A new combined power and desalination system driven by low grade heat for concentrated brine Chennan Li a , D. Yogi Goswami a, * , Andrew Shapiro b , Elias K. Stefanakos a , Gokmen Demirkaya a a Clean Energy Research Center, College of Engineering, ENB 118, University of South Florida, 4202 E. Fowler Avenue, Tampa, FL 33620, USA b GE Global Research Center, One Research Circle Niskayuna, NY 12309, USA article info Article history: Received 20 April 2012 Received in revised form 27 July 2012 Accepted 29 July 2012 Available online xxx Keywords: Multi-effect distillation (MED) Supercritical organic Rankine cycle (SORC) Ejector Concentrated brine Low grade heat Cogeneration abstract A new combined power and desalination system is proposed. This system is driven by low grade heat sources such as solar energy, geothermal or waste heat. This system combines a supercritical organic Rankine cycle (SORC), an ejector and a multi-effect distillation (MED) desalination system, which could be used for seawater or concentrated brine such as frac flowback water produced during natural gas mining. A theoretical model is presented and partially validated based on experimental results from the literature. The thermal performance of the proposed system is analyzed using the model and a para- metric sensitivity analysis is carried out to quantify the performance of this combined power and water system. The combined system has an overall exergy efficiency close to 40% for salt concentration of 35 g/ kg using a low temperature heat source at 150  C The proposed system could treat concentrated brine up to 55 g/kg salt concentration with no additional energy input except heat supplied to the power cycle. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Desalination is not only necessary to overcome fresh water shortage issues of the future [1e3] but also important for the oil- gas-coal industry which generates substantial amounts of waste water during the production of oil, natural gas and coal [4]. Multi- effect distillation (MED), multi-stage flash (MSF) and reverse osmosis (RO) are the dominant desalination processes with RO having the largest installed capacity (see Fig. 1) [5]. When handling brackish water or even seawater, the RO process is energy efficient. However, it requires a stringent pretreatment and dramatic osmotic pressure increase with salt concentration, as shown in Fig. 2. This limits the RO process to high concentration feed water desalination applications. On the other hand, a thermal process such as MED is robust, requires less pretreatment and could handle high concentration water sources. Since thermal desalination is regarded as energy intensive, seawater desalination and frac flowback water desali- nation require more energy than a conventional water treatment due to the higher salt concentration [6,7]. It is estimated that about 8.78 million tons of oil per year is required to produce 1 million m 3 per day of fresh water by desalination [8]. Therefore, researchers are focusing on alternative energy sources and technologies [9e11] such as wind [12], solar PV/wind hybrid system [13] as well as solar thermal technologies including thermal collectors [14], solar ponds [15] and solar stills [16]. It is however important to improve the energy efficiency of thermal desalination. Researchers have tried various methods to improve thermal energy utilization by combining mechanical vapor compressors (MVC) [17e20], thermal vapor compressors (TVC) [21e24], absorption heat pumps [25e29] and adsorption heat pumps [30,31]. Among all these research efforts, Alarcón-Padilla et al. [32] achieved the lowest experimental specific energy consumption by combining a 14 effect MED with a double effect absorption heat pump using 180  C steam as the heat source. A system using heat pumps combined with MED requires heat as well as electricity. If the heat source is used to run a power cycle, no additional heat is needed for the MED process. In this study, a system is proposed that combines MED desali- nation with a Supercritical Organic Rankine Cycle (SORC) and an ejector, which works like a combined heat, power and condensa- tion system where ejector cooling is used to condense the final effect vapor of the MED system. Ejector cooling has been studied by many researchers [33,34] and has some advantages such as fewer movable parts and low operating, installation and maintenance costs. In addition, the ejector cycle can use a wide range of refrig- erants and many different heat sources [35]. The SORC power cycle provides power for the desalination system and therefore elimi- nates the need for additional electricity input. In the present study, the combined system driven by a low grade heat source is * Corresponding author. Tel.: þ1 813 974 0956; fax: þ1 813 974 5250. E-mail address: goswami@usf.edu (D.Y. Goswami). Contents lists available at SciVerse ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.energy.2012.07.050 Energy xxx (2012) 1e14 Please cite this article in press as: Li C, et al., A new combined power and desalination system driven by low grade heat for concentrated brine, Energy (2012), http://dx.doi.org/10.1016/j.energy.2012.07.050