JP2000325744A - Exhaust gas treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an exhaust gas treatment apparatus suitable for reducing SO3 in exhaust gas. SOLUTION: In an exhaust gas treatment apparatus, an NH3 injection device for removing SO3 is arranged only to the exhaust gas flow passage provided to the inlet of a denitration device and a washing device 17 is provided to the GGH heat recovery device 7 arranged to the exhaust gas flow passage provided to the inlet of a dust collector and a high performance demister 16 is provided to the outlet part of an absorbing tower 22. Since NH3 is not injected in the dust collector, no ammonium sulfate is generated and the concn. of soot flowing in th absorbing tower 22 of a desulfurization equipment is not increased and SO3 is condensed in the GGH heat recovery device 7 but can be easily removed by the washing device and SO3 mist contained in exhaust gas is also removed by the high performance demister 16 provided to the outlet of the absorbing tower of the desulfurization equipment and the SO3 mist recovered in the absorbing tower 22 can be recovered as gypsum in the absorbing tower 22 of the desulfurization equipment by the reaction with limestone and, therefore, the concn. of soot at the outlet of the desulfurization equipment is not increased and the concn. of NH3 in waste water is not also increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flue gas treatment system, and more particularly to a flue gas treatment device suitable for reducing SO ₃ in exhaust gas.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional flue gas treatment system. Exhaust gas from the boiler 1 is sent into the denitration device 2, where it reacts with NH ₃ supplied from the pipe 11 to remove nitrogen oxides. After that, the exhaust gas is cooled to a gas temperature of 130 ° C. to 150 ° C. by the air preheater 3 and is introduced into the electric precipitator (EP) 4. The air introduced by the FDF 13 is preheated by the air preheater 3 and supplied to the boiler as fuel air. GGH heat recovery unit 7, desulfurization unit 8
And the heat medium communication pipes 14 and 15 between the
The heat medium is circulated through the heat exchanger to perform heat exchange.

[0003] SO ₃ contained in the exhaust gas is condensed due to a decrease in the temperature of the exhaust gas in the air preheater 3 to generate sulfuric acid. Here, when the boiler fuel is coal-fired, a large amount of dust is included in the exhaust gas, and since the dust contains an alkali component, most of the condensed sulfuric acid adheres to the ash. Neutralized.

On the other hand, since the concentration of dust in exhaust gas discharged from a boiler 1 using heavy oil containing sulfur at a high concentration as fuel is low, and the proportion of alkali in the dust is low, it is cooled by an air preheater 3. No neutralizing action of sulfuric acid condensed from exhaust gas is also not expected. Therefore, NH ₃ is generally injected from the pipe 12 at the inlet of the electrostatic precipitator 4 and solid (N) is formed by a reaction with SO ₃ contained in the exhaust gas.
A method in which H ₄ ) ₂ SO ₄ (ammonium sulfate) is generated and collected by the electrostatic precipitator 4 is used.

In the flue gas treatment system shown in FIG. 5, after removing the above-mentioned ammonium sulfate together with the dust in the exhaust gas by the electric dust collector 4, the pressure is increased by the IDF 5 and the BUF 6, and the heat is recovered by the GGH heat recovery device 7. The temperature of the exhaust gas is reduced to about 90 ° C., and is introduced into the desulfurizer 8. In the desulfurization unit 8, the exhaust gas concentration becomes about 45 which is the water saturation temperature due to the gas-liquid contact with the absorbent.
To ℃. After the SO ₂ in the exhaust gas is removed by the desulfurizer 8, the exhaust gas is heated to about 90 ° C. by the heating medium in the GGH reheater 9, which recovers heat from the exhaust gas by the GGH heat recovery unit 7 and raises the temperature. , Discharged from the chimney 10.

[0006] In the flue gas treating system, SO as the SO ₃ to produce generated by combustion in the boiler 1 ₂
Are oxidized using heavy metal contained in the adhering dust as a catalyst in the process of passing through the boiler 1 and the SO ₂
Is oxidized by the catalyst of the denitration device 2 and two types. SO ₃ produced in the former, but 2-5% of the product SO ₂ in catalytic oxidation by heavy metals, the adhesion state or composition of the dust as a catalytic oxidation ratio of SO ₂ are greatly different. Also, the SO ₃ generated in the latter is initially about 1 to 1
Although it is 2%, it is known that the amount of generation varies depending on the amount of dust adhering to the catalyst.

