JP3801549B2 - Combustion method of low melting point metal containing fuel using circulating fluidized bed combustor - Google Patents

Description

【００３４】
図２は、燃料のアルミニウム含量とコンバスタの差圧とサイクロン内への灰の付着との関係を表す。
図２に示すように、３％とＲＰＦの金属Ａｌの含有量が多い場合、７ｋＰａとコンバスタ差圧を低くして燃焼試験を行った場合、サイクロンの内塔に灰の付着が観察された（条件２）。この付着物は灰色で非常に硬く、ガスの流れの方向に向かって成長していた。
しかし、３％とＲＰＦの金属Ａｌの含有量が多い場合でも、１４ｋＰａとコンバスタ差圧を高くとするとサイクロン内に付着物の堆積は観察されなかった（条件１）。また、１％とＲＰＦの金属Ａｌの含有量が低い場合には、７ｋＰａとコンバスタ差圧を低くしても、サイクロン内に付着物の堆積は観察されなかった（条件３）。
【００３５】
また、図４は、燃料のアルミニウム含量とコンバスタの温度とサイクロン内への灰の付着との関係を表す。図４に示すように、３％とＲＰＦの金属Ａｌの含有量が多く、コンバスタ差圧が１４ｋＰａと高い場合でも、コンバスタの温度を８５０℃とするとサイクロン内に付着物の堆積は観察されなかった（条件１）。
しかし、同様に３％とＲＰＦの金属Ａｌの含有量が多く、コンバスタ差圧が１４ｋＰａと高い場合でも、コンバスタの温度を９００℃とするとサイクロン内に若干の付着物の堆積が観察された（条件４）。
【００３６】
以上の結果は、コンバスタ差圧が低い場合は、溶解、衝突破砕によるＲＰＦ中の溶融した金属Ａｌの微小粒子化が進行しにくいという、上記した本発明者らの見解を裏付けるものである。また、コンバスタ温度が高すぎる場合、サイクロンに灰が付着しやすいという、上記した本発明者らの見解を裏付けるものである。
【００３７】
なお、本試験における運転状況は、ＲＰＦ中の金属Ａｌの量によらず、安定していた。また、燃焼温度は、燃焼炉の高さ方向に対し、均一に温度が分布していた。その他ガス性状等、特に問題は見つからなかった。
【００３８】
【発明の効果】
上記したところから明らかなように、本発明は、循環流動層燃焼装置を用いて、低融点金属を含有する燃料を燃焼させるときに、サイクロン内に灰が付着しない燃焼方法を提供する。
【図面の簡単な説明】
【図１】循環流動層燃焼装置の概念図である。
【図２】燃料のアルミニウム含量とコンバスタの差圧とサイクロン内への灰の付着との関係を表す図である。
【図３】温度の変化に対する金属Ａｌの粘性係数の変化を表すグラフである。
【図４】燃料のアルミニウム含量とコンバスタの温度とサイクロン内への灰の付着との関係を表す図である。
【符号の説明】
１ コンバスタ
２ サイクロン
３ シールポット
４ 流動層熱交換手段
５ 低温粒子循環ライン
６ 高温粒子循環ライン
７ 排ガス熱交換手段
８ バグフィルタ
９ 誘引ファン
１０ 煙突[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion method of a low melting point metal-containing fuel using a circulating fluidized bed combustion apparatus. In particular, the present invention relates to a combustion method for preventing deposits derived from low melting point metals from adhering to the cyclone.
[0002]
[Prior art]
In recent years, a circulating fluidized bed combustion apparatus has been used as a combustion apparatus for efficiently burning, for example, RDF (Refuse Delivered Fuel), municipal waste, and industrial waste.
FIG. 1 is a conceptual diagram of a circulating fluidized bed combustion apparatus. As shown in FIG. 1, the circulating fluidized bed combustion apparatus includes a combustor 1 and a cyclone 2 as main elements. Such a combustion apparatus is described in the following Patent Documents 1 to 3.
