Reaction Fouling Research Articles

Polymer Versus Polymerization Fouling: Basic Deposition Mechanisms During Emulsion Polymerization by the Example of a Vinyl Acetate and Versa 10 Copolymer

AbstractThe deposition process during emulsion polymerization can be classified as both particulate and reaction fouling, but a deeper understanding of the deposition mechanism, especially in combination with the polymerization process, is lacking. Here, a more in‐depth understanding of the deposition mechanism is sought by investigating the fouling formation of a Vinyl acetate and Versa 10 copolymer on a heated stainless steel surface during emulsion polymerization. Its deposition behavior is also compared with the behavior of an already reacted polymer. All possible influencing factors are investigated separately, and the fouling is quantified by the mass based fouling resistance and the fouling layer composition. The fouling rates of both experimental approaches (ongoing reaction versus already reacted polymer) are used to determine the fraction of reaction fouling along the reaction pathway. The solids content and the driving temperature difference are identified as the main factors influencing fouling formation. The deposited material is composed of latex particles and emulsifier with particle size and number depending on the respective equilibrium composition of the fluid phase. The reaction fouling rate is correlated with the proportion of free initiator radicals and the amount of dissolved monomer in the aqueous phase.

Overview of Butadiene Chemical Reaction Fouling in Steam Crackers and Its Control by Carbon Steel Surface Modification

The main objective of the Steam Cracker is to produce monomers prone to polymerization. The drawback is that polymerization can occur in the Steam Cracker itself. The main monomers fouling precursor is Butadiene. All along the separation process, Butadiene concentration and process temperature change. This implies step changes in polymer structure and fouling level. Several techniques are used to control this fouling, including oxygen ingress control, the use of additives such as antioxidants and free radical scavengers. By a catalytic effect, the metal surfaces can also be a polymerization initiator. The objective of passivation is to modify the Carbon Steel surface into stable magnetite and maghemite. Using electrochemistry to characterize different Carbon Steel samples, we were able to improve our passivation procedure. And when applying metal passivation, we were able to increase run length of Depropanizer reboilers limiting the fouling rate and its impact on operation.

Review: Bio-inspired surfaces for fouling resistance

This paper discusses the anti-fouling principle of lotus surfaces in nature and applies it to the production of anti-fouling surfaces, providing information and ideas for the research and application of anti-fouling. We discuss various fouling (Biofouling, Icefouling, Precipitation Fouling, Dust fouling, and Chemical Reaction Fouling) and their anti-fouling solution. Currently, no single engineered surface can solve the solid fouling problem extensively, so this paper mainly reviews various complex micro or macro structures and coatings that play a role in different fouling.

Fouling Pathways in Emulsion Polymerization Differentiated with a Quartz Crystal Microbalance (QCM) Integrated into the Reactor Wall

AbstractEmulsion polymerization fouling at hot interfaces is studied in situ, making use of a quartz crystal microbalance with dissipation monitoring (QCM‐D). The resonator crystal is heated with a ring‐shaped thermal pad from the back, turning it into a plate with elevated temperature. Configured to be one of the walls of a small reactor for emulsion polymerization, this resonator is prone to heat‐transfer fouling, similar to regular heated parts of process equipment. The fouling kinetics is readily quantified with this QCM. During polymerization at constant temperature (80 °C), some deposition is always observed. However, a film with a thickness of less than 1 μm (determined gravimetrically with the QCM) is sometimes found, which stabilizes the surface against the deposition of much thicker layers. When reaction fouling proceeds directly to thick deposits, a small increase in resonance bandwidth often occurs a few minutes prior to the main transition, presumably caused by coagulum formed in the bulk making first contact with the surface. Furthermore, particle fouling is studied with temperature ramps on nonreactive dispersions. Fouling, if present, is readily observed.

