Heat Exchanger Fouling Research Articles

Experimental and numerical investigation of soot deposition on exhaust heat exchanger tube banks

The exhaust heat exchanger is widely used in waste heat recovery systems (WHR) to recover energy from exhaust gas. However, fouling of the exhaust heat exchanger due to the deposition of soot particles reduces the heat transfer efficiency. In this investigation, a deposition performance experimental system and an improved CFD-based soot deposition prediction model were proposed to investigate the deposition characteristics on tube banks in exhaust heat exchangers. Firstly, the test bench is introduced in detail, and the combination of air heater and soot generator was applied in the test bench to provide the particle flow with specified parameters. Then, considering the effect of thermophoresis, diffusion, inertial impaction, and removal mechanisms, an improved prediction model was proposed. Compared with the traditional two-fluid model (TFM), the thermal-hydraulic performance of exhaust heat exchangers is calculated by CFD software in this model, so it is suitable for all dividing wall type heat exchangers. Afterwards, the influence of particle diameter and tube spacing on the tube bank during the 4 h deposition process was experimentally or numerically investigated. It was found that the comprehensive performance of the tube bank is deteriorated by about 0.45%-1.85% after 4 hours of soot deposition. Besides, the deposition amount on the tube bank with smaller tube spacing (1.25D) is lower.

Infrared thermography observations of crystallization fouling in a plate heat exchanger

Heat exchanger performance is significantly reduced in the presence of impurities in one or both fluid streams, frequently by deposits of inversely soluble salts. Accordingly, immense efforts were and still are spent to combat, predict, and investigate such fouling problems to mitigate the reduction of heat transfer performance. In this study, calcium carbonate crystallization fouling in a corrugated plate heat exchanger was investigated. Fouling was monitored using temperature and flow measurements, and, for the first time, coupled with infrared thermography observations. We show a clear and measurable local difference between clean and fouled conditions, regardless of operating conditions. Infrared measurements of temperature permit conclusions about flow distribution and the spatial location of areas with severe fouling. Compared to the clean state, completely skewed isotherms after fouling point out channel blockage and flow obstructions, resulting in large scale flow re-distribution within the channel. The presented results exhibit a clear benefit of this approach for heat exchanger fouling studies and serve as a foundation for future research of dynamic operation, transient response, and computational models.

Statistical Model Identification and Variable Selection for Prediction of Heat Exchanger Fouling

Fly ash generated during boiler combustion are carried away with hot flue gas and deposited over the heat exchanger surfaces. This study was motivated by the decline in the thermal efficiency of the heat exchangers in thermal power plants due to ash fouling. The paper discusses a new computational procedure that has been attempted to identify the best statistical model for predicting heat exchanger fouling and also to choose the most strongly linked covariates. In this context, three different statistical models including multiple linear regression, sliced inverse regression, and random forests regression are used to estimate the cleanliness factor of the heat exchanger. The variables and model are chosen solely on the basis of analytical procedures. Heat exchanger metal tube temperature that highly influences the cleanliness factor is selected using a measure of importance based on random perturbations. Metal temperature above a threshold is selected as a strongly linked covariate. The R package modevarsel is used here to perform the statistical analysis. The value of root mean square error for the cleanliness factor from sliced inverse regression and random forest is 0.0002, indicating that as more feasible in predicting ash fouling.

Experimental Study of Oil Deposition Using a Deposition Simulator (HLPS - Hot Liquid Process Simulator)

Fouling in heat exchangers is a recurring and costly problem for oil refineries. However, the phenomenon is complex and requires experimental evaluation, as oils have varied compositions. In the present study, analyzes were performed in the laboratory using a deposition simulator (HLPS - Hot Liquid Process Simulator). We performed the test with a sample of crude oil. In this test, the deposition was small, which could occur due to the characteristic of the oil.

Shell and Tube Heat Exchanger Fouling Factor via Heat Transfer Research Inc (HTRI) Software

