The objective of this chapter is to present elements desalination cost. The presentation outlines components of direct/indirect and operating cost. A number of case studies are presented for the calculation procedure. Also, a comprehensive review of literature cost data is presented. Economics of desalination processes shows that the production cost is divided into direct/indirect cost and annual operating cost. The direct capital cost covers purchasing cost of various types of equipment, auxiliary equipment, land cost, construction, and buildings. Indirect capital costs includes: freight and insurance, construction overhead, owner's Costs, and contingency. The unit product cost of RO process depends on the capacity. Recent field estimates give $0.55/m3 for the large RO project in Florida, USA, with a capacity of 113,652 m3/d. Examining recent data smaller capacity units give $0.83/m3 and $1.22/m3 for capacities of 40,000 m3/d and 20,000 m3/d, respectively. The most critical parameters in cost evaluation are the fixed charges (amortization) and the energy cost. Other parameters that have lesser effect on the unit product cost include the cost of chemicals. Further, four case studies for the major desalination processes are presented. All calculations are based on recent economic data extracted from the field data and design studies in the literature.

This chapter presents a discussion on modeling and analysis for a single-effect evaporation desalination system. Although, this system offers very limited use in the desalination industry, it constitutes basic elements found in industrial desalination systems. Modeling and analysis of this simple system is necessary to understand the basics and fundamentals of the desalination process, which are also found in actual desalination systems. Detailed results are presented to show the dependence of the factors controlling the fresh water cost that are the thermal performance ratio, specific heat transfer area, and specific cooling water flow rate, on design and operating variables. These variables are the brine boiling temperature, the intake seawater temperature, and water salinity. Analysis of the single-effect evaporation desalination system shows the need for more efficient management of the system energy. Also, systemoperation is recommended at higher boiling temperatures. Proper energy management will result in higher system performance ratios. This will be found in other single-effect systems, which utilize vapor compression, or in multi-effect configurations. System operation at higher boiling temperature results in reduction of the specific heat transfer area and the specific cooling water flow rate. This reduction lowers the first cost, that is, construction cost of the evaporator, condenser, and seawater pump. In addition, the operating cost is lower as a result of reduction in the energy required to operate the seawater-pumping unit.

This chapter presents elements of membrane separation processes and explains principles of membrane separation. The membrane-based processes include reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. There is an inherent difference in the separation mechanism in all filtration processes and the reverse osmosis process. In filtration, separation is made by a sieving mechanism, where the membrane passes smaller particles and retains larger ones. In osmosis or reverse osmosis processes the membrane permeates only the solvent and retains the solute. The microfiltration, ultrafiltration, and nanofiltration processes are used to separate the suspended material. On the other hand, the reverse osmosis process is used to separate dissolved solids. Nanofiltration is used for partial softening of brackish water. The direction of solvent flow is determined by its chemical potential, which is a function of pressure, temperature, and concentration of dissolved solids. Pure water in contact with both sides of an ideal semi-permeable membrane at equal pressure and temperature has no net flow across the membrane because the chemical potential is equal on both sides. The RO process is defined in terms of a number of variables, which includes: osmotic and operating pressure, salt rejection, and permeate recovery. Membrane manufacturing companies define system specifications in terms of the feed quality, which includes salinity and temperature.

This chapter provides an overview of various desalination processes, developments, and the needs for industrial desalination. The industrial desalination processes involve the separation of nearly salt free fresh water from sea or brackish water, where the salts are concentrated in the rejected brine stream. The desalination processes can be based on thermal or membrane separation methods. The thermal separation techniques include two main categories; the first is evaporation followed by condensation of the formed water vapor and the second involves freezing followed by melting of the formed water ice crystals. The former process is the most common in desalination and nearly at all cases it is coupled with power generation units, which may be based on steam or gas turbine systems. The evaporation process may take place over a heat transfer area and is termed as boiling or within the liquid bulk and is defined as flashing. The evaporation processes include multistage flash desalination, multiple effect evaporation, single effect vapor compression, humidification-dehumidification, and solar stills. The desalination processes can also be classified according to the type of main energy form of energy used to drive the process.

This chapter outlines characteristics of major features in RO operation, which includes feed pretreatment, biofouling, and membrane cleaning. The RO feed water may contain various concentrations of suspended solids and dissolved matter. In addition to physical masking of the membrane surface area and blockage of the membrane module, membrane damage can be caused by system operation at excessively low pH values, high chlorine concentration, or presence of other aggressive chemical compounds that would react and destruct the membrane material. Depending on the raw water quality, the pretreatment process may consists of treatment steps such as removal of large particles using a coarse strainer, water disinfection with chlorine or other biocides, media filtration, reduction of alkalinity by pH adjustment and addition of scale inhibitor. Biofouling in RO is a combined result of a number of factors. Biofouling effects on RO performance are characterized by gradual deterioration in the system performance. This includes a period of rapid decline followed by an asymptotic limit. Performance deterioration includes: decrease in the permeate flux, increase in pressure drop, and decrease in salt rejection. Bifouling potential depends on feed water conditions, system design, and operating conditions. Further, biofouling is recognized by indirect effects on the system performance: permeate decline, decrease of salt rejection, or increase of the pressure drop on the feed-side.