CFD investigation of fouling mechanisms in the crude oil preheat network

Fouling phenomena, generally related to heavy crude oils and bituminous petroleum fractions, nevertheless affects significantly the preheat train (PHT) of the light Algerian crude oil. In this study, a two dimensional model was developed using the computational fluid dynamic (CFD) method in order to investigate fouling behavior in the PHT of Algiers refinery. A fouling model was proposed specifically for the studied crude oil. The model includes a pseudo detailed chemical kinetic mechanism and it considers the deposition of inorganic matters. The proposed model was validated using the experimental results from literature. The simulation results show good agreements with the experimental data. The deposition mechanism of the two fouling routes was studied by analyzing the effect of flow velocity on the thermo-hydraulic conditions of near wall regions. The results indicate that the chemical reaction fouling is controlled by kinetic reaction process and the deposition of inorganic species is dominated by mass diffusion. The distribution of the initial fouling rate was evaluated along the entire heat exchangers network. The simulation results show that the inorganic process was predominant at the first heat exchanger and the chemical reaction fouling reaches its maximum at the PHT outlet.

Accounting for local thermal and hydraulic parameters of water fouling development in plate heat exchanger

Abstract The complex phenomenon of fouling when heating water solutions can significantly hamper the performance of heat exchangers. The fouling process is considered in an application for a plate heat exchanger (PHE) with enhanced heat transfer that proved to have much lower fouling tendencies than conventional shell and tube heat exchangers. To eliminate the drawbacks of the dimensional fouling model forms the dimensionless its form is developed. It is based on the equation for transport and chemical reaction fouling mechanism initially proposed for other types of fouling media. Thermo-hydraulic mathematical model of PHE under fouling conditions accounting for the distribution of local process parameters along heat transfer surface is presented. It enables to predict not only thermal performance of PHE, but also pressure losses. The mathematical model consists of the system of differential equations with the nonlinear right-hand side. Its solution is implemented with software for the personal computer. The model application is demonstrated with two practical examples. It confirms models' validity and its acceptable accuracy for practical calculations of PHE in industry and also the possibility of proposed dimensionless model application for different fouling substances with the similar types of fouling mechanism.

Fouling Management of Thermal Cracking Units

ABSTRACTVisbreakers and other thermal cracking units are thermal process units in crude oil refineries that upgrade heavy petroleum, usually residual oils produced from atmospheric or vacuum distillation of crude oil. The associated process streams of these units consist of heavy hydrocarbons with very high viscosities and impurities, resulting in fouling of the heat exchangers used to cool or heat these streams. This paper presents a practical fouling analysis for thermal cracking units in a refinery in Germany. Fouling management at this refinery was initiated as part of the refinery energy-saving program. Following similar analysis of the refinery's crude preheat trains, heat exchanger networks associated in the thermal cracking units were modeled by entering the plant monitoring data, network topology, and heat exchanger geometries into a commercial heat exchanger network simulator, SmartPM. Fouling behaviors of vacuum residue streams and thermal cracker residue streams were identified and quantified. Both chemical reaction fouling and particulate fouling mechanisms were identified to be responsible for the fouling in these streams. Dynamic fouling models were fitted and used to predict fouling of these heavy petroleum streams, which fouled on both the shell and tube sides of the shell-and-tube heat exchangers.

Temporal variations of cathode performance in air-cathode single-chamber microbial fuel cells with different separators

An ideal separator is essential for efficient power production from air-cathode single-chamber microbial fuel cells (MFCs). In this study, we use different kinds of membranes as separators, including Nafion 117 proton exchange membrane, polyethersulfone and poly(vinylidene fluoride) microfiltration membranes. Temporal variations of cathode performance are monitored during the experiment. Results show that MFCs with microfiltration membranes present higher power output but deterioration is still observed after about 600-h operation. With the utilization of appropriate separators (e.g., polyethersulfone membrane), biofouling, cation fouling and chemical scale fouling of the cathodes are alleviated while reaction fouling seems inevitable. Moreover, it is found that Coulombic efficiency (CE) and energy efficiency (EE) are also related to the cathode performance. Despite relatively high oxygen diffusivity (1.49 × 10−5 cm2 s−1), CE and EE of the MFC with 0.1 μm pore-size polyethersulfone membrane can reach 92.8% and 13.7%, respectively, when its average power density registers 403.5 mW m−2. This phenomenon might be attributed to the finding that the overall substrate consumption rate due to oxygen reduction and respiration is almost constant in the air-cathode MFCs. Oxygen leakage into the electrolyte can be inhibited due to the efficient oxygen reduction reaction on the surface of the cathode.

