JPH0323637B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a water treatment method for an ultra-supercritical thermal power plant, and particularly to a method for preventing corrosion products from adhering to water supply system equipment, piping, etc. of an ultra-supercritical thermal power plant. [Background of the Invention] In recent years, demands for improving the efficiency of thermal power plants have become stronger due to the recent soaring price of fossil fuels (the price of oil was more than 20 times higher around the 1970s) and the problem of depletion of oil resources. For this reason, in order to improve efficiency, the existing supercritical pressure thermal power plant (steam conditions: 538℃, 246℃
There is an urgent need to develop an ultra-supercritical thermal power plant with steam conditions that are higher in temperature and pressure than those in Japan (Kg/cm ² ). Most of the system equipment, piping, etc. in conventional supercritical pressure thermal power plants and other power plants are made of steel. Also, high purity water is used as the circulating medium. However, in order to further prevent corrosion of the constituent materials, the PH and Fe content of the feed water is analyzed and measured at the inlet of the economizer, and based on the measured values, a trace amount of a chemical (NaOH , Na ₃ PO ₄ , Na ₂ HPO ₄ , NH ₄ OH,
By injecting N ₂ H ₂ ), the water supply is made alkaline to prevent corrosion of system equipment and piping. However, power plants are exposed to corrosion products (Fe ₃ O ₄ , γ-
Fe ₂ O ₃ , etc.) adheres to the inner surface of boiler water wall tubes, turbines, high-pressure feed water heaters, feed water flow meters, etc. If it adheres, it can cause various problems such as (1) pipe overheating, (2) reduced turbine output, (3) pump overload due to increased differential pressure, and (4) inappropriate flowmeter indication. However, there are drawbacks such as the fact that corrosion products must be removed by pickling, jet cleaning, etc. FIG. 1 shows the relationship between the feed water temperature and the amount of corrosion products deposited in a supercritical pressure thermal power plant. Figure 1 shows that the amount of corrosion products deposited increases as the feed water temperature increases, especially at temperatures above 250°C. Figure 2 shows that when the Fe concentration is kept constant in the laboratory, The relationship between and the amount of Fe deposited is shown. In the experiment, carbon steel was placed in a sample rotating overclave, Fe concentration was 100 ppm, dissolved oxygen was 10 ppb or less, flow rate was 2.4 m/s, pH was 9.3, and temperature was
The Fe adhering to carbon steel was
The amount was measured. As shown in Figure 2, Fe begins to adhere at around 150°C, and increases rapidly above 200°C. This tendency is similar to that of the actual plant shown in FIG. Furthermore, since the temperature and pressure in ultra-supercritical thermal power plants are significantly higher than in supercritical thermal power plants, the temperature of the feed water in supercritical thermal power plants is around 150℃ at the high-pressure water supply inlet. The temperature of the feed water at the inlet of the economizer is around 280°C, but the temperature of the feed water in an ultra-supercritical thermal power plant is over 200°C at the inlet of the high-pressure water supply, which is higher than that in a supercritical thermal power plant even at the inlet of the economizer. Therefore, in ultra-supercritical thermal power plants, a large amount of corrosion products are leached from steel materials in the water supply, increasing the amount of Fe, resulting in a large amount of corrosion products adhering to various equipment and piping in the water supply system. , there are concerns that various problems will occur. [Object of the Invention] The object of the present invention is to solve the problems that arise due to the high temperature and high pressure of the steam conditions in the ultra-supercritical thermal power plant described above, and to eliminate corrosion products in the water supply system of the ultra-supercritical thermal power plant. The object of the present invention is to provide an effective water treatment method to prevent fouling. [Summary of the Invention] The present invention is a water treatment method for an ultra-supercritical thermal power plant, in which the PH and Fe content of the feed water at the inlet of a high-pressure feed water heater installed in the water supply system are measured,
The present invention provides a water treatment method for an ultra-supercritical thermal power plant, which is characterized by controlling the amount of chemicals injected into the water supply system based on these measured values and adjusting the pH of the water supply. The present inventors have developed a system for suppressing the increase in the amount of Fe in the water supply in the water supply system of an ultra-supercritical thermal power plant.
Various methods of preventing corrosion products from adhering to system equipment and piping were investigated. Analysis and measurement of the PH and Fe content of the feed water is carried out at the coal-fired inlet in supercritical pressure thermal power plants, but measurement is difficult in ultrasupercritical pressure thermal power plants because the feed water is at extremely high temperature and pressure. However, since the temperature and pressure at the inlet of the high-pressure feed water heater are lower than at the inlet of the energy saver, it has been found that the feed water can be easily measured and the water quality can be adjusted to a good quality based on the measured values. In other words, the PH and
The amount of Fe is analyzed and measured, and based on the measured value, chemicals (ammonium water NH ₄ OH, hydrazine N ₂ H ₂ , NaOH, Na ₃ PO ₄ , Na ₂ HPO ₄ , etc.) are added to the water supply system.
