Semi empirical modeling of the stationary state of a real causticizing system in a pulp mill

摘要

Causticizing system is an important part of the recuperation cycle of the Kraft pulp production process. In this system, the Na2CO3 in green liquor from the recovery boiler is converted in NaOH which is a component of the digester cooking liquor. The system is composed by one extinction reactor, where CaO is added to green liquor, followed by three reactors. Three semi-empirical models of CENIBRA's causticizing system are proposed to simulate the stationary state. The mass balance is developed considering three types of reaction rate equations, whose coefficients were estimated using industrial data. The following assumptions are used: CSTR reactors, instantaneous slaking reaction, constant temperature and rate reactions as functions of NaOH and Na2CO3 concentrations. The premise is that all non-modeled factors and the system specificities are included in the estimated coefficients. The obtained models were validated using new industrial data and good agreement was achieved.