In a previous life I etched innerlayer cores with cupric chloride.
We had a Chemcut regenerator which used a venturi to suck in the
replenishment components.

We used 50% hydrogen peroxide as the oxidizer.  Peroxide is safer
than chlorine in that it is not a pressurized gas which can kill people
if a pipe cracks.  The liquid does require special handling.  On one
occasion we had an operator attempt to use an empty peroxide barrel
to store spent etch in.  The barrel had enough peroxide left in the bottom
of it to blow the bottom out ot the drum and take off like a rocket.  For
years there was a big dent in the ductwork overhead as a reminder.
After the plant got going we had peroxide delivered in bulk and used
stainless steel distribution piping.  The day-tank in the process center
had redundant level controls to prevent spills.

Using peroxide has it's downside.  Even at 50% strength it is half water.
This effectively dilutes your etchant and limits the amount of copper you
can maintain in solution.  This hurts economy slightly and also will reduce
your etch factor slightly.

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