Spray type desulfurization and dust collector

Technical characteristics of dual alkali desulfurization method

The dual alkali flue gas desulfurization technology was developed to overcome the disadvantage of easy scaling in the limestone lime method. The traditional limestone lime gypsum flue gas desulfurization process uses calcium based desulfurizers to absorb sulfur dioxide and generate calcium sulfite and calcium sulfate. Due to their low solubility, they are prone to scaling and blockage in the desulfurization tower and pipelines. The problem of scaling and blockage seriously affects the normal operation of the desulfurization system, and even seriously affects the normal operation of the boiler system. In order to avoid the adverse factors of using calcium based desulfurizers as much as possible, most calcium based desulfurization processes require corresponding forced oxidation systems (aeration systems), which increase initial investment and operating costs. Using inexpensive desulfurizers can easily cause scaling and blockage problems, while using sodium based desulfurizers alone has high operating costs and difficult to treat desulfurization products. The contradiction between the two is highlighted, and the dual alkali flue gas desulfurization process has emerged, which effectively solves the above contradictions.

1、 Basic principles of craftsmanship

The double alkali method uses sodium based desulfurizers for tower desulfurization. Due to the strong alkalinity of sodium based desulfurizers, the solubility of reaction products after absorbing sulfur dioxide is high, which will not cause supersaturation crystallization and lead to scaling and blockage problems. On the other hand, the desulfurization products are discharged into the regeneration tank for reduction and regeneration with calcium hydroxide, and the regenerated sodium based desulfurizer is then sent back to the desulfurization tower for recycling. The dual alkali desulfurization process reduces investment and operating costs, and is more suitable for desulfurization and dust removal equipment for small and medium-sized boilers undergoing desulfurization transformation.

The dual alkali flue gas desulfurization technology uses sodium hydroxide solution as the starting desulfurizer, and the prepared sodium hydroxide solution is directly injected into the desulfurization tower to wash and remove the flue gasSO₂To achieve the purpose of flue gas desulfurization, the desulfurization product is then reduced to sodium hydroxide by the desulfurizer regeneration pool and sent back to the desulfurization tower for recycling.

2、 Introduction to Process Flow

The flue gas from the boiler first passes through a dust collector for dust removal, and then enters the desulfurization tower from the bottom of the tower through the flue. The method of arranging several layers (depending on the specific situation) of swirl plates in the desulfurization tower has good gas-liquid contact conditions. The alkaline solution sprayed from the top of the tower is atomized on the swirl plates to remove impurities from the flue gasSO₂Fully absorb and react with the sprayed alkaline solution. After desulfurization and washing, the clean flue gas is dehydrated by the demister and enters the heat exchanger. The heated flue gas is discharged into the atmosphere through the chimney by the induced draft fan. The initial double alkali method usually had only one circulating water tank.NaOHLime and fly ash captured during the desulfurization process are mixed in the same circulating pool. When removing the ash and slag in the circulation pool, the ash, reaction generated calcium sulfite, calcium sulfate, lime slag, and unreacted lime are all removed at the same time. The cleared mixture is not easy to be comprehensively utilized and becomes waste residue. To overcome the shortcomings of the traditional double alkali method, it has been improved. The main process is to add sodium hydroxide to the clean water tank at once to make desulfurization solution, which is pumped into the absorption tower for desulfurization. All three products are soluble in water. During the desulfurization process, the fly ash mixed in the flue gas is simultaneously wetted and captured by the circulating liquid. The circulating slurry discharged from the absorption tower flows into the sedimentation tank. Ash residue is regularly removed through sedimentation and can be recycled, such as in brick making. The supernatant overflows into the reaction tank and reacts with the added lime, replacing the sodium hydroxide solution in the circulating water, while generating insoluble calcium sulfite, calcium sulfate, calcium carbonate, etc., which can be removed by precipitation.

3、 Solution to secondary pollution

Using sodium hydroxide as a desulfurizer, the absorption of sulfur dioxide in the desulfurization tower has a fast reaction rate and high desulfurization efficiency, but the desulfurization productsNa₂SO₄It is difficult to handle and can easily cause serious secondary pollution problems. Adopting the dual alkali flue gas desulfurization process, the product obtained by absorbing sulfur dioxide with sodium hydroxide is regenerated with lime, with only a small amountNa₂SO₄Introduced into gypsum slurry, these are mixed with a small amountNa₂SO₄The gypsum solution is pumped into a cyclone separator for solid-liquid separation. The large amount of solid residue with low moisture content separated is sent to the slag yard for stacking, and the solution flows back to the regeneration tank for continued use, so it will not cause secondary pollution.

4、 Process characteristics

Compared with limestone or lime wet desulfurization processes, the double alkali method generally has the following advantages:

（1）useNaOHDesulfurization and circulating water are basicallyNaOHThe aqueous solution has no corrosion or blockage on the water pump, pipeline, and equipment during the circulation process, making it easy for equipment operation and maintenance;

(2) The regeneration of the absorbent and the precipitation of desulfurization slag occur outside the tower, which avoids blockage and wear inside the tower, improves operational reliability, and reduces operating costs; At the same time, efficient plate towers or packed towers can replace empty towers, making the system more compact and improving desulfurization efficiency

（3）Sodium based absorption solution absorptionSO₂Due to its fast speed, a smaller liquid to gas ratio can be used to achieve higher desulfurization efficiency, which is generally achieved in90%above;

（4）For the integrated technology of desulfurization and dust removal, it can improve the utilization rate of lime. The disadvantages are:Na₂SO₃Oxidation side reaction productsNa₂SO₄Difficult to regenerate, requiring continuous supplementationNaOHperhapsNa₂CO₃And increase the consumption of alkali. Additionally,Na₂SO₄The existence of gypsum will also reduce its quality.