Hydrocarbon Processing - April 2021 - 71

Water Management
izing technology is in one of TOTAL's European refineries,
where the crude unit contains both a desalter followed directly by a furnace and then a main fractionator (MF). The neutralizer was injected into the MF overhead to control BW pH.
As shown in FIG. 4, amine recirculation primarily takes place in
two different circuits of the crude unit. These include:
1. In the overhead naphtha reflux
2. With overhead water used as wash water
to the desalter and around the desalter.
However, it is important to note that in some refineries,
there can be several other significant recirculation routes impacting the prevailing steady-state overhead concentrations,
which will not be discussed here.
Using the new method for amine speciation, amines from
the program were examined in several streams around the
crude unit to determine their respective concentrations in the
overhead system, as compared to the injected quantity.
Samples were analyzed by TOTAL and the service provider from the following streams:
* Water samples
° BW
° Desalter wash water (WW)
° Desalter brine (DB)
* Hydrocarbon samples
° Reflux naphtha (RN).
In addition, amines were calculated for the following streams:
* Crude oil: Calculated by difference (CO = WW - DB)
* Injected neutralizer (IN): Based on injection rate
and amine concentration in product.
TOTAL and the service provider agreed to perform a comprehensive set of analysis on a frequent and regular basis to
continuously assess the prevailing amine concentration ratio
and associated salt points in the overhead because pH dependence and other complex factors can often cause the values to
be very dynamical. One example of results-shown in grams
of amine-is presented in FIG. 5.
If there were no amine recycle, then the BW analysis would
match calculated amines from the IN. However, the measured
level of BW amines is 40% higher than that of the IN amines.
This demonstrates that there is significant amine recycle;
therefore, calculations for salt point temperatures based on
injected amine quantity will result in salt point temperatures
that are lower than actual. When controlling tower operations
to maintain a certain safety factor surrounding salt deposition, the difference between amine-partial pressures assumed
to be derived from amine " as injected " and the partial pressures computed based on actual measured circulating amine
can result in unexpected issues with salt-induced corrosion
and fouling. The additional streams shown in FIG. 5 were then
examined to determine the source of the amine recycle and
close the mass balance. No amine was detected in the RN, as
expected, due to a pH of around 6 in the BW. To restate, the
amines in the DB were subtracted from those contained in the
desalter WW to calculate the amines in the crude oil. As the
desalter operates at a pH of about 8, as directionally expected
from FIG. 1, the data treatment indicated that more than 50% of
total amines were entrained with desalted crude oil.
The quantity of amines entrained in the desalted crude oil,
combined with those injected into the overhead system IN,

agrees with the amount analyzed in the BW, with a 2% difference, which is quite good.
To better illustrate the typical propagated error expected
between these two methods, salt points are compared. These
were obtained first by once-through mass balance calculations
based on amine injection rate (IN) and then by computing
them using the measured BW concentrations.
As shown in FIG. 6, the difference in computed salt points
for the two methods is 3.6°C, which is significant. This difference would be especially important regarding the mitigation of
corrosion in cases where the salt point and the water dewpoint
are close to one another. In such cases, the evaluation of amine
recycle factors would be necessary to accurately evaluate system
salt points. The overall concentration ratio factor for amines in
this overhead system (BW/IN) was shown to be 1.4 in FIG. 5.
This exercise was conducted on a regular basis and confirmed over time that the BW/IN ratio varied between 1.1
and 1.4, mainly as a function of desalter pH and unit operService provider
amine-neutralizing technologyb

1
2
2
Desalter

Main
fractionator
From
other
units
Sour water

FIG. 4. Amine recycle paths.
IN
318 g
Service provider
amine-neutralizing technologyb
Amine mass balance
BW/IN = 140%
-does not balance
BW/(IN + RN + CO) = 102% -balances
*Note: CO = WW - DB

Naphtha (RN)
0g

BW
443 g

Crude oil (CO)
117 g
Desalter

Main
fractionator
Brine (DB)
84 g

WW
203 g

Sour water
stripper

From
other
units

FIG. 5. Analytical results.
Hydrocarbon Processing | APRIL 2021

Hydrocarbon Processing - April 2021

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