Membrane Condenser as a New Technology for Water Recovery from

Article pubs.acs.org/IECR

Membrane Condenser as a New Technology for Water Recovery from Humidified “Waste” Gaseous Streams Francesca Macedonio,*,†,‡ Adele Brunetti,† Giuseppe Barbieri,† and Enrico Drioli†,‡,§ †

Institute on Membrane Technology (ITM-CNR), National Research Council, c/o The University of Calabria, Cubo 17C, Via Pietro Bucci, 87036 Rende CS, Italy ‡ Department of Chemical Engineering and Materials, The University of Calabria, Cubo 44A, Via Pietro Bucci, 87036 Rende CS, Italy § WCU Energy Engineering Department, Hanyang University, Seongdong-gu, Seoul 133-791, South Korea ABSTRACT: The potentialities of a membrane condenser for the selective recovery of evaporated wastewater from industrial gases have been investigated in the present paper. Membrane modules have been prepared and their performance has been evaluated in an artificial flue gas stream. A simulation study of the process has been carried out for predicting the membranebased process performance. The achieved results indicate that a 20% water recovery (the amount to make the plant selfsufficient) can be achieved with temperature reductions less than 5 °C if flue gas is in common conditions (i.e., 50 °C < T < 90 °C and 90% < RH < 100%). To verify the results achieved by the simulation analysis a membrane module with microporous hydrophobic PVDF hollow fibers has been built, and its performance has been evaluated by feeding an artificial flue gas stream. The experimental results showed good agreement with the simulation ones, obtaining deviations less than 2.24%.

1. INTRODUCTION In most parts of the globe, available fresh water is disappearing because people are polluting, diverting, pumping, and wasting their limited supply of fresh water at an exponential level as population and technology grows. Water is considered today as “the blue gold”, “the oil” of the 21st century. Like oil, water is a critical lubricant of the global economy; unlike oil, water has no substitute. Uses of water include agricultural, industrial, household, tourist, and environmental activities. Virtually all of these human uses require fresh water. Agriculture accounts for about 70% of worldwide water use, increasing to over 90% in developing countries; it is necessary to produce food, the natural fibres of clothing, biofuels and other goods based on agricultural raw materials. Water use for household purposes is 8% of worldwide water use. These include drinking water, bathing, cooking, sanitation, and gardening. Industrial water withdrawals account for approximately 22% of global water consumption.1 Major industrial users include hydroelectric dams, power plants, ore and oil refineries, and manufacturing plants, where the water used often needs to be of high quality. In a range of industries − from beverages to chemicals and energy, from construction to metals − water is a key part of the manufacturing process. Water is used to cool and heat installations and as a key product ingredient; it is consumed, reused, processed, transformed, and discharged. In industrial processes, recycling and reusing of process streams and in particular of water is necessary to minimize fresh water requirements. Water supply issues are increasing in importance for new and existing industrial plants because the freshwater supply is limited and the forecasts are that by 2025 two-thirds of the people will live in regions with water scarcity. Increasing water stress presents a significant business risk to every companyespecially those that take for granted the uninterrupted delivery of water in their supply chain. A survey © 2012 American Chemical Society

found that, despite that industries and companies worldwide agree that the impact of a water shortage would be severe, only 17% are prepared for such a crisis. The largest single use of water by industry is in power generation which needs water as boiler feedwater, cooling water, and for cleaning purposes. A coal-fired power station requires 1.6 L of water for each kWh, whereas a nuclear power station needs 2.3 L/kWh. A 500 MW thermoelectric power plant that employs once through cooling uses 4.5 × 104 m3/h of water for cooling and other process requirements. For companies considering the development of new thermoelectric power plants, water is a first-order concern.2 In response to these concerns, both the European Union and the U.S. Department of Energy funded research and development to reduce the amount of freshwater used by industrial plants through the recovery of the evaporated wastewater. Water recovery from the atmosphere and, in particular, from the exhaust gases produced in many industrial production processes can represent a real new source of drinkable water. This evaporated “waste” water usually leaves the plant and ends up in the atmosphere, making it a perfect new source of water. It has been estimated that the recovery of 20% of the evaporated water would be enough to make the plant selfsupporting.3 If the industry can close the water cycle by capturing evaporated water and therefore minimizing the request of water, more water can be made available for other purposes. Special Issue: Baker Festschrift Received: Revised: Accepted: Published: 1160

December 24, 2011 July 9, 2012 July 9, 2012 July 9, 2012 dx.doi.org/10.1021/ie203031b | Ind. Eng. Chem. Res. 2013, 52, 1160−1167

Industrial & Engineering Chemistry Research

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Figure 1. Flow-sheet of the process. The numbers in brackets, 1, 2, 3, 4, indicate the stream number used later on in the equations.

