be stably maintained at a required level, and costs can be reduced.

  At the start-up of equipment that generates exhaust gas (for example, a gas engine or a gas turbine), the temperature of the deaeration heat exchanger is low, so that the boiler water cannot be heated sufficiently. Further, at the time of start-up, the temperature of the deaerated water tank is generally low and the dissolved oxygen concentration is high. Even at the initial stage of startup, steam is generated in the boiler, and a water supply request is issued when the water level of the can water drops due to the removal of the steam. In a state where the dissolved oxygen concentration in the degassed water tank is high, it is preferable to avoid or delay the water supply request from the viewpoint of avoiding water supply with a high dissolved oxygen concentration. As the preferable method, the following means are possible.

  (1) A back pressure valve is provided at the outlet to the steam supply pipe for taking out the steam generated in the boiler. As a result, the steam supply to the steam supply pipe at the initial stage of startup is stopped until the steam pressure in the boiler becomes equal to or higher than the set pressure of the back pressure valve (for example, a pressure within the range of 0.4 MPaG to 0.78 MPaG). it can. Thereby, the fall of the water level in a can can be delayed, and it becomes possible to use the vapor | steam which generate | occur | produced at the initial stage of starting as a heat source for heating deaeration.

  (2) A heater for heating the boiler water is provided in the course of supplying the boiler water. Providing a heater in the deaerated water tank and directly heating it is a preferable method because the water immediately before being supplied to the boiler is heated and deaerated. Moreover, the method of directly putting the steam generated in the boiler into the deaerated water tank is a simple and preferable method. When providing a water supply tank, you may provide a heater in a water supply tank. The heater may be installed at the inlet or outlet of the deaeration heat exchanger, and the temperature at the inlet of the decompression unit may be raised to the deaeration set value. The heater for heating and degassing at the initial stage of startup may be either a steam heater or an electric heater.

  The deaeration pump is selected so that the flow rate for continuous water supply is 1.1 to 2 times the boiler's rated water supply. If it is less than 1.1 times, the amount of heat recovered from the exhaust gas will be small, and if the amount of steam used in the load increases and there is a demand for water supply that exceeds the rating, the deaerated water will be insufficient (the water level of the deaerated water tank is the lower limit). The risk increases. Exceeding twice the rated water volume increases the risk that the outlet temperature of the deaeration heat exchanger will not rise to the preferred range, the capacity of the deaeration pump increases unnecessarily, and piping for the boiler water flow path In addition, the depressurization unit and the flush nozzle size in the deaerated water tank become unnecessarily large, and other disadvantages occur.

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing the flow of water supply in the test facility of the example. The boiler 1 absorbs the heat of exhaust gas generated by a gas engine (for example, JMS208 332 kW 60 Hz fuel natural gas 13A approximately 83 m ³ h manufactured by Yenbach) and generates steam by the heat of the exhaust gas (for example, a once-through boiler manufactured by Samsung). With economizer). In the case of the above equipment, the exhaust gas temperature at the exhaust gas boiler inlet during gas engine rated operation was 495 ° C. Exhaust gas generated from an exhaust gas generation source (not shown) is discharged through the exhaust gas passage 2, and the exhaust gas passage 2 is provided with a boiler 1, an economizer 14, and a deaeration heat exchanger 13 in order from the upstream side. ing. In addition, two tanks including a water supply tank 10 and a deaerated water tank 7 are provided, both tanks are kept warm, and the two tanks are connected by a communication pipe 6.

  Boiler water to be supplied to the boiler 1 is first stored in the water supply tank 10 through the raw water flow path 22. A deaeration channel 5 is connected to the lower part of the water supply tank 10, and the other end of the deaeration channel 5 is connected to a flash nozzle 8 in the deaeration water tank 7. A degassing heat exchanger 13 is provided in the middle of the degassing flow path 5, and the boiler water is heated by the degassing heat exchanger 13. A water flow rate adjusting valve 17 and a deaeration pump 9 are provided between the water supply tank 10 and the deaeration heat exchanger 13, and a thermometer 11 and a pressure gauge are provided between the deaeration heat exchanger 13 and the flash nozzle 8. 12. A pressure reducing valve 18 is provided. The amount of boiler water sent by the deaeration pump 9 is adjusted by a water flow rate adjusting valve 17 and a pressure reducing valve 18. The flash nozzle 8 has a structure in which a plurality of small holes are provided in the lower part of the horizontal pipe in the deaerated water tank 7.

