JPH03213123A - Method and apparatus for desulfurizing exhaust gas - Google Patents

Abstract

PURPOSE:To obtain high desulfurization efficiency by a reduced amount of a desulfuerizing agent by adding a process wherein the desulfurizing agent containing coal ash is mixed with water to dissolve soluble alkali in water and a solid is separated to prepare an aqueous alkali solution which is, in turn, sprayed into exhaust gas. CONSTITUTION:A desulfurizing agent is blown in a combustion furnace 1 using coal as fuel to be reacted with sulfur oxide in gas to perform desulfurization in the furnace and water is sprayed into the exhaust gas generated from the furnace from a spray cooler 3 and the desulfurizing agent scattering from the furnace is allowed to react with sulfur oxide in the exhaust gas. At this time, the desulfurizing agent containing coal ash caught from the exhaust gas is suspended in water by a mixer-separator 4 to dissolve soluble alkali in water and a solid is separated from an aqueous alkali solution. The aqueous alkali solution after separation is sprayed from an aqueous alkali solution spray pipe 8 by the spray cooler 3. As a result, high desulfurization efficiency can be obtained by a reduced amount of the desulfurizing agent and the abrasion and closure of a spray nozzle can also be prevented.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to so-called in-furnace desulfurization, in which desulfurization is carried out by injecting an alkaline desulfurization agent such as limestone into a combustion furnace such as a pulverized coal-fired boiler. The present invention relates to an improvement in an exhaust gas desulfurization method and apparatus that can reuse the blown desulfurization agent and obtain a high desulfurization rate with a small amount of desulfurization agent.

[Conventional technology]

Currently, wet methods are the mainstream method for removing sulfur oxides from exhaust gas, but they have problems such as high equipment costs and the need for wastewater treatment equipment.

On the other hand, various dry methods have been put into practical use, and one of them is an exhaust gas desulfurization method that combines in-furnace desulfurization and water spray, as shown in Japanese Patent Application Laid-open No. 141629/1983. has been done.

Furthermore, in JP-A-60-22920, a slurry containing a Ca-based desulfurizing agent is sprayed into the exhaust gas in the flue, and the desulfurizing agent is dried and powdered by the sensible heat of the exhaust gas, and sulfur dioxide gas (So □) A dry desulfurization method is disclosed.

Furthermore, Japanese Patent Application Laid-open No. 62-200107 discloses that a desulfurizing agent is directly introduced into a furnace, and after the flue gas is rapidly cooled by water spray, the collected fly ash lumps containing unreacted desulfurizing agent are crushed and separated. However, an in-furnace desulfurization method is disclosed in which unreacted desulfurization agent is circulated to the furnace.

[Problem to be solved by the invention]

The method described in Japanese Patent Application Laid-Open No. 61141629 is a desulfurization method in which a desulfurizing agent is injected into the furnace to perform in-furnace desulfurization, and water is sprayed into the generated gas to react with the desulfurizing agent scattered in the exhaust gas. Among the desulfurization agents injected into the furnace, the desulfurization agent that did not contribute to in-furnace desulfurization is reused, and the feature is that desulfurization performance can be improved by adding a simple device. have.

In particular, spraying only water into the exhaust gas causes more wear on piping and spray nozzles than the so-called spray dryer semi-dry desulfurization method that sprays a slurry such as slaked lime described in JP-A-60-22920. , no scale formation, etc., and operation and maintenance are easy.

However, in the method described in JP-A-63-141629, absorption of S08 is extremely low until the sprayed water droplets and the desulfurization agent in the exhaust gas meet.
(Since there is no desulfurizing agent, there is no reaction, and the dissolution of SO□ in water is small). Furthermore, water evaporates into the exhaust gas before association occurs, resulting in a decrease in the surface area of water droplets. This has the disadvantage that the surface area of water droplets immediately after spraying is large, and SO□ is hardly absorbed in a state where gas-liquid contact is most likely to occur, that is, SOt absorption is most likely to occur.

Furthermore, the method described in JP-A No. 62-200107 circulates the separated unreacted desulfurizing agent to the furnace, and an aqueous alkaline solution in which the soluble alkali in the desulfurizing agent is dissolved in water is added to the exhaust gas. The technical idea of spraying is neither disclosed nor suggested.

The present invention was made in view of the above points, and consists of mixing a desulfurizing agent containing coal ash with water, dissolving a soluble alkali in the water, separating the aqueous alkali solution from the solid matter, and dissolving the aqueous alkali solution into the exhaust gas. By adding a spraying process, it is possible to efficiently reuse the desulfurizing agent such as limestone that has been blown into the furnace, and it is possible to obtain a high desulfurizing rate with a small amount of desulfurizing agent, while also preventing wear and clogging of spray nozzles, etc. It is an object of the present invention to provide a method and apparatus for desulfurizing exhaust gas that can prevent this.

