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CARBON CAPTURE AND UTILIZATION & SEQUESTRATION (CCUS)
Carbon Capture, Utilization, and Sequestration (CCUS) represents an integrated suite of advanced technologies designed to isolate and permanently sequester or beneficially repurpose carbon dioxide (CO₂) emissions generated from high-intensity industrial operations such as thermal power generation, steel production, cement manufacturing, fertilizers, and oil & gas processing. The primary objective is to mitigate greenhouse gas (GHG) emissions and enable hard-to-abate sectors to progress toward carbon neutrality and national net-zero commitments.
In India, multiple industrial stakeholders—particularly within heavy industries—are actively investigating CCUS pathways as part of their decarbonization strategies. Recognizing its strategic importance, the Government of India, through the Department of Science & Technology (DST), is fostering CCUS development by initiating laboratory-scale research and pilot studies to establish technology readiness and operational viability under Indian process conditions.
As per DST-supported frameworks, CCUS initiatives are mandated to undergo phased development, beginning with laboratory-scale validation to demonstrate proof-of-concept and technical feasibility. Upon successful validation, the technology is slated for scaling and demonstration within industrial settings where it can be integrated with process emission streams—typically routed to flare stacks—to prevent the direct release of CO₂ into the atmosphere.
For industries emitting significant volumes of CO₂ via combustion and flaring operations, the adoption of CCUS solutions is imperative for transitioning to sustainable, low-carbon operations. Captured CO₂ can either be subjected to microalgae-based sequestration or repurposed through utilization pathways, such as enhanced oil recovery (EOR) or chemical synthesis. This dual approach not only curtails atmospheric carbon loading but also adds value to captured CO₂ streams, supporting circular carbon economy models and enhancing industrial sustainability.
Lab Scale Demonstration Project
Preamble
As the proposed activity pertains to a laboratory-scale validation of the carbon capture and utilization (CCUS) technology, a critical prerequisite is the consistent availability of flue gas as the input stream for CO₂ extraction. Unlike industrial setups where flue gas is inherently produced as a byproduct of ongoing operations, our validation framework necessitates the generation of a synthetic flue gas stream. To this end, we will establish a controlled thermochemical decomposition system—specifically, a gasification unit—capable of converting Refuse-Derived Fuel (RDF) into a synthesis gas rich in CO₂ and other gaseous components. This syngas will serve as the flue gas analog required to assess the efficacy of the downstream CCUS process under realistic operational conditions.
Process Description
Refuse-Derived Fuel (RDF) or biomass are subjected to high-temperature thermochemical conversion via gasification at operating temperatures ranging between 900°C and 1100°C to generate a synthesis gas (syngas) predominantly composed of hydrogen (H₂), carbon monoxide (CO), methane (CH₄), and carbon dioxide (CO₂). Size-reduced RDF/biomass fractions, typically greater than 20 mm, are introduced into a fluidized bed gasifier through a top-feed mechanism. Concurrently, steam and hydroxy gas (a stoichiometric mixture of hydrogen and oxygen) are injected in a counter-current arrangement, enhancing the endothermic reactions responsible for the thermal decomposition and gasification of the feedstock.
The produced hot syngas initially transfers its sensible heat via a boiler pre-heater, raising the temperature of boiler feedwater, thereby improving the overall thermal efficiency of the system. Following heat recovery, the syngas is routed through a cyclone separator to efficiently remove entrained particulates and fly ash. Subsequent to particulate removal, the syngas undergoes a multi-stage gas cleaning process comprising:
1. An alkaline scrubbing system for acid gas neutralization and tar removal.
2. A desulphurization scrubber for the selective removal of hydrogen sulfide (H₂S) and other sulfur compounds.
3. A membrane separation unit engineered to selectively extract hydrogen (H₂) from the cleaned syngas stream.
The separated, high-purity hydrogen is collected for downstream utilization or storage. The membrane separation reject stream, rich in combustible gases, is recirculated to the ash melting zone located at the base of the gasifier, where it is combusted at elevated temperatures, facilitating its conversion primarily into carbon dioxide (CO₂) while simultaneously assisting in ash vitrification.
