BTEX Prediction & Removal in Amine Units Luke Burton Chad Duncan Armando Diaz Miguel Bagajewicz.
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Transcript of BTEX Prediction & Removal in Amine Units Luke Burton Chad Duncan Armando Diaz Miguel Bagajewicz.
BTEX Prediction & Removal in Amine Units
Luke BurtonChad Duncan
Armando DiazMiguel Bagajewicz
Project Objective To study means of reducing incineration expenditures
associated to BTEX capture in Amine units, through Process parameter optimization Alternative/Additional Technologies to capture BTEX
Specifics: BTEX content of needs to be kept under the EPA emission limit
of 25 Ton/year . If this is achieved, a reduction in incineration temperature
from 1500 oF to 1350 oF can be accomplished with an associated savings of $303 Thousand.
Alternative Technologies, if they exist, ought to have a lower cost.
Project Methodology Discuss Existing Simulators and compare their capabilities of
predicting Acid Gas flowrate and composition BTEX capture
Determine ways of using these simulators to make approximate predictions
Assess the ability of process parameter manipulation to achieve the reduction of BTEX capture goal.
Study Alternative Technologies Adsorbents Ionic Liquids
Modeling Objective Commercial Simulators seem not to reproduce reliable
results in the case of Amine units, especially when BTEX capture is of interest.
Ideal Objective: Have a simulator that will use the right thermodynamic equation of state and liquid activity coefficients
Achievable Objectives: Use existing simulators and supersede them with additional data and make conclusions.
Amine Plant at Glance
BTEX Problems in Amine Unit
Flash Drum BTEX is emitted to the atmosphere, possible violating EPA
guidelines.
Acid gas stream BTEX present has to be incinerated at high temperatures,
therefore incurring a high fuel cost.
Sweet gas stream Some BTEX will be present, so it is removed in glycol unit.
PRO II Amine Unit Simulation
Same inlet conditions were used: Feed gas (575MMSCF), T (85°F), P (500psia), same compositions.
Results were compared to 92 wt% of CO2 usually found in acid gas stream.
AmineCalc Amine Unit Simulation
Same inlet conditions were used: Feed gas (575MMSCF), T (85°F), P (500psia), same compositions.
Results were compared to 92 wt% of CO2 usually found in acid gas stream.
CO2 Results from Pro II and AmineCalc
Feed Sweet Gas Acid GasComponents AmineCalc Pro/II AmineCalc Pro/II AmineCalc Pro/II
(mol%) Uncontrolled Controlled CO2 9.37 3.12E-09 1.33 99.95 85.54 87.05
Methane 89.57 9.83E+01 96.71 5.00E-02 1.87 0.392Ethane 0.746 0.816 0.804 0.0004 0.0277 8.52E-03
Propane 0.13 0.143 0.14 0.00006 0.00319 1.36E-03i-Butane 0.025 0.0275 2.70E-02 0 0.000326 1.71E-04n-Butane 0.025 0.0272 2.69E-02 0 0.00174 4.59E-04i-Pentane 0.046 0.0505 4.96E-02 0 0.000836 3.66E-04n-Pentane 0.005 0.0055 5.40E-03 0 7.36E-05 3.54E-05
Hexane 0.009 0.00992 9.72E-03 7.11E-07 5.32E-05 2.96E-05Heptane 0.005 0.00552 5.40E-03 0 1.40E-05 1.04E-05Octane 0.01 0.011 1.08E-02 0 2.19E-05 1.24E-05Nonane 0.008 0.00884 8.65E-03 0.00E+00 2.87E-06 2.31E-06Benzene 0.0004 2.40E-05 4.02E-04 5.00E-05 3.41E-03 2.85E-04Toluene 0.0005 0.000311 5.22E-04 1.00E-05 1.94E-03 1.66E-04
Ethylbenzene 0 0 0 0.00E+00 0.00E+00 Xylene 0.0002 9.14E-05 2.06E-04 0.00E+00 1.05E-03 8.99E-05
N2 0.05 9.14E-05 5.38E-02 0.00E+00 1.05E-03 1.04E-03H2O 0 9.14E-05 0.814 0.00E+00 1.05E-03 12.55
MDEA 0 9.14E-05 1.15E-04 0.00E+00 1.05E-03 7.15E-17
Credibility
Which simulator is correct?
