JP6847711B2 - Anticorrosion method and anticorrosion control device - Google Patents

Description

The present invention relates to an anticorrosion method and an anticorrosion control device for a heat exchanger in a device that burns fuel to generate energy.

Devices that generate energy by combustion include industrial boilers, commercial boilers, and various turbines. In such devices, fossil fuels such as coal and heavy oil are often used as fuel. For example, Patent Document 1 discloses a thermal boiler that uses pulverized coal as fuel.

Fossil fuels are a finite resource and are said to be depleted in the future. _{In recent years, reduction of CO 2} emissions has been promoted from the viewpoint of global warming, _{so fossil fuels that emit a large amount of CO 2} and promote global warming are used from the viewpoint of global environmental conservation. It is being regulated.

Therefore, as an alternative to fossil fuels, the use of renewable energy such as waste or biomass is being promoted. Biomass is a general term for biological resources produced from animals and plants. Biomass, which is often used in equipment that produces energy by combustion, is wood-based materials such as construction waste and thinned wood. Construction waste is easier to obtain as a cheaper fuel than thinned wood (unused wood).

Japanese Unexamined Patent Publication No. 2014-228258

In a device that produces energy by combustion, the components inside the device may corrode due to the components contained in the fuel.

For example, Patent Document 1 discloses that the furnace wall of a boiler is sulfurized and corroded due to the sulfur content in coal. In Patent Document 1, the degree of sulfurization corrosion is predicted with high accuracy by the reaction fluid calculation, and the life of the furnace wall tube is evaluated.

For example, in a boiler that generates energy by burning waste or biomass, there is a concern that the material of the heat transfer tube above the boiler will be corroded by the molten salt. A part of the ash generated when the fuel is burned adheres to and accumulates on the heat transfer tube while flowing together with the combustion gas. Molten salt components (K, Na, S, Cl, etc.) are concentrated in the attached ash. Chlorine compounds contained in the molten salt in the adhered ash are known to induce severe corrosion of heat transfer tubes in particular.

In order to prevent corrosion due to the molten salt component, measures such as using a Ni alloy having high corrosion resistance as the material of the heat transfer tube or setting a regulation value for the chlorine content in the fuel are usually taken.

However, Ni alloys are expensive materials and their use increases costs. While cost reduction is achieved with cheap fuel, using expensive Ni alloy does not lead to expansion of the use of cheap fuel. In addition, construction waste materials tend to contain a larger amount of molten salt components than unused wood. Therefore, limiting the chlorine content in the fuel does not lead to the expansion of the use of inexpensive fuel.

The present invention has been made in view of such circumstances, and provides an anticorrosion method and an anticorrosion control device capable of expanding the application of inexpensive fuels and suppressing an increase in cost for anticorrosion. With the goal.

In order to solve the above problems, the anticorrosion method and the anticorrosion control device of the present invention employ the following means.

The present invention is a method for preventing corrosion of a heat exchanger in an apparatus that burns fuel to generate energy, in which a step of acquiring composition information of Na, K, Cl and S in the fuel and the acquired composition information are obtained. Based on the step of identifying a salt composition containing at least one of Na or K that may be present in the combustion ash obtained by burning the fuel and the melting point information of the salt composition, the metal of the heat exchanger. The step of specifying the salt composition includes a step of determining the set temperature range of the salt composition to be lower than the melting point of the salt composition and a step of adjusting the temperature of the metal so as to be within the set temperature range. When the total amount of Cl and S in the fuel is smaller than the chemical ratio to the total amount of Na and K, carbonate is present in the combustion ash, and the total amount of Cl and S is present. However, the present invention provides an anticorrosion method including a step of determining that carbonate cannot be present in the combustion ash when the total amount of Na and K is larger than the chemical quantity theory ratio.

Molten salt components (Na, K, Cl and S) are contained in the combustion ash deposited on the metal surface of the heat exchanger. However, in the above invention, since the temperature of the metal of the heat exchanger is adjusted so as to be lower than the melting point of the salt composition that can be contained in the combustion ash, the formation of molten salt on the metal surface can be prevented. This makes it possible to avoid corrosion of the heat exchanger without limiting the use of expensive corrosion resistant materials and the chlorine content in the fuel.

Multiple salts can be present in the combustion ash produced by burning fuel. The melting point of a salt composition in which a plurality of salts are mixed varies depending on the combination and composition of the mixed salts. Therefore, in order to adjust the metal temperature so that molten salt is not formed, it is important to identify the salt composition that can be present in the combustion ash.

The invention identifies salts containing at least one of Na or K of the type that may be present in the combustion ash. Na and K are molten salt cation components contained in the fuel. Na and K react with the molten salt anion component of Cl or S to form a compound. Therefore, the salt that can be contained in the combustion ash can be specified based on the composition information of Na, K, Cl and S in the fuel.

On the other hand, when the molten salt cation component is present in a larger amount than the chemical quantity theory ratio with respect to the total amount of Cl and S, the excess molten salt cation component can _{react with carbonic acid (CO 2} ) to become a carbonate. The melting point information to be used changes depending on the presence or absence of carbonate. Since biomass tends to contain a large amount of molten salt cation components, more accurate melting point information can be obtained by determining the presence or absence of carbonate when using biomass as a fuel.

In one aspect of the above invention, the step of adjusting the temperature of the metal is the first adjustment for adjusting the heat transfer area of the heat exchanger at the design stage, and the temperature of the metal is measured during the operation of the apparatus. A second adjustment for adjusting the fuel input amount based on the obtained measured value may be included.

By adjusting the metal temperature of the heat exchanger in two steps, the formation of molten salt can be reliably prevented.

The present invention is a method for preventing corrosion of a heat exchanger in an apparatus for burning biomass to generate energy, in which the compositions of Na, K, Cl and S in the biomass are obtained, and the Cl and the above in the biomass. When the total amount of S is less than the chemical biomass ratio to the total amount of Na and K, carbonate is present in the combustion ash, and the total amount of Cl and S is that of Na and K. If more than the stoichiometric ratio of the total amount, the determining that during the combustion ash not exist carbonates, the biomass comprises the Na, the K, the Cl and the S, and the the total amount of Cl and the S is wherein when the total amount of Na and the K greater than the stoichiometric ratio, set the metal surface temperature of the heat exchanger below 518 ° C., the biomass is the Na the K, wherein the Cl and the S, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K, of the heat exchanger of metal Provided is an anticorrosion method for setting the surface temperature to less than 544 ° C.

If the biomass contains Na, K, Cl and S, NaCl, KCl, Na ₂ SO ₄ , K ₂ SO ₄ may be present in the combustion ash. The minimum liquid phase formation temperature of the salt composition in which these salts are present is 518 ° C. Therefore, by adjusting the metal temperature to less than 518 ° C., preferably 515 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

On the other hand, when the molten salt anion component is present in a smaller amount than the chemical quantity theory ratio with respect to the molten salt cation component, carbonates (Na ₂ CO ₃ , K ₂ CO ₃ ) may be further mixed in the combustion ash. The minimum liquid phase formation temperature for such salt compositions is 544 ° C. Therefore, by adjusting the metal temperature to less than 544 ° C., preferably 544 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

When carbonate is contained, the minimum liquid phase formation temperature of the salt composition can be raised by about 30 ° C. as compared with the case where carbonate is not contained. It is preferable that the metal temperature of the heat exchanger is high. According to the above invention, by confirming the presence or absence of carbonate, the metal temperature can be raised as much as possible to improve the energy generation efficiency while suppressing corrosion.

Further, the present invention is a method for preventing corrosion of a heat exchanger in an apparatus for burning biomass to generate energy, in which the compositions of Na, K, Cl and S in the biomass are obtained and the Cl in the biomass is obtained. And when the total amount of S is less than the chemical biomass ratio to the total amount of Na and K, carbonate is present in the combustion ash and the total amount of Cl and S is Na and said. If the total amount of K greater than the stoichiometric ratio, wherein determining that the carbonate during the combustion ash not exist, the biomass comprises the Na, the K and the Cl, include the S When the total amount of Cl and S is larger than the chemical biomass ratio with respect to the total amount of Na and K, the surface temperature of the metal of the heat exchanger is set to less than 658 ° C. the biomass is the Na, wherein the K and the Cl, excluding the S, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K Provided is an anticorrosion method for setting the surface temperature of the metal of the heat exchanger to less than 558 ° C.

If the biomass does not contain S but contains Na, K and Cl, NaCl and KCl may be present in the combustion ash. The minimum liquid phase formation temperature of the salt composition in which these salts are present is 658 ° C. Therefore, by adjusting the metal temperature to less than 658 ° C., preferably 650 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

On the other hand, when the molten salt anion component is present in a smaller amount than the chemical quantity theory ratio with respect to the molten salt cation component, carbonates (Na ₂ CO ₃ , K ₂ CO ₃ ) may be further mixed in the combustion ash. The minimum liquid phase formation temperature for such salt compositions is 558 ° C. Therefore, by adjusting the metal temperature to less than 558 ° C., preferably 555 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

Further, the present invention is a method for preventing corrosion of a heat exchanger in an apparatus for burning biomass to generate energy, in which the compositions of Na, K, Cl and S in the biomass are obtained and the Cl in the biomass is obtained. And when the total amount of S is less than the chemical biomass ratio to the total amount of Na and K, carbonate is present in the combustion ash and the total amount of Cl and S is Na and said. If the total amount of K greater than the stoichiometric ratio, wherein determining that not exist carbonates during combustion ash, the biomass is the Na, wherein the K and the S, include the Cl When the total amount of Cl and S is larger than the chemical biomass ratio with respect to the total amount of Na and K, the surface temperature of the metal of the heat exchanger is set to 800 ° C. or lower. the biomass is the Na, wherein the K and the S, not including the Cl, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K Provided is an anticorrosion method for setting the surface temperature of the metal of the heat exchanger to less than 700 ° C.

