WO2016192273A1 - Ozone-based flue gas treatment system and method - Google Patents

Abstract

A flue gas treatment system and method. The system comprises: a flue gas treatment device (1), internally provided with at least one ozone spray reaction and absorption layer (27) and at least two spray absorption layers (7, 8); a dedusting and demisting device; an ozone supply device; an evaporation and concentration device; and a circulating sedimentation device. The method comprises the following steps: oxidizing flue gas; carrying out wet absorption; supplying ozone; dedusting and demisting; carrying out evaporation and concentration; and carrying out circulating sedimentation.

Description

Ozone-based flue gas treatment system and method Technical field

The invention relates to a flue gas treatment system and method, in particular to a system and a method for simultaneously removing sulfur dioxide, nitrogen oxides, mercury and dust in flue gas and using the waste liquid to produce salt by-products.

Background technique

In recent years, emissions of SO ₂ and NO _x increasing its pollution caused by more and more serious, and produced a series of problems: they are formed by acid rain and photochemical smog and other serious threats to human health, environmental destruction These pollutants have seriously affected the lives of the people and the development of the national economy. The dust emissions of the steel industry account for 25% of the total industrial dust emissions in China, and the soot emissions from the sintering industry account for about 40% of the total emissions from the steel production process. These dusts emitted by the flue gas are also an important source of plutonium, SO ₂ , NO _x and dust damage to human health, harm to nature to be more serious than we expected. Mercury is the only toxic heavy metal that is gaseous at normal temperature and pressure, and has the ability to diffuse over long distances. Therefore, it is considered to be a global pollutant and has attracted much attention. And SO _2, NO _x, dust and mercury emissions from industrial flue gas is a major source of air pollution. Thus, control of industrial flue gas SO _2, NO _x, dust and mercury emissions is imminent.

Based on the removal of SO ₂ , the flue gas desulfurization technology of magnesia has been gradually promoted and applied. The market share has been less than 1% since 2005, and currently exceeds 6%. The wet magnesia desulfurization technology has gained more and more people. Recognition. The magnesium oxide desulfurization process and the preparation of the desulfurization waste liquid to produce the magnesium sulfate by-product not only solve the problem of the desulfurization gypsum treatment caused by the conventional calcium desulfurization, but also can offset the operation and maintenance cost of the partial desulfurization system through the sales of the magnesium sulfate by-product. Both technical and economic perspectives have greater market application advantages than traditional calcium methods. Based on the angle of removal of NO _x, the conventional denitration method of selective non-catalytic reduction (SNCR) and selective catalytic reduction (SCR). Both of these flue gas denitration methods require higher temperatures, and the existing desulfurization equipment is greatly modified. The SCR method has high denitration efficiency and small secondary pollution, but the equipment investment cost is large, the catalyst is needed, and the operation and maintenance cost is high. The SNCR method has less investment and operation cost, but the denitration efficiency is relatively low, and the increasingly strict emission is not achieved. standard.

Based on the angle of removal of NO _x, using the principle of forced oxidation of NO _x in the flue gas of 95% of the water-insoluble NO converted to NO ₂ or N ₂ O ₅ and the like valency of nitrogen oxides, water, or again Absorption of alkaline substances to achieve flue gas denitration. Existing desulfurization equipment can meet the requirements of denitration without large-scale transformation, and has the advantages of low transformation cost, short cycle, small footprint, simple process and strong adaptability. For example, CN1768902A discloses a flue gas denitration method in which ozone (O ₃ ) as an oxidant is first sprayed into a flue to oxidize NO in the boiler flue gas to NO ₂ or N ₂ O ₅ which is easily soluble in water. The flue gas is then washed with water or an alkali solution to remove nitrogen oxides from the flue gas. Although the oxidative denitration method can achieve the purpose of removing nitrogen oxides, the boiler flue gas is first reacted with ozone (O ₃ ) and then subjected to an alkali treatment process, that is, the oxidation zone is separated from the absorption zone, and ozone (O ₃ ) is exceeded. In the flue gas environment of 130 ° C and in the flue gas condition of dust content of 50 ~ 200mg / Nm ³ , it is easy to decompose, or the adsorption dust is inactivated, resulting in reduced denitration efficiency and excessive ozone (O ₃ ) consumption. Increase the operating cost of the denitration system.

From the perspective of by-products, since the conventional magnesium oxide desulfurization waste liquid produces magnesium sulfate using steam as a medium for evaporation, crystallization, and drying, the method of producing magnesium sulfate by using desulfurization waste liquid requires more steam and directly increases. Desulfurization operation costs. Such as CN1733656A provides a kind of "utilizing boiler flue gas A method for preparing a magnesium sulfate heptahydrate fertilizer, wherein the magnesium sulfate solution is concentrated and crystallized by crystallization of magnesium sulfate at a temperature exceeding 60 ° C, and the high temperature crystallization method requires more consumption. The high-quality steam will cause frequent blockage of the slurry conveying pipeline, and it is difficult to achieve continuous and stable production of by-products. For example, CN102745726A provides a "method of producing magnesium sulfate heptahydrate by using desulfurization waste liquid", the crystallization method used. In order to "deliver the obtained liquid into the evaporator, the slurry is discharged after concentration, the evaporation temperature is 100 to 130 ° C, and the discharged slurry is cooled and crystallized at a temperature of 30 to 45 ° C to obtain magnesium sulfate heptahydrate." The crystallization method requires high steam quality, and the consumption is increased if low-grade steam is used. In summary, regardless of either of the above two methods, it takes about 1.2 to 2 tons of steam to produce one ton of magnesium sulfate. The steam price is calculated at 80 yuan/ton, and the steam consumption cost of one ton of magnesium sulfate is about 160 yuan. Therefore, although the comprehensive cost of magnesium desulfurization is more than the calcium method Low, but at present, the method of producing magnesium sulfate by the three-effect evaporation process outside the magnesium desulfurization tower still has waste steam resources, and the desulfurization operation cost is still high.

Summary of the invention

The object of the present invention is to provide an ozone-based flue gas treatment system and method, which can simultaneously desulfurize, denitrify, dedust and remove mercury from flue gas, and can utilize the waste liquid to produce sulfate, thereby realizing comprehensive treatment and resource utilization.

The invention provides a flue gas treatment system, comprising:

Flue gas treatment equipment with internal:

(1) at least one layer of an ozone spray reaction and absorption layer for oxidizing low-cost nitrogen oxides and elemental mercury in the flue gas to high-priced nitrogen oxides and mercury oxide, respectively;

(2) at least two layers of spray absorbing layer for absorbing sulfur dioxide, nitrogen oxides and dust in the flue gas by using an absorbent, and trapping oxidized mercury in the flue gas, thereby Forming an absorption product;

a dust removal and defogging device for performing dust removal and defogging on the flue gas, wherein the dust removal and defogging device is located above all the spray absorption layers;

An ozone supply device for supplying ozone to said ozone spray reaction and absorption layer;

An evaporation concentration device for evaporating and concentrating the absorption product with flue gas to form a concentrated product;

A circulating settling device for receiving concentrated product from the evaporation concentration device and forming a settling product.

According to the system of the present invention, preferably, at least one of the at least two spray absorbing layers of the spray absorbing layer is disposed under the ozone spray reaction and absorption layer for pretreatment of the smoke Gas to absorb sulfur dioxide and dust in the flue gas; and

At least one of the at least two spray absorbing layers of the spray absorbing layer is disposed above the ozone spray reaction and absorption layer for absorbing sulfur dioxide and nitrogen oxides in the flue gas and trapping Mercury oxide in the flue gas.

