a boiler that fires 10 MM Btu/hr using bituminous coal. This boiler emits 2,057 lb CO 2 per hour. To decarbonise, the boiler could be converted to fire natural gas, reducing emissions to 1,206 lb CO 2 per hour – which is a 41.4% reduction in CO 2 emissions just by changing fuels. Emission capture Focusing on the CO 2 lever of the combustion reaction, carbon capture directly removes CO 2 from the process and the air. The advantage of carbon capture is that it allows end users to operate without any major changes to their core business. In these cases, the end users would capture CO 2 emissions at the outlet of their process. The CO 2 would then be compressed and transported by ship or pipeline to a point of use or storage. Compressed CO 2 can be used as a feedstock for various industries or permanently stored in either onshore or offshore underground geological formations or caverns. Reliability enhancement Finally, end users can also decarbonise by leveraging the reliability of their equipment for optimal heat transfer, utilising the available heat lever of the combustion reaction. In this case, end users can reduce unneeded fuel usage by keeping equipment clean and online via proactive and predictive maintenance. The reality is that fouling of equipment can directly impact the heat transfer between the burner flame and the process. Examples include:
and the burner requires 5.8% less fuel. This fuel reduction also directly relates to a 5.8% reduction in CO 2 emissions. Fuel changes An alternative path to decarbonise fired equipment is to consider changes in fuel, which directly relate to the ‘fuel’ lever of the combustion reaction. While it may be more taxing to implement, there are many types of low-carbon fuel sources to consider. The most obvious fuel change is to use hydrogen, which has received a lot of attention recently as a fuel source that generates zero CO 2 emissions, unlike fossil fuels. Currently, there are many sources of hydrogen in discussion: • Brown hydrogen refers to hydrogen generated from coal gasification. • Grey hydrogen refers to hydrogen fuel generated from natural gas without the capture, use and storage of carbon byproducts. Currently, steam methane reforming (SMR) is the most common approach to generate grey hydrogen. • Blue hydrogen refers to hydrogen fuel production from natural gas (grey hydrogen) with specific additional steps to ensure the capture, use and storage of GHGs. The most common example is through SMR with the use of carbon capture, use and storage. • Green hydrogen refers to the production of hydrogen exclusively through renewable energy. An example could be hydrogen generated from
electrolysis at a solar power facility. While hydrogen offers a fuel source with zero CO 2 emissions, much is still needed for a global transition to hydrogen fuel. In the interim, transitions to lower carbon fuel sources provide an opportunity to reduce CO 2 emissions. Figure 3 shows a comparison between various fuels and their direct pounds (lbs) of CO 2 emitted per MM Btu. As an example, consider
Coke-based coal Anthracite coal Petroleum coke Lignite coal Subbituminous coal Waste oil Bituminous coal T yr e-derived fuel
Other petro & misc. Flared natural gas Municipal solid waste Geothermal (avg. all gen.)
0
50
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150
200
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Figure 3 Comparison of CO 2 emissions emitted vs various fuel sources Source: EIA.gov
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