JP7392687B2 - Boiler fuel preheating device and preheating method - Google Patents

Description

The present invention relates to a boiler fuel preheating device and preheating method, and more particularly to a boiler fuel preheating device and preheating method that uses boiler combustion exhaust gas containing sulfur as a preheating heat source.

In steel plants, by-product gases (blast furnace gas, coke oven gas, converter gas, etc.) are inevitably generated during production processes such as pig iron making, steel making, and coke production. These by-product gases are used, for example, to generate steam as boiler fuel, as shown in Figure 3, and the generated steam is used to generate energy in power generation equipment equipped with a steam turbine. , resources are used efficiently.

In addition, the sensible heat of combustion exhaust gas discharged from various combustion systems such as boilers is recovered by heat exchangers, such as the air preheater and B gas heater shown in FIG. 3, to improve thermal efficiency. However, if the combustion exhaust gas contains sulfur (SOx), if the temperature of the combustion exhaust gas is cooled to a low temperature below the sulfuric acid dew point (hereinafter also referred to as the acid dew point), the heat exchange A problem arises in that SOx condenses as sulfuric acid on the surface of the heat transfer tubes, leading to corrosion of the heat transfer tubes.

In response to such problems, for example, Patent Document 1 describes a method for preventing sulfuric acid dew point corrosion of a heat exchanger. In the sulfuric acid dew point corrosion prevention method described in Patent Document 1, a heat exchanger is provided in an exhaust gas duct containing sulfuric anhydride, and when the heat of the high temperature side gas is transferred to the low temperature side gas, the high temperature side in the heat exchanger is In order to thermally communicate the upstream and downstream sides of the high-temperature gas section, heat exchange panels (heat pipes) are installed inside the gas section on the upstream and downstream sides, respectively. It is said to regulate the temperature. This allows the heat of the upstream exhaust gas to be used to raise the temperature of the downstream exhaust gas, thereby preventing condensation of sulfuric acid.

Another measure to prevent acid dew point corrosion is to preheat the cryogenic fluid using a separate heat source before it enters the heat exchanger, increasing the inlet temperature of the cryogenic fluid and increasing the temperature at the surface of the heat exchanger tubes. Methods have been proposed to increase the temperature to avoid acid dew point condensation. For example, Patent Document 2 describes a heat exchange method for SOx-containing combustion exhaust gas. The technology described in Patent Document 2 uses, for example, waste water from a temperature reduction and dehumidification section of a scrubber as a heat source to raise the temperature of combustion air supplied to a heat exchanger for preheating, and cools combustion air at the outlet of the combustion exhaust gas from the heat exchanger. This is a heat exchange method in which the gas temperature is lowered than when the temperature of combustion air is not raised. This makes it possible to improve fuel efficiency while preventing the combustion exhaust gas in the heat exchanger from dropping below the sulfuric acid dew point temperature. If the temperature of the combustion air is not raised, the outlet gas temperature of the combustion gas can only be lowered to about 300℃, but if the temperature of the combustion air is raised, even if the temperature is lowered to 270℃ or around 270℃, there will be no power transmission. It is stated that there will be no point in the thermal tube where the temperature will be below the sulfuric acid dew point.

Japanese Patent Application Laid-Open No. 61-217699 Japanese Patent Application Publication No. 2011-220545

However, in the technique described in Patent Document 1, it is necessary to install a heat exchanger panel in the high temperature side gas section of the heat exchanger, and in the technique described in Patent Document 2, it is necessary to It is necessary to install a temperature raising device before the heat exchanger, which increases the size of the equipment and complicates operation.

The present invention solves the problems of the prior art as described above, prevents corrosion of heat transfer tubes in a heat exchanger, and prevents a decrease in thermal efficiency. The purpose is to provide an apparatus and a preheating method.