According to the system of the present invention, preferably, a first layer of the spray absorbing layer and the second layer of the spray absorbing layer are disposed from the bottom to the inside of the flue gas treating apparatus, and the ozone spray reaction and absorption layer are disposed at Between the first spray absorbing layer and the second spray absorbing layer.

According to the system of the present invention, preferably, the ozone spray reaction and absorption layer is 0.8 to 2.8 meters from the first layer of the spray absorption layer and 1.0 to 2.3 meters from the second layer of the spray absorption layer.

According to the system of the present invention, preferably, the evaporation concentration device comprises an evaporation concentrated spray layer disposed inside the flue gas treatment device and disposed at a flue gas inlet of the flue gas treatment device Above and all spray suction Below the layer.

According to the system of the present invention, preferably, the system further includes a liquid reservoir for receiving the slurry generated by the spray absorbing layer to slurry the slurry generated by the spray absorbing layer with the slurry of the evaporation concentrating device Separated.

According to the system of the present invention, preferably, the system further comprises:

a crystallization apparatus for crystallizing a sedimentation product from a circulating settling apparatus to form a crystalline product;

a centrifugation apparatus for centrifugally separating a crystalline product from a crystallization apparatus to form a mother liquor and a sulfate-containing product;

A drying device for drying the sulfate-containing product from the centrifuge equipment.

The invention also provides a method for the treatment of flue gas by using the above system, comprising the following steps:

Flue gas oxidation step: in the ozone spray reaction and absorption layer, using ozone to oxidize low-cost nitrogen oxides and elemental mercury in the flue gas to form high-priced nitrogen oxides and mercury oxide, respectively;

The wet absorption step: the absorbent sprayed by the spray absorption layer absorbs sulfur dioxide, nitrogen oxides and dust in the flue gas, and captures mercury oxide in the flue gas to form an absorption product;

Ozone supply step: supplying ozone to the ozone spray oxidation reaction layer by the ozone supply device;

Dust removal and defogging step: dedusting and defogging the flue gas treated by the wet absorption step by using a dust removal and defogging device;

Evaporation concentration step: evaporating and concentrating the slurry delivered thereto in an evaporation concentration device, and forming a concentrated product;

Circulation settling step: receiving concentrated product from the evaporation concentration apparatus in a circulating settling apparatus, and sedimenting the concentrated product to form a sedimentation product.

According to the method of the present invention, preferably, in the flue gas oxidation step, the process conditions of the ozone spray reaction and the absorption layer are: a flue gas temperature of 40 to 70 ° C, a dust content of 30 to 50 mg/Nm ³ , and a relative humidity. More than 30%, the moisture content of the flue gas is between 10% and 15%.

According to the method of the present invention, preferably, the method further comprises:

Crystallization step: crystallizing the sedimentation product from the circulating sedimentation apparatus in a crystallization apparatus to form a crystalline product;

Centrifugation step: centrifuging the crystalline product from the crystallization apparatus in a centrifugation apparatus to form a mother liquor and a sulfate-containing product;

Drying step: The sulfate-containing product from the centrifuge equipment is dried in a drying apparatus.

By adopting the system and method of the invention, the simultaneous desulfurization, denitration, dedusting and mercury removal of the flue gas can be realized, and the sulphate can be produced by using the waste liquid, thereby realizing comprehensive treatment and resource utilization. In addition, the system and method of the present invention enable the flue gas to simultaneously undergo an oxidation reaction and an absorption reaction, and the ozone injected as an oxidant induces a chain reaction in an environment containing hydroxide ions, and the ozone initiates a chain reaction to cause flue gas. a water-insoluble NO NO _x in the main component accounted converted to NO ₂ or N ₂ O ₅ and other nitrogen oxides of higher valence state, the flue gas in the conversion of elemental mercury into mercuric oxide, again water or an alkaline substance Absorption, complete the denitrification and mercury removal process. At the same time, the absorbent of the spray absorbing layer removes the sulphur dioxide in the flue gas. According to the preferred technical scheme of the present invention, the oxidation reaction and the absorption reaction can be completely reacted, the denitration and mercury removal efficiency is improved, and the consumption of ozone and absorbent materials is reduced. In addition, with the system and method of the present invention, the original desulfurization absorption tower can be utilized to the maximum extent, saving cost and floor space. According to the preferred technical solution of the present invention, it is possible to solve the problem that the production of magnesium sulfate by the waste gas after magnesium desulfurization consumes more steam, the production cost of the ore is higher, and the operation cost of the desulfurization is increased more.

DRAWINGS

1 is a schematic diagram of a system according to Embodiment 1 of the present invention.

In the figure, 1 is a flue gas treatment tower, 2 is a circulating settling tank, 3 is an evaporative concentrated spray layer, 4 is a liquid accumulator, 5 is an overflow port, 6 is a circulating settling tank discharge port, and 7 is a first layer spray Leaching absorption layer, 8 is the second layer of spray absorption layer, 9 is rotary dust removal and mist eliminator, 10 is flue gas outlet, 11 is slurry circulation tank, 12 is evaporation concentration pump, 13 is first layer spray absorption Layer circulation pump, 14 is the second layer spray absorption layer circulation pump, 15 is the super temperature emergency cooling device circulation pump, 16 is the crystallization tank, 17 is the centrifuge, 18 is the dryer, 19 is the packaging machine, 20 is the mother liquid back Evaporative concentrated spray layer circulation pump, 21 is the slurry tank discharge pump, 22 is the filter, 23 is the flue gas inlet, 24 is the over-temperature emergency cooling device, 25 is the ozone booster pump, 26 is the ozone generator, 27 is the ozone Spray reaction and absorption layer.

detailed description

The present invention will be further described below in conjunction with the drawings and specific embodiments, but the scope of the present invention is not limited thereto.

The "system" described in the present invention is a product, that is, a system collection of devices. In the present invention, the inlet has the same meaning as the inlet, and the two can be replaced. The "relative humidity" as used herein is expressed as a percentage. The "fluid gas moisture content" described in the present invention is an absolute moisture content expressed by weight percent.

In the present invention, the low-valent nitrogen oxides indicate that the nitrogen is a trivalent or lower (including trivalent) nitrogen oxide, including a low-valent nitrogen oxide (NO _X ) such as NO; and the high-priced nitrogen oxide indicates that the nitrogen is a tetravalent The above (including tetravalent) nitrogen oxides include high-valent nitrogen oxides (NO _X ) such as NO ₂ and N ₂ O ₅ .

The "monomeric mercury" as used in the present invention refers to zero-valent mercury (Hg ⁰ ) which exists in the form of a simple substance. The "oxidized mercury" according to the present invention includes HgO, and the mercury in HgO is a divalent oxidation state (Hg ²⁺ ).

The "wet absorption" as used in the present invention refers to an alkaline slurry as a main flue gas treatment absorption component, but is not limited to a flue gas treatment process in which any other component is added. In the flue gas treatment process of the present invention, the composition of the alkaline slurry which functions as desulfurization and denitrification may vary, and the formulation or variation thereof is well known to those skilled in the art.

The words "above", "below", "bottom", "bottom", etc., which are relative positions, are only "above" or "below", and may be set directly above or below. Indirectly set to "above" or "below", that is, not adjacent to "above" or "below", such as B layer above the A layer, only B layer above the A layer, can be adjacent , can also be adjacent, without any restrictions.

