Page 153 - Design of Simple and Robust Process Plants

138 Chapter 4 Process Synthesis and Design Optimization
The following elements are to be considered:

. The design of additive systems
. The option to buy or rent services
. The size and number of storage facilities (if any)
. The integration of the site (complex)

4.2.6.1 Additives
Additives are increasingly supplied in dedicated containers and prepared at the sup-
plier, and at the correct mix and concentration. These containers are also used as
feed vessels and exchanged as soon as they are empty, thus eliminating the loading
and unloading of chemicals, with all the associated safety and environmental risk. It
also avoids feed preparation, which often requires the handling and availability of
additional chemicals and metering facilities, all of which increases the risk of the
facility.

4.2.6.2 Buy or rent services
The supply of external process services is another approach taken. These external
services are not limited to power and water supply, but also might include other
utilities such as steam, cooling water, waste water treatment, refrigeration, industrial
gases, as well as ªdirectº raw material feed streams. These services can be bought
based on a long-term contract covering (next to cost) an availability/reliability con-
tract. Such a contract needs to be beneficial for both partners, and should be evalu-
ated carefully as it must represent an economical balance between cost spending by
the supplier and potential production losses by the consumer. Any over-investment
as a result of high guarantees is a loss which result in higher cost. Current reliability
engineering techniques are sufficiently accurate to quantify and optimize the invest-
ment in availability/reliability of supplies, see Chapter 6 and 7. The services can be
generated at site, and remotely monitored and operated by the supplier. The chemic-
al treatment of cooling water might also be contracted out to receive maximum
attention from an expert company. The benefits from contracting out these services
including equipment are that specialty companies can produce services more
cheaply and more reliably as they have multiple units running and can standardize
on robust designs.

4.2.6.3 Storage facilities
The point for discussion here is the direct supply of raw materials via pipelines ver-
sus the installation of storage facilities. Chemical plants are increasingly built in
clustered locations (complexes), and this facilitates the direct supply of material,
thus minimizing storage and transportation cost and reducing safety risks. When
direct supply is not practical, storage facilities must be designed for both raw materi-
als and products. The economic sizing of these facilities which include storage in
transport depends on: