JPH06246131A - Method and device for wet type flue gas desulfurization - Google Patents

Abstract

PURPOSE:To simplify a gypsum recovery system and to sharply reduce the cost of a desulftrizer and its operating cost by discharging gypsum contg. slurry waste liquid from an oxidizing tank in the lower part of an absorber, mixing the coal ash collected by a dust collector with it and making the mixture a solid waste having specified moisture concentration CONSTITUTION:SO2 contg. waste combustion gas enters, from a duct 1, a dust collector 2, where coal ash in the waste gas is separated and removed to be delivered to a coal ash/gypsum slurry mixer 29 from a discharge pipe 3. And a part of slurry waste liquid mainly consisting of gypsum in an oxidizing tank 22 enters, through a slurry waste liquid draw-out pipe 23, a liquid cyclone 25. where gypsum in the slurry waste liquid is concentrated to form gypsum slurry of high concentration. The gypsum slurry enters, from a concentrated gypsum slurry feed pipe 26, to the coal ash/gypsum slurry mixer 29, where slurry waste liquid contg. coal ash and gypsum is uniformly mixed to turn into solid waste adjusted to have moisture concentration of <=30wt.% which is discharged from a waste discharge pipe 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet flue gas desulfurization method and apparatus, and more particularly to a wet flue gas desulfurization method suitable for treating by-product gypsum in a slurry absorbing liquid in an oxidation tank of a desulfurization tower and its method. Regarding the device.

[0002]

