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Retrofitting recycled stripping gas in a glycol dehydration regeneration unit

  • Adhi Kurniawan , Renanto Handogo EMAIL logo und Juwari Purwo Sutikno
Veröffentlicht/Copyright: 26. März 2021
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Chemical Product and Process Modeling
Aus der Zeitschrift Chemical Product and Process Modeling Band 17 Heft 3

Abstract

Natural gas dehydration is essential in gas processing to avoid serious problems. As a pretreatment in a cryogenic Natural Gas Liquid (NGL) recovery process, it typically uses triethylene glycol (TEG) and followed by a Molecular Sieve dehydration to achieve 1 mg/Sm3 of water moisture in the dehydrated gas. This work studied the retrofitting of the existing dehydration unit to improve its performance in satisfying the gas moisture qualities. The retrofitted process uses recycled stripping gas schemes to achieve high purity TEG while minimizing the use of fresh stripping gas. The results revealed that the recycled stripping gas has provided sufficiently high purity TEG (>99.99%-wt), significantly reduced the heating and cooling duty by 80%, and reduced the electrical duty by 29% compared to the base case. The TAC was reduced by 38.1% from $ 725,245/year to $ 448,670/year. Through this study, the evaluated cases provide similar dehydration results with less equipment, simpler process, more energy-efficient, and better economic numbers. Therefore, a better process was obtained.

Keywords: dehydration unit; high purity TEG; recycled stripping gas; retrofitting; total annual cost
Corresponding author: Renanto Handogo, Chemical Engineering Department, Institut Teknologi Sepuluh Nopember, Surabaya, Indonesia, E-mail:

Funding source: Deputi Bidang Penguatan Riset dan Pengembangan, Kementerian Riset dan Teknologi / Badan Riset dan Inovasi Nasional

Award Identifier / Grant number: 1153/PKS/ITS/2020

Acknowledgment

The authors thank to Deputi Bidang Penguatan Riset dan Pengembangan, Kementerian Riset dan Teknologi/Badan Riset dan Inovasi Nasional for providing the financial support of this study through Penelitian Dasar Unggulan Perguruan Tinggi, Direktorat Riset dan Pengabdian kepada Masyarakat Institut Teknologi Sepuluh Nopember (ITS) Nomor: 1153/PKS/ITS/2020.

  1. Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.

  2. Research funding: Deputi Bidang Penguatan Riset dan Pengembangan, Kementerian Riset dan Teknologi / Badan Riset dan Inovasi Nasional, through Penelitian Dasar Unggulan Perguruan Tinggi, Direktorat Riset dan Pengabdian kepada Masyarakat Institut Teknologi Sepuluh Nopember (ITS) Nomor: 1153/PKS/ITS/2020.

  3. Conflict of interest statement: The authors declare no conflicts of interest regarding this article.

Appendix A

Table A1:

Gas composition used in this study.

Component Volume fraction
CO2 0.0267
N2 0.0183
Methane 0.8319
Ethane 0.0530
Propane 0.0366
i-Butane 0.0100
n-Butane 0.0116
i-Pentane 0.0042
n-Pentane 0.0028
n-Hexane 0.0017
n-Heptane 0.0007
n-Octane 0.0002
n-Nonane 0.0001
n-Decane 0.0000
C11+ 0.0000
H2O 0.0022
Total 1.0000
Table A2:

Operating parameters for the absorption dehydration (conventional).

Input data Unit Min. Max.
Gas flow rate 106 Sm3/d 1.42 4.20
Absorber pressure kPa 4500 6000
Absorber temperature °C 30.0 40.0
Lean TEG pressure kPa 4600 6100
Lean TEG temperature °C 35.0 45.0
Lean TEG purity %-wt 98.6 98.6
Lean TEG flow rate m3/h 2.0 6.0
Energy consumption Unit Value
Reboiler GJ/h 0.690
Lean TEG Cooler GJ/h 0.163
Rich Glycol Heater GJ/h 0.286
Regen Overhead Cooler GJ/h 0.229
Recycled Gas Comp Cooler GJ/h 0.000
Stripping Gas Heater GJ/h 0.000
TEG Circulation Pump GJ/h 0.044
Recycled Gas Compressor GJ/h 0.000
TEG losses Unit Value
From TEG Absorber kg/h 0.151
From Flash Drum kg/h 0.026
From Overhead Regenerator kg/h 0.099
Recycled Gas Discharge Scrubber kg/h 0.000
Table A3:

Operating parameters for the molecular sieve dehydration.

