Page 24 - Coulson Richardson's Chemical Engineering Vol.6 Chemical Engineering Design 4th Edition

INTRODUCTION TO DESIGN
water, compressed air, steam. Facilities will also be needed for maintenance, firefighting,
offices and other accommodation, and laboratories; see Chapter 14. 7
1.3.1. Continuous and batch processes
Continuous processes are designed to operate 24 hours a day, 7 days a week, throughout
the year. Some down time will be allowed for maintenance and, for some processes,
catalyst regeneration. The plant attainment; that is, the percentage of the available hours
in a year that the plant operates, will usually be 90 to 95%.
hours operated
Attainment % D ð 100
8760
Batch processes are designed to operate intermittently. Some, or all, the process units
being frequently shut down and started up.
Continuous processes will usually be more economical for large scale production. Batch
processes are used where some flexibility is wanted in production rate or product speci-
fication.
Choice of continuous versus batch production

The choice between batch or continuous operation will not be clear cut, but the following
rules can be used as a guide.

Continuous

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1. Production rate greater than 5 ð 10 kg/h
2. Single product
3. No severe fouling
4. Good catalyst life
5. Proven processes design
6. Established market

Batch

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1. Production rate less than 5 ð 10 kg/h
2. A range of products or product specifications
3. Severe fouling
4. Short catalyst life
5. New product
6. Uncertain design

1.4. THE ORGANISATION OF A CHEMICAL ENGINEERING
PROJECT
The design work required in the engineering of a chemical manufacturing process can be
divided into two broad phases.
Phase 1. Process design, which covers the steps from the initial selection of the process
to be used, through to the issuing of the process flow-sheets; and includes the selection,