Simon J. Pugh

Fouling in Crude Oil Preheat Trains: A Systematic Solution to an Old Problem

A major cause of refinery energy inefficiency is fouling in preheat trains. This has been a most challenging problem for decades, due to limited fundamental understanding of its causes, deposition mechanisms, deposit composition, and impacts on design/operations. Current heat exchanger design methodologies mostly just allow for fouling, rather than fundamentally preventing it. To address this problem in a systematic way, a large-scale interdisciplinary research project, CROF (crude oil fouling), brought together leading experts from the University of Bath, University of Cambridge, and Imperial College London and, through IHS ESDU, industry. The research, coordinated in eight subprojects blending theory, experiments, and modeling work, tackles fouling issues across all scales, from molecular to the process unit to the overall heat exchanger network, in an integrated way. To make the outcomes of the project relevant and transferable to industry, the research team is working closely with experts from many world leading oil companies. The systematic approach of the CROF project is presented. Individual subprojects are outlined, together with how they work together. Initial results are presented, indicating that a quantum progress can be achieved from such a fundamental, integrated approach. Some preliminary indications with respect to impact on industrial practice are discussed.

Fouling During the Use of Seawater as Coolant—the Development of a User Guide

IHS ESDU recently published its latest “User Guide” to fouling in heat exchange systems, for systems with fresh water as the coolant. ESDU 08002 is the third in a group, following the development of the Crude Oil Fouling User Guide (ESDU 00016) and the Seawater Fouling User Guide (ESDU 03004). ESDU 08002 was developed by IHS ESDU over a period of 5 years under the guidance of the Oil Industry Fouling Working Party, a collaborative team of oil refiners, heat transfer equipment and services suppliers, and universities. It provides designers and operators of cooling-water facilities with a practical source of guidance on the occurrence, the mechanisms, and the mitigation of freshwater fouling in these systems. IHS ESDUs Oil Industry Fouling Working Party was formed in recognition of the huge economic and environmental importance of heat exchanger fouling and the potential benefits that can accrue from better understanding of mitigation strategies. Work is now underway on reboiler and FCCU fouling. The development of the User Guide ESDU 08002 is discussed in this article and its technical content is summarized.

Approximate Design and Costing Methods for Heat Exchangers

Methodologies for the rapid sizing and costing of heat exchangers have been developed under the aegis of ESDU International plc, London. This paper is a summary of a group of design guides (referred to as “data items”) that cover a wide range of heat exchanger configurations. These data items are aimed at providing rapid selection, sizing, and costing at the process design stage. For two-stream exchangers, the C value method has been adopted in which the costs are expressed per unit (Q/ΔT m ), where [Qdot] is the heat load and ΔT m the mean temperature difference. The development and applications of this method are reviewed, with an emphasis on comparisons between various types of exchanger. The nature of variations from the standard cases considered are also discussed. Though the C value method can be applied to two-stream plate-fin exchangers, such exchangers often operate with multiple streams. Approximate calculations for the design of such multistream exchangers can be made using the concept of the volumetric heat transfer coefficient. This methodology can be combined with standard curves of the cost per unit volume as a function of volume to obtain an approximate costing of such exchangers.

Retrofitting Crude Oil Refinery Heat Exchanger Networks to Minimize Fouling While Maximizing Heat Recovery

Abstract The use of fouling factors in heat exchanger design and the lack of appreciation of fouling in traditional pinch approaches have often resulted in crude preheat networks that are subject to extensive fouling. The development of thermal and pressure drop models for crude oil fouling has allowed its effects to be quantified so that techno-economic analyses can be performed and design options compared. The application of these fouling models is described here on two levels: the assessment of increasing heat recovery in stream matches (e.g., by adding extra area to exchangers) and the design of a complete network using the Modified Temperature Field Plot. Application to a refinery case study showed that, at both the exchanger and network levels, designing for maximum heat recovery (e.g., using traditional pinch approaches) results in a less efficient system over time due to fouling effects.

Extraction of Crude Oil Fouling Model Parameters from Plant Exchanger Monitoring

Most of the semi-empirical “threshold fouling” models for crude oil fouling in shell-and-tube exchangers have been developed and validated using data collected at what may be considered to be “point” or localized conditions. In practice, both velocity and wall temperature can vary significantly within a heat exchanger, leading to difficulty in applying the models in exchanger design and extracting fouling information from exchanger performance monitoring. A partial simulation model is presented here, incorporating a linear temperature distribution. This short-cut model is compared with a more detailed simulation in order to establish its reliability. Pressure drop using a smooth layer model is also considered. The short-cut approach is employed in a data reconciliation study of an operating crude preheat train, which indicates that the original threshold fouling model of Ebert and Panchal gives a better description of the observed fouling behavior.

