JPH1176750A - Flue gas treating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with steam to be supplied for evaporation and concentration by providing a heat exchanger for recovering heat from a heating medium on the midway to be fed to a heat recovering part from a re-heating part of a non-leak gas gas heater. SOLUTION: The heat exchanger 31 for recovering heat from the heating medium W to be fed to the heat recovering part 1a from the re-heating part 3 of the non-leak gas gas heater is provided. As a result, the heat exchanger 31 functions as a heater for a circulating slurry for the evaporation and concentration in an evaporator 13, a part of the heat energy of the flue gas is used for the evaporation and concentration and the requirement of the supply of steam is eliminated. That is, as the circulating quantity of the heating medium W is about 1,000 t/h and the temp. of the heating medium W is about 75-80 deg.C at the outlet in the case of a 100 MW thermal power plant, the circulating slurry composed of a desulfurization waste water is heated to about 59 deg.C and the temp. of the heat transfer surface is kept at <=70 deg.C to prevent the generation of gypsum scale.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flue gas treatment facility for performing desulfurization treatment of flue gas containing at least sulfur dioxide gas and performing treatment by evaporative concentration of desulfurization waste water discharged in connection with the desulfurization treatment. More particularly, the present invention relates to a flue gas treatment facility provided with a non-leak gas gas heater of a heat medium circulation type as a gas gas heater for cooling and reheating flue gas.

[0002]

2. Description of the Related Art Generally, smoke from a boiler in a thermal power plant or the like contains sulfur oxides represented by sulfurous acid gas, and must be released into the atmosphere after desulfurization to prevent air pollution. . Conventionally, as a desulfurization apparatus therefor, for example, a wet desulfurization apparatus based on a lime gypsum method that absorbs sulfurous acid gas using a calcium compound such as limestone as an absorbent and produces industrially useful gypsum has been widely used. In addition, as a treatment apparatus for performing post-treatment of so-called desulfurization wastewater discharged from the desulfurization apparatus, the desulfurization wastewater is treated by evaporative concentration using an evaporator to reduce CO2.
2. Description of the Related Art A wastewater treatment apparatus that does not discharge a effluent requiring advanced wastewater treatment including D, heavy metal, and nitrogen treatment (a so-called non-wastewater treatment apparatus) is known.

FIG. 2 is a diagram showing a conventional example of a flue gas treatment facility including a wet desulfurization apparatus based on the lime-gypsum method as described above and a wastewater treatment apparatus for evaporating and concentrating, and this facility will be described below. The untreated flue gas A discharged from the boiler of the thermal power generation equipment and introduced through an air heater (not shown) is usually 130 to 150 ° C., and firstly, the heat recovery unit 1 of a non-leak gas gas heater (GGH) of a heat medium circulation type. And is cooled to a temperature of, for example, 90 to 110 ° C., and then introduced into the desulfurization device 2 as flue gas A1. The non-leak type gas heater has a structure in which smoke is not leaked outside the system or into the heat medium.

[0004] In the desulfurization device 2, an absorbent slurry containing, for example, limestone as an absorbent, and flue gas A come into gas-liquid contact in an absorption tower (not shown), so that at least sulfur dioxide (SO ₂ ) is removed from the flue gas. You. Here, the flue gas is cooled to the dew point of water by the gas-liquid contact, and usually has a temperature of about 50 ° C. Next, the flue gas is sent to a reheating unit 3 of a gas gas heater (GGH), where the flue gas is heated to a high temperature (usually about 90 ° C.) which is more preferable for atmospheric release.
From the chimney not shown.

[0005] In the desulfurization unit 2, the absorbent slurry that has absorbed the sulfurous acid gas is oxidized in a tank (not shown) formed at the bottom of the absorption tower, and further causes a neutralization reaction to become a gypsum slurry containing gypsum. The gypsum slurry is extracted from the tank, and gypsum solid content is separated by a gypsum separation solid-liquid separation unit (for example, a vacuum belt filter) of the desulfurization apparatus 2. At this time, a part of the filtrate discharged from the solid-liquid separation means is reused as a liquid component constituting the absorbent slurry, and the remainder is discharged out of the system as desulfurization wastewater C1 to prevent accumulation of impurities.

