JPH0773659B2 - Exhaust gas desulfurization method and apparatus - Google Patents

Description

The present invention relates to a flue gas desulfurization method and apparatus for removing sulfur oxides (SOx) contained in the exhaust gas of a pulverized coal combustion furnace such as a pulverized coal burning boiler. Specifically, by adding no alkaline agent from outside the system or by adding a small amount of alkaline agent to the coal ash, the sulfur oxides in the exhaust gas are removed mainly by the alkali content in the coal ash, and it is absorbed in powder form. The present invention relates to a method and an apparatus for desulfurizing exhaust gas capable of taking out ash.

[Conventional technology]

A conventional flue gas desulfurization apparatus is usually used in the state of a solution or slurry by mixing an alkali absorbent with water other than the molar equivalent of sulfur oxides to be removed from exhaust gas. Therefore, the sulfur compound produced after desulfurization becomes an aqueous solution or a slurry state, and in order to separate the sulfur compound, solid-liquid separation as gypsum or the like, or evaporation and concentration as sodium sulfite or sodium sulfate to crystallize and separate. is necessary. Transporting such absorbents from another location to the flue gas desulfurizer also increases desulfurization costs.

Conventionally, JP-A-60-22920 discloses that a slurry containing a Ca-based desulfurizing agent is sprayed into the exhaust gas in the flue to dry powder the desulfurizing agent by the sensible heat of the exhaust gas and react with SO _2. A dry desulfurization method is disclosed.

Further, conventionally, there is a method of introducing limestone into a combustion chamber such as a boiler to desulfurize, but in this case, even if the amount of limestone added is more than the molar equivalent of sulfur, the desulfurization rate is as low as 60%, and The amount of ash increases due to the added limestone, and the product is a mixture of limestone and gypsum, calcium sulfite, unreacted limestone, etc., and its utility value is low.

Further, in JP-A-62-200107, a desulfurizing agent is directly charged into a furnace, flue gas is rapidly cooled by water spraying, and then a mass of fly ash containing unreacted desulfurizing agent is crushed and separated. , An in-furnace desulfurization method of circulating an unreacted desulfurizing agent to a furnace is disclosed.

Further, JP-A-63-141629 discloses that in an exhaust gas generated from a combustion furnace in which an alkaline agent is blown into a furnace, only water is sprayed without adding a new alkaline agent, and an unsaturated range of water is obtained. There is disclosed a desulfurization method in which the humidity is increased inside and SOx in the exhaust gas is made to react with the scattered alkali agent. However, in the method described in JP-A-63-141629, the amount of sulfur oxides removed by coal ash is larger than the amount of sulfur oxides removed by the added alkali component. According to the method described in JP-A-63-141629, a desulfurization rate of 80 to 90% is achieved, but the utilization rate of the alkaline agent added is low.

[Problems to be Solved by the Invention]

As described above, the conventional method has various problems because the alkaline agent is put in the furnace or the slurry of the alkaline agent is sprayed in the furnace or in the exhaust gas. That is, the amount of waste increases, and the raw material cost and the transportation cost increase. Further, when using the slurry, there are problems such as wear and blockage of the device.

On the other hand, coal ash is mixed with cement and used for some purposes such as building materials, but most of it is landfilled. Therefore, the method that can take out the coal ash used as a desulfurizing agent in the form of powder similar to conventional coal ash is easy to handle without changing the conventional equipment, and there is no problem of wastewater treatment. , There are many advantages.

In view of the above points, the present invention has been made to solve the above problems, in order to remove the sulfur oxides in the exhaust gas to a predetermined desulfurization rate or more, sufficient desulfurization capacity coal ash has It is an object of the present invention to provide an exhaust gas desulfurization method and device that can be efficiently and inexpensively desulfurized.

[Means and Actions for Solving the Problems]

In order to achieve the above object, the method of claim 1 comprises a first
As shown in the figure, in the method of removing sulfur oxides contained in the exhaust gas discharged from the pulverized coal combustion furnace 1, the coal ash flying from the combustion furnace 1 is supplied to the combustion furnace 1 without supplying a desulfurizing agent to the combustion furnace 1. It is characterized by desulfurizing only with coal ash by spraying water and humidifying it in the unsaturated range of water in the gas.

