Decarbonisation Technology - February 2023

Combustion air Natural gas fuel

Calciner tower & clinker kiln

Natural gas feedstock & steam

Post combustion ue gas


during reforming, cement, glass and steel production. The flue gas streams from these processes are rich in CO2 at about 15%. This can double to 30% if oxy-fuel combustion has been used. This compares with flue gas from a normal gas- or coal-fired combustion process, which typically contains 2-6% CO2 (see Figure 3 ) . Whilst these processes are responsible for high CO2 emissions globally, they are also some of the best processes to target for CO2 capture because removing CO2 from these flue gases is more cost effective per tonne of CO2 sequestered than capturing CO2 from a very dilute flue gas stream, such as the emissions from a gas-fired turbine power plant. The Airovation Technologies CCM process is ideal for treating steam methane reforming flue gases and other flue gases with similarly elevated CO2 concentrations. It benefits from the process intensity, and the reactions respond well to the elevated CO2 concentrations. Conventional SMR carbon capture technologies can stress utilities infrastructure The most widespread technology for carbon capture uses a twin tower process, where CO2 from the flue gas is absorbed into an amine- Figure 3 Difficult to decarbonise industries – cement making Notes: – CO emissions are also associated with the energy and power requirements for this industry sector. – These can potentially be decarbonised with renewable power and electrical heating or microwaves. – CCS to capture CO from the process and/or the associated energy production is possible.

Notes: – In the SMR the air/fuel combustion reaction takes place in a separate part of the process to the reforming reaction. – SMR may alternatively be side-fired or upwards fired. – Shaded area denotes catalyst bed

Figure 2 Steam methane reforming chemistry

CO 2 generation during steam methane reforming Renewable power supplied to an electrolyser can produce green hydrogen, and many new-build hydrogen plants will operate this way. However, the most common hydrogen production process, used to generate about 80% of the world’s hydrogen, is steam methane reforming. There is a legacy of more than 1,000 operational SMRs around the world. Retrofitting CCM, or another carbon capture technology, can decarbonise these assets and extend their life. Steam methane reforming uses natural gas, refinery gas, or naphtha as feedstocks. When these fossil feedstocks are used to generate hydrogen without capturing the CO2 emissions, it is called ‘grey’ hydrogen. If most of the CO2 from the SMR is captured, the hydrogen is referred to as ‘blue’. CO2 is released from the SMR in two locations: firstly, as the feedstock is transformed to hydrogen, CO2 is produced as an unavoidable by-product. Secondly, CO2 emissions from the combustion of fossil fuels (generally a portion of the natural gas feedstock) create the heat required to drive the reforming chemical reactions that convert the feedstock to hydrogen (see Figure 2 ). CO2 is unavoidably released from the process


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