D Bezuidenhoudt, M Gokool and M Stevens
Bosch Projects, South Africa
In today’s sugar industry, due to rising fuel and electrical energy costs and the increased need for cogeneration, steam economy is a critical factor. Previously established options to upgrade vacuum pans for improved performance or steam economy are well known but are expensive and require extensive modifications to the vacuum pans. The recently developed and commercialised dimple tube technology considerably increases batch and continuous vacuum pan performance, in terms of throughput, and has been well received in industry for this reason. It was shown, during this previous work, that during both laboratory testing and full-scale factory testing and performance reviews that throughput of the retrofitted vacuum pans was increased by approximately 30%. During the previous experimental tests and trials conducted to determine real-world performance improvement, the dimple tube technology has shown a significant improvement in heat transfer coefficients in vacuum pans due to the turbulence created on the surface of the tubes. Through experimentation and analysis, the impact of dimple tube technology on energy savings and possible overall process efficiency is quantified, the dimple tubes have been shown to allow a reduction in vapour grade and hence factory steam efficiency. This is due to the established 14% improvement in overall heat transfer coefficient when utilising dimple tubes. This work applies specifically to sugar factories and refineries where energy efficiency could be improved by taking advantage of improved heat transfer coefficients and operating vacuum pans on lower grade steam.