Hydrocarbon Processing - April 2021 - GP-30

PROCESS TROUBLESHOOTING
igation strategy for a given process fouling
event. It also can be used to investigate other alternatives, such as liquid contaminant
or emulsion removal (often via coalescence) or chemical additive treatments. As
such, the HLPS test is an invaluable test for
fouling root-cause determination, as well
as mitigation strategy determination.

both aqueous and hydrocarbon, and the
produced foulant material can be subjected to further analysis to proactively determine the best feed contaminant removal
method for the process. Determination of
fouling tendency using the HLPS is a powerful tool that can help assess the impact
of processing feedstocks and intermediates (aqueous or hydrocarbon-based). In
relation to filtration and other separation
processes, fouling tendency analysis is useful for determining the optimal treatment
method to address fouling issues. This
has a fundamental impact in determining
whether filtration is the most effective mit-

Case study. A natural gas processing
plant in North America was experiencing
severe problems with fouling at its methanol recovery unit distillation column and
prefilters. The feedwater contained between 50 ppm and 70 ppm of suspended

252
Raw
Filtered
Filtered/deoiled

250

Tempreature, °F

248
246
244
242

solids and approximately 1% of hydrocarbons. Fouling of the tower packing and
filter plugging caused excessive maintenance, reduced throughput and decreased
efficiency, and impacted the efficiency of
other units downstream. The methanol
recovery unit was evaluated, including a
comprehensive analysis of the feed components and the process, to find the best
solution for fouling reduction.
The feed composition was first analyzed to understand the nature of the contaminants and the feed itself. Visual observation of feed samples revealed high free
hydrocarbon contamination (1%) and
high suspended and settled solids. X-ray
diffraction (XRD) and energy-dispersive
X-ray spectroscopy (EDS) analyses were
performed on suspended solids from the
feed and showed a wide range of contaminants (TABLE 1). Large amounts of iron
and carbon undetected by XRD analysis
were present in the EDS results, indicating
an amorphous deposit typical of asphaltene precipitation and hydrocarbon-coated solids. The HLPS test system was used
to determine the fouling impact of these
solids and hydrocarbon contaminants.
Three samples were tested by HLPS:
an unaltered sample, a filtered sample and
a filtered sample with free hydrocarbon

240
238
0

100
Time, min

120

140

160

180

200

FIG. 3. Outlet temperature data produced from HLPS testing of treated and untreated aqueous
samples (inlet temperature maintained at 250°F).

TABLE 1. Elemental analysis of
suspended solids in feedwater/methanol,
as detected by EDX and XRD
Element
Hydrogen, H
Carbon, C

0.01

30.89

2.41

Nitrogen, N

29.35

33.48

Sodium, Na

0.92

3.05

Magnesium, Mg

0.04

0.57

0.2

1.22

Silicon, Si

30 MARCH/APRIL 2021 | GasProcessingNews.com

XRD, %

Oxygen, O

Aluminum, Al

FIG. 4. Time-lapse study of phase separation after homogenization of feed samples. After 30
min, the hydrocarbon and water in solution had almost completely divided into separate phases.
After 1 hr, the aqueous phase is clear, indicating the absence of free or emulsified hydrocarbon.

EDX, %

12.59

Phosphorus, P

0.5

1.2

Sulfur, S

1.76

6.85

Chlorine, Cl

1.37

5.23

Potassium, K

0.61

2.34

Calcium, Ca

0.97

3.53

Iron, Fe

22.32

12.68

Copper, Cu

0.29

5.68

Barium, Ba

7.79

9.18

Note: The difference in compositions between the
two sets of data are indicative of non-crystalline solids
not detected by XRD analysis.

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Hydrocarbon Processing - April 2021

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