JP2009247998A - Exhaust gas treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treatment method for preventing the fixation of soot dust to the bag filter of a dust collector when supplying slaked lime to an acidic gas and reducing an acidic gas concentration. <P>SOLUTION: The exhaust gas treatment method is for supplying the slaked lime to the exhaust gas containing the acidic gas and reducing the acidic gas concentration, the supply amount Y<SB>1</SB>of the slaked lime required in order to react with hydrogen chloride and generate CaClOH is calculated by equation (1) on the basis of the hydrogen chloride concentration of the exhaust gas before treated upstream of a slaked lime supply means in the exhaust gas flow, and the slaked lime whose lower limit amount is the supply amount Y<SB>1</SB>is supplied to an exhaust gas flow path. The equation (1) is Y<SB>1</SB>=3.3×10<SP>-3</SP>X<SB>0</SB>×Q, Y<SB>1</SB>is the supply amount (g/h) of the slaked lime required for reacting with the hydrogen chloride and generating CaClOH, X<SB>0</SB>is the hydrogen chloride concentration (ppm) before the treatment, and Q is an exhaust gas flow rate (Nm<SP>3</SP>/h). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to the treatment of acidic gases such as hydrogen chloride and sulfur dioxide contained in exhaust gas discharged from combustion and heating processes in municipal waste incineration facilities, industrial waste incineration facilities, and other combustion devices and heating devices. More specifically, the present invention relates to a method for controlling the supply amount of slaked lime when spraying and supplying slaked lime powder to an exhaust gas flow channel to react with an acid gas and removing it.

Exhaust gas generated during incineration of municipal waste and industrial waste, as well as exhaust gas emitted by other combustion devices and heating devices and discharged during the heating process, contain acidic gases such as hydrogen chloride and sulfur dioxide. In view of the harmfulness of these acidic gases, exhaust gas treatment is performed so that the concentration of acidic gas is less than the regulation value when the exhaust gas is released into the atmosphere. As a method for removing these acidic gases generally used in refuse incineration facilities, etc., after cooling the exhaust gas from approximately 120 ° C. to 200 ° C., spraying slaked lime powder on the exhaust gas flow path or dust collector to react with hydrogen chloride, In a dust collector, there is a method in which the reaction product CaCl ₂ is collected together with dust by a filter and removed from the exhaust gas.

For example, in Patent Document 1, slaked lime (Ca (OH) ₂ ) is blown into the exhaust gas in order to remove hydrogen chloride (HCl) as an acidic gas in the exhaust gas.
2HCl + Ca (OH) ₂ → CaCl ₂ + 2H ₂ O
Under the above reaction, calcium chloride (CaCl ₂ ) is produced, and this calcium chloride is collected together with soot and dust by a filter.

  By the way, slaked lime will supply an amount commensurate with the amount of acid gas in the exhaust gas to be treated. However, if slaked lime is supplied in excess, the product produced by the reaction will be discharged out of the system as fly ash. While it becomes a problem of pollution, even if the supply amount is insufficient, the concentration of acidic gas in the exhaust gas exceeds the regulation value, which becomes a problem of environmental pollution. For this reason, Patent Document 2 and Patent Document 3 propose a supply amount control method for calculating and supplying a slaked lime supply amount necessary for reducing the acidic gas in the exhaust gas to an arbitrary set concentration.

In the supply amount control method described in Patent Document 2, the hydrogen chloride concentration in the exhaust gas at the outlet side of the dust collector is detected, and the supply amount of slaked lime is increased and decreased so that the hydrogen chloride concentration becomes an arbitrary set value. In the supply amount control method described in Patent Document 3, the hydrogen chloride concentration in the exhaust gas at the outlet side of the exhaust gas treatment device is detected, the P operation and the PID operation are combined, the operation signal is calculated, and the control output is sent to the slaked lime supply device. The slaked lime is supplied to the pre-treatment exhaust gas at the inlet side of the exhaust gas treatment device. It is a well-known technique that this operation signal is derived by performing an operation of multiplying the hydrogen chloride concentration by the exhaust gas flow rate and a conversion factor, and calculating a slaked lime supply amount necessary to reduce the hydrogen chloride concentration to an arbitrary set value. It is done as
JP 2004-223349 A JP-A-9-308817 JP 2002-113327 A

However, in the technique disclosed in Patent Document 1, since CaCl ₂ produced by the reaction of hydrogen chloride with slaked lime has high hygroscopicity, it absorbs moisture in the exhaust gas and hydrates CaCl ₂ (H ₂ O ) n, and this hydrate acts as an adhesive substance to aggregate the dust particles or to fix the dust particles to the filter. As a result, the dust filter is used to blow off the dust trapped in the bag filter used as a dust collector, but the dust is stuck to the bag filter, so the dust cannot be fully removed and the filter is clogged. As a result, the differential pressure of the bag filter increases and the load of the attracting blower increases, so that dust particles stick to the inner surface of the flow path, causing clogging in the flow path, reducing the effective flow cross-sectional area, and smooth exhaust gas flow. Problems that become difficult, such as solidification of dust in the hopper part or carry-out conveyor part that receives dust discharged from the bag filter and discharges it, or problems that make it difficult to discharge dust by forming a bridge Yes.

In Patent Documents 2 and 3, the supply amount of slaked lime is assumed to be appropriate, but as in Patent Document 1, the reaction between hydrogen chloride and slaked lime is performed.
2HCl + Ca (OH) ₂ → CaCl ₂ + 2H ₂ O
In this case, CaCl ₂ is generated, so that the same phenomenon as that of Patent Document 1 occurs and causes the same problem.

  The present invention has been made in view of such circumstances, and prevents dust from sticking to a bag filter or peripheral devices when supplying slaked lime to exhaust gas containing acid gas to reduce the acid gas concentration. It is an object of the present invention to provide an exhaust gas treatment method that can be used.

  Prior to the present invention, the following was found as a result of detailed analysis of the dust adhered to the bag filter and solidified by the peripheral device.

(1) CaCl ₂ produced by the reaction between hydrogen chloride and slaked lime powder is highly hygroscopic, and CaCl ₂ absorbs moisture in the exhaust gas and hydrates (CaCl ₂ (H ₂ O) n) are produced. Aggregates or adheres by hydrate to solidify or fix.