<Fume Control System>

The flue gas treatment system of the invention is a flue gas integrated treatment system, which can realize the functions of flue gas desulfurization, denitrification, dehydration, dedusting, dedusting and desulfurization and producing sulfate. The flue gas treatment system of the present invention includes the following devices: a flue gas treatment device, an ozone supply device, a dust removal and defogging device, an evaporation concentration device, and a circulation sedimentation device. The system according to the invention, wherein the flue gas treatment device is preferably a flue gas treatment tower, more preferably a desulfurization tower. Inside the flue gas treatment device, there are: at least two layers of spray absorbing layer, at least one layer of ozone spray reaction and absorption layer, wherein the ozone spray reaction and absorption layer will be low-cost nitrogen oxides in the flue gas and The elemental mercury is oxidized into high-priced nitrogen oxides and oxidized mercury, respectively. The spray absorption layer absorbs sulfur dioxide, nitrogen oxides and dust in the flue gas by an absorbent, and captures mercury oxide in the flue gas to form a suction. Receiving a product; the ozone supply device for supplying ozone to the ozone spray reaction and absorption layer; the dust removal and defogging device for performing dust removal and defogging on the flue gas, wherein the dust removal and defogging device is located at all sprays Above the absorption layer; the evaporation concentration apparatus is for evaporating and concentrating the absorption product with flue gas to form a concentrated product; the circulation sedimentation apparatus is for receiving a concentrated product from the evaporation concentration apparatus and forming a sedimentation product. The system of the present invention may also include a slurry discharge device, an outer tray filter or vacuum filter, a DCS or PLC control device, a crystallization device, a centrifugation device, a drying device, a packaging device, and a sump.

The flue gas treatment device of the present invention is internally provided with more than one layer of ozone spray reaction and absorption layer, and the number of layers of the ozone spray reaction and absorption layer may be determined according to actual requirements for flue gas desulfurization, denitrification and mercury removal, preferably one layer. Ozone spray reaction and absorption layer. In the ozone spray reaction and absorption layer, ozone is sprayed through an ozone atomizing nozzle provided on the layer, and low-cost nitrogen oxides (such as NO) in the flue gas react with ozone spray reaction and ozone sprayed in the absorption layer. After the oxidation reaction is completed, it becomes a high-priced nitrogen oxide (such as NO ₂ , N ₂ O ₅ ) which is easily absorbed by the absorbent, and ozone oxidizes elemental mercury in the flue gas into oxidized mercury, and the oxidized mercury is trapped in the slurry. . The atomized spray member used in the ozone spray oxidation reaction layer is not particularly limited, and those well known in the art can be used. Preferably, the atomized spray component of the present invention is a high pressure and corrosion resistant atomized spray component, and more preferably a high pressure acid and alkali corrosion resistant atomized spray component. According to an embodiment of the present invention, the atomizing spray member is preferably a high pressure atomizing nozzle, more preferably a stainless steel nozzle, and the pressure of ozone ejected from the high pressure atomizing nozzle is preferably in the range of 0.8 to 0.9 MPa. The outlet direction of the ozone atomizing nozzle is preferably perpendicular to the flue gas at 90 degrees, and the spray of the ozone ejecting pipe is ensured to be 100% in the tower.

The key point of the present invention is that the injected ozone acts as an oxidizing agent. In the environment containing hydroxide ions, ozone initiates a chain reaction, and then the chain reaction is transmitted to generate a highly oxidizing hydroxyl radical. The hydroxyl radical acts as a strong oxidant, oxidizing NO to NO ₂ and higher NOx, reacting with water to form nitric acid and nitrous acid, and the generated nitric acid reacts with nitrous acid and hydroxide ions of the alkaline substance in the slurry to form nitrate. To achieve the purpose of denitration. At the same time, hydroxyl radicals also oxidize mercury in the elemental mercury in the flue gas, which can be dissolved in the slurry to achieve the purpose of mercury removal, and greatly improve the reaction efficiency of ozone and reduce the consumption of ozone.

Taking the absorbent used in the spray absorbing layer as magnesium hydroxide as an example, the reaction principle is as follows:

(1) Magnesium oxide powder is dissolved in water to form a magnesium hydroxide slurry as an absorbent.

(2) Sulfur dioxide is absorbed by water and alkali salts.

Mg(OH) ₂ +H ₂ SO ₃ →MgSO ₃ ↓+2H ₂ O

(3) The injected ozone acts as an oxidant to initiate oxidation.

O ₃ +NO→NO ₂ +O ₂

NO ₂ +O ₃ →NO ₃ +O ₂

NO ₂ +NO ₃ →2N ₂ O ₅

(4) Ozone initiates a chain reaction in an environment where the humidity is appropriate and the hydroxide ion is contained.

Chain initiation reaction

O ₃ +OH ^- →HO ₂ ·+O ₂ ·

Chain transfer reaction

HO ₂ ·→O ₂ ^- ·+H ⁺

O ₃ +O ₂ ^- ·→O ₃ ^- ·+O ₂

O ₃ ^- ·+H ⁺ →HO ₃ ·

HO ₃ ·→HO·+O ₂

Produces highly oxidizing hydroxyl radicals.

(5) Hydroxyl radicals act as strong oxidants and oxidize NO.

HO·+NO→HONO

HO·+HONO→NO ₂ +H ₂ O

HO·+NO ₂ →HNO ₃

HO·+HONO→HNO ₃ +H·

(6) Magnesium sulphate is oxidized to magnesium sulfate by oxygen in a slurry tank to achieve the purpose of desulfurization.

(7) The generated nitric acid and nitrous acid react with the hydroxide ions of the alkaline substance in the slurry to form nitrate, which achieves the purpose of denitration.

HNO ₃ +OH ^- →NO ₃ ^- +HO ₂

(8) Mercury removal reaction.

Hg+O ₃ →HgO+O ₂

The flue gas treating device of the present invention is provided with at least two layers of spray absorbing layers, wherein the spray absorbing layer absorbs sulfur dioxide, nitrogen oxides and dust in the flue gas by an absorbent, and traps oxidation in the flue gas. Mercury, thereby forming an absorption product. The absorbent of the present invention may be an alkaline slurry which may be prepared from an oxide or a hydroxide, preferably calcium oxide, magnesium oxide, sodium oxide, calcium hydroxide, magnesium hydroxide or sodium hydroxide. It is prepared by one or several kinds of ammonia water, more preferably magnesium oxide or magnesium hydroxide. The number of layers of the spray absorbing layer may be determined according to the content of nitrogen oxides, sulfur dioxide, and elemental mercury waiting to be removed in the flue gas.

According to a preferred embodiment of the present invention, at least a layer of spray absorbing layer (corresponding to the secondary spray absorbing layer) is disposed inside the flue gas treating apparatus under the ozone spray reaction and absorption layer because it is disposed in the spray absorbing layer. The evaporation concentrated spray layer below the layer also has a preliminary absorption function, and the evaporation concentrated spray layer is equivalent to the first-stage spray absorption layer), and is used for pretreating the flue gas to absorb sulfur dioxide and dust in the flue gas to ensure the flue gas. Before passing through the ozone spray reaction and absorption layer, the alkaline slurry sprayed by the spray absorption layer can not only remove most of the sulfur dioxide and dust in the flue gas, but also appropriately reduce the high temperature flue gas through at least one spray absorption layer. The temperature prevents some ozone from decomposing when it comes into contact with high-temperature flue gas, while providing partial OH ^- to ensure the occurrence of chain reaction.

According to a preferred embodiment of the present invention, in the flue gas treating apparatus of the present invention, at least one spray absorbing layer (corresponding to a three-stage spray absorbing layer) is provided above the ozone spray reaction and absorption layer for absorption. Sulfur dioxide, nitrogen oxides and oxidized mercury in the flue gas to ensure that nitrogen oxides, oxidized mercury and residual sulfur dioxide in the flue gas after the oxidation reaction are absorbed by the alkaline slurry sprayed by the spray absorption layer. Preferably, at least two layers of spray absorbing layers, more preferably two, three or four layers, are disposed above the ozone spray reaction and absorption layer to absorb high-priced nitrogen oxides such as NO ₂ or N ₂ O _{5 ,} and oxidized mercury. Unabsorbed SO ₂ or other impurities.

