Heat Exchanger Fouling Research Articles

A review of experimental methods for solid solubility determination in cryogenic systems

Over the past years, there have been a number of serious explosions in air industry, which have resulted in workers injuries and fatalities. At the same time, there has been an increase in the use of air separation products for industrial activities. The quality of air entering an air separation plant is of crucial importance for its safe and reliable operation and the interest in the solubility data of solids in cryogenic liquid solvents is closely connected to the problem of impurities accumulation in the process plant and storage tanks. Such accumulations, especially in liquid oxygen, may cause fouling and blockage in heat exchangers and pipelines and they may eventually cause serious explosions. For this reason the air contaminants composition in liquid oxygen must be determined with great precision. This paper aims at reviewing experimental methods for determining the solubility of solid compounds that may be present in the cryogenic liquefaction processing of air distillation. A review of the literature data on solubility of solids in liquid oxygen and nitrogen is included as well. Emphasis is given to the difficulties in setting-up measuring apparatuses working at extreme conditions, i.e. low compositions and low temperatures.

다관원통형 열교환기의 파울링 해석기법 개발 연구

Fouling of heat exchangers is generated by water-borne deposits, commonly known as foulants including particulate matter from the air, migrated corrosion produces; silt. clays. and sand suspended in water; organic contaminants; and boron based deposits in plants. The fouling is known to interfere with normal flow characteristics and reduce thermal efficiencies of heat exchangers. This paper describes the fouling analysis technique developed in this study which can analyze the thermal performance for heat exchangers and estimate the future fouling variations. To develop the fouling analysis technique for heat exchangers, fouling factor was introduced based on the ASME O&M codes and TEMA standards. For the purpose of verifying the fouling analysis technique, the fouling analyses were performed for four heat exchangers in several nuclear power plants; two residual heat removal heat exchangers of the residual heat removal system and two component cooling water heat exchangers of the component cooling water system.<br/>

Mitigation of Crude Oil Refinery Heat Exchanger Fouling Through Retrofits Based on Thermo-Hydraulic Fouling Models

Crude oil fouling in refinery preheat exchangers is a chronic operating problem that compromises energy recovery in these systems. Progress is hindered by the lack of quantitative knowledge of the dynamic effects of fouling on exchanger heat transfer and pressure drop. The concept of a thermal ‘fouling threshold’, first introduced by Ebert and Panchal, is revisited here alongside models of hydraulic effects of fouling to provide a graphical tool, the modified temperature field plot, for assessing chronic chemical reaction fouling effects in refinery heat exchangers. Fouling data of varying quality, collected from pilot plant and refinery operation, were compared with two previously published threshold fouling models and one based on the Epstein deposition model. The model by Epstein showed the best agreement, primarily because it can accommodate fouling that is mass transfer as well as reaction controlled. The hydraulic analysis indicated that the simple slab approximation for fouling layers gave a reasonably good mapping between heat transfer and pressure drop effects as long as roughness contributions are not significant. Where roughness effects (or tube blockage) are important, the relationship between thermal and hydraulic performance is not straightforward. A case study, based on the network described by Panchal and Huang-Fu, is used to illustrate the thermo-hydraulic effects of fouling and the application of the modified temperature field plot.

Numero‐Fuzzy Hybrid for Modelling and Simulation of the Fouling of Milk Heat Exchangers

AbstractTo overcome the lack of a selfcontained description of the fouling process in dairy industry, a fuzzy system is integrated in a process model using wellknown numerics thus resulting in a numero‐fuzzy hybrid model. Results concerning the simulation of a dairy plant and a new approach for the study of the applied fuzzy systems are presented.

An experimental study of the air-side particulate fouling in fin-and-tube heat exchangers of air conditioners

An experimental study was conducted to investigate the chronological performance variation such as pressure drop across a heat exchanger and cooling capacity due to the air-side particulate fouling of fin-and-tube heat exchangers for air conditioner evaporators used. Thirty samples of air conditioners used in the field such as inns, restaurants, and offices are collected in chronological order of use. This study was intended to provide factual long-term fouling data under actual operating conditions. It was found that the important parameters to influence the fouling of heat exchangers are the concentration and size of indoor pollutants, the filter efficiency, the hydrophilicity of fin surfaces, fin spacing, and the structure of fins. The pressure drop of heat exchangers increases from year to year due to the deposition of indoor pollutants larger than 1 Μm in size and increases up to 44% in the samples used for 7 years. Also, the air-side particulate fouling degrades the cooling capacity by 10-15% in the samples used for 7 years.

