Process Engineering for a Small Planet E-Book

Norman P. Lieberman

• Herausgeber: John Wiley & Sons
• Kategorie: Fachliteratur
• Sprache: Englisch

Seitenzahl: 455

Veröffentlichungsjahr: 2011

Beschreibung

Methods for more planet-friendly process engineering

Our earth is just one big, complex Process Facility with limited air, water, and mineral resources. It responds to a number of process variables—among them, humanity and the environmental effects of our carbon consumption. What can professionals in the Hydrocarbon Process Industry do to retard environmental degradation? Rather than looking to exotic technology for solutions, Process Engineering for a Small Planet details ready-at-hand methods that the process engineer can employ to help combat the environmental crisis.

Drawing from the author's professional experience working with petroleum refineries petroleum refineries, petrochemical plants, and natural gas wells, this handbook explains how to operate and retrofit process facilities to:

• Reuse existing process equipment
• Save energy
• Reduce greenhouse gas emissions
• Expand plant capacity without installing new equipment
• Reduce corrosion and equipment failures

Covering topics from expanding fractionator and compressor capacity and vacuum tower heater expansion to minimizing process water consumption and increasing centrifugal pump capacity, Process Engineering for a Small Planet offers big ideas for saving our small planet.

Leseprobe

Contents

Cover

Half Title Page

Title Page

Copyright

Dedication

Preface

Foreword

Introduction: Turning of the Tide

Chapter 1: Expanding Fractionator and Compressor Capacity

Saturn’s Coker Fractionator

Objectives of Delayed Coker Expansion

Changing Tray Panels

Reducing the Gas Oil Content of Feed

“Just Desserts”?

Wet Gas Compressor

Wasting Electric Energy

Alternatives to the New Compressor

Keeping Compressor Rotors Clean

Calculating Liquid Injection Rates

Design Details

Chapter 2: Vacuum Tower Heater Expansion

Missing Tray Deck Manways

The Divine Plan Revealed

Heater Draft Limitation

Additional Methods to Increase Vacuum Tower Lift

Velocity Steam in Heater Passes

Chapter 3: Natural-Draft-Fired Heaters

Controlling Excess Combustion Air

Combustible Analyzers

The Power of Positive Thinking

Improving the Air–Fuel Mixing Efficiency

Convective Section Tramp Air Leaks

Air Preheaters

Correct Air Preheater Design

Reducing Heater Capacity Using Air Preheat

Chapter 4: Crude Pre-Flash Towers

Pre-Flash Tower Flooding

The Wages of Sin

Energy Savings with Pre-Flash Towers

Capacity Benefits of Pre-Flash Towers

Pre-Flash Tower External Reflux

Reference

Chapter 5: Amine Regeneration and Sulfur Recovery

Amine Capacity Expansion

Sulfur Plant Capacity Expansion

Sulfur Recovery From Sour Water Stripper Off-Gas

Result of Low Reaction Furnace Temperature

Fractionation Between Nh3 and H2S

Use of Oxygen to Process Nh3-Rich Gas

References

Chapter 6: Treating and Drying Hydrocarbons

Troubleshooting A Salt Dryer

Salt Dryer Internal Condition

Fixing the Water Wash

An Apology

Pipe Distributor Design

Mercaptan Sweetening

Chapter 7: Minimizing Process Water Consumption

Two-Stage Wastewater Stripper

Steam Condensate Recovery

Condensate Drum Balance Line Location

Water Hammer

Measuring Steam Condensate Recovery

Cooling Tower Cycles of Concentration

Chapter 8: Incremental Expansion Design Concept: Reprocessing Waste Lube Oil

Resurrection

A Visit From Mr. Robert White

The Texaco Marine Division Vacuum Tower Design

Wash Oil Grid Coking

Stripping Tray Efficiency

Precondenser Fouling

Pumping Problems

Exchanger Fouling and Heater Overfiring

Transfer Line Sonic Velocity: Myth or Reality?

