Boiler fuel evaluation method

Abstract

To provide a fuel evaluation method for boiler, capable of estimating the degree of molten salt corrosion of a heat transfer pipe according to differences in fuel composition.SOLUTION: A fuel evaluation method for a boiler including a heat transfer pipe 5 provided in a passage through which combustion gas passes includes: a first process for estimating, under the assumption that content ratios of corrosion-related element forming corrosive condensation component deposited and attached on a surface of the heat transfer pipe 5 are different from each other, therefore multiple types of fuels have different compositions, composition of the corrosive condensation component for the assumed fuel by chemical thermodynamic analysis using fuel composition and combustion conditions in the boiler; a second process for estimating, by performing corrosion test using a test piece reflecting all or part of the composition of the corrosiveness condensation component estimated in the first process, a relation between the composition of the corrosive condensation component and a corrosion evaluation value representing the corrosion degree of the heat transfer pipe 5; and a third process for acquiring a relation between fuel composition corresponding to the composition of the corrosiveness condensation component and the corrosion evaluation value on the basis of estimated results of the first process and the second process.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating fuel for a boiler. [Background technology]

[0002] In recent years, in order to reduce CO2, which has a large impact on global warming, efforts have been made to use biomass, waste plastics, and other waste materials as boiler fuels instead of fossil fuels.

[0003] Meanwhile, Patent Document 1 describes a method for evaluating the amount of corrosion in a boiler during the shutdown period of a plant in which the boiler is installed, the method including a deposit sampling step of sampling deposits from the evaluation target portion, a measurement step of measuring at least the amount of sulfur and vanadium contained in the deposits, and a corrosion amount derivation step of determining the amount of corrosion of the evaluation target portion based on the temperature of the evaluation target portion and the measurement results from the measurement step.

[0004] Furthermore, Patent Document 2 describes a method for predicting the degree of sulfidation corrosion of a boiler furnace wall tube, using the amount of corrosion of the furnace wall tube of a boiler that uses pulverized coal as fuel. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-151476 A [Patent Document 2] JP 2014-228258 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, when biomass fuel or waste fuel is used as the boiler fuel, the fuel contains corrosion-related elements such as Na, K, Cl, and S. Low-melting-point chlorides and sulfates such as NaCl, KCl, Na2SO4, and K2SO4 are precipitated as generated ash that adheres to the heat transfer tubes of the boiler superheater, inducing molten salt corrosion (high-temperature corrosion) of the heat transfer tubes. In addition, the content of corrosion-related elements varies depending on the composition of the fuel, and molten salt corrosion may become severe.

[0007] The present invention has been made to solve the above-mentioned problems, and aims to provide a boiler fuel evaluation method that can estimate the degree of molten salt corrosion of heat transfer tubes depending on differences in fuel composition. [Means for solving the problem]

[0008] In order to achieve the above-mentioned object, a fuel evaluation method for a boiler according to one embodiment of the present invention is a fuel evaluation method for a boiler in which a heat transfer tube is provided in a passage through which combustion gas generated by burning fuel passes, the method including: assuming a plurality of types of fuel having different compositions due to different content ratios of corrosion-related elements that form corrosive condensable components that precipitate and adhere to the surface of the heat transfer tube; a first step of estimating the composition of the corrosive condensable components for each of the assumed fuels by chemical thermodynamic analysis using the fuel composition and the combustion conditions in the boiler; a second step of estimating the relationship between the composition of the corrosive condensable components and a corrosion evaluation value that indicates the degree of corrosion of the heat transfer tube by conducting a corrosion test using a test piece that reflects the composition of all or a part of the corrosive condensable components estimated in the first step; and a third step of determining the relationship between the fuel composition corresponding to the composition of the corrosive condensable components and the corrosion evaluation value based on the estimation results of the first and second steps.

[0009] According to this method, in the third step, the relationship between the fuel composition and the corrosion evaluation value is obtained, so that the degree of molten salt corrosion of the heat transfer tube according to the difference in the fuel composition can be estimated.

[0010] In this specification and the claims, the term "corrosion evaluation value" refers to a value indicating the degree of corrosion, and may be the amount of corrosion thinning calculated from a corrosion test for a specified period of time, or may be a value obtained by converting the amount of corrosion thinning into a corrosion rate. Effect of the Invention