One of the factories for manufacturing Carboxymethyl Cellulose (CMC) uses a shell and tube-type heat exchanger as a condenser. The shell and tube (HE) heat exchanger consists of small diameter tubes arranged in a cylindrical shell. In the tube and shell sections, hot (ethanol) and cold (water) fluids will flow so that heat transfer occurs directly. The use of heat exchangers regularly will reduce the performance of the tool. Due to the increasing fouling layer inside the HE, the device will work harder, and the heat process could be more optimal. It is necessary to analyze the performance of the heat exchanger using the parameter value of the fouling factor (Rd). The fouling factor can be calculated using the manual calculation method (via the Kern method) and the HTRI program. The involvement of the mathematical equation in the first method will be configured for the calculation results through process simulation in the HTRI software. Both ways are used for calibration between manual calculations and the HTRI software for the Rd values obtained. The fouling factor can be calculated using the manual method and HTRI software. The two methods used for calibration are manual calculations with HTRI software. The results from this analysis give a decrease in tool performance with a fouling factor of 0,01 Btu/(h.ft2.℉). ABSTRAKSalah satu pabrik pembuatan Carboxymethyl Cellulose (CMC) menggunakan heat exchanger tipe shell and tube sebagai kondensor. Heat exchanger (HE) shell and tube terdiri dari sekumpulan tube berdiameter kecil yang disusun di dalam shell berbentuk silindris. Pada bagian tube dan shell akan dialirkan fluida panas (etanol) dan dingin (air) agar terjadi proses perpindahan panas secara tidak langsung. Penggunaan heat exchanger secara berkala akan mengurangi kinerja alat. Hal tersebut disebabkan oleh adanya lapisan fouling yang terus meningkat di bagian dalam HE sehingga alat akan bekerja lebih berat dan proses perpindahan panas tidak maksimal. Untuk mengatasi fenomena tersebut maka perlu dilakukan analisis kinerja heat exchanger menggunakan parameter nilai fouling factor (Rd). Fouling factor dapat dihitung menggunakan metode perhitungan manual (melalui metode Kern) dan penggunaan program HTRI. Keterlibatan persamaan matematis pada metode pertama akan dikonfigurasi hasil perhitungannya melalui simulasi proses pada software HTRI Kedua metode digunakan untuk kalibrasi antara perhitungan manual dengan software HTRI atas nilai Rd yang didapatkan. Hasil analisis perhitungan dengan kedua metode tersebut menghasilkan penurunan kinerja alat dengan nilai fouling factor sebesar 0,011 Btu/(jam.ft2.℉).

Determination of the Fouling Degree of the Heat Substation Based on Tests of Plate Heat Exchangers

The subject of the following considerations is research on plate heat exchangers. The research concerns the determination of the degree of fouling of plate heat exchangers with mineral deposits in the water. The method proposed in this publication for determining the thermal resistance of fouling is based on the determination of the overall heat transfer coefficient for a clean heat exchanger (operating under laboratory conditions) and a fouled one (operating in a heat substation). With the overall heat transfer coefficients determined, the difference in thermal resistance for the fouled and clean heat exchanger and thus the total thermal resistance of the fouling can be determined. The calculation algorithm presented in the work will allow the creation of software that enables monitoring, thus optimizing work heating centers.

A simple model-based methodology to characterize foulants in heat exchangers using excess thermal and hydraulic loads

Fouling in heat exchangers is unavoidable and causes performance degradation; hence, occasional cleaning is essential. An effective cleaning strategy requires knowledge of foulants that can be obtained by laboratory tests. However, these are unaffordable for small and medium-scale industries. Model-based methods have been proposed for foulant characterization. However, they fail when exchangers are under temperature control and varying inlet conditions. This paper proposes a simple methodology to directly estimate foulants' characteristics using excess thermal and hydraulic loads. Specifically, it first uses changes in the pressure drop and mass flowrate vis-à-vis the exchanger’s clean state to estimate foulant thickness. Subsequently, the estimated thickness is used along with temperature measurements to estimate the thermal conductivity. The methodology is demonstrated on a heat exchanger in two cases– with fouling only on tube side, and on both shell and tube sides. Our results show that the estimates have an error of less than 3% in all cases. A key advantage of the proposed methodology is that it can accommodate setpoint changes and disturbances that are common in industrial practise.

PREDICTION ANALYSIS OF FOULING MODEL ON HEAT EXCHANGER IN THE CRUDE OIL REFINERY

Fouling mainly occurs in the oil industry. Fouling is an unwanted deposit in HE (heat exchanger). Reliable fouling models are scarce, although empirical and theoretical models have been proposed to describe fouling in heat exchangers. The general models of empirical fouling used are linear, falling rate, and asymptotic. The research methodology begins with the acquisition and use of operational fouling data, which is then followed by the use of an asymptotic fouling model and ends with calculating the thickness of fouling in all HE. The object of this research study is all HE in the crude oil refinery HEN (heat exchanger network). The aim of this research is to use the asymptotic fouling model and get the fouling thickness. The fouling resistance from time to time increases, but in the end, it tends to be stationary, where for the final value, the highest fouling resistance is in HE-10, namely 14.8E-03 (m2°C/W), and the lowest value is fouling resistance at HE- 01 is 1.27E-03 (m2°C/W). The thickness of HE fouling in asymptotic conditions indicates that HE undergoes the same deposition process as suppression.Keywords: fouling, heat exchanger, asymptotic, crude oil refinery, heat exchanger network

