When it comes to cleaning of a heat exchanger, there are to ways to do this: offline and online. The advantage of online cleaning is that the heat exchanger will not have to be shut down, and thereby shutdown costs are reduced. This is why online maintenance is often more preferred and therefore all kinds of online cleaning methods were developed in recent years.
One method to remove foulants, developed by a firm called Advanced Heat Transfer Technologies, is the Automatic Tube Brushing (ATB). The operating principal will explained in the light of the following picture.
Figure 7 The principal of the ATB system
The system can be applied to almost any heat exchanger and consists of two main parts. The first is a small nylon bristle brush (white part on the right, within the yellow tube), which is inserted into each tube of the heat exchanger. The size of the brush is chosen in such a way that there is an appropriate fit within the tube. The second part is a special plastic cage (blue part on the left), which is installed at each side of the exchanger tubes. When the exchanger fluid flows through the tubes it takes the brush with it from the cage on the one side to the other one. By reversing the flow direction, the brush will then be taken to other side again. This way the brush moves back-and-forth through the tubes, thereby removing all kinds of foulants. The turning of the flow is done by a third component, a special valve, which is activated by an automatic control panel. This valve normally turns the flow like two or three times a day, depending on the severity of the fouling in the heat exchanger.
The big advantage of the ATB system lies in the fact that after installation no more extra maintenance is needed, so the shutdown and maintenance costs almost disappear. The system keeps the fouling factor of the heat exchanger at a constant low value. In practice, fouling factors of 5 till 10 times lower than without ATB are reported. This way also energy costs are minimized. Furthermore no chemicals are needed to clean the heat exchanger, which is an advantage for the environment.
The disadvantage of the system lies mostly in the installation, which is rather time consuming for big heat transfers and also rather expensive because, partially because of the needed control unit and valves. Capital costs will rise, but a bigger reduction in other costs can be achieved!
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