Input data Unit Min. Max.
Gas flow rate 106 Sm3/d 1.42 4.20
Pressure kPa 4300 5700
Temperature (Absorption mode) °C 30.0 40.0
Temperature (Regeneration mode) °C 280.0 290.0
Regeneration gas flow rate 106 Sm3/d 0.142
Regeneration gas temperature °C 300.0
Energy consumption Unit Value
Regeneration Gas Heater GJ/h 3.550
Regeneration Gas Cooler GJ/h 3.280
Regeneration Gas Compressor GJ/h 0.121
Table A4:

Operating parameters for the absorption dehydration (enhanced regeneration).

Input data Unit Min. Max.
Gas flow rate 106 Sm3/d 1.42 4.2
Absorber pressure kPa 4500 6000
Absorber temperature °C 30.0 40.0
Lean TEG pressure kPa 4600 6100
Lean TEG temperature °C 35.0 45.0
Lean TEG purity %-wt 99.99 99.995
Lean TEG flow rate m3/h 2.0 6.0
Energy consumption Unit Value
Reboiler GJ/h 0.645
Lean TEG Cooler GJ/h 0.165
Rich Glycol Heater GJ/h 0.142
Regen Overhead Cooler GJ/h 0.200
Recycled Gas Comp Cooler GJ/h 0.278
Stripping Gas Heater GJ/h 0.111
TEG Circulation Pump GJ/h 0.044
Recycled Gas Compressor GJ/h 0.074

Figure A1: Molecular sieve dehydration flow diagram – 2 towers in Adsorption and 1 tower in Cooling mode.
Figure A1:

Molecular sieve dehydration flow diagram – 2 towers in Adsorption and 1 tower in Cooling mode.

Figure A2: Typical operating modes in Molecular sieve dehydration.
Figure A2:

Typical operating modes in Molecular sieve dehydration.

Appendix B

Table B1:

Utility and chemical cost summary from Luyben [20].

Utility cost Unit Value
Heating medium $/GJ 9.8
Cooling water $/GJ 2.5
Electricity $/GJ 16.8
Chemical cost Unit Value
TEG make-up $/kg 2.71
Stripping gas $/GJ 3.11
Table B2:

Capital cost estimation summary from Luyben [20].

Equipment type Estimated formula
Separator/Scrubber/Drum 17640 d1.066 l0.802
Heat exchanger 7296 A0.65
Centrifugal compressor (1293)(517.3)(3.11)(hp)0.82/280

Appendix C

Table C1:

Equipment sizing results: Base case (TEG & Mole sieve dehydration).

Equipment name Type Diameter (m) Length (m)
TEG Contactor Column 1.6 5.85
TEG Regenerator Column 0.4 1.00
Flash Drum Separator 0.9 3.60
Regen Overhead Drum Separator 0.6 2.10
Equipment name Type Area (m2)
Heat Exchanger-1 Heat Exchanger 22.6
Heat Exchanger-2 Heat Exchanger 22.6
Regen Overhead Cooler Heat Exchanger 0.6
Reboiler Heat Exchanger 22.6
Rich Glycol Heater Heat Exchanger 5.0
Equipment name Type Diameter (m) Length (m)
Mole Sieve Tower 1 Column 1.92 5.5
Mole Sieve Tower 2 Column 1.92 5.5
Mole Sieve Tower 3 Column 1.92 5.5
Water separator Separator 0.60 2.0
Equipment name Type Area (m2) Duty (GJ/h)
Regen Gas Cooler Heat Exchanger 50 3.280
Regen Gas Heater Heat Exchanger 50 3.550
Equipment name Type Duty (hp)
Regen Gas Compressor Compressor 45
Table C2:

Equipment sizing results: Evaluated case (recycled stripping gas with natural gas).

Equipment name Type Diameter (m) Length (m)
TEG Contactor Column 1.6 5.85
TEG Regenerator Column 0.5 1.00
TEG Stahl Column Column 0.5 1.00
Recycle Gas Absorber Column 0.3 1.00
Equipment name Type Area (m2)
Heat Exchanger-1 Heat Exchanger 22.6
Heat Exchanger-2 Heat Exchanger 22.6
Reboiler Heat Exchanger 22.6
Lean TEG Cooler Heat Exchanger 5.0
Rich Glycol Heater Heat Exchanger 5.0
Regen Overhead Cooler Heat Exchanger 0.6
Recycled Gas Comp Cooler Heat Exchanger 0.6
Stripping Gas Heater Heat Exchanger 5.0
Equipment name Type Diameter (m) Length (m)
Flash Drum Separator 0.9 3.6
Overhead Drum Separator 0.5 0.8
Recycle Comp Suction Scrubber Separator 0.6 2.1
Recycle Comp Disch Scrubber Separator 0.6 2.1
Equipment name Type Duty (hp)
Recycle Compressor Compressor 27.5
Table C3:

Capital cost estimation for main equipment: base case (TEG dehydration).

