Preface

With the country's promotion of self-reform and digital transformation, the sulfuric acid industry is experiencing a wave of intelligent transformation and digital transition [1]. All parties are actively exploring how to enhance the automation level of sulfuric acid plants and how to achieve their digital transformation to meet the demands of rapid social development [2]. At present, Lizhenglai Technology is committed to promoting the digital transformation of sulfuric acid plants. We have widely listened to the opinions of many large-scale sulfuric acid production enterprises and gained a deep understanding of their demands for the intelligent transformation and digital upgrading of sulfuric acid facilities. Industry consensus indicates that one-click start-up is a key criterion for measuring the success of intelligent transformation. We apply the theoretical knowledge accumulated from the research on digital sulfuric acid and combine it with practical experience in sulfuric acid production operations to design a one-click start-up solution for large-scale sulfuric acid plants, aiming to assist enterprises in achieving intelligent transformation and digital transformation [3].

1. Overall thinking

The start-up of a sulfuric acid production unit from sulfur can be roughly divided into five major steps: pre-start-up inspection, start-up preparation, unit start-up, index control, and normal operation. The pre-startup inspection mainly involves checking whether the process conditions, equipment, instruments and electrical systems meet the startup requirements. This is mainly based on on-site inspection and can be confirmed with an electronic OK meter. The start-up preparation mainly focuses on whether the process flow of the device has been completed and whether each basic control point is ready for start-up. This can be ultimately confirmed by using the start-up navigation as shown in Figure 1. The start-up of the device mainly focuses on the intake air for sulfur spraying. Controlling the air-sulfur ratio is the key and difficult point among them. This can be precisely controlled by taking material balance as the entry point. Index control mainly focuses on the process index control of each procedure and can be achieved through automatic adjustment. Normal operation refers to the ability of each control point to operate independently after meeting the indicators, and the load can be increased or decreased as needed. The increase or decrease of load can also be achieved through material balance.

One-click start-up navigation map for the sulfuric acid plant

2. General Requirements

To achieve one-click start-up, the reliability of equipment, electrical systems and instruments, as well as the requirements for automatic operation, are relatively high. The operating equipment should run smoothly and reliably, and at the same time meet the requirements of automatic start and stop. For key pump equipment, there should be a hot standby design, with safety interlocks set up to enable automatic switching. The instrument is reliable in performance and can accurately display parameters such as the temperature, flow rate and pressure of the material. For key control points, redundant design is required, and two of the three or all of them can be met simultaneously. The control valve achieves effective, precise and stable control based on its actual position and regulating function.

3. Driving logic

3.1 Logic of the sulfur incineration conversion section

After the electronic OK meter is confirmed, the start-up preparation for each section is self-built. When the DCS clicks the start-up preparation button, the start-up preparation for the sulfur-burning section is automatically established.

Establish a steam insulation system: The insulation steam of the refined sulfur tank is automatically opened, the insulation steam of the sulfur pipe is automatically opened, and the outlet vent valve of the insulation steam of the sulfur gun is automatically opened.

Establish the sulfur system: The system automatically selects the high-level liquid sulfur storage tank (or manually selects) with the heat preservation steam pressure and the temperature of the refined sulfur tank as the trigger points. Open the bottom valve of the tank, then open the liquid level regulating valve of the refined sulfur tank to control the liquid level of the refined sulfur tank. The liquid level is maintained at around 65% and set automatically.

Establishing a sulfur cycle: With the liquid level of the refined sulfur tank as the trigger point, the outlet valve of the refined sulfur pump can be delayed for three minutes, the reflux valve of the sulfur pipe will open, the isolation valves of the three sulfur guns will close, the refined sulfur pump will automatically start, the frequency conversion will automatically increase, and the flowmeter will normally display at 60% of the device load flow.

Pre-spraying sulfur: The sulfur gun isolation valve automatically opens with the steam pressure of the pipeline insulation and the sulfur tube flowmeter as the trigger points, and the sulfur tube reflux valve automatically closes. The sulfur burning fire detection signal triggers it. After 3 seconds, the sulfur tube reflux valve automatically opens and the sulfur gun isolation valve automatically closes. The three guns switch automatically to ensure smooth operation of each gun.

Automatic setting of sulfur-burning conversion valves: Triggered by the pre-sulfur injection fire detection signal and the water flow rate of the boiler, the vent valve at the fan outlet is fully open, the inlet valve of the sulfur-burning furnace is fully closed, the butterfly valve at the boiler outlet is fully open, the bell cover valve is 80% open, the butterfly valve at the inlet of the first section is fully open, the bypass of the high-temperature superheater flue gas is fully open, the bypass of the hot and hot heat exchanger flue gas is fully closed, the butterfly valve at the outlet of economizer 2 is fully open, and the bypass of the cold and hot heat exchanger is fully closed. (Conversion heating is achieved by closing two valves.)

