The Earth's climate has changed throughout history. The Earth has witnessed seven cycles of glacial advance and retreat in the past. The abrupt end of ice age marked the beginning of the modern climate era and human civilization on the planet. Earth had suitable climate due to the presence of gases such as carbon-dioxide and other greenhouse gases in its atmosphere which maintain the temperature and prevent the planet from experiencing extreme climatic conditions.

Today, the picture has completely changed. Carbon dioxide which once was the reason behind the presence of suitable climate on the planet’s surface is now a biggest threat to its climate. Carbon dioxide concentrations are rising mostly because of the fossil fuels that people are burning for energy. Additionally, deforestation, transportation, industrial manufacturing units and others are some other sources of carbon dioxide.  In 2018, the concentration of carbon dioxide reached highest of last 3 million years i.e. 408 parts per million. 2016 was the warmest year on record. NASA and NOAA data show that global averages in 2016 were 1.78 degrees F (0.99 degrees C) warmer than the mid-20th century average. Eleven percent of all global greenhouse gas emissions caused by humans are caused by deforestation comparable to the emissions from all of the cars and trucks on the planet. This increase in the levels of carbon dioxide is contributing towards global warming and climate change.

Approaches to Mitigate Global Climate Change

In recent times, increasing amount of carbon dioxide is one of the most critical concern for the world. Changes in climate conditions and increasing global warming are stressing on the need to reduce the concentration of carbon dioxide in atmosphere. Hence, there arises a need to find out ways and techniques to address global climate change problem.

Carbon-dioxide Capture & Storage Technologies

Carbon dioxide capture and storage (CCS) is an important approach used for reducing carbon dioxide emissions and thereby is considered to be helpful in mitigating climate change. Carbon Capture and Storage (CCS) is a technology that captures up to 90% of the emissions produced from the use of fossil fuels in electricity generation and industrial processes, preventing the carbon dioxide from entering the atmosphere. CCS involves a series of steps collecting, separating, transporting and then burying the CO2 so that it does not escape into the atmosphere. The choice of CCS technology to be used completely depends upon the source of CO2 generating plant and fuel used. Carbon dioxide capture systems associated with combustion processes include oxyfuel combustion, post combustion and pre combustion.

After post capture, the next step is separation. Carbon dioxide separation technologies such as cryogenic distillation, chemical looping combustion, adsorption, membrane separation, among others can be utilized to remove CO2 gas from fuel gas stream even before it is transported. Once CO2 is separated from the rest of the flue gas components it is transported to the storage site or to the facilities for its industrial utilization or storage.

Carbon Dioxide Capture Systems

Based on the process or power plant application, there are three main approaches for capturing the CO2 generated from a primary fossil fuel (coal, natural gas or oil), biomass, or mixtures of these fuels. These processes include post-combustion, pre-combustion and oxyfuel combustion for capturing the carbon dioxide.

The post-combustion technique involves the separation of carbon dioxide from fuel gas after combustion has taken place. In this process, usually a liquid solvent is used to capture the CO2 present in flue gas. Nitrogen is the main constituent here. These technologies are usually preferred while retrofitting existing power plants. This technique is successful in recovering up to 800t/day of CO2. Next is the pre-combustion technique in which pre-treatment of fuel is done prior combustion. The pre-treatment differs according to the source of CO2. For instance, pre-treatment of coal is done using gasification process. This technique can be employed in Integrated Gasification Combined Cycle (IGCC) power plants where coal is used as a fuel.

While in oxyfuel combustion, oxygen is used in place of air as it reduces the amount of nitrogen present in the exhaust gases which affects the separation process at a later stage. Additionally, use of oxygen instead of air offers reduction of thermal NOx, another advantage for the process.

Carbon Dioxide Separation Processes

This paragraph offers insights pertaining to the carbon dioxide separation technologies which can be used to isolate carbon dioxide from fuel gas before transportation.