(2) When the sulfur dioxide concentration in the exhaust gas is relatively high, CaCl ₂ generated by the reaction of slaked lime and hydrogen chloride further reacts with sulfur dioxide in the exhaust gas to produce gypsum (CaSO ₄ ), and the dust particles are gypsum. Aggregates or adheres to solidify or adhere.

  As a result of analyzing and elucidating the reaction process of these phenomena, it was found that the following measures were effective for preventing solidification and fixation of soot dust for hydrogen chloride and sulfur dioxide.

<Hydrogen chloride HCl>
When slaked lime reacts with hydrogen chloride, it proceeds in the following two stages.

First stage reaction: HCl + Ca (OH) ₂ → CaClOH + H ₂ O
Second stage reaction: HCl + CaClOH → CaCl ₂ + H ₂ O
Therefore, in order not to generate CaCl ₂ having high hygroscopicity, it is effective to terminate the reaction in the first stage reaction. For this purpose, the supply amount of slaked lime necessary and sufficient to generate CaClOH by reacting with hydrogen chloride in the first stage reaction is calculated as the lower limit amount from the hydrogen chloride concentration, and slaked lime is supplied to the exhaust gas flow path. The stage reaction is not carried out and the reaction is terminated in the first stage reaction so that most of the hydrogen chloride becomes CaClOH and does not generate CaCl ₂ .

  CaClOH produced as a result of the termination of the first stage reaction is a harmless solid powder and is not hygroscopic, so it will not stick to the filter and will be easily washed off, collected and disposed of. .

<Sulfur dioxide SO _2>
When the sulfur dioxide concentration in the exhaust gas is relatively high, CaCl ₂ produced by the reaction between hydrogen chloride and slaked lime reacts with the sulfur dioxide and the moisture in the exhaust gas to produce gypsum (CaSO ₄ ) as follows: The Gypsum causes problems such as agglomeration of dust particles and adhesion of dust particles to the filter.

Reaction of CaCl ₂ and SO ₂ : CaCl ₂ + SO ₂ + H ₂ O → CaSO ₄ + 2HCl
Therefore, in order not to generate harmful gypsum (CaSO ₄ ) from SO ₂ , Ca (OH) ₂ and SO ₂ are reacted as follows to generate CaSO ₃ .

Reaction of Ca (OH) ₂ and SO ₂ : Ca (OH) ₂ + SO ₂ → CaSO ₃ + H ₂ O
For that purpose, hydrogen chloride HCl in the exhaust gas is required to react with hydrogen chloride to generate CaClOH so that it is terminated in the first-stage reaction described above and CaCl ₂ is not generated as described above. the supply of sufficient hydrated lime addition to feed is calculated from the hydrogen chloride concentration, for the sulfur dioxide SO ₂ present with HCl in the exhaust gas, to produce an CaSO ₃ by reacting sulfur dioxide and lime In order to calculate and supply the supply amount of slaked lime necessary and sufficient, supply the slaked lime to the exhaust gas passage with the total supply amount of both as the lower limit amount, so that CaCl ₂ and CaSO ₄ are not generated as a result To do.

That is, CaClOH is generated for HCl and CaCl ₂ is not generated. Since CaCl ₂ is not produced, SO ₂ cannot react with CaCl ₂ and reacts with Ca (OH) ₂ to produce CaSO ₃ . This CaSO ₃ is harmless, like CaClOH, and is solid and non-hygroscopic, so it is easily collected and disposed without sticking to the filter.

  As a result of such studies, the present invention provides a method for treating exhaust gas containing an acidic gas according to the following first to fourth inventions.

  The first and second inventions relate to the supply of slaked lime for suppressing the solidification / fixation of soot dust, and the third and fourth inventions supply the slaked lime for suppressing the solidification / fixation of soot dust and the acid gas concentration. About.

<First invention>
An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the hydrogen chloride concentration before treatment of the exhaust gas upstream of the exhaust gas flow from the slaked lime supply means, the supply amount Y _{1 of} slaked lime necessary and sufficient to react with hydrogen chloride to generate CaClOH is calculated by the equation (1),
Exhaust gas treatment method and supplying the slaked lime to the lower limit amount of the supply amount Y ₁ in the exhaust gas line.

Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Q: exhaust gas flow rate (Nm ³ / h)
Here, the expression (1) is an expression derived as follows.

Y ₁ = X ₀ × 10 ⁻⁶ · Q × 10 ³ × 74 / 22.4 = 3.3 × 10 ⁻³ X ₀ · Q
74: Formula weight of slaked lime g / mol
22.4: molar volume of ideal gas 1 / mol
When slaked lime is supplied to the exhaust gas flow path with Y ₁ as the lower limit amount, this slaked lime reacts with hydrogen chloride HCl to produce CaClOH, and does not produce CaCl ₂ . CaClOH is a harmless solid powder and has no hygroscopicity, so dust is not easily attached to the filter and solidifies, and is easily treated by removing it with a filter.

<Second invention>
An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the pre-treatment hydrogen chloride concentration and pre-treatment sulfur dioxide concentration of the exhaust gas upstream of the slaked lime supply means, the slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and to react with sulfur dioxide to produce CaSO ₃ the supply amount _{Y 2} is calculated by equation (2),
Exhaust gas treatment method and supplying the slaked lime to the lower limit amount of the supply amount Y ₂ in the exhaust gas line.

Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
Here, the expression (2) is an expression derived as follows.

Y ₂ = (X ₀ + Z ₀ ) × 10 ⁻⁶ · Q × 10 ³ × 74 / 22.4
= 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q
When slaked lime with Y ₂ as the lower limit is supplied to the exhaust gas flow path, it only generates CaClOH for hydrogen chloride HCl and does not generate CaCl ₂ , so that dust does not adhere to the filter and solidify. . Also with respect to the sulfur dioxide SO ₂ generates CaSO _3, it does not produce CaSO _4. CaSO ₃ is a harmless solid powder, like CaClOH, and dust does not adhere to the filter and solidify. In this way, dust does not adhere to or solidify on the filter or the like, so that it is easily processed by removing with a filter.

<Third invention>
An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the hydrogen chloride concentration before treatment of the exhaust gas upstream of the exhaust gas flow from the slaked lime supply means, the supply amount Y _{1 of} slaked lime necessary and sufficient to react with hydrogen chloride to generate CaClOH is calculated by the equation (1),
Wherein the pretreatment hydrogen chloride concentration, the supply amount Y ₃ of necessary and sufficient calcium hydroxide to reduce the target hydrogen chloride concentration of hydrogen chloride concentration based on the target hydrogen chloride concentration is the target concentration to reduce the exhaust gas treatment (3) A step of calculating by an expression;
An exhaust gas treatment method comprising a step of supplying slaked lime having a larger amount of the supply amount Y ₁ and the supply amount Y ₃ as a lower limit amount to the exhaust gas flow path.

Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
Y ₃ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X (3)
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
Y ₃ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride)
Here, the expression (3) is an expression derived as follows.

Y ₃ = (X ₀ −X ₁ ) × 10 ⁻⁶ · Q · 10 ³ · 74 · K _X /22.4
= 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X
This third invention is a method of adding control of the slaked lime supply amount to prevent solidification and fixation of soot dust, in addition to the method of controlling the slaked lime supply amount for suppressing acid gas concentration that has been conventionally performed, Of the slaked lime supply amount for suppressing solidification / fixation of dust and the slaked lime supply amount for suppressing acid gas concentration, slaked lime is supplied with the larger amount as the lower limit.

In the present invention calculates the supply amount Y ₁ (1) expression of necessary and sufficient hydrated lime to produce a reacted with hydrogen chloride CaClOH, further processing of the exhaust gas flow upstream side of the exhaust gas from the slaked lime supply means Based on the pre-hydrogen chloride concentration and the target hydrogen chloride concentration that is the target concentration to be reduced by the exhaust gas treatment, the supply amount Y _{3 of} slaked lime that is necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration is expressed by equation (3). Calculate. Of the supply amount Y ₁ and the supply amount Y ₃ , slaked lime is supplied to the exhaust gas passage with the larger amount as the lower limit amount.

In such a third invention, when Y ₁ > Y ₃ , slaked lime is supplied to the exhaust gas flow channel with the supply amount Y _{1 of} slaked lime necessary and sufficient for reacting with hydrogen chloride and generating CaClOH as the lower limit. For this reason, CaClOH is not generated with respect to hydrogen chloride HCl, and CaCl ₂ is not generated, so that dust does not adhere to the filter and solidify. Then, in order to provide more slaked lime than the supply amount Y ₃ of necessary and sufficient calcium hydroxide to reduce the hydrogen chloride concentration in the target hydrogen chloride concentration in the exhaust gas line, suppresses hydrogen chloride concentration in the exhaust gas below the target concentration be able to.

Further, in the case of Y ₃ > Y ₁ , slaked lime is supplied to the exhaust gas flow path with the supply amount Y ₃ necessary and sufficient for reducing the hydrogen chloride concentration to the target hydrogen chloride concentration as the lower limit amount. The hydrogen chloride concentration can be suppressed below the target concentration. Then, in order to supply more slaked lime than the supply amount Y _{1 of} slaked lime necessary and sufficient for reacting with hydrogen chloride to generate CaClOH, only CaClOH is generated with respect to hydrogen chloride HCl. ₂ is not generated, so dust does not adhere to the filter and solidify.

Further, in the case of Y ₃ > Y ₁ , if the supply amount Y _{3 of} slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration is set as the supply amount of slaked lime supplied to the exhaust gas flow path, Supply sufficient to prevent the dust from adhering to the filter and solidifying, while suppressing the hydrogen chloride concentration of the catalyst to below the target concentration and generating only CaClOH for hydrogen chloride HCl and not generating CaCl ₂ Since an amount of slaked lime can be supplied, it is more preferable that slaked lime is not used more than a necessary and sufficient amount.

<Fourth Invention>
An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the pre-treatment hydrogen chloride concentration and pre-treatment sulfur dioxide concentration of the exhaust gas upstream of the slaked lime supply means, the slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and to react with sulfur dioxide to produce CaSO ₃ the supply amount _{Y 2} is calculated by equation (2),
Based on the pretreatment hydrogen chloride concentration and the target hydrogen chloride concentration that is the target concentration to be reduced by exhaust gas treatment, the supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration, and the pretreatment carbon dioxide Supply amount Y of slaked lime which is the sum of supply amount of slaked lime necessary and sufficient to reduce the sulfur dioxide concentration to the target sulfur dioxide concentration based on the sulfur concentration and the target sulfur dioxide concentration which is the target concentration to be reduced by exhaust gas treatment ₄ a step of calculating by the equation (4),
The supply amount Y ₂ and of the feed amount Y _4, an exhaust gas processing method for the slaked lime to the quantity with the larger lower limit amount, comprising the step of supplying the exhaust gas passage.

Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
Y ₄ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X
+ 3.3 × 10 ⁻³ (Z ₀ −Z ₁ ) · Q · _KY (4)
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
Y ₄ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration and the sulfur dioxide concentration to the target sulfur dioxide concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Z ₁ : Target sulfur dioxide concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride)
_KY : molar coefficient (reaction with sulfur dioxide)
Here, the expression (4) is an expression derived as follows.

Y ₄ = (X ₀ −X ₁ ) × 10 ⁻⁶ · Q · 10 ³ · 74 · K _X /22.4
_{+ (Z 0 -Z 1) ×} 10 -6 · Q · 10 3 · 74 · K Y /22.4
= 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X
+ 3.3 × 10 ⁻³ (Z ₀ −Z ₁ ) · Q · _KY
In such a fourth invention, when Y ₂ > Y ₄ , the supply amount Y _{2 of} slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and to react with sulfur dioxide to produce CaSO ₃ is reduced. Since slaked lime is supplied to the exhaust gas flow path as a limited amount, it does not generate CaCl ₂ with respect to hydrogen chloride HCl, but does not generate CaCl ₂ but reacts with sulfur dioxide to generate CaSO ₃ and does not generate CaSO ₄ . , Dust does not adhere to the filter and solidify. Then, since the number of slaked lime than the supply amount Y ₄ necessary and sufficient calcium hydroxide to reduce the reduced sulfur dioxide concentration hydrogen chloride concentration in the target hydrogen chloride concentration to the target concentration of sulfur dioxide supplied to the exhaust gas passage, the exhaust gas The hydrogen chloride concentration and sulfur dioxide concentration can be suppressed below the target concentration.

Further, when Y ₄ > Y _2, the slaked lime is set with the supply amount Y _{4 of} slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration and the sulfur dioxide concentration to the target sulfur dioxide concentration as the lower limit amount. Is supplied to the exhaust gas flow path, the hydrogen chloride concentration and the sulfur dioxide concentration in the exhaust gas can be suppressed below the target concentration. Then, in order to supply more slaked lime than the supply amount Y _{2 of} slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ , In other words, it only generates CaClOH, does not generate CaCl ₂ , reacts with sulfur dioxide to generate CaSO ₃ , and does not generate CaSO ₄ , so that dust does not adhere to the filter and solidify.