In order to achieve the above-mentioned object, the present inventor has intensively studied various factors that affect the temperature of high-temperature fluid (boiler combustion exhaust gas) in a countercurrent heat exchanger in a boiler fuel preheating device. As a result, we came up with the idea of dividing the heat exchange chamber (shell), which serves as a flow path for boiler combustion exhaust gas, which is a high-temperature fluid, into two independent regions (heat exchange chambers) consisting of a high temperature region and a low temperature region. Boiler combustion exhaust gas, which is a high-temperature fluid, is supplied to the divided high-temperature region, and a portion of the high-temperature fluid (hereinafter also referred to as branched high-temperature fluid) is supplied from the high-temperature region to the other divided low-temperature region. We came up with the idea of branching and inflowing. This makes it easy to adjust the outlet temperature of the high-temperature fluid in either of the two independent heat exchange chambers to a temperature that exceeds the sulfuric acid dew point of the high-temperature fluid, which is SOx-containing boiler combustion exhaust gas. It has been found that it is possible to prevent sulfuric acid from condensing on the surface of a heat exchange conduction tube through which low-temperature fluid flows.

The present invention was completed based on the above-mentioned findings and further studies. That is, the gist of the present invention is as follows.
[1] A boiler fuel preheating device that heats the boiler fuel by causing SOx-containing boiler combustion exhaust gas, which is a high-temperature fluid, and boiler fuel, which is a low-temperature fluid, to flow countercurrently in a heat exchange chamber, The heat exchange chamber serving as a flow path is divided into two independent regions consisting of a high temperature region and a low temperature region, and a heat exchange heat transfer tube through which the low temperature fluid flows is divided into two independent regions, and the low temperature fluid is connected to the high temperature fluid in the heat exchange chamber. and supplying the high-temperature fluid to the upstream side of the high-temperature region, and directing a part of the high-temperature fluid supplied to the high-temperature region to a predetermined position on the wall surface of the high-temperature region. A preheating device for boiler fuel, characterized in that a branch pipe is provided for drawing out the fuel through an open branch port and flowing the fuel into the upstream side of the low temperature region.
[2] The boiler fuel preheating device according to [1], wherein the branch pipe is provided with a flow rate regulating valve on the outlet side of the branch port.
[3] The boiler fuel preheating device according to [2], wherein the branch pipe is branched from a plurality of positions on the wall surface of the high temperature region.
[4] A thermometer for measuring the outlet temperature of the high-temperature fluid is disposed at least at the outlet of the low-temperature region of the two independent regions, and the thermometer is configured to measure the flow rate that operates the flow rate regulating valve. The boiler fuel preheating device according to [2], characterized in that an adjustment means is connected.
[5] A method for preheating boiler fuel using the boiler fuel preheating device according to any one of [1] to [4], comprising: SOx-containing boiler combustion exhaust gas which is a high temperature fluid; and boiler fuel which is a low temperature fluid. In heating the boiler fuel by countercurrently flowing the fluid in the heat exchange chamber, the heat exchange chamber is divided into two independent regions consisting of a high temperature region and a low temperature region, and the high temperature fluid is supplied to the high temperature region. , supplying the low temperature fluid to a heat exchange heat transfer tube arranged so that the low temperature fluid flows countercurrently to the high temperature fluid, and branching a part of the supplied high temperature fluid from the high temperature region. A method for preheating boiler fuel, characterized in that the boiler fuel is caused to flow into the low temperature region.
[6] Adjusting the flow rate of a portion of the high temperature fluid flowing into the low temperature region so that the temperature of the high temperature fluid at the outlet sides of the high temperature region and the low temperature region exceeds the acid dew point of the high temperature fluid. The method for preheating boiler fuel according to [5], characterized in that:

According to the present invention, in a heat exchanger used as a boiler fuel preheating device, the outlet temperature of the high-temperature fluid can be easily adjusted to a temperature exceeding the sulfuric acid dew point of the high-temperature fluid that is SOx-containing combustion exhaust gas, It is possible to prevent sulfuric acid from condensing on the surface of the heat exchange heat transfer tube through which low-temperature fluid flows, and since no precipitates are attached to the surface of the heat exchange heat transfer tube, it is possible to suppress the decrease in heat exchange efficiency, which has a significant industrial effect. . Further, according to the present invention, since the high temperature fluid adjusted to an appropriate temperature flows into the low temperature region via some of the heat exchange chambers, there is also an effect that the efficiency of heat exchange in the low temperature region is improved.

