Gas Sweetening

Gas Sweetening merupakan salah satu tahapan penting dalam pengolahan gas bumi yang bertujuan untuk mengurangi kandungan komponen gas asam (acid gases), terutama carbon dioxide (CO₂) dan hydrogen sulfide (H₂S).

Kandungan CO₂ dan H₂S perlu dikendalikan karena dapat memberikan dampak terhadap kualitas gas, korosivitas sistem, keselamatan operasi, serta keandalan peralatan dan fasilitas pengolahan gas. Oleh karena itu, proses Gas Sweetening menjadi salah satu bagian penting dalam memastikan gas hasil pengolahan memenuhi spesifikasi yang dipersyaratkan.

Pemilihan teknologi Gas Sweetening tidak hanya ditentukan oleh kandungan acid gas pada feed gas. Beberapa parameter lain yang perlu dipertimbangkan meliputi target acid gas pada gas produk, kapasitas aliran gas, tekanan dan temperatur operasi, karakteristik feed gas, kebutuhan pretreatment, CAPEX, OPEX, serta kompleksitas operasi.

Gas Sweetening Technology Selection
Pemilihan teknologi yang tepat perlu mempertimbangkan hubungan antara kondisi feed gas dan spesifikasi gas produk. Tidak ada satu teknologi yang paling sesuai untuk seluruh kondisi operasi.

1. Pemilihan Teknologi Gas Sweetening

Secara umum, pemilihan teknologi dapat dilakukan dengan melihat hubungan antara konsentrasi acid gas pada feed dan konsentrasi acid gas yang ditargetkan pada outlet gas. Gambar berikut memberikan gambaran awal mengenai area aplikasi berbagai teknologi Gas Sweetening.

Gambar 1. Bagan Pemilihan Teknologi Gas Sweetening

Source: Bergel & Tierno, 2009

2. Karakteristik Teknologi Gas Sweetening

Berbagai teknologi Gas Sweetening memiliki karakteristik, rentang aplikasi, kebutuhan utilitas, tingkat kompleksitas, serta konsekuensi biaya yang berbeda. Perbandingan karakteristik utama berbagai teknologi ditampilkan pada tabel berikut.

ITEM	AMINES	MEMBRANES	HOT POTASSIUM CARBONATE	PHYSICAL SOLVENTS	MIXED SOLVENTS	PHYSICAL ADSORPTION	NON REGENERATIVE SOLVENTS
Acid Gas Content at Inlet	Up to 70% V	Up to 90% V	5% V to 50% V	PCO₂ > 3.5 bara	PCO₂ > 7.6 bara	0.1% V to 2% V	< 0.1% V
Typical Acid Gas Content at Outlet	From 2% V down to deep removal	1% V	≥ 1.5% V (single stage scheme) ≥ 0.1% V (two stage scheme)	1% V	< 0.5% V	50 ppmV	5 to 300 ppmV
Typical Gas Flow Rate (MMSCMD)	From low to more than 10	From very low to more than 10	From low to 7	From 3 to 11	From low to more than 10	From low to 3	Low
Typical Operating Conditions Pressure	Absorber: 5 to 120 bara Regenerator: 1.5 bara	27 bara to 100 bara	Absorber: 69 bara Regenerator: 1.5 bara	Absorber: 69 bara	Absorber: 69 bara Regenerator: 3 bara or lower	Adsorption: 14 to 69 bara	As required
Typical Operating Conditions Temperature	30 to 60°C (absorption)	< 60°C	110 to 120°C	-18°C to Ambient	Ambient to 60°C (absorption)	Adsorption: 30 to 60°C Regeneration: 350°C	Ambient
Typical Hydrocarbon Losses	Less than 1%	1 stage: 8 - 15% 2 stages: 2%	Very low	Absorbs heavy hydrocarbons & aromatics	Absorbs heavy hydrocarbons & aromatics	None	None
Process Turndown Gas Flow Rate	30%	20%	30%	Approximately 30%	Approximately 30%	Low (Note 4)	No limitation
Main Equipment (Note 3)	Contactor Regeneration System (Note 1) Flash Drum Lean/Rich Amine Heat Exchanger Lean Amine Cooler Circulation Pumps	Inlet Pre-Treatment (Note 2) Membrane Skid Recycle Compressor and Coolers (for 2 stages systems)	Contactor Regeneration System (Note 1) Gas/Gas Heat Exchanger Circulation Pumps Lean Solution Cooler (for 2 stage process scheme)	Contactor CO₂ Recycle Flash Drum Flash Drums at different pressures Lean Solvent Pumps Rich Solvent Pumps Vacuum Pump Recycle Compressor (Optional) Chiller (Optional)	Contactor Regeneration System (Note 1) Flash Drum Lean/Rich Solvent Heat Exchanger Lean Solvent Cooler Circulation Pumps Reclaimer (Optional)	Molecular Sieve Vessels Regeneration Gas Heater	Liquid Scavenger Towers
Materials Requirements	SS for certain parts (Lean/Rich Heat Exchanger, Reboiler tubes, Regeneration System overhead)	Pre-treatment: CS or SS (high acid gas content) Membrane Skid: CS	Stainless Steel for certain parts	Carbon Steel	SS for certain parts (Lean/Rich Heat Exchanger)	Carbon Steel	Carbon Steel
Lay Out Requirements	High	Low	High	High	High	Medium	Low
Services Requirements	Heating Medium Power Chemicals (e.g. antifoam)	Pre-treatment requirements (e.g. Power, Refrigeration) For 2 stages: Power (for Compression)	Heating Medium Power Chemicals (e.g. antifoam)	Power Chemicals (e.g. antifoam) Refrigeration (Optional) Heating Medium or Stripping Gas (Optional)	Heating Medium Power Chemicals (e.g. antifoam)	Heating Medium	—
Ease of operation	High complexity	Low complexity (Note 6)	Very High complexity	High complexity	High complexity	Medium complexity	Low complexity
Contaminants	Oxygen, Heavy HC (liquid state), Solid particles, Organic acids	Heavy HC, BTEX, Glycols, Amines, Liquid water	Solid particles, Heavy HC (liquid state)	Solid particles, Heavy HC (liquid state)	Solid particles, Heavy HC (liquid state), Oxygen	Heavy HC (liquid state), Glycols, Amines, Liquid water	Heavy HC (liquid state)
Cost Composition Investment	High	Medium	High	Medium	High	Medium	Low
Cost Composition Operation	Medium	1 stage: Low 2 stages: Medium	Low	Low	Medium	Low	High
Notes	Outlet gas saturated with water.	Gas is dehydrated.	Outlet gas saturated with water. Solution can precipitate.	Gas is dehydrated.	Sulfinol solvent is relatively expensive. Outlet gas almost saturated with water.	Gas is dehydrated.	Outlet gas saturated with water. The spent caustic is a hazardous waste.

