Circulating fluidized bed boiler operation method

Abstract

A method for operating a circulating fluidized bed boiler and a method for producing fluidized sand are provided, which enable effective use of hearth ash, improve operational efficiency, and reduce costs. [Solution] A method for operating a circulating fluidized bed boiler (10), in which the bottom ash produced by burning wood-derived biomass fuel in another circulating fluidized bed boiler (10) is recovered and used as fluidizing sand for the circulating fluidized bed boiler (10).

Description

[Technical Field]

[0001] The present invention relates to a circulating fluidized bed boiler. How to drive Regarding. [Background technology]

[0002] Circulating fluidized bed (CFB) boilers are highly efficient and flexible boilers capable of using a variety of fuels. CFB boilers are characterized by their ability to utilize a wide variety of fuels in proportions tailored to the user's needs. They can be used not only alone, but also in any desired mixed combustion ratio, including biomass and RDF. CFB boilers are environmentally friendly and can burn a wide variety of fuels, including low-rank coal (including high-ash and high-moisture coal), petroleum coke, plutonium sludge, wood chips, waste tires, RPF, and other industrial waste. CFB boilers achieve high combustion efficiency even with difficult-to-burn fuels by recovering unburned fuel using a cyclone and returning it to the furnace. CFB boilers can reduce sulfur oxide (SOx) emissions by adding limestone to the furnace. In circulating fluidized bed boilers, nitrogen oxides (NOx) are also suppressed through low-temperature, two-stage combustion, and soot and dust can also meet environmental law standards by installing a dust collector.

[0003] Patent Document 1 below discloses an example of a circulating fluidized bed boiler. The circulating fluidized bed boiler in Patent Document 1 includes an external circulation fluidized bed furnace that supplies fuel into a combustion chamber through which a fluidizing material circulates and burns it, and a cyclone connected to the external circulation fluidized bed furnace that mainly separates combustion gas from solid fluidizing material. In addition, in this circulating fluidized bed boiler, at least a portion of the cyclone inlet passage that guides a solid-gas two-phase flow mainly consisting of the fluidizing material and combustion gas from the external circulation fluidized bed furnace to the cyclone is provided along the side wall of the external circulation fluidized bed furnace, which is said to achieve high efficiency. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-311503 Summary of the Invention [Problem to be solved by the invention]

[0005] However, there is still room for improvement in the efficiency of operation and cost reduction of conventional circulating fluidized bed boilers.

[0006] Therefore, an object of the present invention is to provide a method for operating a circulating fluidized bed boiler and a method for producing fluidized sand that can effectively utilize furnace bottom ash, improve operational efficiency, and reduce costs. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention proposes the following means. A method for operating a circulating fluidized bed boiler according to one aspect of the present invention is a method for operating a circulating fluidized bed boiler, comprising recovering furnace bottom ash generated by burning wood-derived biomass fuel in another circulating fluidized bed boiler, and using the furnace bottom ash as fluidizing sand for the circulating fluidized bed boiler. The circulating fluidized bed boiler uses the fluidized sand and burns at least one fuel selected from waste tires, waste plastics, paper sludge, and RPF as a main fuel. .

[0008] A method for producing fluidized sand according to one embodiment of the present invention involves burning wood-derived biomass fuel in a circulating fluidized bed boiler and recovering the resulting furnace bottom ash. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a method for operating a circulating fluidized bed boiler and a method for producing fluidized sand that can effectively utilize furnace bottom ash, improve operational efficiency, and reduce costs. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram of a circulating fluidized bed boiler used in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a schematic diagram of a circulating fluidized bed boiler used in this embodiment. The circulating fluidized bed boiler 10 used in this embodiment includes a combustion furnace 11, a fuel supply section 12, a fluidized sand tank 13, an air introduction section 14, a circulation section 15, a duct 16, a heat exchange section 17, a dust collection section 18, and the like.

