S. S. Alalloush, S. A. W. ALI, A. S. GHADEER, M. I. ALODAIL and A. Z. SADAH, Saudi Aramco, Dhahran, Saudi Arabia
This article elaborates on the startup of a refinery’s heavy naphtha reforming unit with an alternative approach to the initial unit design, including an evaluation of several startup techniques to ensure the adequacy and practicality of the selected option. The alternative startup scheme involved additional efforts for the importation of naphtha and the initial offloading of hydrogen (H2) from an external temporary source of H2 (i.e., tube trailers). The chosen option resulted in a successful startup of the gasoline block and other dependent downstream units, along with a quicker startup schedule and financial benefit.
Background. Saudi Aramco’s Jazan refinery complex (JZRC) is a 400,000-bpd full-conversion oil refinery that processes Arabian crude. It is integrated with a 3.8-GW vacuum residue (VR) gasification power block—the integrated gasification combined cycle (IGCC)—that produces H2, steam and other necessary utilities to sustain refinery operations, and the air separation unit (ASU) for additional utilities like nitrogen, oxygen and others (FIG. 1).
The refinery has multiple hydroprocessing and conversion units to satisfy Saudi Arabia’s fuel demand, as well as petrochemical building blocks benzene and paraxylene. The naphtha hydrotreater (NHT), heavy naphtha reformer and its continuous catalyst regeneration (CCR) are parts of the gasoline block operating area at the JZRC (FIG. 2).
The purpose of this unit is to produce an aromatic-rich reformed naphtha cut (reformate) and a H2-rich gas that is consumed by NHTs and diesel hydrotreaters (DHTs), as well as light-naphtha isomerization and aromatics processing units within the refinery. The feed to this operating area is a combination of sour straight-run naphtha from the crude distillation unit (CDU), cracked naphtha from the hydrocracker and imported naphtha from an outside supplier. Due to the presence of contaminants (organic nitrogen, sulfur), the hydroprocessing of reformer feed in the NHT is required to meet final product quality and environmental regulations, and to maintain the health of the downstream catalytic processes that are affected by catalyst poisons (e.g., sulfur, nitrogen, metals).
Heavy-naphtha reforming and the CCR unit are involved in a catalytic process that includes two sections:
The reforming section’s feed comes from the bottom of the NHT fractionation section, after it flows through a series of exchangers to the feed filters. Then, this feed travels through the feed/effluent exchanger, followed by the interstage fired heaters between a series of reactors.
Leaving the last reactor, the effluent passes through heat recovery in the heat/effluent exchanger. The effluent is then cooled prior to the separation section. Finally, the separated produced gas is fed to the compression and absorption section to increase H2 purity and liquid hydrocarbons recovery.
Startup plan and challenges. The original startup plan for the Jazan refinery’s hydroprocessing units was based on H2 availability from the IGCC to start the NHT, followed by the CCR and other downstream-dependent units. Due to the COVID-19 pandemic causing delays in the commissioning and startup of the IGCC, the refinery portion of the JZRC approached the commissioning stage earlier. To follow this design startup scheme, the refinery startup was dependent on the startup of the IGCC.
The fundamental issue that changed the sequence of the gasoline block startup plan was H2 availability from the IGCC. The reforming process produces H2; however, the upstream NHT requires H2 to treat feed for the reformer. This is often an issue in refineries with catalytic reformers as the sole source of H2, which can be started with purchased or stored hydrotreated (sweet) naphtha until they produce the H2 required to start the NHT. In addition, hydrotreated sweet naphtha is difficult to find in the market, as refineries prefer to refine this heavy naphtha into reformate, since it provides a higher product profit.
In the Jazan refinery case, the issue was complicated, as the CCR-supplied catalyst was in the oxidized state and required H2 to reduce (activate) it before feed could be charged to the unit. As a result, the JZRC had to ensure the availability of both H2 (for catalyst reduction) and treated sweet naphtha prior to sending feed to the reforming unit for the CCR startup, followed by the gasoline block startup.
Alternative startup options. To begin operations on the gasoline block units, several startup options were evaluated. This included the analysis of multiple available naphtha feedstocks, the utilization of a tank naphtha route within the unit, the assessment of different H2 sources and modified startup sequences.
Option 1: Imported sweet heavy naphtha through the NHT oxygen stripper. This option evaluated importing sweet heavy naphtha (< 0.5 ppm wt% sulfur) to start the reforming unit first—this would produce H2 to start the NHT unit. In this case, the stored sweet naphtha would be processed through the oxygen stripper column, bypassing the NHT reactor and moving directly to the NHT stripper, followed by the naphtha splitter column and then the reforming unit (FIG. 3).
Option 2: Imported low-sulfur naphtha through the NHT oxygen stripper. This option evaluated importing low-sulfur naphtha (50 ppmwt maximum) to start the reforming unit first—this would produce H2 to start the NHT unit. In this case, the stored sweet naphtha would be processed through the oxygen stripper column, bypassing the NHT reactor and moving directly to the NHT stripper. This would be followed by the naphtha splitter column and then the reforming unit. This option was considered based on the fact that sulfur is a temporary poison for the reforming catalysts, which can be regenerated after a short startup duration. This route is depicted in FIG. 4.