Carbon Dioxide Transport

After separation from flue gas components, the separated CO2 needs to be transported to a storage or utilization site accordingly. An economically feasible transport network is the key feature of any CCS project. The mode of transport of CO2 totally depends upon the volumes separated. Road tankers or ships or pipelines any of these can be used for safe and reliable transport of CO2. Pipelines are considered as the most important means for onshore transport of large volumes of CO2 through long distances. Additionally, pipelines are the most efficient way for CO2 transport when the source of CO2 is a power plant where lifetime is longer than 23 years. For shorter period, road and rail tankers are more effective. The cost of transport varies according to the regional economic condition. However, there arises a need to regularly monitor these pipelines since CO2 is highly reactive in nature and high pressure can adversely impact the metering equipment. Additionally, these equipment needs to be periodically changed to withstand the challenging environmental conditions inside the pipeline. Additionally, the trans-national transport and offshore storage of CO2 should be critically evaluated in order to prevent any kind of legal implications. 

Carbon Dioxide Storage

Finally, after capture, separation and transport the storage of carbon dioxide is done. CO2 can be stored into geological formations such as oil or gas reservoirs, deep saline aquifers, others. Geological storage is regarded as the most viable options for storing large quantities of CO2 needed to efficiently reduce global warming and climate change.

Pre-requisites for the storage of carbon dioxide include permeability, thickness and porosity of reservoir rock and a stable geological environment. The major types of geological formations considered for CO2 storage include depleted oil and gas reservoirs, un-mineable coal beds, saline aquifers, basalts, among others. Potential CO2 leakage is a major concern for geological storage and a comprehensive monitoring program needs to be developed.

Recent Developments

Recently, researchers from Melbourne have come up with a new method for capturing atmospheric carbon dioxide which is damaging our planet and leading to the problems such as climate change and global warming. Using this method, the atmospheric carbon dioxide can be converted into some sort of solid material which could be stored easily. This new technology will evolve as a sustainable and cost-effective plan for transforming CO2 into coal. The process involves a liquid metal catalyst which is efficient in conducting electricity. CO2 gas is dissolved in a beaker along with an electrolyte liquid and the liquid metal. After the introduction of electric charge, carbon dioxide is broken into small pieces of carbon which can later be collected and stored. Additionally, the solid carbon obtained at the end of this process can be used as an electrode. Carbon can hold electrical charge and thus is becoming a supercapacitor which can be used as a component in future vehicles. Moreover, the entire process produces synthetic fuel which can be used for widespread industrial applications.

Conclusion

In order to reduce global greenhouse gases emissions a range of approaches such as improving energy efficiency & conservation, clean fuel technologies, developing renewable sources of energy, implementing CCS are followed depending upon the circumstances and scenario. Although technologies associated with capture and storage of CO2 exist, but the overall cost of using CCS approach is high and should be significantly reduced before it can be deployed. There are multiple hurdles in the path of CCS deployment which need to be addressed in the coming years. These include the absence of investment in CCS, and economic incentives to support the additional high capital and operating costs associated with the carbon capture technology.

According to TechSci research, “Global Carbon Capture & Sequestration Market, By Application (EOR Process, Industrial, Agricultural & Others), By Service (Capture, Transportation & Storage), Competition Forecast & Opportunities, 2013 – 2023, the global carbon capture & sequestration market is projected to grow at a CAGR of over 14%, in value terms, during 2018-2023. Growing needs for alternative energy sources, increasing focus to reduce CO2 emission, re-usage of captured CO2 by industries, formulation of relevant standardization and legalization and increasing investment by government to develop advance carbon capturing and storage technologies are some factors, that will propel the demand for carbon capture & sequestration over the next five years. North America is anticipated to remain a strong contributor in the carbon capture & sequestration market in the forecast period, owing to technological advancement. APAC is expected to register faster CAGR than any other region, backed by increasing number of coal-fired power plants.

Key Players

Most current CCS techniques are uneconomic because they consume too much energy to sequester the carbon, so they have yet to be deployed at scale. Yet start-ups and big companies alike are working to make CCS both viable and profitable. Some of the major players operating in the global CCS technology market include Shell, Chevron, NRG Energy, Climeworks, Global Thermostat, CO2 Solutions, Carbon Engineering, among others.