1 reply to this topic

[BenC]

Hi everyone,

My name is Ben and I'm a senior in chemical engineering. I'll start by giving you my question then all the details of my Aspen Plus simulation. The RadFrac unit I am using is failing to converge mass balances. I know that RadFrac unit specifications can violate mass balances but I can not figure out where/how my specifications are violating the mass balances around the column. Can any of you who are good with Aspen Plus take a look at my specifications and help me identify any problems?

I'm designing a chilled ammonia absorption system to capture CO2 from a 100 MW power plant that produces 0.93 tonnes CO2/MW-h. I'm trying to use Aspen Plus V7.0 to simulate the process with an ELECNRTL fluids package. I'm modeling the system with CO2 absorption occurring by the reaction: NH3 + CO2 + H2O ---> NH4HCO3

For specifications:
CO2 93 tonne/hr (2113 kmol/hr)
1 atm 10degC
Enters the bottom of the RadFrac unit

2200 kmol/hr NH3
3000 kmol/hr H2O
1 atm 5degC
Enters the top of the RadFrac unit

RadFrac: 10 stages; 1 atm on stage 1; No Condenser; No Reboiler; R-1 (NH3 + CO2 + H2O ---> NH4HCO3) with 90% conversion

The project specified that I only have to consider a stream of pure CO2 from the power plant (which pretty much makes the concept of design pointless but it is just a first pass feasibility study).

I have found a power point presentation from the Tsinghua University that is very similar to my project.

You can find it at:

Tsinghua University Presentation

I wish I could attach my aspen file for you but the forum wont let me. If you message me your email I could send it to you.

Thank you
Ben

Hey Ben,
just try to start te simulation in small steps, the streams are quite big, just start with very much smaller streams and the steady rise them.