Effect Glycol in Gas Stream to AGRU

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    THE EFFECT OF GLYCOLS ON THE PERFORMANCE

    OF THE ACID GAS REMOVAL PROCESS

    Torsten Katz  

    Georg Sieder

    Justin Hearn

    BASF SE, Ludwigshafen, Germany

    ABSTRACT

    In some natural gas applications glycols, such as MEG, DEG or TEG, are added into the pipeline or the gas

    conditioning process, either as hydrate inhibitors or for dehydration purposes to protect downstream pipelines.

    These substances have high boiling points and are not supposed to be carried over into the downstream

    process. Proper separator design shall avoid carry-over of these substances into the Acid Gas Removal

    plant.

    Some amine plants however report glycol build-up in the amine solution over time, which can lead to

    performance losses and ultimately to unexpected plant shutdowns. This paper deals with the sources and

    consequences of glycol build-up in the amine unit and delivers some understanding of how the glycol content

    affects the acid gas capture performance. It provides recommendations on how to control the full acid gas

    capture performance over time and how to avoid operational surprises.

    1. INTRODUCTION

    Raw natural gas usually comes from oil wells, gas wells or condensate wells. Besides methane it contains

    further valuable components, such as ethane, propane, butane, and other hydrocarbons. However, unwanted

    components such as water, nitrogen, carbon dioxide, hydrogen sulfide and other trace sulfur components are

    quite common. Before sending the gas to a sales gas pipeline or before liquefaction, some conditioning is

    required, to purify the gas and to fulfill pipeline or LNG specifications.

    Conditioning takes place in several steps and sometimes starts near the wellhead. In many applications

    several wells from one or several fields are feeding raw natural gas via gathering pipelines to one central

    processing plant. Depending on project specifics, the length of the gathering pipeline system can consist of

    thousands of miles of pipes, interconnecting the processing plant to upwards of 100 wells in the area1.

    Monoethylene glycol (MEG) is sometimes injected into the gathering systems. Its high affinity towards water

    suppresses hydrate formation and avoids plugging of pipelines.

    In the central processing plant, the final purification takes place. Here, pipeline or LNG specification of the

    natural gas is ensured, including the adjustment of the acid gas content and the water dew point. A common

    setup is shown in Figure 1:

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    Figure 1: Conditioning setup of a sales gas plant2 

    For sales gas applications, where the natural gas is sent to a pipeline, glycols or silica gels are common

    means for adjusting the water dew point. According to the Gas Processors Association a water content of less

    than 7 pounds per million cubic feet is a recommended value for pipeline quality4. For LNG applications

    molecular sieves are the only option to achieve a water dew point specification of less than 0.5 ppmv, which is

    necessary to avoid freezing in the cryogenic section of the plant. The dehydration unit is usually downstream

    of the acid gas removal unit (ARGU). For AGRUs using amines this is always required, since the gas leaves

    the AGRU under more or less water saturated conditions.

    In some applications, LNG plants receive their feedstock from a common pipeline grid. This is because major

    LNG production facilities always require seaport access, whereas the gas fields may be located far away from

    the processing site. SEGAS LNG in Egypt for example has such a setup. This unusual pipeline/processing

    setup will be found more often in future: most of the US and Canadian LNG production facilities will receive

    their feedstock from the sales gas pipeline grid and do not use dedicated pipelines. For these cases the

    receiving gas has already undergone a full conditioning process, thus the natural gas may have been

    processed by using glycols in the upstream conditioning process.

     Another example for the use of glycols in natural gas applications was presented in last year’s LGRCC:Schroeter et al.

    3  reported about the setup of the In Salah gas plant in Algeria; this unit consists of three

    pre-processing plants, in which - among others - the water dew point of the natural gas is adjusted by using a

    triethylene glycol unit (TEG) before compressing the gas and sending it to a central processing facility, where

    a second TEG dehydration downstream the AGRU is installed:

    InletSeparator

     AGRU(CO2 removal)

      Dehydration  Dew Point

    Control

    Stabilizer

    DEGRegeneration

      Refrigeration

    Raw

    NaturalGas

       I  n   l  e   t   M  a  n   i   f  o   l   d

    HC Liquid HC Liquid

    Recycle gas

    NGL

    Product

    to export

    Sales

    Gasto P/L

    DEG solutionRefrigerant

    CO2

    Incineration CO2 to Atmosphere

    Train-B

    Train-C

    Train-A

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    Figure 2: Overview of the In Salah gas processing plant

    The previous description shows that different glycols are being used at different point in the production chain,

    in most cases downstream the AGRUs but sometimes also upstream of the AGRUs.

    2. GLYCOLS IN NATURAL GAS CONDITIONING

    The most common types of glycols in natural gas application are monoethylene glycol (MEG), diethylene

    glycol (DEG) and triethylene glycol (TEG). Whereas MEG is mainly used as an alternative for methanol for

    hydrate inhibition (direct injection into the pipeline), DEG and TEG are being used for dehydration purposes.

    Table 1: Molecular mass, boiling point and viscosity of MEG, DEG and TEG

    GLYCOL Molecular mass Boiling point at atmospheric pressure Viscosity at 25°C (68 F)

    MEG 62.07 g/mol 197°C, 387 F 16.9 cP

    DEG 106.12 g/mol 244°C; 471 F 35.7 cP

    TEG 150.17 g/mol 285°C; 545 F 49.0 cP

    Due to its higher boiling point, TEG can be more easily regenerated to a higher purity, and hence achieves

    better water removal and lower dew point than either DEG or MEG. A disadvantage of TEG is its higher

    viscosity, which can make liquid handling in plants under low temperature conditions very difficult. In these

    applications, DEG is the preferred glycol. The setup of a glycol dehydration plant looks as follows:

    Hassi R’Mel

    CompressionKrechba

    Teg

    Reg

    Hassi

    Moumene

    Garet el

    Befinat

    Gour 

    MahmoudIn Salah

     4 8 ”

     4 5 5  k

     m

    24” 

    62 km

    38” 

    60 km24” 

    13 km

    CNDG

    Gas Network 

    Phase 2 (future)

    Phase 1 (2004)

    Field Facility

    Central ProcessingFacility

    Wells + Gas gathering

    system

    Hassi R’Mel

    CompressionKrechba

    Teg

    Reg

    Hassi

    Moumene

    Garet el

    Befinat

    Gour 

    MahmoudIn Salah

     4 8 ”

     4 5 5  k

     m

    24” 

    62 km

    38” 

    60 km24” 

    13 km

    CNDG

    Gas Network 

    Phase 2 (future)

    Phase 1 (2004)

    Field Facility

    Central ProcessingFacility

    Wells + Gas gathering

    system

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    Figure 3: Process flow scheme of a glycol plant6 

    To avoid condensation of hydrocarbons in the unit, the lean glycol temperature is recommended to stay 10°R

    (5.5 K) above the gas inlet temperature4, 5

    . Common feed gas temperatures between 5 to 50°C (41 to 122°F)

    result in lean glycol temperatures between 10.5 – 55.5°C (51 – 132°F). Taking a usual TEG flow rate of 6 – 8

    gal/lbH2O into account5, the resulting heat of water condensation for common natural gas pressures (p = 40 –

    75 bara, 580 – 1088 psia) will only marginally contribute to an increase of the feed gas temperature (usually <

    3.6°R or 2 K). Lower feed gas pressures may lead to somewhat higher temperatures in the treated gas.

    However the assumption that the glycol absorber treated gas temperature equals the feed gas temperature

    allows the approximation of the minimum glycol content caused by vapor pressure losses in the treated gas.

    In contrast to amine absorbers, a glycol absorber can never have a water backwash section to reduce vapor

    pressure-induced solvent losses, since the gas would immediately saturate with water again. As a

    consequence, the treated gas exiting the glycol absorber will always be glycol saturated for the pressure and

    temperature conditions in the glycol absorber top, as shown in Figure 4.

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    Figure 4: Differences in glycol and amine absorber top sections

    Even though glycol vapor pressures are very low, a low concentration of glycols will always end up in the

    glycol absorber treated gas phase. Losses by entrainment will further increase the content. Table 2 shows

    two gas compositions, which will be used for a case study in this article,

    Table 2: Glycol treated gas conditions for the case study

    Case 1 Case 2

    CO2  9.62 vol% 1.75

    N2  0.76 vol% 0.50

    CH4  81.3 vol% 96.05

    C2H6  6.10 vol% 1.30

    C3+  2.14 vol% 0.40

    H2O  varies varies

    T 25°C

    77°F

    40°C

    104°F

    p 59 bara

    856 psia

    50 bara

    725 psia

    Case 1 represents a CO2-rich gas, which is also rich in C2 and C3+ components, whereas Case 2 represents

    a leaner gas, coming from a pipeline.

    Figure 5 shows the glycol saturation concentration over the temperature range for gases with compositions

    according to Case 1 and Case 2 for pressures of 50 and 70 bara (725 and 1015 psi). The values have been

    determined by using the commercially available software Multi-Flash7 by using the cubic equation of state PR

    (advanced). Even though the gases are quite different with respect to acid gas content and heavy

    hydrocarbon content, neither of these two parameters has a substantial impact on the glycol solubility, at least

    not for typical LNG feed gas conditions.

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    Figure 5: Glycol content for feed gas conditions

    The glycol content in the gas mainly depends upon the type of glycol and the temperature. Glycol

    concentrations between 1 ppbv up to 100 ppmv are possible.

    Liquid entrainment can further increase the glycol content in the gas. In order to minimize make-up costs,

    special focus should be put on the selection of the demister pad in glycol absorbers.

     As an example, the data from Figure 5 shall be applied on the In Salah Gas plant, which was presented at the

    2012 LGRCC3. The feed gas to the AGRU had a temperature of about 52°C / 126°F at a pressure of 67 barg /

    972 psig. As reported, the gas is being treated with TEG further upstream. Assuming that the AGRU feed gastemperature equals the TEG dewpoint temperature, the gas contains about 350 ppbv of TEG according to

    Figure 5. At 1000 MMSCFD or 49804 kmol/hr, this equals 49804 kmol/hr * 300ppbv*150.17 kg/kmol = 2.61

    kg/hr TEG ingress (5.75 lb/hr), or over a period of 1 year = 22.9 mt. As it will be shown later in this article, the

    losses of TEG via the treated gas and the acid off gas a rather negligible, these 22.9 mt/year will contribute to

    a TEG buildup in the system. Under consideration of a total solution holdup of 1060 mt, this results in an

    annual TEG built-up-prate of 2.1 wt%. A comparison with the results of a figure from Schroeter et al. shows a

    good fit:

    1

    10

    100

    1000

    10000

    100000

    0 10 20 30 40 50 60

      g   l  y  c  o   l   i  n   g

      a  s

       [  p  p   b  v   ]

    temperature [°C]

    TEG

    DEG

    MEG

    TEG

    DEG

    MEG

    104°F32°F 68°F 140°F

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    Figure 6: Comparison of the In Salah glycol built up with results according to Figure 5

    The significantly higher ingress rate for Train 1 in December 2008 may be explained by additional entrainment

    of liquid glycol droplets into the unit.

    4. HOW GLYCOLS AFFECT THE PERFORMANCE OF AGRUS

    If the glycol-contaminated gas is fed to an AGRU, traces of glycols also get into these units. In order to decide

    whether or not glycols affect the performance of an AGRU, BASF made lab measurements with a 45 wt%

    OASE® purple solution by adding 15 wt% MEG, DEG or TEG .

     As Figure 7 shows, glycols have a negative impact on the maximum (= equilibrium) CO 2 capture capacity of

    the solvent. For a given CO2 partial pressure (pCO2) in the gas phase, the measured CO2 equilibrium loadings

    (Loading CO2) in the OASE® solution are lower in the presence of glycols than for the glycol free solution.

    Glycols replace water from the system, one of the major CO2  capture reaction components, and thereby

    move the equilibrium of the bicarbonate formation reaction towards the un-protonated (left) side as shown for

    the example of an MDEA containing solution:

    MDEA + CO2 + H2O ⇔ MDEAH+ + HCO3

    -

    This leads to a reduced CO2 capture capacity.

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    Figure 7: Impact of glycols on CO2 partial pressure and CO2 equilibrium loading

     Also the CO2 mass transfer is negatively affected by the presence of glycols, since they contribute to an

    increased solvent viscosity. With increased viscosity however, the mass transfer of CO2 into

    MDEA-containing solutions slows down.

    Figure 8: Impact of glycols on solution viscosity and temperature

    The implementation of the measured equilibrium and viscosity data into BASF’s in-house simulation tool

    Chemasim allows us simulating the OASE® process in the presence of glycols. In addition to the CO2 loading

    and viscosity the model was updated for all other required physical properties (density, surface tension etc.)

    as well as for the enthalpy model taking the impact of the glycols into account.