Summary

Reference

Chapter 9: Improving Fractionation Efficiency in Complex Fractionators

Leaded Gasoline

Fractionation Problems with A Crude Unit Pre-Flash Tower

Intermediate Reflux Concept

Project Implementation

Diesel Recovery From A Vacuum Tower Feed

Bypassing Stripping Trays

Effect of Using Bottom Stripping Trays

Improving Fractionation Using Picket Weirs

Picket Weir Design

Increasing Internal Reflux

Pressure Optimization

Chapter 10: Increasing Centrifugal Pump Capacity and Efficiency

Hydraulic Limitations

An Olympic Champion

Worn Impeller-To-Case Clearance

Visit to the Pump Repair Bench

The Pep Rally

Other Methods to Increase Pump Capacity

Marginal Cavitation

Effect of Temperature

Effect of Viscosity

Npsh-Limited Pumps

Chapter 11: Eliminating Process Control Valves Using Variable-Speed Drivers

Variable-Speed Electric Motors

Eliminating Control Valves on A Pump Discharge

New Unit Design

Steam Turbines

Variable-Speed Compressors

Spill-Backs Waste Energy

Impeller Downsizing

Estimating Incentive for Variable-Speed Drives

Throttling Motive Force

Chapter 12: Natural-Draft-Fired Heaters

Expansion Requirements

Discussion with Unit Operators

Engineering Analysis

Calculating Refrigeration Compression Work

Horsepower Limited Vs. Suction Volume Limited

Effect of Increasing Suction Pressure

Reducing Refrigerant Condenser Fouling

Adjusting Refrigerant Composition

Summary

Effects of Noncondensibles in Circulating Refrigerant

The Wrapup Meeting

References

Chapter 13: Oversizing Equipment Pitfalls

Scrubbing H2S From Hydrotreater Recycle Hydrogen

Optimizing H2S Absorption Trays

Result of Reduced Absorber Trays

Absorber Overdesign

Consequences of Overdesign

Oversizing Vapor--Liquid Separators with Demisters

How Demisters Work

Effect of Oversizing Demisters

Demister Failure

References

Chapter 14: Optimizing use of Steam Pressure to Minimize Consumption of Energy

Preserving the Potential of Steam to Do Work

Power Recovery From Steam to A Reboiler

Energy Waste in Condensing Steam Turbines

Cogeneration Plants

Extracting Work From Reboiler Steam Using Existing Equipment

Thermodynamics in Action

Steam Turbine Checklist

References

Chapter 15: Expanding Compressor Capacity and Efficiency

Reciprocating Compressors

Pulsation Dampener Plates

Calculating Restriction Orifice Plate ΔP

Adjustable Head-End Unloaders

Gas-Fired Engines

Centrifugal and Axial Compressors

Next Day

Centrifugal Compressor

Cleaning the Centrifugal Compressor Rotor

References

Chapter 16: Vapor–Liquid Separator Entrainment Problems

Level Problems in V-603

Foam-Induced Carryover

Enhancing Deentrainment Rates

Vapor Distribution as an Aid to Deentrainment

Reference

Chapter 17: Retrofitting Shell-and-Tube Heat Exchangers for Greater Efficiency

New Heat Exchanger Developments

Rerunning Slop Oil

Tube-Side Velocity and Metallurgy

Shell-Side Seal Strips

High-Viscosity Fluids

Water Cooler Fouling

Vapor Evolution in Cooling Water

References

Chapter 18: Reducing Sulfur and Hydrocarbon Emissions

The Ertc Conference

Sulfur Emissions From Carib Island

Sulfur Condenser Modifications

Finding Hydrocarbon Leaks in Seawater Cooling Systems

The Dragon

Loss of Draft Due to Air Leaks

Global Sulfur Emissions

Epilogue

Chapter 19: Hydrocarbon Leaks to the Environment

Measuring Leaks Through Valves

Fixing Leaking Valves

Detecting A Leaking Relief Valve

Fixing Leaking Relief Valves

Measuring Flows in Flare Lines

Valve Stem Packing Leaks

Leaks into Cooling Water

Flange Leaks

Air Cooler Tube Leaks

Leaking Pump Mechanical Seals

Fixing Weld Leaks

Chapter 20: Composition-Induced Flooding in Packed Towers: FCU Fractionator Expansion

Flooding of the Slurry Oil Pump–Around Section

Fractionator Vapor Line Quench

Hot Pump Piping Stress Analysis

Shall we Gamble on the Future?

Perception Vs. Reality

References

Chapter 21: Maintenance for Longer Run Lengths

Acid Plant Operating Factor

Lewis Pump Wear Rings

Precipitator Star Wire Failures

Converter Insulation

Operator Psychology

Fixing and Preventing Process Piping Leaks

Using What’s at Hand

Preserving Pump Mechanical Seals

H2S As Supplementary Feedstock

Summary

Chapter 22: Instrument Malfunctions

Control Valve Failures

Loose Instrument Air Connection

The Next Day

Stuck Control Valve

Reducing Cracked Gas Loads to Vacuum Systems

Effect of Residence Time on Cracked Gas Flow

Mislocated Level Tap

Productive Procrastination

Acknowledgment

Chapter 23: Summary Checklist for Reuse of Process Equipment

Equipment Checklists

Equipment Limitations

Safety Note

Checklist Summary

Chapter 24: Water–Hydrocarbon Separation: Corrosive Effects of Water

Becky’S Story

Combating Corrosion

Hydrocarbon–Water Separation Efficiency

Avoiding Water Traps in Strippers

Use of Dump Valves to Prevent Drain Valve Plugging

Current Co2 Levels

A Final Observation

References

Index

Process Engineering for a Small Planet

Copyright © 2010 by John Wiley & Sons, Inc. All rights reserved.

Published by John Wiley & Sons, Inc., Hoboken, New Jersey.

Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:

Lieberman, Norman P. Process engineering for a small planet : how to reuse, re-purpose, and retrofit existing process equipment / Norman P. Lieberman. p.m. Includes bibliographical references and index. ISBN 978-0-470-58794-2 (cloth) 1. Chemical plants–Equipment and supplies. 2. Chemical plants–Remodeling for other use. 3. Salvage (Waste, etc.) I. Title. TP157.L474 2010 660′.283–dc22

2010001896

To the memory of shift foreman Mohamed Lee, born 2012–died 2090, who shouted: “Shamil, you bloody fool! Throttle on the inlet guide vanes to the blower; don’t open the discharge atmospheric vent. Didn’t you read Lieberman’s book? You idiot! You’re wasting amps!”

To my daughter, Irene, who assembled and reassembled this manuscript.

To my wife, Liz, who inspired this project: “Norman! Stop whining about the environment and do something. Maybe write a book.”

To my mother: “Your cousin’s coat is just like new. We’re poor people. We have to get by with what we’ve got. You’ll wear the coat and like it. And your aunt sent it especially for you. Look, even all the buttons still match.”

Preface

Life goes on. And time goes on. The seasons change one into the other. The hills, the rivers, and the seas will survive, but perhaps without us.

It’s a process problem. Our small planet, our home, is a rather large process plant responding to a number of process variables. One of these new process variables is man.

As I explained in my previous book, Troubleshooting Process Plant Controls (John Wiley, 2008), any unconstrained process variable may result in a positive feedback loop. Our human activities in the past 70 years have introduced just such an unconstrained variable into the dynamics of Earth’s operation.

At the heart of the problem is the hydrocarbon refining and petrochemical processing industry—an industry that I, after 46 years of activity, have become identified with, owing to my design, teaching, writing, and field troubleshooting.

I can see in retrospect from the perspective of the process engineer that I have made a significant and sad contribution to the environmental positive feedback loop our little planet has entered. If our Earth is a complex process facility, it’s clear that we can no longer escape the consequences of our actions. But how can we work to mitigate these consequences?

What’s to be done? What can I and my co-workers in the hydrocarbon process industry do to retard environmental degradation? This book, Process Engineering for a Small Planet, focuses on this question. The text is basically technical. As in my other five books, the format includes stories drawn from my personal experiences in petroleum refineries, chemical plants, and natural gas production wells.

The lesson I teach is that we have to learn to use our existing plant facilities to expand production and improve energy efficiency rather than constructing new pumps, compressors, distillation towers, and vessels. The lesson is that we live on a small planet with limited air, water, and mineral resources. But rather than lecture about morality, I have presented a series of technical and engineering examples to best fulfill my mother’s advice: “Norman, we’re poor people! We can’t afford anything new. We’ve got to get by with what we have.’’

