Foaming in EP Industry- A Global Perspective

8/4/2019 Foaming in EP Industry- A Global Perspective

1/18

Foaming in EP Industry- AGlobal Perspective

Arun BhattacharyaTW Services


2/18

2

What is Foaming? A foam is a substance that is formed by trapping many gaseous bubbles in a liquid (or

solid). Foams are extremely complex systems consisting of poly-disperse gas bubblesseparated by draining films.

Several conditions are needed to produce foam: there must be mechanical work,

presence of surface active components (which reduces surface tension) and foamformation rate faster than break-down rate (dictated by various forces e.g.gravitational, osmotic and Laplace pressures).

Foaming problems have been reported in both production and refining applications.However this presentation focuses on production applications (including natural gasprocessing applications) only.

According to a survey conducted among Gas Processing plants in Texas, New Mexicoand Alberta, it was reported that none operates without the usage of anti-foam.

Another US survey revealed that lower 25% of the surveyed plants face the foamingproblem almost daily while median amine plants face an average of seven episodes peryear. This indicates the magnitude of the problem.

Business impact of foaming is huge-often running to millions of dollars in reducedproduction revenues, increased equipment down-time & maintenance costs etc.
http://en.wikipedia.org/wiki/File:Foam_-_big.jpg


3/18

3

Foaming in Crude Oil Systems Commonly Foaming problems have been observed in following EP areas:

- Production Separators- Produced Water Treatment (Gas Floatation units)- Gas Dehydration (Glycols)- Gas Sweetening (Amines)

The root cause of foaming is different for each system.

In crude oil systems, foaming tendency has been found to be in direct proportion toasphaltenes concentration. Naturally occurring surfactants specially short chaincarboxylic acids and phenols of MW


4/18

4

Foaming in Crude Systems- BP Case Study

BPs Sullom Voe Terminal: Several foaming observed in HP & LP separators. Conventional anti-foams did not work at higher GOR. Under severe conditions, separator internals (dixon plates) &demister were not effective.

A foam density profile using gamma ray scans in the separator showed the following across theseparator diameter. Density profile did not change along the separator length.

Based on above, it was estimated that crude contents of foam was between 28%-66% and up to

50% of crude fed could be carried over in foam. It was estimated only 40% of design capacitycould be achieved without any foam control facilities.

A novel foam inhibitor was finally developed and was effective in foam control. Extensive facilitymodifications were carried out to install permanent anti-foam injection facility along with gammaray scanning facility for the separators.

No foam Profile

Profile w/ Foam

Height

Density

Vapor Liquid

Density Density


5/18

5

Foaming in Crude Systems- Kuwait Case Study

Facility for treating onshore dry crude oil consisted of separators and tanks. Mechanicalfoam breakers (inlet degassing element and de-foamer plates) were installed in theseparators. However these proved to be ineffective as excessive foaming was observedin day-to-day operations.

Silicone based anti-foams were tested for foam control which resulted in markeddifference in separator throughput and liquid carry-over in the gas stream almoststopped. The following results were reported.


6/18

6

Foaming in Crude Systems- Some Process

Considerations

Key to Foam control is to prevent it forming in the first place. Hence the focus shouldbe to identify and remove the foam stabilizing element, if possible. Sometimes installingsuitable filter media upstream of separators can solve the problem. However many atime this is not possible.

Surface whips, thermal shocks and ultrasonic techniques have also been proposed forfoam control. However mechanical devices are usually not considered adequate and areoften accompanied by anti-foam injection facilities for foamy crudes.

Difference between anti-foams (chemicals used to inhibit foam formation- before it isformed) and de-foamers (chemicals used to break foams- after it is formed) should beappreciated.

Key process design parameter in equipment sizing for foamy crudes is the retentiontime available/ required to break the foams. Essentially it comes down to the costbenefit between larger equipment costs (offering higher retention time) vis--vis higherfacility operating costs (with anti-foams).

While designing upstream separation facilities for green field projects or supplementalfield development thro brown-field projects, careful considerations for foamingcharacteristics of crude systems should be given. Non-identification of this parametercarries the risk of potentially significant business impact.


7/18

7

Foaming in PW Treatment Systems (Gas

Floatation) Foaming in PW treatment systems can cause excessive liquid carry-over and loss of

separation efficiency.

In produced water treatment, foaming can either be a problem or a benefit, dependingon the amount of foam. For example, a certain amount of foam is beneficial in gas

flotation cells, however excessive foam makes subsequent handling of the recoveredwaste stream more difficult.

