August 2025

Maintenance, Reliability and Inspection

A techno-economic overview of fouling in steam crackers and available solutions

IP: 10.9.227.195

The fouling of petrochemical manufacturing facilities is well documented as negatively affecting plant throughput, energy requirements, environmental footprint and product quality. Studies indicate that process fouling within heat transfer equipment costs some industrialized countries as much as 0.25% of their gross national product. According to a Lund University study, in 2020, direct greenhouse gas (GHG) emissions from the petrochemical sector amounted to 1.8 gigatons of carbon dioxide equivalent (Gt CO2 eq), equivalent to 4% of global GHG emissions.¹ 

Fouled convection sections can increase GHG emissions and create safety hazards. A strong case can be made for highly efficient fouling removal techniques, both from financial stakeholders looking for maximum carbon reduction and external bodies— including government regulators and consumers—pushing for energy efficiency and safety. 

This article examines the causes and effects of fouling in petrochemical manufacturing plants. Ethylene production via steam cracking relies on complex plant equipment and high-energy chemistry and has vulnerabilities in the plant's convection section and other parts. This work provides a valuable model for studying the effects of fouling and the benefits of efficient fouling removal.  

Key findings and conclusions include: 

• Ethylene is a major chemical industry building block, and many new plants are being constructed to meet demand. The key technology for ethylene production is via the steam cracking of naphtha or ethane.  

• The energy intensity of an ethylene cracker is such that a 50°C (122°F) increase above design stack temperatures, as witnessed in a fouled furnace convection bank, can result in an efficiency loss of 1.5%–2%.  

• For a plant section with five furnaces in operation, it is estimated that in the 3 yr after a robotic clean, a cumulative savings of $5.44 MM is possible; as the average cost per furnace is moderate, payback of the initial investment would be within several months (FIG. 1). 

FIG. 1. Cumulative savings from robotic cleaning of a fouled convection bank. Basis—Furnace convection bank fired duty: 109 MW; five cracking furnaces; stack design temperature: 149°C (300°F); actual stack temperature: 199°C (390°F); efficiency loss: 1.86%; and fuel cost: $23/MWh. 

• In certain instances, fouling can cause a reduction in ethylene plant productivity. A 5-d to10-d equivalent throughput loss during an unplanned shutdown can result in $14 MM–$28 MM in lost revenue at an ethylene price of $1,000/t (FIG. 2). If fouling exists in the integrated polymer production sites, the problem compounds, creating even more considerable margin losses for the finished consumer products. 

FIG. 2. Lost revenue for ethylene production via steam cracking. Reduced plant throughput-financial analysis basis: 1 MMtpy capacity; 90% target operating rate (324 d/yr onstream); ethylene prices of $500/t, $750/t and $1,000/t. Source: Enabled Future Ltd. 

• Many existing mechanical, chemical and hydroblasting fouling removal methods fall short of their possible full cleaning potential. The task of efficient fouling removal is painstaking, repetitive and requires high accuracy. The Industry 4.0 (smart manufacturing) robotic approach performs well in other sectors with similar requirements.  

• The author’s company develops custom robotic solutions for fouling remediation and removal where other techniques struggle or have failed. Its robots are equipped with proprietary delivery systems and record in real-time before, during and after fouling removal. These robots are specifically designed to remove > 90% of deposits from tube and fin surface areas back to original equipment manufacturer (OEM) design performance from areas with restricted access, producing minimal waste and achieving close contact cleaning with precision and uniformity. 

The cost of fouling. Fouling profoundly affects the operation of a manufacturing plant, dragging down its efficiency, throughput, profits and environmental footprint. It leaves the operation susceptible to emergency and even catastrophic shutdowns, a dramatic reduction in production and an incremental increase in incidents.  

The fouling of heat transfer equipment is inevitable when producing chemicals, fuels and power. Fouling negatively impacts plant economics and environmental performance and causes safety hazards. Various attempts have been made to quantify fouling costs.^2–6 While there is not yet a comprehensive industry study in the public domain, top-line statistics present a compelling case to reduce or avoid fouling altogether:  

• 1%–5% of the energy consumed by the industrial sector is used to overcome fouling 

• 2.5% of CO2 emissions (0.8 Gt) are caused by fouled heat transfer equipment, accounting for 3%–10% of an individual plant’s carbon footprint.  