A Critical Analysis of the Compensation Effect and Its Application to Heat Exchanger Fouling Studies

Occurrences of the compensation effect in published studies on the initial rate of heat exchanger fouling are discussed. When fouling-rate experiments are performed on a series of related fluids, it is shown that random errors in the measurements can create an apparent compensation effect. This explains some reported occurrences in the literature. Other reported instances of the compensation effect show a systematic variation in apparent activation energy with fluid flow rate. It is shown that these may be the result of analyzing the temperature dependence of the overall rate of reaction. The conditions under which the compensation effect is expected when flow rate is varied are explored using synthetic data generated by a model for chemical reaction fouling.

Exploration of alternative models for the aging of fouling deposits

AbstractThe effect of fouling in heat‐transfer devices (HTDs) is complicated by aging of the fouling deposits. Aging is, like deposition, often sensitive to temperature, so that heat transfer, deposition, and aging are coupled phenomena. Ishiyama et al. (AIChE J. 2010;56:531–545) presented a distributed model of the aging of deposits formed by chemical reaction fouling and illustrated its effect on thermal and hydraulic performance of a HTD operating in the turbulent flow regime. Two‐layer models, simpler than the distributed model, are explored. The deposit is considered to consist of two layers, fresh and aged; this simple picture is shown to be sufficient to interpret thermal and hydraulic aspects of deposit aging when HTDs are operated at constant heat flux (as reflecting laboratory experiments) but not in cases where the constant wall temperature approximation is more realistic. © 2011 American Institute of Chemical Engineers AIChE J, 2011

HiTRAN® Wire Matrix Inserts in Fouling Applications

Fouling characteristics are dictated largely by the properties of the thermal and hydrodynamic boundary layers. As a result, fouling mitigation strategies must take into account the conditions in this region. hiTRAN wire matrix tube inserts are a useful tool in altering the conditions near the tube wall, especially in the laminar and transition flow regions. This review article considers particle image velocimetry and laser doppler velocimetry measurements, which were employed in order to show the hydrodynamic differences between plain tubes and those containing inserts. Measurements indicate that the wall shear rate in tubes containing hiTRAN inserts operating in the laminar flow regime is similar to that for plain bore tubes operating in the turbulent flow regime. Moreover, the increased tube-side heat transfer coefficient that results from the reduction of the thermal boundary layer allows operation with smaller Effective Mean Temperature Differences (EMTDs). This enables the designer to reduce the tube wall temperature to a level below the fouling threshold temperature, e.g., to combat crude oil fouling. The results from the laser analyses into the hydrodynamic boundary layer are backed up by recent research data investigating the effect of hiTRAN inserts on sedimentation and particulate fouling. The thickness of the fouling layer was measured by applying a combination of photographic and laser measurement techniques. The results are compared to plain tube data and are reported as a function of both flow rate and hiTRAN insert packing density. The impact of altering the hydrodynamic and thermal conditions near to the wall is subsequently demonstrated for different fouling mechanisms. Studies of the impact of hiTRAN inserts on biological and chemical reaction fouling in crude oil processing are also reviewed. A better understanding of the threshold shear rates and wall temperatures for different fouling mechanisms is required for any study into the impact of fouling. Combining this knowledge with the principles outlined in this article clearly emphasizes the benefit of using hiTRAN wire matrix inserts as a powerful tool to mitigate 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.