It’s true! We live on a small planet. We’ve got to get by with the plant facilities we already have. This book will suggest how we in the hydrocarbon process industry can conform to mom’s instructions.

For Whom Intended

Since 1983 I have been teaching a seminar entitled “Troubleshooting Process Operations.’’ About 16,000 technical personnel have attended. In the last few years, I have devoted class time to detailing the growing environmental hazards—chiefly CO2, methane, and NOx emissions—that we, as process technicians, engineers, and managers, are generating.

The response to my challenge is the question: What’s to be done? Engineers, operators, production personnel, and management in the hydrocarbon production and processing industry do not design solar panels, windmills, or fuel-efficient cars. We do not develop hydrogen fuel cells or methods to convert algae to biodiesel.

I am asked: “In the scope of our work as process plant personnel, what can we do?’’

Process Engineering for a Small Planet is my response. What can we in the hydrocarbon process industry do to reduce environmental degradation? Can we contribute to the solution, or are we to be swept along by the tide of events?

We are surrounded by propaganda, which is misleading and often simply lies:

Clean coalThe hydrogen economyEthanol as green fuel

Process engineers and operators do not need to look to exotic technology to make our contribution to combating the environmental crisis. Fully 10% of fossil fuels are consumed in the production, refining, and processing of coal, crude oil, and natural gas. Huge amounts of steel, copper, and cement are consumed to construct new, and often unnecessary, process equipment.

Process Engineering for a Small Planet is a handbook of ideas as to how to operate and retrofit existing process facilities to:

Save energy.Reduce greenhouse gas emissions.Expand existing plant capacity but without installing new equipment.Reduce corrosion and equipment failures.

The text is technical. However, as in my other books:

Troubleshooting Refinery Processes, 1980, PennWellTroubleshooting Natural Gas Processing: Wellhead to Transmission, 1985, PennWellProcess Design for Reliable Operations, {2nd ed.,} 1989, GulfA Working Guide to Process Equipment, {3rd ed.,} 2007, McGraw-HillTroubleshooting Process Plant Control, 2008, WileyTroubleshooting Process Operations, {4th ed.,} 2009, PennWell

the format includes stories drawn from personal experiences in petroleum refineries, petrochemical plants, and natural gas wells. The manuscript is devoid of complex mathematics and pedantic paragraphs. Technical text that is presented in a conversational tone is unusual, but Troubleshooting Process Operations, written in this style, has been on PennWell’s best-seller list for 28 years.

Disclaimer

I have represented the technical facts in this book to the best of my understanding. However, references to places, names of refineries, and of individuals have been chosen at random. Any reference to people or places that corresponds to any actual people or places is purely a coincidence. However, all related experiences are technically complete and correct. Perhaps you will recognize one or more of these stories from your own experiences and think it is your story that I am writing—maybe it is and maybe it isn’t. I have seen many of these scenarios in more than one place. As further evidence, in one of my seminars, an attendee came up to me on a break and asked who had given me his story to tell because the circumstances were so similar—it was not his story but it took a while to unravel the confusion. Please contact me if you have a similar question.

Engineering formulas presented here are usually approximations that have been simplified to promote comprehension at the expense of accuracy. References to more detailed texts are provided if accurate calculations are required.

The stories presented are stated in the context of my having initiated the improvements. Often, I was just a participant in implementing other people’s concepts and have failed to assign appropriate credit. Such concepts have not been stolen from my clients—they have simply been borrowed and will be returned one day soon.

Process Problem Inquiries

If you have a process engineering question related to this or any of my other books, please call me at:

1-504-887-7714

Or, you may fax me at:

1-504-456-1835

There is no charge for such consultations. However, please don’t send emails. I can’t type and do not plan to start learning to do so at my advanced age.

Before you phone or fax, you would be best to conduct a field survey to collect the relevant data. While you are collecting the data in preparation for our phone consultation, you may well stumble across the bit of information that you lacked to solve the problem. Then you can forget about bothering me and thus avoid destroying my sense of peace and well-being. However, if you are absolutely determined to send me an email, my address is

[email protected]

NORMAN P. LIEBERMAN

May 2010

Foreword

Mr. Lieberman’s books, his knowledge and understanding of, and expertise in, the field are second to none. His writing is one of the best (if not the best) in the industry, unsurpassed for clarity, and at the same time absorbing and entertaining. You do not doze off reading his books. His hands-on approach makes his writing understandable by all and suitable for all levels, from the director and technical expert all the way to the novice and the nondegreed operator. People who have been in the game for decades will pick up his books and be able to gain new insights. His practical approach will make it possible for every reader to find something that she or he can use and apply immediately in their own fields.

This book represents a slight departure from Lieberman’s normal writing. His writing usually teaches the practical art of chemical engineering and effectively passes on his vast experience to readers, preaching understanding and excellence in engineering. In this book, his teaching is supplemented with a message leading a crusade to “save Planet Earth from destruction, global warming, and environmental hazards.’’ The beauty of this book is that he shows that following good chemical engineering practices paves a path to protecting the Earth. In contrast, he demonstrates how poor engineering and wasteful practices are one of the major hazards to our planet. He gets across the message: Protecting the Earth is not in “their’’ hands; it is not what “they’’ need to do. It is our responsibility as engineers. It is our duty to identify bad and wasteful engineering practices and stand up to them. Do not use the excuse that a manager above you set the tone. Do not hesitate to stand up to her or him. As a professional, fight such a person with good technical work. With his usual practical writing style and Lieberman humor, the author gets this powerful message across very clearly. Better than many of the politicians who talk about it, he is doing something about it. The political solutions that are promoted in the media often lack a good engineering basis. The need is for engineering solutions, not political ones, and it is we who must come up with them.

There is no question that this book will be a great addition to the literature and is much needed by the industry. Unlike his other books, which are used primarily by industry, this book may make some inroads into academia. The “save the Earth’’ message will make it fashionable and popular, and academics frequently welcome new ideas, such as engineering rather than political solutions to our global warming problems. Lieberman’s usual audience of operation engineers, control engineers, process engineers, design engineers, process operators, and research engineers will be very interested—especially once the enormous costs and undertakings of carbon-capture technology are appreciated—and people will be seeking alternative cheaper solutions, such as those the author advocates. His message is universal and I believe will be supported almost unanimously by the process engineering community.

