(504a) How Much Water Can Be Recovered From Evaporated Waste Gaseous Streams?

How
much water can be recovered from evaporated waste gaseous streams?

F. Macedonio^{1, 2}, A. Brunetti^1,2, G. Barbieri¹,
 E. Drioli^{1, 2}

¹
National Research Council - Institute on Membrane Technology (ITM?CNR), Via Pietro BUCCI, c/o The University of Calabria, cubo 17C,
87036 Rende CS, Italy

²
University of Calabria - Department of Chemical Engineering and Materials, cubo 44A, Via Pietro BUCCI, 87036
Rende CS, Italy

Keywords Dehydration, Membrane Condenser, Process Design

In
most part of the globe, the available fresh water is disappearing at an
exponential rate as population and technology grows. Industrial water
withdrawals account for approximately 22% of global water consumption. Major
industrial users include hydroelectric dams, power plants, ore and oil
refineries, and manufacturing plants. In
industrial processes, recycling and reusing of process water streams is useful
to reduce fresh water requirements. More important is the possibility
for the industry to close the water cycle by capturing evaporated water thus
minimizing the request of fresh water and keeping more water available for
other purposes.

In
the present work, microporous
hydrophobic membranes in an innovative membrane contactor configuration are
proposed for the selective recovery of evaporated water exiting industrial plants
in waste gaseous streams. In particular, hydrophobic membranes are
employed in a membrane condenser
(Figure 1). In the proposed system, the feed (super-satured
industrial gas) is brought into contact with the retentate
side of a hydrophobic microporous membrane. The hydrophobic nature of the
membrane prevents the penetration of the liquid into the pores while the gases
pass through the membrane. Therefore, the liquid is recovered on the retentate side of the membrane, whereas the dehydrated
gases on the permeate side of the membrane.

Figure 1. Scheme of the membrane condenser process.

An experimental set up was built (Figure 2) and dehydration
measurements were carried out for effectively evaluating the capability of the
membrane to retain the liquid water.

Figure 2. Photo
of the experimental set up.

In
the built lab plant, the wet gaseous stream is fed directly to the membrane module
placed into a furnace and containing PVDF
commercial membranes. Before entering in the module the relative humidity (RH)
of the feed stream is measured with an RH sensor positioned just at the inlet
of the membrane module. RH and composition of the two (retentate and permeate)
exiting streams are measured by using RH sensors and a gas chromatograph. The process is characterized by a very low
pressure difference between the two membrane sides (0.1-0.3 bar).

The
dehydration (water recovery) measurements were carried out at different values
of temperature and feed pressure. The results achieved with the experimental
tests proved the capability of the proposed system to capture the water present
in the feed stream [1, 2].

A simulation study of the process was
then carried out for comparing the data measured in the experiments with the results
obtained through the simulation.

The comparison between the
experimental tests and the model indicate
a good agreement, with deviations less than 2.24% [1, 2]. This confirmed
the validity of the simulation study done and its suitability for a preliminary
screening of the potentialities offered by the membrane condenser in the
dehydration of gaseous streams. In Figure 3 some of the results achieved
through the modelling are shown.

Figure 3. Recovered water vs temperature reduction for
the flue gas with RH_feed=100%, 50°C<T_feed<90°C.

Figure 3 highlights the amount of
water that can be recovered from the flue gas, at different temperature of the
inlet flue gas and constant RH. As it can be seen, for an inlet temperature of
90°C, a reduction of ca. 2°C is sufficient to recover the 20% (the amount to make the plant self sufficient)
of water whereas this value growths up to 3.6°C only when the flue gas
enters with a temperature of 60°C. The obtained results confirm the
potentialities offered by the membrane condenser in the dehydration of gaseous
streams.

It must be pointed out that the results
here reported are focused on the analysis of the dehydration of flue gas
stream; however the same approach can be suitable for the study of the
dehydration of other gaseous streams, such as the one coming out from cooling
towers, coal gasification, paper and mills, kilns factory, etc.

Acknowledgments

The EU-FP7 is gratefully acknowledged for
co-funding this work through the project ?CapWa - Capture of evaporated
water with novel membranes? (GA
246074). We also wish
to acknowledge Dr. Wolfgang Ansorge (Membrana GmbH) for supplying us samples of
hollow fibres PVDF membranes.

Relevant bibliography

[1] E. Drioli, F. Macedonio, A. Brunetti, G. Barbieri, Membrane Condenser for the recovery of evaporated ?waste?
water from industrial processes. International Workshop on Membrane
Distillation and Related Technologies, October 9 - 12, 2011, Auditorium Oscar Niemeyer - Ravello (SA).

[2] F. Macedonio, A. Brunetti, G. Barbieri, E. Drioli, Membrane Condenser
as a new technology for water recovery from humidified ?waste? gaseous streams. IECR, 2012.  (Submitted)