[Means and effects for solving the problem] In order to achieve the above object, the method for desulfurizing exhaust gas of the present invention is as shown in Figs. 1 to 4. Desulfurization is carried out in the furnace by blowing a desulfurizing agent and reacting with the sulfur oxides in the gas.Water is sprayed into the exhaust gas generated from the furnace, and the flue gas is made to react with the scattered desulfurizing agent and the sulfur oxides in the exhaust gas. In the desulfurization method of It is characterized by being sprayed inside.

In addition, as shown in FIGS. 1 to 4, the exhaust gas desulfurization apparatus of the present invention injects a desulfurization agent into a combustion furnace i that uses coal or the like as fuel, and causes the desulfurization agent to react with sulfur oxides in the gas. Desulfurize,
In an exhaust gas desulfurization device, exhaust gas generated from a combustion furnace 1 is introduced into a spray cooler 3, water is sprayed into the exhaust gas, and the scattered desulfurization agent reacts with sulfur oxides in the exhaust gas. A desulfurizing agent containing coal ash is suspended in water in the coal ash/desulfurizing agent extraction pipe 7 of the cooler 3, and a mixing/separating process is carried out to dissolve the soluble alkali in the water and separate the alkaline aqueous solution from the solid matter. The mixing/separator and the spray cooler 3 are connected via an alkaline aqueous solution spray pipe 8 so that the w1 machines can be connected together or separately, and the spray cooler 3 can be sprayed into the alkaline earth metal exhaust gas after separation. There is.

As shown in Figure 1, SOt, which is generated by the reaction of sulfur in fuel such as coal with oxygen in a combustion furnace 1, is fixed as gypsum using a desulfurizing agent such as limestone that is blown into the combustion furnace 1.・In the desulfurization method that desulfurizes and the desulfurization method that desulfurizes the exhaust gas generated from the combustion furnace 1 by exchanging heat with combustion air in the gas/air heater 2 and then spraying water with the spray cooler 3, The desulfurizing agent containing coal ash is added to the spray cooler 3, and when the desulfurizing agent is discharged from the system, the desulfurizing agent and the water to be sprayed by the spray cooler 3 are mixed [4194], and the desulfurizing agent is After dissolving the alkaline content in water, undissolved solids are separated, and the alkaline aqueous solution is sprayed in the spray cooler 3 to promote the reaction with Sow in the exhaust gas, and then the dust collector 5
SOA is absorbed and adsorbed into the dust layer (desulfurization agent and coal ash) collected and removed from the exhaust gas, and then released into the atmosphere from the chimney 6.

The method of the present invention involves mixing a used desulfurization agent containing coal ash captured from exhaust gas with water, dissolving the alkaline content of the desulfurization agent in water, and then separating the alkaline aqueous solution and undissolved solids. A mixing/separation ja4 is installed to spray the separated alkaline aqueous solution into the spray cooler 3, and even before it is combined with the desulfurization agent in the spray cooler 3, the dissolved alkaline components cause SO2 is absorbed by the reaction formula (2).

Sow +u, o →1I2so,
■HzSOi + R(OH)z −R
-5Oz + 2+120 ■SOx ”H
ID + R'SO3-R・(HSO3) z
■R' 01SO1) z +R' (0)1)
g ””” 2R'SO:l + 21120
■R: Cation Here, ■ and 0 formula are reactions with alkaline components dissolved in water, SO2 dissolved in water according to 0 formula immediately becomes saturated solubility in the absence of alkaline components, and the dissolution and absorption of SO1 is Although it does not progress, by being fixed to sulfite by formulas (1) and 0, dissolution and absorption further progress, resulting in desulfurization.

Equation 0 is a reaction in which the alkaline aqueous solution sprayed in the spray cooler 3 and the desulfurizing agent associate and the alkaline content is dissolved in water, resulting in a reaction that becomes sulfite that remains as a solid after drying. There is.

Mixing and separation of the desulfurizing agent and water can be carried out using, for example, spray cooler 3.
One example is to use a drag chain method for discharging and transporting the ash from the bottom. With this method, it is possible to mix and separate the slurry at the same time, and in the unlikely event that the desulfurization agent dries in the spray cooler. Even if the discharge is insufficient, there is an advantage that the lower discharge part is water-sealed and can be discharged easily.

Further, instead of providing the mixer 10 and the separator 11, as shown in FIG. 2, the mixer 10 and the separator 11 may be provided separately.

As shown in Figure 4 of Saramukoichi 1, when there is not enough desulfurizing agent discharged from the bottom of the spray cooler 3 and there is not enough desulfurizing agent to sufficiently dissolve the alkaline content in the water, it is necessary to collect the desulfurizing agent. The desulfurizing agent discharged from the I machine 5 is also used, mixed and dissolved with water in the mixer 10, the slurry is separated into solid and liquid in the separator 11, and the separated aqueous solution containing alkaline content is sprayed in the spray cooler 3. Configured for use as water. 12 is a coal ash/desulfurization agent supply pipe.