In the flue gas treating apparatus of the present invention, preferably, a first layer of the spray absorbing layer and a second layer of the spray absorbing layer are disposed from the bottom to the top, and the ozone spray reaction and the absorbing layer are disposed in the first layer of the spray absorbing layer Between the layer and the second layer of the spray absorbing layer, to ensure that the hydroxide ion and the ozone sufficiently initiate the chain reaction and the chain transfer reaction, and generate a highly oxidized hydroxyl radical. According to the system of the present invention, preferably, the ozone spray reaction and absorption layer is disposed 0.8 to 2.8 meters upward from the first layer of the spray absorption layer and 1.0 to 2.3 meters from the second layer of the spray absorption layer. According to the system of the present invention, more preferably, the ozone spray reaction and absorption layer is disposed 1.2 to 2.0 meters above the first layer of the spray absorption layer and 1.3 to 1.8 meters from the second layer of the spray absorption layer.

In the flue gas treatment system of the present invention, the ozone spray reaction and the absorption layer are provided An ozone atomizing nozzle for generating ozone by an ozone generator in the ozone supply device, and being conveyed via a pipeline to the ozone atomizing nozzle disposed in the ozone spray reaction and absorption layer, preferably, the ozone generator generates ozone Thereafter, it is conveyed via a line to the ozone atomizing nozzle disposed in the ozone spray reaction and absorption layer, more preferably, pressurized by an ozone booster pump. The material of the pipeline of the ozone generator is preferably a glass fiber reinforced with carbon fibers.

In the flue gas treatment system of the present invention, the process conditions of the ozone spray reaction and the absorption layer are preferably as follows: the flue gas temperature may be 40 to 70 ° C, preferably 50 to 60 ° C, more preferably 55 ° C, and the flue gas dust content is 30 to 50 mg/Nm ³ , preferably 35 to 45 mg/Nm ³ , relative humidity greater than 30%, preferably greater than 40%; flue gas moisture content between 10% and 15%, preferably 12% to 13%. Under the above conditions, the ozone decomposition is slow, the spray absorption layer slurry is alkaline to provide hydroxide ions, and the temperature, humidity and hydroxide ion content are particularly suitable for decomposing more hydroxyl radicals, and the hydroxyl radicals are more than ozone. oxidation of stronger material, the faster the low nitrogen oxides, the oxidation of elemental mercury high nitrogen oxide, mercury oxide, ozone and NO _X to provide optimal reaction environment and Hg, to maximize the efficiency of denitration To save ozone. With the system of the invention, the denitration efficiency can reach more than 85%, and the ozone consumption can be reduced by more than 30%. Further, the hydroxyl radical reacts with the nitrogen oxides in the flue gas to form nitric acid and nitrous acid, and the hydroxyl radical reacts with the elemental mercury in the flue gas to form mercury oxide.

In the flue gas treatment system of the present invention, the temperature of the flue gas to be treated (flue gas inlet temperature) is preferably controlled at 80 to 150 ° C, more preferably between 90 and 120 ° C, and most preferably at 100 ° C, 105. °C or 110 °C to prevent premature decomposition of ozone, while taking full advantage of the heat of high temperature flue gas. The flow rate of the flue gas to be treated is controlled to be less than 5 m/s, more preferably 2 m/s to 4 m/s, and most preferably 3.5 m/s, to ensure that nitrogen oxides and elemental mercury in the flue gas are sufficiently oxidized, and the flue gas The sulfur dioxide in it is fully absorbed.

In the flue gas treatment system of the present invention, the ozone generator generates an ozone concentration in the range of 1 wt% to 15 wt%, and more preferably, the ozone concentration used is 5 wt% to 10 wt%, from the viewpoint of economy, to ensure Ozone is fully utilized.

In the flue gas treatment system of the present invention, the oxidation reaction time is determined by the size of the denitration and mercury removal oxidation zone, and the desulfurization, denitrification, mercury removal, flue gas flow passes through the ozone spray reaction and the absorption layer, and in the denitration, mercury removal oxidation reaction zone The ozone is subjected to an oxidation reaction, and the time of the oxidation reaction is generally from 0.1 to 10 s, preferably from 0.2 to 5 s; more preferably from 0.5 to 2 s.

In the flue gas treatment system of the present invention, the evaporative concentration apparatus is for evaporating and concentrating an absorption product with flue gas to form a concentrated product, and the evaporative concentration apparatus preferably includes at least one evaporative concentrated spray layer. The evaporative concentration apparatus is preferably disposed above the flue gas inlet inside the flue gas treatment apparatus, and the evaporative concentration apparatus is preferably disposed below the spray absorption layer as close as possible to the flue gas inlet to fully utilize the heat of the flue gas. The alkaline slurry sprayed by the evaporation concentration device (preferably including the evaporation concentrated spray layer) is in contact with the high temperature flue gas which has just entered the flue gas treatment device from the flue gas inlet to cool the high temperature flue gas and initially absorb the sulfur dioxide in the flue gas and Dust, etc. (ie, the evaporation concentrated spray layer also has the function of first-stage absorption of the spray layer), and the alkaline slurry is concentrated and evaporated. These slurries are lowered into a slurry circulation tank disposed at the bottom of the flue gas treatment equipment and then sent to an evaporative concentration unit (e.g., an evaporative concentrated spray layer). Preferably, the slurry is delivered to the filter via a slurry tank discharge pump, and the filtered slurry is sent to the evaporation concentration apparatus via an evaporation concentration circulation pump.

In the flue gas treatment system of the present invention, the circulating settling apparatus is for receiving a concentrated product from an evaporation concentration apparatus and forming a sedimentation product. Preferably, the circulating settling device comprises a circulating settling tank and a slurry circulating tank disposed at the bottom of the denitration apparatus. Preferably, the circulating settling device is located in the evaporation concentration device Lower portion; preferably, the circulating settling tank is located above the slurry circulation tank disposed at the bottom of the denitration apparatus. The concentrated product from the evaporation concentration apparatus is received in the circulating settling apparatus, and the concentrated product is subjected to sedimentation to form a sedimentation product (i.e., a mixture of crystals and slurry discharged after preliminary crystallization). The salt of the salt (for example, magnesium sulfate) in the sedimentation product is larger than 0.1 mm; preferably, the solid content of the sedimentation product (mixture of crystal and slurry) discharged from the cycle sedimentation step is more than 30% by weight. The temperature of the circulating settling apparatus is generally controlled at 55 to 70 ° C, preferably 60 to 65 ° C, more preferably 62 ° C or 63 ° C. Preferably, the crystal grains discharged by the cyclic sedimentation step are larger than 0.1 mm, and the sedimentation product (mixture of crystal and slurry) having a solid content of more than 30% by weight is further crystallized into the crystallization apparatus via a discharge port located at the bottom of the flue gas treatment apparatus. Preferably, the slurry overflowed by the circulating settling device can be recycled to the evaporation concentration device for circulating evaporation and concentration, preferably after being filtered by a filtering device, and then passed through an evaporation concentration circulating pump into an evaporation concentration device for re-evaporation.

