Changes in feedstocks processed through hydrotreating and hydrocracking reactors may sometimes lead to lower efficiency, such as thermal maldistribution problems and reduced cycle length. Can you report any recent cases, such as distillate hydrotreaters challenged with meeting T95 diesel specifications, where conversion problems were resolved that can be duplicated with other hydrotreating units facing similar challenges?Mar-2023
Charles Brandl, Honeywell UOP, email@example.com
Maintaining feedstock composition and quality is extremely critical in hydroprocessing units (whether hydrocracking or hydrotreating), and refiners try to operate their respective unit close to its design conditions. If the feedstock gets heavier in terms of composition, distillation, or contaminants, the unit’s operating severity needs to be increased to meet the target design conversion and product specifications. This, in turn, may impact product selectivity, catalyst life, and/or unit performance. With careful catalyst selection and utilising new and improved process and equipment solutions, existing assets could be fully utilised to deliver overall unit objectives.
We have seen one hydrocracking unit where a refiner wanted to increase the unit capacity and process higher end-point feed than design. Due to increased feed rate and higher severity, radial spread in one of the beds was >25-40°C and was also seen in subsequent cycles due to catalyst volume, which was not effectively utilised. As a result, the refiner had replaced the previous generation internals with UOP’s latest generation reactor internals, and in close collaboration with UOP during start-up the refiner lowered the radial spread to ≤4°C. Lower radial spread resulted in meeting design conversion at lower WABT, which was pivotal for the refiner and provided additional operational flexibility to achieve higher distillate yields until the end-of-run conditions.
Ricky Hsu, International Innotech Inc, firstname.lastname@example.org
Cycle lengths of a hydrotreater or hydrocracker are limited by pressure drop of the fixed bed reactor and deactivation of the catalyst. Solid particles in the liquid streams to the reactor, which plug the catalyst bed and the pore opening of the catalyst active sites, are the main cause of ending the reactor operating cycle.
Currently, solid particles are removed from liquid streams mainly by filtration. Conventional filter cartridges and/or filtering screens are normally used to remove only large solid particles (larger than 25-50 μm) from process streams. To remove additional particles from the liquid stream and provide a better fluid distribution, macropore solids are also packed into the top of the reactor. In recent years, reticulated top bed materials have been packed into the top of the reactor to improve solid particle removal and fluid distribution into the catalyst bed. Depending upon the types of reticulated top bed materials, additional solid particles with sizes larger than 1.0 μm are removed from the liquid stream before reaching the active catalyst bed.
Conventional methods are designed to remove micron- size (10-6 μm) solid particles only and are incapable of removing ultra-small nanometer (10-9 nm) particles from the process streams. For example, the reticulated top bed technology can only remove solid particles from 1 to 1,500 μm in size. Unremoved ultra-small particles in the liquid stream tend to plug the pore opening of the catalyst active sites in the downstream reactor. A magnetically induced filter (Universal Filter), developed and commercialised by ShinChuang Technology, is capable of removing essentially all types of solid particles of any size (down to 7 nm or less) with substantially reduced costs and simpler operations. The impact of nanometer particle removal from liquid streams to the reactor is enormous since it protects (or minimises) catalyst active pore openings from plugging, thereby greatly prolonging the catalyst life.
This dual filtration system achieves nearly a total prevention of solid particles in the liquid stream from entering the reactor. Furthermore, the need for spendable macropore filtration packings in the reactor and filter cartridges in front of the reactor are substantially eliminated (or minimised) to save the cost of materials and operations, which include loading/unloading and disposal of the spendable packing materials.
The following commercial examples demonstrate the effectiveness of the Universal Filter in extending the cycle length of hydrotreaters:
- Treating light coal tar feed stream to HDS reactor
• Capacity: 52,000 MT/y light coal tar (92% benzene and 5% toluene)
• Total solid particle removal: 97.6%
• Nm size solid particle removal: 100% (6.6-29.5 nm)
• Types of solid particle removal (in addition to carbon residue): Fe, S, Mn, Mo, Cu (100%); Al, Cr (90%); Ni, Cl (60-70%)
After 45 days’ continuous operation, the filter required no backwashing or regeneration, and the HDS reactor experienced no significant increment pressure drop or activity reduction.
- Treating dirty kerosene feed stream to HDS reactor
• Capacity: 30,000 b/d dirty (low-quality) kerosene stream fed to HDS reactor
• With a conventional basket filter followed by a cartridge filter, the unit was run with only one-fifth of its design capacity for fresh (dirty) feed with four-fifths of a clean recycle stream to minimise plugging problems and pressure drop in the reactor
• With the Universal Filter followed by a cartridge filter, full design capacity was achieved with a 0% recycle stream, generating US$7MM monthly operating profit (or annual profit of more than US$80MM)
• The Universal Filter also keeps conventional filter cartridges cleaner, reducing cartridge replacement from every few days to every few months, with annual cartridge cost savings of approximately US$225,000.
- Treating straight-run naphtha to HDS unit for CCR reformer
• Capacity: 30,000 b/d straight-run naphtha to HDS reactor for a CCR reformer
• After the Universal Filter was installed in the feed stream to the HDS reactor, reactor run time increased from 3-6 months to two years for uninterrupted continuous operation.
The HDS reactor turnaround has reduced from four (every six months) to one (every two years) in two years, and the total annual cost savings for the CCR reformer were estimated to be US$4,290,000 using the Universal Filter. (Each HDS reactor turnaround took 10 days, causing a US$2,860,000 loss in CCR production.)
The Universal Filter technology can be successfully implemented in other hydrotreating/hydrocracking cases for extending cycle length. The only requirement is the solids in the liquid stream contain certain amounts of ferromagnetic substances, such as FeO, FeS, Fe2O3, Ni, NiO, Co, and CoO. In fact, solid particles in the liquid stream to hydrotreaters or hydrocrackers do meet this requirement.
Daniel Gillis, Chevron Lummus Global, Daniel.email@example.com
There are multiple units where hydrocrackers were designed for two years and are now achieving three years or higher in some instances, especially the second stage (of HCR). This has been made possible by novel catalysts regularly extending hydrotreating and cracking cycles, lowering the start-of-run (SOR) temperature without changing the fouling rate. With some tailoring, catalyst innovations can be extended to other units. In addition to catalyst systems, CLG’s latest reactor internals and new ISOCatch inlet baskets can be helpful in extending life where a high axial temperature gradient is an issue. Other processing schemes have been employed, which not only enhanced catalyst life but also offered to produce high-value products such as premium LBO.