The high-temperature flue gases exiting the ash melting section of the gasifier possess substantial residual thermal energy, which is effectively harnessed for power generation using an Organic Rankine Cycle (ORC) turbine system. The ORC technology operates on the principle of utilizing an organic working fluid with a low boiling point relative to water, enabling efficient conversion of medium- to high-grade waste heat into mechanical and subsequently electrical energy.
This electricity generation constitutes a form of renewable energy recovery from industrial waste heat streams, thereby enhancing the overall thermodynamic efficiency and energy integration of the process. The incorporation of the ORC module not only contributes to improved energy utilization and reduced parasitic losses but also supports the broader objectives of sustainable industrial operations through the valorization of residual thermal energy, reinforcing the system's credentials as a high-efficiency, low-emission energy recovery and conversion platform.
The CO₂-enriched flue gas is then directed through a secondary membrane-based gas separation unit to recover high-purity CO₂. This purified CO₂ stream is subsequently introduced into acrylic photobioreactors (PBRs), specifically designed for microalgae cultivation through biological carbon sequestration. The acrylic construction of the reactors optimizes light transmission, promoting enhanced photosynthetic activity and rapid algal biomass proliferation. The assimilated CO₂ is biologically sequestered within the algal biomass, contributing to significant greenhouse gas mitigation. The harvested microalgae biomass possesses versatile downstream applications, serving as a valuable raw material for the plant-based food industry, nutraceutical and pharmaceutical formulations, and as a feedstock for biodiesel production via transesterification processes. This integrated waste-to-energy and carbon utilization pathway exemplifies a circular bioeconomy model, combining renewable energy generation, greenhouse gas abatement, and sustainable biomass valorization.
The Industrial Application
Industries such as Fertilizers, Oil & Gas, Cement, Steel, and Power generation are inherently dependent on fossil fuels to meet their specific process energy requirements. The combustion of these fuels results in the generation of flue gas streams that are typically rich in carbon-based compounds, predominantly carbon dioxide (CO₂), alongside other trace gases.
As part of an integrated decarbonization and resource optimization strategy, these flue gases are directed towards carbon capture processes. Prior to CO₂ capture, the residual thermal energy embedded within the high-temperature flue gas is harnessed via an Organic Rankine Cycle (ORC) Turbine system, which operates on low-to-medium temperature heat recovery principles. This system converts the recovered thermal energy into electrical power, contributing to the overall plant energy efficiency.
Following waste heat recovery, the cooled flue gas is subjected to carbon capture through one of several technically and economically viable pathways. These include:
1. Conventional Absorption-Desorption Systems: Utilizing chemical solvents such as monoethanolamine (MEA) for selective CO₂ absorption, followed by thermal regeneration for CO₂ release.
2.Membrane Separation Technologies: Employing advanced polymeric or inorganic membranes to achieve phase-wise separation of CO₂ from the flue gas mixture, offering modularity and lower operational footprints.
The captured CO₂, once purified, is then repurposed for biological sequestration through microalgae cultivation in controlled photobioreactor systems. These systems leverage photosynthetic assimilation, where microalgae convert CO₂ into biomass using light energy, offering a sustainable route for CO₂ valorization with applications in biofuels, nutraceuticals, and bioplastics.***
The electricity generated via the ORC Turbine is primarily utilized within the plant to support auxiliary loads, including the operation of the carbon capture units, photobioreactors, and ancillary systems.
