CENG 403 - Equipment Design

We will show one way to use heat exchangers that actually achieve the minimum utility usage for the 4SP1 problem shown in the last section of these notes. First let's recap what we know from the use of composite temperature-enthalpy curves for the desired minimum temperature difference of 10°C:

1. There is a pinch at 249°C
2. 127.68 kW must be added to cold stream C2 with an exchanger using hot utilities. That stream will be heated from 239 to 260°C.
3. 250.1 kW must be removed from the hot streams.

Here is a diagram showing changes in the temperatures of the streams and one possible arrangement of heat exchangers.

The text boxes for the three exchangers used to recover heat from the hot streams are numbered 1 to 3 and show the amount of heat that would be exchanged in each. The follwoing table gives information about each of the three exchangers:

Heat Exchanger	Hot	Streams	Cold	Streams	Heat Transferred
	T in °C	T out °C	T in °C	Tout °C	kW
1	249	178.1	116	239	747.8
2	178.1	161.7	137.3	160	173.1
3	160	93	60	137.3	588.9

It can be seen that all three exchangers are feasible and meet the conditions that require the minimum temperature difference to be 10°C.