Many of the primary products that can be produced by gasification are covered in depth in the section Applications of Gasification Technology. One of the great advantages of gasification, however, is the usefulness of not just its main products, but also its byproducts.
Slag from coal gasification is a mixture of a glassy, silica-based phase (a.k.a. frit) and carbon char, the proportions of which vary depending on operating conditions, gasifier, feed, etc. The two parts can be separated—i.e., they are not chemically bonded—into carbon-rich char and vitreous frit. The two parts of slag can both serve useful purposes, a topic explored further in the next section, Useful Byproducts: Slag.
Sulfur and Other Chemicals
In the course of cleaning synthesis gas (syngas), sulfur and other chemicals are removed. For example, hydrogen sulfide (H2S) is separated from the syngas stream and processed into elemental sulfur. This is covered in more detail in the following page Useful Byproducts: Sulfur and Other Chemicals.
Carbon Dioxide (CO2)
CO2 is also removed from the syngas. The capture of CO2 can be done for environmental reasons (carbon capture and storage; CO2 is a greenhouse gas) or because CO2 has a valuable use in enhanced oil recovery (EOR). Read more about EOR on the following page, Useful Byproducts: CO2.
Industrial Gases from Air Separation
Many gasifier system designs require an air separation unit (ASU) to provide nearly pure oxygen streams. This separation of air can also provide a nitrogen stream and small amounts of argon and other rare gases like neon, krypton, and xenon. To read more about the recoverable gases from air separation, visit the following page, Useful Byproducts: Industrial Gases from Air Separation.