JP2013034965A - Wet flue-gas treatment apparatus and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique preventing smoke dust from sticking to a GGH by lowering of SOconcentration in exhaust gas using alkali noticing SOin the exhaust gas of a boiler, in particular to attain high efficiency of a flue-gas treating system.SOLUTION: It becomes possible to prevent the GGH 6 from being occluded with the smoke dust in the exhaust gas or others while satisfying smoke dust concentration regulation by environment regulation to combustion exhaust gas of fossil fuel discharged from flue-gas treatment facilities to the air by spraying powdery alkali absorbent to an exhaust gas flowing path of an exhaust gas inlet side of the GGH 6 arranged while bridging the exhaust gas flowing paths of a front flowing side and a rear flowing side of the wet flue-gas treatment apparatus 7 arranged in the rear flowing side in a dust collector 4 arranged in the exhaust flowing path.

Description

  The present invention relates to a flue gas treatment system for exhaust gas discharged from a thermal power plant or factory, and more particularly to a wet flue gas desulfurization apparatus and method for reducing components and substances contained in SOx, dust and boiler fuel in the exhaust gas. .

FIG. 7 shows a general exhaust gas treatment system of a flue gas treatment system in a thermal power plant. In each figure, the same device is given the same number.
In FIG. 7, the exhaust gas from the boiler 1 is introduced into the denitration device 2, and after nitrogen oxides in the exhaust gas are removed, the air preheater 3 exchanges heat with the combustion air 21 supplied to the boiler 1. The exhaust gas whose gas temperature has been lowered to a certain temperature by the air preheater 3 is then introduced into the dust collector 4 to remove the dust in the exhaust gas. Thereafter, the exhaust gas is boosted by the fan 5 and is heat-exchanged with the wet exhaust gas desulfurization apparatus outlet gas in the gas gas heater (GGH) 6. The exhaust gas whose gas temperature has been reduced to a constant temperature by GGH 6 is then introduced into the wet flue gas desulfurization device 7, and sulfur oxides in the exhaust gas are removed by gas-liquid contact. The exhaust gas cooled to the saturated gas temperature in the wet flue gas desulfurization device 7 is heated in the GGH 6 and discharged from the chimney 8.

In the above-described prior art, the concentration of dust in the exhaust gas at the outlet of the dust collector 4 is generally 20 to 100 mg / m ³ N, although it varies depending on the power plant. The exhaust gas containing the dust is heat-exchanged by the GGH 6, and a part of the dust is removed by the desulfurization absorbing liquid sprayed in the wet flue gas desulfurization apparatus 7 and is discharged from the chimney 8. Soot and dust is generally removed to about 5 to 10 mg / m ³ N in the wet flue gas desulfurization apparatus 7.

  Due to the recent strengthening of environmental regulations, it is necessary to reduce the concentration of dust in the exhaust gas discharged from the chimney 8. As described above, the wet flue gas desulfurization apparatus 7 can remove the soot and can reduce it to a regulation value or less. However, when the rotary GGH6 is adopted as the GGH type, it is inevitable that a part of the untreated exhaust gas leaks to the desulfurization exhaust gas side. When the concentration of dust in the untreated exhaust gas in the rotary GGH6 is high, the wet exhaust gas Even if the soot concentration is lowered below the regulation value by the smoke desulfurization apparatus 7, the regulation value may not be satisfied in the chimney 8 due to the leakage of soot from the untreated exhaust gas side in the rotary GGH 6.

As a countermeasure, reducing the dust concentration in the exhaust gas at the outlet of the dust collector 4 in the exhaust gas flow path on the upstream side of the rotary GGH 6 to reduce the amount of dust leaking to the desulfurization exhaust gas side in the rotary GGH 6 Is possible. On the other hand, the untreated exhaust gas in which the gas temperature has decreased due to heat exchange in the rotary GGH 6 becomes sulfuric acid mist because SO ₃ contained in the exhaust gas becomes lower than the acid dew point. In the rotary GGH6, when the concentration of dust contained in the untreated exhaust gas is high, even if sulfuric acid mist adheres to the dust, the dust remains dry, but when the concentration of dust in the untreated exhaust gas is low It becomes moist, adheres on the heat exchange element of GGH6, and further dust adheres on the heat exchange element, thereby closing the heat exchange element and causing an increase in pressure loss. Thus, in GGH6, the ratio of soot and SO ₃ concentration is an important design factor, and in order to operate stably, the ratio of soot and SO ₃ concentration (D / S) is operated at a certain value or more. This is very important.

