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DETAILED REPORT

SiC MEMBRANE PILOT ULTRAFILTRATION TEST FORPRODUCED WATER TREATMENT

OCELOTE field – HOCOL (COLOMBIA)

August 2012

Prepared by:

Oscar

Andrés

Prado‐

Rubio

Project Manager, LiqTech

David Cardona

Technical profesional, Conconcreto

Revised by:

Tore Svendsen

Application Manager, LiqTech

Linfeng Yuan

Project Manager SiC membranes, LiqTech



2

Table of Contents 1. Introduction ................................................................................................................................ 3

1.1.

Problem description

............................................................................................................

3

1.2. Test objectives ..................................................................................................................... 5

1.3. Test facility .......................................................................................................................... 5

1.4. Facilities description ............................................................................................................ 8

1.5. Experimental methodology ............................................................................................... 13

1.5.1. Operating window identification ‐ Operability investigation .................................... 13

1.5.2. Continuous operation tests ....................................................................................... 14

1.5.3. Chemical cleaning efficiency evaluation ................................................................... 14

1.6. Activities schedule ............................................................................................................. 14

2. Water permeability test ............................................................................................................ 16

3. Experimental evaluation point: Before the skimming tanks ..................................................... 18

3.1. Characteristics of the inlet water – field information ....................................................... 18

3.2. Preliminary tests – conventional ultrafiltration ............................................................ 19

3.3. Operating window identification ‐ Operability investigation ........................................ 20

3.4. Continuous operation ................................................................................................... 25

2.5

Conclusions.................................................................................................................... 30

4. Experimental evaluation point: After the skimming tanks ....................................................... 32

4.1. Characteristics of the inlet water – field information ....................................................... 32

4.2. Operating window identification ‐ Operability investigation ........................................ 33

4.3. Continuous operation ................................................................................................... 37

4.4 Conclusions.................................................................................................................... 41

5. Cleaning in place evaluation ..................................................................................................... 42

6. Final remarks ............................................................................................................................. 43

Evaluation point before skimming tanks: ..................................................................................... 43

Evaluation point after the skimming tanks: .................................................................................. 43

7. Future challenges ...................................................................................................................... 44

8. Appendix: Critical flux estimation ............................................................................................. 45



3

1. Introduction

HOCOL

is

a

private

company,

with

over

half

a

century

of

presence

in

exploration

and

production

of

oil and gas in Colombia. HOCOL currently has exploration projects in the Upper Magdalena Valley,

Lower Magdalena Valley, the Eastern Plains and the Llanos Foothills. Besides, it has engaged

production operations in the states of Huila, Tolima and Meta, pumping the produced crude oil

through their own pipelines in the Alto Magdalena.

Currently, HOCOL has an average production of 32,307 barrels (gross) per day in fifteen fields and

a portfolio of net 2P reserves of 57.7 million barrels and 0.9 giga cubic feet of gas waiting to be

developed efficiently and with high operational excellence. In 2011, the company produced 9.9

million barrels of oil.

HOCOL showed

interest

to

test

new

technologies

for

the

separation

of

oil

in

water

emulsions,

as

a

way to bring innovation into their installations, in that way fulfilling their future expectations in

produced water treatment. A process proposed by the consortium Conconceto/LiqTech, based on

Silicon Carbide (SiC) membrane technology. LiqTech is a Danish company who manufactures the

membrane. For the last 11 years, LiqTech has been at the leading edge in developing and

marketing its own proprietary products to the environmental industry. LiqTech’s core is its ability

to manipulate SiC, which has allowed it making a high value, high performance products for liquid

and gaseous filtration. Conconcreto has joined LiqTech efforts to promote this technology in South

America. Conconcreto is a Colombian company with more than 50 years of experience providing

services in South America, mainly in the construction area. Recently, Conconcreto has created an

innovation

department

to

provide

cutting

edge

technologies

for

domestic

and

industrial

water

treatment. The produced water application is one of the most promising applications of SiC

membranes. LiqTech/Conconcreto and HOCOL have agreed to perform a test of the SiC

membranes for produced water treatment. This test is relevant for the consortium

LiqTech/Conconcreto since it is a great opportunity to improve its understanding of the separation

and at the same time validate the technology under Colombian conditions. The intention of this

test is to gather sufficient data to allow Conconcreto/LiqTech propose a commercial service

solution for the produced water treatment.

1.1. Problem description

The pilot plant testing has been conducted in “Campo OCELOTE”, inside of the crude processing

area referred to as “Fluid Processing Central – CPF” (see Figure 1). During the oil recovery process,

an interesting challenge is to separate the oil and water mixture. This separation is limited by the

stability of the oil in water emulsion. Conventionally, emulsion breakers are added in order to

facilitate the oil separation and to allow the filters to remove the suspended solids. The HOCOL’s

processing area is divided into two sections, first the oil recovery plant and secondly the produced

water treatment plant for reinjection.



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The oil and water mixture coming from all drilling points is sent to the processing area through

two pipelines. Those enter the CPF in a manifold where temperature is adjusted for the

subsequent oil recovery section. The oil treatment process is composed in two (02) Surge tanks,

one (01) Gun barrel and finally two (02) Storage tanks. The outlet stream has an average

concentration of 500 ppm of oil in water (OiW) and total suspended solids (TSS), respectively.

From the oil recovery plant, 55.000 BWPD are sent to water treatment facilities. This section

consists of two skimming tanks, one microflotation unit and two walnut shell filters.

From the skimming tanks there is an oil recovery which is sent back to the oil processing plant. The

treated water goes to the microflotation unit with OiW concentration of around 75 ppm and 500

ppm of TSS.

From the microflotation process, the produced water stream has 7.5 ppm of OiW and 50 ppm of

TSS approximately.

Currently,

the

Microflotation

process

has

been

by

‐passed

and

the

outlet

from

the skimming tanks is sent directly to walnut shell filters. The water at the end of the process

should have a maximum of 5 ppm of OiW and TSS. Finally the produced water is sent to the

storage tanks, and then re‐injected.

Figure 1. Diagram of the fluid processing central CPF at OCELOTE field. Red square shows the oil

recovery plant. Green square shows the produced water treatment plant.



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As an alternative solution for the produced water treatment, the SiC membrane technology offers

reliable performance. This technology exploits the oil droplets and suspended solids size to

achieve the separation. The separation is possible due to the membrane is highly hydrophilic

allowing the water to pass through and retaining the oil drops and suspended solids.

1.2. Test objectives

The objective of the test is to determine the operability of the pilot plant at the field conditions.

Therefore, the necessary information is gathered to evaluate the technical feasibility of this

technology for the produced water treatment which will be reflected in a commercial design. It is

aimed to deliver water with concentrations below 5 ppm of OiW and TSS. The activities involved

during the test are:

Evaluate the

effect

of

the

operation

variables

on

the

separation

performance

at

different

sampling points in the OCELOTE field

Reveal the most appropriate operation conditions given the input water quality and clean

water requirements.

Investigate the inlet characteristics variance at the interesting sampling points in the field.

Investigate the influence of the inlet water quality on the separation performance

Determine the water and oil separation efficiency at field conditions

Determine the total suspended solid separation efficiency at field conditions

Evaluate the sustainable continuous operation of the pilot plant.

1.3. Test facility

The test rig is a Multibrain pilot unit from LiqTech (CFU8), it can be seen in Figure 2. The PID can be

seen in Figure 3.



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Figure 2. Pilot unit located at OCELOTE-CPF. The pilot unit is equipped with a feed pump which

pressurizes the feed stream, a recirculation pump which generates the cross-flow and a pump for

backflush. The pressure and flow rates inside the system are controlled by adjusting the position of

control valves and pump speeds. In addition, the unit is equipped with a BackPulse Hammer (BPH)

The unit consists of three pumps: a feed pump delivering the feed solution into the recirculation

loop, a recirculation pump generating the cross‐flow and a pump sitting at the permeate side for

Backflush. In addition, the pilot unit is equipped with a Back Pulse Hammer (BPH). The BPH system

is a pulse generator, which delivers high frequency water pulses from the permeate side in order

to keep the membrane clean and free of foulants. The filtration membrane element is based on

Silica Carbide (SiC).