AmineCalc renders 99 wt% of CO2 in the acid gas
Pro II renders 94 wt% of CO2 in the acid gas, closer to the 92 wt % reported from field data.
Thermodynamic packages in AmineCalc and Pro II might explain why.
EOS in AmineCalc Uses Peng-Robinson
equation of state.
Not as thorough as Pro II as far as the thermodynamics. Binary interaction coefficient calculated by using simple cubic mixing rule.
Mixing rule have been shown to be incapable of modeling real systems.
bVbbVV
a
bV
RTP
ˆˆˆˆ
EOS in Pro II Pro II uses SRKM equation
of state to calculate the vapor phase enthalpy and density, and liquid and vapor phase entropy.
ω, cij, kij, b, are parameters that are easily obtained.
Binary interaction coefficients mixing rule developed by Prausnitz, and shown to perform better than simple cubic mixing rule.
ˆ ˆ ˆRT a
PV b V V b
12
21
2
2
1
1 1
0.480 1.574 0.76
ijc
iij i j ij ij ji
i j
r
xa a a k k k
x x
T M T
M
BTEX Predictions Feed Sweet Gas Acid Gas
Components AmineCalc Pro/II AmineCalc Pro/II AmineCalc Pro/II(mol%) Uncontrolled Controlled
CO2 9.37 3.12E-09 1.33 99.95 85.54 87.05Methane 89.57 9.83E+01 96.71 5.00E-02 1.87 0.392Ethane 0.746 0.816 0.804 0.0004 0.0277 8.52E-03
Propane 0.13 0.143 0.14 0.00006 0.00319 1.36E-03i-Butane 0.025 0.0275 2.70E-02 0 0.000326 1.71E-04n-Butane 0.025 0.0272 2.69E-02 0 0.00174 4.59E-04i-Pentane 0.046 0.0505 4.96E-02 0 0.000836 3.66E-04n-Pentane 0.005 0.0055 5.40E-03 0 7.36E-05 3.54E-05
Hexane 0.009 0.00992 9.72E-03 7.11E-07 5.32E-05 2.96E-05Heptane 0.005 0.00552 5.40E-03 0 1.40E-05 1.04E-05Octane 0.01 0.011 1.08E-02 0 2.19E-05 1.24E-05Nonane 0.008 0.00884 8.65E-03 0.00E+00 2.87E-06 2.31E-06Benzene 0.0004 2.40E-05 4.02E-04 5.00E-05 3.41E-03 2.85E-04Toluene 0.0005 3.11E-04 5.22E-04 1.00E-05 1.94E-03 1.66E-04
Ethylbenzene 0 0 0 0.00E+00 0.00E+00 Xylene 0.0002 9.14E-05 2.06E-04 0.00E+00 1.05E-03 8.99E-05
N2 0.05 9.14E-05 5.38E-02 0.00E+00 1.05E-03 1.04E-03H2O 0 9.14E-05 0.814 0.00E+00 1.05E-03 12.55
MDEA 0 9.14E-05 1.15E-04 0.00E+00 1.05E-03 7.15E-17
USE OF EXTERNAL DATA
We used the solubility data found in Developments and Applications in Solubility. (Coquelet et. al. 2007)
In this book, the activity coefficients of benzene, toluene, ethylbenzene, and xylene are calculated experimentally for different mixtures of MDEA/DGA and Water.
Contactor Tower Results
Experimental results can be used to calculate how accurate are the simulator results; more specifically the molar composition in the liquid stream.