[0012] The combustion furnace 11 is a furnace in which fuel is burned in a fluidized bed formed by fluidized sand. The fuel supply unit 12 supplies fuel to the combustion furnace 11. The fluidized sand tank 13 stores fluidized sand received from outside and supplies it to the combustion furnace 11. It is preferable to separate and remove large-diameter particles from the fluidized sand before storing it in the fluidized sand tank 13. Large-diameter particles may be separated using a vibrating screen, for example, or may be removed by crushing them to reduce their diameter. The fluidized sand stored in the fluidized sand tank 13 is then fed into the combustion furnace 11 using pneumatic transport equipment or the like.

[0013] The air introduction section 14 introduces air from a plurality of height positions on the bottom side of the combustion furnace 11, for example, and forms a fluidized bed with the fluidized sand. The circulation section 15 extracts the high-temperature mixture produced by combustion in the combustion furnace 11 together with the fluidized sand, separates the fluidized sand, and circulates it to the combustion furnace 11. The remainder of the mixture is sent to a duct 16. The duct 16 leads the remainder from the circulation section 15 to the outside of the system. This remainder includes, for example, fly ash and the like in addition to products such as gases produced by combustion.

[0014] The heat exchanger 17 generates and superheats steam using heat generated in the combustion furnace 11. In this embodiment, the heat exchanger 17 is provided midway along the duct 16, but the installation position of the heat exchanger 17 is not limited to this. The dust collecting section 18 separates and collects fly ash and the like from the mixture after the fluidized sand has been separated and heat has been sufficiently dissipated.

[0015] The combustion furnace 11 of this embodiment is further provided with an extraction section 21, a cooling section 22, a sorting section 23, and a recovery section 24. The extraction section 21 extracts bottom ash, which is the main ash in the combustion furnace 11, from the bottom of the combustion furnace 11. The cooling section 22 cools the extracted high-temperature bottom ash by dissipating heat. The sorting section 23 separates and removes large-diameter particles from the extracted bottom ash, and also removes foreign matter such as metals. Large-diameter particles may be separated using a vibrating screen, for example, or crushed to reduce their diameter.

[0016] The recovery section 24 is composed of, for example, a recovery tank, and recovers and stores the furnace bottom ash that has been sorted in the sorting section 23 and from which large-diameter objects and foreign objects have been removed. The furnace bottom ash recovered in the recovery section 24 may be recharged into the combustion furnace 11 for recycling as fluidized sand, or may be discharged outside the system.

[0017] Next, a method for operating the circulating fluidized bed boiler 10 of this embodiment will be described. In this embodiment, an example will be described in which multiple circulating fluidized bed boilers such as those shown in Fig. 1 are used. Here, the multiple circulating fluidized bed boilers 10 are roughly divided into two groups, and one circulating fluidized bed boiler 10A (hereinafter also referred to as the first circulating fluidized bed boiler 10A) and the other circulating fluidized bed boiler 10B (hereinafter also referred to as the second circulating fluidized bed boiler 10B) are operated using different fuels and operating conditions.

[0018] In this operating method, fluidized sand is produced by recovering the furnace bottom ash generated in the second circulating fluidized bed boiler 10B. The produced fluidized sand is used as fluidized sand for the first circulating fluidized bed boiler 10A, and a fluidized bed is formed in the combustion furnace 11 of the first circulating fluidized bed boiler 10A to combust fuel.

[0019] The first circulating fluidized bed boiler 10A burns fuel containing, for example, waste tires, waste plastics, or paper sludge as a main component, such as at least one of waste tires, waste plastics, paper sludge, and RPF (Refuse-derived paper and plastics densified fuel).

[0020] The second circulating fluidized bed boiler 10B burns wood-derived biomass fuel, which is fuel derived from wood, such as wood chips, wood pellets, forest residues (including bark), wood waste from construction, and palm oil residue (PKS).