Further, in the case of Y ₄ > Y ₂ , the supply amount Y _{4 of} slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration and the sulfur dioxide concentration to the target sulfur dioxide concentration is supplied to the exhaust gas passage. If the supply amount of slaked lime to be supplied is reduced, the hydrogen chloride concentration and sulfur dioxide concentration in the exhaust gas are suppressed to below the target concentration, and CaClOH is not generated with respect to hydrogen chloride HCl, but CaCl ₂ is not generated. Since it reacts to generate CaSO ₃ and does not generate CaSO ₄ , it can supply a sufficient amount of slaked lime to prevent dust from adhering to the filter and solidifying it. It is more preferable because slaked lime is not used.

<Explanation of molar coefficient>
Here, a description will be added regarding the molar coefficient employed in the third and fourth inventions.

In calculating the number of moles of slaked lime required for removing HCl or SO ₂ , which is an acidic component in exhaust gas, the moles per hour of HCl or SO _{2 in} exhaust gas calculated from the concentration of HCl or SO ₂ and the exhaust gas flow rate The coefficient for obtaining the required number of moles of slaked lime per hour by multiplying the number is called the mole coefficient. That is, the number of moles of slaked lime necessary for removal of acidic components = the number of moles of acidic components in exhaust gas × the molar coefficient. Here, the molar coefficient differs depending on the type of acid gas component and the type of slaked lime powder.

The method for obtaining the molar coefficient will be described below by taking HCl as an example of the acidic component. The reaction when slaked lime Ca (OH) ₂ is blown into and reacted with HCl in the exhaust gas is as follows.

HCl + 1 / 2Ca (OH) ₂ → CaCl ₂ + 2H ₂ O
The theoretical amount of slaked lime that is required to react with 1 mol of HCl is 1/2 mol. Here, slaked lime is in powder form (solid form) with respect to HCl present as gas in the exhaust gas, and is a gas phase-solid phase reaction. Therefore, the amount required for the actual reaction is the theoretical required amount. The required amount can be determined experimentally. An experiment was conducted to determine the actual amount of slaked lime. When JIS special slaked lime was used as the slaked lime powder, the equivalent ratio of slaked lime necessary for removing 98% HCl at 160 ° C. (actual supply) The number of moles / theoretical number of moles) was 3. Therefore, the molar coefficient is as follows.

  When removing HCl using special slaked lime, the removal rate is 98% with an equivalence ratio of 3. Therefore, in order to leave 100%, the molar coefficient is 1.53 as follows.

Molar coefficient = (100 ÷ 98) × 3 × 1/2 = 1.53
Moreover, as the slaked lime powder, when using highly reactive slaked lime having a larger specific surface area and higher reaction rate than the special slaked lime, the equivalent ratio of the amount of slaked lime required to obtain a removal rate of 98% at 160 ° C is Therefore, the molar coefficient in this case is as follows.

  When removing HCl using highly reactive slaked lime, the removal rate is 98% at an equivalence ratio of 2. Therefore, in order to remove 100%, the molar coefficient is 1.02.

Molar coefficient = (100 ÷ 98) × 2 × 1/2 = 1.02
In addition, when the acidic component is SO ₂ , the reaction when slaked lime is blown into SO _{2 in} the exhaust gas for reaction and removal is as follows.

SO ₂ + Ca (OH) ₂ + 1 / 2O ₂ → CaSO ₄ + H ₂ O
One mole of slaked lime is theoretically required to react with one mole of SO ₂ . When a molar coefficient for calculating slaked lime necessary for removing SO ₂ was obtained by the same experiment as that for HCl, it was as follows.

When SO _{2 is} removed using special slaked lime, the removal rate is 98% with an equivalent ratio of 2. Therefore, in order to remove 100%, the molar coefficient is 2.04 as follows.
Molar coefficient = (100 ÷ 98) × 2 = 2.04
When SO _{2 is} removed using highly reactive slaked lime, the removal rate is 98% at an equivalent ratio of 2. Therefore, in order to remove 100%, the molar coefficient is 2.04 as follows.

  Molar coefficient = (100 ÷ 98) × 2 = 2.04

  According to the first and second inventions, in reducing the acid gas concentration by supplying slaked lime to the exhaust gas containing acid gas, solidification of the dust can be prevented, and the dust filter can be prevented from adhering to the bag filter and peripheral devices. be able to. Therefore, dust can be sufficiently removed from the bag filter, increasing the differential pressure of the bag filter, clogging in the exhaust gas flow path, and reducing the effective cross-sectional area, making it difficult to smoothly flow exhaust gas. Smoothly, and the problem that it becomes difficult to discharge the dust by forming a bridge in the hopper part or the carry-out conveyor part that receives the dust removed from the bag filter becomes difficult. Acid gas in the exhaust gas can be removed.

  Furthermore, according to the third and fourth inventions, in addition to the effects of the first and second inventions, it is possible to surely suppress the acid gas concentration in the exhaust gas to a regulation value or less.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a schematic configuration of an apparatus in which the method of the present invention is implemented.

  In FIG. 1, reference numeral 1 denotes an incinerator for waste incineration, and an exhaust port is connected to a boiler 2, and the boiler 2 is connected to a dust collector 4 having a bag filter through a temperature reducing tower 3. The dust collector 4 is connected to a chimney 5 on the exhaust side.

In the present embodiment, a control device 6 that controls the supply amount of slaked lime based on the concentration of acidic gas such as HCl and SO ₂ is provided. The flow path 7 connecting the boiler 2 and the temperature reducing tower 3 is provided with a sensor, and the concentration meter 8 measures the concentrations of HCl and SO ₂ and inputs these values to the controller 6. Is done. Further, a slaked lime supply device 10 is connected to a flow path 9 connecting the temperature reducing tower 3 and the dust collector 4 having a bag filter, and the slaked lime supply device 10 receives a command from the control device 6. Thus, a predetermined amount of slaked lime is supplied into the flow path 8.