Among these, Fe in the water supply can be reduced by increasing or decreasing the injection amount of aqueous ammonia or hydrazine.
The present invention was achieved by discovering that the most effective method is to suppress the increase in corrosion products and prevent the adhesion of corrosion products to system equipment, piping, etc. Next, the present invention will be specifically explained based on the accompanying drawings. Figure 3 is a system diagram of an ultra-supercritical thermal power plant. In Fig. 3, 1 is a turbine, 2
is a condenser, 3 is a condenser hot well, 4 is a condensate pipe, 5 is a condensate pump, 6 is a condensate desalination device, 7 is a condensate boost pump, 8A to 8C are low pressure feed water heaters, 9
10 is a deaerator deaeration chamber, 10 is a deaerator water tank, 11 is a water supply pipe, 12 is a boiler water supply pump, 13A to 13
C is a high pressure feed water heater, 14 is a energy saver, 15 is a boiler, 16 is a steam pipe, 17A to 17C is a low pressure feed water heater drain pipe, 18A to 18C is a high pressure feed water heater drain pipe, 19 is a drain pump, 20A ~
20F is an air bleed pipe, and 21A and 21B are drug injection devices. To explain the steps in FIG. 3, water is supplied to the condenser 2, condenser hot well 3, condensate piping 4, condensate pump 5, condensate desalination device 6, condensate boost pump 7,
Low-pressure feed water heaters 8A to 8C, deaerator deaeration chamber 9, deaerator water tank 10, water supply piping 11, water supply pump 1
2. High-pressure water heaters 13A to 13C, energy saver 14
The steam enters the boiler 15, where it is converted into steam, passes through the steam pipe 16, flows into the turbine 1, does work, and returns to the condenser 2 again. The present inventors investigated the relationship between PH and the ratio of corrosion amount in the laboratory, and the relationship between PH and Fe when the Fe concentration is constant.
An experiment was conducted to examine the relationship between the adhesion weight ratio. In an experiment to determine the relationship between PH and the ratio of corrosion amount, carbon steel was placed in an autoclave at a temperature of 280°C, dissolved oxygen of 10 ppb or less, and PH of 9.3.
~10.0. In addition, an experiment to determine the relationship between PH and the ratio of Fe adhesion was carried out using carbon steel installed in a sample rotating oaklave at a temperature of 280°C and dissolved oxygen.
The test was performed at a flow rate of 2.4 m/s at a flow rate of 10 ppb or less, and a pH range of 9.3 to 10.0. As a sample solution, 100 ppm of a corrosion product (main component Fe ₃ O ₄ ) collected from an actual machine was pulverized in a mortar. As a result, the relationship between PH and the ratio of corrosion amount, and the PH and
The relationship between the ratios of Fe adhesion amounts is as shown by curves a and b in FIG. 4, respectively. Here, the corrosion amount ratio is expressed as the corrosion amount value at PH9.3, and the Fe deposition amount ratio is expressed with the Fe deposition amount value at PH10.0 as 1.0. From Figure 4,
It can be seen that as the PH increases, as shown by curve a, the ratio of corrosion amount decreases, while as shown by curve b, the ratio of Fe deposition amount increases. The dotted line c in Fig. 4 is the ratio of the amount of Fe adhesion calculated from the relationship between the ratio of the amount of corrosion and the ratio of the amount of Fe adhesion described above, and the PH is 9.5.
It is clear that the ratio of Fe adhesion amount calculated above is very small for 9.8 or higher. The feature of the present invention is that it was made based on the above study results, and it significantly reduces the amount of Fe in the water supply of the ultra-supercritical thermal power plant water supply system, and prevents corrosion of various equipment and piping. Since the adhesion of products can be prevented, the above-mentioned problems can be solved, and furthermore, (1) the performance and efficiency of the plant can be improved, (2) the pickling interval for removing corrosion products can be extended,
(3) Reduces wastewater treatment costs; (4) Reduces condensate desalination resin regeneration and replenishment costs. [Embodiments of the Invention] Example 1 An embodiment of the present invention will be described with reference to FIG. In ultra-supercritical thermal power plants, the PH and
Analyze and measure the amount of Fe at the high-pressure feed water heater 13A inlet to reduce the Fe concentration in the feed water.
Based on the measured value, chemicals (NH ₄ OH, N ₂ H _2, etc.) are injected from the medicine injection device 21B installed at the inlet of the high-pressure feed water heater 13A to raise the pH of the water supply to 9.5 or more.
