Page 287 - Chemical engineering design

262
CHEMICAL ENGINEERING
Miscellaneous materials (plant supplies)
Under this heading are included all the miscellaneous materials required to operate the
plant that are not covered under the headings raw materials or maintenance materials.
Miscellaneous materials will include:
1. Safety clothing: hard hats, safety glasses etc.
2. Instrument charts and accessories
3. Pipe gaskets
4. Cleaning materials
An accurate estimate can be made by detailing and costing all the items needed, based
on experience with similar plants. As a rough guide the cost of miscellaneous materials
can be taken as 10 per cent of the total maintenance cost.

Utilities (services)

This term includes, power, steam, compressed air, cooling and process water, and effluent
treatment; unless costed separately. The quantities required can be obtained from the
energy balances and the flow-sheets. The prices should be taken from Company records,
if available. They will depend on the primary energy sources and the plant location. The
figures given in Table 6.5 can be used to make preliminary estimates. The current cost
of utilities supplied by the utility companies: electricity, gas and water, can be obtained
from their local area offices.

Shipping and packaging
This cost will depend on the nature of the product. For liquids collected at the site in
the customer’s own tankers the cost to the product would be small; whereas the cost of
packaging and transporting synthetic fibres or polymers to a central distribution warehouse
would add significantly to the product cost.

Maintenance
This item will include the cost of maintenance labour, which can be as high as the
operating labour cost, and the materials (including equipment spares) needed for the
maintenance of the plant. The annual maintenance costs for chemical plants are high,
typically 5 to 15 per cent of the installed capital costs. They should be estimated from
a knowledge of the maintenance costs on similar plant. As a first estimate the annual
maintenance cost can be taken as 10 per cent of the fixed capital cost; the cost can be
considered to be divided evenly between labour and materials.

Operating labour
This is the manpower needed to operate the plant: that directly involved with running the
process.
The costs should be calculated from an estimate of the number of shift and day personnel
needed, based on experience with similar processes. It should be remembered that to
operate three shifts per day, at least five shift crews will be needed. The figures used for