    5. CASE STUDY

    To estimate the impact of glycols on the performance of a full absorption/desorption process, AGRUs with

    LNG spec (50 ppmv CO2  slip at the absorber overhead) according to Case 1 and Case 2 (Table 2) were

    simulated. Simplified flow schemes of the two plants are shown in Figure 9 and Figure 10:

      p

       C   O   2

    Loading CO2 [mol/mol]

    + 15 wt% TEG

    + 15 wt% DEG

    + 15 wt% MEG

    OASE®

       V   i  s  c  o  s   i   t  y

    Temperature [°C]

    + 15 wt%TEG

    + 15 wt%DEG

    + 15 wt% MEG

    OASE®

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    Figure 9: Flow scheme for Case 1 (CO2-rich gas)

    Figure 10: Flow scheme for plant Case 2 (CO2-lean gas)

    Both plant designs have a water backwash section in the absorber top in order to minimize amine losses. This

    of course will also reduce potential glycol emissions. Case 1 uses a two-stage regeneration system, which is

    common for gases with the given high acid gas partial pressure. The HP-flash drum allows for hydrocarbon

    skimming. The Case 2 design is simpler. Due to the low CO2 partial pressure in the feed gas, a conventional

    stripper is sufficient for regeneration, and HP-flash is not required due to the low C3+ content of the gas.

    For both cases the presence of glycols in the regenerator is less severe due to the high temperature / low

    viscosity effect. However, the absorber is significantly affected by increasing glycol concentrations in theOASE

    ® solution.

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    Figure 11: Absorber liquid temperature and CO2 gas phase concentration

    profiles in presence of MEG for Case 1 (CO2-rich gas) conditions 

    With increasing MEG content, the liquid temperature and the CO2 gas phase profile move upwards, indicating

    that eventually the CO2 will break through. The plant is capable of dealing with MEG concentrations in the

    solution loop of up to 9.2 wt%. If MEG accumulates to higher values, the plant no longer meets its CO2 spec

    as shown by the CO2 breakthrough curve for MEG-contaminated amine in Figure 12, left hand side.

    Figure 12: Case 1 (CO2-rich gas) breakthrough curves and corresponding glycol content in feed gas

    The temperature and CO2 concentration profiles of DEG and TEG-contaminated amine solutions for the Case

    1 study show similar characteristics as for MEG. CO2  breakthrough however, already occurs at 8 wt% for

    DEG and 7.4 wt% for TEG, as show in Figure 12 (left hand side), too.

    On the right hand side, Figure 12 shows the glycol feed gas concentrations which cause accumulation of the

    different glycols in the solution. In order to avoid CO2  breakthrough, glycol concentrations in the feed gas

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    have to stay below 350 ppbv (MEG), 19 ppbv (DEG) or 2.3 ppbv (TEG). Any higher glycol content in the feed

    gas will lead to CO2 breakthrough over the long term.

    Figure 11 and Figure 12 present the results of the Case 2 study (low CO2 content in feed gas). Changes in

    the temperature profile for MEG-contaminated OASE® solution are less distinct; the impact on the CO2 profile

    however is still significant. The plant already produces off-spec CO2  above 3 wt% of MEG in the OASE® 

    solution.

    Figure 13: Absorber liquid temperature and CO2 gas phase concentration profiles in

    presence of MEG for Case 2 (CO2-lean gas) conditions

    Interestingly, there is no difference in the maximum acceptable glycol content in the amine solution (Figure

    14) for all types of glycols. This goes back to the viscosity-increasing effects of the glycols, which for higher

    temperatures in the range of 60 to 90°C (140°F – 194°F) affect the mass transfer almost equally for all three

    glycol types (see Figure 8).

    Figure 14: Case 2 (CO2-lean gas) breakthrough curves and corresponding glycol content in feed gas

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    The maximum acceptable glycol contents in the feed gas are 280 ppbv (MEG), 210 ppbv (DEG) and 53 ppbv

    (TEG).

     A further comparison between Case 1 (CO2-rich gas) and Case 2 (CO2-lean gas) shows that a potential DEG

    or TEG contamination of the feed gas is more severe for the CO2-rich gas. This can be explained by a

    discussion of the temperature profiles: For Case 1 (CO2-rich gas) the treated gas outlet temperature almost

    equals the lean amine inlet temperature into the absorber. Thus the treated gas is relatively cold and does not

    allow significant quantities of glycols to be emitted. However, Case 2 (CO2-lean gas) has a temperature bulge

    in the top of the absorber column and the heat of the CO 2 absorption-reaction leads to a strong increase of

    the exiting gas phase temperatures compared to the incoming lean amine temperature. This causes higher

    glycol vapor-pressure losses thus the plant can accept higher glycol content in the feed gas than applications

    with higher CO2 content in the feed gas (Case 1).