2. Description of the Related Art Sulfur oxides, especially sulfur dioxide (SO ₂ ) in flue gas generated by combustion of fossil fuels in thermal power plants is one of the main environmental problems such as air pollution and acid rain. It is one of the causes. For this reason, SO ₂
Research on flue gas desulfurization method for removing methane and development of desulfurization equipment have become extremely important issues. As the desulfurization method, recently, a simple dry desulfurization device having a low cost and a simple system has been developed, but the desulfurization rate is at most 70-80.
%, The wet desulfurization method still predominates. This wet method includes a soda method using a soda compound as an absorbent, a calcium method using a calcium compound, and a magnesium method using a magnesium compound. Among them, the soda method is excellent in reactivity between the absorbent and SO ₂ , but has a problem that soda used is very expensive. For this reason, a method using a relatively inexpensive calcium compound such as calcium carbonate is most often used in a flue gas desulfurization apparatus such as a large-scale boiler for power generation.
Desulfurization systems using this calcium compound as an absorbing liquid are roughly classified into three types, a spray system, a wetting wall system, and a bubbling system, depending on the difference in gas-liquid contact method. Each of the above-mentioned methods has its own characteristics, but the spray method, which has the most achievements and high reliability, is widely adopted worldwide. For this spray type desulfurization system,
Conventionally, it is mainly configured by a cooling tower for cooling and removing dust of exhaust gas, an absorption tower for spraying an absorbing liquid to react with SO ₂ in the exhaust gas, and an oxidizing tower for oxidizing calcium sulfite produced in the absorption tower. However, in recent years, the development of a one-tower type desulfurization tower in which the absorption tower has functions of cooling and oxidation has progressed, and recently, the one-tower type desulfurization system has become the mainstream of the spray type desulfurization apparatus. FIG. 3 shows an example of the configuration of a conventional one-column tower desulfurization system using a spray method. This system is a one-tower type desulfurization tower 8, a dust collector 2, a gas / gas heater 5, a neutralization tank 12, a thickener 13, a dehydrator 16,
The wastewater treatment device 19 is mainly configured. The exhaust gas discharged from the boiler enters the dust collector 2 from the duct 1,
Dust, which is coal ash, is removed. The coal ash separated and removed here is discharged from the ash discharge pipe 3 to the outside of the system. The exhaust gas from which the coal ash has been removed enters the gas / gas heater 5, heats the moisture-saturated exhaust gas sent from the exit duct 7, and sends it to the chimney from the exit duct 4. On the other hand, the heat-exchanged exhaust gas enters the desulfurization tower 8 through the inlet duct 6. In the desulfurization tower 8, the slurry absorption liquid containing calcium carbonate sent from the slurry absorption liquid circulation pump 11 is sprayed from a plurality of spray nozzles 9, and the slurry absorption liquid and the exhaust gas are brought into gas-liquid contact.
The spray nozzles 9 are arranged in a plurality in the horizontal direction and in a plurality of stages in the height direction, and usually one slurry absorbing liquid circulation pump 11 is installed in each stage. Generally, the number of stages of the spray nozzle 9 is often about 4 to 10, but in FIG. 3, two stages are shown for simplification. Here, the slurry absorbing liquid selectively absorbs SO ₂ in the exhaust gas, and calcium bisulfite [Ca (HS
O ₃ ) ₂ ]. Fine calcium carbonate (limestone) which is an absorbent is supplied from the limestone supply pipe 24 to the oxidation tank 22.