Adjust to a range of 9.8. According to this embodiment, it is possible to reduce the Fe concentration in the high-pressure feed water heaters 13A to 13C, thereby reducing the amount of corrosion products attached, and it is possible to obtain high-quality feed water. In addition, Fe at the high-pressure feed water heater 13A inlet and the energy saver 14 inlet
The concentrations are shown in Table 1. Example 2 Water supply in an ultra-supercritical thermal power plant
High-pressure feed water heater 13 for analysis and measurement of PH and Fe content
Based on the measured value, chemicals (NH ₄ OH, N ₂ H _2, etc.) are injected from the chemical injection device 21A at the inlet of the low-pressure feed water heater 8A to raise the pH of the feed water to 9.5.
Adjust to a range of ~9.8. According to this embodiment, it is possible to not only adjust the PH of the feed water downstream from the inlet of the energy saver 14, but also adjust the PH of the feed water of the high-pressure feed water heaters 13A to 13C, where a large amount of corrosion products adhere. , Fe concentration can be reduced, the amount of corrosion products attached can be suppressed, and high quality water supply can be obtained. Table 1 shows the Fe concentrations at the inlet of the high-pressure feed water heater 13A and the inlet of the carbon saver 14. Example 3 Water supply in an ultra-supercritical thermal power plant
High-pressure feed water heater 13 for analysis and measurement of PH and Fe content
In order to minimize the amount of Fe in the water supply, the measurement value was measured from two locations: the drug injection device 21A at the inlet of the low-pressure feed water heater 8A and the drug injection device 21B at the inlet of the high-pressure feed water heater 13A. Adjust the PH to a range of 9.5 to 9.8 by increasing or decreasing the injection amount of drugs (NH ₄ OH, N ₂ H _2, etc.) based on the results. According to this embodiment, it is possible to obtain high-quality feed water by reducing the amount of Fe in the feed water and by significantly reducing the amount of corrosion products adhering to the high-pressure feed water heaters 13A to 13B. . In addition, Table 1 shows Fe at the inlet of the high-pressure feed water heater 13A and the inlet of the energy saver 14.
Indicates concentration. Also, for comparison, we will discuss the case of a supercritical pressure thermal power plant. Analyze and measure the PH and Fe amount at the coal-saving inlet, and based on the measured values, inject chemicals (NH ₄ OH, N ₂ H _2, etc.) from the low-pressure feed water heater inlet to adjust the PH to 9.4. did. Table 1 shows the Fe concentration at the inlet of the high-pressure feed water heater and the inlet of the economizer. As shown in Table 1, Examples 1 and 2 of the present invention,
In case 3, compared to the comparative example, the Fe concentration in the feed water at the inlet of the high-pressure feed water heater and the inlet of the energy saver was significantly reduced, and therefore the adhesion of corrosion products to water supply system equipment and piping was prevented. Ru.

[Table] [Effects of the Invention] According to the present invention, by significantly reducing the amount of Fe in ultra-supercritical pressure thermal power plant system water and preventing corrosion products from adhering to water supply system equipment and piping, etc. Since high-quality water can be obtained, the efficiency of supercritical pressure thermal power plants can be increased.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the feed water temperature and the amount of corrosion products deposited in a supercritical pressure thermal power plant.
Figure 2 is a diagram showing the relationship between temperature and Fe deposition amount, Figure 3 is a system diagram of an ultra-supercritical thermal power plant, and Figure 4 is a diagram showing the relationship between PH and the ratio of corrosion amount with curve a and PH.
Curve b shows the relationship between the ratio of Fe adhesion amount, PH and estimated Fe
It is a diagram showing the relationship between the ratio of adhesion amounts by curve c. 1... Turbine, 2... Condenser, 6... Condensate desalination device, 8A to 8C... Low pressure feed water heater, 13A
~13C...High pressure water heater, 14...Coal economizer,
15... Boiler, 21A, 21B... Drug injection device.

Claims (1)

[Claims] 1. In a water treatment method for an ultra-supercritical thermal power plant, the PH and Fe content of the feed water at the inlet of a high-pressure feed water heater installed in the water supply system are measured, and based on these measured values, A water treatment method for an ultra-supercritical thermal power plant, characterized by controlling the amount of chemicals injected into the water supply system and adjusting the PH of the water supply. 2. A water treatment method for an ultra-supercritical thermal power plant according to claim 1, characterized in that a chemical is injected from the inlet of a high-pressure feed water heater. 3. A water treatment method for an ultra-supercritical thermal power plant according to claim 1, characterized in that the chemical is injected from the inlet of a low-pressure feed water heater. 4. A water treatment method for an ultra-supercritical thermal power plant according to claim 1, characterized in that the chemical is injected from the inlet of a low-pressure feedwater heater and the inlet of a high-pressure feedwater heater. 5. A water treatment method for an ultra-supercritical thermal power plant according to any one of claims 1 to 4, characterized in that the pH of the feed water is adjusted to 9.5 to 9.8 by injecting a chemical. 6. A water treatment method for an ultra-supercritical thermal power plant according to any one of claims 1 to 5, characterized in that the chemical is ammonia water or hydrazine.