In scenarios of excess power generation, the surplus electricity can be strategically diverted for green hydrogen production via water electrolysis. The produced hydrogen is stored and may be deployed as a clean fuel for Fuel Cell Engines or integrated into a Hydrogen-fueled Organic Rankine Cycle (HyORC) Engine, thus enabling further decarbonization of industrial energy systems. This holistic model not only optimizes waste heat recovery and carbon capture but also ensures productive utilization of the captured CO₂ and surplus renewable energy, supporting circular carbon economy objectives and contributing to industrial net-zero targets.
Carbon Sequestration Strategy The sequestration of captured CO₂ via microalgae cultivation in acrylic photobioreactors, while biologically effective, presents significant scalability limitations. These systems are inherently space-intensive due to the low areal productivity of microalgal biomass and the need for controlled light exposure and nutrient delivery. Moreover, the capital expenditure associated with deploying modular acrylic photobioreactor arrays at a meaningful scale is substantial, making it economically viable only for limited CO₂ loads.
Given these constraints, our current photobioreactor infrastructure is optimally designed to handle a sequestration capacity of approximately 2 TPD (tonnes per day) of CO₂ derived from our CCUS system. Beyond this threshold, the marginal costs of expansion outweigh the benefits, necessitating a shift toward alternative valorization pathways for the surplus CO₂. Accordingly, we propose integrating economically viable downstream utilization technologies such as catalytic conversion to methanol or formic acid, mineral carbonation, or polymer precursor synthesis. These approaches not only provide high-throughput carbon fixation capacity but also ensure value-added transformation of captured CO₂ into commercially marketable products, thus reinforcing the techno-economic feasibility of the overall CCUS framework.
Multiple Utilities of CO2
Pure CO₂ captured from industrial has numerous utilization pathways beyond long-term storage (sequestration). These applications align with both circular economy principles and carbon valorization strategies, enabling conversion into high-value products or services. Below is a comprehensive categorization of technically viable and commercially emerging CO₂ utilization options:
1. Chemical Conversion (Carbon-to-Chemical Pathways)
Captured CO₂ can serve as a feedstock in several chemical synthesis reactions:
-Green Methanol Production: CO₂ + Green H₂ → CH₃OH (via catalytic hydrogenation)
▪ Used in fuel blending, chemicals, marine fuels. Urea Synthesis: CO₂ + Ammonia → Urea
▪ Widely used in fertilizer production.
2. Fuels & Energy Carriers CO₂ can be converted into synthetic fuels via power-to-fuels technologies:
- Synthetic Methane (Sabatier Process): CO₂ + H₂ → CH₄
▪ Compatible with existing natural gas infrastructure.
- Dimethyl Ether (DME): CO₂ → DME via methanol intermediate ▪ Clean-burning LPG substitute.
3. Biological Conversion (Biofixation Pathways)
- Algal Biomass Production: CO₂ is assimilated in open ponds ▪ Biomass is converted into biofuels, nutraceuticals, or animal feed.
-Microbial Electrosynthesis: Electroactive microbes convert CO₂ into acetate or ethanol.
4. Mineralization and Construction Materials
- Carbonate Aggregates: CO₂ + Ca/Mg-rich industrial waste → Calcium Carbonates
▪ Used in concrete, bricks, and road base materials.
- CO₂-Cured Concrete: Accelerated curing processes embed CO₂ in cement.
5. Food & Beverage Industry
-Carbonation of Beverages: Food-grade CO₂ used in soda, beer, and sparkling water.
-Modified Atmosphere Packaging (MAP): For increasing shelf life of perishable foods.
6. Refrigeration and Cryogenics
- Dry Ice Production: Solid CO₂ used for cold chain logistics and industrial cleaning.
7. Enhanced Product Applications
- CO₂ for Oil Recovery: CO₂ injection in mature reservoirs (EOR) for residual oil mobilization.
-Fire Extinguishers: CO₂ is a standard suppressant gas in Class B and C fire hazards. 8. Agriculture and Horticulture
-Greenhouse Enrichment: Controlled release of CO₂ to enhance crop yields in polyhouses.