Case Study: Troubleshooting Decrease in Recovery Efficiency
Problem Identification
An existing client brought SRE in to troubleshoot an unexplained decrease in recovery efficiency within their Sulfur Recovery Unit (SRU). The plant had three SRU trains and had been experiencing high H2S levels in the product from the downstream degassing operation.
Steps Taken to Address the Problem
1-Initial Compositional Analysis:
SRE performed a compositional analysis of the process gas and found low conversion across Converter 2.
The SRU was generally well-operated, and no significant changes had occurred since the last test period.
2-Simulation and Catalyst Activity:
Simulations reconfirmed that the catalyst activity in the second converter bed was lower than expected.
Despite the catalyst being replaced only six months prior, the sudden reduction in efficiency was puzzling.
3-Inlet Temperature and Sample Testing:
Further analysis revealed that the converter inlet temperature was above the normal recommendation.
SRE installed a sample probe at the inlet, discovering a different gas composition than at the converter one outlet.
4-Identifying a Leak:
The analysis suggested a hole in the multipass condenser, allowing process gas from the first pass to contaminate the second pass.
This leakage explained the reduced conversion efficiency and increased inlet temperature at Converter 2.
5-Degassing Operation Review:
Before the client shut down to repair the condenser leak, SRE evaluated the degassing pits to understand why H2S levels were up to 200 ppm in the liquid sulfur.
Adjustments to the agitator and pump circulation rates were tested. It was found that the circulation rate was too low for adequate degassing.
One of the two sulfur pumps was found to be barely operational and required a complete overhaul.
6-Repair and Validation:
The condenser and pump repairs were scheduled during a planned shutdown.
SRE assisted with the shutdown and subsequent startup, performing tests to verify the effectiveness of the repairs.
Post-repair tests confirmed that recovery efficiency improved to above the license limit of 98%, and H2S levels in the liquid sulfur returned to specification.
Summary of Findings and Benefits
Operational Improvements: Quick identification and repair of the multipass condenser leak and the sulfur pump issues restored the plant's efficiency.
Financial Savings: Early detection and repair prevented further damage to the SRU and avoided substantial costs associated with contaminated product.
Product Quality: Restored liquid sulfur to meet H2S specifications, ensuring high-quality output.
This case study illustrates SRE's proficiency in diagnosing and resolving complex SRU issues efficiently. By identifying and repairing leaks and optimizing degassing operations, SRE restored the client's recovery efficiency and product quality. Other companies can benefit from SRE's thorough approach and expertise in maintaining and improving SRU operations, avoiding potential downtimes and financial losses.
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7 SRU Catalyst Killers: Identifying and Mitigating Contaminants in Sulfur Recovery Units
Catalysts are the heart of the sulfur recovery process, crucial for ensuring high efficiency and low emissions. However, various contaminants can deactive and damage these catalysts, leading to reduced performance and increased operational costs. This article explores the primary contaminants, their mechanisms, and methods for mitigation, alongside the financial impact of catalyst misuse.
Catalysts in sulfur recovery units (SRUs) facilitate the conversion of hydrogen sulfide (H2S) into elemental sulfur. Over time, contaminants can deactive these catalysts, impacting their effectiveness and lifespan. Identifying and understanding these contaminants is critical for maintaining optimal performance.
Major Contaminants and Their Impact
1- BTEX (Benzene, Toluene, Ethylbenzene, Xylene)
Mechanism: BTEX components are not fully destroyed in the reaction furnace (RF) and polymerize on the Claus catalyst.
Deactivation Type: Permanent.
Mitigation: Ensure complete destruction in the RF, maintain correct temperatures, and monitor BTEX levels in the feed.
2-Methanol
Mechanism: Methanol bypasses the RF via an acid gas bypass, leading to polymerization on the catalyst.
Deactivation Type: Permanent.
Mitigation: Properly control bypass systems and monitor methanol concentrations.
3-Soot and Liquid Sulfur Deposition
Mechanism: Incomplete combustion during startup or improper burner stoichiometry leads to soot formation, plugging converter beds.
Deactivation Type: Temporary.
Regeneration: Heat soak.
Mitigation: Optimize startup procedures and maintain burner efficiency.
4-Sulfation
Mechanism: Excessive free oxygen from the RF or reheaters causes sulfation of the catalyst.
Deactivation Type: Permanent.
Mitigation: Control oxygen levels and ensure proper operation of reheaters.
5- Steam (Hydrothermal Aging)
Mechanism: Long-term exposure to excessive water vapor leads to structural damage.
Deactivation Type: Permanent.
Mitigation: Minimize steam introduction and prevent boiler leaks.
6-Thermal Aging
Mechanism: High temperatures during sulfur fires cause catalyst sintering.
Deactivation Type: Permanent.
Mitigation: Avoid thermal excursions and maintain safe operational temperatures.
7-Heavy Hydrocarbons
Mechanism: Heavy hydrocarbons crack and form coke, blocking catalyst pores.
Deactivation Type: Permanent.
Mitigation: Optimize feedstock composition and prevent heavy hydrocarbon carryover
Avoiding Contamination
Preventing catalyst contamination involves maintaining strict operational controls and regular monitoring:
Ensure proper destruction of contaminants in the RF.
Control bypass systems to prevent methanol and heavy hydrocarbons from entering the catalyst beds.
Optimize startup and shutdown procedures to minimize soot formation.
Maintain proper temperatures to avoid sulfur condensation.
Regularly inspect and repair boiler systems to prevent hydrothermal aging.
Avoid thermal excursions by controlling process temperatures and preventing sulfur fires.