• Fouling and the inability to clean preheat train exchangers, especially on the external shell side, can lead to a decline of as much as 12°C (54°˚F) in furnace inlet temperature. Therefore, the subsequent need to burn extra fuel results in higher costs and an increase in CO2 emissions of > 20%.   

Fossil fuels are under more scrutiny than ever, given the evidence that GHG emissions are causing an increase in global air temperatures, subsequent climate change and adverse weather events. Legislation and voluntary measures are continually being developed to tackle GHG emissions. More than 190 countries have signed the Paris Agreement to limit global warming to 1.5°C above pre-industrialized levels. Each country has pledged to set out a plan for GHG reductions (intended nationally determined contributions) to be enacted within the next decade. 

Punitive measures in the form of carbon taxation, fines and loss of investment all await industries that do not react to remedy the situation. Activist investors are demanding improved economic, environmental and safety performance from businesses engaged in the production and use of fossil fuels. Recently, several high-profile investors have pulled out of these assets altogether. Companies active in the fossil fuels’ supply chain must carry out process intensification and improvements to meet the expectations of their stakeholders and avoid penalties. Addressing fouling in the most cost-effectively and efficient way has never been more important.  

The cleaning process. There is a range of fouling removal methods for heat transfer equipment and chemical reactors. Some specialist measures for ethylene plants include protective coatings and anti-foulants. These compounds, however, have failed to prevent coking and fouling of transfer line exchangers (TLEs) immediately downstream of the furnace. The failure concerning TLEs may be due to premature degradation of the treatments in the ethylene furnace, which sees temperatures in the range of 538°C–927°C (1,000°F–1,700°F).  

Cleaning maintenance contractors vary from small local companies with straightforward mechanical and hydroblasting methods to larger, more sophisticated companies with several de-fouling methods in their portfolio. Many manufacturing plant operators tend to operate on a fixed budget, even if this means a less than complete removal of fouling rather than opting for an expensive but more thorough approach. In the long term, this does not make economic sense. Even a fraction of a per cent deviation in planned output results in millions of dollars in decreased revenue. This is even before the costs of additional energy costs, reduced equipment lifetime, higher capital expenditures (CAPEX), and the potential for safety issues or incidents are considered. Ideally, operators would choose a plant cleaning method that ensures that no additional plant slowdown, shutdown or loss of yield, attributable to fouling, occur.  

Such an approach requires a top-down management strategy rather than a siloed approach, which penalizes the maintenance department for having a higher cost structure. 

The difficulty here is that the term “clean” is subjective. How clean is clean? With no descriptor or mandate such as an American Petroleum Institute (API) document to guide plant operators, it inevitably falls back to a slightly misguided philosophy of “it’s been done this way for so long, so why change?” philosophy. 

One such “out of sight, out of mind” asset are the horizontal convection banks that sit above the vertical radiant tube section. Methods typically used to remove fouling from deep within each finned convection bank—which can consist of up to 12 rows of bare, finned or studded tubes—include relatively crude approaches such as mechanical and abrasive blasting techniques, which are slow, messy, hazardous, and can cause wear and risk damage to equipment.  These techniques tend to miss > 20% of the foulant when applied in isolation due to their inability to remove fouling from all finned heat transfer tubes. 

The manual spray injection of chemicals can remove greater proportions of foulant than mechanical techniques, but as they take the least path of resistance, efficacy cannot be measured until after the unit is back in service, which is not ideal. Manual spray injections also rely on organic chemicals and solvents that pose challenges with emissions of volatile organic compounds (VOCs), reducing the ability to ensure that worker exposure is kept to legislated limits and the need to comply with tightening toxic substances legislation [i.e., the U.S. Toxic Substances Control Act (TSCA) and the European Directive on the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH)]. 

