This leads to the next question, “
How to prevent low cooling water supply flow from impacting the performance of a vacuum system?”
Design for the Correct Cooling Water Flow Rate
Although this does not help with a system already installed, on new installations it's very important that the vacuum system manufacturer is provided an accurate cooling water flow rate.
Cooling Water Balance / Booster Pumps
Checking the cooling water balance in the overall system will help identify if there is any flow being restricted on one system and not on another. Balancing the cooling water will insure cooling water flow is going to the correct systems. Another option would be to install a booster pump to help increase the cooling water flow rate to the design flow rate and help maintain overall performance.
Compensating with Colder Cooling Water Inlet Temperatures
Reducing the cooling water inlet temperature will help overcome a decrease in the cooling water flow rate. Temperature and humidity will limit the effectiveness of cooling towers. Colder water may be available from an alternate source.
Reduction in Process Loading
Cutting back on the process load will reduce the loading on the condensers and remove duty from the cooling water loop. This can help compensate for the reduction in cooling water flow rate to some degree but will have an impact on production.
Cleaning the condensers on both the shell side and tube side helps to both maximize cooling water flow and the heat transfer rate. Cleaning the condensers helps the condenser’s capacity by ensuring its best operation and minimizing the impact.
New Condensers / Redesign of Ejectors
In an existing system there are only so many things that can be done to compensate for low cooling water flow rate. At some point condensers and systems need to be redesigned if the cooling water flow rate is going to be lower than design for extended periods of time. It may be prudent to investigate replacement ejectors, using new interstage pressures to compensate for cooling water limitations. The equipment manufacture should be consulted to see what changes are applicable for a specific system.