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High-level block scheme

High-level block scheme showing the integration between the hydrocracker and the steam cracker.

If the new catalyst caused the hydrogen content of the hydrowax to decrease then the steam cracker’s ethylene yield or the furnace’s run length would have been severely curtailed, and so the technologists were keen to ensure that their new catalyst system could maintain the hydrowax quality as well as improving the middle distillate yield. 

Although taking such an integrated approach added substantial complexity to the catalyst selection process, post-project calculations show that it has enhanced the combined economics of Pernis and Moerdijk by some $5 million a year. In this interview, three of the unit’s technologists discuss the steps they took to ensure that the new catalyst system had a positive effect at both sites.

DISCUSSION PARTICIPANTS

Jeroen Groenhagen, Senior Technologist, Shell Pernis, was responsible for the catalyst selection study, and loading and starting up the hydrocracker after the new catalyst package’s installation.

Bastiaan van Hasselt, Hydroprocessing Team Leader, Shell Pernis, has 15 years’ experience in hydrocracking and played a key role in the project.

Jelle Sietsma, Hydrocracking Technologist, Shell Pernis, was involved in loading, starting up and monitoring the hydrocracker after the new catalyst package’s installation.

straight talk

Q: How did you evaluate the impact of the new catalyst?

Groenhagen: We performed a catalyst selection study. However, such studies usually only consider improving the kerosene and gas oil outputs, the level of conversion and the cycle length. Here, we had another level of complexity because we also had to consider the integration aspect: the quality of the hydrowax was an important parameter.

Van Hasselt: We could have simply tuned the catalyst package to improve middle distillate yield, which is the goal for most refiners, but we needed to consider the bigger picture. The hydrogen content of the hydrowax was particularly important because it determines the ethylene and pitch yields, and the furnace run length. If our new catalyst were to alter the hydrowax’s hydrogen content, this might adversely affect Moerdijk’s economics, so we had to find a balance. 

Q: What catalyst have you installed in the unit?

Sietsma: The unit has a completely new cracking catalyst from Criterion Catalyst & Technologies called Z-FX10, which uses a special zeolite technology designed to increase middle distillate yield, product quality and catalyst stability.

Van Hasselt: In the pretreatment section, where we remove the impurities that could poison the sensitive cracking catalyst, we have a carefully designed combination of demetallisation, hydrodenitrogenation and hydrodesulphurisation catalysts. Criterion tuned the pretreatment section to ensure that we achieve the right cycle length and quality.

straight talk 2

Q: As this was the catalyst’s first commercial application, what steps did you take to verify how it would perform in your unit and with your specific feed?

Groenhagen: We ran a full pilot-plant testing programme at the Shell Technology Centre in Amsterdam, the Netherlands, to compare the novel cracking catalyst with the existing catalyst. This was important because it gave us confidence that the catalyst package would deliver what it was designed to. 

It also verified the quality of hydrowax that we would be sending to Moerdijk. This was vital because the lower the hydrogen content in the hydrowax, the more easily the furnaces in the steam cracker coke up.

Even the slightest deterioration in hydrowax quality can have a huge impact on ethylene yield, furnace run length and coke make, so we really needed to understand that parameter’s behaviour over the run length of the catalyst and what it would mean in margin or dollar terms.

Q: How has the catalyst been performing?

Sietsma: When we first started up, the catalyst was slightly more selective towards middle distillates than anticipated. Criterion helped us to fine-tune the process conditions and, within a short time, the unit was meeting the performance guarantees.

Van Hasselt: We are now nine months into the cycle, and so far it has performed very well. The catalyst has been delivering on-specification products, increased middle distillate yield, and there have been no surprises.

Even the slightest deterioration in hydrowax quality can have a huge impact on ethylene yield, furnace run length and coke make, so we really needed to understand that parameter’s behaviour over the run length of the catalyst and what it would mean in margin or dollar terms.

straight talk

Q: How valuable has the project been for both plants? 

Sietsma: At Pernis, we have been able to maximise our middle distillate yield: we now make more kerosene and diesel than before, and less naphtha, while operating at a similar conversion severity.

There are clear advantages for Moerdijk too. Because we were able to optimise the hydrowax quality for their specific processes, they have been able to enhance the ethylene and pitch yields, and maximise the furnace run length. 

By balancing the objectives of both units, we have enhanced Shell’s overall margin, we call this enterprise economics, by some $5 million per year.

Q: Because there is a clear trend across the industry towards refinery–petrochemical integration, other plants may find themselves in a similar situation to you. What advice would you offer to them?

Groenhagen: Align the economics that you use: that is really important. Normally, when we do catalyst selections, we only look at the refinery impact and that is relatively straightforward, especially because we have our own economic models to use. However, if the refinery site model is not connected to the petrochemicals site model, you have to be extremely careful. 

Sietsma: If there is anything unusual about your application, whether it is an unusual feed or a novel catalyst, for example, you might want to consider pilot plant tests as part of your management of change process. These can give substantial insights into how the catalyst package will perform in the commercial facility and minimise the risk of surprises when you start up. 

Van Hasselt: Engage all of your stakeholders and do it as early as possible. This was key to the success of our project. Because we brought all parties in at the right time, they have been extremely co-operative and the project has delivered enormous value for the two sites.