277175 How Much Water Can Be Recovered From Evaporated Waste Gaseous Streams?

Wednesday, October 31, 2012: 12:30 PM
401 (Convention Center )
Francesca Macedonio1,2, Adele Brunetti1,2, Giuseppe Barbieri1 and Enrico Drioli1,2, (1)Institute on Membrane Technology of the National Research Council - (ITM-CNR), Rende, Italy, (2)University of Calabria, Rende, Italy

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

F. Macedonio1, 2, A. Brunetti1,2, G. Barbieri1,  E. Drioli1, 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 RHfeed=100%, 50°C<Tfeed<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)


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