Low-temperature Multi-effect Desalination Research Articles

Performance analysis of an open absorption heat pump and thermal desalination system for heat and water recovery of coal-fired flue gas based on zero liquid discharge

An innovative combined system based on an open absorption heat pump and low-temperature multi-effect desalination system is proposed to provide fresh water and domestic hot water in order to achieve zero liquid discharge from coal-fired power plants and recover the waste heat of flue gas. This system takes into consideration the evaporation of desulfurization wastewater by flue gas. By using a 600 MW unit as an example, energy and exergy analysis is used to examine the impacts of flue gas humidity, temperature, mass, generator pressure, solution concentration, and boiler load on system performance. The findings showed that because coal-fired power plants produce a significant amount of dry flue gas, an increase in gas humidity has little effect on product supply. As a result, little variation in the combined system is caused by the desulfurization wastewater spray evaporation, which allows power plants to achieve zero liquid discharge with only a small loss in exergy efficiency of about 6%. The recovery of sensible heat rather than latent heat benefits from an increase in the bulk of dry flue gas. The recovery of heat and water benefits more from an increase in operating load or flue gas temperature than the open absorption heat pump system itself. The generator pressure and rich solution concentration have negligible effects on heat and water recovery. The open absorption heat pump system's increasing exergy efficiency trend and the boiler operating loads are also related. The exergy efficiency of the generator is the highest by about 75%, that of the desalination system is the lowest by about 29%, and the exergy destruction of the absorber is the highest by about 43%. The findings are likewise applicable to coal-fired power stations with various levels of electrical output.

Performance Analysis of Solar Thermal Powered Supercritical Organic Rankine Cycle-Assisted Low-Temperature Multi-Effect Desalination Coupled With Mechanical Vapor Compression

Abstract Power and freshwater demand are increasing as populations around the world keep growing. Due to the environmental impact of using fossil fuels and limited resources, using solar thermal in desalination application is a valuable option. In this paper, an innovative new design of low-temperature multi-effect desalination coupled with mechanical vapor compression (LT-MED-MVC) powered by supercritical organic Rankine cycle (SORC) utilizing a low-grade solar heat source using evacuated tube collectors is analyzed. The proposed design has the potential to desalinate water of high salt concentrations or brine with high salinity more than 100,000 ppm or effluent streams from a power plant with low energy consumption and high efficiency when compared to other systems. The performance of the LT-MED-MVC was found to be better than similar systems found in the literature. The specific power consumption for the system is lower than 4 kW h/m3 for seawater feed salinity of 100,000 ppm, 14 forward feed effects, and a recovery rate of 50%. The overall system efficiency is about 14%. The impact of increasing the number of effects, motive steam temperature, pressure of SORC, and salt concentration on the specific power consumption, solar collector area, and the system efficiency are also analyzed.

Thermodynamic, economic, and sensitivity analysis of salt gradient solar pond (SGSP) integrated with a low-temperature multi effect desalination (MED): Case study, Iran

Integration of a salt-gradient solar pond (SGSP) with multi-effect-desalination (MED) system for southern part of Iran is in present study. The proposed system was evaluated from thermodynamic and economic standpoints. Also, sensitivity analysis based on the important parameters of the system is performed. Economic analysis is performed for the first time based on the Iran’s Plan and Budget Organization (PBO) price lists and local suppliers. Annual productivity of the proposed system for each month was evaluated and overall productivity of the system throughout a year calculated by about 20,000 m3/year. The economic results indicated that the period of return (POR) of the intended system is around 6 years. The solar pond construction costs such as excavation, transportation, salt and lining, were considered based on the local prices (Bandar Abbas city) and PBO. The cost of constructing a solar pond was evaluated about 12 $/m2. Also, sensitivity analysis was elucidated to realize the effects of salt price and transportation cost on the system. Finally, the results showed that by reducing the salt price and eventually considering it’s for free, POR will be reduced by about 45%, while by considering transportation cost equal to zero, POR will be reduced by about 25%.

Numerical investigation on steam flow and resistance to thermodynamic losses inside the full-scale low-temperature multi-effect desalination evaporator

Numerical investigation on steam flow and resistance to thermodynamic losses inside the full-scale low-temperature multi-effect desalination evaporator

Combined concentrated solar power plant with low-temperature multi-effect distillation

This study analyzes a technological concept for simultaneously generating power and desalinating water in a Middle East and North Africa country. An innovative, low-temperature, multi-effect desalination (LT-MED) process integrated with a concentrating solar power (CSP) plant was assessed and analyzed. A combined power and seawater desalination plant was modeled for the city of Aqaba by the Red Sea in Jordan. Parabolic-trough collectors using indirect steam generation with thermal energy storage connected with power and desalination blocks were designed. The designed plant was modeled and simulated using EBSILON Professional, a discrete energy balance simulation software, under several operating conditions, to analyze the results. An economic feasibility analysis of the combined CSP+LT-MED plant was also conducted. The simulation results showed the broad variability of the cogeneration system in terms of electricity generation and water production. The output power of the CSP plant without water production reached 58.7 MWel in June. The output power accompanied with distilled-water production with a mass flow rate of 170 m3/h was approximately 49.5 MWel. Furthermore, the number of desalination stages had the strongest influence on distillate production but limited the operational flexibility of the power plant due to the temperature gradients within the desalination stages. The distilled-water mass flow reached 498 m3/h for 10 stages. The research showed that the design successfully worked with up to €78.84 million, earned from selling the produced electricity. However, owing to highly subsidized water tariffs in Jordan (80% less than the actual cost), the integration of water desalination into the CSP plant was not economically feasible.

