Heat Exchanger Fouling Research Articles

Application of machine learning in monitoring fouling in heat exchangers in chemical engineering: A systematic review

AbstractThe present work consists of a systematic literature review that examines studies on using machine learning to monitor fouling in heat exchangers in the chemical engineering area. The research was conducted in four renowned databases: SCOPUS, Science Direct, IEEE, and Web of Science. The main objective of the investigation was to identify the most prevalent machine learning methods, evaluate their performance, and analyze the challenges associated with their implementation and prospects. Using the StArt software, seven relevant scientific papers from the established review protocol. The most frequently identified methods were support vector machine (SVM) and k‐nearest neighbours (k‐NN), followed by decision tree. However, long‐term and short‐term predictors and long short‐term memory (LSTM) and non‐linear autoregressive with exogenous inputs (NARX) algorithms were the most successful, followed by Gaussian process regression (GPR), SVM, k‐NN, and improved grey wolf optimization–support vector regression (IGWO‐SVR) algorithms. Although these methods inspire confidence, it is important to highlight that they are still in the software testing phase. Key gaps identified include the need for further studies on real industrial applications and the integration of advanced sensors and measurement systems. Future directions point to developing more robust and generalized algorithms capable of dealing with the complexity of real systems.

Mitigation of fouling with swirling flow induced in 3-D double-sided straight channel for printed circuit heat exchanger

Fouling should be considered in the design of a printed circuit heat exchanger (PCHE) for industrial applications. The swirling flow, which is known to mitigate fouling in heat exchangers, can incorporate this aspect; however, realizing these flow characteristics in compact heat exchangers such as PCHE is difficult. Thus, this study proposed a three-dimensional (3-D) designed PCHE channel. To induce swirling flow, it was designed to face two semicircular straight channels with angles such that the interaction between the mainstreams in different flow directions induced a swirling flow. Compared to conventional two-dimensional (2-D) PCHE channels (straight, zigzag, and airfoil channels), the swirling flow induced in the proposed 3-D PCHE channel uniformly increased the wall shear stress while minimizing flow separation or recirculation. This minimized the low wall shear stress that was more likely to be fouled. A comparative evaluation of the thermal-hydraulic performance of the investigated channels was conducted by comparing the volume goodness factors under the equal hydraulic diameter. The proposed 3-D channels exhibited the potential to mitigate fouling, as well as a thermal-hydraulic performance comparable to that of conventional 2-D PCHE channels. Therefore, the proposed 3-D channel can be suggested as an advanced PCHE design option for high thermal-hydraulic performance and mitigation of fouling. Furthermore, because the swirling flow is known to mitigate fouling in heat exchangers as well as the heat transfer deterioration of sCO2, a double-sided straight channel with swirling flow is expected to be competitive.

Modelling the Relationship between Water Jetting Parameters and Material Failure in Heat Exchanger Tubes

The Zeeland-Flemish region has a robust process industry where heat exchangers (HEX) are essential for managing heat transfer. However, Fouling in HEX occurs when deposits of contaminants form on surfaces affecting heat transfer. HEX maintenance/cleaning can harm the material of construction (MoC). This study explores how altering Water Jetting (WJ) parameters affects MoC failure mechanisms. This knowledge can optimize processes to prevent unwanted MoC failure while achieving desired fouling control. In this study, a three-factorial experiment was designed to investigate how increased water pressure and flow rates impact the structural health of copper used in HEX tubes during WJ cleaning. Then, we compared these results with experiments using steel as the MoC. Statistical and mathematical analysis were employed to understand the effect of process parameters on damage mechanisms and identify the most influential parameter. For copper samples, we observed that higher water pressure consistently increased damage across all flow rates, following a linear trend of α_p =0.001(gm loss/gm sample. Kpsi). Flow rate's impact on damage exhibited logarithmic behavior, which can be split into two ranges. At low to medium flow levels, increased flow rates raised damage at a rate of α_f =0.007(gm loss/gm sample. gpm). However, at high flow rates, the increase in flow had no effect on the damage as it was attributed solely to pressure. Comparing steel and copper at high pressure levels, it was found that steel experienced a lower linear increase in damage, β_f =0.0036(gm loss/gm sample. gpm), compared to α_f for copper. These results offer insights for optimizing water jetting cleaning processes to minimize material damage during HEX maintenance, enhancing overall efficiency.

