During the operation of the sulfuric acid production plant, unorganized emissions of acidic gases are inevitable, mainly including sulfur dioxide (SO₂), sulfur trioxide (SO₃), and sulfuric acid mist. These acidic gases not only cause severe pollution to the surrounding environment but also harm the respiratory system, skin mucous membranes, and other healthy tissues of the human body. At the same time, they cause equipment corrosion, shorten the service life of the equipment, and increase the operating costs of the enterprise. With increasingly strict environmental protection requirements, effectively controlling the unorganized emissions of acidic gases from the sulfuric acid production plant has become an urgent need for sulfuric acid manufacturing enterprises.

1. Sources of Unorganized Acidic Gas Emissions from Sulfuric Acid Production Plant

The sulfuric acid production process is the transformation of sulfur into sulfuric acid. All equipment, pipelines, and valves in contact with it become sources of unorganized emissions.

1) Sealing leakage of moving equipment: For example, the mechanical seals of sulfuric acid circulation pumps and liquid sulfur pumps, under the erosion, wear, and corrosion of the medium, the sealing surfaces are prone to gaps, causing acidic liquids or gases to escape;

2) Leakage at static sealing points: For instance, the flange gaskets and valve stuffing boxes, due to material aging, improper installation, or stress changes, cannot effectively block the medium, especially in process sections with significant temperature and pressure fluctuations, the leakage risk significantly increases.

3) Corrosion perforation of equipment body: Some carbon steel equipment or pipelines that have not undergone proper anti-corrosion treatment, after long-term contact with acidic media, will corrode and eventually develop perforation leaks. Due to the frequent start-stop of the plant, the welds at the connections between equipment or between equipment and pipelines will be pulled apart due to thermal expansion and contraction, resulting in leaks.

4) Process requirements, during normal operation of the plant, to ensure the efficient and stable operation of the device, analysts will regularly sample and analyze the exhaust gas and sulfuric acid to ensure the authenticity and reliability of the sampling data. They will also manually replace samples in dead corners, resulting in a large amount of acidic gas leakage; operators will also regularly inspect and eliminate condensate acid in the equipment, during the inspection and elimination process, a large amount of acidic gas leaks.

5) Volatilization of acid tanks/cylinders and loading/unloading: The circulating acid tank of the sulfuric acid production plant is connected with the absorption tower. During operation, the circulating acid tank generates acid mist, due to poor sealing, it spreads into the air. When the breathing valve of the concentrated sulfuric acid storage tank fails or the seal is not tight, the liquid level fluctuates in the tank, and the acid mist is discharged through the breathing valve; during the loading/unloading process of sulfuric acid, if a closed loading/unloading system is not used or the sealing of the loading/unloading port is not good, a large amount of acid mist will escape.

2. Solutions for Unorganized Acidic Gas Emissions

2.1 Optimize Process Design

During the design stage of the sulfuric acid production plant, advanced and mature process technologies should be adopted to reduce the risk of unorganized emissions from the source. For sections prone to leakage, such as circulating acid tanks and sulfuric acid loading/unloading tanks, a sealed structure or a negative pressure suction device should be installed to collect the acidic gas and transfer it to the internal system of the plant or the tail gas treatment system. For sampling points of exhaust gas and sulfuric acid, sealed sampling devices should be installed to return the supposed-to-be-vented exhaust gas or sulfuric acid back into the system. At the acid discharge ports of the equipment, automatic condensate acid discharge devices should be installed to ensure no residual condensate acid remains in the equipment and to reduce the labor intensity of the operators, while maximizing safety.

2.2. Select Corrosion-resistant Sealing Equipment

Due to the strong corrosiveness of the sulfuric acid medium, suitable equipment and sealing materials should be selected to reduce the probability of leakage:

1) Upgrade of equipment materials: Key equipment such as circulation pumps, heat exchangers, and valves should use corrosion-resistant materials, such as fluororesin, stainless steel, or special alloys like duplex stainless steel or Hastelloy. This extends the service life of the equipment.

2) Upgrade of sealing technology: Moving equipment should adopt modular mechanical seals or dry gas seals for efficient sealing technology. Static sealing points should use corrosion-resistant gasket materials (such as polytetrafluoroethylene gaskets, metal wound gaskets), and the sealing structure design should be optimized to improve sealing reliability.

3) Install leakage monitoring devices: Install online leakage monitoring sensors (such as gas detectors, acid gas detectors) at key sealing points to monitor leakage conditions in real time. Once a leakage exceeds the standard, an alarm signal will be promptly sent, facilitating prompt handling by maintenance personnel.

4) Strictly control the frequency of start-up and shutdown: The majority of equipment and pipelines' leaks are closely related to the frequent start-up and shutdown of the device. During the start-up and shutdown process of the equipment, temperature and pressure fluctuate significantly, causing thermal expansion and contraction of the equipment, which can cause permanent damage to the equipment.

2.3 Unorganized Emission Collection System

Effectively collect the unorganized emitted acidic gases within the device. Set local air collection hoods at vulnerable leakage points such as storage tanks, circulating acid tanks, pump valve sealing points, etc. Through negative pressure suction, the emitted acidic gases are collected and treated by the purification system.

For areas with scattered leakage points and difficult local collection, an overall ventilation and air exchange system is adopted. By setting roof exhaust fans and side wall intake ports, a negative pressure environment is formed in the space, allowing the diffused acidic gases to be discharged.

2.4 Acidic Gas Purification Treatment

Apply appropriate purification technologies to the collected unorganized acidic gases to ensure compliance with emission standards:

1) Spray Absorption Method: Introduce the collected acidic gases into an absorption tower, where they come into countercurrent contact with sprayed absorption liquid (such as sodium hydroxide solution). Acidic gases such as SO₂ and SO₃ react chemically with the absorption liquid to form sulfates or sulfites, thereby achieving gas purification. This technology is suitable for handling high-concentration acidic gases and has advantages such as high processing efficiency and low operating costs. The absorption liquid can be recycled or discharged in compliance with standards. The collected acidic gases can also be directly introduced into the device's exhaust system for treatment and discharged through the chimney.

2) Activated Carbon Adsorption Method: Utilize the porous structure and surface activity of activated carbon to adsorb acidic gas molecules, achieving gas purification. For small amounts and low-concentration acidic gases collected, activated carbon is filled in the collection pipe, and the acidic gases are adsorbed by the activated carbon and then discharged directly into the atmosphere. The activated carbon can be restored to its adsorption performance through thermal regeneration or chemical regeneration and can be recycled.