Sarma V. Pisupati

In the John and Willie Leone Family Department of Energy and Mineral Engineering in the College of Earth and Mineral Sciences, Sarma Pisupati and his research group are pursuing exciting projects to develop clean coal technologies and coal/biomass conversion processes.

Oxy Coal Combustion

One approach that has generated considerable interest is the burning of coal in O2 and recycled flue gas mixture to produce a near-pure stream of CO2 in the flue gas that can be easily sequestered or utilized in downstream applications. Thus, in this approach N2 in the oxidizer (air) is replaced by the CO2. However, due to differences in thermal properties of CO2 and N2, an oxidizer with a mixture of 30% O2/70% CO2 (molar basis) has been shown to produce similar flame characteristics. The char generated in a CO2 medium has similar reactivity to that of char generated in an inert gas atmosphere. However, very few studies have explored char reactivity, CO, and NOx emissions in increased gas concentrations of O2 and CO2. The challenges that Pisupati's group is addressing are to:

• Distinguish the effect of CO2 during pyrolysis on:
  • Coal particle heat-up rate
  • Coal-N split between char and volatile phase
  • Resultant char properties
• Establish the effect of char-CO2 reaction on particle temperature, burnout and CO emission
• Sulfur capture performance of limestones under oxy-combustion conditions at high pressures

Gasification Behavior of Various Size and Density Fractions

Another approach for clean coal power generation is using Integrated Gasification Combined Cycle (IGCC). Using this method, coal is gasified at high pressure and temperature using oxygen and steam to produce carbon monoxide and hydrogen mixture (synthesis). The carbon monoxide is reacted with water to produce additional hydrogen and carbon dioxide (shift reaction). The synthesis gas is cleaned and burned in a gas turbine generating power. The gases exiting the gas turbine are used to produce steam using a heat recovery steam generator (HRSG) which is then used in a steam turbine generating additional power. Hence it is combined cycle. IGCC plants are more efficient in converting coal to electricity than conventional coal plants and thus produce less CO2 per unit of electricity generated. One of the challenges in coal gasification is to achieve high conversion of carbon and less deposition of ash in the subsequent gas coolers. The goal of this project is to better understand the impact of the non-homogeneous nature of coal-on-coal gasification systems and to develop better modeling tools to improve reliability and efficiency of coal gasifiers. It is well known that the mineral and organic components in coals, known as macerals, vary widely in their composition, distribution, and occurrence. These components have a different physical and chemical makeup. When ground to the fine sizes required for advanced gasification systems, some of these components will separate to form particles enriched in individual minerals or macerals which respond completely differently than the aggregate or average coal particles. These outliers can lead to process inefficiencies, fouling, and other reliability problems. Coals will be fractionated by hardness and density and those fractions will be characterized, gasified, and the resulting information will be used to develop validated computer models.

Sarma Pisupati's Group is collaborating with researchers from U.S. DOE, West Virginia University, Carnegie Mellon University, SRI International, Niksa Energy Associates, REM Engineering Services, and Leonardo Technologies, Inc.

Co-Gasification of Coal and Biomass

Coal has a relatively low cost and a high energy density but its major drawbacks are its high emissions of environmentally harmful compounds (sulfur dioxide, nitrogen oxides and carbon dioxide), and its low hydrogen-to-carbon ratio, hindering its direct use for combustion and its gasification for synthetic gas production. On the other hand, biomass as gasification feedstock although giving a high hydrogen yield, has the disadvantage of low energy density, high moisture content, seasonal limitation and poor reliability in supply, tar production due to low gasification temperature. Blending biomass and coal as feedstock can reduce the shortcomings of each fuel taken alone and boost the efficacy of the overall system. Therefore, co-gasification of coal and biomass offers a better prospect for cleaner coal utilization and a way to dispose wastes/biomass in an economical, safe, and environmentally friendly manner.

Agglomeration of Ash in Fluidized Bed Systems

Conventional coal plants and thus produce less CO2 per unit of electricity generated. One of the challenges in coal gasification is to achieve high conversion of carbon and less deposition of ash in the subsequent gas coolers. The goal of this project is to better understand the impact of the non-homogeneous nature of coal-on-coal gasification systems and to develop better modeling tools to improve reliability and efficiency of coal gasifiers. It is well known that the mineral and organic components in coals, known as macerals, vary widely in their composition, distribution, and occurrence. These components have a different physical and chemical makeup. When ground to the fine sizes required for advanced gasification systems, some of these components will separate to form particles enriched in individual minerals or macerals which respond completely differently than the aggregate or average coal particles. These outliers can lead to process inefficiencies, fouling, and other reliability problems. Coals will be fractionated by hardness and density and those fractions will be characterized, gasified, and the resulting information will be used to develop validated computer models.

Sarma Pisupati's Group is collaborating with researchers from U.S. DOE, West Virginia University, Carnegie Mellon University, SRI International, Niksa Energy Associates, REM Engineering Services, and Leonardo Technologies, Inc.

Co-Gasification of Coal and Biomass

Coal has a relatively low cost and a high energy density but its major drawbacks are its high emissions of environmentally harmful compounds (sulfur dioxide, nitrogen oxides and carbon dioxide), and its low hydrogen-to-carbon ratio, hindering its direct use for combustion and its gasification for synthetic gas production. On the other hand, biomass as gasification feedstock although giving a high hydrogen yield, has the disadvantage of low energy density, high moisture content, seasonal limitation and poor reliability in supply, tar production due to low gasification temperature. Blending biomass and coal as feedstock can reduce the shortcomings of each fuel taken alone and boost the efficacy of the overall system. Therefore, co-gasification of coal and biomass offers a better prospect for cleaner coal utilization and a way to dispose wastes/biomass in an economical, safe, and environmentally friendly manner.

Agglomeration of Ash in Fluidized Bed Systems

Possible causes for initiation and propagation of ash agglomeration in fluidized bed gasification and combustion are being identified through a systematic literature survey as well as thermodynamic, mathematical modeling and experiments. Various chemical and physical parameters affect ash agglomeration simultaneously. A useful tool for the industry would be an integrated model capable of making predictions based on both the fuel composition (chemistry) as well as the reactor configuration (physics), under a given set of operating conditions.

A two-particle collision model based on particle-level variations in chemical composition and particle hydrodynamics is being developed. Starting with an initial particle size distribution, this model is to be used to predict kinetics of agglomerate growth. Effects of particle composition on slag formation tendencies are being studied using FactSage, thermodynamic simulation software, on four specific gravity separated fractions of Pittsburgh seam coal. The slag formation tendencies are investigated under both oxidizing and reducing conditions. The amount and viscosity of slag are being estimated and incorporated into the agglomeration model developed using Stokes‘ criterion. Basic fluid and particle dynamic effects are being incorporated into the model based on kinetic theory of granular flow. Further, validation of the mineral matter transformations and the model developed will be done in a bench scale reactor.