A multi-objective optimization approach for integrating isomerization hydroprocessing unit with hydrogen network

The isomerization unit improves the light naphtha research octane number with better environmental impacts. Recent developments in increasing the octane number in the isomerization unit are leading to increased demand for refinery hydrogen. However, the disconnected hydrogen network and increasing the octane number in isomerization unit has led to a shortfall of hydrogen to meet the hydrogen demand. The present work is an integrated approach to the isomerization process in refineries and hydrogen network design. Modeling and optimization of the overall hydrogen network objective to minimize the total consumption of fresh hydrogen and maximize the isomerization octane number using a goal programming multi-objective optimization approach is presented. The model is introduced for two cases, reuse/recycling and hydrogen regeneration networks. The global network model is a multi-objective nonlinear programming model, and is optimized using Lingo optimization software version 14. The results showed that by integrating the isomerization model with the hydrogen reuse/recycling network, the fresh hydrogen saving was 20.871 kmol/h compared to 7.772 kmol/h in the case of neglecting the isomerization model. On the other hand, a significant reduction of 447.898 kmol/h in fresh hydrogen was achieved in the hydrogen regeneration network when including the isomerization model compared to that achieved when neglecting the isomerization model (343.261 kmol/h). In addition, the optimum operating conditions, feed specifications and hydrogen consumption of the isomerization unit that gives the maximum research octane number and the minimum fresh hydrogen were determined for both the reuse/recycling and hydrogen regeneration network cases.