Modification and Performance Evaluation of a Laboratory-scale Alcohol Reboiler

Author : Tolentino, Joel Hassan G.
Major Adviser : Demafelis, Rex B. 
Committee Members : Acda, Reynaldo I.; Abrigo Jr., Casiano S.; Valencia, Sixto A.
Year : 1993
Month : July
Type : Thesis
Degree: BS
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An existing laboratory-scale alcohol reboiler was modified to minimize the occurrence of uncondensed steam and tested. Prior to repairing the reboiler, a series of tests were conducted to identify for the problems’ cause. Upon analysis of the data obtained and investigation of the equipment design, it was decided to improve the reboiler tube side by increasing its number of passes.

The number of tube passes of the reboiler was increased from two to six by adding baffles in the entrance and return headers. Testing the equipment showed an improvement in the amounts of condensed steam and vapor produced. But still the uncondensed steam was not totally eliminated. This is explained by the decrease in the driving force for heat transfer due to the discovery that the temperature of steam supplied was only at 100 °C, not at the saturation temperature of steam at 10 psig which is about 115 °C.

In the five trials conducted, the average amount of condensed steam has increased from 7.768 to 15.213 lbm/hr.This showed a 95.84 % increase. The vapor: reboiler food ratio has increased from 0.0558 to 0.1152. This showed an increase of 106.45%.

Moreover, heating of the mixture to boiling took about 15 minutes and all the steams supplied were condensed in the modified equipment while in the previous design preheating test about an hour and uncondensed steam was already observed.

The increased number of the tube passes increased the residence time of steam because of the longer path provided for the steam to travel inside that gave it more time to release its heat and the simultaneous decrease in the condensing steam flowrate while traveling through the longer path. The increase in velocity of steam due to the decrease in the cross-sectional area per pass created a more turbulent flow. both observation imply an increase in the heat transfer rate. This explains the increase in the amount of condensed steam and vapor produced.

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