Please explain the double alkali desulfurization

The desulfurization process mainly consists of 5 parts:

1) Preparation and replenishment of absorbents.

2) Absorbent slurry spraying.

3) The fog droplets in the tower are in contact with the flue gas and mix.

4) Reduction of sodium base by slurry in the regeneration pool.

5) Gypsum dehydration.

Due to the strong alkalinity of the sodium-based desulfurizer, the solubility of the reaction products after absorbing sulfur dioxide is large, and it will not cause supersaturated crystallization and cause fouling and blockage.

Summary. 1) Preparation and replenishment of absorbents.

2) Absorbent slurry spraying.

3) The fog droplets in the tower are in contact with the flue gas and mix.

4) Reduction of sodium base by slurry in the regeneration pool.

5) Gypsum dehydration.

The process flow of double alkali desulfurization.

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1) Preparation and supplementation of absorbents; 2) Absorbent slurry spraying. 3) The fog droplets in the tower are in contact with the flue gas and mix. (4) Reduction of sodium base by slurry in the regeneration pond next to the branch; (5) Gypsum dehydration treatment with partners.

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The cupola furnace consumes 35 tons of coke per day, and the hourly flow rate of sulfur is 20,000 cubic meters, how much lime and lye need to be replenished every day, and the impact on the replacement and the change of chemical reaction when the sandan is not added in time, and the flue gas emission is less than 30 cubic milligrams per hour.

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Write down the specific process flow.

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**Auspicious solution. The double alkali flue gas desulfurization process is similar to the reaction mechanism of lime leakage lime and other wet desulfurization processes, and the main reaction is that the SO2 in the flue gas is first dissolved in the absorption solution, and then dissociated into H+ and HSO3-; Na2CO3 or NaOH liquid is used to absorb SO2 in flue gas to generate HSO32-, SO32- and SO42-.

Due to the strong alkalinity of the sodium-based desulfurizer, the solubility of the reaction products after absorbing sulfur dioxide is large, which will not cause supersaturated crystallization of tung pants and cause scaling and blockage. The desulfurization process mainly includes five parts: (1) pure and high preparation and supplementation of absorbent; 2) Absorbent slurry spraying. (3) The fog droplets in the tower are mixed with the flue gas contact attitude scale; 4) Reduction of sodium base by slurry in the regeneration pool. 5) Gypsum dehydration.

Control of the pH value of the absorbent solution.

In the case of good scrubber coverage, it is also important to be able to control the pH value of the whole system well. At present, there is a lack of corresponding operating skills and related knowledge in the operation of the desulfurization system, and the pH value of the absorption liquid cannot be accurately controlled, which leads to damage to the equipment or poor use effect of the desulfurization system, and the result is that the flue gas pollutants fail to meet the emission standards.

1. With the increase of the pH of the absorbent solution (circulating clear water pool) at the inlet of the tower, the desulfurization efficiency will gradually increase, but when the pH is increased, a certain amount of sodium hydroxide solution needs to be added to the system to maintain the stable operation of the system. In order to effectively control the amount of NAOH replenishment in the system, it is best to control the pH of the absorbent liquid (circulating clear water tank) at the inlet of the tower during operation.

2. When the pH of the absorbent liquid (circulating clear water pool) at the inlet of the tower is controlled, and when the pH of the regeneration pool is controlled, the supersaturation of calcium sulfate at the inlet of the tower can be reduced to the nearest 1, which greatly reduces the possibility of scaling in the tower.

The double alkali method is to use sodium-based desulfurizer for in-tower desulfurization, which is strongly alkaline by Qi Lu in sodium-based desulfurizer, and the solubility of the reaction product is large after absorbing sulfur dioxide, which will not cause supersaturated crystallization in the high cavity zone, and the problem of fouling and blockage caused by round decay. On the other hand, the desulfurization product is discharged into the regeneration tank and regenerated with calcium hydroxide, and the regenerated sodium-based desulfurizer is then beaten back to the desulfurization tower for recycling. The double-alkali desulfurization process reduces the investment and operating costs, and is more suitable for the desulfurization transformation of small and medium-sized boilers.

Answer: (1) Preparation and supplementation of absorbents; 2) Absorbent slurry spraying. 3) The fog droplets in the tower are in contact with the flue gas and mix. 4) Reduction of sodium base by slurry in the regeneration pool. 5) Gypsum dehydration. The double alkali flue gas desulfurization process is similar to other wet desulfurization processes such as limestone and lime, and the main reaction is that the SO2 in the flue gas is first dissolved in the absorption solution, and then dissociated into H+ and HSO3-; Na2CO3 or NaOH liquid is used to absorb SO2 in flue gas to generate HSO32-, SO32- and SO42-.

