MODIFICATION IN NCG REMOVAL & CLANDRIA EQUALIZING SYSTEM TO IMPROVE CONTINUOUS PAN EFFICIENCY

Abstract

The function of vacuum pan is to initiate the process of crystallization in sugar mother liquor under vacuum. The crystallization in vacuum pans involves simultaneously two processes i.e. mass transfer and evaporation. The process is carried out in both batch and continuous system. The pan design should be such that it efficiently meets the requirement of energy conservation, better mass transfer (exhaustion) and improved circulation. This presentation covers the basic requirements of better design of continuous pan which includes circulation ratio, hydrostatic head, heating surface to volume ratio, graining volume ratio etc. Further advantages of continuous pans over batch pans are also discussed. The factors which influence operation of vacuum pans have also been identified. To improve the evaporation, heat transfer and mass transfer, the very important parameter is the proper distribution of mass/vapor in the calandria. This factor is specially significant while operating pans on low steam/vapor pressure. This paper is a case study regarding the improving upon in operation of continuous pan in Mirpurkhas Sugar Mills. We observed that boiling in central chambers of continuous pans was sluggish. After detailed monitoring of pans operation, it was found that it was mainly due to the fact that the non- condensable gases were not removed efficiently and calandria is not properly equalized and vapors do not reach to the farthest point from the steam entry. Some modifications were done in the non-condensable gases removal and equalizing system of calandria. This modification has resulted in improved boiling efficiency in pan and we achieved optimum utilization of the capacity and better exhaustion of the mother liquor.