KR102556853B1 - Carbon Dioxide Removing System From Exhaust Gases - Google Patents

Abstract

The present invention includes a dust collector for receiving exhaust gas discharged from an exhaust gas source and removing dust from the exhaust gas; a carbon dioxide absorption tank receiving the exhaust gas that has passed through the dust collector, reacting with the carbon dioxide absorbent containing sodium hydroxide solution to remove carbon dioxide and sulfur oxides from the exhaust gas, and discharging processed gas; a primary precipitation tank receiving the reaction liquid from the carbon dioxide absorption tank and precipitating foreign substances by a flocculation reaction with a coagulant; It relates to a system for removing carbon dioxide from exhaust gas, characterized in that it comprises a; secondary precipitation tank for recovering calcium carbonate by reacting the reaction liquid introduced from the primary precipitation tank with calcium oxide.

Description

Carbon Dioxide Removing System From Exhaust Gases

The present invention relates to a system capable of removing carbon dioxide from exhaust gases such as power plants and providing high-purity calcium carbonate.

In power plants using fossil fuels, a large amount of CO ₂ is included in flue gas after combustion. At this time, NOx generation due to the high-temperature combustion process is removed with a denitrification facility (SCR or SNCR), and even if the case of relatively expensive LNG power generation is excluded, the sulfur in the fuel depends on the type of fossil fuel used as fuel. Due to the components, SOx is generated after combustion, and dust containing ash and heavy metals is removed by an electric precipitator (EP).

A large-scale desulfurization facility (FGD) is operated to suppress the emission of SOx into the atmosphere, and sulfur components are removed in the form of CaSO ₄ from a huge absorption tower using limestone as an absorbent. Among these flue gases, CO ₂ (366 ton/hr, based on one 500 MWH power plant) is more than 100 times greater than the SOx generated and removed, which is being emitted into the atmosphere as it is (2.6 million ton/year, 366*24 hours*). 300 days)

In order to remove or reduce such a huge amount of CO ₂ , it is predicted that the facility and operation will be impossible from the scale and the generation of wastewater will be enormous with an absorbent method such as limestone.

Therefore, it is required to develop an adsorbent capable of excellent adsorption capacity for carbon dioxide and low-cost CO ₂ degassing or easy resource conversion from a feasible facility in terms of economic feasibility and scale. It is desirable to suppress the occurrence.

Even though most of the CO ₂ resource circulation system is removed from the EP by various components contained in the fuel, the exhaust gas is contaminated with dust or sulfur oxides containing heavy metals. Purity issues must be addressed so that impurities can be removed.

Republic of Korea Patent Registration No. 10-1415865

The present invention has been made to solve the above problems, and is intended to provide a system capable of efficiently removing sulfur oxides as well as carbon dioxide from exhaust gas and producing high-purity calcium carbonate as a result.

A system for removing carbon dioxide from exhaust gas according to the present invention (hereinafter referred to as "the system of the present invention") for achieving the above object is a dust collector that removes dust from the exhaust gas by receiving the exhaust gas discharged from the exhaust gas source. Device; a carbon dioxide absorption tank receiving the exhaust gas that has passed through the dust collector, reacting with the carbon dioxide absorbent containing sodium hydroxide solution to remove carbon dioxide and sulfur oxides from the exhaust gas, and discharging processed gas; a primary precipitation tank receiving the reaction liquid from the carbon dioxide absorption tank and precipitating foreign substances by a flocculation reaction with a coagulant; It is characterized by including; a secondary precipitation tank for receiving the reaction solution from the primary precipitation tank and reacting with calcium oxide to recover calcium carbonate.

As an example, a nitrogen oxide removal unit receiving exhaust gas discharged from an exhaust gas source and removing nitrogen oxides from the exhaust gas is further included at a front end of the dust collector.

As an example, the processing gas discharged through the carbon dioxide absorption tank is discharged to the outside through a heat exchanger.