Option 3: CDU straight-run naphtha with a temporary H2 generator. Another option was to arrange a temporary H2 generator system. The NHT would be started utilizing straight-run naphtha from the CDU, followed by the startup of the reformer. This option was similar to the design case; however, instead of H2 supplies from the IGCC, the temporary H2 generator would be used to start the NHT and reforming units. This route is similar to the unit design depicted in FIG. 5.
The basis of decision. Based on the team’s evaluation, it was identified that Options 2 and 3 contained several associated risks and challenges. The implementation of Option 2 would have required an urgency in the startup of the NHT unit, as the reforming reactor’s catalyst coke content would have increased rapidly and without regeneration. The reactor’s catalyst would then deactivate to the extent that it would eventually stop the reformer. The challenge with Option 3 was the availability of a temporary H2 generator facility to reliably produce sufficient H2 to sustain the operations of both the NHT and CCR.
Based on the evaluation of options and the type of challenges associated with each one, the JZRC team selected Option 1—importing sweet naphtha and H2 tube trailers—as the best option in terms of lowest risk, shortest duration and lower economic impact.
Selected option implementation and bottlenecks. Although Option 1 was the most viable in terms of associated risks, duration and economic impact, additional challenges were identified when this option was further explored. The availability of sweet naphtha in the refined products market was the biggest challenge, as refineries would rather upgrade naphtha to a finished product or blend it in their gasoline pool. Furthermore, to bring H2 in tube trailers, the distance between the JZRC and the nearest capable H2 production facility was approximately 1,600 km (995 mi). Moreover, there were a limited number of H2 tube trailers available from the H2 supplier and no existing provision/facility to offload the pressurized H2 from the tube trailers to the refinery system.
In light of these challenges, the team aimed to quantify the necessary H2 needed for unit startup and catalyst reduction, along with proper logistics planning, including the transportation of tube trailers from the production source to the offloading refinery site. In parallel, the team benchmarked several H2 offloading facilities in other refineries around Saudi Arabia to design the optimum H2 offloading facility for the JZRC. This was followed by detailed engineering design, along with safety assessments of the design via a series of risk assessments and hazard and operability (HAZOP) analysis sessions. As a result of these efforts, a robust H2 offloading facility was constructed, commissioned and operated in a safe and reliable manner to provide the required H2 for unit startup. Moreover, a planned implementation was completed to ensure (especially during the startup of the units’ compressors) that H2 would be continously available until the unit feed introduction and H2 production. A sketch of the H2 offloading facility is shown in FIG. 6.
Takeaway. In light of the selected alternative approach to start the heavy naphtha reforming unit, the JZRC performed a safe and smooth commissioning and startup of the gasoline block. This led to the startup of other associated units such as the DHT and the sulfur recovery unit. This resulted in earlier production benefits and financial profits on the refinery side prior to the startup of the IGCC. HP
ACKNOWLEDGMENTS
The authors would like to thank Saudi Aramco’s Process and Control Systems Department management and also the JZRC’s management for their cooperation and work toward implementation of these new technologies.
Saeed S. AlAlloush is an Engineering Consultant within Saudi Aramco’s Process and Control Systems Department. He has more than 20 yr of experience in the oil refining industry, primarily with the fluid catalytic cracking process. He has also published and presented several papers, and has been granted three U.S.-registered patents. AlAlloush earned an MS degree in chemical engineering from the University of Tulsa in Oklahoma.
Syed Abdul Wahab Ali is a Operation Engineer within Saudi Aramco’s Jazan Refinery Department, specializing in naphtha block hydroprocessing and reforming units. He is a professional chemical engineer with 12 yr of industry experience, and an active member in international engineering bodies such as Engineers Australia and IChemE, UK. He earned an MS degree in chemical engineering from the University of the Punjab in Lahore, Pakistan, and an MBA degree from Bahauddin Zakariya University in Multan, Pakistan.
Abdulelah S. Ghadeer is an Operation Engineer within Saudi Aramco’s Jazan Refinery Department, specializing in naphtha hydroprocessing, reforming, and aromatics extraction and processing units. He is a chemical engineer with 10 yr of industrial experience in refining and petrochemicals facilities. Ghadeer earned a BS degree in chemical engineering from King Fahd University of Petroleum and Minerals in Dhahran, Saudi Arabia, and an MS degree in refining and petrochemicals from the IFP School in Rueil-Malmaison, France.
Mohammed I. Alodail is a Process Engineer within Saudi Aramco’s Process & Control Systems Department, specializing in naphtha hydroprocessing, isomerization and reforming units. He has 6 yr of industrial experience in refining facilities. He earned a BS degree in chemical engineering from King Fahd University of Petroleum and Minerals in Dhahran, Saudi Arabia.
Ahmed Z. Sadah is a Process Engineer within Saudi Aramco’s Process & Control Systems Department, specializing in naphtha hydroprocessing, reforming, isomerization and other processing units. He is a chemical engineer with 5 yr of industrial experience in refining and petrochemicals facilities. He earned a BS degree in chemical engineering, with a concentration in polymer science and engineering, from Michigan State University in East Lansing, Michigan.