1. The main heat energy sources and utilization of the sulfuric acid production unit from sulfur

1.1 Thermal energy inherent in sulfur: The sulfur entering the sulfur burning furnace is usually in a liquid state. To ensure its fluidity, the temperature of the liquid sulfur is generally controlled at 135-145℃. This part of the heat will enter the system along with the liquid sulfur and serve as part of the thermal energy of the device.

1.2 Heat energy inherent in the air: Under working conditions, air enters the system through a blower. At this time, the temperature of the air is determined by the ambient temperature, and there is a significant difference between winter and summer, with the highest temperature reaching around 40℃. In the system, a portion of the oxygen in the air is consumed, and the remaining air is discharged from the outlet of the secondary suction tower. Affected by the acid temperature of the upper tower of the secondary suction tower, the discharge temperature is generally around 65-75℃, and in some cases, it can even be higher. Therefore, the air will carry away heat from the system.

1.3 Compression heat energy of the fan: After air is compressed by a blower, compression heat energy is generated. Generally, the pressure increase of an air blower is 48 to 52kPa, and the temperature rise of air compression is approximately 37 to 50 degrees Celsius. If the fan is set in front of the tower, some of this heat will be carried away by the drying circulating acid. The temperature of the air leaving the tower is affected by the temperature of the acid entering the tower and is generally around 60℃. If the fan is set up after the tower, the air is first heated by the drying circulating acid, and then compressed and raised in temperature by the fan. The outlet temperature can reach about 110℃. This part of the heat accounts for about 2% of the system heat and can be effectively utilized by the boiler when entering the system.

1.4 Heat of sulfur combustion: Sulfuric acid burns in the sulfur-burning furnace, releasing a large amount of heat energy. This part of the heat energy is called sensible heat and accounts for about 53% of the total system heat. Most of this heat energy is directly absorbed by the boiler to generate medium-pressure saturated steam, a part enters the next process to maintain the thermal balance of the conversion system, and is eventually utilized by the economizer, while a small part enters the low-temperature heat recovery system and is carried away by the air.

1.5 Sulfur Dioxide conversion heat: Sulfur dioxide reacts with oxygen to form sulfur trioxide, releasing a large amount of heat. This part of the heat is called medium-temperature heat energy, accounting for about 17% of the entire system's thermal energy. This part of the heat is mainly absorbed by steam in the superheater to generate superheated steam and maintain the thermal balance of the conversion system.

1.6 Sulfur trioxide absorbs heat: Sulfur trioxide reacts with water to form sulfuric acid, releasing a large amount of heat. This part of the heat energy is called low-temperature heat energy, accounting for about 24% of the entire system's heat energy. Due to the relatively low temperature of this part of the heat energy, it is difficult to utilize. In traditional processes, only a small portion of this heat is utilized by desalinated water, while the majority is carried away by circulating water, which not only fails to generate value but also increases energy consumption. The current low-temperature heat recovery process can recover over 80% of the low-temperature thermal energy for the production of low-pressure saturated steam and heating of desalinated water, while significantly reducing the consumption of circulating water.

1.7 Heat of dilution of sulfuric acid: The heat of dilution of sulfuric acid only accounts for a very small part of the system's heat. In the low-temperature heat recovery system, the dilution heat is effectively utilized, while in the dry adsorption system, it is carried away by the circulating water.

2. Thermal energy optimization of the sulfuric acid production unit from sulfur

2.1 Post-tower setting of the fan: It can utilize more compressed heat energy, and the steam production rate of the system can be increased by about 4%. However, the post-tower fan has higher requirements for corrosion resistance of the fan. If the acid mist at the outlet of the drying tower is not properly controlled, it is easy to corrode the equipment. At the same time, as the air temperature rises, the air volume increases. When ensuring the same air velocity in the empty tower, the air volume will increase, the size of the drying tower will increase, and the energy consumption of the fan will also increase accordingly. Considering the long-term cycle, the fan has more advantages after the tower.

2.2 Increase the acid temperature of the air entering the drying tower: Under the premise that the air moisture and acid mist meet the standards, appropriately increase the acid temperature of the air entering the drying tower. The acid temperature of the air entering the tower determines the temperature of the air leaving the tower. After the acid temperature is increased, the temperature of the air leaving the tower also increases accordingly. This temperature can be effectively utilized by the boiler. At the same time, the usage of drying circulating water also decreases accordingly.

2.3 Increase the concentration of sulfur dioxide: Under the premise of ensuring the conversion rate, appropriately increasing the concentration of sulfur dioxide in flue gas will reduce the total amount of air accordingly, and the heat carried away by the air will also decrease accordingly.

2.4 Reduce the temperature of the flue gas entering the secondary suction tower: The heat of the flue gas entering the secondary suction tower is not utilized and is all carried away by the circulating water. Under the premise of ensuring that the economizer does not produce condensation acid, appropriately reducing the temperature of the flue gas will relatively reduce the heat entering the secondary suction tower, and the usage of circulating water for the secondary suction will also relatively decrease.

2.5 Reduce the temperature of the acid produced by low-temperature heat recovery: The acid produced by low-temperature heat recovery enters the dry absorption system. The heat of this part of the acid can only be carried away by the circulating water. If the HRS preheater can recover more heat from the acid, the thermal energy utilization of the system will be higher.

2.6 Increase the feed water temperature of the deaerator: In the dry suction system, a desalted water heater is added to replace the acid cooler, raising the feed water temperature of the deaerator. This reduces the steam consumption of the deaerator, decreases the circulating water consumption of the dry suction system, and increases the thermal energy utilization rate of the system.

2.7 Optimize the secondary suction tower process. Besides the flue gas heat energy from the economizer and the acid-producing heat energy from low-temperature heat recovery, the secondary suction system also has the heat energy absorbed and released by the sulfur trioxide converted from the second rotation that has not been utilized. If the secondary suction process is optimized to control the acid temperature at the bottom of the tower higher, allowing the acid feed water to be heated to generate steam or the desalinated water to be heated, the heat can be effectively utilized. The utilization of thermal energy in the entire sulfuric acid plant will reach a new level.