The use of cryogenic substances such as solid CO2 (dry ice) offers the benefits of being safe with ventilation and having a zero secondary waste profile. The downsides are the expense of the cryogen, which requires gas separation processes and refrigeration techniques with high utility requirements, and the fact that neither can clean past the first two rows of a convection bank. 

The use of manual high-pressure water blasting lances is a commonly employed technique offered by both smaller and larger contractors. The downside is that it is carried out manually and is a line-of-sight (LOS)-only technique where incidents of refractory damage have been inadvertently caused by operator carelessness or fatigue. Deposits mixed with water cascade down between tube rows creating a mud-like paste that cements itself after run-off. The pressure of the water and contact with the equipment can be less than uniform; and, as with manual dry ice and chemical methods, this method is only able to deliver its pressure to the second tube row at best. Tube and insulation damage have occured, as well as under-scale corrosion due to aggregate formation, as the water reacts with the foulant. Hydroblasting generates high volumes of wastewater that may be classified as hazardous, increasing the expense of disposal. 

The use of pre-programmed robotics (FIG. 3) offers a safer step-change improvement over more mature manual lancing systems. Customized robots can reach > 95% surface area cleanliness of convection banks between every tube row, regardless of fouling levels, with cleaning standards verified using real-time digital video capture.  

FIG. 3. The author’s company’s robotic cleaning technology.  

The author’s company is the only service globally offering such robotic cleaning systems. Its robots use proprietary lance and nozzle technologies, achieving very close tube surface contact in situ. The versatile robots are used with air and high-pressure water. While very high pressures are involved [e.g., up to 1,000 bar (15,000 psi)], the total volume of water is much lower than in standard hydroblasting. 

There is minimal risk of refractory damage as the rotary jet on the lance is specifically angled towards the finned tubes. The robot has sensors programmed to stop prior to the refractory wall. The water absorption rate during the robotic cleaning service has been examined in a collaborative report based on trials around the world.  

ETHYLENE CASE STUDY  

Ethylene value chain. Ethylene is a major building block of the chemical industry (FIG. 4); it is an intermediate product that is highly reactive and serves as a key feedstock for several high-revenue chemicals. These chemicals have complex value chains comprising unique technologies with many processing steps. Key ethylene derivatives include polyethylene (PE), polyethylene terephthalate (PET) and polyvinyl chloride (PVC), as well as a broad range of specialty chemicals. Virtually every industry contributing to gross domestic product (GDP) growth relies on products derived from an ethylene-based chemical. Global ethylene capacity was 223.86 MMt in 2022 and is expected to grow at an annual average growth rate of > 6% from 2022–2027.7 Millions of tons of new ethylene capacity are being built to meet this demand. 

FIG. 4. The ethylene chemical value chain. Source: Enabled Future Ltd. 

Ethylene manufacturing via steam cracking. An ethylene plant is a multi-billion-dollar complex; the steam cracker is the central processing unit, but it is embedded in a flow sheet containing more than 300 individual units operating at temperatures from –73°C to 2,012°C (–100°F to 1,100°F). The major functions of the different plant sections are to clean and prepare feedstocks for conversion; remove toxic elements such as sulfur; separate component gases which are not required for the cracking reaction but have value elsewhere; heat and pressurize feedstocks to reaction conditions; perform cracking chemistry; and separate the product mixture into single components, compressed and delivered as pure high-pressure streams. The plant’s output amounts to millions of dollars of product every day, and it is of paramount importance to avoid the erosion of margins due to process inefficiencies.  

The ethylene production process entails the use of pyrolysis or cracking furnaces to produce ethylene from various gaseous and liquid petroleum feedstocks. Typical gaseous feedstocks include ethane, propane, butane and mixtures thereof (FIG. 5). These chemicals are referred to as saturated hydrocarbons: carbons saturated with hydrogen (H2). The cracking reaction removes some of the H2 and produces unsaturated hydrocarbons (olefins). Typical liquid feedstocks include naphtha, kerosene, gasoil and crude oil. Product slates vary by feedstock. Ethylene from ethane is the simplest process with the highest yields of ethylene and the fewest byproducts. European and Asian feedstocks are typically mixed feeds of heavier streams (naphtha, gasoil and kerosene). Such processes using liquid feedstocks have a lower yield, but a wide range of valuable byproducts. 