Even if the fuel does not contain Cl, there is a risk that the metal of the heat exchanger will corrode due to sulfurization and carburizing. Therefore, it is necessary to adjust the metal temperature in order to suppress corrosion. If the biomass does not contain Cl but contains Na, K and S, Na ₂ SO ₄ and K ₂ SO ₄ may be present in the combustion ash. The minimum liquid phase formation temperature of the salt composition in which these salts are present is lower than 850 ° C and higher than 800 ° C. Therefore, by adjusting the metal temperature to 800 ° C. or lower, preferably 700 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

On the other hand, when the molten salt anion component is present in a smaller amount than the chemical quantity theory ratio with respect to the molten salt cation component, carbonates (Na ₂ CO ₃ , K ₂ CO ₃ ) may be further mixed in the combustion ash. The minimum liquid phase formation temperature for such salt compositions is 700 ° C. Therefore, by adjusting the metal temperature to less than 700 ° C., preferably 650 ° C. or lower, the formation of molten salt can be prevented and corrosion of the heat exchanger can be suppressed.

Further, the present invention is an anticorrosion control device which is connected to a device for combusting fuel to generate energy and controls anticorrosion of the heat exchanger of the device, wherein Na, K, Cl and S in the fuel. An acquisition unit for acquiring composition information, and a specific unit for specifying a salt composition containing at least one of Na or K that may be present in combustion ash obtained by burning the fuel based on the acquired composition information. When the total amount of Cl and S is smaller than the chemical ratio to the total amount of Na and K, carbonate is present in the combustion ash, and Cl and When the total amount of S is larger than the chemical quantity theory ratio with respect to the total amount of Na and K, a determination unit for determining that no carbonate is present in the combustion ash, and at least of Na and K. A library that stores information on the multidimensional melting point of the salt composition containing one of them, and fuel information that correlates the temperature of the metal of the heat exchanger and the amount of fuel input, and the salt composition specified in the specific part. Based on the information in Provided is an anticorrosion control device including a unit and an adjusting unit for adjusting the amount of fuel input so that the temperature of the metal falls within the set temperature range.

In one aspect of the present invention, the adjusting unit may have a receiving unit that receives the measured temperature of the metal, and the input amount of the fuel may be adjusted so that the received measured temperature falls within the set temperature range. ..

According to the present invention, the formation of molten salt on the metal surface can be prevented by adjusting the temperature of the metal of the heat exchanger so that the temperature is lower than the melting point of the salt composition that can be contained in the combustion ash. As a result, it is possible to expand the application of inexpensive fuels and suppress the increase in costs for anticorrosion.

It is a schematic block diagram of the biomass combustion boiler which concerns on one Embodiment. It is a figure which shows the procedure of the anticorrosion method which concerns on one Embodiment. It is a figure which shows an example of the multi-dimensional melting point diagram. It is a figure which shows an example of the multi-dimensional melting point figure. It is a figure which shows an example of the multi-dimensional melting point figure. It is a figure which shows an example of the multi-dimensional melting point diagram. It is a figure which shows an example of the multi-dimensional melting point figure. It is a schematic block diagram of the anticorrosion control device which concerns on one Embodiment. It is the schematic of the adhered ash layer. It is a figure which shows the result of having analyzed the actual ash situation of the actual machine of a biomass combustion boiler. It is a figure which shows the result of having analyzed the actual ash situation of the actual machine of a biomass combustion boiler. It is a figure which illustrates composition information of biomass. It is a figure which illustrates the relationship between the cation component (K ₂ O + Na ₂ O) and the anion component (2Cl + SO _{4) in a fuel.}

Hereinafter, an embodiment of the anticorrosion method and the anticorrosion control device according to the present invention will be described with reference to the drawings. The present invention may be applied to devices that burn fuel to generate energy and have heat exchangers that are concerned about corrosion by molten salts. Such devices include biomass combustion boilers, waste combustion boilers, incinerators, and recovery boilers. Heat exchangers that may be corroded by molten salt are heat transfer tubes such as heaters, reheaters, and economizers. Molten salt components that may corrode heat exchangers are sodium (Na), potassium (K), chlorine (Cl), sulfur (S) and carbonic acid (CO ₃ ).

In this embodiment, the anticorrosion method and the anticorrosion device applied to the biomass combustion boiler will be illustrated.

FIG. 1 shows a schematic configuration diagram of the biomass combustion boiler 1. The biomass combustion boiler 1 includes a fuel supply unit 2 that supplies fuel (biomass) F, a furnace 4 that burns the supplied fuel with a burner 3 to generate heat, an upper position of the furnace 4, and the vicinity of a gas discharge port 5. It is equipped with 6 groups of heat transfer tubes (evaporator, overheater, reheater, coal saver) arranged in.

The combustion gas G generated by burning the biomass in the fireplace 4 flows above the fireplace 4, exchanges heat with the heat transfer tube group 6, and then is discharged from the gas discharge port 5 to the exhaust gas treatment facility and the like downstream. The high-temperature steam generated by the heat exchange in the heat transfer tube group 6 is supplied to a steam turbine (not shown) to drive the steam turbine.

