The following sequnce of pictures illustrates the lifting and erection
of an acid plant stack.
Lifting of any large piece of equipment is a
dangerous operation. Countless things can go wrong if the lift is not planned and
executed properly. An acid plant stack is often the first major piece of equipment
to be erected since this provide better access for the large cranes required.
A stack lift is not a heavy lift but its length does make it an event to be
watched.
In this case three cranes are used to perform
the lift. One crane is use at the base of the stack to lift and guide the bottom.
Two cranes are used at the top of the stack the perform the lift.
A frame work is used in the inside of the stack to attach the liftng cables.
This ensure that the top of the stack is not damaged during the lift.
Generally, as much of the platforms and ladders are attched
to the stack while it is still on the ground since it is easier and safer to perform the
work on the ground than after the stack is erected.
The stack must be design properly so the no
damage to the stack occurs when it is first lifted. Normally, a stack is subjected
to wind loads, earthquake loads, etc. When a stack is first lifted from the
horizontal position there is a risk that the stack will buckle in the middle. The
walls of the stack must be thick enough to prevent this buckling. Reinforcing rings
are also utilized to ensue that the stack does not buckle.
As the stack comes to the vertical position the
crane at the bottom must guide the base of the stack to its foundation.
During this lift workers were stationed at the
top of the stack. This is not normal practice and posses a risk to the workers.
Eventually workers will be required at the top of the stack to release the lifting
cable and remove the lifting frame.
The stack is finally lifted in the vertical
position and is guided on to the foundation. The cranes will remain attached to the stack
until the base of the stack is secured to the foundation.