JP2002361035A - Boiler flue gas treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide simple flue gas treatment equipment which is capable of suppressing the occurrence of the in-tube wall wear by a high-velocity fluidized slurry and the local corrosion by V<5+> ions by drastically lowering the concentration of the soot and V<5+> ions in the waste gas of a boiler. SOLUTION: A soot recovering and reducing column 15 of a tray foaming system is arranged downstream of a heat recovering side GGH 6 and cleaning water is injected into the heat recovering side GGH 6 by a high-pressure injecting device 9. The cleaning liquid used for cleaning is fed into the soot recovering and reducing column 15 by a circulating pump 16 and is brought into gas-liquid contact with the waste gas discharged from the GGH 6 together with another absorbent liquid, by which the greater part of the soot in the waste gas is captured. The equipment is so constituted that the SO3 <2-> ions eluted into the absorbent liquid reduce the V<5+> ions eluted from the soot to V<3+> ions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a boiler flue gas treatment apparatus for removing dust and sulfur while maintaining the temperature of exhaust gas containing dust generated by combustion of fuel in a boiler to some extent.

[0002]

2. Description of the Related Art Recently, in response to increasing interest in environmental problems, for example, the problem of air pollution, domestic thermal power boilers use nitrogen oxides (NO, NO ₂ , NO. hereinafter referred to as nO _x), soot, sulfur oxides (sO _2, sO _3, as hereinafter referred to as sO _x) air pollutants such is not released into the atmosphere, flue gas treatment to recover these substances Equipment is installed.

FIG. 4 is a schematic diagram showing a schematic configuration of a conventional flue gas treatment apparatus for a heavy oil fired boiler. The exhaust gas discharged from the boiler 1 is NO _{x in the} denitration device 3, then the dust is collected in the electric dust collector (EP) 5, and the SO _x is further reduced in the desulfurization device 7.
Are arranged to be removed respectively. As shown in the figure, a gas / gas heater (hereinafter abbreviated as GGH) 6 is usually provided in the flue to improve the desulfurization performance and to heat and dry the purified exhaust gas and release it to the atmosphere. Is provided, and the exhaust gas on the outflow side of the desulfurization unit 7 is heated by the heat recovered from the exhaust gas on the inflow side of the desulfurization unit 7.

The provision of such a flue gas treatment device makes it possible to remarkably reduce air pollutants contained in flue gas discharged from the chimney 8 into the atmosphere. However, since installation of such a flue gas treatment apparatus requires a large amount of capital investment cost, for example, it is economical to provide the above-mentioned complete flue gas treatment apparatus in a thermal power boiler in an economically developing country. In many cases, there is a demand for a simpler, less expensive, and more effective flue gas treatment device.

FIG. 5 is a schematic diagram showing a schematic configuration of a flue gas treatment apparatus for a heavy oil fired boiler according to the prior art developed in response to such a demand. The flue gas treating apparatus is not equipped with a denitration apparatus and an electrostatic precipitator, the improvement of the NO _x combustion method, also, dust is to be removed or reduced by the desulfurization apparatus which gave dust collecting function. In this way, even if the equipment for smoke exhaust treatment is reduced by almost half and the capital investment cost is significantly reduced, it is possible to maintain the temperature of the exhaust gas and prevent the occurrence of air pollution.

[0006]

As described above, equipment investment is
In the flue gas treatment equipment that reduces capital costs, denitration and collection
Since the dust function is supplemented by other alternative means,
Avoid some technical problems
Can not. For example, in the above-mentioned flue gas treatment device,
Since no ammonia is injected, a relatively large amount
SO_ThreeIs included. In addition, heavy and low quality oils with high sulfur
When burned, the exhaust gas contains 1000-3000 ppm SO_TwoContains
You. By the way, the dust contained in the exhaust gas of heavy oil fired boilers
V inside_TwoO _FiveWhich acts as an oxidation catalyst
And SO_Two1-2% of SO is oxidized to SO_ThreeChange to
After all, in the exhaust gas, 10 to 60 ppm of SO_ThreeContains
You. In addition, the exhaust gas contains 10% moisture.

As shown in FIG. 7 showing the SO ₃ concentration versus sulfuric acid dew point temperature characteristic, the sulfuric acid dew point temperature for SO ₃ concentration of 10 to 60 ppm is about 130 to 150 ° C. As can be seen from the comparison with -200 ° C and the outflow-side exhaust gas temperature of 70-90 ° C, high-concentration sulfuric acid contained in the exhaust gas is condensed in the heat recovery-side device of GGH6 and condenses on the surface.
Thus, when the inner surface of the heat recovery-side device of the GGH 6 becomes wet with the liquefied sulfuric acid, dust in the exhaust gas easily adheres.