Figure 2. Scheme of the membrane condenser process for the recovery of evaporated “waste” water from flue gas as feed.

an energy efficient alternative for molecular separations because of its high energy efficiency, reliability (no moving parts) and small footprint. Membrane operations, properly designed and operated, can perform the selective removal of water vapor from gas streams and can produce water with high purities without additional heating. These advantages make membrane technology an interesting and promising alternative to remove water vapor from flue gases in coal-fired power plants, as well as in the waste streams coming out from cooling towers (or geothermal well) and in paper or board mill.9 Up to now, both dense membranes10 and porous hydrophilic11−13 membranes were used for this purpose. In the case of dense membrane the gas is dehumidified via diffusion. Sijbesma et al.10 tested two membrane materials for flue gas dehydration through dense membranes of PEBAX and SPEEK. Their results showed, on one hand, the technical viability of flue gas dehydration, on the other the superior performance of composite hollow fiber membranes with a top layer of SPEEK with respect to PEBAX. The disadvantage of these membranes is that they operate at high pressure, since a pressure difference is necessary to promote the permeation of the water vapor through the membrane. This, in turn, means compression, high energy consumption and high costs. Hydrophilic polymer membranes provide another membrane-based alternative for water recovery from gaseous streams. In hydrophilic membrane-based dehumidification systems, the membrane is a barrier between the humid gas phase and a liquid-coolant phase (often water). The coolant temperature, combined with a transmembrane pressure difference, establishes a water flux from the humid gas into the

Currently there is not an available commercial technology for evaporated wastewater recovery from industrial processes. There is the possibility, in principle, to recover water from flue gas by condensation with plastic heat exchangers. An example can be found in the project “Recovery of water f rom boiler f lue gas” funded by the U.S. Department of Energy, under Award No. DE-FC26−06NT42727.2,4 The objective of this project was to develop condensing heat exchangers to recover water vapor from flue gas at coal-fired power plants. The condensing heat exchanger apparatus developed and tested consisted of a long rectangular duct containing water-cooled heat exchangers arranged in series. Hot flue gas entered the apparatus from the back end of the boiler and was cooled as it passed through the heat exchangers. The produced water can then be used for plant operations such as cooling tower or flue gas desulfurization makeup. Condensation in flue gas is a complicated phenomenon since heat and mass transfer of water vapor and various acid vapors simultaneously occur in the presence of noncondensable gases. As a consequence, the condensed water is relatively dirty and corrosive. Moreover, several design and process parameters affect flue gas water vapor condensation rates, such as cooling water inlet temperature and flue gas water vapor content. Another technique available to remove water vapor from gas streams is using a desiccant drying system.5−8 A desiccant system, widely used and accepted, has as disadvantages the regeneration of the desiccant and the low quality of the produced water. Other researchers have proposed and used membrane-based systems for water recovery from air. Membrane technology is 1161

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calculated. Afterward, the temperature T3 at the exit of the condenser is calculated iteratively together with the physicochemical properties of the flue gas and the supersaturation degree (section 3 in Figure 1). At the temperature T3, the flow rate of water vapor W higher than the saturation limit (i.e., the maximum water vapor that the gas is able to hold without it condensing) is condensed and the amount of water that can be recovered from the flue gas can be calculated with the following equation:

coolant medium. Some membrane materials such polyethersulphone, mixed cellulose ester (e.g., cellulose triacetate) and polyvinylchloride were used in hydrophilic membrane-based dehumidifiers. The advantage in the use of these materials for separating water vapor from the vapor/gas mixture is their strong affinity to the water molecules.13 The strong affinity leads to the high permeation difference between water vapor and the other components of the gaseous streams. Zhang et al.13 affirm that the permeability ratio of water to air ranges from 460 to 30 000 for such hydrophilic membranes. In other words, gases other than water vapor can hardly permeate through these membranes. The aim of the present work is to investigate, for the first time, the potentialities of microporous hydrophobic membranes for the selective recovery of evaporated wastewater from industrial gases. The proposed solution is characterized by a very low pressure difference between the two membrane sides and the condensed water is retained in the retentate stream. A simulation study of the process has been carried out for predicting the membrane-based process performance. In addition, a membrane module has been prepared and its performance evaluated in an artificial flue gas stream. The experimental results have been compared with the ones achieved through the simulation.

