Precombustion capture

Precombustion CO₂ capture involves removing all or part of the carbon content of a fuel before burning it. The fuel is processed to produce a gas stream that primarily consists of CO₂ and hydrogen.

The CO2 is then captured for storage and the hydrogen is combusted in a conventional gas turbine combined cycle to generate electricity, resulting in a flue gas that only consists of water vapour.

The first step of Precombustion is to convert the original solid fuel into a synthesis gas that primarily consists of carbon monoxide (CO) and water (H₂O). The synthesis gas is then cleaned of particles that could otherwise damage the gas turbine or cause problems in the subsequent processing steps.

Next, the carbon monoxide is reacted with steam in a shift reactor to produce CO₂ and hydrogen:

CO + H₂0 <-> CO₂ + H₂

After the shift reaction, the gas primarily consists of CO₂ and hydrogen. The CO₂ is then separated in an absorption process. The CO₂ is transported to a storage site and the remaining hydrogen-rich gas is combusted in a gas turbine, which produces water vapour as the main flue gas.

Considerations for commercial viability

Most of the process equipment required for Precombustion is readily available and commonly used in ammonia plants, refineries and other industrial processes. An advantage of the Precombustion system is that it could be optimized for generating electricity, hydrogen or chemicals, or even a combination of all three. However, to make pre-combustion truly viable for commercial use in power plants, further development of the gas turbine and the gasifier is required.