[0011] Advantageous Effects of Invention According to the present invention, there is an advantage in that it is possible to provide a boiler fuel evaluation method capable of estimating the degree of molten salt corrosion of a heat transfer tube according to differences in fuel composition. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram showing an example of a boiler to which the boiler fuel evaluation method of the present embodiment is applied. [Diagram 2] FIG. 2 is a diagram showing an example of a chemical thermodynamic analysis flow in the first step of the boiler fuel evaluation method shown in FIG. [Diagram 3] FIG. 3 is a diagram showing an example of a fuel composition used in the boiler shown in FIG. [Figure 4] FIG. 4 is a diagram showing the analysis results in the first step. [Diagram 5] Figure 5 is a phase diagram plotting the analysis results for each of the 28 types of fuel in the first step. [Figure 6] FIG. 6 shows in tabular form the “coated ash composition” of the corrosive condensable components to be coated on the test specimens used in the corrosion test, as well as the material and shape of the test specimens, the test temperature, the test time, and the gas conditions of the simulated gas on the heat transfer tube surface. [Figure 7] FIG. 7 is a diagram in which the values ​​of the corrosion thinning amounts of the test pieces No. 1 to No. 12 in the first specific example are plotted in correspondence with the corrosive condensation components No. 1 to No. 12 shown in the phase diagram of FIG. [Figure 8] FIG. 8 is a diagram in which the corrosion thinning amounts entered in FIG. 7 are plotted in correspondence with the analysis results in FIG. [Figure 9]FIG. 9 is a diagram showing an example of the range of the content ratio of corrosion-related elements (S, Cl) that is within the corrosion danger range in the case of the first specific example. [Figure 10] FIG. 10 is a diagram in which the values ​​of the corrosion thinning amounts of the test pieces No. 1 to No. 12 in the second specific example are plotted in correspondence with the corrosive condensation components No. 1 to No. 12 shown in the phase diagram of FIG. [Figure 11] FIG. 11 is a diagram in which the corrosion thinning amounts entered in FIG. 10 are plotted in correspondence with the analysis results in FIG. [Figure 12] FIG. 12 is a diagram showing an example of the range of the content ratio of corrosion-related elements (S, Cl) that is within the corrosion danger range in the case of the second specific example. [Figure 13] FIG. 13 is a diagram showing an example of a chemical thermodynamic analysis flow in the first step of the boiler fuel evaluation method when the boiler is of a single-stage combustion type. [Figure 14] FIG. 14 is a schematic diagram showing another example of a boiler to which the boiler fuel evaluation method of the present embodiment is applied. [Figure 15] FIG. 15 is a diagram showing an example of a chemical thermodynamic analysis flow in the first step of the boiler fuel evaluation method shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following, the same or corresponding elements are denoted by the same reference numerals throughout the drawings, and duplicated descriptions thereof will be omitted. In addition, the drawings of Figs. 1 and 14 show each component diagrammatically for ease of understanding, and shapes, dimensional ratios, etc. may not be shown accurately. In addition, the present invention is not limited to the following embodiments.

[0014] (Embodiment) FIG. 1 is a schematic diagram showing an example of a boiler to which the boiler fuel evaluation method of the present embodiment is applied.

[0015] The boiler 1 shown in FIG. 1 is a two-stage combustion type boiler, and includes a combustion chamber (furnace) 2a having a primary combustion region R1 and a secondary combustion region R2 therein, a main body 2 in which a gas flow path is formed, a plurality of burners 3, a plurality of secondary air supply ports 4, and a heat transfer tube 5 constituting a superheater. The burners 3 and the secondary air supply port 4 are connected to the combustion chamber 2a, and the heat transfer tube 5 is disposed in a flue (a passage through which combustion gas passes) above the combustion chamber 2a. The burners 3 burn fuel that is blown in together with the primary air. Note that the primary combustion region R1 and the secondary combustion region R2 are not necessarily limited to the regions shown in the figure.

[0016] In the combustion chamber 2a, the fuel injected from the burner 3 is mixed with the primary air, and most of the fuel is burned in the primary combustion region R1 (primary combustion reaction), and the unburned fuel is burned in the secondary combustion region R2 by the secondary air blown out from the secondary air supply port 4 (secondary combustion reaction). The high-temperature combustion gas thus generated is led from the combustion chamber 2a to the flue and heat-exchanged in the heat transfer tube 5 (hereinafter also referred to as the "flue heat transfer tube 5"). The combustion gas generated in the boiler 1 is finally discharged from a chimney (not shown).

[0017] Next, a method for evaluating fuel for a boiler according to the present embodiment will be described. An example of the boiler fuel evaluation method of this embodiment is a fuel evaluation method for a boiler 1 in which a heat transfer tube 5 is provided in a passage through which combustion gas generated by burning fuel passes, and includes the first to third steps described below, and may further include a fourth step described below.

[0018] [1st process] In the first step, multiple types of fuels with different compositions due to different content ratios of corrosion-related elements that form corrosive condensed components that precipitate and adhere to the surface of the heat transfer tube 5 are assumed, and the composition of the corrosive condensed components is estimated for each of the assumed fuels by performing a chemical thermodynamic analysis using the fuel composition and combustion conditions in the boiler 1. The chemical thermodynamic analysis in this first step is a flow of multiple reactions that simulates phenomena within the boiler 1 related to the corrosion of the heat transfer tube 5 according to the structure of the boiler 1, and a flow of multiple reactions (chemical thermodynamic analysis flow) including the combustion reaction of the fuel and the condensation reaction of the combustion gas on the surface of the heat transfer tube 5 is set, and a thermodynamic equilibrium calculation is performed for each reaction.

[0019] Fig. 2 is a diagram showing an example of a chemical thermodynamic analysis flow in the first step of the boiler fuel evaluation method shown in Fig. 1. This flow is a flow of a plurality of reactions simulating a phenomenon in the boiler 1 related to corrosion of the heat transfer tube 5.

[0020] In this example, in the first step, multiple types of fuels having different compositions are assumed to be multiple types of fuels having different content ratios of corrosion-related elements (e.g., S, Cl) that form corrosive condensable components that adhere to the heat transfer tube 5, and steps S1 to S3 are performed for each fuel to estimate the composition of the corrosive condensable components for each fuel. That is, the composition of the corrosive condensable components for each fuel is estimated.

[0021] 2, first, a primary combustion reaction analysis is performed in the primary combustion region R1 (step S1). Specifically, the composition and amount of each of the primary combustion gas phase and the condensed phase generated by the primary combustion are estimated by thermodynamic equilibrium calculation using the fuel composition (fuel element composition) and combustion conditions such as the amount of primary air and the combustion reaction temperature T1.

