There is probably no other industry that has come under such intense scrutiny as the oil refining industry. Still, there is no denying that processing crude oil into useful petroleum products such as gasoline, diesel fuel and heating oil is an important part of the world’s economy. Furthermore, the oil refining industry has made substantial changes to be more environmentally friendly both in its product line and process facilities.
One of the by-products of clean fuel production is liquid molten sulfur. As environmental legislation mandates stricter controls on refined products, oil refineries must remove more sulfur from their refined products, such as diesel fuel. The recovered sulfur, sold to other industrial companies, finds use in other products such as fungicides, black gunpowder, detergents and phosphate fertilizers, and for rubber vulcanization.
Leaking Liquid Sulfur
For one major United States refinery, the sulfur recovery process was causing problems in its process line. Sulfur has a high melting temperature of 250-degrees-Fahrenheit and must be constantly heated at or above this temperature to keep it in a liquid state for pipeline transportation. But molten sulfur also has an upper temperature limit of 300-degrees-Fahrenheit where the viscosity increases and it begins to re-solidify. Trying to control this narrow temperature range and maintain the sulfur in a molten liquid state can be very difficult, and as a result, the refinery was experiencing reliability issues with its pumps and specifically for the mechanical seals.
Immediately after installation and start-up, the pump’s mechanical seal would begin to leak. Within weeks, a large pile of hardened sulfur would form around the pump base causing huge housekeeping issues along with environmental disposal problems. Not only did the plant have to contend with continually cleaning-up the leaking sulfur, it also had to make sure that the sulfur was disposed of in an environmentally safe manner.
In searching for a solution to its problem, the refinery tried several different sealing configurations, but the leaking still occurred. Since the standard seal designs were not providing a solution, the refinery turned to EagleBurgmann, a manufacturer of mechanical seals, to solve the problem. After assessing the situation, EagleBurgmann realized that the typical seal configuration would not work for this application and a new approach was needed.
According to Jeff Batinick, a Territory Manager at EagleBurgmann, the refinery resigned itself to dealing with the housekeeping mess, although they were not happy about it. “The plant would operate the pump for an extended period of time, while the hardened sulfur formed around the pump,” said Batinick. “When an opportunity arose, they would replace the seal and clean-up the sulfur. This bad-actor pump and seal configuration was a never-ending headache for the refinery.”
The Sealing Situation
EagleBurgmann immediately began to investigate the problem. Batinick worked with engineers at the refinery to get all the details of the application and process conditions.
The existing seal was a typical rotating bellows design with a carbon bushing outboard of the seal faces and a steam jacket around the bushing, but no steam quench was being used between the bushing and seal faces.
Although a traditional steam 5 PSIG quench had been employed in the past to prevent sulfur leakage from accumulating and solidifying around the seal faces, the quench line would become plugged with sulfur and tended to accelerate the formation of solid sulfur around the pump; therefore, it was eliminated. Because of the barrier fluid contamination of the sulfur, a double seal was not a viable option.
Batinick explained that since the sulfur product temperature in the pump was at 280-degrees-Fahrenheit and with a pump speed of 3600 RPM, the refinery engineers and incumbent seal manufacturer theorized that the heat generation in the seal gap was significant enough that the sulfur migrating across the seal faces was reaching its upper solidification temperature (300-degrees- Fahrenheit). A steam quench on the atmospheric side of the seal faces was keeping the sulfur at this upper temperature. Without the quench, the solidification was still occurring but at a much lesser rate
“In either case, the result was a domino effect,” said Batinick. “Sulfur leaking past the faces was accumulating and solidifying around the atmospheric side of the faces, causing them to hang-up, and ultimately leading to additional and accelerated sulfur leakage.”
A Non-Traditional Approach
After examining the situation at the refinery, Batinick approached EagleBurgmann’s Engineering Department to find the best solution. EagleBurgmann’s engineers recommended a pusher seal instead of a metal bellows seal to eliminate the sulfur build-up. “We looked at the application and, although a bellows seal is the traditional approach, we knew that what was required here was ‘out-of-the-box’ thinking,” Batinick said.
The key to EagleBurgmann’s non-traditional approach was its ability to think beyond the standard product offerings. “In mature industries such as refining, the industry gets ‘hooked’ into ‘canned’ solutions to problems,” commented Batinick. “Most seal manufacturers would say, ‘If it is a sulfur application, then you must use a bellows seal.’ EagleBurgmann looked at it differently. With over 180 years of experience, we can provide innovative solutions, not just the standard offering, to our customers.”
EagleBurgmann’s LH9UC pusher seal is a slurry seal design. It features a stiff, single-coil, stationary spring that loads-up the faces to resist hang-up, it has the dynamic o-ring on the OD of the spring-loaded, stationary face with the spring on the atmospheric side, and it uses faces with large clearances between their ID and the sleeve OD to resist hang-up if sulfur starts to accumulate on the atmospheric side. The other unique feature is the segmented carbon (Espey-type) bushing on the atmospheric side of the faces that can be utilized for a high-pressure (30-40 PSIG) steam quench.
Steam at 35 PSIG has a saturation temperature of 260 degrees-Fahrenheit, which is near the lower solidification temperature for sulfur.
Therefore, introducing a steam quench between the faces and the segmented carbon bushing at this pressure and temperature and controlling it with a needle valve on the flange drain line would:
- Equalize the temperature around the faces to create a better environment for the sulfur in the seal gap, resulting in more even transfer of the seal-generated heat away from the faces to keep the temperature in the gap below the upper solidification temperature
- Improve the heat transfer capability of the seal, since steam conducts heat better than air, which is an insulator
- Prevent the sulfur from reaching the lower solidification temperature as it leaks across the faces
- Move the sulfur leakage away from the ID of the faces to prevent it from accumulating, solidifying and hanging-up the faces
“With this seal configuration, we were able to keep the steam flowing out of the drain line at a fairly high rate to prevent the steam from cooling and condensing,” Batinick explained. “Any sulfur leaking past the seal faces to the atmospheric side is ‘swept’ away, which prevents the sulfur from accumulating and solidifying.”
Sealing the Deal
In order to install this solution, the refinery had to make a few design modifications to its process line. Engineers from the refinery and EagleBurgmann worked as a team to minimize equipment modifications. EagleBurgmann’s engineers made recommendations both for the equipment design and for implementing environmental controls.
“Teamwork – among EagleBurgmann’s engineers and with the refinery – made this a successful outcome,” said Batinick. “We were present for the seal installation and start-up, and we provided training and support. As long as the refinery follows our operating procedures, there should be no issues with the seal.”
Within two weeks after the pump start-up – the time when sulfur would start to accumulate around the pump – there were no signs of sulfur leakage. Housekeeping is now a non-issue for the refinery and although it has had other pump issues, none of them were related to the seal. The refinery is so pleased with EagleBurgmann’s solution that it is currently in the process of modifying a second pump to accommodate the pusher seal and is considering retrofitting several other pumps in the facility.
“In this situation, the refinery was faced with an unacceptable predicament – not only were the leaking pumps causing housekeeping issues but the sulfur was posing environmental concerns, too,” stated Batinick. “In our search for a solution, we took a non-traditional approach.
“EagleBurgmann does not have a ‘one-size-fits-all’ mentality when dealing with customers,” Batinick continued. “For the refinery, using a pusher seal was not the standard solution, but it was the answer to the problem. And we didn’t just show up with the seal and drop it off at the front door – we provided the assistance and training to guarantee that the seal would work at start-up and into the future.”
For more information, please contact Alton Smith, Senior Regional Manager at firstname.lastname@example.org.