In the chemical industry, sulfur recovery plants play a crucial role. However, this device also faces many potential risks, such as equipment failure, improper operation, and external threats. In order to ensure the safety and stability of the sulfur recovery process, we must develop and implement strict safety prevention strategies. These strategies not only include regular equipment inspections and maintenance, but also professional training for operators and improvement of emergency plans. Through these measures, we can effectively reduce potential risks in sulfur recovery plants and ensure the safety and stability of the chemical industry.
Compared to typical petroleum refining facilities, the main risks faced by sulfur recovery plants are not combustion or explosion (although these hazards also exist), but rather from toxic gas leaks and corrosion, which pose significant threats to safety production. As a senior sulfur recovery unit manufacturer, Ruichang has over 20 years of experience in sulfur recovery unit production and has provided professional sulfur recovery equipment to more than 100 enterprises. Next, we will introduce the safety hazards in sulfur recovery plants and share corresponding preventive measures to help more manufacturers build safe sulfur recovery unit.
Unlike typical petroleum refining facilities, the main hazard of sulfur recovery plants is not combustion and explosion (although this hazard also exists), but the harm of toxic gases (hydrogen sulfide, ammonia) to human health. H2S exists in various parts of the sulfur recovery unit and is the main hazard factor of the sulfur recovery unit.
H2S is a colorless strong neurotoxic gas that can cause sudden coma, respiratory and cardiac arrest, and result in electrocution death after poisoning. H2S exists in various parts of the sulfur recovery plant and is the main hazard factor of the sulfur recovery plant. So how is H2S distributed in the sulfur recovery plant?
Distribution of H2S in sulfur recovery unit
The sulfur recovery plant uses H2S as raw material to produce sulfur, so H2S is a widely distributed and highly concentrated substance in the sulfur recovery plant, so its potential hazards are also enormous. Among them, the acidic gas pipeline has the highest concentration of H2S. Generally, the concentration of acidic gas in sulfur recovery plants is higher than 40%, and some even reach over 90%. If a leak occurs, the consequences will be unimaginable. In addition, for the entire device, most of the pipelines contain varying concentrations of H2S or substances such as SO2 and COS, some of which, although not high in concentration, can be fatal.
The toxicity of hydrogen sulfide has such a significant impact, so what potential risks exist during the start-up and shutdown of sulfur recovery plants and normal production processes?
1: Shutdown phase
The shutdown process of sulfuric acid plants is usually divided into H2S blowing, SO2 blowing (adjusted by changing the air distribution ratio), and catalyst burning. H2S purging is to prevent catalyst deactivation, SO2 purging is to carry as much internal sulfur as possible, and catalyst burning is to burn the carbon deposits on the surface of the catalyst, ensuring catalyst activity and preparing for start-up.
During the shutdown process, even if the blowing process is completely carried out, it is impossible to completely remove all the sulfur inside the system. This will result in sulfur combustion during burning, which releases a large amount of heat and causes reactor overheating. Once overheating occurs, it is difficult for the temperature to drop in a short period of time, which will inevitably cause damage to the catalyst and even equipment, thereby affecting normal production.
2. Startup phase
If the blowing and burning process of the sulfur recovery plant is not thoroughly carried out during the shutdown phase, the unit may experience sulfur condensation or catalyst coking blocking the gas path during the shutdown process. This will cause process blockage during the start-up phase, and when acidic gas enters the system, the explosion-proof membrane of the combustion furnace will burst, causing a large amount of toxic gas to leak and seriously threatening life safety.
3 Acidic gas with hydrocarbons (amines)
The most widely used sulfur recovery plant is the partial combustion method, in which incomplete air distribution is used for the combustion furnace. If acidic gas carries hydrocarbons (amines), due to insufficient air, it will cause severe coking of hydrocarbons (amines), especially amine substances, which will form glossy tar coking. This increases the burning load during the shutdown of the sulfur unit and prolongs the shutdown time. More importantly, excessive carbon accumulation can cause blockages in the device during normal operation, leading to the rupture of the explosion-proof membrane and the leakage of toxic gases.
