JP2000300951A - Facility and method for treatment of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a facility and a method for treatment of exhaust gas which are high in removal efficiency of dioxins and little in deterioration of a carbonaceous adsorbent. SOLUTION: Gas components of an exhaust gas guided to an absorbing tower 3 are measured by a measuring means 9. The charge amount of a desalting agent from a desalting agent storing equipment 6 via a line L7, the charge amount of SO2 from an SO2 storing equipment via a line L9 and the charge amount of a desorbing gas via a line L12 are adjusted so that the SO2 concentration becomes at least 5 ppm and the Cl/SO2 mol ratio becomes at most 10 by controlling respectively valves V1, V3 and V5 by a controller 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas treatment method and apparatus for adsorbing and removing harmful substances including dioxins and their precursors with a carbonaceous adsorbent.

[0002]

2. Description of the Related Art Sulfur oxide (SOx) contained in exhaust gas,
As a method for treating nitrogen oxides (NOx), halogen compounds, heavy metals, and dioxins, there is known a treatment method in which carbon dioxide is adsorbed and removed. As a pretreatment of such an adsorption treatment, there is a technique of injecting slaked lime or the like into exhaust gas to solidify a halogen compound, particularly hydrogen chloride (HCl) and SOx as a calcium salt, and removing the solid content with a dust collector.

[0003]

The hydrogen chloride in the exhaust gas is not completely removed even by such a pretreatment, and the residue is adsorbed and removed by the carbonaceous adsorbent. However, when HCl is present in excess, there is a problem that the dioxin removal efficiency is deteriorated. There is also a problem that HCl degrades the performance of the carbonaceous adsorbent.

[0004] In view of the above problems, it is an object of the present invention to provide an exhaust gas treatment apparatus and method which have high removal efficiency of dioxins and the like and cause less deterioration of the carbonaceous adsorbent.

[0005]

Means for Solving the Problems To solve the above-mentioned problems, the present inventor has set forth the relationship between the sulfur oxide concentration in the exhaust gas led to the carbonaceous adsorbent, the molar ratio of chlorine / sulfur oxide, and the dioxin adsorption rate. And the relationship with the residual chlorine remaining after desorption regeneration. As a result, a sulfur oxide concentration of 5
It has been found that by maintaining the molar ratio of chlorine / sulfur oxide at 10 ppm or more, the dioxin removal rate can be kept high, and the deterioration of the carbonaceous adsorbent can be prevented.

The present invention has been made based on the above findings, and an exhaust gas treatment apparatus according to the present invention has a harmful substance containing dioxin and its precursor contained in exhaust gas adsorbed on a carbonaceous adsorbent. An exhaust gas treating apparatus for removing, comprising: (1) a sulfur oxide introducing means for introducing a sulfur oxide into the exhaust gas; and (2) a carbonaceous adsorbent into which the exhaust gas after introducing the sulfur oxide is guided and filled. An adsorption tower that adsorbs and removes harmful substances in exhaust gas with an adsorbent; and (3) a desorption tower that heats the carbonaceous adsorbent in the adsorption tower to desorb and decompose the adsorbate and regenerate the carbonaceous adsorbent (4) a measuring means for measuring the chlorine content and the sulfur oxide concentration of the exhaust gas before introduction into the adsorption tower, and (5) a sulfur oxide charging means based on the chlorine content and the sulfur oxide concentration by the measuring means. Control of sulfur oxide input Te, or 5ppm sulfur oxide concentration of exhaust gas introduced into the adsorption tower, characterized in that it comprises a control means for adjusting the molar ratio of chlorine / sulfur oxides to 10 below, the.

On the other hand, the exhaust gas treatment method according to the present invention
(1) a sulfur oxide charging step in which sulfur oxide is charged into the exhaust gas; and (2) a harmful substance in the exhaust gas by introducing the exhaust gas after charging the sulfur oxide into an adsorption tower filled with a carbonaceous adsorbent. (3) a desorption / decomposition step in which the carbonaceous adsorbent in the adsorption tower is heated in the desorption / decomposition tower to desorb / decompose the adsorbate and regenerate the carbonaceous adsorbent; ,
(4) The chlorine content and the sulfur oxide concentration of the exhaust gas before introduction into the adsorption tower are respectively measured, and based on these, the sulfur oxide introduction amount in the sulfur oxide introduction step is controlled to be introduced into the adsorption tower. When the sulfur oxide concentration of the exhaust gas is 5 ppm or more, chlorine /
A control step of adjusting the molar ratio of the sulfur oxide to 10 or less;
It is characterized by having.

