JP4298398B2 - Method for suppressing emission of N2O and NOX in a combustion apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention can simultaneously perform desulfurization and N ₂ O and NO _X emission suppression in a furnace of a combustion apparatus that burns fuel such as coal, heavy oil, petroleum coke, biomass, and industrial waste by fluidized bed combustion. Regarding the method.
[0002]
[Prior art]
Fluidized bed combustion using coal, heavy oil, petroleum coke, biomass, industrial waste, etc. as fuel, generates a large amount of nitrous oxide (hereinafter referred to as N ₂ O), one of the greenhouse gases. Development is needed.
As a method for suppressing N ₂ O, N ₂ O decomposition by a catalyst, N ₂ O adsorption by active coke, partial temperature increase by blowing auxiliary fuel gas into a combustion device, N ₂ O decomposition particles in the furnace A method by addition is known. In addition, by using porous alumina particles as N ₂ O decomposition particles and mixing them with quartz sand, which is a fluidized medium for fluidized bed combustion, at a constant mixing rate, the fuel is burned to reduce the amount of N ₂ O emissions. Can be reduced.
Moreover, the discharge amount of N ₂ O can also be reduced by mixing an excessive desulfurizing agent with the fluid medium.
[0003]
However, according to the method of mixing porous alumina particles or excess desulfurizing agent, there is a problem that the emission amount of nitrogen oxide (NO _x ), which is one of pollutant gases, increases. This is because the porous alumina particles or desulfurization agent suppresses the conversion to N ₂ O by converting the nitrogen (N) content in the coal into nitrogen oxides, but on the other hand, the conversion to NO _X It is thought to promote.
In order to suppress the NO _X emissions, a method of removing with a catalyst outside the furnace has been proposed, in this method, it is necessary to significantly modify the existing combustion device, the considerable expense There is a problem that the cost for suppressing the emission amount of N ₂ O and NO _X is increased.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems, and does not require any major equipment modification, and at the same time, effectively releases N ₂ O and NO _X while desulfurizing in the furnace. It is an object of the present invention to provide a method that can be suppressed.
[0005]
[Means for Solving the Problems]
The inventors of the present invention have found that when an excessive amount of desulfurizing agent is present in the fluidized bed of the combustion apparatus, NO _X tends to increase, and due to the contact between the desulfurizing agent and the fuel, Focusing on the fact that NO _X increases, and when using a separate fluid medium from the desulfurizing agent, the present invention has been discovered by focusing on separating the desulfurizing agent and the fluid medium.
[0006]
That is, the present invention provides a combustion apparatus in which a fluidized bed containing a fluidized catalyst is arranged in the lower stage and a desulfurization layer containing a desulfurizing agent is arranged in the upper stage, after the fuel is burned in the fluidized bed in the lower stage, A method for simultaneously suppressing emission of N ₂ O and NO _X by performing desulfurization of exhaust gas in a desulfurization layer , wherein the particle size of the fluidized catalyst particles is larger than the flow rate of the gas passing through the fluidized bed. The particle size of the fluidized catalyst particles is such that the terminal velocity of the desulfurizing agent is large, and the particle size of the particles of the desulfurizing agent is smaller than the flow rate of the gas passing through the fluidized bed. This is a method for suppressing the emission of N ₂ O and NO _X in the combustion apparatus .
[0007]
Specifically, the combustion device is a bubble fluidized bed combustion device , the average particle size of the fluid catalyst is 0.05 mm to 5 mm, and the average particle size of the desulfurizing agent is 0.01 mm to 2 mm.
[0008]
Moreover, the said combustion apparatus is a circulating fluidized bed combustion apparatus , the average particle diameter of a fluid catalyst is 0.02 mm-2 mm, and the average particle diameter of a desulfurization agent is 0.01 mm-2 mm.
[0009]
Since the particle size of the fluidized catalyst particles is such that the terminal velocity of the particles is larger than the flow velocity of the gas passing through the fluidized bed, the fluidized catalyst particles flow together with the gas passing through the fluidized bed. The inconvenience of being discharged from the layer can be prevented.
In this way, the fluidized catalyst can be kept in the fluidized bed against the gas passing through the fluidized bed.
[0010]
Further, since the particle size of the particles of the desulfurizing agent is such that the terminal velocity of the particles is smaller than the flow velocity of the gas passing through the fluidized bed, the desulfurizing agent is combined with the gas passing through the fluidized bed. Discharged.
In this way, since the desulfurizing agent is discharged by the gas passing through the fluidized bed, the desulfurizing agent does not stay for a long time , and generation of NO _x can be suppressed.