  In the apparatus of this embodiment having such a configuration, the exhaust gas discharged from the incinerator 1 is heat-recovered by the boiler 2, and after the exhaust gas temperature is cooled from about 120 ° C. to about 200 ° C. by the temperature reducing tower 3, the acid gas is removed. Processing is performed. The slaked lime powder is sprayed into the exhaust gas flow path 9 upstream of the bag filter used in the dust collector 4 to neutralize the acid gas, and the reaction product is removed from the exhaust gas together with soot dust in the bag filter of the dust collector 4. The reaction product and dust collected in the bag filter are removed by jetting off the gas, and collected and disposed of.

<First embodiment>
The first embodiment is a form in which supply control of slaked lime is performed with a supply amount necessary and sufficient to suppress solidification / fixation of dust as a lower limit amount.

In controlling the amount of slaked lime powder supplied, in FIG. 1, the hydrogen chloride concentration or the hydrogen chloride concentration and the sulfur dioxide concentration in the exhaust gas are measured in the flow path 7 upstream of the temperature reducing tower 3 in FIG. Measure with a densitometer 8. In the control device 6, the amount of hydrogen chloride in the exhaust gas, or the amount of hydrogen chloride and sulfur dioxide is obtained from these gas concentrations and exhaust gas flow rates, and the amount of slaked lime necessary and sufficient to generate CaClOH by reacting with the hydrogen chloride is obtained. Calculated as the supply amount. Alternatively, the amount of slaked lime that reacts with hydrogen chloride to produce CaClOH and reacts with sulfur dioxide to produce CaSO ₃ is calculated as a necessary and sufficient supply amount.

  The control device 6 receives a signal from the densitometer 8, calculates a necessary and sufficient amount of slaked lime as a supply amount, and outputs an operation signal to the slaked lime supply device 10 so as to supply slaked lime exceeding the necessary and sufficient supply amount. .

(1) The slaked lime supply amount for detecting only the hydrogen chloride concentration and reacting slaked lime with this hydrogen chloride to produce CaClOH is Y ₁ or more according to the following equation (1).

Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
here,
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
is there.

By supplying slaked lime at Y ₁ or more, all hydrogen chloride reacts with slaked lime to produce CaClOH and remains in this state, and does not produce CaCl ₂ . For this reason, the dust is easily treated by being removed by the filter without adhering and solidifying the filter.

(2) Hydrogen chloride concentration and sulfur dioxide are also detected, and slaked lime is reacted with hydrogen chloride to produce CaClOH, and at the same time, sulfur dioxide is reacted with sulfur dioxide to produce CaSO _3. 2) Y ₂ or more according to the formula.

Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
here,
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
It is.

By supplying more than Y ₂ slaked lime, all hydrogen chloride reacts with slaked lime to produce CaClOH and stays in this state and does not produce CaCl _2, while sulfur dioxide produces CaSO ₃ and produces CaSO ₄ . do not do. For this reason, the dust is easily treated by being removed by the filter without adhering and solidifying the filter.

<Second embodiment>
In the second embodiment, the larger one of the supply amount necessary and sufficient for suppressing solidification and fixation of dust and the supply amount necessary and sufficient for suppressing the concentration of hydrogen chloride and sulfur dioxide is set as the lower limit amount. It is the form which controls supply of slaked lime.

(3) The amount of slaked lime for detecting the hydrogen chloride concentration and generating CaClOH to suppress the generation of CaCl ₂ and to suppress the hydrogen chloride concentration in the exhaust gas to a target concentration or less is the same as the previously described Y ₁ And the larger one of Y ₃ by the following equation (3) is set as the lower limit amount.

In this case, in addition to the above-described calculation of Y ₁ by the equation (1), the target hydrogen chloride concentration is suppressed based on the pretreatment hydrogen chloride concentration and the target hydrogen chloride concentration to be reduced by exhaust gas treatment. calculating a necessary and sufficient supply amount Y ₃ (3) expression of slaked lime for.

Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
Y ₃ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X (3)
here,
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
Y ₃ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride)
And
Of the supply amount Y ₁ and the supply amount Y ₃ , slaked lime having the larger amount as the lower limit amount is supplied to the exhaust gas passage.

In such an embodiment, in any case of Y ₃ > Y ₁ and Y ₁ > Y ₃ , the hydrogen chloride concentration in the exhaust gas becomes equal to or lower than the target concentration, and solidification / adherence of dust can be suppressed.

(4) Detect hydrogen chloride concentration and sulfur dioxide concentration, react slaked lime with hydrogen chloride to produce CaClOH, and react with sulfur dioxide to produce CaSO ₃ to produce CaCl ₂ and CaSO ₄ The amount of slaked lime supplied to suppress the hydrogen chloride concentration and sulfur dioxide concentration in the exhaust gas to below the target concentration while suppressing the larger of the above-mentioned Y ₂ and Y ₄ according to the following equation (3), the lower limit amount And

In this case, in addition to the above-described calculation of Y ₂ by the equation (2), based on the pre-treatment hydrogen chloride concentration, the pre-treatment sulfur dioxide concentration, and the target hydrogen chloride concentration and the target sulfur dioxide concentration, which are target concentrations to be reduced by exhaust gas treatment. calculates a necessary and sufficient supply amount Y ₄ of slaked lime by equation (4).

Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
Y ₄ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X
+ 3.3 × 10 ⁻³ (Z ₀ −Z ₁ ) · Q · _KY (4)
here,
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
Y ₄ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration and the sulfur dioxide concentration to the target sulfur dioxide concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Z ₁ : Target sulfur dioxide concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride)
_KY : molar coefficient (reaction with sulfur dioxide)
And
Of supply amount Y ₂ and the supply amount Y _4, and supplies the slaked lime to the quantity with the larger lower limit amount in the exhaust gas line.

In such an embodiment, in any case of Y ₄ > Y ₂ and Y ₂ > Y ₄ , the hydrogen chloride concentration and the sulfur dioxide concentration in the exhaust gas are equal to or lower than the target concentrations, and the solidification / adhesion of dust is suppressed. be able to.

<Removal test of hydrogen chloride and sulfur dioxide in waste incinerator exhaust gas>
In FIG. 1, simulated waste is combusted in a waste incineration test furnace 1 with an exhaust gas flow rate of 180 Nm ³ / h, the bag filter of the dust collector 4 provided in the subsequent stage is controlled to 160 ° C., and the upstream flow of the exhaust gas flow of the bag filter The HCl concentration and the SO ₂ concentration are continuously measured in the path 7, the supply amount of the slaked lime powder is determined by the control device 6 based on each control logic, and the slaked lime powder is blown into the channel 9 upstream of the bag filter. Then, the HCl concentration and SO ₂ concentration were measured at the outlet of the bag filter, and the removal status of HCl and SO ₂ was investigated. The actual supply amount of slaked lime is referred to as the actual supply amount.