4 Acidic gas with liquid
Acidic gas carrying liquid is a common problem in sulfur recovery plants, where the liquid mainly refers to water. Once liquid phase water enters the combustion furnace, due to the temperature of the combustion furnace being at least 800 ℃ or above, the liquid phase suddenly changes to the gas phase, causing a sudden increase in the volume of gas entering the combustion furnace. This will cause a sudden rise in pressure inside the furnace, leading to the rupture of the explosion-proof membrane and the leakage of toxic gases.
5. Blockage of cooler
The cooler is an important equipment in the sulfur recovery plant. Usually, sulfur vapor flows through the pipeline and cooling water flows through the shell. However, due to various reasons, leaks often occur between the tube plates of the cooler. Once leaked, sulfur vapor will directly solidify upon contact with cooling water, causing equipment blockage. In severe cases, it will cause an increase in system pressure, leading to the rupture of explosion-proof membranes and the leakage of toxic gases.
6. Inappropriate air distribution
The air distribution ratio is an important operating condition for sulfur recovery plants. Only by matching appropriate air with acidic gas can the maximum sulfur recovery rate be achieved, that is, maintaining a 2:1 ratio of H2S and SO2 in the process gas. At the same time, the air distribution rate also needs to provide the air required for the combustion of hydrocarbon substances carried in the acidic gas.
A large air distribution will reduce the sulfur recovery rate and seriously pollute the environment; Low air distribution can also reduce sulfur recovery rate and lead to incomplete combustion of hydrocarbon substances, resulting in carbon deposits and system blockages, posing a threat to safety production.
7. Changes in Acid Gas Flow and Concentration
In sulfur recovery plants, the flow rate and concentration of acidic gas usually vary, but this variation is allowed within a certain range. If this change exceeds the allowed range, there will be a continuous large range of changes in the air distribution ratio, which is unfavorable for normal operation and can cause sulfur blockage in severe cases.
8. fan malfunction
Usually, a fan is used in the sulfur recovery plant to provide air to the combustion furnace, and like other moving equipment, the fan is also on standby. The fan is a crucial equipment in the sulfur recovery plant. Once the air is stopped during normal production, a large amount of acidic gas will directly enter the exhaust system, causing serious impact. In addition, the hydrocarbons in the acidic gas will also undergo incomplete combustion at high temperatures, resulting in carbon deposition and system blockage. During the device switching process, if there is a slight deviation in operation, it may also cause the fan to reverse, resulting in the backflow of acidic gas and directly threatening human life safety.
9. Deoxygenation water interruption
In the Claus sulfur recovery unit, a waste heat boiler is installed after the combustion furnace to recover energy in the form of steam. Deoxidized water is used for steam generation. Once interrupted, it can cause water shortage in the boiler, and in severe cases, it can lead to dry burning and boiler explosion.
10. Gas Stop or Liquid Carry
Regardless of whether the sulfur recovery device is equipped with a tail gas treatment unit, the final stage is equipped with a tail gas incinerator. Incinerators typically burn sulfur tail gas at high temperatures using gas as fuel.
If the gas is suddenly interrupted, it will extinguish the incinerator flame due to the lack of fuel gas supply, affecting normal production.
If gas carries liquid, it will cause insufficient air supply, carbon accumulation in the incinerator, and sometimes combustion in the pipeline, burning the pipeline and causing equipment accidents or gas leaks, threatening safety production.
11. High temperature blending valve malfunction
To control the inlet temperature of the converter and improve the conversion rate, a high-temperature blending valve is usually installed at the inlet of the converter in the sulfur recovery unit. By extracting high-temperature gas from the middle of the combustion furnace and mixing it with the gas at the outlet of the combustion furnace, the required population temperature of the converter is achieved.
