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Fouling in oil refineries is a prevalent and persistent problem that affects the performance and efficiency of refining processes. The preheat train of the crude distillation unit (CDU) is the key process for energy efficiency in refineries and, consequently, the focus of application of Hexxcell’s technology to save fuel, reduce CO2 emissions and maximise throughput. Other processes can also significantly benefit from it.


Managing fouling in oil refineries requires a proactive and systematic approach to monitoring, cleaning, and mitigating the accumulation of deposits. The use of digital solutions, such as predictive maintenance and advanced monitoring, can help to minimize the negative impacts of fouling and ensure consistent and efficient refining operations.

Preheat trains in CDUs are key processes for the energy efficiency of the refinery. These extensive networks of heat exchangers aim to recover up to 70% of the energy required to preheat crude oil before entering the distillation column by exchanging heat with the hot streams coming out from it. The rest is provided in furnaces by burning fuel, normally natural gas. As fouling builds up in the train, the inlet temperature to the furnace (coil inlet temperature, CIT) decreases.

Additional fuel must be burned in the furnaces to maintain the desired inlet temperature to the distillation column (or coil inlet temperature, COT), which is critical to achieve the desired yields. If the furnace reaches the maximum capacity, the plant throughput must be reduced to meet the desired COT, leading to significant economic losses. In other cases, the hydraulic impact of fouling, rather than the thermal, is the cause of throughput losses.

Hexxcell’s technology has been extensively applied to help reduce the negative impact of fouling in preheat trains by closely monitoring the condition of the network, predicting future scenarios, optimising operations and cleaning schedules, and uncovering the impact of crude oil blends on fouling propensity. For an average-size refinery (100,000 – 150,000 bbl/d), typical benefits of applying Hexxcell’s technologies include $1-2 M/yr savings in fuel, reduction of over 8-10% in CO2 emissions of the CDU, production increase of 0.5-3%, and total financial impact of several millions of dollars per year.

While the preheat train is the main actor in refineries, substantial benefits can be achieved in other processes, such as vacuum distillation units (VDUs) requiring preheat, preheaters in cokers or FCCs, auxiliary exchangers in stabilisers, etc.


Fouling impacts operations and economics across petrochemical processes. In critical exchangers (even single units), the undesired build-up of deposits incurs in large additional energy consumption, utility demand (e.g. steam, water), and even reduced production. In such cases, the benefits of applying Hexxcell’s technology have been identified in the range of $400 - $500 k/year.


The decay in performance because of fouling deposition reduces heat exchange performance resulting in worsened heat integration between units and higher pressure drops. The impact of fouling in critical heat exchangers at the system level includes:

  • Reduced production and yields because of limitations in water cooling circuits, pre-heats, boilers, and condensers (e.g. due to undesired side-reactions, limitations in control of reactors, distillation efficiency, etc.)
  • Lost opportunity of using high margin feeds
  • Additional consumption of steam or need of higher-pressure steam
  • Additional consumption of cooling water
  • Additional fuel consumption and CO2 emissions in fired-heaters
  • Need of additional heat transfer area (spare exchangers) to allow for continuous operation
  • “Cascade” effect in highly heat-integrated processes

With experience in preheaters, reactor cooling exchangers, quenching circuits, or reboilers in separation units, among others, Hexxcell has quantified the impact of fouling in critical exchangers in over $1 MM/yr in energy and utility consumption and $50 - $100 k/day in undesired downtime. Advanced monitoring and predictive maintenance can help reduce such impact by detecting faults and unexpected events earlier, warning ahead of time of possible production limitations, performing “what if” scenarios and rigorously accounting for techno-economic trade-offs when making cleaning decisions.


The gradual buildup of fouling affects large-scale power generation plants by gradually reducing energy recovery and causing operational issues. While some problems are long-standing in the industry (e.g. cruds in nuclear plants, fouling in boilers and condensers in coal-fired plants), new issues related to raising cooling water temperatures as a result of climate change and global warming are creating new challenges that need addressing.


Fouling is a major issue in power generation plants, affecting various equipment in the primary circuit such as boilers in coal-fired plants or nuclear reactors, the condensers in the secondary circuit, and the water-cooling circuits. Depending on the system, fouling can be composed of corrosion particles (e.g. cruds in nuclear reactors), dust, or inorganic scales. This leads to reduced power generation, increased downtime, and additional maintenance costs.

