Fouling In Plate Heat Exchangers Research Articles

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).

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.

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.

Calcium Chelation by Phosphate Ions and Its Influence on Fouling Mechanisms of Whey Protein Solutions in a Plate Heat Exchanger.

Fouling of plate heat exchangers (PHEs) is a recurring problem when pasteurizing whey protein solutions. As Ca2+ is involved in denaturation/aggregation mechanisms of whey proteins, the use of calcium chelators seems to be a way to reduce the fouling of PHEs. Unfortunately, in depth studies investigating the changes of the whey protein fouling mechanism in the presence of calcium chelators are scarce. To improve our knowledge, reconstituted whey protein isolate (WPI) solutions were prepared with increasing amounts of phosphate, expressed in phosphorus (P). The fouling experiments were performed on a pilot-scale PHE, while monitoring the evolution of the pressure drop and heat transfer coefficient. The final deposit mass distribution and structure of the fouling layers were investigated, as well as the whey protein denaturation kinetics. Results suggest the existence of two different fouling mechanisms taking place, depending on the added P concentration in WPI solutions. For added P concentrations lower or equal to 20 mg/L, a spongy fouling layer consists of unfolded protein strands bound by available Ca2+. When the added P concentration is higher than 20 mg/L, a heterogeneously distributed fouling layer formed of calcium phosphate clusters covered by proteins in an arborescence structure is observed.

Predicting the distribution of whey protein fouling in a plate heat exchanger using the kinetic parameters of the thermal denaturation reaction of β-lactoglobulin and the bulk temperature profiles.

Fouling of plate heat exchangers (PHE) is a severe problem in the dairy industry, notably because the relationship between the build-up of protein fouling deposits and the chemical reactions taking place in the fouling solution has not yet been fully elucidated. Experiments were conducted at pilot scale in a corrugated PHE, and fouling deposits were generated using a model β-lactoglobulin (β-LG) fouling solution for which the β-LG thermal denaturation reaction constants had been previously determined experimentally. Then 18 different bulk temperature profiles within the PHE were imposed. Analysis of the fouling runs shows that the dry deposit mass per channel versus the ratio R=kunf/kagg (with kunf and kagg representing, respectively, the unfolding and aggregation rate constants computed from both the identification of the β-LG thermal denaturation process and knowledge of the imposed bulk temperature profile into the PHE channel) is able to gather reasonably well the experimental fouling mass data into a unique master curve. This type of representation of the results clearly shows that the heat-induced reactions (unfolding and aggregation) of the various β-LG molecular species in the bulk fluid are essential to capture the trend of the fouling mass distribution inside a PHE. This investigation also illustrates unambiguously that the release of the unfolded β-LG (also called β-LG molten globule) within the bulk fluid (and the absence of its consumption in the form of aggregates) is a key phenomenon that controls the extent of protein fouling as well as its location inside the PHE.

Investigation of Fouling in Plate Heat Exchangers at Sugar Factory

Investigation of Fouling in Plate Heat Exchangers at Sugar Factory

Experimental study on microbial fouling characteristics of the plate heat exchanger

Iron bacteria (IB) and slime-forming bacteria (SFB) are the most common in circulating cooling water. In order to study on the characteristics of microbial fouling in plate heat exchangers, an experimental study was carried out for the fouling characteristics of IB and SFB. The fouling characteristics in the plate heat exchanger under the different flow velocity, temperature and concentration were investigated for these two bacteria and the mixture of them. The results show that the asymptotic value of fouling resistance and the time of reaching the asymptotic value decreases with the increase of fluid velocity. The asymptotic value of fouling resistance increases with the increase of concentration. And the influence of temperature is different for the two kinds of bacteria. When these two bacteria are mixed, the IB and the SFB grow synergistically because the IB have strong ability in microbial fouling and the SFB have the high secretion rate of extracellular polymeric substances.

