An evaluation of multi-effect desalination with a thermal vapour compression system in terms of thermo-economics

Experimental investigation of a desalination system using porous carbon tube as a humidification media with swirl flow

Study of steam parameters on the performance of a TVC-MED desalination plant

Novel Tri Hybrid Desalination Plants

A lab-scale MED dealing with salinity wastewater: the study of optimal operation schemes and parameters

Water desalination and air conditioning consumes huge amount of energy that mostly come from fossil fuels, which produces harmful emissions detrimental to the environment. This work is concerned with the use of a new hybrid cooling and water desalination system driven by solar thermal energy. The system primarily consists of an evacuated tube solar collector, LiBr absorption chiller, and a humidification-dehumidification (HDH) unit. Seawater is used to cool the condenser and absorber of the chiller as well as the condenser of the HDH unit. The heat rejected by the absorber is used to drive the HDH unit. Thermodynamic model of the system has been formulated and simulated using engineering equation solver (EES) software. The results show that the coefficient of performance (COP) of the chiller nearly remain constant with increase in seawater temperature at the absorber inlet. The average COP of the chiller is found to be 0.76. The hybrid system efficiency increases with increase in the seawater temperature mainly due the effect of latent heat of water condensation. The rate of fresh water production increases with increase in the seawater inlet temperature. This resulted in a higher outlet temperature at the absorber exit, leading to a higher energy input to the HDH unit. Gained output ratio (GOR) increases with increase in seawater temperature. This is due to the direct proportionality of the GOR to the amount of fresh water produced. The results also revealed that increasing the flow rate of seawater causes the decrease in the fresh water production due to the corresponding decrease in the temperature of the seawater.

Desalination is a method of producing water from sea or brackish water for drinking, Industry, and irrigation in arid and semi-arid countries, multi-effect desalination with thermal vapour compression (MED-TVC) is a thermal desalination process which has high exergy efficiency compared to other thermal processes. This paper presents the parametric study of a proposed plant modelled using the IPSEpro software package which was validated against data from Kish Island 1536 t/d operational data, where very good agreement between the model results and operational data were found. Then the model was scaled up to produce 24000 t/d to provide fresh water to Zawya City in Libya. The results show that as seawater temperature and salinity increases, exergy efficiency and GOR also increase, and the exergy destruction associated with the steam ejector was around 40%. In addition, the effect of number of effects was investigated, and the results showed that as number of effects increases the exergy efficiency and GOR increase.

Based on the pinch theory and energy cascade utilization principle, the performance of a multi-effect shipboard vertical tube climbing film desalination system combined thermal vapor compression with different preheating configuration has been analyzed. The mathematical model is established for thermodynamic simulation, in which various thermodynamic losses caused by boiling point elevation and pressure drop are considered, and the effective heat transfer temperature difference and the hot side temperature difference are used to analyze the influences of heating steam temperature, final effect evaporation temperature, and concentration ratio on thermal performance including gained output ratio (GOR)—specific heat transfer area for different preheating configuration. The results show that the internal average effective heat transfer temperature difference determines characteristics of multi-effect distillation (MED) system. While for system with similar average effective heat transfer temperature, the temperature difference of hot side is the controlling parameter. And the energy cascade utilization principle shows the controlling attribute in MED thermodynamic system, as GOR is improved mainly due to utilization of the secondary energy and residual energy of the heating steam for preheating process.

Exergy analysis of the solar multi-effect humidification–dehumidification desalination process

