a plant produces any 2 of 3 products (make1, make2, make3). Plant knows
how much to produce over a period of time of each product. normally
product 1 is set to zero. product 2 can be stored in any of three tanks
(tank1, tank2, tank3). product 3 can only be stored in tank4. Tanks
have minimum volumes known as heels and maximum volumes. Liftings of
products (2 & 3) need to be scheduled to maintain steady production
without "runout" of room. Liftings have maximum volume/lifting. Lifting
frequency should be minimized to save cost.

If production is known say for three weeks ahead, how best to estimate
when and how much to lift? how to rotate filling of tanks1,2, & 3 with
product 2?

solver is one approach.

counting number of lifts 0 with =COUNTIF(J9:J29,"0") , and using
solver to minimize this cell still produces 21 daily lifts. How would
you get solver to produce lifts every 3-4 days or so as tanks working
capacity offer 4+ days of production before "runout" of room.

cheers,
deano