Use of non-crystallising particles to mitigate crystallisation fouling

Fouling in heat exchangers is of paramount importance considering its impact on the overall performance of a process plant. Fouling can be controlled by using different methods that affect the deposition rate and/or the removal rate. The use of larger particles (of the order of several millimetres) in fluid bed heat exchangers has been quite successful for heat transfer with severely fouling fluids. In this study, we will investigate the role of much smaller (micron size), non-crystallising particles on crystallisation fouling in a heat exchanger. This will be done by measuring global fouling resistance and pressure drop across the heat exchanger. The smaller particles have been found to be effective in mitigating the crystallisation fouling substantially by lowering the deposition rate and by increasing the removal rate.

Deposition of micron-sized particles on flat surfaces: effects of hydrodynamic and physicochemical conditions on particle attachment efficiency

An experimental study of micron-sized particle deposition on flat surfaces is presented, aimed at delineating the effects of hydrodynamic and physicochemical interactions on particle transport and attachment efficiency, and at obtaining a better understanding of the particle sticking probability, a concept employed in modelling particulate fouling of industrial heat exchangers. Dilute particle suspensions are employed in a parallel-plate-laminar-flow channel, and hydrodynamic and physicochemical conditions are systematically varied. Deposition rates are determined by optical microscopy and image analysis techniques. It is observed that if gravity forces are present (in a horizontal channel) they control deposition at low wall shear stresses. As the hydrodynamic wall shear stress increases particle deposition rates are significantly reduced due to the effect of hydrodynamic lift or drag forces inhibiting transport or attachment. In general, for hydrodynamic conditions similar to those encountered in industrial heat exchangers, it appears that the particle sticking probability is significantly lower than unity.

Analysis of Deposits to Study the Effect of Particles on Crystallisation Fouling

Understanding the process of fouling is of utmost importance considering its usually considerable impact on the overall performance of a process plant. Crystallisation fouling is one of the most commonly encountered problems in industry. Despite significant advances made by crystallographers in understanding mechanisms of crystallisation, researchers working in the filed of fouling in heat exchangers have tended to ignore certain basic features of crystallization. Generally the rate of crystallization fouling is simply taken as a function of concentration difference occurring in heat exchangers and reaction rate constant. The aim of this study was to analyse crystalline deposits forming on the heat transfer surface and hence determine the effect of particles on crystallization fouling. It was found that deposit formation pattern changed significantly when particles of the crystallizing material were introduced into the process solution. These particles settled on the heat transfer surface and provided new nucleation sites for crystal growth. As a result, many additional crystals were formed and the rate of crystallization enhanced significantly. In contrast, particulate fouling by these particles was found to be insignificant. Based on these results, it is argued that there is a need to modify the crystallization fouling models to incorporate the enhancement effects of the particles.

Experimental determination of carbon dioxide and nitrous oxide co-solubility in liquid oxygen

Knowledge of solid solubility in condensed gases is of great practical interest, e.g. in designing the cryogenic processes involving separation of gas mixtures into their components. Great attention has been paid to developing and implementing an operational procedure in order to reduce the probability of accidents in low temperature industry. The interest in the solubility data is closely connected to the problem of accumulation of impurities in process plant and storage tanks. Such accumulations in liquid oxygen may cause fouling and blockage in heat exchangers and pipelines and it may eventually cause serious explosions, for instance that occurred in Bintulu, Malaysia, in 1997 [J. Loss Prevent. Process Ind. 14 (2001) 167]. Solubility data for pure compounds in liquid solvents are available for various systems, but co-solubility data are drastically lacking. As an attempt to begin filling this gap, the CO 2–N 2O co-solubility has been measured in liquid oxygen at 90.44 K. For this purpose a new device named “atomiser–injector”, was designed, constructed and tested in our laboratory.

Numerical simulation of the fouling process

Fouling of heat transfer surfaces causes serious technical and economic problems in industry. The goal of this work is to simulate the aforementioned fouling process using the CFD code FLUENT. The obtained numerical results assist in designing and running heat exchangers. Based on models for the calculation of deposition and removal mass rates [S. Krause, Internat. Chem. Engrg. 33 (1993)], the crystallization fouling of calcium sulfate on flat heat transfer surfaces was simulated. The induction period, which occurs with almost all fouling processes, was therefore not considered. The simulation of real crystal growth requires a continuous variation of the geometric flow model and therefore considerable computational effort. For that reason fictitious crystal growth was simulated instead. This numerical simplification enabled an unsteady simulation to be obtained, of the fouling process and a realistic description of the temporal modification of both the flow and temperature field due to the continuous crystal growth. Based on experimental results of Hirsch [M. Bohnet et al., in: T.R. Bott et al. (Eds.), Understanding Heat Exchanger Fouling and its Mitigation, United Engineering Foundation and Begell House, New York, 1997, pp. 201–208], a model was developed which enables the calculation of the density of the fouling layer not only as a function of the local position within the fouling layer, but also as a function of the time-dependent total thickness of the fouling layer. In addition a model was developed, that enables a realistic distribution of the heat flux along the heat transfer surface during the simulation. Both models provide a more exact description of the complicated fouling process. Results of the numerical simulation are the prediction of the fouling resistance as a function of time and the calculation of the temperature distribution within the fouling layer. In view of the complexity of the fouling process during the incrustation of heat transfer surfaces and the fact that not all influences from the used models could be considered the agreement between calculated and experimentally obtained data is satisfactory.

