Case Study - Process Capabilty - Fermenter Performance

In this case study, as part of an six sigma initiatiative looking at flavour performance in a brewery, it was noted that fermenting vessels that had been in use for 30 years were not keeping up with the required cooling performance. 

The fermenters were required to maintain between 14-16⁰C but were only achieving 15-17⁰C.  They were also required to crash cool to 4⁰C in 24 hours. They were only achieving 8⁰C in 72 hours.  An ultrasonic flowmeter was strapped to the cooling jacket flowrate and it was found that the flow was 4.3 to 6 m3/h.  Themal Calculations indicated that a flow rate of 10 to 12 m3/h were required to meet the crash cooling duty.

Physical examination of the vessels showed them to be early cylindro-conical vessels, built with a unique "trickle jacket".  The inner fermenter vessel was surrounded by a unflooded outer jacket. At the top of this jacket was a gutter that was filled with chilled water and allowed to over flow to wet the outer surface of the fermenter vessel and cool it. 

At some point unknown in the past spray nozzles has been fitted to the chilled water inlet.
It was suspected that these were to "throw" the chilled water away from the inlet and achieve better surface coverage of the vessels. 

Thermographic images were taken of several of the Fermenters. This showed cooling water wetting about 7.5% of the vessel jackets (the black areas) but leaving 92.5% of the jacket unwetted and uncooled (red areas). 

The cost to carry out modifications to each vessel to improve coolant distribution was budgeted at £30,000.  As a conclusion it was demonstrated that it was more cost effective to install larger modern external flooded jacket multi purpose fermenters rather correct the old fermenters.