fraction of recovered water =

n H2O,feed −

PH2O(T3)(n feed − n H2O,feed) P − PH2O(T3)

n H2O,feed

(1)

where nH2O,feed is the number of water moles in the feed flue gas, nfeed is the total number of feed flue gas moles, PH2O(T3) is the partial pressure of water at the temperature T3. Finally, also the condenser heat duty and the transfer area are calculated. The condenser heat duty is the heat required to condense the vapor or part of it. In the studied system, the condenser has to cool the whole flue gas flow rate from its inlet temperature T2 to the temperature T3, which is the temperature needed to have the required water recovery. The total heat duty Q needed to condense water vapor (QI) and to cool the flue gas (QII), has been calculated with the equations from 2 to 4:

2. MEMBRANE CONDENSER TECHNOLOGY The selective recovery of evaporated wastewater from industrial gases is carried out through hydrophobic microporous membranes. In particular, the hydrophobic membranes are utilized in what we called a “membrane condenser”. Figure 1 and Figure 2 schematize the flow sheet of the process and the principle of the membrane condenser. The flue gas is slightly compressed through a blower (0.1≤ ΔP ≤ 0.5 bar) and then fed to the membrane condenser. The latter consists of a condenser for cooling the flue gas until a supersaturation state, and of a membrane contactor (MC) unit. In the MC, the feed (that is the supersatured flue gas) is brought into contact with one side (retentate side) of a hydrophobic microporous membrane. The hydrophobic nature of the membrane prevents the penetration of the liquid into the pores, whereas the dehydrated gases will pass through the membrane. Therefore, the liquid water is recovered on the retentate side of the membrane, whereas the other gases are in the permeate side.

Q I = Wλ v

(2)

QII = Fc pv(T2 − T3)

(3)

Q = Q I + Q II

(4)

where W is the water vapor flow rate [kg/h] higher than the saturation limit (i.e., the water recovered through the process), F the flue gas flow rate [kg h−1], cpv is the specific heat capacity [kJ kg−1 K−1] and λv is the water latent heat of condensation [kJ kg−1]. In the investigated process, as a first assumption, cooling water is available at 90 °F (32 °C), and being returned at 120 °F (49 °C) has been considered as coolant medium in the condenser. The simulations have been carried out considering a dry stream of flue gas as feed and analyzing the effect of such important variables like temperature, relative humidity (RH), and pressure on the fraction of recovered water and on the power needed to drive the process. Table 1 summarizes the operating conditions simulated and the composition of the considered flue gas, just before entering the blower. 3.2. Experiments on Dehydration of Flue Gas. To verify the suitability of the simulation study aforementioned as a useful tool for a preliminary analysis of the potentialities of the membrane condenser for the dehydration of wet gaseous streams and to effectively evaluate the capability of the membrane to retain the liquid water, some experimental measurements on membrane modules were carried out. A membrane module containing 10 hollow fibers, for an effective membrane area of ca. 50 cm2, was built and its performance was evaluated. The microporous hydrofobic PVDF commercial membranes used were kindly supplied by MEMBRANA GmHB (Germany). Dehydration measurements have been

3. METHODS 3.1. Simulation of the Membrane-Based Flue Gas Dehydration System. The modeling of the processes provides a useful tool for predicting their performance. The simulations have been carried out considering ideal gas behavior and dry flue gas as feed, humidified at various levels of RH%. Input values of the algorithm developed in this work are the feed flue gas composition, flow rate, physico-chemical properties, temperature, and pressure. Also the morphological parameters of the membranes are known. These values are used for the calculation of the vapor pressure, relative humidity (RH), and dew point of the feed flue gas (section 1 in Figure 1). Then, knowing the desired discharge pressure of the blower (section 2 in Figure 1), the power needed to drive the blower together with the discharge temperature T2, relative humidity, and dew point of the flue gas at the exit of the blower are 1162