[0022] Next, a secondary combustion reaction analysis is performed in the secondary combustion region R2 (step S2). Specifically, the composition and amount of the secondary combustion gas phase and the condensed phase generated by the secondary combustion are estimated by thermodynamic equilibrium calculation using the composition of the primary combustion gas phase, the amount of secondary air, the combustion reaction temperature T2, etc.

[0023] Next, a condensation reaction analysis is performed on the flue heat transfer tube 5 (step S3). Specifically, the composition and amount of each of the gas phase and condensed phase (corrosive condensed components) on the surface of the flue heat transfer tube 5 are estimated by thermodynamic equilibrium calculation using the composition of the secondary combustion gas phase, the condensation reaction temperature (surface temperature of the flue heat transfer tube 5) T3, etc.

[0024] Fig. 3 is a diagram showing an example of a fuel composition used in the boiler 1 shown in Fig. 1. Here, biomass fuel is shown as an example, and the target fuel has a sulfur (S) content (amount of S in the fuel) in the range of 0.01 to 0.1 wt%, and a chlorine (Cl) content (amount of Cl in the fuel) in the range of 0.01 to 1.0 wt%.

[0025] FIG. 4 is a diagram showing the analysis results in the first step. In FIG. 4, the analysis results in the range P1 surrounded by the rectangle ABCD are the analysis results when the content ratios of sulfur (S) and chlorine (Cl) are in the above-mentioned ranges. Here, the analysis results are obtained when the content ratios of chlorine (Cl) are 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, and 1.0 [wt%] for the content ratios of sulfur (S) in the range P1. That is, FIG. 4 shows the analysis results (corrosive condensed components) for 28 types of fuels with different content ratios of sulfur (S) and chlorine (Cl), which are corrosion-related elements. The analysis results outside the range P1 are shown for reference.

[0026] In Fig. 4, the analysis results, such as ◯, ◇, and △, indicate the corrosive condensed components contained in the condensed phase on the surface of the flue heat transfer tube 5, which are obtained by the thermodynamic equilibrium calculation in step S3 in Fig. 2. As shown in Fig. 4, for example, ◯ indicates that NaCl, KCl, and Na2SO4 are contained as corrosive condensed components. ◇ indicates that Na2SO4 and K2SO4 are contained as corrosive condensed components. △ indicates that Na2SO4, KCl, and K2SO4 are contained.

[0027] In the first step, the composition and amount of corrosive condensable components adhering to the flue heat transfer tube 5 are estimated by performing a chemical thermodynamic analysis using the composition of each of the 28 types of fuel. Each fuel contains 0.06 wt% Na and 0.66 wt% K. These Na and K are contained in the ash content of the fuel (see FIG. 3). The combustion reaction temperature T1 inputted to the thermodynamic equilibrium calculation in step S1 of FIG. 2, the combustion reaction temperature T2 inputted to the thermodynamic equilibrium calculation in step S2, and the condensation reaction temperature T3 inputted to the thermodynamic equilibrium calculation in step S3 are each an assumed temperature in an actual boiler, and in this example, temperatures having the relationship T1=T2>T3 are used.

[0028] Fig. 5 is a phase diagram plotting the analysis results for each of the 28 types of fuel in the first step. In Fig. 5, the analysis results are shown as black circles, and the amount (large or small) of corrosive condensable components is roughly indicated by the size (large or small) of the black circle. According to the analysis results of the first step, it can be seen that when a fuel with a composition in which the content ratio of corrosion-related elements (S, Cl) falls within the range P1 in Fig. 4 is used, the composition of the corrosive condensable components adhering to the flue heat transfer tube 5 falls within the range P2 in Fig. 5.

[0029] In the phase diagram of FIG. 5, the corrosive condensation components at corner E are all NaCl, at corner F are all KCl, at corner G are all Na2SO4, and at corner H are all K2SO4. That is, the direction of the arrow a indicates the ratio of Na and K contained in the corrosive condensation components, the part of side GE is 100% Na and 0% K, and the part of side FH is 0% Na and 100% K. The direction of the arrow b indicates the ratio of Cl2 and SO4 contained in the corrosive condensation components, the part of side EF is 100% Cl2 and 0% SO4, and the part of side GH is 0% Cl2 and 100% SO4. In FIG. 5, there are black circles showing multiple analysis results overlapping each other. That is, the six black circles on the side GH where Cl2 is 0% correspond to the 18 analysis results in which the corrosive condensable components consist of Na2SO4 and K2SO4, as indicated by ◇ in Fig. 4. Also, in the phase diagram in Fig. 5, the melting point isotherms of the corrosive condensable components are shown by curves, and these melting point isotherms (curves) are shown by reference to publicly known information.

[0030] The corrosivity of the corrosive condensation component strongly depends on the hierarchical relationship between its melting point and the heat transfer tube temperature (the surface temperature of the heat transfer tube 5). For this reason, it is preferable to plot the composition of the corrosive condensation component estimated by the chemical thermodynamic analysis (first step) on a phase diagram, and select the composition of the corrosive condensation component to be subjected to the corrosion test (second step) described later, taking into consideration the hierarchical relationship between the melting point on the phase diagram and the heat transfer tube temperature. Here, the melting point on the phase diagram refers to the "liquidus temperature", "solidus temperature", "eutectic temperature", "peritectic temperature", etc., and the melting point of the corrosive condensation component can be estimated from its composition by using such a phase diagram.