This chapter analyzes the performance of multiple effect evaporation systems combined with various types of heat pumps. The analysis includes performance of the following systems: parallel feed multiple effect evaporation with thermal or mechanical vapor compression heat pumps; forward feed multiple effect evaporation with thermal, mechanical, absorption, or adsorption vapor compression heat pumps. The performance of the parallel feed systems is compared against industrial data. However, the forward feed system presents only results of system design, since there are no industrial units for these systems. Further, discussion focuses on modeling and performance analysis of the forward feed multiple effect evaporation with thermal vapor compression. The analysis included a step-by-step calculation method for the multiple effect evaporation- thermal vapor compression (MEE-TVC) system, detailed mathematical model, performance as a function of the top brine temperature and the number of effects, and comparison against the stand-alone forward feed MEE system. Results show an increase up to 50% in the thermal performance ratio and a similar decrease in the specific flow rate of cooling water.

This chapter analyzes the characteristics of major associated processes in thermal desalination, which includes: venting, steam Jet Ejectors, demisters, and MSF Weirs. Venting in the thermal desalination is driven by steam ejectors for removal of the non-condensable gases during startup and operation. During maintenance and other shut down procedures, the flashing chambers in MSF or the evaporation effects in MEE are opened to ambient air. Therefore, air removal is one of the main activities in the startup procedure. The startup ejectors have higher capacity and are capable of processing large air volumes over a short period of time. Conventional jet ejector has three main parts: the nozzle, the suction or mixing chamber, and the diffuser. The nozzle and the diffuser have the geometry of converging/diverging venturi. The diameters and lengths of various parts forming the nozzle, the diffuser, and the suction chamber together with the stream flow rate and properties define the ejector capacity and performance. The ejector capacity is defined in terms of the flow rates of the motive fluid and the entrained stream. Their sum gives the mass flow rate of the compressed gases. Further, wire mesh mist eliminator or demisters is a simple porous blanket of metal or plastic wire that retains liquid droplets entrained by the gas phase. Demisters are used in distillation or fractionation, gas scrubbing, evaporative cooling, evaporation and boiling, and trickle filters. Today, the wire mesh mist eliminator is widely used in thermal desalination plants. The main features of wire mesh mist eliminators are low-pressure drop, high separation efficiency, reasonable capital cost, minimum tendency for flooding, high capacity, and small size. The performance of wire mesh eliminators depends on many design variables such as supporting grids, vapor velocity, wire diameter, packing density, pad thickness, and material of construction.

This chapter evaluates the performance of the multiple effect evaporation desalination processes. Performance analysis of various configurations shows that the best performance is obtained for the parallel/cross flow multiple effect evaporation (MEE). However, the parallel flow system has similar performance characteristics; moreover, its design, construction, and operation is simpler. Operation of both systems is favored at higher temperatures because of the drastic reduction in the specific heat transfer area. However, operation at lower temperatures gives higher thermal performance ratio and lower specific flow rate of the cooling water. Final selection of the most efficient and least expensive system and operating conditions necessitate full system optimization. The developed models should prove to be highly valuable in selecting and determining the characteristics of the optimum system. Comparison of the multistage flash desalination (MSF), forward feed, parallel, and parallel/cross flow MEE systems show several advantages of the forward feed MEE over the other systems. It is certain that the engineering design of the forward feed MEE is more energy efficient since it has the lowest specific power consumption, specific heat transfer area, and specific cooling water flow rate. Advantages of the forward feed MEE over the MSF system are found in the lower number of effects and specific power consumption. The forward feed and parallel flow MEE systems have similar or higher thermal performance ratio than the MSF system, however, the number of effects is only 12 for the MEE systems, while it is equal to 24 stages in the MSF system. Also, the MSF system has higher specific power consumption, which is required for pumping the brine circulation stream.

This chapter focuses on evaluation of the single effect evaporation system combined with various types of heat pumps. The single-effect thermal vapor-compression desalination process is of very limited use on industrial scale. However, thermal vapor compression is used with the multiple effect evaporation (MEE) system, which is known as MEE-thermal vapor compression (TVC). TVC system design and analysis provides the basis for the more complex system of multiple effect evaporation with thermal vapor compression. The mathematics for the TVC system includes material and energy balance equations for the condenser and evaporator. Also, the model includes heat transfer equations for the condenser and evaporator as well as an empirical equation for the steam jet ejector. The analysis of the system is made as a function of variations in the thermal performance ratio, the specific heat transfer area, and the specific flow rate of cooling water. The analysis is performed over a range of the boiling temperature, the motive steam pressure, and the compression ratio. The analysis of the system performance by the mathematical models shows consistency of predictions and industrial practice. The specific power consumption is found to vary over a similar range, 9-17 kWh/m3 at 60 ºC. In addition, the predicted evaporator specific heat transfer area is close to the industrial practice, with values between 400-600 m2/(kg/s) at 60 ºC. The temperature values predicted by the model are also found consistent with reported industrial data. Further, the absorption heat pump combined with the single effect evaporation desalination process is analyzed as a function of the design and operating parameters.

This chapter analyzes and evaluates the performance of the multistage flash desalination (MSF) system. This is made through a discussion of the process developments of MSF; standard features of the brine circulation MSF process; modeling and analysis of the single stage flashing system, the once through multistage system, and the brine circulation multistage system; and features and performance of novel configurations, which include MSF with brine mixing and MSF with thermal vapor compression. The MSF process is an innovative concept, where vapor formation takes place within the liquid bulk instead of the surface of hot tubes. The chapter also presents a novel system for the multi-stage flash desalination. The system is based on the conventional MSF configuration. It includes two of its basic elements; the brine heater and the heat recovery section. The cooling water stream, typical of the MSF system, is also eliminated. The new system adopts a direct brine recycle stream from the brine stream leaving the last flashing stage. This stream is mixed with the intake seawater stream in an insulated and vented tank. Accordingly, the temperature of the feed stream is adjusted to meet summer and winter operating conditions.