According to a preferred embodiment of the invention, the flue gas treatment system of the invention further comprises crystallization equipment for crystallizing the settled product from the circulating settling apparatus to form a crystalline product. The sedimentation product (mixture of crystal and slurry) discharged from the circulation settling tank discharge port of the circulating sedimentation apparatus is further crystallized in a crystallization apparatus to obtain a crystal slurry. The sedimentation product entering the crystallization apparatus is cooled in the crystallization apparatus, preferably by cooling, to further form a crystal slurry in a supersaturated state, and the crystallization temperature is generally controlled at 20-30 ° C, preferably 20-25 ° C, most preferably It is 22 ° C or 23 ° C; the crystal grains (for example, magnesium sulfate grains) formed in the crystallization step are preferably more than 0.15 mm, more preferably more than 0.2 mm. The particle size of the present invention is determined by sieving (see GB/T21524-2008). In order to prevent grain sedimentation, preferably, a stirring device is arranged in the crystallization device, and the salt crystal is gradually grown in the crystallization device, and is separated from the stirrer to settle at the bottom of the crystallization device, and the crystal slurry is discharged through the discharge pump and sent to the centrifugal device. in. The discharged crystal slurry has a solid content of more than 40% by weight.

According to a preferred embodiment of the invention, a centrifugation device is also included for centrifuging the crystalline product from the crystallization apparatus to form a mother liquor, and a sulfate-containing product. In order to ensure sufficient centrifugation, the centrifugal speed is controlled at 1,500 to 2,000 rpm, preferably 1600 to 1,800 rpm. For batch operation, the centrifugation time of each batch of material is controlled to 5 to 30 minutes, preferably 5 to 10 minutes. For continuous operation, the centrifugation time of each batch of material is controlled to be from 10 to 30 minutes, preferably from 10 to 15 minutes. The sulfate-containing product obtained in the centrifugation step has a water content of less than 2% by weight. The mother liquor separated in the centrifugation step can be recycled to the evaporation concentration apparatus, for example, by an evaporation concentration circulation pump to the evaporation concentration apparatus.

According to a preferred embodiment of the invention, a drying device is also included for drying the sulfate-containing product from the centrifugation device. Preferably, it can be carried out by vacuum drying or by passing heated air. The drying temperature is 90 to 150 ° C, preferably 100 to 130 ° C, more preferably 110 to 120 ° C; and the drying pressure is 0.01 to 0.5 MPa, preferably 0.05 to 0.2 MPa. The moisture content of the precipitate after drying by the drying apparatus is less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight. In a specific embodiment, the air is heated into a vibrating fluidized bed by a saturated steam having a temperature of 120 ° C and a pressure of 0.2 MPa, and the sulfate-containing product is sufficiently dried to be a finished product under the action of mechanical vibration.

In the flue gas treatment system of the present invention, a dust removal and defogging device may be further included, and the dust removal and defogging device of the present invention is disposed above the entire spray absorption layer (i.e., above the topmost spray absorption layer). The dust removing and mist removing device of the present invention comprises a dust removing and mist removing device and a dust removing liquid spray layer disposed under the dust removing and mist removing device, and a dust removing liquid special nozzle is disposed on the dust removing liquid spray layer, and the dust removing liquid is sprayed, and the dust removing of the present invention The liquid spray layer is disposed 0.3 to 1 meter below the dust removal and mist eliminator, preferably 0.4 to 0.9 meters, more preferably 0.5 to 0.8 meters. Preferably, the dusting liquid spray layer is disposed within a range of 0.5 to 0.8 meters above the topmost spray absorbing layer, more preferably 0.6 meters. Dust removal of the present invention The mist eliminator is preferably a rotary dust eliminator, more preferably a high efficiency rotary dust defogger, and those known in the art can be used, and will not be described herein.

After the flue gas treated by the dust removing and defogging device of the present invention, the flue gas dust content can be very low, and the mist droplet content can be no more than 25 mg/Nm ³ .

The flue gas treatment system of the present invention further includes a liquid reservoir, preferably for receiving a slurry generated by the spray absorption layer to separate the slurry produced by the spray absorption layer from the slurry of the evaporation concentration device .

The flue gas treatment system of the present invention may further comprise a slurry circulation device for receiving a slurry containing sulfate, nitrate, and oxidized mercury formed from the spray absorption layer, which is low in mercury nitrate due to reactivity limitation. The slurry containing sulfate, nitrate, and oxidized mercury is circulated into the spray absorbing layer. Preferably, the slurry in the spray absorbing layer is a slurry prepared by using magnesium oxide or magnesium hydroxide, and the slurry circulation device is for receiving a slurry containing magnesium sulfate, magnesium nitrate and oxidized mercury formed from the spray absorbing layer, and The slurry containing magnesium sulfate, magnesium nitrate, and oxidized mercury is recycled to the spray absorbing layer.

The flue gas treatment system of the present invention may further comprise an outer plate filter (plate and frame filter) or a vacuum filter for filtering out solid particles in the slurry, such as magnesium sulphate, calcium sulfate, and flue gas. dust. The filtered clean slurry is sent to a settling tank or water treatment tank.

In the flue gas treatment system of the present invention, a slurry discharge device may be further included to discharge the slurry after desulfurization, denitrification, demercuration and dedusting in which the pH value in the column reaches a prescribed value.

In the flue gas treatment system of the present invention, DCS or PLC control equipment may also be included, and the whole set of equipment is automated as much as possible to save manpower, improve the automation level of equipment and process, and reduce man-made operational errors.

According to the flue gas treatment system of the present invention, preferably, the flue gas satisfies any of the following conditions:

(1) The flue gas is smoke from a sintering machine, a pellet, or a kiln;

(2) sulfur dioxide content of the flue gas is ^{300mg / Nm 3 ~ 20000mg / Nm} 3, NO X content of ^{100mg / Nm 3 ~ 500mg / Nm} 3 and an oxygen content of 8 ~ 20vt%.

<Method of flue gas treatment>

The method for treating flue gas by using the above system of the present invention comprises the following steps: a flue gas oxidation step, a wet absorption step, an ozone supply step, a dust removal and defogging step, an evaporation concentration step, and a circulation sedimentation step. Optionally, the flue gas denitration method of the present invention further comprises a slurry discharge step, a slurry circulation step, a filtration step, a crystallization step, a centrifugation step, a drying step, and the like.

The flue gas oxidation step of the present invention is to use the ozone spray reaction and the ozone emitted from the absorption layer to oxidize the low-temperature nitrogen oxides and elemental mercury in the flue gas to form high-priced nitrogen oxides and mercury oxide, and the ozone spray reaction and absorption The number of layers of the layer can be determined according to the actual requirements for flue gas denitration, preferably a layer of ozone spray reaction and absorption layer. Preferably, the flue gas oxidation step of the present invention comprises: in the ozone spray reaction and absorption layer, spraying ozone by providing an ozone atomizing nozzle. The process conditions of the ozone spray reaction and the absorption layer are as described above and will not be described here.

The wet absorption step of the present invention absorbs sulfur dioxide, nitrogen oxides and dust in the flue gas by the absorbent sprayed from the spray absorption layer, and traps mercury oxide in the flue gas to form an absorption product. Preferably, the absorbent is an alkaline slurry, and the alkaline slurry is preferably prepared from an oxide or a hydroxide, more preferably calcium oxide, magnesium oxide, sodium oxide, calcium hydroxide, magnesium hydroxide or hydrogen. It is prepared by one or several kinds of sodium oxide and ammonia water, and most preferably is prepared by magnesium oxide or magnesium hydroxide. The number of layers of the spray absorbing layer may depend on the amount of nitrogen oxides, mercury and sulfur dioxide in the flue gas waiting to be removed. The invention is in a flue gas treatment device, in oxygen At least one spray absorbing layer is disposed above and below the reaction and absorption layers. As mentioned above, it will not be described here.