[0031] [Second process] In the second step, a corrosion test is performed using a test piece that reflects the compositions of all or a part of the corrosive condensable components estimated in the first step, thereby estimating the relationship between the compositions of the corrosive condensable components and a corrosion evaluation value that indicates the degree of corrosion of the heat transfer tube 5. In the following example, a desired composition of a part of the corrosive condensable components is selected from the compositions of all the corrosive condensable components estimated in the first step, and a corrosion test is performed using a test piece that reflects each of the compositions of the selected part of the corrosive condensable components, but the corrosion test may also be performed using a test piece that reflects each of the compositions of all the corrosive condensable components estimated in the first step.

[0032] In this example, several desired corrosive condensation components are selected from among the corrosive condensation components shown by black circles in the phase diagram of Figure 5, and test pieces having the compositions of the selected corrosive condensation components are prepared and subjected to a corrosion test (laboratory corrosion test). In this example, the corrosive condensation components numbered (1) to (12) in Figure 5 were selected. Here, by selecting corrosive condensation components that are appropriately separated in the phase diagram of Figure 5, the number of test pieces to be prepared can be reduced.

[0033] FIG. 6 shows the corrosive condensable components applied to the test pieces used in the corrosion test in the form of a table as the "applied ash composition," and also shows in the form of a table the material and shape of the test pieces, the test temperature, the test time, and the gas conditions of the simulated gas on the surface of the heat transfer tube 5. The numbers (No.) of the "applied ash composition" in FIG. 6 are the numbers of the test pieces, and correspond to the corrosive condensable components of the numbers (1) to (12) in FIG. 5. Here, the material of the flue heat transfer tube 5 (2.25Cr-1Mo steel material) is used for each test piece. In addition to the corrosive condensable components, each test piece is applied with an applied ash containing SiO2, which is a noncorrosive substance, so that the amount of corrosive condensable components contained in the applied ash of each test piece is equal. That is, in this corrosion test, only the composition of the corrosive condensable components caused by the difference in the composition of the fuel is considered, and the amount (precipitation amount) of the corrosive condensable components is not considered.

[0034] Test pieces No. 1 to No. 12 were prepared and subjected to a test in which they were exposed to the gas conditions shown in Figure 6 at 600°C (condensation reaction temperature T3) for 100 hours, and the amount of corrosion thinning (unit: mm) was calculated. This amount of corrosion thinning can be calculated by dividing the amount of weight loss of the test piece before and after the test by the area and density of the test piece. The amount of corrosion thinning of each test piece No. 1 to No. 12 is shown below.

[0035] Corrosion loss of test piece No. 1: 0.006 (mm) Corrosion loss of test piece No. 2: 0.074 (mm) Corrosion loss of test piece No. 3: 0.094 (mm) Corrosion loss of test piece No. 4: 0.079 (mm) Corrosion loss of test piece No. 5: 0.094 (mm) Corrosion loss of test piece No. 6: 0.073 (mm) Corrosion loss of test piece No. 7: 0.071 (mm) Corrosion loss of test piece No. 8: 0.060 (mm) Corrosion loss of test piece No. 9: 0.096 (mm) Corrosion loss of test piece No. 10: 0.119 (mm) Corrosion loss of test piece No. 11: 0.134 (mm) Corrosion loss of test piece No. 12: 0.114 (mm) FIG. 7 shows a diagram in which the corrosion thinning values ​​(unit: mm) of the test pieces No. 1 to No. 12 are plotted in correspondence with the corrosive condensation components No. 1 to No. 12 shown in the phase diagram of FIG.

[0036] That is, the test pieces No. 1 to No. 12 simulate the compositions of the corrosive condensable components estimated in the first step to be precipitated on the surface of the heat transfer tube 5 when fuels of different compositions are used, and in the second step, it is possible to estimate the relationship between the composition of the corrosive condensable components and the corrosion evaluation value (the above-mentioned amount of corrosion thinning) of the heat transfer tube 5. Note that the amount of corrosion thinning calculated from the 100-hour corrosion test as described above may be converted into a corrosion rate and used as the corrosion evaluation value.

[0037] [3rd step] In the third step, based on the estimation results in the first and second steps, the relationship between the fuel composition corresponding to the composition of the corrosive condensable components and the corrosion evaluation value (amount of corrosion thinning) of the heat transfer tube 5 is obtained.

[0038] For example, FIG. 8 shows a diagram in which the corrosion thinning amounts entered in FIG. 7 are entered in correspondence with the analysis results for range P1 in FIG. 4. As a result, FIG. 8 shows the corrosion evaluation values ​​(corrosion thinning amounts) of the heat transfer tubes 5 for each fuel with a different content of corrosion-related elements (S, Cl) in range P1, i.e., for each fuel with a different composition. In other words, the relationship between the composition of each fuel and the corrosion evaluation value (corrosion thinning amount) of the heat transfer tubes 5 can be obtained. Therefore, the degree of molten salt corrosion of the heat transfer tubes 5 according to the difference in fuel composition can be estimated.

[0039] [4th step] In the fourth step, based on the relationship between the composition of each fuel obtained in the third step and the corrosion evaluation value (amount of corrosion thinning) of the heat transfer tube, the range of fuel compositions for which the corrosion evaluation value is equal to or greater than a predetermined value is determined as the corrosion danger range.

