Chemical Engineering April 2012 - 61

DESIGNING FOR SAFETY, MATERIALS
MANAGEMENT AND COST SAVINGS
Simulation software can aid in a number of tasks including the following:
* Tune production planning to optimize raw material costs, inventories, usage rates and
projected sales
* Simulate the usage of a chemical to maximize worker safety and minimize inventory
costs
* Project scenarios for changes in costs of materials and labor, usage rates, material
transport and vessel transfer
intermediate materials, that must
be formulated, produced and stored
ahead of time. Keeping track of these
intermediate materials can be complex.
One key ingredient in paint is
a grind of solids that must be held in
suspension before completing the formulation.
Selection of the equipment
to produce the intermediate - starting
with a cleaned system to avoid
inter-batch contamination, proper
emulsion preparation, and cleaning of
the equipment prior to the next intermediate
- can all be improved with
the use of material-flow simulation.
As a rule, simulation can help a processor
minimize the amount of work
involved with controlling inventories
and the flow of materials. This keeps
complex material flows from overwhelming
the process and causing errors.
It also ensures that the plant will
not produce products that have no orders
or even prospects of orders. Also,
work-process minimization makes it
possible for the plant to operate on an
efficient just-in-time basis. Ultimately,
the goal is to complete a product formulation,
transfer it into a shipping
container, and then send it on its way,
leaving as little finished product in inventory
as possible.
Simulation software can map out a
number of scenarios to streamline inventory
control and material costs. It
can accept inputs for product orders,
raw material inventories, in-process
mix, and the timing required to formulate
and return intermediate materials.
In all, simulation software helps
to set up a work and material flow
that makes sense.
Managing raw material costs
Simulation can also be used to tune
production planning to optimize raw
material costs, inventories, usage
rates and projected sales - all with
the goal of ensuring that neither raw
materials nor finished products sit in
inventory longer than necessary.
To consider raw material costs, it
is important for the engineer to understand
usage rates. While volume
pricing is an important means to control
costs, another consideration is
how much material will be used and
stored. That's because the inventory
cost of stored material can offset any
savings from volume purchasing.
Consider, for example, the way auto
assembly plants use and inventory
brake fluid. A hydroscopic material
cannot be inventoried and stored in
the same way as other chemical ingredients
can. Some manufacturers bring
the material in 250-gal totes, which
cost a couple cents more per gallon
than 55-gal drums. On the other hand,
material in 55-gal drums is difficult to
protect from the air during use. Still
other manufacturers prefer bulk storage
tanks that hold thousands of gallons
of brake fluid, for two reasons.
First, it is the easiest way to limit
contact with air even though it raises
inventory costs. Second, it can make
sense as a strategy for materials that
are difficult to resupply.
A material's total supply cost,
however, includes not just the material's
purchase price and capital cost
to store and supply onsite, but also
non-valued-added costs. Relocation of
drums or totes from delivery point to
storage location to usage point may be
small compared to capital costs for a
bulk system during the first year of
operation. However, the return-on-investment
curves may cross at a point
in the future. This may be surprising
if an accurate evaluation of all factors
- raw material supply (including
materials not received by drum or
tote, such as in pails or by bulk tanker
trucks), return shipping costs, disposal
costs and so on - is available.
Designing for safety
Chemical processes often employ or
create hazardous materials during
processing. Engineers must take both
worker and community safety into
account when designing a CPI plant.
Safety considerations often mirror
material-cost-management considerations.
For example, sulfuric acid is
both extremely corrosive and hydroscopic.
Safety, as well as prudent cost
management, suggests avoiding 55-gal
drums to minimize chemical handling
and to eliminate the disposal costs of
used drums. An alternative is to use
250-gal totes, which cost more to buy
and also create inventory costs, along
with a tote-return cost to the supplier.
Bulk deliveries become a third option
to consider, with employee safety considerations
and reduced material costs
offset by increased capital investment
and material inventory costs.
Small versus large quantities isn't
necessarily the issue. Depending upon
utilization, examination of bulk storage
requirements is needed. Bulk
storage could be utilized regardless of
whether it's for frequent, infrequent
or quantity-usage limits. The goal is to
reduce chemical handling, especially
for chemicals that are hazardous.
Drum use requires a dedicated
drum-storage area. Someone needs to
go get the drum, transport it to where
it will be used, open it and then use a
siphon tube or drum pump to extract
the material. Drum use makes material
handling more frequent and increases
the potential for worker exposure
(more risk). Tote use means less
handling; and piping directly from the
tote minimizes exposure risk as only
attaching and detaching the pipe is
needed. Where chemicals are hazardous
due to instability, however, smaller
containers may be the best option to
reduce quantities onsite.
Simulation software analyzes costs
of materials and transport, cleaning of
drums and disposal. Use of a drum or
tote may initially be more cost-effective,
but if production rates increase, a
bulk storage system may pay for itself.
Total cost includes costs of materials,
usage rates and labor.
There is risk with all methods of
chemical retrieval and transfer - from
point of delivery to end point of application
in the process. Simulation helps
evaluate risk factors for all methods of
delivery, storage and retrieval in conjunction
with cost. The goal is to simulate
to find out which storage option is
the most safe and least costly for the
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