Equipment name Type Capital cost ($)
TEG Contactor Column 120,046
TEG Regenerator Column 8426
Flash Drum Separator 44,043
Overhead Drum Separator 18,554
Heat Exchanger-1 Heat Exchanger 55,368
Heat Exchanger-2 Heat Exchanger 55,368
Overhead Cooler Heat Exchanger 5235
Reboiler Heat Exchanger 55,368
TEG Cooler Heat Exchanger 20,769
Rich Glycol Heater Heat Exchanger 20,769
Total 403,944
Table C4:

Capital cost estimation for main equipment: base case (mole sieve dehydration).

Equipment name Type Capital cost ($)
Mole Sieve Tower 1 Column 138,761
Mole Sieve Tower 2 Column 138,761
Mole Sieve Tower 3 Column 138,761
Regen Gas Cooler Heat Exchanger 92,772
Regen Gas Heater Heat Exchanger 142,265
Water separator Separator 17,842
Regen Gas Compressor Compressor 168,491
Total 841,654
Table C5:

Operating cost estimation for main equipment: base case (TEG dehydration).

Running hours (h) Consumption (GJ/h) Energy unit cost ($/GJ) Utility cost ($)
Heater duty 8640 0.975 9.8 82,606
Cooler duty 8640 0.392 2.5 8465
Electrical duty 8640 0.044 16.8 6436
Running hours (h) Consumption (kg/h) Chemical unit cost ($/kg) Chemical cost ($)
TEG make-up 8640 0.2755 2.71 6541
Table C6:

Operating cost estimation for main equipment: base case (mole sieve dehydration).

Running hours (h) Consumption (GJ/h) Energy unit cost ($/GJ) Utility cost ($)
Heater duty 4380 3.55 9.8 152,380
Cooler duty 4380 3.28 2.5 35,916
Electrical duty 8760 0.121 16.8 17,792
Table C7:

Capital Cost estimation for main equipment: Evaluated case (Recycled Stripping Gas with natural gas).

Equipment name Type Capital cost ($)
TEG Contactor Column 120,046
TEG Regenerator Column 8426
TEG Stahl Column Column 8426
Recycle Gas Absorber Column 4888
Heat Exchanger-1 Heat Exchanger 53,368
Heat Exchanger-2 Heat Exchanger 53,368
Reboiler Heat Exchanger 55,368
Lean TEG Cooler Heat Exchanger 20,769
Rich Glycol Heater Heat Exchanger 20,769
Regen Overhead Cooler Heat Exchanger 5235
Recycled Gas Comp Cooler Heat Exchanger 5235
Stripping Gas Heater Heat Exchanger 20,769
Flash Drum Separator 44,043
Recycle Comp Suction Scrubber Separator 18,554
Recycle Comp Discharge Scrubber Separator 18,554
Recycle Compressor Compressor 112,511
Total 574,326
Table C8:

Operating Cost estimation for main equipment: Evaluated case (Recycled Stripping Gas with natural gas).

Running hours (h) Consumption (GJ/h) Energy unit cost ($/GJ) Utility cost ($)
Heater duty 8640 0.898 9.8 76,035
Cooler duty 8640 0.6425 2.5 13,878
Electrical duty 8640 0.1179 16.8 17,118
Running hours (h) Consumption (kg/h) Chemical unit cost ($/kg) Chemical cost ($)
TEG make-up 8640 0.2017 2.71 4723
Running hours (h) Stripping gas consumption (Sm3/h) Stripping gas unit cost ($/GJ) Stripping gas cost ($)
Stripping gasa 8640 131.8 3.11 145,475

  1. aGas heating value: 40.96 MJ/Sm3.

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Received: 2020-12-02
Accepted: 2021-03-09
Published Online: 2021-03-26

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https://doi.org/10.1515/cppm-2020-0111
Schlagwörter für diesen Artikel
dehydration unit; high purity TEG; recycled stripping gas; retrofitting; total annual cost

Artikel in diesem Heft

  1. Frontmatter
  2. Research Articles
  3. Viscosity prediction of hydrocarbon binary mixture using an artificial neural network-group contribution method
  4. Design of an environmentally friendly fuel based on a synthetic composite nano-catalyst through parameter estimation and process modeling
  5. Numerical study of coupled natural convection to surface radiation in an open cavity submitted to lateral or corner heating
  6. A comparative study of thermodynamic models to describe the VLE of the ternary electrolytic mixture H2O–NH3–CO2
  7. Murphree vapor efficiency prediction in SCC columns by computational fluid dynamics analysis
  8. Retrofitting recycled stripping gas in a glycol dehydration regeneration unit
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