Multi-effect Desalination System Research Articles

Development and analysis of a novel biomass-based integrated system for multigeneration with hydrogen production

Energy and exergy analyses of an integrated system based on anaerobic digestion (AD) of sewage sludge from wastewater treatment plant (WWTP) for multi-generation are investigated in this study. The multigeneration system is operated by the biogas produced from digestion process. The useful outputs of this system are power, freshwater, heat, and hydrogen while there are some heat recoveries within the system for improving efficiency. An open-air Brayton cycle, as well as organic Rankine cycle (ORC) with R-245fa as working fluid, are employed for power generation. Also, desalination is performed using the waste heat of power generation unit through a parallel/cross multi-effect desalination (MED) system for water purification. Moreover, a proton exchange membrane (PEM) electrolyzer is used for electrochemical hydrogen production option in the case of excess electricity generation. The heating process is performed via the rejected heat of the ORC's working fluid. The production rates for products including the power, freshwater, hydrogen, and hot water are obtained as 1102 kW, 0.94 kg/s, 0.347 kg/h, and 1.82 kg/s, respectively, in the base case conditions. Besides, the overall energy and exergy efficiencies of 63.6% and 40% are obtained for the developed system, respectively.

Thermo-Economic Optimization of an Idealized Solar Tower Power Plant Combined with MED System.

Based on the reversible heat engine model, theoretical analysis is carried out for economic performance of a solar tower power plant (STPP) combined with multi-effect desalination (MED). Taking total revenue of the output power and the fresh water yield per unit investment cost as the economic objective function, the most economical working condition of the system is given by analyzing the influence of the system investment composition, the receiver operating temperature, the concentration ratio, the efficiency of the endoreversible heat engine, and the relative water price on the economic parameters of the system. The variation curves of the economic objective function are given out when the main parameter is changed. The results show that the ratio of water price to electricity price, or relative price index, has a significant impact on system economy. When the water price is relatively low, with the effect numbers of the desalination system increasing, and the economic efficiency of the overall system worsens. Only when the price of fresh water rises to a certain value does it make sense to increase the effect. Additionally, the threshold of the fresh water price to the electricity price ratio is 0.22. Under the conditions of the current price index and the heliostat (or reflector), the cost ratio and the system economy can be maximized by selecting the optimum receiver temperature, the endoreversible heat engine efficiency, and the optimum concentration ratio. Given the receiver surface temperature and the endoreversible heat engine efficiency, increasing the system concentration ratio of the heliostat will be in favor of the system economy.

Decentralized stand-alone Multi Effect Desalination (MED) system using fixed focus type Scheffler concentrator for the remote and arid rural regions of Sultanate of Oman

Rising population and industrialization made desalination of prime importance in physically water scarce Sultanate of Oman for fulfilling the gap between the rising demand and supply of fresh water. Almost 80-85% of the installed and planned desalination plants in the Sultanate are based on Combined Cycle Gas Turbine (CCGT) power plants while remaining are standalone which includes about 5-7% of the installed plants for rural arid and dry regions. All the installed and planned desalination plants utilises fossil fuels for their operation and are based on Reverse Osmosis (almost 90-95% of the plants) and Multi Stage Flash technologies. Sultanate of Oman is a tropical country with most of the regions being arid and dry receiving solar energy most abundantly. But the utilisation of solar energy in the country is mostly limited to installations based on photovoltaic systems. Only recently solar thermal Enhanced Oil Recovery plant with 1 GWth power output has been undertaken in the country at Amal oil field. A pilot standalone Multi Effect Desalination (MED) plant using fixed focus type Scheffler concentrator for remote and arid rural regions of country has been discussed in this paper to address this gap. This pilot plant has been designed for producing 100 kg/day output based on three stage cross flow type multi effect desalination technology with two 16 m2 Scheffler concentrators and operates in the temperature limits of 170 – 90°C. Preliminary testing carried out on the system during summer and winter period has shown that with available insolation above 700 W/m2, steam at a pressure of 8 to 8.5 bar could be generated in a batch experiment after 2-3 hours from starting the operation for 42 to 55 kg of water in the header of the system. This steam generated is further utilised for desalination in three stages. The initial lag period for the system is measured to be 35-50 minutes depending on the quantity of water in the header, wind speed and solar insolation. System comes out of the lag period when solar insolation reaches just above 650-700 W/m2. The desalination output for the system is measured between 60-65 litres per day for the summer period. Batch type intermittent operation, tracking errors, optical concentration losses, receiver convection losses, brine heat losses are few of the reasons observed based on the analysis for the lower output from the system. Experimentation has given a direction to make operation of the system from batch to continuous production while reducing optical and convection losses through appropriate rectifications for increasing overall yield of the system.

