Crude Oil Fouling

Deposit Characterization, Measurements, and Modeling

Francesco Coletti, Geoffrey Hewitt

• Publisher: Gulf Professional Publishing
• Year: 2014
• Print ISBN:
  9780128012567
• eBook ISBN:
  9780128013595
• Topic: Technology & Engineering
• Subtopic: Industrial Management
• Index: Technology & Engineering

With production from unconventional rigs continuing to escalate and refineries grappling with the challenges of shale and heavier oil feedstocks, petroleum engineers and refinery managers must ensure that equipment used with today's crude oil is protected from fouling deposits Crude Oil Fouling addresses this overarching challenge for the petroleum community with clear explanations on what causes fouling, current models and new approaches to evaluate and study the formation of deposits, and how today's models could be applied from lab experiment to onsite field usability for not just the refinery, but for the rig, platform, or pipeline. Crude Oil Fouling is a must-have reference for every petroleum engineer's library that gives the basic framework needed to analyze, model, and integrate the best fouling strategies and operations for crude oil systems. - Defines the most critical variables and events that cause fouling - Explains the consequences of fouling and its impact on operations, safety, and economics - Provides the technical models available to better predict and eliminate the potential for fouling in any crude system

Chapter One

Introduction

F. Coletti¹, H.M. Joshi², S. Macchietto³, and G.F. Hewitt^{4 1}Chief Technology Officer, Hexxcell Ltd, UK ²Principal Heat Transfer Engineer, Shell, USA ³Professor of Process Systems Engineering, Imperial College London, UK ⁴Professor of Chemical Engineering, Imperial College London, UK

Abstract

Crude oil fouling is a long-standing problem in oil refineries that impacts operations, energy efficiency, and costs and has severe environmental and health and safety implications. Chapter 1 introduces the topic of crude oil fouling and starts with a description of fouling in a typical crude distillation unit. The chapter continues with a discussion of the impact of fouling on the operation of a crude oil distillation unit, both from an operational and economic point of view. Health and safety aspects are also discussed.

Keywords

Cost of fouling; Crude distillation unit; Crude oil fouling; Fouling economics; Fouling impact; Preheat train; Refinery

Stringent environmental policies and tightening refining margins in a highly competitive market are forcing oil companies worldwide to increase their focus on the efficient utilization of energy. Refinery efficiency is so critical that it has been reported to be capable of moving the share price of major oil and gas companies. In this perspective, the efficiency of heat exchange equipment and heat exchange networks is of paramount importance. Fouling, the deposition of unwanted material on heat transfer surfaces, is a major cause of inefficiencies with severe effects on refinery economics, operability, health and safety, and environmental impact.

Fouling is a long-standing problem in the process and energy industry. Taborek (1995) tracked the origin of the first industrial concern about fouling back in the 1880's USA power industry and the first mention of fouling in the open literature is in a paper by Orrok (1910). Fouling has been described both as “the major unresolved problem in heat transfer” (Taborek et al., 1972) and “a nearly universal problem in heat exchanger equipment design and operation” (Watkinson, 1988). Indeed fouling is ubiquitous in the oil industry.

In upstream operations, hydrate formation, asphaltene precipitation, and wax deposition from crude oil not only reduce the thermal efficiency of heat exchangers but also, more importantly, restrict flow, causing blockages that significantly impact operations. In some cases also oil pipelines are affected to the extent of becoming plugged. Wax deposition typically occurs when crude is cooled to a point at which the paraffins normally contained in solution start aggregating and eventually depositing on the surfaces.

In oil refineries, the feed/effluent heat exchangers in naphtha hydrotreaters, the slurry exchangers in fluid catalytic cracking units, and the furnace and exchangers in the visbreaker unit are all known to be affected by severe fouling problems. However, the largest share, about 50% (Van Nostrand et al., 1981), of the total fouling-related costs for the whole refinery originates in the preheat train (PHT) of the atmospheric distillation unit (here referred to as crude distillation unit or CDU).

The PHT is an extensive network of heat exchangers used to reduce energy requirements in the CDU, which is where primary fractionation of all the crude processed in the refinery is performed. If the PHT is not working efficiently, more fuel must be burnt at the downstream furnace that heats the crude to the required temperature for the distillation. The average energy involved with this process has been estimated to be over 192 TWh per year (6.94 × 10¹⁷ J per year) for refineries in the United States (DOE, 2006). This makes the CDU the largest energy utilizer in the refinery and one of the largest in the whole process industry. By comparison, the total primary energy consumed by Ireland in 2013 was 169 TWh.

Although there are only a few—largely outdated—studies that deal with the economic costs of fouling in oil refineries, there is little doubt that fouling has an enormous impact on the refinery’s bottom line. Van Nostrand et al. (1981) estimated that process-side fouling cost the United States refineries US$ 1.36bn per year, and US$ 861 MM of that in the crude PHT alone. Adjusting for inflation to 2014 this is equivalent to US$ 3.6bn and US$ 2.26bn, respectively.

The environmental impact is even more staggering with fouling in refineries estimated to be responsible for 88 MM t of CO₂, or 2.5% of total worldwide anthropogenic emissions in 2009 (Müller-Steinhagen et al., 2009a).

How much of this inefficiency can be eliminated, and at what cost, is the key question. Fouling mitigation can provide increased capacity and reduced greenhouse gas emissions without significant capital expenditure. A study made in 2006 for the US Department of Energy (DOE) indicates that potential fuel savings up to 55% can be achieved in oil refineries by improving operating practices and capital equipment (DOE, 2006). Among the suggested improvements it was found that fouling mitigation in the PHT and fired heater in atmospheric distillation units could lead to a 15% fuel saving (1/3 from existing technology, 2/3 from technology in the R&D stage). As fuel consumption in the atmospheric furnace represents around 4% of the total refinery throughput (Yeap et al., 2004), a potential saving of 15% equates to a sizable 500,000 bbl per day potential savings worldwide, equivalent to the daily production of a large refinery, or (for oil at US$80 bbl⁻¹) a value of US$14.6bn per year. However, much still needs to be done to tap into these savings, starting from the way heat exchangers are designed, crudes are blended, and operations are managed. To improve these aspects, it is widely recognized that a more fundamental understanding of the underlying fouling phenomena is needed.

Over the years, several projects have been coordinated to study the complex and interacting phenomena involved in different types of fouling (Pilavachi and Isdale, 1993; Pritchard, 1988a). F...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Preface
• Nomenclature
• Chapter One. Introduction
• Chapter Two. Basic Science of the Fouling Process
• Chapter Three. Experimental Generation of Fouling Deposits
• Chapter Four. Deposit Characterization and Measurements
• Chapter Five. Modeling of Fouling from Molecular to Plant Scale
• Chapter Six. Concluding Remarks
• Appendix 1
• References
• Index