Foreword

As a key upstream facility and energy supply unit in the chemical industry, the production efficiency and cost management of sulfur acid plants directly determine the economic returns of enterprises. In the production process of sulfur acid production, the ratio of oxygen and sulfur plays a decisive role in the production capacity, energy efficiency and stability of process parameters. However, the manual control method commonly used in sulfur acid making plant is difficult to achieve accurate adjustment of oxygen to sulfur ratio, which not only reduces production efficiency and increases energy consumption, but also affects the stability of process parameters and brings hidden dangers to the safe operation of the plant. Therefore, it is of great significance to study and implement the automatic control strategy of oxygen to sulfur ratio in sulfur acid making plant to improve the operation efficiency, reduce the production cost and enhance the market competitiveness of enterprises.

Background and objectives of the control scheme

In the process of producing acid from sulfur, the oxygen/sulfur ratio (that is, the proportion of sulfur reacting with oxygen in the air) is a crucial process parameter. The fine adjustment of this ratio will directly affect the output of sulfuric acid, the efficiency of steam generation, and the energy consumption and cost of the entire production process. In the traditional production mode, it usually relies on manual adjustment to control the oxygen/sulfur ratio, but this method is slow in response and insufficient in adjustment accuracy, and often cannot meet the automation and autonomous operation advocated by the modern sulfuric acid industry, as well as the strict requirements for the stability and real-time performance of process indicators. Therefore, it is urgent to develop a safe, advanced, stable and adaptable oxygen/sulfur ratio automatic control scheme. Based on the combination of process principles, automation technology and stable measuring instruments, the solution realizes real-time monitoring and automatic control of the oxygen/sulfur ratio, ensuring the precise control of the ratio of air and sulfur in the production process, thereby maximizing the output of sulfuric acid and steam generation efficiency, significantly reducing unnecessary energy consumption and production costs. Further enhance the economic benefits and market competitiveness of enterprises. At the same time, through the implementation of automatic control, it can effectively reduce the interference of human factors on the production process and ensure the consistency and stability of the process parameters, which is the core function necessary to realize the automatic operation of the sulfur acid making plant.

Effects of oxygen-sulfur ratio on production

In the design of each sulfur acid production equipment, the SO2 concentration at the outlet of the sulfur burner has been set, and the domestic standard is usually 11.5%. Since the volume fraction (dry basis) of oxygen in the air is 20.948%, the sum of the initial SO₂ concentration and the initial oxygen concentration in the flue gas produced by sulfur combustion is a constant value.

This gives the formula: b=20.948-a, where a represents the initial SO₂ volume fraction (%) and b represents the initial oxygen volume fraction (%).

Therefore, the oxygen/sulfur ratio R is really only a function of the initial SO2 volume fraction. R=20.948/11.5-1=0.824.

Oxygen/sulfur ratio has many effects on the production process. If the oxygen/sulfur ratio is low, it indicates an excessive supply of sulfur, which will lead to a lower conversion rate and incomplete combustion of sulfur, resulting in sublimed sulfur, resulting in excessive exhaust gas and production accidents. Although a higher oxygen/sulfur ratio ensures complete combustion of sulfur, too much oxygen consumption will result in wasted energy, more heat carried away by the flue gas, and less steam recovery, thereby increasing costs. (For every 0.1% reduction in SO₂ concentration, the production cost of tons of acid will increase.) Therefore, it is crucial to control the oxygen/sulfur ratio at the optimal balance point, which not only ensures the complete combustion of sulfur to increase the yield, but also avoids the excessive consumption of oxygen resulting in energy waste, which is the key to reducing production costs.

Logic of automatic control of oxygen-sulfur ratio

After confirming the SO₂ concentration at the outlet of the sulfur burner, the conversion efficiency is also considered during the operation of the unit to determine the optimal oxygen/sulfur ratio, thereby maximizing the efficiency of the unit. The two key variables in the oxygen/sulfur ratio are sulfur and air. The amount of sulfur is determined by the load of the unit and is set to a fixed value in the automatic control system. The supply of oxygen depends on the air flow provided by the fan (that is, the air volume), which will change with the atmospheric pressure, temperature, humidity and the speed of the fan, so in the automatic control, the air volume is set as a dynamic variable. The control goal of oxygen/sulfur ratio is to maintain the stability of the air volume, and maintain the optimal oxygen/sulfur ratio by automatically adjusting the speed of the fan when the environmental parameters or load change.

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