FIG. 5. Typical feedstock yields for the steam cracking process.⁸ 

The chemical bonds are strong and cracking them open takes considerable energy. The resulting free-radical species are highly reactive and undergo rapid reactions to regain stability. Free radical chemistry occurs in three stages: initiation, propagation and termination. The key primary reactions for ethane cracking are shown in FIG. 6. Further secondary reactions (not shown) occur that result in products with longer carbon chains and coke.  

FIG. 6. The key primary reactions for ethane cracking. 

Steam cracker plants have three broad sections (FIG. 7):  

1. The radiant section, where heat transfer relies more on radiation 
2. The convection section  
3. The TLE.  

FIG. 7. Simple flow diagram of a typical steam cracker facility.⁹ 

Steam serves the dual purposes of lowering hydrocarbon partial pressure, which increases the yields of primary products (ethylene and propylene) and reduces coke formation.  

After the furnace, the effluent passes through the TLE where it is initially cooled to between 204°C and 315°C (400°F and 600°F). Further cooling then occurs in the quenching tower or the primary fractionator. After sufficient cooling, the stream must be compressed before being fractionated into the various products. Compression is usually performed with interstage cooling and temperature control to keep the cracked gas below 100°C (212°F) to prevent the olefin product from reacting (i.e., polymerization) and causing equipment fouling. On specification, ethylene and byproducts are either integrated into downstream chemical production or sold via pipeline or compressed freight.  

Today, a greenfield ethylene facility requires a total fixed investment of billions of dollars. Within this footprint, thousands of individual pieces of equipment can become fouled, and the combined effect on the process economics is considerable. 

Ethylene plant technology is mature but subject to continuous incremental improvements. Licensor agreements with producers often govern the maintenance of steam crackers until a specific production milestone is achieved. A key technology development of late has been to increase the scale of steam crackers up to 1 MMtpy–1.5 MMtpy, thereby rendering older, smaller ethylene plants less competitive due to economies of scale and bringing a focus on debottlenecking, improved process maintenance and integration into key product slates and grades to remain competitive. Improved fouling removal procedures play a key role. 

Ethylene plant fouling. Fouling in petrochemical plants can occur in reactors and other process units, process lines, compressors, pumps and heat transfer equipment. There are thousands of individual pieces of equipment in an ethylene plant that can become fouled. Various mechanisms are involved. Due to high temperatures, the cracking of hydrocarbons can lead to free radicals, which react to form coke, which partially and completely blocks tubes and process lines. Emulsions are also a major nuisance in steam cracking plants. They form due to mixing between lighter hydrocarbons and polymerized materials, which meet in the quench tower and separator. Emulsions can pass through process lines and transfer from one unit to another, causing all kinds of disruptions (e.g., from pressure drop to off-spec products). Other fouling processes include chemical reactions, biological processes, crystallization, corrosion, particulate build-up (sedimentation), precipitation and metal salt accumulation. Each of the main fouling issues is outlined below:  

• Gas-side fouling. Gas-side fouling of finned tubes in a convection section can be attributed to several factors. Primarily, it is caused by the deposition of particulates present in the fuel gas. These particulates can be dust, particles of ceramic fiber or other contaminants. Additionally, chemical reactions within the gas can lead to the formation of compounds that adhere to tube surfaces. Over time, this build-up reduces heat transfer efficiency.  

• TLEs. TLEs are usually shell-and-tube exchangers but other designs—including horizontal and vertical tubes or concentric tubes—are also possible. Fouling is caused by condensation and coke formation. Corrosion also occurs due to the accumulation of boiler feed water (BFW) solids, leading to a pH level that is high enough to penetrate the protective magnetite layer.10 Anti-fouling treatments such as amine neutralized sulfonates employed in the furnace coils can protect TLEs to a certain degree but are insufficient, especially for TLEs located just downstream of the furnace.¹¹ The failure of the TLEs may be due to premature degradation of the treatments in the ethylene furnace which sees temperatures in the range of 535°C–935°C (900°F–1,706°F).  

