Fouling in heat exchangers of crude distillation units

Lead Research Organisation: University of Cambridge
Department Name: Chemical Engineering and Biotechnology

Abstract

Crude oil distillation accounts for a large fraction of the energy used in oil refining. Every effort is made to reduce this huge energy consumption by exchanging heat between the input and output streams to the distillation tower in a train of heat exchangers commonly referred to as the crude preheat train . Unfortunately, crude oil contains components which lead to drastic fouling of the heat exchangers in the crude preheat train. Such fouling leads to enormous costs, not only in the costs of loss of energy recovery but also in the costs of loss of product and mitigation measures. In the USA alone, preheat train fouling is estimated to cost around $1.2 billion per annum. The most important components causing fouling are the asphaltenes, which are complex polynuclear aromatic compounds which carry most of the trace element content of the crude oil. Though the importance of the problem has led to a large amount of work being done, this has not led to an understanding of the processes of ashphalene transport and deposition. What is proposed is a study (carried out by a multi-disciplinary team) which covers the scales from molecular to plant systems. The first step is to understand more precisely the asphaltene contents and compositions in crude oil and deposits (Sub-Project A). Using nano-rheoemetry, the interfacial behavior of the depositing species can be studied (Sub-Project B). Using the information on chemical and physical properties of asphaltenic materials, modelling structures can be developed both of the molecular properties (Sub-ProjectD) and of the heat and mass transfer effects (Sub-Project C ). It is an essential part of the project to carry out actual measurements on fouling and the plan is to make such measurements using a small scale (rotating cell) apparatus (Sub-Project E) and an annulus flow facility simulating heat exchanger conditions (sub-Project G). Finally, technology transfer will be achieved through participation of ESDU International Ltd. in the project (Sub-Project H); ESDU has close contacts with the refining industry and is already developing software which is used by this industry and into which the key results of the project can be subsumed to ensure rapid take-up by the companies involved.

Publications

10 25 50
 
Description Fouling of heat exchangers causes losses in energy transfer, reduced throughput and can cause loss of process integrity. The Crude Oil Fouling Project was a collaboration between Bath, Imperial and Cambridge supported by industry and considered different aspects of crude oil fouling in order to develop mitigation routes based on fundamental understanding.



The Cambridge work focused on (i) developing numerical methods for determining plant-scale cleaning strategies and (ii) developing a fluid dynamic gauging device for working with crude oil at high temperature and pressure.



In strand (i) we developed numerical techniques for simulating fouling in refinery preheat train networks, incorporating real fouling behaviour, control actions, and different cost structures as part of a large optimisation problem. The capacity to determine optimal exchanger cleaning schedules was demonstrated with case studies drawn from industry. The simulation tools can also be used to asses and rank network retrofit and other exchanger revamping options.



A new method for modelling deposit ageing in crude oil fouling was also developed.



In strand (ii) we demonstrated that fluid dynamic gauging could be used, in principle, to study fouling layers at high temperature and pressure, over a wide range of flow rates. A device was designed to work on the crude oil fouling test rig being constructed at Imperial College. The capacity to make thickness measurements with an accuracy of 10 micron was demonstrated at lower pressures: the project finished before the device could be installed and tested on the Imperial rig. The technology has allowed other collaborators to use dynamic gauging in related applications.



Computational fluid dynamics simulations of the dynamic gauging were constructed and can be combined with the thickness measurements to determine the rheology of fouling layers.
Exploitation Route Both the exploitation routes above are directly relevant to industry, both for operating existing plant and designing new ones. Case studies have demonstrated the applicability of the scheduling software tool. The dynamic gauging devices can be used in industrial and commerical R&D on fouling and on cleaning, as well as a way of testing attachment of layers to surfaces and treated surfaces. The network simulation tool provides refinery operators with a tool to quantify the likely effect of fouling on their systems, and can be used by operators planning production as well as in design of more robust systems. This is being exploited in the development of the SmartPM software tool by IHS.

