Carbon capture, utilization, and storage (CCUS), or carbon capture and sequestration/storage (CCS), is a groundbreaking process that aims to reduce the amount of carbon dioxide (CO2) in the atmosphere. CO2 is a byproduct of many industrial and commercial activities like power generation, manufacturing, and automobiles.
The process aims to capture and store carbon to use in a responsible manner. In recent years, CCS technologies have emerged to have a significant potential to reduce carbon dioxide and capture 90%-100% of their carbon dioxide. The technologies aim to couple with a method of using the CO2 as either a feedstock for other industrial processes, as a process gas itself, or different recovery processes in the oil and gas exploration and production.
Renewable energy sources, carbon-neutral or negative industrial processes, and energy-efficient machines and equipment have gained massive traction among the public and private sectors. CCS is so important to these aims because it will reduce the rate of CO2 emission in the atmosphere. We need a CCS to reduce the cumulative amount of CO2 in the atmosphere to reduce the harmful effect of greenhouse gases on climate change.
According to recent reports from Global Carbon Capture and Sequestration/Storage (CCS), newer built chemical plants or ones being constructed can potentially capture triple the amount of CO2 produced by the United States. Forty million metric tons carbon capture potential by these plants per annum compared to 5 million metric tons produced by the United States in 2019.
There is a different set of technologies at work in each capture, utilization, and sequestration step. They are usually packaged together to make the whole process work and are broadly categorized as follows:
In the post-combustion process, carbon dioxide is absorbed by an absorbent at the source of CO2 production. In pre-combustion, the carbon content is converted to CO2 by gasifying the fuel. Gasification is a process in which the fossil fuel (carbon-based fuels) is converted to gases like hydrogen, nitrogen, carbon dioxide, and carbon monoxide in the presence of a gasifying agent like sub-stoichiometric oxygen or air and steam. This helps to “clean” the fuel before the combustion takes place.
Although being adopted by the industrial facilities, it is in the nascent stage of development for the power plants. The assumption is that it will be available for new constructions. However, retrofitting the existing power plants will be a very costly capital expenditure for the power producers. In the case of oxy-fuel combustion systems, the fuel is burned in the presence of pure oxygen. The carbon dioxide generated is as purest to the high level so that it can be stored easily without having to go through further post-processing scrubbers to remove flue gases.
The captured CO2 is then transported either through pipelines or through other modes of transportation to the storage sites. Interestingly, many abandoned oil and gas well sites, formations, fields, old coal beds, and salt caverns are among the best storage sites because they prevent leakage of gases into the atmosphere and keep the formation fluid within bounds.
The vicinity of a geological formation that can store the CO2 is one of the most important factors of the CCS because it reduces the transportation cost and makes it more economically feasible.
Certain challenges associated with CCS cause a high market entry barrier. First and foremost is the high cost of the subsystems and regulatory requirements for infrastructure, including pipelines, making it a high capital expenditure. Second is the high cost of transportation because CO2 needs to be maintained at high pressure and very low temperatures for pumping through a pipeline, thus increasing pumping costs. CO2 needs to be maintained at high pressure, which increases the infrastructure’s strain due to the requirement for high-pressure piping while low-pressure oil and gas pipelines cannot be used for this purpose.
Another significant issue is that in the presence of impurities, the corrosion rate of pipeline increases. Corrosion can result in catastrophic failure and leakages. The cryogenic temperatures CO2 further complicates this situation during transportation, making the metal brittle and easy to fail.
The third challenge is related to storage. Most of the storage is underground, so the geological formation should be appropriate for the storage. If the required geological formation is not available, the liquid CO2 shall be pumped to the farthest distances, making the pumping and infrastructure costs prohibitively expensive. Currently, it is thought that limitations on the geological formation are not a high constraint for companies to enter the market because of the abundant orphaned oil and gas sites and coal mines available for storage. There is a long-sought-out discussion on the effect of CO2 storage underground resulting in a heightened risk of seismic activity. One way of mitigating this risk is above-ground mineralization of CO2.
We can use CO2 from the CCS either in conventional or unconventional pathways. CO2 is converted to a chemical like Urea or Polycarbonate polyols in conventional utilization. Another utilization is making construction materials like concrete which will be one the highest consumers of CO2 apart from Urea used to make fertilizers.
It is estimated that using CO2 in cement making will utilize 0.1 to 1.4 Gt CO2 from the CCS program.
Enhanced oil recovery is another arena where CO2 from the CCS program is used. Like waterflood applications, the CO2 is pumped through injection wells around the oilfield to increase the production of oil, where CO2 will push the oil through the production well.