Chlor-Alkali sulfuric Acid re-concentration

I am the Operations Manager for a CHlor-Alkali company. Our process requires the use of concentrated sulfuric acid (98%) for the drying of the chlorine gas prior to liquification. During this process the concentration drops to approximately 85% at which time the chlorinated acid cannot be used further.

I am looking for a way of re-concentrating the acid to approximately 90% and forming a closed system.

Reconcentrating of dilute sulfuric acid to 98% is not considered worthwhile and hence not done in majority of plants.

Concentrating from 85% to 90% or above is possible but expensive. A simple way is to mix with Oleum and bring up the concentration. This would result in the increase of total acid quantity. Some acid could be disposed off as 98% acid. This wold be a simpler method than to concentrate the acid.

I did concentrated sulfuric acid but by a foolish way of my own which seemed to be working

I placed the dilute acid in a beaker [beakers on eBay or Amazon [affil link] and placed the beaker in another larger one which was filled with water at a constant level and heated

the outer water reaches 100C and also the inner acid
so water evaporates from the acid while the acid is with a boiling point of 180

pretty foolish way but it seemed to be working in an inverse logarithmic speed.