Woven Metal Products (WMP), in partnership with Haldor Topsoe Inc., has jointly developed an outlet support grid (OSG) for gas-phase, fixed-bed catalytic reactors, such as straight-run naptha and coker naptha units. The OSG is also used in hydrogen plants in high-temperature and low-temperature shifts and the methanation reactor. There are many advantages of the OSG, which would replace an existing elephant stool, including:
- Pressure-drop reduction over the reactor of about 50 percent.
- Reduction in use of ceramic balls by as much as 75 percent.
- Faster unloading and loading, as the use of ceramic balls are eliminated.
- Easy access to inspect inside the elephant stool and outlet pipe.
OSG design
The catalyst support grid consists of a modified outlet collector, outlet brackets, outlet connector rods, skirt section and a top grid section that can be wire mesh or profile wire, all of which sits in the bottom of the reactor. Side and top views of the grid are shown in Figure 1 and Figure 2, respectively.
Flexible and easy sealing
The catalyst support grid has been designed without the need to use packing rope or insulation to seal the vessel wall. A good seal between the support grid and the vessel head performs well over thermal cycles and is critical in preventing support ball or catalyst migration over the life of the grid through many shutdowns.
Top manway hatch innovation
The OSG design includes an inspection hatch located at the top of the outlet collector. This allows for access to the outlet collector and outlet piping for inspection during maintenance outages without having to disassemble and remove the entire catalyst support grid.
No-weld installation
A no-weld installation results in no approval requirements from local pressure vessel authorities for modifying equipment. This also results in a lower required installation time, and the catalyst support grids are easily retrofitted to existing vessels. The outlet collector is fitted with three tabs that prevent the grid from shifting horizontally, which would result in an inadequate grid-vessel seal. Due to the no-weld design, the installation is typically carried out by the catalyst-loading contractor. The contractor employees are well trained and equipped for confined-space entry and have experience with numerous catalyst-containing vessels.
Tried and tested
The first generation of the OSG was installed in 2001 and is still operating successfully. Thirty units are now using the OSG, which are all designed for more than 50 years of service. The following data is from a low-temperature reactor (shift catalyst), where a 50-percent reduction in the overall reactor pressure drop was achieved: The OSG was installed without any safety incidents, and the installation took about two shifts. On top of the new bottom support grid, a 4-inch layer of 3/4-inch ceramic balls and a 4-inch layer of 1/4-inch ceramic balls were loaded. The active catalyst was loaded on top of the 1/4-inch ceramic balls.
Final takeaway
This new, innovative OSG reduces the reactor start of run pressure drop, which may be utilized to increase the feed rate, increase the recycle gas rate or simply increase the cycle length before a pressure drop in a naphtha hydro treater becomes a limitation. The faster unloading/loading and in-section help reduce downtime and increase profitability.
For more information, visit www.wovenmetal.com or call (800) 624-6537.