  A deaerated water channel 23 is connected to the lower part of the deaerated water tank 7, and the other end of the deaerated water channel 23 is connected to the boiler 1. A boiler pump 4 and an economizer 14 are provided in the middle of the deaerated water passage 23, and the deaerated water is preheated by the economizer 14 and then supplied to the boiler 1. The steam generated in the boiler 1 is supplied to a steam use location (not shown) through a steam supply pipe 15, and a back pressure valve 20 is provided at an outlet portion to the steam supply pipe 15. The back pressure valve 20 is set so that the steam pressure becomes 0.78 MPaG, thereby substantially eliminating the water supply requirement until the same set pressure is reached.

  A flash steam channel 16 is connected to the upper portion of the deaerated water tank 7, and heat recovery heat exchange is performed in the middle of the flash steam channel 16 to heat the raw water flowing through the raw water channel 22 with the heat of the flash steam. A pressure regulating valve 19 for regulating the pressure of the vessel 3 and the deaerated water tank 7 is provided.

  A heater 21 is provided in the deaerated water tank 7. The heater 21 is for performing heat degassing instead when the flash degassing cannot be performed, such as at the initial start of a gas engine (not shown). By operating the heater 21 when the dissolved oxygen concentration in the deaerated water tank 7 is high, the water temperature in the deaerated water tank 7 is raised and the dissolved oxygen is removed.

  When a gas engine (not shown) is performing a rated operation, the boiler inlet exhaust gas temperature is 495 ° C., and the exhaust gas heats the boiler 1, the economizer 14, and the deaeration heat exchanger 13 in this order. During operation of the gas engine and the boiler 1, the deaeration pump 9 is continuously operated, and the boiler water stored in the water supply tank 10 is sent to the deaeration heat exchanger 13. In the deaeration heat exchanger 13, the boiler water is heated and the pressure is increased. The temperature and pressure of the boiler water are detected by a thermometer 11 and a pressure gauge 12 provided in front of the pressure reducing valve 18, and the water pressure at the inlet of the pressure reducing valve 18 is detected by both the water flow rate adjusting valve 17 and the pressure reducing valve 18. Adjust temperature and flow rate. The boiler water passing through the pressure reducing valve 18 is reduced in pressure by the restriction of the pressure reducing valve 18, but the temperature does not change, and thus flash steam is generated. The flash steam is injected from the flash nozzle 8 to separate dissolved oxygen, and the deaerated water after the separation is accumulated in the deaerated water tank 7.

  The rated output of the boiler 1 is 0.28 t / h, and since the blow in the boiler was not performed during the test, the amount of water supply and the amount of steam generated are almost the same. When the water level in the boiler 1 is lowered due to the steam generated by the boiler 1, the deaerated water stored in the deaerated water tank 7 by operating the boiler pump 4 is sent through the deaerated water channel 23. Water is supplied to the boiler 1 after preheating with the economizer 14.

  Since the amount of boiler water that is continuously supplied to the deaerated water tank 7 is larger than the amount of water supplied from the deaerated water tank 7 to the boiler 1, some of the deaerated water passes through the communication pipe 6. It returns to the water supply tank 10 through it. Since the deaerated water returning to the water supply tank 10 is high in temperature and has a low dissolved oxygen concentration, an effect of increasing the temperature of boiler water stored in the water supply tank 10 and an effect of reducing the dissolved oxygen concentration are obtained. It is done.

  The flash steam generated in the deaerated water tank 7 is sent to the heat recovery heat exchanger 3 through the flash steam flow path 16, and the heat recovery heat exchanger 3 also preheats the boiler water. .

Example 1
Gas engine rated operation, continuous feed water flow rate of 0.4t / h by deaeration pump, feed water temperature 60 ° C, deaeration water tank pressure atmospheric pressure, flash by changing decompression part inlet temperature and decompression part inlet pressure The dissolved oxygen concentration of deaerated water was measured. FIG. 2 shows dissolved oxygen concentrations when the inlet temperature of the decompression section is 101 ° C., 102 ° C., 105 ° C., 107 ° C., 110 ° C., 115 ° C., and 120 ° C. FIG. 3 shows the dissolved oxygen concentration when the pressure in the decompression section is 0.01 MPaG, 0.03 MPaG, 0.1 MPaG, 0.2 MPaG, 0.3 MPaG, and 0.5 MPaG.

