40, 41, 42 Research DWR SEP13 Version 3.indd - SLIDEBLAST.COM
RESEARCH
Developing membrane distillation for use on desalination brines _________ Samer Adham, Joel Matar, Altaf Hussain and Arnie Janson, ConocoPhillips Global Water Sustainability Center (GWSC), Qatar ___ Editor’s note: Membrane distillation is the subject of a great deal of research and development around the world, as D&WR has often reported. In Qatar, the emphasis is on using it to produce a high-quality distillate from high-salinity brines rejected from thermal desalination. The team has proved the viability of the process and is now testing it under real field conditions
MEMBRANE DISTILLATION (MD) is an emerging hybrid thermal-membrane process that can use low-grade waste heat and/or renewable energies to generate a vapor pressure difference across a membrane and produce a high quality distillate from high salinity rejected brines. Although it has inherent advantages over both reverse osmosis (RO) and thermal desalination processes, as an emerging technology, MD cannot compete directly with these established technologies on a broad scale of applications. To become commercially viable, a niche application has to be identified wherein MD can be more cost-effective. The treatment of rejected brines from thermal desalination plants is potentially a niche market where MD can be more cost-effective than existing desalination technologies. In Qatar, the thermal desalination facilities are coupled with power plants, which means that both hot rejected brines and lowgrade waste heat are potentially available, making the MD process an ideal technical solution to be implemented in Qatar. A consortium composed of ConocoPhillips Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity & Water Company (QEWC), has been formed to undertake a two-phase testing program with the overall aim of assessing the suitability of MD to treat rejected brines from thermal desalination plants in Qatar. Phase I of the program consisted of evaluating the performance of different membranes using seawater from the Arabian Gulf and brines from thermal desalination plants. This was done using a state-of-theart MD bench scale unit designed and assembled at
GWSC by the research team. The results of Phase I can be found in previous works presented by the GWSC research team 1, 2. The objective of Phase II of the testing program is to benchmark two MD technologies side by side while treating brine from a thermal desalination plant under real field conditions in Qatar. For this phase, two MD pilot units of 1,000 L/d capacity each were purchased from Germany (Memsys) and Sweden (XZero) and shipped to Qatar. This article presents the results of the tests conducted in Phase II-A at QU and highlights from Phase II-B currently ongoing at a thermal desalination plant in Doha, Qatar. The goal of Phase II-A was to test the two MD pilot units on various solutions (tap water, sodium chloride and brine from a local thermal desalination plant) and identify the optimum operating conditions for Phase II-B of the testing program. In Phase II-B, the two MD pilot units were relocated to a local thermal desalination plant for further long-term testing with brine under real field conditions and continuous operation. The MD Process MD is a mass transfer process driven by a partial vapor pressure difference due to a temperature gradient across a hydrophobic porous membrane. Due to the hydrophobic nature of the membrane, only vapor molecules are transported through the pores, preventing the passage of any liquid solutions 3. A temperature difference as low as 10°C between the warm and cold streams can be sufficient to produce high quality distillated water.
