Process Engineering E-Book

Norman P. Lieberman

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

Seitenzahl: 216

Veröffentlichungsjahr: 2017

Beschreibung

This is not your average technical book! Using a humorous and easy-to-understand approach to solving common process engineering problems, this unique volume is the go-to guide for any veteran or novice engineer in the plant, office, or classroom. Textbooks are often too theoretical to help the average process engineer solve everyday problems in the plant, and generic handbooks are often out of date and not comprehensive. This guide focuses on the most common problems that every engineer faces and how to solve them. The "characters" walk the reader through every problem and solution step-by-step, through dialogues that literally occur every day in process plants around the world. With over half a century of experience and many books, videos, and seminars to his credit, Norm Lieberman is well-known all over the world and has helped countless companies and engineers through issues with equipment, processes, and training. This is the first time that this knowledge has appeared in a format like this, quite unlike anything ever published before in books on process engineering. This is a must-have for any engineer working in process engineering.

Leseprobe

Contents

Cover

Title page

Copyright page

Dedication

Other Books By Norman Lieberman

Introduction

Part I

Chapter One: Process Operations & Design

Increasing Cooling Water Flow Thru an Elevated Condenser or Cooler

Hot Vapor By-Pass Pressure Control

Stalling a Thermosyphon Reboiler

Optimizing Fractionator Pressure

Adjusting Steam Turbine Speed to Minimize Steam Consumption

Steam Condensate Drainage from Reboilers Blowing Condensate Seal

Effect of Reflux on Fractionator Top Temperature

Centrifugal Pump Head Vs. Flow Performance Curves

Condensate Back-Up in Condensers-the Effect of Sub-Cooling

Distillation Tray Downcomer Back-Up and Liquid Flooding

Effect of foam on Level Indication in Distillation Towers

Split Liquid Levels in Vertical Vapor - Liquid Separators

Optimizing Excess Air in a Fired Heater to Minimize Fuel Consumption

Distillation Tray Dumping or Weeping with Valve Cap Tray Decks

Fired Heater - Tube Failures

Low Air Flow in a Fin Fan Forced Draft Air Cooler

Measuring Air Flow For an Aerial Fin Fan Aerial Cooler

Measuring Cooling Tower Efficiency Approach to Wet Bulb Temperature

Adjusting Heater Stack Damper for Optimum Energy Efficiency

Preventing Tray Dumping by Use of Bubble Cap Trays

Demister Fouling in Vapor-Liquid Seperator Vessels

Effect of Temperature on Liquid Level Indication

Draw-Off Nozzle Capacity Limits

On-Stream Repair of Tube Leaks in Surface Condenser

When Are Vortex Breakers Required?