The ozone supply step of the present invention is to supply ozone to the ozone spray reaction and absorption layer by an ozone supply device. Specifically, ozone is generated by an ozone generator in the ozone supply device, and after being pressurized, is sent to the ozone atomizing nozzle disposed in the ozone spray reaction and absorption layer via a pipeline, and then injected into the flue gas treatment device. Preferably, the pipeline of the ozone generator is made of glass fiber with a surface covering carbon fiber. The concentration of ozone generated by the ozone generator is in the range of 1 wt% to 15 wt%, and from the viewpoint of economy, the ozone concentration used is more preferably 5 wt% to 10 wt% to ensure that the ozone is sufficiently utilized.

The dust removing and defogging step of the present invention is to perform dust removal and defogging on the flue gas treated by the wet absorption step by using a dust removing and defogging device. The dust removing and defogging device of the present invention and the dust removing and defogging process are as described above, and are not described herein again.

In the evaporation concentration step of the present invention, the slurry of sulfate, nitrate, and oxidized mercury is concentrated by evaporation in an evaporation concentration apparatus to form a concentrated product. As mentioned above, it will not be described here.

The cyclic settling step of the present invention receives the concentrated product from the evaporation concentration zone in a circulating settling apparatus and settles the concentrated product to form a settled product. Other specifics are as described above and will not be described here.

Optionally, the method of flue gas treatment of the present invention further comprises a crystallization step of crystallizing the settled product from the cycle settling apparatus in a crystallization apparatus. The sulfate (e.g., magnesium sulfate) forms a crystalline product by controlling the crystallization temperature and the crystallization time. As mentioned above, it will not be described here.

Optionally, the method of flue gas treatment of the present invention further comprises a centrifugation step of centrifuging the crystalline product from the crystallization apparatus in a centrifuge apparatus to form a mother liquor and a sulfate (e.g., magnesium sulfate) product. As mentioned above, it will not be described here.

Optionally, the method of flue gas treatment of the present invention further comprises a drying step of drying the sulfate (e.g., magnesium sulfate) product from the centrifuge equipment in a drying apparatus. As mentioned above, it will not be described here.

Optionally, the method for treating flue gas of the present invention may further comprise a slurry circulation step for receiving a slurry containing sulfite, sulfate, nitrite, nitrate, and oxidized mercury formed from the spray absorption layer, and It is circulated into the spray absorbing layer.

Optionally, the method of flue gas treatment of the present invention may further comprise a slurry discharge step for discharging a slurry containing sulfate, nitrate, and oxidized mercury having a pH value up to a prescribed value in the column.

Optionally, the method for treating flue gas according to the present invention further comprises a filtering step of filtering out solid particles in the slurry, such as magnesium sulfite, calcium sulfate, and flue gas, by using an outer plate filter or a vacuum filter. dust. The filtered clean desulfurization solution is sent to a settling tank or a water treatment tank.

The process conditions of the above slurry circulation step, slurry discharge step, and filtration step are not particularly limited, and process conditions well known in the art can be used.

The flue gas treatment system and method of the invention can be applied to the traditional wet calcium method, the magnesium method, the sodium method, the potassium method and the ammonia method, as long as the traditional tower structure and process are modified according to the structure and process provided by the invention. Structure, process can be. The salt is preferably one or more of a magnesium salt, a calcium salt, a sodium salt, a potassium salt or an ammonium salt, preferably a magnesium sulfate salt, more preferably magnesium sulfate, including magnesium sulfate monohydrate, magnesium sulfate trihydrate, and five. Magnesium sulfate in water and anhydrous magnesium sulfate. For the skilled person, a different type of magnesium sulphate product can be obtained by using a conventional extended drying time or extending the size and size of the process equipment in the drying stage so that the material stays longer or shorter in the dryer.

When the system and method of the present invention, when the amount of the flue gas treatment is to be 1,000,000Nm ³ / h, the flow rate of the flue gas is less than 5m / s, the flue gas NO _X concentration of 500mg / Nm about ^3, SO ₂ concentration of 1000-3000mg / Nm ^3, _the NO _x concentration in the flue gas after treatment is required 100mg / Nm ³ or so, the use of denitration O ₃ as the oxidant, the ozone consumption is preferably 260 ~ 460kg / h, preferably from 300 to 360kg/h.

The system and method of the present invention are described in conjunction with the accompanying drawings, which are intended to illustrate the invention and not to limit the scope of the invention.

The raw materials used in the following examples of the invention are as follows:

The alkaline slurry is a magnesium hydroxide slurry;

The O ₃ product has an ozone concentration of 10% by weight;

Example 1

1 is a schematic diagram of a system in accordance with an embodiment of the present invention. The figure shows:

The flue gas treatment system of the invention comprises a flue gas treatment tower 1, an ozone supply device, a dust removal and defogging device, an evaporation concentration device, a circulation sedimentation device and the like. The ozone supply device includes an ozone generator 26 and an ozone boost pump 25. The exhaust gas treatment tower 1 is provided with an over-temperature emergency cooling device 24, an evaporation concentrated spray layer 3, a liquid reservoir 4, a first layer spray absorption layer 7, an ozone spray reaction and an absorption layer 27, in order from bottom to top. The second layer spray absorbing layer 8 and the rotary dust removing demister 9. The flue gas to be treated enters the flue gas treatment tower 1 from the flue gas inlet 23 of the flue gas treatment tower 1, and is cooled and initially absorbed by the evaporation concentrated spray layer 3, and then absorbed into the flue gas through the first layer of the spray absorption layer 7. The sulphur dioxide and dust are then oxidized by the ozone spray reaction and the absorption layer 27 to oxidize the low-cost nitrogen oxides and elemental mercury to the high-priced nitrogen oxides and the oxidized mercury, respectively, and the oxidized flue gas is sprayed through the second layer. The absorption layer 8 performs desulfurization, denitrification and demercuration, and the desulfurization, denitrification and demercuration flue gas enters the rotary dust removal and mist eliminator 9 and is discharged through the flue gas outlet 10. Set in the evaporation concentrated spray layer 3 The sump 4 between the first spray absorbing layer 7 and the first spray absorbing layer 7 is for receiving the slurry for receiving the first spray absorbing layer 7 and the second spray absorbing layer 8, and concentrating the slurry with the evaporation concentrate The slurry of the layer 3 is separated. The ozone spray reaction and absorption layer 27 was 1.8 m from the first spray absorbing layer 7; the spacing between the first spray absorbing layer 7 and the second spray absorbing layer 8 was 2.8 m. The slurry circulation tank 11 disposed at the bottom of the flue gas treatment tower 1 is provided with an alkaline slurry, and is passed through an evaporation concentration circulation pump 12, a first layer spray absorption layer circulation pump 13, and a second layer spray absorption layer circulation pump 14 to pass alkaline. The slurry delivery line is delivered to each of the spray absorbing layers (evaporation concentrated spray layer 3, first layer spray absorbing layer 7, and second layer spray absorbing layer 8). The slurry circulation tank 11 is connected to the evaporation concentrated spray layer 3 through a slurry discharge pump 21, a filter 22, and an evaporation concentration circulation pump 12. Ozone is generated in the ozone generator 26 and is piped to the nozzles of the ozone spray reaction and absorption layer 27 by the ozone booster pump 25. An over-temperature emergency cooling device 24 is further disposed below the first spray absorbing layer 7 of the flue gas treatment tower 1, and the over-temperature emergency cooling device 24 is connected to the slurry circulation tank 11 through a pipeline through an over-temperature emergency cooling device circulating pump 15. through.

