Modelling parallel trains

Yesterday I was working with a customer and we were trying to make one of his models more elegant. One of the bits that looked pretty ugly, I felt anyways, was the way the recombining of parallels trains was handled. This was a case with 3 parallel compression trains, each of them taking one third of the capacity. The way this was modelled is shown above.

Replacing the mixer, the 2 Balance blocks and the 4 SET operations by a single TEE operation makes for a much nicer PFD. You simply set the flow fractions of the two non-modelled trains to -1. The only negative here is that your "other train" streams are not nicely showing as though they are mixing to form the combined stream. Besides the visual advantage, this technique also has the advantage that if none of the trains carry any flow, the combined flow will calculate fine. If you use a mixer, the mixed flow will be OK, but the temperature will not be calculated.