An application of dynamic simulation for 16.2 MIGD MSF desalination plant

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

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

Conventional seawater desalination processes like the multi-stage flash (MSF) and multi-effect distillation (MED) are environmentally unsustainable. They consume large amounts of fossil fuels which are a major cause of climate change. Further, desalination plants discharge highly concentrated brine which can cause eutrophication and damage the marine life. Qatar, being a country that faces freshwater scarcity, is highly dependent on desalination for municipal water consumption. On average the daily production capacity of all desalination plants in Qatar is 1.5 million cubic meters per day. This incurs heavy costs on both the economy and the environment. It is expected that by 2020, desalination fuel costs will reach $2.55 billion. Conventional desalination can be made more sustainable by integrating it with solar energy. However, assessing the environmental competitiveness of this solution should be done in a systematic way and reflect the overall system performance. Simplistic models like merely calculating CO2 emissions are not enough and only allow for modest conclusions. Based on a previous literature review by the authors, it was found that the MED process with thermal vapor compression (TVC) is an excellent choice to couple with solar thermal energy that is provided from a concentrating solar collector. The authors also developed a configuration for solar-driven MED with TVC that is simpler in component choices and relies 100% on solar energy to provide the superheated steam required for the MED-TVC process. A model was developed for a 7-effect MED-TVC pilot plant and was validated with actual plant data. Current literature on desalination mainly focuses on membrane technologies and almost completely neglects thermal desalination. In the Arabian Gulf region, thermal desalination is predominant and hence it is required to assess its sustainability from a view point and further investigate how coupling renewable energy can reduce the environmental impacts. This work quantifies the environmental impacts of solar desalination in Qatar using life cycle assessment (LCA). Our work is based on the proposed MED-TVC solar-driven plant. The objective of this study is to assist decision making by providing information about the potential environmental impacts of solar desalination, propose system improvements and suggest references for comparison between different renewable energy-driven desalination processes in general. We identified five impact categories: global warming, freshwater eutrophication, water use, mineral resource scarcity and fossil resource scarcity. GaBi tool was used to carry the LCA. Ecoinvent database, GaBi databases, academic literature and expert opinions were used to construct a comprehensive life cycle inventory for the plant. ReCiPe method was used to assess potential impacts in the five categories. This method was used because it includes characterization factors unique to Qatar and also because it was widely used in the literature hence comparisons can be made. The functional unit was 1 m3 of freshwater at the plant. The results of the LCA are then computed, grouped and weighted. Comparisons with similar desalination systems are also made. The findings of this work are highly relevant to Qatar National Vision 2030 as they provide detailed findings on the environmental impacts of solar-desalination which is a promising solution for the problem of water scarcity in Qatar.

Conventional seawater desalination processes like the multi-stage flash (MSF) and multi-effect distillation (MED) are environmentally unsustainable. They consume large amounts of fossil fuels which are a major cause of climate change. Further, desalination plants discharge highly concentrated brine which can cause eutrophication and damage the marine life. Qatar, being a country that faces freshwater scarcity, is highly dependent on desalination for municipal water consumption. On average the daily production capacity of all desalination plants in Qatar is 1.5 million cubic meters per day. This incurs heavy costs on both the economy and the environment. It is expected that by 2020, desalination fuel costs will reach $2.55 billion. Conventional desalination can be made more sustainable by integrating it with solar energy. However, assessing the environmental competitiveness of this solution should be done in a systematic way and reflect the overall system performance. Simplistic models like merely calculating CO2 emissions are not enough and only allow for modest conclusions. Based on a previous literature review by the authors, it was found that the MED process with thermal vapor compression (TVC) is an excellent choice to couple with solar thermal energy that is provided from a concentrating solar collector. The authors also developed a configuration for solar-driven MED with TVC that is simpler in component choices and relies 100% on solar energy to provide the superheated steam required for the MED-TVC process. A model was developed for a 7-effect MED-TVC pilot plant and was validated with actual plant data. Current literature on desalination mainly focuses on membrane technologies and almost completely neglects thermal desalination. In the Arabian Gulf region, thermal desalination is predominant and hence it is required to assess its sustainability from a view point and further investigate how coupling renewable energy can reduce the environmental impacts. This work quantifies the environmental impacts of solar desalination in Qatar using life cycle assessment (LCA). Our work is based on the proposed MED-TVC solar-driven plant. The objective of this study is to assist decision making by providing information about the potential environmental impacts of solar desalination, propose system improvements and suggest references for comparison between different renewable energy-driven desalination processes in general. We identified five impact categories: global warming, freshwater eutrophication, water use, mineral resource scarcity and fossil resource scarcity. GaBi tool was used to carry the LCA. Ecoinvent database, GaBi databases, academic literature and expert opinions were used to construct a comprehensive life cycle inventory for the plant. ReCiPe method was used to assess potential impacts in the five categories. This method was used because it includes characterization factors unique to Qatar and also because it was widely used in the literature hence comparisons can be made. The functional unit was 1 m3 of freshwater at the plant. The results of the LCA are then computed, grouped and weighted. Comparisons with similar desalination systems are also made. The findings of this work are highly relevant to Qatar National Vision 2030 as they provide detailed findings on the environmental impacts of solar-desalination which is a promising solution for the problem of water scarcity in Qatar.

