• An innovation assessment model was developed to demonstrate how different processes for desalination can be used in a cost-optimized manner. 
• As part of this process, the change in the design of a specific component will impact the cost and performance of a desalination unit. 
• This evaluation was expanded through the use of a stochastic value of innovation analysis to determine how changes in other components along the side of the component of interest will affect desalination.

Access to large quantities of pure water suitable for drinking and for industrial applications is becoming more challenging. As sources of fresh water continue to decline, the focus moves to developing technologies to purify readily available sea water.

From an industrial perspective, using seawater is not feasible and will lead almost undoubtedly to corrosion due to the high concentration of chloride anions. Finding additive options to protect against chloride corrosion has proven to be challenging.

In a previous TLT article,¹ researchers synthesized a three-dimensional cryptand-like-triazolo cage that has been found to have a strong affinity for chloride anions in an aqueous medium. This triazolo cage displayed a preference for extracting chloride anions compared to other anions. A triazolo coated, mild steel sample exhibited good performance when immersed in a saturated sodium chloride solution for two weeks at ambient temperature. No evidence of corrosion was found.

The use of reverse osmosis (RO) remains the best method for desalination of sea water (see Figure 3). Dr. Alexander Dudchenko, associate staff scientist in the applied energy division at the SLAC National Accelerator Laboratory in Menlo Park, Calif., says, “The objective has been to find a cost-effective technique for treating high-salinity water that exhibited a brine concentration greater than 75 grams per liter of total dissolved solids. Standard RO techniques cannot readily treat such waters due to high osmotic pressure and current systems being limited to 60-70 bar. Although many novel processes have been proposed for treating high salinity waters, there is large uncertainty in the feasibility of scaling these systems and their costs. Critically, it is not clear which areas of these systems require further innovation to ensure they can reduce costs relative to the current industrial state of the art.”


Figure 3. Desalination of sea water is a very challenging process due to the high cost involved. A recent study has provided a new approach for operators of desalination units to maximize cost performance. Figure courtesy of SLAC National Accelerator Laboratory.

One of the issues faced by the desalination producers is how to balance higher capital costs with higher operating costs. Dudchenko says, “The two key applications for desalination are municipal and industrial systems. Municipalities are limited in not being able to raise capital to pay for the large desalination systems they require. Industrial plants typically utilize small systems which have lower upfront costs but higher operating costs. Ideally, there is need for innovations that provide a tunable way to shift from a capital intensive system design to an operationally intensive design, while retaining an overall low cost of treating water across the lifespan of the processes.”

Ultimately, Dudchenko feels that a balance needs to be achieved in developing an optimal design that maximizes cost performance for a specific desalination application. A study has been published that uses new analytical methods to help engineers evaluate the technical and financial considerations needed in designing a desalination plant.

Innovation assessment model
Dudchenko and his colleagues including Meagan Mauter, associate professor of civil and environmental engineering at Stanford University in Palo Alto, Calif., devised a method that uses three distinct approaches. He says, “Our objective was to demonstrate how cost-optimization tools can be used to find areas of innovation in high-salinity treatment processes, using osmotically assisted RO and multi-stage gap distillation as examples.”

Initially, the researchers determined how changes in component performance or cost affect the levelized cost of water (LCOW) for a specific desalination unit. Dudchenko says, “LCOW is the sum of capital and operating expenses amortized over the lifespan of the process divided by the total volume of treated water produced by the process. By evaluating the value of innovation (VoI), which is defined as the percentage change in system LCOW over the percent change in component performance or cost, we can assess how changing the design of a component impacts the cost and performance of the desalination unit.”

This technique captures the trade-off in innovation of a specific parameter versus a change in cost. A second modified approach evaluates the cost in developing a new component used in a desalination unit with the potential performance improvement.

Examination of a change in one component is limiting because a desalination unit is complicated and contains numerous components. Dudchenko says, “Our third approach is to conduct a stochastic value of innovation analysis (SVoIA) on each component in a specific desalination unit. The reason is we need to take into account innovations that may occur in other components along the side of the component of interest. We first calculate a system LCOW for reference design and then determine how a percentage change in cost or performance for each component of interest changes LCOW. This is repeated for thousands of the reference designs, each made of components with different performance and cost metrics. This allows us to quantify if improving a given component will always result in significant LCOW reduction even as other components improve.”

The tools developed by the researchers were used to hypothetically evaluate a high pressure reverse osmosis (HPRO) system operating up to 300 bar applied pressure. Dudchenko says, “The desalination industry considers HPRO to be the ‘holy grail.’ Our approach was to use a multistage HPRO model and apply a cost-escalation function that is a function of applied pressure between 85 and 300 bar. The purpose of our approach was to determine by how much costs of HPRO components can increase before the process does not make economical sense. In general, component costs of up to seven times higher than current RO systems would yield lower overall costs, assuming the performance of the current state-of-the art process does not improve. If significant improvements in other processes occur, that cost penalty could be significantly lower. At this stage, there are no commercial HPRO units in service.”

The researchers intend to apply their approach in a wide range of processes as a means to figure out what technology improvements will lead to more cost effective desalination. Additional information can be found in a recent article² or by contacting Dudchenko at avd@slac.stanford.edu or Mauter at mauter@stanford.edu.

REFERENCES
1. Canter, N. (2019), “Binding chloride anions,” TLT, 75 (10), pp. 16-17. Available at here.
2. Dudchenko, A., Batholomew, T. and Mauter, M. (2021), “High-impact innovations for high-salinity membrane desalination,” Proceedings of the National Academy of Sciences, 118 (37), e2022196118.