Fouling in petroleum process streams is an injurious deposition on heat transfer surfaces. The deposits are composed of: organic fouling reaction products, high molecular weight process stream components, coke and inorganic salts. Fouling afflicts many process units: FCC, crude, coker, reformer units, etc. The fouling of hydrodesulfurizer preheat exchangers is often particularly vexing. As fouling occurs, heat transfer is reduced, pressure drop is increased and process flow is blocked. Commonly, hydrodesulfurizers employ feed-effluent exchangers to preheat the feed and cool the effluent. Hot hydrodesulfurizer effluent flows through the exchanger tubes and cooler feed flows through the shell. Severe fouling problems often assail the feed in the shell side. If constant mass flow is maintained, then the loss of exchanger heat transfer due to fouling increases the heating burden placed on the furnace. In addition, more cooling duty must be provided for the effluent. On the other hand, if the furnace and cooling duties are maintained constant, then the process throughput must be decreased.