[0012]
In a combustion apparatus that performs fluidized bed combustion, quartz sand or the like is generally used as a fluid catalyst. In this invention, it is preferable to use porous alumina as the fluid catalyst. With this porous alumina, the amount of N ₂ O discharged can be effectively reduced.
[0013]
Further, in the present invention , an air flow disturbing member is disposed at a position separated from the fluidized bed inside the desulfurization layer of the furnace so as to disturb the flow of the exhaust gas containing the desulfurizing agent discharged from the fluidized bed. There is a way.
According to this method, for example, the flow of the exhaust gas containing the desulfurizing agent can be disturbed by disposing an airflow disturbing member such as a baffle plate above the desulfurizing layer spaced from the fluidized bed. As a result, the desulfurization agent can be kept in the furnace for a long time in a state of being separated from the fluidized bed, and a sufficient reaction time can be given to the desulfurization agent, so that the desulfurization agent can be effectively used.
As the desulfurizing agent, those containing Ca as a main component can be used.
For example, limestone, ready-mixed concrete sludge, dolomite, shells, concrete structures, wastes thereof, and the like whose main component is calcium carbonate (CaCO ₃ ) can be used.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings.
Note that fluidized bed combustion includes circulating fluidized bed combustion and bubbling fluidized bed combustion. Hereinafter, description will be made on the assumption that bubbling fluidized bed combustion is performed.
In addition, the lower part of the furnace that causes fluidized bed combustion is sometimes referred to as the “rich layer” to distinguish it from the “fluidized bed”. In this specification, this part is collectively described as “fluidized bed”. And
[0015]
[First embodiment]
FIG. 1 is a schematic view of a combustion apparatus for carrying out an emission control method according to the first embodiment of the present invention.
A combustion apparatus 1 that combusts fuel by fluidized bed combustion includes a furnace 11, a fuel supply unit 12 that supplies fuel particles to the furnace 11, and a desulfurization agent circulation unit 13 that circulates the desulfurization agent particles 111a discharged from the furnace 11. And a desulfurization agent supply unit 14 for newly supplying the desulfurization agent particles 111 a to the furnace 11.
In the present invention, as fuel, heavy oil, petroleum coke, biomass, industrial waste, etc. can be used in addition to coal. Moreover, as a desulfurization agent, what contains Ca as a main component, for example, limestone, ready-mixed concrete sludge, dolomite, a shell, a concrete structure, its waste, etc. can be used.
[0016]
At the bottom of the furnace 11, a wire mesh-like or perforated plate-like dispersion plate 113 is provided, and a fluidized bed 112 is formed on the dispersion plate 113. A free board portion (desulfurization layer) 111 is provided above the fluidized bed 112.
The fuel supply unit 12 includes a hopper 121 that stores fuel particles, and a controller 122 that controls the amount of fuel particles supplied from the hopper 121 to the furnace 11.
[0017]
Further, the desulfurization agent supply unit 14 is provided with a hopper 141 for storing desulfurization agent particles 111 a supplied to the furnace 11 and a controller 142 for controlling the amount of the desulfurization agent particles 111 a supplied from the hopper 141 to the furnace 11. It has been.
The desulfurizing agent particles 111a may be batch-fed into the furnace 11 from the hopper 141, or may be mixed with fuel particles and supplied to the furnace 11. Further, as shown in FIG. 1, the desulfurization agent particles including the unreacted portion are collected from the discharged desulfurization agent particles by a dust collector 131 such as a cyclone, and the collected desulfurization agent particles are supplied to the controller 132. Then, it may be returned to the furnace 11.
[0018]
FIG. 2 is a partially enlarged view of the fluidized bed 112. The fluidized bed 112 is filled with porous alumina particles 112b that are fluidized catalysts. When air is fed into the fluidized bed 112 through the dispersion plate 113 and the fuel particles 112a are supplied from the fuel supply unit 12, the mixture of the porous alumina particles 112b and the fuel particles 112a becomes fluidized. Then, combustion is performed while maintaining the temperature in the fluidized bed 112 at a predetermined temperature (for example, 850 ° C.).
The diameter d2 of the porous alumina particles 112b is preferably such that the porous alumina particles 112b are not discharged from the fluidized bed 112 by the gas passing through the fluidized bed 112.
[0019]
FIG. 3 is a partially enlarged view of the free board unit 111.
