Page 35 - Plant design and economics for chemical engineers

18 PLANT DESIGN AND ECONOMICS FOR CHEMICAL ENGINEERS

established within narrow limits before a detailed-estimate design is developed:

1. Manufacturing process
2. Material and energy balances
3. Temperature and pressure ranges
4. Raw-material and product specifications
5. Yields, reaction rates, and time cycles
6. Materials of construction
7. Utilities requirements
8. Plant site

When the preceding information is included in the design, the result
permits accurate estimation of required capital investment, manufacturing costs,
and potential profits. Consideration should be given to the types of buildings,
heating, ventilating, lighting, power, drainage, waste disposal, safety facilities,
instrumentation, etc.
Firm process designs (or detailed designs) can be prepared for purchasing
and construction from a detailed-estimate design. Detailed drawings are made
for the fabrication of special equipment, and specifications are prepared for
purchasing standard types of equipment and materials. A complete plant layout
is prepared, and blueprints and instructions for construction are developed.
Piping diagrams and other construction details are included. Specifications are
given for warehouses, laboratories, guard-houses, fencing, change houses, trans-
portation facilities, and similar items. The final firm process design must be
developed with the assistance of persons skilled in various engineering fields,
such as architectural, ventilating, electrical, and civil. Safety conditions and
environmental-impact factors must also always be taken into account.

Construction and Operation
When a definite decision to proceed with the construction of a plant is made,
there is usually an immediate demand for a quick plant startup. Timing,
therefore, is particularly important in plant construction. Long delays may be
encountered in the fabrication of major pieces of equipment, and deliveries
often lag far behind the date of ordering. These factors must be taken into
consideration when developing the final plans and may warrant the use of the
Project Evaluation and Review Technique (PERT) or the Critical Path Method
(CPM).? The chemical engineer should always work closely with construction
personnel during the final stages of construction and purchasing designs. In this
way, the design sequence can be arranged to make certain important factors

$For further discussion of these methods consult Chap. 11.