Technical Paper Refinery Process Fouling Control Abstract Modern refineries strive for reliability and pro- cessing flexibility, with longer run lengths and min- Fouling of refinery process equipment is a common imal equipment fouling, to allow the processing of problem resulting in severe economic penalties, as lower quality feedstocks, which offer favorable well as significant safety and environmental con- economic incentives. cerns. For more than 30 years, GE Water & Process GE has developed the technology, the applications Technologies has invested extensively in the iden- expertise, and the global industry experience to tification and understanding of fouling mecha- effectively treat and minimize fouling throughout nisms, as well as how to minimize the fouling in the refinery. Typical problem areas include crude process equipment. The result of these efforts has preheat exchangers and furnaces, hydrotreater been the development of proven chemical treat- exchangers and reactor beds, FCCU slurry ex- ment programs that are unique to each applica- changers, and thermal cracking process ex- tion. changers and furnaces. Multiple factors impact fouling including equip- This paper will cover the following topics related to ment design; flow rates; temperatures; cracking refinery process fouling: units operational severity; fluid characteristics; Fouling mechanisms caustic addition, can impact crude preheat fouling and coker furnace fouling; and upstream process- Exchangers – cleaning, bypassing, pretreating es, such as desalter operation. Consequently, each Economic penalties process unit and fouling control program is unique. GE has developed state-of-the-art analyt- Environmental and safety impact ical tools and sophisticated monitoring techniques Antifoulant chemistries to identify and track process fouling, as well as quantify the impact and economic benefits of a Crude (crude blends) quality chemical treatment program. Analytical tools Heat exchangers are used to recover heat from Monitoring tools and techniques product streams to preheat the feedstock, mini- mizing the furnace fuel needed to raise the feed to Value of a comprehensive treatment program the required process temperature. Fouling in the exchanger train and the related reduction of heat Background transfer can cause significant energy loss and in- crease operating costs. Fouling can also become Since the early 1980’s, chemicals have been used so severe that unit capacity and production limits to help reduce fouling. Early on, the benefits of are reached. chemical treatment were difficult to demonstrate due to limitations in monitoring and program justi- In a crude preheat exchanger system, the hot fication, combined with a developing understand- preheat section is usually the area of greatest ing of fouling mechanisms. concern. The hottest exchangers or exchangers with the highest heatflux typically show the high- Find a contact near you by visiting www.ge.com/water and clicking on “Contact Us”. * Trademark of General Electric Company; may be registered in one or more countries. ©2012, General Electric Company. All rights reserved. TP1194EN.doc Feb-12 est fouling rates. This is also the case for the hy- Many factors contribute to the economic impact drotreater feed/effluent exchangers and the slurry of refinery process fouling, including those de- exchangers. scribed below. A correctly designed and applied chemical treatment program can help significant- Intermediate cleanings can be applied, although ly reduce costs and penalties related to equip- throughput reductions are typically required if an ment fouling. online clean is carried out or even a shutdown is necessary to clean an exchanger that cannot be Energy Cost: Fouling in exchanger networks will isolated and bypassed. This represents significant reduce the amount of heat recovered from prod- economic penalties, if not planned in the normal uct streams. This in turn, requires more heat to be refinery operation. supplied by the furnace to compensate for the lower feed temperature. Also, the higher loading Mechanical changes and spiral metal inserts, of the furnace often reduces furnace efficiency which vibrate as fluid flows through the tube have and increases the fouling or coking tendency of been used to control the fouling rate. However, the furnace. Both effects further increase fuel de- other problems such as hydraulic limitations have mand and energy costs. been encountered. Maintenance Cost: High fouling rates can lead to Introduction excessive equipment cleaning requirements and costs. Mechanical cleaning, using high pressure Heat exchangers are used to recover sensible jetting, is typical. It requires equipment opening heat from process streams leaving reactors, distil- and often heat exchanger bypassing. In cases lation columns etc. to preheat the feedstock and where the exchangers cannot be bypassed, a unit minimize the external energy demand to provide shutdown may be required to clean the equip- the required heat for the process. Of the total pro- ment and a substantial production loss needs to cessing cost, energy is a major part, particularly in be added to the total cost of cleaning. Opening distillation processes, which can directly influence the equipment also increases the risk of damage refinery profitability. Controlling, or minimizing, and additional repair costs, as well as safety and heat exchanger fouling can dramatically lower environmental concerns. overall operating costs. Throughput Loss: Fouling of the preheat ex- Typically, refiners acknowledge and accept the changers will increase the heat duty of the fur- gradual diminishing performance from their heat nace up to the point that the maximum furnace transfer equipment, as fouling inevitably builds. capacity is reached. As that limit is approached, However, when fouling becomes so severe that the unit throughput will need to be cut back grad- throughput restrictions occur, the economic pen- ually in order to unload the furnace, and again, alty is no longer acceptable. Units are then shut- significant production losses are incurred. down, or the equipment is by-passed for cleaning, incurring high maintenance costs and production Process stream fouling can lead to increased losses, as well as increased environmental and pressure drop in the exchangers and furnace. In safety concerns. some cases the fouling is so severe that the hy- draulic limits are reached, the throughput is re- Economic Impact of Fouling duced, and significant processing incentives are lost. In the case of a hydrotreater, reactor fouling Fouling of refinery process heat exchange sys- will also cause pressure drop problems resulting in tems can cause significant economic penalties. similar consequences. Minimizing operating costs, sustaining throughput, Feed Flexibility: The fouling rate can be greatly and maintaining equipment reliability are primary goals in today’s difficult economic climate, with influenced by the crude type or blend. Some more difficult crude slates and blends, stringent crudes contribute to such severe fouling problems regulatory mandates, and greater environmental that they are not considered for processing in cer- and safety focus than ever before. tain refineries. These “opportunity” crudes offer an attractive economic incentive to the refinery that can process them. Page 2 Loss Opportunity: Modern refinery operation can remain and cause deposition in the preheat strives to maximize the run-length between shut- train. downs and plan shutdown activities so as to min- imize downtime and production losses. Unit A caustic solution is sometimes injected into the flexibility and equipment reliability are key factors desalted crude for distillation tower overhead cor- in avoiding unscheduled shutdowns, which might rosion control. However, this practice can also en- hinder contract fulfillment or the ability to capital- hance the potential for fouling in downstream ize on “opportunity” crudes. exchangers and coking in downstream process furnaces. Equipment fouling in the distillation column, can lead to poor product separation and quality, with In an FCC slurry system, catalyst fines can con- dramatic economic consequences. tribute to significant fouling. In a hydrotreater, severe fouling can impact con- Additionally, inorganic salts in the effluent side of version generating off-spec, lower value products, the hydrotreater feed/effluent exchangers can and can also result in throughput reductions. become a serious problem. In an FCCU, severe slurry fouling may force the Organic: Organic fouling in a crude unit results refinery to run a lower main fractionation tower from the precipitation of organic components bottoms temperature, dropping valuable products which become insoluble in the system, such as into the less valuable slurry. asphaltenes, and high molecular weight hydro- carbons (i.e. paraffins). The asphaltenes can be- Safety: Regular equipment opening for cleaning come unstable because of the blending of increases the risk of leakages, specifically during incompatible crudes and/or the heating of the flu- the start-up. Although difficult to quantify, the id. The precipitated organic molecules can sit at economic penalties associated with a fire or ex- the metal surface and dehydrogenate, forming plosion, and moreover personnel injuries, can be coke. The coke formation can also result from enormously high. thermal degradation of hydrocarbons due to long heating periods. Fouling Mechanisms Organic fouling on the feed