FIG. 1 is an explanatory diagram schematically showing the outline of the preheating device of the present invention. It is an explanatory view showing the outline of other examples of the preheating device of the present invention typically. FIG. 2 is an explanatory diagram schematically showing an example of equipment arrangement around a boiler in a steelworks power plant.

In the boiler fuel preheating device of the present invention, the SOx-containing combustion exhaust gas is used as a high-temperature fluid, the fuel is used as a low-temperature fluid, and the sensible heat of the combustion exhaust gas, which is a high-temperature fluid, is recovered using a countercurrent heat exchanger, and the sensible heat is recovered from the combustion exhaust gas, which is a high-temperature fluid. (boiler fuel).

As the fuel, by-product gas from a steel mill can be used, and it is preferable to use blast furnace gas (B gas), coke oven gas (C gas), converter gas (LD gas), or the like. Although it is not necessary to apply the fuel preheating method of the present invention to all fuel gases, it is particularly preferable to apply the present invention to blast furnace gas because its calorific value is small. Combustion exhaust gas (boiler combustion exhaust gas) after these fuels are burned in a boiler contains sulfur (SOx). Note that the temperature of the boiler combustion exhaust gas is in the range of 300 to 700°C, but when the fuel preheating of the present invention is performed after the combustion exhaust gas is used to preheat the combustion air as shown in Figure 3, the temperature is 300 to 500°C. It is about ℃. On the other hand, the temperature at the inlet side of the boiler fuel is about the same as the outside temperature.

The countercurrent heat exchanger used in the boiler fuel preheating device of the present invention is preferably a commonly used shell-and-tube heat exchanger. In a conventional shell-and-tube heat exchanger, there are multiple heat exchange conduction tubes through which low-temperature fluid flows, and the low-temperature fluid is arranged in a countercurrent direction to the heat exchange chamber, which is the flow path for high-temperature fluid. do.

In the boiler fuel preheating device 10 of the present invention, as shown in FIG. 1, the heat exchange chamber 2, which is a flow path (duct) for the high temperature fluid 1, is divided into two independent regions 21 and 22. One of the two independent regions is called a high temperature region 21 and the other is called a low temperature region 22. Then, the above-described high-temperature fluid 1 is supplied to the upstream side of the high-temperature region 21. Note that the boundary between the high temperature region 21 and the low temperature region 22 is sealed with heat-resistant packing to seal each region.

In the boiler fuel preheating device 10 of the present invention, a branch pipe 3 is disposed between the high temperature region 21 and the low temperature region 22. Branch ports (for example, branch ports 31 and 32) are provided at predetermined positions on the wall surface of the high temperature region 21 described above. Then, a portion of the high temperature fluid 1 is extracted (branched) from each of these branch ports, and flows into the upstream side of the low temperature region 22 as a portion 12 of the high temperature fluid via the branch pipe 3 . The temperature of the branched high-temperature fluid (part of the high-temperature fluid) 12 extracted from the high-temperature region 21 is higher than the acid dew point of the high-temperature fluid. By using the inflowing branched high-temperature fluid 12 as a heat source, it becomes possible to adjust the temperature of the flowing fluid (combustion exhaust gas) so as not to drop below the acid dew point.

As the branched high temperature fluid 12 to flow into the low temperature region 22, the same boiler combustion exhaust gas supplied to the high temperature region 21 may be directly flowed in, but in that case, the fluid temperature is too high compared to the low temperature fluid, and the heat Exchange efficiency decreases. Therefore, in the present invention, heat is exchanged in the high temperature region 21 of the heat exchange chamber, and the high temperature fluid whose fluid temperature has decreased to an appropriate temperature is extracted and made to flow into the low temperature region 22 as the branched high temperature fluid 12.

