White Paper Heat Exchanger Fouling Mitigation Facing a squeeze on margins and worries about carbon emission legislation, most refiners are very focused on running as efficiently as possible. The drive for efficiency has led some to install new automation systems and examine their manufacturing processes. Many are also paying close attention to something else: their heat exchangers. Heat exchanger fouling — the build-up of dirt deposits on the metal surfaces of heat exchangers — is a critical and growing problem for refiners. Fouling in PetroChem plants is a major economic and environmental problem worldwide. Estimates have been made of fouling costs as high as 0.25% of the gross national product (GNP) of the industrialized countries. Many millions of tonnes of carbon emissions are the result of this inefficiency. Crude oil fouling in oil refineries is the single biggest industrial fouling problem. Costs associated with refinery pre-heat train fouling worldwide are estimated to be of the order of $4.5 billion. There has never been a better opportunity to capture the cost and operational benefits of cleaner processing. And, as extracted crudes become heavier and dirtier and buyers chase lower-cost heavy “opportunity crudes”, operators should prepare for the challenges this increased fouling potential will bring.
Transcript
White Paper
Heat Exchanger Fouling Mitigation
Facing a squeeze on margins and worries about carbon
emission legislation, most refiners are very focused on running
as efficiently as possible. The drive for efficiency has led some to
install new automation systems and examine their manufacturing
processes. Many are also paying close attention to something
else: their heat exchangers. Heat exchanger fouling —
the build-up of dirt deposits on the metal surfaces of heat
exchangers — is a critical and growing problem for refiners.
Fouling in PetroChem plants is a major economic and environmental problem worldwide. Estimates have been made of fouling costs as high as 0.25% of the gross national product (GNP) of the industrialized countries. Many millions of tonnes of carbon emissions are the result of this inefficiency.
Crude oil fouling in oil refineries is the single biggest industrial fouling problem. Costs associated with refinery pre-heat train fouling worldwide are estimated to be of the order of $4.5 billion.
There has never been a better opportunity to capture the cost and operational benefits of cleaner processing. And, as extracted crudes become heavier and dirtier and buyers chase lower-cost heavy “opportunity crudes”, operators should prepare for the challenges this increased fouling potential will bring.
Economic and EnvironmEntal imPactSThe huge costs associated with fouling in crude pre-heat exchangers are categorised as follows:
Energy costs and environmental impact. This corresponds to the additional fuel required for the furnace due to the reduced heat recovery in the preheat train as exchangers foul. Energy losses due to increased pressure drop (pumping power) may also be significant. The use of more fuel leads to additional production of CO2 with the associated environmental impact.
Production loss during shutdowns due to fouling. If the pre-heat train throughput is furnace-limited, a typical 10% loss of production due to taking a heat exchanger out of service in a 100,000 US barrel/day plant would cost $20,000 per day (assuming $2 per US barrel of marginal lost production). After shutdown, there is an additional cost due to out-of specification production after production is restarted.
Equipment capital expenditure. This includes excess surface area, costs for stronger foundations, provisions for extra space, increased transport and installation costs, costs of anti-fouling equipment, costs of installation of on-line cleaning devices and treatment plants, increased cost of disposal of the (larger) replaced bundles and, finally, the (larger) heat exchangers.
maintenance costs. This includes staff and other costs for removing fouling deposits and the cost of chemicals or other operating costs of anti-fouling devices. There are also economic and environmental penalties associated with disposal of cleaning chemicals after cleaning.
crudE oil Fouling in PrE-HEat train ExcHangErS Crude oil from storage tanks is fed to the heat exchangers of the crude pre-heat train, initially at ambient temperature. The crude oil is then typically heated to around 250°C (480°F) at entry to the furnace. From the furnace, the crude is fed to a distillation column where valuable product streams, such as kerosene, gasoline and gases, are separated and collected.
The most damaging fouling arises from asphaltene deposition from the crude oil onto the metal surfaces of the pre-heat train hot end heat exchangers. This fouling leads to a decline in furnace inlet temperature by perhaps as much as 30°C (54°F), and a subsequent need to burn extra fuel in the furnace to make up the temperature necessary for efficient distillation. Fouling also causes a significant decrease in the crude unit throughput, cutting production.
