When a project is originally designed, the designer must decide
whether a natural draft or mechanical draft tower offers the best
economic result.
Mechanical draft towers are substantially less costly to
purchase, but have the disadvantage of having a continuous
auxiliary power draw. They are also physically smaller and
shorter.
Natural draft towers consume no auxiliary power, but are very
expensive to purchase and erect. They are very large and tall.
Often times, plants do not have enough "real estate" to fit such a
large structure.
One must do an economic analysis to establish which option is
the best choice, economically.
They are also simpler, not having any moving parts