Two types of compounds are commonly used for controlling foam, silicones and poly-glycol esters. These compounds work by disrupting the gas/liquid interface thusbreaking down the foam. These compounds have low solubility in both oil and water.

Typical treatment concentrations are 5 -25ppm. In PW treatment applications, thesecompounds stay with the recovered oil froth, which is returned to the produced oilstream. Therefore only small amounts of the de-foamers are discharged in theproduced water.


8/18

8

Foaming in Glycol Dehydration System

High Glycol loss from gas dehydration circuit is a common operating problem in globalEP industry. Glycol loss is broadly categorised under the following heads:

Vaporisation Losses both from Contactor and Regenerator. Equilibrium glycol loss fromContactors is usually around 5% of total loss and is primarily due to high gas temperature.

Vaporisation loss from the still is mainly due to high still temperature and high stripping gas

rate. Carryover losses both from Contactor and Still Column: Primarily due to foaming, high gas

velocity and inadequate mist-mat capacity (at high foaming rates, even a well designed mist-mat can not stop excessive liquid carry-over).

Mechanical Losses- usually negligible for well maintained plants.

Foaming in Glycol system usually results from the following main causes:

Condensate Carry-over from upstream units as a result of poor separation efficiency/

inadequate inlet separation devices/ inadequate skimming facility to prevent condensate carry-over to regen system. TEG degradation products (due to higher reboiler temp- typically above 204C) , if not filtered

properly, will tend to accumulate in the system and cause foaming.


9/18

9

Benchmarking Glycol Dehydration Performance

As it is difficult to predict and benchmark extent of foaming in glycol systems, industryfocus remained on total glycol loss data. However following may be noted in thisregard:

As stated earlier, some glycol losses are unavoidable which are governed by

thermodynamic equilibrium and glycol solubility in hydrocarbon gases (dependenton operating P,T, Composition).

Higher pressure and lower temperature combinations tend to reduce glycol losseswhile lower pressure and higher temperatures tend to increase these losses. It hasbeen suggested that glycol losses start to become appreciable at gas densities>100 kg/m3 and gas temperature>49C.

Feed gases with high CO2 content will tend to offer higher glycol losses(particularly at >62 bar, as CO2 becomes dense phase). The following limits arenot applicable for such scenario (mostly applicable for CO2 flood/EOR conditions).

Following are the various Industry guides/ benchmarks for total glycol loss data(complied from various sources).


10/18

10

Referenced Benchmark Performance

Sl.

No

Quoted

Glycol LossReference

120-60

lit/MMSm3

DEP 20.04.10.10-Gen (Dec 1994).The quoted losses are typical for properly designed and maintained dehydration unit.

Suggested that the typical entrainment loss with bubble cap trays is of the order of 10

lit/MMSm3 (included in the above figure).2

0.05-0.30gal/MMSCF

GPSA.The lower figure for HP-LT mode and the higher figure for LP-HT mode.

3 -do- Worley design guide

4 25 lit/MMSm3 BP Guideline for Glycol dehydration Unit for North Sea (UK) operations.

50.13

gal/MMSCF

TOTAL guidelines for properly operated unit.

Suggested to use this figure for Technical audit/ benchmarking purposes.

60.1

gal/MMSCF

North American Gas Industry accepted norm, as quoted by:- Pipeline & Gas J, July 1988 (Improving Gas Dehydrator Efficiency, Randy

Neal);- Oil & gas J, Sept 1981(Avoiding excessive glycol costs in operation of gas

dehydrators);- Simmons Charles); Hydrocarbon Processing, April 1977 (Operators Talk-

glycol dehydration, Ballard Don).Typically these cases refer to onshore/pipeline operations.


11/18

11

Some Reported Performances

1 25 lits/MMSm3Shell Expro (UK, Brent platform).The operating pressure was between 115-138 bara (gas density=140-170 kg/m3).

2 Negligible Shell NAM offshore (Netherlands) , 136 barg, 30C, Sulzer Mellapack 250Y.

30.25

gal/MMSCF

Shell Gulf of Mexico (USA) Operating data.Suggested solubility losses in the order of 0.02-0.06 gal/MMSCF and about 0.2gal/MMSCF for inefficient operation.

40.16-0.35

gal/MMSCFARCO Oil & Gas (USA), based on five most efficient packing test data (Structurepacking proven superior for TEG gas drying; Kean et al, Oil & Gas J, Jul 2006).

