(200b) Techno-Economic Optimization of a Supercritical Pulverized Coal Power Plant With Integrated CO2 Capture and Utilization Processes

Kasule, J., West Virginia University
Bhattacharyya, D., West Virginia University
Turton, R., West Virginia University
Zitney, S. E., National Energy Technology Laboratory

The CO2 captured from future supercritical pulverized coal (SCPC) power plants can be utilized for producing value-added products, thereby improving overall plant economics and operating efficiency. The CO2 utilization processes vary significantly in terms of cost of the raw materials and catalysts, value and demand of the products, and the operating conditions.  Most SCPC plants have low-level utilities that are usually wasted resulting in lower thermodynamic efficiency. A portion of these low-level utilities can be utilized for converting CO2 into value-added products thereby improving the overall thermodynamic efficiency of the SCPC plant. Therefore, an optimal synthesis of CO2 utilization processes will need to consider the trade-offs between various CO2utilization processes taking into account the low-level utilities that can be spared in a given SCPC power plant.

In this project, the SCPC power plant is considered as a source of utilities and low-level waste heat for the CO2 capture and utilization processes.  The CO2 capture unit is based on the well-known monoethanolamine (MEA) solvent-based process.  A number of promising CO2 utilization processes such as the tri-reforming process, chemical and photochemical reduction of CO2 to methanol and electrochemical reduction of CO2 have been developed and validated with the available experimental data. The tri-reforming process is a combination of steam reforming, CO2 reforming, and catalytic partial oxidation of methane. In the tri-reforming process, the energy requirement for the endothermic reforming reactions is partially obtained from the exothermic partial oxidation reaction. In the photocatalytic reduction of CO2, CO2 is reduced to produce methanol in a steady-state optical-fiber photo reactor comprised of TiO2-coated fibers. Electrochemical reduction of CO2 to a number of value-added chemicals is also modeled. Electrochemical reduction of CO2 is very promising especially when excess energy from solar or wind power generation is available. Both aqueous and non-aqueous processes have been modeled by considering the trade-off between the concentration overpotential and ohmic polarization. Chemical reduction of CO2 to methanol is also modeled. If there are multiple technologies for producing the same chemical, most of the promising technologies are modeled. For example, methanol can be synthesized in several ways.  First,gas-phase methanol synthesis can take place at a temperature of 260oC and 50 atm pressure in presence of copper catalyst. Second, methanol synthesis can be carried out in liquid phase at 120oC and 30 atm using a slurry of zinc catalyst. A third approach for synthesizing methanol is by the Carnol process where H2 is produced by thermal cracking of methane followed by the methanol synthesis reaction. Since a given chemical can oftentimes be produced at various pressures and temperatures, one CO2utilization process may be favored over another based on the available waste energy from the SCPC plant and heat generated, if available. 

The steady-state models of the SCPC power plant and the CO2 capture process are developed in Aspen Plus® while the models of the CO2 utilization processes are developed using Aspen Plus and Aspen Custom Modeler®. The CO2 capture and utilization models are integrated with the SCPC plant using an Excel interface. For superstructure optimization, the process models are interfaced with ModeFrontier®, a powerful software for optimization, by using an Excel link. A techno-economic optimization study is then performed using a Genetic Algorithm (GA) in ModeFrontier to maximize the profitability of the SCPC power plant.