  On the other hand, even when the Tubular non-leakage type GGH6 is adopted as the model of GGH6, if the concentration of the dust in the untreated exhaust gas is low in the operation of the plant, the dust becomes wet and adheres to the surface of the heat transfer tube. There is a problem that causes an increase in loss.

Also, a denitration device, an air preheater, GGH, an electrostatic precipitator and a desulfurization device are arranged in this order from the upstream side in the boiler exhaust gas flow path, and calcium carbonate is introduced between the denitration device and the air preheater. There is an invention that discloses a method for removing high-concentration SO ₃ (Patent Document 1).

In addition, a NOx removal device, an air preheater, an electrostatic precipitator, a GGH and a desulfurization device are arranged in this order from the upstream side in the boiler exhaust gas flow path, and the dust exhausted from the boiler exhaust gas is placed between the electric dust collector and the GGH. In a flue gas treatment apparatus having a structure for charging powder, there is a problem that dust in the exhaust gas adheres to the GGH over time, and in particular, wetted SO ₃ adheres with the dust when the exhaust gas temperature decreases. Therefore, by introducing the same type of powder as dust into the exhaust gas flow path on the upstream side of GGH, the ratio of dusts is increased and the SO ₃ is kept dry without moistening the SO ₃ to the GGH heat transfer element. An invention has been disclosed that prevents adhesion of soot and dust and can be easily scraped off even if dust adheres to the heat transfer element of the GGH. Are (Patent Document 2).

Furthermore, by placing a denitration device, air preheater, GGH, dry dust collector and desulfurization device in order from the upstream side in the boiler exhaust gas flow path, by introducing alkali such as sodium carbonate between the GGH and the dry dust collector, An invention (Patent Document 3) in which SO ₃ in an exhaust gas that easily adsorbs mercury by reducing SO ₃ in the GGH outlet gas is reduced, and even a small amount of mercury in the exhaust gas is effectively adsorbed and removed by a dry dust collector. is there.

JP 2003-126649 A JP 2002-204925 A International Publication No. WO2008 / 078721

In the inventions described in the above Patent Documents 1 to ₃ , paying attention to SO ₃ in boiler exhaust gas, the concentration of SO ₃ is lowered using alkali powder or the like, so that dust or the like adheres to the air preheater, GGH or dust collector. This is a technology that prevents this.

  However, in the invention described in Patent Document 2, the ash collected by the electric dust collector is again put in front of the air preheater, and is collected and circulated by the electric dust collector. Electric dust collector has a large capacity. In addition, when ash is put in front of the electrostatic precipitator, the ash is collected by the wet flue gas desulfurization device, and the purity of the by-product gypsum is lowered. It is not desirable to put it in front of the vessel.

  Further, in the invention described in Patent Document 1, alkali powder is used, but it is put in front of the air preheater upstream of the electrostatic precipitator, and unreacted (unused) alkaline powder is collected by electrostatic precipitator. It is not an economical method because it is collected and disposed of in a container.

The problem of the present invention is to focus on SO ₃ in boiler exhaust gas by a technique different from the invention described in the above patent document, and reduce the concentration of SO _{3 in} exhaust gas using an alkali, so that dust adheres to GGH. This is a technology to prevent, and in particular, aims to improve the efficiency of the flue gas treatment system.

The above object of the present invention is achieved by the following means.
The invention described in claim 1 includes a dust collector for removing dust contained in exhaust gas discharged from a combustion apparatus such as a boiler, and a substance derived from sulfur oxides in the exhaust gas and components contained in the boiler fuel. A wet flue gas desulfurization device that is removed with a calcium carbonate-based desulfurization agent, and a GGH that is arranged over the exhaust gas flow path on the exhaust gas inlet side and the outlet side of the wet flue gas desulfurization device and performs heat exchange with the exhaust gas. In the flue gas treatment facility, an alkali absorbent charging part for spraying a powdery alkali absorbent is provided in the exhaust gas flow path downstream of the dust collector and in the exhaust gas flow path of the exhaust gas introduced into the GGH. This is a flue gas treatment facility.

