Boiler system

Abstract

To provide a boiler system that can suppress generation of condensation water in a preheater and has an enhanced effect of improvement of efficiency by the preheater.SOLUTION: A boiler system according to one aspect of the present disclosure includes: a boiler that mixes and burns hydrogen and air and generates steam by using heat obtained through the combustion; a preheater that warms air to be supplied to the boiler by using heat of combustion gas discharged from the boiler via a heat transfer body; an air bypass flow passage for supplying air to the boiler while bypassing the preheater; and a control device reducing air passage amount that is a flow rate of air passing through the preheater by increasing air bypass amount that is a flow rate of air passing through the air bypass flow passage when a dew point temperature difference obtained by subtracting a water dew point temperature of the combustion gas from a temperature of a portion with the lowest temperature of the heat transfer body becomes lower than a preset allowable temperature.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a boiler system.

Background Art

[0002] Some boiler systems include a preheater. In the preheater, the air supplied to the boiler is heated by the heat of the combustion gas discharged from the boiler. As a result, the heat of the combustion gas can be recovered, improving the efficiency of the boiler system (see, for example, Patent Document 1 below).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in recent years, hydrogen, which does not emit carbon dioxide during combustion, has attracted attention as a fuel for boiler systems. However, when hydrogen is used as a fuel for a boiler system, a large amount of water is generated by the combustion of hydrogen. Therefore, the combustion gas will contain a lot of moisture, and condensed water is likely to occur in the preheater, and there is a risk of corrosion of the preheater and the pipes connected to the preheater.

[0005] As a countermeasure, it is conceivable to review the design conditions of the preheater so that condensed water does not occur, and suppress the temperature drop of the combustion gas when passing through the preheater. However, in this case, the heat of the combustion gas cannot be sufficiently recovered, and the effect of improving the efficiency of the boiler system by the preheater cannot be fully exerted.

[0006] Therefore, an object of the present disclosure is to provide a boiler system using hydrogen as a fuel, which can suppress the generation of condensed water in the preheater and has a high effect of improving efficiency by the preheater. [Means for solving the problem]

[0007] A boiler system according to one aspect of the present disclosure includes: a boiler that burns hydrogen mixed with air to generate steam by the heat of combustion; a preheater that heats the air supplied to the boiler via a heat transfer element using the heat of the combustion gas discharged from the boiler; an air bypass channel that supplies air to the boiler by bypassing the preheater; and a control device that, when the dew point temperature difference obtained by subtracting the water dew point temperature of the combustion gas from the temperature of the coldest part of the heat transfer element falls below a preset allowable temperature, increases the air bypass amount, which is the flow rate of air passing through the air bypass channel, and decreases the air passage amount, which is the flow rate of air passing through the preheater. [Effects of the Invention]

[0008] This configuration makes it possible to suppress the generation of condensate in the preheater and provide a boiler system that offers a high efficiency improvement effect from the preheater. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram of the boiler system. [Figure 2] Figure 2 is a flowchart of the air bypass amount adjustment program. [Modes for carrying out the invention]

[0010] (Overall structure) The boiler system 100 according to the embodiment will be described below. First, the overall configuration of the boiler system 100 will be described. Figure 1 is a schematic diagram of the boiler system 100. As shown in Figure 1, the boiler system 100 includes a boiler 10, a preheater 20, an air bypass passage 30, and a control device 40. These components will be described in order below.

[0011] Boiler 10 is a device that burns hydrogen mixed with air, generating steam from the heat of combustion. Hydrogen is supplied to boiler 10 via a hydrogen supply channel 11, and air (outside air) is supplied via an air supply channel 12. The combustion gas generated by burning hydrogen is discharged from boiler 10 to the outside of the boiler system 100 via a combustion gas discharge channel 13. Furthermore, water tubes 14 are located inside boiler 10. Water is supplied to water tubes 14, and as the supplied water passes through water tubes 14, it is heated by the heat generated by the combustion of hydrogen and turns into steam.

[0012] The preheater 20 is a device that heats the air supplied to the boiler 10 using the heat from the combustion gas discharged from the boiler 10. The preheater 20 is located on the air supply channel 12 and the combustion gas discharge channel 13. The preheater 20 also includes heat transfer elements 21. The preheater 20 in this embodiment is of the rotary regenerative type, and the part called the element in the rotary regenerative type corresponds to the heat transfer elements 21 in this embodiment. Note that the preheater 20 is not limited to the rotary regenerative type, and the number of heat transfer elements 21 is also not limited.

