Jan-2001

Revamp options for improved diesel

Integration of cocurrent and countercurrent reactor systems into existing hydrotreaters makes various revamp options possible, providing opportunities for meeting changing specifications for diesel

Gary L Hamilton, ABB Lummus Global
Bert van der Linde, Shell Global Solutions
Dave DiCamillo, Criterion Catalyst Company

Article Summary

Continuing challenges facing refiners in producing improved quality diesel product have focused considerable attention on various hydroprocessing options – from adjusting diesel feedstock properties via different blending and/or adjusted feedstock cut points, to the use of higher activity catalysts, hydrotreater revamps, and possibly even the installation of new hydrotreating facilities.

One way or another, improving the quality of diesel does not come free of charge. There is no single right answer or solution, as experience has shown that refiner-specific (or more appropriately, refinery-specific) needs and issues play a considerable role in deciding how best to achieve improved diesel quality goals with minimum investment. In addition, by their very nature, the diesel quality goals will also strongly influence the right case-specific solution.

The SynAlliance, consisting of Shell Global Solutions, ABB Lummus Global, and Criterion Catalyst Company LP, has developed various options and approaches to improving diesel quality. The technology involved is referred to as SynTechnology, consisting of various reactor system designs in conjunction with advanced high activity SynCat catalysts. By employing the right combination of catalyst(s) and reactor system, the SynAlliance has developed optimised solutions for producing improved quality diesel.

Through the use of reactor system technology that can include both cocurrent and countercurrent reactors, various revamp options are available.

In order to meet new and changing hydroprocessing objectives, particularly with regard to existing units, it is key to maximise the performance of the reactor system by optimising the hydrogen partial pressure and, in doing so, obtain the highest hydrogen partial pressure for a given existing systemís operating pressure. In this way, maximum performance can be obtained from the right catalyst(s) while minimising revamp investment. Reactor systems utilising both cocurrent and countercurrent contacting of distillate with hydrogen-rich gas have been proven as an effective means to achieving an optimum hydrogen partial pressure profile throughout the reactor system.

Specific information about the Lummus patented countercurrent reactor system is contained in the references in this article.

Meeting the need
It is essential to develop solutions in close cooperation with a refiner’s engineering, planning and operations personnel. It is most important to define ways to maximise re-use of existing equipment/systems, determine the optimum selection and/or blend of feedstocks to be treated and determine the optimum way in which to utilise the available hydrogen within site-specific limitations.

Experience has demonstrated that this approach will lead to the best fully integrated solution that meets diesel product quality objectives at minimum investment within the framework of an acceptable revamp implementation plan.

SynTechnologies include SynHDS, SynShift and SynSat.
SynHDS technology is primarily focused on producing ultra low sulphur diesel and is capable of meeting sulphur specifications of <10wppm.
SynShift is a selective ring opening technology for processing even the most difficult-to-treat feedstocks for the purpose of density reduction, T95 reduction (shift), cetane improvement and aromatics (polynuclear or total) reduction.

SynSat is specifically focused on aromatics saturation, providing added density reduction and cetane improvement. SynShift and SynSat can be combined for deep HDA and T95 reduction, along with other process objectives.

Whether for new units or revamps, the key to an optimised yet flexible no-regret solution is to be found in selecting the right reactor configuration, operating conditions, and catalyst or catalyst combination. Various high-activity SynCat catalysts are available including CoMo, NiMo, NiW and noble metal-containing.

A wide number of different reactor system configurations have been designed and implemented. These have included a single-stage system with a cocurrent reactor, or integrated two-stage systems with a cocurrent first-stage reactor together with either a cocurrent or countercurrent second-stage reactor. In such integrated two-stage systems, interstage flashing/stripping has been utilised, and its use will depend on the specific processing objectives and required SynCat catalyst(s).

Reactor systems have also been designed and implemented that have staged investment configurations, using a cocurrent reactor initially with the ability to modify the system at a future date to a two-stage configuration if required as a result of changing product specifications.

Typical reactor configurations are depicted in Figure 1. It should be noted that the number of catalyst beds in each reactor stage can vary depending on feedstock type/quality and diesel objectives.

Table 1 provides a general guide to applying the right reactor system and associated SynTechnology.
In addition to the above hydroprocessing objectives, cold flow properties improvement via SynFlow technology can also be achieved, if required, within each of the reactor system configurations.

Revamp opportunities
Depending on an existing unit’s operating pressure, catalyst volume, and available makeup hydrogen and recycle gas capabilities, the number and type of revamp options will vary and be highly dependent on the revamp objectives concerning not only diesel quality, but also unit capacity.