• Gas compressors. Fouling can occur on the balance drum and discharge lines, diffusers, inlet guide vanes and labyrinths seals between the wheels. The effect is gas leaking, increased polymer and emulsions formation, and knock-on fouling in the quench system and the fractionation towers.¹²  

• Dilution steam system (DSS). In an ethylene plant, fouling in the DSS creates many difficulties, including increased steam consumption, reduced efficiency, increased wastewater costs, reduced pygas yields and unplanned downtime for cleaning.¹³ 

• Quench water and quench oil systems. Fouling in quench systems is common and is caused by high pour-point material build-up. It is especially problematic in gas-based crackers because there may not be a quench oil tower which would otherwise remove coke fines and tars.¹⁴ Additional measures such as the fitment of redistillation units are required. These separate out and route lower pour point hydrocarbons back into the quench tower to moderate the pour point. This adds to the plant’s CAPEX, operational expenditures (OPEX) and maintenance requirements. 

• Cracking furnace coils. Coking is to be expected when hydrocarbon molecules are being smashed at high temperatures and pressures where free radical reaction mechanisms are operating. It is further promoted by impurities (e.g., sodium, nickel, iron oxide) in naphtha feed streams but also forms due to reactions at the tube surface. Heat flux resistance and pressure drop due to coke build-up necessitate a decoking exercise at some point. Excessive coking in the furnace coils leads to a need for more frequent decoking cycles, increased particulate waste inventory, reduced operating rates, lower product yield, shortened furnace life and higher maintenance costs.¹⁵ 

• Fractionation trains. Depending on plant configuration, polymer build-up in the de-ethanizer and de-propanizer causes bottlenecks, which are exacerbated by acetylene feed impurities. This can result in a severe capacity loss due to premature flooding, high tower pressure drop, abrupt and severe tower bottom level reductions during furnace feed slate switches, separation efficiency reduction such as high concentration of heavy components in the pygas, and difficulties controlling quench oil viscosity. 

There are numerous mechanisms by which fouling can prevent an ethylene plant from running smoothly. Controlling fouling is a time-consuming and expensive endeavor. 

Planned shutdowns for each unit vary widely from months to years, meaning that fouling can build up in certain areas. Workarounds are employed to avoid accelerating the maintenance schedule, effectively patching a problem rather than solving it—this is far from ideal. In the next section, the economic downside potential from fouling in a gas-fed cracker is considered.  

Financial losses due to fouling. The effects of fouling on ethylene plants’ cash cost of production and CAPEX are typically considered in five key areas:  

1. Maintenance costs: Increased costs due to planned and unplanned maintenance due to fouling. 
2. Energy costs: Fouling increases energy costs due to reduced heat transfer efficiency. 
3. Yield: Fouling affects conversion of feedstock in the steam cracker. 
4. Annual operating rate: Unplanned downtime, leading to falling behind on the production plan operating target set by market conditions. 
5. Total CAPEX (total fixed investment): Equipment overdesign to account for fouling. 

Each of these areas directly impacts the cost of production. The most significant issues are those that impact the energy requirements of the plant—e.g., utility costs and the total plant output (i.e., loss of yield or operating rate). 

Financial costs of heat exchanger inefficiency. An ethylene plant requires a vast amount of energy for its operation. A mega-scale cracker (> 1 MMtpy) has a heat requirement of > 5,000 kWh/t of ethylene. As a result, the heat transfer efficiency in the plant is of paramount importance.  