[0013] In this embodiment, the heat transfer element 21 rotates so as to pass through the air supply channel 12 and the combustion gas discharge channel 13. The rotation axis 22 of the heat transfer element 21 is parallel to the direction of airflow and combustion gas flow within the preheater 20. As a result, as the heat transfer element 21 rotates, the portion of the heat transfer element 21 that is located on the combustion gas discharge channel 13 and has absorbed heat from the combustion gas moves onto the air supply channel 12, supplying the heat absorbed from the combustion gas to the air. Consequently, the heat from the combustion gas is recovered into the air supplied to the boiler 10, improving the efficiency of the boiler system 100.

[0014] The air bypass passage 30 is a passage that supplies air to the boiler 10 by bypassing the preheater 20. The air bypass passage 30 is positioned to connect the portion of the air supply passage 12 upstream of the preheater 20 and the portion downstream of the preheater 20. The air bypass passage 30 is equipped with an air bypass amount adjustment damper 31. By changing the opening of this air bypass amount adjustment damper 31, the flow rate of air supplied to the boiler 10 by bypassing the preheater 20 (hereinafter referred to as "air bypass amount") can be adjusted. Note that increasing the air bypass amount decreases the flow rate of air passing through the preheater 20 (hereinafter referred to as "air passage amount"), and decreasing the air bypass amount increases the air passage amount.

[0015] The control device 40 is a device that controls each component of the boiler system 100. The control device 40 includes a processor, volatile memory, non-volatile memory, and an I / O interface. The non-volatile memory of the control device 40 stores the air bypass amount adjustment program, which will be described later, and various data, and the processor performs calculations using the volatile memory based on each program.

[0016] In this embodiment, a temperature sensor 41 is provided near the outlet of the preheater 20 on the combustion gas discharge passage 13. The control device 40 is electrically connected to this temperature sensor 41 and can acquire the temperature of the combustion gas that has passed through the preheater 20 (hereinafter referred to as "combustion gas outlet temperature") based on the measurement signal received from the temperature sensor 41. Furthermore, the control device 40 is electrically connected to an air bypass amount adjustment damper 31 and can adjust the amount of air bypass by transmitting a control signal to the air bypass amount adjustment damper 31.

[0017] The functions of the elements disclosed in this specification can be executed using a circuit or processing circuit including a general-purpose processor, a dedicated processor, an integrated circuit, an ASIC (Application Specific Integrated Circuits), a conventional circuit, and / or a combination thereof that is configured or programmed to execute the disclosed functions. Since a processor includes transistors and other circuits, it is regarded as a processing circuit or a circuit. In the present disclosure, a circuit, unit, or means is hardware that executes the listed functions or hardware programmed to execute the listed functions. The hardware may be the hardware disclosed in this specification or other known hardware that is programmed or configured to execute the listed functions. When the hardware is a processor considered to be a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used for configuring the hardware and / or the processor.

[0018] (Air bypass amount adjustment program) Next, the air bypass amount adjustment program will be described. The air bypass amount adjustment program is a program for adjusting the air bypass amount and is executed by the control device 40. FIG. 2 is a flowchart of the air bypass amount adjustment program.

[0019] As shown in FIG. 2, when the air bypass amount adjustment program is started, the control device 40 acquires the combustion gas outlet temperature (step S1). As described above, the control device 40 can acquire the combustion gas outlet temperature based on the measurement signal received from the temperature sensor 41.

[0020] Subsequently, the control device 40 calculates the dew point temperature difference (step S2). Here, the "dew point temperature difference" refers to the temperature obtained by subtracting the water dew point temperature of the combustion gas from the temperature of the lowest temperature part of the heat transfer body 21 (hereinafter referred to as the "heat transfer body minimum temperature").

[0021] Generally, the coldest part of the heat transfer body 21 is located near the air inlet of the preheater 20. The lowest temperature of the heat transfer body may be measured directly, but in this embodiment, it is estimated based on the combustion gas outlet temperature obtained in step S1. Specifically, the control device 40 stores map data or a mathematical formula indicating the relationship between the lowest temperature of the heat transfer body and the combustion gas outlet temperature, and estimates the lowest temperature of the heat transfer body based on the map data or the mathematical formula and the combustion gas outlet temperature obtained in step S1.

[0022] Also, the water dew point temperature of the combustion gas can be calculated based on the amounts of hydrogen and air supplied to the boiler 10. However, the water dew point temperature of the combustion gas may be set as a fixed value. Note that when the dew point temperature difference becomes negative, that is, when the lowest temperature of the heat transfer body is lower than the water dew point temperature of the combustion gas, condensed water will be generated when the combustion gas contacts the coldest part of the heat transfer body 21. For example, if the water dew point temperature of the combustion gas is 80°C, when the lowest temperature of the heat transfer body becomes lower than 80°C, the dew point temperature difference becomes negative and condensed water may be generated.