[0008] As described above, this smoke exhaust treatment device is a simple device without a dust collector. Therefore, the flue gas produced by burning heavy oil has several times the number of exhaust gas treatment devices equipped with EP5. It contains more than ten times the concentration of about 300 to 500 mg / m ³ N dust, and if a large amount of dust adheres to the inner surface of the GGH 6 heat recovery side device, a serious accident such as obstruction of the flue may be caused. Therefore, when operating this apparatus, it is necessary to periodically wash and remove dust adhering to the inner surface of the GGH 6 using high-pressure jet water or the like.

FIG. 6 is an enlarged view of the latter part of the smoke exhaust treatment device shown in FIG. Since the concentration of dust in the exhaust gas is low in the exhaust gas treatment device equipped with the EP, the cleaning and removal of the dust attached to the inner surface of the GGH 6 may be performed at intervals of six months to one year. Due to the high concentration of dust in it, it must be performed frequently at half-month to two-month intervals. The cleaning water for cleaning the inner surface of GGH6 is pH2.
Because of the following strongly acidic aqueous solution, the material constituting the inside of the GGH 6 must be strong in acid resistance, and the processing cost of the cleaning water used for frequent cleaning of the GGH 6 becomes enormous.

Further, as described above, a part of the dust in the exhaust gas adheres and accumulates on the inner wall surface of the GGH 6, but most of the dust is conveyed to the desulfurizer 7 downstream. Therefore, the amount of dust contained in the absorption liquid treated by a simple device is several times or more than that of a smoke exhaust treatment device equipped with EP, and its concentration is several%.
Can be estimated. Generally, dust contains high concentrations of metal oxides such as Al ₂ O ₃ , SiO ₂ , and Fe ₂ O ₃ , and these fine particles are mixed in lime-gypsum slurry that flows at high speed. Then, the wear in the desulfurization device 7 becomes severe, so that a measure for preventing the wear is required. That is, the portion of the desulfurization device 7 where the high-speed fluidized slurry collides must be covered with a wear-resistant coating material, so that the impeller renewal timing of the circulation pump is hastened. Incidentally, it is known that the wear rate due to the high-speed fluidized slurry is proportional to about the cube of the flow rate of the slurry and the concentration of the solid component.

Further, as described above, dust in the exhaust gas of a heavy oil fired boiler contains vanadium oxide (mostly V ₂ O ₅ ), and is generated when this V ₂ O ₅ is dissolved in water. V ⁵⁺
Since ions have strong acidity, stainless steel containing Mo (JIS SUS316L, etc.) that is often used in desulfurization equipment 7
To cause local corrosion such as pitting and crevice corrosion. FIG. 8 shows stainless steel (JIS SUS316) versus V ⁵⁺ ion concentration.
It is a corrosion characteristic figure which shows the relationship with crevice corrosion rate of L).
As is apparent from the figure, crevice corrosion of stainless steel is V
⁵⁺ ion concentration is generated at about several tens ppm, and ^{V5 +}
At ion concentrations, crevice corrosion of stainless steel increases in proportion to the logarithm of the ^{V5 +} ion concentration.

The problems of the simple exhaust gas treatment apparatus described above can be summarized as follows. 1) A lot of trouble and cost are required for cleaning sulfuric acid and dust adhering in GGH6. 2) Wall wear occurs due to the high-speed flow of dust, which has significantly increased in the desulfurizer 7.

3) Local corrosion occurs on the stainless steel wall material due to the increased V ⁵⁺ ions contained in the dust. The present invention has been made to solve such a problem in the prior art, and it has been proposed that dust and V ⁵⁺ in boiler exhaust gas are eliminated.
An object of the present invention is to provide a simple flue gas treatment apparatus capable of significantly reducing the ion concentration and suppressing the inner wall wear of the pipe due to the high-speed fluidized slurry and the occurrence of local corrosion due to V ⁵⁺ ions.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a gas / gas supply system between a heat recovery side device and a desulfurization device.
It is provided with a dust collection and reduction tower that is used as an absorbing liquid that collects washing water that has washed the inside of the heat recovery side device of the gas heater and collects dust contained in exhaust gas by gas-liquid contact, A neutralizing agent for neutralizing the acidity is added to the washing water recovered from the heat recovery side device, or the absorption liquid in the dust collection and reduction tower is changed to alkaline and used as the absorption liquid for the desulfurization device.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, in a dust collection and reduction tower installed on the downstream side of GGH, an absorbent containing washing wastewater for washing the inner wall surface of GGH is brought into gas-liquid contact with exhaust gas,
By melting the SO ₂ in the flue gas in the absorption liquid, causing the SO ₃ ^2-ion according to the following reaction formula.