As an example, the carbon dioxide absorbent is characterized in that an illite extract is included.

One example is characterized in that sodium tetraborate is further included.

One example is characterized in that water glass is further included.

One example is characterized in that hydrogen peroxide is further included.

As described above, the present invention has an advantage in that the system can be efficiently operated without a desulfurization facility or without a load on the desulfurization facility by using a carbon dioxide absorbent capable of simultaneously treating carbon dioxide and sulfur oxides.

In addition, by allowing the collected carbon dioxide to be recovered as high-purity calcium carbonate without impurities, it has the advantage that it can be used by itself throughout the industry, such as papermaking, construction, and steelmaking, without limiting the demand.

1 is a block diagram showing the system of the present invention;
2 is a diagram showing the carbon dioxide absorption mechanism of the carbon dioxide absorbent applied to the present invention,
Figure 3 is a graph showing the experimental results on the removal of sulfur oxides,
4 is a graph showing experimental results regarding the removal of carbon dioxide.

In the following, preferred embodiments according to the present invention will be described in detail.

As shown in FIG. 1, the system 1 of the present invention includes a dust collector 4 for receiving exhaust gas discharged from an exhaust gas emission source 2 and removing dust from the exhaust gas; a carbon dioxide absorption tank (7) receiving the exhaust gas passing through the dust collector (4), removing carbon dioxide and sulfur oxides from the exhaust gas by reacting with a carbon dioxide absorbent containing sodium hydroxide solution, and discharging processed gas; a primary precipitation tank (8) receiving the reaction solution from the carbon dioxide absorption tank (7) and precipitating foreign substances by coagulant reaction with the coagulant; It is characterized in that it includes; a secondary precipitation tank (9) for receiving the reaction solution from the primary precipitation tank (8) and reacting with calcium oxide to recover calcium carbonate.

In addition, a nitrogen oxide removal unit 3 receiving the exhaust gas discharged from the exhaust gas emission source 2 and removing and discharging nitrogen oxides from the exhaust gas is further included at the front end of the dust collector 4.

The emission source 2 is a concept that collectively refers to a place, facility, etc. that emits exhaust gas mixed with nitrogen oxides, sulfur oxides, and carbon dioxide as various pollutants such as a power plant.

The nitrogen oxide removal unit 3 is configured to remove nitrogen oxides from the exhaust gas discharged from the emission source 2, and the nitrogen oxide removal unit 3 removes nitrogen oxides from the exhaust gas by applying various known technologies. to be discharged, for example, SCR denitrification technology can be applied.

The dust collector 4 receives the exhaust gas that has passed through the nitrogen oxide removal unit 3 and removes dust from the exhaust gas, and removes dust from the exhaust gas by electric dust collection. The dust is a concept including particulate contaminants, ash, heavy metals, and the like.

The desulfurization unit 5 shown in FIG. 1 is configured to remove sulfur oxides from exhaust gas, and in the system 1 of the present invention, simultaneous removal of sulfur oxides and carbon dioxide in the carbon dioxide absorption tank 7 described below is performed. By using a possible carbon dioxide absorbent, the desulfurization unit 5 can be selectively bypassed, thereby simplifying the system and controlling the load of the desulfurization unit 5.

Since there are various known techniques for removing sulfur oxides in the desulfurization unit 5, a detailed description thereof will be omitted.

The heat exchanger 6 allows heat exchange while passing the processed gas through the desulfurization unit 5 or the carbon dioxide absorption tank 7, and various known technologies exist in the case of the heat exchanger 6. , its detailed description is omitted.

The carbon dioxide absorption tank 7 receives the exhaust gas that has passed through the dust collector 4 and reacts with the carbon dioxide absorbent containing sodium hydroxide solution to remove carbon dioxide and sulfur oxides from the exhaust gas, and the heat exchanger 6 Corresponds to a configuration in which processing gas is discharged into the furnace.