7

Figure 3. PID-diagram of the test unit. The LiqTech Multibrain CFU08 is an industrial pilot unit for

water filtration applications



8

1.4. Facilities description

The pilot unit was located inside CPF area, beside the Microflotation unit, this location allow

having the connections for the first and second test points very close to the pilot plant.

The following figure shows the localization of the pilot unit inside the CPF area.

Figure 4. General Layout of CPF area (The precise location is indicated with the red circle in the

layout)



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The connections for the first and second point of operation with the pilot unit were suitable by

HOCOL, installing a valve for control the feed flow rate (as can be seen in Figure 5 and Figure 6).

Figure 5. First point of connection, outlet surge tanks.

Figure 6. Second point of connection, outlet skimming tanks.

The equipments that complement the pilot plant are:

Transformer: the voltage in the field is 480V. Therefore was necessary to install an

electrical transformer to reduce the voltage to 440V (see Figure 7).



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Figure 7. Electrical transformer, 480V to 440V, 32A.

Panels: as protection for the equipment, there are different electrical panels that allow

connecting the pilot plant, heater, a pump and the computers that use 440V and 110V

(Figure 8 and Figure 9).

Figure 8. Electric panel for connection 220V and 110V.



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Figure 9. Electric panel for connection 440V.

Cleaning in place unit (CIP): Consist of two plastic tanks with 250 liters of capacity, with a

configuration of pipelines and valves that allow connecting the feed, permeate and

retentate hose’s. In these tanks the chemical cleaning solution with alkaline and acid is

prepared for

the

membrane

cleaning

(Figure

10).

Figure 10. Cleaning in place unit (CIP).

Prefilter: this equipment filters the water through a mesh, where particles with size larger

than 300 micrometers are retained. This is a protection device which avoid that these



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particles enter the pilot unit, in that way preventing the obstruction the feed channels.

There is a small pump (8 m3/h) to generate flow if necessary (Figure 11).

Figure 11. Prefilter is showed in the left side, pump shown in the right side.

Storage tanks: There are two plastic tanks, the first with 1000 L of capacity, used for feed

of produced water. The emulsion is kept in the tank by strong agitation and temperature

regulation. The second tank with a capacity of 2000 L, is employed for clean water storage

to be used for the membrane washing.

Figure 12. In the left side of the picture is showed the feed tank, and in the right side the clean water

tank.



13

1.5. Experimental methodology

In order to evaluate the influence of operating variables on the separation behavior, a stepwise

methodology is proposed. The separation performance is assessed in terms of well‐established

indexes like: flux, permeate quality, recovery and sustainability. The most appropriate operating

conditions are estimated from an analysis of the independent experiments based on the

mentioned indexes. The following inputs, that define the membrane performance, can be

controlled by the membrane pilot unit:

Flow conditions: cross‐flow velocity

Driving force: transmembrane pressure (TMP)

Cleaning: combination of the available cleaning strategies (backpulse hammer,

backflush and cleaning in place)

The separation efficiency is determined by the membrane characteristics, the mixture properties

and how the system is operated. During the filtration of any mixture (e.g. emulsions, suspensions,

solutions), the solvent flux through the membrane is always lower than the pure water flux due to

two tightly coupled phenomena referred to as concentration polarization and fouling.

In order to determine the best way to operate the process, it is important to identify the influence

of the operating conditions on the mentioned phenomena, thus on the separation performance.

For that purpose, an experimental design is used.

1.5.1. Operating window identification - Operability investigation

In order to minimize the number of experiments, a hierarchical structure is employed. The

operating mode selected for the experiments is constant flux, which can be automatically

controlled (in a selected experiment the constant TMP mode is tested, which analogous to the

constant flux operation). The influence of flux increments is evaluated through a conservative

stepwise strategy. This is necessary in order to avoid an initial irreversible fouling and at the same

time more carefully follow the separation performance. In that way viable and reproducible

results can be obtained. An additional advantage of this procedure is that the membrane has an

appropriate time to get used to the environment. The first series of experiments on a new type of

water application are initiated with the smallest flux possible and maximum cross flow velocity.

For this

pilot

unit,

the

transmembrane

pressure

should

be

kept

below

0.3

bars

and

the

cross

‐flow

should be kept as high as 2 m/s (50 m3/h).

The used methodology is called “step up‐down” method for the estimation of the sustainable

flux1. The experiment starts with an initial flux which is gradually increased; each increment is

followed by a relaxation period. After each increment, the transmembrane pressure will increase

as a consequence of the higher desired flux. The transmembrane pressure should reach a

relatively stationary average value, indicating a situation where there is equilibrium between the

1 Beier, S.P. and Jonsson, G. Critical Flux Determination by Fux Stepping. AIChE Journal 56(7). 1739‐1747.



14

amount of material being deposited on the membrane surface and material being removed by the

cross‐flow and employed cleaning strategy. This equilibrium is achieved due to the efficiency of

the equipment to remove the reversible fouling.

The idea of the experiments is to find the so called critical flux, since exceeding that point is not

possible to achieve a stationary operation, meaning that there is not equilibrium between the

fouling formation and removal by the cleaning strategy (cross‐flow, backflush or backpulse). Above

the critical flux it is very difficult to maintain a sustainable production due to the formation of a

dominating irreversible fouling. After considerable irreversible fouling, there is a loss of separation

performance which cannot be recovered. It is not recommended to operate the equipment above

the critical flux, thus it is an important parameter to identify. During the experiments for each flux

conditions, the physical cleaning variables are tested such as frequency and intensity. The

frequency of the cleaning strategies has a big influence on the operating cost of the pilot plant.

The separation performance is followed using quantitative measurements of the total suspended

solids and oil in water. The analyses are performed following the standard protocols used in the

field laboratory (ANTEK)2.

The determination of the critical flux methodology is applied at two different points in the

produced water treatment, before and after the skimming tanks. As a preliminary experiment, the

first evaluation point includes a test of conventional ultrafiltration.

1.5.2. Continuous operation tests

Once

the

operating

conditions

are

identified,

the

sustainable

operation

is

evaluated

using

continuous operation. The initial tests are performed at moderated operating time, increasing the

operation window. During the continuous tests, the water quality is determined regularly.

1.5.3. Chemical cleaning efficiency evaluation

As a parallel activity to the experimental design, the efficiency of the chemical cleaning is

evaluated. The objective of the chemical cleaning is to remove the accumulated organic matter,

solids and precipitated salts in both surface and internal structure of the membrane. Thus, recover

the initial stable separation potential of the membrane. The cleaning efficiency is quantified

through

the

water

permeability

assessment.

Using

the

test

results,

the

recommended

cleaning

strategy is refined in order to match an acceptable water permeability recovery at field conditions.

1.6. Activities schedule

The activities are organized in four main areas; every one of these has a time line defined,

including labor, resources and troubleshooting that were necessary for the correct development

of the project.

2 ANTEK is a certified laboratory that makes all quantitative measurements in the field.



15

In the following figure, the time line for every area is depicted.

Figure 13. Work schedule for the test period at OCELOTE field-HOCOL

The Assembly and Installation of the pilot unit and was started 27/06/2012. The installation of the

pilot plant was delayed due to the absence of 440V in the field. HOCOL had promised 440V but at

the end there was no way to provide it in the field. Therefore, a transformer was installed. This

activity took

a week.