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cases, to promote the permeation of gases through the membrane a few low pressure drops (0.1−0.3 as relative pressure) are necessary between the two membrane sides. For this scope a back pressure controller is placed on the retentate side and the pressure is measured by means of a manometer. All the lines connecting the module with the rest of the instrumentation placed out of the furnace are thermally insulated in order to avoid any undesired condensation. The experimental device operates in such a way that all the water vapor condensation and recovery is going to take place in the membrane surface and not in the pipes. This can be done with an appropriate control of membrane surface temperature and vapor flow rate. The control of these parameters is also fundamental for minimizing the solubilization of all the pollutants present in the gaseous streams. The dehydration measurements were carried out at different values of temperature and feed pressure. Table 2 summarizes the operating conditions used in the experiments.

Table 1. Feed Flue Gas Characteristics flue gas composition flue gas (dry stream)

N2 CO2 O2 NOx SO2 HCl/HF

71.8 13.6 3.4 150−300 50−100 1−7.00

vol% vol% vol% vppm vppm vppm

relative humidity 16.2% < RH < 100% pressure 1 bar temperature 50 °C < T < 90 °C 0 bar < pressure drop through the membrane < 0.5 bar

carried out on this module by using the experimental set up shown in Figure 3. The dry gaseous stream coming out from a cylinder with a standard composition has been fed by means of mass flow controllers to a humidifier, set at a defined temperature value. The stream has been, thus, humidified and its relative humidity measured by means of a RH sensor located just at the outlet of the humidifier. This stream is usually saturated (RH = 100%). Whether the desired level of RH was lower than 100%, the saturated stream exiting from the humidifier was mixed with a dry stream having the same composition. By balancing the flow rates of these two streams it was possible to control the final RH of the stream to be fed to the module. This stream is fed directly to the module placed into the furnace at a temperature lower than the one of the humidifier. Before entering in the module, the RH of the feed stream is measured with a RH sensor positioned just at the inlet of the membrane module. The gases, with a defined level of RH are fed to the module where the separation occurs: the membrane allows the liquid water to be retained in the retentate side and collected at the bottom of the furnace in a flow meter, whereas the dehydrated stream is recovered in the permeate side and its flow rate is measured by means of a bubble soap flow meter. In dependence on the operating conditions used during the experiments, the permeate stream could contain a certain level of RH, lower than the feed one, and a part of the gaseous stream fed to the module could not pass through the membrane remaining in the retentate side. Indeed, for both these streams, RH sensors are placed at the outlet of the permeate and retentate sides, respectively, and their compositions are eventually analyzed by using a GC (Agilent). In such

Table 2. Operating Conditions Used in the Experiments feed stream (dry) composition, % molar feed stream relative humidity, % feed flow rate, mL min−1 feed pressure, bar flue gas temperature, °C membrane module temperature, °C

N2:CO2:O2 = 78:17:5 100 253.9; 507.8 1; 1.1; 1.2; 1.3 53−55.2 40−47

The flue gas considered in the experiments had a composition different than the one presented in the simulation analyses that will be presented in the next section. In this case, in fact, components such as SO2, HCl, and HF were not added to the feed mixture. This choice was done since the aim of the experiments was to evaluate the effective capability of this new condenser, based on membrane technology, to recover water from gaseous streams. We suppose that the presence of those compounds could cause eventual changes in the performance of the module and a more detailed experimental analysis is necessary for analyzing this further aspect. To well compare the experimental results with the simulations, the latter were repeated considering the composition reported in Table 2.