Exploration of plasma‐activated water (PAW) as a cleaning‐in‐place (CIP) solution for fouling removal and microbial reduction

AbstractThe rapid fouling and bacterial contamination of equipment, heat exchangers, and pipelines are major concerns in food manufacturing plants. The process of cleaning‐in‐place (CIP) in the food manufacturing industry involves hazardous chemicals such as sulfuric acid, chlorine, sodium hydroxide, and potassium hydroxide. This study aims to investigate the cleaning efficiency of a novel environment‐friendly solution, plasma‐activated water (PAW), for removing dairy and plant‐based fouling and for biofilm reduction. PAW was produced by exposing water to plasma, which is a partially ionized gas generated by applying electricity to air. PAW prepared in this study had a pH, electrical conductivity (EC), and oxidation–reduction potential (ORP) of 2.5 ± 0.1, 1170. 1 ± 202.2 μS/cm, and 589.0 ± 2.4 mV, respectively. Holding PAW at different temperatures (20–75°C) did not change pH, ORP, and EC significantly, while nitrite and nitrate concentrations in PAW did not show a consistent trend with temperature. The treatment time and temperature of PAW were optimized for cleaning fouled coupons (stainless‐steel type 304 and 316) using model fouling fluids (MFF) with dairy (whey) and plant‐based (oat) proteins using full‐factorial design. The optimized PAW combinations (15 min/75°C and 5 min/75°C) were found to be as effective for fouling removal as compared to CIP controls (conventional caustic and acid solutions). Optimized PAW also showed significant biofilm reduction of Listeria innocua on stainless‐steel coupons with/without fouling, with at least 4.4 log and 4.0 log reductions in L. innocua biofilms when attached to MFF‐whey and MFF‐oat, respectively.Practical applicationsPlasma‐activated water (PAW) can inactivate a wide spectrum of microorganisms on various food and food contact surfaces. We propose the use of environment‐friendly plasma‐activated water (PAW), which can be prepared on‐site and on‐demand for cleaning‐in‐place (CIP) operations in the food industry. The results of this study suggest the potential of PAW as a promising CIP alternative for cleaning and sanitizing surfaces soiled by fouling deposits in dairy and plant‐based industries.

14th Heat exchanger fouling and cleaning conference

14th Heat exchanger fouling and cleaning conference

Industrial scale fouling of heat exchangers in isocyanate production

The fouling of a commercial stainless steel (AISI 316L) during the manufacture of polymeric methylene diphenyl diisocyanate (pMDI) has been studied using laboratory‐based fouling apparatus that simulates commercial production conditions. The goal of the work is to understand the mechanisms behind the corrosion and fouling during isocyanate production with a view to improving process efficiency, not only in this process, but also others using similar plant and processes. Steel coupons were exposed to a solution of pMDI and solid amine hydrochloride, with hydrogen chloride gas being bubbled through the reaction cell. A number of different conditions were investigated, the variables being pMDI concentration, HCl gas flow duration, immersion time and temperature. Following the fouling experiments the coupons were removed from the fouling rig, photographed, and examined by XPS and ToF‐SIMS; principal component analysis was used to extend the ToF‐SIMS analysis to identify organic fouling products. The extent of fouling is shown to be relatively insensitive to pMDI concentration, but significantly influenced by continual HCl flow and increased temperature, features which increase the extent of substrate corrosion thought to be a precursor to the fouling process itself. Both XPS and ToF‐SIMS confirm the formation of various nickel chlorides in the corrosion process. Urea and metal corrosion products are found to co‐exist on certain (random) areas of the coupon surface.

Experimental and mechanism studies on high CaCO3 fouling inhibition of PTFE coating with enhanced stability and anti-corrosion

Surface coatings are an effective technique for mitigating fouling in heat exchangers. In this study, a stable polytetrafluoroethylene (PTFE) coating was prepared with improved corrosion resistance and CaCO3 fouling inhibition rate. The prepared PTFE coating remains strongly stable even undergoing tape stripping, sandpaper abrasion, water impacting and immersion. The corrosion-suppression efficiency of the coating is 95.09 % compared to the stainless steel surface. Fouling tests reveal that the coating possesses an inhibition rate of 86.25 %, and it retains a high level of fouling inhibition rate even after 100 cycles of tape stripping and 400 mm of sandpaper abrasion. Additionally, molecular dynamics simulation was performed to gain insight into the anti-fouling mechanism of the PTFE coating. The results demonstrate the presence of two dense adsorption layers of water molecules in close proximity to the metal surface, which is found to be a crucial role in facilitating the adsorption of CaCO3 ions due to their strong attraction (Einteraction = -15.47 eV) towards the ions. In contrast, the weaker interaction (Einteraction = -1.52 eV) between PTFE and water molecules results in the absence of dense water adsorption layers on the PTFE coating. Consequently, the PTFE coating effectively reduces the rate of ion adsorption on the metal surfaces in the initial stage of CaCO3 fouling formation.