Combustion gas contains combustion ash. The combustion ash adheres to each heat transfer tube of the heat transfer tube group while the combustion gas is flowing. The heat transfer tube is made of a metal material such as low alloy steel (2Cr), SUS304, or SUS310. SUS means stainless steel, and both SUS304 and SUS310 are a type of stainless steel.

FIG. 2 shows the procedure of the anticorrosion method according to the present embodiment. The anticorrosion method according to the present embodiment determines a step of acquiring fuel composition information (S1), a step of specifying a salt composition that may exist in combustion ash (S2), and a set temperature range of the metal of the heat transfer tube. The step (S3) and the step (S4) of adjusting the metal temperature of the heat transfer tube are included.

S1: Step of acquiring fuel composition information Wood fuel (pellets, chips), rice straw fuel, PKS (Perm Kernel Shell) and the like are used as the biomass of the fuel. In this step, at least the composition information of Na, K, Cl and S in the fuel is acquired.

The composition information can be obtained by analysis using, for example, a high temperature combustion method, a high frequency inductively coupled plasma (ICP) method, an ion chromatography (IC) method, an atomic absorption method, an XRF (X-ray diffraction method), or the like. As the composition information, the composition information provided by the fuel distributor may be used. When obtained by analysis, composition information is preferably obtained after fuel purchase or prior to fuel use.

In the high-temperature combustion method, a sample (fuel) is heated to about 1350 ° C. in an oxygen stream, total sulfur is oxidized and vaporized, collected with a hydrogen peroxide solution, and then titrated with a sodium hydroxide standard solution. This is the method (see Japanese Industrial Standard JIS M 8813). The high temperature combustion method can quantify S (combustible S, nonflammable S) contained in the fuel.

The ICP method is a method in which an inductively coupled plasma generated by argon gas heats a sample (fuel) and atomizes and thermally excites the element to identify and quantify the element. The ICP method can quantify Na and K contained in the fuel.

The IC method is a method using liquid chromatography (ion exchange chromatography) in which an ion exchange resin is used as a stationary phase and an aqueous solution of an electrolyte is used as a mobile phase (eluent). Cl can be identified and quantified for the peak of the obtained chromatogram by matching the retention time with the standard solution. The fuel is pretreated with a combustion device or the like and then subjected to chromatography.

S2: Step of specifying the salt composition that can be present in the combustion ash Based on the composition information acquired in S1, the salt composition that can be present in the combustion ash is specified. The salt composition that may be present in the combustion ash comprises at least one of Na or K. The salt composition that can be present in the combustion ash is a composition consisting of one kind of salt or a composition in which a plurality of salts are mixed.

In the same step, for example, when Na, K and Cl are contained in the fuel, it is specified that a salt composition containing NaCl and KCl may be present in the combustion ash. For example, if the fuel contains Na, K and S, it is specified that a salt composition containing _{Na 2} SO ₄ and K ₂ SO _{4 may be present in the combustion ash.} For example, if the fuel contains Na, K, Cl and S, it is specified that a salt composition containing _{NaCl, KCl, Na 2} SO ₄ and K ₂ SO _{4 may be present in the combustion ash.}

The step (S2) of identifying the salt composition that may be present in the combustion ash _{determines whether or not carbonates containing Na or K (Na 2} CO ₃ , K ₂ CO ₃ ) can be present in the combustion ash. Including the process of In the determination step, when the total amount of Cl and S in the fuel is smaller than the stoichiometric ratio with respect to the total amount of Na and K based on the composition information acquired in S1, carbonate is contained in the combustion ash. Determine that it can exist. In the same step, based on the composition information obtained in S1, when the total amount of Cl and S is larger than the stoichiometric ratio to the total amount of Na and K, carbonate cannot be present in the combustion ash. judge.

S3: Step of determining the set temperature range of the metal of the heat transfer tube Based on the melting point information of the salt composition specified in S2, the set temperature range of the metal is set to the temperature at which the salt composition specified in S2 does not become a molten salt (melting point). Less than). The lower limit of the set temperature range is not particularly limited, but is usually set to a temperature equal to or higher than the saturation temperature due to the pressure of the water / steam system, and is approximately 300 ° C. or higher.

When the salt composition specified in S2 contains only one kind of salt, the set temperature range is determined in the range of the temperature (less than the melting point) at which the specified salt does not become a molten salt. When the salt composition specified in S2 contains a plurality of salts, the melting point information of the multi-dimensional salt composition can be obtained by using the multi-dimensional melting point diagram related to the specified salt. Then, based on the melting point information, the set temperature range is set in the temperature range in which the multidimensional salt composition does not become a molten salt. The temperature range in which the multidimensional salt composition does not become a molten salt can be obtained by reading the lowest liquid phase formation temperature from the multidimensional melting point diagram.

3 to 7 show an example of a multi-dimensional melting point diagram. The number shown in the figure is the melting point (° C.).

