Title : Membrane system for hydrogen recovery in a hydrotreating unit
Abstract:
Hydrogen is the backbone of many processes in the refinery, such as hydrotreating. The atmospheric residue desulfurization (ARDS) unit is one of the hydrotreating processes to remove sulfur compounds from the fuel. This step is essential because combusting high-sulfur fuel can produce sulfur dioxide, which contributes to acid rain. However, the ARDS unit requires excessive amounts of hydrogen, and its purge gas usually contains significant amounts of unreacted hydrogen. In this study, the stream will be recycled back to the ARDS unit rather than being wasted as boiler fuel. The membrane technology was selected for this purpose due to its lower capital investment and reduced energy input. The membrane works based on differences in solubility and diffusion among molecules.
A commercial membrane made of polysulfone was integrated into one of the ARDS units at Kuwait refinery. The study was performed using the Honeywell® UniSIM® process simulator to estimate the quantity and quality of the recycled hydrogen. Unfortunately, the software does not have a membrane unit, so the module was built manually using a component splitter, adjust functions, and a spreadsheet. The system was solved by assuming the membrane area and guessing the permeate cut values. Results show that the single-stage membrane with an area of 2,050 m2 can recover up to 92% of hydrogen with a product purity of 98 mol%. This recycled hydrogen reduced the requirement for fresh hydrogen by 24%. An economic assessment was also performed to compare the cost of recycling hydrogen via the membrane compared to producing fresh hydrogen by the steam-methane reforming (SMR) process. The estimated capital investment of the membrane system is $ 4.1M, with an operating fee of $ 620k to recycle 12,900 tons of hydrogen per year. It was predicted that the membrane unit would have a payback period of 6 months, which is very attractive to the refinery.
