Page 11 - Applied Process Design For Chemical And Petrochemical Plants Volume III

66131_Ludwig_CH10A 5/30/2001 4:06 PM Page 1

Chapter

10

Heat Transfer

Heat transfer is perhaps the most important, as well as the this text is to provide the designer with a basis for manually
most applied process, in chemical and petrochemical plants. checking the expected equations, coefficients, etc., which
Economics of plant operation often are controlled by the will enable the designer to accept the computer results. In
effectiveness of the use and recovery of heat or cold (refriger- addition, the text provides a basis for completely designing
ation). The service functions of steam, power, refrigeration the process heat transfer equipment (except specialized
supply, and the like are dictated by how these services or utili- items such as fired heaters, steam boiler/generators, cryo-
ties are used within the process to produce an efficient con- genic equipment, and some other process requirements)
version and recovery of heat. and sizing (for mechanical dimensions/details, but not for
Although many good references (5, 22, 36, 37, 40, 61, 70, pressure strength) the mechanical hardware that will accom-
74, 82) are available, and the technical literature is well repre- plish this function.
sented by important details of good heat transfer design prin-
ciples and good approaches to equipment design, an Types of Heat Transfer Equipment Terminology
unknown factor that enters into every design still remains. This
factor is the scale or fouling from the fluids being processed The process engineer needs to understand the terminol-
and is wholly dependent on the fluids, their temperature and ogy of the heat transfer equipment manufacturers in order
velocity, and to a certain extent the nature of the heat transfer to properly design, specify, evaluate bids, and check draw-
tube surface and its chemical composition. Due to the ings for this equipment.
unknown nature of the assumptions, these fouling factors can The standards of the Tubular Exchanger Manufacturers
markedly affect the design of heat transfer equipment. Keep Association (TEMA) 107 is the only assembly of unfired
this in mind as this chapter develops. Conventional practice is mechanical standards including selected design details and
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presented here; however, Kern has proposed new thermal Recommended Good Practice and is used by all reputable
concepts that may offer new approaches. exchanger manufacturers in the U.S. and many manufac-
Before presenting design details, we will review a sum- turers in foreign countries who bid on supplying U.S. plant
mary of the usual equipment found in process plants. equipment. These standards are developed, assembled, and
The design of the heat transfer process and the associated updated by a technical committee of association members.
design of the appropriate hardware is now almost always The standards are updated and reissued every 10 years.
being performed by computer programs specifically devel- These standards do not designate or recommend thermal
oped for particular types of heat transfer. This text does not design methods or practices for specific process applications
attempt to develop computer programs, although a few but do outline basic heat transfer fundamentals and list sug-
examples are illustrated for specific applications. The impor- gested fouling factors for a wide variety of fluid or process
tant reason behind this approach is that unless the design services.
engineer working with the process has a “feel” for the The three classes of mechanical standards in TEMA are
expected results from a computer program or can assess Classes R, C, and B representing varying degrees of mechan-
whether the results calculated are proper, adequate, or “in ical details for the designated process plant applications’
the right ball park,” a plant design may result in improperly severity. The code designations [TEMA 1988 Ed] for
selected equipment sizing. Unless the user-designer has some mechanical design and fabrication are:
knowledge of what a specific computer program can accomplish, on
what specific heat transfer equations and concepts the program is RCB—Includes all classes of construction/design and
based, or which of these concepts have been incorporated into the pro- are identical; shell diameter (inside) not exceeding 60 in.,
gram, the user-designer can be “flying blind” regarding the results, and maximum design pressure of 3,000 psi.
not knowing whether they are proper for the particular con- R—Designates severe requirements of petroleum and
ditions required. Therefore, one of the intended values of other related processing applications.

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