Modeling and Simulation of Either Co-Current or Countercurrent Operated Reverse-Osmosis-Based Air Water Generator.

Marc Fill,Mirko Kleingries

doi:10.3390/membranes11120913

Abstract

Technologies for obtaining drinkable water are becoming more important as global water consumption steadily increases and climate change progresses. One possibility for obtaining water is the extraction of water vapor from ambient air by means of air water generators (AWG). Previous studies in the field of AWG have mainly dealt with the condensation of humidity on cold surfaces with a cooling system or with absorption and thermal desorption. In this paper, another possibility for AWG is investigated, specifically AWG using absorption and reverse osmosis. For this purpose, models have been set up for an absorber operated in countercurrent and reverse osmosis membrane modules operated in co-current and countercurrent. With these models, simulations with different boundary conditions were then carried out using the programming language Python. The simulations have shown that the reverse osmosis membrane modules operated in countercurrent generally have a lower energy demand and require fewer reverse osmosis stages than those operated in co-current.

Highlights

air water generators (AWG) systems based on absorption and reverse osmosis were investigated in terms of specific energy demand
The absorber was modeled in countercurrent, whereby the state and process variables as well as the key figures were calculated in each finite element, and the reverse osmosis process was modeled for both co-current and countercurrent operations
In the case of co-current reverse osmosis membrane modules and fixed booster pump pressures, the specific energy demand is between ∼230–1500 kWh/m3, and for co-current operation with variable booster pump pressures, it is between ∼230–1480 kWh/m3

Summary

Introduction

There is enough fresh liquid water on the earth’s surface in the form of lakes and rivers to supply humankind. This amount corresponds to a volume of about 90,000 km3 [4]. In many regions affected by water shortages, large facilities that provide clean water in sufficient quantities do not exist, and transport by land or air seems not feasible. Another potential source is the atmosphere, where the water is stored in the form of water vapor. The earth’s atmosphere contains so much water vapor that in its liquid state it would have a volume of about 13,000 km, which is about one seventh the volume of fresh water on the earth’s surface [4]

Methods

Results

Conclusion