Evaporator liquor brix sensor : final report 2017/003

Abstract

A Pro-M-tec Ultrasonic Time of Flight (TOF) sensor was installed for trials at Victoria Mill in 2017. The TOF instrument calculates the brix of a liquid using the measurement of temperature and velocity of an ultrasonic signal through a liquid. The single sensor was located in a spool piece on the discharge line from final evaporator liquor pumps.

The prime objective was to examine the instrument’s suitability for liquor brix measurement on mill evaporators. In addition, its performance with water, juice, pan products and caustic cleaning solutions would also be assessed.

Using the instrument with calibrations as supplied, tests were performed with water and sugar solutions over an extended range up to 77°Bx, and with low temperature caustic cleaning solutions. Under normal evaporator operation, stable and almost linear predictions for brix were found for liquor from 65°Bx to 74°Bx and temperatures between 55°C and 65°C. Below 50°Bx the original calibrated ultrasonic velocity response compared to a digital laboratory refractometer brix was non linear (parabolic) and subject to large errors. Outside the 65°Bx to 74°Bx ranges for liquor, results diverged from the reference instrument, but did not experience some of the erratic responses experienced with microwave instruments. Caustic brix response was almost linear at low concentrations, but tended to be overestimated. Other solutions including aerated high grade molasses and magma appeared beyond the capability of the instrument.

Using experimental data, Wilmar developed multivariate calibration algorithms which enhanced the range and accuracy of the instrument for sugar solutions. The new equations enabled the instrument to be used to measure the brix of juice and liquor for control purposes, and provided an indicative brix to use with caustic solutions.