A circulating settling tank 2 is further disposed above the slurry circulating tank 11 inside the flue gas treatment tower 1 and below the over-temperature emergency cooling device 24, and an overflow port 5 is provided at the top of the circulating settling tank 2, and the overflow port 5 passes through the slurry discharge pump 21 The filter 22 and the evaporation concentration circulation pump 12 are in communication with the evaporation concentrated spray layer 3. The circulation settling tank discharge port 6 provided at the bottom of the circulating settling tank 2 is connected to the crystallization tank 16, and the crystallization tank 16 is provided with a centrifuge 17, a dryer 18 and a packaging machine 19. The centrifuge 17 is also in communication with the evaporative concentration spray layer 3 through a mother liquor back evaporation concentrated spray layer circulation pump 20 and an evaporative concentration circulation pump 12.

The process flow of Embodiment 1 of the present invention is:

a. The inside of the flue gas treatment tower 1 is provided with a slurry circulation tank 11 containing an alkaline slurry (the slurry in this embodiment is made of magnesium oxide powder and industrial tap water is added to make hydrogen and oxygen). As a flue gas absorbent, the alkaline slurry is transported to the first through the first layer of spray absorbing layer circulating pump slurry circulating pump 13 and the second layer of spray absorbing layer circulating pump 14 via the alkaline slurry conveying line. a layer of spray absorbing layer 7, a second layer of spray absorbing layer 8 and sprayed downward;

b. The flue gas to be treated enters the flue gas treatment tower 1 from the flue gas inlet 23 of the flue gas treatment tower 1 and rises, and the high temperature flue gas is cooled and concentrated to absorb sulfur dioxide and dust through the evaporation concentrated spray layer 3, and then The alkaline slurry sprayed by the spray absorbing layer 7 is neutralized by countercurrent contact to remove most of the SO ₂ and dust in the flue gas to form a preliminary purified flue gas, and the temperature of the flue gas is lowered;

c. The O ₃ product produced by the ozone generator 26 is pressurized by the ozone booster pump 25, sent to the ozone spray reaction and absorption layer 27 through the ozone transfer line and sprayed downward, and the above-mentioned preliminary purified flue gas and ozone spray The O ₃ countercurrent contact in the reaction and absorption layer 27 undergoes an oxidation reaction, oxidizes the low-priced nitrogen oxides in the flue gas into high-priced nitrogen oxides and removes them from the flue gas, and at the same time, the elemental substance in the flue gas Mercury is oxidized to oxidized mercury and removed from the flue gas to form an ozone oxidizing flue gas;

d. Ozone oxidation flue gas continues to rise, and a neutralization reaction occurs in countercurrent contact with the alkaline slurry sprayed from the second spray absorption layer 8 to obtain a slurry containing magnesium sulfate, magnesium sulfite, magnesium nitrate and magnesium nitrite, and oxidized. Mercury is also trapped in the slurry and forms ozone oxidative desulfurization, denitrification and mercury removal flue gas;

e. Ozone oxidative desulfurization, denitrification and mercury removal, the flue gas continues to rise, and the fine particles and droplets entrained in the flue gas are removed by the rotary dust eliminator 9 in the process, the flue gas drives the rotating blades in the rotary dust demister The group rotates at a high speed, and under the centrifugal force generated by the high-speed rotation of the rotating blade group, the droplets and the fine particles collide with each other to form larger particles and are smashed to the inner wall of the rotary dust removing demister and flow down the wall; The mister 9 is equipped with a dust-removing liquid, and the atomized dust-removing liquid can trap extremely fine dust, and at the same time, it can interact with the mist to achieve a flocculation effect and aggravate the fog. The quality of the drop causes it to fall, and the ozone oxidizing desulfurization, denitration and mercury removal flue gas is discharged into the qualified flue gas through the flue gas outlet 10 after being dedusted and defogged;

f. The slurry containing magnesium sulfate, magnesium sulfite, magnesium nitrate and magnesium nitrite formed during the entire flue gas treatment process falls into the slurry circulation tank 11 at the bottom of the flue gas treatment tower 1, and the nitrite reacts with oxygen in the environment. The nitrate is formed, and the pH of the pool circulation tank 11 is controlled between 5 and 7. The slurry in the lower portion of the slurry circulation tank 11 is discharged through the slurry tank discharge pump 21, and then filtered by the filter 22 and sent to the evaporation by the evaporation concentration circulation pump 12. The concentrated spray layer 3 is concentrated by evaporation, and the circulation amount accounts for 50 vt% of the total output of the slurry circulating tank slurry; the slurry of the upper portion of the slurry circulating tank 11 passes through the first layer of the spray absorption layer circulation pump 13, and the second layer of the spray absorption layer. The circulation pump 14 is sent to the first layer of the spray absorption layer 7 and the second layer of the spray absorption layer 8, the circulation of the two accounts for 50vt% of the total output, the volume ratio of the two is 1:1;

g. The slurry in the evaporation concentrated spray layer 3 passes through the high-temperature flue gas, and the concentrated product is formed and descends to the circulating settling tank 2. The slurry overflowed from the overflow port 5 of the circulating settling tank 2 passes through the slurry tank discharge pump 21 and enters the filter. 22, after being filtered, sent to the evaporation concentrated spray layer 3 by the evaporation concentration circulating pump 12 for recycling;

h, the temperature of the circulating settling tank 2 is controlled at 60 ° C, and the sedimentation product (grain containing magnesium sulfate crystal, magnesium nitrate) having crystal grains larger than 0.1 mm and solid content exceeding 30 wt% discharged from the circulating sedimentation tank discharge port 6 at the bottom of the circulating settling tank 2 The mixture with the slurry enters the crystallization tank 16, and the solution in the crystallization tank 16 is cooled by circulating the cooling water at a temperature of 20 to 30 ° C to achieve temperature crystallization of the magnesium sulfate supersaturated state, and a magnesium sulfate crystal having a crystal grain size larger than 0.15 mm is formed. Magnesium nitrate is still dissolved in the slurry; in order to prevent crystal sedimentation, a stirring device is arranged in the crystallization tank 16, and the stirring device is an electric stirring device;

i. The crystal slurry having a solid content of more than 40% by weight obtained by further crystallization from the crystallization tank 16 is sent to the centrifuge 17 for separation, and the centrifuge 17 is separated to obtain a water content of less than 2% by weight. The magnesium sulfate product and the mother liquor, the mother liquor is passed through the mother liquor back to the evaporation concentration spray layer circulation pump 20 and the evaporation concentration circulation pump 12 to the evaporation concentrated spray layer 3 for cyclic evaporation and concentration;

j. The magnesium sulfate product having a water content of less than 2% by weight is sent to the dryer 18, and the air is heated and sent to the dryer 18 (ie, the vibrating fluidized bed) by a saturated steam having a temperature of 120 ° C and a pressure of 0.2 MPa. Under the action, the magnesium sulfate crystal is fully dried into a magnesium sulfate product and sent to the automatic packaging machine 19 for packaging, and finally a magnesium sulfate product having a quality above the industrial qualified product is obtained;

k. The liquid collector 4 collects the slurry from the first spray absorbing layer 7 and the second spray absorbing layer 8, and further recycles after treatment. The sump 4 also separates the slurry produced by the first spray absorbing layer 7 and the second spray absorbing layer 8 from the slurry produced by the evaporation concentrated spray layer 3;

1. When a smoke accident occurs, the over-temperature emergency cooling device circulation pump 15 will be automatically activated, and the evaporation concentration circulation pump 12, the first-layer spray absorption layer circulation pump 13, and the second-layer spray absorption layer circulation pump 14 will be closed. And the ozone boosting pump 25, the slurry in the slurry circulating tank 11 is sent to the over-temperature emergency cooling device 24 through the over-temperature emergency cooling device circulating pump 15 for cooling the flue gas to ensure equipment safety.

The above-mentioned flue gas treatment system and method are applied to a 1.5 million-ton pellet fire gas treatment experiment, and the experimental operating parameters, the flue gas emissions, and the quality of the produced magnesium sulfate are shown in Table 1-3.

