Vacuum Unit Performance
SUMMARY
Inaccurate feed characterisation and process modelling errors are major contributors to poor performance in a vacuum unit as refiners switch to heavier crude types.
TEXT
Refinery grassroots or revamp vacuum units frequently fail to meet expected product yield, product quality or run length targets. Real performance versus design is often 3-6 wt% lower in vacuum gas oil (VGO) product yield on whole crude, with much higher VGO metals and microcarbon, and 12 to 24-month run lengths instead of 48 to 60-month targets. Lost profitability can be tens or hundreds of millions of US dollars per year. Designers blame a low VGO yield, poor VGO quality or short run lengths on crude blend, refiner operations, equipment suppliers’ errors or numerous other perceived causes; rarely is it attributed to a lack of know-how by the designer. In this age of easy-to-use computer simulations, there is a belief that even an inexperienced engineer will be able to design a successful vacuum unit if appropriately sophisticated software is utilised. Experience proves otherwise. Low VGO product yield and poor vacuum unit reliability are becoming more common even though the global refining industry is becoming more competitive.
Today, most design engineers are experts in running process simulations and equipment models, yet almost none have validated them by comparing model output to actual measured performance. Many designers rarely have first-hand experience of the results of their work. The office-based approach presumes model results represent actual unit performance...