A review of recent advancements in the crystallization fouling of heat exchangers

A review of recent advancements in the crystallization fouling of heat exchangers

14th Heat Exchanger Fouling and Cleaning Conference - 2022, Wagrain, Austria

14th Heat Exchanger Fouling and Cleaning Conference - 2022, Wagrain, Austria

Laminar cross-flow convective heat transfer of a finned cylindrical tube in the presence of particle deposition and deposit erosion

Cross-flow finned tube heat exchangers are extensively used in a variety of industrial and commercial applications. Although the fins increase surface area and hence enhance heat transfer rate, the fouling potential also increases due to the more complex geometry leading to performance deterioration. This paper presents an integrated numerical model to study the effect of fouling on convective heat transfer of a finned cylindrical tube. In this model, fluid flow, particle transport, particle deposition, deposit erosion and heat transfer are all accounted for in a fully coupled manner. Moreover, the fluid-deposit interface is captured using a level-set method and the interfacial velocity is derived from the net effect of combined particle deposition and deposit erosion. In such a way, the evolution of deposit layer is implicitly tracked in a fixed mesh, and its influences on fluid flow and heat transfer are considered by updating the thermophysical properties of the deposit region. Based on this integrated model, comprehensive parametric studies are conducted to investigate the effects of tube orientation angle (β), Reynolds number (Re), Damkholer number (Da), erosion number (Er), particle Peclet number (PeC) and thermal Peclet number (PeT) and dimensionless critical shear stress (τ*crit). It is found that the amount of deposits accumulated increases for a lower β within the range of 0°-45°, a higher β in the range of 45°-90°, a higher Re, a higher Da, a lower Er, a lower PeC and a lower τ*crit. Heat transfer deteriorates as the insulating deposit layer grows thicker and at a higher PeT. This study demonstrates the capabilities of the developed model, and provides fundamental insights on the coupled fouling and heat transfer processes of cross-flow finned tube heat exchangers in the trend towards miniaturization.

Interaction of Heat Transfer Enhancement and Fouling in Operating Heat Exchangers

Interactions of heat transfer enhancement and fouling can occur due the change in nature of the surface, operating condition, or the fluid itself. Interactions arising relating to higher clean heat transfer coefficients, and higher wall shear stresses of the enhanced surfaces are discussed in this paper. On the lab-scale, enhancement was often achieved by static elements, such as wire wrapping on a heated rod in an annular flow. Lab-scale tests of necessity suffered from effects of relatively short duration of runs, and re-circulation of a batch of liquid with the danger of changing the fluid composition during experiment. Nevertheless, initial fouling rate results consistent with expected trends could be achieved for hydrocarbon fouling, and particulate fouling. There is a continued need to better represent and compare performance of plain and enhanced surfaces over prolonged operating periods in industrial heat exchangers, using commercial enhancement technologies. Example case studies are discussed which demand different methods of comparing performances. A daily averaged cost analysis is identified as a possible systematic approach on the evaluation of the economic benefit of the use of enhancement devices. This is illustrated for a case study example where tube insert is used as an enhancement option.

Chemical Cleaning of Crude Oil Fouling Deposits; Applying the Coke Spectrum

Fouling of heat exchangers and refining equipment by crude oil deposits is a chronic operating problem. In general, many such deposits are narrowly defined as coke fouling, for which the prescribed cleaning has traditionally been high-pressure water blasting. The results for this type of cleaning are mixed at best. Heat exchangers are often returned to service at conditions less than 85% clean performance, driving the need for more efficient cleaning regimens. A detailed characterization of 62 field-based crude oil fouling deposits from hydrocarbon process units was presented by the authors in 2019. This paper demonstrated that such deposits are exceptionally complex, resulting in the introduction of the Coke Spectrum. Here, these deposits are revisited, and chemical cleaning methods are applied. Chemical cleaning encompasses a variety of applications. Circulation, ultrasonic immersion, and clean-in-place techniques were reviewed on laboratory-scale samples to determine what chemical cleaning agents are most effective toward the various categories of foulant making up the Coke Spectrum. Combination techniques which employ both chemical and mechanical applications simultaneously or in sequence are considered in depth. The correlation between chemical composition and the effectiveness of the cleaning method is explored with considerations for scaling from laboratory to industrial application.

