Types and scale of carbon capture usage and storage

[edit] Introduction

Carbon capture, usage and storage (CCUS), also referred to as carbon capture, utilisation and storage, is carbon capture and storage (CCS) combined with carbon capture and usage (CCU), the same capture techniques but covering both eventualities of the post capture product, usage and storage.

The global capacity for CCUS is currently around 40 million metric tons of CO2 or carbon per year, whilst global CO2 or carbon emissions in 2022 were estimated at around 37 billion metric tons.

[edit] Types of usage

Carbon dioxide (CO2) is also now often also referred to just as carbon. Its use after it is has been captured loosely falls in to one of three categories; mineralisation, chemical or biological usage. These however differ by nature in that some technologies or methods such as mineralisation can sink carbon permanently, whilst others make use of carbon in products only for it to be released later, so are only temporary or mid-term solutions.

[edit] Mineralisation

Mineralisation in the natural world is a geological, slow and methodical way of sequestering CO2. Hydrolysis of CO2 in moist air or water can drive chemical weathering in rocks. Carbonates are made of 1 atom of carbon and 3 atoms of oxygen with an electric charge of −2. Carbonate minerals are a set of minerals made from carbon, oxygen, and a metal element.

There are around 80 known natural carbonate minerals, most are rare but the most common include; calcite which is the primary mineral in limestone and marble, and dolomite which is the same where the calcite is replaced and aragonite, which is more recent deposits containing shells. Other more common carbonate minerals are metal ores: siderite (iron ore) rhodochrosite (manganese ore; strontianite (strontium ore) smithsonite (zinc ore) witherite ( barium ore) and cerussite (lead ore).

Carbon dioxide is emitted as a by-product of clinker production for the cement industry. The calcium carbonate (CaCO3) is calcinated and converted to lime (CaO), which is the primary component of cement. Fossil fuel combustion also emits carbon dioxide (CO2). The carbon dioxide (CO2) emitted can be captured from the processes, recycled and injected into fresh concrete during mixing, where the CO2 undergoes a chemical reaction and transforms into a mineral.

[edit] Chemical

Chemical use of CO2 (carbon) is relatively common in small quantities in many many different applications, most of which could make use of recycled or captured carbon. CO2 is used in aerosol propellants, dry ice refrigeration, fire extinguishers, as inert agents in welding, and in carbonated drinks, which eventually lead to its release. It is also used in the process of making metal castings, and to make urea fertiliser and some special polymers, all of which can be replaced with recycled and captured CO2. In the future when hydrogen production is more common and green, CO2 could be combined with H2 to make synthetic fuels, syngas and methanol. The production of methanol and ethanol create opportunities for sinking of CO2 in products, but as liquid fuels are eventually burnt they are not permanent sinks. As syngas and methanol are basic chemical feed-stocks this can lead to the production of many different chemicals, polymers and polycarbonates, if in relatively small quantities.

[edit] Biological

Biological use of CO2 relates to the promotion of plant growth and can be captured in soils by using biochar to increase soil quality. It can also be used in the production of Algae and thus as a potential fuel.

[edit] Types of storage

Simply storing CO2 for the long term after it is has been captured generally involves one of two processes; enhanced oil recovery (EOR) and aquifer storage.

[edit] Enhanced Oil Recovery (EOR)

Enhanced Oil Recovery (EOR) ironically is relatively common because it is a method to draw more oil and gas from reserves and was first trialled in the 1970's. One technique is to inject CO2 (carbon) into the depths of an oil well over 700m deep with pressure, where it acts as a solvent releasing oil and gas from the rock strata, it can also be injected along with water. Injected CO2 can also be used as a secondary drive mechanism pushing out anything remaining in an oil or gas well, storing it in the voids that are left.

[edit] Aquifer sequestration

Aquifers sequestration makes use of natural geological formations containing brine (salt water) in a porous rock. These are usually underneath a layer of rock which is non-porous, referred to as caprock. Many of these formations can be found throughout the globe and are normally extremely large and deep.

CO2 or carbon can be pumped down into the rock, displacing the brine in the formation and forming a subterranean plume at the top of the void, the CO2 slowly dissolves into the brine. Over many millions of years the CO2 can mineralise into rock is the same way as natural carbonate minerals are formed, thus sequestering the carbon permanently.

[edit] Scale

In 2023, there are around 35 commercial facilities that apply CCUS technologies to industrial processes, fuel transformation and power generation. They are located in the US, Brazil, Canada, Australian, Qatar, Saudi Arabia, Norway, China and Hungary, with a total capacity of storing just under 40 million metric tons of CO2 or carbon per year. With global emission in 2022 set at around 37 billion metric tons, if it were theoretically possible to locate facilities at all emissions points (which in reality it is not) this would mean a scaling up of the technology to increase capacity by at least 1000 times. The largest facility in 2022 is the Shute Creek Gas Processing Plant, in the United States which has a capacity of capturing around 7 million metric tons of CO2 or carbon per year.

Because of the difficulty in capturing emissions the technology is restricted to large point emission locations, such as power plants and is therefore only likely to be a part of the solution in reducing emissions. Likewise because of the differing levels of sequestration possible via the different types of CCUS, aquifer sequestration and mineralisation in construction products are often seen as having the most potential because these could be carried out at a significant scale.