HETP in absorbers depends on many factors, such as packing type, liquid viscosity, absorption factor, et cetera,
Different packings give different interfacial areas (m2/m3) and liquid viscosity depends on temperature, amine type and amine concentration.
20 - 30 years ago, when I was often involved in the design of HDS and HCU which usually included an amine absorber, I remember that we used HETP = 3 m (three meters) for DEA or MDEA over 2 inch random packing (2" Pall rings or IMTP50).
This is just to give you a rough idea. For different amine and different packing type & area one would need to adjust that HETP.
You best contact the vendor of your particular packing for a more exact HETP number based on present knowhow.