Energy efficiency improvements with vertical shell and tube juice heaters at Millaquin Mill

A NEW SECONDARY juice heater station was installed at Millaquin Mill for the 2017 season to improve the process energy efficiency and provide surplus bagasse for operation of the refinery in the non-crush. A set of four vertical shell and tube heaters were installed for consecutive heating of secondary juice with V3, V2 and V1 vapours in three of the heaters with the fourth heater on cleaning or standby. The operation of the secondary juice heaters was monitored during the 2017 season. The measured overall heat transfer coefficients (OHTCs), fouling rate factors and pressure drops were compared with values calculated using accepted methods. The measured OHTCs did not correspond accurately with the generalised correlation widely used in the Australian industry. When a more rigorous method was used to calculate the OHTC, the measured values corresponded more accurately with the predictions. A fouling rate factor of 0.001 was more appropriate for a first stage juice secondary heater using V3 steam at Millaquin. This differs significantly from the fouling rate factor reported in other literature for primary and secondary horizontal heaters. The measured total pressure drop across the heaters was compared with the predicted pressure drop using factors of 2.5, 2.0 and 1.5 velocity heads per pass to estimate the loss in the return headers. The factor of 1.5 was found to more accurately predict the observed values. The installation of the juice heaters resulted in a reduction in the factory steam%cane from 47.7% to 44.0%.