As mentioned above, the carbon dioxide absorbing tank 7 uses a carbon dioxide absorbing agent that simultaneously removes carbon dioxide and sulfur oxides, so that exhaust gas that has not passed through the desulfurization unit 5 can flow in, as shown in the drawing. Although it has not been done, the reaction can be performed by introducing the exhaust gas that has passed through the desulfurization unit 5.

The carbon dioxide absorbent is characterized by comprising an aqueous solution of sodium hydroxide and an illite extract.

The sodium hydroxide aqueous solution is characterized in that a mixture gas containing high-temperature, high-concentration carbon dioxide and COS (hydrocarbon, O ₂ , SOx) can be simultaneously removed. That is, sulfur oxides (SOx) as well as carbon dioxide are simultaneously absorbed from power plant exhaust gas.

The principle of removing sulfur oxides and carbon dioxide from the sodium hydroxide aqueous solution is shown in the following reaction formula. That is, sulfur trioxide (sulfurous acid) and sulfur dioxide are removed by reacting with sodium hydroxide and being extracted with anhydrous sodium sulfate and sodium sulfite, respectively, as shown below.

And carbon dioxide is removed by reacting with sodium hydroxide to produce sodium carbonate as shown in the following reaction formula. In addition, the generated sodium carbonate reacts with excess sulfur oxides to further increase the sulfur oxide removal effect, and the produced carbon dioxide is removed by sodium hydroxide.

1) 2NaOH + SO ₃ = Na ₂ SO ₄ + H ₂ O

2) 2NaOH + SO ₂ = Na ₂ SO ₃ + H ₂ O

3) 2NaOH + CO ₂ = Na ₂ CO ₃ + H ₂ O

4) NaOH + CO ₂ = NaHCO ₃

The illite is a mineral that is found to be buried in large quantities in the Yeongdong region of Korea, represented by {K _0.75 [Al _1.75 (Mg Fe ₂ +) _0.25 ] (Si _3.50 Al _0.50 ) O ₁₀ (OH) ₂ }. The layer charge is lower than that of muscovite mica, and the charge is due to isomorphic substitution reduction of Al ³⁺ and Si ⁴⁺ in the tetrahedral plate. Some isomorphic substitutions occur in the octahedral plate.

Illite is non-expandable due to the strong bonding force by K + existing between layers, and the layer spacing is 10 Å. Therefore, it is a mineral that is extracted from the liquid phase, has a total cationic charge, and is easily converted into a chelation compound, and in the present invention, it is appropriate to use undifferentiated illite to easily extract such a metal foreign material.

The extract extracted from illite is an extract containing various metal oxides such as potassium oxide, and serves as a reaction enhancer by providing minerals that are easily converted into chelation compounds in a liquid phase. That is, in the absorption of carbon dioxide containing SOx in the sodium hydroxide aqueous solution, the illite extract is further added to increase the absorption efficiency.

The reaction formula with sodium hydroxide of illite extract as a reaction enhancer is as shown below. Only the main components of illite have been described, and oxides of minor components such as Ca, Fe, Mg, Mn, Ti and P ₂ O ₅ also contribute to the formation of stable metal chelation compounds in the liquid phase.

1) 2NaOH + SiO ₂ = Na ₂ O. SiO ₂ + H ₂ O

2) 2NaOH + K ₂ O = Na ₂ O + 2KOH

3) Na ₂ O + Al ₂ O ₃ + H ₂ O = 2NaAlO ₂ + H ₂ O

The illite extract is characterized in that it is prepared by adding illite powder to water heated to 40 to 100 ° C and stirring. That is, it can be obtained by adding illite powder to heated water to precipitate solids while stirring, and separating and filtering the supernatant.

In addition, the present invention provides an example in which the carbon dioxide absorbent further includes sodium tetraborate (Na ₂ B ₄ O ₇ .10H ₂ O) and water glass (Na ₂ SiO ₃ ).

