CN105498509A - Calcium-magnesium combined desulphurization and denitrification method realizing deep removal of flue gas pollutants - Google Patents

Abstract

The invention discloses a calcium-magnesium combined desulfurization and denitrification method satisfying the deep removal of flue gas pollutants. The invention relates to the field of environmental protection, and is a new technology developed for deep desulfurization and denitrification of industrial flue gas. The desulfurization equipment corresponding to the present invention is composed of multiple zones, including a main desulfurization zone, a deep desulfurization zone and a high-efficiency dust and fog removal zone. In the main desulfurization area, the conventional calcium method (lime or limestone) is used for desulfurization, so that the flue gas can achieve a desulfurization efficiency of more than 90% under economical and reasonable conditions; then, the flue gas passes through the deep desulfurization area, and the magnesium desulfurization process is used. In the case of a relatively low liquid-gas ratio, the sulfur dioxide in the flue gas is removed to below 30mg/m3 to achieve its ultra-low emission requirements. In addition, an oxidation and denitrification accelerator can also be added in the deep desulfurization area to simultaneously realize the desulfurization and denitrification functions. Compared with the prior art, the invention has high desulfurization efficiency and low cost, and the reaction intermediate product can be recycled.

Description

A calcium-magnesium combined desulfurization and denitrification method that meets the deep removal of flue gas pollutants

technical field

The invention relates to the field of environmental protection, in particular to a calcium-magnesium combined desulfurization and denitrification method that satisfies the deep removal of flue gas pollutants.

Background technique

At present, the air pollution situation in our country is severe, which has caused serious harm to human health. SO2 is one of the main pollutants that cause air pollution. Effective control of SO2 in industrial flue gas is an urgent environmental protection issue. In recent years, domestic and foreign industrial waste gas, especially air pollutants from coal-fired power plants have put forward ultra-low emission requirements, requiring SO2 emission to be less than 35mg/m3.

Looking at the mainstream technologies currently used, it can be found that whether it is desulfurization in the furnace or flue gas purification, the core is the reaction of calcium-based compounds with SO2 to form gypsum (CaSO4). These methods have the advantages of simple process, safe and reliable production and operation, wide range of applicable coal types, high desulfurization efficiency, high utilization rate of absorbent, abundant and cheap source of desulfurizer-limestone. However, it is difficult to meet the current ultra-low emission requirements by using calcium desulfurization alone. It is necessary to increase the desulfurization efficiency by increasing the number of spray layers, increasing the liquid-gas ratio, and increasing the volume of the slurry tank, especially when the desulfurization efficiency is high. If measures such as increasing the liquid-gas ratio continue, the desulfurization efficiency will increase very slowly, thereby greatly increasing equipment investment and energy consumption. Therefore, the cost of using calcium alone to control the depth of desulfurization is relatively high.

At present, as a wet flue gas desulfurization technology, the magnesium oxide desulfurization method is being widely promoted and applied in the world. The magnesium oxide desulfurization technology is mature, and the desulfurization efficiency is as high as 98%, which can easily meet the requirements of emission standards. In addition, the magnesium oxide desulfurization system does not scale, the system is safe and reliable, the work efficiency is high, and the by-products can be recycled; the desulfurization agent uses magnesium oxide powder, the source of raw materials is sufficient, the transportation is convenient, and the price is relatively low. However, for large-scale desulfurization, because the amount of magnesium oxide consumed by desulfurization and the generated magnesium sulfate wastewater to be treated are both high, there are problems in terms of economy. However, if it is used in combination with calcium desulfurization and only used in deep desulfurization areas, its advantages will be more obvious.

To sum up, calcium desulfurization is difficult to meet the current ultra-low emission requirements, while magnesium desulfurization is difficult to apply to large-scale desulfurization, and the cost is high. Therefore, it is necessary to explore a desulfurization method with low cost, suitable for large-scale desulfurization and high desulfurization efficiency, which has good industrial value.

Contents of the invention

The object of the present invention is to provide a combined calcium-magnesium desulfurization and denitrification technology that satisfies the deep removal of flue gas pollutants in order to overcome the above-mentioned defects in the prior art.

The purpose of the present invention can be achieved through the following technical solutions: a calcium-magnesium combined desulfurization and denitrification method that satisfies the deep removal of flue gas pollutants. zone and deep desulfurization zone, including the following steps:

(1) After the industrial flue gas is dedusted, it is input into the main desulfurization area, and the flue gas is pre-desulfurized by calcium desulfurization in the main desulfurization area to obtain low-sulfur flue gas;

(2) The low-sulfur flue gas obtained in step (1) enters the deep desulfurization zone, where magnesium desulfurization is used to desulfurize the low-sulfur flue gas, and then it is discharged into the atmosphere after demisting treatment.

