- Email: [email protected]
Basics of Process Operations and Engineering
1 Basics of Process Operations and Engineering The truth is you’ve wasted 4 years in University qualifying for an engineering degree or have wasted 2 years in an operator training class. That’s not my fault. But now, as a process engineer in a refinery, or as an operator in a petrochemical complex, you need to understand how pumps, compressors, heat exchangers, distillation towers, air coolers, fired heaters, steam boilers, turbines, and vacuum ejectors actually work to do your job. The reason you did not understand your professor about how process equipment works is that he didn’t understand it himself. Everything I write is based on my own experience and field observations. For example: 1. Increasing excess combustion air in a fired heater will cool off the tubes in the firebox, but increase the heater absorbed process duty. 2. Nitric oxides (NOx) can be reduced by increasing air flow to the secondary air register and reducing air flow to the primary air register. 3. Preheating combustion air to a heater will often reduce its heat absorption capacity. 4. The energy to spin a steam turbine does not come from the steam’s pressure, but from the steam’s heat content. 5. But, superheating steam to a steam turbine will cause the turbine to slow down. 6. A steam vacuum ejector is really a multistage gas compressor, but there are no moving mechanical components. 7. One way to stop a distillation tower from flooding is to increase the reboiler duty. 8. With a constant reboiler duty, lowering a distillation tower’s top temperature with more reflux increases the vapor flow. 9. Ancient bubble cap trays have a better tray fractionation efficiency than modern trays, and also a lower pressure drop. 10. When starting a centrifugal pump, monitor the pump suction pressure, not its discharge pressure. 11. The feet of head produced by a centrifugal pump does not vary with the density of the liquid pumped. 12. Increasing the load on an ordinary alternating current motor-driven pump does not affect its speed. 13. Centrifugal, motor-driven American pumps, run 20% faster than European pumps. Why? Because they are American pumps.
Understanding Process Equipment for Operators and Engineers. https://doi.org/10.1016/B978-0-12-816161-6.00001-1 © 2019 Elsevier Inc. All rights reserved.
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UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
14. A butane reboiler will have more capacity, if its tubes are pitted and corroded, than a reboiler with brand new tubes. 15. A tiny amount of air or CO2 in steam will reduce a steam reboiler, or a steam turbine surface condenser, capacity by 50%. 16. The latent heat of condensation of steam increases a lot as the steam pressure is reduced. 17. The auto-ignition temperature of gasoline is much higher than tar. 18. Hydrogen heats up as it expands, but all other gases cool off, as they expand. 19. Centrifugal compressors surge when the gas molecular weight is reduced. 20. Partly closing a cooling water outlet valve from an exchanger elevated 60 ft above grade can increase its water flow. 21. A rising level in a boiler can cause the boiler’s indicated level to be reduced, and the boiler feed water level control valve to open, even though the water level is already excessive. 22. A gas flow meter will read a reduction in gas flow rate, even though the actual volume of gas flow has not changed, if the gas molecular weight is reduced. 23. A pressure above atmospheric can develop in the upper portion of a heater’s firebox, even though a substantial vacuum exists in the lower portion. 24. Thermosyphon circulation rates may be reduced, as the exchanger heat input increases. 25. An effective way to improve a distillation tower fractionation efficiency is to reduce the tower’s operating pressure. 26. The motor amps increase with molecular weight for a centrifugal compressor, but decrease with a higher molecular weight for a reciprocating compressor. 27. Fouled fin tubes on a forced draft air cooler which greatly reduces cooling air flow through the tube bundle does not increase the amp load on the fan’s motor driver. 28. The outlet pressure of a heat exchanger can be higher than the inlet pressure, even though both pressure points are at the same elevation. 29. Closing a by-pass valve around a condenser will usually reduce the condenser’s upstream pressure. The preceding points are all somewhat counterintuitive. I’ll explain the process basis for each of them in the following chapters. The application of these and other concepts I have discussed in subsequent chapters have led to the solution of many process problems and enhanced the capacity and efficiency of hundreds of process units. I think most people are like me. I find it difficult to learn new stuff by reading, listening, or just watching. But, when I apply my own hands, and my own mind, to a particular problem, I remember and understand the solution for the rest of my life. And, as someone, who has been practicing solving process engineering problems in the field, without any hiatus, since 1964, that’s a lot of learning opportunities. We are fortunate to work in an industry where the nature of the equipment has barely changed in the past six decades. Becoming a proficient process operator, or process
Chapter 1 • Basics of Process Operations and Engineering
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engineer, is still largely a matter of time and determination. And, I suspect, that will always be true as long as we try to alter the nature of hydrocarbons, minerals, water, and air to our own human purposes.