4. RESULTS AND DISCUSSION 4.1. Simulation ResultsWater Recovery Factor. The amount of water that can be recovered from a hot flue gas, at different initial relative humidities, is shown in Figure 4 as a

Figure 3. Scheme of the experimental set up. (MFC, mass flow controller; GC, gas chromatograph). 1163



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higher is the reduction of the temperature of the flue gas. However, in this case, a lower amount of water with respect to the previous situation (Tfeed = 90 °C) can be recovered from flue gas if cooling water is used as coolant in the condenser. Anyway, temperature reductions from 3.5 to 5.6 °C are sufficient to achieve a 20% water recovery if the RH of the feed flue gas ranges from 90 to 100% (Table 4), which are the typical conditions of the common flue gases. Table 4. Temperature Reduction Required to Achieve a 20% Water Recovery from Flue Gas. 60% ≤ RH ≤ 100%, T = 50 °C

Figure 4. Recovered water vs temperature of the flue gas before entering the membrane module. Feed flue gas with 16.2% ≤ RH ≤ 100% and T = 90 °C.

function of the required temperature reduction of the feed (i.e., the flue gas). The achieved results show that the amount of water that can be recovered increases with Tfeed reduction, as expected. For the same temperature reduction, the percentage of recovered water increases with an increase of the RH of the feed flue gas. Moreover, in the case of hot flue gas, recovery factors as high as 97% can be achieved using cold water as coolant in the condenser, and temperature reductions ranging from 1.9 °C (for RH=100%) to 5.1 °C (for RH = 90%) are sufficient to achieve a 20% water recovery (that is the amount necessary to make the plant self-sufficient) (see Table 3).

RHfeed [%]

T reduction [°C] for 20% water recovery

100 92 90 80 70 60

3.45 5.12 5.57 7.89 10.5 13.9

A part from the RH%, the amount of water that can be recovered by the membrane condenser also depends on the temperature of the flue gas fed to the module. Figure 6

Table 3. Temperature Reduction Required to Achieve a 20% Water Recovery from Flue Gas. 16.2% ≤ RH ≤ 100%, T = 90 °C RHfeed [%]


100 90 80 70 60 50 40 30 20 16.2

1.93 5.11 8.53 12.2 16.4 21.1 26.5 33.2 41.9 46.2

Figure 6. Recovered water vs temperature of the flue gas before entering the membrane module. Feed flue gas with RH = 100%, 50 °C ≤ T ≤ 90 °C.

highlights the amount of water that can be recovered from the flue gas, at different temperatures of the inlet flue gas and constant RH. As can be seen, for an inlet temperature of 90 °C, a reduction of ca. 2 °C is sufficient to recover the 20% of water, whereas this value increases to 3.6 °C when the flue gas enters with a temperature of 60 °C (Table 5). Indeed, the temperature reduction required to obtain the same percentage of water recovery decreases Tfeed increases. A positive effect on the amount of water recovered can be exercised by the feed pressure which increases the partial pressure of the water vapor in the feed side, reaching easily the

In Figure 5 is shown what happens for a cold flue gas. Also in this case a greater amount of water can be recovered as much

Table 5. Temperature Reduction Required to Achieve a 20% Water Recovery from Flue Gas. RHfeed = 100%, 60 °C ≤ Tfeed ≤ 90 °C

Figure 5. Recovered water vs temperature of the flue gas before entering the membrane module. Feed flue gas with 60% ≤ RH ≤ 100%, T = 50 °C. 1164

Tfeed [°C]


90 80 70 60

1.93 2.95 3.43 3.55 dx.doi.org/10.1021/ie203031b | Ind. Eng. Chem. Res. 2013, 52, 1160−1167


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supersaturation and, thus, the condensation. In addition, the higher pressure drop ΔP favors the passage of the other gases through the membrane pores, increasing the water vapor molar fraction in the feed side. Figure 7 reports the effect of pressure

Figure 9. Power needed to drive the process vs recovered water. Feed flue gas with 16.2% ≤ RH ≤ 100% and T = 90 °C.

of water recovery decreases with RH (Figure 4). This is directly connected to the definition of relative humidity that is the amount of water vapor in the gaseous mixture at a specific temperature with respect to the maximum water vapor that the gaseous mixture is able to hold without condensing it, at that given temperature. A high RH means a greater amount of water contained in the feed stream. As a consequence, a higher volume of water has to be condensed, requiring a higher heat duty QI (i.e., the energy needed to condense water vapor, eq 2), for achieving the same percentage of water recovery (i.e., 20%). This represents the main contribution to the total energy duty Q since the energy required to cool down the rest of the gases (QII) is negligible with respect to QI. To obtain the same volume of recovered water, the energy required decreases as the RH of the feed stream increases (Figure 10).