The calcium method desulfurization described in step (1) uses one or more of limestone powder, lime or calcium carbide slag as a desulfurizer, which is dissolved in water and configured to have a mass concentration of 5-20% and a pH value of 5.5-6.5. Slurry (if the pH is greater than 6.5, it is easy to scale, so it should not be too high; if the pH is less than 7, it can still desulfurize), pump it into the main desulfurization area and mix it with the flue gas to remove the sulfur in the flue gas. The desulfurization liquid-gas ratio is 3 -8L/m ³ .

Step (1) When the concentration of sulfur dioxide in the flue gas input to the main desulfurization zone is 500-5000 ^mgm3 , remove more than 90% of the sulfur dioxide in the flue gas through the main desulfurization zone, and make the concentration of sulfur dioxide in the flue gas discharged from the main desulfurization zone Below 300mg/m ³ , the calcium desulfurization can be operated under the most reasonable process conditions. The desulfurization product is converted into gypsum through oxidation and crystallization.

The magnesium method desulfurization described in step (2) uses magnesium oxide or magnesium hydroxide slurry as a desulfurizing agent, which is dissolved in water, configured into a slurry with a mass concentration of 1-10% and a pH value of 6.5-9, and pumped into a deep desulfurization The zone is fully contacted and mixed with the flue gas to remove sulfur in the flue gas. The desulfurization liquid-gas ratio is 1-3L/m ³ . Through this treatment, the system can achieve deep desulfurization under the condition of very low magnesium consumption, and can greatly Significantly reduce the operating pressure of calcium desulfurization in the main desulfurization area.

The deep desulfurization zone described in step (2) can remove the sulfur dioxide in the flue gas from the main desulfurization zone to within 30 mg/m ³ .

In the deep desulfurization zone, a denitrification enhancer is added to the desulfurizer slurry used for magnesium desulfurization to perform denitrification.

The denitrification enhancer includes one or more of ozone, hydrogen peroxide, magnesium peroxide or magnesium persulfate and other halogen-free or alkali metal-free oxidants; the pH of magnesium oxide has the ability to activate these oxidants to absorb denitrification, and has a relatively Good denitrification effect; the addition amount of the destocking enhancer is such that the mass concentration in the desulfurizer slurry used for magnesium desulfurization is: 1%-15%.

The by-product of desulfurization and denitrification obtained in the deep desulfurization zone is magnesium sulfate or magnesium nitrate solution, and the obtained magnesium sulfate or magnesium nitrate solution is used as a buffer in the main desulfurization zone, which can improve the desulfurization effect of the main desulfurization zone.

Pass the obtained magnesium sulfate and magnesium nitrate solution into the desulfurization liquid circulation tank, precipitate with ammonia water, and obtain magnesium hydroxide which can be recycled; the ammonium sulfate produced by regeneration is replaced by lime into ammonia water for recycling; The calcium sulfate precipitate is washed and collected together with desulfurization gypsum.

The main desulfurization zone and the deep desulfurization zone are located in an integrated device or in two independent tower devices.

From bottom to top, the integrated equipment includes the tower kettle area, the main desulfurization area, the deep desulfurization area, and the dust and fog removal area; the raw material flue gas enters the equipment from the main desulfurization area,

Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects:

(1) Compared with the traditional limestone-gypsum desulfurization process, the desulfurization efficiency is significantly improved;

(2) Due to the high-efficiency removal effect of magnesium oxide in the deep desulfurization zone, it is avoided to increase the number of spray layers, increase the liquid-gas ratio, and increase the volume of the slurry pool to achieve ultra-low emissions, which reduces the cost and makes the system operate at a very low level. In the case of low magnesium consumption, deep desulfurization can be realized, and the operating pressure of calcium desulfurization in the main desulfurization zone can be greatly reduced;

(3) Magnesium oxide does not scale, therefore, the equipment is not easy to corrode, and the maintenance cost is reduced;

(4) In the deep desulfurization zone, one or more of the oxidizing agents that do not contain halogens or alkali metals such as ozone, hydrogen peroxide, magnesium peroxide, and magnesium persulfate can be added to denitrify at the same time, and the pH of magnesium oxide has the ability to activate these The ability of oxidant to absorb denitrification has better denitrification effect;

(5) The desulfurization and denitrification by-products obtained in the deep desulfurization zone can be directly used as a buffer for the desulfurization liquid in the main desulfurization zone, which can improve the desulfurization effect of the main desulfurization zone; ammonia water can also be used for precipitation, and the obtained magnesium hydroxide can be recycled After use, the ammonium sulfate generated by the regeneration is converted into ammonia water by using lime for recycling.

