Dynamic Absorption Model for Off-Gas Separation

摘要

Modeling and simulations will aid in the future design of U.S. advanced reprocessing plants for the recovery and recycle of actinides in used nuclear fuel. The specific fuel cycle separation process discussed in this report is the off-gas treatment system. The off-gas separation consists of a series of scrubbers and adsorption beds to capture constituents of interest. Dynamic models are being developed to simulate each unit operation either as a stand-alone model or in series with multiple others. The model described herein is a thermodynamic equilibrium and kinetics model for countercurrent, multistage absorption of gaseous species from a gas stream into a liquid stream. The generic equilibrium model can be used for different gas species as long as the key constants and assumptions are changed. The kinetic model, however, is unique to the gas species, and is currently based on NO and NO2. The model for NOx absorption is designed to enable modeling the performance of a counter-current NOx absorber used to capture NOx in a used fuel dissolver off-gas stream, for recycle back to the dissolver. Inputs include liquid and gas stream constituents, column properties, liquid and gas phase reactions, number of stages, and inlet conditions. It simulates absorption by mass transfer and chemical reaction. The assumption of each stage being a discrete well-mixed entity was made. Therefore, the model is solved stagewise. The simulation output includes component concentrations in both phases as a function of time from which the rate of absorption is determined. Temperature of both phases is output as a function of time as well. The model will be able to be used as a standalone model or in series with other off-gas separation unit operations. The current model is being generated based on NOx absorption; however, a future goal is to develop a CO2 specific model. The model will have the capability to be modified for additional absorption systems. The off-gas models, both adsorption and absorption, will be made available via the server or web for evaluation by customers.