Hyundai Oil bank

When striving to increase the throughput of a hydrocracker or other conversion unit, the amount of vacuum gas oil (VGO) that the high-vacuum unit (HVU) can generate is often a critical constraint. To overcome this, some refiners lift more from the short residue into the VGO, but that brings with it metals and other contaminants that can affect the conversion unit’s reliability. Fortunately, with Shell’s deep-flash technology, the VGO yield of an HVU can often be increased substantially without affecting the downstream units’ reliability through a low-cost revamp, as a recent project for Hyundai Oilbank demonstrates.

When Hyundai Oilbank conceived the notion of building a 20,000-bbl/d Group II base oil manufacturing plant, its integration with the adjacent Daesan refinery in South Korea was key. To make the project work, Hyundai Oilbank needed to revamp the hydrocracker to provide the right amount of feed at the right quality. However, even after doing that, the hydrocracker would be short by about 5,000 bbl/d, but the Shell Global Solutions team identified an opportunity to produce additional feedstock for the hydrocracker by going further back into the processing stream and revamping the HVU.

“We identified various ways in which Hyundai Oilbank could get more VGO to the hydrocracker,” explains Kaushik Majumder, Team Lead and Licensing Technology Manager – Distillation, Shell Global Solutions. “Essentially, these centred on two main options. The first was a major revamp of the existing vacuum distillation unit (VDU) to convert it to a deep-flash HVU. The second involved a minor revamp of the VDU and adding a new deep-flash HVU in parallel to co-process atmospheric residue (AR) and vacuum residue (VR) from the VDU.

“Shell Global Solutions conducted cost–benefit analyses of these options. Hyundai Oilbank then selected the option involving a major revamp, as this provided the lowest-capital-cost option, but, says Majumder, it was also the most technically challenging and the riskiest in terms of the project economics owing to the potential for significantly extending the planned turnaround of the crude distillation unit (CDU) and the HVU.

"We were very impressed with the quality of their solution and their responsiveness"

“The biggest limitation was the furnaces,” says Majumder. “Hyundai Oilbank had two furnaces feeding the existing HVU and to meet the project goals we needed to increase their duty significantly. So, we revamped both extensively, including adding tubes in the convection section and switching completely to gas firing instead of dual-fuel firing. This was critical to the success of the project.” 

Other important changes were upsizing the transfer line and the column feed inlet nozzle. The team also replaced the existing vapour horn type feed inlet device with a Shell Schoepentoeter* Plus inlet device (see boxed text overleaf) to reduce the entrainment of VR to VGO (hydrocracker feed) and to ensure better vapour distribution. “This was very important for the performance of the unit because we were almost at the maximum limit of the transfer line velocity,” says Majumder.

In addition, the team took all the possible steps to minimise the vacuum column pressure drop to help maximise distillate yield. The pumparound and wash-bed packing were replaced with the latest-generation, low pressure drop structured packing and the existing chimney trays were replaced with Shell’s proprietary low pressure drop draw-off trays.

The team also installed new spray distributors and made minor plant modifications outside the column to support the main revamp, such as upgrading the heat exchangers, pumps etc.

“Unlocking more barrels of VGO from the HVU was key to the economics of our lubricant base oils project because the HVU and the hydrocracker are configured to work with the new base oil plant as a value chain,” says Dalho Kang, Refinery Manager, Hyundai Oilbank.

“Shell Global Solutions provided us with a detailed set of creative options that would help us to unlock more barrels of VGO from the HVU and then went on to evaluate each one against our objectives. Once we had selected our preferred option, they licensed the technology to us and guaranteed its performance. We were also very impressed with the quality of their technology solution and their responsiveness,” Kang concludes.

The execution of the HVU revamp by Hyundai Oilbank was exceptionally efficient. The full scope was delivered within the budgeted days and cost, which confirmed that the full revamp option was the best decision for this project. After start-up, all the performance guarantees, including VGO yield and quality, were fully met.

Minimum-scope versus maximum-scope HVU revamps

Many refiners have a strategic need to maximise the throughput of their conversion units and an HVU revamp can often be an extremely attractive solution. But some are often unaware that the scope of such a project can vary enormously according to the unit’s current bottlenecks and the customer’s specific objectives, writes Kaushik Majumder, Team Lead and Licensing Technology Manager – Distillation, Shell Global Solutions.

“In my opinion, no HVU could be revamped more than Hyundai Oilbank’s. We really pushed at the limits of what is achievable. But some projects do not need to push as hard and can achieve their objectives through a relatively simple revamp in which we only introduce a new feed inlet device and change the wash bed. We would call that a minimum-scope revamp.

For example, we recently worked with a non-Shell refinery in India where the VGO yield was limited owing to excessive entrainment of metal from the short residue. Unlike at Hyundai Oilbank, we found that changes would not be required to the furnace and most of the packing could stay. They wanted to produce more VGO and had the capacity in the column, furnace and transfer line to do so. Revamping this unit only required modifications to the column internals and replacing the existing feed inlet device with a Shell Schoepentoeter Plus.

We implemented these changes within the turnaround window, and our customer has reported that the unit now generates 8% more VGO of the desired quality.

Whether the project involves maximum scope, minimum scope or something in-between, an HVU revamp can often be an extremely compelling project. Typically, the capital cost is relatively low, the payback time is short and the hardware changes can often be made within an existing refinery turnaround window.

Having said that, HVU revamps can often be very challenging and, if they are not engineered properly, it may be impossible to meet the desired revamp objectives. At Shell Global Solutions, we have delivered almost 50 new designs or revamps since 1985 and that track record brings with it invaluable experience.”

For more on minimum-scope HVU revamps, see Low-capital-cost revamps of high-vacuum units (HVU).

The Shell Schoepentoeter Plus

The Shell Schoepentoeter Plus is a key component that Shell Global Solutions has introduced in most of its HVU revamps since the device was developed in 2010. This is an advanced version of the Shell Schoepentoeter, a versatile, low pressure drop, vane-type feed inlet device. The conventional device has proven to be one of the most effective technologies available on the market for efficient de-entrainment in critical services such as deep-cut vacuum distillation and the new “plus” device provides yet more efficient de-entrainment, especially at higher vapour loadings, owing to its innovative vane design for minimising liquid re-entrainment.

This technology has an excellent track record. For example, a recent inspection of a Shell Schoepentoeter Plus in a deep-cut vacuum column in 2010 revealed it was mechanically and functionally robust after five years of on-target performance.

*Schoepentoeter is a Shell trademark.

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