FactorS inFluEncing Fouling Fouling in refineries and petrochemical plants is a function of many variables. Factors affecting fouling in crude oil pre-heat exchangers include process conditions (temperature, pressure, flow rate), exchanger and piping configuration, crude oil composition, corrosion and inorganic contaminants. Effective control of these variables may minimise fouling in crude oil units.
Experimental studies have shown the existence of “fouling thresholds” for chemical reaction (asphaltene) fouling in
particular crudes and crude blends. These thresholds are both temperature and velocity dependent. Given the existence of fouling thresholds it was possible to develop EXPRESSplus™ for heat exchanger design.
imProving Plant modElling and PrEdiction Chemical reaction fouling is essentially dynamic in nature but the design of heat transfer equipment is often still based on the summation of time-independent resistances to heat transfer (such as the TEMA values). Although the TEMA tables were originally only considered to be rough guidelines for heat exchanger design, they are unfortunately often treated as
FrEquEntly aSkEd rEFinEry oPEration quEStionS• What is the most cost-effective maintenance/cleaning
strategy if we operate the refinery with similar throughput and average API?
• What effect will running heavier crudes have on maintenance?
• Can we flag severe fouling events in real time, or even predict and prevent?
• What can we save in capital, maintenance, energy, CO2 if we re-engineer heat exchangers or change plant piping payout? Does this justify the project?
• Are there any benefits in using alternative heat exchanger types or install tube inserts? How big are those benefits?
• What happens if we switch the crude from tube-side to shell-side in heavily fouling heat exchangers?
• We use anti-fouling chemicals – what are they saving us?
• We want to use anti-fouling chemicals – what could they save us?
accurate values. This may cause considerable errors, not least because the transient character of the fouling process is neglected. Conditions in initially over-designed heat exchangers often promote deposition, thus making fouling a self-fulfilling prophecy.
The application of dynamic fouling methods in EXPRESSplus™ illustrates that, with reliable plant monitoring data, it is often possible to either design heat exchangers with much reduced or even no fouling or identify cases where mitigation devices might be essential.
Unfortunately, reconciled data that are inferred from sparse measured monitoring data are often in error due to the approximate heat exchanger models in conventional software. These data are then used to make various operational decisions and can lead to significant errors. By incorporating the rigorous heat exchanger technology of EXPRESSplus™ into smartPM™ and running in data reconciliation mode, more reliable temperatures can be then reported to the plant operator to enable better decision making.
For the exchanger designer or process engineer exploring better exchanger designs for lower fouling, EXPRESSplus™ generates “parameter plots” that illustrate graphically the constraints on overall thermal duty, pressure drops, bundle vibration and acceptable tubeside velocities are met. A further constraint represents the fouling threshold. EXPRESSplus™ allows the designer to identify exchanger geometries in which fouling is likely to be minimised and then provides operability information on the performance of that geometry, including fouling propensity, under various operating conditions.
The advantage of using the EXPRESSplus™ program for investigating design is that the designer obtains a visual guide on the effect of making particular changes similarly it is possible to investigate the effects of changes of operating conditions and modification on fouling thresholds.
rEducEd Fouling HitS tHE bottom linE – imProvEd marginSincreased capacity – Most refineries know what pre-heat train fouling is costing them. For example, at one refinery in France the increase in effective on-stream time due to reduced fouling/cleaning was about 10 days/yr, which translates to about 3% extra production. Even at modest refinery margins, the revenue improvement is huge. Another UK refinery estimates a direct fouling cost of £2-3 million per annum in lost throughput due to firing constraints alone.
Energy cost savings – Reduced fouling rates mean higher average Furnace Inlet Temperatures, which means lower fuel use in the reboiler (fired heater) and lower emissions. Savings in the use of non-reusable fuel will result in the reduction of CO2. The refinery may benefit from either selling or banking its carbon (GHG) emissions credits. Emissions from a fired heater can increase by over 20% as extra fuel is burnt to make up the loss of heat recovery.
maintenance cost reductions – Reducing the frequency of heat exchanger cleaning through ‘smarter’, targeted cleaning scheduling can yield very significant cost, operational and safety benefits. Many refineries today use simplistic scheduling that misses opportunities to improve effectiveness whilst reducing costs.
caSE StudyFrench oil company Total revamped one of their refinery crude distillation units to improve efficiency. Soon after the plant restarted, it was clear that due to the application of conventional design methods the preheat train was experiencing very heavy fouling. This led to a significant throughput reduction as the furnace bottlenecked. Financial losses were estimated to be around $1.5 million over three months after start-up.