    The combination of the maximum allowable glycol content in the feed gas, according to the heat and mass

    balances of Case 1 and Case 2 (Figure 12 and Figure 14), with the glycol vapor pressure of the feed gases

    (Figure 5) allows for the determination of the maximum temperature under which a DEG or TEG unit, or MEG

    injection, can be operated (or more precisely: where the glycol dewpoint of the incoming feed gas into the

     AGRU absorber lies) without causing production of off-spec CO2.

    Figure 15: Maximum glycol dewpoint temperature for AGRU absorber feed gas

    Figure 15 shows that the following:

    •  A gas according to Case 1 (CO2-rich gas) must have a DEG dewpoint of < 1°C/34°F or TEG dewpoint

    of < 4°C/39°F, without causing production of off-spec. treated gas in the AGRU.

    •  A gas according to Case 2 (CO2-lean gas) can have a DEG dewpoint of < 20°C/86°F or TEG dewpoint

    of < 35°C/95°F, without causing production of off-spec. treated gas in the AGRU.

    •  MEG treatment of the gas upstream the AGRU absorber will cause off-spec production for Case 1 and

    Case 2 for relevant MEG dewpoint temperatures > 0°C / 32°F.

    To treat gases with glycol dewpoint temperatures above the values according to FIGURE 15, additional glycol

    mitigation measures are necessary to allow production of on-spec CO2 in the long term.

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    6. OPTIONS FOR MITIGATION

    There are several options to reduce the impact of glycols coming into the AGRU with the feed gas. To decide

    which option is best applicable, the knowledge about the use of any glycol upstream of the AGRU is very

    important: which type of glycol was applied at which temperature, what is the resulting glycol vapor pressure

    in the feed gas etc. As shown in the previous chapter, not considering glycol in the feed gas can lead to

    malperformance of the AGRU. Even though this point may only be reached after several years of operation,

    mitigation measures usually will be required – sooner or later. In the following, several options are presented:

    Option 1: 

    Consider the glycol content in the feed gas during the design phase; additional margins in the solvent

    circulation rate, heat exchanger duties and absorber height can compensate for glycol ingress into the AGRU

    within a certain range. As a consequence mainly CAPital EXpenditures (CAPEX) will increase.

    Option 2: 

    Instead of increasing the CAPEX there is also an option to go ahead with a standard design of the AGRU by

    accepting increased OPerational EXpenditures (OPEX). Not installing a water-backwash section in the

    absorber top will slightly increase the vapor pressure losses of glycol exiting the absorber top compared to a

    plant with backwash section. Omitting the backwash section is therefore a means to tolerate higher tolerable

    glycol content in the feed gas. However, it will also lead to increased amine losses (higher OPEX) and is

    therefore not the most preferred mitigation measure. Also, this glycol mitigation measure is limited to a certain

    glycol feed gas concentration range only.

    Option 3:

    Continuous, or intermittent bleeding of solvent, and substituting it by fresh solvent, offers another option to

    operate the plant at full capacity and to balance the incoming glycol quantities with the exiting quantities. To

    minimize accompanying amine losses, the stream with the highest glycol to amine ratio should be selected.

    This stream is usually the lean amine stream. Increased OPEX and potentially complicated solvent disposal

    are unwanted consequences of this approach.

    Practically, it is expected that a combination of a slight adjustment of the plant design and allowing a bleed

    stream is the most cost-effective way to mitigate the impact of glycols on the performance of the AGRU.

    Option 4: 

    Thermal reclamation of glycol containing amine solutions is extremely difficult and depends very much on the

    solvent components and glycols in use. The vapor pressure curves (see FIGURE 16) show that for MDEA

    containing solvents, MEG boils in-between MDEA and one activator component, which makes thermal

    separation difficult, DEG and MDEA have more or less exactly the same vapor pressure and therefore cannot

    be thermally separated at all with reasonable effort. TEG is the heaviest boiling component and therefore

    requires evaporation of all other components first. This is very costly.

    Thermal reclamation always requires vacuum distillation in order to avoid thermal degradation of the amines.

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    Figure 16: Vapor pressure curves for thermal reclamation

    Option 5:

    Reclamation by applying ion exchange is a possible way to separate amines from glycols. In the case, theamines (and not the glycols) will be removed from the solution, which makes it a very costly method.

    Option 6:

    Option 6 offers the most sophisticated way to deal with glycols in gas conditioning: removing them in a

    pre-treatment step upstream of the AGRU. This requires additional equipment. A water scrubber is the

    easiest and most beneficial way of doing so.

