CCUS in General
Carbon Capture, Utilization, and Storage or often addressed as CCUS is a technology that can capture carbon from large emitting sources such as industries and power generators, to be used or stored underground. In the case that the carbon is that utilized or stored within the same site as the capture site, the CO2 is transported in a compressed liquid state. CCUS is one of the key technologies which help to reduce emissions especially in the hard-to-abate sectors. Currently, around 40 commercial capture facilities are in operation globally, with a total annual capture capacity of more than 45 Mt CO2.
Carbon recycling refers to the process by which carbon, in various forms such as carbon dioxide (CO2) or organic carbon, is reused or transformed into different compounds within the Earth's biosphere, lithosphere, atmosphere, and hydrosphere. This process is vital for maintaining the carbon balance in the environment and sustaining life on Earth.
Carbon recycling occurs through various natural processes and human activities:
- Photosynthesis: Plants, algae, and some bacteria use sunlight, water, and CO2 to produce carbohydrates during photosynthesis. This process removes CO2 from the atmosphere and incorporates carbon into organic matter, which can then be consumed by other organisms.
- Respiration: Organisms, including plants, animals, and microbes, release CO2 into the atmosphere through respiration when they break down organic matter to obtain energy.Decomposition: Dead organisms and organic matter are broken down by decomposers like bacteria and fungi. During decomposition, carbon is released back into the atmosphere as CO2 or incorporated into the soil as organic carbon.
- Fossil Fuel Formation and Combustion: Over millions of years, the remains of plants and animals can become fossil fuels like coal, oil, and natural gas through geological processes. When humans extract and burn these fossil fuels for energy, carbon that was sequestered underground is released into the atmosphere as CO2, contributing to climate change.
- Carbon Sequestration: Some natural processes and human activities can remove CO2 from the atmosphere and store it in long-term reservoirs. For example, forests and oceans act as carbon sinks, absorbing CO2 from the atmosphere through photosynthesis or chemical reactions.
- Carbon Capture and Storage (CCS): This technology captures CO2 emissions from industrial processes and power plants before they are released into the atmosphere. The captured CO2 is then transported and stored underground in geological formations to prevent it from contributing to climate change.
There are four main types of capture process. Depending on the industrial process, the type of power plant, or the geographical conditions, pre-combustion capture, post combustion capture, oxy-fuel combustion, or direct air capture (DAC) is applied.
A. PRE-COMBUSTION CAPTURE
Pre-combustion capture is a process in which carbon is extracted from a fossil fuel (i.e., gas, oil, or coal) before it is burnt. This is done by a pre-treatment process called ‘gasification’, in which the fuel is heated under low pressure with a limited amount of oxygen. The product is called ‘synthesis gas’, or just ‘syngas’, and is used in gas turbine generators at power plants. Precombustion recovery is mainly used in industrial facilities, such as natural gas processing, whilst the application to power plants is still limited to a few integrated gasification combined cycle (IGCC) coal plants.
B. POST-COMBUSTION CAPTURE
Oxy-fuel combustion uses almost pure oxygen instead of air to burn fossil fuel. This produces an exhaust gas consisting of water vapour and CO2, which can be easily separated, after being dried and compressed, to produce high-purity CO2. It is a relatively cost-intensive technology that requires large-scale equipment to be installed. However, it can be used in combination with other separation/recovery technologies.
C. OXY-FUEL COMBUSTION
Post-combustion carbon capture removes CO2 after the fossil fuel has been burned. The CO2 is separated from the exhaust flue gas before it is released to the atmosphere. CO2 can be recovered using several different methods: liquid solvent, sorbent-based, and membrane-based methods.
D. DIRECT AIR CAPTURE (DAC)
Direct air capture (DAC) technologies extract CO2 directly from the atmosphere. There are currently two major technological approaches. One is a liquid system, in which a hydroxide solution reacts with CO2 to remove it from the air. Another approach is based on solid sorbents, similar to the post-combustion capture process. Solid sorbent filters chemically bind with CO2. When the filters are heated, they release the concentrated CO2.
Both are technically feasible but are highly energy- and cost-intensive. Compared to the flue gas at fixed point capturing, the CO2 intensity in the atmosphere is 200–300 times more dilute. This results in low capturing efficiency and is, therefore, more expensive. It is, however, the only technology that can capture CO2 already released into the atmosphere. This makes DAC not only a potential carbon-neutral technology but even a potential carbon-negative technology.
