Detection of Fouling in Heat Exchangers using Model Comparison

Fouling of heat exchangers is a severe problem in the industrialized world. The effects of fouling are reduced energy efficiency and increased greenhouse gas emissions. In fact, any heat transfer process has a risk of fouling on the heat transfer surface. The fouling can in some cases be cleaned physically, chemically or burned off; in other cases it may not be possible to clean the heat exchanger and a new one will be needed. For those heat exchangers that are cleaned there is normally only a certain number of times that they can be cleaned before new ones will be required. Although early fouling detection may not have a significant impact on the lifetime of heat exchangers it can help in preventing the situation where their efficiency becomes so low that it affects the process the heat exchanger is used in, resulting in reduced economy of operation. The aim of this Ph.D. project was to develop and implement fouling detection methods that only require flow and temperature measurements that can easily be obtained during normal operation of heat exchangers and without interrupting the process. In the scope of the project six different methods have been tested on either counter or cross flow heat exchangers. The measurements are either real measurements or simulated data series from accurate heat exchanger models where fouling can be simulated. Statistical methods are then applied on the data. The findings clearly show that methods developed in the project can be used to detect fouling well before a typical design limit is reached.