Page 31 - Plant design and economics for chemical engineers

14 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

reactors have been used for each reaction. Then radically new and simplified
reactors were developed based on a better understanding of the chemical and
physical steps involved.

DESIGN-PROJECT PROCEDURE

The development of a design project always starts with an initial idea or plan.
This initial idea must be stated as clearly and concisely as possible in order to
define the scope of the project. General specifications and pertinent laboratory
or chemical engineering data should be presented along with the initial idea.

Types of Designs
The methods for carrying out a design project may be divided into the following
classifications, depending on the accuracy and detail required:

1. Preliminary or quick-estimate designs
2. Detailed-estimate designs
3. Firm process designs or detailed designs

Preliminary designs are ordinarily used as a basis for determining whether
further work should be done on the proposed process. The design is based on
approximate process methods, and rough cost estimates are prepared. Few
details are included, and the time spent on calculations is kept at a minimum.
If the results of the preliminary design show that further work is justified,
a detailed-estimate design may be developed. In this type of design, the cost-
and-profit potential of an established process is determined by detailed analyses
and calculations. However, exact specifications are not given for the equipment,
and drafting-room work is minimized.
When the detailed-estimate design indicates that the proposed project
should be a commercial success, the final step before developing construction
plans for the plant is the preparation of a firm process design. Complete
specifications are presented for all components of the plant, and accurate costs
based on quoted prices are obtained. The firm process design includes blueprints
and sufficient information to permit immediate development of the final plans
for constructing the plant.

Feasibility Survey
Before any detailed work is done on the design, the technical and economic
factors of the proposed process should be examined. The various reactions and
physical processes involved must be considered, along with the existing and
potential market conditions for the particular product. A preliminary survey of
this type gives an indication of the probable success of’the project and also