Brine heat recovery unit for Multi Effect Desalination (MED) system based on Scheffler Concentrator using shell and coil heat exchanger

Three stage standalone solar thermal Multi Effect Desalination (MED) pilot plant for remote and arid rural regions of Sultanate of Oman using fixed focus type Scheffler concentrator producing 100 litres per day has been set up at author’s institute. Preliminary tests carried out on this plant yielded lower outputs of 60-65 litres per day. Heat loss through high temperature brine discharged at 85°C was observed as one of the reasons for lower yield. Literature reviewed and analysis shown that desalination outputs can be increased with increased feed water inlet temperature. To recover this heat and preheat the feed water supplied, brine heat recovery unit using counter flow type shell and coil heat exchanger has been proposed in this paper. Helically coiled heat exchanger has been selected for its compactness, higher heat transfer area per unit volume, higher inside heat transfer coefficient and lower fouling rates due to induced turbulence. The operating parameters of this heat exchanger will handle hot brine at 80-85°C and 1 bar pressure. In the present work, heat load, number of turns, coil length and pressure drop calculations are done for estimating the theoretical values based on heat transfer & fluid mechanics principles using numerical correlations from the literature reviewed. The steady state analysis has shown that that coil pitch, inside tube diameter, mass flow rate through the coil and shell affects the heat transfer rates. Practical dimensional constraints have been taken into consideration while finalising the dimensions of the heat exchanger. Overall effectiveness of 84.6% has been calculated for the proposed heat exchanger.

Modeling and simulation of a solar field based on flat-plate collectors

This paper outlines the development of models of a solar field designed to provide thermal energy to a Multi-Effect Desalination (MED) plant. The dynamic model can be used both for simulation and control purposes. Some of these models have been developed based on static and dynamic energy and mass balances, and some others are based on step response methods (experimental tests). The solar field comprises a flat-plate collector field, an air cooler, a heat exchanger and the corresponding pipelines and interconnections. The main purpose of the solar field is to feed the MED unit with hot water within a specific temperature range using two thermal storage tanks as input buffers to the MED system. The main achievement of this paper is that the developed model provides an adequate tradeoff between complexity and performance.

A novel solar-biomass based multi-generation energy system including water desalination and liquefaction of natural gas system: Thermodynamic and thermoeconomic optimization

Abstract In this study, an inventive multi-generation energy system utilizing solar and biomass energy as a complementary fuel are proposed and analyzed, by means of a thermodynamic and thermoeconomic investigation and multi-objective optimization. For supplying electricity, heating and cooling power, a Rankine cycle including a turbine, a heater and a double effect absorption chiller, for liquefaction of natural gas, a Linde-Hampson cycle, for desalination of sea water, a multi-effect desalination system, for solar energy exploitation, a parabolic Trough solar collector and for combustion of biomass, a burner is utilized. Results outline that, the studied system has potential to generate 16.11 kW electricity, 28.94 kW heating power, 23.41 kW cooling power, 8.8 kg/h fresh water and 0.02 m3/h liquefied natural gas with the energy and exergy efficiencies of 46.8%, 11.2%, and product cost rate of 15.16 $/h. A comprehensive modeling is accomplished by applying mass, energy, exergy and thermoeconomic balances to all component of the multi-generation energy system. The investigation becomes more comprehensive with a sensitivity analysis in order to survey the dependency of the thermodynamic and thermoeconomic performance upon the decision variables such as stack gasses temperature, temperature difference of evaporator1, evaporator2 temperature and Turbine inlet temperature. Finally, optimized performance of the system is determined using Genetic Algorithm and deriving Pareto front considering the exergy efficiency and product cost rate as objective functions. The optimized multi-generation energy system could yield the exergy efficiency of 9.9% and the product cost rate of 13.32 $/h.