Fouling Management at TotalEnergies through Use of HTRI SMARTPM™: Case Study of a Project Proposal for Cleaning Schedule Optimization

Heat exchanger fouling is problematic in crude oil refining, impacting energy consumption, greenhouse gas emissions, plant capacity, and maintenance budget. As part of the digital transformation journey at TotalEnergies and with advances in research on hydrocarbon fouling, advanced fouling monitoring and prediction tool (HTRI SmartPMTM) was implemented throughout TotalEnergies to better manage fouling in heat exchangers. The SmartPM software performs advanced data reconciliation, including simulation of detailed exchanger operational data using proprietary HTRI shell-and-tube heat exchanger calculation methods. After deployment and adoption of the software for fouling monitoring and reporting, the predictive functionalities have been applied to several feasibility studies concerning energy efficiency and CO2 emissions reduction projects. The present work describes the predictive study of the cleaning schedule of a refinery. The result of this study is an industrial project proposal on the installation of new bypasses across selected exchangers, leading to an economically optimized cleaning strategy, savings in the fuel consumption of the crude preheat furnace, and the reduction in CO2 emissions associated to its combustion.

Coatings to Reduce Fouling in Plate Heat Exchangers: Two Case Studies

Fouling of heat exchangers in the chemical industry, oil & gas industry, district heating, power plants, among others, results in a loss of performance which leads to production stops for cleaning and therefore increased operation costs. One approach to mitigate fouling is to alter the properties of the metal surface. A coating to be successful in any plate heat exchanger (PHE) application needs to have a good adhesion to the metal but also keep the heat transfer through the metal plates as unaltered as possible. This requires a thin coating with a relatively good thermal conductivity. The plates in a PHE are subjected to plate-to-plate contact point wear when in operation which also puts an extra requirement for the coating. To be suitable, the coating needs to have a good mechanical stability to resist this plate-to-plate wear. Alfa Laval has a long experience in coating plates for diverse applications and in this paper two case studies will be presented. One in the paper industry and the other in the biofuel industry. A new type of multilayer Teflon™ coating from Chemours was used, specifically designed to show excellent fouling release properties along with limited thicknesses (30–50 microns).

Novel Surface Treatment to Mitigate Fouling in Heat Exchangers and Process Equipment

The global impact of climate changes due to greenhouse gas emissions cannot be overemphasized. To combat this, engineers are striving to develop innovative enhancements for heat transfer and fouling reduction in process equipment as a pathway to reduce CO2 emissions. A novel surface application of Minimox® treatment, a water-based suspension of rare-earth oxides, is a promising solution. The self-protective alloy treatment, unlike a traditional continuous coating, has no measurable thickness, does not impose any operating temperature limits, protects from high temperature oxidation, and decreases surface energy and polarity that leads to low fouling and coking rates. Minimox can be applied by dipping or spraying to both external and internal surfaces, including non-conventional tubing shapes. A post-application curing at 400 °C for 1 h is needed to ensure maximum fouling mitigation efficacy. Laboratory tests conducted to simulate operating conditions in a Coker furnace show that the Minimox-treated tubes reduce coke formation by about 80% as compared to untreated tubes. In addition, adhesion of coke to the Minimox treated tubes was significantly lower than for the untreated tubes. Field data collected in refinery applications involving Coker furnace tubes and a vacuum column wash bed are promising, lending support the laboratory results.

Economic and Environmental Implications of Fouling in Crude Preheat Trains

The economic, environmental and safety consequences of fouling are the key reasons for industrial and research interest in heat exchanger fouling and cleaning. The implication of fouling in crude oil refineries has changed in the recent decades due to better monitoring tools, use of fouling mitigation devices, optimization of the use of antifoulants, optimization of process conditions, better blending of crudes, better design of heat exchangers and selection of exchanger tube materials. This brings a need for the economic impact of fouling in crude refinery preheat train to be revisited. The estimation of the cost of fouling in crude preheat train is discussed via updating the assumptions previously used in literature. The updated fouling cost estimate for the crude preheat train in the US refining sector is likely to be in the range of 1–1.2 B US$ per year for 2019. It is shown that the cost of fouling needs to be associated with a relevant refining profit or a crude refining margin as it is possible for the refinery to processes crudes with higher fouling problems after compensating the fouling cost with the price of the crude.