Supplied within. The slurry absorbing liquid that has generated calcium bisulfite is accumulated in the oxidation tank 22, and the calcium sulfite in the slurry absorbing liquid is oxidized by the air supplied from the air blowing pipe 21 to generate gypsum (CaSO ₄ ). A part of the slurry absorbing liquid in the oxidation tank 22 in which calcium carbonate (CaCO ₃ ) and gypsum coexist is sent to the spray nozzle 9 again by the slurry absorbing liquid circulating pump 11, and a part of the slurry absorbing liquid is discharged from the slurry waste liquid discharging pipe 23. -Sent to the gypsum recovery system. The reaction in the desulfurization tower is shown below. (Reaction in spray section) SO ₂ + H ₂ O → H ₂ SO ₃ (Chemical formula 1) CaCO ₃ + 2H ₂ SO ₃ → Ca (HSO ₃ ) ₂ + CO ₂ + H ₂ O ... (Chemical formula 2) Ca (HSO ₃ ) ₂ + O ₂ + 2H ₂ O → CaSO ₄・ 2H ₂ O + H ₂ SO ₄ (1 part) (Chemical formula ₃ ) (Reaction in oxidation tank) Ca (HSO ₃ ) ₂ + O ₂ + 2H ₂ O → CaSO ₄・ 2H ₂ O + H ₂ SO ₄ ...... (Chemical formula 4) CaCO ₃ + H ₂ SO ₄ + H ₂ O → CaSO ₄・ 2H ₂ O + CO ₂ …… (Chemical formula 5) The gypsum produced in the oxidation tank 22 is extracted as a slurry waste liquid and neutralized. After neutralizing by adding alkali in tank 12,
The thickener 13 deposits gypsum particles in the slurry waste liquid.
In the neutralization tank 12, caustic soda is usually added as a neutralizing agent, so that it must be uniformly stirred by a stirrer. Then, by uniformly stirring, the chlorine and fluorine compounds accumulated in the slurry waste liquid are neutralized, and it is possible to prevent chlorine compounds and fluorine compounds from depositing in the oxidation tank 22. Under normal desulfurization operating conditions,
The large particle size of gypsum in the slurry waste liquid is about 50 μm, and the small particle size is about several μm. for that reason,
Thickener should be deposited for a sufficient time, eg 5
The diameter of the thickener in the desulfurization equipment of a 00 MW thermal power plant is about 10 m. The concentrated gypsum slurry enters the dehydrator 16 through the gypsum slurry discharge pipe 15. Here, the gypsum is finally solid-liquid separated and discharged from the gypsum discharge pipe 18 for processing. When the gypsum is dehydrated and treated as a solid waste, the water content in the gypsum needs to be 10% or less, so the processing time of the slurry absorbing liquid in the dehydrator 16 must be lengthened, and 500 MW is required. In a large scale plant, 5 to 10 dehydrators 16 are required. The drainage generated in the dehydrator is partially returned from the return pipe 17 to the oxidation tank 22, and the other is sent together with the supernatant liquid of the thickener 13 to the drainage treatment device 19 to be detoxified and then the drainage pipe 2
It is discharged from 0 to the outside of the system. As shown in FIG. 3, the conventional desulfurization system has a very complicated system of gypsum recovery system and many reaction tanks, and the installation area is the same as the absorption system of SO ₂ in order to arrange the desulfurization system. It was necessary to make it compact and manageable. In Japan, gypsum is used as a raw material for gypsum board, etc. instead of being a waste, and thus the above-mentioned complicated gypsum recovery system is required. However, many coal-fired boilers are being constructed or planned in anticipation of future power demand, and when a wet limestone-gypsum desulfurization unit is built, the gypsum supply will exceed demand. ,
It is expected that gypsum will also be treated as waste. Further, even in foreign countries, there are few cases where only gypsum is collected, and it is desired to make the gypsum collection system as compact as possible on the basis of discarding. As conventional techniques, for example, JP-A-55-97225 and JP-A-3-8411.
No. Gazette and the like.