| 40 | Desalination & Water Reuse | August-September 2013
reSeArcH
reSULTS Phase II-A of the testing program has been completed. The main experimental conditions tested in Phase II-A were: Feed water TDS: up to 90,000 ppm Feed temperature: 40-60°C Cooling temperature: 15-40°C The effect of feed salinity on distillate flux was initially investigated. Table 1 shows the salinity level of the three different solutions (synthetic and actual brine) tested on the pilot unit. The flux was stable for all tested solutions and excellent salt rejection of >99.99% was observed. Figure 1 also shows the results of membrane productivity at these different salinity levels compared with tap water (TDS 99.99 >99.99 >97.46
literature reported flux reduction with the MD process when treating salinities above 70,000 ppm TDS 4,5. coNcLUSIoNS The results from Phase II-A indicate the viability of using MD in Qatar to treat brines from thermal desalination plants. This may contribute to augmenting the capacity of existing thermal desalination plants, significantly contributing to long-term water sustainability in Qatar. Phase II-A was carried out at QU on various solutions, including sodium chloride (NaCl) and brine from a local thermal desalination plant. The main results of Phase II-A are: Distillate was of high quality for all feed salinities tested (TDS
Developing membrane distillation for use on desalination brines _________ Samer Adham, Joel Matar, Altaf Hussain and Arnie Janson, ConocoPhillips Global Water Sustainability Center (GWSC), Qatar ___ Editor’s note: Membrane distillation is the subject of a great deal of research and development around the world, as D&WR has often reported. In Qatar, the emphasis is on using it to produce a high-quality distillate from high-salinity brines rejected from thermal desalination. The team has proved the viability of the process and is now testing it under real field conditions
MEMBRANE DISTILLATION (MD) is an emerging hybrid thermal-membrane process that can use low-grade waste heat and/or renewable energies to generate a vapor pressure difference across a membrane and produce a high quality distillate from high salinity rejected brines. Although it has inherent advantages over both reverse osmosis (RO) and thermal desalination processes, as an emerging technology, MD cannot compete directly with these established technologies on a broad scale of applications. To become commercially viable, a niche application has to be identified wherein MD can be more cost-effective. The treatment of rejected brines from thermal desalination plants is potentially a niche market where MD can be more cost-effective than existing desalination technologies. In Qatar, the thermal desalination facilities are coupled with power plants, which means that both hot rejected brines and lowgrade waste heat are potentially available, making the MD process an ideal technical solution to be implemented in Qatar. A consortium composed of ConocoPhillips Global Water Sustainability Center (GWSC), Qatar University (QU) and Qatar Electricity & Water Company (QEWC), has been formed to undertake a two-phase testing program with the overall aim of assessing the suitability of MD to treat rejected brines from thermal desalination plants in Qatar. Phase I of the program consisted of evaluating the performance of different membranes using seawater from the Arabian Gulf and brines from thermal desalination plants. This was done using a state-of-theart MD bench scale unit designed and assembled at
GWSC by the research team. The results of Phase I can be found in previous works presented by the GWSC research team 1, 2. The objective of Phase II of the testing program is to benchmark two MD technologies side by side while treating brine from a thermal desalination plant under real field conditions in Qatar. For this phase, two MD pilot units of 1,000 L/d capacity each were purchased from Germany (Memsys) and Sweden (XZero) and shipped to Qatar. This article presents the results of the tests conducted in Phase II-A at QU and highlights from Phase II-B currently ongoing at a thermal desalination plant in Doha, Qatar. The goal of Phase II-A was to test the two MD pilot units on various solutions (tap water, sodium chloride and brine from a local thermal desalination plant) and identify the optimum operating conditions for Phase II-B of the testing program. In Phase II-B, the two MD pilot units were relocated to a local thermal desalination plant for further long-term testing with brine under real field conditions and continuous operation. The MD Process MD is a mass transfer process driven by a partial vapor pressure difference due to a temperature gradient across a hydrophobic porous membrane. Due to the hydrophobic nature of the membrane, only vapor molecules are transported through the pores, preventing the passage of any liquid solutions 3. A temperature difference as low as 10°C between the warm and cold streams can be sufficient to produce high quality distillated water.
| 40 | Desalination & Water Reuse | August-September 2013
reSeArcH
reSULTS Phase II-A of the testing program has been completed. The main experimental conditions tested in Phase II-A were: Feed water TDS: up to 90,000 ppm Feed temperature: 40-60°C Cooling temperature: 15-40°C The effect of feed salinity on distillate flux was initially investigated. Table 1 shows the salinity level of the three different solutions (synthetic and actual brine) tested on the pilot unit. The flux was stable for all tested solutions and excellent salt rejection of >99.99% was observed. Figure 1 also shows the results of membrane productivity at these different salinity levels compared with tap water (TDS 99.99 >99.99 >97.46
literature reported flux reduction with the MD process when treating salinities above 70,000 ppm TDS 4,5. coNcLUSIoNS The results from Phase II-A indicate the viability of using MD in Qatar to treat brines from thermal desalination plants. This may contribute to augmenting the capacity of existing thermal desalination plants, significantly contributing to long-term water sustainability in Qatar. Phase II-A was carried out at QU on various solutions, including sodium chloride (NaCl) and brine from a local thermal desalination plant. The main results of Phase II-A are: Distillate was of high quality for all feed salinities tested (TDS