[0008] With this configuration, by introducing sulfur oxide into the exhaust gas introduced into the adsorption tower, the sulfur oxide concentration of the exhaust gas is increased, and the molar ratio of chlorine / sulfur oxide is reduced. Each is controlled to a suitable range obtained by the above-mentioned knowledge.

Further, prior to the sulfur oxide input means, a desalinating agent inputting means for inputting a desalinating agent which reacts with the chlorine compound to solidify the chlorine compound into the exhaust gas, and the exhaust gas after the inputting of the desalinating agent are led. A dust collector for removing a solid content in the exhaust gas, wherein the control means controls the amount of the desalinating agent charged by the desalting agent charging means and the amount of sulfur oxide charged by the sulfur oxide charging means, respectively. Thus, an exhaust gas treatment device that adjusts the sulfur oxide concentration of the exhaust gas introduced into the adsorption tower to 5 ppm or more and the molar ratio of chlorine / sulfur oxide to 10 or less may be used.

[0010] Alternatively, before the sulfur oxide charging step, a desalting step of charging a desalinating agent that reacts with the chlorine compound to solidify the chlorine compound into the exhaust gas and removing a solid content with a dust collector is further provided. The control step controls the amount of the desalting agent charged in the desalting step and the amount of sulfur oxide charged in the sulfur oxide charging step to control the sulfur oxide concentration of the exhaust gas introduced into the adsorption tower to 5 ppm or more, An exhaust gas treatment method in which the molar ratio of sulfur oxide is adjusted to 10 or less may be used.

By adjusting the input amount of the desalting agent, chlorine /
Since the molar ratio of the sulfur oxide can be reduced, the control to a suitable range obtained by the above-described findings is further facilitated.

[0012] Sulfur oxide input may include returning a portion of the adsorbate desorbed from the carbonaceous adsorbent in the desorption cracker. Since the main component of the adsorbate desorbed from the carbonaceous adsorbent in the desorption cracking column is sulfur oxide, it is possible to reduce the input amount of sulfur oxide by returning it.

[0013]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
1 is an overall schematic diagram showing a preferred embodiment of an exhaust gas treatment apparatus according to the present invention.

This apparatus comprises a dust collector 1 for removing solids from exhaust gas, a heat exchanger 2 for recovering heat from the exhaust gas and cooling the exhaust gas, and an active carbon filled as an adsorbent therein. Move vertically downward to form a moving layer,
An adsorption tower 3 for adsorbing harmful substances to activated carbon by bringing exhaust gas into contact with the moving bed by cross-flow and a chimney 4 for discharging the treated exhaust gas to the atmosphere are arranged in series. These are connected by lines L1 to L4, respectively.

From the adsorption tower 3, a desorption / decomposition tower 5 for regenerating the activated carbon by heating the activated carbon in an inert gas and desorbing the adsorbed substance through a line L5 for taking out and transporting the activated carbon therein. The regeneration activated carbon outlet of the desorption cracking tower 5 and the activated carbon inlet of the adsorption tower 3 are connected by a line L6 composed of a belt conveyor or the like, forming a circulation line of activated carbon between the adsorption tower 3 and the desorption cracking tower 5. are doing.

A line L7 is connected to a line L1 for introducing exhaust gas into the dust collector 1, and a desalinating agent storage facility 6 for storing a predetermined desalinating agent such as quicklime is provided with a flow control valve V1. . A line L3 connecting the heat exchanger 2 and the adsorption tower 3 has an ammonia storage facility 7 for storing ammonia gas or ammonia chemicals such as ammonia water.
And a line L having flow control valves V2 and V3, respectively, for example, in which the SO ₂ storage facility 8 in which SO ₂ gas is stored.
Measuring means 9 for measuring gas components such as Cl component and SO ₂ concentration in the exhaust gas introduced into the adsorption tower 3 while being connected by 8, L9.