[0040] For example, if a range in which the amount of corrosion thinning is 0.075 (mm) or more is set as the corrosion danger range in Fig. 8, the range of fuel compositions in which the content ratio of corrosion-related elements (S, Cl) falls within range Q1 can be set as the corrosion danger range as shown in Fig. 9. This makes it possible to reduce corrosion of the heat transfer tube 5 by designing the fuel composition so that the content ratio of corrosion-related elements (S, Cl) does not fall within range Q1, i.e., so that the range of the fuel composition does not fall within the corrosion danger range.

[0041] In the above example, in the second step, the corrosion test was performed taking into consideration only the composition of the corrosive condensable components resulting from differences in fuel composition, without taking into consideration the amount (amount of deposition) of the corrosive condensable components, but it is preferable to perform the corrosion test taking into consideration both the composition and the amount (amount of deposition) of the corrosive condensable components. As described above, a first specific example will be used to describe a corrosion test taking into consideration only the composition of the corrosive condensable components, and a second specific example will be used to describe a corrosion test taking into consideration both the composition and the amount (amount of deposition) of the corrosive condensable components.

[0042] In the second specific example, the ratio of corrosive condensable components to non-corrosive substances (SiO2) contained in the applied ash of each test piece is changed according to the amount of corrosive condensable components, and the relative ratios of each component (NaCl, KCl, Na2SO4, K2SO4) in the corrosive condensable components are set to the same ratios as in the above-mentioned corrosion test, thereby creating test pieces that reflect the composition and amount (amount of precipitation) of corrosive condensable components that arise due to differences in fuel composition, and then conducting a corrosion test.

[0043] Here, the ratio of corrosive condensation components contained in the applied ash of each test piece is as follows: Specified ratio exceeding 90%: Test piece No. 6 Specified ratio of more than 80% and less than 90%: Test piece No. 10 Specified ratio exceeding 60% and not exceeding 80%: Test piece No. 12 Specified ratio between 40% and 60%: Test pieces No. 5, No. 9, and No. 11 Specified ratio exceeding 20% ​​and not exceeding 40%: Test pieces No. 4 and No. 7 Specified ratio exceeding 0% and not exceeding 20%: Test pieces No. 1, No. 2, No. 3, and No. 8 In this way, test pieces No. 1 to No. 12 were prepared and subjected to a test in which they were exposed to the gas conditions shown in Figure 6 at 600°C for 100 hours. The corrosion thinning amount of each test piece was calculated as follows.

[0044] Corrosion loss of test piece No. 1: 0.018 (mm) Corrosion loss of test piece No. 2: 0.037 (mm) Corrosion loss of test piece No. 3: 0.053 (mm) Corrosion loss of test piece No. 4: 0.072 (mm) Corrosion loss of test piece No. 5: 0.061 (mm) Corrosion loss of test piece No. 6: 0.056 (mm) Corrosion loss of test piece No. 7: 0.064 (mm) Corrosion loss of test piece No. 8: 0.052 (mm) Corrosion loss of test piece No. 9: 0.084 (mm) Corrosion loss of test piece No. 10: 0.082 (mm) Corrosion loss of test piece No. 11: 0.078 (mm) Corrosion loss of test piece No. 12: 0.071 (mm) FIG. 10 shows a diagram in which the corrosion thinning values ​​(unit: mm) of the test pieces No. 1 to No. 12 are plotted in correspondence with the corrosive condensation components No. 1 to No. 12 shown in the phase diagram of FIG.

[0045] That is, the test pieces No. 1 to No. 12 simulate the compositions and deposition amounts of the corrosive condensable components estimated in the first step to be deposited on the surface of the heat transfer tube 5 when fuels of different compositions are used, and in the second step, it is possible to estimate the relationship between the composition and deposition amount of the corrosive condensable components and the corrosion evaluation value (the above-mentioned corrosion thinning amount) of the heat transfer tube 5. Note that the corrosion thinning amount calculated from the 100-hour corrosion test as described above may be converted into a corrosion rate and used as the corrosion evaluation value.

[0046] In this case as well, in the third step, based on the estimation results of the first and second steps, the relationship between the fuel composition corresponding to the composition of the corrosive condensable component selected in the second step and the corrosion evaluation value (amount of corrosion thinning) of the heat transfer tube 5 is determined.

[0047] For example, FIG. 11 shows a diagram in which the values ​​of the corrosion thinning amount entered in FIG. 10 are entered in correspondence with the analysis results for range P1 in FIG. 4. As a result, FIG. 11 shows the corrosion evaluation value (corrosion thinning amount) of the heat transfer tube 5 for each fuel with a different content of corrosion-related elements (S, Cl) in range P1, i.e., for each fuel with a different composition. In other words, the relationship between the composition of each fuel and the corrosion evaluation value (corrosion thinning amount) of the heat transfer tube 5 can be obtained. Therefore, the degree of molten salt corrosion of the heat transfer tube 5 according to the difference in fuel composition can be estimated.

[0048] In this case as well, in the fourth step, based on the relationship between the composition of each fuel obtained in the third step and the corrosion evaluation value (amount of corrosion thinning) of the heat transfer tube, the range of fuel compositions for which the corrosion evaluation value is equal to or greater than a predetermined value is determined as the corrosion danger range.

[0049] For example, if a range in which the amount of corrosion thinning is 0.070 (mm) or more is set as the corrosion danger range in Fig. 11, the range of fuel compositions in which the content ratio of corrosion-related elements (S, Cl) falls within range Q2 can be set as the corrosion danger range as shown in Fig. 12. This makes it possible to reduce corrosion of the heat transfer tube 5 by designing the fuel composition so that the content ratio of corrosion-related elements (S, Cl) does not fall within range Q2, i.e., so that the range of the fuel composition does not fall within the corrosion danger range.