The invention according to claim 2 comprises the GGH as the GGH, wherein the wet flue gas desulfurization device comprises a GGH for exchanging heat of the exhaust gas in each exhaust gas flow path of the exhaust gas inlet portion and the exhaust gas outlet portion of the wet flue gas desulfurization device. A soot concentration measuring device for measuring the soot concentration in the exhaust gas passage downstream from the GGH at the exhaust gas outlet of the exhaust gas in the exhaust gas passage upstream of the GGH at the exhaust gas inlet of the wet flue gas desulfurization device sO ₃ and sO ₃ concentration measuring apparatus for measuring the concentration provided, the two ratios of dust concentration to the sO ₃ concentration measured by the measuring device, the exhaust gas of the wet flue gas desulfurization apparatus to be larger than the preset value The flue gas treatment facility according to claim 1, further comprising a control device for charging an alkali absorbent from an alkali absorbent charging portion provided in an exhaust gas flow path at an inlet portion.

  According to the third aspect of the present invention, the dust contained in the exhaust gas discharged from the combustion apparatus such as the boiler is removed by a dust collector, and further, the substances resulting from the components contained in the sulfur oxide and the boiler fuel are wet-exhausted. A flue gas treatment method for removing heat with a calcium carbonate-based desulfurization agent in a flue gas desulfurization apparatus and exchanging heat with the flue gas by GGH arranged over the exhaust gas flow path on the exhaust gas inlet side and the outlet side of the wet flue gas desulfurization apparatus In the exhaust gas treatment method, the powdery alkali absorbent is sprayed on the exhaust gas flow path of the exhaust gas introduced into the GGH after removing the dust with the dust collector.

The invention according to claim 4 uses, as the GGH, a GGH that performs heat exchange of exhaust gas in each exhaust gas flow path of the exhaust gas inlet portion and the exhaust gas outlet portion of the wet flue gas desulfurization device. Measure the soot concentration in the exhaust gas flow path downstream of the GGH at the exhaust gas outlet and the SO ₃ concentration in the exhaust gas flow path upstream of the GGH at the exhaust gas inlet of the wet flue gas desulfurization device, Introducing an alkali absorbent into the exhaust gas flow path at the exhaust gas inlet of the wet flue gas desulfurization apparatus so that the ratio of the soot concentration to the SO ₃ concentration measured by the control device is greater than a preset value. It is a flue gas processing method of Claim 3 characterized by the above-mentioned.

(Function)
In the exhaust gas treatment facility and method of the present invention, the exhaust gas temperature in GGH is increased by spraying the powdered alkaline absorbent into the exhaust gas from which the dust is sufficiently removed in the dust collector in the exhaust gas flow channel upstream of the GGH. Even if sulfuric acid mist is generated at a temperature lower than the dew point, it is possible to prevent the sulfuric acid mist from adhering to the GGH heat exchange element by adhering to the powdery alkali absorbent, that is, to prevent the sulfuric acid mist from clogging.

As described above, in the invention described in Patent Document 2, the ash collected by the electric precipitator is again put in front of the air preheater, and is collected and circulated by the electric precipitator. For this reason, power for ash recirculation is required, and the electrostatic precipitator has a large capacity, whereas in the present invention, the alkaline powder is introduced in front of the electrostatic precipitator, Is economical because it passes through an electrostatic precipitator and is recovered by a wet flue gas desulfurization device and reused for SO ₂ removal.

  In addition, when ash is put in front of the electrostatic precipitator, the ash is collected by the wet flue gas desulfurization device, and the purity of the by-product gypsum is lowered. The body (such as calcium carbonate) is desirable.

  According to the first and third aspects of the present invention, the powdered alkali absorbent is sprayed on the exhaust gas flow path on the exhaust gas inlet side of the GGH, whereby the fossil fuel released from the flue gas treatment facility to the combustion exhaust gas is discharged. It is possible to prevent GGH from being clogged with soot and the like in exhaust gas while satisfying soot concentration regulation due to environmental regulations.