An operating economics-driven perspective on monitoring and maintenance in multiple operating regimes: Application to monitor fouling in heat exchangers

Process monitoring is required to ensure consistent product quality and safe operation. Equipment degradation leads to changes in the process model causing plant-model mismatch, e.g., fouling in heat exchangers. This is particularly important for slow drifting industrial processes, where monitoring just the process variables is insufficient, as controllers continuously seek to track key process variables to ensure that they adhere to strict design conditions, despite increased operating costs to compensate for the model degradation. An objective of this work is to develop a straightforward operating economics-driven monitoring algorithm to track process drifts and equipment degradation in multiple operating regimes by monitoring deviations in model parameters along with the states. A 2014 estimate put the economic cost of fouling in heat exchangers for US industries at $14 billion per year. To mitigate this expenditure, and highlight the importance of this work, illustrative examples involving both simulated synthetic data and experimental data from a double-pipe heat exchanger are used. Traditional state estimation methods are integrated with cost contours based on operating economics to accurately track equipment degradation by monitoring deviations in model parameters, even when drastic changes in input conditions are present. Tracking process drifts and equipment degradation while evaluating the economic impact helps determine the urgency of cleaning and maintenance that is required.

Experimental Investigation of Polymer-Induced Fouling of Heater Tubes in the First-Ever Polymer Flood on Alaska North Slope Part II

Summary A polymer flood pilot has been ongoing in the Schrader Bluff viscous oil reservoir at Milne Point on the Alaska North Slope. The results from the pilot are encouraging. However, a major concern of the operator is the influence of polymer on the production system after breakthrough, especially the fouling in heat exchangers. This work applies a multiexperimental approach to study the severity of polymer-induced fouling in both dynamic and static states of produced fluids to determine safe operating conditions. Dynamic scale loop (DSL) tests were conducted to study fouling due to polymer at different skin temperatures (165–350°F) in a dynamic state of fluid flow where the fluids’ flow mimics the residence time of fluids in the heat exchanger of the field pilot. Static deposit tests were also conducted at similar skin temperatures of 165–250°F using a novel experimental apparatus designed and built in-house. It was found that at higher skin temperatures of 250–350°F, tube blocking was observed in the DSL tests, whereas the tests at 165–200°F did not show any tube blocking, even in a more extended test period. The deposit test showed that the deposit rate generally increases with skin temperature, and the presence of polymer aggravates the fouling. The copper tube performs best when the skin temperatures are 165–200°F, while the stainless steel tube performs best at a skin temperature of 250°F. These experiments also manifested the influence of the cloudpoint of the solution as the deposit rate increased significantly when the skin temperature was higher than the solution cloudpoint. The study provides a source of practical guidance to the field operations.

Monitoring fouling in heat exchangers under temperature control based on excess thermal and hydraulic loads

Fouling affects heat exchangers’ performance leading to additional utility requirements and economic penalties. Performance monitoring is required to ensure that exchangers operate within allowable limits. Conventional techniques use overall heat transfer rate to monitor thermal performance. These techniques fail when the heat transfer rate remains constant, which is the case anytime a heat exchanger has feedback control on temperature. In this paper, we propose an approach to monitor fouling in heat exchangers that have closed-loop control. Our approach is based on excess pressure drop and thermal load. A monitoring chart is also proposed based on combined hydraulic and thermal performance indicators. The proposed monitoring charts are demonstrated on two case studies – a cooler with a utility on the tube-side and a heater with the utility on the shell-side. The results show that even when setpoints and flowrates change due to process requirements, the proposed approach can effectively monitor fouling and identify if the operation is within allowable performance bounds. The results can be used to schedule the cleaning of the exchangers at an appropriate time so as to avoid excessive economic losses.