[0003]

SUMMARY OF THE INVENTION In the above-mentioned prior art, when recovering the gypsum produced in the oxidation tank, a neutralization tank, thickener, dehydrator, wastewater treatment facility, etc. are provided in order to recover only the gypsum alone. It is necessary, the desulfurization process is complicated, a large area for installing these equipments is required, and the power cost to operate these equipments is also extra. The recovery system should be as simple as possible, equipment cost,
It was necessary to reduce the installation area and operating power costs.

An object of the present invention is to provide a wet flue gas desulfurization method and an apparatus thereof in which the desulfurization process is extremely simple by omitting the gypsum recovery system of the wet flue gas desulfurization apparatus and treating the gypsum produced as a solid waste. To provide.

[0005]

In order to achieve the above object of the present invention, a slurry waste liquid containing gypsum is discharged from an oxidation tank provided in the lower part of an absorption tower of a wet flue gas desulfurization apparatus, and a dust collector The solid waste is prepared by mixing the coal ash collected in 1. and adjusting the water concentration in the mixture to 30% (weight) or less. Desirably, if the water concentration in the mixture is set to about 25%, the handling as solid waste becomes easier. If the water content of the waste, which is a mixture of coal ash and gypsum slurry, greatly exceeds 30%, no problem will occur if the gypsum slurry concentration is concentrated by a liquid cyclone or the like and then mixed with coal ash. Also, if the pH of the slurry absorption waste liquid is low, or if chlorine compounds or fluorine compounds are present and it is necessary to add additives (neutralizing agents, etc.), add the additives in the high-concentration slurry liquid line at the liquid cyclone outlet. This eliminates the need to newly install a neutralization tank or the like. Therefore, in the wet flue gas desulfurization apparatus of the present invention, the gypsum recovery system can be largely omitted, and at the same time, the desulfurization operation cost can be significantly reduced. The present invention is a desulfurization tower that absorbs and removes sulfur oxides in exhaust gas by gas-liquid contact with exhaust gas containing sulfur oxides discharged from a combustion device that uses coal as fuel, and a slurry absorbing liquid that contains calcium carbonate, At least one oxidation tank for storing the reacted slurry absorbing solution in the lower part of the desulfurization tower and oxidizing it to produce gypsum, and wet flue gas for desulfurization by recirculating the slurry absorbing solution from the oxidation tank to the desulfurization tower In the desulfurization method, a slurry waste liquid containing gypsum is discharged from the oxidation tank, and mixed with coal ash collected by the exhaust gas system of the combustion device to prepare a solid waste having a water concentration of 30% by weight or less. It is a wet flue gas desulfurization method. Then, in the wet flue gas desulfurization method of the present invention, after separating and removing water from the slurry waste liquid containing gypsum and concentrating the gypsum, mixing and adjusting with coal ash to obtain a solid waste having a water concentration of 30% by weight or less. You can also It also includes a step of recirculating the low-concentration slurry absorption liquid, which is obtained by separating gypsum from the slurry waste liquid, into the oxidation tank. Further, according to the amount of coal ash collected in the exhaust gas system of the combustion apparatus, the amount of slurry waste liquid containing gypsum discharged from the oxidation tank is adjusted and controlled to form solid waste having a water concentration of 30% by weight or less. You can also Moreover, after separating the water content of the slurry waste liquid containing gypsum and adding a neutralizing agent to the concentrated gypsum slurry, coal ash is added to adjust the mixture to obtain a solid waste having a water content of 30% by weight or less. Is also possible. The present invention is a desulfurization tower that absorbs and removes the above sulfur oxides by gas-liquid contacting an exhaust gas containing sulfur oxides discharged from a combustion device that uses coal as a fuel, and a slurry absorbing liquid that contains calcium carbonate. At least 1 that accumulates the reacted slurry absorption liquid in the lower part of the desulfurization tower and oxidizes it to form gypsum
A wet flue gas desulfurization device comprising at least one oxidation tank and a means for recirculating the slurry absorbing liquid from the oxidation tank to a desulfurization tower, which discharges the coal ash collected in the exhaust gas system of the combustion device. At least a mixer for mixing and controlling a pipe, a discharge pipe for discharging a slurry waste liquid containing gypsum from an oxidation tank, and a coal ash discharged from the above-mentioned coal ash discharge pipe to adjust and control the water concentration to 30% by weight or less. It is a wet flue gas desulfurization device provided. Furthermore, the wet flue gas desulfurization apparatus of the present invention comprises a discharge pipe for discharging the coal ash collected in the exhaust gas system of the combustion device, a discharge pipe for discharging the slurry waste liquid containing gypsum from the oxidation tank, and a discharge of the slurry waste liquid. From a liquid cyclone that produces concentrated gypsum slurry from the slurry waste liquid provided at the outlet of the pipe, a pipeline mixer that supplies additives to the concentrated gypsum slurry and mix in the pipeline, and from the pipeline mixer A mixer is provided for mixing the concentrated gypsum slurry containing the discharged additive and the coal ash discharged from the coal ash discharging pipe to adjust and control the water concentration to 30% by weight or less.