HENRY KISTER

FLUOR

Introduction: Turning of the Tide

Morning had broken, like the first sunrise. The hidden fjord was bright and still in the sunshine. I paddled my red kayak easily between sheer rock walls cut by the strong hand of a long vanished glacier, toward the distant snow-capped peak. Space and time had lost all meaning.

Enclosed by the towering fjord, with no possible landing beach, I reversed course and headed back to camp. Paddling hard, I glanced at a tree growing from the cliff wall. The tree hadn’t moved. In 20 minutes I had not progressed 20 feet. The tide had turned against me.

The tide would turn again, but then it would be night, which would bring a cross-wind and a rip-tide. Allowing the tide to sweep me farther into the fjord was an option with unknown consequences. Trapped in the fjord at midnight, with the black waves rebounding from the granite walls, was a fatal prospect.

What was I to do? I paddled with all my strength. Alone and afraid, I prayed for divine deliverance. But the Universe is vast, and the Creator did not answer my plea right away, but left me there awhile to think.

As a species we too are trapped, with time and tide turning against us. A tide of solar energy stored as carbon has carried us into a dead-ended technology. Oxidizing fossilized carbon to provide energy for 7 billion people in our growing industrialized economy is madness. Timing is uncertain, but the outcome can be calculated.

Like my experience in the misty fjords in Alaska, we’ll have to rely on our own resources and with the tools at hand. Otherwise, the tide of greenhouse gas from tar sands, shale oil, coal, peat, natural gas, methane hydrates, heavy crude oil, and nitrous oxides will sweep us into oblivion.

Some are waiting for new technology. Clean coal. CO2 sequestration. Biodiesel from fermented cellulose. Some are waiting for Divine intervention. Others are hoping for offshore drilling. But I can’t wait. Let’s all face the truth. We must make progress with what we have at hand today.

The hydrocarbon process industry is at the center of the crisis. I just visited a coke gasification plant in Kansas. The plant converts petroleum coke to hydrogen. Great! Except that it vents 1 mol of CO2 per mole of H2. Suppose that this process becomes the long-term solution to the energy crisis in the United States? Tar sands, ethanol, shale oil, natural gas to liquids, fuel cells, the hydrogen economy—are all just as bad.

There are 10,000 to 20,000 senior leaders in the hydrocarbon processing industry. As far as tenure goes, I’m in the top rank: 45 years in refining, petrochemicals, and natural gas processing. Perhaps society as a whole cannot alter our carbon-dependent economy. But we, the process engineers in the hydrocarbon industry, can make a difference.

My book is not a solution. It’s not even a plan, or a start, or the beginning. It’s just a prayer whispered into the wind.

Let’s use the process equipment that we have. Let’s use our chemical engineering skills to avoid building new facilities, but operate our existing plants in an efficient manner. The expansionist economy we have created has to be reversed. How can this be done? Well, I’ve 45 years’ worth of experience to share with you.

I paddled my kayak back for five hours and eventually won through. It was a struggle the whole way. Nor will it be easy for us to escape the mortal grip of the carbon economy that we, the process engineering community, have created. But I, for one, am going to try. This book is my contribution to that goal. If we don’t try, we will surely fail. Ladies and gentlemen, the tide of time is not on our side.

Process Engineering for a Small Planet: How to Reuse, Re-Purpose, and Retrofit Existing Process Equipment, By Norman P. Lieberman Copyright © 2010 John Wiley & Sons, Inc.

Chapter 1

Expanding Fractionator and Compressor Capacity

Last night, in my dreams, I traveled through time and space. The universe was vast: dark and still. In my dream I ascended Mount Olympus, where King Zeus, son of Cronus, Queen Hera, the Earth Mother, and Pallas Athena, Goddess of Wisdom, reign over the affairs of man and beast. Father Zeus and other immortals had gathered around a pool of crystal clean water. Peering into the pool, I could see images of my home, New Orleans, submerged beneath the waves of the Gulf of Mexico. King Zeus rippled the water with a wave of his hand. Now I could see Greenland, bare of its ice cap. Zeus waved his divine hand again and Kansas appeared. Not green with corn and soybeans, but as a desiccated windblown desert.

Athena, Goddess of Wisdom, looked sadly at me and said, “Thus have humankind’s actions destroyed the creation of the Titans; the Blue Planet; the Pearl of the Universe. Look deeply into the sacred waters and learn the folly of human ways.”

And as I obeyed the command of the daughter of Zeus, I saw a six-drum delayed coker in Los Angeles. Father Zeus spoke thus: “Norman,” Zeus commanded, “Tell me about your life.”

“It’s a long story, Son of Cronus,” I said.

“Not a problem,” responded Zeus, “We have all eternity.”

“Okay. Well, I was born in 1942 in Brooklyn. I married and had three children. I studied chemical engineering and graduated in 1964 from… .”

“Norman,” King Zeus interrupted, “I know all that. What I’m interested in is the C-301A, the new coker fractionator you designed for the Saturn refinery in Los Angeles.”

“Well, this was a 26-ft-I.D. by 112-ft tangent-to-tangent tower that… .”

“Tangent to tangent was 112 ft and 4 in.,” Hera corrected.

“Yes, Immortal Queen Hera, it was 112 ft and 4 in. C-301A was a new tower. The largest coker fractionator on Earth.”

“And how about C-301, the existing 17-ft-I.D. tower?” asked Pallas Athena.

My exit interview had taken an unpleasant turn. In 45 years, I had designed hundreds of distillation towers. Why did Zeus have to select this tower—the project that I would least like to dwell upon? Especially the fate of the old C-301 coker fractionator.

“Rulers of Heaven, it was all so long ago. Anyway, it wasn’t my fault. I had a contract for $132,000. Don, the project manager, told me what Saturn wanted. It was Don’s fault. Not mine. The scope of work was defined by my client. I’ve forgotten the details. How about my revamp of the El Dorado polypropylene plant? Would you like to hear about… .”