Organic pollutants in industrial coastal basins are generated from a number of sources including coastal effluents and loading/unloading offshore stations. Such pollutants may adversely affect the quality intakes of other strategic coastal facilities such as coastal thermal desalination plants. In United Arab Emirates, many of such desalination plants are located along one coast hosting refineries as well as other coastal facilities. Loading and unloading of oil tankers are also practiced from offshore stations. A number of organic pollutants are generated from these sources and can potentially threaten the quality of intake seawater of the nearby desalination plants. This paper presents the results of a fate transport modeling study for two selected organic pollutants; Phenol and PCB-180 (HeptachloroBiphenyl) in an industrial coastal basin located in United Arab Emirates. A number of parameters involved in the transport processes were determined from lab experiments while most other parameters were estimated from a numerical sensitivity study. The model results depict contour maps of dissolved concentrations of the two considered pollutants for three different wind conditions in summer and winter. The obtained results and observations constitute useful information for the desalination plants' operators due to the effect of intake quality on the quality of final distillate produced from thermal desalination processes.

Overview of hybrid desalination systems — current status and future prospects

Chapter 3 - Single Effect Evaporation-Vapor Compression

A review of geothermal integrated desalination: A sustainable solution to overcome potential freshwater shortages

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

The two major thermal processes which are employed in large scale desalination plants are MSF (multi-stage flash) and MED-TVC (multi-effect distillation coupled with thermal vapor compression). This chapter provides a brief description on these processes, their performances and challenges. The operational and design developments which have been associated with the thermal desalination processes are explained. Salient features of conventional power water cogeneration cycles in which the MSF/MED-TVC distillation plant operates are highlighted. Challenges that have to be addressed to enhance developments of thermal desalination processes such as introduction of innovative methods to reduce specific energy consumption are also discussed.

Simulation and economic evaluation of a coupled thermal vapor compression desalination process for produced water management

Preliminary thermoeconomic analysis of combined parabolic trough solar power and desalination plant in port Safaga (Egypt)

Desalination is the sole proven technique that can provide the necessary fresh water in arid and semi-arid countries in sufficient quantities and meet the modern needs of a growing world population. Multi effect desalination with thermal vapour compression (MED-TVC) is one of most common applications of thermal desalination technologies. The present paper presents a comprehensive thermodynamic model of a 24 million litres per day thermal desalination plant, using specialised software packages. The proposed model was validated against a real data set for a large-scale desalination plant, and showed good agreement. The performance of the MED-TVC unit was investigated using different loads, entrained vapour, seawater temperature, salinity and number of effects in two configurations. The first configuration was the MED-TVC unit without preheating system, and the second integrated the MED-TVC unit with a preheating system. The study confirmed that the thermo-compressor and its effects are the main sources of exergy destruction in these desalination plants, at about 40% and 35% respectively. The desalination plant performance with preheating mode performs well due to high feed water temperature leading to the production of more distillate water. The seawater salinity was proportional to the fuel exergy and minimum separation work. High seawater salinity results in high exergy efficiency, which is not the case with membrane technology. The plant performance of the proposed system was enhanced by using a large number of effects due to greater utilisation of energy input and higher generation level. From an economic perspective, both indicators show that using a preheating system is more economically attractive.

Desalination technologies and industry have advanced significantly in the past two decades to meet the growing freshwater demands stimulated by the compounding issues of both water quality and quantity in many regions of the world. As desalination processes are energy demanding, there have been many efforts dedicated to improve energy-efficiency of the process units, enhance energy conservation and recovery, and increase renewable energy integration in desalination plants. This research-review article highlights recent key advances and discusses possible venues for further development in desalination energy portfolio to reduce specific energy consumption and, via integration with solar energy, to minimize the environmental footprint associated with freshwater production. First, an overview of current desalination technologies and their energy requirements are presented followed by a discussion on opportunities for improving energy efficiency and energy recovery in both membrane and thermal desalination technologies. Then, various combinations of renewable energy driven desalination plants are discussed with some recent highlights in solar energy driven membrane, thermal and hybrid desalination processes. Technological readiness levels for novel desalination processes, their perceived impact and expected near-future developments in renewable energy integrated desalination technologies are presented. Finally, the potential for solar driven desalination as a cost-competitive freshwater supply alternative is discussed.

In many parts of the world, desalination is the only viable and economic solution to the problem of fresh water shortage. The current commercial desalination technologies rely on fossil fuels and are thus associated with high greenhouse gas emissions that are a major cause of climatic changes. Solar thermal-driven multi-effect distillation with thermal vapor compression is a clean alternative to conventional desalination technologies. To comprehend this process, as well as its features and limitations, extensive modeling is required. In this work, we proposed a plant design based on a solar field with a linear Fresnel collector that supplies heat to a multi-effect distillation plant with thermal vapor compression. The solar desalination plant model is implemented in the Engineering Equation Solver (EES). The system performance is investigated and a control strategy for reducing electric pumping is proposed. Results showed that 1 m2 of the solar field produces 8.5 m3 of distillate per year. The proposed control strategy resulted in a 40% reduction in electric pumping energy. Our results highlight the versatility of the linear Fresnel collector when coupled with thermal desalination.