Management of Crude Preheat Trains Subject to Fouling

Crude oil refinery preheat trains are designed to reduce energy consumption, but their operation can be hampered by fouling. Fouling behaviors vary from one refinery to the next. Effective management of preheat train operation requires inspection of historical plant performance data to determine fouling behaviors, and the exploitation of that knowledge in turn to predict future performance. Scenarios of interest can include performance based on current operating conditions, modifications such as heat exchanger retrofits, flow split control, and scheduling of cleaning actions. Historical plant monitoring data are frequently inconsistent and usually need to be subject to data reconciliation. Inadequate data reconciliation results in misleading information on fouling behavior. This article describes an approach to crude preheat train management from data reconciliation to analysis and scenario planning based around a preheat train simulator, smartPM, developed at Cambridge and IHS. The proposed methodology is illustrated through a case study that could be used as a management guideline for preheat train operations.

Design of Shell-and-Tube Heat Exchangers to Achieve a Specified Operating Period in Refinery Preheat Trains

Fouling dominates the design of heat exchangers used in crude oil preheat trains. It also dominates the lifetime cost of the trains, where the most important cost factor is lost profit through reduced production. Thus, the design objective should be the identification of geometries that provide acceptable performance throughout a desired operating period. This paper suggests a new design approach for shell-and-tube heat exchangers in refinery preheat trains that uses dynamic crude oil fouling models rather than conventional fouling factors to yield designs that are capable of achieving a specified operating period between cleaning operations.

Considering In-Tube Crude Oil Boiling in Assessing Performance of Preheat Trains Subject to Fouling

Oil refinery preheat trains can exhibit unwanted two-phase flow behavior. An example is boiling of crude oil inside heat exchangers, when the local pressure is not high enough to keep crude in a liquid state. This often arises when the pump is undersized. Understanding the two-phase behavior and assessing the boiling heat transfer coefficients would result in a better prediction and estimation of exchanger fouling. Where single-phase modeling is used under boiling conditions, the anomalous behavior leads to unrealistic estimates of fouling resistance, and can severely underpredict the increased pressure drop and consequent loss of crude throughput. There is little public information on fouling in two-phase flows as laboratory experiments are very costly, despite the importance of this in refinery heat exchangers and furnaces. Indeed, the importance of crude boiling is likely to increase as lighter crudes such as shale oils are processed. These lighter crudes are often blended with heavier crudes to maintain an appropriate refining average density. This paper consists of two sections. The first section uses industrial monitoring data to illustrate fouling behavior for a heat exchanger that undergo both boiling and fouling. The second section discusses simulations to evaluate thermohydraulic behavior when the crude undergoes boiling. The analysis requires coupled heat transfer, and hydraulic and surface fouling aspects; a commercial preheat train network simulator, SmartPM, was used for this study.

Effect of flow distribution in parallel heat exchanger networks: use of thermo-hydraulic channeling model in refinery operation

Abstract Parallel branches are commonly observed in industrial heat exchanger networks (HENs). Despite the important relationship between flow distribution and network efficiency, not all parallel branches comprise of flow controllers or not least, flow measurements. When the network is subject to fouling, uncontrolled flow branches can introduce undesired phenomenon such as thermo-hydraulic channeling (THC) [presented at the 2007 HEFC conference; Ishiyama et al., Effect of fouling on heat transfer, pressure drop and throughput in refinery preheat trains]. Recent analysis of crude preheat train heat exchangers has shown the need to use THC models, in particular, for situations where there is insufficient flow measurement data, especially in nonsymmetric branches. This paper revisits the THC model and highlight practical importance of the THC phenomenon through analysis of plant data. The hydraulic aspect of the analysis is strongly linked to the knowledge of deposit thermal conductivity. A case study of a section of a crude refinery HEN is used to illustrate the use of thermo-hydraulic models in data reconciliation to understand flow imbalances caused due to differences in operating conditions and fouling of heat exchangers in each branch of a parallel network.AbstractParallel branches are commonly observed in industrial heat exchanger networks (HENs). Despite the important relationship between flow distribution and network efficiency, not all parallel b...

Quantifying implications of deposit aging from crude refinery preheat train data

Abstract Heat exchanger fouling has been studied for some time in the petroleum industry. As understanding of fouling dynamics and mitigation methods improves, refinery fouling mitigation strategies are changing. The implications of deposit aging in refinery units have not been addressed in detail: aging refers to where the deposit undergoes physical and chemical conversion over time. In the 2009 Heat Exchanger Fouling and Cleaning conference, Wilson et al. [Ageing: Looking back and looking forward] presented a simple framework illustrating how deposit aging impacts heat exchanger thermal and hydraulic performance. This paper presents insights into deposit aging gained from analysis of refinery monitoring data. Two case studies are presented: (i) one from the Preem refinery in Sweden where stream temperature, flow and gauge pressure measurements indicated a higher deposit thermal conductivity in exchangers located in the hotter section of the preheat train. (ii) US refinery stream temperature, flow and plant cleaning log data, showing an increased resistance to cleaning when deposits are exposed to high temperature for a prolonged period. The use of deposit aging analysis to improve exchanger operation is discussed.