This method is used to treat the tail gas of sulfuric acid production in some small sulfuric acid production units in China.

In this method, the sulfuric acid tail gas is ammonia washed, and the obtained (NH4) 2so3-nh4hso3-h2o absorption solution is recycled. Part of the absorption solution is led out directly as a product without acid hydrolysis, neutralization and other treatment. The method has the advantages of simple equipment, less investment, and can save a lot of acid and alkali. The product can be used as fertilizer after dilution. According to the operation of existing production, the basic conditions are summarized as follows;

① The absorption tower adopts porcelain ring packed tower, and the tower is lined with ceramic tiles;

② The alkalinity of absorption mother liquor should be controlled at 12 ~ 16 titer, and the absorption rate should be more than 90%;

③ When the relative density of the absorption mother liquor is 1.17 ~ 1.18, it can be led out as a product, and the total sulfate content in the mother liquor is about 350g / L;

④ When the alkalinity is appropriate, the spray density of absorption solution is 14m3 / (M2 · h), and the absorption efficiency can exceed 95%. The reduction of spray density will lead to the reduction of efficiency.

Ammonia ammonium sulfate process

Process principle

The absorption principle of ammonia ammonium sulfate method is the same as that of other methods in ammonia method. NH3 absorbs SO2, and the generated (NH4) 2so3-nh4hso3 absorption cycle is used to wash the waste gas containing SO2. The difference is that in the absorption process of the latter, it is necessary to prevent and inhibit the occurrence of oxidation side reactions as much as possible, and avoid oxidizing NH4) 2so3 in the absorption solution to NH4) 2so3-nh4hso4, so as to maintain the absorption efficiency of SO2 by the absorption solution; In the ammonia ammonium sulfate method, the oxidation product is the end product of the method, so it is necessary to promote the oxidation of circulating absorption solution in the absorption process. As a result, ammonia ammonium sulfate method is different from ammonia acid method and ammonia ammonium sulfite method in process and equipment. {ammonia treatment}

Ammonia ammonium sulfate process is generally used to treat SO2 in combustion flue gas, because generally, the oxygen content in flue gas is sufficient to oxidize all (NH4) 2so3 in absorption liquid to (NH4) 2SO4. However, the oxidation rate of the absorption solution directly affects the absorption rate of SO2. The oxidation of the washing solution changes sulfite into sulfate. The more complete the oxidation, the lower the ability of the solution to absorb SO2. In order to ensure the SO2 absorption capacity of the absorption solution, sufficient sulfite concentration shall be maintained in the absorption solution. Sulfite cannot be completely oxidized in the absorption tower. Therefore, a special oxidation tower needs to be set behind the absorption tower to ensure the full oxidation of ammonium sulfite.

Process and equipment

In order to promote the oxidation of absorption liquid in the absorber, some measures should be taken to strengthen the oxidation in the design and process conditions of the absorber. The absorption equipment shall be equipment easy to absorb oxygen, such as packed tower, and the gas velocity and solution concentration in the tower shall be controlled lower; The absorption solution shall maintain a high S / C value and make the temperature of the absorption solution higher. Catalytic oxidizing substances such as activated carbon and manganese ions shall be used to promote oxygen dissolution and sulfite oxidation. In the oxidation tower, compressed air is generally used to make the solution have a large enough oxygen dissolution rate. In the structure of the oxidation tower, in order to ensure sufficient contact surface between air and solution, a rotary atomizer shall be set in the tower to make the air entering the tower rotate and atomize, resulting in fine bubbles dispersed in the solution and increasing the gas-liquid contact area.

The process of ammonia ammonium sulfate process is mainly divided into absorption, oxidation and post-treatment.

Recommended waste gas treatment devices: activated carbon adsorption device / activated carbon absorption tower, waste gas purification tower, alkali spray tower and acid mist purification tower.

The combustion flue gas is exhausted after two-stage absorption. Part of the circulating absorption liquid is led out from the absorption system to the neutralization tank and neutralized with NH3. The neutralization solution is pumped into the oxidation tower and filled with compressed air for oxidation. The oxidized solution is added with NH3 in the pH adjustment tank, which is called alkaline, so that the heavy metals contained in the flue gas become hydroxide precipitation and removed. Ammonium sulfate product can be obtained after ammonium sulfate mother liquor is concentrated, crystallized, separated and dried.

The main product of this method is ammonium sulfate. Compared with other methods of ammonia method, less equipment is used, no acid is consumed, and no SO2 by-products are produced. Therefore, there is no need to process and store SO2 equipment. Therefore, the method is relatively simple and the investment is less. At present, ammonium sulfate fertilizer has a poor market abroad, but it still has a good market in China. It is especially suitable for use in alkaline soil in North China. In addition, the application of nitrogen phosphorus compound fertilizer can be expanded by preparing nitrogen phosphorus compound fertilizer from sulfur ammonia. There are imported devices in France.