  Also, whether or not there is an increase in the differential pressure between the inlet and outlet (whether there is an increase in the differential pressure) and whether there is solidification of dust in the hopper part of the bag filter after the bag filter is wiped off confirmed.

In order to change the concentration of acid gas components in the exhaust gas at the bag filter inlet, the content of chlorine or sulfur in the simulated waste was changed as necessary.
・ Types of slaked lime
Two types of slaked lime powder, JIS special slaked lime and highly reactive slaked lime, were used.
The physical properties of JIS special slaked lime and highly reactive slaked lime are shown below.
High-reactivity slaked lime has a small particle size and a large specific surface area compared to special slaked lime, and thus a high reaction rate is obtained. Therefore, the acid gas concentration can be reduced with a small supply amount.

Physical properties of JIS special slaked lime and highly reactive slaked lime

Specific surface area (m ² / g) Average particle diameter (μm) Apparent specific gravity (g / cm ³ )
JIS special name slaked lime 15-16 8-10 0.55-0.58
Highly reactive slaked lime 35-45 5-6 0.43-0.45

-Explanation of molar coefficient Next, the number of moles will be explained. As can be seen from the following reaction formula (1),
2HCl + Ca (OH) ₂ → CaCl ₂ + 2H ₂ O (1)
Hydrogen chloride reacts with 1/2 equivalent of slaked lime.

  For example, in hydrogen chloride removal, the equivalent ratio (number of moles actually supplied / number of theoretical moles) required to obtain a 98% hydrogen chloride removal rate by experiment was found to be 3 for JIS special slaked lime. is doing. Therefore, the molar coefficient is as follows.

When HCl is removed using special slaked lime, the removal ratio is 98% at an equivalent ratio of 3, so the molar coefficient = (100 ÷ 98) × 3 × 1/2 = 1.53
Hereinafter, the molar coefficient for each type of slaked lime and each type of acid gas is as follows.

When removing SO ₂ using special slaked lime, the equivalent ratio is 2 and the removal rate is 98%. The molar coefficient is (100 ÷ 98) × 2 = 2.04.
When HCl removal is performed using highly reactive slaked lime, the removal ratio is 98% at an equivalent ratio of 2, so the molar coefficient = (100 ÷ 98) × 2 × 1/2 = 1.02.
When removing SO ₂ using highly reactive slaked lime, the equivalent ratio is 2 and the removal rate is 98%, so the molar coefficient = (100 ÷ 98) × 2 = 2.04.
<Experiment 1> See Table 1. In Experiment 1, the concentration of acidic gas in the exhaust gas was 200 to 1500 ppm in HCl and 15 to 30 ppm in SO ₂ in the exhaust on the upstream side of the bag filter. The target concentration of HCl concentration at the bag filter outlet was set to 100 ppm. Table 1 shows the experimental situation and results.

In Table 1, Y ₁ represents the supply amount of slaked lime necessary and sufficient to react with HCl to produce CaClOH, and Y ₃ represents the amount of slaked lime necessary and sufficient to make the HCl concentration at the bag filter outlet 100 ppm. The supply amount is shown.
・ Test No. Description ○ - ○ -A: tests were actually supplied the supply amount Y ₃ calculated as the supply actual amount No. It is.

○ - ○ -B: the supply amount Y ₁ calculated actually supplied as the supply actual amount Test No. It is.
-Meaning of the arrow (→ or ←) in the column for actual supply

→ ○: It was actually supplied the supply amount Y ₃ calculated as the feed actual amount, and shows the supply quantity.

○ ←: it actually supplies the supply amount Y ₁ calculated as the feed actual amount, and shows the supply quantity.
During · Table 1 shows in comparison the supply amount Y ₁ and required supply actual amount blown.
-HCl concentration and SO ₂ concentration indicate measured values at the bag filter outlet.
・ Increased differential pressure between bag filter inlet and outlet
○: No increase in differential pressure ×: Shown as an increase in differential pressure.
-Whether there is solidification of dust in the hopper of the bag filter
○: not solidified ×: indicated as solidified.
-From the results of Experiment 1, the following was found.

(1) was calculated based on the concentration of HCl bag filter upstream, if the actual supply amount that is actually supplied slaked lime than the required supply amount Y ₁ of necessary and sufficient hydrated lime to produce a CaClOH reacts with HCl is small In addition, the bag filter differential pressure increased and the dust solidified in the hopper. Further, actually the actual supply amount necessary and sufficient supply amount Y ₁ equal to or that supplied slaked lime, if greater, the bag filter differential pressure increase and solidification has not occurred.

(2) Analysis of soot dust The soot dust was sampled and the composition of the crystal phase was analyzed by X-ray diffraction. When no increase in the bag filter differential pressure or solidification of the dust occurs, CaClOH and CaSO ₃ are detected, and CaCl ₂ is not detected. Almost all of the hydrogen chloride reacted with slaked lime to produce CaClOH, which was completed in the first stage reaction (HCl + Ca (OH) ₂ → CaClOH + H ₂ O), and it was confirmed that no CaCl ₂ was produced.

In addition to CaClOH and CaSO ₃ , CaCl ₂ was detected when the bag filter differential pressure increased and the dust solidified. When the amount of slaked lime is relatively small, the reaction proceeds to the second stage reaction (HCl + CaClOH → CaCl ₂ + H ₂ O), producing highly hygroscopic CaCl _2. It was confirmed that pressure increase and dust solidification in the hopper were caused.

First stage reaction: HCl + Ca (OH) ₂ → CaClOH + H ₂ O
Second stage reaction: HCl + CaClOH → CaCl ₂ + H ₂ O
Which test No. In Example 1, the HCl concentration at the bag filter outlet was below the target concentration, and it was confirmed that the hydrogen chloride concentration was sufficiently reduced by supplying slaked lime.

<Experiment 2> See Table 2. In Experiment 2, the concentration of acidic gas in the exhaust gas was 200 to 500 ppm in HCl and ₂₀ to 25 ppm in SO ₂ in the exhaust gas upstream of the bag filter. The target concentration of HCl concentration at the bag filter outlet was 50 ppm. Table 2 shows the experimental situation and results.