In addition to the illite extract, the sodium hydroxide aqueous solution is to further include sodium tetraborate and water glass. As sodium tetraborate and water glass are further added in this way, carbon dioxide and the absorbent component react directly, so the reaction rate is much faster and the mass transfer coefficient is increased.

Moreover, since sodium tetraborate and water glass have high viscosities, absorbed gaseous carbon dioxide cannot escape and quickly melts into a liquid state and reacts with carbonic acid, thereby doubling the absorption rate of carbon dioxide.

In addition to this, the present invention suggests an example in which hydrogen peroxide (H ₂ O ₂ ) is further added as a reaction-promoting additive.

The reaction formula of sodium tetraborate and hydrogen peroxide in aqueous sodium hydroxide solution is as follows.

1) Na ₂ B ₄ O ₇ + H ₂ O = Na ₂ O + 2B ₂ O ₃

2) 2NaOH + H ₂ O ₂ = Na ₂ O + H ₂ O + 0.5O ₂

Therefore, the carbon dioxide absorption mechanism is shown in FIG. 1 and the following reaction formula.

1) CO ₂ (g) + CO ₂ (aq) + Na ₂ O + 2OH- = CO ₂ (g) + CO ₃ -- + 2NaOH = CO ₂ (aq) + CO ₃ --

2) CO ₃ -- + H ₂ O + CO ₂ (aq) = 2HCO ₃ -

3) CO ₂ (aq) + OH- = HCO ₃ -

4) HCO ₃ - + OH- = CO ₃ - + H ₂ O

The primary precipitation tank 8 receives the reaction solution from the carbon dioxide absorption tank 7 and precipitates foreign substances by coagulant reaction with the coagulant, so that foreign substances such as heavy metals, ash, and SS are removed from the reaction solution by coagulation. This is to increase the purity of the calcium carbonate obtained in the secondary precipitation tank 9 at the rear, and although not shown in the figure, it is to regenerate a regenerated carbon dioxide absorbent without impurities when regenerating the reaction solution.

The type of coagulant is not limited, and for example, calcium hydroxide (Ca(OH) ₂ ) may be applied.

The secondary precipitation tank 9 corresponds to a configuration in which calcium carbonate is recovered by receiving the reaction solution from the primary precipitation tank 8 and reacting with calcium oxide.

In the secondary precipitation tank 9, CaO is added according to the equivalent number of carbon dioxide captured as carbonic acid in the reaction solution so that high-purity, high-value-added precipitated calcium carbonate, which is a useful resource, is produced. In addition, the reaction solution from which foreign substances and captured carbon dioxide are removed through the primary precipitation tank 8 and the secondary precipitation tank 9 can be reused as a regenerated carbon dioxide absorbent.

In order to achieve the purpose of reducing carbon dioxide, costs such as the size of additional facilities or absorbents and operational convenience must be considered, and the cost of energy input is also one of the important items. Therefore, the cost of the carbon dioxide absorbent provided according to the present invention has a mechanism for recovering the absorption capacity by precipitating calcium carbonate again after the chemical absorption reaction of carbon dioxide, but not shown in the drawings, but slightly in the piping and absorption tower through the circulation system. There is no loss except for the loss of, and there is almost no heat energy loss, such as the temperature of the filtrate being maintained at 60 ° C or higher after calcium carbonate precipitation by the heat of dilution generated when CaO is added in the secondary precipitation tank 9. Rather, an exothermic reaction develops. Of course, calcium carbonate has almost no solubility in alkaline water even at a high temperature of 60 ℃ or higher, but only affects the size or crystal form of the precipitate according to the temperature.

Although not shown in the drawing, a portion of the calcium carbonate obtained in the secondary precipitation tank 9 can be sent to the desulfurization unit 5 to be used to remove sulfur oxides, and in addition to high value-added precipitated products, the calcium carbonate thus obtained Since it has a very high impurity-free purity, it can be used by itself throughout the industry, such as papermaking, construction, and steelmaking, without restrictions on demand sources, and can be recycled as resources by producing high-purity carbon dioxide and slaked lime through the sintering process. In addition, such pure calcium carbonate can be used at least in landfills of abandoned mines as a pollution-free resource that is not affected by the natural world.

