Date of Defense
Dr. Andrew Kline
Dr. Peter E. Parker
Dr. Betsy M. Aller
Several issues exist with the current fermentation tank cooling system in use in building 121 at Pfizer. The fouling caused by the current cooling medium significantly reduces the heat transfer in the system, while at the same time causing corrosion. Over time, this reduced heat transfer efficiency causes an increase in operating costs, as the cooling water required increases. The corrosion in the coils steadily worsens, until the coils must be replaced at an estimated cost of $300,000. In addition to the cost associated with the replacement of the coils, the event of an unexpected coil rupture due to corrosion would result in unscheduled downtime and containment issues. This downtime would affect production schedules throughout the entire facility, and could ultimately result in a loss of income if production deadlines are not met. In an effort to deal with these issues, a heat transfer spreadsheet was created to model the current system. This spreadsheet is capable of predicting fouling as a function of time, which would allow for the scheduling of regular maintenance intervals to ensure clean coils. Using this heat transfer spreadsheet, a close loop cooling system was designed to address both the fouling and containment issues associated with the current process. The new system would utilize a much cleaner fluid on the inside of the coils, thus eliminating the need for periodic coil replacement. Also, the proposed system would provide secondary containment in the event of a system contamination.
If a closed loop cooling system is desired, it is recommended that Pfizer implement the following design per fermentation tank: • Shell and tube heat exchanger, stainless steel construction • Clean water as the coolant within the coils • Methanol brine as the secondary coolant within the heat exchanger Based on this system and a 20 year plant life, the following costs would be incurred per heat exchanger: • Cost of purchased equipment (heat exchanger and two pumps): $130,000 Installation costs: $485,000 Annual cost of methanol brine usage: $789,000 Overall NPV: -$2,860,000 • • The calculated NPV is negative because no income was associated with the implementation of this project. It is important to realize that expansion of the building would most likely be necessarily to ensure adequate space for piping and maintenance. It is recommended that further structural analysis of the current building be performed in an effort to determine the feasibility of locating the heat exchangers within the current building. It is also recommended that if a closed loop system is implemented, the fouling be closely monitored using the heat transfer spreadsheet to ensure maintenance is performed at the proper intervals.
Moseley, Dustin and Tate, Nathan, "Closed Loop Cooling Systems for Fermentation Tanks" (2008). Honors Theses. 1831.
Honors Thesis-Campus Only