Designers can find short- and long-term savings by using a non-traditional approach.
by Mike Pemberton
November 21, 2015

According to the U.S. National Oceanic and Atmospheric Association (NOAA), the ocean holds 97 percent of the world's water while the remainder is found in rivers, lakes, underground pockets or glaciers, often in difficult locations to access. As a result, with global population growth, there is a pressing need to limit water use, streamline water treatment processes and increase the efficiency of desalination technology. Desalination is capital and energy intensive, but demand for the process has grown rapidly in the Middle East.

A 2009 United Nations report titled "The Role of Desalination in Addressing Water Scarcity" states that desalination has been in use for 50 years and has become an indispensable process for ensuring that potable water is available across the region. Due to the continuous growth in capacity, the Middle East has almost half of the world's desalination capability, which supplies the majority of its freshwater demand, according to the UN report.

The area's estimated average annual rainfall is 10.2 centimeters, which is about a tenth of the global average of 103.3 centimeters, according to climate experts. At the same time, the region has experienced a high rate of population growth, which has more than tripled in the last 34 years, according to the Al-Hayat Arabic daily.

For these reasons and others, such as aging water treatment facilities, water resources are becoming increasingly scarce.

Considering the cost of running pipelines and building desalination plants, it is important the pumping stations, booster stations and pipelines are designed and built to ensure maximum efficiency and reduced life-cycle costs. Energy and maintenance costs are typically the greatest expenses over a system's lifetime. While these systems have historically been designed with efficiency in mind, the use of pipe modeling software that identifies the optimum design and lowest life-cycle cost for pumps and piping is becoming more popular. These software packages ensure that all possible iterations of pump and pipe sizing are considered. There are thousands of iterations of pump and pipe dimensions that can work for a given design, but software models aimed at the lowest capital costs and minimum energy usage can identify the best combinations over the short and long term.

Case Study

Cost is the biggest challenge with desalination, especially considering water transportation costs and potential environmental factors. Comparative modeling has shown that cost reductions can be achieved by rethinking traditional design criteria for the pumping station and transport pipeline

For example, one desalination plant was designed new around 2008 to run the 145 kilometer length from Ain Dar to Khurais in Saudi Arabia. According to a white paper titled "Application of Numerical Optimization of Seawater Pumping Systems" by Joseph Thorpe, an engineering specialist with Aramco Services Company in Houston, Texas, and Jeffry Olsen, Vice President of Applied Flow Technology, the treated seawater transfer system was designed to deliver 2.14 million barrels per day (62,400 gallons per minute [gpm]) starting in 2009 with the ability to raise the flow rate to 3.0 million barrels per day (87,500 gpm), a 17 percent increase, by 2019.

Using advanced pipe modeling software to identify the lowest life-cycle cost resulted in a capital cost savings of $37 million and a total life-cycle cost savings of $104 million over 20 years, according to the report. Additionally, the report states the original design would have resulted in a system that cost 5 percent more in capital and 12 percent more than the final design over the 20-year life cycle. The original design called for a 64-inch pipeline whereas the final design used a 6.25 percent lower diameter pipe of 60 inches, which allowed the system to keep the pumpage at an incrementally higher pressure.

Ultimately, with reduced-diameter piping and less steel required, fabrication costs were significantly reduced, and an entire booster station was eliminated , providing major capital and life-cycle cost savings.

By utilizing piping design optimization software and performing the due diligence to determine the best few configurations, an optimized design was selected for this project. Traditional design philosophy often calls for over-sizing of pumps and ancillary equipment to ensure there will always be enough capacity, both now and in the future, with the end-result being higher-than-necessary first costs and life-cycle costs.

For this project, the report noted that using stronger steel allowed the 60-inch diameter pipe to support higher pressures along the entire pipeline. Being able to transport at a higher pressure eliminated the booster station. The pipeline savings when combined the savings from eliminating the booster station dwarfed the cost of the design software modeling and engineering hours that enabled a new design to emerge, which, in effect, transformed the project from a cost and impact standpoint.

Environmental Impact

According to information provided by the Sustainable Sanitation and Water Management organization, the most commonly used desalination methods are thermal distillation technologies and membrane technologies, primarily reverse osmosis (RO). Each approach varies in energy consumption, operating cost and ability to process seawater or brackish water.

The process is crucial in the Middle East. For example, the Royal Embassy of Saudi Arabia states the country is the world's largest producer of desalinated water. There are 27 desalination stations that provide more than 70 percent of the water used in cities, industry and for electrical generation.

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