In the present invention, the load of the boiler is monitored and the amount of high-temperature fluid (boiler combustion exhaust gas) flowing into a heat exchange chamber divided into two independent areas is appropriately distributed according to the amount of boiler fuel and boiler combustion exhaust gas. do. This makes it possible to maintain the hot fluid (boiler combustion exhaust gas) temperature at a temperature above the acid dew point temperature over the entire region of the heat exchanger.

Note that the branch port is provided at at least one location on the wall surface of the high temperature region 21 along the flow path of the high temperature fluid 1. Although FIG. 1 shows an example in which they are provided at two locations (branch ports 31 and 32), it goes without saying that the present invention is not limited to this. By providing branch ports at multiple locations along the flow path of the high-temperature region 21, high-temperature fluids 1 with various fluid temperatures can be extracted, and the temperature of the portion 12 of the high-temperature fluid flowing into the low-temperature region can be easily adjusted. becomes. Note that it is preferable that the portion 12 of the high-temperature fluid extracted from the high-temperature region 21 has a fluid temperature of about 200 to 300°C.

Furthermore, in the boiler fuel preheating device 10 of the present invention, it is preferable to arrange thermometers 211 and 221 at the respective exits of the high temperature region 21 and the low temperature region 22 to measure the temperature on the exit side of the fluid (combustion exhaust gas). In the present invention, based on the outlet temperature of the fluid (boiler combustion exhaust gas) measured by the thermometers 211 and 221, the temperature of the high-temperature fluid (boiler combustion exhaust gas) is prevented from falling below the acid dew point of the boiler combustion exhaust gas. , it is preferable to adjust the flow rate of the portion 12 of the high temperature fluid flowing from the high temperature region 21 to the low temperature region 22.

Therefore, flow rate regulating valves 311 and 321 are provided corresponding to the branch ports 31 and 32, respectively, and the regulating means Preferably, the inflow rate is adjusted via 33.

Furthermore, at the respective outlets (outlet sides) of the high temperature region 21 and the low temperature region 22, sensors (density meters) 212 and 222 are installed to measure the concentration of sulfuric anhydride (SOx) in the discharged high temperature fluid (boiler combustion exhaust gas). It is preferable to provide the following in order to grasp the acid dew point of the boiler combustion exhaust gas.

Furthermore, in the boiler fuel preheating device 10 of the present invention, a heat exchange heat transfer tube 5 through which the low temperature fluid 4 flows is arranged so as to flow countercurrently to the high temperature fluid 1 having the heat exchange chamber 2 as a flow path. As shown in FIG. 1, the arrangement is such that the low temperature fluid 4 passes from the low temperature region 22 to the high temperature region 21 of the heat exchange chamber 2 in this order. In the schematic diagram of FIG. 1, only one heat exchange tube 5 is shown, but in reality, a number of tubes are used as a flow path for the low temperature fluid 4 depending on the capacity of the heat exchanger. It goes without saying that the actual heat exchange heat transfer tube 5 is used.

In addition, the heat exchange tube 5 used in the preheating device of the present invention is a carbon steel tube for boilers and heat exchangers (STB340, etc.) specified in JIS G 3461, and for boilers and heat exchangers specified in JIS G 3461. Any commonly used tubes such as alloy steel pipes (STBA12, etc.) can be used.

In order to monitor sulfuric acid condensation (condensation) on the surface of the heat exchange tube 5, a thermometer 213 that measures the surface temperature of the heat exchange tube 5 near the outlet of the high temperature region 21 and a thermometer 213 that measures the surface temperature of the heat exchange tube 5 near the outlet of the high temperature region 21 are used. It is preferable to provide a thermometer 223 for measuring the surface temperature of the heat exchange tube 5 near the outlet of the tube.