Double-alkali desulfurization refers to the desulfurization method that uses two alkaline substances, NaOH and lime (calcium hydroxide), as desulfurizers.

There is generally only one circulating pool for double-alkali desulfurization, and the soot captured in the process of dedusting and desulfurization is mixed in the same circulating pool, and the soot, the reaction product calcium sulfite, calcium sulfate and lime slag and the lime slag that is not completely reacted are removed at the same time when the ash in the circulating water pool is removed, and the ash slag is a mixture that is not easy to be used to form waste slag. The main process is: sodium hydroxide solvent is added to the clear water pool at one time to make sodium hydroxide desulfurization liquid (circulating water), and the pump is pumped into the desulfurization dust collector for desulfurization.

All three products are soluble in water. In the desulfurization process, the flue ash mixed with the flue gas is moistened by the circulating water at the same time and captures into the circulating water, and the circulating water discharged from the desulfurization dust collector becomes gray water (dilute mortar). It flows into the sedimentation tank together, and the flue ash is regularly removed by precipitation, such as making internal combustion bricks.

The supernatant overflows into the reaction pool and reacts with the added lime, and the displaced sodium hydroxide is dissolved in the circulating water, and insoluble calcium sulfite, calcium sulfate and calcium carbonate are generated at the same time, which can be removed by precipitation; Yes, it is a good raw material for making cement.

Introduction to sodium-alkali desulfurization process.

The sodium-calcium double alkali method [Na2CO3--Ca(OH)2] uses soda ash to absorb SO2, lime reduction and regeneration, and the absorbent is recycled after regeneration, and there is no wastewater discharge.

Under the principle of advanced technology, reliable operation and economic reasonableness, in order to minimize one-time investment, energy saving and consumption reduction and convenient system maintenance, the process flow as shown in Figure 1 is designed.

The flue gas is dusted through the bag filter and then enters the desulfurization tower. The flue gas spirals upwards in the guide plate and contacts with the desulfurization liquid, atomizing the desulfurization solution into droplets of diameter to form a good atomization absorption zone. The flue gas and the alkaline desulfurizer in the desulfurization solution are fully in contact with the reaction in the atomization zone to complete the desulfurization absorption and further dust removal of the flue gas.

After desulfurization, the flue gas directly enters the fan through the air outlet on the side of the tower and is discharged by the chimney.

The desulfurization solution adopts the external circulation absorption method. The desulfurization liquid that absorbs SO2 flows into the regeneration tank, and the new lime water is regenerated for regeneration, and the grout after the reaction flows into the sedimentation regeneration tank for precipitation, when the sediment of one sedimentation regeneration tank is full, the slurry switches to another sedimentation regeneration tank, and then the sediment precipitated by this regeneration tank is manually cleaned up, and the waste residue is dried and transported for treatment. The regenerated and precipitated liquid in the circulating tank is pumped into the desulfurization tower by the circulating pump for recycling.

In addition, because the slag belt water will lose a part of the sodium ions in the desulfurization solution, a small amount of soda ash or waste lye needs to be added to the circulating tank.

Principles of chemical reactions.

The basic chemical principle can be divided into two parts: the desulfurization process and the regeneration process.

Absorbs SO2 in the tower

na2co3＋so2＝na2so3＋co2 （1）

2naoh＋so2＝na2so3+h2o （2）

na2so3＋so2＋h2o＝2nahso3 （3）

The above three formulas vary depending on the pH of the absorption solution, and when the alkalinity is high (pH 9), the main reaction is (2); When the alkalinity is slightly reduced, equation (1) is the main reaction; When alkaline to neutral or even acidic (5 pH 9), the reaction is carried out according to formula (3).

Regenerate with slaked lime.

ca（oh）2 ＋na2so3＝2naoh＋caso3

ca（oh）2 ＋2nahso3＝na2so3＋caso3• h2o＋1 h2o

In the lime slurry (lime reaches saturation), NaHSO3 reacts with Ca(OH)2 to release Na, and SO32- reacts with Ca2, and the resulting CaSO3 precipitates in the form of hemihydrate compounds to regenerate Na. Na2CO3 is only a starting alkali, and it actually consumes lime after starting, and theoretically does not consume soda ash (but it will bring some when cleaning the slag, so there is a small amount of loss).

Recycled desulfurizers such as NaOH and Na2SO3 are recycled.