CCUS: Carbon Capture, Use and Sequestration – Principles and Practice

Article by Rami Elias Kremesti M.Sc., CSci, CEnv, CWEM

The Problem

Combustion of fossil fuels (coal or biogas) and biomass or the production of steel and cement generates CO2 and H2O + Heat which is used to generate steam in thermal fossil fuel power stations or for transport. In a power station, the steam turns a turbine and electricity is generated.
The Equation is: CxHyOz + O2 -> CO2 + H2O + Heat (+ N2 + NOx + SOx)
CO2 is a powerful green house gas
When air is used for combustion, N2 and NOx are also produced in the flue gas.
If coal that has sulphur in it is used, SOx is also produced

The Solution

Separate the N2 from the CO2 in the flue gas and capture/store/use the CO2. This is known as Post-Combustion CCS.
Separate O2 from N2 in ambient air and use pure O2 for the combustion reaction then only CO2 and H2O is produced. This is called Oxy-Combustion.
CO2 can be stored in geological formations
CO2 can be used in Enhanced Oil Recovery
CO2 can be used as a Carbon source monomer for synthesizing larger molecules
Reacting CO2 with NaOH produced Soda Ash or Sodium bi-Carbonate
CO2 could potentially be stored in so called smart materials called Metal Organic Frameworks (MOF’s)

The Chemistry of CCUS

Amine gas treating, also known as amine scrubbing, gas sweetening and acid gas removal, refers to a group of processes that use aqueous solutions of various alkylamines such as Mono-Ethanol-Amine MEA (commonly referred to simply as amines) to remove hydrogen sulfide (H2S) and/or carbon dioxide (CO2) from combustion flue gases.
It is also possible to combust the fossil fuel incompletely to produce CO and H2 called Syngas.
Calcium looping processes for capturing CO2 from large emissions sources are based on the use of CaO (lime) particles as sorbent in circulating fluidized bed reactors.
Gas separating membranes are also being proposed that can separate CO2 from N2 and even recover H2O.

Amine Based CCUS Process Flow Sheet

Schematic of Amine Bsaed Carbon Capture Absorber-Regenrator Units

DAC – Direct Air Capture

Direct air capture (DAC) is the use of chemical or physical processes to extract CO2 directly from the ambient air.
Most commercial techniques use a liquid solvent—usually amine-based or caustic—to absorb CO2.
In a cyclical process designed in 2012 by professor Klaus Lackner, the director of the Center for Negative Carbon Emissions(CNCE), dilute CO2 can be efficiently separated using an anionic exchange polymer resin called Marathon MSA, which absorbs air CO2 when dry, and releases it when exposed to moisture.
Some DAC processes used Bipolar ion exchange membranes to extract the CO2 which is a process also used in Direct Ocean CO2 capture.

Schematic of Direct Air CO2 Capture - DAC

Figure 1: Schematic of DAC

Uses of CO2

CO2 is a non-polar acidic relatively inert gas
It can be used to decrease the pH or neutralize alkaline waters
If CO2 is reduced to CO it can be used a monomer building block
Labs around the world are trying to synthesize bio-plastics out of CO2
Plants/Trees turn CO2 and Water into Lignin and Cellulose
Farms can use CO2 as a fertilizer/agro-stimulant in green houses
CO2 is used in soft drinks as a source of fizziness
CO2 is injected at a low dose in aquariums to feed the plants/algae
CO2 gas can be used to enhance oil recovery (EOR) by pressurising oil formations

Pioneers in CCUS

GE Power/ALSTOM
Shell
ARAMCO
INEOS
Linde Engineering
Scrubbing Agents from BASF
Occidental Petroleum
NOVO-MOF AG

Real Life CCUS Projects

China’s largest carbon capture and storage plant at Guohua Jinjie coal power station was completed in January 2021. The project is expected to prevent 150,000 tons of carbon dioxide emissions annually at a 90% capture rate.
In 2020, Norway announced “Longship” (“Langskip” in Norwegian). This 2,7 billion euro CCS project will capture and store the carbon emissions of Norcem’s cement factory in Brevik.
After the success of their pilot plant operation in November 2011, the Abu Dhabi National Oil Company and Abu Dhabi Future Energy Company moved to create the first commercial CCS facility in the iron and steel industry. CO2 is a byproduct of the iron making process. It is transported via a 50 km pipeline to Abu Dhabi National Oil Company oil reserves for EOR. The facility’s capacity is 800,000 tonnes per year. As of 2013, more than 40% of gas emitted by the crude oil production process is recovered within the oil fields for EOR.
The UK is investing in CCUS projects in various clusters like the Humber, Mid West and the Solent.

References

https://en.wikipedia.org/wiki/List_of_carbon_capture_and_storage_projects

https://en.wikipedia.org/wiki/Carbon_capture_and_storage

https://www.ge.com/gas-power/future-of-energy/carbon-capture-storagehttps://en.wikipedia.org/wiki/Direct_air_capture

About The Author

Rami Elias Kremesti is a passionate water/waste water treatment and power station chemist. He lives in the UK and has worked on power station and water treatment projects worldwide. He is a polyglot, enjoys reading, writing, cooking and playing guitar. He has two lovely teenage daughters Krassi and Lulu that are the love of his life. He is based in High Wycombe, the water treatment capital of the UK. Rami is a passionate Social and Peace activist and the founder of AMALID.ORG and BONKA.BG.

Rami Elias Kremesti with a gypsy Roma matriarch in Trankovo Village, Bulgaria.