There are two major methods of transporting captured CO2 to storage locations or utilization sites, shipping and pipelines. CO2 is typically compressed to a pressure of about 8 megapascals, reducing the transportation cost. CO2 pipelines are already in use for the transport of CO2 to enhanced oil recovery sites, but there are also efforts to utilize existing natural gas pipelines. Other feasible options for rather limited volumes of CO2 are trains and roads.
An essential part of making CCUS an economically sustainable concept is the utilization of CO2. Changing CO2 from an environmental burden that has to be disposed of somewhere to an economical asset that can be traded as any other resource, would create a new value cycle. This value cycle would offer a positive incentive for emitters to invest in
CO2 capturing and makes CCUS less dependent on public funding. There are multiple approaches to utilizing CO2 as a resource. The food and beverage industry, fuel industry, construction industry, and agriculture are four sectors spearheading the research and development to find feasible applications. Products from these sectors are all essential on a global scale. This means that if CO2-utilising products can be made for these sectors, the market will automatically be huge and the products will not require long-distance transportation.
Storing CO2 involves the injection of captured CO2 into a deep underground geological reservoir of porous rock overlaid by an impermeable layer of rocks, which seals the reservoir and prevents the upward migration of CO2and its escape into the atmosphere. There are several types of reservoirs suitable for CO2 storage. To geologically store CO2, CO2 must first be compressed, usually to a dense supercritical fluid. The reservoir must be at a depth of 800 meters or greater to retain the CO2, where the injected CO2 will be in a dense supercritical state. Potential CO2 reservoirs can be categorised into three types as follows:
- Deep saline formations: Layers of porous and permeable rocks saturated with salty water (brine), which are widespread in both onshore and offshore sedimentary basins.
- Depleted oil and gas reservoirs: Porous rock formations that have trapped crude oil or gas for millions of years before being extracted and which can similarly trap injected CO2.
- Deep coal seams: Solid coal has a very large number of micropores into which gas molecules can diffuse and be tightly adsorbed. Adsorption is the main storage mechanism in coal seams at high pressure.
Fig 1. Tomokomai CCS Demonstration Project (Source: ACN Archives)
From 2016 to 2019, Japan implemented its initial comprehensive carbon capture and storage (CCS) initiative. This project, ‘Tomakomai CCS Demonstration Facility', successfully captured and stored carbon dioxide (CO2) emitted by a coastal oil refinery located on Hokkaido Island in Japan. The goal is to showcase the feasibility of a comprehensive CCS system, encompassing the entire process from CO2 capture to injection and storage [1]. An annual injection and storage of at least one hundred thousand tons of CO2 is taking place in offshore saline aquifers in the Tomakomai port region. Japan CCS Co., Ltd. (JCCS) has been assigned the responsibility of executing this project by the New Energy and Industrial Technology Development Organization (NEDO), with the Ministry of Economy, Trade and Industry (METI) Japan providing subsidies to cover the operational expenditures. The CCS demonstration project has reached its goal of injecting a cumulative total of 300,000 mt of CO2 on November 22, 2019, ensuring safe operation [2].
Japan has taken a significant stride towards achieving carbon neutrality by 2050. In June 2023,the country announced the selection of its first seven carbon capture and storage projects. These projects aim to store 13 million metric tons of CO2 annually within Japan and in other countries by the year 2030 [3]. Japan aims to establish and operate CCS businesses by 2030, with the objective of augmenting its annual CO2 storage capacity by 6 million to 12 million metric tons.This initiative is part of Japan's long-term CCS roadmap plan [3]. The seven chosen initiatives focus on various sectors including electricity generation, oil refining, steel production, chemical manufacturing, pulp and paper production, and cement production. These projects aim to capture carbon dioxide emissions from industrial clusters in Hokkaido,Kanto, Chubu, Kinki, Setouchi, and Kyushu regions. The overall objective is to store around 6 to 12 million metric tons per annum of CO2 by the year 2030 [4]. The projects, with five of them targeting CO2 storage in Japan and the remaining two in Asia and Oceania, seek to achieve a combined CO2 storage capacity of over 13 million metric tons per annum (Mtpa). JOGMEC aims to reach a CO2 storage capacity of around 120 to 240 million metric tons per annum by 2050 through these projects [4].
