K. Thu, Y.-D. Kim, G.L. Amy, W.G. Chun, K.C. Ng
Applied Energy, 104, 810-82, (2013)
Hybrid desalination, Adsorption, Multi-effect distillation, Low-temperature waste heat
This paper describes the development of a simple hybrid
desalination system of a Multi-Effect Distillation (MED) and an
adsorption (AD) cycle operating at sub-atmospheric pressures and
temperatures. By hybridizing the conventional MED with an AD cycle,
there is a symbiotic enhancement of performances of both cycles. The
performance enhancement is attributed to (i) the cascade of adsorbent’s
regeneration temperature and this extended the usage of thermal energy
emanating from the brine heater and (ii) the vapor extraction from the
last MED stage by AD cycle which provides the effect of lowering
saturation temperatures of all MED stages to the extent of 5 °C,
resulting in scavenging of heat leaks into the MED stages from the
ambient. The combined effects of the hybrid cycles increase the water
production capacity of the desalination plant by nearly twofolds.
In
this paper, we demonstrate a hybrid cycle by simulating an 8-stage MED
cycle which is coupled to an adsorption cycle for direct vapor
extraction from the last MED stage. The sorption properties of silica
gel is utilized (acting as a mechanical vapor compressor) to reduce the
saturation temperatures of MED stages. The modeling utilizes the
adsorption isotherms and kinetics of the adsorbent + adsorbate
(silica-gel + water) pair along with the governing equations of mass,
energy and concentration. For a 8-stage MED and AD cycles operating at
assorted temperatures of 65–90 °C, the results show that the water
production rate increases from 60% to twofolds when compared to the MED
alone. The performance ratio (PR) and gain output ratio (GOR) also improve significantly.