[0006]

[Function] In the conventional wet flue gas desulfurization method, the gypsum produced in the oxidation tank of the absorption tower is individually recovered, so the process of the gypsum recovery system is complicated, and the equipment cost and the operating cost occupy a large proportion. . On the other hand, if the present invention is applied, it can be disposed of as solid waste simply by mixing the coal ash and the gypsum slurry liquid at a predetermined ratio, so that the gypsum recovery system of the desulfurization device can be greatly simplified. You can Further, when the additive is added, it is not necessary to newly install a neutralization tank by setting a line mixer for mixing in the pipe between the additive supply port and the coal ash and gypsum slurry mixer.

[0007]

Embodiments of the present invention will be described below in more detail with reference to the drawings. FIG. 1 is a schematic diagram showing an example of the configuration of the wet flue gas desulfurization apparatus of the present invention. In the figure, S
The combustion exhaust gas containing O ₂ enters the dust collector 2 from the duct 1,
Here, the coal ash in the exhaust gas is removed. As the dust collector 2, an electric dust collector or a multi-cyclone dust collector is generally used. The coal ash separated and removed here is sent from the ash discharge pipe 3 to the coal ash and gypsum slurry mixer 29. Exhaust gas from which coal ash has been removed is gas and gas heater 5
The exhaust gas, which has entered and which has been saturated with water and which has been sent from the outlet duct 7, is heated and sent from the outlet duct 4 to the chimney. On the other hand, the heat-exchanged exhaust gas is introduced into the desulfurization tower 8 through the inlet duct 6.
to go into. In the desulfurization tower 8, the slurry absorbing liquid containing calcium carbonate sent from the slurry absorbing liquid circulating liquid pump 11 is sprayed from a plurality of spray nozzles 9. Here, the sprayed slurry absorption liquid absorbs SO ₂ gas by gas-liquid contact with the exhaust gas, is oxidized in the oxidation tank 22, and finally a slurry absorption liquid containing gypsum is generated. A part of the slurry waste liquid in the oxidation tank 22 mainly containing gypsum enters the liquid cyclone 25 through the slurry waste liquid discharge pipe 23. here,
The gypsum in the slurry waste liquid is concentrated to become a high-concentration gypsum slurry, and enters the coal ash and gypsum slurry mixer 29 from the concentrated gypsum slurry supply pipe 26. On the other hand, the low-concentration slurry absorption liquid that is not concentrated by the liquid cyclone 25 or the like is recycled from the dilute slurry liquid supply pipe 27 to the oxidation tank 22. Here, the coal ash from the dust collector 2 and the slurry waste liquid containing gypsum are uniformly mixed. Chlorine compounds and fluorine compounds contained in the slurry absorption waste liquid are adsorbed and fixed in the coal ash by mixing the coal ash and the slurry absorption waste liquid. In a commonly used coal base, the ratio of coal ash and gypsum slurry is 5 to 10: 1. When the ratio of gypsum slurry to coal ash is small as described above, it is not necessary to use the liquid cyclone 25. Absent. In addition, when the pH of the slurry absorption waste liquid is low or when there are many chlorine compounds or fluorine compounds,
A neutralizing agent or the like is added from the additive supply pipe 28 in the middle of the concentrated gypsum slurry supply pipe 26 to process the gypsum slurry liquid in advance, and then sent to the coal ash and gypsum slurry mixer 29. further,
By installing the pipe line mixer 31 between the additive supply pipe 28 and the coal ash / gypsum slurry mixer 29, it is possible to sufficiently neutralize the neutralizer etc. in the line of the pipe without newly installing a neutralization tank. Additives can be mixed. As described above, if the present invention is applied, it can be treated as a solid waste simply by mixing a slurry liquid containing coal ash and gypsum, so the process becomes very simple and the desulfurization equipment cost and desulfurization operation cost can be reduced. It can be significantly reduced.
FIG. 2 shows the relationship between the water concentration of the waste produced in the coal ash and the gypsum slurry mixer 29 and the elution rate of chlorine compounds and fluorine compounds. The sample produced by the mixer 29 of coal ash and gypsum slurry was allowed to stand for 1 day, 10 g of this sample was dissolved in 100 cc of water, and the elution rate of the chlorine compound and the fluorine compound eluted in water 100 hours later was determined. And the standard is when the water content in the waste is 25% (1)
And showed it. As shown in the figure, when the water concentration was 25% or less, the elution rates of chlorine and fluorine compounds were almost constant and almost constant. However, the water concentration is 30%
If it exceeds, the dissolution rate will decrease sharply. If the water content exceeds 30%, the waste produced in the coal ash and gypsum slurry mixer becomes sticky with water, and the harmful components in the waste liquid are not sufficiently adsorbed in the coal ash. On the other hand, if the slurry liquid containing gypsum is mixed under the condition that the water content is 25% or less, all the water on the surface of the coal ash is adsorbed in the coal ash, and at the same time, the harmful components are also adsorbed and stably immobilized. To be done. As described above, by using the present invention, it is possible to mix coal ash and gypsum slurry liquid and dispose as waste, so that the gypsum recovery system can be greatly simplified, desulfurization equipment cost and operation The cost can be significantly reduced, and the installation area of the gypsum recovery system can be significantly reduced.

[0008]

According to the wet flue gas desulfurization method and apparatus of the present invention, the coal ash and the slurry liquid containing gypsum can be mixed and disposed of as solid waste, which greatly simplifies the gypsum recovery system. Therefore, the desulfurization apparatus cost and the operating cost can be significantly reduced, and the installation area of the gypsum recovery system can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a wet flue gas desulfurization apparatus exemplified in an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the amount of water in wastes and the elution rates of chlorine and fluorine compounds exemplified in the examples of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a conventional wet flue gas desulfurization apparatus.

[Explanation of symbols]

 1 ... Duct 2 ... Dust collector 3 ... Ash discharge pipe 4 ... Exit duct 5 ... Gas / gas heater 6 ... Entrance duct 7 ... Exit duct 8 ... Desulfurization tower 9 ... Spray nozzle 10 ... Slurry absorbing liquid circulation pipe 11 ... Slurry absorbing liquid circulation pump 12 ... Neutralization tank 13 ... Thickener 14 ... Supernatant liquid discharge pipe 15 ... Gypsum slurry (slurry waste liquid) discharge pipe 16 ... Dehydrator 17 ... Return pipe 18 ... Gypsum discharge pipe 19 ... Wastewater treatment device 20 ... Drain pipe 21 ... Air blow Mixing pipe 22 ... Oxidation tank 23 ... Slurry waste liquid extraction pipe 24 ... Limestone supply pipe 25 ... Hydrocyclone 26 ... Concentrated gypsum slurry supply pipe 27 ... Dilute slurry liquid supply pipe 28 ... Additive (neutralizing agent) supply pipe 29 ... Coal Ash and gypsum slurry mixer 30 ... Waste discharge pipe 31 ... Piping line mixer