On the other hand, the desorption / decomposition tower 5 is connected to a line L10 for introducing an inert gas, and is connected to branched lines L11 and L12 for introducing the generated desorption gas. The line L11 has a flow control valve V4 and is connected to the line L1.
It has a flow control valve V5 and is connected to the line L3.

The flow control valves V1 to V5 and the measuring means 9 are connected to a control device 10 for controlling the flow control valves V1 to V5 based on the gas components measured by the measuring means 9.
It is connected to the.

Here, the results of an experiment conducted by the present inventor to investigate the relationship between the concentration of SO ₂ and Cl in the exhaust gas led to the adsorption tower 3, the concentration of Cl remaining in the activated carbon, and the dioxin removal rate will be reported.

In the experiment, activated carbon (about 7 mm in diameter) was
(φ, length about 9 mm) 28 m ³ is filled, the retention time in the adsorption tower 3 is set to 50 hours, then desorption / regeneration is performed, and the cycle is returned to the adsorption tower. Was done.

FIG. 2 shows the relationship between the SO ₂ concentration of various general exhaust gases used in the experiment and the Cl / SO ₂ molar ratio. In the figure, the exhaust gas in the high SO ₂ concentration region (100 to 1000 ppm) is an exhaust gas from a steel sintering furnace, a coal boiler, or the like.
Exhaust gas in the two concentration ranges (10 to 100 ppm) is exhaust gas from refuse incinerators and the like. On the other hand, the exhaust gas in the low SO2 concentration range (1 ppm or less) is an exhaust gas from an RDF (Refuse Derived Fuel) incinerator that incinerates a solid fuel manufactured by drying and forming refuse. These exhaust gases are clear from FIG.
Between the SO ₂ concentration x in the exhaust gas and the Cl / SO ₂ molar ratio y, y =
a × x ^b is established, a is 50~400, b is -1～-
It was found to be in the range of 1.5.

FIG. 3 is a graph showing the relationship between the concentration of SO ₂ in the exhaust gas, the amount of Cl remaining in 1 g of activated carbon after the treatment test for 2000 hours, and the dioxin adsorption rate at that time.

As is clear from FIG. 3, the higher the SO ₂ concentration, the lower the amount of Cl remaining in the activated carbon. And activated carbon 1
When the residual Cl concentration per g is 2,000 μg or less, the adsorption performance of activated carbon does not largely change, and the adsorption performance of dioxin becomes 96% or more.
The adsorption performance of activated carbon declined rapidly. Therefore, the residual
In order to keep the Cl concentration below 2000 μg, SO ₂
It was found that the concentration should be maintained at 5 ppm or more.

FIG. 4 is a graph showing the relationship between the Cl / SO ₂ molar ratio in the exhaust gas and the dioxin removal rate. As is clear from FIG. 4, when the Cl / SO ₂ molar ratio is low, that is, when SO ₂
In but present in excess to conditions as compared to Cl, has been able to achieve high dioxin removal ratio, when Cl / SO ₂ molar ratio is high, i.e., Cl is present in excess compared to SO ₂ The dioxin removal rate decreased. It has been found that in order to maintain the dioxin removal rate at 95% or more, it is necessary to maintain the Cl / SO ₂ molar ratio at 10 or less.

Based on this knowledge, the operation of the exhaust gas treatment apparatus according to the present invention, that is, in the exhaust gas treatment method according to the present invention, when the SO ₂ concentration in the exhaust gas guided to the adsorption tower 3 is 5 ppm or more, and the Cl / SO ₂ The molar ratio is maintained at 10 or less.

Hereinafter, the operation of the exhaust gas treating apparatus according to the present invention, that is, the exhaust gas treating method according to the present invention will be described in detail with reference to FIG.

When the exhaust gas to be treated flows through the line L1, the desorbed gas generated in the desorption / decomposition tower 5, which will be described later, is mixed via the line L11, and at the same time, quicklime etc. Is supplied via line L7. The controller 10 controls the valve V
1 and V4 are adjusted by controlling each. The introduced quicklime reacts with HCl and SOx in the exhaust gas to generate calcium salts, which are solidified. The exhaust gas containing the calcium salt thus solidified is guided to the dust collector 1, and the calcium salt and dust contained in the exhaust gas are removed.