Numerical analysis of a protection technique for tube erosion in utility boilers

Mitigation of fouling and particulate deposition in heat exchangers is the foremost concern of this critical review study. Formation of vindictive scale, sludge and fouling layers on heat transfer surfaces have severe influence on thermo-hydraulic performance and overall efficiency of heat exchangers. Fouling on gas or liquid side prevent heat transfer from bulk fluid to the solid surfaces resulting lower thermal performance of heat exchangers. Furthermore, fouling layers on heat transfer surfaces induce blockage to the fluid flow and hence increase pumping power by amplifying pressure drop. The use of various system operating variables in controlling fouling and particulate deposition is comprehensively discussed. The influence of flow rate or velocity, temperature, concentration, material surfaces and other miscellaneous factors on reduction of fouling and particle deposition is extensively investigated. It was concluded that higher flow velocity induces strong shear force across heat transfer surface which in results eradicate deposits and reduces the fouling resistance at the expense of higher pressure drop. The enhancement in fouling concentration leads to the higher fouling resistance and materials with lower thermal conductivity yield inferior fouling resistance. To conclude, this review study will be exceedingly useful for designers to design heat exchangers with higher overall efficiency under the influence of fouling.

Use of crude oil fouling threshold data in heat exchanger design

The existence of a `threshold' below which chemical reaction fouling of heat transfer surfaces by crude oil does not occur has been identified by Ebert and Panchal [Fouling Mitigation of Industrial Heat-Exchange Equipment, Begell House, 1997, 451–460] and clearly demonstrated by Knudsen et al. [Understanding Heat Exchanger Fouling and its Mitigation, Begell House, 1999, 265–272]. This phenomenon has important implications for the design and operation of heat exchangers in refinery pre-heat trains used for the processing of crudes. In this paper we show how a consideration of the fouling threshold condition can be incorporated into the design procedures for shell-and-tube heat exchangers. We then proceed to show how fouling can be mitigated through attention to heat exchanger design, particularly the choice of configuration. The cost of improperly designed units, based on the conventional use of `fouling factors', is demonstrated.

Evaluation of laboratory crude oil threshold fouling data for application to refinery pre-heat trains

`Threshold' models for crude oil fouling present a logical framework for analysing chronic fouling problems in refinery pre-heat trains. Few complete data sets of fouling thresholds in crude oil exist: this paper presents a modelling (correlation) study of the data set obtained by Knudsen et al. [Understanding Heat Exchanger Fouling and its Mitigation, Begell House, New York, 1999, p. 265] for threshold fouling experiments performed in a pilot plant. The threshold fouling equation proposed previously by Ebert and Panchal, and extended by Panchal et al. [Understanding Heat Exchanger Fouling and its Mitigation, Begell House, New York, 1999, p. 273] has been modified following a critique of some of its underlying assumptions. These previous efforts in developing threshold fouling equations were based on observed fouling rates, extrapolated to yield operating conditions that presumably exhibit zero fouling. This study represents an attempt to model measured physical parameters that actually resulted in no observable fouling. The validity of such a model to describe threshold fouling conditions in refinery pre-heat exchangers is discussed.

Statistical aspects of fouling processes

Fouling in heat exchangers is traditionally characterized by deterministic (linear or nonlinear) kinetic models of fouling deposition and removal processes. This deterministic approach to fouling does not reflect the real situation of heat exchangers subject to fouling. The observations in a real situation of fouling of heat exchangers, when compared with the results obtained from predictive models, show a large discrepancy. This discrepancy in the fouling literature is normally referred to as uncertainty of the process. In this paper an attempt is made to model this uncertainty by characterizing the fouling as a correlated random process. The deterministic kinetic models (available in the literature) are randomized by treating their parameters as random quantities. Three fouling patterns are characterized by Rf(t) = Bt for the linear process, Rf(t) = mtn for the power law process with a falling rate (0 n ≤ 1) and Rf(t) = Rf∗[1 − exp (—t/τ)] for an asymptotic process, where t &gt; 0 and B, m, Rf∗ and τ are the random process parameters with associated distributions. Fouling causes the performance loss of heat exchangers which can be tolerated up to a certain limit (i.e. critical level of fouling, Rfc), and thus it is of interest to find P[R(t) ≤ Rfc] = P(T &gt; t) where T is the time to reach Rfc. Such distributions are developed in this paper, which are validated against the available data in the literature. It is demonstrated that alpha, modified alpha and Weibull are the most appropriate models to characterize the time to reach a critical level of fouling, if the underlying random fouling growth laws are linear, power law and asymptotic respectively. Knowledge of these distributions and the methods to determine their parameters is useful for devising appropriate maintenance and cleaning schedules in a probabilistic framework.

