I am working on heat pump assisted reactive distillation column. Trying to develop aspen plus model of vapor re-compression in reactive distillation column. the process includes three recycle streams ( one from separation column, one reflux stream and one reboil stream). I have used direct substitution method to converge the flowsheet. All blocks converge to desired results. But simulation ends with the error "solver block didn't converge in 100 iterations" and " solver block didn't converge normally in the final pass." increasing the no of iterations have no effect as depicted in convergence history chart. chart becomes linear. Not able to solve this error despite trying number of options. If anyone can help with this, it would be a great favor.