Working Principle

In view of the inadequate sealing performance of the circulating tank pump seat, in order to ensure that the circulating acid tank does not produce negative pressure when the level drops, each circulating tank of the sulfuric acid unit must be communicated with the atmosphere, which leads to the discharge of acidic toxic gases such as SO₂, SO₃ and sulfuric acid fog into the environment. These gases in the atmosphere not only pollute the environment, but also affect human health. According to the "Petrochemical Combustible Gas and Toxic Gas detection alarm Design Standard" (GB/T50493-2019), China has implemented strict detection standards for toxic acidic gases emitted by the petroleum industry since 2020. As a part of the petrochemical field, the detection of combustible gases and toxic gases in the sulfuric acid industry should also follow this standard, which puts forward strict requirements for the discharge of acidic gases and toxic pollutants. This includes emission limits for pollutants such as sulfur dioxide SO₂ and sulfuric acid fog, as well as regulations on the unorganized emission limits of air pollutants at the boundaries of enterprises, aimed at reducing environmental pollution. Not only new enterprises must meet this standard, but also existing enterprises must gradually meet and maintain this emission standard through technological transformation and upgrading. In addition, the environmental protection department will regularly monitor the acid toxic gas emissions of enterprises to ensure that the acid toxic gas emissions of enterprises meet the standards. However, in the process of conversion analysis in acid production, a large amount of acidic toxic gas will be released. The World Health Organization's International Center for Research on Cancer (IARC) has classified sulfuric acid as a G1 carcinogen, which is directly judged to be an extremely harmful medium. It was measured that each cycle tank emitted about 30m³/h into the environment due to the analyzed SO₂ and acid fog. Each unit emits about 480,000 m³ of acid gas into the environment throughout the year, causing serious environmental pollution and equipment corrosion.

In the drying circulation pump tank and the secondary suction tower circulating acid pump tank, the circulating liquid is fed into the drying tower and the secondary suction tower through the action of the pump to absorb SO₃ in the flue gas, thus producing sulfuric acid. In this absorption process, the circulating acid dissolves SO₂ and SO₃ in the flue gas, and then returns to the circulating acid pump tank of the secondary suction tower through the self-return line at the bottom of the tower. The circulating liquid in the pump tank will release part of SO₂ and SO₃, forming the exhaust gas in the drying tower circulating pump tank and the second suction tower circulating acid pump tank. The concentrated sulfuric acid in the circulating acid pump tank of the drying tower is pumped to the drying tower to dry the air. At this time, its w(H₂SO₄) is reduced, and the concentration of concentrated sulfuric acid provided by the circulating acid pump tank of the secondary suction tower is adjusted. In this process, the concentrated sulfuric acid dissolved SO and S0 enters the circulating acid tank of the drying tower and releases the exhaust gas containing SO₂ and SO₃. At the same time, the evaporation of concentrated sulfuric acid in the pump tank also forms acid fog in the exhaust gas. Therefore, the main components in the exhaust gas include SO₂, SO₃, and acid fog.

Current Situation

At present, the sulfuric acid production plant connects the drying circulation tank and the secondary suction tower circulation tank to the main fan inlet by using carbon steel pipes, and uses the negative pressure effect of the main fan to recover the generated acidic gas and reintroduce it to the acid production system to produce sulfuric acid. Since the circulating acid pump tanks of the drying tower and the secondary suction tower are lined with acid-resistant bricks, these bricks cannot withstand the vibration load, so the pump cannot be mounted directly on the pump tank, and a separate pump frame must be installed. Due to the irremediable gap between the pump frame and the pump tank, after some time of use, we found that the connection pipe could not achieve a complete seal with the dry pump seat and the secondary suction seat. As a result, hydrated air seeps into the pump tank through these gaps and mixes with the acid to form a dilute acid. The acid sludge produced after the dilute acid corrodes the pipe blocks the passage, resulting in the acid gas cannot be pumped to the main fan inlet. This eventually leads to the direct discharge of acidic gases into the atmosphere, causing serious pollution to the environment. In order to solve this problem, some sulfuric acid plants have improved the original waste gas recovery process and adopted the method of fan suction.

In view of the gap between the pump tank and the pump frame, it is necessary to maintain a small negative pressure inside the pump tank to prevent the leakage of exhaust gas into the atmosphere. At present, the exhaust gas desulfurization tower equipped with sulfuric acid equipment, its fan impeller and bearing are made of 316L stainless steel, and the wind housing is made of plastic. However, after the transformation, we found that the water and acid fog in the acid gas in the pump tank will form dilute acid, causing serious corrosion to the fan impeller, resulting in the impeller unable to maintain dynamic balance. In addition, condensed condensed acid inside the fan increases the vibration of the fan, the seal at the connection between the wind casing and the inlet back cover often leaks dilute acid and a small amount of exhaust gas, and the connection bolts are frequently corroded; Dilute acid and exhaust gas leakage are also frequent at the sealing material of the shaft and the wind housing, and the corrosion of the shaft and exhaust gas contact part is particularly serious, and the impeller and connecting bolts are usually replaced once a month. Each replacement of the impeller must be thoroughly washed with clean water, and then reset the action balance calibration to prepare for the next use. During the operation of the fan, it is also necessary to periodically discharge the dilute acid in the housing of the fan. These technical improvements are not only inconvenient to operate, the maintenance frequency is tight, the maintenance cost is high, and the exhaust gas is easily leaked into the atmosphere during the maintenance process, and the condensing acid in the fan also makes the maintenance environment become harsh. Therefore, how to effectively recover the acid gas in the circulation tank has become a difficult problem faced by the industry. The SAW-C100 acid aspirator developed by our company is designed to solve this problem.

 

 

Product Characteristics

No moving parts, use the main fan outlet air to provide power source.

Using corrosion-resistant materials to avoid dilute acid corrosion, long service life.

The suction negative pressure of the circulation tank can be adjusted to prevent the wet air from entering the circulation tank and corroding the pump seat.

The acid gas produced in the circulation tank can be efficiently recovered to the tail gas system to achieve zero acid gas emission at the plant site.

Automatic operation, simple operation, maintenance-free, simple installation, one installation has been benefited.

 

Product Performance

Name: Acid Mist Aspirator

Installation position: drying cycle tank, two suction cycle tank, one suction cycle tank

Suction power: main fan outlet air

Suction capacity: 100m³/h

Suction negative pressure: Max. -2000Pa; Suction pressure adjustable

Air consumption: 50~200m³/h

Material: 316 stainless steel and corrosion-resistant plastic

Fog removal efficiency: 95%