Abstract
Multistage membrane distillation units connected in series for water desalination is considered. The influence of the number of stages and the module length per stage on the overall economics is investigated via simulations using a validated model. Depending on the degree of feed salinity, a suboptimal condition occurs at a structure size of 40 ~ 35 stages with an average module length of 15 ~ 12 m. The corresponding specific operating and fixed costs are $8 ~ 12.5/m
3
and $0.97~−.8/m
3
, respectively. For a high salinity feed, the optimum specific operating cost increases due to reduced mass production. Membrane porosity and thickness showed a pronounced effect on cascade structure economics. The specific operating cost can be further reduced by an average of 60% using permeate heat recovery systems.