A simulation model for settling tanks with varying cross-sectional area

ABSTRACT

A quasi-one-dimensional model of the process of continuous sedimentation in clarifier-thickeners (settlers) with variable cross-sectional area is presented. The partial differential equation (PDE) model extends the settler model advanced by Bürger et al. (2013), which assumes a constant cross section. A reliable numerical method that handles the special features of the nonlinear PDE is presented along with an advantageous time-step condition for continuous and batch sedimentation under the condition of a variable cross-sectional area. Simulations of continuous sedimentation show the effect of change of cross-sectional area in the concentration inside the vessel and in the underflow. Simulations of batch settling in cones illustrate the versatility of the numerical scheme to include a vertex, where the area shrinks to zero.

KEYWORDS:

• Clarifier-thickener
• continuous sedimentation
• nonlinear conservation PDE
• numerical method
• secondary clarifier

Additional information

Funding

Raimund Bürger and Julio Careaga are supported by BASAL project CMM, Universidad de Chile and Centro de Investigación en Ingeniería Matemática (CI²MA), Universidad de Concepción. In addition Raimund Bürger is supported by Fondecyt project 1170473; Fondef project ID15I10291, and project CONICYT/FONDAP/15130015.