As shown in FIG. 8, a typical case might be a cracking furnace with a fired duty of 109 MW, which has a design stack temperature of 149°C (300°F). After several years, the stack temperature increased by 50°C (122°F) to 199°C (390°F). The efficiency loss is 1.83%. This means that at a fuel cost of €20/MWh ($23.20/MWh), the fuel consumption in this furnace is increased by 4 MW, equalling a fuel cost of €323,303/yr ($375,000/yr) for just one furnace. If the plant has five furnaces in operation, this adds up to €1.61 MM/yr ($1.87 MM/yr). This loss of efficiency can easily be avoided by adopting a cleaning and maintenance regime that returns the plant back close to design conditions. Efficiency loss can be avoided by robotic cleaning of the convection section, which has a payout of < 1 yr. Based on the date model employed here, over a 3-yr period after the clean, approximately €4.69 MM ($5.44 MM) can be saved in OPEX (FIG. 8).   

FIG. 8. Cumulative savings from robotic cleaning of a fouled convection bank. Basis—Furnance convection bank fired dury: 109 MW; five cracking furnaces; stack design temperature: 149°C (300°F); actual stack temperature: 199°C (390°F); efficiency loss: 1.86%; and fuel cost: $23/MWh (€20/MWh). 

Ethylene plant throughput costs. If the costs of energy losses in a fouled plant seem dramatic, those associated with downtime and loss of product revenue are far more significant. Ethylene plants are designed to operate at least 8,000 hr/yr. FIG. 9 shows the sensitivity of revenue loss due to loss of throughput (shown as days of operation slowdown equivalent) and lowered operating rates. This is based on a 1-MMtpy plant with a planned average annual operating rate of 90%, with three different ethylene prices ranging from $500/t–$1,000/t. In these scenarios, even a 5-d equivalent slowdown due to fouling results in losses between $7 MM and $14 MM. 

FIG. 9. Lost revenue for ethylene production via steam cracking. Reduced plant throughput financial analysis: 1 MMtpy, 90% target operating rate (324 d/yr onstream), and ethylene prices of $500/t, $750/t and $1,000/t. 

At historical average U.S. ethylene prices of $750/t, a plant would lose approximately $10 MM in revenue for 5 d of lost throughput compared with the planned 90% operating rate. For a 10-d loss at the same ethylene price, the plant would lose $21 MM. Prices of ethylene of more than $1,800/t have been witnessed over the last decade in the European region and $1,500/t in the U.S.16,17 Even at a conservative value of $1,000/t, 10 d of lost throughput starts to push the loss of revenue towards $30 MM. 

FIG. 9 shows the lost revenue or ethylene prodction via steam cracking. The reduced plant throughput-financial analyis basis details are: 1 MMtpy; 90% target operating rate (324 d/yr onstream); ethylene prices of $500/t, $750/t and $1,000/t.  

Fouling throughout a petrochemical complex—with downstream PVC, PET and polyolefin units—would cause compounding economic effects on the facility’s economics and squeeze finished product margins to an even greater degree. The effects in a large oil refinery, where daily revenues are in the order of tens of millions of dollars, is an order of magnitude higher than in an ethylene plant. 

The losses described even at the lowest end, for the cheapest ethylene price, far outweigh the costs of a deep clean using the most advanced methods available. Strategically, manufacturing plants would see improved financial performance if they viewed such costs as a part of their overall plant economics, rather than simply a part of the maintenance budget, with pressure to reduce such costs year-over-year. 

Takeaways. Fouling within manufacturing plants places a considerable burden on performance. Loss of production wipes millions of dollars in revenue from the bottom line, creating supply shortages and safety hazards, and exacerbating a plant’s negative environmental and CO2 footprint. With ever-increasing pressure on energy and chemical-producing sectors to become more environmentally friendly, efficient fouling mitigation and removal methods are increasingly important. The existing paradigm and historical mindset of seeing cleaning as a cost within the maintenance department rather than an investment opportunity—which over time will greatly increase the financial performance of the organization—create a roadblock to the adoption of modern techniques and innovation that must be addressed and overcome. Investors are more environmentally conscious and are switching their funds from businesses involved in the production and use of fossil fuels to those with more sustainable activities. Even now, global refining groups have linked bonuses with CO2 reduction incentives.  

Many manufacturers have announced time frames whereby inefficient and hazardous human entry is to be replaced with robotics. Therefore, it is imperative that companies in the oil and gas and petrochemicals sectors immediately demonstrate to the financial markets their commitment to eliminate process inefficiencies caused by fouling of heat transfer equipment and reactor units. 

