With xxxxxx from Tropsoe

Revolutionary steps in catalyst research have made it possible to go down to ultra low sulphur diesel by minimum process changes in an existing unit, and Topsøe’s experience is that is can be economically advantageous to revamp an existing hydrotreater rather than building a grassroots plant.

The decision of whether to revamp an existing hydrotreater or build new hydrotreating capacity may be influenced by several factors e.g. existing unit pressure and capacity, feedstock properties (straight or cracked stock, feed endpoint, sulphur content), present and future crude slate, expectations on future regulation of sulphur and aromatics, plant location (Middle East, North Africa, Europe, USA etc.), and corporate clean fuels goal

It is not necessary to consider only the same licensor for the revamp as an original licensor. Rather it is important to select a licensor that through understanding of the interplay between catalyst and process solutions to arrive at the optimal solution. Topsøe has revamped 57 diesel hydrotreaters for production of ULSD, and all 57 hydrotreaters were not originally licensed by Topsøe.

Things to consider before revamping a low-pressure unit

For a revamp to be successful it is necessary to make a thorough study as it can be difficult to predict bottlenecks. Examples of bottlenecks are compressor limitations, pump limitations, amine flow limitations, H2S handling limitations, wash water limitation, metallurgy limitations etc.

There are many things to consider and it is not easy for the refiner to gather experts within all these fields, whereas licensors can. Topsøe approach is to prepare a revamp study including a test run to collect data about the performance of the existing hydrotreater. In this study, Topsøe summarises the pros and cons of different revamp cases including a detailed economic study. The client can then make an informed decision about the revamp configuration to implement.

Catalyst selection is a vital part of the revamp. A broad range of high activity catalysts is necessary for optimum product yield, conversion, extent of desulphurisation etc. Change in the catalyst may require change in the process, e.g.: changing MW in recycle gas has an influence on compressor performance. It is important that the licensor is also a catalyst supplier and can help predicting these issues and help solving them.

Reactor internals are important for optimum utilisation of modern catalyst systems and are critical for ULSD production. A change to high efficiency reactor internals will be a natural part of an ULSD revamp.

Revamping a low-pressure unit - industrial example

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. The feed was a blend of kerosene, AGO, LVGO and Heavy Cat. Cracker Naphtha (HCCS). Operating conditions were

            Unit pressure, bara                        30

            Treat gas rate, Nm3/m3                 150

            Diesel feed sulphur, wt%                0.3 - 0.5

            Feed cut-point, °C                        348

BP's original understanding was that a new high-pressure unit for 10 wppm diesel production 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. 

Revamp modifications included a new reactor in series with the existing reactor, 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.

Both reactors were filled with a new charge of Topsøe's CoMo catalyst. A successful test run was completed to demonstrate the revamped unit's capabilities for production of 10wppm sulphur diesel.

The catalyst activity obtained was excellent during the entire first catalyst cycle, and the client decided to purchase Topsøe CoMo catalysts for the two subsequent catalyst cycle.