[0016] _{SO 2 + H 2 O → H} 2 SO 3 ...... (1) V 2 O 5 + 2H 2 SO 3 → V 2 O 3 + 2H 2 SO 4 ...... (2) Thus, SO ₃ ^2-ion Strong oxidizing and corrosive pentavalent vanadium ion V dissolved in absorbing solution
⁵⁺ can be reduced to a non-corrosive trivalent vanadium ion V ³⁺ . When a calcium compound such as lime is added to the dust collection and reduction tower, the absorption liquid contains
Due to the presence of Ca ²⁺ ions, the substance produced by the above formula (1) is replaced by calcium sulfite (CaS) instead of sulfite (H ₂ SO ₃ ).
O ₃ · nH ₂ O), but in most cases, sulfite has a reducing property, and in any case, performs a reducing action on V ⁵⁺ ions.

Further, in the dust collection and reduction tower, the absorbing liquid containing the GGH washing wastewater is brought into gas-liquid contact with the exhaust gas,
Most (90-95% or more) dust in exhaust gas can be collected. In addition, as the gas-liquid contact method, any method such as a spray injection method (spray) method of an absorbing liquid, a platen foaming (bubbling) method in an exhaust gas absorbing liquid, and the like may be used.

The dust collected in the absorbing solution in the dust collection and reduction tower is collected by a concentration separation method such as a sedimentation method and a centrifugal separation method. The supernatant liquid when recovering the dust, since in the case of lime-free additive has a strongly acidic solution because it contains the remaining SO ₃ ^2-ions consumed in the reduction of V ⁵⁺ ions, this as one likes Cannot be discarded. Therefore, in the present invention, lime water, lime powder or lime slurry is added to the absorbent discharged from the dust collection and reduction tower to change it to neutral or alkaline, and then used as an absorbent for injection into a desulfurizer. . In this way, not only does harmful waste liquid need not be discharged, but also the exhaust gas
SO ₂ can be absorbed and the vanadium ion V ⁵⁺ can be reduced by the SO ₂ . At this time, if the generated sulfuric acid is reacted with the lime slurry to produce gypsum, the desulfurization reaction proceeds more quickly and the desulfurization efficiency can be improved.

In the present invention, the above dust collection and reduction tower is used.
To collect dust with the same efficiency as an electric dust collector
(1/10 to 1/20 reduction) and therefore high-speed fluidized slurry
Wall wear due to
V contained in dust⁵⁺Ion to V ³⁺Can be reduced to ions
To prevent local corrosion of the desulfurizer wall material.
Can be controlled.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an enlarged view of a rear part of a flue gas treatment apparatus according to a first embodiment of the present invention. In the present embodiment, a dust collection and reduction tower 15 of a shelf-stage foaming type is arranged downstream of the heat recovery side GGH 6, and the cleaning liquid that has been washed by injecting cleaning water into the heat recovery side GGH 6 by the high-pressure water injection device 9 is circulated by a circulation pump. Water is supplied to the inside of the dust collection and reduction tower 15 at 16 and GGH is supplied together with other absorbing liquid.
A gas-liquid contact is made with the exhaust gas discharged from 6 to collect most of the dust in the exhaust gas. The SO ₃ ²⁻ ions dissolved into the absorbing solution by the gas-liquid contact reduce V ⁵⁺ ions eluted from the dust to V ³⁺ ions. The collected dust is concentrated and separated and discharged and collected from the dust collection system 17.

As described above, since the washing water collected from the GGH 6 has a strong acidity, lime water is supplied and added from the lime water supply device 14 to a part of the absorbing solution collected in the dust collection and reduction tower 15. After that, the mixture is made neutral or alkaline, and then supplied to the absorption liquid discharge system of the desulfurization unit 7. The absorbing solution discharged from the desulfurizing device 7 is desulfurized by the desulfurizing solution circulating pump 11.
Reflux inside. In the middle of the circulation path of the absorption liquid, together with the gypsum mud absorption and sulfuric acid and lime water generated in it is generated by compounding SO ₂ in the flue gas is separated is supplied to the gypsum recovery unit 13, lime water Lime water is supplied from the supply device 14.

FIG. 2 is an enlarged view of a rear part of a smoke exhaust treatment device according to a modification of the first embodiment of the present invention. In the present modification, lime water is supplied and added from the lime water supply device 14 in the middle of the reflux path for refluxing the absorbent to the dust collection and reduction tower 15 to make it neutral or alkaline. Thereby, the corrosiveness of the dust collection and reduction tower 15 due to the acidic absorbing liquid can be reduced, so that the wall material forming the dust collection and reduction tower 15 can be made of an inexpensive metal material.