Solar Rankine Cycle (SRC) powered by Linear Fresnel solar field and integrated with Multi Effect Desalination (MED) system

Abstract The Linear Fresnel (LF) solar filed was considered to support part of the required thermal energy of the Solar Rankin Cycle (SRC). Multi Effect Desalination (MED) system was applied in order to produce distillate water by using the SRC thermal energy. Two typical low temperature MED systems with 14 effects and two Gain Output Ratios (GORs) of 9.8 and 12 were considered to be feed by the steam (70 °C) at the outlet of the turbine replacing the condenser of SRC. Two thermal storage capacities of 6 and 12 h were considered in SRC calculations. Two LF solar fields were considered to operate with different mass flow rates and aperture areas. An economic analysis was also used to determine the water and electricity costs of the SRC/MED plant. The electricity unit cost of the SRC/MED plant was compared to electricity cost of a reference SRC plant (SRC/Ref) without MED and comprising a once-through cooling condenser with cooling temperature of 35 °C. The amount of annual fuel saving and the unit cost of the water and electricity were determined under different scenarios of MED unit GORs and for two thermal storage capacities.

Seven-effect 2 × 4500 m3/d low-temperature multi-effect desalination plant. Part I: Design, installation and commissioning

Seven-effect 2 × 4500 m3/d low-temperature multi-effect desalination plant. Part I: Design, installation and commissioning

A low-temperature multi-effect desalination system powered by the cooling water of a diesel engine

This paper introduces a medium-size low-temperature multi-effect desalination (LT-MED) system. Powered by the cooling water of a 1000kW diesel power generator set, the system can produce 60tons of fresh water per day. First, the thermodynamic and heat transfer model of the LT-MED system is derived. Second, an integrated four-effect tower distiller is designed and built. The system is installed in the Guishan Island, Zhuhai, Guangdong, China, and tested comprehensively. In the operation, the evaporation temperature of each effect is linearly proportional to the heat load of the power generator. Additionally, the evaporation temperature in each effect distiller rose linearly when the heat load was gradually increased. The variation of evaporation pressure was consistent with the evaporation temperature. When the heat load of the power generator increases from 300kW to 530kW, the fresh water production rate increases from 1.26m3/h to 2.30m3/h. The conductivity of the fresh water is usually <100μS/cm. Because of electricity and freshwater co-production, the system is environmental friendly and is particularly useful for islands and offshore platforms.

Conceptual design and experimental investigation involving a modular desalination system composed of arrayed tubular solar stills

A novel conceptual design of a low temperature multi-effect desalination (LT-MED) system is presented in this paper. The LT-MED system operates at vacuum pressure and is composed of several modules of tubular solar still (TSS) cells, each of which can independently produce freshwater. To verify the performance of the modules in different stages of the system, an experimental TSS was fabricated and tested under different vacuum pressures and heating conditions from 20 to 80kPa and 100 to 300W, respectively. The results showed that the energy utilization efficiency exceeded 0.7 in most cases, with a maximum value of approximately 0.81, which was nearly double that of a basin still operated at normal pressure. A 5-effect modular MED system for practical application with a capacity of 86kg/d was proposed according to the presented theoretical and experimental work. A structural design and control scheme were also presented. Performance and economic analyses indicated a wide applicability of the system, especially for remote and desert regions.

IAEA coordinated research activity on nuclear desalination: the quest for new technologies and techno-economic assessment

A coordinated research project (CRP) on new technologies for seawater desalination using nuclear energy was conducted by the International Atomic Energy Agency (IAEA). The CRP goal was to quest for innovative seawater desalination technologies which can be integrated with the existing nuclear power plants, could make seawater desalination using nuclear energy more viable, and promote the exchange of technical information on national programs in the field of seawater desalination using nuclear energy. Other activities carried out within this CRP include conducting preliminary feasibility analysis for nuclear seawater desalination based on national site specifics, economic and life cycle assessment of nuclear seawater desalination projects, and scoping of new ideas to improve the IAEA Desalination Economic Evaluation Program (DEEP). Among other outcomes, the CRP identified several potential technologies which can make nuclear desalination a more viable option such as: heat pipe, the low temperature Multi-Effect Desalination (MED), enhanced Reverse Osmosis (RO) at elevated temperature, and hybrid low temperature desalination processes. This paper summarises the activities carried out by participating Member States and the results achieved. Elaboration on different nuclear desalination technologies is provided. It also presents an overview of the financial model suggested for further improvement of the IAEA DEEP tool.

