An ambitious step to the future desalination technology: SEAHERO R&D program (2007–2012)
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In Republic of Korea, seawater engineering and architecture of high efficiency reverse osmosis (SEAHERO) research and development (R&D) program started from 2007 to lead the top seawater reverse osmosis (SWRO) plant technologies for desalination with the fund of US $165 million for 6 years including test-bed plant construction. There are three technical strategies for SEAHERO R&D program called 3L, which represents large scale, low fouling, and low energy, respectively. Large scale means design, construction, and operation of the largest unit SWRO train [daily water production rate = 8 MIGD (36,000 m3/day)] in the world. Low-fouling strategy targets the decrease of RO membrane fouling by 50%. The specific target for low energy is total energy consumption of whole SWRO plant (including intake, pretreatment, SWRO systems, and so on) less than 4 kWh/m3. The core parts for SWRO plant, such as 16 in. diameter RO membrane and energy recovery device, were developed and will soon be introduced to a test-bed including the largest unit SWRO train. The next step of SEAHERO is real field scale test-bed application of the unit technologies developed for the past 4 years (2007–2010) such as strategic pretreatment, energy-saving technology, and reliable system monitoring.
KeywordsDesalination Reverse osmosis SEAHERO Large scale Low fouling Low energy
Korean government (especially ministry of Land, Transport and Maritime affairs) selected seawater reverse osmosis (SWRO) desalination technology as one of global top 5 technologies which will bloom Korean economy in 2006. Center for Seawater Desalination Plant (CSDP) funded by Korean government launched SEAHERO research and development (R&D) program from August 31st, 2007. SEAHERO is an abbreviation for seawater engineering and architecture of high efficiency reverse osmosis. SEAHERO R&D program (SEAHERO hereafter) is targeting to get the top level of SWRO plant technologies in the world and will be carried out with the fund of US $165 million for 5 years (Kim et al. 2009a).
SEAHERO consists of four core technology (CT) projects, including development of platform technologies for SWRO plant construction (CT 1: platform technology), development of SWRO membranes and high pressure pump component manufacturing and system optimization technologies (CT 2: plant units localization and system optimization), development of large-scale SWRO plant design and construction technology [CT 3: engineering–procurement–construction (EPC)], and development of innovative operation and maintenance (O&M) technology for large-scale SWRO plant (CT 4: O&M). More detailed information about the four CTs can be obtained from the official web page of SEAHERO (http://www.seahero.org).
Large scale To design and construct the largest unit SWRO train [daily water production rate = 8.0 MIGD (36,000 m3/day)] in the world. The daily production rate of the largest unit train at the moment is 5.2 MIGD, and it is in Point Lisas SWRO plant, Trinidad and Tobago (GWI 2007) and a desalination plant with unit train size of 6.84 MIGD (31,000 m3/day) will soon be constructed in Antofagasta, Chile (GWI 2009a).
Low fouling To reduce membrane fouling by 50% in terms of silt density index (SDI) and a new fouling index developed through CT 1 project.
Low energy To lower energy consumption of whole SWRO plant (including intake, pretreatment, SWRO systems, and so on) less than 4 kWh/m3.
The 3L is finally accomplished by designing, constructing, and operating a test-bed, which is defined as a whole system for the real field application of developed unit technologies. The capacity of the test-bed is 10 MIGD (45,000 m3/day). The test-bed will include an 8 MIGD unit SWRO train, which will be the largest unit train in the world.
Energy consumption in SWRO plant as a function of plant size
0.3 MGD (1,135 m3/day)
10 MGD (37,850 m3/day)
50 MGD (189,250 m3/day)
Introduction of 16 in. diameter SWRO membrane will accelerate the economies-of-scale in large SWRO plant. A 16 in. diameter SWRO module can produce more than three times larger amount of fresh water than an 8 in. diameter module, which is current market standard of spiral wound RO module (Kim et al. 2009a). The diameter of 16 in. RO module assures more than 10% of capital cost saving compared to the case of 8 in. diameter module (Hallan et al. 2008). One of the most splendid products of SEAHERO is the production of 16 in. SWRO membrane module with high permeability. The production rate and the nominal salt rejection of the module is 136.1 m3/day and 99.7% in the test condition of 32,000 mg/l sodium chloride solution, 8% of recovery, 25°C of temperature and 6.5–7.0 of pH as reported in the web page of CSM filter (http://www.csmfilter.com/upload/csm/swe/prod1_2010114134121.pdf), which is a company member of SEAHERO. This SEAHERO-brand SWRO membrane module will be installed in the test-bed.
Membrane fouling has been a critical problem in worldwide desalination plants using RO membrane to separate salts from seawater (Barger and Carnahan 1991). Since the membrane fouling leads to performance deterioration such as lowered permeate flux and salt rejection, it has been hindering RO application (Tang et al. 2010). In order to reduce the membrane fouling, numerous research topics have been studied such as mechanism of membrane fouling, optimization pre-treatment process or system, development of cleaning method or materials, development of membrane fouling index, and others (Prihasto et al. 2009).