According to the second and fourth aspects of the invention, in addition to the effects of the first and third aspects of the invention, the dust concentration in the exhaust gas flow path downstream of the GGH and the exhaust gas flow upstream of the rotary GGH. based on the sO ₃ concentration in the road, the ratio of measured sO ₃ dust versus concentration concentration, larger than the ratio of the predetermined dust concentration / sO ₃ concentration of the alkaline absorption agent from the alkaline absorbent charged portion The exhaust dust concentration of the flue gas desulfurization facility does not exceed the regulation value by being introduced into the exhaust gas passage between the GGH and the wet flue gas desulfurization device.

It is a figure which shows the system | strain of the flue gas processing system used as this invention. It is a figure which shows rotation type GGH rotation among the flue gas processing systems used as this invention. It is a figure which shows GGH and the wet flue gas desulfurization apparatus circumference | surroundings among the flue gas processing systems used as this invention. It is a figure which sprays the powdery alkali absorbent used as the application example of this invention on the entrance-exit side of GGH. It is a figure which sprays the powdery alkali absorbent used as the application example of this invention on the entrance-outlet side of GGH, and sprays water on the exit side of GGH. It is a figure which sprays the powdery alkali absorbent used as the application example of this invention to the entrance side of GGH, and sprays the mixture of a powdered alkali absorbent and water to the exit side of GGH. It is a figure which shows the system | strain of the conventional smoke removal processing system. Is a diagram showing the relationship between D (dust concentration) / S (SO ₃ concentration) in the flue gas treatment system.

  A system diagram of a flue gas treatment system according to the present invention is shown in FIG.

  In FIG. 1, the exhaust gas from the boiler 1 is introduced into the denitration device 2, and after nitrogen oxides in the exhaust gas are removed, the air preheater 3 exchanges heat with the combustion air 21 for the boiler 1. The exhaust gas whose gas temperature has been reduced to a constant temperature by the air preheater 3 is then introduced into the dust collector 4 to remove the dust in the exhaust gas. Thereafter, the exhaust gas is pressurized by the fan 5, and the powdery alkali absorbent is introduced into the exhaust gas flow path from the powdery alkali absorbent charging equipment 9 and introduced into the GGH 6. The exhaust gas on the inlet side of the wet flue gas desulfurization device 7 has a gas temperature lowered to a constant temperature by heat exchange with the outlet gas of the wet flue gas desulfurization device 7 in the GGH 6, and is then introduced into the wet flue gas desulfurization device 7. The sulfur oxide in the exhaust gas is removed by gas-liquid contact. The exhaust gas cooled to the saturated gas temperature in the wet flue gas desulfurization device 7 is heated in the GGH 6 at the outlet of the wet flue gas desulfurization device 7 and discharged from the chimney 8.

FIG. 2 shows a configuration diagram around the rotary GGH 6. An SO ₂ · SO ₃ concentration meter 16 for measuring the SO ₂ concentration and SO ₃ concentration in the exhaust gas is disposed in the exhaust gas flow path on the upstream side of the rotary GGH 6, and FIG. 8 shows D (soot concentration) / S (SO ₃ (Concentration) curve.
In the Dry zone region of FIG. 8, the dust is kept dry and no clogging of the GGH6 element occurs, but in the Wet zone region, the dust becomes moistened and problems such as clogging of the GGH6 element occur. Therefore the raw exhaust gas inlet of the SO ₃ concentration of GGH6 measured, from dust concentration in the outlet gas of the D / S curve and dust collector 4 shown in FIG. 8, the powder necessary to keep the dust is dry The amount of charged alkaline absorbent is controlled. Moreover, since the SO ₃ concentration in the exhaust gas depends on the SO ₂ concentration in the exhaust gas and the oxidation rate of the denitration catalyst, it is possible to calculate the SO ₃ concentration based on the SO ₂ concentration at the untreated exhaust gas inlet on the GGH 6 inlet side. It is.

