entropy Article Desalination Processes’ Efficiency and Future Roadmap Muhammad Wakil Shahzad * , Muhammad Burhan, Doskhan Ybyraiymkul and Kim Choon Ng Water Desalination and Reuse Centre, King Abdullah University of Science & Technology, Thuwal 23955-6900, Saudi Arabia; [email protected] (M.B.); [email protected] (D.Y.); [email protected] (K.C.N.) * Correspondence: [email protected] Received: 6 December 2018; Accepted: 14 January 2019; Published: 18 January 2019 Abstract: For future sustainable seawater desalination, the importance of achieving better energy efficiency of the existing 19,500 commercial-scale desalination plants cannot be over emphasized. The major concern of the desalination industry is the inadequate approach to energy efficiency evaluation of diverse seawater desalination processes by omitting the grade of energy supplied. These conventional approaches would suffice if the efficacy comparison were to be conducted for the same energy input processes. The misconception of considering all derived energies as equivalent in the desalination industry has severe economic and environmental consequences. In the realms of the energy and desalination system planners, serious judgmental errors in the process selection of green installations are made unconsciously as the efficacy data are either flawed or inaccurate. Inferior efficacy technologies’ implementation decisions were observed in many water-stressed countries that can burden a country’s economy immediately with higher unit energy cost as well as cause more undesirable environmental effects on the surroundings. In this article, a standard primary energy-based thermodynamic framework is presented that addresses energy efficacy fairly and accurately. It shows clearly that a thermally driven process consumes 2.5–3% of standard primary energy (SPE) when combined with power plants. A standard universal performance ratio-based evaluation method has been proposed that showed all desalination processes performance varies from 10–14% of the thermodynamic limit. To achieve 2030 sustainability goals, innovative processes are required to meet 25–30% of the thermodynamic limit. Keywords: standard primary energy; primary energy; standard universal performance ratio; desalination 1. Introduction The world’s demand for increasingly scarce water is escalating rapidly, challenging its accessibility for the life cycle and putting the global population at risk. The increase in water demand is mainly due to the rapid growth of population and economic development. Water security underpins the life cycle, economic growth and sustainability all over the world. In 2000, overall world water demand was 4000 billion cubic meter and it is estimated to increase over 58% by 2030. The water demand is expected to be much higher in developing countries, where over 93% additional water projections are estimated as compared to developed countries [1–6]. Conventional water sources also called renewable resource such as surface water and ground water are not able to patch up the gap between supply and demand of fresh water. This growing gap can only be filled by non-conventional and non-renewable sources such as wastewater treatment and seawater desalination. In some parts of the world, even after the application of wastewater reuse, still there is shortfall of water that only can be filled by seawater desalination processes. During last Entropy 2019, 21, 84; doi:10.3390/e21010084 www.mdpi.com/journal/entropy Entropy 2019, 21, 84 2 of 14 Entropy 2019, 21, x 2 of 14 20years, years, steady steady growth growth in desalination in desalination capacities capacities installation installation has hasbeen been observed observed that thatis expected is expected to rise to risein the in near the near future future to fulfil to fulfil world world water water demand. demand. Installed Installed desalination desalination capacities capacities are projected are projected to be todoubled be doubled by 2030 by in 2030 the inGulf the Cooperation Gulf Cooperation Countries Countries (GCC) (GCC) as well as as well in the as inworld the worldas shown as shown in the inFigure the Figure1a. Presently,1a. Presently, 150 countries 150 countries are operating are operating over over19,500 19,500 desalination desalination plants plants to produce to produce 100 100million million cubic cubic meters meters per per day day to tofulfill fulfill the the demand demand of of a apopulation population of of 300 300 million throughout the world.world. Based on current processes, the share in thethe worldworld desalinationdesalination marketmarket andand theirtheir respectiverespective publishedpublished specificspecific energyenergy consumptions,consumptions, seawaterseawater reversereverse osmosisosmosis (SWRO)(SWRO) 60%60% atat 3.5 Kilowatt hours perper cubiccubic metermeter (kWhm-3)(kWhm-3) and thermally driven processes 40% at 1717 kWhm-3,kWhm-3, the totaltotal desalinationdesalination energy consumption isis predictedpredicted andand presentedpresented inin FigureFigure1 1b.b. It It can can bebe noticednoticed thatthat withwith thethe projectedprojected expansion of desalination capacities, the energy consumption for desalination is expected to reach to 2.4 Gigawatt hours (GWh)(GWh) inin 20302030 asas comparedcompared toto onlyonly 1.41.4 GWhGWh inin 20182018 [[7–14].7–14]. (a) (b) Figure 1. (a) World andand Gulf Cooperation Countries (GCC) desalination capacitiescapacities trendtrend fromfrom 19851985 toto 2030 and ((b)) energyenergy consumptionconsumption byby desalinationdesalination processesprocesses [[1–14].1–14]. The energy utilized in desalination processes is in the majority (80%) produced by thermoelectric processesprocesses thatthat consumeconsume huge huge amount amount of of water water for for heat heat rejection rejection to complete to complete the thermodynamic the thermodynamic cycle. Itcycle. is estimated It is estimated that aroundthat around 15% 15% of water of water is evaporated is evaporated in in cooling cooling towers towers to to produce produce thethe requiredrequired power.power. WorldWorld electricityelectricity demanddemand isis expectedexpected toto increaseincrease twofoldtwofold toto 3434 terawattterawatt hourshours (TWh) in 2035 as compared to 20102010 productionproduction level.level. Correspondingly, inter-linked water demand is expectedexpected to increaseincrease toto 790790 billionbillion cubiccubic metersmeters (bcm)(bcm) byby 20352035 asas comparedcompared toto 583583 bcmbcm inin 2010.2010. ThisThis highhigh waterwater demand in thermoelectricthermoelectric power generation is due to lowlow efficienciesefficiencies ofof conventionalconventional cycles.cycles. In thethe past,past, typical power plants plants were were operated operated at at 28–30% 28–30% energetic energetic efficiency efficiency that that is isrecently recently increased increased to 50% due to rapid development in combustion processes and cascading operations as shown in Figure 2 [15–20]. Recently, General Electric (GE) in partnership with EDF made history and set a Guinness Entropy 2019, 21, 84 3 of 14 Entropyto 50% 2019 due, 21 to, x rapid development in combustion processes and cascading operations as shown3 of 14 in Figure2[ 15–20]. Recently, General Electric (GE) in partnership with EDF made history and set a WorldGuinness Records World title Records for operating title for the operating world’s the most world’s efficient most combined-cycle efficient combined-cycle power plant power at 62.22%. plant Theseat 62.22%. gradual These improvements gradual improvements in power plant in power efficiencies plant efficiencieswill help to will save help fossil to savefuel, fossilCO2 emissions fuel, CO2 andemissions additional and additionalwater consumption water consumption [21,22]. [21,22]. FigureFigure 2. 2. CombinedCombined cycle cycle efficiency efficiency and and environment environment impact impact trend trend from from 1870–2018 1870–2018 [15–22]. [15–22]. ItIt can can be noticednoticed thatthat over over a a century century (1880–1970), (1880–1970), there there was was not not much much improvement improvement in power in power plant plantefficiency efficiency due to due inefficient to inefficient combustion combustion and singlyand singly operated operated processes. processes. The The major major improvement improvement was wasobserved observed during during 1970–2000 1970–2000 due todue implementation to implementation of efficient of efficient combined combined cycle gas cycle turbines gas turbines (CCGT) (CCGT)coupled coupled with heat with recovery heat boilerrecovery operated boiler steam operated turbines. steam Noticeable turbines.improvement Noticeable improvement was also observed was alsowhen observed thermally when driven thermally desalination driven processes desalination were integrated processes withwere CCGT integrated power with plants CCGT due to power better plantsutilization due to of better low pressure utilization steam of low in waterpressure production steam in beforewater dumpingproduction into before the condenser.dumping into Today, the condenser.combined CCGTToday, and combined desalination CCGT processes and desalination are considered processes as most are efficientconsidered cycle as formost power efficient and watercycle forproduction. power and In conventionalwater production. combined In conventional CCGT power combined and desalination CCGT power plants, and primary desalination fuel is supplied plants, primaryto the gas fuel turbine is supplied