Common Problems and Optimization Solutions for Sulphur Recovery Unit in Refinery

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Sulphur recovery unit in refinery has been widely used in recent years. In order to make tail gas emissions meet the emission standards, the Claus sulphur recovery process technology is constantly optimized and improved, and the trend toward high efficiency, quality, environmental protection, and the economy is gradually evolving. Claus process for sulfur recovery is very mature and has a history of nearly one hundred years. The Claus sulfur recovery process is a process to recover sulfur from the H2S-containing gas produced during the desulfurization process. It realizes the recovery of sulfur products and chemical raw materials in other industries while obtaining good economic benefits. The Claus sulphur recovery process solves the problem of industrial waste gas pollution in the atmosphere and realizes the simultaneous and coordinated development of environmental protection and benefits. It is a relatively mature acid gas sulfur recovery process. Sulphur recovery unit equipment is widely used in various petrochemical companies such as coking plants, power plants, oil refineries, coal gasification plants, methanol plants, and fertilizer plants.

Ruichang has been committed to building efficient and stable sulphur recovery unit equipment for customers for many years. After the sulfur recovery unit in refinery was put into production, we carried out a number of technical transformations in response to the problems and deficiencies in the actual operation. The modified sulfur recovery unit equipment has a better operating effect, ensuring the safe and stable operation of the device. Now enumerate the typical problems existing in the actual operation of the sulfur recovery unit in the refinery, and give the optimized solutions by Ruichang.

Common Problems and Optimization Solutions

1. The ignition air and fuel gas pressure of the sulfur recovery unit is low, resulting in ignition difficulties.

The ignition fuel gas pressure of the sulphur recovery unit in refinery is designed to be 0.026Mpa, and the ignition air pressure is 0.03Mpa. During the ignition process of the sulfur recovery unit in refinery, the ignition is difficult due to the low pressure. Even after ignition, as the fuel gas volume increases during the furnace heating process, the large pressure difference between the ignition fuel gas and the main fuel makes the furnace temperature of the furnace difficult to control. In addition, the ignition air comes from the compressed air produced by the blower, and the pressure is lower than that of the fuel gas, which can easily cause backfire at the ignition gun and burn the ignition gun.

Optimization solution by Ruichang

In order to solve the problem of low ignition air and fuel gas pressure in the sulfur recovery device, the design team changed the ignition air from blower air to instrument air, which increased the ignition air pressure. In addition, the ignition fuel gas is changed from behind the regulating valve to before the regulating valve, and a stop valve is added for regulation to stabilize the ignition fuel gas pressure and ensure the stability of combustion after ignition.

Since the ignition air pressure and the ignition fuel gas pressure are basically the same and stable, during the furnace heating process, the occurrence of backfire is avoided and the safe and stable operation of the furnace is ensured. At the same time, the sulfur output is increased, the cost of replacing the ignition system is saved, and the economic benefit is increased.

2. In the refinery sulfur recovery process, the concentration of H2S in the acid gas is low.

Before equipment optimization, the highest hydrogen sulfide concentration was 17.1%, the lowest was 6.3%, and the annual average concentration was 12.5%. In the sulfur recovery process, the CO2 content in the acid gas is relatively high, designed to be 80%. It will react with H2S in the furnace to produce COS and CS2, which will reduce the sulfur recovery rate and increase the sulfur content in the tail gas. Due to the low concentration of feed gas, less combustible gas components, higher carbon content, and the larger amount of oxygen required, under insufficient air, it is easy to cause carbon deposits in the bed, resulting in a larger difference in catalyst bed stratification.

Optimization solution by Ruichang

Optimize the operation in the low-temperature methanol washing section, increase the amount of stripped nitrogen in the hydrogen sulfide concentration tower, flash out excess carbon dioxide as much as possible, and reduce the pressure of the first section of the thermal regeneration tower from the original 0.25MPa to 0.23MPa. Distill a part of the CO2 in the methanol into the hydrogen sulfide concentration tower to reduce the CO2 content in the acid gas and increase the concentration of hydrogen sulfide as much as possible. After a period of testing, the optimized sulfur recovery equipment of the refinery has a maximum hydrogen sulfide concentration of 21.2%, a minimum of 9.5%, and an annual average concentration of 13.4%, thereby increasing the sulphur recovery output of the sulphur recovery unit equipment.

3. The content of methanol is high.

The alcohol content is high. The main effect of combustion in the acid gas combustion furnace is to increase the temperature of the reaction furnace and the heat load of the waste heat boiler and at the same time increase the air consumption. In the case of insufficient air, unburned hydrocarbons may precipitate carbon on the catalyst or produce impurities such as mercaptans, sulfides, sulfites, etc., which affect the activity of the catalyst and easily cause black sulfur in the pipeline to block the liquid sulfur pipeline.

Optimization solution by Ruichang

Before the acid gas enters the sulfur recovery unit, an acid gas scrubber is added to scrub the methanol in the acid gas. The sulphur recovery unit equipment optimized by Ruichang was put into use, which greatly reduced the risk of acid gas carrying methanol causing load reduction or system pressure increase due to insufficient airflow. At the same time, the operation of the equipment was stabilized to ensure its continued stability run.

4. Sulphur recovery unit in refinery is corroded seriously, and the exhaust gas temperature is lower than the set temperature.

Corrosion on sulfur recovery equipment
Corrosion on sulfur recovery equipment

The steam drum level of the acid gas burner and tail gas incinerator designed by the Claus sulfur recovery device is provided by the medium pressure boiler feed water heated by the boiler feedwater preheater. Due to a large amount of water entering the boiler feedwater preheater, the maximum temperature of the tail gas at the outlet of the incinerator is 160°C, which is lower than the design temperature of the tail gas of 230°C, and sulfite is easily formed. Sulfite corrodes the pipes seriously, causing frequent leakage of equipment and affecting the long-term normal operation of the sulfur recovery unit in the refinery.

Optimization solution by Ruichang

Add a boiler feed water bypass pipeline to the boiler feedwater preheater, and use a bypass valve to control the liquid level of the steam inlet drum. Turn down the pipeline valve passing through the preheater, adjust the temperature with the regulating valve, reduce the water intake of the medium pressure boiler, reduce heat loss, increase the temperature of the exhaust gas, make the temperature meet the design requirements, and prevent the subsequent pipeline from blocking the pipeline due to low temperature caused by crystallization.

By continuously improving the process technology of the sulphur recovery unit in refinery, and optimizing and adjusting the operation method, Ruichang not only solved the problems in the production of the recovery unit but also ensured the long-term stable operation of the recovery equipment. This not only increases the output of sulfur but also reduces the emissions of sulfur dioxide. While protecting the environment, significant economic and social benefits have been achieved.

For more production issues and optimization solutions of sulfur recovery equipment in refineries, please contact us for better advice.

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