The exhaust gas from which the solid content has been removed is led to the heat exchanger 2 by the line L2 and cooled to 140 to 160 ° C. When the cooled exhaust gas flows through the line L3,
Ammonia drug from the ammonia storage facility 7 through a line L8, via a line L9 from SO ₂ storage facilities 8 SO ₂
However, a desorption gas is supplied from a desorption / decomposition column 5 described later via a line L12. These input amounts are adjusted by the control device 10 controlling the valves V2, V3, and V5, respectively. In particular, input of SO ₂ and desorption gas, 5 ppm is SO ₂ concentration in the gas in the adsorption tower 3 inlets before measuring by the measuring means 9 with input of dechlorinating agent described above
Thus, the Cl / SO ₂ molar ratio is adjusted to be 10 or less.

Specifically, SO in the gas before the entrance of the adsorption tower 3
_{When the} concentration of _{2 and the} molar ratio of Cl / SO ₂ satisfy this condition, each input amount is maintained as it is. When the SO ₂ concentration in the exhaust gas is lower than 5 ppm, the valve V3 is opened to increase the supply amount of SO ₂ from the line L9, or the valve V5 is opened to release the desorbed gas from the line L12. or increase the injection volume, or the addition of SO ₂ in the exhaust gas flowing through the line L3 by performing both SO ₂
Increase concentration. As a result, the Cl / SO ₂ ratio is lower than before injection. However, if it is desired to reduce the consumption of added SO ₂ or to reduce the load of desulfurization treatment in the adsorption tower, the valve V
By controlling 1 to increase the supply amount of the desalting agent and lowering the Cl concentration in the exhaust gas introduced into the line L3, the Cl / SO ₂ ratio can be reduced. The exhaust gas that needs such adjustment includes the exhaust gas of the RDF furnace described above.

In the adsorption tower 3, NOx in the exhaust gas is decomposed by reacting with ammonia added by the catalytic action of the activated carbon, and SOx, halogen compounds, dioxins, heavy metals and the like are adsorbed and removed by the activated carbon. . At this time, since the SO ₂ concentration and the Cl / SO ₂ molar ratio of the exhaust gas are adjusted to satisfy the above-mentioned conditions, the dioxin removal rate can be maintained high, and aging due to the accumulation of Cl in activated carbon. Can be prevented. The exhaust gas from which the harmful substances have been removed is discharged from the chimney 4 to the atmosphere via the line L4.

On the other hand, the activated carbon in the adsorption tower 3
And heated to 400 to 450 ° C. in an inert gas in the desorption / decomposition tower 5. As a result, the adsorbed dioxin is decomposed, and SO ₂ , HCl and the like are eliminated. The main component in the desorbed gas is SO ₂ .

The embodiment having both the desalinating agent storage facility 6 and the SO ₂ storage facility 8 has been described above.
In the case of treating exhaust gas having a low concentration, the concentration and the molar ratio may be adjusted only by injecting SO ₂ without performing the treatment for charging the desalting agent. Further, the desorbed gas may be processed or collected in another processing system without returning to the exhaust gas processing line. Also, the ammonia storage facility is not essential.

As the carbonaceous adsorbent of the present invention, activated carbon, activated coke, activated char, etc. obtained by oxidizing, heat-treating or activating coal with steam or the like are generally used, and these are vanadium. What carried metal compounds, such as iron, manganese, etc. can also be used.

[0034]

As described above, according to the present invention,
Since the SO ₂ concentration and Cl / SO ₂ molar ratio of the exhaust gas introduced into the adsorption tower are adjusted to the specified ranges, the dioxin adsorption efficiency is maintained, and the deterioration of the carbonaceous adsorbent is prevented over time. Can be. In particular, the SO ₂ concentration in RDF furnaces is low,
l Suitable treatment is possible for exhaust gas with high concentration.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the entire configuration of an exhaust gas treatment apparatus according to the present invention.

FIG. 2 is a graph showing the relationship between the SO ₂ concentration of general exhaust gas and the Cl / SO ₂ molar ratio.

FIG. 3 is a graph showing the relationship between the SO ₂ concentration of exhaust gas, the residual Cl concentration of activated carbon, and the dioxin adsorption rate.

FIG. 4 is a graph showing the relationship between the Cl / SO ₂ molar ratio of exhaust gas and the dioxin adsorption rate.