Effect of input parameters intensity and duration on dynamic performance of MED-TVC plant

Multi-Effect-Desalination (MED) may be exposed to fluctuations (disturbances) in input parameters during operation. Therefore, there is a requirement to analyze the transient behavior of such MED systems. In this work, a dynamic model is developed and used to examine the effect of abrupt and ramp changes in the main operational parameters on the plant behavior and performance. The results show that the disturbance intensity variation has a major role in the desalination plant behavior. For the current MED-TVC configuration, it is recommended to limit the reduction in the seawater cooling flow rate to under 12% of the designed steady-state value to avoid dry out in the evaporators. A reduction in the motive steam flow rate and cooling seawater temperature of more than 20% and 35% of the nominal operating values, respectively, may lead to flooding in the evaporators and a complete plant shutdown. On the other hand, the disturbance period has a minimal effect on plant performance if it avoids the critical values of the disturbance intensity that can cause plant shutdown. Simultaneous combinations of two different disturbances with opposing effects result in a modest effect on the plant operation and they can be used to control and mitigate the flooding/drying effects of the disturbances. For simultaneous combinations of disturbances with similar effect, the plant needs an accurate control system to avoid an operational shutdown.

Exergy Analysis and Optimization of Multi-effect Distillation with Thermal Vapor Compression System of Bandar Abbas Thermal Power Plant Using Genetic Algorithm

Multi-effect distillation desalination system with thermal vapor compression is one of the systems of producing fresh water based on distillation desalination. This type of desalination system is one of the most appropriate and economic types of desalination systems for low to high capacities of seawater and brackish water in which evaporation and distillation have occurred in a vacuum and in temperature below 70 °C. This research provides a mathematical model in the steady-state conditions for multi-effect distillation desalination system with thermal vapor compression in Bandar Abbas thermal power plant in south of Iran. The genetic algorithm is used for maximizing the produced fresh water and minimizing total exergy destruction rate. Exergy analysis shows that the thermo-compressor and effects are the main sources of exergy destruction in the system (more than 80%). The actual operating data in summer and winter were used for the exergy destruction study. The results show that the exergy destruction in winter is more than summer. Parametric analysis for studying the effects of key parameters shows that increasing the top brine temperature leads to increase in the total exergy destruction of the system. The optimization of the system with two-target genetic algorithm causes distillate production to increase by 16.62%, and the total exergy destruction rate decreases by 3.58%.

Application of transcritical CO2 in multi-effect desalination system: energetic and exergetic assessment and performance optimization

Application of transcritical CO2 in multi-effect desalination system: energetic and exergetic assessment and performance optimization

Optimal operating conditions analysis for a multi-effect distillation plant according to energetic and exergetic criteria.

In order to reduce the energy cost while improving the process operation, a study which aims to analyze the influence of the operational parameters variations and determine the optimal operating conditions of a pilot multi-effect desalination system (MED) at CIEMAT-Plataforma Solar de Almerıía (PSA) has been performed. An equation-based object-oriented mathematical model of the experimental MED plant, implemented using the modeling language Modelica and previously developed, calibrated and validated, has been adapted to carry out this study. Firstly, an energetic and exergetic analysis of the process under nominal conditions has been carried out, revealing the key sources of energy and exergy consumption. On the one hand, the thermal energy contained in the mass outflows are the main responsible source of the high energy consumption, on the other hand the entropy generation and the heat exchanged with the environment are the responsible of the exergy degradation. Secondly, a study on the influence of the operational parameters shows that the production of the real plant under nominal conditions is far from the maximum simulated values and some operational parameters have not a great influence in the process with respect to the rest. Finally, using a genetic optimization algorithm implemented in the modeling tool, a optimization process taking into account different energy and exergy performance criteria, sets optimal operational set points.

Thermo-economic analysis of a multiple-effect desalination system with ejector vapour compression

A new formulation for the evaporation, flashing, condensation processes taking place in the effects of thermal desalination systems which simulates the operation of both forward and parallel/cross configurations is coupled with an exergo-economic model based on the SPECO method. The thermo-economic model uses accurate properties for the seawater, brine, pure water and vapour and is solved with an equation solver which does not require the development of a specific solution algorithm as in most previous studies. This flexible model is used to analyze the influence of the number of effects N and the temperature difference ΔTe between effects on the technical and economic performance of multi-effect desalination systems with ejector vapour compression. In particular, it is shown that the performance calculated by an earlier black-box approach is not attainable by technically and economically realistic systems. It is also shown that for each feed configuration and a given number of effects there exists an optimum value of ΔTe which minimizes the cost of the produced potable water. This last result forms the basis of a procedure that combines black-box results with the optimum value of ΔTe and can be used to select the appropriate system for any specific application.

