Hydrocarbon Processing - April 2021 - 72

Water Management
ating conditions. It also confirmed that the neutralizer is always present in the atmospheric tower through desalter recycling. Defining a standard recycle ratio (BW/IN) is needed
to properly and practically evaluate daily salt points based on
the amine injection rate. This is especially important because
the amine speciation methodology requires time to obtain
results subsequently used to perform the amine balance. To
have enough safety margin, TOTAL and the service provider
agreed to use an ongoing recycle ratio of 1.5 and calculate, on
a daily basis, the amine salt point based on both the injected
amount only and then a second salt point based on amine expected by including the recycle factor of 1.5.
Because of the recycle ratio factor and its impact on salt
point computation, it is important to choose the right neutralizing amine and to exploit its recycle behavior to ensure that
no salt fouling and associated corrosion occurs in the tower or
in the overhead condenser system.
A second benefit from the recycle factor is the global injection rate of the amine-neutralizing programs, which is very
often less than when using classical amines at a constant pH
target range; therefore, reducing treatment program costs,
while maintaining the benefits of better corrosion control and
system performance. In this case, when moving from a commodity amine to a neutralizing amine, the injection rate based
on the use of a lower neutralizer strength amine (FIG. 1) was
80

°C

66.4

+3.6°C

62.8
60

40
Based on injection

Based on analysis
Amine salt point

FIG. 6. Salt point temperatures.

Amine 2-Service provider technologyb

Amine 1

3
2
3
PF

Desalter

MF
3

From
other
units

2
Sour water stripper

FIG. 7. Recirculation of service provider amine in a PF column.

APRIL 2021 | HydrocarbonProcessing.com

proposed to be 20% higher. However, due to the recycling
advantage of the amine, the actual injection rate represents
about 80% of the previous injection rate, which confirmed
this program to be very cost effective.
Case 2: Crude unit with preflash (PF). After this first success, TOTAL and the service provider decided to apply the
same technology and approach in a more complex unit with
a PF column upstream from the furnace and the MF column.
The behavior of amines injected into the overhead of both
the PF and the MF is different than in the case previously
presented, with a more complex recycle scenario. Because of
the different configuration of the unit, it was decided to once
again implement a similar type of analytical plan to evaluate
the recycling effect and its consequences, with respect to computed salt deposition potentials before adopting the amineneutralizing program.
This was critical because overhead water acidity is a key
driver of amine selection. Light organic acids (e.g., acetic
acid) are more likely to condense in the overhead of a PF than
in the downstream fractionator overhead. This behavior can
then drive a higher neutralization demand. This is true even
in the absence of problematical chloride levels. Conversely,
chlorides are more likely to condense in the overhead of a MF
because hydrolyzing chlorides from mineral salts in crude oil
need the additional time and temperature provided by passage
through the crude furnace.
As represented in FIG. 7, when Amine 2 is injected into
the overhead of the MF, it can recycle with BW through the
desalter as wash water and route to the PF overhead system
rather than to the MF one where it was originally injected.
Similarly, Amine 1 injected into the overhead of the PF recycles through the PF overhead but does not end up in the MF
overhead. Unlike Case 1, this causes preferential cycle-up of
oil soluble amines in the PF but not generally in the MF. This
difference-caused by recycle loop behavior-should drive
program design with the goal to manage salt points in both
overheads simultaneously. To achieve these goals, granular
and frequent amine speciation with following salt point calculations are of prime importance.
By using an amine-neutralizing productb (Amine 2 in the
MF overhead FIG. 7), operators can manage salt points in the
MF overhead and it plays a role in PF overhead pH control
through recycling. Recycling reduces the required injection
rate of Amine 1 in the overhead of the PF (even possibly
down to 0 in certain operating cases). It also allows the use of
a classical primary amine because fewer condensed salts are
expected due to overall lower hydrochloric acid condensation.
This behavior depends on the bottom temperature of the PF
column and on the amine boiling point.
TOTAL and the service provider decided to adopt a similar analytical plan as used in Case 1 to evaluate the recycle of
amines for Case 2. The following streams were sampled with
the same type of analysis as before:
* Water samples
° MF BW
° PF BW
° Desalter WW
° Desalter effluent

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Hydrocarbon Processing - April 2021

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