Things I Worry About Troubleshooting Refinery Process Equipment is the most complex activity that mankind can undertake. I’ve been at it for 54 years, and I barely know what I’m doing. The main problem is that process equipment is normally not designed correctly in the first place. The original design errors are then compounded with: • • • • • •
Corrosion Foulings Mis-operation Variable ambient condition Unexpected feed stocks Altered product spec’s
In spite of my very long experience to the contrary, I often pray for help to solve process problems. However, instead of waiting for divine intervention, I’ve found it’s better to understand some basic process principles such as: • • • • • • • • • •
How wind affects draft? How reboiler duty affects thermosyphon circulation? How noncondensables cause vapor binding in steam condensers? What determines tray fractionation efficiency? The real function of steam in a steam stripper. How centrifugal pumps convert power to pressure? How steam turbines and steam engines are explained by thermodynamics? Effect of reflux on vapor flows in a distillation column. What causes centrifugal compressors to surge? How not to blow up a fired heater which has become flooded with fuel, and with fire and black smoke being emitted from its stack?
I also talk a lot about safety, and the last chapter in this text addresses that particular problem based on my many bad refinery experiences.
The Future Without Refineries My world, the world dominated by vehicles burning hydrocarbons, will be gone in 20 or 30 years. Much of what I know about delayed cokers, visbreakers, fluid catalytic crackers, hydrocracking, and naphtha reforming will no longer be relevant to mankind’s future in transportation.
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UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
I suppose even after gasoline and diesel will no longer be required, the human race will still need to process hydrocarbons for: • • • • • • • • •
Jet fuel Asphalt roads Lube oils Plastics Petrochemicals Carbon anodes Roofing shingles Baby oil Waxes
Still, the majority of petroleum refining process technology will be lost and forgotten—a relic of the past. However, I am quite sure that the human race will persist, as long as we require industrial technology as a species, to use: • • • • • • • •
Centrifugal pumps Heat exchangers Gas compressors Vapor-liquid separators Electric motors Distillation columns Control valves Pipes, valves, and fittings
I imagine, if by chance, that I am reincarnated as a Process Engineer, in the year 3018, I will not feel out of place, or the skills I acquired in my current life cycle will be entirely outmoded. If, on the other hand, I find myself in the netherworld, and am greeted by the Devil himself, I will also feel quite at home. Once Satan realizes my vast experience in Sulfur Plants and Fired Heaters, I am confident he will enroll me in Hell’s Process Engineering Department.
Safety Note Hydrocarbon leaks in water cooling service can cause explosive mixtures to form below the distribution decks in cooling towers. Especially when cooling butane streams, this can, and has (Amoco Oil—Texas City), caused cooling towers to ignite. Check your cooling water outlets for combustible vapors perhaps once a month. The instrument that the operators use to issue vessel entry permits can be employed for this purpose. Vapors tend to accumulate beneath the distribution decks. Sludge buildup on these decks is another indication and result of hydrocarbon leaks into the cooling water return. Note From Author: If you have questions relating to this text or your work in general, please email me at [email protected].
Understanding Process Equipment for Operators and Engineers. https://doi.org/10.1016/B978-0-12-816161-6.00001-1 © 2019 Elsevier Inc. All rights reserved.
