ESTIMATION OF pH OF SUGAR CANE JUICES A . T HIGH TEMPERATURE
A Philips digital pH-meter (PW9422) equipped with a Philips high temperature pH-electrode (CH 85D-SD) and platinum 100 thermometer was used in the autocalibrate mode to standardise itself using 2 NBS-buffers (phthalate and borax solutions). The instrument automatically identifies each buffer and uses the current temperature to select the exact buffer value from its look-up table. Temperature compensation for electrode slope changes due to temperature changes was also automatic.
THE VOLATILISATION AND CONDENSAliON OF ACETIC ACID DURING CANE JUICE EVAPORATION
Severe corrosion problems associated with vapour condensates have been experienced at Felixton Sugar Mill over the past few seasons. Routine analyses from the 1989/90 season .onw~rd.s have pinpointed the problem as being due to acetic aCid m the condensate. The acetic acid has been shown to originate from the acetyl hydrolysis of the hemicellulose fraction of bagasse during liming in the diffuser. Laboratory trials were devised to investigate the amount of volatilis~tionand .c~mdensati~nofacetic acid from juice under varying conditions of bnx, temperature and impurity concentrations. The results showed that a combination of high brix and high temperature increased the volatilisation of acetic acid. This explained why Felixton, with 2nd effect Kestner evaporators operating above atmospheric pressure was experiencing corrosion problems in the vapour 2 con~ densate. Experiments on the condensation of the vapour showed that the acetic acid was concentrated in the first part of the vapour to condense, explaining the severe localised corrosion found in the factory. A computer model was developed using ionic equilibrium and relative volatility constants for comparison with the experimental data. This model can explain several of the experimental observations.
MECHANICAL VAPOUR RECOMPRESSION AT PONGOLA
Four performance test runs were carried out on a 31 t h-I mechanical vapour recompression unit at Pongola, compressing vapour from 145 kPa abs to 196 kPa abs. The test results are examined and the overall effect on the steam balance is assessed. A saving of approximately 6 t h-I of high pressure steam is achieved reducing extraneous fuel costs by about RlOO 000 per season. Capital cost of the' installation is given.