Testing a mathematical model for initial chemical reaction fouling using a dilute protein solution

AbstractA 1 wt% lysozyme solution was used as a model fluid to test a previously formulated mathematical model for the initial chemical reaction fouling rate of a heat transfer surface. The experimental results showed that, at a given wall temperature, a maximum initial fouling rate existed over a range of fluid velocities. The maximum rate and the fluid velocity at which it occurred both increased as the wall temperature increased. These observations were consistent with the model. Quantitatively, the average absolute percent deviation between the experimental results and the optimum model predictions was 23,3%. The decrease in initial fouling rate with increasing velocity at high fluid velocities was even greater than predicted by the model.

Fouling of heat exchangers

1. Introduction. 2. Basic principles. 3. The cost of fouling. 4. General models of fouling. 5. Fluid flow and mass transfer. 6. Adhesion. 7. Particulate deposition. 8. Crystallisation and scale formation. 9. Freezing fouling or liquid solidification. 10. Fouling due to corrosion. 11. Chemical reaction fouling. 12. Biological growth on heat exchanger surfaces. 13. The design, installation, commissioning and operation of heat exchangers to minimise fouling. 14. The use of additives to mitigate fouling. 15. Heat exchanger cleaning. 16. Fouling assessment and mitigation in some common industrial processes. 17. Obtaining data. Index.

Chemical reaction fouling: A review

Recent research on fouling of organic fluids is renewed. Fouling in organic mixtures can be caused by numerous reactions, including autoxidation, polymerization and thermal decomposition. Understanding of autoxidation processes and their link to fouling has developed markedly in the past few years. By contrast, for fouling under non-oxidative conditions, the chemical and physical processes have not been adequately explored.

A study of autoxidation reaction fouling in heat exchangers

AbstractThe mechanism of autoxidation reaction fouling in single phase liquid heat transfer under turbulent flow conditions was studied using model solutions of indene in lube oil recirculated through a tubular fouling probe which permitted both thermal and mass deposition measurements. The fouling rate was initially constant, and then accelerated as polyperoxide gums reached their solubility limit. Deposit composition and morphology in the tubular device are compared with results obtained in an annular probe with a short heated length. The initial fouling data collected over surface temperatures of 180−255°C and flow velocities of 0.5–2.6 m/s (Re = 3000 − 16000) gave reasonable agreement with a boundary layer reaction model.

Regression analysis of a chemical reaction fouling model

AbstractA previously reported mathematical model for the initial chemical reaction fouling of a heated tube is critically examined in the light of the experimental data for which it was developed. A regression analysis of the model with respect to that data shows that the reference point upon which the two adjustable parameters of the model were originally based was well chosen, albeit fortuitously.

Chemical reaction fouling of organic fluids

AbstractChemical reaction fouling of heat exchangers involves deposition that is caused by chemical reactions which occur in the fluid, or on the surface itself. The factors which influence fouling of organic fluids via autoxidation and thermal decomposition processes are described and the dependence of the rate of thermal fouling on chemical effects and process variables demonstrated. Mitigation techniques are outlined in brief.

Performance of two heat transfer fouling probes for various fluids

AbstractThe predictions of two commonly used fouling monitoring devices, namely a heated rod in an annulus and a coiled wire in cross‐flow are compared. As fouling fluids, heptane with dissolved styrene (to simulate chemical reaction fouling), heptane with suspended particles (to simulate particulate fouling) and Kraft pulp black liquor (where both the above fouling mechanisms may occur) have been used.

Optimal design of a heat exchanger undergoing reaction fouling

AbstractThe design of heat exchangers which resist fouling is examined. It is shown that for asymptotic reaction fouling in a uniform wall temperature exchanger with outlet fluid temperature kept constant, it is possible to obtain an optimum combination of exchanger size and tube‐side temperature. This optimum minimises the amount of fouling in the system. An equation which gives a good approximation to the optimum is derived, and its limitations discussed.