Introduction

Coletti, Francesco; Joshi, Himanshu M.; Macchietto, Sandro; Hewitt, Geoff

doi:10.1016/b978-0-12-801256-7.00001-4

Cited by 14 publications

(16 citation statements)

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“…Moreover, the increasing thickness of the deposits over time leads to a reduction in the cross-sectional area with a consequential rise of the pressure drop. In 1972, Taborek et al indicated fouling as the major unresolved problem in heat transfer, but its relevance is still very high because of its impact in terms of energy losses, fuel consumption and emissions [ 29 , 30 ]. A similar influence of fouling on thermal and hydraulic resistances also takes place in steam cracking reactors, where the formation of coke on the inner wall of the tubular reactors represents the major reason of process inefficiency [ 31 ].…”

Section: Introductionmentioning

confidence: 99%

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

2021

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The almost ubiquitous, though undesired, deposition and accumulation of suspended/dissolved matter on solid surfaces, known as fouling, represents a crucial issue strongly affecting the efficiency and sustainability of micro-scale reactors. Fouling becomes even more detrimental for all the applications that require the use of membrane separation units. As a matter of fact, membrane technology is a key route towards process intensification, having the potential to replace conventional separation procedures, with significant energy savings and reduced environmental impact, in a broad range of applications, from water purification to food and pharmaceutical industries. Despite all the research efforts so far, fouling still represents an unsolved problem. The complex interplay of physical and chemical mechanisms governing its evolution is indeed yet to be fully unraveled and the role played by foulants’ properties or operating conditions is an area of active research where microfluidics can play a fundamental role. The aim of this review is to explore fouling through microfluidic systems, assessing the fundamental interactions involved and how microfluidics enables the comprehension of the mechanisms characterizing the process. The main mathematical models describing the fouling stages will also be reviewed and their limitations discussed. Finally, the principal dynamic investigation techniques in which microfluidics represents a key tool will be discussed, analyzing their employment to study fouling.

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Section: Introductionmentioning

confidence: 99%

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

2021

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“…Fouling in crude oil preheat exchangers presents refineries with major operational, environmental, and safety challenges, concerning issues such as reduced heat transfer, rising pressure drop, excess CO 2 emissions, waste disposal, hazards related to approaching furnace limits, crane operation, and personnel health and safety. These could result in substantial economic penalties amounting to about $12.5MM per annum for a 100 000 bbl/day refinery . Such fouling concerns are as old as heat exchangers themselves and have been scrutinized from molecular to large industrial scales using either empirical studies on deposit generating rigs (hot wires, microbomb reactors, , batch stirred cells, , and flow loops , ) or field studies on refinery preheat exchangers. − The studies were carried out as follows: the analysis of process data and characterization of foulant samples.…”

Section: Introductionmentioning

confidence: 99%

Cross Sectional Examination of a Fouled Tube Removed from a Crude Oil Preheat Exchanger

Behranvand

Mozdianfard

Díaz-Bejarano

et al. 2019

Ind. Eng. Chem. Res.

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A first attempt is presented to characterize intact foulant of a refinery preheater. A tube was removed from an exchanger located post-desalter and preflash-drum at a 4-year shutdown, and dissected into undisturbed cutout rings. Following visual inspection, elemental analysis (x-ray maps and line scans) was carried out and radial concentration profiles of the existing elements were established. A stratified coloured foulant layer inside the tube appeared in sine waves fluctuating at both axial and angular directions, likely evidencing for the first time a shadow effect and erosion process. Results agreed with our studies on a comparable exchanger of the same refinery. They confirm the proposed deposition mechanism and simulation results, indicating: formation of a stratified foulant consisting inorganics ranging 50wt%; presence of an acute inorganic deposition period along the chronic organic-inorganic fouling; and identification of foulant phases arrangement, amongst possible conductivity mixing models, as cocontinuous and effective medium theory structures.

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“…4 In other areas, such as refining applications, fouling can be caused by more than one mechanism at the same time. 2 Its consequences on the operation of chemical processes are of major concern.…”

Section: Introductionmentioning

confidence: 99%

“…6 This is most evident in the preheat train (PHT) of the crude distillation unit (CDU), which processes all the crude oil that comes into the refinery under extreme conditions, such as high temperature, varying range of composition, and high amounts of contaminants. 2 In this case, the extra thermal resistance in the heat exchangers reduces the coil inlet temperature (CIT) to the furnace, to compensate because more fuel is burned, increasing the amount of carbon emissions and the operational cost. If no mitigating action is performed in the HEN, the operational cost of refining operations can increase by several million dollars per year.…”

Section: Introductionmentioning

confidence: 99%

Integration of Optimal Cleaning Scheduling and Control of Heat Exchanger Networks Undergoing Fouling: Model and Formulation

Santamaria

Macchietto

2018

Ind. Eng. Chem. Res.

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The performance and operability of heat exchanger networks (HENs) is strongly affected by fouling, which involves the deposition of unwanted material, which reduces the heat-transfer rate and increases the pressure drop, the operational costs, and the environmental impact of the process. Periodical cleaning and control of the flow rate distribution in the HEN are used to mitigate the effects of fouling and restore the performance of the units. The optimal cleaning scheduling has been formulated as a mixed-integer linear programming (MILP) or mixed-integer nonlinear programming (MINLP) problem and is solved using various approaches. The optimal control has been formulated as a nonlinear programming (NLP) problem and is used to define the flow rate distribution of the network. Both problems share the same objective: minimization of the total cost of the operation. In principle, the simultaneous solution of the optimal control problem and the optimal cleaning scheduling problem should provide greater savings than the independent or sequential solution of the two problems, since the interactions of the two mitigation alternatives are considered. However, these two problems have been typically considered separately, because of modeling and solution challenges. Also, it is not quite clear what additional benefit a simultaneous solution may bring. The challenges for solving the integrated problem are the large scale of the associated optimization problem and the different time scales involved in each operational layer. Here, a general and efficient formulation is proposed, using a continuous time discretization scheme for the integrated problem of scheduling and control of HENs subject to fouling. A dynamic model of the heat exchangers is proposed that is sufficiently detailed to represent the physics of interest with novel modifications to address simultaneously their control and scheduling in a network. The problem is formulated as a MINLP and solved using deterministic optimization algorithms. The flexibility of the model and variations of the formulation are demonstrated with two small case studies. The formulation complexity versus scale and advantages are analyzed. The results show that considering the two problems simultaneously has a very strong synergistic effect, with over a 20% decrease in operational cost achieved, in comparison to using either fouling mitigation alternative individually.

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Introduction

Cited by 14 publications

References 0 publications

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

Cross Sectional Examination of a Fouled Tube Removed from a Crude Oil Preheat Exchanger

Integration of Optimal Cleaning Scheduling and Control of Heat Exchanger Networks Undergoing Fouling: Model and Formulation

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