57-40/75/12-25

lit/MMSm3

Operating data from 3 fields operated by TOTAL (locations undisclosed).Operating P,T conditions were: 50/55/26 barg, 61/60/25 C (TEG inlet temp); 30-40/26/18C (Gas inlet temp).

6 3 mg/Nm3 Sulzer quoting revamping experience with Mellapack-plus packing (NewFrontiers inGlycol Contactor design, Brunet et al, GPA Amsterdam, Sept 2001).

7 60 lit/MMSm3ONGC Bombay Offshore (India) Operating data for BPA platform (7% CO2).;Operating P=103 bar, Gas inlet temp=43 C, Glycol inlet temp=51C


12/18

12

Effects of Foaming on Packed Bed Efficiency


13/18

13

Effects of Foaming on Packed Bed Pr Drop


14/18

14

Foaming in Glycol Systems- Some Process

Considerations

Key to Foam control in glycol dehydration system is to operate the plant within designlimits and identification/rectification of the root cause of the problem.

Use of anti-foams on a long term basis is not recommended as it continues to build-upin the closed circuit and over the time hardens the foam structure (particularly if glycol

degradation products are available in the system). A case has been reported whereprolonged use of antifoams totally reduced their effectiveness and entire glycolinventory was to be replaced.

Often carry-over of condensates from upstream process equipment causes foaming.Upstream equipment adequacy should be checked when frequent foaming problemsare reported and remedial actions to improve separation efficiency should be initiated.

Carbon filters are effective in adsorbing condensates in glycol streams (a slip-stream,around 10% of lean glycol rate, is usually directed towards activated carbon bed).However if not properly maintained, carbon particles may enter the circulating glycolstream which can act as foam-stabilizer.

Regeneration temperature should be properly maintained (


15/18

15

Foaming in Amine Systems

Solvent foaming is a well known and #1 operating problem in Natural gas processing(Gas Sweetening) industry yet contaminants who actually cause the problem areseldom, if ever, are quantified.

Some startling facts on impacts due to foaming in Natural Gas Processing plants: Two of the most recognized area of revenue loss due to foaming are production

loss and solvent loss. In one plant:

Production loss of over $2M/year was reported. Over $500,000/year was spent to control foaming in amine unit. Particle filters were changed every hour to control foaming, costing over

$400,000 / year. On average, amine inventories are changed 3 times/year. ......

Indirect costs associated with foaming were probably higher than direct costs.These included downstream process damage and environmental violations.

Numerous case studies are available in literature describing various attempts madeby EP Industry to tackle this problem- success stories came sometimes withchanges in operating practices and sometimes with costly retrofits.


16/18

16

Key factors

Clean solvents do not foam. Foaming is caused by solvent contamination by carriedover solids, erosion-corrosion products. liquid hydrocarbons, well treating chemicals,corrosion inhibitors, lubricants, acidic amine degradation products and antifoamadditives. Solvent make-up water can also be a major source of foaming as it maycontain corrosion inhibitors and chelating agents (used to treat boiler feed water).

Most severe solvent contaminants are not visible. Check for Heat-Stable Salts (formate,oxalate, acetate, thio-cyanate, sulphate etc) which decrease amine solutions gascarrying capacity and increase viscosity , thus increasing Operating costs.

Difficult to identify root cause. Filtration system design is a key component yet all its functionality not fully understood.

A single filter may be effective in removing organic contaminants yet ineffective in anti-foam additives.

While antifoam agents reduce foaming tendency, they increase foam stability.Continued treatment with antifoams will initially knock back the foam, but will make thesolution sensitive to smaller amounts of foam promoters. The best remedy is toeliminate the need for antifoam agents by removing liquid hydrocarbons and othersurface active materials from the inlet gas. Activated carbon should be used to removeamine degradation products.


17/18

17

Predict Foaming in AGRU


18/18

18

Closing Remarks

Foaming creates undesirable, difficult to predict/control and highly expensiveoperational upset conditions.

Foaming mitigation is not an exact science- experience plays a big role.

Aspects of foaming, its impact on operations and possible mitigating measuresshould be kept in mind while designing and operating EP facilities.

There is no one-fits-all solution for foaming problems- each problem is unique andshould be analysed in its own merit.

Thank you for this invitation !

Foaming in EP Industry- A Global Perspective

Documents

Transcript of Foaming in EP Industry- A Global Perspective