(424c) Green Coal Production from Biomass

Green Coal Production from Biomass

Stanislav Barskov¹, Dr. Prashanth R. Buchireddy², Dr. John L. Guillory², Dr. Mark E. Zappi¹

¹ Department of Chemical Engineering University of Louisiana Lafayette, Lafayette, LA

²Department of Mechanical Engineering University of Louisiana Lafayette, Lafayette, LA

Coal, one of the most abundant natural resources has been extensively utilized for U.S. power generation in the last fifty years. Today, over 50% of U.S. power is generated by combustion of coal in the power plants. When combusted in the power plants, coal emits substantial amounts of greenhouse gases into the atmosphere. As a result, federal government has mandated environmental agencies to establish strict regulations and propose solutions on the reduction of the greenhouse gases emissions. One of the emerging solutions to reduce greenhouse emission is co-firing biomass with coal. The main advantages of the biomass is that it is considered carbon neutral and has a lower nitrogen, sulfur, and ash content than coal. The lower content of nitrogen, sulfur, and ash results in significantly lesser amount of emissions when biomass is combusted. The disadvantages of co-firing biomass are that biomass has lower heating value, density, and higher moisture content when compared to coal. Additionally, difficulties with fuel preparation, handling, storage, transportation, milling, and feeding in for co-firing with coal in the power plants further hinder biomass utilization as an alternative energy source.

One of the way to address the aforementioned issues associated with biomass co-firing is through torrefaction. Torrefaction is a thermal pre-treatment of the biomass in temperatures between 230-320 °C in an absence of an oxidizing agent and under atmospheric pressure. During torrefaction approximately 30% of the biomass is converted into volatile organic compounds and gases containing 10% of biomass energy. However, 70% of the mass and 90% of the energy is still retained in the original biomass. Therefore, energy densification is achieved via torrefactions by a factor of 1.3 on mass basis. The torrefied product has improved fuel properties such as increased mass energy density, hydrophobicity, uniformity, and grindability compared to the fresh biomass. This properties allow for effective utilization of torrefied biomass in coal fired power plants using existing burners and without major modifications.

Research is being conducted at University of Louisiana Lafayette using an indirectly heated rotary drum pilot scale torrefaction reactor utilizing pine wood chips as a primary lignocellulosic material. The effect of various parameters including temperature, raging in between 240 - 320 °C, residence time, ranging in between 30 - 100 minutes, carrier gas (N₂, CO₂, Steam), particle size, moisture content, ranging in between 10 - 30% on torrefaction product is being evaluated and the results will be presented in this conference. Additionally, analysis of volatiles and gases is being carried out to evaluate the overall process efficiency. Lastly, mass and energy balances on the pilot scale torrefaction process would be presented. Conducting research on a pilot scale and utilizing alternative energy sources would put U.S. one step closer to achieving perfection in clean power generation, and establishing energy independence from the rest of the world.