Answer: Carbon Capture, Storage and Utilization (CCUS)
Carbon Capture, Utilization and Storage (CCUS) is a suite of technologies that capture CO2 emissions from sources like power plants and industrial facilities, then either permanently store the CO2 underground or convert it into useful products. CCUS is essential for decarbonizing hard-to-abate sectors and achieving net-zero targets.
Overview of CCUS Process
The CCUS process involves three main steps:
- Capture: Separating CO2 from emission sources or atmosphere
- Transport: Moving captured CO2 to storage/utilization sites
- Storage/Utilization: Permanent sequestration or conversion to products
Step 1: Carbon Capture Technologies
A. Post-Combustion Capture
- CO2 captured from flue gases after fuel combustion
- Uses chemical solvents (amines like MEA) to absorb CO2
- Solvent heated to release pure CO2, then recycled
- Application: Existing power plants, industrial facilities
- Efficiency: Can capture 85-95% of CO2
B. Pre-Combustion Capture
- Fuel converted to hydrogen and CO2 before combustion
- Gasification: Coal/biomass + steam → syngas (CO + H2)
- Water-Gas Shift: CO + H2O → CO2 + H2
- CO2 separated, hydrogen burned for energy
- Application: IGCC plants, hydrogen production
C. Oxy-Fuel Combustion
- Fuel burned in pure oxygen instead of air
- Produces flue gas with high CO2 concentration (80-90%)
- Easier to capture without dilution by nitrogen
- Application: New power plants, cement kilns
D. Direct Air Capture (DAC)
- Captures CO2 directly from ambient air
- Uses large fans and chemical filters (solid sorbents or liquid solvents)
- Can remove historical emissions (negative emissions)
- Challenge: Low CO2 concentration in air (420 ppm) makes it energy-intensive
- Companies: Climeworks, Carbon Engineering
| Capture Method |
CO2 Concentration |
Energy Penalty |
Maturity |
| Post-Combustion |
10-15% |
25-35% |
Commercial |
| Pre-Combustion |
20-40% |
15-25% |
Commercial |
| Oxy-Fuel |
80-90% |
20-30% |
Demonstration |
| Direct Air Capture |
0.04% |
High |
Early stage |
Step 2: Carbon Transport
Captured CO2 must be transported from capture sites to storage or utilization locations.
Transport Methods:
- Pipelines: Most common method for large volumes; CO2 compressed to supercritical state; extensive networks exist (8,000+ km globally)
- Ships: For offshore storage or long distances; CO2 liquefied at low temperature; similar to LNG transport
- Trucks/Rail: For smaller volumes or pilot projects; CO2 in liquid or compressed form
Transport Considerations:
- CO2 purity requirements (>95%)
- Impurities can cause corrosion
- Pipeline routing and safety
- Infrastructure investment needs
Step 3A: Carbon Storage (Sequestration)
Permanent storage of CO2 in geological formations to prevent atmospheric release.
Storage Options:
| Storage Type |
Description |
Capacity |
| Depleted Oil/Gas Fields |
Inject into exhausted hydrocarbon reservoirs; well-characterized geology |
400+ Gt CO2 |
| Saline Aquifers |
Deep saltwater formations; largest storage potential |
1,000+ Gt CO2 |
| Enhanced Oil Recovery (EOR) |
CO2 injected to extract residual oil; economic benefit offsets cost |
300+ Gt CO2 |
| Unmineable Coal Seams |
CO2 adsorbs to coal; releases methane (ECBM) |
Limited |
| Basalt Formations |
CO2 reacts with basalt to form carbonate minerals |
Emerging |
Storage Requirements:
- Depth >800m for supercritical CO2
- Impermeable caprock to prevent leakage
- Monitoring for long-term integrity
- Site characterization and risk assessment
Step 3B: Carbon Utilization (CCU)
Converting captured CO2 into valuable products, creating economic incentives for capture.
Utilization Pathways:
- Enhanced Oil Recovery (EOR): CO2 injection extracts additional oil; most mature application
- Building Materials: CO2 cured concrete, aggregates (CarbonCure, Solidia)
- Chemicals: Methanol, urea, polymers, carbonates
- Synthetic Fuels: E-fuels combining CO2 with green hydrogen
- Carbonation: Beverages, food industry
- Algae Cultivation: CO2 for biofuel production
- Greenhouses: Enhanced plant growth
Global CCUS Status: 40+ commercial facilities | 150+ Mtpa capture capacity planned by 2030 | Major projects: Sleipner (Norway), Boundary Dam (Canada), Gorgon (Australia)
Challenges and Barriers
- High Cost: $50-100/tonne CO2 (reducing with scale)
- Energy Penalty: 15-35% additional energy for capture
- Infrastructure: Limited pipeline and storage networks
- Public Acceptance: Concerns about storage safety
- Policy Support: Need for carbon pricing, incentives
CCUS in India
- Mission Innovation participant for CCUS
- Research by NTPC, ONGC, GAIL
- Potential storage in Deccan basalts, offshore formations
- Important for decarbonizing steel, cement industries
Conclusion
CCUS involves capturing CO2 through post-combustion, pre-combustion, oxy-fuel, or direct air capture methods; transporting via pipelines, ships, or trucks; and either storing permanently in geological formations (depleted fields, saline aquifers) or utilizing in products (EOR, building materials, chemicals, fuels). While technically proven, CCUS faces challenges of cost, energy penalty, and infrastructure needs. It is essential for decarbonizing hard-to-abate sectors (steel, cement, chemicals) and achieving net-zero targets. With growing policy support and cost reduction through learning, CCUS is expected to scale significantly in the coming decades as a critical climate solution.
Sources: Module 1 & 4 Notes | IEA CCUS Report | Global CCS Institute | IPCC SR15