- Email: [email protected]
Learning Process Engineering Principles
38
Learning Process Engineering Principles
Most of what I have needed to learn to achieve my objective of becoming an effective process engineer, I did not acquire in University or Graduate School. I did not learn very much about process engineering employed as a design engineer in Chicago for 16 years. My foundation of process knowledge is built on the times I worked as an operator during the two long strikes in the American Oil Refinery in Texas City in 1974 and 1980. The strikes lasted 4–5 months. As a salaried employee, I worked as a scab. Twelve hour days. Seven days a week. In 1974, on the Sulfuric Acid Alkylation Unit. In 1980, on the Sulfur Recovery Unit that I had previously designed. Had it not been for this opportunity to observe, operate, and repair pumps, turbines, reactors, heat exchangers, and distillation towers, I would not have developed the process insight to the problems that I have today. The other major source of my process knowledge is derived from childhood experiences. I enjoyed being a child. I continue to regret and resist growing up into an adult. As a child I had an inordinate fascination in such phenomena as: 1. How did the air lift filter pump in my aquarium circulate water? 2. What was the function of the small conical vent on top of our steam radiator that heated our fifth floor apartment? 3. When my mom poured Coke over the rust stains in our bathroom sink, why did the rust dissolve? 4. Why did a drop of water on a very hot, smooth frying pan dance around and not evaporate, while water on a cooler, scratched pan, would instantly boil away? 5. When it was windy outside, why did the water level in our toilet bowl oscillate? 6. Why did water come out of the kitchen tap cloudy, but clear up after standing for 5 min? 7. Why, when my dad opened a warm bottle of beer too fast, did the beer explode violently out of the bottle? Now I can correlate these childhood observations with refinery process technology: 1. Air lift pump—Similar to thermosyphon circulation in reboilers and steam generators. 2. Radiator vent—A noncondensable vent installed below the lower pass partition baffle on the channel head of steam shell and tube heaters.
Understanding Process Equipment for Operators and Engineers. https://doi.org/10.1016/B978-0-12-816161-6.00038-2 © 2019 Elsevier Inc. All rights reserved.
305
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UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
3. Removing rust stains with coke—This is an example of carbonic acid corrosion of iron due to CO2 contamination of steam, due to the decomposition of carbonates in boiler feed water. 4. Water on a hot pan—Same as a heat flux limitation in a reboiler with smooth tubes and high pressure steam. 5. Erratic toilet water level—Caused by the draft that wind develops as it blows across the top of a fired heater’s stack. Typically, 0.1–0.2 in. of water. 6. Cloudy tap water—Air dissolved in water in higher pressure and cooler temperature. 7. Beer bottle foam-over—Sudden reduction in a distillation tower pressure causes the tower to flood and carry-over.
Function of a Process Engineer I quit American Oil in 1980 and went to work as the Technical Service Manager at the Good Hope Refinery. I had a dozen young chemical engineers in my group. They were bright boys, but like me, had not learned much in University that would aid them in their job (Note: In 1980, very few women studied Chemical Engineering. Now it’s about 50/50.). The first thing I explained to the boys as they began work was that our principal job was to solve problems in the plant. Our function was not to: • • • • • • • • •
Write reports Attend meetings Interact with vendors Do environmental impact studies Run computer models Provide data for the planning department Have lunch with chemical vendors Evaluate new refining technology Participate in seminars in New Orleans Our job was to solve plant problems that the operators could not solve themselves.
How to Learn I didn’t learn to drive sitting at a desk in high school. My dad taught me in our brown 1959 Oldsmobile. The operators in our plant were actually “trained on the job.” They started working in parallel with an older guy. They followed him around for a few weeks. Then, the experienced operator followed and observed the newer operator for another week to correct any of his or her mistakes. It’s really no different when learning any skill. Most everyone is like me. I can only learn while doing. It’s the ancient apprentice concept. When a new process engineer started work at the Good Hope Refinery in my group, I would give him his first assignment.
