Economic Performance

Capital Expenditure (CAPEX)

CAPEX Structure

• Absorber column: Represents approximately 10% of total process unit equipment costs​
• High-pressure equipment: Thick-walled vessels required for 35-60 bar operation increase capital costs​
• Refrigeration system: Represents 25-35% of total CAPEX; significant investment in compressors, heat exchangers, and refrigerant inventory​
• Overall CAPEX: Higher than ambient-temperature physical solvent processes (e.g., Selexol) or chemical absorption (e.g., aMDEA) due to refrigeration requirements​​

CAPEX Optimization with Structured Packings (vs. traditional tray design):​

• Absorber diameter reduction: 25-27%
• Absorber CAPEX reduction: 39% (structured packing absorber costs 61% of tray design)
• Overall process unit equipment CAPEX reduction: 7%
• Additional benefits: Lower pressure drop, higher liquid handling capacity

Operating Expenditure (OPEX)

Major operating cost components:

1. Refrigeration energy: Largest single operating cost (40-50% of total OPEX)
2. Compression power: Syngas compression, CO₂ compression, recycle gas compression (30-35% of OPEX)
3. Steam consumption: Methanol regeneration reboiler duty (10-15% of OPEX)
4. Electricity: Pumps, auxiliaries (5-10% of OPEX)
5. Methanol make-up: Minimal (<2% of OPEX due to low solvent cost)

OPEX Reduction with Process Optimization:​ Structured packing implementation achieves 17% overall OPEX savings:

• Refrigeration duty reduction: 19%
• Electricity consumption reduction: 16%
• Steam consumption reduction: 18%

Energy Costs

Specific Energy Consumption:​

• Non-optimized design: 755 kJ/kg CO₂ captured (specific exergy consumption)
• Optimized design: 662 kJ/kg CO₂ captured (12% improvement through systematic heat integration and process optimization)
• Energy breakdown: ~60% refrigeration, ~30% compression, ~10% thermal regeneration

CO₂ Capture Cost Sensitivity:

• Optimal CO₂ capture range: 90-98% (nearly linear cost increase)​
• Beyond 98-99% capture: Exergy consumption increases dramatically due to finite CO₂ solubility in methanol​
• Economic optimum typically at 95-97% CO₂ capture for CCS applications​

Optimal Application Envelope

Low-temperature methanol wash is most economically attractive when:​​

• Feed pressure: >30 bar (physical absorption efficiency increases with pressure)
• Acid gas concentration: >20% total acid gases (high loading favors physical absorption)
• Purity requirements: Ultra-low sulfur specifications (<0.1-1 ppmv) required for downstream catalytic processes
• Feedstock: Coal, lignite, or heavy hydrocarbon gasification producing syngas with multiple contaminants
• Product requirements: Need for separate H₂S and CO₂ streams with high individual purities
• Integration opportunities: Synergy with cryogenic processes or where cold syngas product is beneficial
   

Commercial Track Record

Low-temperature methanol wash technology was first deployed at large scale in the 1950s at Sasol's Fischer-Tropsch plant in South Africa, where three identical purification units with a combined capacity of 164 MMscfd were installed for coal gasification gas treatment using licensed Rectisol® technology. Sasol subsequently expanded operations with two larger facilities, each employing systems capable of treating over 1 billion standard cubic feet per day across four independent trains.​

Licensed Rectisol® installations: Air Liquide (ex-Lurgi) reports >110 commercial references worldwide (including operating units, projects under construction, and completed engineering studies), with over 35 installations commissioned since 2005. Combined installations from both Linde plc and Air Liquide licensors exceed 85 operating units as of 2006, with current installations estimated at 100-120+ units.

Generic technology deployment: Beyond licensed Rectisol® units, numerous non-licensed generic low-temperature methanol wash installations have been deployed, particularly in China's coal chemical industry since the 2000s. These domestically-engineered implementations utilize the same fundamental cold methanol absorption principles for coal-to-methanol, coal-to-chemicals, and coal-to-SNG projects. The total global installation base (combining licensed and generic implementations) likely exceeds 200-250 operating units as of 2026.

Low-temperature methanol wash represents the benchmark acid gas removal technology for coal gasification applications globally, with particular concentration in South Africa (Sasol), China (coal-to-chemicals, largest deployment region), and North America (IGCC and synfuels projects).

The process also removes trace contaminants including NH₃, HCN, CS₂, mercaptans, BTX aromatics, and metal carbonyls. This comprehensive contaminant removal capability makes it particularly suitable for syngas from coal or heavy hydrocarbon gasification, which typically contains these impurities.

H₂S > COS > CO₂ > CO > H₂ > N₂