FIG. 3 is a quaternary melting point diagram (EK Akopov and AG Bergman, Zhur. Neorg. Khim., 4 [7] of the KCl-NaCl-K ₂ SO _{4- Na 2} SO _{4 system salt composition.} ] 1655 (1959)).

According to FIG. 3, for example, _{a quaternary salt composition in which KCl, NaCl, K 2} SO ₄ and Na ₂ SO ₄ are mixed does not become a molten salt at a temperature of less than 518 ° C. (that is, a solid salt state). Melting point information that can be maintained) is obtained.

According to FIG. 3, for example, melting point information that a binary salt composition in which KCl and NaCl are mixed does not become a molten salt at a temperature lower than 658 ° C. can be obtained.

Figure 4 is _a ternary melting diagram of _{KCl-Na 2 CO 3 -Na 2} SO 4 based salt composition (A.G.Bergman and A.K.Sementsova, Zhur.Neorg.Khim., 3 [2] 395 (See (1958)).

According to FIG. 4, for example, _{melting point information that a ternary salt composition in which KCl, Na 2} CO ₃ and Na ₂ SO ₄ are mixed does not become a molten salt at a temperature of less than 544 ° C. can be obtained.

FIG. 5 is a _{ternary melting point diagram of a KCl-K 2} SO _4- Na ₂ CO ₃ salt composition (AK Sementsova and AG Bergman, Zhur. Obshchel. Khim., 26, 995 (1958). )).

According to FIG. 5, for example, _KCl, 3 ternary salt composition is K 2 SO ₄ and _Na 2 CO ₃ to mixed melting point information is obtained that does not become molten salt at a temperature below 546 ° C..

Combining the melting point information obtained from FIGS. 4 and 5, the multidimensional salt composition in which the fuel contains Na, K, Cl and S and contains carbonate does not become a molten salt at temperatures below 544 ° C. Melting point information can be obtained. Note that, unlike FIG. 3, FIGS. 4 and 5 do not cover all the compounds to be considered, but from FIG. 3, NaCl and KCl, Na ₂ SO ₄ and K ₂ SO ₄ show similar behaviors. It can be used as an approximate temperature.

FIG. 6 is a quaternary melting point diagram (RN Nyankovskaya, Doklady Akad. Nauk S.S.S.R., 83, 420) of the KCl-NaCl-K ₂ CO _{3- Na 2} CO _{3 system salt composition.} (See (1952)).

According to FIG. 6, for example, _{melting point information that a quaternary salt composition in which KCl, NaCl, K 2} CO ₃ and Na ₂ CO ₃ are mixed does not become a molten salt at a temperature of less than 558 ° C. can be obtained.

FIG. 7 is a quaternary melting point diagram (AK Sementsova, KA Bvdoklmova, and AG) _{of the K 2} SO _4- Na ₂ SO _4- K ₂ CO _{3- Na 2} CO _{3 salt composition.} . Bergman, Zhur. Neorg. Khim., 4, 146 (1968)).

According to FIG. 7, for example, _{a quaternary salt composition in which K 2} SO ₄ , Na ₂ SO ₄ , K ₂ CO ₃ and Na ₂ CO ₃ are mixed does not become a molten salt at a temperature of less than 700 ° C. Information is available.

According to FIG. 7, for example, _{melting point information that a binary salt composition in which K 2} SO ₄ and Na ₂ SO ₄ are mixed does not become a molten salt at a temperature of 800 ° C. or lower can be obtained.

S4: Step of adjusting the metal temperature of the heat transfer tube The metal temperature is adjusted so as to be within the set temperature range determined in S3. The metal temperature is designed from the exhaust gas temperature and the steam temperature at the time of design. If the water / steam cycle temperature is fixed, install the metal at a position where the exhaust gas temperature is low in order to lower the metal temperature. Exhaust gas temperature and steam temperature are controlled by adjusting the load during operation such as when changing fuel after design.

In S4, both the first adjustment for adjusting the heat transfer area of the heat transfer tube at the design stage and the second adjustment for adjusting the fuel input amount during the operation of the biomass combustion boiler may be performed. At the time of the second adjustment, the metal temperature of the heat transfer tube is measured, and based on the obtained measured value, the fuel input amount may be controlled so that the metal temperature falls within the set temperature range determined in S3. By doing so, corrosion due to the molten salt can be prevented more reliably.

Next, an anticorrosion control device for implementing the anticorrosion method according to the present embodiment will be described. FIG. 8 shows a schematic configuration diagram of the anticorrosion control device 10. The anticorrosion control device 10 includes an acquisition unit 11, a specific unit 12, a determination unit 13, a library 14, a determination unit 15, and an adjustment unit 16.

The acquisition unit 11 acquires composition information of the fuel supplied to the biomass combustion boiler. The composition information includes at least information on Na, K, Cl and S.

The identification unit 12 receives the composition information acquired by the acquisition unit 11, and based on the composition information, identifies a salt composition containing at least one of Na or K that may be present in the combustion ash.