Determination of Heat Transfer Correlations for Fluids Flowing through Plate Heat Exchangers Needed for Online Monitoring of District Heat Exchanger Fouling

This article deals with the problem of estimating the degree of fouling of plate heat exchangers (PHEs) used in district heating substations (where the working medium is water). A method for calculating the thermal resistance of fouling is proposed based on a comparison of the thermal resistance of a fouled and clean heat exchanger. The thermal resistance of the heat exchanger for both fouled and clean apparatuses is determined as the inverse of their overall heat transfer coefficient. In the method, the heat transfer coefficients necessary to determine the overall heat transfer coefficient of the clean exchanger are calculated using a modified Wilson method. Moreover, the heat transfer coefficients on the clean heat exchanger plates’ cold water side are determined based on experimental tests. The computational algorithm presented in this paper will make it possible to develop software to monitor and thus optimise the operation of district heating substations.

A numerical analysis of ash fouling characteristics in elliptical tube bundles

Ash fouling in flue gas heat exchangers (FGHE) detrimentally affects waste heat recovery systems' performance and efficiency by impeding heat transfer, increasing operational resistance, and escalating maintenance costs. The main purpose of this study is to develop an improved particle deposition model for predicting ash fouling characteristics and to explore the fouling reduction performance of elliptical tube bundles (ETB) at various system parameters. The findings reveal that ETB can efficiently reduce operation resistance and ash fouling in FGHE with an insignificant loss in heat exchanger efficiency, especially at large eccentricities (E) and/or low flue gas velocity (vinlet). The most cost-effective E is 0.78, which decreases ash deposit and pressure drop by 66.4% and 48.4%, respectively, at the expense of a 14.2% Nusselt number reduction at vinlet = 10 m/s. Ash fouling reveals three distinctive hotspots: Hotspot 1 located approximately at ±30°, Hotspot 2 at the flow stagnation area, and Hotspot 3 roughly at ±150°. The deposit layer thickness at these hotspots varies between rows and with the E, vinlet and particle diameter (dp). The layer thickness at the flow stagnation regions increases with any of the E, vinlet, and dp. The study also found that medium-sized particles (dp = 5 μm) are the easiest to deposit on tube surfaces, followed by large particles (dp = 10 μm). Small particles (dp = 1 μm) are the least likely to deposit due to their small inertia. Medium-sized and large particles deposit primarily at the windward side of the tubes, while small particles tend to deposit more on the leeward side as they can be easily drawn into the recirculation zones behind those tubes. Increasing the E would significantly alleviate fouling by medium-sized and large particles but does not significantly change the ash fouling situation of small particles.

Modeling Strategies for Crude Oil-Induced Fouling in Heat Exchangers: A Review

Semi-empirical fouling models have proven more effective in predicting the fouling behavior of crude oils in heat exchangers. These models have aided refineries in optimizing operating conditions to minimize or eliminate fouling in preheat exchangers. Despite their complexity, the models continue to improve in approximating real behavior by taking into account previously neglected aspects. This paper summarizes these findings from various studies along with highlighting different factors which were considered to enhance the predictability of the models. A critical analysis is presented to emphasize that activation energy in the deposition term varies depending on the physical processes involved and may not conform to the precise definition of activation energy. Two primary modeling approaches for crude oil fouling have emerged, i.e., deterministic and threshold models. Threshold models have gained more attention due to their fewer adjustable parameters. The stability or compatibility of crude oils has a substantial impact on asphaltene deposition, which is a major contributor to fouling. However, incorporating this factor into fouling models has received little attention. The inclusion of parameters for inorganic fraction and ageing has increased predictability by accurately estimating the fouling thickness. The use of CFD to analyze fouling mechanisms is promising, particularly for complex geometries. The dynamic and moving boundary modeling approach has potential to broaden the applicability of fouling models.

Experimental/Numerical Investigation and Prediction of Fouling in Multiphase Flow Heat Exchangers: A Review

Fouling build-up is one of the most challenging problems for heat exchangers in industry. The presence of fouling leads to a degradation of system efficiency, an increase in operating cost, and possibly, a harmful environmental impact. For this reason, fouling analysis has become an extremely important research subject in order to have a safe and efficient operation. The analysis is more difficult where phase change of fluids is involved during the heat transfer process, as in the case of boilers and condensers, which are critical units in industrial facilities. Due to the lack of a comprehensive review of fouling analysis for the case of multiphase heat exchangers, this paper examines available approaches and techniques used for fouling characterization, modeling, monitoring, and prediction in heat exchangers for both single-phase and multiphase heat exchangers with a focus on fouling in thermal desalination systems. It also gives an overview of heat exchanger condition monitoring solutions available in the market.