Falling-film evaporators - role in steam saving (a perspective of Almoiz Industries, Pakistan)

The energy efficiency of a sugar mill depends to a large extent on the performance of the evaporators. The conventional Robert evaporators used in most cane sugar factories work with high ?T, thus usually the 1st or 2nd vapours are required for juice heating and boiling of the massecuite. To operate the sugar plant with high efficiency, one of the pre-requisites is that the evaporators work on very low ?T, so that the lower stage vapours can be utilized for heating and boiling. Falling-film evaporators (FFEs) have the required characteristics to work on a narrow ?T to improve the steam economy. Currently, the Pakistani sugar cane industry is facing multiple challenges for its survival and those can only be addressed by improving efficiencies both in agriculture and processing. Therefore, Almoiz Industries set up a state-of-the-art project in Pakistan having high energy-efficient values either as steam % cane or in-house power consumption. These factors lead towards availability of extra electrical power, which can be used for any other diversified allied operation such as power export to the utility or using the surplus power for steel making etc. Similarly, it helped in saving bagasse, which can be used for different purposes during the off season. To reduce steam consumption, a complete set of seven FFEs was installed. All vapours from the 1st effect to 5th, including condensate, were used for heating juice and boiling massecuites to reduce steam consumption per tonne of cane. The operation of FFEs is based on small ?T, due to which the vapour temperature in each effect increases and allows the use all types of vapours. Although there were operational difficulties in the beginning, these were resolved over time. A minimum 35% steam on cane with a refinery and 33kW/t of cane electrical consumption is achieved at maximum rate of cane crushing. The operation of FFEs proved that all vapours from 1st effect to 5th can be used, which results in steam consumption reduction of the plant and saving of bagasse. Saved bagasse can be used for power export and other allied businesses. Key words Bagasse saving, use of all vapours, design, problems, solutions