The experimental phase was divided in two tests: the first sample point used feed water from the

outlet of surge tanks, and the second used water from the outlet of skimming tanks. The order of

the tests was imposed by HOCOL. All these activities were started the 10/07/2012 and finished

03/08/2012.

Closing Operation consisted in un‐mounting of the equipment, cleaning and shut down of the pilot

unit. These activities were started the 04/08/2012 and finished 06/08/2012.



16

2. Water permeabil ity test

The

ultrafiltration

membrane

used

for

the

experiments

was

LiqTech‐

103377.

The

water

permeability is used to evaluate the state of the membrane. The permeability is defined as the

ratio between the flux and the applied transmembrane pressure.

In the field, the membrane permeability is estimated according to the water quality available.

There is a limitation since there is not a drinking water line available (see Figure 14a). The cleanest

source available is the outlet of the walnut shell filter 2. This water is not in optimal conditions

neither for cleaning nor for water permeability estimation but there is no other initial water

source. The quality of this water changes a lot as it can be as bad as it is shown in Figure 14b,

which is an extreme case seen in the at the beginning of the experiments.

(a) (b)

Figure 14. Quality of the water available in the field. (a) Drinking water, the color is due to a severe

oxidation of the pipelines. (b) Example of bad quality water from the walnut shell filter 2 (not all the

time was bad ).

The water flux was estimated as a function of the TMP. The results are shown in the Figure 15. It

can be seen how the flux increases very fast by raising the pressure at low TMPs. At higher TMP,

the slope tends to settle. The results are clearer by looking the permeability in Figure 16.

The initial permeability changed from 1550 to 4500 LMH/bar at the lowest TMP evaluated.

However, it rapidly stabilizes around 3000 LMH/bar at TMPs higher than 0.1 bar. At moderate

TMP, a high

recovery

is

achieved

and

the

permeability

tends

to

decrease.

It

is

believed

that

this

effect is due to the quality of the water that was coming from the walnut shell filter (OiW: 1 ppm

and TSS: 3.3 ppm, this average information was provided by the Latin‐American treatment

personal, at HOCOL).

Despite the water quality, the results agree with the expected value of 3000 LMH/bar, reported by

LiqTech3.

3 LiqTech International A/S. CoMem Conduit – OD146mm diameter Round Channels data sheet.



17

Figure 15. Water permeability test using water from the walnut shell filter 2 (12/07/12).

Figure 16. Water permeability test using water from the walnut shell filter 2 (12/07/12).

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

800.00

900.00

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

W a t e r f l u x ( L M H )

Transmembrane pressure (bar)

0.00

500.00

1000.00

1500.00

2000.00

2500.00

3000.00

3500.00

4000.00

4500.00

5000.00

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

P e r m e a b i l i t y ( L M H / b a r )

Transmembrane pressure (bar)

Field

Perm



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3. Experimental evaluation point: Before the skimmingtanks

The test in this evaluation point took place between the 11/07/2012 to 28/07/2012. This period

included testing time and maintenance of the pilot plant due to some unexpected situations.

3.1. Characteristics of the inlet water – field information

In the field, the oil in water and total suspended solids are quantified twice per day. The average

values during the testing days are shown in the following plots. The place where the inlet is taken

is a point where the 3 shown streams are combined.

Figure 17. Oil in water average concentration at the outlet of the oil recovery section. ST: Surge tank,

GB: Gun Barrel (Information provided by Latin-American treatment personal, at HOCOL)

It can be seen in Figure 17 that the OiW outlet concentration of the surge tank 1 is considerably

higher than the other units. The surge tank 2 manages the lowest variance and the Gun barrel

manages lower outlet concentrations, however it has a substantial variance. According to this

record, heavy oil load has been received especially in the middle and at the end of the experiment,

the heaviest load has been seen during the period with continuous operation of the pilot plant.

0.00

100.00

200.00

300.00

400.00

500.00

600.00

700.00

O I W

( p p m )

ST 1

ST 2

GB



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On the other hand, the total suspended solids concentrations show lower variance and the

concentrations are below 20ppm (see Figure 18). However, there is an atypical event at the end of

the test where there is a tremendous increase in the TSS concentration (six times higher

concentrations). This event took place during the continuous evaluation of the operating point.

It has to be mentioned that these concentrations are average of two samples per day. Therefore,

they do not really represent the variance that can be seen in the field, but give an overview of the

challenges faced during the experiments.

Figure 18. Total suspended solids evolution in the lines at the outlet of the oil recovery section. ST:

Surge tank, GB: Gun Barrel. (Information provided by Latin-American treatment personal, at

HOCOL)

3.2. Preliminary tests – conventional ultrafiltration

The purpose of the first experiment was to provide a fast indication of the fouling challenge in this

evaluation point. The idea was to determine the sustainable flux during conventional

ultrafiltration. An inspection of this data would provide relevant information about how fast the

flux is limited by irreversible fouling. At the same time, this point is a comparison standard to

evaluate the efficiency of the in situ cleaning strategies.

The ultrafiltration test has shown that the critical flux without any in situ cleaning mechanism

occur at relatively low TMP. The summary of the results are shown in the Table 1. For this

experiment, the operating and relaxation time per operating point were 60 and 30 minutes,

0.00

20.00

40.00

60.00

80.00

100.00

120.00

140.00

T S S ( p p m )

ST 1

ST 2

GB



20

respectively. The permeate flow rate increase was initially 0.5 m3/h, but it was decreased along

the experiment.

Table 1. Results from the conventional ultrafiltration operation mode.

Crossflow

(m3/h)

Critical TMP*

(bar)

Critical Flux Average inlet concentration

LMH Permeate (m3/h) TSS (ppm) OiW (ppm)

30 0.7 150 1.2 28.38 117.53

*This TMP has been already affected by an initial irreversible fouling during the experiment

From the preliminary results, it was evidenced that irreversible fouling is formed at relatively low

TMPs and LMH. It has been seen that completely unsustainable operation is achieved already at

170 LMH. These results have been influenced by the initial fouling generated by the quality of the

clean water available in the field (during the permeability test).

From this experiment it can be stated that there is a need of using the in situ cleaning strategies

for this application. The cleaning frequency should be moderate in order to avoid irreversible

fouling formation.

3.3. Operating window identification - Operability investigation

A sequence of experiments were performed in order to determine the sustainable operation

conditions of the plant according to the given water quality. The initial strategy was to emulate

continuous operation by having around 500 L of produced water in the feed tank and recirculating

both retentate and permeate streams. In that way, it was expected to have approximately

constant inlet concentration for each experiment (the variation would be due to the accumulated

material within the equipment). In this scenario, strong agitation and temperature regulation were

provided. The first 3 tuning experiments were performed in this way.

Nevertheless, it was noticed that there was a considerable oil inlet concentration decrease along

the experiments (see Figure 21). This was mainly due to the oil tendency to stick to the feed tank

surface and to some extend within the equipment. Therefore, it was decided to perform the

remaining tuning experiments using a continuous feed stream to the feed tank, while the

retentate and permeate where disposed out of the system. This operation mode brought new

challenges due to the variance of the inlet oil and suspended solid concentrations along the tuning

experiments. Besides,

it

introduces

the

inlet

concentrations

as

variables

within

the

experimental

design. On the other hand, this strategy was advantageous due to the constant monitoring of the

inlet concentrations along the experiments, providing more information about the system, which

is relevant for the plant design and operation.

Due to the variable quality of the clean water used for washing and permeability estimation

between experiments, it was decided that as long as the water coming from the walnut shell filter

2 showed bad aspect, the permeate water would be used for those purposes. This water was

collected in one of the 2000L tanks available.



21

The tuning experiments at constant flux started using a low recovery and it was increased step

wise between experiments. The summary of the operating conditions for the experiments are

shown in the Table 2. For the last experiment the constant TMP operating mode was tested. Only

the results certified by ANTEK laboratory are reported.