Chapter 38 • Learning Process Engineering Principles
307
“Reid, we’re short of reboiler duty on our Crude Unit gasoline debutanizer. Ask Mr. Walker, the area supervisor, to explain the problem to you as he understands it. He will show you where the reboiler is located.” Reid Burt came back to my office the following morning, “Mr. Lieberman, Mr. Walker showed me the reboiler. He says the problem is he can’t get enough 150# steam flow to the reboiler. He used to be able to get 14,000 pounds an hour flow, but now all he can get is 9,000. He showed me that the steam inlet control valve is wide open. I made a sketch of the reboiler, but I don’t know what else to do? We didn’t study steam reboilers at LSU. Should I try to model the debutanizer on the Aspen Simulation Program?” And I would say, “Reid. Let me get my tools and my bag of pipe fittings. We’ll go out together and look the job over in the field. Go get your gloves and hard hat.” Reid and I would then measure the pressures and skin temperatures in the 300 steam condensate drain line and in the 600 condensate collection header. And I would explain, as we made the measurements together, the cause of the low steam flow. “Reid, water is backing up in the reboiler channel head. The problem is vapor lock. The excessive pressure drop in the condensate drain line is causing the water to partly flash back to steam. The evolved steam restricts the flow of water, which backs-up over the tubes in the reboiler. This reduces the heat transfer surface area and reboiler duty.” From this exercise, Reid would learn how to make field pressure and temperature measurements. He would also learn the technical concept of the effect of condensate back-up. I would explain the design error. That is, the omission of a condensate pump to prevent excessive steam evolution in the condensate flow in the 300 line.
Interfacing With Operators Up until the 20th century, most technical knowledge was transmitted not through institutions or books, but by the apprentice system. My example cited before, when I said, “Let me get my tools and we’ll go out to the reboiler together,” was an example of this ancient instructional technique. Another technique of comparable value is to interface with the plant operators. Especially when it relates to controls (level, flow, temperature, pressure). Working with operating personnel is the best way to understand how control loops and control valves work, and their wide range of malfunctions. Especially, how control loop design interacts with process problems and occasionally creates a “Positive Feedback Loop.” For example, I had no idea of how instrument air is connected to a control valve diaphragm, until it was explained to me by an older operator on my Alky Unit in Texas City in 1975. Another example of learning from operators is the need for “Starting NPSH” for centrifugal pumps. A concept that I’ve discussed in detail in this text. Operators all understand the need to increase flow from the discharge of a centrifugal pump slowly, to avoid
308
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
cavitation. From this observation, I have devised the numerical method for calculating, for design purposes, the starting NPSH requirement for a centrifugal pump. This is the extra elevation of a vessel needed to accelerate the liquid, on start-up, in the pump’s suction line.
Learning From Maintenance Personnel A lot of people, like me, have a problem visualizing a three-dimensional object from a book. I do much better in my comprehension when I can see the actual equipment. A Shell and Tube Heat Exchanger is a good example. I never quite understood how the floating head on such an exchanger was actually attached to the tube sheet using a “Split Ring Assembly,” until John Brundrett, the maintenance manager in Texas City, showed it to me during an FCU turnaround. I had heard a lot about the clearance between the impeller and the pump case, and knew this was important. But until a shop maintenance technician explained this to me, I never really understood it. I learned how centrifugal compressors work by watching a 10,000 BHP Solar-Centar rotor overhauled in a repair shop in Dallas, while listening to a 2-h monolog from the craftsman cleaning and rebalancing the rotor’s three wheels. When I put the compressor back on-line at the Texas, Laredo Natural Gas Compression Station the following week, I had a better understanding as to how the machine actually functioned.
Inspecting Tower Internals My main field of work as a process design engineer is retrofitting refinery distillation towers and designing new fractionators. I have designed 3000 ID jet fuel steam strippers and a 260 –000 Delayed Coker Fractionator. I draw the tower internal details to scale on blue lined graph paper at 1 in. per foot. Old process design engineers have a saying, “The Devil is in the Details.” As I draw these details, I have a picture in my mind of how this particular feature looked in a tower I had inspected. What had gone wrong with the installation? Are the dimensions I am specifying being adhered to in practice? Have I made a reasonable provision for fouling? Certainly, I will base the tower ID and the number of fractionation trays on the Aspen computer model output. But, that does not provide insight as to where iron sulfide and salt deposits will require an extra inch of downcomer clearance, or, when extra downcomer bracing brackets are needed. When I inspect tower internals, I try to understand how the condition of the trays relates to operating problems I have experienced in distillation service. Seeing out-of-level tray decks and slanted weirs correlate with low tray fractionation efficiency, I have learned from the inspections, not to take computer-generated distillation results to necessarily represent the actual distillation tower performance.
Chapter 38 • Learning Process Engineering Principles
309
Learning From Performance Tests My favorite way to learn basic process principles is by following a three-step program: • • •
Step 1—Measure a variable in the field, such as the feet of head developed by a pump. Step 2—From the pump curve, the measured flow, and the density of the fluid, calculate the feet of head that the pump should have been able to develop. Step 3—Determine the cause of any difference.