In addition, the system (1) of the present invention does not directly capture and then store or recycle carbon dioxide, does not require large-scale facilities, does not generate wastewater or has few factors, and produces calcium carbonate of very low solubility by a 1: 1 reaction with carbonic acid quickly. As the entire amount is precipitated at a high rate, the conversion energy cost in a small-scale sedimentation tank is rather converted into heat energy by the exothermic reaction of calcium carbonate. It becomes. High-purity precipitated calcium carbonate, also a conversion product, can be expected to have high added value in terms of market size and price.

A preferred embodiment of the carbon dioxide absorbent will be described based on experimental examples below.

1,350 g of yellow-phase illite pulverized with 1,000 mesh was added to 15 L of RO water heated to 60 ° C and stirred for 30 minutes. Then, 150 g of sodium tetraborate was added and stirred for 10 minutes to dissolve well (temperature drop of about 10 ° C), and then 300 g of sodium hydroxide was slowly added and stirred. Stir.

The temperature of the reaction solution naturally dropped and was stirred until it reached room temperature. Stirring was stopped at room temperature and allowed to stand overnight, and the supernatant was filtered to prepare an adsorbent.

540 g of illite of the yellow phase pulverized with 325 mesh was put into 6 L of RO water heated to 60 ° C. and stirred for 30 minutes. Add 300g of sodium tetraborate and stir for 30 minutes (temperature drop of about 20℃ in the reaction solution). When it was, 300 g of water glass was added and stirred for 1 hour.

After the temperature of the reaction solution naturally dropped to below 60 ° C, 90 g of hydrogen peroxide was added and stirred until the reaction solution reached room temperature. Stirring was stopped at room temperature and allowed to stand overnight, and the supernatant was filtered to prepare an adsorbent.

<Exhaust gas analysis equipment>

NOVA 9K (MRU Emission Monitoring System, Germany) was used, and the sensor, measurement range, and resolution for each measurement object are as follows.

- O ₂ (EC) : 0 ~ 21 Vol% / 0.2%

- CO ₂ (NDIR) : 0 ~ 40 Vol% / 0.3%

- SO ₂ (EC) : 0 ~ 2,000 ppm / 5ppm

* E.C: electrochemical sensor, NDIR: non-dispersive infrared sensor

<Exhaust gas analysis method>

-. SO ₂ analysis

Ignition coal was put in the meseta dissociation firewood stove and ignited, and after 5 minutes, lignite was raised by 1Kg to start combustion. After about 15 minutes, 3 kg of lignite, which had been evenly sprayed with 100 g of the liquid desulfurization catalyst prepared in Example 1, was further raised and combustion was started in earnest.

In order to suck in some of the exhaust gas exhausted through the flue, make a hole in the middle of the flue, connect a silicone hose, completely seal the gap with silicone, and inhale the exhaust gas through a diaphragm pump to adjust the flow meter to 35L/min and experiment. The reactor was blown into the reactor through the In-Let pipe of the gas trap adapter. The exhaust gas discharged through the Out-Let pipe of the gas trap adapter was connected to NOVA 9K, and the amount of SO ₂ was measured.

-. CO ₂ analysis

After preparing an N ₂ bombe and a CO ₂ bombe with a heating device, adjust the flow meter to 30L/min of N ₂ and 5L/min of CO ₂ , respectively, and mix the gas through the Y-shaped adapter to in-let pipe of the gas trap adapter. was blown into the reactor through The CO ₂ concentration was measured at the Out-Let of the gas trap adapter, and 1 L of the CO ₂ chemical adsorbent prepared in Example 2 was introduced into the reaction tank through the dropping funnel, and then the CO ₂ concentration was measured.