Naphtha Injection to Centrifugal Compressor

Internal Overflow from Total Trap-Out Chimney Tray

Vacuum Ejector – Loose Steam Nozzle

Effect of Tramp Air Leaks on Heater Efficiency

Effect of a Single Fouled Tray

Steam Turbine – Surface Condenser Outlet Temperature

Water Accumulation in Turbine Case

Chapter Two: Crude Distillation

How to Adjust Pumparound Flows

How Top Reflux Rate Affects Flooding on Top Trays

Desalter - Adjusting Mix Valve Pressure Drop

Causes of Tray Deck Fouling

Minimizing Flash Zone Pressure

How to Adjust Bottoms Stripping Steam Rate

Overhead Condenser Corrosion

On-Line Spalling of Crude Pre-Heat Exchangers

Effect of Reflux on Overhead Accumulator Temperature

Removing Trays from Pre-Flash Towers

Total Trap-Out Chimney Tray

Side Draw-Off Limitations

Packed Towers

Rules of Thumb for Packed Towers

Controlling Ago Draw-Off Rate

Filming Amine Plugs Overhead Vapor Line

Stripping Tray Pressure Drop Profile

Protecting Crude Tower Stripping Trays from Damage Due to Water in Steam

Chapter Three: Engineering Basics

Draft in Fired Heaters

Turbine Exhaust Surface Condenser Outlet Temperature

Adjusting Steam Turbine to Save Steam

Distillation Tray Downcomer Seal

Bernoulli’s Equation

Properties of Steam

Measuring Flows

Head Loss in pipelines

Irene Explains Horsepower

Refrigeration

Packed Towers Vs. Trayed Towers

Condensing Steam Turbine Exhaust

Maximizing Lmtd in Heat Exchangers

Chapter Four: Routine Refinery Operating Problems

Pump Bearings Lubrication

Pressure Measurement Problems in Vapor Lines

Negative Pressure Drops

Coked-Up Thermowells

Centrifugal Compressor Surging

Commisioning Steam Turbine

Refrigeration Systems

Seal Pan Drain Hole

Measuring Steam Flow Without a Steam Meter

Air Leak on Suction of Cooling Water Pump

Chapter Five: Refinery Safety

Auto-Ignition of Hydrocarbons

Failure of Mechanical Pump Seals

Sampling Tar Safely

Dangers of Iron Sulfides

H

2

S Fatalities

Fired Heater – Positive Pressure

Refinery Explosions & Fires

Flooding Fire Box with Fuel

Routing Relief Valves to the Flare

Isolating Equipment with Gate Valves

Explosive Limit of Hydrogen

Climate Change

Danger of Carbon Steel Piping Spool Pieces

Screwed Connections

Dangers of Steam Deaerators

Connecting Steam Hose to Hydrocarbon System

Process Vessel Collapse Under Vacuum During Start-Up

Acid Gas K.O. Drum

Safety Note

Part II

Chapter Six: Pitfalls in Computer Modeling

Basis for Process Engineering Calculations

Underlying Assumptions in Distillation Technology

Tray Fractionation Efficiency

Heat Exchanger Train Performance

Heat Exchanger Pressure Drop

Packed Towers

Air Coolers

Fired Equipment

Piping Systems

Centrifugal Pumps – NPSH

Rotating Equipment

Summary

References

Value of a Chemical Engineering Degree to the Process Engineer in a Refinery

Chapter Seven: Latent Heat Transfer

Propane-Butane Splitter Reboiler

Heat Flux Limitations

Chapter Eight: Hydraulics

Fluids Other Than Water

Rotational Energy

Pressure Drop Through an Orifice

Effect of Fluid Density on Orifice Pressure Drop

Head Loss in Piping

Factor Affecting Orifice Coefficients

Compressible Fluids

Chapter Nine: Air Coolers

Measuring Air Flow

Air Recirculation

Vane Tip Clearance Problems

Cleaning Tube Bundle

Effect of Fouling on Reverse Air Flow

Effect of Adding Rows of Tubes

Changing Fan Blade Tips & Speed

Slipping Belts

Air Humidification

Induced Draft Fans

Chapter Ten: Extracting Work from Steam

An Isentropic Expansion

Steam Turbines

The Potential Energy of Steam

Condensing Steam at Low Pressure

The Meaning of Entropy

The Norm Lieberman Refinery Troubleshooting Seminar Video Presentation

Index

End User License Agreement

Guide

Cover

Copyright

Contents

Begin Reading

List of Illustrations

Chapter 6

Figure I

Figure II

Figure III

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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106

Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])

Process Engineering: Facts, Fiction, and Fables

Norman P. Lieberman

This edition first published 2017 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2017 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.

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Limit of Liability/Disclaimer of WarrantyWhile the publisher and authors have used their best efforts in preparing this work, they make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation any implied warranties of merchantability or fitness for a particular purpose. No warranty may be created or extended by sales representatives, written sales materials, or promotional statements for this work. The fact that an organization, website, or product is referred to in this work as a citation and/or potential source of further information does not mean that the publisher and authors endorse the information or services the organization, website, or product may provide or recommendations it may make. This work is sold with the understanding that the publisher is not engaged in rendering professional services. The advice and strategies contained herein may not be suitable for your situation. You should consult with a specialist where appropriate. Neither the publisher nor authors shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages. Further, readers should be aware that websites listed in this work may have changed or disappeared between when this work was written and when it is read.

Library of Congress Cataloging-in-Publication DataISBN 978-1-119-37027-7

To Allen and Irene Hebert, whose dedication and determination have been tirelessly applied to assemble this text. And who jointly originated the concept for assembling my cast of cartoon characters into book format.