  On the other hand, as described above, in the rotary GGH 6 having the configuration shown in FIG. 2, the leakage of the exhaust gas from the untreated exhaust gas side to the treated exhaust gas side is unavoidable, and powdery alkali absorption sprayed on the untreated exhaust gas side of the rotary GGH 6 Part of the agent leaks into the treated exhaust gas and is treated as dust. Therefore, the dust concentration in the outlet gas of GGH6 is measured by the dust concentration meter 10 installed at the outlet of the treated exhaust gas side of the rotary GGH6. If the dust concentration in the outlet gas exceeds the regulation value by any chance. Is performed by the control device 23 for the spray amount of the powdered alkaline absorbent from the powdered alkaline absorbent charging equipment 9, so that the concentration of the outlet dust in the outlet gas of the GGH6 does not exceed the regulation value.

Here place the _SO 2 · SO ₃ concentration meter 16 for measuring the SO ₂ concentration and the SO ₃ concentration in the exhaust gas in the exhaust gas line of the upstream side of the rotary GGH6, SO ₂ · in the GGH6 inlet side exhaust gas Based on the SO ₃ concentration and the soot concentration in the outlet gas of GGH6, the control device 23 controls the outlet soot concentration in the outlet gas of GGH6 so as not to exceed the regulation value from the relationship shown in FIG.

  In the present invention, a Tubular type non-leakage type GGH of a type in which a heat medium made of a fluid flows between two GGHs instead of the rotary type GGH can be used.

  FIG. 3 shows a configuration around GGH 6 and wet flue gas desulfurization apparatus 7. By adding a powdery alkali absorbent such as calcium carbonate to the exhaust gas flow path before the upstream flow of GGH6, the apparent D / S passing through the GGH6 increases, and the dust in the exhaust gas remains dry. it can. Further, the powdery alkaline absorbent is removed from the exhaust gas by the absorbent 12 sprayed by the absorbent circulating pump 11 in the wet flue gas desulfurization apparatus 7 and taken into the absorbent 12. On the other hand, the wet flue gas desulfurization apparatus 7 also uses a slurry 13 in which a powdered alkali absorbent and water are mixed as a desulfurization absorbent, so that the powder taken into the absorbent 12 from the exhaust gas in the wet flue gas desulfurization apparatus 7. The gaseous alkali absorbent can be reused as a desulfurization absorbent.

Application examples of the present invention are shown in FIGS. 4, 5 and 6, respectively.
In the application example shown in FIG. 4, in addition to the exhaust gas channel on the inlet side of the rotary GGH 6, the powdered alkali absorbent is supplied from the powdered alkali absorbent charging facility 9 to the exhaust gas channel between the GGH 6 and the wet flue gas desulfurization device 7. By spraying, it becomes possible to remove part of the sulfur oxide in the exhaust gas flow path on the inlet side of the wet flue gas desulfurization apparatus 7. As a result, the concentration of sulfur oxide in the exhaust gas flow path on the inlet side of the wet flue gas desulfurization device 7 is lowered, and the desulfurization performance required in the wet flue gas desulfurization device 7 can be lowered. It becomes possible to reduce the capacity | capacitance of the absorption liquid circulation pump 11 of the apparatus 7. FIG.

  In addition to the exhaust gas channel on the inlet side of the rotary GGH 6, the application example shown in FIG. 5 is also applied to the exhaust gas channel between the GGH 6 and the wet flue gas desulfurization device 7 from the powdered alkaline absorbent charging equipment 9. Oxidation of sulfur in the exhaust gas in the exhaust gas flow path on the inlet side of the wet flue gas desulfurization device 7 by spraying the absorbent and further spraying water 14 to the exhaust gas flow channel between the GGH 6 and the wet exhaust gas desulfurization device 7 Part of the object can be removed. As a result, the sulfur oxide concentration in the exhaust gas on the inlet side of the wet flue gas desulfurization device 7 becomes low, and the desulfurization performance required in the wet flue gas desulfurization device 7 can be lowered. The capacity of the absorption liquid circulation pump 11 can be reduced.