<Experimental Example 1> SOx removal performance measurement

After burning lignite in a firewood stove, the amount of SOx generated in exhaust gas was measured and the amount of SOx reduction was measured through the above experimental device.

The experimental results are shown in FIG. 2, and as shown in the graph, it can be seen that the SOx reducing ability is expressed by the action of the absorbent of Example 1 from approximately 37 minutes to 91 minutes.

<Experimental Example 2> CO ₂ Removal Ability Measurement

In the above experimental device, 14% CO ₂ Gas was injected into the main reactor through N ₂ Bombe and CO ₂ Bombe, and then 1L of CO ₂ chemical absorbent prepared in Example 2 was put in and passed through the input gas to reduce CO ₂ was measured.

As the experimental results are shown in FIG. 3, the first descending curve on the graph indicates that Example 2 is injected and CO ₂ is reduced, and while the CO ₂ is reduced, the rising curve shows that the lid of the reactor is opened and the outside air is released. Although not mentioned in the present invention after CO ₂ is increased by allowing the inflow, it can be seen that CO ₂ is reduced again as a result of introducing a regenerated absorbent obtained by regenerating the previously used absorbent of Example 2.

<Experimental Example 3> Production of CaCO ₃ and Regeneration of CO ₂ Absorbent

In Experimental Example 2, 1L of the absorbent that absorbed CO ₂ (solution temperature: 32°C) was transferred to a 2L Beaker, and 62.16 g of CaO (assay 90%) was added while stirring. As was precipitated, grayish brown CaO particles were rapidly dissolved, and then the solid was filtered and dried with hot air to obtain 100.1 g of white CaCO ₃ . The filtrate was again used as the CO ₂ absorption regeneration solution of Experimental Example 2.

As described above, although the present invention has been described with limited embodiments and drawings, the present invention is not limited to the above embodiments, of course, from the above description by a person having ordinary technical knowledge in the field to which the present invention belongs. Of course, various modifications and variations may be possible.

1: system of the present invention 2: emission source
3: nitrogen oxide removal unit 4: dust collector
5: desulfurization unit 6: heat exchanger
7: carbon dioxide absorption tank 8: primary sedimentation tank
9: 2nd sedimentation tank

Claims (7)

a dust collector for receiving the exhaust gas discharged from the exhaust gas source and removing dust from the exhaust gas;
A sodium hydroxide aqueous solution by receiving the exhaust gas passing through the dust collector; an illite extract prepared by adding illite powder to water heated to 40 to 100° C. and stirring; Sodium tetraborate and water glass, which doubles the absorption rate of carbon dioxide by reacting with carbonic acid while the absorbed gaseous carbon dioxide cannot escape and melts into a liquid state; It is composed of hydrogen peroxide, but the illite powder is added to water heated to 40 to 100 ° C. and stirred, then sodium tetraborate is sequentially added and stirred, sodium hydroxide is added and stirred, and water glass is added and stirred a carbon dioxide absorption tank for removing carbon dioxide and sulfur oxides from the exhaust gas by reacting with the carbon dioxide absorbent prepared by adding hydrogen peroxide, stirring, and filtering the supernatant, and discharging the treated gas;
a primary precipitation tank receiving the reaction liquid from the carbon dioxide absorption tank and precipitating foreign substances by a flocculation reaction with a coagulant;
a second precipitation tank receiving the reaction solution from the first precipitation tank and reacting with calcium oxide to recover calcium carbonate;
Carbon dioxide removal system from exhaust gas, characterized in that it comprises a. According to claim 1,
The system for removing carbon dioxide from exhaust gas, characterized in that the front end of the dust collector further includes a nitrogen oxide removal unit for receiving exhaust gas discharged from an exhaust gas emission source and removing and discharging nitrogen oxides from the exhaust gas. According to claim 1,
Carbon dioxide removal system from exhaust gas, characterized in that the processing gas discharged through the carbon dioxide absorption tank is discharged to the outside through a heat exchanger. delete delete delete delete