“Norman,” Zeus thundered, “Thou hast sinned. Man was made in God’s image, the steward of the Earth. Have you been a good steward of this small planet, unique unto all the heavens?”

SATURN’S COKER FRACTIONATOR

In 1966, I had revamped the Amoco viscous polypropylene unit at El Dorado to increase its capacity by 60%. Amoco was going to build a new plant to get the extra 60%. But I realized that I could “de-bottleneck” the unit by 60% by converting a natural-circulation refrigerant evaporator into a forced-circulation refrigerant evaporator (see Chapter 12). All I needed was a new refrigerant pump and some 6-in. piping. But Zeus wasn’t interested in that project.

Actually, I remembered the coker project in Los Angeles in detail. However, my plan to blame Don, the project manager for this fiasco, was a nonstarter in the eyes of the Immortals. So here’s what happened. Maybe you can say a prayer for me.

OBJECTIVES OF DELAYED COKER EXPANSION

Figure 1-1 is a simplified sketch of a refinery delayed coker. The coker had a capacity of 60,000 bsd, as limited by the flooding in the fractionator. The objective of the expansion project was to increase the capacity to 75,000 bsd. I had been retained to prepare a process design to achieve this 25% expansion. My plan was to reuse the existing C-301 fractionator by:

Figure 1-1Simplified process flow diagram of a delayed coker.

Increasing the fractionator operating pressure by 8 psig.Reducing the recycle of coker gas oil to the coke drum by leakproofing the gas oil pan chimney tray.Minimizing the use of unneeded purge steam used at various points associated with the coke drums.Increasing heat extraction on the gas oil pump-around loop.Drilling holes near the tray rings and tray panel seams in the tray panels that did not have any room for valve caps, to optimize the hole area at 13 to 15% of the tray active area.Sloping the tray downcomers, to increase the tray deck area.Reducing the outlet weir heights to a minimum on the critically loaded trays.

CHANGING TRAY PANELS

As an alternative to modifying the existing tray panels, one could change the tray panels without modifying the existing tray rings supports and still reuse existing downcomers. When done properly, an increase of 5 to 15% in the tray vapor-handling capacity will result. Changes that are required include:

Cutting off the bottom edge of the downcomers (about the bottom 4 in.) and restricting the downcomer bottom to preserve the downcomer seal.Adding a push-type valve tray panel below the downcomers.Replacing the tray panels with Provalves (from Koch-Glitsch) or MVG Grid Trays (from Sulzer-Nutter).

Part of the extra capacity results from using the area under the downcomer for vapor flow. Part comes from pushing the liquid across the tray deck, which equalizes the liquid level on the tray deck and thus promotes more even vapor flow to each tray.

REDUCING THE GAS OIL CONTENT OF FEED

My other proposals would decrease Saturn’s excess coker feed by reducing the gas oil content of the delayed coker’s feed. The coker feed pumps used a gas oil for seal flush material. These were older pumps, with archaic mechanical seals. Four pumps were involved. Each had both an in-board and out-board mechanical seal, for a total of eight seal flush points. Each seal flush point consumed about 3 gpm of gas oil:

(Note: An idle pump uses 60% of the seal flash used by a running pump.)

Thus, 1% of coker feed was recycled gas oil. I could change the older seals to modern seals that use high-pressure nitrogen as a barrier fluid. Changing the seals would be inexpensive compared to the cost needed to replace the existing pumps. (Note: The Eagle-Burgman seal is a good choice.)

I had also noted that the vacuum tower stripping section was not using enough stripping steam. By increasing the flow of the vacuum tower bottoms stripping steam, I could reduce the gas oil content of the delayed coker feed from 12% to 10%. This would reduce the coker feed rate by about 1200 bsd.

Finally, the flowmeters on the coker heater pass orifice meter connections were purged with gas oil. There were eight passes, each with two orifice tap connections. Rather than continuously purging these 16 orifice tap connections, seal pots packed with gas oil could be used. This would reduce the gas oil content of coker feed a further 250 bsd. Overall, these three indirect methods would decrease the required delayed coker capacity by an additional 3 to 4%.

I had thought that combining all these modest changes would increase the coker capacity by 20 to 25%, or about 72,000 to 75,000 bsd. I knew that raising the fractionator pressure, which would also increase the fractionator capacity, would not be an acceptable option if it also raised the coke drum pressure. The problem was that each increase of 8 psi in coke drum pressure would also reduce the delayed coker liquid yields by about 1.5 liquid volume percent. However, I had also observed that the current differential pressure between the coke drums and the fractionator was about 12 psi. Most of this ΔP (see Figure 1-1) was due to not having full ports in the coke drum overhead vapor valves. The valve port sizes were only 70% of the line sizes. This means that the flow area through the orifice was only half of the flow area through the process lines. As ΔP varies with

I could eliminate the majority of the pressure loss through the coke drum vapor lines by replacing the existing vapor valves with full ported valves. Thus, the coke drum pressure would barely change, even though the fractionator pressure would increase from 20 psig (35 psia) to 28 psig (43 psia).

Tower capacity varies inversely with the square root of the absolute pressure. Thus, my single idea of increasing the fractionator pressure by 8 psi would increase the tower’s capacity by 11%:

“JUST DESSERTS”?

Don, the Saturn project manager, obtained a cost estimate of $8 million for my design. But my design was rejected by Saturn for several reasons:

I could not provide an absolute guarantee that the existing coker fractionator would not flood at 75,000 bsd of feed.The Saturn project planning department had budgeted $100 million for this project and capital investment allocations could not be transferred to next year.The Saturn plant manager, Larry Overbourne, wanted a new tower.

“It’s okay, Norm,” Don explained. “We realize that a new contract is required. I’ve already generated a new purchase order for your additional work. Just design the new coker fractionator so that it won’t flood at 80,000 bsd and 20 psig operating pressure. The bigger the better. That’s the way Mr. Overbourne thinks.”

“But, Don,” I responded, “I’ve spent so much time on the revamp of C-301. I think it will do the job. The capacity of the unit will be limited by the size of the coke drums to less than 75,000 bsd anyway. Mr. Overbourne's 80,000 bsd feed rate target is completely unrealistic. The coke drums will limit unit capacity to… .”