Note that, in the present invention, the division of the heat exchange chamber 2 is not limited to the two independent regions described above, the high temperature region 21 and the low temperature region 22. If it is permissible to heat the temperature of the fuel, which is a low-temperature fluid, to a desired preheating temperature according to the temperature and amount of the combustion exhaust gas, a heat exchange chamber (shell) is added to the high-temperature region 21 and the low-temperature region 22. For example, as shown in FIG. 2, a medium temperature region 23 may be provided and divided into three independent regions. In this case, it is preferable that the branched high-temperature fluids 12 and 13 branched (extracted) from the branch ports 31 and 32 of the high-temperature region 21 flow into the low-temperature region 22 and the medium-temperature region 23 via the branch pipe 3.

Further, the present invention utilizes the boiler fuel preheating device 10 having the above-described configuration to cause the SOx-containing boiler combustion exhaust gas, which is the high-temperature fluid 1, and the boiler fuel, which is the low-temperature fluid 4, to flow countercurrently in the heat exchange chamber, This is a boiler fuel preheating method for heating boiler fuel.

In the boiler fuel preheating method of the present invention, SOx-containing boiler combustion exhaust gas, which is the high-temperature fluid 1, is supplied to the high-temperature region 21 of the heat exchange chamber, and the high-temperature fluid 12 is branched from the high-temperature region 21 and flows into the low-temperature region 22. let Thereby, the temperature of the high-temperature fluid in the low-temperature region can be adjusted so as not to fall below the acid dew point of the high-temperature fluid. In addition, in the present invention, the outlet temperature of the high temperature fluid in each area is measured by the thermometers 211 and 221 disposed at the outlet of each area of the heat exchange chamber, and the high temperature fluid is adjusted according to the obtained outlet temperature. The flow rate of the branched high temperature fluid 12 flowing into the low temperature region 22 is adjusted so that the acid dew point of the fluid is exceeded. It is preferable to adjust the flow rate by inputting the obtained outlet temperature into the adjusting means 33 and operating the flow rate regulating valves 311 and 321 disposed on the outlet sides of the branch ports 31 and 32.

In addition, instead of adjusting the amount of the branched high-temperature fluid (boiler combustion exhaust gas) 12 to be extracted with the flow rate adjustment valve, by changing the extraction position of the high-temperature fluid from the branch port 31 to the branch port 32, for example, the high-temperature fluid to be extracted can be adjusted. It is also possible to change the temperature of the fluid and obtain the same effect.

Note that the acid dew point of the high-temperature fluid changes mainly depending on the sulfur content, so it is preferable to constantly measure the sulfur content of the high-temperature fluid to understand the acid dew point of the high-temperature fluid. Boiler combustion exhaust gas usually contains SO ₂ sulfur of about 0.00001 to 0.001 ppm, and the acid dew point is in the range of 90 to 130°C. Therefore, from the viewpoint of preventing sulfuric acid condensation on the surface of the heat exchange tube through which the low temperature fluid flows, it is preferable to adjust the temperature of the high temperature fluid in each region of the heat exchange chamber to a temperature of 180°C or higher, which is higher than the acid dew point. .

Boiler fuel was preheated using the boiler fuel preheating device 10 of the present invention shown in FIG. As the low temperature fluid (boiler fuel) 4, blast furnace gas (B gas; flow rate: 340,000 Nm ³ /h) at a temperature of 40° C. was supplied to the heat exchange tube 5 . In addition, the material of the heat exchange heat transfer tube 5 was STB350. As high temperature fluid (boiler combustion exhaust gas) 1, boiler combustion exhaust gas (flow rate: 820,000 kg/h) with a temperature of 350° C. was supplied to the high temperature region 21. A portion of the high-temperature fluid was extracted from a branch port 31 disposed at a predetermined position on a wall along the flow path of the high-temperature region 21 and flowed into the upstream side of the low-temperature region 22 via the branch pipe 3. Note that the temperature of the branched high-temperature fluid 12 extracted from the branch port 31 was 300°C. During operation, the branch high-temperature fluid 12 is extracted by operating the flow rate adjustment valve 311 so that the outlet temperature of the high-temperature fluid (boiler combustion exhaust gas) as measured by the thermometer 221 installed on the outlet side of the low-temperature region 22 is 180°C or higher. The flow rate was adjusted.