Investigation of CaCO3 fouling in plate heat exchangers

An experimental investigation, coupled with theoretical modeling of CaCO3 fouling in plate-and-frame type heat exchangers (PHEs) have been conducted. Four different plates, made of SS-304, are used in two different surface patterns (chevron and zig-zag) of varying corrugation severity (waviness depth and pitch) and area enhancement. They were further characterized in clean, non-fouled convection by their measured heat transfer coefficients and friction factors in the Reynolds number range of 600–6000. The flow-fouling experiments delineate the effects of temperature and plate-surface geometry on growth rates and stabilization of fouling resistance, along with the anti-fouling behavior of plates coated with a hydrophobic PTFE (Teflon) film. Moreover, the microscopic structure of fouling deposits is mapped in a scanning-electron microscope. Corrugated plates with the largest height-to-pitch ratio and hydraulic diameter are found to have the lowest fouling growth rate and resistance; Teflon-film coating of plate surface is also found to mitigate fouling relative to the performance of bare stainless steel plates. Finally, a semi-empirical fouling model, based on the Prandtl–Taylor analogy, has been devised to describe the experimental data and provide a predictive tool.

Accounting for the thermal resistance of cooling water fouling in plate heat exchangers

Of the many different approaches available to mitigate fouling, the use of enhanced heat transfer surfaces is a principal method. The flow in channels of plate heat exchangers (PHEs) has high levels of turbulence due to the channels intricate geometry. In principle therefore, this type of heat transfer augmentation should lead to fouling mitigation. The effects of process parameters on fouling in PHE channels are studied in this article. The asymptotic behaviour of water fouling is examined specifically and the net rate of fouling accumulation is described as the difference between the fouling deposition rate and the fouling removal rate. An equation is proposed to account for how the fouling resistance varies with time. The conclusion is that for scaling there exist threshold conditions on wall shear stress, wall temperature and salt content, beyond which fouling deposition starts. The fouling deposition rate expression proposed for tubes incorporating heat transfer enhancement as used by Yang and Crittenden is adapted to be used in a new model for PHEs. Comparison with experimental data published in the literature reveals good agreement with the proposed model. The model can then be used to predict cooling water fouling development over time for all the heat exchangers in a chosen industrial circuit.

Mitigation of Fouling in Plate Heat Exchangers for Process Industries

Among different methods for mitigation of fouling the use of enhanced heat transfer surfaces is one of the major categories. Heat transfer enhancement is one of the main features of Plate Heat Exchanger (PHE) and mitigation of fouling render even more advantages to the use of this type of heat transfer equipment in different applications at process industries. In present study the period of fouling deposit formation in PHEs and influencing it factors are investigated. To estimate development of fouling thermal resistance with time the Equation is proposed. The pictures of fouling deposit distribution along the plate of PHE for fresh water heating are analyzed. The conclusion is, that for scaling fouling there exist some threshold conditions on wall shear stress, wall temperature and salt content, after which fouling deposition starts. The expression of fouling deposition rate proposed for the tubes with heat transfer enhancement by Yang and Crittenden is used. Comparison with available in literature experimental data have shown good agreement with proposed model, when one its parameter is adjusted. For certain cooling water circuit of a big industrial enterprise this parameter can be determined by data about fouling in one heat exchanger. After that the model can be used for prediction of cooling water fouling development with a time in all heat exchangers of this circuit.

Experimental observation of surface morphology effect on crystallization fouling in plate heat exchangers

In this study, stainless steel test plates with different surface roughness and textures, which are used as the heat transfer surface of a plate heat exchanger, are tested individually in calcium carbonate fouling experiments. The present experimental results clearly indicate a strong correlation between the surface roughness and the amount of crystallization fouling deposit. Through detailed image analysis, four stages of the formation of crystallization fouling are identified, and the impact of the surface morphology on the extent of crystallization fouling is described qualitatively.

Design and performance of a low-frequency non-intrusive acoustic technique for monitoring fouling in plate heat exchangers

The fouling of plate heat exchangers (PHE) is a serious problem in the food industry. Fouling reduces both PHE efficiency and food quality and can also give rise to microbiological problems. In order to monitor fouling inside PHE in real time, a new acoustic technique, using multiple optimized non-intrusive sensors, was developed for experimental on-line trials. Low-frequency acoustic waves were propagated through the plates, and these waves were analyzed to measure their ability to detect fouling inside the PHE. By comparing the evolution of the acoustic wave parameters (e.g. power and delay), an indicator of the fouling rate is obtained for each zone inside the exchanger. The results of this analysis show that low-frequency acoustic waves are sensitive to PHE fouling.