FIG. 3 is an enlarged view of the latter part of the flue gas treatment apparatus according to the second embodiment of the present invention. In this embodiment, the gas-liquid contact of the dust collection and reduction tower 15 employs a spray injection method. By employing this method, it is possible to eliminate the occurrence of a differential pressure across the dust collection and reduction tower 15. In the conventional example, the dust concentration in the absorption liquid of the desulfurization device 7 is 2 to 4%,
Since ^{V5 +} ion concentration is 100-1000ppm, it is called Ni-Cr-Mo alloy or super stainless steel as wall material
Ni-Cr-Mo-containing stainless steel was used, and the area where dust and dust collided had to be coated with an abrasion-resistant material. The renewal period of the circulation pump was as short as 2-3 years. In the example, it is not necessary to use the above expensive material,
No coating is required. Although the initial capital investment cost and operating cost of the dust collection and reduction tower 15 are newly required, the total facility cost over the 10-year operating period estimated to be the service life is 20 to 30.
% Reduction. G is a simple exhaust gas treatment device.
A large amount of washing water is consumed for washing sulfuric acid and dust adhering to the GH 6, and this washing water is reused as an absorbent used for dust collection in the dust collection and reduction tower 15, and
Since a part of the GGH 6 is used as an absorbing solution of the desulfurizer 7, even if the number of times of cleaning the GGH 6 is increased in order to prevent a rise in differential pressure and a decrease in heat transfer efficiency, a large load is not required for the treatment.

[0024]

As described above, according to the first aspect of the present invention, between the heat recovery side device and the desulfurization device, the cleaning water for cleaning the inside of the heat recovery side device of the gas / gas heater is recovered. Therefore, since a dust collection and reduction tower was used as an absorbing solution for collecting dust contained in exhaust gas by gas-liquid contact,
Inexpensive equipment can efficiently collect dust, and even if a large amount of washing water is used, it can be effectively used and ^{V5 +} ions contained in the dust can be reduced to ^{V3 +} ions. Local wall corrosion of the wall material can be suppressed.

According to the second aspect of the present invention, the neutralizing agent for neutralizing the acidity is added to the washing water recovered from the heat recovery side device of the gas / gas heater, so that the wall material of the dust recovery and reduction tower can be made more efficient. It can be made of an inexpensive metal material. According to the third aspect of the present invention, since the absorption liquid in the dust collection and reduction tower is changed to alkaline and used as the absorption liquid for the desulfurization apparatus, the maintenance cost of the desulfurization apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a rear part of a flue gas treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a rear part of a smoke exhaust treatment device according to a modification of the first embodiment of the present invention.

FIG. 3 is an enlarged view of a rear part of a smoke exhaust treatment device according to a second embodiment of the present invention.

FIG. 4 is a schematic diagram showing a schematic configuration of a flue gas treatment device for a heavy oil fired boiler according to the related art.

FIG. 5 is a schematic diagram showing a schematic configuration of a flue gas treatment device for a heavy oil fired boiler according to the related art.

FIG. 6 is an enlarged view of a rear part of the smoke exhaust treatment device shown in FIG. 5;

FIG. 7: SO ₃ concentration vs. sulfuric acid dew point temperature characteristics

FIG. 8 is a corrosion characteristic diagram showing the relationship between the V ⁵⁺ ion concentration and the crevice corrosion rate of stainless steel.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Boiler 6 Gas / gas heater (GGH) 7 Desulfurization device 8 Chimney 9 High pressure water injection device 11 Desulfurization absorption liquid circulation pump 13 Gypsum recovery device 14 Lime water supply device 15 Dust recovery reduction tower 16 Circulation pump 17 Dust recovery system

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) B01D 47/06 F-term (Reference) 4D002 AA02 AC01 BA02 BA14 CA01 DA05 DA12 DA66 EA01 FA03 4D032 AA21 AC07 BB05 DA01

Claims (3)

[Claims] 1. An exhaust gas containing dust generated by combustion of fuel in a boiler is guided to a heat recovery side device of a gas / gas heater to recover heat, and then guided to a desulfurization device to remove sulfur oxides. In a boiler flue gas treatment device that is configured to be discharged through a heating-side device of a gas heater, between the heat-recovery-side device and the desulfurization device, recovering cleaning water that has washed the inside of the heat-recovery-side device, A boiler flue gas treatment apparatus, comprising a dust collection and reduction tower used as an absorbing liquid for collecting dust contained in exhaust gas by gas-liquid contact. 2. The boiler flue gas treatment apparatus according to claim 1, wherein a neutralizing agent for neutralizing the acidity is added to the washing water recovered from the heat recovery side device of the gas / gas heater. 3. The boiler flue gas treatment apparatus according to claim 1, wherein the absorption liquid in the dust collection and reduction tower is made alkaline and used as an absorption liquid for a desulfurization apparatus.