Page 71 - Design of Simple and Robust Process Plants

3.3 Design Philosophies 55
Summary
. JIP is a concept to minimize storage, and is based on quality production and
supply chain optimization.
. JIP aims to minimize the stored products to base components, and supply
additives during loading or at the customer's location.
. Design of storage capacity at the plants and at the customer's location is
based on processing reliability, transportation frequency cargo size and relia-
bility, and customer delivery requirements.
. The methodology is available for the optimization of design and operation
based on Monte Carlo simulations.

3.3.10
Design for Total Quality Control (TQC)

3.3.10.1 Prevent versus cure
The concept of JIP can only be applied if we are able consistently to produce at speci-
fication.

Elimination of check and lot tanks Prevent versus cure, which is part of TQC,
makes it attractive to eliminate corrective provisions such as the check tanks and lot
tanks in plants. These tanks are installed in plant recycle systems to cope with off-
specification products.
In the past, most batch plants were unable to produce consistent batches, and
therefore more batches were produced and the whole was blended in a so called lot
tank The solution for this is to use feed forward control (in general to be double-
checked with separate measurements) with a feedback adjustment in the process.
The disturbances (whether internal or external) should be incorporated in the feed
forward controllers to achieve TQC (see Figure 1.3 in Chapter 1). It should not be
underestimated that operational errors are also often a cause for off-specification
situations, and these must be covered by the application of automation.

Prevent upsets Many provisions are installed in plants to cope with unplanned
situations. The release of a component to the environment is mostly covered with
add-on provisions such as scrubbers, incinerators, flares, emergency tanks, etc.
However, all of these provisions are expensive, and the best way to handle the situa-
tion is to modify the design into a preventive action, triggered by a question such as:

what provision is needed to prevent an upset?

A higher design pressure of a vessel in order to prevent release, or release through a
safety device into another process vessel, are often cheap solutions. The following is
a typical example (Figure 3.5). The safety provisions on an ammonia storage facility
asked for a very large scrubber with water, and the recovery of unlikely, but poten-
tially diluted, solution. Removal of the safety device was accomplished by preventing
upsets. In this particular situation, a potential fire was the limiting case. Elimination