Jump menu

Main content |  back to top

Refinery operators can increase margins by processing lower-quality feedstocks to produce high-value products, but, for this approach to succeed, operators must optimise the performance of their hydrocracking units.

The principal challenge is to balance the cost and the quality of a feedstock against the effects it will have on the hydrocracker’s catalyst  system.

The ultimate aim is to improve refinery margins while using the catalyst fill effectively and prolonging the cycle as much as possible.

Managing this requires a clear understanding of the hydrocracker and how it will operate during each cycle.

The catalyst choice and the selection of reactor internals influence the efficiency of any hydrocracking process.

The catalyst usage has to be managed to derive the best performance in terms of activity and stability, while the right choice of internals promotes efficient distribution of gas and liquids within the reactor.

Zeeland refinery in the Netherlands is a joint venture between Total and LUKOIL.

Criterion Catalysts & Technologies (Criterion) has provided hydrocracking catalysts to the hydrocracker  for almost 15 years and has gained a clear understanding of the process challenges it faces in balancing feedstock quality and the performance of the hydrocracker catalyst system.

Criterion offers a detailed and in-depth technical service to help the refinery overcome these operational challenges.

This service includes operating data evaluations, special studies and process-related advice.

A key tool for supporting these activities is a hydrocracking kinetic model that is used to simulate hydrocracker catalyst performance.

Hydrocracking refinery

Zeeland refinery has a turnaround every five years, and the hydrocracker operates on the basis of an optimised 19-month turnaround to fit this schedule.

The 19-month turnaround means having two intermediate catalyst change-outs in the five-year period.

Running this way calls for close monitoring of the operation and regular evaluation of the hydrocracker unit’s data to ensure that its performance is in line with the operational targets.

The focus for the hydrocracker unit at this facility is on improving throughput, achieving the desired cycle length and managing the quality of the products from a variable feedstock.

Throughput at Zeeland refinery has increased significantly in past years and this has been achieved not by upgrading the hydrocracker, but by increasing the activity of the catalyst and installing Shell Global Solutions reactor internals in the pretreatment reactor.

Thanks to the combination of higher activity catalyst and the new reactor internals, no additional catalyst changeout was necessary when the throughput increased, and this has enabled Zeeland refinery to keep its original catalyst changeout scheme.

The catalyst choice and the selection of reactor internals influence the efficiency of any hydrocracking process.

A key part of maintaining the changeout scheme has been developing a new pretreatment catalyst specifically for heavier and dirtier feedstocks.

This involved making the demand for more active and stable catalysts a focus of the research and development process within Criterion and close technical collaboration with the research and development groups in the Shell  technology centres in Amsterdam, the Netherlands, and Houston, USA.

In its last cycle, Zeeland refinery used Criterion’s newest pretreatment catalyst,

CENTERA® DN-3620, and was one of the first clients to do so.

This catalyst was developed specifically for heavier feedstocks and illustrates how closely research and development is connected to the market.

DN-3620 is a Type 2 NiMo alumina catalyst based on the latest CENTERA technology platform.

Criterion applied nanotechnology methods, a detailed understanding of metal–support interactions and the impact of particle size and pore-size distribution on performance to create a high-activity catalyst with outstanding stability (Figure 1).

This combination of features is essential when processing heavier, more-metalcontaminated feeds.

According to Cees Koopman, Senior Process Engineer at Zeeland refinery, “The drive at the Zeeland refinery is to operate the hydrocracker unit so that it uses every drop of activity from the Criterion catalyst.

Our determination to get the best from the unit has made it possible to increase margins consistently during a period of global economic downturn.

The key to this has been a clear understanding of what is happening in the unit.”  

Feedstock composition and variability are two of the main factors affecting hydrocracker performance.

The crude unit at Zeeland refinery does not produce sufficient vacuum gas oil (VGO) to supply the hydrocracker, so the operators bring in VGO from the open market.

The quality of the imported VGO is a key factor in unit performance and product quality.

Too much nitrogen or other catalyst poison in the VGO has a detrimental effect on catalyst activity and selectivity.

The cycle length for a hydrocracker is usually determined by the pretreatment catalyst’s deactivation rate, which depends, in turn, on the feed quality and the process operating conditions.

The feed to the hydrocracker at Zeeland refinery is a combined stream of hot VGO from the crude and vacuum distillation units, and imported VGO.

Very poor quality VGO substantially reduces the cycle length, so it is vital to check the VGO’s quality before using it.

In the worst case, an unplanned change-out may be required, which would mean an additional 10-day shutdown, a fresh catalyst charge and loss of production.

Theo Visser, Senior Technologist Hydroprocessing, Shell Global Solutions, says, “During the cycle before the application of CENTERA DN-3620, the deactivation rate for the pretreatment catalyst at Zeeland refinery increased significantly.

Criterion compared the conditions in the hydrocracker with those in earlier cycles and examined parameters such as feed properties and

process conditions to determine why.”

CENTERA DN-3620

The stability of CENTERA DN-3620 compared with the previous catalyst by reference to the weighted average bed temperature. The data from this commercial application shows that DN-3620 is twice as stable as CENTINEL GOLD DN-3300, itself a market leader.

 

The study, which included analyses of imported VGO samples, resulted in several key recommendations for operating the hydrocracker unit at Zeeland refinery:

  1. Systematically analyse imported feeds to check for a high Conradson   carbon ratio and asphaltene and nitrogen content.
  2. Analyse and set limits for the hot VGO colour targeting a normal specification of ASTM Colour 4 for all feedstocks processed on the vacuum distillation unit, as this indicates minimal asphaltene entrainment.
  3. Investigate inconsistency in feed Conradson carbon ratio values.
  4. Make minor operational adjustments to reduce the negative effect of poorquality feeds on catalyst activity.

One of the most important tools for analysing hydrocracker unit performance is the Shell Global Solutions kinetic hydrocracking model HyStar.

This powerful tool estimates how a specific catalyst package for a particular hydrocracker will perform in terms of activity, stability, product yields and properties.

The software uses information about the specific design feedstock and the operating conditions at the refinery to deliver a solution tailored to that facility.

“The model describes the kinetic behaviour of a wide range of pretreatment and hydrocracking catalysts,” Visser explains.

“The model is based on numerous catalyst testing projects from Shell’s research and development groups, and industrial experience from more than 30 years. It is regularly updated.”

The kinetic model provides information on  vital factors about the process, including how a particular feedstock will affect the activity and stability of the catalyst; the likely yield  structure; and the predicted product properties.

This is a very powerful tool when a refinery is running on a wide variety of imported feeds.

As Visser points out, results from the model require expert interpretation.

“No matter how sophisticated the model is, we have to remember that it is a model. The results must be interpreted by hydrocracking experts who know the customer’s operation in detail.

Balancing feedstock, product properties and cycle length to meet a customer’s need is a challenge where we can deliver added value.”

At Zeeland refinery, the model helped to reveal the key issues behind the increased deactivation rate and enabled the operators to establish a new workflow to prevent the issue from recurring.

“The success of this monitoring and modelling approach relies on a technical collaboration that combines the wealth of knowledge that the Zeeland refinery operators have of the unit and how it operates with Shell Global Solutions and Criterion’s catalyst expertise and understanding of technical issues.

” Koopman adds.

When it became clear that the new catalyst would enable the Zeeland refinery unit to reach its run target with activity to spare, the operators were able to run the vacuum distillation unit harder and yield a heavier VGO feed for the hydrocracker or to adjust the specifications for the imported VGOs.

This has helped to increase the refinery’s margins significantly.

The performance of CENTERA DN-3620 at Zeeland refinery emphasises the need for catalysts with high stability as well as high activity; catalyst activity is only valuable for as long as it is retained.

By combining a catalyst that offered high activity and stability with a strong technical support programme from Criterion, the Zeeland refinery operators were able to overcome the specific challenges they faced and to optimise their operations.

 

CENTERA is a Criterion Catalysts & Technologies trademark.

Page Tools

Discover more

Criterion Catalysts & Technology
Criterion is the world’s largest supplier of hydroprocessing catalysts, which includes catalysts for hydrotreating, hydrocracking, hydrogenation and isomerization.
CRI Catalyst Company
CRI Catalyst Company serves the chemical and petrochemical industry by supplying catalysts, technology, and services to meet a wide range of requirements.
Receive the latest digital edition direct to your mailbox.