Description of drawings

Figure 1 is a schematic diagram of the process of the present invention.

Among them, 1 is the main desulfurization area, 2 is the deep desulfurization area, 3 is the dust and fog removal area, 4 is the desulfurization liquid circulation pool, and 5 is the tower kettle area.

detailed description

The embodiments of the present invention are described in detail below. This embodiment is implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating procedures are provided, but the protection scope of the present invention is not limited to the following implementation example.

Example 1

As shown in Figure 1 , this embodiment adopts integrated equipment, which includes tower kettle area 5, main desulfurization area 1, deep desulfurization area 2, and dust and mist removal area 3 from bottom to top. The solution in the deep desulfurization zone 2 is passed into the desulfurization liquid circulation pool 4, and ammonia water is added to obtain magnesium hydroxide for recycling. The specific steps are as follows:

(1) The concentration of sulfur dioxide in raw flue gas is 500mg/m ³ , the concentration of nitrogen oxides is 150mg/m ³ , of which nitric oxide is 80mg/m ³ , nitrogen dioxide is 70mg/m ³ , and the flue gas temperature is 180°C ; The raw flue gas is discharged into the main desulfurization zone 1 with a flow rate of 100m ³ /h; the main desulfurization zone adds a desulfurizer solution with a flow rate of 300L/h. The desulfurizer solution is made by dissolving lime in water, and its concentration is 20 wt%, pH 6.5, after the reaction, low-sulfur flue gas is obtained, the concentration of sulfur dioxide in it is 50mg/m ³ , and the removal rate is 90%.

(2) The desulfurizing agent solution after the reaction in the main desulfurization area 1 falls in the tower kettle area 5, and the desulfurizing agent solution is extracted from the tower kettle area 5 by a circulation pump, and is returned to the top of the main desulfurization area 1 through the pipeline, Carry out recycling of desulfurizer solution;

(3) The low-sulfur flue gas is discharged into the deep desulfurization zone 2, and the absorbent slurry with a flow rate of 100L/h is added. The absorbent slurry is a magnesium hydroxide slurry formed by adding water to magnesium hydroxide, and its concentration is 10wt%. It is 9, and hydrogen peroxide is added in the slurry simultaneously (making the solution contain hydrogen peroxide concentration to be 1%), after carrying out deep desulfurization and denitrification, obtain exhaustable flue gas;

(4) Discharge the obtained slurry after treatment in the deep desulfurization zone 2 into the desulfurization liquid circulation pool 4, and add 15% ammonia water in the desulfurization liquid circulation pool 4 (the ratio of the added volume to the volume of the solution to be regenerated is 1:3), The resulting precipitate is magnesium hydroxide, and after adding water, it becomes a magnesium hydroxide slurry and circulates to the deep desulfurization zone 2; a sufficient amount of lime is added to the generated solution to make the solution turn into ammonia water and calcium sulfate precipitation again, and the calcium sulfate precipitation is carried out Recycle;

(5) Discharge the exhaustable flue gas into the dust and mist removal area 3, and discharge it into the atmosphere after deep dust and mist removal treatment.

After testing, the concentration of sulfur dioxide in the flue gas discharged into the atmosphere is 6mg/m ³ , the concentration of nitric oxide is reduced to 30mg/m ³ , the concentration of nitrogen dioxide is reduced to 10mg/m ³ , the concentration of sulfur dioxide meets the emission requirements, and desulfurization The rate is 98.8%.

Example 2

This embodiment adopts integrated equipment, which are dust and mist removal area, deep desulfurization area, main desulfurization area, and tower kettle area from top to bottom. The solution in the deep desulfurization area is passed into the desulfurization liquid circulation pool, and ammonia water is added to obtain magnesium hydroxide for recycling. The specific steps are as follows:

(1) The concentration of sulfur dioxide in raw flue gas is 5000 mg/m ³ , the concentration of nitrogen oxides is 450 mg/m ³ , of which nitrogen monoxide is 250 mg/m3, nitrogen dioxide is 200 mg/m ³ , and the flue gas temperature is 180°C; The raw flue gas is discharged into the main desulfurization zone at a flow rate of 100m ³ /h; the main desulfurization zone adds a desulfurizer solution with a flow rate of 800L/h, which is prepared by dissolving lime in water, and its concentration is 5wt% , the pH is 5.5, after the reaction, low-sulfur flue gas is obtained, and the concentration of sulfur dioxide in it is 300 mg/m ³ , and the removal rate is 94%. ;