The fluid dynamic gauging devices allow fouling layers to be studied in new ways and this is being exploited by licensing or constructing devices for other users.
Sectors Chemicals,Education,Energy,Environment

URL http://opus.bath.ac.uk/22885/
 
Description In this project a fluid dynamic gauging tool was designed for making measurements in crude oil under conditions of high pressure (up to 30 bara) and moderately high temperature (up to 270C). Proof of concept was demonstated, fundamental principles understood and a prototype constructed. We demonstrated that fluid dynamic gauging could be peformed in fast moving liquids and constructed a prototype (but the project ended before it could be commissioned). The device operated in a new mode, which can be used for other high pressure systems (e.g. membranes) and also at very low pressures. This capability has been exploited in subsequent projects studying fouling, cleaning and surface testing. Beneficiaries: Academic research groups, Industrial R&D, industrial manufacturing Contribution Method: The project confirmed that fluid dynamic gauging could be peformed reliably in flowing systems in annular geometries and other configurations. The expertise developed was exploited in other projects. The high pressure and high temperature design specification led to novel approaches to sealing and mechanical design. Numerical simulation of the flow fields also highlighted key fluid mechanics aspects. In this phase of the Crude Oil Fouling Project, our task was to construct a numerical simulation of the operation of refinery preheat trains incorporating the dynamics introduced by fouling and cleaning. This simulation was then used to identify the best schedule of cleaning operations, to support cleaning-based fouling mitigation strategies. The simulation was designed to be flexible, robust, and capable of being expanded to include control aspects and also to be used in retrofitting studies. We also expanded the modelling approach to include deposit ageing. We developed a numerical simulation tool can be used to analyse the thermal peformance of crude oil refinery preheat trains subject to fouling, to optimise cleaning operations including complex control aspects, subject to a range of different cost and environmental impact structures. The potential was demonstrated with a series of industrial case studies where plant operating data sets were used to generate local fouling models, demonstrating the potential to apply these methodology to any refinery (as these plants are all different). Substantial cost and carbon dioxide savings are achievable. Beneficiaries: Academic research; industrial researcher; oil refinery operators: other heat transfer applications; Contribution Method: We developed appropriate calculation approaches for modelling the sets of equations describing network heat transfer, fouling dynamics, the optimisation problem associated with scheduling cleaning operations and the inclusion of control issues. A key aspect was the development of robust algorithms. A substantial body of industrial fouling data was processed and new insights into fouling behaviour, particularly that associated with ageing, was identified. The simulation also allows fouling to be considered at the network design and retrofit stages, which is important for building flexiblity into oil refinery operations.
First Year Of Impact 2007
Sector Agriculture, Food and Drink,Chemicals,Education,Energy,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description CASE Studentship on scanning dynamic gauging
Amount £42,500 (GBP)
Organisation Procter & Gamble 
Sector Private
Country United States
Start 08/2008 
End 09/2012
 
Description Industrial CASE Studentship Fouling and cleaning of food membrane systems - held by University of Bath
Amount £85,000 (GBP)
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 10/2007 
End 09/2011
 
Description Portugese Foundation for Science and Technology International PhD Studentship
Amount £75,000 (GBP)
Organisation Portuguese Foundation for Science and Technology (Portugal) 
Sector Public
Country Portugal
Start 01/2013 
End 06/2014
 
Title High pressure fluid dynamic gauging 
Description Fluid dynamic gauging is a non-contact technique for measuring the thickness of soft solid layers on solid or membrane surfaces, immersed in liquids (which may be opaque, stagnant or flowing) in situ and in real time. In the Crude Oil Fouling research project a version of this technique was developed for measuring the thickness of layers in the micron to millimetre range on the outside of cylinders in flowing liquids at pressures up to 30 bar and 270 Centigrade. 
Type Of Material Improvements to research infrastructure 
Year Produced 2007 
Provided To Others? Yes  
Impact The tool has been used to measure, for the first time, the thickness of fouling layers growing on membrane surfaces, in real time. A version of this tool has been developed for aseptic operation, and for studying biofilms. 
 
Description Fouling and cleaning of food membrane systems 
Organisation University of Bath
Country United Kingdom 
Sector Academic/University 
PI Contribution Demonstration of the fluid dynamic gauging technique in flowing systems and high pressure led to a CASE PhD studentship at the University of Bath with Dr Michael Bird supported by Danisco and Tetra Pak. The project investigated fouling and cleaning in membrane processing units. This CASE PhD Studentship was based at Bath with input from Cambridge on the design and commissioning of devices for studying fouling and cleaning in food membrane test cells.
Start Year 2007
 
