Fouling mitigation strategies for heat exchanger network

Fouling of heat transfer equipment has been defined by some authors as one of the "greatest unsolved problem of chemical engineering". Fouling is indeed a very serious problem, which affects most of the industries that use heat transfer in their processes. The main effects of fouling are related to reduction in the thermal and hydraulic performance of the affected heat transfer equipment. The cost associated with this problem is immense. Every year, billions of dollars are expended by the industry in fouling related costs in the form of extra capital cost, extra energy consumption, maintenance cost and lost production. Fouling also has an environmental impact, which is both a result of the extra energy consumption brought about by the reduction in heat recovery efficiency and the cleaning actions necessary to remove fouling deposits. There are then strong incentives to develop techniques to mitigate the effects of fouling deposition in heat exchanger networks. Numerous approaches have been proposed to mitigate the detrimental effects of fouling on the performance of heat recovery networks. Existing techniques, based on different principles, are used to mitigate of fouling in both existing heat exchanger networks and prospective new designs. The success achieved by these fouling mitigation techniques, however, has been limited. Many of the existing mitigation methods provide only palliatives to the effects of fouling, without really solving the problem. Other methods can worsen the fouling problem rather than mitigate it. Perhaps the lack of effectiveness of many established fouling mitigation techniques stems from the reactive approach used to combat the fouling deposition problem. Most of these approaches consider fouling deposition as a problem that cannot be avoided. These methods seem to condemn heat exchanger networks to suffer fouling deposition. Therefore, no attempt is made to try to avoid the occurrence this problem. Instead, provisions are made to apply corrective measures once fouling deposits commence to affect the performance of the heat transfer equipment. Contrary to common belief, fouling deposition in heat transfer equipment is not an inevitable problem. Numerous field and laboratory observations have confirmed that, under appropriate operating conditions, fouling deposition occurs at just negligible levels. The role that operating variables have on the rate of fouling deposition has been the subject of intensive research. It is now a well-known fact that the severity of many fouling mechanisms is significantly affected by variables such as wall temperature, flow velocity and composition. In this thesis, a novel fouling mitigation methodology is developed. The proposed mitigation strategies are intended to be used during the different stages of the life cycle of heat exchanger networks, i.e., synthesis, operation and retrofit. The proposed strategies use a pro-active approach to deal with the fouling problem. Instead of applying palliatives to the effect of fouling deposition, the new approach tries to avoid, or at least reduce, the occurrence of fouling in heat exchanger networks. For this purpose, the proposed methodology exploits the effect that some operating variables have on the rate of fouling depositions. When compared with traditional mitigation strategies, the new methodology leads to better solution in many aspects, including higher economic savings.