CLEAN COAL TECHNOLOGY & INDUSTRY EMISSIONS REDUCTIONS

- Nikhil Kaitwade

Associate Vice President, Future Market Insights

Coal is the most polluting of all fossil fuels. When burnt, it emits greenhouse gases, causes acid rain, and pollutes the environment. With all of the talk about hydropower, nuclear energy, as well as biofuels, one might be forgiven for assuming that filthy coal is on its way out. But that is not the fact in reality. What comes into the entire scenario here is the huge amounts of carbon emissions. With the increasing carbon emissions, particularly from industrial activities, the trend has shifted towards the usage of clean coal technologies for the sustainable development of various industries and also to achieve the carbon emissions target worldwide.

According to Future Market Insights, the global demand for clean coal technology is expected to reach US$ 3.8 billion by 2022, exhibiting growth at a CAGR of 4% during the forecast period 2022-2032. Rapid rise in power consumption as well as a shift away from renewable energy sources is expected to fuel market expansion in the coming years.

Clean coal technologies are advanced coal utilization methods of the next generation that are aimed to improve the environmental acceptability as well as efficiency of coal mining, preparation, and also use. Such techniques are being developed to reduce the negative environmental effect of coal energy production and to alleviate global climate change by reducing greenhouse gas emissions. Although new rules and rigorous emission standards favour renewable energy sources, coal is expected to remain a critical power generation source globally. As a result, companies are focusing on sophisticated CO₂ reduction strategies to reduce emissions and dispel clean coal illusions. Increasing demand for improved process methods such as capture and gasification that aid in the use of coal with little environmental effect is expected to enhance the need for clean coal technology across various sectors globally.

In this blog, we will discuss the various types of clean coal technology. We will highlight how carbon can be captured and separated to reduce emissions, the different ways of storing and using the existing carbon in various industries and various coal gasification techniques, and how it is getting popular all across the globe.

Capture and separation of carbon dioxide

There are several methods for capturing carbon dioxide from the gas streams, but none have been optimized at the scale needed in coal-burning power stations. Historically, the emphasis has been on acquiring pure CO₂ for industrial applications rather than lowering CO₂ levels in power plant emissions. But with growing environmental concerns like the EU carbon neutrality target by 2050, industrial emissions are required to be restricted. Hence, industries have started to capture the CO₂ emissions and hence reuse them later on. The capturing of CO₂ is mainly done in ways: Post-combustion capture, Oxyfuel combustion, and Pre-combustion capture.

Post-combustion capture: Since nitrogen makes up the majority of the flue gas while there is only a paltry 14% to 16% carbon dioxide content, carbon dioxide capture from the flue gas streams after burning in the air is far more challenging and costly than that from natural gas streams. Absorption of carbon dioxide occurs as flue gases travel via an amine solution in the primary process, which handles it just like any other pollutant. The solution can be heated to release it afterward. The removal of CO₂ from natural gas is another application for this amine scrubbing method.

This method is still not being used in a lot of commercial-scale power plants. For instance, a $100 million Alstom pilot project handled less than almost 2% of the plant's off-gas for CO₂ recovery at the 1,300 MWe Mountaineer power station in West Virginia, which releases 8.5 Mt CO₂ annually. The project used chilled amine technology. Around 20% of the plant's CO₂ was intended to be captured and separated. However, these plants were shelved in 2016 owing to a lack of government backing. Hence, industries would be in need of a lot of government support to lower their CO₂ emissions in the first place.

Oxyfuel combustion: When coal is burnt in oxygen instead of air, the flue gas is primarily composed of CO₂, making amine scrubbing a much more effective method for capturing it. This method also costs roughly half as much as capturing from traditional plants. Many oxyfuel systems are in use in the USA and other countries. For instance, the FutureGen 2 project makes use of oxy-combustion. An air separation plant, a boiler island, as well as a compressor, and purifying unit for ultimate flue gas are all features of such a plant.

Another example is the Integrated Gasification Combined Cycle (IGCC) plant that uses steam with coal to create carbon monoxide (CO) and hydrogen, which are then burnt in a gas turbine with just a secondary steam turbine (i.e., a combined cycle) to create electricity. If oxygen is used to fuel the IGCC gasifier instead of air, the flue gas will then include highly concentrated CO₂, which can easily be recovered after burning, thus reducing emissions by almost 38%.

Pre-combustion capture: The IGCC method will be further developed by adding a shift reactor for oxidizing the carbon monoxide with water, resulting in a gas stream primarily composed of carbon dioxide and hydrogen, with some nitrogen. Before burning, the CO₂ along with Hg and H2S contaminants is separated (with around 85% CO₂ recovery), as well as the hydrogen alone will become the fuel for power generation (or other purposes), whereas the concentrated pressured carbon dioxide is easily disposed of. No commercial-scale power plants are using this technique currently, but there is one demonstration project being thought of by industries.

Some units have already successfully captured carbon dioxide from coal gasification at low marginal costs. One example is the Great Plains Synfuels Plant in North Dakota, which gasifies 6 million metric tonnes of lignite annually to create synthetic natural gas that is clean and safe.