Comparison of Crystallization Fouling in Plate and Double-Pipe Heat Exchangers

Comparison of Crystallization Fouling in Plate and Double-Pipe Heat Exchangers

Comparison of Crystallization Fouling in Plate and Double-Pipe Heat Exchangers

The selection of fouling resistances to design plate-and-frame heat exchangers is usually based on experience or guesswork. The primary aim of this study was to compare fouling resistances for plate heat exchangers with values obtained in a parallel double-pipe heat exchanger under comparable operating conditions. The double-pipe heat exchanger was selected because it represents a shell-and-tube heat exchanger in a simplified form. Correction factors for plate heat exchangers have been obtained by comparing the performance of the two heat exchanger types during calcium sulfate crystallization fouling. Fouling was investigated in both heat exchangers for two conditions: (1) particles present in the process solution were allowed to enhance the crystallization process and (2) particles present in the process solution were removed by an in-line 1-μm filter. For similar flow velocities, the plate heat exchanger was found to foul significantly less than the double-pipe heat exchanger, i.e. 20-25 times less in the presence of particles and around 15 times less when the particles were filtered out. When data for similar overall shear forces are compared, results for both heat exchanger types are much closer, even though the plate heat exchanger still seems to perform somewhat better. Fouling in plate-and-frame heat exchangers was also found to depend significantly on plate design. This will add a further complication in direct comparison with shell-and-tube heat exchangers.

Fouling of Nearly Incompatible Oils

The fouling of heat exchangers by asphaltenes in petroleum crude oils is found to be caused not only by incompatible crude oil mixtures but also by mixtures that are nearly incompatible. It is reasoned that the tendency for asphaltenes to adsorb on heated metal surfaces increases as the oil mixture approaches compositions at which asphaltenes precipitate. Based upon data for mixtures of Forties and Souedie crude oils, this region of near-incompatibility occurs for ratios of the solubility blending number to the insolubility number that are between 1.0 and 1.4. These numbers can be measured on individual oils using the oil compatibility model and tests and calculated for mixtures.

Membrane Filtration of Corn Steep Water

ABSTRACTMembrane filtration is a cost‐effective alternative to heat pasteurization of corn steep water. Trials were done in an operating ethanol plant with commercial spiral‐wound modules. Flux increased with transmembrane pressure and became independent of pressure at &gt;10 psi (69 kPa) with flux being higher at higher cross‐flow velocities. Average flux at 4× concentration factor over 24‐hr operating cycles was 34 L/m2/hr under optimum conditions. Capital cost of the membrane system is expected to be lower because it eliminates the heat pasteurizer and centrifuge and reduces cooling requirements. Operating cost of the microfilter are about one‐third of a heat pasteurization system and provides the opportunity to recover insoluble protein and starch for use in corn gluten feed. Microfiltered steep water could improve ethanol fermentation efficiency and reduce fouling of heat exchangers in the fermenters, beer still, and steep evaporators.

Calcium Sulfate Precipitation in the Presence of Nondominant Calcium Carbonate: Thermodynamics and Kinetics

This study addresses the fouling of heat exchangers by coprecipitating inorganic salts. It investigates the effects of nondominant CaCO3 on thermodynamics and kinetics of CaSO4 precipitation as well as on scale structure. Even though precipitating salts coexist in industrial water systems, because of the complexity of the fouling process, research has primarily been concentrated on a single salt precipitation. In addition, all thermodynamic predictive models and softwares only consider the effect of coexisting salts through the ionic strength by Debye−Huckel or modified forms of that. The results of this investigation indicate that the presence of a coprecipitating salt with a common ion affects the solubility constants of the salts, and therefore application of the solubility data obtained under a single salt precipitation is questionable for coprecipitating salts with common ions. Also, the kinetics of precipitation is affected by the presence of a common ion, and the traditional method of kinetic analy...

Petroleum Stability and Heteroatom Species Effects in Fouling of Heat Exchangers by Asphaltenes

Petroleum stability effects on heat exchanger fouling were studied using mixtures of heavy oil containing asphaltenes, and carrier fluids consisting of a fuel oil cut with varying amounts of added aliphatic or aromatic fluid. Fouling was measured in a recirculation loop using an annular, electrically heated probe. The effects of carrier fluid composition, dissolved oxygen, and heteroatomic species additions were investigated. Insolubles formed in the mixtures, measured by hot filtration, and deposits on the probe had compositions similar to asphaltenes. Fouling rates were correlated with instability indices, and with the concentrations of suspended asphaltenes.