The determination unit 13 receives the composition information acquired by the acquisition unit 11 and determines whether or not carbonate may be present in the combustion ash based on the composition information. In the determination unit 13, when the total amount of Cl and S is smaller than the stoichiometric ratio to the total amount of Na and K, carbonate is present in the combustion ash, and the total amount of Cl and S is Na and K. It is programmed to determine that carbonate cannot be present in the combustion ash if it is greater than the stoichiometric ratio to the total amount of.

The library 14 stores multidimensional melting point information of a salt containing at least one of Na and K, and fuel information that correlates the temperature of the metal of the heat transfer tube with the fuel input amount. The multi-dimensional melting point information is, for example, a multi-dimensional melting point diagram.

The determination unit 15 receives information on the specified salt composition from the specific unit 12. The determination unit 15 receives the determination result from the determination unit 13. Based on the acquired composition information and the determination result of the determination unit, the set temperature range of the metal is determined from the multidimensional melting point information related to the salt composition that can be present in the combustion ash. The set temperature range does not include the temperature at which the salt composition that may be present in the combustion ash becomes a molten salt.

The adjusting unit 16 receives information on the set temperature range from the determining unit 15, and based on the information, adjusts the amount of fuel input to the fuel supply unit 2 of the biomass combustion boiler 1 so that the metal temperature falls within the set temperature range. Send a command to do.

The adjusting unit 16 may have a receiving unit that receives the measured temperature of the metal. The adjusting unit 16 sends a command to the fuel supply unit to adjust the fuel input amount so that the received measured temperature falls within the set temperature range.

It is preferable that the adjusting unit 16 has a receiving unit (not shown) for receiving the measured temperature of the metal. For example, a temperature measuring means such as a thermoelectric pair is installed in the metal, and the temperature information measured by the temperature measuring means is received by the receiving unit. Then, the fuel input amount is adjusted so that the received measured temperature falls within the set temperature range.

The anticorrosion control device 10 is composed of, for example, a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a computer-readable storage medium, and the like. Then, as an example, a series of processes for realizing various functions are stored in a storage medium or the like in the form of a program, and the CPU reads this program into a RAM or the like to execute information processing / arithmetic processing. As a result, various functions are realized. The program is installed in a ROM or other storage medium in advance, is provided in a state of being stored in a computer-readable storage medium, or is distributed via a wired or wireless communication means. Etc. may be applied. Computer-readable storage media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, semiconductor memories, and the like.

Next, the grounds for setting the procedure of the anticorrosion method according to the present embodiment as described above will be described.

Combustion gas contains combustion ash. Molten salt components (Na, K, S and Cl) that may corrode metal when biomass is burned are contained in the combustion ash.

While the combustion gas G is flowing, the combustion ash particles adhere to the surface (metal) of the heat transfer tube 6a and accumulate to form the adhered ash layer 20. FIG. 9 shows a schematic view of the attached ash layer 20. The attached ash layer 20 is composed of combustion ash particles (fly ash) FA and voids V. The void V is composed of a molten salt component and a gas.

As shown in FIG. 9, even after the adhered ash layer 20 is formed, the molten salt component MS permeates into the adhered ash layer 20 from the combustion gas G flowing on the surface side of the adhered ash layer 20. Therefore, the molten salt component MS is concentrated inside the adhered ash layer. Usually, when a molten salt component (particularly Cl) comes into contact with a metal in the state of a molten salt, severe corrosion is induced.

On the other hand, as a result of diligent research, the inventor of the present application causes corrosion of the metal even if the molten salt component is concentrated in the adhered ash layer 20 if the molten salt component is present as a solid salt in the portion in contact with the metal. We obtained the finding that it can be greatly suppressed.

FIGS. 10 and 11 show the results of analyzing the actual ash condition of the actual biomass combustion boiler. The analysis is a surface analysis using EPMA. FIG. 10 is a diagram showing the Cl distribution in the adhered ash layer formed by accumulating actual ash. FIG. 11 is a diagram in which the phenomenon of FIG. 10 is reproduced by calculation. The calculation was performed by thermodynamic calculation incorporating the Shile solidification calculation. The software used is ChemSheever 1.89. FIG. 11A is a diagram showing the relationship between the molten salt component melt amount distribution (relative value) and the temperature in the adhered ash layer (° C.). FIG. 11B is a diagram showing the relationship between the combustion ash composition (relative value) and the temperature inside the adhered ash layer (° C.).

The temperature inside the attached ash layer 20 was lowest in the innermost layer 21 on the surface side of the heat transfer tube 6a and increased toward the outer layer 23. The temperature inside the innermost layer 21 was about 410 ° C.-525 ° C., the temperature inside the inner layer 22 was about 535 ° C.-650 ° C., and the temperature inside the outer layer 23 was about 660 ° C.-700 ° C.

