H. Eldessouky et al., STEADY-STATE ANALYSIS OF THE MULTIPLE EFFECT EVAPORATION DESALINATIONPROCESS, Chemical engineering & technology, 21(5), 1998, pp. 437-451
Mathematical modeling of the multiple effect evaporation (MEE) desalin
ation process has been carried out to determine the effects of the imp
ortant design and operating variables on the parameters controlling th
e cost of producing fresh water, The model assumes the practical case
of constant heat transfer areas for both the evaporators and feed preh
eaters in all effects. In addition, the model considered the impact of
the vapor leak in the venting system, the variation in thermodynamic
losses from one effect to another, the dependence of the physical prop
erties of water on salinity and temperature, and the influence of nonc
ondensable gases on the heat transfer coefficients in the evaporators
and the feed preheaters. The modified fixed-point iterative procedure
is used to solve the large number of highly nonlinear equations descri
bing the MEE desalting system. The algorithm consists of 10 calculatio
n blocks and 6 logical blocks. The algorithm is implemented using L-A-
S computer aided language. Results show that the heat transfer coeffic
ients increase with the boiling temperature. Also, the heat transfer c
oefficient in the evaporator is always higher than that in the feed pr
eheater at the same boiling temperature. The plant thermal performance
ratio is nearly independent of the top brine temperature and strongly
related to the number of effects. The specific heat transfer area inc
reases by raising the number of effects and reducing the top brine tem
perature, The effect of the top brine temperature on the specific heat
transfer area is more pronounced with a larger number of effects. The
required specific heat transfer areas at a top brine temperature of 1
00 degrees C are 30.3% and 26% of that required at 60 degrees C when t
he number of effects are 6 and 12, respectively. The specific now rate
of cooling water is nearly constant at different values of top brine
temperature and tapers off at a high rate as the number of effects is
increased. Two correlations are developed to relate the heat transfer
coefficients in the preheater and the evaporator to the boiling temper
ature. Design correlations are also developed to describe variations i
n the plant thermal performance, the specific heat transfer area, and
the specific flow rate of cooling water in terms of the top brine temp
erature and the number of effects.