[0050] As in the second example, it is common to perform a corrosion test taking into consideration both the composition and the amount (amount of deposition) of the corrosive condensation components, but in the case of this embodiment, in each of the first and second examples, a similar tendency was obtained in the magnitude relationship of the corrosion thinning amount calculated from the results of the corrosion test. Also, for the corrosion danger range in each example, the range Q1 in Fig. 9 and the range Q2 in Fig. 12 corresponding thereto can be set to a similar range.

[0051] In the above example, in the first step, fuels with different compositions were assumed to be fuels with different content ratios of corrosion-related elements (S, Cl) that form corrosive condensable components, but fuels with different content ratios of other corrosion-related elements (e.g., Na, K) may also be assumed.

[0052] In the above example, biomass fuel is exemplified as the fuel for the boiler, but the fuel is not limited to this. The fuel varies depending on the boiler, and may be, for example, waste fuel such as waste plastic, fossil fuel such as coal, or a mixture of these. Depending on the fuel used, corrosive condensed components that adhere to the heat transfer tube and the corrosion-related elements that form them may be other than those mentioned above.

[0053] (Modification) In the above example, the boiler 1 is a two-stage combustion type boiler, but the case of a single-stage combustion type boiler will be described.

[0054] A single-stage combustion boiler can be considered to have a configuration in which, for example, the secondary air supply port 4 is not provided in the boiler 1 shown in Fig. 1. An example of a chemical thermodynamic analysis flow in the first step of the boiler fuel evaluation method in this case is shown in Fig. 13.

[0055] In this case, in the first step, a primary combustion reaction analysis is performed in the primary combustion region R1 (step S11). Specifically, for each of a plurality of types of fuels having different content ratios of corrosion-related elements, the composition and amount of each of the primary combustion gas phase and condensed phase generated by the primary combustion are estimated by thermodynamic equilibrium calculation using the fuel composition (fuel element composition) and combustion conditions such as the amount of primary air and the combustion reaction temperature.

[0056] Next, a condensation reaction analysis is performed on the flue heat transfer tube 5 (step S12). Specifically, the composition and amount of each of the gas phase and the condensed phase on the surface of the flue heat transfer tube 5 are estimated by thermodynamic equilibrium calculation using the composition of the primary combustion gas phase, the condensation reaction temperature (surface temperature of the flue heat transfer tube 5), etc.

[0057] In this way, in the case of the single-stage combustion type, step S2 for performing the secondary combustion reaction analysis is omitted from the flow of the two-stage combustion type shown in FIG.

[0058] Also, for example, in the case of a three-stage combustion boiler, a tertiary air supply port is provided further downstream in the gas flow path (flue) than the secondary air supply port. In this case, in Fig. 2, a step of performing a tertiary combustion reaction analysis is inserted after step S2 of performing a secondary combustion reaction analysis, and then step S3 of performing a condensation reaction analysis in the flue heat transfer tube 5 is performed. In this way, in the case of an n-stage combustion boiler (n is an integer of 1 or more), the boiler fuel evaluation method of this embodiment can be applied.

[0059] (Other variations) FIG. 14 is a schematic diagram showing another example of a boiler to which the boiler fuel evaluation method of the present embodiment is applied.

[0060] The boiler 20 shown in Fig. 14 includes a combustion vessel 22 constituting a fluidized bed furnace 21. The lower part of the combustion vessel 22 is partitioned by partition walls 41, 42 into three types of cells: a combustion cell 61, a circulation cell 62 located outside the combustion cell 61, and a heat recovery cell 63 located outside the circulation cell 62. The internal circulating fluidized bed 23 is formed by fluidizing the fluidized medium 24 filled in each of the cells 61, 62, 63 with fluidizing gas (G1, Gw). As the fluidized medium 24, for example, silica sand can be used.

[0061] Fuel F1 is supplied to the combustion cell 61 from a fuel inlet (not shown) above the cell 61. A secondary air supply port (not shown) for blowing in secondary air G2 is provided above the fuel inlet.

[0062] The heat recovery cell 63 is provided with an immersed heat transfer tube 64. The heat medium passing through the immersed heat transfer tube 64 recovers heat.

[0063] The bottom of the combustion vessel 22 is provided with a large number of air holes. Below the combustion vessel 22, wind boxes 71, 72, 73 are provided which communicate with the inside of the combustion vessel 22 through the air holes. The wind boxes 71, 72, 73 are provided corresponding to the respective cells 61, 62, 63. Fluidizing gas (G1, Gw) whose flow rate is independently adjusted is supplied to each of the combustion cell 61, the circulation cell 62, and the heat recovery cell 63 through the wind boxes 71, 72, 73. The fluidizing gas G1 supplied to the wind boxes 71, 72 of the combustion cell 61 and the circulation cell 62 is air, the fluidizing gas G1 supplied to the wind box 73 of the heat recovery cell 63 is air, and Gw is the combustion gas (exhaust gas) discharged from the exhaust port 32.

