Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes

Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Two main technologies are currently installed in PLN consist of thermal processes and membrane processes. Thermal processes include multistage flash distillation (MSF) and multi-effect distillation (MED) while the membrane process used is reverse osmosis (RO). The number of RO installed in PLN has rapidly increased in the last decade reached nearly 57% from about 46 units of desalination technology installed in PLN. In 2017, the total of installed capacity is 2,486 m3/h and around 70% of the desalination units are in the capacity range of ≤ 50 m3/h. Therefore, This paper focuses mainly on desalination units with a capacity of ≤ 50 m3/h, which is the most widely used capacity in PLN. The primary goal of this paper is to asses the contribution of the various factors for water production costs. The results of the study show that, the energy cost is responsible for around 60% to 70% of the produced water cost in thermal processes and about 30% of the produced water cost in RO, and RO is the right choice for the PLN power plants because energy consumption and costs at RO are lower than MSF and MED.

This work presents a detailed thermo-economic analysis of unit water costs from dual-purpose cogeneration plants. The power levelized cost was first calculated for stand-alone steam, nuclear, and combined-cycle power plants. The cost of energy needed to operate the desalination systems connected to power plants was evaluated based on two different approaches: power- and heat-allocated methods. Numerical models based on the heat and mass balances of the power and desalination plants’ components were developed and validated. Comprehensive and updated data generated using Desaldata libraries were correlated to estimate the capital, labor, overhead, and maintenance costs for different desalination systems. The levelized water cost produced by multi-effect distillation, multi-effect distillation with vapor compression, multi-stage flash, and reverse osmosis systems connected to different power plants was estimated. The impact of various controlling parameters, including the price of natural gas, nuclear power plant installation cost, and the desalination capacity on water cost, was investigated. For all simulated cases, the levelized water cost evaluated using the heat-allocated method was found to be lower by 25–30% compared to that estimated using the power-allocated method. The cost of water produced using reverse osmosis remains below that produced by other desalination technologies. However, using the heat-allocated method to estimate the levelized water cost narrows the gap between the costs of water produced by multi-effect distillation and that produced by seawater reverse osmosis. The results also show that the use of the multi-effect distillation process in a cogeneration configuration rather than multi-effect distillation with vapor compression can result in a lower water cost. The profit analysis shows slight differences between the profit of a power plant connected to a reverse osmosis system and the profit of a power plant connected to a plain multi-effect distillation system.

Novel Tri Hybrid Desalination Plants

Hybrid systems in seawater desalination-practical design aspects, status and development perspectives

Desalination is probably the only means for fresh water supply to countries in decertified climate. The majority of GCC counties rely on desalinated water for fresh water supply to major cities. Over 70% of the desalinated water in the GCC comes from thermal desalination plants including Multi Stage Flash (MSF) and Multi Effect Distillation (MED). The new trend in the desalination plant in the GCC is 30% Reverse Osmosis (RO) and 70% thermal. However, these percentages vary from one to another country depending on feed water quality and expertise. For example, Oman Sea has lower salinity than the Gulf water and hence Oman uses more RO for desalination than MED and MSF. This decision is also driven by economy as RO process less energy intensive and hence the produced water is less expensive as compared to thermal plants. On the contrary, Qatar and Kuwait use more MSF followed by MED due to the high salinity and low quality feed water. This is also because trials of RO in both Qatar and Kuwait were not successful because of the problems of membrane fouling and restrict pre-treatment requirements due to the quality of the water intake.The advantages of RO over thermal technologies are well known in terms of lower energy consumption and the cost of produced water; but are not yet taken advantage of in the GCC zone. One of the reasons is blamed on high feed water salinity and bad water quality; other reasons such as lack of experience, red tides and reliability are contributed to the dominance of thermal plants. However, field experience showed that good pretreatment and optimized RO design may overcome the problems of high feed salinity and bad water quality. Several RO plants, such as Fujairah in UAE, are good examples of a working RO technology in the harsh water environment. Good RO design includes design and optimization of both pretreatment and post-treatment. Field experience showed that most of RO plants failure was due to inefficient pretreatment which resulted in providing low quality water to the RO membrane that caused fouling. Fouling, including biological and scaling, can be handled once an efficient pretreatment process is available. Recent advances in pre-treatment techniques include the combination of Forward Osmosis (FO) with RO among other methods. Recent studies by the authors including commercial implantations have shown that the combination of FO with RO addresses the most technical challenge of RO process and that is fouling, which results in lower energy consumption and less chemical additives. Experience showed fouling in FO process in reversible, i.e. can be removed by backlashing while fouling in conventional RO process is irreversible.In this study, the feasibility of integrating FO with RO process for the desalting of the Gulf water in Qatar is presented. The results are expressed in terms of specific energy consumption, process recovery, produced water quality, chemical additives and overall process cost.The implementation of RO for desalination is not only reducing the cost of desalination but also the environmental impact. More R&D should be done to provide useful data about RO application and suitability for the Gulf water. The R&D should be focused on laboratory to market development of RO technology using rigorous lab scale and pilot plant testing program.