CFD analysis of Gypsum crystallization fouling in 2D plate heat exchangers

CFD analysis of Gypsum crystallization fouling in 2D plate heat exchangers

Experimental and numerical analysis of fine particle and soot formation in a modern 100 MW pulverized biomass heating plant

The formation of soot, organic, and inorganic aerosols has a profound effect on the environmental and technological feasibility of biomass combustion. In this work, the soot and aerosol processes are examined for a modern pulverized wood-burning 100 MWth district heating plant. Experimental data was collected from two locations inside the furnace (30% and 100% thermal loads), including measurements for fine particle (PM1) number size distribution, number concentration, and chemical composition. The experiments were complemented with Computational Fluid Dynamics (CFD) simulations and Plug-Flow Reactor (PFR) modeling. The measurements and modeling are combined in a comprehensive analysis, providing fundamental understanding on the aerosol processes inside the furnace. The wood-powder combustion is efficient under both thermal loads, indicated by the low unburned carbon content in fly-ash, and the low CO, NO and soot emissions (<0.3 mg/Nm3). The fine particles consist mainly of K2SO4, and of lesser amounts of alkali salts (NaCl, KCl), and Ca and Mg compounds (oxides or sulfates). A large concentration of KOH/K2CO3 vapor may exist in the flue gas and play a significant role in the heat exchanger fouling. The applied modeling tools are shown to provide accurate estimations for the composition and formation regions of fine particles inside the industrial biomass furnaces.

Dynamic simulation of once-through multistage flash (MSF-OT) desalination process: Effect of seawater temperature on the fouling mechanism in the heat exchangers

Scale formation of carbonates and sulphates is one of the most well-known types of crystallization fouling in heat exchangers. Tackling crystallization fouling in Once-Through Multistage Flash Desalination (MSF-OT) is one of the most challenging tasks in the desalination industry. In this paper, a fouling model is developed and then incorporated into a MSF model to investigate the fouling behaviour under variable seawater temperature. The proposed dynamic model investigates the crystallization of calcium carbonate and magnesium hydroxide at the inside tube surface areas by considering the attachment and removal mechanisms. The results show that the fouling rate is higher at high constant seawater temperature. Overall, the fouling rate is lower at the seasonal variation of the seawater temperature, resulting in a higher performance ratio (PR). The results also show that although the brine heater duty increases in winter due to low seawater temperature, the drop of fouling rate in cold months may save some energy.

Effect of fouling resistance in heat exchanger and the crystal form of CaCO3 in hard circulating cooling water with electrostatic field and alternating current electric field.

The effect of high voltage electrostatic field and high voltage alternating current electric field on the heat exchanger surface fouling under the conditions of hard water was investigated. The Ca2+ concentration in two water conditions was 12 mmol/L. The Mg2+ concentration was 10 mmol/L and 12 mmol/L respectively. The HCO3- concentration changed with the Mg2+ concentration. X-ray diffraction and scanning electron microscope results confirmed that the main crystal phases of the scale samples consisted of calcite and aragonite. The high voltage electrostatic treatment can promote scale growth under both water quality conditions. However, the high voltage alternating current electric field treatment shows a good scale inhibition effect under both water quality conditions, and the scale inhibition effect is best when both Ca2+ and Mg2+ concentrations are 12 mmol/L, and the average scale inhibition rate reaches 47.58%. When the calcite content of the scale sample is significantly higher than that of aragonite, Mg2+ affects the growth and solubility of crystals. Conversely, the high voltage alternating current electric field treatment can effectively extend the fouling induction period of the adherent scale on the heat exchanger surface, which is favorable for heat exchanger fouling.

Computational Fluid Dynamics Simulation of Fouling of Plate Heat Exchanger by Phosphate Calcium

A computational fluid dynamics (CFD) model was developed for fouling of calcium phosphate in heat exchangers which can consider the tendency of fluid components to precipitate and the surface properties of the materials. In the CFD model the precipitation of inversely soluble mineral due to the temperature increase in the near-surface region of the heated wall was modeled based on the saturation ratio. The precipitates form small, spherical particles that can adhere on the wall surface. The wall function model developed for adherence was modified to consider the turbulent viscosity modeled by CFD. The model was tested against experiments made with simulated milk ultrafiltrate, which is an aqueous solution simulating the mineral composition of milk. This preliminary adhesion CFD model paves the route to build a more comprehensive model for predicting the likely profile of milk deposition in heat exchangers.