Further, the method of claim 2 is, as shown in FIG. 2, a method of removing sulfur oxides contained in the exhaust gas discharged from the pulverized coal combustion furnace 1, in which the coal ash collected by the dust collector 3 is removed. After activating by pulverizing into fine powder, the powder is re-introduced into the exhaust gas and dispersed in the exhaust gas in a powder state. It is used as a desulfurizing agent together with coal ash, and is characterized by spraying water on these powders and humidifying them within the unsaturated range of water in the gas for desulfurization.

Further, as shown in FIG. 3, the method of claim 3 activates the coal ash collected by the dust collector 3 in FIG. 2 by further pulverizing the coal ash into fine powder.
Activated by adding coal in an amount equal to or less than the molar equivalent of sulfur oxides in the exhaust gas to the coal ash collected by, and coating the coal ash, or pulverizing the coated product into fine powder. It is characterized by that. 6
Is an exhaust gas superheater, which is used to reheat the gas leaving the desulfurization tower as a measure to prevent the dust collector and the flue from being blocked and corrosive.

Further, as shown in FIG. 4, in the method of claim 4, instead of activating the coal ash collected by the dust collector 3 in FIG. 2 by further pulverizing it into fine powder, the dust collector 3 is activated.
The coal ash collected by the above is reacted by adding an alkali in an amount equal to or less than the molar equivalent of sulfur oxide in the exhaust gas, and gypsum / lime, and transforming the coal ash into a porous or acicular fine structure. It is characterized in that it is activated by performing a treatment for enhancing the desulfurization activity or by pulverizing this substance into a fine powder.

Furthermore, the method of claim 5 is the method of claim 1, 2, 3 or 4, as shown in FIGS.
The step of spraying water with the water spray nozzle 12 is made into at least two stages, and after the spray water on the upstream side is completely evaporated, the water spray of the next stage is performed.

And the apparatus of Claim 6 installs the desulfurization tower 2 provided with the water spray nozzle 12 in the exhaust gas duct 11 of the pulverized coal combustion furnace 1, as shown in FIG. The exhaust gas duct 11 or the desulfurization tower 2 is characterized in that a coal ash circulation line 13 for recharging a part of the ash collected by the dust collector is connected.

The apparatus of claim 7 is characterized in that, as shown in FIG. 2, the crusher 7 is installed in the coal ash circulation line 13 of claim 6.

Further, the apparatus of claim 8 is, as shown in FIG. 3 or FIG. 4, an activation treatment apparatus 5a for adding alkali to the coal ash circulation line 13 of claim 6 and mixing with coal ash, or It is characterized in that an activation treatment device 5b for adding alkali and gypsum / lime to react with coal ash is installed.

In the method and apparatus of the present invention, Ca is used as the alkali.
(OH) ₂ , CaO, NaOH, Mg (OH) _{2 and the} like are used.

In addition, the term “activation” in the present invention refers to the following.

(1) Crushing of collected coal ash.

(2) To coat the surface of the collected coal ash particles with a small amount of alkali. Or crush this thing.

(3) A small amount of alkali and a small amount of gypsum / lime are added to the collected coal ash to cause a reaction, and the surface area of the ash is increased or the reactivity is increased as a structure such as ettringite or zeolite.

Or crush this thing.

In the method of the present invention, when a relatively low desulfurization rate is sufficient, the amount of input alkali is set to 0 to desulfurize only the coal ash in the combustion exhaust gas, or the collected coal ash is crushed and reactivated. After being converted, it is mixed with the fly ash from the combustion exhaust gas and desulfurized.

In order to ensure a higher desulfurization rate, in order to further activate the collected coal ash, before crushing the collected coal ash,
Alternatively, the water-soluble alkaline agent is removed after pulverization, a molar amount of less than the stoichiometric amount of sulfur is added, and the mixture is sprinkled on coal ash and re-supplied in a dry powder state, and mixed with coal ash flying from combustion exhaust gas. Desulfurization improves the total desulfurization rate. Further, alkali and gypsum / lime are added to the collected coal ash to cause a reaction, the reaction activity is improved, and the same is re-introduced to improve the desulfurization rate.

Further, the desulfurization rate can be improved by efficiently contacting the powder with the spray water, so that repeating the water spray leads to an improvement in the overall efficiency.

The desulfurization method of the present invention, the distribution of the alkali content contained in the particles of the coal ash, and all the metal elements contained as components of the coal ash have a more or less desulfurization effect, and the cause of the coal ash. It is considered that this is due to the desulfurization action due to the micropores and the like on the structure generated from.