[0064] Here, the flow rates of the fluidizing gases (G1, Gw) supplied to the wind boxes 71, 72, 73 are adjusted so as to generate a circulating flow of the bed material 24. That is, the superficial velocity of the fluidizing gas G1 in the circulation cell 62 is set equal to or lower than the superficial velocity of the fluidizing gas G1 in the combustion cell 61, and the superficial velocity of the fluidizing gas G1 in the combustion cell 61 is set higher than the superficial velocity of the fluidizing gas (G1, Gw) in the heat recovery cell 63. As a result, the bed material 24 in the combustion cell 61 moves to the circulation cell 62 by passing under the partition wall 41, the bed material 24 in the circulation cell 62 moves to the heat recovery cell 63 by jumping over the partition wall 42, and the bed material 24 in the heat recovery cell 63 moves to the combustion cell 61 by passing under the partition walls 41, 42. In this manner, the bed material 24 circulates.

[0065] In this fluidized bed furnace 21, primary combustion is carried out in a combustion cell 61 to which fuel F1 is supplied, and combustion gas and pyrolysis residue, etc. are generated. The pyrolysis residue and unburned fuel F1 are discharged from an outlet 25 to the outside of the furnace.

[0066] The combustion gas generated in the combustion cell 61 rises together with the fluidized gases G1, Gw that have passed through the circulation cell 62 and the heat recovery cell 63, and secondary air G2 is further supplied to perform complete combustion (secondary combustion) in the secondary combustion region R20, and the combustion gas (exhaust gas) Gw passes through the flue 30 and is discharged from the exhaust port 32. The flue 30 is provided with a flue heat transfer tube 31, and heat is recovered by a heat medium passing through the flue heat transfer tube 31. Here, a condensation reaction occurs on the surface of the flue heat transfer tube 31, whose surface temperature is lower than the combustion gas temperature.

[0067] The fuel evaluation method for the boiler 20 also includes the first to third steps, and may further include a fourth step, similar to the above-described boiler 1. Here, a case where the target of corrosion evaluation is the immersed heat transfer tube 64 will be described.

[0068] In the first step, multiple types of fuel with different compositions are assumed, and for each of these assumed fuels, the composition of the corrosive condensable components that precipitate and adhere to the surface of the immersed heat transfer tube 64 is estimated by chemical thermodynamic analysis using the fuel composition.

[0069] FIG. 15 is a diagram showing an example of a chemical thermodynamic analysis flow in the first step of the fuel evaluation method for the boiler 20.

[0070] In this case, in the first step, a primary combustion reaction analysis is first performed in the combustion cell 61 (step S21). Specifically, for each of a plurality of types of fuels having different content ratios of corrosion-related elements, the compositions and amounts of the primary combustion gas phase and the condensed phase generated by the primary combustion are estimated by thermodynamic equilibrium calculation using the fuel composition (fuel element composition) and combustion conditions such as the amount of primary air (fluidizing gas G1 supplied to the combustion cell 61) and the combustion reaction temperature.

[0071] Next, a secondary combustion reaction analysis is performed in the secondary combustion region R20 (step S22). Specifically, the composition and amount of the secondary combustion gas phase and the condensed phase generated by the secondary combustion are estimated by thermodynamic equilibrium calculation using the composition of the primary combustion gas phase, the amount of secondary air G2, the combustion reaction temperature, etc.

[0072] Next, a condensation reaction analysis is performed in the flue heat transfer tube 31 (step S23). Specifically, the composition and amount of each of the gas phase and the condensed phase on the surface of the flue heat transfer tube 31 are estimated by thermodynamic equilibrium calculation using the composition of the secondary combustion gas phase, the condensation reaction temperature (the surface temperature of the flue heat transfer tube 31), etc.

[0073] Next, a condensation reaction analysis is performed on the immersed heat transfer tube 64 (step S24). Specifically, the composition and amount of each of the gas phase and condensed phase (corrosive condensed components) on the surface of the immersed heat transfer tube 64 are estimated by thermodynamic equilibrium calculation using the composition of the gas phase on the surface of the flue heat transfer tube 31, the condensation reaction temperature (surface temperature of the immersed heat transfer tube 64), and the like.

[0074] In this case, the second to fourth steps can be performed in the same manner as in the case of the above-mentioned boiler 1. That is, in the second step, several desired compositions of corrosive condensable components are selected from the compositions of corrosive condensable components adhering to the surface of the immersed heat transfer tube 64 estimated in step S24 of the first step, and a corrosion test is performed using a test piece reflecting the composition (or composition and deposition amount) of the selected corrosive condensable components, thereby estimating the relationship between the composition (or composition and deposition amount) of the corrosive condensable components and the corrosion evaluation value indicating the degree of corrosion of the immersed heat transfer tube 64.

[0075] Then, in the third step, a relationship between the fuel composition corresponding to the composition of the corrosive condensable component selected in the second step and the corrosion evaluation value is obtained based on the estimation results in the first and second steps, which makes it possible to estimate the degree of molten salt corrosion of the immersed heat transfer tubes 64 according to differences in fuel composition.

[0076] Furthermore, in the fourth step, a corrosion danger range is set, and the fuel composition is designed so that the range of the fuel composition does not fall within the corrosion danger range, thereby making it possible to reduce corrosion of the immersed heat transfer tubes 64.

[0077] In addition, in this boiler 20, when the object of corrosion evaluation is the flue heat transfer tube 31, there is no need to perform step S24 in the first step, and it is sufficient to perform the second step and subsequent steps on the corrosive condensed components adhering to the surface of the flue heat transfer tube 31 estimated by the condensation reaction analysis of the flue heat transfer tube 31 in step S23.

