I have never experienced the described issue personally but I do use a lot of oxygen absorbers in our products and silica beads in some machinery.
Oxygen absorbers are just little packets full of silica beads that absorb and retain moisture over time, they do have a max of how much moisture they will absorb however. Forgive me I am in the US and don't use the metric system all that often. 9 kg is roughly 20 lbs, we have vacuum sealed packaging that goes up to 40 lbs (18.14 kg) of product. We use an oxygen absorb pad that is about 2" x 3", so not all that big and they work just fine for us. I wouldn't over think it, just find the size you think will fit your needs and you will be fine. They aren't all that expensive so running a batch as a trial wont hurt that much and you can find them all over online. Just make sure to get food grade rated ones.
Hope that helped,