By Gerrill Griffith // Technical Contact: Dr. Madhava Syamlal
Computational Fluid Dynamics (CFD) is the use of applied mathematics, physics and computational software to describe how a gas or a liquid flows. The CFD simulations require high performance computers such as NETL’s Joule 2.0 Supercomputer. At NETL, it is a critical knowledge tool that is helping to find cleaner, more efficient ways to power the nation. There are many examples at NETL of how CFD has been used to develop devices and processes aimed at energy innovations.
MHD Modeling & Simulation
Magneto-hydrodynamic (MHD) power generation or direct power extraction (DPE) is a process to generate electrical energy directly from the products of fuel combustion without an intermediate mechanical device (dynamo). The electric power is produced from the interaction of the ionized fluid with an applied external magnetic field. MHD power generation systems could be more efficient than traditional fossil power systems, especially when a carbon capture system is integrated. Work will continue to improve accuracy and include the use of laser induced photoionization to increase the conductivity of the gas within a generator channel. The model developed at NETL will help engineers to predict and understand the behavior of such systems.
Vortex Chamber Research
Vortex chambers allow for the operation of rotating fluidized beds that can provide a unique fluidization regime where particles experience centrifugal forces much higher than the force of gravity allowing particles to experience intensified gassolid contact, gas-solids separation, and solids-solids segregation. With a focus on segregation of oxygen carriers and ash in Chemical Looping Combustion, numerical simulations were conducted to understand the flow behavior and particle segregation in a vortex chamber. The information from numerical simulations will be used to guide and help interpret the experimental tests of vortex chambers in the lab.
Chemical Looping Modeling & Simulation
Chemical Looping Combustion (CLC) is being investigated by NETL as a way to use fossils fuels at a lower cost and with lower greenhouse gas emissions than more conventional approaches. In chemical looping combustion, the fuel is combusted with a solid oxygen carrier, eliminating the need for separating CO2 from the flue gas as in the case of combustion in air. NETL researchers used CFD to predict the performance of three CLC designs. Based on the simulations, two separate modifications were identified as possible solutions. The proposed modifications were experimentally tested and proven effective.
CFD for Development of Integrated Waste Treatment Units
NETL used CFD modeling to help develop an Integrated Waste Treatment Unit (IWTU), a first-of-its-kind, 53,000-square-foot facility designed to treat 900,000 gallons of aqueous, radioactive sodium-bearing waste that has been stored in underground storage tanks at a spent nuclear fuel reprocessing facility located at DOE’s Idaho Nuclear Technology and Engineering Center (INTEC). IWTU uses a steam-reforming technology to convert the sodium-bearing liquid into a solid, granular material before packaging it in stainless steel canisters for long-term storage. This reforming process uses two fluidized beds to treat the sodium-bearing waste and reform process gases. Fluidized beds suspend solid fuels on upwardblowing jets of air during the combustion process, causing a turbulent mixing of gas and solids and providing more effective chemical reactions and heat transfer.
Developing new small-scale systems that convert solid fuel to power and chemicals to suit local conditions and that can be deployed at low financial risk is an important NETL objective. NETL scientists developed an MFiX-based reactor optimization code that enables users to determine optimal reactor design and operating conditions before any physical hardware is constructed. NETL rapidly transforms computational reactor designs into a physical test unit using 3D manufacturing. Researchers use the physical units to validate simulation and design optimization. If discrepancies are found, researchers use this knowledge to refine the simulation optimum, and a new physical system can be created and operated in a day. This method of CFD-based design and rapid prototyping using 3D manufacturing is expected to radically change small-scale system development.
Carbon Capture Simulation
To develop sorbent-based CO2 capture for conventional coal-fired power plants, NETL conducted CFD simulations for a pilot-plant unit that addressed several challenges including the presence of vertical heat transfer tube banks, patented multi-stage design, and the complex chemical reactions that take place inside the system.
A model built with the help of NETL’s multiphase CFD solver, MFiX, was first validated with data from several small-scale experiments. The figure below shows a validation study for a fully resolved flow over an array of vertical tubes. Simulations were performed with square and triangular tube arrangements and results were compared with experimental data found in the literature. Good agreement was found in terms of hydrodynamics and bubble statistics. The validated model was used to predict the performance of a 1 MW carbon capture reactor, well before the unit was operated.