Front page continued (72) Inventor Hirofumi Yoshikawa 3-36 Takaracho, Kure City, Hiroshima Prefecture Babcock-Hitachi Kure Research Institute

Claims (7)

[Claims] 1. A desulfurization tower that absorbs and removes sulfur oxides in exhaust gas by gas-liquid contact between exhaust gas containing sulfur oxides discharged from a combustion device using coal as a fuel and a slurry absorbing liquid containing calcium carbonate. , At least one oxidation tank for accumulating the reacted slurry absorption liquid in the lower part of the desulfurization tower and oxidizing it to produce gypsum, and a wet exhaust for recirculating the slurry absorption liquid from the oxidation tank to the desulfurization tower for desulfurization In the smoke desulfurization method, a slurry waste liquid containing gypsum is discharged from the oxidation tank and mixed with coal ash collected in the exhaust gas system of the combustion device to prepare solid waste having a water concentration of 30% by weight or less. A wet flue gas desulfurization method characterized by: 2. The method according to claim 1, wherein water in the slurry waste liquid containing gypsum is separated and removed to concentrate the gypsum, and then mixed with coal ash to prepare solid waste having a water concentration of 30% by weight or less. Characteristic wet flue gas desulfurization method. 3. The wet flue gas desulfurization method according to claim 2, further comprising the step of recirculating the low-concentration slurry absorption liquid obtained by separating the gypsum content from the slurry waste liquid into the oxidation tank. 4. The amount of slurry waste liquid containing gypsum discharged from the oxidation tank is adjusted and controlled according to the amount of coal ash collected in the exhaust gas system of the combustion apparatus according to claim 1, and the water concentration is 3%.
A wet flue gas desulfurization method, characterized in that solid waste is 0% by weight or less. 5. The method according to claim 2, wherein the water content of the gypsum-containing slurry waste liquid is separated, the neutralizing agent is added to the concentrated gypsum slurry, and then coal ash is added to adjust the mixture so that the water content is 30% by weight. % Or less solid waste, a wet flue gas desulfurization method. 6. A desulfurization tower for absorbing and removing the above sulfur oxides by gas-liquid contacting an exhaust gas containing sulfur oxides discharged from a combustion device using coal as a fuel with a slurry absorbing liquid containing calcium carbonate, At least one oxidation tank for accumulating the reacted slurry absorbing solution in the lower part of the desulfurization tower and oxidizing it to produce gypsum, and a wet method including at least a means for recirculating the slurry absorbing solution from the oxidation tank to the desulfurization tower In the flue gas desulfurization device, a discharge pipe for discharging coal ash collected in the exhaust gas system of the combustion device, a discharge pipe for discharging slurry waste liquid containing gypsum from the oxidation tank, and a discharge pipe for the coal ash. A wet flue gas desulfurization apparatus comprising a mixer for mixing and controlling coal ash to adjust and control the water concentration to 30% by weight or less. 7. A discharge pipe for discharging coal ash collected in an exhaust gas system of a combustion device, a discharge pipe for discharging a slurry waste liquid containing gypsum from an oxidation tank, and a discharge pipe for the slurry waste liquid according to claim 6. A liquid cyclone that produces concentrated gypsum slurry from the slurry waste liquid provided at the outlet, a pipe line mixer that supplies additives to the concentrated gypsum slurry and mixes in the pipe line, and is discharged from the pipe line mixer. Wet exhaust, characterized in that a concentrated gypsum slurry containing an additive is mixed with coal ash discharged from the coal ash discharge pipe to provide a mixer for adjusting and controlling the water concentration to 30% by weight or less. Smoke desulfurization equipment.