[0021] In so-called biomass-fired CFBs such as the second circulating fluidized bed boiler 10B, a large amount of bottom ash is extracted and disposed of as industrial waste rather than reused in order to prevent the generation of clinker due to the concentration of Na and K derived from the fuel. However, when the components of the bottom ash were examined, the inventors discovered that it contained a large amount of silica sand, which is effective as a fluidizing material. On the other hand, in a CFB such as the first circulating fluidized bed boiler 10A that uses waste tires as the main fuel, the Na·K concentration in the furnace bottom ash is relatively low. Therefore, the inventors came to the conclusion that it might be acceptable to use the furnace bottom ash of the second circulating fluidized bed boiler 10B as fluid sand, even though the amount of Na·K carried over would increase. Therefore, in the operating method according to this embodiment, the bottom ash of a so-called biomass-fired CFB (second circulating fluidized bed boiler 10B), which would have conventionally been treated as industrial waste, is reused as fluid material for a CFB (first circulating fluidized bed boiler 10A) that uses waste tires or the like as its main fuel.

[0022] The furnace bottom ash of the second circulating fluidized bed boiler 10B produced by burning wood-derived biomass fuel contains a large amount of silica sand and a small amount of impurities that are not useful for combustion or that inhibit combustion. Silica sand is a heat-resistant heat medium, and by flowing at high speed together with the fuel inside the circulating fluidized bed boiler 10, the fuel can be burned uniformly and over a wide area inside the circulating fluidized bed boiler 10, allowing for efficient combustion of the fuel. Therefore, furnace body ash that is generated in the second circulating fluidized bed boiler 10B and contains a large amount of silica sand can be suitably used as fluid sand for the first circulating fluidized bed boiler 10A, for example.

[0023] Although not particularly limited, the SiO2 (silica) content of the hearth ash used for fluidized sand is preferably 40% by mass or more. If the SiO2 content is 40% by mass or more, when a fluidized bed is formed, the thermal efficiency is good and the ash can be effectively used as fluidized sand. However, the SiO2 content may be less than 40% by mass.

[0024] Furthermore, the hearth ash used in this fluidized sand preferably contains at least one of, and particularly both, an Al2O3 content of 7% by mass or less and a CaO content of 15% by mass or less. The use of such hearth ash can prevent a decrease in the ash melting temperature and the formation of clinker, and can maintain good thermal efficiency. However, the Al2O3 content may be more than 7% by mass, and the CaO content may be more than 15% by mass.

[0025] On the other hand, the bottom ash produced by burning wood-derived biomass fuel contains sodium and potassium. As the content of these components increases, the melting temperature of the ash decreases, making it more likely to produce deposits called clinker. However, fuels such as waste tires, waste plastics, paper sludge, and RPF burned in the first circulating fluidized bed boiler 10A are highly combustible fuels. The ash produced by burning these fuels is less likely to have increased concentrations of sodium and potassium, and these effects are less likely to occur when burned.

[0026] Therefore, in the operating method of this embodiment, the hearth ash generated in the second circulating fluidized bed boiler 10B can be suitably used as fluidizing sand for the first circulating fluidized bed boiler 10A. This suppresses the generation of clinker, and the specified hearth ash recovered as described above can be used as fluidizing sand for the circulating fluidized bed boiler, thereby making effective use of the hearth ash.

[0027] The furnace bottom ash generated in the second circulating fluidized bed boiler 10B, i.e., the furnace bottom ash generated by burning wood-derived biomass fuel, is collected in the collection section 24. In this embodiment, the furnace bottom ash in the collection section 24 of the second circulating fluidized bed boiler 10B is, for example, transported as appropriate, stored in the fluidized sand tank 13 of the first circulating fluidized bed boiler 10A, and supplied as fluidized sand to the combustion furnace 11 of the circulating fluidized bed boiler 10A.

