Sulfur recovery units—or SRUs—play an important role when converting toxic hydrogen sulfide into harmless elemental sulfur. However, within this process, sulfurcrete deposits appear and present a challenge by causing blockages and corrosion in sulfur condensers.
The sulfur condenser belongs to the shell and tube boiler, which is a special type of heat exchanger. The main function of this equipment is to cool and condense the sulfur generated in the upstream reaction section.
Sulfurcrete, with a hardness comparable to granite, consists of elemental sulfur, salts formed from sulfur, CO2, SO2, NH3, and Claus catalyst dust. It's a familiar problem for Claus plant operators, as it tends to accumulate and obstruct tubes in sulfur condensers, resulting in the formation of sulfuric acid traces and subsequent corrosion. The removal of sulfurcrete is a notoriously difficult and time-consuming task, requiring extensive downtime for SRUs.
Traditional methods, such as drilling, often cause damage to the equipment and are less effective due to the material‘s hardness. Additionally, sulfurcrete is insoluble in most common solvents, making washing a big waste of time as it doesn't work. Despite the prevalence of this issue in the approximately 1,000 Claus plants worldwide, no real solution had been found—which is why mycon developed the TubeMaster system.
1. The Challenges of Sulfurcrete in Sulfur Recovery
The Importance of Sulfur Recovery Units
Sulfur recovery units play a critical role in processing sour gas, which contains high levels of hydrogen sulfide (H2S). H2S is a toxic and corrosive gas that poses significant environmental and safety concerns. SRUs convert H2S into elemental sulfur, which can be safely stored, transported, and used in various industrial applications.
The Claus process, the most widely employed method for sulfur recovery, relies on thermal and catalytic reactions to convert H2S into sulfur. The efficiency of SRUs is vital to meeting environmental regulations, reducing greenhouse gas emissions, and minimizing health risks.
The Formation and Impact of Sulfurcrete
Sulfurcrete forms under specific conditions within Claus plants, particularly in areas with lower temperatures, such as sulfur condensers. The condensation of sulfur and the presence of salts from CO2, SO2, and NH3, along with dust from Claus catalysts, results in the formation of this hard, granite-like material.
Sulfurcrete deposits cause several problems in SRUs, including:
- Obstruction of tubes in sulfur condensers which leads to reduced heat transfer efficiency and decreased sulfur recovery.
- Formation of sulfuric acid traces beneath the sulfurcrete layer, causing corrosion and equipment damage.
- Increased maintenance and downtime requirements for removing the sulfurcrete deposits.
The Limitations of Traditional Removal Methods
Traditional methods for removing sulfurcrete, such as drilling and washing, have proven to be less than optimal. Drilling is time-consuming and can cause damage to the tube’s surfaces, leading to increased wear, reduced lifespan, and the increased potential for future deposit formation. Washing with common solvents is generally ineffective, as sulfurcrete is insoluble in most solvents, particularly those that are easy to handle.
2. Blasting for Sulfurcrete Removal: The TubeMaster Solution
The TubeMaster system uses abrasive blasting agents to clean SRUs, with the specific blasting agent selected based on the desired surface condition. mycon's specially designed nozzles are precisely adjusted to meet the requirements of each application.
The TubeMaster system removes even the hardest deposits, leading to improvements in surface quality and the efficiency of heat exchangers. By enhancing the surface condition, TubeMaster also makes future cleanings easier, as deposits are less likely to adhere to the improved surfaces.
The system has been tested on various types of pipes, including steel, stainless steel, bronze, red bronze, copper, brass, titanium, aluminum, plastic, and graphite. For curved pipes, specific criteria must be considered during the blasting process.
TubeMaster AS: The Semi-Automated Solution
The TubeMaster AS, a semi-automated version of the system, is designed to achieve high cleaning quality through precisely controlled cleaning speeds. This method reduces the consumption of blasting media but also minimizes the physical strain on the operators. It can be used for cleaning both vertically and horizontally oriented shell-and-tube heat exchangers.