In SEAHERO, the specific target for the low-fouling strategy is 50% of fouling reduction as mentioned in “Introduction” part of this paper. Fouling reduction in principle can be interpreted to the increase in membrane replacement period. The assurances of 50% increased membrane replacement period can be a reasonable specific target for low fouling. However, the membrane replacement period (usually more than 5 years) cannot be estimated during the R&D period of SEAHERO until 2012. The product of SEAHERO should be estimated by Korean government at the end of the R&D period since SEAHERO is a government-funded R&D program. Therefore, 50% reduction of silt density index (SDI) and a new fouling index developed in SEAHERO is selected as a specific target for low fouling instead the increase in membrane replacement period.
There are lots of unit processes for pretreatment system. The most important thing in design of pretreatment system is to select best combinations of these unit processes targeting highest RO feed water quality with lowest cost, which can be called strategic pretreatment. Selection of good combinations of pretreatment processes depends on field conditions such as feed water quality, temperature, and fouling durability of RO membrane. In SEAHERO program, factors affecting design of optimal pretreatment strategies and the economic evaluation of SWRO system with regard to various antifouling strategies were investigated (Prihasto et al. 2009; Choi et al. 2009a, b, c; Jeong et al. 2010).
Reliable system monitoring technologies for SWRO system can be applied to avoid severe troubles such as irreversible fouling, scaling, and unexpected system failures, which will be more promising. In SEAHERO program, estimation technologies of system performance by using plant operation data (i.e., pressure, flow rate, temperature, total dissolved solids concentration, and pH) were developed (Kim et al. 2009f, 2011), and application of biosensor to select the most problematic biofoulant in SWRO processes were investigated (Lee et al. 2009a, b).
In SEAHERO, a new fouling index was developed in order to support to achieve the strategic pretreatment and reliable system monitoring. It gives information on fouling potential by particles, hydrophilic organic matters, and hydrophobic organic matters, respectively (Choi et al. 2009a, b, c; Yu et al. 2010; Hong et al. 2010). The new fouling index is expected to be more useful than common indices such as silt density index (SDI) and modified fouling index (MFI) as well as MFI-UF and MFI-NF. In addition, more fundamental efforts to elucidate fouling mechanisms were made by developing new and advanced membrane characterization techniques such as atomic force microscopy (AFM) and dynamic hysteresis analysis (DH) (Yang et al. 2010; Lee et al. 2011).
Energy consumption (kWh/m3) of SWRO system according to ERD type and system size
Small SWRO system
Large SWRO system
In SEAHERO, specific target for low energy is energy consumption of the test-bed including intake, pretreatment, and SWRO system less than 4 kWh/m3, which is not the smallest value among SWRO plants in the world. There are several SWRO plants whose total power demands are less than 4 kWh/m3. These plants are large in capacity and under the high temperature condition (e.g., higher than 25°C). Considering the test-bed size is rather small and seawater temperature in South Korea varies from 2 to 28°C, the target of 4 kWh/m3 can be a challenging objective. Moreover, the power demand of Fukuoka SWRO plant with capacity of 50,000 m3/day, which is exactly the same as the SEAHERO test-bed, was reported as 5.5 kWh/m3 (GWI 2007).
System optimization is based on the fundamental understanding of SWRO system, and a good simulator can give a good strategy for energy saving such as control of operation conditions (i.e., selection of optimal recovery rate and trans-membrane pressure in accordance with feed water quality and temperature). In SEAHERO program, various types of simulators for monitoring and prediction of SWRO process performance and cost estimation were developed (Kim et al. 2009b, c, d, e; Lee et al. 2009a, b; Oh et al. 2009). Using these simulators, several energy-saving methodologies were suggested using stochastic control approaches which considered feed water temperature and operating pressure as control parameters. The methodologies showed how to improve the performance of SWRO desalination process as well as how to save the energy during the operation of the SWRO systems.
Together with the simulation techniques, an IT-based technology for real-time monitoring of energy consumption in SWRO plants has been developed in SEAHERO program, which enables a precise control of energy usage. Small-size digital power meters coupled with a wireless communication module were designed and developed to send real-time information on electricity usage of important equipments (i.e., high pressure pump, ERD booster pump, intake, and pretreatment pumps, etc.). The information obtained by these wireless power meters can be used to operate a SWRO plant with the optimized energy consumption. Furthermore, a preventive maintenance of the equipments is possible by analyzing this real-time energy usage information.
In order to get further, SEAHERO carried out the researches on the combination of RO and forward osmosis (FO). As a result, application of FO to brine treatment was investigated (Tang and Ng 2008; Tan and Ng 2008), and the combination of RO and FO can result in more energy-saving compared to conventional RO system (Choi et al. 2009a, b, c).
Conclusion: the next step of SEAHERO
The SEAHERO test-bed has two distinguished features. First, it has the world largest unit RO train as discussed earlier. Second, it will be the first SWRO plant in the world, which is firstly constructed for the R&D purpose and then used for a drinking water production facility after the R&D period. SEAHERO is going to develop the future desalination technology step by step, remaining footprints such as the leading-edge 3L technologies and the distinguished test-bed.
This research was supported by a grant (07SeaHeroA01-01) from the Plant Technology Advancement Program funded by the Ministry of Land, Transport and Maritime Affairs, Korea.
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