The high-temperature blending valve is essentially a three-way valve that controls the temperature of the converter by adjusting the valve body opening to control the heat flux. Due to the high working temperature of the high-temperature mixing valve, it is prone to malfunction and often experiences jamming. Once the high mixing valve gets stuck, the airflow temperature cannot be controlled, the sulfur conversion rate will significantly decrease, and it will also affect normal production or cause abnormal shutdown. For sulfur recovery units, abnormal shutdowns are terrifying because they often fail to blow and burn, causing system blockages and even greater trouble.
12. chimney blockage
H2S and SO2 can react even in the absence of a catalyst, although the reaction rate is slow and the amount of sulfur generated is small, over time it can clog equipment or pipelines. A chimney is installed in the sulfur recovery unit to discharge sulfur tail gas.
In devices without exhaust gas treatment facilities or using incineration exhaust gas treatment methods, due to the high content of H2S and SO2 in the exhaust gas, sulfur often blocks the chimney pipeline, causing the entire sulfur system to be blocked, affecting safety production, and in severe cases, forced shutdown.
13. Exhaust gas malfunction
To meet the sulfur tail gas emission standards, modern sulfur enterprises are equipped with tail gas treatment units. The most widely used among them is the SCOT hydrogenation process, which converts SO2 in the tail gas into H2S through the hydrogenation process of the tail gas under the action of a specialized catalyst. After absorbing H2S with a solvent and desorbing it, it is re used as raw material to enter the sulfur unit, in order to improve the sulfur conversion rate and reduce pollution. The key to its control is the conversion of SO2 in the exhaust gas, and the factors that affect it mainly include catalyst performance, reaction temperature, hydrogenation amount, etc. The amount of hydrogenation is of utmost importance, with a large amount of hydrogenation. Although it can ensure the complete conversion of SO2, it will increase the burden on the tail gas incinerator, and in severe cases, cause the incinerator to overheat and be damaged. If the hydrogenation amount is too small, SO2 cannot be completely converted, and it will react with H2S in the process gas to generate sulfur, which can block the equipment and, in severe cases, cause accidents in the sulfur reaction unit.
14. Risk factors during the sampling process
The sulfur recovery unit achieves the optimal conversion rate of sulfur in the Claus reaction by adjusting the air distribution rate, because the content of H2S and hydrocarbons in acidic gas varies over time. If a high conversion rate is required, the air distribution rate needs to be adjusted at any time. To determine whether the air distribution rate is appropriate, it is necessary to analyze the content of H2S and SO2 in the process gas to help operators make correct judgments. Therefore, it is very important to analyze the gases in the sulfur production process.
Safety prevention measures for the sulfur recovery unit
There are many factors that affect the safe operation of the sulfur recovery plant. To ensure safe production, increase the sulfur recovery rate and protect the environment, an interlock control system is generally installed in the sulfur production unit. The most widely used automatic control interlock system in the sulfur production unit is the risk control system. In the sulfur production unit, the flow and concentration of acidic gas are constantly changing. If the air supply is adjusted manually, the adjustment frequency is too high and it is also difficult to be accurate, resulting in an inappropriate supply of air and increasing the probability of danger or pollution.
During the production process of the sulfur recovery plant, there are numerous risks. In addition to adopting the automatic control interlock system of the sulfur unit, the following safety precautions also need to be paid attention to.
To ensure the safe operation of the sulfur recovery plant, the following basic measures should be taken:
- Only regular inspections of the equipment are required. All pipeline inspections must also strictly follow the regulations of the pressure pipeline management system to minimize the risk of leakage.
- Fixed H2S detection alarm devices should be set scientifically and reasonably, and ensure an adequate number to enable early detection of any leakage and minimize losses as soon as possible.
- Complete protective equipment should be provided, including portable alarm devices, positive pressure respirators, and other filtering breathing equipment.
- The handling steps in the event of a severe leakage situation are emphasized. The principle is that after detecting a leakage, relevant personnel should be informed first, and complete protective equipment should be worn. The leakage source should be cut off promptly. It is strictly forbidden to carry out activities such as cutting off the leakage source or rescue without the protection of safety equipment.
