Singapore is the most active desalination market in the Southeast Asian region with a total desalination capacity of 100 million gallons per day (mgd), which is growing at 19 per cent annually. Desalination of seawater has been an important component of Singapore’s long-term strategy for water self-sufficiency. The Tuaspring desalination plant, commissioned in September 2014, is one of the largest in Asia and twice the capacity of the existing SingSpring desalination plant, which had commenced operations in 2005. Together, these plants are able to meet about 25 per cent of the total water demand in Singapore.
The Tuaspring plant presents a good example of a cost-effective and energy-efficient model for desalination. The plant has deployed one of the most advanced pretreatment membrane technologies for seawater desalination and has a 411 MW power plant to meet its energy needs. The advanced technologies are capable of achieving quality standards that are fit for both industrial and domestic use. It is the first ultrafiltration membrane to achieve NSF International certification for crytosporidium removal efficiency. Further, simultaneous execution of the desalination and the power plant has resulted in significant cost savings, as well as operations and maintenance (O&M) improvements. The plant has been completed within two years of commencing construction because of thorough and detailed planning.
Owing to factors such as advanced technology and on-site power generation, treated water from the Tuaspring plant is priced at 0.45 cents per cubic metre (m3) for the first year, which is lower than SingSpring’s first-year price of 0.78 cents per m3. Hyflux Limited, the project owner and operator, will sell the water under a 25-year water purchase agreement to the Public Utilities Board (PUB), Singapore’s national water agency.
Distinguishing features
The Tuaspring desalination plant has a capacity to supply about 70 mgd of treated water, while the SingSpring desalination plant supplies up to 30 mgd. The plant has several distinguishing characteristics that make it more cost-effective as compared to the SingSpring desalination plant. Its compact design has reduced the footprint per cubic metre by more than 30 per cent as compared to SingSpring. In addition, the Tuaspring plant has one of the largest pretreatment ultrafiltration membrane facilities (318,000 m3 per day) in the world.
The plant uses the advanced Hyflux Kristal ultrafiltration membrane technology for the pretreatment process, which offers better water quality, ease of operation, lower operating cost, a smaller footprint and greater stability while dealing with poor or varying feed water conditions. Not only does the high quality pretreatment solution enhance the operational performance, but it also extends the lifespan of the downstream reverse osmosis (RO) membranes and consumes less chemicals and energy. In contrast, conventional pretreatment technologies such as in-filter dissolved air flotation and filtration, chemical dosing and cartridge filtration, which are used by the SingSpring desalination plant, require regular operator intervention to maintain the desired quality.
To further enhance the operational efficiency and optimise production costs, a dual-fuel natural gas-cum-distillate oil-fired combined cycle power plant (CCPP) is being built in a single-shaft configuration and integrated into the Tuaspring desalination plant. As the gas turbine, steam turbine and generator are installed on a single shaft, the O&M of the plant is simpler and more convenient. The plant has a design capacity to produce a power output of more than 390 MW under site-ambient conditions and a net efficiency of 58.5 per cent. Apart from providing electricity, the plant will also draw cooling water from the sea to the desalination facility, thus optimising the balance of energy for the overall plant. By combining the desalination plant with a CCPP, the project has been able to realise significant capital cost savings and reduce its operating costs in the form of single intake and outfall, and associated pumps for both the plants. Further, on-site power generation is expected to reduce the plant’s O&M costs and generate revenues through the sale of excess power.
The project, worth nearly S$1.05 billion, has been financed through a combination of debt and equity on an approximately 60:40 basis. The project was awarded in 2011 and the overall cost was estimated at S$890 million. The cost increase of 18 per cent was attributable to Hyflux’s choice of high efficiency turbines for the power plant. The power plant, which is being set up by Siemens, is estimated to cost S$500 million, accounting for approximately 50 per cent of the total project cost. While the desalination component of the project is covered by a water purchase agreement with the PUB, no power purchase agreement for the integrated power plant was found to be feasible in Singapore’s liberalised electricity market.
Economic benefits
Desalinated water is expected to play a big role in reducing Singapore’s dependence on imported water from Malaysia. The commencement of the Tuaspring desalination plant is a major step towards achieving self-sufficiency in water supply before 2061 when the import agreement with Malaysia expires. The advanced ultrafiltration and dual-phase RO technologies deployed by the plant enable the production of potable water that meets drinking water standards. Its pretreatment membranes are designed to remove impurities as small as 0.01 micron. Hence, the treated water produced by the plant will be used for both domestic and industrial purposes.
The Tuaspring plant is not only self-sufficient in meeting its energy requirements but also produces desalinated water at a lower cost. Thus, there is no doubt that significant synergies have been achieved by the simultaneous execution of the two plants. However, being a first-of-its-kind plant in Singapore, the project is expected to face challenges in terms of its financial viability. As per the plan, the energy produced by the power plant will be utilised to run PUB’s two desalination plants in Tuas. Together, these plants are expected to consume about a quarter of the CCPP’s capacity. Hence, the excess power generated at the plant will be sold to the local power grid. However, with the existing oversupply situation in Singapore’s electricity market, it will be difficult to supply power to the grid at competitive prices. In addition, since a single power plant will meet the power requirements of both the desalination plants, additional energy will have to be purchased to meet the demand during the plant’s maintenance period to ensure uninterrupted operations. These factors are expected to affect the long-term financial viability of the project.
Conclusion
Singapore is envisaged to meet nearly 30 per cent of its total water demand from desalination by 2060, with the remaining demand coming from other sources. It is not only ramping up its existing desalination capacity, but is also exploring new cost-effective technologies such as Memstill (based on membrane distillation) and variable salinity (integration of seawater desalination and NEWater) to convert seawater into potable water.
The Tuaspring desalination plant is likely to result in significant cost savings in the form of reduced electricity bills and lower maintenance costs. However, given Singapore’s liberalised wholesale electricity market as well as substantial investments in technology, the success of the project will also depend on the revenues derived from the sale of excess power. Although Hyflux has committed to sell the excess power generated at the plant to the local grid, it remains to be seen to what extent the company will succeed in this endeavour.