Financial Impact of Catalyst Misuse
Catalyst deactivation leads to significant financial burdens due to reduced efficiency, increased maintenance costs, and potential unscheduled shutdowns. Misuse can result in:
Increased operational costs due to frequent catalyst replacements.
Higher energy consumption and lower process efficiency.
Downtime for maintenance and catalyst regeneration or replacement.
How We Can Help: Performance Testing and Optimization
Sulfur Recovery Engineering (SRE) offers comprehensive performance testing and optimization services. Our experts can:
Conduct thorough assessments to identify contamination sources.
Provide tailored solutions to prevent and mitigate catalyst deactivation.
Offer regular monitoring and maintenance programs to ensure long-term efficiency and reliability.
Protect your catalysts and ensure optimal performance of your sulfur recovery units. Contact SRE today to schedule a consultation and learn how we can help you maintain peak efficiency and minimize operational costs.
The Heat Is On! – Why Temperature Plays an Important Role in Sulfur Recovery
The iconic skyline of Alberta’s natural gas sector is marked by labyrinthine tubes and tunnels, pipes and platforms. Atop it all—like candles on the cakes of carbon—are sputters of live flame, alighting the morning sky.
Far more than just a deterrent to low-flying aircrafts (and birds), the powerful heat of the reaction furnace ensures sulfur extraction is maximized, and the purity of outflow is an optimal makeup for cleanliness and machine reliability.
Too Hot to Handle:
Working with sour water means bringing all the good along with the bad. Side reactions inside the reaction furnace will invariably produce unwanted products like CO, H2, COS, and CS2. Luckily, other contaminants such as BTEX, Mercaptans, NH3, HCN, Methanol, and HCs may be destroyed in the reaction furnace with proper calibration and sufficient heat.
While 900℃ (1650℉) is the minimum temperature for flame stability, heats of 1050℃ (1920℉) or above are capable of destroying the unwanted contaminants. Bear in mind the reaction furnace is kinetically limited based on residence time, turbulence, and temperature, as well as burner efficiency.
Through the Fire and Flames:
In our Sulfur Recovery experience, combustion air flow rates are nearly always off by at least 10–20%. While this is standard, we must work to ensure this margin of possible error is not exacerbated. Proper mixture of gasses and the installation of a high-efficiency burner can increase reaction furnace temperatures up to 100℃, which helps to reach the target temperatures mentioned previously.
This is crucial not only for efficiency, but for optimal refinery health. Proper burn-off of ammonia in the reaction furnace is essential, as residuals can carry over to the condensers and converters, bringing with them the risk of forming ammonia salts. These salts will negatively impact heat transfer and recovery efficiency. As with most sulfur recovery unit issues, you won’t know there is a problem until it is too late.
As with any efficient furnace system, management of both inflow and output should be carefully monitored, with changes to procedure made according to the changes in both. Ensure your plant is optimized for the feed it receives. For example, when H2S qualities are low in gas plants, a front side split configuration is often best for ensuring minimal additions of air and nitrogen to the system.
Conclusion:
Sulfur recovery isn’t always easy, but it is undoubtedly important. In the end, you should run your reaction furnace like you would your bathtub: the hotter, the better; the better, the cleaner! Learn more about how we can help you optimize your Sulfur Recovery by contacting us at our website, subscribing to our newsletter, or by giving us a call today.
Sulfur Pit Degassing
Why do we degas? Crude oil and natural gas contain sulfur compounds which get concentrated as they makes their way to the SRU in the
Why do we degas? Crude oil and natural gas contain sulfur compounds which get concentrated as they makes their way to the SRU in the form of hydrogen sulfide (H2S). H2S is present in liquid sulfur in two forms: dissolved and chemically bound (known as polysulfides or H2Sx). The residual H2S content in produced liquid sulfur can be in excess of 600 ppm and the Lower Explosive Limit (LEL) for H2S in air is 4% which is easily reached if liquid sulfur is not degassed. The main goal then of degassing is to reduce the potential safety risk to people, the environment, and equipment. Increasing product purity may also be a reason for degassing to lower levels. The industry standard for safe handling of sulfur product is 10 ppm or less.
Degassing typically consists of two stages, an agitation stage followed by a sweeping stage. Air is typically used in both stages as it is readily available and cheap, oxygen also promotes the direct oxidation of hydrogen sulfide and polysulfides. That being said, other gasses such as nitrogen, steam, and Claus tail gasses can also be used for sweeping the released H2S from the pit.
There are several processes that can be seen in industry and that have been implemented around the world. It is likely that if you have worked in a sulfur plant that you have experience with one or more of these processes.
Comprimo (Formerly Exxon) Degassing Process
Air used for sparging and sweeping
Catalyst added to pit to promote decomposition of polysulfides
Aquisulf (SNEA)
Aquisulf catalyst
Multiple compartments
Shell
Uses air for agitation
Stripping column within the pit
Enersul HySPEC
Series of CSTRs (Continuous Stirred Tank Reactors)
Air used to sweep and catalyst added
Fluor D’GAASS
Pressurized above-ground contactor
Air used for agitation
CSI ICOn
Fixed catalyst bed contactor before or after pit
Operates at pressure of SRU
Finally, we’ll talk about operation and troubleshooting fundamentals. Knowing the basics of degassing chemistry, such as the kinetics, effects of catalyst, and flow characteristics provide a solid foundation for any issues that you may encounter. The next step is knowing your design, understanding how your particular process works compared to others is necessary to being able to identify problem areas. Lastly, ensure that your data is accurate and reliable when monitoring KPIs. To help with this, get onsite verification of your process, including fact checks of technical drawings and data, and liquid sulfur testing.
Reach out to us at SRE for more information on troubleshooting tips and support as well as some interesting case studies from our experience.
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