In Table 2, Y ₁ indicates the supply amount of slaked lime necessary and sufficient to react with HCl to produce CaClOH, and Y ₃ indicates the amount of slaked lime necessary and sufficient to make the HCl concentration at the bag filter outlet 50 ppm. The supply amount is shown.

Test No. The explanation of the meaning of the arrow (→ or ←) in the supply actual quantity column is the same as in Table 1.
- than in Experiment 1, for the HCl concentration of the bag filter outlet to a lower 50 ppm, requires sufficient supply amount Y ₃ of slaked lime is more calculated.
-From the results of Experiment 2, the following were found.

(1) Calculated based on the HCl concentration on the upstream side of the bag filter, when the actual supply amount that actually supplied slaked lime is smaller than the supply amount Y _{1 of} slaked lime necessary and sufficient to react with HCl to produce CaClOH, Increased bag filter differential pressure and solidified dust in the hopper. Further, actually the actual supply amount necessary and sufficient supply amount Y ₁ equal to or that supplied slaked lime, if greater, the bag filter differential pressure increase and solidification has not occurred.

(2) Dust analysis The same results as in Experiment 1 were obtained.

When there is no increase in the bag filter differential pressure or solidification of the dust, CaClOH and CaSO ₃ are detected, and CaCl ₂ is not detected. Almost all of the hydrogen chloride reacted with slaked lime to produce CaClOH, which was completed in the first stage reaction (HCl + Ca (OH) ₂ → CaClOH + H ₂ O), and it was confirmed that no CaCl ₂ was produced.

In addition to CaClOH and CaSO ₃ , CaCl ₂ was detected when the bag filter differential pressure increased and the dust solidified. When the amount of slaked lime is relatively small, the reaction proceeds to the second stage reaction (HCl + CaClOH → CaCl ₂ + H ₂ O), producing highly hygroscopic CaCl _2. It was confirmed that pressure increase and dust solidification in the hopper were caused.

  Which test No. In Example 1, the HCl concentration at the bag filter outlet was below the target concentration, and it was confirmed that the hydrogen chloride concentration was sufficiently reduced by supplying slaked lime.

<Experiment 3> See Table 3. In Experiment 3, the concentration of acidic gas was 200 to 510 ppm for HCl in the exhaust gas on the upstream side of the bag filter, and 70 to 100 ppm for SO ₂ . The target concentration of HCl concentration at the bag filter outlet was 50 ppm, and the target concentration of SO ₂ concentration was 50 ppm.

In Experiment 3, the SO ₂ concentration was higher than in Experiments 1 and _2, and an experiment was performed in consideration of the reaction between slaked lime and SO ₂ . Table 3 shows the experimental situation and results.

In Table 3, Y ₂ represents the supply amount of slaked lime necessary and sufficient to react with HCl to produce CaClOH and to react with SO ₂ to produce CaSO _3. Y ₄ represents HCl at the bag filter outlet. The supply amount of slaked lime necessary and sufficient to make the concentration 50 ppm and the SO ₂ concentration 50 ppm is shown.
・ Test No. Description ○ - ○ -A: tests were actually supplied the supply amount Y ₄ calculated as the supply actual amount No. It is.

○ - ○ -B: the supply amount Y ₂ calculated and actually supplied as the supply actual amount Test No. It is.
· Meaning → ○ arrows in the supply actual amount of columns (→ or ←): It supply amount Y ₄ calculated and actually supplied as the supply actual amount, and shows the supply quantity.
○ ←: it actually supplies the supply amount Y ₂ calculated as supplying actual amount, and shows the supply quantity.
During · Table 3 shows in comparison the supply amount Y ₂ and required supply actual amount blown.
-From the results of Experiment 3, the following were found.

(1) Supply amount Y of slaked lime necessary and sufficient to react with HCl to produce CaClOH and react with SO ₂ to produce CaSO ₃ calculated based on the HCl concentration and SO ₂ concentration upstream of the bag filter ₂ indicates that when the actual supply amount of slaked lime actually supplied was small, the bag filter differential pressure increased and the dust solidified in the hopper. Further, actually the actual supply rate equal to or required amount Y ₂ which supplied the slaked lime, if greater, the bag filter differential pressure increase and solidification has not occurred.

(2) Analysis of soot When there is no increase in the bag filter differential pressure or solidification of soot, CaClOH and CaSO ₃ are detected, and CaCl ₂ is not detected. Almost all of the hydrogen chloride reacted with slaked lime to produce CaClOH, which was completed in the first stage reaction (HCl + Ca (OH) ₂ → CaClOH + H ₂ O), and it was confirmed that no CaCl ₂ was produced.

When the bag filter differential pressure increase and soot solidification occurred, CaCl ₂ and CaSO ₄ were detected in addition to CaClOH and CaSO ₃ in the soot composition. When the amount of slaked lime is relatively small, the reaction proceeds to the second stage reaction (HCl + CaClOH → CaCl ₂ + H ₂ O), producing highly hygroscopic CaCl ₂ and further producing CaSO ₄ , so dust Was fixed and solidified, and it was confirmed that bag filter differential pressure increased and dust solidification occurred in the hopper.

Which test No. In addition, the HCl concentration and SO ₂ concentration at the outlet of the bag filter were below the target concentrations, and it was confirmed that the hydrogen chloride concentration and sulfur dioxide concentration were sufficiently reduced by supplying slaked lime.

<Experiment 4> See Table 4. In Experiment 4, the concentration of acidic gas was 200 to 510 ppm for HCl in the exhaust gas on the upstream side of the bag filter, and 70 to 110 ppm for SO ₂ . The target concentration of HCl concentration at the bag filter outlet was 100 ppm, and the target concentration of SO ₂ concentration was 50 ppm. Table 4 shows the experimental situation and results.

In Table 4, Y ₂ represents the supply amount of slaked lime necessary and sufficient to react with HCl to produce CaClOH and to react with SO ₂ to produce CaSO _3. Y ₄ represents HCl at the bag filter outlet. The supply amount of slaked lime necessary and sufficient to make the concentration 100 ppm and the SO ₂ concentration 50 ppm is shown.

Test No. The explanation of the meaning of the arrow (→ or ←) in the supply actual quantity column is the same as in Table 3.
This experiment 4 is the case where the acid gas concentration in the exhaust gas is similar to that in the experiment 3, and the target concentration of SO ₂ concentration in the exhaust gas at the bag filter outlet is as high as 100 ppm.
From the results of Experiment 4, the following was found.