[0003]
The combustor 1 stores particles of fluid material such as silica sand. Further, air is sent into the combustor 1 from the bottom of the combustor 1. Due to the flow of the air from the lower part to the upper part of the combustor, the fuel introduced into the combustor 1 is rolled up together with the particles to form a so-called high-speed fluidized bed. The fuel repeatedly burns effectively by repeated contact with the particles in the high-speed fluidized bed. The combustion temperature at this time is usually 800 ° C. to 900 ° C.
Particles or the like forming a high-speed fluidized bed in the combustor are sent to the cyclone 2 where they are separated into particles such as a fluidized material and exhaust gas. The separated unburned matter is further separated in the seal pot 3 and circulates to the combustor 1 through the fluidized bed heat exchange means 4 (low temperature particle circulation line 5) and directly circulated to the combustor 1 (hot particles) To the circulation line 6). By returning the particles cooled by the fluidized bed heat exchange means 4 to the combustor 1, the combustion temperature in the combustor 1 is adjusted.
[0004]
The ash produced in the combustor 1 is extracted as necessary, discharged out of the system, and processed separately. The exhaust gas separated from the unburned portion by the cyclone 2 is heat-exchanged by the exhaust gas heat exchanging means 7, and then passes through the bag filter 8 that removes the dust in the gas, and is then passed through the chimney 10 by the induction fan 9. To the atmosphere.
[0005]
By the way, some of these fuels contain a low melting point metal such as aluminum. For example, in order to increase the airtightness, an aluminum layer is provided inside the paper container, but it is practically impossible to separately remove aluminum in the waste containing such a paper container. . When a fuel containing such a low-melting-point metal is burned, the low-melting-point metal contained in the fuel may adhere as ash in the cyclone 2, particularly on the inner cylinder of the cyclone provided at the outlet of the cyclone 2. .
[0006]
Such deposits are very hard and may need to be destroyed together with the refractory material forming the cyclone 2 to remove it. Generally, the energy generated in such a combustion device is used as a power generation device or other heat source. Therefore, stopping the combustion device in accordance with the removal work of such deposits is important for the operation of the entire plant. Because it has an impact, it is very uneconomical. Furthermore, when such a deposit falls, there is a possibility that the cyclone 2 is not able to operate the combustion apparatus.
[0007]
[Patent Document 1]
JP-A-9-89214 [Patent Document 2]
Japanese Patent Laid-Open No. 2002-5413 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-162002
[Problems to be solved by the invention]
An object of the present invention is to provide a combustion method for preventing adhesion of deposits derived from a low melting point metal in a cyclone when a fuel containing a low melting point metal is burned using a circulating fluidized bed combustion apparatus. And
[0009]
[Means for Solving the Problems]
The present invention comprises a combustor that contains fluid material particles therein to form a high-speed fluidized bed, and a cyclone that is provided at the outlet of the combustor and separates unburned matter and exhaust gas discharged from the combustor, A combustion method of a low-melting-point metal-containing fuel using a circulating fluidized bed combustion device that circulates and inputs unburned matter collected by the cyclone into the combustor, and the more the low-melting-point metal content in the fuel is, Provided is a combustion method for preventing the accumulation of deposits in the circulating fluidized bed combustion apparatus by increasing the differential pressure of the combustor.
[0010]
Here, the “differential pressure” of the combustor is the difference between the pressure at the bottom of the combustor and the pressure at the outlet of the combustor, and corresponds to the amount of particles retained in the combustor. That is, as compared with the outlet of the combustor, a higher pressure is applied to the bottom of the combustor by the weight of the fluid material particles housed in the combustor. For this reason, the amount of particles in the combustor can be expressed as a differential pressure of the combustor. For example, the differential pressure is 14kPa in the combustor, equivalent to sand about 1.4t per 1 m ² is present in the combustor.
[0011]
Further, although not particularly limited, examples of the low melting point metal include aluminum, lead, and zinc. A fuel formed from waste paper or plastic, generally called RPF (Refuse Paper and Plastic Fuel), contains such a low melting point metal.
[0012]
According to the present invention, the greater the content of the low melting point metal in the fuel, the more the combustor differential pressure is increased, so that the ash derived from the low melting point metal does not adhere to the cyclone and the circulating fluidized bed combustion apparatus operates. Can continue.
[0013]
The combustor differential pressure P (kPa) with respect to the low melting point metal content X (% by weight) of the fuel is preferably determined within the range given by the following equation (1).
