CCS and Power Systems
Advanced Energy Systems - Gasification Systems
Performer: National Energy Technology Laboratory
Project No: FWP-2012.03.03
Program Background and Project Benefits
Coal and biomass gasification is an approach to cleaner power generation and other uses of these resources. Currently, the service life of gasifiers does not meet the performance needs of users. Gasifiers fail to achieve on-line availability of 85-95 percent in utility applications and 95 percent in applications such as chemical production. The inability to meet these goals has created a potential roadblock to widespread acceptance and commercialization of advanced gasification technologies.
Gasifier output is a hot gas mixture consisting primarily of hydrogen and carbon monoxide (CO), known as synthesis gas (syngas). The syngas cooler is one of the key components identified as negatively impacting gasifier availability. Ash originating from impurities in gasifier carbon-containing feedstock is at the root of many problems, attacking or fouling syngas components and causing unplanned shutdowns for repair, replacement, or cleaning. Gaps in the understanding of how fuel properties impact carbon conversion, slag viscosity, and downstream fouling and the potential advantages of fuel flexibility on availability rates and sustainability using different feedstocks are additional factors contributing to lower efficiency and capacity factor.
To address these issues the Gasification Program is using an integrated approach to leverage the U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL)-Regional University Alliance (RUA) and URS partners’ capabilities to combine theory, computational modeling, laboratory experiments, and industrial input to develop physics based methods, models, and tools to support the development and deployment of advanced gasification based devices and systems.
This research will enhance the ability of researchers to predict gasifier performance, including rates of carbon conversion and fly ash generation, and to address fouling rates in syngas coolers. The impact of volatile organic oxides and iron content and its oxidation state on plastic viscosity will be established. The impacts and limitations of using various coal grades and petcoke in entrained gasifiers, in terms of optimizing slag fluidity to ensure drainage along gasifier walls and limit refractory degradation to an acceptable limit will be determined. This will reduce plugging and fouling throughout the syngas cooling system and should help gasification technology achieve wider accessibility by allowing for a greater understanding of the role fuel properties have on gasifier RAM. These benefits will support the NETL Gasification Program goals of 90 percent IGCC availability and greater cost efficiency.
The main goal of this project is to improve the reliability, availability, and maintainability of gasification plants by developing tools to evaluate the impact of fuel properties on slag and refractory interactions. By evaluating ash deposition from carbon feedstock, plugging and fouling throughout the syngas cooling system can be reduced. To achieve this goal, four major areas of research are being pursued concurrently:
Model Development: The modeling effort involves developing a heuristic spreadsheet-based reduced ROM with the capability to predict the effects of the distributive properties of fuels used in entrained-flow gasifiers on key gasifier performance indicators, so that the ROM may be used as a tool to investigate syngas cooler fouling and the amount of unconverted carbon.
Devolatization and Char Kinetics: The objective of the devolatization and char kinetics effort is to measure pyrolysis kinetics for various density and size fractions of Pittsburgh #8 coal and, at high temperature and pressure, characterize the changes to char particles during pyrolysis (early stages)—including particle size, density, char reactivity in carbon dioxide (CO2), and mineral matter transformations—and identify the critical conversion(s) at which the particle fragmentation occurs.
Slag Viscosity and Unburnt Carbon: The slag viscosity and unburnt carbon effort is focused on measuring slag viscosities as a function of temperature and CO/CO2 ratio for laboratory manufactured synthetic ash to determine how slag infiltrates into a refractory material subjected to a temperature gradient.
Particle Deposition: The particle deposition effort is focused on conducting ash particle deposition experiments at conditions relevant to existing convective syngas coolers and using the data to generate a comprehensive model of ash deposition probability as a function of feedstock size and density fractions, ash particle size, particle temperature, particle velocity, surface temperature, and contact angle.