Page 164 - Chemical process engineering design and economics

Process Heat Transfer

Heat transfer is a frequently occurring process operation. Within a process
two general types of heat exchange occur. One type is the exchange of heat be-
tween two process streams. The heat exchanger where this occurs is frequently
called an interchanger. In the second type, heat exchange occurs between the
process and the surroundings, which requires a heat-transfer fluid. Water is the
most common fluid. If the temperature is sufficiently high, then it may be eco-
nomical to recover work from a process stream by generating high pressure steam
and then expanding the steam through a turbine. This occurs in processes for syn-
thesizing methanol where superheated steam is generated when cooling the re-
former exit stream.
After the process analysis is completed, the heat-exchange requirements of
the process will be specified. The next step is to calculate the heat-exchanger sur-
face area which will allow you to calculate its installed cost. The cost calculation
proceeds according to the following steps:

1. select a heat-transfer fluid
2. evaluate and select a heat-exchanger type
3. locate the shell-side and tube-side fluids
4. specify the terminal temperatures of the fluid streams
5. determine the overall heat-transfer coefficient
6. calculate the heat-exchanger surface area
7. estimate the total installed cost

To calculate the heat-transfer surface area requires a calculation procedure.
The approach used here will be to use a simple procedure. A detailed procedure
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