Table 2. Summary of the operating conditions for the tuning experiments. The experiments labels stand

for Dynamic Ultrafiltration (DUF). It is referred as dynamic due to the operation of the in situ cleaning

strategies.

Test* Crossflow

(auto)

Feed pump

(auto)

Backpulse

(s)

Backflush

(s)

Permeate Retentate

04V04(%) 03V01(%) 03V02(%)

DUF 1 30 29‐38 60 300 40‐90 100 100

DUF 2 30 30‐50 60 300 60‐100 100 70‐100

DUF 3 30 32‐56 60 300 100 60 60

DUF 4

30

28‐42

60

300

80

‐100

40

50

*DUF – Dynamic Ultrafiltration

As an example of the results obtained, the dynamic behavior of the 3th experiment (DUF 3) is

shown in Figure 19 and Figure 20. It can be seen that the backpulse and backflush operation

disturb the system having the noise effect. This disturbance is rejected by the constant flux

controller that manipulates the feed pump. From the flux values in the figure, the challenge of the

separation can be seen due to the low fluxes obtained from the beginning.

Figure 19. Flux profile during the critical flux determination (DUF3)

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

400.00

13:55:12 15:07:12 16:19:12 17:31:12 18:43:12

P e r

m e a t e f l u x ( L M H )

Time (h:m:s)



22

Figure 20. TMP profile during the critical flux determination (DUF3)

The summary of the tuning experiment results are depicted in Table 3. The minimum flux

condition is the starting point. The maximum flux conditions correspond to the point where the

maximum permeate flow was evaluated.

Table 3. Summary of the tuning experiments before the skimming tanks. Values taken by inspectionfrom the display during operation, before the BPH.

Point Min. flux conditions Maximum flux conditions

Average inlet

(ppm)*

Initial

PERM

** LMH TMP REC PERM LMH TMP REC PERM OiW TSS

DUF 1 63 0.10 7 720 200 0.35 19 700 106.50 22.11 1860

DUF 2 125 0.15 17 750 280 0.90 24 310 70.50 3.5 600

DUF 3 175 0.60 33 310 276 1.55 28 172 74.32 7.25 1250

DUF 4 150 0.55 40 260 435 0.95 62 435 65.39 4.07 1500

* From our measurements

** The variance in the initial permeability is highly correlated to the quality of the cleaning water

The results depicted in Table 3 give the range of operating conditions achievable given the inlet

concentrations. It can be seen that the operating window was extended for the last experiments,

where higher TMPs were tested. Despite the first experiment was performed using the highest

average inlet concentrations, it has shown the best permeabilities. This result is expected since the

membrane was new. The second and third experiments are interesting since they have similar

water quality in oil concentration but different suspended solids concentration (TSSDUF3 is more

than 2 times TSSDUF2). The impact in the permeability is evident at minimum and maximum flux

conditions; there is a reduction around 50% from DUF2 to DUF3. This effect is visible in the

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

13:55:12 15:07:12 16:19:12 17:31:12 18:43:12

T M P ( b a r )

Time (h:m:s)



23

maximum flux tested, where a much higher TMP is required in DUF3 to achieve basically the same

flux. It has to be accounted for that during DUF 3 the inlet concentration decreased along the

experiment while during DUF 4 it increases.

The last experiment showed the highest flux at moderate TMPs, with inlet concentrations

comparable to the second experiment. This is an indication that effect of the suspended solids on

the process does not depend entirely of the concentration.

The water quality during the tuning experiments is shown Figure 21 and Figure 22. The data are

certified by ANTEK laboratory. The samples 1‐5 were taken the 20/07/2012 (DUF 3) and the

remaining samples the 21/07/2012 (DUF 4). According to the data reported by the field, the

measured inlet OiW concentrations were considerably lower, between 30% and 65% of the

average values reported by the field laboratory4. This confirms the variability of the concentrations

measured in

the

field,

and

why

average

concentrations

do

not

entirely

represent

the

system.

Figure 21. Oil in water concentration at the inlet and outlet of the pilot plant for the tuning experiments

For the DUF 3 experiment, it can be seen how the OiW concentration decreases along the test.

The situation that generated the change in the feed strategy, as mentioned previously (notice that

the concentration increases in DUF4). The OiW outlet concentration does not necessarily follow

the trend in the inlet concentration in the evaluated flux conditions. From the reported values, all

4 In the field, Latinametican chemical treatment also measures the concentrations along the process.

0

0.5

1

1.5

2

2.5

3

3.5

0

20

40

60

80

100

120

140

160

180

0 1 2 3 4 5 6 7 8 9 10 11 12 13

O i l i n w a t e r o u l t e t ( p p m )

O i l i n w a t e r i n l e t ( p p m )

Sample (1 hour difference)

DUF 3 ‐ inlet DUF 4 ‐ inlet DUF 3 ‐ oulet DUF 4 ‐ outlet



24

permeate water fulfill the required the target (max 5 ppm). The maximum outlet concentration is

around 3 ppm. The oil removal from the inlet stream during the tuning experiments was between

83.6 and 99.4%.

Regarding the total suspended solids concentrations, there is no concentration decrease along the

experiment DUF 3 (see Figure 22). Interestingly, the reduction in the TSS is seen when the feed is

in continuous mode (DUF4). For both experiments, the inlet concentration is between 3 and 10

ppm. The TSS concentrations in the permeate stream are very low, in some cases below the

detectability of the instrument. It means that the equipment is not able to distinguish between

distillated water and the permeate samples. The TSS removal during the tuning experiments was

between 82.3% and 100%. Notice that the 82.3% is the last point in Figure 22, and does not

entirely represent the overall behavior, for all the other samples the TSS removal was above 95%.

Some examples

of

the

water

quality

during

DUF

3 and

DUF

4 can

be

seen

in

Figure

23.

Figure 22. Total suspended solids concentration at the inlet and outlet of the pilot plant for the tuning

experiments

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9 10 11 12 13

T o t a l s u s p e n d e s

s o l i d s o u t l e t ( p p m )

T o t a l s u s p e n d e d s o l i d s i n l e t ( p p m )

Sample (1 hour difference)

DUF 3

‐inlet DUF

4

‐inlet DUF

3

‐oulet DUF

4

‐outlet



25

(a) DUF 3 (b) DUF 4

Figure 23. Pictures of the inlet water and treated water during the tuning experiments

The shown flux ranges correspond to the tested values. The purpose of the experiments is to

determine a sustainable operation of the system. The precise value for each inlet concentration

can be estimated from a rigorous analysis of the experimental data. However, a qualitative

inspection of the data provides sufficient preliminary information in order to plan the continuous

experiments. From the analysis, it was seen that the sustainable operation was in the

neighborhood

of

0.7

to

1

bar

for

the

evaluated

concentrations.

Higher

TMP´s

would

require

a

considerable increase in the feed channels pressure in order to keep the constant permeate flux.

3.4. Continuous operation

The continuous operation of the system was evaluated at three different operating times (6, 12

and 27 hours). Besides, the system was operated at constant TMP. The biggest challenge for these

experiments is to achieve stable operation given the disturbances in the inlet concentrations. This

issue is particularly difficult to handle due to the frequency and amplitude of the disturbances.

A summary of the pilot plant inputs is shown in the Table 4. Taking advantage of the longer

operation

time,

the

influence

of

different

crossflow,

backpulse

frequency

and

recovery

values

were tested. In other situations the recovery was manipulated in order to increase productivity or

handle disturbances.



26

Table 4. Summary of the operating conditions for the continuous operation of the treatment before the

skimming tanks.

