Have You Ever Tracked the “C-Factor”?
A good friend just called looking for a second opinion on a closed loop heating water system. This is a rather large water system — well over a million gallons — so it warrants more attention than most systems. This led me to think about “extra-value services” that we would look to provide with those types of systems.
I was reminded of data we would collect around critical heat exchangers. These were typically pieces of equipment with rather high heat flux rates. In power plants, the condensers were where the money was saved or lost, but they generally do not have high heat flux rates. There were usually other heat exchangers, like the ones in air compressors or lube oil heaters, that had higher heat flux rates and could be affected by poor water treatment long before the condensers ever showed reduced performance. Think of these pieces of equipment as the “canary in a coal mine.” These heat exchangers would give us a heads-up if we were headed towards trouble.
Since heat exchangers usually consist of many small diameter tubes, the surface area of the tubes was quite high in relation to the amount of water in the exchanger. Even a small amount of deposition from any source on the walls of the tubes could greatly increase the resistance of water getting through the exchanger. Sounds straightforward and it is. So how could we use this to monitor a heat exchanger’s performance?
There is a calculation we used called the “C-Factor.” It allows for a simple calculation to be used to create a number telling the user if a piece of heat exchange equipment (or, really, any other piece of equipment which has water flowing through it) is staying clean or getting fouled. The calculation we used was simple:
Flow Rate (FR) is expressed as gpm and Pressure Drop (PD) is expressed as psi. “SQRT” is the function “square root” of the value in the parenthesis.
For monitoring purposes, the initial value should be for a clean system. This value should be compared to a “design value.” Then, operating data could be regularly collected — weekly or monthly, depending on your service visits. I have seen systems using the same pressure gauge (piped to both the inlet and outlet with isolation valves on each side), reducing the error between the readings from two pressure gauges. Operators who work in this area probably collect this data in a log sheet during their rounds. The more data you have, the better you can monitor a system.
So, if a system gets fouled, the flow rate might stay the same but the pressure on the discharge of the heat exchanger will be decreasing. This will create a higher pressure drop causing the C-Factor to decrease. Tracked over time, this information should be useful in demonstrating effective water treatment or determining when equipment needs to be cleaned. (This works for scale and microbio concerns as well.)
The C-Factor is another tool to help you show that your systems are well taken care of. If you have problems, you could determine how bad the situation is and evaluate program changes, then get real-time feedback as to how those changes are working and improving the system.
Give this a try at one of your challenging plants.
