Dear Mondolfi,
I'm not a Hysys user. I've used Aspen and other programs for amine simulations before. Here's an idea....have you checked whether you specified the H2S and your other gas components as a Henry's component? This is something I've encountered in Aspen that makes a difference in...
It is not typical to have a spare heat exchanger. Nor is it typical to have plugging this frequently.
What is causing the plugging of the exchanger? Iron Sulfide? Iron Carbonate?
You may want to track down the source. Your amine vendor may be able to give you some assistance.