Test Crossflow

(auto)

Feed pump

(manual)

Backpulse

(s)

Backflush

(s)

Permeate

Retentate

04V04(%) 03V01

(%)

03V02

(%)

CDUF 2‐ 6h 30 35‐40 60‐90 300 100 40 45

CDUF 4‐ 12h 30‐35 30‐32 60‐120 300 100 55‐60 55‐60

CDUF 5‐ 27h 30‐40 30‐35 60‐90 300 100 40‐70 45‐70

For the continuous operation, the results are shown in table 5. Different exogenous events

affected the length of the experiments. First of all, it can be noticed that the inlet concentrations

are substantially higher than during the tuning experiments. Despite of this situation, the obtained

fluxes are

within

the

expected

values.

During

the

experiment

CDUF

4,

there

was

a problem

with

a

valve in the retentate line that forced a shut down. The operation was recovered after 2 hours.

This prolonged shut down had a negative effect in the plant performance. In the last continuous

experiment (CDUF 5) there was an atypical situation that generated an unsustainable condition.

Since the last continuous experiment is the most interesting, it will be discussed further.

Table 5. Summary of the continuous experiments before the skimming tanks

Point Minimum flux conditions Maximum flux conditions

Average inlet

(ppm) Initial

PERM*

LMH

TMP

REC

PERM LMH TMP REC PERM OiW

TSS CDUF 2 185 0.70 51 250 495 0.95 81 540 221.20 7.33 1200

CDUF 4 135 0.70 35 190 370 0.35 54 925 722.56 16.74 484

CDUF 5 200 0.65 63 280 610 0.60 87 1000 367.91 13.14 2400

* The variance in the initial permeability is highly correlated to the quality of the cleaning water

The operation of the CDUF 5 is shown in Figure 24 and Figure 25. Initially a conservative TMP of

0.4 bar was used, obtaining stable operation for approx 9 hours at an average of 490 LMH with a

recovery of 70%. This was possible due to the quality of the inlet water. Later, the TMP was slightly

raised further increasing the flux and the recovery. At this point, 5 hours of stable operation was

achieved at 0.55 bar with 590 LMH and 80% recovery. This operation window represents the best

evaluated case.

At 10:00 am, there was a material recirculation from the sludge treatment plant trough the line

used for the feed. This material is characterized by high OiW and TSS content, beyond the limits

managed in the produced water treatment plant. The impacts of this event are clear on the flux

and permeate quality. In order to evaluate the plant performance without chemical cleaning, it

was decided to continue the experiment. Nine hours after the incident, the flux had decreased

more than 50% and reached a new stationary operation point at 240 LMH.



27

Figure 24. Flux profile during the continuous experiment CDUF 5

Figure 25. TMP profile during the continuous experiment CDUF 5

0

100

200

300

400

500

600

700

800

900

1000

19:54:46 00:42:46 05:30:46 10:18:46 15:06:46 19:54:46

F l u x ( L M H )

Time (h:m:s)

‐1

‐0.5

0

0.5

1

1.5

19:54:46 00:42:46 05:30:46 10:18:46 15:06:46 19:54:46 T M P ( b a r )

Time (h:m:s)



28

The OiW concentration behavior during the continuous tests is depicted in Figure 26. Comparing

the inlet concentrations with the average values reported by the field laboratory, there are big

differences (between 40 and 60%, only in the average values, see Figure 17). Evidently, the

difference at certain points is even higher with the actual concentration being up to 5 times the

average. These concentrations are considerably higher than the values used for the equipment

tuning. Meaning that during some periods the pilot plant was operated at higher TMP´s than

recommended. As a consequence, some oil was able to pass through the membrane. This effect

can be seen along the continuous experiments and it is critical in CDUF 5 after the incident, where

the amount of oil in the permeate stream is far beyond the desired value. Despite the plant

achieved a new stationary operation point, the permeate water quality indicates that the

membrane was saturated with oil. The OiW removal is between 67.4% and 99.5% for most of the

data, with atypical values of 23.4 and 53.4% after the incident in CDUF 5.

The non

satisfactory

OiW

concentration

in

the

treated

water

was

also

influenced

by

some

non

complete recovery of the water permeability between experiments. Due to time constraints, it

was decided to continue the experiments being aware of the possible consequences.

Figure 26. Oil in water concentration at the inlet and outlet of the pilot plant for the continuous

operation

0

50

100

150

200

250

0

200

400

600

800

1000

1200

1400

0 5 10 15 20 25

O i l i n w a t e r o u t l e t ( p p m )


Sample

CDUF 2

‐inlet CDUF

4

‐inlet CDUF

5

‐inlet

CDUF 2 ‐ outlet CDUF 4 ‐ outlet CDUF 5 ‐ outlet



29

Figure 27. Total suspended solids concentration at the inlet and outlet of the pilot plant for the

continuous operation

In Figure 27, the suspended solid concentrations during the continuous operation are shown.

These values are similar to the average values reported by the field laboratory (see Figure 18).

Operation at higher TMP’s does not have a significant effect in the concentration in the permeate

TSS concentration, due to the incompressible nature of the suspended solids. Despite the

concentration picks, the TSS concentrations in the treated water are kept below 2 ppm. The

suspended solid removal during the continuous experiments is between 92.5 and 100%.

Some pictures of the continuous experiments are shown in Figure 28. In the Figure 28(b), the

operation was satisfactory and the quality evident. In Figure 28(c), the difference between the

expected feed water and the recirculated sludge can be seen. Due to the low residence time in the

machine the effect in the permeate quality is immediate. After the incident, the water looks like in

Figure 28 (d).

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

5

10

15

20

25

30

0 5 10 15 20 25

T o t a l s u s p e n d e d s o l i d s o u t l e t ( p p m )

T o t a l s u s p e n d e d s o l i d s i n l e t ( p p

m )

Sample

CDUF 2 ‐ inlet CDUF 4 ‐ inlet CDUF 5 ‐ inlet

CDUF 2 ‐ outlet CDUF 4 ‐ outlet CDUF 5 ‐ outlet



30

(a) CDUF 2 – satisfactory performance (b) CDUF 5 – satisfactory performance

(c) CDUF 5 – incident time (left the sludge fed) (d) CDUF 5 – after incident

Figure 28. Pictures of the inlet water and treated water during the continuous experiments

2.5 Conclusions

From this first testing it can be concluded:

From the laboratory analysis of the average inlet water characteristics, it can be seen that

there is considerable variance from day to day, where the concentration can easily

increase more than 100%

The need of the in situ cleaning strategies is evident, since the sustainable fluxes where

increased more than 3 times (depending on the inlet concentration and nature).



31

The tuning experiments showed a preliminary indication that the concentration and

nature of the suspended solids in this field can be a limiting flux factor, since duplicating

the TSS had a significant effect in the TMP necessary to obtain the same flux. This result is

also influenced by the slope in the inlet concentration. There is a considerable variance in

the nature of the treated water since it comes from several oil wells in the area.

The qualitative analysis of the obtained data indicated that the best sustainable operation

can be achieved with TMP´s between 0.7 and 1 bar.

The tuning experiments showed that the OiW and TSS target concentrations where

achieved, not higher than 5 ppm. The oil and TSS removal were up to 99.4 % and 100%,

respectively.

During the continuous operation of the plant, large disturbances were evidenced in the

feed concentration, even atypical situations. These variables have a significant influence in

the plant performance, implying a significant reduction in the flux. Despite new stationary

operating points were achieved; the oil content in the water indicated the need of a

premature chemical cleaning. The accidental recirculation of the sludge is the worst water

in the field to treat, and still good oil and TSS removal were achieved (up to 99.5 % and

100%, respectively). The recommended operating conditions are 30‐40 m3/h of crossflow,

60 s of backpulse frequency and 300 s of backflush. These results indicate how important

is to monitor the inlet concentrations in order to have an appropriate plant operation. It is

relevant to notice that the OiW and TSS loads during the tuning experiments were

considerably lower than during the continuous operation. Therefore, it is expected that a

longer trial time would provide the necessary information for an improved plant

operation.