In this case, the heat medium W (usually water) of the gas gas heater circulated by the heat medium circulation pump 4 is also heated by the heat of the steam D in the heat medium heater 5 in this case. To be heated. Further, a reservoir tank (not shown) for storing the heat medium W is connected to the suction side of the heat medium circulation pump 4 so as to absorb pressure fluctuations of the heat medium circulation system.

For example, in the case of a 1000 MW thermal power generation facility, the steady-state circulation flow rate of the heat medium is 1000 t /
h and the temperature of the circulating heat medium is
About 75 to 80 ° C. at the outlet of the heat recovery unit 1 or at the inlet of the reheating unit 3
It is about.

Next, post-treatment of the desulfurization waste water C1 is performed by a waste water treatment device including a pre-treatment device 11 without discharging a discharged liquid in this case. That is, the desulfurization effluent C1 is first introduced into the pretreatment device 11, where pretreatment including coagulation sedimentation and the like is performed, and as a desulfurization effluent C2 from which suspended solids are removed, the evaporative concentration circulation line is used. 12 is sent.
The evaporating and condensing circulation line 12 is a piping line in which a part of the slurry C3 collected at the bottom of the evaporator 13 is forcibly circulated by the evaporator circulation pump 14. Then, the sent desulfurization wastewater C2 is sent to a nozzle 16 in an evaporator 13 through a heater 15 (heat exchanger) via the evaporative concentration circulation line 12 together with a part of the slurry C3, 13 and the water evaporates.

Here, the heater 15 is a so-called shell-and-tube heat exchanger for heating the circulating slurry composed of the desulfurization wastewater C2 by the supplied high-temperature steam E. For example, in the case of a thermal power generation facility of 1000 MW, the circulating flow rate at steady state by the evaporator circulation pump 14 is about 1000 m ³ / h, the temperature of the circulation slurry is about 55 ° C. at the inlet of the heater 15, Exit 15 at 59
It is about ° C. The upper part of the evaporator 13 is provided with a condenser 17.
And connected to the vacuum pump 18 at 55 ° C.
The pressure is set to a negative pressure (about 0.2 ata) so that the water evaporates by heating from about 30 ° C. to about 59 ° C.

[0010] Since the desulfurization wastewater C2 is a gypsum saturated solution, the solid content of gypsum may precipitate on the heat transfer surface of the heater 15 and form a scale, which may be fixed.
According to the applicant's research, it has been found that such a scale can be prevented by the following operations. That is, as a so-called seed crystal for promoting crystallization of gypsum in the slurry C3 of the evaporator 13, for example, gypsum recovered by the desulfurization unit 2 is at least 4000 pp in the desulfurization wastewater C2.
m, and the temperature of the steam E may be controlled so that the temperature of the heat transfer surface in the heater 15 is 70 ° C. or less.

The water C4 (steam) of the slurry C3 evaporated in the evaporator 13 is cooled by the cooling water F in the condenser 17 and condensed, and recovered as high-purity water C5 containing almost no gypsum. It is stored in a tank 19. The water C5 in the recovery tank 19 is reused, for example, as makeup water constituting the absorbent slurry of the desulfurization device 2.

On the other hand, the slurry C collected at the bottom of the evaporator 13
Reference numeral 3 denotes a concentrated slurry containing a large amount of dissolved salts precipitated by the evaporation of water, and a part of the concentrated slurry is sequentially drawn out by a slurry pump 20. In this case, the water is further removed by a dryer 21 to remove solids G. Will be collected as In this case, a drum dryer type dryer is used as the dryer 21. Further, the slurry C3 extracted from the bottom of the evaporator 13 can be mixed with dust or cement such as fly ash collected from flue gas by a dust remover (not shown) and solidified.

[0013]

By the way, the above-mentioned conventional flue gas treatment equipment is excellent in that the desulfurization wastewater is evaporated and concentrated by the evaporator to eliminate the discharge liquid as described above. However, from the viewpoint of further improving economic efficiency, there are the following problems to be improved.

That is, in order to evaporate water in the evaporator 13, a large amount of heat energy corresponding to the latent heat is required, and a large amount of steam E is required. Was a major obstacle for For example, in the case of a 1000 MW thermal power generation facility, about 10 t / h of steam E to be supplied to the heater 15 is required.

Accordingly, the present invention provides a desulfurization apparatus, a wastewater treatment apparatus for evaporating and condensing desulfurization wastewater from the desulfurization apparatus,
It is an object of the present invention to provide a flue gas treatment facility including a heat medium circulation type non-leak gas gas heater, which eliminates the need for steam conventionally supplied for evaporation and concentration.