In the free board portion 111 provided above the fluidized bed 112, desulfurization agent particles 111a are retained. The particle size d3 of the desulfurizing agent particles 111a may be set to a size that is at least discharged from the fluidized bed 112 by a gas such as air or exhaust gas that passes through the fluidized bed 112. Further, the particle size d3 of the desulfurization agent particles 111a may be set to a size such that at least a part of the particle size d3 is conveyed to the exhaust gas rising in the furnace 11 and discharged from the furnace 11.
The particle diameters d2 and d3 of the above-mentioned particles are measured in consideration of the kind of the porous alumina particles 112b and the kind of the desulfurizing agent particles 111a, the supply amount of air, the flow rate of air passing through the fluidized bed 112, exhaust gas, and the like. And can be determined by experience.
[0020]
The particle diameters d2 and d3 can be determined based on the relationship between the flow velocity of gas such as air or exhaust gas passing through the fluidized bed and the terminal velocity of the particles. In general, the terminal velocity of a particle is closely related to the viscosity, density and particle size of the particle. The termination speed increases as the particle diameter increases, and the termination speed decreases as the particle diameter decreases.
[0021]
As an example, a method for determining the particle size d3 of the desulfurizing agent particles 111a will be described with reference to FIG.
FIG. 4 is a graph showing the relationship between the particle size of the desulfurizing agent particle 111a and the terminal velocity, where the vertical axis represents the terminal velocity of the desulfurizing agent particle 111a and the horizontal axis represents the particle size of the desulfurizing agent particle 111a.
In the graph of FIG. 4, the superficial velocity of the gas passing through the fluidized bed 112 is indicated by a one-dot chain line. Therefore, by selecting the particle size d3 so that the terminal velocity is smaller than the superficial velocity of the gas passing through the fluidized bed 112, the desulfurizing agent particles 111a are brought out of the fluidized bed 112 together with the gas passing through the fluidized bed 112. It can be made to be discharged. According to the graph of FIG. 4, for example, when the superficial velocity of the reference gas is 0.22 m / s, the particle diameter d3 is preferably 0.1 mm or less.
As described above, the particle diameters of the fluid catalyst and the desulfurizing agent particles may be determined based on the superficial velocity of the gas. Specifically, in the bubbling fluidized bed combustion apparatus, the average particle diameter of the fluid catalyst is 0.05 mm to 5 mm and a desulfurizing agent having an average particle diameter in the range of 0.01 mm to 2 mm are preferably used. In the circulating fluidized bed combustion apparatus, the fluid catalyst having an average particle diameter of 0.02 mm to 2 mm and an average particle diameter of the desulfurizing agent of 0.01 mm to 2 mm is preferably used.
[0022]
[Second Embodiment]
FIG. 5 is a schematic view of a combustion apparatus that implements the emission control method according to the second embodiment of the present invention.
In FIG. 5, the same parts and members as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
In this embodiment, a plurality of baffle plates 151 are arranged above the free board portion 111 of the furnace 11. Then, the exhaust gas is disturbed by the baffle plate 151 so that at least a part of the desulfurization agent particles 111a that have risen in the furnace 11 together with the exhaust gas is temporarily retained in the vicinity of the baffle plate 151. Yes.
Therefore, since the desulfurization agent particles 111a remain in the furnace 11 until the reaction is sufficiently performed, the desulfurization agent particles 111a can be effectively used.
Note that the airflow disturbing member is not limited to the baffle plate 151, and other members such as a net member or a porous member may be used as long as the flow of the exhaust gas can be disturbed to temporarily retain at least a part of the desulfurizing agent particles 111a. Can be used.
[0023]
[Third embodiment]
FIG. 6 is a schematic view of a combustion apparatus that implements the emission control method according to the third embodiment of the present invention.
In the combustion apparatus 2 used in this embodiment, the inside of the furnace 21 is divided into two stages, upper and lower. A fluidized bed 212 for burning fuel supplied from the hopper 221 of the fuel supply unit 22 via the controller 222 is provided in the lower stage, and a desulfurization layer 211 for desulfurizing exhaust gas is provided in the upper stage.
The desulfurization layer 211 is filled with desulfurization agent particles such as limestone, but unlike the previous embodiment, the particle size is such that the desulfurization agent particles are not discharged out of the furnace 21 by the exhaust gas. . The desulfurization agent particles are input to the desulfurization layer 211 from the hopper 231 of the desulfurization agent supply unit 23 via the controller 232.
[0024]
According to this embodiment, fuel particles are burned in the fluidized bed 212 while air is supplied to the fluidized bed 212 through the dispersion plate 213. The exhaust gas rises in the furnace 21 and reaches the desulfurization layer 211, and desulfurization is performed in the desulfurization layer 211.
