The source of the cooling water for a condenser should be considered when looking at potential origins of debris. The cooling water is normally sourced from a cooling tower, a river or lake, or in some cases the ocean. When that water is sourced from a natural body, it always has the potential to include trash or waste from that body of water including debris like leaves and sticks. These types of debris are less common in cooling tower systems, because that water is treated, although cooling towers are not free of debris concerns. Pieces of the cooling tower boards or pieces of the structure itself can make its way into the cooling water supply. Because of the induced air flow through a cooling tower, they are prone to sucking in debris, which can eventually find its way into the condenser.

It’s important to note that often process systems with multiple condensers will have some of them piped in series. In this case, the first condenser will have a tendency to gather all the debris where as any debris that can pass through the first condenser will also tend to pass through any downstream condensers. Because of this orientation a high pressure drop across the first condenser and lower pressure drops across any downstream condensers, is a sign that debris is present as opposed to some other fouling mechanism.

One of the best ways to address debris is to prevent it from entering the system in the first place. Placing a strainer on the cooling water line can help capture any debris and prevent it from reaching a system’s condensers. This in-line strainer should be placed between the water source, whether it be a cooling tower or natural body of water and the system’s condensers. Often this is placed upstream of the system’s pumps to prevent that debris from entering the pumps and damaging them. Another often overlooked item is the need to clean out any installed strainer on a periodic basis to ensure that it does not plug up with debris and fail.

If debris does make it into the system’s condensers, it must then be removed. To remove debris from a condenser you can physically open the condenser and clean out the debris. This is often achieved by opening up the channel covers or by accessing the waterbox via manways once the condenser has been drained and properly locked out. While this

Another way to remove debris from a condenser is by back flushing. Back flushing is achieved by reversing the cooling water flow through the condenser by manipulating previously installed cooling water valves and piping. By reversing the direction of the water flow, any debris that may have lodged in the condenser will then be removed by the reverse flow. Back flushing is often done intermittently to remove debris so that when the cooling water flow is put back to its normal direction the debris that was negatively impacting the condenser has been flushed out of the system.

Change in Cooling Water Direction - Condensers are designed with the cooling water flow to be in a specific direction. Changing the direction of the cooling water through the condenser will have a negative impact on the condenser’s capacity in most instances, and should be done only on an intermittent basis.

Series Flow – When systems with multiple condensers are piped with the cooling water in series, back flushing the first condenser only will result in any debris that was in the first condenser being flushed into the downstream condensers. Because of this, the cooling water flow through the entire system is often reversed as opposed to each condenser being back flushing individually. The entire system is back flushed so that each condenser does not need to have its own back flush piping/valves and to simplify the back flushing process. When the water is reversed though the entire system, it can be expected that the vacuum system will not work as designed. The colder cooling water needed in the first condenser of the system will pass through multiple condensers first resulting in a much hotter temperature to the first condenser. This can break the performance of the system’s ejectors while the back flushing is occurring.

Debris Type – We discussed debris in this article as debris is the primary reason to back flush a condenser. Other types of fouling like process side fouling, hard water scaling or mineral deposits will not be improved by back flushing. While back flushing can be extremely effective, it’s conditional on the type of fouling present in the condenser.

Because of these concerns, it’s not uncommon for the systems load rates to be reduced while back flushing is occurring. Back flushing is also sometimes scheduled during cooler weather or during colder parts of the day to minimize its impact as the colder cooling water temperatures will help negate or offset the temporary reduction in performance while the system is being back flushed. If you suspect debris or fouling in your condenser or want to know why your system is struggling, please don’t hesitate to contact Graham’s Service Department for assistance.