Multi objective optimization of the MED-TVC system with exergetic and heat transfer analysis

The mathematical model to predict the performance and the exergetic efficiency in a multi-effect desalination system with thermal vapor compression (MED-TVC system) has been presented. The energy and the concentration conservation law were developed for each effect, considering the boiling point elevation and the various thermodynamic losses by developing the mathematical models. These analyses led to the determination of the thermodynamic properties at different points and to the gain output ratio (GOR) values. Then, a heat transfer equation was developed in each effect and the required heat transfer areas were determined. Finally, irreversibility analysis was performed, from which the exergy destruction (considering chemical and physical exergy) and the exergetic efficiency were calculated. To obtain the optimum point of a system, multi-objective optimization was used. Determination of the best trade-off between GOR and heat transfer area was the final goal of this optimization. The optimum design led to a selected system with the lowest heat transfer area (and related cost) and the highest GOR.

Thermoeconomic analysis of an integrated multi-effect desalination thermal vapor compression (MED-TVC) system with a trigeneration system using triple-pressure HRSG

In this research, thermoeconomic analysis of a multi-effect desalination thermal vapor compression (MED-TVC) system integrated with a trigeneration system with a gas turbine prime mover is carried out. The integrated system comprises of a compressor, a combustion chamber, a gas turbine, a triple-pressure (low, medium and high pressures) heat recovery steam generator (HRSG) system, an absorption chiller cycle (ACC), and a multi-effect desalination (MED) system. Low pressure steam produced in the HRSG is used to drive absorption chiller cycle, medium pressure is used in desalination system and high pressure superheated steam is used for heating purposes. For thermodynamic and thermoeconomic analysis of the proposed integrated system, Engineering Equation Solver (EES) is used by employing mass, energy, exergy, and cost balance equations for each component of system. The results of the modeling showed that with the new design, the exergy efficiency in the base design will increase to 57.5%. In addition, thermoeconomic analysis revealed that the net power, heating, fresh water and cooling have the highest production cost, respectively.

Allocation of thermal vapor compressor in multi effect desalination systems with different feed configurations

Multi-Effect Desalination system with thermal vapor compression (MED-TVC) is a promising large-scale thermal water production technique. In MED, multiple evaporators are used where vapor is formed in each one using the heat generated from condensing steam/vapor in the previous effect, resulting in high Performance Ratio (PR). A thermal Vapor compressor is used with the MED system to extract a portion of the formed vapor formed in an effect and mix it with motive steam to reduce the rate of steam from a power plant and decrease the pressure in the effects. The top brine temperature of MED system is limited to a value around 65°C to avoid scale formation on the outer surface of tubes in the evaporator.In this study, a mathematical model is developed to identify the optimum location of the thermal-vapor-compressor (TVC or ejector) attached to the Multi Effect Evaporation system. Both forward and parallel feed configurations are investigated. The performance of the system is evaluated using the main performance indicators such as performance ratio (PR), surface area of the evaporators and condenser, and the specific cooling water flow rate needed for condensing the vapor that reaches the down condenser.Locating the TVC at the middle effect resulted in the best unit performance regardless of the number of effects. That is, the highest PR, lowest specific cooling water flow rate are resulting from placing the ejector (TVC) at N/2 where N is the number of effects. Changing the TVC location did not affect the specific heat transfer area, which means that the plant capital cost is not affected by placing the TVC in its optimum location within the practical range of TBT.

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.

The application of Linear Fresnel and Parabolic Trough solar fields as thermal source to produce electricity and fresh water

In the present paper, the integration of the Multi Effect Desalination (MED) system with the Solar Rankine Cycle (SRC) was considered in order to produce electricity and water. Parabolic Trough Collector (PTC) and Linear Fresnel (LF) solar fields were investigated as the thermal source of the SRC and a Natural Gas Boiler (NGB) was considered to supply part of the SRC required thermal energy during the non-availability of the solar thermal energy. A simple optimization approach was used in order to obtain the SRC plants with minimum electricity and water generation costs. A Thermal Storage System (TES) was also considered in the calculations of the present paper. For both PTC/SRC and LF/SRC plants, the required Solar Multiple (SM), electricity generation cost and water production cost were determined for different percentages of the solar share. A comparison between the PTC and LF solar fields was conducted in order to determine the required solar field and land area for producing the specific electricity and fresh water rates. Finally, a sensitivity analysis was performed to determine the importance of each cost parameters on the final electricity and water unit of costs for both PTC and LF base SRC plants.