In this embodiment, since it is possible to prevent the fuel and the desulfurizing agent from coming into contact with each other, it is possible to effectively suppress the generation of NO _X and simultaneously suppress the generation of N ₂ O. it can.
[0025]
[Example]
Next, specific examples of the present invention according to the first embodiment will be described. The conditions of the examples and comparative examples are as follows.
[0026]
(Example)
・ Fuel: Coal particle diameter d1 = 297 μm to 1000 μm
Ingredients Carbon 80.13%, Hydrogen 6.50%, Oxygen 11.06%, Nitrogen 1.74%, Sulfur 0.57%
Calorific value 6470Kcal / kg
Supply amount The amount that the oxygen concentration of the exhaust gas was 4% was supplied.
・ Air flow rate: 0.22m / s
Fluid catalyst: porous alumina particle diameter (average particle diameter) d2 = 399 μm
Components _{Al 2 O 3 84.7%, SiO} 2 2.2%, MgO 0.0%
CaO 0.8%, TiO ₂ 1.1%, Fe ₂ O ₃ 5.8%
SO ₃ 3.8%, Others 1.6%
Supply amount 220 cc filling / desulfurization agent in bulk volume so that the height of the stationary layer is 10 cm: Limestone particle diameter d3 = 53 μm to 105 μm
Component CaCO ₃ 96.9%, MgCO ₃ 1.4%, SiO ₂ 0.6%, Al ₂ O ₃ 0.8%, Fe ₂ O ₃ 0.3%
Supply method Input amount supplied in batch input or mixed with fuel The ratio of the molar amount of Ca in the supplied limestone to the molar amount of S in the supplied coal (Ca / S ratio) is greater than 0 and less than 5 Supplied to.
[0027]
(Comparative Example 1)
The fuel and air flow rates are the same as in the above embodiment.
Fluidized catalyst: quartz sand particles Quartz sand particle size (average particle size) d2 = 273 μm
Supply amount 220 cc filling / desulfurization agent in bulk volume so that the height of the stationary layer is 10 cm: Limestone particle diameter d3 = 420 μm to 590 μm
Ingredients are the same supply method as in Example 1. Input amount supplied in batch or mixed with fuel Ratio of Ca molar amount of supplied limestone to molar amount of S of supplied coal (Ca / S ratio) is 0 It was supplied so as to be 5 or less.
(Comparative Example 2)
It is the same as Comparative Example 1 except that the particle size d3 of the limestone particles is set to 145 μm to 250 μm.
[0028]
In the above Examples and Comparative Examples 1 and 2, the concentration of each component in the exhaust gas is analyzed by removing the discharged coal combustion ash and limestone particles with a cyclone at the outlet of the furnace 11 and a silica filter, followed by ice cooling. The exhaust gas was passed through a stainless steel pipe and cooled and dehumidified.
The concentrations of N ₂ O, O ₂ , CO ₂ , CO, and N ₂ are determined by collecting dust and dehumidified exhaust gas in a gas pack and then gas chromatograph with TCD (thermal conductivity detector) (Shimadzu Corporation) Discontinuous measurement was performed using GC-8A).
[0029]
The O ₂ concentration is a magnetic O ₂ concentration meter (POT-101 manufactured by Shimadzu Corporation), and the CO ₂ and CO concentrations are infrared gas concentration measuring devices (CGT-7000 manufactured by Shimadzu Corporation or CGT- manufactured by Shimadzu Corporation). 10-1A) was used for continuous measurement.
Further, NOx (NO + NO ₂ ) was continuously measured using a chemiluminescence type NOx measuring device, SO ₂ was an infrared type SO _{2 and} an infrared type SO ₂ meter (URA-107 manufactured by Shimadzu Corporation) was continuously measured. .
[0030]
The result of the measurement performed in this manner is shown in the graph of FIG.
FIG. 7A is a graph showing the relationship between the desulfurization amount (SO ₂ emission amount) and the NO _X emission amount in the above-mentioned Examples and Comparative Examples 1 and 2, and FIG. 7B is the above-described Example. 4 is a graph showing the relationship between the desulfurization amount (SO ₂ emission amount) and the N ₂ O emission amount of Comparative Examples 1 and ₂ .
[0031]
As shown in FIG. 7A, the NO _X emission amounts of the example and the comparative examples 1 and 2 increase as the SO ₂ emission amount decreases, that is, toward the left of the graph. However, in the method of the present invention, a small increase in the slope of the NO _X emissions compared to the two comparative examples 1 and 2, and, as compared NO _X emissions and about 180Ppm～200ppm, and two comparative examples It remains fairly low.