“Norm, the new purchase order for your work is $132,000—a lump sum,” Don said. I couldn’t think what to say. That’s a lot of money and I knew I could do the entire design in just two weeks. So I changed the subject.

“Look, Don, the wet gas compressor will not be big enough. Not with the fractionator running at only 20 psig and 80,000 bsd of feed. That’s my main reason for raising the coker fractionator pressure by 8 psig. The resulting higher wet gas compressor suction pressure, from 10 psig to 16 psig, will allow me to raise the unit charge from 60,000 bsd to maybe close to 75,000 bsd. Also, I could… .”

“No, Norm. You’re not listening,” Don interjected. “Mr. Overbourne also wants a new 12,000-hp compressor.”

“But, Don, there’s nothing wrong with the existing 9000-hp compressor. Anyway, the electrical substation won’t handle the extra load.”

“Lieberman,” Don concluded in a firm voice, “I’ve a meeting to go to. So let’s wrap this up. Listen to me:

First point. The $100 million includes the cost of all electrical work, especially a new substation.Second point. If you don’t want the work, Wild Horse Engineering will be happy to take over.Third point. You should show more respect for Saturn management.”

So I signed the contract. And now I had to answer for the new C-301A fractionator. But it wasn’t my fault. Maybe Moses dropped the tablet with the Eleventh Commandment: “Thou shall not waste the resources of the Earth.” But that’s not my fault either. It’s all Don’s fault. He led me into temptation.

WET GAS COMPRESSOR

I guess it’s true. The Immortals know the evil that dwells in our hearts.

“Norman,” said the Son of Cronus, “did you know that 16,000 tons of iron ore had to be torn from your small planet to fabricate the new fractionator? Plus 16,000 tons of No. 9 coal. All for what purpose?”

“Well, Master of Mt. Olympus. All for no purpose. As you see, I would trade all of the $132,000 just to get my kayak to the shore. And the L.A. delayed coker was limited to 70,000 bsd of feed by the capacity of the existing coke drums, which with relatively minor process changes, the old C-301 tower could have handled.”

I could see, though, that it was best not to mention again that it wasn’t my fault. Not only because Zeus didn’t believe me, but because in my heart I knew—and had always known—the truth.

“Zeus, forgive me. I am at fault,” I admitted.

“And how about, Norman, the new K-301-A, 12,000-horsepower wet gas compressor?” inquired Athena.

“To answer that question, I’ll have to refer to the second law of thermodynamics.”

“Yes, the second law of thermodynamics.” Hera seemed pleased. “The Titans created the laws of thermodynamics when they separated light from darkness. Yes, they created the laws of science for humankind to use and not to abuse. But you have perverted science in sinful ways.”

I had told Don that the capacity of the coke drums was inconsistent with a new and much larger, 12,000-hp centrifugal compressor. It would not really matter, I explained, if the compressor were oversized if we used a variable-speed driver. There were three variable-speed options:

Steam turbine. We could install a 400-psig motive steam turbine, exhausting to a surface condenser operating under vacuum conditions. But Don said that the refinery was short of cooling water and the proposed surface condenser would consume 8000 gpm of cooling water.Gas-fired turbine. There was plenty of coker fuel gas to burn. But this would require a permit, as a new emission source, from the state of California, which could take years.Variable-speed motor drive. This would involve the purchase of a relatively expensive motor, as the frequency of electric power to the motor would have to be varied. Unfortunately, Larry Overbourne, the refinery manager, did not like variable-frequency speed control of large motors in critical services.

So we would have to use an ordinary 15,000-hp motor. (The compressor rating was to include a 10% capacity safety factor, and the motor was sized for 110% of the compressor load.) I tried to explain to Don that we could never need a 15,000-hp electric motor. It was way too large for the capacity of the coke drums.

“Norm,” Don responded, “our Mississippi refinery has a 15,000-hp compressor and we want one of the same size. After all, they have the same-size coke drums as we do.”

As the Saturn refinery in Mississippi is close to my home in New Orleans, Don flew from LAX to Louis Armstrong International Airport. We drove to Mississippi. Figure 1-2 summarizes what we saw. The compressor suction valve was almost closed. The pressures were:

Figure 1-2Energy loss across a compressor suction throttle valve.

Compressor suction: 2 psig (17 psia)Compressor discharge: 265 psig (280 psia)Pressure upstream of the suction throttle valve: 20 psig (35 psia)

Compression work per mole is proportional to the compressor suction pressure, as follows:

where p1 and p2 are, respectively, the compressor suction and discharge pressure in psia. The exponent 0.20 is calculated from k (the ratio of the specific heats) as follows:

Assume that we have two cases:

Case I: suction pressure = 17 psia, suction valve 20% openCase II: suction pressure = 35 psia, suction valve 100% open

Case I requires roughly 40% more horsepower than case II. This means that approximately 30% of the motor driver horsepower is lost across the compressor suction throttle valve when it is 20% open.

WASTING ELECTRIC ENERGY

I explained to Don that 2500 kW were being wasted at the Mississippi plant by the suction throttle valve. To generate 1 kW of electric power may require 9000 Btu/hr of fuel. In older power stations, it is likely to be 10,500 Btu/hr. Therefore, the waste in energy was

There are 6,300,000 Btu in a barrel of fuel oil. Therefore, the Mississippi wet gas compressor was wasting about 80 bsd worth of fuel a day. A typical family in the United States consumes 0.20 barrel of crude oil a day. Therefore, the suction throttle valve was wasting the amount of crude oil that 400 families would use each day.

But Don said, “Interesting, but irrelevant. Saturn has already issued the purchase order for the new compressor and motor. I’d better be careful, though, not to oversize the new compressor’s suction throttle valve.”

“Don, Saturn could pay a 10% cancelation fee for the compressor. The electric power saved could be exported to Los Angeles. Think of all the CO2 emissions we could avoid. The concentration of greenhouse gases has been increasing at 0.5%, compounded annually, since 1975. We’ve got to draw the line somewhere. Why not here? Why not today?”

“Norm, I told you, Mr. Overbourne wants the new compressor.”