  Furthermore, in the application example shown in FIG. 6, in addition to the exhaust gas flow channel on the inlet side of the rotary GGH 6, the powdered alkali absorbent and water mixture are also introduced into the exhaust gas flow channel between the GGH 6 and the wet flue gas desulfurization device 7. By spraying the mixture of the powdery alkaline absorbent and water from the facility 15, it becomes possible to remove a part of the sulfur oxide in the exhaust gas in the exhaust gas passage on the inlet side of the wet flue gas desulfurization apparatus 7. . As a result, the sulfur oxide concentration in the exhaust gas on the inlet side of the wet flue gas desulfurization device 7 becomes low, and the desulfurization performance required in the wet flue gas desulfurization device 7 can be lowered. The capacity of the absorption liquid circulation pump 11 can be reduced.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Denitration apparatus 3 Air preheater 4 Dust collector 5 Fan 6 GGH (gas gas heater)
7 Wet flue gas desulfurization device 8 Chimney 9 Powdered alkaline absorbent charging equipment 10 Dust concentration meter 11 Absorbent circulating pump 12 Absorbing liquid 13 Desulfurized absorbent slurry 14 Water 15 Powdered alkaline absorbent and water mixture charging equipment 16 SO ₂・ SO ₃ concentration meter 21 Combustion air 23 Controller

Claims (4)

A dust collector that removes soot and dust contained in exhaust gas discharged from a combustion apparatus such as a boiler, and a substance derived from sulfur oxides in the exhaust gas and components contained in boiler fuel are removed with a calcium carbonate desulfurization agent. In a flue gas desulfurization device and a flue gas treatment facility provided with a GGH that is arranged over an exhaust gas flow path on the exhaust gas inlet side and the outlet side of the wet flue gas desulfurization device and performs heat exchange with the exhaust gas,
An exhaust gas flow path on the downstream side of the dust collector, the exhaust gas flow path of the exhaust gas introduced into the GGH is provided with an alkali absorbent charging portion for spraying a powdery alkaline absorbent. Smoke treatment equipment. The GGH is composed of GGH that performs heat exchange of the exhaust gas in each exhaust gas flow path of the exhaust gas inlet portion and the exhaust gas outlet portion of the wet flue gas desulfurization device, and from the GGH in the exhaust gas outlet portion of the wet flue gas desulfurization device SO ₃ for measuring the SO ₃ concentration before downstream side of the exhaust gas flow path from the GGH in the exhaust gas inlet part of the dust concentration measuring device for measuring the dust concentration and the wet type exhaust gas desulfurization system on the downstream side end of the exhaust passage A concentration measuring device is provided, and the ratio of the soot concentration to the SO ₃ concentration measured by the two measuring devices is set in the exhaust gas flow path at the exhaust gas inlet of the wet flue gas desulfurization device so as to be larger than a preset value. The flue gas treatment facility according to claim 1, further comprising a control device for charging the alkali absorbent from the provided alkali absorbent charging section. Dust contained in exhaust gas discharged from combustion equipment such as boilers is removed by a dust collector, and substances derived from sulfur oxides and components contained in boiler fuel are further removed in a wet flue gas desulfurization system. In the flue gas treatment method in which heat is exchanged with the exhaust gas in the GGH disposed over the exhaust gas flow path on the exhaust gas inlet side and the outlet side of the wet flue gas desulfurization apparatus,
A method for treating flue gas, comprising: spraying a powdery alkali absorbent on an exhaust gas flow path of exhaust gas introduced into the GGH after dust is removed by the dust collector. As the GGH, GGH that performs heat exchange of the exhaust gas in each exhaust gas flow path of the exhaust gas inlet portion and the exhaust gas outlet portion of the wet flue gas desulfurization device is used, and after the GGH in the exhaust gas outlet portion of the wet flue gas desulfurization device. The soot concentration in the exhaust gas flow channel on the flow side and the SO ₃ concentration in the exhaust gas flow channel on the upstream side of the GGH at the exhaust gas inlet of the wet flue gas desulfurization device are measured, and the measured SO is measured by the control device. _The alkali absorbent is introduced into the exhaust gas flow path of the exhaust gas inlet of the wet flue gas desulfurization apparatus so that the ratio of the soot concentration to the ₃ concentration is larger than a preset value. Smoke treatment method.

Images