Usually, in a dry state in which coal ash is not sprayed with water, the desulfurization ability is low even if the temperature is lowered, and it is not enough to be used in a desulfurization device. However, by spraying with water to wet the surface of the particles, the desulfurization capacity is greatly increased, and desulfurization of 30 to 60% is possible.
This depends on the type of coal, the composition of ash, the state of combustion, etc., but some of the coal ash tried showed an absorption capacity of around 50% (see Table 1 below). .

The following has been clarified for various types of coal so far by photographs of the microscopic aspect of combustion ash of specific coal types and analysis of the distribution state of elements in the ash. That is, the elements in the coal ash are distributed almost uniformly in the particles, and few are unevenly distributed. On the other hand, the immobilization reaction of sulfur oxides occurs only on the surface of coal ash particles. Therefore, by crushing the coal ash of the absorbent to increase the surface and re-inject, the surface capable of immobilization reaction increases,
The absorption capacity per unit weight is increased. As components in the ash, in addition to Fe ₂ O ₃ , CaO, MgO, Na ₂ O, K ₂ O, oxides such as Al, Si, Ti, etc. It has reactivity and helps to fix sulfur content. Exhaust gas is flowing in the flue with ash dispersed in the exhaust gas. When water is sprayed into this exhaust gas, water evaporates and the temperature of the entire exhaust gas gradually drops. However, an amount that is higher than the saturation temperature, preferably 5 ° to 15 ° C. higher than the saturation temperature is sprayed. Further, in spraying, it is preferable that the coal ash particles be uniformly wetted as much as possible. For this purpose, a plurality of spray nozzles, which are evenly arranged in the cross section of the entire flow path, are arranged, and, as shown in FIGS. 5 to 7, a plurality of spray nozzles are arranged in at least two stages in the flow direction. By so doing, it is advantageous to improve the absorption performance by increasing the chances of the particles getting wet. Furthermore, the spray of the next stage is performed in a state where the spray water of the previous stage is completely evaporated. This is because the absorption reaction is increased by the presence of water.

As shown in the above-mentioned JP-A-60-22920, an alkali is slurried and sprayed, and the amount of water such that the gas becomes unsaturated with water at the outlet of the absorption section and the powder becomes a dry state. Although there is a method of adding a slurry, the amount of particles dispersed in the exhaust gas and the surface area thereof can be significantly increased as compared with this conventional method, which is effective in increasing the absorption rate.
The reason is that when the amount of powder is large relative to the amount of water, it becomes difficult to disperse the particles, and the amount of powder is limited.

The desulfurization section requires a space until the water completely evaporates due to the relationship between the flow velocity and the residence time. Therefore, increasing the cross-sectional area shortens the flow path.

Next, if the reaction alkali amount of coal ash is insufficient, Na
Add soluble alkali such as OH in the form of an aqueous solution before regrinding to make up for the lack of alkali. As this amount, the remaining amount of the sulfur oxide absorbed by the coal ash may be supplemented. The molar equivalent of the usual amount of alkali used to the sulfur oxide is 1 or more, but in this case, it may be 1 or less.

In addition, as one of the methods for improving the activity of coal ash, by adding an alkaline agent and a small amount of Ca (OH) ₂ and gypsum to the coal ash and adding water, curing is performed at 80 to 100 ° C for 5 to 15 hours. Ettringite (3CaO ・ Al ₂ O ₃ / 3CaSO ₄・ 32H ₂ O) or calcium monosulphoaluminate hydrate (3CaO ・ Al
₂ O ₃ · CaSO ₄ · 12H ₂ O), which can be used very effectively when the powder is pulverized and used. The reason is that the needle-like structure develops and the surface area increases extremely (more than 10 times).

Therefore, in the state where the alkaline component in the ash and SO ₂ have reacted, the crystals are broken and the surface is renewed, and a new reaction surface is generated. Therefore, the desulfurization performance is improved. In this case, the added Ca (OH) ₂ is 10 to 30 wt% with respect to the coal ash flying from the combustion furnace side, and the added dihydrate gypsum is 10 to 30 wt% with respect to the coal ash flying from the combustion furnace. Is desirable. Note that CaO may be used instead of Ca (OH) ₂ .

Reactions such as the above can be performed using Na, K, Mg, Fe other than calcium.
There are elements such as, etc. (different as materials), and for example, a material such as zeolite is generated to increase the adsorption surface. The present invention also includes reusing the reactants, including such.