Advanced Fouling Management through Use of HTRI SmartPM: Case Studies from Total Refinery CDU Preheat Trains

Heat exchanger fouling is a persistent problem contributing to process economics, plant capacity, environmental concerns, and safety. Advances in research on hydrocarbon fouling have changed the impact of fouling in crude refinery operations, through the use of rigorous performance monitoring and process optimization methods, use of fouling predictive models, use of fouling mitigation technologies (e.g., use of tube inserts), etc. This work presents case studies from two TOTAL refineries preheat trains where the exchangers are subject to fouling. TOTAL has implemented performance monitoring and predictive maintenance software (HTRI SmartPM™) throughout their refineries to improve existing fouling management practice. The software performs advanced data reconciliation, including simulation of detailed exchanger operational data using HTRI shell-and-tube heat exchanger calculation methods and inferring fouling resistance for individual shells for shells-in-series based on dynamic fouling behavior. Dynamic fouling models are used to assess the impact of fouling on the overall network performance. Several heat exchangers in the network have tube inserts (Turbotal® and Spirelf® inserts from Petroval), and their performances are monitored and predicted. The case studies demonstrate successful implementation of SmartPM software in TOTAL Normandy and Grandpuits refineries, enabling economically feasible, technically viable, and environmentally desirable decision-making for refinery operation.

A Review of Crystallization Fouling in Heat Exchangers

A vast majority of heat exchangers suffer from unwanted deposition of material on the surface, which severely inhibits their performance and thus marks one of the biggest challenges in heat transfer. Despite numerous scientific investigations, prediction and prevention of fouling remain unresolved issues in process engineering and are responsible for large economic losses and environmental damage. This review article focuses specifically on crystallization fouling, providing a comprehensive overview of the state-of-the-art of fouling in heat exchangers. The fundamentals of the topic are discussed, as the term fouling resistance is introduced along with distinct fouling behaviour, observed in laboratory and industrial environments. Insight into subsequent phases of the fouling process is provided, along with the accompanying microscale events. Furthermore, the effects of fluid composition, temperature, flow velocity, surface condition, nucleate boiling and composite fouling are comprehensively discussed. Fouling modelling is systematically reviewed, from the early work of Kern and Seaton to recently used artificial neural networks and computational fluid dynamics. Finally, the most common fouling mitigation approaches are presented, including design considerations and various on-line strategies, as well as off-line cleaning. According to our review, several topics require further study, such as the initial stage of crystal formation, the effects of ageing, the interplay of two or more fouling mechanisms and the underlying phenomena of several mitigation strategies.

Numerical Investigation of Short Elliptical Twisted Tube for Reduced Fouling Rate in Steam Cracking Furnaces

In the steam cracking industry of natural gas or naphtha, fouling of tubular heat exchangers by cokes is a major issue. This growing carboneous layer has two major negative effects: 1) it increases pressure drop and 2) reduces heat transfer from the tube wall to the processed fluid. Using the open-source Computational Fluid Dynamics software OpenFOAM, this study numerically investigates wall shear stress, pressure drop and heat transfer performances of swirl decaying flow generated by different elliptical cross-section twisted tube. One of the objectives is to determine if minor modifications of tube geometry can generate swirling flow which could enhance wall shear stress at a reduce pressure drop penalty. For a Reynolds number ranging from 10, 000 to 100, 000, it is shown that the investigated geometries could enhance heat transfer by 90% at an increased pressure drop of 128% which yields a Performance Evaluation Criterion (PEC) of 1.44. The comparison between the performances of the different geometries is carried out using a newly defined PEC based on the bulk temperature, along with the usual PEC.

RF‐LSTM‐based method for prediction and diagnosis of fouling in heat exchanger

AbstractFouling degrades the thermal and hydraulic performances of the heat exchanger (HE), leading to failure if undetected. It occurs due to the accumulation of undesired material on the heat transfer surface. Knowledge about the HE fouling dynamics is required to plan mitigation strategies, ensuring a sustainable and safe operation. This paper aims to propose a feature‐based technique to predict the fouling status of the HE based on historical data. Three thermal and two hydraulic features are extracted from the HE. Random forest (RF) is employed to detect the dominant features using the Gini index. These dominant features are used to predict the fouling resistance using a deep neural network based on the Long Short‐Term Memory (LSTM) model. Also, these dominant features provide reliable inferences to reason out the fouling dynamics. A diagnostic flag is derived based on the dominant feature and is used to diagnose the ongoing fouling phenomena, which is vital to formulate mitigation. The proposed technique is investigated on the data acquired from the HEs used in a thermal power plant (Case 1) and petroleum refinery (Case 2). Prediction accuracy of 99% and 97% is observed for Cases 1 and 2, respectively. Experimental results illustrate that RF enables the LSTM to achieve faster training and reliable prediction of fouling.