Performance study of a pilot-scale low-temperature multi-effect desalination plant

A 30t/d low-temperature multi-effect evaporation seawater desalination (LT-MED) system was designed based on the mathematical model, and the corresponding pilot device was constructed in Tianjin, China. Whole-process tests were carried out, and the effects of key operating parameters, including motive steam pressure, maximum operating temperature, temperature difference, spray density, non-condensing gas extraction method, and steam ejector flow, on desalination performance were analyzed. Results showed that the device successfully met product water design requirements; total dissolved solids were less than 5mg/L. Water production initially increased as motive steam pressure increased, then stabilized when pressure exceeded 21% of the design value. Water production reached its maximum when heat transfer temperature difference and spray density ranged from 3°C to 4°C and from 240L/(mh) to 300L/(mh), respectively. Unlike in parallel mode, water production increased by 3.64% when vacuum pumping was operated in series mode. Water production and gain output ratio increased, and system energy consumption reduced when a thermo-vapor compressor was introduced. The results provide a useful reference for the design of other large-scale seawater desalination systems.

Experimental Studies on a Solar Low Temperature Multi-Effect Distillation Desalination System

Solar energy has been widely used in desalination systems. A low-temperature multi-effect desalination system driven by solar is constructed for a series of experimental studies. The results show that water production rate grows with solar radiation, and maintains at a high level between 12am to 4pm. The optimized heat water flow is 1400 kg/h and appropriate cooling water temperature is 24 °C, respectively.

Steam driven large multi effect MVC (SD MVC) desalination process for lower energy consumption and desalination costs

It has been published and demonstrated in operating plants that the low-temperature multi effect desalination process (LT MED) when operated on turbine backpressure steam requires minimal energy consumption yielding specific desalination energy costs approaching values of optimal RO energy costs. However due to variations in electricity demand, the operation of large steam turbines at base load is in most cases impractical. As a result, in order to allow variations in electricity supply and full capacity of the desalination extraction, steam extracted from the turbines at higher pressures than the back pressure is commonly used. The extraction steam pressure of these turbines is in the range of 1.5–4.5 barg. (Typically as required for process steam at refineries and for MSF desalination plants). The LT MED process when utilizing such extraction steam incorporates thermo compressors (steam ejectors) in order to take advantage of the excessive extraction steam pressure, thereby increasing the economy ratio of the MED (decreasing energy consumption). Thermo compressors (ejectors) as a rule have a relatively low adiabatic efficiency, thus limiting the potential of the MED to increase the economy ratio even more. In this paper an approach of using a novel large centrifugal compressor driven by an auxiliary steam turbine utilizing the extraction steam is incorporated instead of the thermo compressor for large LT MED plants. The centrifugal compressor and auxiliary turbine having a much higher efficiency than the thermo compressor results in significant energy savings, thus lowering the desalination costs. This paper will also describe the thermodynamic advantages, the specific investment and desalination costs comparison, and the resulting desalination cost reduction potential of the steam-driven multi effect MVC process.

Advanced MED process for most economical sea water desalination

The low temperature horizontal tube multi-effect desalination (MED) process is thermodynamically the most efficient of all thermal distillation processes. A comprehensive multi-disciplinary development and design approach resulted in prevention of corrosion and scale formation on the plant’s heat transfer surfaces. It also allows the successful and most economical use of aluminum alloys for heat transfer tubes, as well as carbon steel epoxy coated shells for the evaporator body. The ability to use economically low grade heat, such as waste heat, exhaust steam from power station turbines as the primary heat source for MED, yields very low specific energy costs for sea water desalination. Recent developments of very economical low temperature deep pool nuclear heat reactors, when acting as the primary energy source for large MED plants, yield very low specific desalination energy costs. The combination of economical specific MED plant costs with low energy cost, together with the inherent durability of low temperature MED avoiding the necessity of comprehensive sea water pretreatment (such as with RO plants) make the MED process one of the best candidates for safe and durable large capacity economical desalination options. This paper describes the design principles and various energy considerations that result in this uniquely economical MED process and plant. It also provides an overview of various cases of waste heat utilization, and cogeneration MED plants operating for many years.

Engineering relations for economic production functions of solar low-temperature multi-effect desalination

Three simple and accurate engineering relations summarize the engineering results of a computational model related to the process of the solar low-temperature multi-effect desalination. The relations providing the heat transfer surface the installed electrical power and the thermal energy are useful in facilitating the adjustment of the economic production function of the desalination process according to different price systems.

Coupling of a power plant with a low temperature Multi-effect desalination plant

The low-temperature heat discarded by a large power plant can produce large quantities of desalted seawater at low cost. This paper describes a system in which a horizontal tube multi-effect (HTME) desalination process is coupled to a large power plant (either nuclear or non-nuclear) in such a manner as not to interfere with the power cycle. The resulting product water is produced at a cost approximating present prices of water sold by water companies.