Other Books By Norman Lieberman

Introduction

I started work as a process engineer for the American Oil Company in 1965. Now, after 52 years, I’m still a process engineer. Still working in the same way, on the same problems:

Distillation Tray Efficiency

Shell & Tube Heat Exchangers

Thermosyphon Reboilers

Draft in Fired Heaters

Steam Turbine Operation

Vacuum Steam Ejectors

Centrifugal Pump Seals

Surge in Centrifugal Compressors

Reciprocating Compressor Failures

Process Safety

Fluid Flow

Most of what I need to know to do my job, I have still to learn. And I’m running out of time! So, with the help of my little friends in this book, I’ve recorded what I have learned so far. I hope this will help you in solving process problems.

The difficulty of being a process engineer is that our job is to solve problems. Not with people, but with equipment. Within minutes, or hours, or days, the validity of our efforts are apparent. More like plumbing, less like other branches of technology.

Most things I’ve tried as a process engineer haven’t worked. But those that have been successful I remember, and use again. And it’s insights from these successful plant trials and projects that I have shared with you in my book.

One thing’s for certain. The money paid for this book is nonrefundable. But should you have process questions, I’ll try to help.

Norm [email protected]

PART I

CHAPTER ONEPROCESS OPERATIONS & DESIGN

CARL & CLARE

Hello! I’m Clare! I work for Carl. We troubleshoot refinery process equipment! We’re a team!

Hi! I’m Carl! I know everything, because I’m really, extremely, smart! Clare is my associate!

INCREASING COOLING WATER FLOW THRU AN ELEVATED CONDENSER OR COOLER

Clare! Let’s open the cooling water outlet valve to get more water flow.

No, Carl! The Condenser is 60 feet above grade. The pressure at P1, is under vacuum! Opening that valve will give us less cooling water flow!

NO! Opening a valve will always increase flow!

Sorry, Carl! Opening that valve reduces the pressure at P1, further below the atmospheric pressure. This causes the air to flash-out of the cooling water, which chokes back water flow!

Clare! WRONG! I’m really smart! Anyway, where’s the test to prove you’re right?

OK. I’ll close the valve and you’ll see the temperature at T1 will go down. But don’t close it too much! Otherwise, you will throttle the water flow. Then, T1 will get hotter!

But Clare! How do I know how to adjust that stupid valve?

Carl, dear! Set the valve to hold a backpressure of about 3″ Hg. That’s minus 0.10 atmosphere. At 100 °F, that will stop air evolution from the water, but not throttle the water flow too much!

HOT VAPOR BY-PASS PRESSURE CONTROL

Clare! Close the hot vapor by-pass valve! We need to lower the tower pressure. Do it now!

Sorry, Carl! When I closed the valve the tower pressure went up … not down!

No, Clare! Closing the valve will cool off the reflux drum! The pressure at P2 will drop, and draw down the pressure at P1. Understand?

But Carl! How about the pressure drop across the air cooler? It increases as more flow is forced through it. True, the pressure at P2 will always fall! But the pressure at P1 may go up or down—depending on the air cooler DP!

But, but …? Closing the hot vapor by-pass is supposed to lower the tower pressure, according to my design manual!

But suppose the tubes get full of salts and scale? Then what? Also, Carl, we now have a vacuum in the reflux drum, which can be quite dangerous! Air could be sucked into the drum and an explosive mixture could form! Don’t forget there’s pyrophoric iron sulfide deposits (Fe(HS)2) in the drum! They’ll auto-ignite at ambient temperatures!

STALLING A THERMOSYPHON REBOILER

Clare! Open the steam supply valve! Quick! We need more reboiler heat. The reflux drum is going empty!

Sorry, Boss! That won’t help! The Once-Thru Thermosyphon Reboiler is STALLED OUT!

Clare! More steam flow will have to give us more heat to the reboiler! Open that valve!

Opening the steam valve will not increase steam flow when the reboiler is STALLED-OUT!

STALLED-OUT? What does that mean?

Stalled-out means heat duty is limited by the process flow to the tube-side of the reboiler! The process flow rate to the reboiler is real low now and limiting the steam condensation rate!

How do you know that, Clare? Do you have X-ray vision?

