1. BTEX Prediction & Removal in Amine Units
Luke Burton
Chad Duncan
Armando Diaz
Miguel Bagajewicz

2. 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 oF can be accomplished with an associated savings of $303 Thousand.
Alternative Technologies, if they exist, ought to have a lower cost.

3. 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

4. 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.

5. Amine Plant at Glance

6. 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.

7. 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.

8. 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.

9. CO2 Results from Pro II and AmineCalc
Feed
Sweet Gas
Acid Gas
Components
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
0.392
Ethane
0.746
0.816
0.804
0.0004
0.0277
8.52E-03
Propane
0.13
0.143
0.14
1.36E-03
i-Butane
0.025
0.0275
2.70E-02
1.71E-04
n-Butane
0.0272
2.69E-02
4.59E-04
i-Pentane
0.046
0.0505
4.96E-02
3.66E-04
n-Pentane
0.005
0.0055
5.40E-03
7.36E-05
3.54E-05
Hexane
0.009
9.72E-03
7.11E-07
5.32E-05
2.96E-05
Heptane
1.40E-05
1.04E-05
Octane
0.01
0.011
1.08E-02
2.19E-05
1.24E-05
Nonane
0.008
8.65E-03
0.00E+00
2.87E-06
2.31E-06
Benzene
2.40E-05
4.02E-04
5.00E-05
3.41E-03
2.85E-04
Toluene
0.0005
5.22E-04
1.00E-05
1.94E-03
1.66E-04
Ethylbenzene
Xylene
0.0002
9.14E-05
2.06E-04
1.05E-03
8.99E-05 N2
0.05
5.38E-02
1.04E-03
H2O
0.814
12.55
MDEA
1.15E-04
7.15E-17

10. 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.

11. 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.

12. 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.

13. BTEX Predictions Feed Sweet Gas Acid Gas Components AmineCalc Pro/II
Feed
Sweet Gas
Acid Gas
Components
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
0.392
Ethane
0.746
0.816
0.804
0.0004
0.0277
8.52E-03
Propane
0.13
0.143
0.14
1.36E-03
i-Butane
0.025
0.0275
2.70E-02
1.71E-04
n-Butane
0.0272
2.69E-02
4.59E-04
i-Pentane
0.046
0.0505
4.96E-02
3.66E-04
n-Pentane
0.005
0.0055
5.40E-03
7.36E-05
3.54E-05
Hexane
0.009
9.72E-03
7.11E-07
5.32E-05
2.96E-05
Heptane
1.40E-05
1.04E-05
Octane
0.01
0.011
1.08E-02
2.19E-05
1.24E-05
Nonane
0.008
8.65E-03
0.00E+00
2.87E-06
2.31E-06
Benzene
2.40E-05
4.02E-04
5.00E-05
3.41E-03
2.85E-04
Toluene
0.0005
3.11E-04
5.22E-04
1.00E-05
1.94E-03
1.66E-04
Ethylbenzene
Xylene
0.0002
9.14E-05
2.06E-04
1.05E-03
8.99E-05 N2
0.05
5.38E-02
1.04E-03
H2O
0.814
12.55
MDEA
1.15E-04
7.15E-17

14. 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.

15. 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.
Sweet Gas
Amine
Contactor Data 575MMSCFD Feed and 702 MGal/hr MDEA
Tray 6 T (F)
145
Tray 6 P (psia)
250 G L2 V L1
Benzene (mol%)
4.00E-04
8.67E-06
9.13E-06
Toluene (mol%)
5.00E-04
5.42E-06
5.02E-04
5.65E-06
Ebenzene (mol%)
Xylene (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
Feed Gas
Liquid tray 5
Vapor tray 6
Bottoms liquid

16. Contactor Tower Results
Flash G L2 L1 V L2 G V L1

17. Contactor Tower Results
Flash G L2 L1 V

18. 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.
Acid Gas
Vapor tray 3
Liquid tray 2
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%)
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
Rich Amine
Lean Amine

19. RESULTS BTEX Concentration from Experimental Results Component
Contactor
Calculated
Pro II xi
Benzene
1.17E-06
8.67E-06
Toluene
5.99E-07
5.42E-06
EthylBenzene
Xylene
2.78E-07
3.16E-06 yi
2.46E-04
2.85E-04
1.46E-04
1.66E-04
8.10E-05
8.99E-05
BTEX Concentration from Experimental Results
Component
Regenerator
Calculated
Pro II xi
Benzene
4.79E-05
9.13E-06
Toluene
9.96E-05
5.65E-06
EthylBenzene
Xylene
5.44E-05
2.97E-06 yi
2.80E-04
4.00E-04
9.55E-04
5.02E-04
2.35E-04
2.02E-06

20. 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.

