Carbon Capture: an Introduction to the Mature and Emerging Technologies

Among the numerous carbon capture technologies, the dominant two are pre- and post-combustion. New, more cost-effective CO₂ capture technologies are emerging, and are required in order to attain the SDS objectives. IFPEN and Axens are addressing this situation through the development of the DMX™ process technology, for instance.

Mature pre-combustion and post-combustion technologies

The two main carbon capture technologies, according to the distribution of CCS projects worldwide, are pre-combustion and post-combustion (figure 1). Due to their low representation in the distribution of CCS projects worlwide, the other two technologies – oxy-fuel combustion and direct air capture (DAC) – will not be detailed in this article, although they are currently attracting significant development.

Figure 1 - Distribution of CCS projects worldwide (Source: Concawe report no. 18/20 - September 2020)

• Pre-combustion consists in removing the CO₂ from the synthetic gas (syngas) before combustion for power generation. This pre-combustion system is applicable to many industrial processes such as fertilizer manufacturing, refineries, hydrogen production, etc.
• The post-combustion carbon capture technology consists in treating exhaust gas from fuel combustion (such as coal, fuel oil, gas, biomass or waste). Such flue gases are encountered in many industrial sectors such as power generation, steel manufacturing, cement plants, waste incinerators, crude oil refineries and chemical plants.

Pre- and post-combustion carbon capture solutions (figure 2) involve a wide range of technical processes with chemical and physical absorption at the top, and also adsorption on selected solids, membrane or cryogenic processes.

Figure 2 - Pre-combustion and post-combustion CO₂ capture routes

These technologies are the most advanced comparatively with other solutions, with a Technology Readiness Level (TRL) of over 5 on a scale ranging from 1 for the initial idea (basic principles observed) to 11 for mature technologies (proof of stability attained). To meet the aforementioned Sustainable Development Scenario (SDS) deadlines, sufficient maturity levels and further developments are required.

Today, the most common process technology for either pre- or post-combustion applications is based on absorption in solvents that will selectively pick up the CO₂ present in the gas. This process is illustrated in figure 3. The feed gas is washed in a counter-current in an absorption column with the solvent. The CO₂-rich solvent at the bottom of the absorber is then thermally regenerated to release the absorbed CO₂.

Figure 3 - Typical absorption process for CO₂ removal

As a rule, acid gas solubility reflects the ability of the CO₂ to dissolve in the solvent. The higher the gas solubility, the more gas can be treated in the same amount of solvent. The choice of solvent type (chemical, physical or hybrid) for a given application will mainly depend on CO₂ partial pressure in the gas to be treated.

As illustrated in figure 4, chemical solvents are clearly more suited to gases with low CO₂ partial pressure as encountered in post-combustion applications. CO₂ solubility will indeed be higher at low partial pressure in chemical solvents than in physical solvents leading to lower solvent circulation rates and lower overall energy consumption.

Figure 4 - CO2 solubility trends in solvents versus CO2 partial pressure

The selection of solvent type at higher CO₂ partial pressure (ppCO₂) will be case-dependent and driven by many parameters such as the level of impurities in the gas, energy consumption, the treated gas specification, quantity of equipment, utilities available at the site, and others.

Some typical conditions of industrial gases for post-combustion and pre-combustion applications are summarized below:

Find out more about Pre-combustion and Post-combustion technologies by downloading our dedicated Whitepaper.

Emerging Carbon Capture technologies: the example of DMX™

New generations of chemical solvents have emerged in recent years reducing the energy used in carbon capture and offering strong resistance to the presence of oxygen and contaminants. They will therefore bring benefits in terms of design and operating costs of the carbon capture unit.

Solvent-based technologies can be further segregated based on the type of solvent used for carbon dioxide capture, including:

• activated amines,
• amine blends,
• ionic liquids, and
• biphasic solvents.

A biphasic solvent is used in the case of the DMX™ technology developed by both IFPEN and Axens based on the use of an amine blend which forms two immiscible liquid phases under certain temperature and pressure conditions when loaded with CO₂.

The DMX™ technology is built on very solid foundations since it benefits from over 60 years’ experience in CO₂ removal on natural gas acquired by Axens and IFPEN through the licencing of the Advamine™ processes. 

Benefiting from prior developments through the Octavius and Valorco projects, including several laboratory experiments and pilot-scale testing, the DMX™ technology is now being demonstrated at laboratory scale and is ready to test industrially.

The DMX™ technology (figure 5) represents a real breakthrough for post-combustion CO₂ capture based on absorption by a demixing solvent.

Figure 5 - The demixing principle

This second-generation process has several benefits:

• A regenerable solvent with a much higher cyclic capacity than commercially available solvents
• High solvent thermal stability with low degradation rate, making regeneration possible at higher temperature, and therefore producing CO₂ directly under pressure, leading to significant CO₂ compression cost savings for downstream sequestration or liquefaction
• Solvent stability also induces lower corrosion risks and therefore allows cheaper steel to be used 
• A high capture rate (>90%) is achievable with high purity of produced CO₂ (>99%)
• Low steam energy consumption
• All these solvent properties lead to a 30% reduction in the energy penalty and in the total CO₂ capture cost (figure 6)

Figure 6 - Reduction of energy penalty with DMX™ solvent