Apr 24 2018
3 min read
In today’s complex environment, refineries and petrochemical plants around the world are on the lookout for advanced solutions to help them reach operational excellence. Working towards this goal Axens recently introduced three brand-new EquiFlow® high-efficiency reactor internals.
This includes Hy-Tray™, the latest generation of distributor trays, Hy-Quench-XM™ and Hy-Quench-NG™, two compact quench systems, and Hy-Clean®, a new smart filtering tray system.
Let’s dive into a typical case study and see how these new internals can help to achieve your goals.
A European refiner was encountering different operating problems with its hydrocracking unit.
The catalyst cycle lengths were shortened and the unit had to be shutdown once a year in order to overcome pressure drop issues.
Here is what Axens technical experts found after they carried out an audit.
The audit led to observe two phenomena happening in the hydrocracking unit.
First, impurities and inorganic matter were responsible for crust formation and plugging. As a result, pressure drop issues happened in the first catalytic bed of the reactor increasing the catalyst change-out frequency.
Second, the temperature profile was not optimized because of hot spots and a poor vapor/liquid distribution throughout the catalytic bed.
The Radial Differential Temperature (ΔT) was too high, the poor temperature distribution in the reactor reduced catalyst activity, selectivity and ultimately stability, leading to shorter cycle lengths and performance losses.
These two phenomena needed to be addressed to extend the unit cycle length.
Illustration of a non-optimized radial temperature profile with hot spots
As a first move, EquiFlow® Hy-Clean™ filtering trays were installed at the top of the reactor to prevent plugging by retaining feed impurities such as fines, rust and inorganic matter that are responsible for crust formation. These filtering baskets can then be removed and cleaned to be reused.
To go further, Hy-Tray™ distributor trays, a dispersive system that goes under the chimney tray, were installed. Developed along with IFPEN and drawing on 15 years of extensive R&D based on Computational Fluid Dynamics (CFD) and Gamma ray Tomography, this system enabled a close-to-ideal vapor/liquid distribution throughout the catalytic bed.
Finally, quench system Hy-Quench-XM™ was set up. This quench system is more compact and designed to mix in a perfect fashion the effluents from the upper catalytic bed with a hydrogen quench stream injected into the reactor. It helps to get a homogeneous temperature of the mixture, made of the effluent and the hydrogen, and to distribute it uniformly before entering the lower catalytic bed. Hy-Quench-XM™ also enables to decrease the Radial Differential Temperature and to increase the catalyst volume loaded in the reactor up to 10%. These two benefits contribute to extend the unit cycle length.
To finish with, this multi-stage solution was easily implemented because welding procedures were not required.
Since the installation of the three high-efficiency reactor internals in the hydrocracker unit, the ratio of radial ΔT over axial ΔT has remained constant and extremely low throughout the whole cycle in all beds. The radial ΔT was reduced by 10°C thus increasing the catalyst cycle length by 20%.
By limiting fouling and pressure drop issues and increasing the catalyst cycle length, the on-stream factor was significantly increased and the catalyst replacement cost was reduced
Upgrading the hydrocracking unit with internal reactors also creates economical value. Based on our experience, an 84% conversion hydrocracker unit operating at 320t/h can come out on an additional profit of $1.5M per year.
