Page 30 - Plant design and economics for chemical engineers

CHAPTER
2

PROCESS
DESIGN

DEVELOPMENT

A principle responsibility of the chemical engineer is the design, construction,
and operation of chemical plants. In this responsibility, the engineer must
continuously search for additional information to assist in these functions. Such
information is available from numerous sources, including recent publications,
operation of existing process plants, and laboratory and pilot-plant data. This
collection and analysis of all pertinent information is of such importance that
chemical engineers are often members, consultants, or advisors of even the
basic research team which is developing a new process or improving and revising
an existing one. In this capacity, the chemical engineer can frequently advise the
research group on how to provide considerable amounts of valuable design data.
Subjective decisions are and must be made many times during the design
of any process. What are the best methods of securing sufficient and usable
data? What is sufficient and what is reliable? Can better correlations of the data
be devised, particularly ones that permit more valid extrapolation?
The chemical engineer should always be willing to consider completely
new designs. An attempt to understand the controlling factors of the process,
whether chemical or physical, helps to suggest new or improved techniques. For
example, consider the commercial processes of aromatic nitration and alkylation
of isobutane with olefins to produce high-octane gasolines. Both reactions
involve two immiscible liquid phases and the mass-transfer steps are essentially
rate controlling. Nitro-aromatics are often produced in high yields (up to 99
percent); however, the alkylation of isobutane involves nume;ous side reactions
and highly complex chemistry that is less well understood. Several types of * -

1 3