Some of these issues are currently being exacerbated by global warming. Cooling water normally comes from a natural body of water. After removing thermal energy from the system, the water is pumped back to the water source at warmer temperature, which is restricted by environmental laws. As temperatures in rivers and seas increase due to global warming, plants are noticing a gradual reduction in the cooling margin, which may reach critical levels in specific geographical areas during hot seasons of the year. In this context, fouling in the cooling circuity exchangers becomes even more relevant, leading to reduced production and even shutdown. As a result, adequate monitoring and prediction of the remaining cooling margin is becoming increasingly important to minimise undesired downtime.


Many food factories, and particularly those producing dairy products, undergo fast fouling build-up, leading to operational issues in a matter of days or even hours. In these processes, energy efficiency and operational issues, common to other industries, are accompanied (sometimes even dwarfed by) health-related considerations. Here too, advanced monitoring tools can help improve the process efficiency and economics.


Food processes are inherently prone to fouling as a result of the raw materials involved. Proteins, fats, or colloids are precursors that very easily deposit on heat transfer surfaces. The fast formation of fouling requires very frequent cleaning of the heat transfer equipment. As opposed to other industries, energy consumption may not be the main driver for taking actions. Other important considerations, such as avoidance of microbial growth or cross-contamination (in multi-product plants), play a major role in the decision-making.

Examples of food processes undergoing severe fouling are milk factories (and milk derivatives), breweries, or sugar factories. Although fouling management and cleaning optimisation is highly constrained, these industries tend to “overclean” to be on the safe side, leaving room for improvement. Advanced monitoring can help adjust the cleaning cycles depending on feeds processed by accurately characterising the current condition and quickly reacting to any unexpected event. Predictive maintenance optimisation can help plan ahead, capturing trade-offs such as cleaning methods (mechanical cleaning, cleaning-in-place or CIP, etc.), duration of cleanings, time frequency, or operating costs.


Fouling is a complex and multi-faceted problem that can have significant impact on the performance, efficiency, and economics of biofuel production. For example, fouling in bioethanol plants can lead to costs in the range of $1.5 – 5 MM/yr and additional emissions of 7 – 25 kton CO2/yr, according to estimations performed by Hexxcell for an average-size plant.


Fouling in in biofuels production plants occurs as a result of the accumulation of impurities, organic matter, microorganisms, and/or inorganic deposits on surfaces of process equipment. This buildup can have detrimental effects on heat transfer efficiency, flow dynamics, and overall system performance. In particular, bioethanol plants suffer the effects of fouling in a number of ways:

  • Reduced heat exchange performance resulting in worsened heat integration between units
  • Higher pressure drops
  • Reduced Ethanol yield
  • Damaged units (erosion)
  • Plugging of tubes and trays
  • Products potentially unable to meet specification
  • Increased energy consumption in the dryer

Multi-effect evaporators, heat-integrated with the beer-column and its reboiler, have been identified as the pieces of equipment where fouling has a greater impact, requiring very frequent cleaning; other heat exchangers, such as the mash cooler, beer column preheater or the fermenter cooling exchanger, also suffer the effects of fouling, although its impact is noticed over longer time periods (several months).

According to Hexxcell’s estimations, fouling in those units may lead to additional costs of $1.5- 5 MM/yr, additional water use of 30 – 90 kton/yr and additional CO2 emissions of 7 – 25 kton/yr for an average capacity plant. The application of Hexxcell’s technology could help cut these costs by 20-40%. Based on U.S. metrics, this translates in a 0.5 -2 CI score reduction.

Pulp & Paper

Fouling is a common issue in pulp and paper plants, where it can have a significant impact on the efficiency and performance of process equipment. Energy intensive processes, such as black liquor production and evaporation, are particularly affected by the gradual reduction in heat transfer efficiency.


Fouling occurs when unwanted materials, such as wood fibers, dirt, and chemicals, accumulate on the surfaces of heat exchangers, boilers, and other process equipment. This buildup can lead to decreased performance, increased operational costs, and reduced overall plant’s profitability. Other undesired consequences are decreased process yields and product quality, which can result in the need to reprocess the product, leading to further operational costs. In addition to reducing efficiency, fouling can also increase downtime for cleaning and maintenance.
This can be costly in terms of lost production and labour costs, as well as potential damage to equipment.

The problem is particularly relevant in energy-intensive processes. An example is black liquor evaporators, where fouling due to deposition of organic (lignin, fibres, etc) and inorganic (calcium, sodium or aluminium silicate scales) form rapidly after the dry-solids content go above 50%. Black liquor requires a minimum of 75-80% dry solids to meet the desired specifications. As a result, fast deposit build-up is almost inherent to the process. Accurate monitoring and predictive tools can indeed help optimise the management of fouling and cleaning cycles.