(2) The desulfurizing agent solution after the reaction in the main desulfurization area falls into the tower kettle area, and the desulfurizing agent solution is extracted from the tower kettle area through a circulation pump, and is returned to the top of the main desulfurization area through the pipeline, and the desulfurizing agent solution is desulfurized. recycling;

(3) Low-sulfur flue gas is discharged into the depth desulfurization zone, adding flow is the absorbent slurry of 300L/h, and this absorbent slurry is the magnesium hydroxide slurry that magnesium hydroxide adds water and forms, and its concentration is 1wt%, and pH is 6.5. At the same time, add hydrogen peroxide to the slurry to maintain the hydrogen peroxide content in the absorption liquid at about 0.5%. After deep desulfurization and denitrification, exhaustable flue gas is obtained;

(4) the solution obtained after treatment in the deep desulfurization zone is magnesium sulfate and magnesium nitrate, and the magnesium sulfate or magnesium nitrate solution of gained is used as the buffering agent of the main desulfurization zone, which can improve the desulfurization effect of the main desulfurization zone;

(5) Discharge the exhaustable flue gas into the dust and mist removal area 3, and discharge it into the atmosphere after deep dust and mist removal treatment.

After testing, the concentration of sulfur dioxide in the flue gas discharged into the atmosphere is 20mg/m ³ , the concentration of nitric oxide is reduced to 45mg/m ³ , the concentration of nitrogen dioxide is reduced to 15mg/m ³ , the concentration of sulfur dioxide meets the emission requirements, and the concentration of sulfur dioxide The removal rate is 99.6%.

Example 3

Field test 1: Take the actual flue gas of a coal-fired power plant as the treatment object, draw 100m ³ /h of actual flue gas from the flue, in which the concentration of sulfur dioxide is 800mg/m ³ , the concentration of nitric oxide is 200mg/m ³ , The nitrogen dioxide concentration was 180 mg/m ³ (ozone injection). The desulfurization agent in the main desulfurization area is limestone powder, the solution concentration is about 10%, the desulfurization liquid-gas ratio is 5L/m ³ , the desulfurization agent in the deep desulfurization area is magnesium oxide, the pH value of the desulfurization liquid is controlled at 7, the slurry concentration is The liquid-gas ratio is 2L/m ³ , and 1% hydrogen peroxide is added in the deep desulfurization zone. Using the same steps as in Example (1), desulfurization and denitrification treatment was performed on raw flue gas. Through testing and analysis, it is concluded that the desulfurization efficiency of the main desulfurization zone reaches about 90%, and after passing through the deep desulfurization zone, the concentration of sulfur dioxide at the outlet is 25mg/m ³ , the concentration of nitrogen monoxide is reduced to 60mg/m ³ , and the concentration of nitrogen dioxide is reduced to 10 mg/m ³ .

Example 4

Field test 2: Take the actual flue gas of the power plant as the treatment object, draw 10000m ³ /h of actual flue gas from the flue, in which the concentration of sulfur dioxide is 1800mg/m ³ , the concentration of nitrogen monoxide is 250mg/m ³ , and the concentration of carbon dioxide The nitrogen concentration was 200 mg/m ³ (ozone injection). The desulfurization agent in the main desulfurization area is lime, the concentration of the slurry is 8%, and the desulfurization liquid-gas ratio is 4L/m ³ . After passing through the main desulfurization area, the residual sulfur dioxide content in the flue gas is 200 mg/m ³ . Magnesium, the slurry concentration is ² %, the desulfurization liquid-gas ratio is 2L/m ³ , and ¹ % hydrogen peroxide is added. 8 mg/m ³ .

Example 5

Laboratory simulation test 1: The simulated flue gas flow rate is 500ml/min, the concentration of sulfur dioxide is 1000mg/m3, and the flue gas temperature is about 180°C.

The simulated flue gas passed through the solution containing 10% limestone and 2% magnesium hydroxide slurry in turn. The concentration of sulfur dioxide at the outlet was measured by a flue gas analyzer to be about 20 mg/m ³ , and the desulfurization efficiency was 98%.

Pass the simulated flue gas alone through a solution containing 10% limestone, use a flue gas analyzer to measure the concentration of sulfur dioxide at the outlet is about 100mg/ ^m3 , and the desulfurization efficiency is about 90%; pass the simulated flue gas alone through a solution containing 3% magnesium oxide When in the solution, the measured outlet sulfur dioxide concentration is about 30mg/m ³ , and the desulfurization efficiency is 97%.

This example shows that the calcium-magnesium combined process can be used to solve the problems existing in meeting the ultra-low emission in the single calcium desulfurization method.