Figure 7. Recovered water vs temperature of the flue gas before entering the membrane module. Feed flue gas with RH = 92%, T = 50 °C, 0.1 bar ≤ ΔP ≤ 0.5 bar.

on the amount of recovered water, considering the case of a stream not completely saturated that enters the module at 50 °C. As can be seen, the recovered water increases with the growing of the pressure drop between the two membrane sides due to the increasing of the process driving force. A ΔP = 0.1 bar allows the 20% of the water contained in the feed to be recovered reducing the temperature of ca. 5 °C and this value increases at 25% for a ΔP = 0.3 bar. 4.2. Simulation ResultsEnergy Consumption. The suitability of a process as potential alternative to the well consolidated technologies, as in the case of the condensers, strongly depends on the energy consumption associated to the process itself. In the case of membrane condensers, the energy consumption of the process is due both to the power required to drive the compression and to the heat duty required to condense the vapor or part of it. The achieved results showed that the energy consumption of the system is mainly due to the heat required to condense the water vapor (Figure 8).

Figure 10. Power needed to drive the process vs recovered water. Feed flue gas with 16.2% ≤ RH ≤ 100% and T = 90 °C.

Similar trends were observed also for cold flue gas (Figure 11 and 12). In this case, to achieve a 20% water recovery from a flue gas with a temperature equal to 50° and 60% ≤ RH ≤ 100%, the power needed was less than 60 kJ/m3 of inlet flue gas. Figure 13 shows the power needed to drive the system at different temperature (Tfeed) of a satured (RH = 100%) feed flue gas. It can be seen that, in this case, the power needed for achieving the same percentage of recovered water increases with initial feed temperature, although the temperature reduction required to obtain the desired percentage of water recovery decreases with Tfeed (Figure 6). This is due to the fact that, at increasing temperature and constant RH, the amount of water vapor in the gaseous mixture is higher. Therefore, for achieving the same percentage of water recovery (i.e., 20%), a

Figure 8. Power needed to drive the process per m3 of treated flue gas vs recovered water. Feed flue gas with at RH = 100% and T = 90 °C.

As a matter of fact, the higher is the percentage of water recovered, the higher is the total power required. The power needed to drive the process and required to achieve the desired water recovery, as a function of the RH% of the flue gas stream fed to the module is shown in Figure 9. The power needed for achieving the same percentage of recovered water increased with the RH, although the temperature reduction required to have the same percentage 1165



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5. EXPERIMENTAL MEASUREMENTS AND COMPARISON WITH THE MODEL RESULTS The comparison between the results obtained through the simulations and those of the experimental measurements is reported in Figures 15 and 16. In the graphs, the fraction of

Figure 11. Power needed to drive the process vs recovered water. Feed flue gas with 60% ≤ RH ≤ 100% and T = 50 °C.

Figure 15. Recovered water vs feed pressure. Feed flue gas with RH = 100%, T = 55.2 °C, and 1 bar ≤ P ≤ 1.3 bar.

Figure 12. Power needed to drive the process vs recovered water [m3/ h]. Feed flue gas with 60% ≤ RH ≤ 100% and T = 50 °C.

Figure 16. Recovered water vs feed pressure. Feed flue gas with RH = 100%, T = 53 °C and 1 bar ≤ P ≤ 1.3 bar.

recovered water with respect to the feed pressure and at various temperature reductions is shown. Figure 15 reports the results for a flue gas with a temperature equal to 55.2 °C. Figure 16 reports the results for a flue gas with a temperature equal to 53 °C. In both cases, the lines are referred to the simulations, the points to the experimental measurements. It can be observed that a good agreement between experimental tests and model exists, with deviations less than 2.24%. This confirms 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.

Figure 13. Power needed to drive the process vs recovered water. Feed flue gas with RH = 100% and 50 °C ≤ T ≤ 90 °C.

higher volume of water has to be condensed requiring a higher heat duty (Figure 14).