I often tell my clients, “I am an expert in refinery distillation technology.” But how have I become an expert? • •
•
Step 1—I run a computer model of a distillation tower using 80% tray efficiency. Step 2—Using plant data (i.e., reflux rate, reboiler duty, product analysis), I reduce the tray efficiency in my model to match the observed distillate and bottom products lab analysis. Step 3—I crawl through the tower to understand why my calculated tray efficiency in Step 2 is only 30%, when the industry standard for this particular service is 80%.
For heat exchangers, I calculate heat transfer coefficient (“U”) based on observed temperatures and flows. I will then calculate the clean “U,” based on Heat Transfer Research Institute (HTRI) computer program. Let’s say: Observed“ U ” ¼ 40btu=h=ft2 =° F HTRI Clean“ U ” ¼ 90btu=h=ft2 =° F
The difference the reader might conclude is fouling. But maybe not. Next, I repeat my field measurements after the heat exchanger is cleaned. The clean observed “U” ¼ 60! Now what? I will then examine the design of the tube bundle for problems such as: • • • • •
Excessive shell side clearances. Lack of dummy tubes to reduce shell side bypassing. Leaking channel head pass partition baffle. Tube viscosity higher than I used in my calculations. Twenty percent of tubes were plugged as leakers, but the maintenance department did not record this.
Conclusion Process Engineering is more of a craft than a science. Therefore, instructors who author textbooks and teach engineering classes, who lack field experience in troubleshooting process problems, are ill equipped to fulfill their objective. That objective being to prepare young men and women to understand and solve process plant problems. Unless an
310
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
engineer understands process equipment malfunctions, especially process control problems, he or she is not ready to design new equipment or function as a plant supervisor. Modern use of computer technology is neither harmful nor beneficial. It is largely irrelevant to the learning experiences that you and I must have to efficiently operate and design heat exchangers and fractionators. Although I’m getting old, my rate of learning the craft of process engineering has not diminished with the passage of the years. I learn something new; something exciting and interesting, with every troubleshooting and retrofit design project. As a Process Engineering Division Manager, I also learned something of great importance and of growing relevance. That being, to say to the young engineer who reported to me, “Let me get my tools, and we’ll go out into the plant together and work on the problem. Pick up that bag of ¾00 fittings I left in Tommy’s office and the new digital vacuum gauge from Bobby.”
Learning Process Engineering Principles
Most of what I have needed to learn to achieve my objective of becoming an effective process engineer, I did not acquire in University or Graduate School. I did not learn very much about process engineering employed as a design engineer in Chicago for 16 years. My foundation of process knowledge is built on the times I worked as an operator during the two long strikes in the American Oil Refinery in Texas City in 1974 and 1980. The strikes lasted 4–5 months. As a salaried employee, I worked as a scab. Twelve hour days. Seven days a week. In 1974, on the Sulfuric Acid Alkylation Unit. In 1980, on the Sulfur Recovery Unit that I had previously designed. Had it not been for this opportunity to observe, operate, and repair pumps, turbines, reactors, heat exchangers, and distillation towers, I would not have developed the process insight to the problems that I have today. The other major source of my process knowledge is derived from childhood experiences. I enjoyed being a child. I continue to regret and resist growing up into an adult. As a child I had an inordinate fascination in such phenomena as: 1. How did the air lift filter pump in my aquarium circulate water? 2. What was the function of the small conical vent on top of our steam radiator that heated our fifth floor apartment? 3. When my mom poured Coke over the rust stains in our bathroom sink, why did the rust dissolve? 4. Why did a drop of water on a very hot, smooth frying pan dance around and not evaporate, while water on a cooler, scratched pan, would instantly boil away? 5. When it was windy outside, why did the water level in our toilet bowl oscillate? 6. Why did water come out of the kitchen tap cloudy, but clear up after standing for 5 min? 7. Why, when my dad opened a warm bottle of beer too fast, did the beer explode violently out of the bottle? Now I can correlate these childhood observations with refinery process technology: 1. Air lift pump—Similar to thermosyphon circulation in reboilers and steam generators. 2. Radiator vent—A noncondensable vent installed below the lower pass partition baffle on the channel head of steam shell and tube heaters.
Understanding Process Equipment for Operators and Engineers. https://doi.org/10.1016/B978-0-12-816161-6.00038-2 © 2019 Elsevier Inc. All rights reserved.
