Emilio Diaz-Bejarano

Detection of changes in fouling behavior by simultaneous monitoring of thermal and hydraulic performance of refinery heat exchangers

Abstract Monitoring of pre-heat trains in oil refineries is a crucial activity to assess the gradual decay in performance of heat transfer equipment due to fouling. It is also important to assist in operational decisions with respect to fouling mitigation options and cleaning strategies. In this paper, a novel graphical representation of time varying operational data is proposed to monitor crude oil fouling. This dynamic thermo-hydraulic plot, named the TH-λ plot, simultaneously captures both thermal and hydraulic performance and presents it in a way easily interpreted by field engineers. Its features and applications are demonstrated here for typical situations using data generated using an advanced dynamic simulation model for shell-and-tube heat exchanger undergoing fouling. The results show that consideration of thermal and hydraulic effects, together with process dynamics, is essential to adequately monitor performance, detect changes in fouling behaviour and properly interpret available data. They also show this is achievable using only measurements of inlet and outlet streams to heat exchangers.

Organic and inorganic fouling in heat exchangers – Industrial case study: Analysis of fouling state

A comprehensive model-based thermo-hydraulic methodology is used to investigate fouling behaviour in refinery heat exchangers where high concentration of inorganics in the deposits was reported. The method combines a data-driven analysis of plant measurements (including pressure drop) with a model-based analysis using advanced models of shell-and-tube heat exchangers undergoing fouling. A deposit model capable of tracking composition and deposition history was extended to include thermal-conductivity mixing models appropriate for various deposit structures. Substantial new and useful information can be extracted from the plant measurements in comparison to current practice: the thickness, the effective conductivity, and the radial conductivity and composition profiles of the deposits, reflecting the exchanger operation history. Episodes of rapid and acute fouling, and deposition of inorganic materials could be identified and quantified. A validation of the approach was carried out by (i) a comparison of averaged predicted and experimental inorganic weight fractions in a mixed deposit sample collected at the end of run, and (ii) an initial comparison of predicted radial inorganics profiles and experimental ones (obtained with SEM-EDX) in deposits from similar exchangers. Both steps yielded surprisingly good agreement. The study indicates that the method employed represents a new powerful, model-based analysis tool for monitoring, diagnosis and troubleshooting of fouling in heat exchangers.

Crude Oil Fouling Deposition, Suppression, Removal, and Consolidation—and How to Tell the Difference

ABSTRACT Crude oil fouling on heat transfer surfaces is often described as the result of two competing mechanisms: a deposition and a deposition-offsetting mechanism. There is uncertainty about whether the offsetting mechanism is suppression (due inhibition of attachment or back-diffusion of foulant from near the wall into the bulk) or removal of foulant already deposited, due to (i) difficulties in experimentally identifying and isolating the key phenomena and (ii) the cumulative measurement of deposition rates by monitoring thermal exchange rates (or resistance) alone. Here, the question is addressed of whether it is conceptually possible to distinguish such phenomena, and if so, in which conditions. A recently developed two-dimensional (2D) deposit model and a thermohydraulic model of a heat exchanger tube are used to assess the system response to removal, suppression, aging, and consolidation (for which a new model is proposed). It is shown that while suppression or removal lead to undistinguishable behavior during overall deposit growth, thermal and hydraulic responses will differ in certain conditions, for which an experimental procedure is suggested. Simultaneous consideration of thermal and hydraulic effects and accurate characterization of the deposit aging and consolidation processes are suggested as a way to allow the unambiguous identification of the dominant deposition-offsetting mechanism.

Model-based monitoring of thermal-hydraulic performance of refinery heat exchangers undergoing fouling

Abstract Monitoring of fouling is key to assess the performance of refinery heat exchangers, estimate resulting economic costs, and assist in planning of mitigation and cleaning. Such monitoring typically addresses just thermal performance, while hydraulic limitations are often also important. A dynamic thermo-hydraulic plot (TH-λ) for simultaneous monitoring the thermal and hydraulic performance of heat exchangers was recently presented. The features and benefits of the plot were illustrated for fixed inlet conditions. In this work, a model-based monitoring solution is presented which enables the application of the TH-λ plot with time-varying inputs. The TH-λ concept is integrated with a software framework that describes a shell-and-tube heat exchanger using a high-fidelity dynamic, distributed system model undergoing fouling. A method is presented to decouple the variations in exchanger performance due to changes in inlet conditions from those due to changes in fouling rates and/or deposit properties. The method and its benefits are illustrated with a case study using typical refinery data.

Modelling and Prediction of Shell-Side Fouling in Shell-And-Tube Heat Exchangers

ABSTRACT Fouling is a challenging, longstanding, and costly problem affecting a variety of heat transfer applications in industry. Mathematical models that aim at capturing and predicting fouling trends in shell-and-tube heat exchangers typically focus on fouling inside the tubes, while fouling on the shell side has generally been neglected. However, fouling deposition on the shell side may be significant in practice, impairing heat transfer, increasing pressure drops, and modifying flow paths. In this paper, a new model formulation is presented that enables capturing fouling on the shell side of shell-and-tube heat exchangers including the effect of occlusion of the shell-side clearances. It is demonstrated by means of an industrial case study in a crude oil refinery application. The model, implemented in an advanced simulation environment, is fitted to plant data. It is shown to capture the complex thermal and hydraulic interactions between fouling growth inside and outside of the tubes, the effect of fouling on the occlusion of the shell-side construction clearances, and to unveil the impact on shell-side flow patterns, heat transfer coefficient, pressure drops, and overall exchanger performance. The model is shown to predict the fouling behavior in a seamless dynamic simulation of both deposition and cleaning operations, with excellent results.

Condition-based chemical cleaning of crude oil deposits – a conceptual model

Abstract Chemical cleaning represents a less expensive option than mechanical cleaning (e.g. hydro-blast). While the latter typically complete removes the fouling deposits, the effectiveness of chemical cleaning depends on many factors (choice of chemical, deposit composition and ageing, etc.) and often leaves the surface only partially clean. This affects the rate of fouling when operations resumes. To assess the benefits of chemical cleaning it is important to capture the trade-offs between the effectiveness of cleaning agent and time and results produced. A novel chemical cleaning model is presented which takes into account deposit conditions, effectiveness of the chemicals used and processing time to describe the thermal and hydraulic performance achieved.