Carl! Look at the reboiler outlet. It’s 450°F! The tower bottoms are only 330°F. Most of the 300°F liquid from tray #1 is leaking past the draw pan, and dumping into the bottoms’ product!

OK, Clare, OK! But still, the steam inlet valve is only 50% open! Won’t opening it 100% help some?

No, Sir! The pressure at P1 on the steam inlet line is 500 PSIG! The same as the steam supply pressure. There is zero DP across the steam supply valve. The valve position, with no DP, is IRRELEVANT!

I guess we should have used a total trap-out chimney tray for tray #1! I remember you suggested that last year, Clare. Perhaps you’d like a transfer to the Process Design Division? They would probably love to have you! I remember that in the old days we had bubble cap trays, which could never leak and cause this loss in thermosyphon circulation, or stalling-out.

OPTIMIZING FRACTIONATOR PRESSURE

Clare! The best way to optimize tower pressure is to target for the lowest pressure!

Why is that, Carl?

Because, Clare, as we learned at university, the lower the pressure, the greater the RELATIVE VOLITILITY between propane and butane!

But Carl! Suppose the lower tower pressure causes entrainment? Then, a lower pressure will reduce tray separation efficiency and make fractionation worse!

Well! What do you suggest? It takes too long to wait for lab sample results.

Carl, I suggest:

At a constant reflux rate, start lowering the fractionator pressure.

Now, watch the delta T (T1 - T2).

That tower pressure, that maximizes delta T, will give the best split between butane and propane. But make the moves slowly!

Clare! You really should take a more positive attitude towards your engineering degree, and show more respect for the principle of relative volatility!

ADJUSTING STEAM TURBINE SPEED TO MINIMIZE STEAM CONSUMPTION

Clare! Always run steam turbines at a constant speed! In the U.S., 3,600 rpm, Europe 3,000 rpm!

I’m sorry, Carl! But I don’t agree!

Exactly what’s your problem? All process plants run their turbines at 5% below their maximum rated speed. That’s best!

Carl! The best way to set the speed of the turbine is to slow the turbine down until the control valve on the discharge of the pump it’s driving is in a mostly wide-open but still controllable position!

All to what purpose?

Well, Carl, for each 3% speed reduction, the steam required to drive the turbine will fall by 10%. Work varies with speed cubed: W ~ (speed)3 … That’s the Affinity Law!

Thanks, Clare! I’ll write new instructions for the operators!

Carl! Actually, you can get rid of the control valve on the discharge of the pump, and run just on governor speed control, to adjust the upstream level or the pump discharge flow and pressure. That will save even more of the motive steam.

STEAM CONDENSATE DRAINAGE FROM REBOILERS BLOWING CONDENSATE SEAL

Clare, listen up! Open that condensate drain valve more. We need more heat to the reboiler!

Sorry, boss! I think opening the condensate drain valve more will reduce reboiler duty! I’m not too sure!

Not sure? Can’t you just follow my instructions for once? It’s getting late!

Carl, here’s the problem! If I open the drain valve too much, we’ll blow the condensate seal. Steam will blow through the reboiler tubes, without condensing. If I open the valve too little, we will suffer from condensate back-up!

I’m confused! Then how do we know whether to open or close that stupid condensate drain valve?

Well, if we close the valve, and T1 goes up, it means we were previously blowing the condensate seal! If we close the valve and T1 goes down, it means we were previously suffering from steam condensate back-up!

OK! Let’s optimize the drain valve position to maximize the reboiler outlet temperature, and go to lunch. I’m hungry! Seems like it’s all a balance between condensate back-up and blowing the condensate seal. Kinda like eating too much or too little.

EFFECT OF REFLUX ON FRACTIONATOR TOP TEMPERATURE

Clare, dear! To lower the tower top temperature, one should always raise the reflux rate. It’s a basic idea of Process Control!

Sorry to disagree again, Carl! It ain’t necessarily true!

Now Clare! Read any distillation textbook. They all agree with me! What’s your problem?

It’s this: If the top tray is at its flood point, raising top reflux must increase reboiler duty, because the reflux comes from the reboiler. This will increase vapor flow to the top tray!

So what? The reflux will cool off that extra vapor! The reflux will knock back the heavier components in the vapor. What’s your problem, Clare?