The powder floating in the exhaust gas has the effect of aggregating by water spraying, and the relatively fine powder agglomerates and becomes large and easily sediments. Therefore, the amount of coal ash settled in the desulfurization section increases. This phenomenon is advantageous in reducing the load on the subsequent dust collector, but is disadvantageous in that the space retention time is shortened for desulfurization in the absorption section. In order to reduce this drawback, the flow velocity should be set a little faster to reduce sedimentation, or an upward flow should be used to extend the holding time. Therefore, it is desirable that the absorbing part allows the exhaust gas to flow vertically.

In the method of the present invention, the state of the exhaust gas is saturated humidity or less, the structural material can be slightly graded compared to the wet desulfurization device, it is possible to use an inexpensive material, but desirably, in the absorption part. It is desired to protect the material by exchanging heat between the incoming exhaust gas and the exhaust gas at the outlet of the absorption section or by heating the exhaust gas at the outlet. By heating, the material of the subsequent device can be inexpensive.

〔Example〕

 Examples of the present invention will be described below.

Example 1 As shown in Table 1, coal having a ash content of 15.5 wt% and an S content of 0.34 wt% (referred to as coal type A) was used as a pulverized coal combustion boiler shown in FIG.
Burned at 15. The flue gas was introduced into the desulfurization tower 2, water was sprayed, the water was humidified in the unsaturated range of water, and the desulfurization performance was measured.

The SOx concentration generated in the exhaust gas before entering the desulfurization tower 2 was 249 ppm. The desulfurization rate was as shown in Table 1 when water was sprayed on the exhaust gas and the exhaust gas temperature after desulfurization was set to 60 ° C and 70 ° C.

Example 2 Using coal having an ash content of 4.8 wt% and an S content of 0.47 wt% (referred to as coal type B), the measurement was performed under the same conditions as in Example 1. The results are shown in Table 1.

The ground coal ash and the coal type of coal ash increases the Blaine specific surface area and 20hr ground in a ball mill from 3000 cm ² / g to 6000 cm ² / g in Example 3 Example 1, according to the flow shown in FIG. 2, the combustion It was mixed with exhaust gas from the furnace, introduced into a desulfurization tower, sprayed with water, and humidified in an unsaturated range of water in the gas to perform desulfurization treatment. The ratio (weight) of the coal ash in the exhaust gas from the combustion furnace and the crushed coal ash was 1: 2. As shown in Table 2, assuming that the desulfurization rate is 45 to 55% in the case of only coal ash that is not ground, the desulfurization ability in the case of this example was 60 to 70%.

Example 4 Coal ash was coated by adding an aqueous solution in which 0.5 to 0.8 molar equivalent of NaOH of sulfur oxide in the exhaust gas was dissolved to the coal ash of coal type in Example 1 and coating the coal ash in FIG. According to the flow shown, it was mixed with the exhaust gas from the combustion furnace, introduced into the desulfurization tower, sprayed with water, and humidified within the unsaturated range of the water in the gas for desulfurization treatment. The ratio (weight) of the coal ash in the exhaust gas from the combustion furnace and the alkali-coated coal ash (excluding the alkali) was 1: 2. As shown in Table 2, the desulfurization ability in this example is 60-
It was 95%.

Example 5 Coal ash of coal type in Example 1, NaOH of 0.8 molar equivalent of sulfur oxide in exhaust gas, 10 wt% gypsum with respect to coal ash flying from the combustion furnace, coal ash flying from the combustion furnace On the other hand, 20 wt% of Ca (OH) ₂ and water were added to cause the ettringite reaction, and the coal ash was mixed with the exhaust gas from the combustion furnace according to the flow shown in Fig. 4, introduced into the desulfurization tower, and sprayed with water. By humidifying in the unsaturated range of water in the gas,
It was desulfurized. The ratio (weight) of the coal ash in the exhaust gas from the combustion furnace and the coal ash subjected to the ettringite reaction (excluding alkali, gypsum and Ca (OH) ₂ ) was 1: 2.
As shown in Table 2, the desulfurization ability in this example was 80 to 90%.

[Effects of the Invention] Since the present invention is configured as described above, the following excellent effects are achieved.

(1) Since it is desulfurization using only coal ash or desulfurization mainly using coal ash, raw material costs can be saved and operating costs are low.

(2) Only water is sprayed into the exhaust gas, and the exhaust gas is unsaturated, so the amount of heat for reheating may be small.

(3) The coal ash discharged is in a state of being slightly moist, but it is in the form of dry powder, and the ash processing device conventionally used can be used as it is.

(4) Moisture content evaporates due to the heat generated by the pulverization of coal ash, so it is easy to re-input coal ash.