[0023] Subsequently, the control device 40 determines whether the dew point temperature difference is lower than the allowable temperature (step S3). Here, the "allowable temperature" is a preset value and is the temperature for avoiding the water dew point considering the variation in the temperature range inside the preheater 20. The allowable temperature is set, for example, in the range of 5°C or more and 10°C or less.

[0024] In step S3, if it is determined that the dew point temperature difference is lower than the allowable temperature (YES in step S3), the control device 40 increases the air bypass amount and decreases the air passage amount (step S4). The control device 40 can increase the air bypass amount and decrease the air passage amount by transmitting a control signal to the air bypass adjustment damper 31.

[0025] For example, suppose the allowable temperature is set to 5°C, the dew point temperature of the combustion gas is 80°C, and the minimum temperature of the heat transfer element is 83°C. In this case, the dew point temperature difference is 3°C, which is below the allowable temperature of 5°C. In such a case, since the dew point temperature difference is 3°C and not negative, condensation would not normally occur. However, in this embodiment, the amount of air bypassed is increased to account for fluctuations in each temperature.

[0026] Increasing the amount of air bypassed and decreasing the amount of air passing through reduces the amount of air in contact with the heat transfer element 21, which raises the minimum temperature of the heat transfer element and suppresses the temperature drop of the combustion gas in the preheater 20. As a result, the dew point temperature difference increases, and the generation of condensation water in the preheater 20 can be suppressed.

[0027] After step S4, or if it is determined in step S3 that the dew point temperature difference is not below the allowable temperature (NO in step S3), the process returns to step S1 and repeats the steps described above. This concludes the flow of the air bypass amount adjustment program.

[0028] As described above, according to the boiler system 100 of this embodiment, when there is a risk of condensation forming in the preheater 20, the amount of air bypassed and the amount of air passing through can be increased to suppress the formation of condensation in the preheater 20. Furthermore, since the boiler system 100 of this embodiment can suppress the formation of condensation in the preheater 20 by adjusting the amount of air bypassed, the preheater 20 can be designed with an emphasis on the efficiency of the boiler system 100 rather than the formation of condensation.

[0029] For example, when the boiler system 100 is operating at the design point and the amount of air bypass is zero, the preheater 20 may be designed so that the dew point temperature difference is zero or less. In other words, the preheater 20 may be designed so that the combustion gas outlet temperature becomes very low. In this case, if the amount of air bypass is zero, condensation will be generated in the preheater 20, but in this embodiment, the amount of air bypass is adjusted so that no condensation is generated in the preheater 20. Furthermore, the design of the preheater 20 as described above allows for a large temperature drop of the combustion gas in the preheater 20, resulting in sufficient heat recovery from the combustion gas and fully demonstrating the effect of the preheater 20 in improving the efficiency of the boiler system.

[0030] As an example, the preheater 20 (air bypass amount, heat transfer area of ​​the heat transfer element 21, rotational speed of the heat transfer element 21, etc.) is designed to satisfy the following three conditions: (i) At the design point of the preheater 20 (for example, when the boiler 10 is operating at 110% load) and the air bypass amount is zero, the dew point temperature difference is negative. (ii) At the operating point of the preheater 20 (for example, when the boiler 10 is operating at 100% load) and when the air bypass amount is adjusted by the air bypass amount adjustment damper 31, the dew point temperature difference is an appropriate value (approximately 5°C to 10°C). (iii) At both the design point and the operating point of the preheater 20, the low-temperature mean edge temperature of the heat transfer element 21 (the average temperature of the heat transfer element 21 near the air inlet and combustion gas outlet of the preheater 20) is higher than the water dew point temperature of the combustion gas. By designing the preheater 20 in this manner, the operating point of the preheater 20 will be an optimal design that allows for a minimum margin relative to the water dew point.

[0031] However, the preheater 20 does not have to be designed as described above. For example, when the boiler system 100 is operating at the design point and the amount of air bypass is zero, the preheater 20 may be designed so that the dew point temperature difference is slightly greater than zero. Even in this case, the effect of the preheater 20 in improving the efficiency of the boiler system can be fully realized.