Example 6

Laboratory simulation test 2: the simulated flue gas flow rate is 500ml/min, the concentration of sulfur dioxide is 1000mg/m ³ , and the concentration of nitrogen oxides is 150mg/m ³ (of which nitric oxide is 80mg/m ³ and nitrogen dioxide is 70mg/m ³ ), the smoke temperature is around 180°C. The specific experiment is as follows:

The flue gas is first passed into a solution containing 10% limestone, and then into a solution of 2% magnesium oxide, wherein 1% hydrogen peroxide is added to the magnesium oxide solution, and the measured concentration of sulfur dioxide at the outlet is about 0mg/ ^m3 , and the concentration of nitric oxide The concentration of nitrogen dioxide is about 30mg/m ³ , the concentration of nitrogen dioxide is 2mg/m ³ , the desulfurization efficiency reaches 100%, and the removal efficiency of nitrogen monoxide reaches 62.5%.

This shows that, in the case of adding hydrogen peroxide, the sulfur dioxide in the flue gas can be further reduced to achieve its ultra-low emission requirements, and at the same time realize the function of simultaneous denitrification.

Claims (10)

1. meet calcium-magnesium combined desulfurization and denitration method of flue gas pollutant deep removal, it is characterized in that, the method comprises following step:

(1) industrial smoke is after dedusting, inputs main desulfurization zone (1), adopts the desulfurization of calcium method to carry out pre-desulfurization to flue gas, obtain low-sulfur flue gas in main desulfurization zone (1);

(2) step (1) gained low-sulfur flue gas penetration depth desulfurization zone (2), adopts magnesium processes desulfurization to carry out deep desulfuration to low-sulfur flue gas in deep desulfuration district (2), then through demist process, is disposed in air.

2. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1, it is characterized in that, calcium method desulfurization described in step (1) is using one or more of agstone, lime or carbide slag as desulfurizing agent, soluble in water, being configured to mass concentration is 5 ~ 20%, and pH value is the slurries of 5.5 ~ 6.5, pumps into main desulfurization zone (1) and fully contacts rear mixing with flue gas, slough the sulphur in flue gas, desulfurization liquid-gas ratio is 3-8L/m ³.

3. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1, it is characterized in that, step (1) sulfur dioxide concentration inputted in the flue gas of main desulfurization zone (1) is 500-5000mg/m ³in situation, remove the sulfur dioxide of in flue gas more than 90% through main desulfurization zone (1), and make sulfur dioxide in flue gas concentration that main desulfurization zone (1) is discharged lower than 300mg/m ³.

4. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1, it is characterized in that, magnesium processes desulfurization described in step (2) is using magnesia or magnesium hydroxide slurry as desulfurizing agent, soluble in water, being configured to mass concentration is 1 ~ 10%, and pH value is the slurries of 6.5 ~ 9, pumps into deep desulfuration district (2) and fully contacts mixing with flue gas, slough the sulphur in flue gas, desulfurization liquid-gas ratio is 1-3L/m ³.

5. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1, it is characterized in that, the sulfur dioxide in flue gas coming from main desulfurization zone can take off to 30mg/m by the deep desulfuration district (2) described in step (2) ³within.

6. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1 or 4, it is characterized in that, in magnesium processes desulfurization desulfurizer therefor slurries, add denitration hardening agent in described deep desulfuration district (2), carry out denitration.

7. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 6, it is characterized in that, described denitration hardening agent comprises one or more in ozone, hydrogen peroxide, peromag or persulfuric acid magnesium; The addition of described denitration hardening agent is the mass concentration making them in magnesium processes desulfurization desulfurizer therefor slurries: 1%-15%.

8. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1 or 6, it is characterized in that, described deep desulfuration district (2) gained desulphurization denitration accessory substance is magnesium sulfate or magnesium nitrate solution, is used by the magnesium sulfate of gained or the magnesium nitrate solution buffer as main desulfurization zone (1).

9. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 8, it is characterized in that, the magnesium sulfate of gained and magnesium nitrate solution are passed into doctor solution circulatory pool (4), with ammonia precipitation process, obtaining magnesium hydroxide can recycle; Regenerate the ammonium sulfate that produces then to recycle lime and again replace and become ammoniacal liquor, recycle; The calcium sulfate precipitation produced, after washing, is collected together with desulfurated plaster.

10. a kind of calcium-magnesium combined desulfurization and denitration method meeting flue gas pollutant deep removal according to claim 1, it is characterized in that, described main desulfurization zone (1) and deep desulfuration district (2) are arranged in integration apparatus or two independently tower.