CHAPTER 4

Understanding Process Conditions

Don Scott

ENCH 430

1/24/06

The ability to make an economic analysis of a chemical process

based on a PFD is not proof that the process will actually work.

It is usually easier to adjust temperature and/or pressure than

it is to change composition.

HOWEVER

A decision to operate outside the pressure range of 1 to 10 bar

must be justified

$$$$$$$$$$$$

A decision to operate above 400º C must be justified

Microstructure of steel pipe after 28 years service at 773K,

shows several creep pores (dark) and carbides(white).

A decision to operate outside the range of 40°C to 260°C, thus

requiring special heating/cooling media, must be justified.

$$$$$$$$$$$$

$$$$$$$$$$$$

Conditions outside the favored temperature and pressure ranges

are identified as “conditions of special concern.”

Items for justification

• Favorable equilibrium conversion

• Increase reaction rates

• Maintain a gas phase

• Improve selectivity

Also, consider tables 4.1,2,3 on pages 120-122

Changes in process conditionsfor a stream passing through a

single piece of equipment

• Table 4.4 on page 124

• Table 4.5 on page 128 process conditions matrix.