In this study, four new indirect heat pump assisted mechanical vapor compression humidification-dehumidification (HDH) systems are proposed and their superiorities over the reference system are demonstrated from thermodynamics and thermoeconomics viewpoints. The proposed models are configured based on an HDH unit and a simple cascade heat pump, an HDH unit and a heat pump with an ejector, an HDH unit and a cascade heat pump with an ejector, and an HDH unit and a vapor injection heat pump. Although employing a heat pump with cascade and ejector configurations improved gain-output-ratio (GOR) and specific power consumption (SPC) values in comparison with the base system, the performance metrics of such layouts are still inferior to those of the HDH unit coupled with the vapor injection heat pump. It is found that the desalination unit with vapor injection mechanism has the highest GOR and the lowest SPC values of 9.22 and 71.29 kWh/m3, respectively, under constant electrical power of 31.26 kW. Overall, proposal of the cascade heat pump, heat pump with an ejector, cascade heat pump with an ejector, and a vapor injection heat pump instead of the conventional heat pump improved GOR by 4.83%, 10.03%, 11.52%, and 14.25%, respectively. Meantime, the SPC of the HDH unit coupled with a simple heat pump decreased by 4.6%, 9.1%, 10.26%, and 12.46% when a cascade heat pump, a heat pump with an ejector, a cascade heat pump with an ejector, and a vapor injection heat pump were used instead of the conventional heat pump, respectively. Also, it is found that a maximum improvement of 14.13% can be achieved in exergy efficiency with a cost penalty of only 1.59 $/m3. Also, it was found that with the use of a simple cascade heat pump instead of the simple heat pump, the exergy efficiency can be enhanced by 4.9%, while the unit cost of the distilled water (UCDW) was degraded by 51.32%. Likewise, the HDH unit coupled with the cascade heat pump with an ejector was resulted in high UCDW compared to the base system, while its exergy efficiency was not enhanced so significantly. Variation of exergy efficiency versus the intermediate temperature had a maximum value of 1.93% (for the HDH unit coupled with a simple cascade heat pump) and 2.05% (for the HDH unit coupled with a cascade heat pump with an ejector) at Tint = 315 K. Moreover, it was found that the UCDW can be decreased with the rise of the intermediate temperature and cascade heat exchanger temperature difference as the fresh water cost rate decreases as a result, while the exergy efficiency can be increased with the rise of the cascade heat exchanger temperature difference.

A comprehensive study was conducted to elucidate the effect of operating conditions on the performance of a multi-effect vacuum membrane distillation pilot plant. A theoretical assessment of the energy and exergy efficiency of the process was achieved using a mathematical model based on heat and mass transfer, which was calibrated using experimental data obtained from the pilot plant. The pilot plant was a solar vacuum multi-effect membrane distillation (V-MEMD) module comprising five stages. It was found that a maximal permeate mass flux of 17.2 kg/m2·h, a recovery ratio of 47.6%, and a performance ratio of 5.38% may be achieved. The resulting gain output ratio (GOR) under these conditions was 5.05, which is comparable to previously reported values. Furthermore, the present work systematically evaluated not only the specific thermal energy consumption (STEC), but also the specific electrical energy consumption (SEEC), which has been generally neglected in previous studies. We show that STEC and SEEC may reach 166 kWh/m3 and 4.5 kWh/m3, respectively. We also observed that increasing the feed flow rate has a positive impact on the process performance, particularly when the feed temperature is higher than 65 °C. Under ideal operational conditions, the exergetic efficiency reached 21.1%, and the maximum fraction of exergy destruction was localized in the condenser compartment. Variation of the inlet hot and cold temperatures at a constant differential showed an interesting and variable impact on the performance indicators of the V-MEMD unit. The difference with the lowest inlet temperatures exhibited the most negative impact on the system performance.

Using the potential of energy losses in gas pressure reduction stations for producing power and fresh water

Thermo-economical and environmental analyses of a Direct Contact Membrane Distillation (DCMD) performance

Effective energy management by combining gas turbine cycles and forward osmosis desalination process

Humidification dehumidification process is an attractive small scale water desalination technique in which desalinated water is produced by mimicking the nature’s water cycle. Various modifications to the basic HDH system can be vital in improving the productivity and reducing the production cost of the fresh water. In this study, a closed-air-open-water water-heated (CAOW-WH) cycle and a closed-air-open-water air-heated (CAOW-AH) cycle are modeled and optimized. Effects of mass flow ratio, humidifier and dehumidifier effectiveness, relative humidity, top and bottom temperatures (main concern of study) on the gain output ratio (GOR), the recovery ratio (RR), entropy generation in the system have been analyzed and presented. It has been observed that an optimal mass flow ratio exists for both the cycles, which maximizes the GOR of the system. Moreover, effectiveness of the humidifier and the dehumidifier is an important parameter, which determines the productivity of the systems. Furthermore, a higher GOR can be obtained at low Tmin and high Tmax and at high Tmin and low Tmax for systems heated by a water heater, whereas the GOR of the air heated HDH system increases with increasing both the Tmin and the Tmax for values of humidifier and dehumidifier effectiveness of 0.8. This study provide extended design charts for building an optimum HDH system to produce a pre-determined rate of desalinated water.

Transient mathematical modelling and investigation of radiation and design parameters on the performance of multi-effect solar still integrated with evacuated tube collector