ALTERNATIVES TO THE NEW COMPRESSOR

“Pallas Athena, the new 15,000-hp motor was not my fault. I tried my best. There was just nothing I could do.”

“Do you not fear the shades of Hades?” asked Athena.

“Not really. It’s probably like the Good Hope refinery, in St. Charles Parish, Louisiana, where I used to work.”

“Norman, look unto thy heart. Were there no alternatives to the new, larger centrifugal compressor?” asked the daughter of Zeus.

“Creator of Wisdom, I did have a few ideas along those lines:

The air-cooled condensers just upstream of the compressor knockout drum were dirty. I could have cleaned their exterior to increase airflow. This would have lowered the reflux drum temperature shown in Figure 1-1. The reduced reflux drum temperature would alter the vapor–liquid equilibrium so as to produce less vapor. Also, compression work is reduced, as the compressor suction temperature is reduced, in proportion to the reduction in absolute temperature (°R or °K).The tube side of the air coolers could have been water-washed on-stream. Not only would this have improved cooling, but more important, the tube-side pressure drop could have been reduced. At a constant fractionator pressure, this would have raised the wet gas compressor suction pressure. Each 1 psi reduction in condenser Δp would have reduced the suction volume by over 4%. Further, the lower Δp value and the resulting higher reflux drum pressure would alter the vapor–liquid equilibrium so as to produce less vapor.The compressor could be kept clean by spraying about 1 wt% of heavy coker naphtha into the suction of the machine. Enough naphtha is used, depending on its molecular weight, to keep the compressor effluent slightly below its dew-point temperature—the idea being to keep the rotator wheels wet, which retards dry-out of salt deposits on the final stage wheels.Most of the time, cooler ambient conditions in Los Angeles prevent the coker from being limited by the wet gas compressor. During late afternoon summer days, water can be sprayed as a fine mist into the inlet of the forced-draft air fans. This will cool the air by 10 to 15°F due to the evaporation of the water, rather like the swamp coolers used in the south western United States. I’ve also seen the Russians use this technique in Lithuania and it works fine. It’s a nice trick to use to reduce the flow of wet gas during peak ambient temperature periods.Changing from trays to beds of structured packing in the fractionator would reduce the fractionator Δp. This would raise the compressor suction pressure by an equivalent amount, but without raising the coke drum pressure.The interstage compressor water coolers were badly fouled. They could have been cleaned with inhibited, dilute hydrochloric acid to remove the hardness deposits on the water side. This would have reduced the vapor load to the compressor’s second stage by increasing the flow of cooling water and thus decreasing the interstage knockout drum temperature. Alternatively, a chelating solution could have been circulated through the cooling water circuit, to clean the entire cooling-water circulating system.The air-cooled compressor discharge condenser could also have been cleaned, on both the tube and air sides. This would have reduced the discharge condenser pressure drop and thus reduced the compressor discharge pressure. This is relatively unimportant, as a 10-psi reduction in discharge pressure is equivalent to a 1-psi reduction in suction pressure as it affects the wet gas compressor compression ratio.The existing motor had a habit of tripping off on electrical overload. This could have been because the full-limit amperage (FLA) trip point setting was accidentally set too low. Alternatively, and more likely, the insulation integrity of the copper coil windings had deteriorated, and the motor would have to be rewound. This is not uncommon in larger motors that have seen many years of service close to their FLA point.Improving the cleanliness of the compressor rotor by the heavy coker naphtha spray at the suction would also help the motor. As the cleaner rotor would require less horsepower to spin, the amperage load on the motor would also be reduced.Another option would have been to modify the. …”

“Enough!” commanded Zeus.

“Merciful King of the Immortals, I sent the plant manager, Mr. Overbourne, an email with my suggestions for reusing the existing wet gas compressor and motor. But I never received a reply.”

“That email! Unfortunately, it was lost in cyberspace,” Zeus explained.

“But Master of Thunder, that’s not my fault. I think it was returned by a Mailer Demon.”

“Your sin is one of omission. You should have asked for an appointment with Overbourne. You should have insisted on your ideas. The construction of the new motor and compressor consumed resources on your little planet that will take eons to replace. Just the wasted electrical power produced more carbon dioxide emissions than Adam and Eve, who lived for 900 years,” Queen Hera explained.

“Queen Hera, where’s Larry Overbourne now?” I asked.

Zeus’s countenance darkened, “Vengeance shall be mine. Seek for him across the River Styx, in the House of Hades.”

I just hung up the phone. Don was telling me that my new fractionator and compressor designs are working great. Demonstrated capacity is overdesign and all products are on-spec.

Unfortunately, the refinery is cutting the crude run because gasoline demand is slipping due to the economic turndown. Also, the coke drums themselves are cracking due to the shortened coke drum cycles. So the extra capacity isn’t needed. But still, Saturn’s management is pleased with the project. I just didn’t have the heart to tell Don what the ultimate top management thought about our work.

KEEPING COMPRESSOR ROTORS CLEAN

Of the preceding list of items to improve a compressor’s efficiency and capacity, the one from which I have seen the most beneficial results is the injection of a liquid spray into the suction of the compressor. This is such a beneficial practice when compressing most process and natural gas streams that I have often wondered why it is not a standard feature in most centrifugal compressor’s original installations.

When I was first asked, as a young process design engineer at the old American Oil Company in 1965, to design a liquid injection system for the suction of a multistage recycle hydrogen centrifugal compressor, I was quite confused by the assignment. All compressors that I had seen were equipped with compressor K.O. (knockout) drums, to prevent liquid from damaging the compressor internals. Both entrained droplets and slugs of liquid will damage the valve plates on a reciprocating compressor. A broken valve plate will, in practice, disable the affected reciprocating compressor cylinder and lead to a loss of compression efficiency and capacity. Slugs of liquid (but not necessarily entrained droplets of liquid) will also damage both the rotor and stator of a centrifugal compressor. Hence the need for the K.O. drum ahead of the compressor’s suction.