305
306
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
3. Removing rust stains with coke—This is an example of carbonic acid corrosion of iron due to CO2 contamination of steam, due to the decomposition of carbonates in boiler feed water. 4. Water on a hot pan—Same as a heat flux limitation in a reboiler with smooth tubes and high pressure steam. 5. Erratic toilet water level—Caused by the draft that wind develops as it blows across the top of a fired heater’s stack. Typically, 0.1–0.2 in. of water. 6. Cloudy tap water—Air dissolved in water in higher pressure and cooler temperature. 7. Beer bottle foam-over—Sudden reduction in a distillation tower pressure causes the tower to flood and carry-over.
Function of a Process Engineer I quit American Oil in 1980 and went to work as the Technical Service Manager at the Good Hope Refinery. I had a dozen young chemical engineers in my group. They were bright boys, but like me, had not learned much in University that would aid them in their job (Note: In 1980, very few women studied Chemical Engineering. Now it’s about 50/50.). The first thing I explained to the boys as they began work was that our principal job was to solve problems in the plant. Our function was not to: • • • • • • • • •
Write reports Attend meetings Interact with vendors Do environmental impact studies Run computer models Provide data for the planning department Have lunch with chemical vendors Evaluate new refining technology Participate in seminars in New Orleans Our job was to solve plant problems that the operators could not solve themselves.
How to Learn I didn’t learn to drive sitting at a desk in high school. My dad taught me in our brown 1959 Oldsmobile. The operators in our plant were actually “trained on the job.” They started working in parallel with an older guy. They followed him around for a few weeks. Then, the experienced operator followed and observed the newer operator for another week to correct any of his or her mistakes. It’s really no different when learning any skill. Most everyone is like me. I can only learn while doing. It’s the ancient apprentice concept. When a new process engineer started work at the Good Hope Refinery in my group, I would give him his first assignment.
Chapter 38 • Learning Process Engineering Principles
307
“Reid, we’re short of reboiler duty on our Crude Unit gasoline debutanizer. Ask Mr. Walker, the area supervisor, to explain the problem to you as he understands it. He will show you where the reboiler is located.” Reid Burt came back to my office the following morning, “Mr. Lieberman, Mr. Walker showed me the reboiler. He says the problem is he can’t get enough 150# steam flow to the reboiler. He used to be able to get 14,000 pounds an hour flow, but now all he can get is 9,000. He showed me that the steam inlet control valve is wide open. I made a sketch of the reboiler, but I don’t know what else to do? We didn’t study steam reboilers at LSU. Should I try to model the debutanizer on the Aspen Simulation Program?” And I would say, “Reid. Let me get my tools and my bag of pipe fittings. We’ll go out together and look the job over in the field. Go get your gloves and hard hat.” Reid and I would then measure the pressures and skin temperatures in the 300 steam condensate drain line and in the 600 condensate collection header. And I would explain, as we made the measurements together, the cause of the low steam flow. “Reid, water is backing up in the reboiler channel head. The problem is vapor lock. The excessive pressure drop in the condensate drain line is causing the water to partly flash back to steam. The evolved steam restricts the flow of water, which backs-up over the tubes in the reboiler. This reduces the heat transfer surface area and reboiler duty.” From this exercise, Reid would learn how to make field pressure and temperature measurements. He would also learn the technical concept of the effect of condensate back-up. I would explain the design error. That is, the omission of a condensate pump to prevent excessive steam evolution in the condensate flow in the 300 line.
Interfacing With Operators Up until the 20th century, most technical knowledge was transmitted not through institutions or books, but by the apprentice system. My example cited before, when I said, “Let me get my tools and we’ll go out to the reboiler together,” was an example of this ancient instructional technique. Another technique of comparable value is to interface with the plant operators. Especially when it relates to controls (level, flow, temperature, pressure). Working with operating personnel is the best way to understand how control loops and control valves work, and their wide range of malfunctions. Especially, how control loop design interacts with process problems and occasionally creates a “Positive Feedback Loop.” For example, I had no idea of how instrument air is connected to a control valve diaphragm, until it was explained to me by an older operator on my Alky Unit in Texas City in 1975. Another example of learning from operators is the need for “Starting NPSH” for centrifugal pumps. A concept that I’ve discussed in detail in this text. Operators all understand the need to increase flow from the discharge of a centrifugal pump slowly, to avoid
308
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
cavitation. From this observation, I have devised the numerical method for calculating, for design purposes, the starting NPSH requirement for a centrifugal pump. This is the extra elevation of a vessel needed to accelerate the liquid, on start-up, in the pump’s suction line.