What you say is true, boss. Up to a point. The INCIPIENT FLOOD POINT! Above that point, extra vapor promotes ENTRAINMENT. The result is droplets of heavy liquid blow up through the trays, increasing the boiling range of the top product and temperature at the top of the tower.

That’s BAD! Because then the tower top temperature will go up, as the reflux rate is increased. Worse, the top reflux rate, and reboiler duty will then increase more, and make the problem even worse!

Yes, Carl! I call this getting caught up in a POSITIVE FEED-BACK LOOP! The reflux needs to be switched to manual and partly closed to break the feed-back loop.

CENTRIFUGAL PUMP HEAD VS. FLOW PERFORMANCE CURVES

Clare! Where did you get that pump curve from? It’s wrong!

From plant data on the new giant vacuum tower residual pump. I plotted observed flow vs. pump discharge pressure!

Well! It’s contrary to the manufacturer’s curve! The head and flow are both going down, at a low flow. Impossible, I’d say!

The pump is never supposed to operate at such a low flow. But, Carl, you purchased this oversized pump yourself!

Oh! Well then, I guess it’s OK to run it below point “A”, as we have lots of excess head anyway!

No, Carl! It’s not OK. Below point “A”, the pump vibrates in a most alarming manner!

No need to mention this to Carl … but Norm first saw this in 1991, at the Coastal Refinery in Aruba! Norm still complains to this day that those pump vibrations loosened the fillings in his teeth! Imagine what that did to the pump’s mechanical seal? The pump had a minimum flow spill-back, but when Norm opened it, the pump lost suction and cavitated is a most alarming manner.

CONDENSATE BACK-UP IN CONDENSERS-THE EFFECT OF SUB-COOLING

Clare! Let’s get condenser “B” cleaned. Look how high its outlet temperature is!

Actually Carl, it’s “A” that’s really underperforming!

But the outlet flow of “B” is hotter than “A”?

Well, that’s true! But only because “A” is suffering from CONDENSATE BACK-UP and sub-cooling! About 40% of the tubes in “A” are submerged in liquid, but only 10% of the tubes in “B” are covered in liquid!

So, Clare, I suppose that now you have X-ray vision too? How can you know that “A” is suffering from condensate back-up?

Just run your hand along that channel head cover! You can feel the temperature gradient; where the channel head feels cooler, is the liquid level. Tubes covered in liquid, can’t condense any vapors! Because the vapor is not even in contact with any of the tubes.

You know Clare, this kind of reminds me about the condensate back-up problem we had in the channel head of our steam reboilers! Kinda the same process problem!

DISTILLATION TRAY DOWNCOMER BACK-UP AND LIQUID FLOODING

Clare, let me explain what causes downcomers to flood! It’s because the downcomers are too small! That is, downcomer loading exceeds 175 GPM per square foot of downcomer cross sectional area!

I certainly agree, Carl! But there are many other reasons for downcomer flooding. Shall I explain?

Such as?

Well, Carl! Such as loss of the downcomer seal! If the weir height is adjusted wrong, it may be lower than the downcomer clearance! Then the downcomer seal would be lost! Vapor would blow up the downcomer and prevent liquid from draining out of the downcomer!

Easy enough to prevent! Just keep the bottom of the downcomer real close to the tray deck below. No problem!

No, Carl! Restricting the downcomer clearance will cause too much head loss under the downcomer, and also increase downcomer back-up! Also, if tray #1 gets too dirty, the flowing vapor pressure drop through tray #1 will go up. This will push up the liquid level in downcomer “A”! And Carl, if tray #2 leaks really bad, the bottom of downcomer “A” will become UNSEALED! This would also cause vapor to blow up downcomer “A” and retard liquid drainage from tray #1!

I guess this would cause tray #1 to flood. That’s bad!

Not only tray #1! With time, all the trays above would also flood!

OK, Clare! Just be careful, when you inspect the tray installations, that you have a ″ overlap, between the top edge of the weir and the lower edge of the downcomer from the tray above! And make real sure the weir and bottom edge of the downcomer are LEVEL!

EFFECT OF FOAM ON LEVEL INDICATION IN DISTILLATION TOWERS

Clare, I’ve just checked the level in the tower. It’s 2 ft. below the reboiler return nozzle. It’s fine!