3.2 Logic of the dry suction section

The electronic OK meter confirms that the DCS clicks the start-up preparation button, and the start-up preparation for the dry suction section is automatically established.

Mother acid filling: Automatically open the valves for drying, secondary suction, and HRS mother acid filling. The tank farm automatically opens the inlet and outlet valves of the pump. Manually select which large tank to use to start the pump. Fill the liquid level of the drying circulating acid tank, secondary suction circulating acid tank, and HRS circulating acid tank to 85% according to the actual situation. Stop the pump and close the valve.

Circulating water circulation: The circulating water pool automatically replenishes water to the liquid level. The inlet and outlet valves of the acid cooler's circulating water automatically open, the circulating water pump starts automatically, and the pump outlet valve opens automatically. Water enters the acid cooler, and the feed water pressure, flow rate, and PH at the acid cooler outlet all return to normal (the circulating water system also has a separate start-up preparation logic).

Low-temperature heat recovery system water supply The deaerator liquid level is the trigger point. The HRS evaporator vent valve is opened, the steam production valve is closed, the heater inlet regulating valve is opened, the HRS evaporator feed water pump starts automatically, the boiler outlet valve is opened, water is filled in the evaporator, and the liquid level reaches 75% (depending on the actual situation). The water supply to the evaporator is reduced to 10 m3/h, and the boiler fixed discharge is opened to control the stability of the boiler liquid level. The low-temperature heat recovery system also has a separate start-up preparation logic.

Establish a separate acid cycle

Drying cycle: With the liquid level of the drying acid tank as the trigger point, the bypass valve of the drying acid cooler opens, the valve for producing drying acid in HRS closes, the valve of the second suction circulation acid tank of the drying series closes, and the drying circulation acid pump starts automatically to control the acid volume going up the tower to the index value of 850 m3/h. Maintain the liquid level at around 55%. If the liquid level is insufficient, add mother acid again.

Secondary suction circulation: Triggered by the liquid level in the secondary suction acid tank, the bypass of the secondary suction acid cooler is opened, including the HRS acid bypass. The acid production valve is closed, the valve of the HRS secondary suction circulation acid tank is closed, and the inlet valve of the HRS secondary suction acid is closed. The secondary suction circulation acid pump starts automatically to control the acid volume entering the tower to the index value of 800 m3/h. Maintain the liquid level at around 55%. If the liquid level is insufficient, add mother acid again.

HRS acid circulation: With the liquid level of the drying acid tank and the boiler as the trigger points, the HRS acid production valve closes, and the cooling water of the HRS acid pump and the air at the shaft seal automatically open. The shaft seal air controls the pressure and flow rate, and the HRS acid pump starts automatically to control the acid volume in the first stage of the tower to the index value (1200m3/h). Maintain the liquid level at around 60%. If the liquid level is insufficient, add mother acid again.

Establish acid circulation: Take the flow rate of the second suction to the tower and the first acid flow rate of HRS as the trigger points. Open the valve of the second acid in HRS to control the acid flow rate to the tower at 60m ³ /h. Open the valve of the second suction circulating acid tank in HRS to keep the liquid level of the circulating acid tank stable. Establish HRS and secondary acid absorption cycles.

4. Conclusion

This paper conducts in-depth research and analysis on the one-click start-up technology of the sulfur-to-acid plant. Through the one-click start-up technology scheme designed and simulated for verification in this paper, the rapid and stable start-up of the sulfur-to-acid plant and the efficient and stable production process can be successfully achieved. The practical application of this technical solution can bring revolutionary changes to the future development of the sulfuric acid production industry from sulfur. It can not only significantly enhance the production efficiency of sulfuric acid and energy utilization efficiency, but also effectively reduce production costs and safety risks. This solution not only demonstrates broad application prospects and important social value, but also provides a new demonstration for the digital transformation of the sulfuric acid industry.

References

[1] Yang Lingguo Digital Transformation Empowers and Boosts Traditional industries [N]. Guiyang Daily. May 26, 2022 (004).

[2] Chen Xinyi, Zhang Hua, Jia Junjun, et al. Exploration and Research on the Digital Transformation of Industrial Production Standards under the Digital Economy [J]. China Standardization, 2023, 48-52

[3] Fan Xiaoxiang Application of New Technologies and Equipment in Sulfuric Acid Production Plants from Sulfur [J]. Chemical Safety and Environment, 2020, 15-17.