(1) Supply amount Y of slaked lime necessary and sufficient to react with HCl to produce CaClOH and react with SO ₂ to produce CaSO ₃ calculated based on the HCl concentration and SO ₂ concentration upstream of the bag filter ₂ indicates that when the actual supply amount of slaked lime actually supplied was small, the bag filter differential pressure increased and the dust solidified in the hopper. Further, actually the actual supply rate equal to or necessary and sufficient supply amount Y ₂ which supplied the slaked lime, if greater, the bag filter differential pressure increase and solidification has not occurred.

(2) Analysis of soot When no increase in bag filter differential pressure or solidification of soot has occurred, CaClOH and CaSO ₃ are detected, and CaCl ₂ and CaSO ₄ are not detected. Almost all of the hydrogen chloride reacted with slaked lime to produce CaClOH, which was completed in the first stage reaction (HCl + Ca (OH) ₂ → CaClOH + H ₂ O), and it was confirmed that no CaCl ₂ was produced.

When the bag filter differential pressure increase and soot solidification occurred, CaCl ₂ and CaSO ₄ were detected in addition to CaClOH and CaSO ₃ in the soot composition. When the amount of slaked lime is relatively small, it proceeds to the second stage reaction (HCl + CaClOH → CaCl ₂ + H ₂ O), producing highly hygroscopic CaCl ₂ and further producing CaSO ₄ , so dust Was fixed and solidified, and it was confirmed that bag filter differential pressure increased and dust solidification occurred in the hopper.

Which test No. In addition, the HCl concentration and SO ₂ concentration at the outlet of the bag filter were below the target concentrations, and it was confirmed that the hydrogen chloride concentration and sulfur dioxide concentration were sufficiently reduced by supplying slaked lime.

  As described above, by controlling the supply amount of slaked lime, hydrogen chloride and sulfur dioxide are removed from the exhaust gas to below the target concentration, and solidification and fixation of the dust are suppressed, increasing the differential pressure of the bag filter and solidifying the dust. It was confirmed that the occurrence of troubles due to the above could be suppressed.

It is a schematic block diagram of the apparatus of one Embodiment of this invention.

Explanation of symbols

7 (Exhaust gas) channel 9 (Exhaust gas) channel 10 Slaked lime supply device

Claims (4)

An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the hydrogen chloride concentration before treatment of the exhaust gas upstream of the exhaust gas flow from the slaked lime supply means, the supply amount Y _{1 of} slaked lime necessary and sufficient to react with hydrogen chloride to generate CaClOH is calculated by the equation (1),
Exhaust gas treatment method and supplying the slaked lime to the lower limit amount of the supply amount Y ₁ in the exhaust gas line.
Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Q: Exhaust gas flow rate (Nm ³ / h) An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the pre-treatment hydrogen chloride concentration and pre-treatment sulfur dioxide concentration of the exhaust gas upstream of the slaked lime supply means, the slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and to react with sulfur dioxide to produce CaSO ₃ the supply amount _{Y 2} is calculated by equation (2),
Exhaust gas treatment method and supplying the slaked lime to the lower limit amount of the supply amount Y ₂ in the exhaust gas line.
Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Q: Exhaust gas flow rate (Nm ³ / h) An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the hydrogen chloride concentration before treatment of the exhaust gas upstream of the exhaust gas flow from the slaked lime supply means, the supply amount Y _{1 of} slaked lime necessary and sufficient to react with hydrogen chloride to generate CaClOH is calculated by the equation (1),
Wherein the pretreatment hydrogen chloride concentration, the supply amount Y ₃ of necessary and sufficient calcium hydroxide to reduce the target hydrogen chloride concentration of hydrogen chloride concentration based on the target hydrogen chloride concentration is the target concentration to reduce the exhaust gas treatment (3) A step of calculating by an expression;
An exhaust gas treatment method comprising a step of supplying slaked lime having a larger amount of the supply amount Y ₁ and the supply amount Y ₃ as a lower limit amount to the exhaust gas flow path.
Y ₁ = 3.3 × 10 ⁻³ X ₀ · Q (1)
Y ₃ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X (3)
Y ₁ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH (g / h)
Y ₃ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride) An exhaust gas treatment method for reducing acid gas concentration by supplying slaked lime to exhaust gas containing acid gas,
Based on the pre-treatment hydrogen chloride concentration and pre-treatment sulfur dioxide concentration of the exhaust gas upstream of the slaked lime supply means, the slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and to react with sulfur dioxide to produce CaSO ₃ the supply amount _{Y 2} is calculated by equation (2),
Based on the pretreatment hydrogen chloride concentration and the target hydrogen chloride concentration that is the target concentration to be reduced by exhaust gas treatment, the supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration, and the pretreatment carbon dioxide Supply amount Y of slaked lime which is the sum of supply amount of slaked lime necessary and sufficient to reduce the sulfur dioxide concentration to the target sulfur dioxide concentration based on the sulfur concentration and the target sulfur dioxide concentration which is the target concentration to be reduced by exhaust gas treatment ₄ a step of calculating by the equation (4),
The supply amount Y ₂ and of the feed amount Y _4, an exhaust gas processing method for the slaked lime to the quantity with the larger lower limit amount, comprising the step of supplying the exhaust gas passage.
Y ₂ = 3.3 × 10 ⁻³ (X ₀ + Z ₀ ) · Q (2)
Y ₄ = 3.3 × 10 ⁻³ (X ₀ −X ₁ ) · Q · K _X
+ 3.3 × 10 ⁻³ (Z ₀ −Z ₁ ) · Q · _KY (4)
Y ₂ : Supply amount of slaked lime necessary and sufficient to react with hydrogen chloride to produce CaClOH and react with sulfur dioxide to produce CaSO ₃ (g / h)
Y ₄ : Supply amount of slaked lime necessary and sufficient to reduce the hydrogen chloride concentration to the target hydrogen chloride concentration and the sulfur dioxide concentration to the target sulfur dioxide concentration (g / h)
X ₀ : Hydrogen chloride concentration before treatment (ppm)
X ₁ : Target hydrogen chloride concentration (ppm)
Z ₀ : Sulfur dioxide concentration before treatment (ppm)
Z ₁ : Target sulfur dioxide concentration (ppm)
Q: Exhaust gas flow rate (Nm ³ / h)
K _X : molar coefficient (reaction with hydrogen chloride)
_KY : molar coefficient (reaction with sulfur dioxide)

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