Desalination process options

Some idea of typical operation costs of desalination processes is given in Figure 4.12, plotted against the salt concentration of the water to be desalted. Although the cost data are by now a little old, the relative costs as between the various processes are still roughly right. It can be seen that, for all but the lowest concentrations, reverse osmosis is the least expensive option. 

While the cost of membrane based desalination has decreased over time with improving process efficiency, the cost of concentration disposal has remained relatively constant. Furthermore, disposal cost is unlikely to decrease in the future due to the simplistic and low-tech nature of the equipment required for concentrate management, and the range of nontechnical factors and limitations that determine the feasibility for each option (Mickley 2009). 

Another interesting possibility is the use of pressure-driven membrane processes, in particular MF and UF are becoming standard and very efficient pretreatment options for sea- and brackish-water desalination. Also, for wastewater treatment, MF/UF pretreatment technology can efficiently reduce the highly fouling nature of the feed. 

In addition to this, SMRs are a preferred option for non-electric applications that require a proximity to the customer (such as seawater desalination, district heating and other process heat applications). 

Except for the BN GT 300 (17), all sodium and lead-bismuth cooled reactor concepts use a Rankine superheated steam cycle, and a number of them provide options for the extraction turbines to support seawater desalination, district heating, or process heat cogeneration. The BN GT 300 (17) uses a gas-turbine cycle. 

IRIS (International consortium led by Westinghouse, USA) 1000 343 (279 desalination option) 140,000 Yes, flexible 2012-2015-First-of-a-kind plant Pre-application licensing process started in October 2002 Yes -11% (BOL, without Xe) Yes Lifetime core option was considered. 

In addition, an economic analysis of the desalination plant was performed to investigate economic viability of the SMART desalination plant. The results show that SMART is competitive with other power options, particularly with a gas fired combined plant, within a limited range of electricity generation. The calculated unit cost of fresh water production under desalination capacity of 40,000 mVday using the MED process were in the range of 0.56-0.88 /m for 80% plant availability, which is close to the results of studies performed in other countries. These results indicate that SMART can be considered as a competitive choice for seawater desalination. 

In addition to calculating the expenses of a complete process, one can also calculate the economic impact of modifying a process. Consider the precooler we added to the desalinator, shown in Figures 3.24 and 3.29. The precooler saves energy and thus lowers operating cost, but it requires an additional capital cost. Is a precooler justified economically Let s apply mathematical modeling to compare the two options no precooler and precooler. 

A problem common to all membrane processes is that posed by the retentate in which impurities are concentrated. In some cases, retentate can be discharged with wastewater. Other options include evaporation of the water followed by disposal or incineration of the residue, reclamation of chemicals from industrial wastewater, and disposal in deep saline water aquifers. For the special case of desalination of seawater by reverse osmosis, the retentate is returned to the ocean, which has the potential to cause problems due to excess salinity. 

Some SMRs offer the possibility of very long core lifetimes with reduced core power density, burnable absorbers or high conversion ratio in the core. An infrequent refuelling interval may provide certain guarantees of sovereignty for those countries that have a less developed infrastructure and would prefer to lease fuel rather than master an autonomous fuel cycle [7]. SMRs are also the preferred option for near-term (desalination of seawater or district heating) and advanced (e.g. hydrogen production) process heat applications [7]. 

Utilities have requirements for a range of options for future NPPs. This includes options in plant size (e.g., large or mid-size), plant type (PWR, BWR, PHWR, HTGR, ALMR, etc.), design philosophy (e.g, active vs. passive safety), and plant purpose (power production, process steam, district heating, desalination). 

Figure 7.1 shows the two major treatment options to obtain RO-quality water from sewage and seawater. The key in water reclamation is to first treat the sewage biologically and use MF/UF membrane filtration to remove suspended solids. Two membrane filtration alternatives are available for water reclamation tertiary filtration (TF) of the effluent from a conventional activated sludge (CAS) process and an integrated membrane bioreactor (MBR). For seawater desalination, pretreatment must be provided if the source is open seawater. The current practice involves multimedia filtration, but membrane filtration has also been considered. 

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