In an industrial scale, the plant operation can be adapted to handle the concentration

peaks. One option is to reduce the plant productivity (lower TMP) during abnormal

conditions. It is expected that using this strategy the plant can operate longer time

avoiding a premature chemical cleaning. The alternative is to have a flexible stages design

that allows modifying the plant configuration to guarantee the permeate quality. Both of

these strategies would require continues measurement of OiW content.



32

4. Experimental evaluation point: After the skimmingtanks

The test in this evaluation point took place between the 30/07/2012 to 03/08/2012.

4.1. Characteristics of the inlet water – field information

In the field, the oil in water and total suspended solids are quantified twice per day. The average

values during the testing days are shown in the following plots. The place where the inlet is taken

is a point where the outlet of the 2 skimming tanks is combined.

Figure 29. Oil in water concentration at the outlet of the oil recovery section. SK: Skimming tank

(Information provided by Latin-American treatment personal, at HOCOL)

In contrast to the previous feed point, the variance in the inlet concentration is not that high.

There is only one pick the 31st of July during the tuning experiments. The two skimmers behaved

similarly. The average concentration at the inlet of the skimming tanks in those days was between

200 ppm and 400 ppm, the skimming tanks were able to remove around 85% of the oil.

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

O I W

( p p m )

SK 1

SK 2



33

Figure 30. Total suspended solids concentration at the outlet of the Skimming tanks. SK: Skimming

tanks. (Information provided by Latin-American treatment personal, at HOCOL)

The TSS concentration follows the behavior of the OiW. The variance is moderated having a pick

the 31st of July as well. The purpose of the skimming tanks is to recover the remaining oil in the

water. However, part of the suspended solids is removed too. In these days, approximately 60% of

the solids were removed with the oil. According to the current understanding of the nature of the

suspended solids by the people in the field, parts of the suspended solids are hydrocarbons of

interest (soluble in xylene) and are supposed to be recovered in the skimmers.

4.2. Operating window identification - Operability investigation

The experiments were carried out using a constant feed coming from the skimming tanks and at

constant permeate operation mode. The water for washing and permeability estimation was taken

from the walnut shell filter 2. During this part of the experiment, the water quality from the filter

was exceptionally good (below 1 ppm OiW/TSS). Once again, the tuning experiments started using

a low recovery and it was increased step wise between experiments.

The operating conditions for the tuning experiments are shown in Table 6.

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

T S S ( p p m )

SK 1

SK 2



34

Table 6. Summary of the operating conditions for the tuning experiments

Test Crossflow

(auto)

Feed pump

(auto)

Backpulse

(s)

Backflush

(s)

Permeate Retentate

04V04(%)

03V01(%)

03V02(%)

DUF 1 30 28‐38 90 300 100 70‐80 70‐80

DUF 2 30 29‐50 90 300 55‐90 50‐60 50‐60

DUF 3 30 28‐58 90 300 60‐100 40 40

As an example of the results obtained, the dynamic behavior of the 3rd experiment (DUF 3) is

shown in Figure 31.

Figure 31. Flux and TMP profile during the critical flux determination

It can be seen that for the given inlet concentration of the last tuning experiment, higher fluxes

are achievable compared to the previous feed point and the noise is reduced. The summary of the

results for the tuning experiments are depicted in Table 7.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0

100

200

300

400

500

600

700

800

900

1000

17:45:36 18:28:48 19:12:00 19:55:12 20:38:24 21:21:36 22:04:48

T M P ( b a r )

F l u x ( L M H )

Time (h:m:s)

LMH TMP



35

Table 7. Summary of the tuning experiments before the skimming tanks. Values taken by inspection

from the display during operation before de BPH

Point

Minimum flux conditions Maximum flux conditions Average inlet

(ppm)

Initial

PERM* LMH TMP REC PERM LMH TMP REC PERM OiW TSS

DUF 1 250 0.2 31 1250 501 0.35 46 1200 8.30 3.17 1700

DUF 2 250 0.15 40 1300 692 0.95 71 767 38.58 6.02 1300

DUF 3 315 0.15 74 1600 816 1.65 85 490 22.23 3.21 2400


From the table can, it be seen that the initial and final fluxes where increased as well as the

recovery between experiments. High permeabilities are evidenced at minimum flux conditions, a

situation that changes for the maximum flux conditions. Considering the reduced OiW and TSS

load in

the

feed,

the

fluxes

do

not

increase

in

the

same

ratio.

Comparing

the

fluxes

from

DUF

2

and DUF 3 at similar TMPs, the results are comparable despite the differences in the inlet

concentrations (results not shown in the table). The last tuning experiment has shown the highest

flux and recovery (816 LMH and 85%, respectively). The influence of the OiW and TSS

concentrations is not clearly visible from the results.

The water quality during the tuning experiments is shown in Figure 32 and Figure 33. The data 1‐5

were taken the 30/07/2012 (DUF 1), 6‐13 taken the 31/07/2012 (DUF 2) and 14‐22 taken the

1/08/2012 (DUF 3).

Figure 32. Oil in water concentration at the inlet and outlet of the pilot plant for the tuning experiments

0

1

2

3

4

5

6

7

8

910

0

10

20

30

40

50

60

70

0 5 10 15 20 25



Sample

DUF 1 ‐ inlet DUF 2 ‐ inlet DUF 3 ‐ inlet

DUF 1 ‐ outlet DUF 2 ‐ outlet DUF 3 ‐ outlet



36

Comparing the average oil concentration measured during the experiments (Table 7) and the

values reported by the laboratory in the field (Figure 29), our values are between 50% and 100%

higher. There is not a clear trend in the OiW inlet concentrations. Regarding the outlet

concentration, there is only one value that is slightly above the desired limit. The oil removal from

the inlet stream during the tuning experiments was between 55.8 and 100%, but the lowest is an

atypical data since most of them are above 95%.

Figure 33. Total suspended solids concentration at the inlet and outlet of the pilot plant for the tuning

experiments

The suspended solid concentrations are more in accordance with the values reported by the

laboratory in the field, where the biggest difference is 21%. The TSS removal from this inlet stream

is considerable superior compared to the previous feed point, achieving between 91.2% and 100%.

The remarkable low concentrations in the treated water has to be highlighted, in several cases the

removal was 100%. Some examples of the water quality during DUF 2 and DUF 3 can be seen in

Figure 33.

From the inspection of the tuning results, it is expected to have the sustainable operation using

TMPs between 0.8 and 1 bar. Pictures of the treated water can be seen in Figure 34.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25

T S S o u l e t ( p p m )

T S S i n l e t

( p p m )

Sample

DUF 1 ‐ inlet DUF 2 ‐ inlet DUF 3 ‐ inlet

DUF 1

‐outlet DUF

2

‐outlet DUF

3

‐outlet



37

(a) DUF 2 (b) DUF 3


4.3. Continuous operation

The continuous operation of the system was evaluated for 26 hours without a chemical cleaning.

The system was operated at constant TMP. The biggest challenge is still to achieve stable

operation given

the

disturbances

in

the

inlet

concentrations.

A

summary

of

the

pilot

plant

inputs

is

shown in the Table 8.

Table 8. Summary of the operating conditions for the continuous operation of the treatment after the

skimming tanks.

Test Crossflow

(auto)

Feed pump

(manual)

Backpulse

(s)

Backflush

(s)

Permeate Retentate

04V04(%) 03V01

(%)

03V02

(%)

CDUF 26 h 30‐40 28‐45 60‐90 300 80‐90 40‐50 40‐50

For the

continuous

operation,

the

results

are

shown

in

Table

9 and

data

shown

in

Figure

35

and

Figure 36. Only one point is evaluated due to time constraints. When the experiment started, a

moderate TMP was chosen to start with. Based on the tuning experiments it should provide a flux

of approximately 500 LMH. The initial flux was around 400 LMH which declined with time and

achieved stable operation at around 340 LMH after 5 hours of operation. This flux was maintained

all night slightly increasing the TMP. After 19 hour of operation, it is decided to operate at

constant flux conditions with a target of 440 LMH. The system achieved a new stationary

operating point at a TMP of 1.2 bar. The sustainable flux was very similar to the fluxes obtained for

the previous feed point. However, the operation in this point was more stable and potentially



38

longer operating time between chemical cleanings, specially using the constant permeate

operating mode.