(5) Since the crushed ash that is re-input can be input to the flue, it has almost no effect on the boiler.

(6) The equipment cost can be reduced because the equipment can be manufactured with an inexpensive material.

(7) There is no drainage and no wastewater treatment facility is required.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an embodiment of the exhaust gas desulfurization apparatus of the present invention, FIGS. 2 to 4 are flow sheets showing other embodiments of the exhaust gas desulfurization apparatus of the present invention, and FIGS. FIG. 7 is an explanatory view showing an example of a desulfurization tower, and FIG. 8 is a first embodiment of the present invention,
It is a flow sheet of the apparatus used in 2. 1 ... Combustion furnace, 2 ... Desulfurization tower, 3 ... Dust collector, 4 ... Chimney, 5a, 5b ... Activation treatment device, 6 ... Exhaust gas heater,
7 ... Crusher, 11 ... Exhaust gas duct, 12 ... Water spray nozzle, 13 ... Coal ash circulation line, 15 ... Pulverized coal combustion boiler

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location F23J 15/00 6908-3K F23J 15/00 B (72) Inventor Yasunori Shibata Kawasaki Town, Akashi City, Hyogo Prefecture No. 1-1 Kawasaki Heavy Industries Ltd. Technical Research Institute (72) Inventor Fumio Uemura 3-1-1 Higashikawasaki-cho, Chuo-ku, Kobe, Hyogo Prefecture Kawasaki Heavy Industries Ltd. Kobe Factory (72) Inventor Shigeharu Ito Kobe, Hyogo Prefecture 3-1, 1-1 Higashikawasaki-cho, Chuo-ku Kawasaki Heavy Industries Ltd. Kobe factory

Claims (8)

[Claims] 1. A method for removing sulfur oxides contained in an exhaust gas discharged from a pulverized coal combustion furnace, in which coal ash flying from the combustion furnace is sprayed with water without supplying a desulfurizing agent to the combustion furnace. The desulfurization method of exhaust gas, wherein the desulfurization is performed only with the coal ash by humidifying the water in the gas in an unsaturated range. 2. A method for removing sulfur oxides contained in an exhaust gas discharged from a pulverized coal combustion furnace, wherein the coal ash collected by a dust collector is further pulverized into fine powder for activation, and then the exhaust gas is discharged. It is used as a desulfurizing agent together with the coal ash flying from the combustion furnace without supplying the desulfurizing agent to the combustion furnace in a state of being re-introduced into the exhaust gas and dispersed in powder form in the exhaust gas. A desulfurization method of exhaust gas, characterized by spraying and desulfurizing by humidifying in a unsaturated range of water in gas. 3. Instead of activating the coal ash collected by the dust collector by further pulverizing the coal ash into fine powder, the coal ash collected by the dust collector has a molar equivalent of sulfur oxide or less in the exhaust gas. 3. Activated by adding an amount of alkali and coating with coal ash or pulverizing the coated product into fine powder.
Exhaust gas desulfurization method described. 4. Instead of activating the coal ash collected by the dust collector by further pulverizing the coal ash into fine powder, the coal ash collected by the dust collector has a molar equivalent of sulfur oxide or less in exhaust gas. To add a certain amount of alkali and gypsum / lime to react them, and to transform coal ash into a porous or needle-like fine structure to enhance desulfurization activity, or to pulverize this into fine powder. The method for desulfurizing exhaust gas according to claim 2, wherein the method is activated by 5. A step of spraying water in at least two stages,
The desulfurization method of exhaust gas according to claim 1, 2, 3 or 4, wherein after the upstream spray water is completely evaporated, the next stage water spray is performed. 6. An exhaust gas duct (11) for a pulverized coal combustion furnace (1)
A desulfurization tower (2) equipped with a water spray nozzle (12) is installed in the exhaust gas duct (11) or the desulfurization tower (2) on the upstream side of the desulfurization tower (2), and a part of the dust collector trapped ash is collected. A flue gas desulfurization device, characterized in that a coal ash circulation line (13) for re-charging is connected. 7. A crusher (7) in the coal ash circulation line (13).
The exhaust gas desulfurization apparatus according to claim 6, wherein the exhaust gas desulfurization apparatus is installed. 8. An activation treatment device (5a or for adding alkali to a coal ash circulation line (13) to mix with coal ash or for adding alkali and gypsum / lime to react with coal ash. 5b) is installed, The exhaust gas desulfurization apparatus of Claim 6 characterized by the above-mentioned.