[0028] In the fluidized sand of this embodiment, it is preferable to separate and remove large particles from the furnace bottom ash when the furnace bottom ash is collected in the collection section 24 or when the fluidized sand is stored in the fluidized sand tank 13. Although not particularly limited, in this embodiment, it is preferable to separate and remove large particles with a particle size of 3000 μm or more. Removing the large particles improves the fluidity when the sand is used as fluidized sand for the circulating fluidized bed boiler 10, thereby improving the combustion efficiency of the circulating fluidized bed boiler 10. However, the fluidized sand may contain particles (large particles) with a particle size of 3000 μm or more.

[0029] According to the above-described method for operating the circulating fluidized bed boiler 10, the furnace bottom ash generated by burning wood-derived biomass fuel in the second circulating fluidized bed boiler 10B is used as fluidizing sand for the circulating fluidized bed boiler 10A to be operated. Therefore, the amount of bottom ash generated in the second circulating fluidized bed boiler 10B that is disposed of as waste can be reduced or eliminated. As a result, the operating method of this embodiment can effectively utilize the bottom ash, improving operational efficiency and reducing costs.

[0030] According to the method for producing fluidized sand, the fluidized sand for the first circulating fluidized bed boiler 10A is produced by recovering the furnace bottom ash generated by burning wood-derived biomass fuel in the second circulating fluidized bed boiler 10B, making it easy to produce fluidized sand for the circulating fluidized bed boiler 10.

[0031] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, a plurality of circulating fluidized bed boilers shown in FIG. 1 are used, but the structure of the circulating fluidized bed boiler is not particularly limited.

[0032] Furthermore, in the above embodiment, an example has been described in which fuel containing waste tires, waste plastics, or paper sludge as its main component is used as fuel for the first circulating fluidized bed boiler 10A. However, it is also possible to use wood-based biomass fuels such as wood chips, wood pellets, forest residues (including bark), construction wood waste, palm residues (PKS), etc. as part or all of the fuel for the first circulating fluidized bed boiler 10A in the above embodiment.

[0033] In this case, it is preferable to reduce or remove the sodium and potassium content by contacting the hearth ash with an aqueous liquid such as water or by washing the hearth ash with an aqueous liquid.

[0034] In addition, the above embodiment has mainly described an example in which only hearth ash produced by burning wood-derived biomass fuel in the second circulating fluidized bed boiler 10B is used as fluid sand for the first circulating fluidized bed boiler 10A, but this is not particularly limited. The fluid sand for the first circulating fluidized bed boiler 10A in the embodiment can also be a mixture of fluid sand made from hearth ash produced by burning wood-derived biomass fuel (the hearth ash of the second circulating fluidized bed boiler 10B) and other fluid sand (supplement sand) different from this fluid sand. [Example]

[0035] Examples of the present invention will be described below.

[0036] [Examples 1 to 3] A long-term combustion test was conducted using two circulating fluidized bed boilers 10A and 10B installed independently of each other. The two circulating fluidized bed boilers 10A and 10B had the configuration shown in FIG. 1. In the combustion test, a fixed fuel was continuously combusted in the circulating fluidized bed boilers 10A and 10B. The combustion test was conducted three times, with combustion periods of 21 days (Example 1), 46 days (Example 2), and 41 days (Example 3) for each combustion test. The combustion conditions for each circulating fluidized bed boiler 10A and 10B were kept as constant as possible, although there were fluctuations during the combustion period.

[0037] The first circulating fluidized bed boiler 10A combusted fuel containing 40% by mass of waste tires, 30% by mass of wood chips, and 30% by mass of paper sludge. The combustion conditions were a furnace bottom temperature of 850 to 900°C. The fluidized sand used in this circulating fluidized bed boiler 10A was the furnace bottom ash generated by combustion in the second circulating fluidized bed boiler 10B. The second circulating fluidized bed boiler 10B burned wood chips as fuel. The combustion conditions were a furnace bottom temperature of 770 to 820°C.