Learning From Maintenance Personnel A lot of people, like me, have a problem visualizing a three-dimensional object from a book. I do much better in my comprehension when I can see the actual equipment. A Shell and Tube Heat Exchanger is a good example. I never quite understood how the floating head on such an exchanger was actually attached to the tube sheet using a “Split Ring Assembly,” until John Brundrett, the maintenance manager in Texas City, showed it to me during an FCU turnaround. I had heard a lot about the clearance between the impeller and the pump case, and knew this was important. But until a shop maintenance technician explained this to me, I never really understood it. I learned how centrifugal compressors work by watching a 10,000 BHP Solar-Centar rotor overhauled in a repair shop in Dallas, while listening to a 2-h monolog from the craftsman cleaning and rebalancing the rotor’s three wheels. When I put the compressor back on-line at the Texas, Laredo Natural Gas Compression Station the following week, I had a better understanding as to how the machine actually functioned.
Inspecting Tower Internals My main field of work as a process design engineer is retrofitting refinery distillation towers and designing new fractionators. I have designed 3000 ID jet fuel steam strippers and a 260 –000 Delayed Coker Fractionator. I draw the tower internal details to scale on blue lined graph paper at 1 in. per foot. Old process design engineers have a saying, “The Devil is in the Details.” As I draw these details, I have a picture in my mind of how this particular feature looked in a tower I had inspected. What had gone wrong with the installation? Are the dimensions I am specifying being adhered to in practice? Have I made a reasonable provision for fouling? Certainly, I will base the tower ID and the number of fractionation trays on the Aspen computer model output. But, that does not provide insight as to where iron sulfide and salt deposits will require an extra inch of downcomer clearance, or, when extra downcomer bracing brackets are needed. When I inspect tower internals, I try to understand how the condition of the trays relates to operating problems I have experienced in distillation service. Seeing out-of-level tray decks and slanted weirs correlate with low tray fractionation efficiency, I have learned from the inspections, not to take computer-generated distillation results to necessarily represent the actual distillation tower performance.
Chapter 38 • Learning Process Engineering Principles
309
Learning From Performance Tests My favorite way to learn basic process principles is by following a three-step program: • • •
Step 1—Measure a variable in the field, such as the feet of head developed by a pump. Step 2—From the pump curve, the measured flow, and the density of the fluid, calculate the feet of head that the pump should have been able to develop. Step 3—Determine the cause of any difference.
I often tell my clients, “I am an expert in refinery distillation technology.” But how have I become an expert? • •
•
Step 1—I run a computer model of a distillation tower using 80% tray efficiency. Step 2—Using plant data (i.e., reflux rate, reboiler duty, product analysis), I reduce the tray efficiency in my model to match the observed distillate and bottom products lab analysis. Step 3—I crawl through the tower to understand why my calculated tray efficiency in Step 2 is only 30%, when the industry standard for this particular service is 80%.
For heat exchangers, I calculate heat transfer coefficient (“U”) based on observed temperatures and flows. I will then calculate the clean “U,” based on Heat Transfer Research Institute (HTRI) computer program. Let’s say: Observed“ U ” ¼ 40btu=h=ft2 =° F HTRI Clean“ U ” ¼ 90btu=h=ft2 =° F
The difference the reader might conclude is fouling. But maybe not. Next, I repeat my field measurements after the heat exchanger is cleaned. The clean observed “U” ¼ 60! Now what? I will then examine the design of the tube bundle for problems such as: • • • • •
Excessive shell side clearances. Lack of dummy tubes to reduce shell side bypassing. Leaking channel head pass partition baffle. Tube viscosity higher than I used in my calculations. Twenty percent of tubes were plugged as leakers, but the maintenance department did not record this.
Conclusion Process Engineering is more of a craft than a science. Therefore, instructors who author textbooks and teach engineering classes, who lack field experience in troubleshooting process problems, are ill equipped to fulfill their objective. That objective being to prepare young men and women to understand and solve process plant problems. Unless an
310
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
engineer understands process equipment malfunctions, especially process control problems, he or she is not ready to design new equipment or function as a plant supervisor. Modern use of computer technology is neither harmful nor beneficial. It is largely irrelevant to the learning experiences that you and I must have to efficiently operate and design heat exchangers and fractionators. Although I’m getting old, my rate of learning the craft of process engineering has not diminished with the passage of the years. I learn something new; something exciting and interesting, with every troubleshooting and retrofit design project. As a Process Engineering Division Manager, I also learned something of great importance and of growing relevance. That being, to say to the young engineer who reported to me, “Let me get my tools, and we’ll go out into the plant together and work on the problem. Pick up that bag of ¾00 fittings I left in Tommy’s office and the new digital vacuum gauge from Bobby.”