Steady-state simulation of a continuous moving bed reactor in the pulp and paper industry

Abstract

This paper is concerned with the mathematical modeling and simulation of the steady-state operation of an industrial moving bed heterogeneous reactor for the kraft pulping of Eucalyptus globulus. The cooking takes place in a single-vessel hydraulic digester adapted for isothermal cooking (ITC), a further development of the modified continuous cooking (MCC) process. A heterogeneous model is used to take into account the different phases, each with distinct profiles of temperature and concentration of organic (lignin, cellulose and hemicellulose) and inorganic (effective alkali and sulfide) compounds. The numerical solution of the model is based on a non-uniform discretization strategy to cope with special geometric and operational features of the digester. The decrease in bulk porosity caused by the compaction of the bed and the progressive increase in the voidage of chips as a result of chemical reactions are incorporated into the model as well as the resulting implications in the entrapped and free liquor flows. The model presented here can be used in optimization studies and has been validated with data from an industrial mill.