21. 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.

22. 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 MMSCFD
104 °F
887 psig
10gal/min glycol
382 °F

23. 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.

24. 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”

25. Contactor Tower on Dehydration Unit
Results
Contactor Tower on Dehydration Unit
Feed
Dry Gas
Components
GlyCalc
Pro II
Milagro Data
Methane
98.9
98.880
Ethane
0.8164
0.816
0.7994
Propane
0.1605
0.16
0.160
0.1556
Isobutane
0.0263
2.630E-02
2.619E-02
2.51E-02
n-Butane
0.0262
2.620E-02
2.603E-02
2.53E-02
Neopentane
0.0003
N/A
5.213E-03
3.00E-03
Isopentane
0.0086
8.581E-03
8.30E-03
n-Pentane
0.0053
5.290E-03
5.286E-03
5.10E-03
2,2-Dimethylbutane
2.838E-04
3.00E-04
2,3-Dimethylbutane
0.0006
5.524E-04
6.00E-04
2-Methylpentane
0.0017
1.571E-03
1.60E-03
3-Methylpentane
0.0009
8.094E-04
9.00E-04
n-Hexane
0.0016
1.600E-03
1.584E-03
1.50E-03
Heptanes
0.0051
5.070E-03
5.029E-03
5.20E-03
Octanes
5.920E-03
2.895E-03
5.00E-03
Nonanes
5.582E-04
Decanes plus
0.0004
3.524E-04
1.10E-03
Nitrogen
0.0569
5.690E-02
5.687E-02
5.29E-02
Carbon Dioxide
0.0000
Oxygen
Water
4.860E-03
5.804E-03
Benzene
3.000E-04
2.720E-04
2.189E-04
Toluene
5.000E-04
4.220E-04
3.281E-04
4.000E-04
Ethylbenzene
Xylene
6.000E-04
3.930E-04
2.459E-04
2,2,4-Trimethylpentane
1.000E-04
9.980E-05
9.912E-05
1.00E-04
Cyclopentane
Cyclohexane
9.000E-04
8.880E-04
8.744E-04
Methylcyclohexane
1.000E-03
9.840E-04
9.851E-04

26. 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.

27. BTEX Solutions

28. 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

29. 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.

30. Parameter Adjustments
It is our belief that this route will not solve the emission problems.

31. Second Solution Solvents can be used: Alternative Technology
Water
Alternative Technology
Adsorbents
Activated Carbon
Silica Aerogels
Macroreticular Resins
Ionic Liquids

32. Removal by Solvent
Removal By Water

33. 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

34. 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

35. 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

36. Silica Aerogels (SAG) SA can be used up to 14 cycles!
Hydrophobic material that has low density ( g/cm3), high porosity, and high surface area ( m2/g).
SA can be used up to 14 cycles!

37. 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
84.42%
Nitrogen
78.11%
Oxygen
20.95%
Argon
0.93%
Water
15.08%

38. 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.

39. 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

40. 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).

41. Thermal Oxidizers Analysis Without BTEX (Constant Air Excess Assumed)
Fuel Cost
Thermal 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)
Cost per day
161
$814
$2,000
Saving per Year ($)
$303,000
**Cost of Methane at $5/MMBtu**

42. SAG Adsorption Process
Column 1
Column 2
To Amine Unit/ Oxidizer
To Design
Acid Gas/Raw Gas
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.

43. 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.

44. 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

45. Silica Aerogels Acid 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

46. Macroreticular Resins Acid 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

47. 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.

48. 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.

49. Amine Unit First batch costs
Amine Unit Cost
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
$2,168,000
Condenser Fan Electricity
$11,000
Total
$31,969,000
Amine Unit First batch costs
First batch amine
$596,000
Total
Equipment Costs
Absorption tower
$1,336,000
Stripping tower
$210,000
Heat exchangers
$527,000
Pump
$42,000
Condensers
$115,000
Reboilers
$126,000
Total
$2,355,000
Hydrocarbon Losses
$/year
Methane loss
$329,203
Ethane loss
$13,290
Total Annualized Cost
$32,508,000

50. Ionic Liquid Conclusion

51. Ionic Liquid Conclusion

52. QUESTIONS?