Table 9. Summary of the continuous experiments after the skimming tanks

Operating

point

Minimum flux conditions Maximum flux conditions Average inlet (ppm) Initial

PERM* LMH TMP REC PERM LMH TMP REC PERM OiW TSS

CDUF 26h 310 0.6 63 490 440 1.2 68 390 20.36 2.86 1700


Figure 35. Flux profile during the continuous experiment CDUF 26h

0

100

200

300

400

500

600

700

800

13:55:12 18:43:12 23:31:12 04:19:12 09:07:12 13:55:12

F l u x ( L M H )

Time (h:m:s)



39

Figure 36. TMP profile during the continuous experiment CDUF 26h

The water quality during the continuous experiment is shown in Figure 37 and Figure 38.

Figure 37. Oil in water concentration at the inlet and outlet of the pilot plant for the continuous

operation

‐0.5

0.0

0.5

1.0

1.5

2.0

13:55:12 18:43:12 23:31:12 04:19:12 09:07:12 13:55:12

T M P ( b a r )

Time (h:m:s)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0

5

10

15

20

25

30

35

40

45

0 2 4 6 8 10 12



Sample

CDUF 1 ‐ inlet CDUF 1 ‐ outlet



40

It can be seen in Figure 37 that at the beginning of the experiment the OiW concentration was

rather constant for 18 hours. Only at the end there was a considerable increase in the

concentration. Despite this moderate variation, the OiW content in the treated water was kept

below 1 ppm. The oil removal was between 96.3% and 100%.

Figure 38. Total suspended solids concentration at the inlet and outlet of the pilot plant for the

continuous operation

The suspended solids inlet concentration was stable at the beginning of the experiment whereas

some disturbances appeared towards the end. The TSS removal was 100% in most of the cases,

only one point showed a lower removal (96.4 %). Some pictures of the continuous operation of the

plant are depicted in Figure 39.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

0 2 4 6 8 10 12

T o t a l

s u s p e n d e d s o l i d s ( p p m )

T o t a l

s u s p e n d e d s o l i d s ( p p m )

Sample

CDUF 1 ‐ inlet CDUF 1 ‐ outlet



41

(a) OiW content (b) Suspended solids


4.4 Conclusions

From this first testing it can be concluded:

From the laboratory analysis of the average inlet water characteristics, it can be seen that

there is

considerable

variance

from

day

to

day,

where

the

concentration

can

easily

amplify

several times (eight for OiW and two for TSS).

The tuning experiments of the second sampling point (after skimming tanks) showed

improvements in the maximum flux compared to the first feed point evaluated (before

skimming tanks), around 30%. However, this result is not linearly correlated with the

changes in the inlet concentrations for both points.

The qualitative analysis of the obtained data indicated that the best sustainable operation

can be achieved with TMP´s between 0.8 and 1 bar.

The tuning experiments shown that the OiW and TSS target concentrations where

achieved, not higher than 5 ppm. The oil and TSS removal were up to 100%.

During the continuous operation of the plant, moderate disturbances were evidenced in

the feed concentration. Stationary operation was achieved at moderate flux conditions

first 340 LMH and later 440 LMH, using 30 m3/h cross flow, a backpulse frequency of 60 s,

a backflush frequency of 300 s. At this feed point, it is not that relevant to monitor the

inlet concentration, since the Skimming tanks act storage tanks that buffer the inlet

disturbances. During the continuous operation, the OiW and TSS target were achieved

(concentration below 5 ppm). From the tuning experiments it is expected to have better

fluxes.



42

5. Cleaning in place evaluation

The

cleaning

strategy

was

evaluated

through

the

water

permeability

evaluation.

The

results

of

the

experiments are depicted in Figure 40. The initial water permeability of the membrane was 2800

LMH/bar at a TMP= 0.2 bar and using a cross flow of 30 m3/h. The fouling load in each of the

experiments was different mainly due to changes in inlet concentrations, cleaning water quality,

TMP, recovery and operation time. Initially the cleaning strategy consisted of one washing cycle:

1. Flushing with water

2. Alkaline cleaning: 30 min with 1% NaOH, 50 m3/h crossflow


4. Acid cleaning: 30 min with 1% Oxalic acid, 50 m3/h crossflow


Figure 40. Flux recovery after chemical cleaning. The initial water permeability was 2800 LMH/bar.

One cleaning cycle was enough during the first operation days. However, a loss of cleaning

efficiency was evidenced the 14/07/2012 and 21/07/2012. The 21/07/2012, was decided to use 2

washing cycles in order to recover the water permeability. It is acceptable to have a flux recovery

above 70%. After the continuous tests performed on the 24/07/2012, it was difficult to recover

permeability, even after the 2 washing cycles. However, the desired permeability was restored

after the 26/07/2012. Those dates correspond to the second sampling point (after skimming

tanks). It can be concluded that the type of fouling evidenced in the field is reversible to the

desired point in most of the cases.

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

R e c o v e r y ( % )



43

6. Final remarks

Evaluation point before skimming tanks:

5.1.1 Inlet water quality

Variance in the inlet water quality: high

Variance in the outlet water quality: low

5.1.2 Operability

Monitoring level required: significant

Changes in the operating conditions: significant

Chemical cleaning frequency: largely depends on the atypical events faced during continuous

operation

Longer operation might show other operation challenges (i.e. scaling and irreversible fouling)

5.1.3 Other aspects

Technical feasibility: it is recommended to include a buffer tank to assist the membrane

operation.

Membranes arrangement: parallel/series configuration with multiple membrane housings

could be exploited

Evaluation point after the skimming tanks:

5.2.1 Inlet water quality

Variance in the inlet water quality: moderate

Variance in the outlet water quality: negligible

5.2.2 Operability

Monitoring level

required:

low

Changes in the operating conditions: low

Chemical cleaning frequency: considerable lower than in the first evaluation point. The

appropriate frequency can be estimated from and OPEX analysis

5.2.3 Other aspects

Technical feasibility: high

Membranes arrangement: parallel/series configuration could be exploited



44

7. Future challenges

It is important to understand further the characteristics of the feed streams, not only

concentrations. This information is not only relevant for the operation but to improve the

cleaning strategies.

The methodology used for the determination of the operative window is impaired by

fluctuations in the inlet concentrations, making the estimation of the sustainable

operation more difficult. Further developments in the tuning strategy are needed.

The variance in the inlet concentration is probably the biggest obstacle to tune the system

and to operate in continuous. Monitoring of the inlet concentration is relevant for the

appropriate operation.

In

the

field

there

are

interactions

between

the

pilot

plant

and

the

existing

installations

at

industrial scale. Further electric protection for the system can avoid damage.

There is a lack of understanding of the interactions between the added chemicals in the

actual treatment and the membrane. Besides, the interactions between the acid and

alkaline solutions and the chemicals added. These topics remain for investigation.



45

8. Appendix: Critical flux estimation

The

critical

flux

was

estimated

using

two

different

methodologies

described

in

literature

5

,

referred

to as average pressure and fouling rate methods. Details of the methods can be found in the

mentioned paper. According to the employed methodology during the experiments, the flux is

increased step wise aiming to find where the production becomes unsustainable for the given

input water quality. As mentioned extensively along the report, the variance in the inlet

concentration is the biggest obstacle to determine the critical flux. Therefore, it is better to aim for

identification of the critical flux window for each of the evaluated test points.