According to FIGS. 10 and 11, the Cl content in the adhered ash layer 20 was extremely low in the innermost layer 21 and the outer layer 23, and higher in the inner layer 22. As a result, it was confirmed that the attached ash layer 20 can be divided into three layers, the innermost layer 21, the inner layer 22, and the outer layer 23, in this order from the heat transfer tube 6a side. Although not shown in the figure, S and K of the attached ash layer 20 were also measured in the same manner as Cl. As a result, the distribution of S and K was not as biased as that of Cl, and a certain amount was also present in the innermost layer 21 and the outer layer 23.

According to FIG. 11, there is no melting in the innermost layer 21 and the outer layer 23, and the molten salt is present only in the inner layer 22.

According to the above results, the distribution of Cl, which causes particularly severe corrosion, was biased, and Cl was hardly present in the innermost layer 21. Since Cl contained in the solid salt is accompanied by a very slow intersolid phase transfer at the contact point, the corrosion rate is low, and the corrosion rate of metal by Cl contained in the molten salt having a high transfer rate in the phase is high. This fact suggests that if the state of the adhered ash layer 20 in FIG. 10, that is, the state in which the molten salt containing Cl does not permeate into the metal side (innermost layer 21) can be maintained, the corrosion of the metal can be significantly suppressed. ing.

In the above embodiment, the metal temperature is set in the range of the temperature at which the molten salt is not formed (less than the melting point of the salt composition) in order to prevent the molten salt containing Cl from penetrating into the metal side. Since the innermost layer 21 is covered with the inner layer 22 and the outer layer 23, it is less susceptible to the high temperature combustion gas G than the outer layer 23 and the inner layer 22. By adjusting the metal to a temperature at which the molten salt is not formed, the molten salt component in the innermost layer 21 maintains the state of the solid salt, and the solid salt can block the permeation of the molten salt from the inner layer 22. As a result, metal corrosion is suppressed.

FIG. 12 illustrates the composition information of biomass. Bituminous coal (coal) contained more anionic components (Cl and S) than cation components (Na and K). Waste (waste fuel from paper mills) had a smaller ratio of anionic components to cation components than coal. The wood chips (biomass) contained more cationic components than anionic components.

FIG. 13 shows the relationship between the cation component (K ₂ O + Na ₂ O) and the anion component (2Cl + SO _{4) in the fuel.} In the figure, ◆ plot is waste fuel, ● plot is wood fuel. According to FIG. 13, the total amount of anionic components in waste fuel was larger than the stoichiometric ratio to the total amount of cation components. In wood fuel, the total amount of anionic components was less than the stoichiometric ratio to the total amount of cation components.

When there are more anionic components than cation components, such as coal and waste, the cation components (Na, K alkali metals) react with Cl and S to preferentially form chlorine compounds and sulfates. (Verified). Therefore, almost no carbonate is formed.

On the other hand, when the amount of cation component is larger than that of anion component such as biomass, _{it is presumed that the surplus cation component reacts with carbon dioxide gas (CO 2} ) to form a carbonate.

As can be seen from FIG. 12, the fuel usually contains a plurality of molten salt components. Therefore, a plurality of combinations of salts that may be present in the combustion ash are also conceivable. The multidimensional composition in which a plurality of salts are mixed has different melting points depending on the combination of salts and the content ratio. Therefore, in order to determine the set temperature range of the metal temperature, it is necessary to specify the salt composition that may be present in the combustion ash.

Further, as described above, since the combustion ash of the biomass fuel is more likely to contain carbonate as compared with the case where coal and waste are used as fuel, it is also necessary to determine the presence or absence of carbonate. ..

By identifying the salt composition that can be present in the combustion ash and further determining the presence or absence of carbonate, it becomes possible to select appropriate melting point information (multidimensional melting point diagram). As a result, the metal temperature can be adjusted more reliably so that molten salt is not generated in the innermost layer 21, and the anticorrosion effect can be enhanced.

According to the present invention, by preventing the formation of molten salt on the metal surface, corrosion of the metal in the heat transfer tube can be prevented. According to the present invention, corrosion due to chlorine can be avoided regardless of the use of expensive metal as a heat transfer tube material, fuel restriction, or the like. As a result, it is possible to expand the application of inexpensive fuels and suppress an increase in costs for anticorrosion.

When the molten salt is solidified and adheres to the surface of the adhering ash layer 20 and the heat transfer tube 6a in a close contact state, there is a concern of corrosion risk due to sulfurization or carburizing even if the fuel does not contain Cl. Therefore, it is preferable to apply the anticorrosion method according to the present invention even if the fuel does not contain Cl.