P ≧ 2 × X + 3.5 (1)
Further, it is more preferable that the differential pressure P (kPa) of the combustor is determined within the range given by the following equation (2) with respect to the low melting point metal content X (wt%) of the fuel.
P ≧ 3.5 × X + 3.5 (2)
[0014]
Further, when the content X is 1% by weight, the differential pressure is set to a certain value of 7 kPa or more, and when the content X is greater than 1% by weight and 3% by weight or less, the differential pressure is It can also be larger than a certain value.
[0015]
The amount of the low melting point metal contained in the fuel such as RPF is usually about 1% by weight, and at most about 3% by weight. Therefore, it is sufficient if the differential pressure of the combustor is about 10 kPa, more preferably about 14 kPa. In addition, the effects of the present invention can be obtained.
[0016]
According to the combustion method of the present invention, the low melting point metal contained in the fuel does not adhere to the inside of the cyclone.
This can be explained as follows from the results of the inventors' EPMA analysis (Electron Probe Micro-Analysis: X-ray microanalyzer) and XRD analysis (X-ray Diffraction: X-ray diffraction). That is, the low melting point metal contained in the fuel is considered to behave as follows in the combustion apparatus, but the present invention is not limited to such a mechanism. For convenience of explanation, the case where the low melting point metal is aluminum (hereinafter referred to as “Al”) will be described.
[0017]
1. The temperature in the combustor is usually 800 to 900 ° C., and the melting point of metal Al is 660 ° C., which is lower than this. For this reason, the metal Al contained in the fuel charged into the furnace is dissolved. At the same time, an oxide film of Al ₂ O ₃ is formed on the surface.
2. In the high-speed fluidized bed, the surface is covered with an oxide film, and when the fluid material particles collide with the dissolved Al, the dissolved Al adheres to the fluid material particles. Alternatively, Al is crushed into fine particles.
3. Metal Al adhering to the surface of the fluidized material particles forms a eutectic salt with Ca or the like to form a film. Further, the metal Al that has entered the recessed portion of the fluidized material particles is oxidized only on the exposed surface, and maintains the metal form.
4). Al or the like repeats such a process of micronization in the high-speed fluidized bed until it flows into the cyclone. According to the present invention, in order to apply a high differential pressure to the combustor, Al is sufficiently microparticulated to about 10 to 20 μm in the high-speed fluidized bed.
5). Since the flow of particles is intense in the cyclone, the metallic Al adhering to the fluidized material particles is released. The released metal Al forms an oxide film of Al ₂ O ₃ , and if the Al particles formed are sufficiently small, they are scattered into the flue at the rear of the cyclone. Al finely divided into fine particles in the high-speed fluidized bed is not collected by the cyclone but scattered to the rear flue.
[0018]
However, when the combustor differential pressure is low, it is considered that the reduction of the mass of Al in the high-speed fluidized bed may not be sufficiently performed. At this time, the Al particles cannot be scattered into the flue and are collected by the cyclone. It is thought that such Al accumulates in the cyclone and forms a strong deposit.
[0019]
Here, the change of the viscosity coefficient of metal Al with respect to the change of temperature is shown in FIG. 3 with the viscosity coefficient at 850 ° C. as a reference. As shown in FIG. 3, when the temperature is increased, the viscosity of the molten metal Al decreases. For this reason, when the combustion temperature of the combustor is increased, the viscosity of the metal Al decreases, and the metal Al easily enters the recess of the fluidized material in the combustor.
[0020]
In fact, when the fluidized bed boiler was operated at a high combustor temperature, it was found from the results of analysis by EPMA of the present inventors that large metal Al was present in the particles above the combustor. When these particles enter the cyclone, the metal Al is liberated by the impact of swirling and collision, but it is considered that the particles do not become sufficiently fine particles and adhere to the cyclone. In other words, when the combustor temperature is relatively low, it is considered that the metal Al becomes fine particles independent of the particles found on the fluidized material and other combustors and easily passes through the cyclone.
[0021]
Thus, since the adhesion of ash increases when the combustion temperature of the combustor is high, there is a high possibility that the ash is taken into the wall surface of the cyclone inner cylinder when passing through the cyclone inner cylinder. On the other hand, if the temperature is too low, the burn-out property of the fuel is lowered, which is not preferable. For this reason, the combustion temperature of the combustor is preferably 700 ° C. or higher and 870 ° C. or lower, and particularly preferably 840 ° C. or higher and 860 ° C. or lower.
[0022]
In addition, according to the combustion method concerning this invention, there is also no problem that particle | grains granulate. Particle granulation refers to a phenomenon in which fluidized material particles forming a high-speed fluidized bed become enormous with the operation of the circulating fluidized bed combustion apparatus. The cause of this phenomenon can be considered as follows. The dissolved Al acts as a binder, and the fluidized material particles are bonded together to be granulated. Alternatively, in the course of combustion, the formation of a film of Al, Ca, etc. on the surface of the fluidized particles is repeated, whereby the fluidized material particles become larger and granulated.
[0023]
According to the present invention, since a high differential pressure is applied to the combustor, the concentration of particles in the high-speed fluidized bed is high, and the flow state of the particles is good. For this reason, particles collide violently and many times. For this reason, it is considered that the bonds between the particles are broken, or the film formed on the particles is worn and not granulated.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, although embodiment of this invention is described, this invention is not limited to this.
The combustion method according to the present invention can be performed using the above circulating fluidized bed combustion apparatus. The same elements as those described above are not described here to avoid duplication.
[0025]
As the fuel in the present invention, a volatile component (VM) measured based on the coal and coke industrial analysis method (applicable for solid fuel not defined in the standard) defined in Japanese Industrial Standard (JIS M8812) and A fuel having a fixed carbon (FC) ratio (FC / VM) of 0.5 or less is preferable. Such fuel includes, for example, RDF obtained by solidifying municipal waste and RPF. The amount of the low melting point metal contained in these fuels can be measured by a method such as ICP analysis (Inductively Coupled Plasma).
[0026]
The combustor differential pressure P (kPa) with respect to the low melting point metal content X (% by weight) of the fuel is preferably determined within the range given by the above formula (1), and more preferably the above formula. Set to the range given by (2).
[0027]
As described above, the amount of the low melting point metal contained in the fuel such as RPF is usually about 1% by weight, and at most about 3% by weight. Therefore, the differential pressure of the combustor is about 10 kPa, more preferably about 14 kPa is sufficient.
[0028]
It should be noted that a pressure measuring device is provided at each of the bottom of the combustor and the upper outlet of the combustor, and by measuring the pressure at the bottom of the combustor and the upper outlet of the combustor, the differential pressure of the combustor can be measured or monitored. it can.
[0029]
Although the combustion temperature in the combustor at this time is related to the value of the differential pressure, it is usually about 700 to about 1000 ° C., preferably about 800 to about 900 ° C., more preferably about 830 to about 870 ° C. . According to the following experimental example, when the differential pressure is 14 kPa, 830 to 870 ° C. is suitable as the temperature condition for reliably preventing the low melting point metal from adhering to the cyclone. The speed of the air flowing in the combustor (hereinafter referred to as “superficial velocity”) is usually about 1 to about 10 m / second, preferably about 2 to about 8 m / second, more preferably about 4 to about 6 m / second. Seconds. The air ratio is usually about 1.0 to about 2.0, preferably about 1.1 to about 1.6, and more preferably about 1.2 to about 1.4.
[0030]
In addition, silica sand, fuel combustion ash, and the like can be used as particles of the fluidized material stored in the combustor. The average particle diameter of these particles is usually 0.001 to 0.5 mm, preferably 0.1 to 0.3 mm, and more preferably 0.15 to 0.25 mm.
[0031]
【Example】
A combustion test was performed based on the above-described embodiment.
In this test, a circulating fluidized bed combustion apparatus having a height of 21 m and a cross-sectional shape of 400 mm × 400 mm and having a whole refractory material structure was used. Two types of RPF were used as fuel. These were all in the form of pellets having a diameter of about 8 mm and a length of about 10 mm, and contained 3.0% by weight and 1.0% by weight of metal Al, respectively.