[0078] (summary) A boiler fuel evaluation method according to one embodiment of the present invention is a fuel evaluation method for a boiler in which a heat transfer tube is provided in a passage through which combustion gas generated by burning fuel passes, the method including: assuming a plurality of types of fuel having different compositions due to different content ratios of corrosion-related elements that form corrosive condensable components that precipitate and adhere to the surface of the heat transfer tube; a first step of estimating the composition of the corrosive condensable components for each of the assumed fuels by chemical thermodynamic analysis using the fuel composition and the combustion conditions in the boiler; a second step of estimating the relationship between the composition of the corrosive condensable components and a corrosion evaluation value that indicates the degree of corrosion of the heat transfer tube by conducting a corrosion test using a test piece that reflects the composition of all or a part of the corrosive condensable components estimated in the first step; and a third step of determining the relationship between the fuel composition corresponding to the composition of the corrosive condensable components and the corrosion evaluation value based on the estimation results of the first and second steps.

[0079] According to this method, in the third step, the relationship between the fuel composition and the corrosion evaluation value is obtained, so that the degree of molten salt corrosion of the heat transfer tube according to the difference in the fuel composition can be estimated.

[0080] The second step may involve plotting the compositions of all the corrosive condensable components estimated in the first step on a predetermined phase diagram, selecting desired compositions of the corrosive condensable components from the plotted compositions of the corrosive condensable components, and performing the corrosion test using test pieces reflecting the compositions of the selected corrosive condensable components. In this case, the number of test pieces to be prepared can be reduced by selecting compositions of the corrosive condensable components that are appropriately separated from each other on the phase diagram.

[0081] The first step may involve estimating the composition of the corrosive condensed component as well as its amount of precipitation, and the second step may involve performing the corrosion test using a test piece that reflects the composition of the corrosive condensed component as well as its amount of precipitation, thereby estimating the relationship between the composition and amount of precipitation of the corrosive condensed component and the corrosion evaluation value.

[0082] The method may further include a fourth step of determining a range of fuel compositions in which the corrosion evaluation value is equal to or greater than a predetermined value as a corrosion danger range based on the relationship between the fuel composition and the corrosion evaluation value obtained in the third step. In this case, the fuel composition can be designed so as not to fall within the corrosion danger range, thereby reducing corrosion of the heat transfer tube.

[0083] The chemical thermodynamic analysis in the first step may be a flow of a plurality of reactions simulating phenomena within the boiler related to corrosion of the heat transfer tube depending on the structure of the boiler, the flow of the plurality of reactions including a fuel combustion reaction and a condensation reaction of the combustion gas on the surface of the heat transfer tube being set, and a thermodynamic equilibrium calculation may be performed for each of the reactions.

[0084] From the above description, many improvements and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as merely illustrative and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present invention. Details of the structure and / or function thereof may be substantially changed without departing from the spirit of the present invention. [Industrial Applicability]

[0085] INDUSTRIAL APPLICABILITY The present invention is useful as a boiler fuel evaluation method or the like that can estimate the degree of molten salt corrosion of a heat transfer tube depending on differences in fuel composition. [Explanation of symbols]

[0086] 1,20 Boiler 5 Heat transfer tube 64 Submerged Heat Transfer Tube

Claims

1. A fuel evaluation method for a boiler having a heat transfer tube provided in a passage through which combustion gas generated by burning fuel passes, comprising the steps of: A first step of assuming a plurality of types of fuels having different compositions due to different content ratios of corrosion-related elements that form corrosive condensed components that precipitate and adhere to the surface of the heat transfer tube, and estimating the composition of the corrosive condensed components for each of the assumed fuels by chemical thermodynamic analysis using the fuel composition and the combustion conditions in the boiler; A second step of estimating a relationship between the composition of the corrosive condensation components and a corrosion evaluation value indicating the degree of corrosion of the heat transfer tube by performing a corrosion test using a test piece reflecting all or a part of the composition of the corrosive condensation components estimated in the first step; A third step of determining a relationship between a fuel composition corresponding to a composition of the corrosive condensed component and the corrosion evaluation value based on the estimation results of the first step and the second step. Boiler fuel evaluation methods.

2. The second step comprises: Plotting the compositions of all the corrosive condensable components estimated in the first step on a predetermined phase diagram, selecting a desired composition of a portion of the corrosive condensable components from the plotted compositions of the corrosive condensable components, and performing the corrosion test using a test piece reflecting the composition of the selected corrosive condensable components. The boiler fuel evaluation method according to claim 1.

3. The first step comprises: The composition of the corrosive condensation component and the amount of the precipitation thereof are estimated, The second step comprises: The corrosion test is performed using a test piece that reflects the composition and amount of precipitation of the corrosive condensation component, thereby estimating the relationship between the composition and amount of precipitation of the corrosive condensation component and the corrosion evaluation value. The boiler fuel evaluation method according to claim 1 or 2.

4. A fourth step of determining a range of fuel compositions in which the corrosion evaluation value is equal to or greater than a predetermined value as a corrosion danger range based on the relationship between the fuel composition and the corrosion evaluation value obtained in the third step. The boiler fuel evaluation method according to any one of claims 1 to 3.

5. The chemical thermodynamic analysis in the first step A flow of a plurality of reactions simulating phenomena in the boiler related to corrosion of the heat transfer tube in accordance with a structure of the boiler, the flow of the plurality of reactions including a fuel combustion reaction and a combustion gas condensation reaction on the surface of the heat transfer tube, is set, and a thermodynamic equilibrium calculation is performed for each of the reactions. The boiler fuel evaluation method according to any one of claims 1 to 4.

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