A novel hybrid polygeneration system supplying energy and desalinated water by renewable sources in Pantelleria Island

In this paper a thermoeconomic analysis of a novel hybrid Renewable Polygeneration System connected to a district heating and cooling network is presented. The plant is powered simultaneously by solar and geothermal sources, producing electricity, desalinated water, heat and cooling energy. System layout includes Parabolic Through Collector (PTC) field, geothermal wells, Organic Rankine Cycle (ORC) unit and a Multi-Effect Desalination (MED) system. Cooling and thermal demands are calculated by suitable building dynamic simulation models, calibrated for Pantelleria Island. Electrical demand is obtained by measured data. A detailed control strategy has been implemented in order to prevent any heat dissipation, to match the appropriate operating temperature levels in each component, to avoid a too low temperature of geothermal fluid reinjected in the wells and to manage the priority of space heating and cooling process. A 1-year dynamic simulation has been performed and results analyzed on daily, monthly and yearly basis. The system achieved an SPB equal to 8.50 and it resulted capable to cover the energy demands of a small community. Moreover, the plant is capable to cover the fresh water demand of the Pantelleria Island.

Modeling, simulation, parametric study and economic assessment of reciprocating internal combustion engine integrated with multi-effect desalination unit

Due to thermal nature of multi-effect desalination (MED), its integration with a suitable power cycle is highly desirable for waste heat recovery. One of the proper power cycle for proposed integration is internal combustion engine (ICE). The exhaust gas heat of ICE is used to produce motive steam for the required heat for the first effect of MED system. Also, the water jacket heat is utilized in a heat exchanger to pre-heat the seawater. This paper studies a thermodynamic model for a tri-generation system composed of ICE integrated with MED. The ICE thermodynamic model has been used in place of different empirical efficiency relations to estimate performance – load curves reasonably. The entire system performance has been coded in MATLAB, and the results of proposed thermodynamic model for the engine have been verified by manufacturer catalogue. By increasing the engine load from 40% to 100%, the water production of MED unit will increase from 4.38 cubic meters per day to 26.78 cubic meters per day and the tri-generation efficiency from 31% to 56%. Economic analyses of the MED unit integrated with ICE was performed based on Annualized Cost of System method. This integration makes the system more economical. It has been determined that in higher market prices for fresh water (more than 7 US$ per cubic meter), the increase in effects number is more significant to the period of return decrement.

Exergy Based Optimization of a Biomass and Solar Fuelled CCHP Hybrid Seawater Desalination Plant

Integrated energy systems utilizing renewable sources are a sustainable and environmentally substitution for conventional fossil fired energy systems. A CCHP hybrid seawater desalination plant with two inputs such as biomass and solar energy and four useful outputs such as cooling, heating, power and distillated water is presented and investigated in this paper. The proposed system includes evacuated tube solar collectors, biomass burner, organic rankine cycle (ORC), absorption chiller, heater and multi effect desalination system (MED). The results showed that the proposed system is able to produce 802.5KW as power, 10391 KW as heating, 5658 KW as cooling and 9.328 kg/s distillated water. Energy efficiency of the system is 61 %, the exergy efficiency is 7 % and the main sources of exergy destructions are biomass burner, evacuated tube solar collectors and vapor generator. Exergy optimization is carried out in order to find the optimum point of system.

A thermodynamic model for exergetic performance and optimization of a solar and biomass-fuelled multigeneration system

Integrated energy systems utilizing renewable sources are sustainable and environmentally substitutes for conventional fossil-fired energy systems. A new multigeneration plant with two inputs, such as biomass and solar energy, and four useful outputs, such as cooling, heating, power, and distilled water, is presented and investigated in this paper. The proposed system includes evacuated tube solar collectors, biomass burners, the organic rankine cycle (ORC), absorption chillers, heaters, and a multi-effect desalination system (MED). The results showed that the proposed system can produce 802.5 kW for power, 10391 kW for heating, 5658 kW for cooling, and 9.328 kg/s for distilled water. The energy efficiency of the system is 61%, while the exergy efficiency is 7% and the main sources of exergy destructions are biomass burner, evacuated tube solar collectors, and the vapour generator. Exergy optimization is carried out to find the optimum point of the system.