Sulfurcrete Removal With TubeMaster
In Claus plants, sulfur condensers are typically operated at temperatures between 257 and 320°F (125 and 160°C). At higher temperatures, sulfur becomes highly viscous, impeding its free flow from the condenser. Conversely, at temperatures below 257°F (125°C), the temperature difference to the sulfur solidification point (approximately 246°F (119°C)) becomes too small, reducing the efficiency of the condenser.
Operating at higher temperatures may simplify the process, but it comes at the cost of reduced sulfur recovery, as some sulfur vapor passes through the condenser unrecovered. This trade-off is often unacceptable due to stringent regulations regarding sulfur recovery. However, multiple stages can be used.
Although operators have tried various methods to mitigate the problem of plugging in sulfur condensers, none have provided a complete solution. Eventually, tubes in the sulfur condensers accumulate sulfurcrete deposits, leading to a reduction in the heat transfer and blockages.
3. Comparison to Other Cleaning Methods
Although TubeMaster may be more expensive than other cleaning methods, such as high-pressure water, it offers numerous advantages that often outweigh its higher price.
These advantages include:
- Removal of even the hardest deposits
- Gentle on the surface and the tube with no reduction in wall thickness
- Dry cleaning process
- Improved surface quality within pipes
- Energy savings
- Extended operating times
- Environmentally friendly cleaning with the recovery of used materials
TubeMaster is particularly great for sour gas processing, where it's essential to keep equipment dry during and after cleaning and where it's beneficial to reduce downtime.
TubeMaster has been successful in various applications, as in the Gulf States and at one of the world's largest low-density polyethylene (LDPE) producers, where a sulfur condenser required a perfect cleaning for an IRIS inspection. In this case, dry cleaning was necessary due to the presence of sulfur, and mechanical alternatives failed to produce satisfactory results, even after intensive trials.
TubeMaster offers an effective solution for cleaning tubes with diameters as small as 3 mm (0.1 in.), removing deposits ranging from soft materials like oils and fats to hard substances such as sulfurcrete. The cleaning process does not result in any reduction of wall thickness, leaving the original wall thickness intact. Additionally, it enables in-place cleaning of equipment, eliminating the need for disassembly and re-assembly. The cleaned surfaces often exhibit better smoothness after treatment, reducing adhesion and extending the intervals between cleanings.
TubeMaster's additives and blasting process can be optimized for specific applications. Mycon provides consultation and support during the initial implementation of the TubeMaster system at a customer's site, ensuring seamless integration. The company also offers ongoing training and support to operators, enabling them to maximize the benefits of the system in their facilities.
5. Environmental and Economic Benefits
The TubeMaster system delivers several environmental and economic benefits for sulfur recovery plants, including:
- By improving the efficiency of sulfur condensers, TubeMaster enables Claus plants to comply with stringent environmental regulations and minimize sulfur emissions.
- The improved heat transfer efficiency in cleaned sulfur condensers results in reduced energy consumption, lowering operating costs and contributing to a greener operation.
- TubeMaster's abrasive blasting agents can often be recovered, reducing waste generation, and lowering the environmental impact of the cleaning process.
Sulfur recovery is a crucial aspect of sour gas processing and a primary concern for the petrochemical and refining industries. The buildup of sulfurcrete deposits in sulfur condensers has long posed significant challenges for these operations. Traditional cleaning methods, such as drilling and washing, have proven inadequate and often damaging to the equipment.
The TubeMaster system, developed by mycon, offers a game-changing solution to this persistent problem. By employing abrasive blasting technology, TubeMaster efficiently and effectively removes sulfurcrete deposits without causing damage to the equipment surfaces. The result is improved heat transfer efficiency, reduced corrosion, and extended operating times for sulfur recovery units. The system is also environmentally friendly, with the potential for abrasive agent recovery and reuse.