Table 1 1.5 million tons of pellets flue gas treatment system operating parameters

Serial number	parameter	unit	Numerical value
1	Flue gas treatment tower inlet flue gas volume (working conditions)	m 3 /h	240000
2	Flue gas treatment tower inlet flue gas volume (standard condition wet basis)	Nm 3 /h	166718

3	Flue gas treatment tower inlet smoke temperature	°C	120
4	SO 2 inlet concentration	Mg/Nm	2000
5	Inlet nitrogen oxide concentration	Mg/Nm	450
6	Inlet dust concentration	Mg/m 3	98
7	Inlet mercury concentration	Gg/m 3	10
8	Design desulfurization rate	%	≥96
9	Design denitration rate	%	≥84
10	Magnesium to sulfur ratio	Mg/S	1.02
11	Total resistance of flue gas treatment tower	Pa	<1000

Table 2 Exhaust emissions from flue gas treatment experiments

Serial number	project	Quantity		unit
1	Flue gas treatment tower outlet flue gas volume (working conditions)	176117	Nm 3 /h
2	exhaust temperature	50	°C
3	SO 2 emission concentration	<50	Mg/Nm 3
4	NOx emission concentration	<70	Mg/Nm 3
5	Average outlet dust concentration	Mg/m 3	3
6	Mercury concentration at export	Gg/m 3	0.01
7	Export fog content	Mg/m 3	20
8	Highest desulfurization efficiency	%	98.9
9	Maximum denitration efficiency	%	90.4
10	Highest dust removal efficiency	%	96.9
11	Highest mercury removal efficiency	%	99.9
12	Magnesium sulfate output	1.1	t/h
13	Magnesium sulfate quality	>98	% mass percentage

In this experiment, the amount of flue gas is 240,000 m ³ /h, the concentration of sulfur dioxide at the inlet is 2000 mg/Nm ³ , the concentration of nitrogen oxide is 450 mg/Nm ³ , the concentration of dust is 98 mg/m ³ , and the concentration of mercury is 10 μg/m ³ . System and method After desulfurization, denitrification, demercuration and dedusting, the concentration of sulfur dioxide is less than 50mg/Nm ³ , the concentration of nitrogen oxide is less than 70mg/Nm ³ , the concentration of dust is 3mg/m ³ , the concentration of mercury is as low as 0.01μg/m ³ , and the content of mist is 20mg/m ³ , all emission levels are lower than the national requirements, and even meet more stringent emission standards.

In the production process of by-product magnesium sulfate, the main content of MgSO ₄ ·7H ₂ O is as high as 98.5%, which satisfies the use standard of industrial grade magnesium sulfate.

Table 3: The quality of magnesium sulfate produced by the flue gas treatment experiment

Serial number	project	Quantity		unit
1	Main content (calculated as MgSO 4 ·7H 2 O)	98.5	% mass percentage
2	Iron (in terms of Fe) content	0.005	% mass percentage
3	Chloride (as Cl) content	0.30	% mass percentage
4	Heavy metal content	0.0005	% mass percentage
5	Water insoluble content	0.08	% mass percentage

The measurement method of magnesium sulfate quality adopts "Chemical Industry Standard of the People's Republic of China HG/T 2680-2009".

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It should be considered as the scope of protection of the present invention.

Claims (10)

1. A flue gas treatment system characterized by comprising:

   Flue gas treatment equipment with internal:

   (1) at least one layer of an ozone spray reaction and absorption layer for oxidizing low-cost nitrogen oxides and elemental mercury in the flue gas to high-priced nitrogen oxides and mercury oxide, respectively;

   (2) at least two layers of spray absorbing layer for absorbing sulfur dioxide, nitrogen oxides and dust in the flue gas by using an absorbent, and trapping oxidized mercury in the flue gas to form an absorption product;

   a dust removal and defogging device for performing dust removal and defogging on the flue gas, wherein the dust removal and defogging device is located above all the spray absorption layers;

   An ozone supply device for supplying ozone to said ozone spray reaction and absorption layer;

   An evaporation concentration device for evaporating and concentrating the absorption product with flue gas to form a concentrated product;

   A circulating settling device for receiving concentrated product from the evaporation concentration device and forming a settling product.
2. The system of claim 1 wherein at least one of said at least two spray absorbing layers is disposed beneath said ozone spray reaction and absorption layer for pre-treatment Treating flue gas to absorb sulfur dioxide and dust in the flue gas; and

   At least one of the at least two spray absorbing layers of the spray absorbing layer is disposed above the ozone spray reaction and absorption layer for absorbing sulfur dioxide and nitrogen oxides in the flue gas and trapping Mercury oxide in the flue gas.
3. The system according to claim 2, wherein a first layer of spray absorbing layer and a second layer of spray absorbing layer are disposed inside the flue gas treating apparatus from bottom to top, said ozone spray reaction and absorption layer It is disposed between the first spray absorbing layer and the second spray absorbing layer.
4. The system of claim 3 wherein said ozone spray is reversed The first layer of the spray absorption layer should be 0.8 to 2.8 meters from the absorption layer and 1.0 to 2.3 meters from the second layer of the spray absorption layer.
5. The system of claim 1 wherein said evaporative concentration device comprises an evaporatively concentrated spray layer disposed within the flue gas treatment device and disposed in the flue gas of the flue gas treatment device Above the inlet and all below the spray absorbing layer.
6. The system of claim 1 further comprising an accumulator for receiving slurry produced by the spray absorbing layer to slurry the spray absorbing layer with said evaporative concentration device The slurry is separated.
7. The system of any of claims 1-6, wherein the system further comprises:

   a crystallization apparatus for crystallizing a sedimentation product from a circulating settling apparatus to form a crystalline product;

   a centrifugation apparatus for centrifugally separating a crystalline product from a crystallization apparatus to form a mother liquor and a sulfate-containing product;

   A drying device for drying the sulfate-containing product from the centrifuge equipment.
8. A method for performing flue gas treatment using the system of any one of claims 1-7, comprising the steps of:

   Flue gas oxidation step: in the ozone spray reaction and absorption layer, using ozone to oxidize low-cost nitrogen oxides and elemental mercury in the flue gas to form high-priced nitrogen oxides and mercury oxide, respectively;

   The wet absorption step: the absorbent sprayed by the spray absorption layer absorbs sulfur dioxide, nitrogen oxides and dust in the flue gas, and captures mercury oxide in the flue gas to form an absorption product;

   Ozone supply step: supplying ozone to the ozone spray oxidation reaction layer by the ozone supply device;

   Dust removal and defogging step: dedusting and defogging the flue gas treated by the wet absorption step by using a dust removal and defogging device;

   Evaporation concentration step: evaporating and concentrating the slurry delivered thereto in an evaporation concentration device, and forming a concentrated product;

   Circulation settling step: receiving concentrated product from the evaporation concentration apparatus in a circulating settling apparatus, and sedimenting the concentrated product to form a sedimentation product.
9. The method according to claim 8, wherein in the step of oxidizing the flue gas, the process conditions of the ozone spray reaction and the absorption layer are: a flue gas temperature of 40 to 70 ° C and a dust content of 30 to 50 mg / Nm ³ , The relative humidity is greater than 30%, and the moisture content of the flue gas is between 10% and 15%.
10. The method according to claim 8 or 9, wherein the method further comprises:

    Crystallization step: crystallizing the sedimentation product from the circulating settling device in a crystallization apparatus to form a crystalline product;

    Centrifugation step: centrifuging the crystalline product from the crystallization apparatus in a centrifugation apparatus to form a mother liquor and a sulfate-containing product;

    Drying step: The sulfate-containing product from the centrifuge equipment is dried in a drying apparatus.

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