1
2
3
4
5
6
T1
S1
S2
S3
S4
Feed GasLiquid tray 5
Vapor tray 6
Bottoms liquid
Contactor Tower
Sweet Gas Amine
Contactor Data 575MMSCFD Feed and 702 MGal/hr MDEATray 6 T (F) 145
Tray 6 P (psia) 250 G L2 V L1
Benzene (mol%) 4.00E-04 8.67E-06 4.00E-04 9.13E-06Toluene (mol%) 5.00E-04 5.42E-06 5.02E-04 5.65E-06
Ebenzene (mol%) 0 0 0 0Xylene (mol%) 2.00E-04 3.16E-06 2.02E-06 2.97E-06
Flow Rate (g-mol/hr) 2.86E+07 8.87E+07 2.85E+07 8.88E+07
Contactor Tower Results
1
2
3
4
5
6
T1
S1
S2
S3
S4
GL2
L1
V
Flash
G
L2
L1
V
Contactor Tower Results
Flash
G
L2
L1
V
1
89.219
53.120389.6
2
1
2
12
12
10*
1
1
1
1
LP
TV
xLGyx
LPPT
V
xLGyx
xLP
PxTVxLGy
PxTPy
xLVyxLGy
TBTEX
LBTEX
GBTEX
BTEX
satBTEX
LBTEX
GBTEX
BTEX
BTEX
satBTEXBTEXL
BTEXGBTEX
satBTEXBTEXBTEX
BTEXBTEXLBTEX
GBTEX
Regenerator Tower Results
Experimental results can be used to calculate how accurate are the simulator results; more specifically the molar composition in the acid gas stream.
Regenerator Tower
Acid Gas
Vapor tray 3Liquid tray 2
Rich Amine
Lean Amine
Contactor Data 575MMSCFD Feed and 702 MGal/hr MDEA
Tray 2 T (F) 211 Tray 2 P (psia) 15.5
V' L1 V Benzene (mol%) 2.01E-05 8.67E-06 2.85E-04 Toluene (mol%) 1.17E-05 5.42E-06 1.66E-04
Ebenzene (mol%) 0 0 0 Xylene (mol%) 6.37E-06 3.16E-06 8.99E-05
Flow Rate (g-mol/hr) 3.78E+07 8.87E+07 2.66E+06
RESULTS
BTEX Concentration from Experimental Results
ComponentContactor
Calculated Pro II
xi
Benzene 1.17E-06 8.67E-06
Toluene 5.99E-07 5.42E-06
EthylBenzene 0 0
Xylene 2.78E-07 3.16E-06
yi
Benzene 2.46E-04 2.85E-04
Toluene 1.46E-04 1.66E-04
EthylBenzene 0 0
Xylene 8.10E-05 8.99E-05
BTEX Concentration from Experimental Results
ComponentRegenerator
Calculated Pro II
xi
Benzene 4.79E-05 9.13E-06
Toluene 9.96E-05 5.65E-06
EthylBenzene 0 0
Xylene 5.44E-05 2.97E-06
yi
Benzene 2.80E-04 4.00E-04
Toluene 9.55E-04 5.02E-04
EthylBenzene 0 0
Xylene 2.35E-04 2.02E-06
CONCLUSION It is our belief that Pro II produces good answers for flows and CO2
concentrations in the amine unit.
Pro II and AmineCalc overestimates the solubility of BTEX in the contactor.
• We do not have the right thermodynamics in Pro II or AmineCalc, or any simulator.
• Despite the above, we have a credible way of estimating solubilities based on experimental data.
Glycol Dehydration Units
Unit removes water from sweetened natural gas.
Glycols such as DEG or TEG usually used for these tasks.
Two commercially available simulators: GlyCalc and Pro II.
Interfaces for Glycalc and Pro II are shown.
Glycol Dehydration Units
Unit removes water from sweetened natural gas.