Description IHS-ESDU International Plc 
Organisation Esdu International
Country United States 
Sector Private 
PI Contribution In the Crude Oil Fouling project we worked on two topics of direct relevance to IHS; the measurement of the thickness of fouling layers, and the modelling and simulation of crude oil heat exchangers subject to fouling. Both topics are directly relevant to IHS work in this area. The simulation work generated a software tool which IHS subsequently partnered through to commercialisation in the commercial tool, SmartPM.
Collaborator Contribution ESDU International (now part of the IHS) group were the leaders of the industrial support for the Crude Oil Fouling Project. They co-ordinated industrial input and organised (and co-hosted) several of the meetings. The simulation work generated a software tool which IHS subsequently partnered through to commercialisation in the commercial tool, SmartPM. IHS had considerable input on this.
Impact Publications - see elsewhere IHS have incorporated the learnings in their technical literature. SmartPM software tool - a highly flexible software tool for managing energy efficiency in oil refinery preheat trains, particularly those subject to fouling.
Start Year 2006
 
Description Imperial College London 
Organisation Imperial College London
Country United Kingdom 
Sector Academic/University 
PI Contribution Imperial College was one of the university partners in the Crude Oil Fouling research project. Our fluid dynamic gauging device was designed for operation on the fouling pilot plant apparatus at Imperial. This aspect of the project was led by Imperial. We led the tranche of the project on process modelling and simulation, organising and dividing the activities in this area.
Collaborator Contribution The Imperial team provided overall leadership of the Crude Oil Fouling research project. In the fouling pilot plant apparatus testing work Imperial provided leadership and co-ordination of the activity, and we worked closely with them on the design of the fluid dynamic gauging system for the unit in their labs. In the process modelling and simulation work, the Imperial team concentrated on pilot plant and individual unit modelling, complementing our work on network behaviour and system optimisation. Several jointly authored papers resulted from this collaboration.
Impact Publications - see else where. A fluid dynamic gauging device that can operate with crude oil at higher temperature and pressures. Software/simulation tools for modelling and predicting the impact of fouling in oil refinery crude oil heat exchangers and networks thereof. A good working relationship.
Start Year 2006
 
Description University of Bath 
Organisation University of Bath
Country United Kingdom 
Sector Academic/University 
PI Contribution In the Crude Oil Fouling research project we managed the process modelling and optimisation activity, taking results from parts including the small scale testing activity at Bath and implementing them into unit and plant scale models. There was regular exchange between the partners for this.
Collaborator Contribution The Bath group provided data and insight provided by their small scale testing activity. In addition to data and knowledge transfer, co-authored publications resulted.
Impact Publications - see elsewhere. The Bath group have collaborated with us on applying the fluid dynamic gauging technique to membrane and biofilm systems (John Chew moved from our group to Bath). The Bath group was one of the co-organisers of the 2014 Fouling and Cleaning in Food Processing conference held in Cambridge in April 2014.
Start Year 2006
 
Title Fluid dynamic gauge for high temperature and pressure operation 
Description In this part of the Crude Oil Fouling Project, a version of the fluid dynamic gauging tool was developed for making measurements at high pressure (30 bara) and temperature (up to 300 C) on the crude oil fouling apparatus being constructed at Imperial College 
Type Of Technology Physical Model/Kit 
Year Produced 2009 
Impact This product introduced the capability of making reliable measurements under challenging operating conditions for real fluids. The technology has allowed fluid dynamic gauging systems to be designed for other applications, including aseptic conditions. 
 
Title Numerical simulation of fouling in oil refinery heat exchanger networks 
Description The numerical simulation developed in this project constitutes a powerful simulation tool for analysing the operation of oil refinery preheat trains. Functionality includes data reconciliation, heat transfer prediction, control and operability aspects, and optimisation. The numerical code was subsequently developed into a piece of commercial code, SmartPM, in collaboration with IHS-ESDU 
Type Of Technology Software 
Year Produced 2012 
Impact The SmartPM software is the first truly flexible tool which allows oil refinery operators to (a) establish the level of fouling in their heat exchanger networks, (b) establish the most economically attractive cleaning scheduling programme to mitigate fouling, and (c) to compare cleaning programmes with other mitigation options such as network retrofitting or cleaning chemicals. Proof of impact is its adoption by several oil majors. The technology reduces financial costs as well as greenhouse gas emissions. 
URL http://www.ihs.com/info/st/e/smartpm.aspx
 
Description Provision of training 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Prof A. Paul Watkinson (UBC) delivered an industrial training course 'Crude Oil Fouling in Refineries: Current Understanding and Mitigation Methods' at Jesus College, Cambridge, from 10-11 April 2008. The 40 delegates included workers on the Crude Oil Fouling Project as well as industrial researchers and practising engineers from industry across the UK, EU and USA.

The level of shared knowledge across the sector rose notably.

All the workers on the Crude Oil Fouling Project benefitted from this comprehensive survey and review of knowledge in the area.
Year(s) Of Engagement Activity 2008