chapter  8
Scale Formation in Sugar Juice Heat Exchangers
Pages 24

To understand fouling in sugar juice heat exchangers, it is rst necessary to look at the sugar manufacturing process as a whole (Figure 8.1), where raw sugar is produced from sugarcane. The rst step in the process is the harvesting and transport of sugarcane to the mills, where the cane is shredded and then crushed on the milling train to squeeze out the juice. The leftover plant material is called bagasse, and it is used to re the boilers to create process steam and electricity. After the cane is crushed, the juice is heated to ∼76°C, incubated to remove starch and then heated to 100°C, and claried to remove soluble and insoluble impurities, such as plant material, dirt, and scale-forming ions. During clarication, calcium hydroxide (as milk of lime or lime saccharate) is added to raise the pH (from ∼5.4 to ∼7.6-7.8) and to form calcium phosphate with the phosphate already present in the juice. If the phosphate levels in the juice are low and the juice is poorly clarifying, phosphoric acid can be added. Calcium phosphate is used to remove both soluble and insoluble impurities, and it forms ocs in the process. A sodium polyacralyate copolymer is added to aid

8.1 Introduction .................................................................................................. 135 8.2 Experimental ................................................................................................ 137

8.2.1 Factory Juices ................................................................................... 137 8.2.2 Evaporator Scale ............................................................................... 137

8.3 Results ........................................................................................................... 139 8.3.1 Composition of Factory Juices .......................................................... 139 8.3.2 Scale Analysis ................................................................................... 141

8.3.2.1 XRF .................................................................................... 141 8.3.2.2 X-Ray Powder Diffraction ................................................. 142 8.3.2.3 Surface Analysis ................................................................ 143 8.3.2.4 Cross-Sectional Analysis ................................................... 147

8.4 Discussion ..................................................................................................... 150 8.5 Conclusion .................................................................................................... 154 Acknowledgments .................................................................................................. 154 References .............................................................................................................. 155

the occulation of the calcium phosphate ocs [1,2]. Once the juice is claried, it is drawn from the top of the clarier and sent to the evaporators, where the claried juice is concentrated from 12 to 65 wt% sucrose to form syrup [3]. Within each evaporator unit, the juice is boiled in stainless steel tubes heated by circulating steam in a multieffect arrangement, and approximately 40% of the tube height is submerged in sugar juice during processing. The juice typically passes through ve such evaporator units before being transferred to crystallization pans. The evaporators are where the majority of the fouling occurs.