Chemical Engineering October 2016 - 60

age finished chemical products or
their feedstocks as the ever-present
threat of a catastrophic spill hangs
precariously over their heads. The
complexity of chemicals processing
facilities (Figure 1) demands excellence
with regard to safety and security.
Because of the many transfer
points in the manufacturing and
handling supply chains in the chemical
process industries (CPI), operators
must constantly ensure that
their liquid-transfer equipment and
loading systems are of the highest
quality and reliability.
This includes the loading arms,
hoses and disconnects that are
used to transfer chemical products
and feedstocks from, for example,
barges, railcars, transport vehicles
and pipelines to storage tanks, and
from production lines to bottling,
packaging and tote-filling operations.
This article details the operation
of various types of dry-disconnect
couplers, and illustrates how
selecting the proper style of coupler
can help increase safety, optimize
flowrates and prevent the types
of costly and dangerous chemical
spills or accidents that the NRC
so fervently monitors.
Know what is needed
In general, designing and constructing
a loading system for chemicals
is a complex process. Many different
variables must be accounted
for, and no two systems are ever
exactly alike. For example, will finished
products or raw feedstocks
be loaded onto or unloaded from
railcars, barges, pipelines or tanker
trucks? Will the loading and unloading
take place from bottom outlet
valves on the transport vehicles, or
will they be top-loading operations,
which will require the use of loading
arms and support structures? All of
these questions are critical considerations
and their answers will help
determine which specific loadingsystem
components will be required.
This also means that the engineers
who fashion these systems and their
individual components must work
closely with users to create systems
that meet unique needs, while also
building units that deliver reliability
and safety. Before a loading system
POPPET-STYLE VERSUS BALL-VALVE DRY
DISCONNECT COUPLERS
The differing operational mechanisms of poppet and ball-valve dry-disconnect couplers are
described in the sections below.
Poppet Style Design
When utilizing poppet-style disconnects, liquid transfer is initiated when the poppets are
opened by the operator (Step 1). The liquid transfer is completed when the operator closes
the poppets (Step 2). However, at this time, a small amount of liquid can be trapped, and
during disconnection, it is possible that the trapped liquid can escape, leading to a minor
product spill (Step 3).
Ball-Valve Style Design
The operation of double ball-valve dry disconnects allows a convex ball to seat with a concave
ball when the valve is opened (Step 1). This straight-through design allows the liquid
to transfer through the adaptor and coupling with no reduction in flowrate (Step 2). Upon
disconnection there are no cavities created in which product can nest, meaning no product
will be spilled. This no-spill operation is accomplished through the use of five independent
and redundant mechanical interlocks that require deliberate sequential action by users,
thereby eliminating unintentional spills and catastrophic chemical releases.
is ever installed and the first ounce
of chemical transferred, the following
are some of the most important
operational considerations that must
be taken into account:
* Is it a top-, bottom- or sideloading
application? Knowing the
configuration will help determine
the overall design of the system
* What are the ambient weather
conditions where the system will
be used, and will the equipment
encounter extremely cold or hot
temperatures? Environmental
conditions must always be taken
into consideration when working
with chemicals that possess
unique traits
* Do the products being handled
produce extreme temperatures
that must be accounted for? If
so, proper metals and elastomers
for these temperature conditions
must be used
* What type of products will the
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
OCTOBER 2016
loading system be used for?
Temperature, corrosiveness and
viscosity are just some of the
considerations here
* Will any type of cleaning or purging
procedure be employed?
* What materials of construction
(metals, elastomers and so on)
are most compatible with the
products to be handled? Materials
that are not compatible with
products to be handled are more
susceptible to failures that can
lead to catastrophic spill incidents
* How long must the loading arms
be? The precise dimensions
of the loading system must be
known and the system designed
to exactly meet those parameters
* Will railcars or trucks need to be
spotted from various distances,
requiring more flexibility?
* What level of product flowrates
will be required? Loading and unloading
times must be optimized,
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Chemical Engineering October 2016

Table of Contents for the Digital Edition of Chemical Engineering October 2016