[0032]
Further, as shown in FIG. 7B, the N ₂ O emission amounts of the example and the comparative examples 1 and 2 decrease as the SO ₂ emission amount decreases, that is, toward the left of the graph. However, in the method of the present invention, the N ₂ O emission amount is also about 25 ppm to 40 ppm, which is considerably lower than the two comparative examples 1 and 2.
As can be seen from the graphs of FIGS. 7A and 7B, in the present invention, NO _X and N ₂ O emissions are simultaneously suppressed in the furnace 11 while maintaining the desulfurization amount in the exhaust gas. Is something that can be done.
[0033]
Although preferred embodiments of the present invention have been described, the present invention is not limited to the above-described embodiments.
For example, as a fluidized bed combustion type combustion apparatus capable of implementing the method of the present invention, various combustion apparatuses such as a normal pressure type, a pressure type, a bubbling type, and a circulation type can be used.
[0034]
【The invention's effect】
According to the present invention, it is possible to simultaneously suppress the emission amounts of N ₂ O and NO _X at a low cost while desulfurization is performed in a furnace without significantly modifying an existing combustion apparatus. .
[Brief description of the drawings]
FIG. 1 is a schematic view of a combustion apparatus for carrying out an emission suppressing method according to a first embodiment of the present invention.
2 is a partially enlarged view of a fluidized bed in the combustion apparatus of FIG. 1. FIG.
3 is a partially enlarged view of a free board portion in the combustion apparatus of FIG. 1. FIG.
FIG. 4 is a graph for determining the particle size of desulfurizing agent particles, and shows the relationship between the particle size and the terminal velocity.
FIG. 5 is a schematic view of a combustion apparatus for carrying out an emission suppressing method according to a second embodiment of the present invention.
FIG. 6 is a schematic view of a combustion apparatus for carrying out an emission control method according to a third embodiment of the present invention.
FIG. 7 is a graph for explaining the effect of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Combustor 11 Furnace 111 Free board part 111a Desulfurization agent particle 112 Fluidized bed 112a Fuel particle 112b Porous alumina particle (fluid catalyst)
113 Dispersion plate 12 Fuel supply unit 121 Hopper 122 Controller 13 Desulfurization agent circulation unit 131 Dust collector 132 Controller 14 Desulfurization agent supply unit 141 Hopper 142 Controller 151 Baffle plate (air flow disturbance member)
2 Combustor 21 Furnace 211 Desulfurization layer 212 Fluidized bed 213 Dispersion plate 22 Fuel supply unit 221 Hopper 222 controller 23 Desulfurization agent supply unit 231 Hopper 232 controller

Claims (5)

In a combustion apparatus in which a fluidized bed containing a fluidized catalyst is arranged in the lower stage and a desulfurized layer containing a desulfurizing agent is arranged in the upper stage, after burning the fuel in the fluidized bed in the lower stage, desulfurization of exhaust gas in the upper desulfurized bed Is a method for simultaneously suppressing emission of N ₂ O and NO _X ,
The particle size of the fluidized catalyst particles is a particle size at which the terminal velocity of the fluidized catalyst particles is larger than the flow rate of the gas passing through the fluidized bed,
N ₂ O and NO _X in a combustion apparatus, wherein the particle size of the desulfurizing agent particles is set to a particle size at which the terminal velocity of the desulfurizing agent particles is smaller than the flow rate of the gas passing through the fluidized bed. Emission control method. 2. The combustion apparatus according to claim 1, wherein the combustion apparatus is a bubbling fluidized bed combustion apparatus , wherein the average particle diameter of the fluidized catalyst is 0.05 mm to 5 mm, and the average particle diameter of the desulfurizing agent is 0.01 mm to 2 mm. A method for suppressing emission of N ₂ O and NO _X in the combustion apparatus described in 1 above. The combustion apparatus is a circulating fluidized bed combustion apparatus , wherein the fluid catalyst has an average particle diameter of 0.02 mm to 2 mm and an average particle diameter of the desulfurizing agent is 0.01 mm to 2 mm. A method for suppressing emission of N ₂ O and NO _X in the combustion apparatus described in 1 above. The method for suppressing emission of N ₂ O and NO _X in a combustion apparatus according to any one of claims 1 to 3, wherein the fluid catalyst is particulate porous alumina. The air flow disturbing member is disposed inside the desulfurization layer so as to disturb the flow of exhaust gas containing the desulfurization agent discharged from the fluidized bed. A method for suppressing emission of N ₂ O and NO _{X in} a combustion apparatus.

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