Gasificaton Transport: A Multiphase CFD Approach & Measurements

Abstract

OBJECTIVEThe objective of this project was to develop predictive theories for the dispersion and mass transfer coefficients and to measure them in the turbulent fluidization regime, using existing facilities. A second objective was to use our multiphase CFD tools to suggest optimized gasifier designs consistent with aims of Future Gen. CONCLUSIONSWe have shown that the kinetic theory based CFD codes correctly compute:(1) Dispersion coefficients (2) Mass transfer coefficients Hence, the kinetic theory based CFD codes can be used for fluidized bed reactor design without any such inputs.We have also suggested a new energy efficient method of gasifying coal and producing electricity using a molten carbonate fuel cell. The principal product of this new scheme is carbon dioxide which can be converted into useful products such as marble, as is done very slowly in nature. We believe this scheme is a lot better than the cancelled FutureGen, since the carbon dioxide is safely sequestered. OBJECTIVEThe objective of this project was to develop predictive theories for the dispersion and mass transfer coefficients and to measure them in the turbulent fluidization regime, using existing facilities. A second objective was to use our multiphase CFD tools to suggest optimized gasifier designs consistent with aims of Future Gen. SUMMARY OF ACCOMPLISHMENTS • Dispersion coefficientsThe dispersion coefficient is a measure of the quality of mixing. We have identified two types of solids dispersion coefficients: those due to random particle oscillations, "laminar" type, and those due to cluster or bubble motion, "turbulent" type. A literature review shows that dispersion coefficients in fluidized beds differ by more than five orders of magnitude. To understand the phenomena, two types of hydrodynamics models that compute turbulent and bubbling behavior were used to estimate radial and axial gas and solids dispersion coefficients. The 6 autocorrelation technique was used to compute the dispersion coefficients from the respective computed turbulent gas and particle velocities.The computations show that the gas and the solids dispersion coefficients are close to each other in agreement with measurements. The simulations show that the radial dispersion coefficients in the riser are two to three orders of magnitude lower that the axial dispersion coefficients, but less than an order of magnitude lower for the bubbling bed at atmospheric pressure. The dispersion coefficients for the bubbling bed at 25 atmospheres are much higher than at atmospheric pressure due to the high bed expansion with smaller bubbles. The computed dispersion coefficients are in reasonable agreement with the experimental measurements reported over the last half century and those measured at IIT and in the NETL riser in Morgantown (Jiradilok et al., 2007(Jiradilok et al., , 2008).• Optimized gasifier designs (Gasifier -fuel cell)For carbon capture fossil fuel electric power generation plants will have to be made more efficient. Department of Energy vision 21 c...

Co2 Capture From Flue Gas by Potassium-Based Sorbent in Circulating-Turbulent Fluidized Bed

“…At an initial time, the volume fraction of the mixture consisted of uniformly mixed 58 percent of 100 and 50 m particles. A nearly spherical bubble has occurred at 0.2 s, then it has split at 0.5 s. This behavior is very similar to bubble formation of single size 877 m particles in a KRW fluidized bed [131]. At 1 s, the bed expansion has reached the top of the bed.…”