[0038] In each combustion test, the bottom ash generated in the second circulating fluidized bed boiler 10B was recovered and used without being returned to the combustion furnace 11. The recovered bottom ash was used to produce fluidized sand by removing large particles of 3000 μm or more using a vibrating screen. The fluidized sand was fed into the fluidized sand tank 13 of the first circulating fluidized bed boiler 10A and used at a rate of 1 ton per day.

[0039] A portion of the bottom ash recovered from the second circulating fluidized bed boiler 10B was sampled and the particle size distribution before removing large particles was measured. The bottom ash had the particle size distribution shown in Table 1. A component analysis was also carried out on a portion of the sampled bottom ash, and the results are shown in Table 2. The total of the proportions in Table 2 is less than 100% by mass, but the remainder less than 100% was made up of components not listed in the table. As is clear from Tables 1 and 2, the bottom ash recovered in the second circulating fluidized bed boiler 10B contained large particles of 3000 μm or more in diameter. The bottom ash also contained a large amount of silica sand components such as silicon dioxide, as well as components that cause clinker generation, such as sodium and potassium.

[0040] [Table 1]

[0041] [Table 2]

[0042] In the combustion tests of Examples 1 to 3, fluidized sand was used, which was produced by separating and removing large particles of 3000 μm or more from the furnace bottom ash of the second circulating fluidized bed boiler 10B, and no problems such as clogging occurred when used in the first circulating fluidized bed boiler 10A. Furthermore, in the combustion tests of Examples 1 to 3, no operational problems such as clogging due to clinker generation or signs of abnormalities such as a drop in the furnace bottom temperature were observed in the first circulating fluidized bed boiler 10A. When the inside of the boiler was inspected after the end of each test period, no clinker generation or an increase in the amount of ash adhering to the heat exchanger or the like was found. Furthermore, for Examples 1 and 2, the sodium and potassium concentrations of the bottom ash of the first circulating fluidized bed boiler 10A were measured during operation, and it was confirmed that the sodium and potassium concentrations were approximately the same as the sodium and potassium concentrations of the blank product (the bottom ash of the second circulating fluidized bed boiler 10B) before use as fluidized sand, and it was determined that there was no concentration of sodium and potassium.

[0043] (Addendum) The embodiment can be understood, for example, as follows. <1> A method for operating a circulating fluidized bed boiler according to one aspect of the present invention is a method for recovering furnace bottom ash produced by burning wood-derived biomass fuel in another circulating fluidized bed boiler and using the furnace bottom ash as fluidizing sand for the circulating fluidized bed boiler.

[0044] In this method of operating a circulating fluidized bed boiler, the hearth ash of another circulating fluidized bed boiler is used as fluidizing sand for the circulating fluidized bed boiler being operated. The hearth ash generated by burning wood-derived biomass fuel in the other circulating fluidized bed boiler contains a large amount of silica sand and little impurities. Therefore, it can be suitably used as fluidizing sand for the circulating fluidized bed boiler.

[0045] Furthermore, by recovering the hearth ash generated in other circulating fluidized bed boilers and using it as fluidized sand, it is possible to reduce or eliminate the amount of hearth ash to be disposed of as waste. As a result, according to the operating method of a circulating fluidized bed boiler of the present invention, it is possible to effectively utilize the hearth ash, improve operational efficiency, and reduce costs.

[0046] <2> the above <1> In the method for operating a circulating fluidized bed boiler described in the above, the circulating fluidized bed boiler may be one that uses the fluidized sand to burn at least one fuel selected from waste tires, waste plastics, paper sludge, and RPF.

[0047] The bottom ash produced by burning wood-derived biomass fuel in other circulating fluidized bed boilers contains sodium and potassium. As these contents increase, the melting temperature of the ash decreases, making it more likely for a deposit called clinker to form. However, waste tires, waste plastics, paper sludge, and RPF are easily combustible fuels, and the concentrations of sodium and potassium are less likely to increase, making these effects less likely to occur when burned. As a result, the operating method of the present invention suppresses the generation of deposits and allows the specified bottom ash recovered as described above to be used as fluidizing sand for the circulating fluidized bed boiler, thereby making effective use of the bottom ash.

