Heat transfer and heat transfer fouling in Kraft black liquor evaporators

A large number of experiments have been performed with New Zealand Forest Products Kraft black liquor to measure heat transfer coefficients and fouling rates during convective and subcooled flow boiling heat transfer as a function of surface temperature, bulk temperature, velocity, and solids concentration. Results from experiments with two chemical fouling inhibitors, with Teflon surface coating and in plate and frame heat exchangers, also are presented. The fouling deposits are analyzed with respect to appearance, composition, and process conditions for which they were obtained. With the assumption of chemical reaction-controlled fouling, a deposition model is developed and compared with the experimental data.