Juice Clarifiers

Rapid Design

You can do an online rapid design of a short retention clarifier right now

Introduction

A clarifier is used to separate out the solids suspended in the cane juice. These solids originate from sand adhering to the cane stalks as well as from material inherent in the cane stalk. The separation takes place by allowing the solid particles to settle out onto a tray. The solids are swept from the tray into a mud compartment, from which it is pumped to filters for desweetening and dewatering.

In the past multitray clarifiers, such as the Dorr, Graver, Bach and RapiDorr were popular, but the SRI clarifier is almost standard for all new installations. The SRI clarifier is a single tray clarifier (also known, oddly, as a trayless clarifier), characterised by short juice retention times (usually 40 minutes or less). The benefits of the single tray short retention clarifier are:

Flocculent usage and operability appear to be no different from multitray clarifiers (See Jullienne and Montocchio SASTA 1996, pg 277)

Design

The main design parameters are upflow velocity and the residence time

Upflow Velocity

The upflow velocity is calculated as half the initial settling rate of the mud in the juice. The initial settling rate is the slope of the steeply downward sloping part of the settling curve below. In the case of a greenfield project where the settling characteristics of the mud are unknown, the upflow velocity can be assumed in the range 65 to 80 mm/min (Most SRI clarifiers in South Africa operate with an upflow velocity below 72mm/min).

Residence Time

The residence time is usually on the range of 40 to 45 minutes.

Sizing

Given the volumetric juice flow and the above two parameters; the cross sectional area (hence diameter) and the operating depth of the clarifier can be calculated.