Let’s assume that there is a small amount of entrained liquid in the suction of a centrifugal compressor. Actually, according to Stokes' law, that’s not an assumption but a certainty. Let’s further assume that this entrained liquid contains a tiny amount of salts. Again, that’s not an assumption, but a certainty, if we are compressing:

Coker off-gasFCU (fluid cracking unit) wet gasRefinery hydrotreater recycle gasNaphtha reformer off-gasNatural gas upstream of the glycol dehydration scrubber

As the gas is compressed, one might think that the higher pressure would prevent any droplets of entrained liquid from evaporating. However, the heat of compression is always a bigger factor promoting compressed gas to dry out, and it offsets the effect of the higher pressure entirely. Thus, as the inevitable droplets of liquid in the inlet gas evaporate, salts and other solids may slowly accumulate on the compressor wheels.

My most vivid experience of this common problem occurred at the Laredo compression station in south Texas in 1986. We were compressing natural gas from 600 psig to 1100 psig using a centrifugal compressor comprised of four wheels. The gas contained entrained brine (i.e., salt water). After several months of operation, I would begin to notice a gradual loss of compressor capacity. Not only would the compressor’s capacity and efficiency diminish with time, but when the compressor lost about 30% of its capacity, the compressor would start to vibrate and then trip off on the high rotor vibration automatic shutdown switch. When, subsequently, the machine was disassembled, I observed that:

The first wheel was very clean.The second wheel had minor salt deposits.The third wheel was badly encrusted with both salt and a heavy grease.The final and fourth wheel was very slightly fouled with salt.

Clearly, the brine was drying out on the third wheel. The resulting deposits were restricting the gas flow through the machine: thus the loss of capacity.

CALCULATING LIQUID INJECTION RATES

A typical application in a refinery for suppressing salt formation on a centrifugal compressor’s rotor, would be hydrogen recycle for a naphtha hydrosulfurizer. To calculate the amount of the liquid injection to the suction of the compressor:

Assume that the entrainment rate is zero from the K.O. drum.Select the type of liquid to be employed. I would just use the naphtha stabilizer bottoms rather than an expensive specialty aromatic chemical.Calculate the amount of naphtha that is required in the compressor’s suction to reach the dew-point temperature at the discharge from the final wheel of the stage.Note that each stage of compression (i.e., not each wheel) should be treated separately.To calculate the amount of naphtha required, take into account both the latent heat of evaporation of the naphtha and the increase in the dew-point temperature of the compressed gas, due to the gas’s increased molecular weight, from the injected naphtha.A typical spray wash flow is 1 wt% of the gas flow. I do not add any safety factors to the amount calculated above, as ignoring the effect of entrainment in the feed gas in effect adds a safety factor to this calculation.

DESIGN DETAILS

Then I call my Bete nozzle rep and have him select an appropriate mist nozzle for this application, I will typically specify:

Δp = 20 psiNozzle to be extractable on-stream, through a packing gland316 (L) stainless steelExternal filter, with mesh openings of one-third the maximum free passage of the mist nozzle

Running without the spray while it is being cleaned for a few hours is okay. However, forgetting to shut off the naphtha spray when the compressor trips off is definitely not okay. Thus, the FRC regulating the spray wash flow should be tripped when the compressor is shut down.

I realize that changing the fractionator tray panels and adding a mist injection system to a wet gas compressor is not entirely consistent with the objective of using what we have. But these methods are a far better alternative to erecting a giant new coker fractionator tower or installing a new oversized wet gas centrifugal compressor equipped with a huge new motor, requiring a new electrical substation. This is what ethical engineering design is all about!

Troubleshooting Method

In this book I detail a large number of successful examples as to how process problems were resolved, with a minimum input of new equipment. These examples are all genuine and true to life, sometimes taken out of the actual context, but without altering the technical content of the incident. However, what is not true is that I solved all these problems myself. On occasion, the solution was later found by an engineer or operator with whom I had been working.

My failure to solve some problems is usually due to spending only a day or two on a subtle or complex issue. Or, too frequently, I have made a wrong initial assumption and could not resolve the issue until this flawed assumption was discarded.

Still, almost invariably, the man or woman who has defined the correct solution after my departure has credited my troubleshooting method as contributing to their success. This method is as follows:

Look over the equipment in the field until you become familiar with the function, location, and nomenclature.Discuss the problem with the hourly operators in detail.Carefully measure all parameters that may interact with the problem. Defining which such parameters to measure is often the most difficult and important key to solving the problem.Calculate the effect of process changes on the parameters.Observe the effect of the process changes on the parameters. That is, change things and see what happens.Does the observed change equal the calculated change? If not, why the difference?

The difference between the observed and predicted parameters is most often the key observation that will reveal the true nature of the problem. So often, in retrospect, the nature of the problem is disturbingly simple. Often, I’ve become angry at myself for stumbling over an obvious issue. But with age I’ve come to understand that it’s my technique, not knowledge or experience, that is my fundamental contribution to the hydrocarbon process industry.

Process Engineering for a Small Planet: How to Reuse, Re-Purpose, and Retrofit Existing Process Equipment, By Norman P. Lieberman Copyright © 2010 John Wiley & Sons, Inc.

Chapter 2

Vacuum Tower Heater Expansion

“Father Zeus, what happened to H-501-A, the new vacuum heater at Saturn’s El Segundo refinery?” I asked.

A section of this new, 200 million Btu/hr vacuum heater had fallen off a truck on I-10 east of Los Angeles and rolled down a hill. The damage took months to repair. It happened during a freak ice storm and was thus designated by the All Farm Insurance company to be “an Act of God.”

I had been hostile to the H-501-A heater replacement project from the start. Let me explain with reference to Figure 2-1.

Figure 2-1Diesel left in vacuum tower feed increases heater fuel consumption.

I had been retained by Saturn to improve the performance of its vacuum tower. The problem was excessive vertical vapor velocities in the flash zone of the vacuum tower. The high vertical velocity was promoting entrainment of black asphaltine molecules, which contaminated the gas oil product. The entrainment velocity factor, C, is calculated as follows:

where

C=entrainment velocity, ft/sec

V=superfacial vapor velocity, ft/sec

DV=vapor density

DL=liquid density

A C factor above 0.45 will lead to uncontrolled entrainment. A C factor below 0.15 will produce very little entrainment. I design vacuum tower flash zones for a C factor of 0.35 ft/sec. The C