[0032] Furthermore, the control device 40 of this embodiment estimates the minimum temperature of the heat transfer element based on the combustion gas outlet temperature and calculates the dew point temperature difference based on the estimated minimum temperature of the heat transfer element to determine whether the dew point temperature difference is below the allowable temperature. However, the control device 40 may store map data or the like showing the relationship between the dew point temperature difference and the combustion gas outlet temperature, and obtain the dew point temperature difference based on the map data or the like and the combustion gas outlet temperature to determine whether the dew point temperature difference is below the allowable temperature. Similarly, the control device 40 may determine whether the dew point temperature difference is below the allowable temperature based on the difference between the combustion gas outlet temperature and the temperature of the combustion gas before passing through the preheater 20 (combustion gas inlet temperature), or it may determine whether the dew point temperature difference is below the allowable temperature based on the amount of hydrogen consumed.

[0033] (summary) The first item disclosed herein is a boiler system comprising: a boiler that burns hydrogen mixed with air to generate steam by the heat of combustion; a preheater that heats the air supplied to the boiler via a heat transfer element using the heat of the combustion gas discharged from the boiler; an air bypass channel that supplies air to the boiler by bypassing the preheater; and a control device that, when the dew point temperature difference obtained by subtracting the water dew point temperature of the combustion gas from the temperature of the coldest part of the heat transfer element falls below a preset allowable temperature, increases the air bypass amount, which is the flow rate of air passing through the air bypass channel, and decreases the air flow rate, which is the flow rate of air passing through the preheater.

[0034] With this configuration, if there is a risk of condensation forming in the preheater, the amount of air bypassed and the amount of air passing through can be increased to suppress the formation of condensation in the preheater. Furthermore, since the formation of condensation in the preheater can be suppressed by adjusting the amount of air bypassed, if the preheater is designed with efficiency as the priority over condensation prevention, the effect of the preheater in improving the efficiency of the boiler system can be fully realized.

[0035] A second item disclosed herein is a boiler system according to the first item, wherein the control device acquires the combustion gas outlet temperature, which is the temperature of the combustion gas that has passed through the preheater, and determines whether the dew point temperature difference has fallen below the allowable temperature based on the acquired combustion gas outlet temperature.

[0036] This configuration makes it easy to determine whether the dew point temperature difference has fallen below the allowable temperature.

[0037] A third item disclosed herein is the boiler system described in the first or second item, wherein the allowable temperature is set in the range of 5°C to 10°C.

[0038] By setting the allowable temperature to 5°C or higher, the generation of condensed water in the preheater 20 can be suppressed. On the other hand, by setting the allowable temperature to 10°C or lower, the decrease in the efficiency of the boiler system can be suppressed.

[0039] The fourth item disclosed herein is a boiler system according to any one of the first to third items, wherein the preheater is designed such that the dew point temperature difference is zero or less when the boiler system is operated at the design point and the amount of air bypass is zero.

[0040] This configuration allows for the suppression of condensation generation in the preheater while more fully realizing the effect of the preheater on improving the efficiency of the boiler system.

[0041] The fifth item disclosed herein is a boiler system according to any one of the first to fourth items, wherein the preheater is designed such that the low-temperature mean edge temperature of the heat transfer element is higher than the dew point temperature of the combustion gas at both the operating point and the design point.

[0042] This configuration ensures that the preheater's operating point has an optimal design that allows for a minimum margin of safety relative to the water dew point. [Explanation of Symbols]

[0043] 10 Boilers 20 Preheater 21 Heat transfer element 30 Air bypass channel 40 Control device 100 Boiler Systems

Claims

1. A boiler that burns hydrogen mixed with air, and generates steam from the heat produced by combustion, A preheater that heats the air supplied to the boiler via a heat transfer element using the heat from the combustion gas discharged from the boiler, An air bypass channel that supplies air to the boiler by bypassing the preheater, A boiler system comprising: a control device that, when the dew point temperature difference obtained by subtracting the water dew point temperature of the combustion gas from the temperature of the coldest part of the heat transfer element falls below a preset allowable temperature, increases the air bypass amount, which is the flow rate of air passing through the air bypass channel, and decreases the air passage amount, which is the flow rate of air passing through the preheater, the system The preheater is designed such that the dew point temperature difference is zero or less when the boiler system is operating at its design point and the amount of air bypass is zero.

2. The boiler system according to claim 1, wherein the control device acquires the combustion gas outlet temperature, which is the temperature of the combustion gas that has passed through the preheater, and determines whether the dew point temperature difference has fallen below the allowable temperature based on the acquired combustion gas outlet temperature.

3. The boiler system according to claim 1, wherein the allowable temperature is set in the range of 5°C or more and 10°C or less.

4. The boiler system according to claim 1, wherein the preheater is designed such that the low-temperature mean edge temperature of the heat transfer element is higher than the water dew point temperature of the combustion gas at both the operating point and the design point.

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