Glycols such as DEG or TEG usually used for these tasks.
Two commercially available simulators: GlyCalc and Pro II.
Interfaces for Glycalc and Pro II are shown.
Milagro Data:49 MMSCFD104 °F887 psig10gal/min glycol382 °F
GlyCalc Contactor Tower
In contactor tower, VLE calculations using Kremser-Brown approximation.
Approximation used to calculate K-values.
Contactor tower not rigorously modeled by using stage by stage flash calculation.
L and V is assumed to be average in every stage.
GlyCalc Regenerator For regenerator, manual notes:
“to avoid complex heat and material balances that would be needed if the regenerator were rigorously modeled, a simple empirical calculation is used”
ResultsContactor Tower on Dehydration Unit
Feed Dry GasComponents GlyCalc Pro II Milagro Data
Methane 98.8880 98.9 98.880 98.9160Ethane 0.8164 0.816 0.816 0.7994Propane 0.1605 0.16 0.160 0.1556
Isobutane 0.0263 2.630E-02 2.619E-02 2.51E-02n-Butane 0.0262 2.620E-02 2.603E-02 2.53E-02
Neopentane 0.0003 N/A 5.213E-03 3.00E-03Isopentane 0.0086 N/A 8.581E-03 8.30E-03n-Pentane 0.0053 5.290E-03 5.286E-03 5.10E-03
2,2-Dimethylbutane 0.0003 N/A 2.838E-04 3.00E-042,3-Dimethylbutane 0.0006 N/A 5.524E-04 6.00E-04
2-Methylpentane 0.0017 N/A 1.571E-03 1.60E-033-Methylpentane 0.0009 N/A 8.094E-04 9.00E-04
n-Hexane 0.0016 1.600E-03 1.584E-03 1.50E-03Heptanes 0.0051 5.070E-03 5.029E-03 5.20E-03Octanes 0.0003 5.920E-03 2.895E-03 5.00E-03Nonanes 0.0006 N/A 5.582E-04 3.00E-04
Decanes plus 0.0004 N/A 3.524E-04 1.10E-03Nitrogen 0.0569 5.690E-02 5.687E-02 5.29E-02
Carbon Dioxide 0.0000 0 0 0Oxygen 0.0000 0 0 0Water N/A 4.860E-03 5.804E-03 N/A
Benzene 3.000E-04 2.720E-04 2.189E-04 3.000E-04Toluene 5.000E-04 4.220E-04 3.281E-04 4.000E-04
Ethylbenzene 0 0 0 0Xylene 6.000E-04 3.930E-04 2.459E-04 3.00E-04
2,2,4-Trimethylpentane 1.000E-04 9.980E-05 9.912E-05 1.00E-04Cyclopentane 0 0 0 0Cyclohexane 9.000E-04 8.880E-04 8.744E-04 9.00E-04
Methylcyclohexane 1.000E-03 9.840E-04 9.851E-04 1.10E-03
Conclusions GlyCalc produces better results for BTEX in dehydration
unit.
We believe Glycalc would be able to predict the amount of BTEX present in dehydration unit.
GlyCalc would not be able to accurately predict duty in regenerator due to its simple correlation used for energy balance.
BTEX Solutions
Reduction Possibilities Two different ways to remove amine exist
Reduce absorption in amines Certain parameters can obtain this
Remove BTEX prior/post amine unit treating Solvent Alternative Technologies
First Solution
Changes in parameters such as amine flow rate, temperature and pressure of towers, etc. may reduce BTEX capture.
We performed a few simulations in Pro II to get a preliminary sensitivity analysis for the affect of temperature.
Parameter Adjustments
It is our belief that this route will not solve the emission problems.
