Can we make coal from biomass?

It is generally accepted that most coal that we used today were formed from plant materials.

If that were so, can we make coal from the hundreds of millions of tons of agricultural waste available worldwide?

Yes. It is possible to convert biomass into a material very similar to coal through a process called torrefaction.

Torrefaction refers to the slow heating of biomass in an inert (no air/oxygen) environment in the temperature range of 200–300°C. The resulting material resembles coal in many aspects so much that torrefied biomass is often called green coal.

Torrefaction is different from combustion, a process in which the entire energy present in the biomass is converted into heat and all you have left is ash. In the case of torrefaction, you preserve most of the energy in the biomass while transforming it into a material that could replace coal for power generation and heating applications.

By the way

Not surprisingly, many coal power plants around the world are keenly experimenting the use of torrefied biomass blended with coal to reduce overall CO2 emissions.