The critical flux is estimated using two different methods. Additionally, the step up‐down test

allows identifying when the irreversible fouling starts forming. Small description of the methods is

presented bellow.

a) Average pressure: this method evaluates the average TMP against the average flux along

the experiment. The critical flux is determined by the deviation from linearity, meaning

the presence of a maximum flux.

b) Fouling rate method: this method evaluates the fouling rate (dP/dt) against the average

flux along the experiment. The critical flux is determined for a notable increase in the

fouling rate by increasing the flux.

c) Irreversible fouling: it should be understood as the onset of the irreversible fouling. This

method evaluates the difference TMP for the same flux level steps. When fouling starts to

get irreversible, the TMP cannot be restored when moving from the next step due to the

higher flux

in

between.

It should be mentioned that not all the experiments behave as in the ideal case. It is believed that

the concentration changes along the experiments are the main reason.

8.1 Evaluation before the skimming tanks

For this test point, there are four tuning experiments. The first one does not use the in situ

cleaning strategies, so it is called conventional ultrafiltration (CUF). The remaining experiments use

the backpulse and backflush, so they are referred to as dynamic ultrafiltration (DUF). Good

examples of the obtained plots are shown in Figure 41 and Figure 42. A summary of the results for

all experiments

are

shown

in

Table

10.

5 Beier, S.P. and Jonsson, G. Critical Flux Determination by Fux Stepping. AIChE Journal 56(7). 1739‐1747.



46

Figure 41. Average pressure method for critical flux estimation. Results of experiment DUF4 (Critical

flux at 0.8 bar)

Figure 42. Fouling rate method results for critical flux estimation. Results from CUF experiment

(Critical flux 150 LMH)

0

50

100

150

200

250

300

350

400

450

0.72 0.74 0.76 0.78 0.80 0.82 0.84 0.86

A v e r a g e f l u x ( L M H )

Average TMP (bar)

0

2

4

6

8

10

12

14

16

18

100 110 120 130 140 150 160 170 180 190 200

d P / d t ( b a r / h )

Flux (LMH)



47

Table 10. Critical flux estimation from the tuning experiments before the skimming tanks.

Experiment

Critical flux

Method (Avg P)

Critical flux

Method (dP/dt) Irreversible

fouling flux

(LMH) Flux

(MLH)TMP

(bar) dP/dt

(bar/h)Flux

(MLH)TMP

(bar)dP/dt

(bar/h)

CUF 187.5 0.54 15.63 150 0.65 1.96 150.00

DUF 1* 186.5 0.24 2.09 186.5 0.24 2.09 155.69

DUF 2* 240.23 0.69 2.05 240.23 0.69 2.05 182.30

DUF 3 218.56 0.95 6.53 205.03 0.97 26.21 170.84

DUF 4 352.41 0.80 0.72 352.41 0.80 0.72 341.61

* Critical flux not achieved, then maximum value depicted

Due to time constraints performing the experiment, the critical flux is not achieved in all cases.

However, the information gathered was used in the following experiments. It can be seen in Table

10, that

the

critical

flux

was

not

achieved

in

DUF1

and

DUF2.

Therefore,

the

maximum

evaluated

flux is shown. The results are presented in Figure 43 and Figure 44.

Figure 43. Critical flux from the tuning experiments before the skimming tanks

Only for the conventional ultrafiltration, both methods gave considerable different results

(approx. 25%). From the experiments, it can be seen that the critical flux lies between 200 and 350

LMH. This range is broad and totally depends on the concentrations given during the tuning

experiments. For this reason, the operating TMP is considered as a better way to delimit the

operating window since the operation mode is constant TMP. In Figure 44, the critical TMP

Avg. P

dP/dt0

50

100

150

200

250

300

350

400

CUFDUF 1

DUF 2DUF 3

DUF 4

C r i t i c a l f l u x ( L M H )

Experiment



48

window can be identified between 0.7 and 1 bar. This confirms the conclusions obtained in the

field for this testing point.

In most

of

the

cases

the

onset

of

the

irreversible

fouling

formation

is

lower

than

the

critical

flux

(see Table 10). For that reason, the continuous experiments were performed using a conservative

TMP and sustainable operation was achieved due to the in situ cleaning strategies.

Figure 44. Critical TMP from the tuning experiments before the skimming tanks

8.2 Evaluation after the skimming tanks

For the test after the skimming tanks, there are three tuning experiments. All the experiments use

the backpulse and backflush, and referred to as dynamic ultrafiltration (DUF). Good examples of

the obtained plots are depicted in Figure 45 and Figure 46. The summary of the results of all

experiments are shown in Table 11.

Table 11. Critical flux estimation from the tuning experiments after the skimming tanks

Experiment

Critical flux

Method (Avg P)

Critical flux

Method (dP/dt) Irreversible

fouling flux

(LMH) Flux

(MLH)

TMP

(bar)

dP/dt

(bar/h)

Flux

(MLH)

TMP

(bar)

dP/dt

(bar/h)

DUF 1* 405.03 0.32 ‐0.14 405.03 0.32 ‐0.14 N/A

DUF 2* 573.24 0.69 1.94 573.24 0.69 1.94 486.32

DUF 3 703.28 1.24 11.25 600.97 0.88 1.97 536.87

* Critical flux not achieved, then maximum value depicted

Avg. P

dP/dt0

0.2

0.4

0.6

0.8

1

CUFDUF 1*

DUF 2*DUF 3

DUF 4

C r i t i c a l T M P

( b a r )

Experiment



49

Figure 45. Average pressure method for critical flux estimation. Results of experiment DUF3 (Critical

flux at 1.24 bar)

Figure 46. Fouling rate method results for critical flux estimation. Results from DUF experiment

(Critical flux 645.86 LMH)

In the average pressure method (Figure 45), the deviation from linear behavior occurs in the

maximum flux evaluated. In the second method the critical flux lies between the last two

evaluated points, and then the last with relatively low fouling rate is selected (notice that the

second plot has only 4 points, this is due to a lost in the data for this experiment). The results

from Table 11 are depicted in Figure 47 and Figure 48. Notice that the first two experiments, DUF1

and DUF2, did not achieve the critical flux.

0

100

200

300

400

500

600

700

800

0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

A v e r a g e F l u x ( L M H )

Average TMP

(bar)

0

2

4

6

8

10

12

400 450 500 550 600 650 700 750

d P / d t ( b a r / h )

Average flux (LMH)



50

Figure 47. Critical flux from the tuning experiments after the skimming tanks

From the experiments, it is difficult to determine if both methods are giving the same results since

only one experiment achieved the critical flux. In that case, the obtained critical fluxes are slightly

different (approx. 16%). For this testing point, it is estimated to have sustainable fluxes between

600 and 700 LMH. Nevertheless, this result depends on the evaluated concentrations. The limited

information was collected in this evaluation point due to time constraints. For evaluation of this

point, more conservative sustainable fluxes are expected. This was confirmed during continuous

operation where

the

system

operated

at

maximum

440

LMH.

Figure 48. Critical TMP from the tuning experiments after the skimming tanks

Avg. P

dP/dt0

200

400

600

800

DUF 1*DUF 2*

DUF 3

C r i t i c a l f l u x ( L M H )

Experiment

Avg. …

dP/dt0

0.5

1

1.5

DUF 1*DUF 2*

DUF 3

C

r i t i c a l T M P ( b a r )

Experiment

Avg. P

dP/dt



Once again, it is relevant to determine the TMP operating window. It can be seen in Figure 48 that

the TMP operating window lies between 0.8 and 1.2 bar. This confirms as well the proposed

operating window investigated during continuous operation. Finally, the onset of the irreversible

fouling formation occurs again at fluxes lower than the identified critical fluxes (see Table 11).

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