  It was found that the dissolved oxygen concentration rapidly increased when the pressure at the inlet of the decompression part was lower than 103 ° C., and the decrease in dissolved oxygen concentration was small even when the temperature was increased to 115 ° C. or higher. It was also found that the dissolved oxygen concentration increased rapidly when the pressure at the inlet of the decompression part was less than 0.03 MPaG, and the decrease in dissolved oxygen concentration was small even when the pressure was increased to 0.4 MPaG or more.

Example 2
The flow rate of continuous feed water is set to 0.28 t / h (same as the rated output of steam) and 0.8 t / h (about 2.9 times the rated output of steam). An attempt was made to measure the dissolved oxygen concentration of flash degassed water at a pressure of 0.15 MPa. The other conditions were the same as in Example 1. However, when the flow rate of the continuous water supply was 0.28 t / h and 0.8 t / h, the pressure at the inlet of the pressure reducing part did not reach 110 ° C., so the measurement was stopped. As a result of measuring the water temperature in the water supply tank at this time, the average temperature was 60 ° C. when the flow rate of continuous water supply was 0.28 t / h and 85 ° C. when the flow rate was 0.8 t / h. Since the average temperature of the water supply tank in Example 1 where the flow rate of continuous feed water is 0.4 t / h was 71 ° C., the reason that the inlet temperature of the decompression section did not reach 110 ° C. was that the flow rate was 0.28 t / h. This is because the temperature inside the water supply tank 10 is too low, and when the flow rate is 0.8 t / h, the flow rate is too high.

The flow figure which showed the flow of the water supply in the test equipment of the Example of the present invention The graph which showed the decompression part entrance temperature and dissolved oxygen concentration in an example The graph which showed the pressure reduction part inlet pressure and dissolved oxygen concentration in an Example

Explanation of symbols

1 boiler
2 Exhaust gas passage
3 Heat exchanger for heat recovery 4 Boiler pump
5 Flow path for deaeration
6 Communication pipe
7 Deaerated water tank 8 Flash nozzle 9 Deaeration pump 10 Water supply tank 11 Thermometer
12 Pressure gauge 13 Heat exchanger for deaeration 14 Economizer 15 Steam supply pipe
16 Flash steam channel 17 Water flow rate control valve 18 Pressure reducing valve 19 Pressure control valve 20 Back pressure valve 21 Heater 22 Raw water channel 23 Deaerated water channel

Claims (4)

A deaeration heat exchanger that heats boiler water, a depressurization unit that generates flash steam by depressurizing heated and pressurized boiler water, a deaeration water tank that accumulates boiler water degassed by flash steam generation, and the deaeration Prepare a water supply tank to store boiler water before sending it to the heat exchanger, pass water from the water supply tank to the heat exchanger for deaeration, and flush the boiler water heated by the heat exchanger for deaeration In the boiler heating deaerator that removes dissolved oxygen from the boiler water, a part of the deaerated water is returned from the deaerated water tank to the water tank by connecting the deaerated water tank and the water tank through a communication pipe. In this way, water that is 1.1 to 2 times the rated output of the boiler is continuously supplied from the water supply tank to the heat exchanger for deaeration, and a part of the deaerated water is transferred from the deaeration water tank to the water supply tank. While continuing to reflux, the temperature of the boiler water at the inlet of the pressure reducing section is 103 ° C. to 115 ° C., the water pressure is 0.03 MPaG to 0.4 MPaG, and the pressure in the deaerated water tank is adjusted to atmospheric pressure. Heating deaerator for boiler The boiler degassing apparatus according to claim 1, wherein a flash steam passage for discharging flash steam is connected to the deaeration water tank, and heat is exchanged with the boiler water in the middle of the flash steam passage. A heat deaerator for a boiler, wherein a heat exchanger for heat recovery is provided. The boiler degassing apparatus according to claim 1 or 2, wherein a steam valve for shutting off the steam supply to the steam use location side is provided in the middle of the steam supply pipe for sending the steam generated in the boiler to the steam use location side. In addition, when the water temperature or water pressure at the inlet of the pressure reducing unit is lower than a predetermined range, the steam supply to the steam use location side is stopped until the steam pressure in the boiler reaches a predetermined pressure. Heat deaerator. The boiler degassing apparatus according to any one of claims 1 to 3, wherein a heater for heating the boiler water is provided in the middle of a path for supplying the boiler water, and the water temperature or water pressure at the inlet of the decompression unit is predetermined. When the temperature is lower than the above range, the boiler degassing apparatus is characterized in that the degassing of the boiler water is promoted by using the heating by the heater together.

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