Two workers in refinery

As much as six years can elapse from completing the configuration study to the unit starting up and much can change in that time. Market conditions may have shifted or there may have been changes in emissions legislation or product-quality specifications. For example, if the market demand for middle distillates has outstripped the initial forecasts, the owner may be keen to increase capacity or, if some product streams are achieving an unanticipated margin, modify for a different product slate.

Shell Global Solutions has worked with several refiners, including, for example, Valero and Marathon, to revamp their newly started up hydrocrackers. These projects made relatively small adjustments but their impacts were substantial: they ensured that the new assets continue to be relevant to the prevailing market conditions and provide substantial bottom line benefits.

Technology focus 

Revamping an existing hydrocracker or hydrotreater is substantially more complex than building a new one and is a highly specialised area that calls for advanced process engineering skills and wide-ranging operating experience. A selection of the actions taken during a revamp is shown below. New technologies may be installed, including:

  • state-of-the-art reactor internals that can enable a greater catalyst volume to be loaded into the reactor; n latest-generation catalysts to help improve product yields and cycle lengths;
  • high-capacity distillation trays to help improve throughput cost-effectively;
  • additional rotating equipment, such as turbines, pumps and compressors, to support the increased capacity; and/or n higher-capacity relief valves to help remove hydraulic constraints. A revamp may require operational changes, for example: n realigning the process configuration to modify the conversion; n optimising the feedstock selection and preparation; and/or
  • running the unit to the limit of its design constraints to achieve capacity creep.

Studies and reviews often are required, including:

  • dynamic simulations for reactor thermal stability checks during normal and upset conditions; and/or
  • material reviews of corrosion rates in, for example, wash-water loops and fired equipment.

Existing equipment is not replaced unless there is a strong economic case, so recycle gas compressors and recycle gas turbines, for example, are rarely replaced. Moreover, care is taken to avoid the additional duty triggering the need for more steam-raising capacity.