■

CONCLUSIONS The potentialities of membrane technology for the separation and recovery of evaporated “waste” water from industrial processes were presented in this work. The proposed membrane technology uses hydrophobic membranes in a membrane condenser configuration. In this system, water condensation and recovery occurs in the retentate side of the membrane module, whereas the dehydrated stream is recovered on the permeate side of the membrane. The carried out simulations allowed us to predict membrane module performance in terms of fraction and amount of recovered water, independent of the effect of temperature and relative humidity of the inlet flue gas. The achieved results are encouraging because they indicate that a 20% water recovery (the amount

Figure 14. Power needed to drive the process vs recovered water [m3/ h]. Feed flue gas with RH = 100% and 50 °C ≤ T ≤ 90 °C. 1166



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(11) Scovazzo, P.; Hoehn, A.; Todd, P. Membrane porosity and hydrophilic membrane-based dehumidification performance. J. Membr. Sci. 2000, 167, 217−225. (12) Scovazzo, P.; Burgos, J.; Hoehn, A.; Todd, P. Hydrophilic membrane-based humidity control. J. Membr. Sci. 1998, 149, 69−81. (13) Zhang, L. Z.; Zhu, D. S.; Deng, X. H.; Hua, B. Thermodynamic modeling of a novel air dehumidification system. Energy Build. 2005, 37, 279−286.

for a self-sufficient plant) can be achieved with temperature reductions less than 5 °C for a flue gas in the most common conditions (i.e., 50 °C < T < 90 °C and 90% < RH < 100%). The simulation study was validated by experimental analysis confirming its validity and suitability for a screening of the potentialities offered by the membrane condenser in the dehydration of gaseous streams, It must be pointed out that the simulations here reported are focused on the analysis of the dehydration of flue gas stream; however the same simulation approach can be suitable for the study of the dehydration of other gaseous streams, such as those coming out from cooling towers, coal gasification, paper and mills, kilns factory, etc. The water obtained by condensation assisted by membranes can represent a new source of water. However, further research is necessary regarding the proper composition of the recovered water because acid compounds in the flue gas stream can negatively affect its quality. In principle, acid condensation can be limited by lowering as much as possible the contact time between liquid and vapor, eventually through the optimization of the feed flow rate.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +39 0984 492012. Fax.: +39 0984 402103. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The EU-FP7 is gratefully acknowledged for cofunding 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 fiber PVDF membranes.

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REFERENCES

(1) ″WBCSD Water Facts & Trends″. http://www.wbcsd.org/ includes/getTarget.asp?type=d&id=MTYyNTA (accessed 2009-0312). (2) Jeong, K.; Kessen, M. J.; Bilirgen, H.; Levy, E. K. Analytical modeling of water condensation in condensing heat exchanger. Int. J. Heat Mass Transfer 2012, 53, 2361−2368. (3) Judd, S.; Jefferson, B. Membrane for Industrial Wastewater Recovery and Re-use; Elsevier Science Ltd: Oxford, UK, 2003. (4) Feeley, T. J.; Pletcher, S.; Carney, B.; McNemar, A. T. Department of Energy/National Energy Technology Laboratory’s Power PlantWater R&D Program, Power-Gen International 2006, 2006. (5) Ito, A. Dehumidification of air by a hygroscopic liquid membrane supported on surface of a hydrophobic microporous membrane. J. Membr. Sci. 2000, 175 (1), 35−42. (6) Isetti, C.; Nannei, E.; Magrini, A. On the application of a membrane air−liquid contactor for air dehumidification. Energy Build. 1997, 25 (3), 185−193. (7) Liu, X. H.; Zhang, Y.; Qu, K. Y.; Jiang, Y. Experimental study on mass transfer performances of cross flow dehumidifier using liquid desiccant. Energy Convers. Manage. 2006, 47 (15−16), 2682−2692. (8) Zurigat, Y. H.; Abu-Arabi, M. K.; Abdul-Wahab, S. A. Air dehumidification by triethylene glycol desiccant in a packed column. Energy Convers. Manage. 2004, 45 (1), 141−155. (9) Beerlage, M. A. M.; Zeijsink, A. G. L. Preparation of water from flue gases, WO 0,056,426, 2000. (10) Sijbesma, H.; Nymeijer, K.; van Marwijk, R.; Heijboer, R.; Potreck, J.; Wessling, M. Flue gas dehydration using polymer membranes. J. Membr. Sci. 2008, 313, 263−276. 1167


Membrane Condenser as a New Technology for Water Recovery from

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