[0016]

In order to achieve the above object, a flue gas treatment facility of the present invention comprises a desulfurization device for bringing flue gas into gas-liquid contact with an absorbent slurry to absorb at least sulfur dioxide in the flue gas. A desulfurization treatment system that evaporates and concentrates a desulfurization wastewater obtained by extracting a part of the liquid constituting the absorbent slurry of the desulfurization device with an evaporator, and a heat recovery unit provided upstream of the desulfurization device. A flue gas treatment facility having a heat medium circulation type non-leak gas gas heater for recovering heat from smoke and reheating flue gas after desulfurization processing by a reheating unit provided downstream of the desulfurization device with the recovered heat; In the above, a heat exchanger for recovering heat from a heating medium being sent from a reheating unit to a heat recovery unit of the non-leak gas gas heater is provided as a heater for heating the desulfurization wastewater for evaporation in the evaporator. Features To.

[0017]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of the smoke exhaust treatment facility of the present embodiment. The same elements as those in the conventional configuration shown in FIG. 2 are denoted by the same reference numerals, and redundant description will be omitted.

The present embodiment is characterized in that a heat exchanger 31 for recovering heat from the heating medium W being sent from the reheating unit 3 of the non-leak gas gas heater to the heat recovery unit 1a is provided instead of the conventional heater 15. It is characterized by having. In addition, it is preferable that the capacity (heat transfer area) of the heat recovery unit 1a of the non-leak gas gas heater be slightly larger than that of the conventional heat recovery unit, as described later. In this case, a bypass line that does not pass through the heat exchanger 31 is provided, and the flow control valve 32 is connected to the bypass line.

In the flue gas desulfurization facility of the present embodiment, the heat exchanger 3
1 sufficiently functions as a heater for a circulating slurry for evaporating and condensing in the evaporator 13 and consequently heat energy of flue gas (which has been conventionally used for evaporating water during gas-liquid contact in a desulfurizer). ) Is used for heating for evaporative concentration, so that there is no need to supply steam E as in the conventional case, and the amount of steam used as a whole equipment can be greatly reduced.

That is, for example, in the case of a thermal power generation facility of 1000 MW, the circulation flow rate of the heat medium W is about 1000 t / h, and the temperature of the heat medium W
Since the temperature is about 5 to 80 ° C., the heat exchanger 31 can sufficiently heat the circulating slurry composed of the desulfurization wastewater to the above-mentioned temperature (about 59 ° C.) and raise the temperature of the heat transfer surface to 70 ° C.
It is also possible to prevent the above-mentioned gypsum scale from being generated by maintaining the temperature below ℃.

The temperature of the heat medium W at the inlet of the heat recovery unit 1a of the gas gas heater is reduced to about 70 to 75 ° C. by heat absorption in the heat exchanger 31 as a result, and as a result, the heat recovery unit 1a Even if the capacity of the heat recovery unit is the same as the conventional one, the heat recovery effect (cooling performance) increases, and the smoke discharge temperature at the smoke discharge outlet of the heat recovery unit 1a increases from approximately 110 ° C. to 105 ° C.
To a degree.

On the other hand, the temperature of the heat medium W at the outlet of the heat recovery unit 1a is slightly lower than the conventional one due to the increase of the heat recovery effect in the heat recovery unit 1a, and hardly causes any problem. In addition, in the desulfurization device 2, the flue gas is cooled until it is saturated with water vapor generated by evaporating the moisture of the absorbent slurry (that is, to the dew point of water), so the flue gas outlet of the heat recovery unit 1a (that is, the desulfurization device) (Inlet side 2), the flue gas temperature is 110
Even if the temperature is lowered from about ℃ to about 105 ℃, the temperature on the outlet side of the desulfurization apparatus 2 hardly changes, which is not a problem.

In addition, the fact that the exhaust gas temperature at the inlet side of the desulfurization unit 2 drops from about 110 ° C. to about 105 ° C. in the desulfurization unit 2 rather accelerates the absorption reaction of the sulfur dioxide gas in the desulfurization unit 2 and improves the performance of the desulfurization treatment. And the effect of reducing the amount of evaporation of water due to the gas-liquid contact between the smoke exhaust and the absorbent slurry, so that the amount of makeup water in the desulfurization apparatus 2 can be reduced (the amount of industrial water used can be reduced).