[Explanation of symbols]

1: dust collector, 2: heat exchanger, 3: adsorption rate, 4: chimney, 5
... elimination decomposing column, 6 ... dechlorinating agent reservoir facilities, 7 ... ammonia storage facilities, 8 ... SO ₂ storage facilities, 9 ... measuring means, 10 ... controller, L1 to L12 ... lines, V1 to V5 ... flow regulation valve .

Claims (6)

[Claims] 1. An exhaust gas treatment apparatus for removing harmful substances including dioxin and its precursor contained in exhaust gas by adsorbing the carbonaceous adsorbent, wherein a sulfur oxide is introduced into the exhaust gas. Means, an exhaust tower into which the exhaust gas after the introduction of the sulfur oxide is introduced, and an adsorption tower for adsorbing and removing harmful substances in the exhaust gas by the carbonaceous adsorbent filled therein; and heating the carbonaceous adsorbent in the adsorption tower. To remove adsorbed material
A desorption / decomposition tower that decomposes and regenerates the carbonaceous adsorbent; measuring means for measuring the chlorine content and sulfur oxide concentration of the exhaust gas before introducing the adsorption tower, respectively; chlorine content and sulfur oxide by the measuring means Based on the concentration, the amount of sulfur oxide introduced by the sulfur oxide introduction means is controlled so that the concentration of sulfur oxide in the exhaust gas introduced into the adsorption tower is 5 ppm or more and the molar ratio of chlorine / sulfur oxide is 10%.
An exhaust gas treatment apparatus, comprising: control means for adjusting the following. 2. A desalting agent inputting means for inputting a desalinating agent which reacts with a chlorine compound to solidify the chlorine compound into the exhaust gas, prior to the sulfur oxide inputting means; A dust collector to which the exhaust gas is guided and which removes a solid content in the exhaust gas, wherein the control means comprises: 2. The method according to claim 1, wherein the sulfur oxide concentration of the exhaust gas introduced into the adsorption tower is adjusted to 5 ppm or more and the chlorine / sulfur oxide molar ratio is adjusted to 10 or less by controlling the amount of the oxides. Exhaust gas treatment equipment. 3. The method according to claim 1, wherein the sulfur oxide charging means includes a means for returning a part of the adsorbed substance desorbed from the carbonaceous adsorbent in the desorption cracking tower.
An exhaust gas treatment device according to item 1. 4. An exhaust gas treatment method for removing harmful substances, including dioxins and their precursors, contained in exhaust gas by adsorbing the carbonaceous adsorbent, wherein a sulfur oxide is introduced into the exhaust gas. An adsorption step in which the exhaust gas after the introduction of the sulfur oxide is introduced into an adsorption tower filled with a carbonaceous adsorbent to adsorb and remove harmful substances in the exhaust gas, and a carbonaceous adsorbent in the adsorption tower is removed. A desorption / decomposition step of heating and desorbing / decomposing the adsorbate in the desorption / decomposition tower and regenerating the carbonaceous adsorbent; and measuring a chlorine content and a sulfur oxide concentration of the exhaust gas before the introduction of the adsorption tower, respectively. Then, based on these, controlling the sulfur oxide input amount in the sulfur oxide input step, the sulfur oxide concentration of the exhaust gas introduced into the adsorption tower 5ppm or more,
A control step of adjusting the chlorine / sulfur oxide molar ratio to 10 or less. 5. A desalting step of adding a desalinating agent for reacting with a chlorine compound and solidifying the chlorine compound into the exhaust gas before removing the sulfur oxide, and removing a solid content with a dust collector. The control step comprises controlling the amount of the desalting agent charged in the desalting step and the amount of sulfur oxide charged in the sulfur oxide charging step, respectively, to thereby control the sulfur oxides of the exhaust gas introduced into the adsorption tower. A concentration of 5 ppm or more,
The exhaust gas treatment method according to claim 4, wherein the molar ratio of chlorine / sulfur oxide is adjusted to 10 or less. 6. The method according to claim 4, wherein the sulfur oxide charging step includes a step of returning a part of the adsorbed substance desorbed from the carbonaceous adsorbent in the desorption cracking tower.
An exhaust gas treatment method according to item 1.