Revamp of an existing diesel hydrotreater or build new diesel hydrotreaing capacity?

During recent years refiners in Europe and U.S. have been busy completing their clean fuels projects to meet the regulatory deadlines for ultra low sulphur diesel (ULSD). Topsøe has been leading this hydrotreating revolution and has to date designed 92 units for ULSD and sold more than 22,000 tonnes of catalyst for ULSD service including to units that were not originally licensed by Topsøe.

Topsøe clients have taken different approaches to their ULSD projects based on their refineries needs. The most basic decision that refiners must first make is whether to revamp their existing distillate hydrotreater or build new distillate hydrotreating capacity. This decision may be influenced by the following considerations:

• Existing unit design pressure and capacity
• Feedstock properties (straight or cracked stock, feed endpoint, sulphur content)
• Present and future crude slate
• Ability to reuse existing distillate hydrotreater as gasoline desulphurization unit
• Expectations on future regulation of sulphur and aromatics
• Plant location (Middle East, North Africa, Europe, USA etc.)
• Corporate clean fuels goal

No matter which approach the refiner chooses, the project team must have the necessary knowledge within the catalyst, process, and engineering fields to properly evaluate various project options. Furthermore, the project team must have a clear understanding of the interplay between catalyst and process solutions to arrive at the optimal solution. Since it is during the early scoping phase when the key decisions having the biggest impact on project cost are made, the licensor's participation during this critical phase is vital. An experienced licensor can add value during this critical phase by bringing to the table:

• An in-depth understanding of the kinetics governing deep desulphurization of diesel
• A unique understanding of the key cost drivers for a project
• High activity catalysts

Survey of Licensed ULSD Units

To get an understanding of the variations in key ULSD design parameters such as unit design pressure, product sulphur target and catalyst selection, a survey of the Topsøe licensed units is presented in the following table.

Table 1: ULSD Unit Design Survey

One clear trend is that higher pressure units are typically designed to use NiMo catalyst while the very low pressure units are designed predominantly to use CoMo units. Recent developments in Topsøe's proprietary catalyst preparation technology BRIM^TM have allowed Topsoe to design some units for very low pressures. Details of the key design criteria behind the success of BRIM^TM catalysts have been discussed elsewhere [1].

The investment cost for an ULSD unit is of course highly site-specific. A typical Capex cost for a grassroots ULSD unit ranges from 1,000 - 2,000 EUR per bpsd capacity. The high end of this range reflects the projects with a high complexity, e.g. with an additional HDA or dewaxing stage.

For revamps, the capital investment is naturally even more unit specific. Revamps conducted by Topsøe have typically been in the range of 250 - 500 EUR per bpsd capacity.

Clean fuel projects are rarely driven by economical justifications, but typically out of necessity due to dictation by local environmental regulations or corporate clean fuel goals. Currently, the most stringent environmental regulation (EURO V) requires the diesel product to contain less than 10wtppm S.  Almost 75% of the units that Topsøe have designed or revamped are targeting to meet EURO V specifications or tighter specifications set by certain IOC's who wish to be prepared for further strengthening of the clean fuels specifications in the future.

In many of the revamp projects, the refiner has taken advantage of the opportunity to increase the total processing capacity. This is a typical way of establishing a return on investment and justifying a clean fuel project. A specific example is Bharat Petroleum (BPCL), who wished to revamp their diesel hydrotreating unit in Mahul, India, to produce ULSD. Following the recommendations of the Topsøe experts, BPCL was able to increase the design load of the unit by 43% securing thereby an estimated payback time of 1-1½ years [2].

In the following, an industrial case is presented to exemplify the complexity of the decision making process when a refiner has to take a decision of whether to revamp an existing unit or to build a new one.

Industrial Case: Low-pressure ULSD Production at BP, Coryton, UK

The Catalytic Hydrodesulphurisation (CHD) unit at the BP Coryton, UK refinery (Now owned by Petroplus), was built in 1968 and has been revamped extensively since then to a capacity, which is more than three times the original capacity. Before the latest revamp the unit was co-producing 50 wppm diesel and 0.2 wt% heating oil in blocked mode. The feed was a blend of kerosene, AGO, LVGO and Heavy Cat. Cracker Naphtha (HCCS). Operating conditions were:

In response to the developing 10 wppm diesel market, BP initiated a project for production capacity increase of ULSD at Coryton.

The original understanding was that a new high-pressure unit was required, and five licensors were invited to bid for this unit. Topsøe was selected out of two licensors, both confident of revamping the low-pressure unit for ULSD production. 

The economics of a revamp vs. building a new grassroots hydrotreater (including the project approach, pilot plant testing and the design phase) were described in detail [3]. A key analysis performed by the BP/Topsøe project team showed that investment in a tailored feed revamp had about twice the internal rate of return as a new high-pressure unit. Further technical and economic analysis revealed that it was economically justified to add additional reactor volume to achieve longer run length and process higher endpoint feeds.

An important aspect of the project was to incorporate BP's operating experience related to the unit limitations and reliability, some of which would be even more constraining under ULSD production. Revamp modifications in this respect included a new compressor rotor, addition of a wash water system and a new stripper pre-flash drum and re-tray to off-load product stripper flood limit.

To manufacture 10 wppm sulphur diesel, a new reactor was added in series with the existing reactor. Both reactors were filled with a new charge of Topsøe's CoMo catalyst TK-574. A successful test run was completed to demonstrate the revamped unit's capabilities for production of 10wppm sulphur diesel.

The catalyst activity obtained during the entire first catalyst cycle was satisfactory, and the client decided to purchase Topsøe CoMo catalysts for the two subsequent catalyst cycles. Figure 1 shows the product sulphur versus run days for the second catalyst cycle. Due to market conditions, continues production of ULSD with < 10 wppm sulphur commence during the second catalyst cycle.

Figure 1: Product sulphur versus run days for the second catalyst cycle

Figure 2: Normalised WABT versus run days for the second catalyst cycle

Conclusion

The revamp project at the BP Coryton refinery demonstrate the capabilities of Topsøe's high efficiency reactor designs and high activity HDS catalysts to extend the capabilities of an existing hydrotreater to make ultra low sulphur diesel.  In depth knowledge of deep HDS reaction kinetics and engineering design is the key to successful, low-cost ULSD project implementation.

References

[1]: "Next generation BRIM^TM catalyst technology",

      Lars Skyum, Per Zeuthen, Barry Cooper, ERTC 2008

[2]: "Hydrotreater revamp case study. Making the most of what you have."

      Torkil Hansen,  ERTC 2010 Istanbul.

[3]: "Systematic Approach for the Revamp of a Low Pressure Hydrotreater",

      Jamie Townsend, Tim Shooter and Gordon Low, 7th ERTC, Paris, November 2002