Opportunities of improvement of the MED seawater desalination process by pretreatments allowing high-temperature operation

Abstract

a b s t r a c tIn this work, the effect of increasing the top brine temperature (TBT) in a multi-effect distillation (MED) process and its influence on the main design and operational parameters, as gain output ratio (GOR) and specific heat transfer area is investigated. To that end, a detailed and advanced steady-state mathematical model for MED process with forward feed arrangement is developed and validated against data found in the literature. First, a comprehensive sensitivity analysis including key design parameters is carried out. The model is then used to simulate three different heating steam temperatures of 70°C, 100°C and 120°C with a variable number of effects between 9 and 34 and mean temperature difference between effects within 2°C-4°C. Results showed that, given a mean temperature difference between effects, the simultaneous increase in the number of effects and heating steam temperature leads to a significant improvement of the GOR, and a reduction of the specific heat transfer area. Particularly, for a mean difference of temperature between effects of 2.5°C, if the heating steam temperature is increased from 70°C to 120°C, the GOR is improved about 70%, the specific heat transfer area is reduced a 11% and the specific thermal energy consumption a 45%. This analysis provides meaningful results for the preliminary design of MED plants with high-temperature operation.

Boosting the performance of a Reverse Electrodialysis – Multi-Effect Distillation Heat Engine by novel solutions and operating conditions

“…Two plate heat exchangers are used to cool down the concentrate and distillate streams to 25 °C before leaving the unit, using cooling water. The model of the FF-MED, implemented in Engineering Equation Solver (EES), has been adapted from [37] to be suitable for the simulation of this process, in a wide range of operating conditions and with a high number of effects. The model has been validated in [37].…”

Correlations for estimating the specific capital cost of multi-effect distillation plants considering the main design trends and operating conditions

“…This model follows the standard approach for forward-feed MED plants and is already described with detail in Ref. [6]. The model considers feed preheaters and distillate flashing boxes and is based on mass and energy balances applied on each component of the plant.…”

“…This analysis concluded to a very accurate expression (R 2 equal to 0.9935) as a function of the number of effects (N) and the heat source temperature (T), shown in Eq. (6).…”

“…1. Specific MED cost as a function of plant capacity up to 10,000 m 3 /day Equation 1 has some other limitations, especially when the MED plant design deviates from the norm (recent designs introduce higher number of effects and/or higher temperatures of heat supply [6], as well as application of MED in fields other than seawater desalination [7]). The most important design parameters with a high contribution on the MED capital cost are the number of effects and the heat exchanger (HEX) area [8], which also define the top brine temperature (TBT).…”

Performance Analysis of a RED-MED Salinity Gradient Heat Engine

“…Thus, they use correlations for the calculation of the physical-chemical properties of the adopted saline solution related to seawater. The model here presented is a steady-state model for a forward feed MED plant thoroughly described and validated in [55], including purposely developed correlations for the physical-chemical properties of the NaCl aqueous solution (BPE, latent heat of vaporization, enthalpy, density, specific heat, etc.). Also, the working range for several parameters has been enlarged, e.g., the heating steam temperature can range between 60 • C and 100 • C and the recovery ratio between 10 and 70%.…”