[0048] <3> the above <1> or <2> In the method for operating a circulating fluidized bed boiler described in the above, it is preferable to obtain the fluidized sand by separating and removing large particles having a particle size of 3000 μm or more from the furnace bottom ash. By separating and removing large particles from the furnace bottom ash in this manner, the fluidity of the ash can be improved when it is used as fluidizing sand in a circulating fluidized bed boiler, and as a result, the combustion efficiency of the circulating fluidized bed boiler can be improved.

[0049] <4> the above <1> Or <3> In the method for operating a circulating fluidized bed boiler described in any one of the above, it is preferable to use the furnace bottom ash having an SiO2 content of 40 mass % or more as the fluidizing sand. If the SiO2 content is high like this, the thermal efficiency is good and it can be effectively used as fluid sand.

[0050] <5> the above <1> Or <4> In the method for operating a circulating fluidized bed boiler described in any one of the above, it is preferable to use the furnace bottom ash having an Al2O3 content of 7 mass % or less as the fluidizing sand. <6> Also, the above <1> Or <5> In any one of the above methods for operating a circulating fluidized bed boiler, the bottom ash having a CaO content of 15 mass % or less is preferably used as the fluidizing sand. If the Al2O3 content and CaO content are low, the melting temperature of the ash will not drop and clinker will not be generated, and the thermal efficiency will be good, allowing the sand to be used effectively as fluidized sand.

[0051] <7> In a method for operating a circulating fluidized bed boiler 10 for producing fluidized sand according to one embodiment of the present invention, wood-derived biomass fuel is combusted in the circulating fluidized bed boiler, and the resulting furnace bottom ash is collected. In this way, by burning wood-derived biomass fuel in a circulating fluidized bed boiler and recovering the resulting furnace bottom ash, fluidizing sand for a circulating fluidized bed boiler can be easily produced.

[0052] <8> the above <7> In the method for producing fluidized sand described in the above, it is preferable to separate and remove large particles having a particle size of 3000 μm or more from the recovered furnace bottom ash. In this way, fluid sand that can easily improve the fluidity in a circulating fluidized bed boiler can be produced. [Explanation of symbols]

[0053] 10, 10A, 10B Circulating fluidized bed boiler 11 Combustion furnace 12 Fuel supply section 13 Fluidized sand tank 14 Air intake section 15 Circulation section 16 Duct 17 Heat exchange section 18 Dust collection section 21 Extraction section 22 Cooling section 23 Sorting Department 24 Collection Department

Claims

1. A method for operating a circulating fluidized bed boiler, comprising: A furnace bottom ash generated by burning wood-derived biomass fuel in another circulating fluidized bed boiler is recovered, and the furnace bottom ash is used as fluidizing sand for the circulating fluidized bed boiler. A method for operating a circulating fluidized bed boiler, wherein the circulating fluidized bed boiler uses the fluidized sand and burns at least one fuel selected from waste tires, waste plastics, paper sludge, and RPF as a main fuel.

2. 2. The method for operating a circulating fluidized bed boiler according to claim 1, wherein the fluidized sand is obtained by separating and removing large particles having a particle size of 3000 μm or more from the furnace bottom ash.

3. SiO ２ 2. The method for operating a circulating fluidized bed boiler according to claim 1, wherein the furnace bottom ash has a content of 40 mass% or more and is used as the fluidizing sand.

4. Al ２ O ３ 2. The method for operating a circulating fluidized bed boiler according to claim 1, wherein the bottom ash has a content of 7% by mass or less and is used as the fluidizing sand.

5. 2. The method for operating a circulating fluidized bed boiler according to claim 1, wherein the furnace bottom ash having a CaO content of 15% by mass or less is used as the fluidizing sand.

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