Carbon sequestering technology to gain traction in the next few years

Early breakthroughs in carbon capture and storage (CCS) focused on a single source connected to a specific storage location. An emphasis on hubs that combine, dehydrate, as well as transport CO₂ fluxes from various sources, has emerged as a result of economies of scale. In North America alone, there are currently roughly 15 hubs being established. The Northern Lights Project being developed in the North Sea off Norway is one of the most significant hubs currently under development. It combines CO₂ streams that are produced by plants, starting at 0.8 Mt/yr and growing to roughly 5 Mt/yr. The initiative, created by Shell, Equinor, and Total, would compress as well as liquefy CO₂ at source facilities before shipping it to a storage location in a special CO₂ ship.

The three primary types of carbon sequestration are coal seam storage, deep saline aquifers, and oil and gas replacements, particularly enhanced oil recovery (EOR). The expense of the second option may be outweighed by immediate economic benefits. Deep saline aquifers hold the vast bulk of the potential for storage. Around 55 million tonnes of carbon dioxide had been sequestered through monitoring up until 2017. As per the IEA’s Energy Technology Perspectives, by the end of 2022, 19 large-scale operational initiatives had a combined potential capture capacity of 30 Mt CO₂ annually, but only 28% of the captured CO₂ was being stored with proper verification and monitoring. This CO₂ is mostly a result of the treatment of natural gas.

Coal seams are another way to sequester CO₂ and use it for other purposes. Storage in coal seams differs from storage in oil-gas systems and saline aquifers because CO₂ is deposited in the coal matrix rather than stored inside the pores of rocks as it is in saline aquifers as well as oil-gas systems. The qualities of the coal have a significant impact on whether carbon dioxide will soak into it. The economics of improved coal bed methane recovery with CO₂ disposal is not always as favorable as they are for better oil recovery, but the opportunity is enormous as coal seam gas is progressively exploited. Hence, more and more industries are slowly shifting towards these processes to lower their emissions and gain sustainable growth in the coming years.

Coal gasification technology to help carbon get converted into syngas

Coal gasification is a thermo-chemical process that uses steam as well as oxygen to transform lignite into a synthesis gas (syngas). It has been around for a long and is considered an effective clean coal technology. Since syngas is mostly made of carbon monoxide and hydrogen, most other unclean contaminants are frequently eliminated. It is anticipated that the coal gasification process will be utilized more frequently for the manufacture of chemical raw materials and electricity, particularly because it offers clean coal technology with greater energy efficiency.

For example, Chiyoda Corporation offers various industries with effective coal gasification projects. Chiyoda provides plant technology to enhance coal usage efficiency and reduce the environmental effect in various industrial plants that use coal-gasified syngases by leveraging their extensive expertise in gas purification as well as conversion facility construction from petroleum and natural gas projects. They have extensive expertise and technological capabilities in the field of chemical plant building and provide the best technique for producing chemical raw materials using syngas generated by coal gasification. 

Underground coal gasification (UCG), another method that has been available ever since the 19th Century but hasn’t yet achieved widespread commercial viability, has one operational plant in Uzbekistan and is now being tested in pilot projects in South Africa and Australia. It is regarded as a novel method of utilizing coal power without the typical environmental effects. UCG is now a practical means to reach the massive coal deposits that are too deep to mine, because of technological advancements and the growing price of gas. Estimates indicate that up to 85% of the world’s coal reserves cannot be reached using conventional mining methods. Opening them up for exploitation might have severe consequences for carbon dioxide emissions and global warming, but the industry claims these resources can be obtained cleanly.

Conclusion

Next-generation, cutting-edge methods for using coal that is called ‘clean coal technologies' are intended to increase the efficiency as well as acceptability of coal mining, preparation, and usage from an environmental standpoint. These techniques are being introduced to diminish the damaging environmental effects of coal energy production and to slow down global warming by cutting greenhouse gas emissions.

There are recent developments that will decrease prices while simultaneously improving carbon capture efficiency. One modification would be to switch from utilizing water as that an absorbent to employing solid adsorbents. For instance, at Georgia Tech, one such absorbent was created by creating solid hollows out of polyethyleneimine-silicon dioxide (PEI), which flue gas then travels through. Such solid hollows are just as effective at absorbing carbon dioxide as the liquid absorbents. Scientists put the fibers under hot water to cause the carbon dioxide to escape and be stored.

Metal-organic frameworks (MOFs) are another helpful invention produced at UC Berkeley. With a huge interior surface area as well as the ability to absorb CO₂, MOFs are composed of diamine and magnesium molecules (two amino groups) inserted into the pores. By guaranteeing CO₂ links to a diamine in such a way that enables other CO₂ molecules to connect to the close-by diamine molecule, MOFs are capable of soaking carbon dioxide. To liberate the CO₂ from the fibers, high temperatures are needed. Thus, with these innovations in the domain of clean coal technology, various industries should utilize these techniques at the earliest, especially the cement and steel manufacturing units as it is the most difficult for them to reduce carbon emissions during their production methods.

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