1 Biomass combustion boiler (device that burns fuel to generate energy)
2 Fuel supply unit 3 Burner 4 Fireplace 5 Gas outlet 6 Heat transfer tube (heat exchanger)
10 Anticorrosion control device 11 Acquisition unit 12 Specific unit 13 Judgment unit 14 Library 15 Decision unit 16 Adjustment unit

Claims (7)

A method of preventing corrosion of heat exchangers in a device that burns fuel to generate energy.
The step of acquiring the composition information of Na, K, Cl and S in the fuel, and
A step of identifying a salt composition containing at least one of Na or K that may be present in the combustion ash obtained by burning the fuel based on the acquired composition information.
A step of determining the set temperature range of the metal of the heat exchanger to be lower than the melting point of the salt composition based on the melting point information of the salt composition, and
The process of adjusting the temperature of the metal so that it falls within the set temperature range, and
Including
The step of identifying the salt composition is
When the total amount of Cl and S in the fuel is less than the stoichiometric ratio to the total amount of Na and K, carbonate is present in the combustion ash and the Cl and S A method for preventing corrosion, which comprises a step of determining that carbonate cannot be present in the combustion ash when the total amount is larger than the stoichiometric ratio with respect to the total amount of Na and K. The process of adjusting the temperature of the metal is
The first adjustment to adjust the heat transfer area of the heat exchanger at the design stage,
A second adjustment that measures the temperature of the metal during operation of the device and adjusts the fuel input amount based on the obtained measured value, and
The anticorrosion method according to claim 1. It is an anticorrosion method for heat exchangers in equipment that burns biomass to generate energy.
Obtaining the composition of Na, K, Cl and S in the biomass,
When the total amount of Cl and S in the biomass is less than the stoichiometric ratio to the total amount of Na and K, carbonate is present in the combustion ash and the total amount of Cl and S is present. However, when it is larger than the stoichiometric ratio with respect to the total amount of Na and K, it is determined that carbonate cannot be present in the combustion ash.
The biomass is the Na, the K, wherein the Cl and the S, and the total amount of the Cl and the S is, when greater than the stoichiometric ratio to the total amount of the Na and the K, the heat Set the surface temperature of the metal of the exchanger to less than 518 ° C.
The biomass is the Na, the K, wherein the Cl and the S, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K, the heat An anticorrosion method that sets the surface temperature of the metal of the exchanger to less than 544 ° C. It is an anticorrosion method for heat exchangers in equipment that burns biomass to generate energy.
Obtaining the composition of Na, K, Cl and S in the biomass,
When the total amount of Cl and S in the biomass is less than the stoichiometric ratio to the total amount of Na and K, carbonate is present in the combustion ash and the total amount of Cl and S is present. However, when it is larger than the stoichiometric ratio with respect to the total amount of Na and K, it is determined that carbonate cannot be present in the combustion ash.
The biomass is the Na, wherein the K and the Cl, excluding the S, and the total amount of the Cl and the S is, when greater than the stoichiometric ratio to the total amount of the Na and the K , The surface temperature of the metal of the heat exchanger is set to less than 658 ° C.
The biomass is the Na, wherein the K and the Cl, excluding the S, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K , An anticorrosion method for setting the surface temperature of the metal of the heat exchanger to less than 558 ° C. It is an anticorrosion method for heat exchangers in equipment that burns biomass to generate energy.
Obtaining the composition of Na, K, Cl and S in the biomass,
When the total amount of Cl and S in the biomass is less than the stoichiometric ratio to the total amount of Na and K, carbonate is present in the combustion ash and the total amount of Cl and S is present. However, when it is larger than the stoichiometric ratio with respect to the total amount of Na and K, it is determined that carbonate cannot be present in the combustion ash.
The biomass is the Na, wherein the K and the S, not including the Cl, and the total amount of the Cl and the S is, when greater than the stoichiometric ratio to the total amount of the Na and the K , Set the surface temperature of the metal of the heat exchanger to 800 ° C or lower,
The biomass is the Na, wherein the K and the S, not including the Cl, and the total amount of the Cl and the S is, when less than the stoichiometric ratio to the total amount of the Na and the K , An anticorrosion method for setting the surface temperature of the metal of the heat exchanger to less than 700 ° C. An anticorrosion control device that is connected to a device that burns fuel to generate energy and controls the anticorrosion of the heat exchanger of the device.
An acquisition unit that acquires composition information of Na, K, Cl, and S in the fuel, and an acquisition unit.
Based on the acquired composition information, a specific part that identifies a salt composition containing at least one of Na or K that may be present in the combustion ash obtained by burning the fuel, and a specific portion.
Based on the obtained composition information, when the total amount of Cl and S is smaller than the stoichiometric ratio with respect to the total amount of Na and K, carbonate is present in the combustion ash and Cl is present. And a determination unit that determines that carbonate is not present in the combustion ash when the total amount of S is larger than the stoichiometric ratio with respect to the total amount of Na and K.
A library in which multidimensional melting point information of a salt composition containing at least one of Na and K and fuel information correlating the temperature of the metal of the heat exchanger and the fuel input amount are stored.
Based on the information of the salt composition specified in the specific portion and the determination result of the determination unit, the set temperature range of the metal is determined from the multidimensional melting point information related to the salt composition that may be present in the combustion ash. A decision-making part that determines the salt composition to be below the melting point,
An adjusting unit that adjusts the amount of fuel input so that the temperature of the metal falls within the set temperature range.
Anticorrosion control device equipped with. The adjusting unit has a receiving unit that receives the measured temperature of the metal.
The anticorrosion control device according to claim 6, wherein the input amount of the fuel is adjusted so that the received measured temperature falls within the set temperature range.

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