Therefore, according to the configuration of this embodiment, the heat energy of the exhaust gas is effectively used for heating for evaporative concentration in the evaporator 13 and the heat balance of the gas gas heater and the like is obtained. In addition to having little effect on the performance of the desulfurization treatment and improving the desulfurization performance, instead of the conventional heater 15 for evaporative concentration, the heating medium W is replaced with the high-temperature side fluid in the conventional equipment. By performing a very simple design change or modification such as adding a pipe line for flowing the heat medium W through the heat exchanger 31 to be used, the amount of steam used is significantly smaller than before, The practically excellent effect that desulfurization treatment having substantially the same or higher performance and wastewater treatment associated therewith can be performed can be obtained.

In order to keep the temperature of the heat medium W at the inlet of the reheating unit 3 of the gas gas heater unchanged at all compared with the conventional case, it is necessary to increase the capacity (heat transfer area) of the heat recovery unit 1a slightly. The flow rate of the steam D in the heating medium heater 5 may be slightly increased. In this way, the temperature of the exhaust gas B after treatment can be maintained exactly the same as before, and in this case,
As a whole, the amount of heat recovered from the flue gas is increased, so that a large reduction in the amount of used steam is realized.

In this case, the amount of evaporation in the evaporator 13 due to the variation in the amount of the desulfurized wastewater C1 is controlled by operating the opening of the flow rate control valve provided in the bypass line to the heat exchanger 31. It is easily possible by adjusting the flow rate of the heat medium W.

[0027]

In the flue gas treatment equipment of the present invention, the heat exchanger functions sufficiently as a heater for evaporative concentration in the evaporator, and as a result, the heat energy of the flue gas (at the time of gas-liquid contact in the desulfurization unit). A part of the water used for evaporation of water) is used for heating for evaporative concentration, eliminating the need to supply steam for evaporative concentration as in the past. Overall steam usage can be significantly reduced.

Further, since the temperature of the flue gas at the inlet side of the desulfurization unit is lower than before, the absorption reaction of the sulfur dioxide gas in the desulfurization unit is rather accelerated to improve the performance of the desulfurization treatment. Since it has the effect of reducing the amount of evaporation of water due to gas-liquid contact, it is possible to realize a reduction in the amount of makeup water in the desulfurization device (a reduction in the amount of industrial water used).

Therefore, according to the present invention, a heat exchanger using a heat medium of a gas gas heater as a high-temperature side fluid is provided in place of the conventional heater for evaporative concentration with respect to the conventional equipment,
By making a very simple design change or modification, such as adding a piping line for flowing the heat medium of the gas gas heater, the amount of steam used is much smaller than before, and the performance is almost the same as or higher than the conventional one. A practically excellent effect that desulfurization treatment and accompanying wastewater treatment can be performed is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire configuration of a flue gas treatment facility as an example of the present invention.

FIG. 2 is a diagram showing an entire configuration of a conventional smoke exhaust treatment facility.

[Explanation of symbols]

 1a Heat recovery unit of gas gas heater 2 Desulfurization unit 3 Reheating unit of gas gas heater 13 Evaporator 31 Heat exchanger C1 Desulfurization wastewater W Heat medium

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Susumu Okino 4-6-22 Kannonshinmachi, Nishi-ku, Hiroshima-shi, Hiroshima Inside Hiroshima Research Laboratory, Mitsubishi Heavy Industries, Ltd.

Claims (1)

[Claims] 1. A desulfurization apparatus for bringing flue gas into gas-liquid contact with an absorbent slurry to absorb at least sulfur dioxide in the flue gas, and desulfurization by extracting a part of a liquid constituting the absorbent slurry of the desulfurization apparatus. A wastewater treatment device for evaporating and condensing wastewater by an evaporator and a heat recovery unit provided upstream of the desulfurization device recovers heat from the flue gas, and the recovered heat is provided downstream of the desulfurization device. In a flue gas treatment facility having a heat medium circulation type non-leak gas gas heater for reheating flue gas after desulfurization treatment by a reheating unit, as a heater for heating desulfurization waste water for evaporation in the evaporator, A flue gas treatment facility comprising a heat exchanger for recovering heat from a heat medium being sent from a reheating section of a non-leak gas gas heater to a heat recovery section.