Molecular Sieve Dehydration units are used for dehydration of natural gas prior to gas processing or transportation. A molecular sieve dehydration system consists of multiple adsorbers which remove water during adsorption cycle until they get saturated with water. Regeneration of a saturated adsorber is performed by passing a hot regeneration gas stream through the adsorber. The hot regeneration gas after passing though the adsorber is then cooled before sending to regeneration gas compression. If an aircooled exchanger is used to cool the hot regeneration gas, heat available in the hot spent regeneration gas ends up in the atmosphere. In this context, an in-house study was performed to examine techno-economic viability of waste heat recovery from the hot spent regeneration gas using a modified regeneration scheme at one of the gas processing sites.

The modified scheme involves installation of a new waste heat recovery (WHR) exchanger to exchange the heat available in the hot regeneration gas with regeneration heater's inlet regeneration gas thereby reducing the fuel gas consumption in the regeneration heater as well as power consumption in regeneration gas cooler fans. The study comprised design and operation data collection and analysis followed by assessment of key challenges. The key challenges include performance of the heater in WHR case (i.e. lower fuel gas consumption), space availability for the new WHR exchanger and modifications in the existing system. A thermodynamic model was developed for running various operating scenarios and estimating the WHR potential, including heater's specific fuel gas consumption analysis at varying temperatures, to establish realistic fuel gas savings.

Overall, the study has indicated significant energy savings with good financial indicators for the proposed regeneration scheme. It has also showed reduction of peak heat duty of heater & cooler, thus providing an additional advantage of reduced CAPEX for future projects.

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