Influence of Surface Properties and Characteristics on Fouling in Plate Heat Exchangers

The scope of the present work was to investigate the influence of surface properties of corrugated heat exchanger plates on calcium sulpate crystallization fouling from aqueous salt solutions. The applied surface treatment technologies for the heat exchanger plates are ion beam implantation, ion sputtering, carbo-nitriding & oxidizing, and Ni-P-PTFE coating. Ten pairs of Alfa Laval M3 heat exchanger plates were treated with these techniques and used for this study. Other process parameters such as temperature, solution composition, flow velocity, and the corrugation inclination angle of the plates were kept constant in order to allow for a comparison between the different surface treatments. To evaluate the influence of surface roughness on CaSO4 crystallization fouling, one pair of plates was electropolished. Surface energy and surface roughness measurements were carried out to characterize the treated surfaces.

Effect of Geometry and Flow Conditions on Particulate Fouling in Plate Heat Exchangers

This article describes particulate fouling experiments performed on small-scale and full-scale plate heat exchangers for three different corrugation angles (30 deg, 45 deg and 60 deg). The velocity effect has been studied as well as the particle type and concentration effects. The test duration ranges between 20 and 1,500 h in order to reach asymptotic behavior. The results clearly indicate that the corrugation angle has a major influence on the asymptotic fouling resistance. Increasing the corrugation angle leads to lower values for the fouling resistance. Furthermore, for a given corrugation angle, the asymptotic fouling resistance is inversely proportional to the velocity squared. Finally, the asymptotic fouling resistance is proportional to the particle concentration. Fouling mitigation can be obtained by taking into account at the design stage the heat exchanger geometry and fluid velocity.

Effect of Suspended Particles on Crystallization Fouling in Plate Heat Exchangers

The presence of suspended particles in solutions significantly affects the crystallization rate. This study investigates the effects of calcium sulphate (crystallizing) particles and alumina (noncrystallizing) particles on calcium sulphate crystallization fouling in a plate heat exchanger. Calcium sulphate particles are formed during the preparation of calcium sulphate solution due to breakage of calcium sulphate crystals growing on the heat transfer surface. These suspended particles settle on the heat transfer surface and act as nuclei. The availability of extra nucleation sites increases the crystallization rate significantly. These particles can be removed with a filter, and the removal of the particles prevents this extra assistance available for crystallization. Therefore, the crystallization rate is reduced markedly. Alumina particles were purposely added during the preparation of calcium sulphate solutions. These particles attach loosely to the heat transfer surface compared with crystalline deposits which adhere strongly. Therefore, calcium sulphate crystals growing on these particles are removed easily. Also, alumina particles settling on the growth faces of calcium sulphate crystals may act as a distorting agent. This slows down the growth of the crystals.

Crystallization Fouling in Plate Heat Exchangers

Crystallization fouling of calcium sulfate was investigated in a plate and frame heat exchanger. The effects of flow velocity, wall temperature, and CaSO4, concentration on the fouling rates have been investigated and the distribution of scale along the heat transfer surface has been observed. The measured fouling curves are compared with predictions from a surface reaction controlled model.

Particulate Fouling in Plate Heat Exchangers

Particulate fouling in an Alfa-Laval P20 plate heat exchanger was investigated using a suspension of aluminum oxide particles in heptane. Process parameters such as flow velocity, heat flux, and particle concentration were varied over a considerable range. In this paper, the influence of the above parameters on the asymptotic fouling resistance is discussed. Measured values of fouling resistance are compared with results for a double-pipe heat exchanger and with the prediction of a fouling model from the literature.

Cooling Water Fouling in Plate Heat Exchangers

Heat exchangers using cooling water are designed with fouling resistance applicable to tubular equipment, in most cases TEMA recommended values. Plant experiences indicate that plate heat exchangers produce substantially lower fouling rates due to turbulence induced by the plate corrugations. Furthermore, plate exchangers are more severely penalized by fouling resistance than tubular exchangers because of the high heat transfer coefficients typical of plate exchangers. To supply reliable folding data to the designer, APV Company. Ltd. sponsored a research project to study fouling in plate exchangers with Heat Transfer Research. Inc. (HTRI). The test fluid was a typical, treated cooling-tower water. Results of these experiments, described in this paper, show that at typical operating conditions the fouling resistances for plate exchangers are substantially lower than those used for tubular equipment.