For this reason, particularly in the case of fuels having a high sulfur content, the variation range of the amount of generated SO ₃ is large, and it is difficult to control the amount of NH ₃ injected. For example, if the sulfur content is 4%, S
The O ₂ concentration will be about 2000 ppm, and the resulting SO ₃ concentration may exceed 100 ppm. Since NH ₃ required for the reaction with SO ₃ is 2 mol per 1 mol of SO ₃ , the supply amount is required to be 200 ppm or more.

If the molar ratio of NH _{3 to} SO ₃ becomes twice or less, NH ₄ (HSO ₃ ) (ammonium acid sulfate) is produced, and this acid ammonium sulfate has a very strong adhesion. The dust adheres to the inside of the IDF 5 and the BUF 6 disposed in the electric precipitator 4 and on the downstream side of the smoke exhaust treatment system, and causes the deterioration of the dust collection performance and the vibration of the fan.

Therefore, it is necessary to supply NH ₃ so as to always be in excess with respect to the SO ₃ concentration. However, SO
_{Since the three} concentrations cannot be measured continuously, the boiler 1 and the denitration device 2
Since the amount of production differs depending on the operating conditions, it was necessary to supply NH ₃ in a large excess.

Unreacted NH resulting from a large excess supply
₃ is absorbed removed absorbent including calcium carbonate and the like to be sprayed toward the exhaust gas for SO ₂ absorption in the desulfurization apparatus 8 of flue gas treatment system downstream side, is dissolved in the absorbing liquid. Part of the absorbent is discharged as wastewater after purification treatment by a wastewater treatment device.However, when discharging wastewater to the sea or river, the amount of nitrogen content is reduced to prevent eutrophication of the sea or river. It is regulated, and it is necessary to install expensive denitrification equipment in the wastewater treatment equipment.

[0011] the cost of purchasing the flue gas treatment system NH ₃ to remove the SO ₃ by thus NH ₃ injection equipment of the NH ₃ injection device, it is necessary to provide a denitrification device further waste water treatment apparatus. In addition, the generated ammonium sulfate becomes dust, which is collected by the electric precipitator 4, and a part of the dust passes through the electric precipitator 4 and flows into the desulfurization device 8. Since this ammonium sulfate has a very fine particle size of about 0.5 μm, the desulfurization device 8
, The dust concentration at the entrance of the chimney 10 is increased.

In some cases, it is necessary to take operational measures to raise the gas temperature at the outlet of the air preheater 3 to a value higher than the dew point of SO ₃ without injecting NH ₃ into the exhaust gas. GGH reheater 9 used for raising exhaust gas temperature
And a GGH heat recovery unit 7 for supplying thermal energy to the GGH reheater 9 via a heat medium cannot be installed. Because, even if the gas temperature at the outlet of the air preheater 3 is maintained at the dew point or higher, when the GGH heat recovery device 7 is installed, the gas temperature decreases due to heat exchange in the GGH heat recovery device 7 and becomes lower than the dew point.
Sulfuric acid condenses on the heat transfer tubes of the GGH heat recovery unit 7 for heat recovery. Therefore, the heat transfer tube of the GGH heat recovery unit 7 becomes clogged,
As a result of the corrosion, the operation of the flue gas treatment system becomes impossible.

For example, SO₃Fig. 4 shows the relationship between concentration and dew point.
You. SO in the gas at the inlet of the air preheater 3 ₃The concentration is 100pp
m, the dew point is expected to be 150 ° C,
Air preheater 3 outlet gas temperature should be 153 ℃ or more
Driving SO₃Of the air preheater 3
In the GGH heat recovery unit 7 installed on the side, a desulfurization device
8 GGH reheater 9 installed at the exit
0 ° C.) and the gas temperature drops, so SO₃
Below the dew point.

Here, there is a method in which the gas temperature at the outlet of the air preheater 3 is set to about 200 ° C. so that the gas temperature at the outlet of the GGH heat recovery unit 7 becomes 153 ° C. or more, but this greatly reduces the boiler efficiency. This is uneconomical.

[0015]

In the flue gas treatment system shown in FIG. 5 for injecting NH ₃ into exhaust gas in order to remove SO ₃ in the exhaust gas, the system is connected to a downstream device after the NH ₃ injection section. The influence was not taken into account, and the dust concentration at the outlet of the desulfurization device 8 increased, and it was necessary to install a denitrification device in the wastewater treatment device after desulfurization.

An object of the present invention is to provide a flue gas treatment system for removing SO ₃ in exhaust gas without introducing NH ₃ .

[0017]

SUMMARY OF THE INVENTION The object of the present invention is to provide a dust collector provided in an exhaust gas flow path without injecting NH ₃ into the dust collector.
The problem can be solved by providing a water washing device in the H heat recovery unit and a high-performance mist removal device at the outlet of the absorption tower of the desulfurization device.