A range of fouling removal techniques are available, but each has its place. However, the use of robotics for precise, fast operation and avoidance of human labor in hazardous environments is consistent with the manufacturing sector’s move towards Industry 4.0/smart manufacturing approaches. Gains will be made in financial performance, reliability and environmental terms, as robotics are increasingly providing the most promising method for maximum process efficiency. In the future, it will be possible to install access for a robotic cleaning system as a permanent feature in the plant, built in from its first day of operation and ensuring constant housekeeping to prevent heavy fouling from ever forming. Companies that lead the way in adopting Industry 4.0 cleaning technologies that involve robotics, zero and minimal waste techniques combined with monitoring, measuring and recording of performance can expect to rank in the top percentile as they improve their competitive advantage globally and avoid future penalties on energy consumption.  

ACKNOWLEDGMENTS  

The author would like to thank Dr. Michelle Lynch, Enabled Future Ltd., for technical writing and techno-economic analysis; and Khevna Naran, 108 Blocks, for technical writing and chemical engineering.   

LITERATURE CITED  

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2 IHS Markit, “Heat exchanger fouling,” ESDU Case Study, online: https://www.esdu.com  

3 Pugh, S. and E. Ishiyama, “Managing fouling in refinery networks,” Digital Refining, July 2015.  

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5 Statista, “Global GDP at current prices from 2012–2022 (in billions USD),” online: https://www.statista.com/statistics/268750/global-gross-domestic-product-gdp/  

6 Garrett-Price, B. A., S. A. Smith, R. L. Watts and J. G. Knudsen, Fouling of heat exchangers: Characteristics, costs, prevention, control and removal, Noyes Publications, Park Ridge, New Jersey, 1985. 

7 GlobalData, “Ethylene industry installed capacity and capital expenditure forecasts, including active and planned plants to 2027,” GlobalData, 2023. 

8 Gonzalez, B., “The impact of Saudi ethane price increases on competitiveness,” S&P Global, 2016, online: https://www.spglobal.com/commodity-insights/en/news-research/blog/chemicals/011916-the-impact-of-saudi-ethane-price-increases-on-competitiveness  

9 Rosli, M. N. and N. Aziz, “Simulation of ethane steam cracking with severity evaluation,” IOP Conference Series: Materials Science and Engineering, Bandung, Indonesia, October 2016. 

10 Robinson, J. O., “Avoiding waterside corrosion problems in ethylene plant steam systems,” AIChE Spring Meeting and Global Congress on Process Safety, March 31, 2014. 

11 Kisalus, J. C., “Method for reducing fouling in ethylene cracking furnaces,” European Patent EP0391620B1, 1989, online: https://patents.google.com/patent/EP0391620B1  

12 Snider, S., “Ethylene plant cracker gas compressor fouling,” AIChE Spring National Meeting, EPC Conference, Houston, Texas, 2006.   

13 Pall Corp., “Ethylene processing: Dilution steam system,” 1997, online: https://www.pall.com/content/dam/pall/chemicals-polymers/literature-library/non-gated/HCP-24.pdf  

14 Dork Ketal, “Effective, economical emulsion and fouling control for ethylene plants.” 

15 Brayden, M, T. H. Wines and K. Del Guidice, “Improve steam cracking furnace productivity and emissions control through filtration and coalescence,” Pall Corp. Fuel and Chemicals, 2006, online: https://www.pall.com/content/dam/pall/chemicals-polymers/literature-library/non-gated/GDS138.pdf  

16 Waldheim, J., “US ethylene spot prices fall to nine-year low,” ICIS, March 20, 2018, online: https://www.icis.com/resources/news/2018/03/20/10204214/us-ethylene-spot-prices-fall-to-nineyear-low/  

17 Weddle, N., “Chemical profile: Europe ethylene,” ICIS, May 10, 2013, online: https://www.icis.com/resources/news/2013/05/10/9667019/chemical-profile-europe-ethylene/   

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