Question

A process has five streams, two that need to be heated and three that need to be cooled, as described in the table.

Attempt to graph the hot and cold stream composite temperature-enthalphy curves.

Stream	Supply Temperature (°C)	Target Temperature (°C)	Heat Capacity Flow Rate (kW/°C)	Heat Load (kW)
Cold 1	30	200	4	-680
Cold 2	50	250	2	-400
Hot 1	200	50	3	450
Hot 2	240	100	1.5	210
Hot 3	120	119	300	300

Answer 1

The above images are composite curves, Consider low temperature process, First assume DT_min for calculation purposes, it is best to take values from 3-5 ⁰C , if higher value of  DT_min is choosen heat recovery decreases and heat and cold utilities increases, that is capital and energy cost increases but less area of heat exchanger is needed.

Temperature enthalphy graphs are called composite curves.

Heat availibility in the process is called hot utility curve

Heat demand in the process is called cold utility curve