In addition, as shown in FIG. 3, the desulfurization agent containing coal ash discharged from the dust collector 5 may be supplied to the mixer/separator 4.

〔Example〕

Examples and comparative examples of the present invention will be described below.

Comparative Example 1 The following experiment was conducted according to the flow shown in FIG. Coal with a sulfur content of 0.5 wt% was burned in a combustion furnace, and limestone was blown into the combustion furnace as a desulfurization agent so that the Ca/S molar ratio was 3. As a result, in the combustion furnace, 420 ppm
The SO□ concentration of was reduced to 240 ppm.

This exhaust gas was introduced into a spray cooler installed downstream, and only water with a pH of 7.5 was sprayed. The desulfurization effect at this time was as shown in FIG.

Example 1 The following experiment was conducted according to the flow shown in FIG. Coal with a sulfur content of 0.5 wL% was burned in a combustion furnace, and limestone was blown into the combustion furnace as a desulfurization agent so that the Ca/S molar ratio was 3. As a result, in the combustion furnace, 420 ppm
The SOtkM degree of was reduced to 240 ppm.

The desulfurization agent containing coal ash discharged from the lower part of the spray cooler installed downstream is placed in a mixer, slurried with water, and this slurry is passed through a fractionator II machine before being mixed with alkaline water t8i11 ( p old 2.5) was sprayed into the exhaust gas in the spray cooler. The desulfurization effect at this time is the fifth
It was as shown in the figure.

Note that 8T on the horizontal axis in FIG. 5 is the value obtained by subtracting the moisture saturation temperature from the temperature after exhaust gas cooling.

As is clear from Comparative Example 1 and Example 1, the desulfurization effect in the spray cooler is approximately 15% greater when using an alkaline aqueous solution with a desulfurizing agent mixed and separated compared to when using only water.
It can be seen that the desulfurization rate has been improved.

〔Effect of the invention〕

Since the present invention is configured as described above, it has the following effects.

fl+ Since the alkali is dissolved in the water sprayed into the exhaust gas, the desulfurization performance can be improved compared to the case where only water is sprayed.

(2) Since the used desulfurization agent is effectively used, the utilization rate of the desulfurization agent can be improved.

(3) What is sprayed is an aqueous solution in which an alkali is dissolved, and there is no concern about scaling or abrasion of the spray nozzle, etc., compared to the conventional method of injecting a desulfurizing agent slurry.

[Brief explanation of drawings]

Fig. 1 is a flow sheet showing one embodiment of the exhaust gas desulfurization device of the present invention, Figs. 2 to 4 are flow sheets showing other embodiments of the device of the present invention, and Fig. 5 is a flow sheet showing a conventional water spray device. in the case of,
and is a graph showing the relationship between ΔT (temperature after exhaust gas cooling - moisture saturation temperature) and desulfurization rate in the case of spraying desulfurization agent mixed separated water (alkaline aqueous solution) in the present invention. 1... Combustion furnace, 2... Gas/air heater, 3...
Spray cooler, 4... Mixer/separator, 5... Dust collector, 6... Chimney, 7... Coal ash/desulfurization agent extraction pipe, 8
...Alkaline aqueous solution spray pipe, 0...Mixer, 1...Separator, 12...Coal ash/desulfurization agent supply pipe Figure 6 (4$ S#, T↑East 5 Makutomo - Water) Famous Japanese bottle, Izumi) (de1

Claims (1)

[Scope of Claims] 1 A desulfurizing agent is injected into a furnace using coal or the like as fuel, and is reacted with sulfur oxides in the gas to desulfurize the furnace, and water is sprayed into the exhaust gas generated from the furnace and dispersed. In an exhaust gas desulfurization method that involves reacting a desulfurizing agent containing coal ash with sulfur oxides in the exhaust gas, the desulfurizing agent containing coal ash captured from the exhaust gas is suspended in water to dissolve the soluble alkali in the water, and then the alkali A method for desulfurizing exhaust gas characterized by separating an aqueous solution and solids and spraying the separated aqueous alkaline solution into the exhaust gas. 2 A desulfurizing agent is injected into a combustion furnace (1) that uses coal, etc. as fuel and reacts with sulfur oxides in the gas to desulfurize the furnace, and the exhaust gas generated from the combustion furnace (1) is introduced into a spray cooler (3). In an exhaust gas desulfurization device that sprays water into the exhaust gas and causes the scattered desulfurization agent to react with sulfur oxides in the exhaust gas, coal ash and
The desulfurization agent extraction pipe (7) is equipped with a mixing/separator for suspending the desulfurization agent containing coal ash in water, dissolving the soluble alkali in the water, and separating the alkaline aqueous solution from the solid matter. A mixer/separator and a spray cooler (3
) are connected to each other via an alkaline aqueous solution spray pipe (8).