Total decided to implement an in-house study of the problem following methods developed by IHS ESDU in their collaborative research work with Total and other major oil companies. The methods successfully highlighted the rogue exchangers and pointed to retrofit options that were subsequently adopted. Total presented the findings of their study at a major international conference. Total’s paper concluded that the predictions of rogue heat exchangers predicted by the methods were subsequently found to be very close to the true situation. They recommended that designers use the methods, built into the EXPRESSplusTM program, to identify rogue exchangers and identify retrofit scenarios.
Fouling rESEarcHIHS ESDU has been working closely for over 10 years with leading international oil companies and with leading international fouling researchers. The collaboration has led to the development and continual improvement of new techniques and tools for design and operation for the mitigation of fouling. New crude oil fouling analysis solutions were developed by IHS ESDU and incorporated into our graphically-driven heat exchanger design and analysis software EXPRESSplusTM.
Figure 1. Parameter plot from EXPRESS program showing constraints for heat transfer, flow velocity and pressure drops
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EXPRESSplusTM has been applied successfully to numerous pre-heat trains worldwide processing a wide range of crude blends, including heavy opportunity crudes. EXPRESSplusTM is used to track and model the fouling process and identify ways of reducing or even eliminating fouling and reducing the need to clean heat exchangers, usually through retrofit options.
Since 2007, IHS ESDU has facilitated and been the technology transfer partner in the world-leading crude oil fouling research program CROF. This program saw the UK Government research funding body provide over $4 million to the world-leading multi-disciplinary team of engineering, chemical and thermodynamic analysts and experimentalists at the UK’s Imperial College, Cambridge University and Bath University. Now, EXPRESSplusTM is complemented by new, next generation pre-heat train simulation software developed by a team in the Department of Chemical Engineering at Cambridge University and funded within the CROF program.
This simulator – smartPMTM – incorporates the heat exchanger technology within EXPRESSplusTM and uses fouling process physics to optimise preheat train performance and cleaning scheduling for most efficient operation – the first truly ‘smart’ Predictive Maintenance solution for preheat train operators.
iHS ESdu Fouling SolutionSThe ESDU division of IHS offers unique software and services for energy efficiency studies for oil and gas customers. A key area of expertise is fouling of heat exchangers: this is a chronic operational problem with severe negative impacts on cost, safety, health and environment.
IHS ESDU is driving the crude fouling knowledge curve, working with the oil companies and world-leading researchers. The collaboration led to the development and continual improvement through implementation experience of new techniques and tools for design and operation for the mitigation of fouling.
New crude oil fouling analysis solutions developed by IHS ESDU has led to the development of heat exchanger design and analysis and simulation software that has now been applied successfully to numerous pre-heat trains worldwide processing a wide range of crude blends, including heavy opportunity crudes.
The state-of-the art pre-heat train fouling analysis and reduction simulator smartPMTM (smart Predictive Maintenance) was originally developed at Cambridge University. It takes plant monitoring data extracted from the CRM to report past performance and predict future refinery throughput, energy use, emissions and optimum heat exchanger maintenance/cleaning schedules.
The smart technology then allows “what if” scenario planning, for example to assess economic benefits of better heat exchanger design (identified using EXPRESSplusTM); the use of anti-foulant chemicals, or to assess cost and operational penalties through refining new crude blends. Optimum maintenance scheduling can then be reported to Asset Management Software, and historic and future pre-heat train emissions, including quantified forecasts of emission reduction opportunities, can be reported to the IHS Environmental Business Intelligence software.
iHS ESdu SErvicES tEam For EnErgy EFFiciEncy StudiESIHS ESDU has assembled a global consulting team with a range of key skills and experience to identify and resolve a refiner’s fouling challenges. Other key areas of focus in energy efficiency projects include:
• Heat exchanger network optimization for minimum energy use
• Electrical power saving through optimum use of adjustable speed pumps
• Combined heat and power (CHP) system optimization through total site analysis
• Fresh water minimization through optimum wastewater use, and
• Industrial energy performance measurement and monitoring.
Design and operationalparameters
Cost data andoperational strategies smartPM Refining
solutions
Figure 2. smartPMTM pre-heat train fouling analysis and reduction simulator