That is, according to the present invention, in order to remove dust, nitrogen oxides and sulfur oxides contained in exhaust gas from a combustion device such as a boiler, the denitration device, the dust collector, In a desulfurization apparatus provided with an absorption tower and a flue gas treatment apparatus having a heat recovery unit and a reheater of a gas gas heater arranged before and after the desulfurization apparatus, an NH ₃ injection apparatus for removing SO ₃ is provided by a denitration apparatus. A flue gas treatment device that is installed only in the exhaust gas channel at the inlet, a cleaning device is installed in the GGH heat recovery device that is installed in the exhaust gas channel at the dust collector inlet, and a high-performance mist removal device is installed at the outlet of the absorption tower. It is.

The high-performance mist removing device can be constituted by a spray device for fine droplets and a mist eliminator, or can be constituted by a wet EP.

[0020]

[Action] Since NH ₃ is not injected into the dust collector, ammonium sulfate is not generated, and the concentration of the dust flowing into the desulfurizer does not increase.
In the GGH heat recovery unit, SO ₃ is condensed, but can be easily removed by a water washing device, and SO ₃ mist contained in exhaust gas is also removed by a high-performance mist removal device at an outlet of an absorption tower of a desulfurization device. SO recovered in the tower
_{The three} mist can be recovered as gypsum by reaction with limestone in the absorption tower of the desulfurization device. Therefore, the concentration of the dust at the outlet of the desulfurizer does not increase, and the concentration of NH ₃ in the wastewater does not increase.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. In a flue gas treatment system for a boiler using a sulfur-containing fuel, SO ₃ without injecting NH ₃ is used.
FIG. 1 shows a flue gas treatment system having a _three- removal device.

In the flue gas treatment system shown in FIG. 1, similarly to the flue gas treatment system shown in FIG. 5, a boiler 1, a denitration device 2, an air preheater 3, an electric precipitator 4, an IDF 5, a BUF
6, a GGH heat recovery unit 7, a desulfurization unit 8, a GGH reheater 9, a chimney 10, an NH ₃ supply pipe 11, an FDF 13, and heat medium communication pipes 14, 15.

In the present invention, NH ₃ is not injected into the exhaust gas upstream of the electrostatic precipitator, a cleaning device 17 is provided in the GGH heat recovery device 7, and a mist removal device is provided at the outlet of the absorption tower of the desulfurization device 8. SO ₃ not inject NH ₃ by providing the 16
Is removed.

FIG. 2 shows the structure of the absorption tower 22 of the desulfurization unit 8 shown in FIG. 1. A washing unit 17 is provided at the inlet of the GGH heat recovery unit 7 and a mist removal unit 16 is provided at the outlet of the absorption tower 22. Is provided.

FIG. 3 shows a system of a water washing device of the washing device 17. Sulfuric acid and dust condensed on the heat transfer tube of the GGH heat recovery unit 7 form a wet state, and can be easily removed by washing with water.

In the washing device of the washing device 17, a washing pipe 19, a water spray type (full cone) nozzle 20 attached to the washing pipe 19 and a washing valve 21 are usually provided.
A plurality of these are installed in the GH heat recovery unit 7 so that the entire surface can be washed.

As shown in FIG. 2, water is sprayed on the mist removing device 16 by the spray device 23 to enlarge the SO ₃ mist, and then the mist is removed by the mist removing device 24 at the subsequent stage.

In the absorption tower 22, the absorption liquid is sprayed from the spray nozzle 25 of the absorption liquid, and comes into contact with the exhaust gas to absorb the sulfur oxides. The absorbing liquid sprayed from the spray nozzle 25 is supplied to the absorbing liquid storage tank 2 provided at the lower part of the absorbing tower 22.
6 and supplied to the spray nozzle 25 again by the circulation pump 27.

As shown in FIG. 1, the exhaust gas from the boiler 1 exits the air preheater 3 and is introduced into the electric precipitator 4, but the exhaust gas before flowing into the electric precipitator 4 is injected with NH ₃ . Since it is not performed, SO ₃ is introduced into the GGH heat recovery unit 7 in a gaseous state. Since the exhaust gas temperature decreases in the GGH heat recovery unit 7, SO ₃ is condensed to form a sulfuric acid mist, and a part thereof adheres to the heat transfer tube of the GGH heat recovery unit 7. As a result, the surface of the heat transfer tube becomes wet, and if dust in the exhaust gas adheres to the heat transfer tube, the sulfuric acid mist is strongly adhered and cannot be removed by the soot blower. A cleaning device 17 is provided to perform periodic cleaning.