As a result of heat exchange under these conditions, the low temperature fluid (boiler fuel) was heated to 270°C. Further, the outlet temperature of the high temperature fluid (boiler combustion exhaust gas) of the low temperature region 22 into which a part of the above-described high temperature fluid was introduced was 200° C., which was higher than the acid dew point of the boiler combustion exhaust gas.

Further, when the heat exchanger was inspected after operating the boiler under these conditions for one year, no acid corrosion was found in the heat exchange tube.

1 High temperature fluid 2 Heat exchange chamber 3 Branch pipe 4 Low temperature fluid 5 Heat exchange heat transfer tube 10 Boiler fuel preheating device 12, 13 Branch high temperature fluid (part of high temperature fluid)
21 High temperature region 22 Low temperature region 23 Medium temperature region 31, 32 Branch port 33 Adjustment means
211, 221, 231 Thermometer (combustion exhaust gas thermometer)
212, 222 SOx concentration meter (sensor)
213, 223 Heat exchange heat transfer tube surface thermometer
311, 321, 331 Flow control valve

Claims (6)

A boiler fuel preheating device that heats the boiler fuel by causing SOx-containing boiler combustion exhaust gas, which is a high-temperature fluid, and boiler fuel, which is a low-temperature fluid, to flow countercurrently in a heat exchange chamber, comprising:
The heat exchange chamber, which serves as a flow path for the high-temperature fluid, is divided into two independent regions consisting of a high-temperature region and a low-temperature region,
A heat exchange heat transfer tube through which the low-temperature fluid flows is disposed in the heat exchange chamber so that the low-temperature fluid flows countercurrently to the high-temperature fluid, and
supplying the high temperature fluid to the upstream side of the high temperature region;
A branch pipe is provided for extracting a part of the high temperature fluid supplied to the high temperature region through a branch port opened at a predetermined position on a wall surface of the high temperature region and flowing into the upstream side of the low temperature region. A boiler fuel preheating device characterized by: 2. The boiler fuel preheating device according to claim 1, wherein the branch pipe is provided with a flow rate regulating valve on the outlet side of the branch port. The boiler fuel preheating device according to claim 2, wherein the branch pipe is branched from a plurality of positions on the wall surface of the high temperature region. A thermometer for measuring the outlet temperature of the high-temperature fluid is disposed at least at the outlet of the low-temperature region of the two independent regions;
3. The boiler fuel preheating device according to claim 2, wherein the thermometer is connected to a flow rate adjustment means for operating the flow rate adjustment valve. A boiler fuel preheating method using the boiler fuel preheating device according to any one of claims 1 to 4,
In heating the boiler fuel by causing SOx-containing boiler combustion exhaust gas, which is a high-temperature fluid, and boiler fuel, which is a low-temperature fluid, to flow countercurrently in a heat exchange chamber,
dividing the heat exchange chamber into two independent regions consisting of a high temperature region and a low temperature region;
supplying the high-temperature fluid to the high-temperature region and supplying the low-temperature fluid to a heat exchange heat transfer tube disposed such that the low-temperature fluid flows countercurrently to the high-temperature fluid;
A method for preheating boiler fuel, characterized in that a part of the high temperature fluid supplied is branched from the high temperature region and flows into the low temperature region. The flow rate of a portion of the high temperature fluid flowing into the low temperature region is adjusted so that the temperature of the high temperature fluid at the outlet sides of the high temperature region and the low temperature region exceeds the acid dew point of the high temperature fluid. The boiler fuel preheating method according to claim 5.

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