50 70 90 110 130 150 1700.25
0.27
0.29
0.31
0.33
0.35
BTEX Emission Versus Amine Temp
BTEXCO2 Cutoff
Amine Temperature (◦F)
Bte
x E
mis
sio
n (
lb-m
ol/
hr)
Second Solution Solvents can be used:
Water
Alternative Technology Adsorbents
Activated Carbon Silica Aerogels Macroreticular Resins
Ionic Liquids
Removal by Solvent Removal By Water
0 20 40 60 80 100 120 140 160 180 2000.00000
0.00500
0.01000
0.01500
0.02000
0.02500
0.03000
0.03500
Benzene Composition Vs. Water Flow
Water Flow (MMSCFD)
Ben
zen
e M
ola
r C
om
posit
ion
CONCLUSION Manipulating the amine unit parameters (T, P, and flow
rates) will not lead to the order of magnitude changes needed to reduce the emission.
This conclusion is based both on considering results of Pro II directly and calculations based on experimental results.
Water is also not a good solvent to remove BTEX due to separation complications.
This leads to the investigation of other alternative technologies
Activate Carbon Activated Carbon has a
density of about 350 kg/m3 and surface area of 500 m2/g
Can only be used 2 cycles before 50% adsorption reduction occurs
Macroreticular Resins Macroreticular resins have an
adsorption of BTEX of about: 350 mg BTEX/1000 mg of
adsorbent *(Lin (1999))
Can adsorb and desorb BTEX for 42 cycles before a 10% reduction in adsorption
Silica Aerogels (SAG) Hydrophobic material that
has low density (0.3-0.05 g/cm3), high porosity, and high surface area (500- 1000 m2/g).
SA can be used up to 14 cycles!
Incineration Results From Pro/II, it was calculated how much fuel gas
(methane) will be needed to fully incinerate the acid gas stream at 1500°F by using a Gibbs reactor.
These calculations were based from on the following field data:
Air Fuel Acid Gas
Flowrate (ft^3/hr) 355,888 23,162 504,042
Methane 0% 100% 0.50%
Carbon Dioxide 0% 0% 84.42%
Nitrogen 78.11% 0% 0%
Oxygen 20.95% 0% 0%
Argon 0.93% 0% 0%
Water 0% 0% 15.08%
Flame Temperature Verification
We took initial and final moles from Pro II. Reaction was carried while keeping the vent gas temperature at 1500°F.
Pro II results agreed with field data within 1.3% margin of error.
Pro II results agreed with hand calculations within .64% margin of error.
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f
o
f
o
f
o
f
o
i
o
i
o
i
o
i
o
T
TCOffCO
T
T
fN
T
T
fO
T
TOHffOH
T
TCOfiCO
T
T
iN
T
T
iO
T
TCHfiCH
HdTCpNdTCpNdTCpNHdTCpN
HdTCpNdTCpNdTCpNHdTCpN
Excess Air Limits The Limit of excess is such that the mole percent of
oxygen released to the atmosphere must be between 1-3% (Lewandowski, 2000). Lower limit due to formation of CO below 1% O2
Upper limit exist to reduce formation of NOx which occur above 3% oxygen
This data is backed by Ignacio plant data with O2 level of 2% in outlet stream
Flame Temperature VOC
The flame of incinerator must be risen to a temperature, Auto Ignition Temperature, high enough to combust VOC’s:
In order to incinerate at this temperature, long residence times in incinerator must be used A common rule of thumb for 99% incineration efficiency at .5
seconds is to add 400°F onto AIT.
Compound AIT (°F)
Benzene 1097
Ethylbenzene 870
Toluene 997
Xylene 924* (Lewandowski, 2000).
Fuel CostThermal Oxidizers Analysis
With BTEX
Amount of CH4 (MMft^3/year) Cost per year Cost per Day
221 $1,117,00 $3,000
Without BTEX (Constant Air Excess Assumed)
Amount of CH4 (MMft^3/year) Cost per year Cost per day
161 $814 $2,000
Saving per Year ($)
$303,000
**Cost of Methane at $5/MMBtu**
SAG Adsorption Process
One tank opened while the other is closed, and they will run for 12 hr periods.From the columns, the BTEX can be removed by using three different designs. These columns could be used up front of amine unit or in Acid Gas.