Chapter 4 - Renewable Energy-Powered Membrane Technology: Cost Analysis and Energy Consumption

Various hybrid desalination systems have been proposed during the last two decades to improve the produced water quality, energy efficiency, water production rate and sustainability among others, receiving therefore a rapid industrial implementation. Desalination processes are energy intensive and this energy is mostly provided by fossil fuels, especially for large scale commercial plants. No doubt, the use of renewable energy (RE) sources is a way forward to decrease the environmental and related health impact to produce and supply freshwater in remote regions with severe water shortage and an unfavourable or unfeasible connection to the public electrical grid. However, most installed renewable energy desalination plants have small capacities, yet facing several issues for long term operation. Therefore, this study restricts to the use of fossil fuel based energy source for desalination and provides a thorough analysis summarising the design, operation, and performance, techno-economic and associated challenges of hybrid seawater desalination systems based on several experimental/real plant and simulation studies reported since 2000. It includes mature membrane-based and thermal-based desalination technologies, namely Reverse Osmosis (RO), multistage flash (MSF), and multi-effect distillation (MED), and a number of emerging hybrid membrane-thermal water desalination technologies. Future opportunities in hybrid systems, including RO/MSF and RO/MED are also highlighted.

This chapter addresses the description and thermodynamic analysis for the integration of desalination plants into the power cycle described in Chap. 4. The systems chosen for this study combine a Concentrating Solar Power plant using parabolic-trough collector technology for electricity generation with various desalination plants, giving rise to what is known as a parabolic-trough concentrating solar power and desalination (PT-CSP + D) plant. The description of the PT-CSP plant, based on the Andasol-1 (Blanco-Marigorta et al., 2011) commercial plant, is detailed in Chap. 4, showing all the model equations. The desalination technologies selected to combine with the PT-CSP plant were multi-effect distillation (MED) and reverse osmosis (RO), as discussed in Chap. 1. On one hand, the simultaneous production of water and electricity using an RO plant connected to a CSP plant seems the simpler option. On the other hand, the integration of a low-temperature MED (LT-MED) plant is an interesting alternative because it allows replacement of the conventional power-cycle condenser by using exhaust steam as the thermal energy source for the desalination plant. However, to satisfy demand, while providing a certain performance, the LT-MED plant inlet temperature should be around 70 °C (corresponding to 0.031 bar absolute), meaning that the steam does not completely expand through the turbine and therefore the power-cycle efficiency is low compared with a stand-alone electricity-generating plant. This is the reason why another alternative to the MED plant, MED with thermal vapour compression (TVC), is considered. In this case, the steam expands completely in the turbine until it reaches the permitted value for the condenser conditions. However, part of the steam circulating through the turbine is extracted and used as high-pressure steam; this, together with the low-pressure steam coming from one of the MED effects, generates the inlet steam required in the first stage of the desalination plant. Moreover, in this study, a new concept of CSP + MED plants is evaluated (which, until now, has not been studied in published works), a thermally fed LT-MED plant with steam coming from a thermocompressor (LT-MED + TVC). In this case, the low-pressure steam (the entrained vapour) used by the thermocompressor comes from the exhaust steam of a PT-CSP plant instead of one of the MED effects. In each of the systems studied, desalinated water production is evaluated as well as the power and efficiency of the dual thermal solar power and desalinated water cycle.

Performance analysis of hybrid system of multi effect distillation and reverse osmosis for seawater desalination via modelling and simulation

The Multi-effect distillation (MED) associated with thermal vapor compression (TVC) process has recently been applied for a number of desalination plants in the GCC countries and emerged as a strong competitor to the multistage flash distillation (MSF) process. The MED/TVC desalination process is characterized by low power consumption compared to the MSF process. It is currently operated at low TBT of 65°C to avoid scale formation compared to MSF technology which operate at top brine temperature of 110°C, this lead to lower tendency to scale formation and less fouling risk. The use of more efficient pretreatment to MED/TVC desalination plants such as nano-filtration or high performance additive antiscalant would allow operating MED at higher TBT which allow increasing the performance ratio. A simulation steady-state program has been established to analyze the thermodynamic behavior of parallel feed flow MED/TVC unit at a wide range of TBT from 65°C up to 125°C and different number of effects with different condition of motive steam pressure on the performance ratio, and specific heat transfer and therefore the best design of MED for the future different design options were considered to optimize the operational of MED system to enhance the economics and performance of MED technology.

Techno-economic assessment of a hybrid RO-MED desalination plant integrated with a solar CHP system

The relationships within the Energy-Water nexus are inherently complex, necessitating sophisticated methods to optimize and manage these interactions effectively. Metamodeling emerges as a crucial technique in abstracting these complex relationships into a manageable analytical form. This study adopts a systematic approach to construct Life Cycle Assessment (LCA) metamodels, aimed at examining the interactions within the water-energy nexus of various desalination technologies. A critical aspect of the developed methodology is the selection of sampling points that align with LCA scenarios through a tailored designed experiment (DoE) model. These scenarios, which include Reverse Osmosis (RO), Electrodialysis (ED), and Multi-Effect Distillation (MED), are evaluated using a set of indicators the Energy-Water nexus, across tradeoff nexus policies. The results signify the impact of considering the Energy-Water Nexus on optimizing desalination processes, compared to evaluating energy and water metrics independently. In policies where nexus considerations were not integrated—focusing solely on cumulative energy or exclusively on water footprint—the RO with Wind Turbine (RO[WT]) scenario emerged as the optimal solution. This configuration consumed 7.540 MJ and 1.654 m³ of water and a carbon footprint of 0.719 kg CO2eq per cubic meter of desalinated water. Conversely, policies that incorporate a nexus approach favor the adoption of MED with Thermal Solar (MED[TS]) scenario. Characterized by its moderate energy consumption of 2.226 MJ, and a water footprint of 2.226 m³, per cubic meter. These findings illustrate the critical role of employing Energy-Water Nexus frameworks through metamodeling in minimizing the environmental impacts associated with desalination processes.

On the brine re-utilization of a multi-stage flashing (MSF) desalination plant

Distillation vs. membrane filtration: overview of process evolutions in seawater desalination