Gasification Facilitates CO2 Capture
Carbon dioxide (CO2) capture, utilization, and storage (CCUS) will play a crucial role in the wide-ranging carbon management actions needed for the United States to achieve ambitious goals for a greenhouse gas (GHG)-neutral economy by 2050, a carbon-pollution-free power sector by 2035, and a 50% reduction from 2005 levels in economy-wide net GHG pollution by 2030. Clean hydrogen produced by gasification is expected to contribute to the wide-ranging decarbonization of power generation and industry sectors needed to meet these goals, mandating extensive application of CO2 capture at gasification facilities.
Historically, the focus of emissions control was on sulfur dioxide and particulates, where a typical pulverized coal (PC) or coal gasification power plant was required to incorporate supporting technology to remove these pollutants to meet specific emissions regulations. Stricter limits on these as well as a broad range of pollutants including mercury ensued over time. Currently, the climate crisis has concentrated attention on CO2 emissions from fossil fuel-based power production, given that 85% of GHG emissions are energy related, and 95% of those gas emissions are CO2.
Gasification research and development at DOE/NETL is focused on technological solutions that can make significant contributions towards economy-wide decarbonization, taking full advantage of the inherent strengths of gasification in facilitating efficient and low-cost CO2 capture.
Gasification vs. Combustion in CO2 Emissions
In a conventional PC combustion-based power plant, air and fuel are mixed, combusted and then exhausted at near atmospheric pressure. Since air contains a large amount of nitrogen which substantially dilutes the combustion exhaust gases, CO2 is considerably diluted in the exhaust, and being near ambient pressure, the exhaust gases are of low density. Removing the CO2 following combustion is known as "post-combustion" CO2 capture, which is made relatively difficult, energy-intensive, and expensive because of the dilution and low pressure of the exhaust gases.
On the other hand, in gasification oxygen is normally supplied to the gasifiers and just enough fuel is combusted to provide the heat to gasify the remainder; moreover, gasification is often performed at elevated pressure. The resulting syngas is typically at higher pressure and not diluted by nitrogen, allowing for much easier, efficient, and less costly removal of CO2 (and other pollutants as well, demonstrated by the extremely low emissions of sulfur and nitrogen oxides in addition to low levels of particulate matter and other contaminants such as heavy metals characteristic of gasification processes). Gasification and integrated gasification combined cycle (IGCC)'s unique ability to easily remove CO2 from the syngas prior to its combustion in a gas turbine (called "Pre-Combustion" CO2 capture) is one of its great advantages over conventional combustion.
The following figure demonstrates that even without taking into account the advantages IGCC has in ease of carbon capture it still emits less carbon dioxide emissions than the coal-fired PC plants.
In carbon capture plant scenarios, the benefits of IGCC over PC plants in CO2 emissions maintains a similar favorable trend as shown below. However, it should be noted that current estimates of levelized cost of electricity associated with baseline IGCC and PC cases show significantly higher costs for the gasification-based cycles, which were informed by recent examples of gasification-based power plants which incurred very high capital and developmental costs..