Column 1
Column 2
To Amine Unit/ Oxidizer
To Design
Acid Gas/Raw Gas
Comparison of Two Designs
Removing the BTEX present in the columns by blowing air through the columns.
Instead of burning the air/BTEX stream, run the stream through a condenser, and then pass it through a flash.
Activated Carbon Acid Gas
Desorb and Burn
Columns $372,000
Blower $7,000
Piping $379,000
Total FCI $636,000
Materials $257,000
Labor $38,000
Fuel $5,000
Total Operating Cost $451,000
Total Annualized Cost $493,000
Activated Carbon cost $4 per kg.
Used Pro-II Results from Milagro Type Plant
This design would have an additional cost of $191,000
In order for a saving of $100,000 to be reached price would have to be reduced to $1.15 per kg
71% discount needed
Silica AerogelsAcid Gas
Silica Aerogels cost $37 per kg from Cabot.
Used Pro-II Results from Milagro Type Plant
This design would produce a savings of $76,000
In order for a saving of $100,000 to be reached price would have to be reduced to $34 per kg
8% discount needed
Desorb and Burn
Columns $373,000
Blower $7,000
Piping $258,000
Total FCI $638,000
Materials $164,000
Labor $37,000
Fuel $5,000
Total Operating Cost $206,000
Total Annualized Cost $227,000
Macroreticular ResinsAcid Gas
Macroreticular resins cost $43 per kg from Dow Chemical.
Used Pro-II Results from Milagro Type Plant
This design would produce a savings of $61,000
In order for a saving of $100,000 to be reached price would have to be reduced to $35 per kg
19% discount needed
Desorb and Burn
Columns $165,000
Blower $7,000
Piping $117,000
Total FCI $289,000
Materials $181,000
Labor $37,000
Fuel $5,000
Total Operating Cost $223,000
Total Annualized Cost $242,000
Conclusions from Adsorption
There exist a saving of $303,000 in reducing the flame temperature from 1500°F to 1350°F.
This savings can then be used to design adsorption columns to remove BTEX.
Out of all the adsorbents studied silica aerogels proved to be the best adsorbent on the basis of savings and reduced cost.
Ionic Liquid Background
Ionic liquids can be used to remove carbon dioxide.
The expense of using these liquids will be examined in comparison with that of the amine unit.
Amine Unit CostAmine Unit First batch costs
First batch amine $596,000 Total $596,000
Equipment CostsAbsorption tower $1,336,000Stripping tower $210,000Heat exchangers $527,000Pump $42,000Condensers $115,000Reboilers $126,000 Total $2,355,000
Operation Costs $/year
Process water that is lost $2,873,000
Process amine that is lost $415,000
Heat at the reboiler $26,502,000
Electricity for pump $2,168,000Condenser Fan Electricity $11,000
Total $31,969,000
Hydrocarbon Losses $/yearMethane loss $329,203Ethane loss $13,290
Total Annualized Cost$32,508,000
Ionic Liquid Conclusion
0.00% 0.50% 1.00% 1.50% 2.00% 2.50% 3.00% 3.50% 4.00% 4.50% 5.00%$0
$5,000,000
$10,000,000
$15,000,000
$20,000,000
$25,000,000
$30,000,000
$35,000,000
TAC versus % Methane Loss
% Methane Lost
To
tal
An
nu
ali
ze
d C
ost
Current Design 2.37% Loss
Amine TAC
IL TAC
Ionic Liquid Conclusion
$0 $5 $10 $15 $20 $25 $30 $35 $40 $45 $50$0
$500,000
$1,000,000
$1,500,000
$2,000,000
$2,500,000
FCI versus IL cost
IL Cost, $/kg
FC
I
Amine FCI
IL FCI
QUESTIONS?