Session: 13-02: Hydrogen Production and Storage

Paper Number: 169420

169420 - Thermodynamic and techno-economic analysis of produced water desalination systems for clean hydrogen production 

Abstract: 

To achieve favorable techno-economics for clean hydrogen production, it is critical to satisfy ultrapure input water requirements (2.5-2050 ppm) alongside economical process infrastructure and effective thermal management. Renewables-powered electrolysis and carbon capture enabled fossil fuel reforming require withdrawals of up to 20 and 30 liters of ultrapure water, respectively, to produce 1 kg of hydrogen. With adequate treatment, water requirements for clean hydrogen production can be met via on-site desalination of oilfield-produced water (PW). PW is a hypersaline byproduct of shale oilfield mining, typically disposed of through deep well injection, causing seismicity, aquifer contamination, and soil pollution. Conventional thermal desalination techniques such as Mechanical Vapor Compression (MVC), although energy- and capital-intensive in operation, are the only suitable conventional dewatering options for the application owing to their insensitivity to feed concentrations. In contrast, traditional membrane desalination systems such as reverse osmosis (RO) are not suitable for feed concentrations above 75,000 ppm because of burst pressure limitations. Osmotically Assisted Reverse Osmosis (OARO) is a novel membrane desalination technique that has been conceptualized as suitable for treating hypersaline PW and provides an energy-efficient alternative to thermal-based techniques. OARO enhances the permissible feed salinity range of conventional RO by introducing an additional draw solution stream to alleviate transmembrane osmotic pressure difference requirements.

The present study provides a thermodynamic and techno-economic performance comparison between MVC and coupled OARO-RO. Both systems were designed as hypersaline PW desalination units that generate fresh water (FW) suitable for clean hydrogen production. In-house experimental and computationally validated analytical models were utilized to model and optimize the coupled OARO-RO system. These models are based on an extension of the heat and mass transfer analogy and incorporate the effects of non-ideal solution behavior, non-ideal membrane selectivity, varying permeate concentration, and concentration polarization. Single-effect MVC was modelled based on first-order thermodynamic models, which also included the effects of variations in relevant thermophysical solution properties with temperature and salinity. The inlet and outlet stream properties, overall freshwater recovery, pressure requirements, membrane sizing, heat exchanger sizing, specific work input (kWh/m3 of FW produced) and 2nd law efficiency were determined for both desalination techniques from the corresponding analytical models. Based on the calculated performance parameters, the unit water costs (UWC) for each technique were determined from capital and operating expenditures with depreciation, system integration, and amortization. Additionally, the costs of pre-treatment, post-treatment, and brine disposal were calculated.

For every 1000 liters of PW treated from the Permian Basin (100,000 ppm), 470 liters of ultrapure water (2.5-2050 ppm) and 15-24 kg of clean hydrogen can be obtained using the present technology, with the desalination brine (177,158 ppm) being suitable for environmentally benign Zero-Liquid Discharge. Coupled OARO-RO and MVC were characterized by a specific energy consumption of 7.5 and 20.6 kWh/m3FW. Consequently, the integrated OARO-RO process resulted in a 64% reduction in energy consumption for the specified application, while maintaining water treatment costs at $7.4/m3FW, comparable to those of MVC. This would contribute to ~ 15-22 cents/kg of clean hydrogen production.  The major UWC contribution was from the membrane capital cost for membranes in OARO, whereas it was from electricity operating expenses for MVC. Overall, the present study provides a detailed energetic and economic comparison of different hypersaline desalination techniques that could facilitate the production of clean energy from oilfield waste.

Presenting Author: Vishnu Sree Shanthanu Katakam The University of Texas at Austin

Presenting Author Biography: I am Vishnu Sree Shanthanu Katakam, a Mechanical Engineering PhD student working under Dr Vaibhav Bahadur at The University of Texas at Austin. My research work includes areas related to Desalination and Green Hydrogen.