    For the Case 1 scenario, some scrubber simulations were performed assuming 1 ppmv of MEG in the feed

    gas. Figure 17  shows the configuration. The water-wash section can be designed with a pump- around

    allowing a significant removal rate of glycol so that only a small portion of make-up water is needed. Per 100MMSCFD feed gas, roughly 0.7 GPM of make-up water are needed to reduce the MEG content down to 10

    ppbv, which is lower than the critical concentration of MEG (< 350 ppbv) where some impact has to be

    expected on the performance.

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    Figure 17: Performance of the removal of MEG (1 ppmv in feed gas) for Case1 using a water wash

    Option 7: 

     Another option to avoid getting glycols into amine operated AGRUs is to replace them by alternative

    processes. Instead of MEG, methanol offers an alternative, which due to its lower boiling point is much easier

    to handle in an AGRU than MEG. In other applications, glycols have been replaced by adsorption processes

    operating with silica gels such as Sorbead®. Next to dehydration, they also allow recovering natural gas

    liquids (NGL), which for some applications increases their attractiveness. They also facilitate the operation of

    pipelines, since glycol fouling is not an issue any more. 

    7. SUMMARY

    Glycols in natural gas applications are widely used for hydrate suppression or dehydration purposes. Even

    though they have relatively low vapor pressures, traces of glycols will end up in the natural gas. Gas phase

    concentrations between several ppbv up to several hundred ppmv are possible. The use of demisters can

    only reduce liquid entrainment of glycols into the natural gas. Gas phase losses, however, will always

    contribute significantly to the overall glycol losses.

    In most natural gas applications, glycols are being used downstream of AGRUs, some companies however

    operate glycol units upstream of AGURs. For these applications it is important to know the glycol dewpoint of

    the natural gas at the AGRU inlet in order to determine the absolute glycol ingress to the amine units. Major

    quantities of the incoming glycols will accumulate in the amine units up to significant concentrations (> 15

    wt%), since glycols are heavy boiling components and do not easily leave the system. They have a negative

    impact on the acid gas capture capacity and on the absorption kinetics and thus may limit the treatment

    capacity of a natural gas conditioning plant.

    To mitigate the effects of glycols, several countermeasures are possible. These range from accepting

    glycols in the feed to the AGRU and considering extra design margins to the AGRU, bleeding part of the

    glycol-containing solvent or avoiding significant glycol ingress to the units. This can be done either by

    applying a water-wash step upstream of the AGRU or by replacing glycol processes by alternatives, such as

    methanol (hydrate inhibition) or silica gels (dehydration). Reclaiming of glycol contaminated amine is anotherpossible but costly mean.

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    In any case, the knowledge that the natural gas to be treated in an AGRU will contain glycols, requires

    adequate glycol mitigation measures to avoid running into operational surprises, once the AGRU is in

    operation for several years.

    REFERENCES

    1. NaturalGas.Org: http://www.naturalgas.org/naturalgas/processing_ng.asp

    2. Tanaka K., Fujimura Y., Katz T., Spuhl O.: HiPACT – Advanced CO2 capture technology for green

    natural gas exploration; LRGCC conference proceedings 2010

    3. Schroeter R.W. et al.: Investigation Considerations on CO2 Removal at the In Salah Gas Plant

    HiPACT –; LRGCC conference proceedings 2012

    4. GPSA Handbook, 10th

     edition

    5. Hernandez-Valencia V.N., Hlavinka M.W., Bullin, J.A.; Glycol Units for Maximum Efficiency;

    Bryan Research & Engineering Technical Papers;

    http://www.bre.com/portals/0/technicalarticles/Design%20Glycol%20Units%20for%20Maximum%20

    Efficiency.pdf

    6. http://en.wikipedia.org/wiki/Glycol_dehydration

    7. Multiflash: DLL Version 4.0.08 February 2011, Infochem

    http://www.bre.com/portals/0/technicalarticles/Design%20Glycol%20Units%20for%20Maximum%20Efficiency.pdfhttp://www.bre.com/portals/0/technicalarticles/Design%20Glycol%20Units%20for%20Maximum%20Efficiency.pdfhttp://en.wikipedia.org/wiki/Glycol_dehydrationhttp://en.wikipedia.org/wiki/Glycol_dehydrationhttp://www.bre.com/portals/0/technicalarticles/Design%20Glycol%20Units%20for%20Maximum%20Efficiency.pdfhttp://www.bre.com/portals/0/technicalarticles/Design%20Glycol%20Units%20for%20Maximum%20Efficiency.pdf