That unit does not exist even in reality: there is no reason to mix several stream at different temperature (i.e., getting a quenching effect) and then vaporise. You should feed at stage 20. I suggest checking the temperature at which MeOH, AA, and recycle are fed. If this temperature it is far lower than the reboiler temperature, there is no reason to put into the boiler, it is better to flash it in stage 20 and then heat up only the residue liquid fraction.

Beyond this comment, you can handle this in Aspen Plus. You should implement a RadFrac without reboiler. The reboiler will be an external reboiler. The feed will be the resulting stream from the mixing of the stream you need to collect, including the liquid from the bottom of the RadFrac. You need to set that the vapour fraction (alpha) is one at the outlet of the heat exchanger. Please, pay attention and check always that Aspen properly calculated the outlet temperature (dew point) and that the stream leaving the heat exchanger is only vapour since you don't want a residue liquid. I hope that there is a "purge" somewhere and not reported in the picture otherwise you get accumulations in the system due to the recycle.