Session: 11-02: Process Heat for Desalination and Industrial Decarbonization

Paper Number: 142132

142132 - Air Gap Diffusion Distillation as a Thermal Brine Concentrator 

Abstract: 

Desalination technologies are a promising solution to meet the growing demand for clean water and address the depletion of natural freshwater reserves. However, the main challenge with current desalination technologies such as reverse osmosis (RO) is that they generate a hyper-saline byproduct (concentrated waste > 6 wt%) that is difficult to dispose. Seawater desalination in coastal areas from brine disposal via ocean discharge, but this has negative consequences for marine life while inland desalination is limited by cost-effective brine disposal options. To address this, zero liquid discharge (ZLD) has emerged as an alternative method for brine treatment by recovering between 90-98% of the water and leaving behind solid waste for easier disposal. Mechanical vapor compression is an electrically driven process that serves as the state-of-the-art technology used to achieve ZLD. However, the challenges associated with MVC are the high capital cost from corrosion-resistant surfaces and the use of high-grade electricity.  Thus, there is a need for a more cost-effective approach to achieve ZLD that can rely on alternative forms of energy beside high-grade electricity.

This presentation will discuss the development of a cost-effective technology, namely air gap diffusion distillation (AGDD), that is constructed from polymeric surfaces and capable of desalinating brine up to a salinity of 20 wt% or ZLD. The main components are a condenser channel and an evaporator surface, both of which are separated by an air gap to enable this thermally-driven process at ambient pressure. The feed enters the condenser channel at a salinity of 7 wt% and flows upward where it is preheated by condensed water vapor on the external surface of the channel. After leaving the condenser channel, the feed is further heated by an external energy source to the desired evaporation temperature. The heated feed then flows down the evaporator surface where water vapor diffuses across the air gap to produce permeate (pure water). The remaining brine leaving the evaporator is then cooled down to the desired temperature before recirculating it back into the condenser channel; this is repeated (multiple passes) until the brine reaches a salinity of 20 wt%. Like other thermal desalination technologies, this system incorporates heat recovery via a counterflow configuration to recover a portion of the latent heat and reduce overall energy consumption. The experimental results are used to validate a couple heat and mass transport model of AGDD and further optimize the process design. Overall, this work demonstrates AGDD as an alternative method for brine concentration to help achieve ZLD goals in a cost-effective manner compared to other technologies.

Presenting Author: Walter Parker Georgia Institute of Technology

Presenting Author Biography: Walter received his B.S. in Mechanical Engineering at the University of California, Davis in 2018 and his M.S. in Mechanical Engineering at Carnegie Mellon University (CMU) in 2020. In summer 2021, Walter was a GEM Fellow at the National Renewable Energy Lab, where he developed thermal models for building applications. Currently, he is a Ph.D. student in Mechanical Engineering at Georgia Tech, with a research focus on thermally driven desalination systems for clean water production.

Authors:

Walter Parker Georgia Institute of Technology
Akanksha Menon Georgia Institute of Technology