Source: Bergel & Tierno, 2009

Notes:

1. Regeneration System includes: Regeneration Column (Still), Condenser, Accumulator, Reflux Pumps and Reboiler.

2. Inlet pre-treatment depends on gas composition. Simple pre-treatment includes: coalescing filter, non-regenerable adsorbent (activated carbon) guard bed, dust filter and heater. Enhanced pre-treatment could include a LTS Unit (mechanical refrigeration), a Joule-Thompson Expansion Unit or a Regenerable Adsorption System.

3. Inlet and Outlet Scrubbers, Filters not indicated.

4. Adsorption/cooling cycles must be lengthened.

5. CS: Carbon Steel. SS: Stainless Steel.

6. Membrane unit only. Complexity increases with recycle compression (two stage membrane process) and enhanced pre-treatment schemes.

3. Batas Maksimum Impurities pada Produk Gas

Selain pemilihan teknologi, spesifikasi gas produk merupakan salah satu parameter penting dalam menentukan tingkat penghilangan impurities yang diperlukan. Batas maksimum impurities dapat berbeda tergantung pada jenis produk gas dan kebutuhan penggunaannya.

Parameter	Pipeline	LNG	GTL	LPG
H₂S (ppmv)	4	2-4	2-4	1-10
Total Sulfur (ppmv)	20-50	10-50	10-50	50
CO₂	2%-8%	50 ppmv	50-1000 ppmv	500 ppmv

Source: UOP, 2009

4. Kesimpulan

Pemilihan teknologi Gas Sweetening perlu dilakukan berdasarkan kondisi feed gas dan spesifikasi gas produk yang ingin dicapai. Kandungan acid gas, target outlet, kapasitas gas, kondisi operasi, kebutuhan pretreatment, serta aspek investasi dan operasi menjadi pertimbangan utama dalam menentukan teknologi yang sesuai.

Tidak semua teknologi memiliki rentang aplikasi yang sama. Amines, physical solvents, mixed solvents, potassium carbonate, molecular sieves, membranes, maupun teknologi non-regenerative memiliki karakteristik dan kebutuhan operasi yang berbeda.

Engineering Perspective

Pemilihan Gas Sweetening bukan hanya mengenai kemampuan menghilangkan H₂S dan CO₂, tetapi juga mengenai bagaimana mencapai spesifikasi gas secara reliable, efficient, safe, and economically viable.

References

Bergel, M., & Tierno, I. (2009). Sweetening Technologies – A Look at the Whole Picture. TECNA Estudios y Proyectos de Ingeniería S.A.

UOP. (2009). Gas Treating and Processing.