The washing pipe 19 and the nozzle 20 in the washing apparatus 17 shown in FIG. 3 can be made of resin such as polypropylene or Teflon in consideration of acid resistance. According to the present embodiment, the washing water amount is about 50 liter / min.
・ M ² , but if the entire heat transfer tube surface is washed at the same time, the amount of water will increase. Therefore, the washing operation is performed by dividing and operating a plurality of sets of the washing pipe 19, the nozzle 20 and the washing valve 21 sequentially. The method is desirable.

The cleaning time by the cleaning device 17 is generally about 10 minutes once per day / day, and ΔP (GG
If necessary, the heat transfer tube 18 is re-cleaned based on the pressure loss (ΔP) of the exhaust gas flow of the H heat recovery unit 7).

Further, it is desirable that the heat transfer tube 18 of the GGH heat recovery unit 7 shown in FIG. 2 be a bare tube so that a sufficient cleaning effect can be obtained, and it is desirable to use a sulfuric acid corrosion resistant material. Since the washing wastewater can be collected in the absorption tower 22 and used as makeup water, the amount of water used in the entire desulfurization device 8 does not increase.

The sulfuric acid mist that has passed through the GGH heat recovery unit 7 flows into the absorption tower 22 of the desulfurization unit 8, but the sulfuric acid mist is collected by gas-liquid contact in the absorption tower 22 because the particle size of the sulfuric acid mist is as small as 1 μm or less. Therefore, the mist removing device 16 is installed at the outlet of the absorption tower 22. As the mist removing device 16,
A system in which water is sprayed by the spray device 23 to enlarge the SO ₃ mist and then collected by the mist removal device 24 at the subsequent stage can be employed. The mist collected by the mist removal device 24 is collected in the absorption tower 22 by a device (not shown). In addition, there is also a method of employing a wet EP as the mist removing device 24.

[0034]

According to the present invention, in a flue gas treatment system, SO ₃ in exhaust gas can be removed without injecting NH ₃ in an electric precipitator, so that utility can be reduced. Therefore, a denitrification device in the wastewater treatment device is not required.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flue gas treatment system according to an embodiment of the present invention.

FIG. 2 is a partial view of a GGH heat recovery unit and a desulfurization device of the flue gas treatment system of FIG.

FIG. 3 is a partial view of a flushing device of the flue gas treatment system of FIG. 1;

FIG. 4 is a graph showing the relationship between the concentration of SO _{3 in} exhaust gas and the dew point.

FIG. 5 is a diagram illustrating a smoke exhaust treatment system according to the related art.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 boiler 2 denitrification device 3 air preheater 4 electric precipitator 5 IDF 6 BUF 7 GGH heat recovery device 8 desulfurization device 9 GGH reheater 10 chimney 11, 12 NH ₃ supply pipe 13 FDF 14, 15 heat medium communication pipe 16 Mist removing device 17 Rinse device 18 Heat transfer tube 19 Rinse pipe 20 Full cone nozzle 21 Rinse valve 22 Absorption tower 23 Spray device 24 Mist remover 25 Spray nozzle 26 Absorbing liquid storage tank 27 Circulation pump

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Sayuki Saito 6-9 Takaracho, Kure-shi, Hiroshima Babcock-Hitachi Inside the Kure Plant (72) Inventor Naomi Oda 6-9 Takaracho, Kure-shi, Hiroshima Babcock-Hitachi Co., Ltd. F-term in the Kure Plant (reference) 4D002 AA02 AA12 AC01 BA02 BA03 BA14 BA16 CA01 CA13 DA05 DA07 DA16 EA02 EA09 FA03 GA01 GB03 GB06 HA03 HA08

Claims (3)

[Claims] 1. A denitration device, a dust collector, and an absorption tower in order from an upstream side of an exhaust gas passage to remove dust, nitrogen oxides, and sulfur oxides contained in exhaust gas from a combustion device such as a boiler. In a flue gas treatment device in which a heat recovery unit and a re-heater of a gas gas heater are arranged before and after the desulfurization device and the desulfurization device provided, an NH ₃ injection device for removing SO ₃ is provided with an exhaust gas at the inlet of the denitration device. Smoke exhaust, which is provided only in the flow channel, provided with a cleaning device in the GGH heat recovery device disposed in the exhaust gas channel at the dust collector inlet, and provided with a high-performance mist removal device at the outlet of the absorption tower. Processing equipment. 2. The smoke exhaust treatment device according to claim 1, wherein the high-performance mist removal device comprises a spray device for fine droplets and a mist eliminator. 3. The smoke exhaust treatment device according to claim 1, wherein the high-performance mist removal device uses a wet-type electrostatic precipitator.