[0032]
In this test, as shown in Table 1, the combustor differential pressure was set to 14 kPa or 7 kPa according to each RPF, the combustor temperature was 850 ° C. or 900 ° C., the air ratio was about 1.2, and no additive was added. Each was subjected to a 20 hour combustion test. At this time, the superficial velocity was 5.5 m / s. Note that silica sand having an average particle diameter of 0.2 mm was used as the fluid material particles.
[0033]
[Table 1]

[0034]
FIG. 2 shows the relationship between the aluminum content of the fuel, the combustor differential pressure, and the ash deposition in the cyclone.
As shown in FIG. 2, when the content of metal Al of 3% and RPF is large, ash adhesion was observed on the inner tower of the cyclone when the combustion test was performed with a combustor differential pressure reduced to 7 kPa ( Condition 2). The deposit was gray and very hard and grew in the direction of gas flow.
However, even when the metal Al content of 3% and RPF was large, no deposits were observed in the cyclone when the combustor differential pressure was increased to 14 kPa (Condition 1). When the metal Al content of 1% and RPF was low, no deposits were observed in the cyclone even if the combustor differential pressure was reduced to 7 kPa (Condition 3).
[0035]
FIG. 4 shows the relationship between the aluminum content of the fuel, the temperature of the combustor, and the adhesion of ash in the cyclone. As shown in FIG. 4, even when the metal Al content of RPF is 3% and the combustor differential pressure is as high as 14 kPa, no deposits were observed in the cyclone when the combustor temperature was 850 ° C. (Condition 1).
However, even when the metal Al content of RPF is high at 3% and the combustor differential pressure is as high as 14 kPa, some deposits are observed in the cyclone when the combustor temperature is 900 ° C. (conditions) 4).
[0036]
The above results support the above-mentioned view by the present inventors that when the combustor differential pressure is low, the formation of fine particles of molten metal Al in the RPF due to melting and impact crushing is difficult to proceed. Moreover, when combustor temperature is too high, the above-mentioned inventors' view that ash tends to adhere to a cyclone is supported.
[0037]
In addition, the driving | running condition in this test was stable irrespective of the quantity of metal Al in RPF. Further, the combustion temperature was uniformly distributed with respect to the height direction of the combustion furnace. Other problems such as gas properties were not found.
[0038]
【The invention's effect】
As is apparent from the above, the present invention provides a combustion method in which ash does not adhere to a cyclone when a fuel containing a low melting point metal is burned using a circulating fluidized bed combustion apparatus.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a circulating fluidized bed combustion apparatus.
FIG. 2 is a diagram showing the relationship between the aluminum content of fuel, the differential pressure of the combustor, and the adhesion of ash into the cyclone.
FIG. 3 is a graph showing changes in the viscosity coefficient of metal Al with respect to changes in temperature.
FIG. 4 is a diagram showing the relationship between the aluminum content of fuel, the temperature of the combustor, and the adhesion of ash into the cyclone.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Combustor 2 Cyclone 3 Seal pot 4 Fluidized bed heat exchange means 5 Low temperature particle circulation line 6 High temperature particle circulation line 7 Exhaust gas heat exchange means 8 Bag filter 9 Induction fan 10 Chimney

Claims (4)

A combustor that contains fluidized material particles therein to form a high-speed fluidized bed, and a cyclone that is provided at the outlet of the combustor and separates unburned matter discharged from the combustor and exhaust gas, is captured by the cyclone. A method for burning low-melting-point metal-containing fuel using a circulating fluidized bed combustion device that circulates and feeds the collected unburned matter into the combustor
A combustion method for preventing deposition of deposits in the circulating fluidized bed combustion apparatus by increasing the differential pressure of the combustor as the content of the low-melting point metal in the fuel increases , wherein the differential pressure P of the combustor (KPa) is defined as a range given by P ≧ 2 × X + 3.5 with respect to the low melting point metal content X (wt%) of the fuel.   When the content X is 1% by weight, the differential pressure is set to a certain value of 7 kPa or more, and when the content X is greater than 1% by weight and 3% by weight or less, the differential pressure is set to the certain value. The combustion method according to claim 1, wherein a larger value is set. The combustion method of Claim 1 or 2 whose combustion temperature of the said combustor is 700 degreeC or more and 870 degrees C or less. The combustion method according to claim 1 , wherein the low melting point metal is aluminum.

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