1
2
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
14. A butane reboiler will have more capacity, if its tubes are pitted and corroded, than a reboiler with brand new tubes. 15. A tiny amount of air or CO2 in steam will reduce a steam reboiler, or a steam turbine surface condenser, capacity by 50%. 16. The latent heat of condensation of steam increases a lot as the steam pressure is reduced. 17. The auto-ignition temperature of gasoline is much higher than tar. 18. Hydrogen heats up as it expands, but all other gases cool off, as they expand. 19. Centrifugal compressors surge when the gas molecular weight is reduced. 20. Partly closing a cooling water outlet valve from an exchanger elevated 60 ft above grade can increase its water flow. 21. A rising level in a boiler can cause the boiler’s indicated level to be reduced, and the boiler feed water level control valve to open, even though the water level is already excessive. 22. A gas flow meter will read a reduction in gas flow rate, even though the actual volume of gas flow has not changed, if the gas molecular weight is reduced. 23. A pressure above atmospheric can develop in the upper portion of a heater’s firebox, even though a substantial vacuum exists in the lower portion. 24. Thermosyphon circulation rates may be reduced, as the exchanger heat input increases. 25. An effective way to improve a distillation tower fractionation efficiency is to reduce the tower’s operating pressure. 26. The motor amps increase with molecular weight for a centrifugal compressor, but decrease with a higher molecular weight for a reciprocating compressor. 27. Fouled fin tubes on a forced draft air cooler which greatly reduces cooling air flow through the tube bundle does not increase the amp load on the fan’s motor driver. 28. The outlet pressure of a heat exchanger can be higher than the inlet pressure, even though both pressure points are at the same elevation. 29. Closing a by-pass valve around a condenser will usually reduce the condenser’s upstream pressure. The preceding points are all somewhat counterintuitive. I’ll explain the process basis for each of them in the following chapters. The application of these and other concepts I have discussed in subsequent chapters have led to the solution of many process problems and enhanced the capacity and efficiency of hundreds of process units. I think most people are like me. I find it difficult to learn new stuff by reading, listening, or just watching. But, when I apply my own hands, and my own mind, to a particular problem, I remember and understand the solution for the rest of my life. And, as someone, who has been practicing solving process engineering problems in the field, without any hiatus, since 1964, that’s a lot of learning opportunities. We are fortunate to work in an industry where the nature of the equipment has barely changed in the past six decades. Becoming a proficient process operator, or process
Chapter 1 • Basics of Process Operations and Engineering
3
engineer, is still largely a matter of time and determination. And, I suspect, that will always be true as long as we try to alter the nature of hydrocarbons, minerals, water, and air to our own human purposes.
Things I Worry About Troubleshooting Refinery Process Equipment is the most complex activity that mankind can undertake. I’ve been at it for 54 years, and I barely know what I’m doing. The main problem is that process equipment is normally not designed correctly in the first place. The original design errors are then compounded with: • • • • • •
Corrosion Foulings Mis-operation Variable ambient condition Unexpected feed stocks Altered product spec’s
In spite of my very long experience to the contrary, I often pray for help to solve process problems. However, instead of waiting for divine intervention, I’ve found it’s better to understand some basic process principles such as: • • • • • • • • • •
How wind affects draft? How reboiler duty affects thermosyphon circulation? How noncondensables cause vapor binding in steam condensers? What determines tray fractionation efficiency? The real function of steam in a steam stripper. How centrifugal pumps convert power to pressure? How steam turbines and steam engines are explained by thermodynamics? Effect of reflux on vapor flows in a distillation column. What causes centrifugal compressors to surge? How not to blow up a fired heater which has become flooded with fuel, and with fire and black smoke being emitted from its stack?
I also talk a lot about safety, and the last chapter in this text addresses that particular problem based on my many bad refinery experiences.
The Future Without Refineries My world, the world dominated by vehicles burning hydrocarbons, will be gone in 20 or 30 years. Much of what I know about delayed cokers, visbreakers, fluid catalytic crackers, hydrocracking, and naphtha reforming will no longer be relevant to mankind’s future in transportation.
4
UNDERSTANDING PROCESS EQUIPMENT FOR OPERATORS AND ENGINEERS
I suppose even after gasoline and diesel will no longer be required, the human race will still need to process hydrocarbons for: • • • • • • • • •
Jet fuel Asphalt roads Lube oils Plastics Petrochemicals Carbon anodes Roofing shingles Baby oil Waxes
Still, the majority of petroleum refining process technology will be lost and forgotten—a relic of the past. However, I am quite sure that the human race will persist, as long as we require industrial technology as a species, to use: • • • • • • • •
Centrifugal pumps Heat exchangers Gas compressors Vapor-liquid separators Electric motors Distillation columns Control valves Pipes, valves, and fittings
I imagine, if by chance, that I am reincarnated as a Process Engineer, in the year 3018, I will not feel out of place, or the skills I acquired in my current life cycle will be entirely outmoded. If, on the other hand, I find myself in the netherworld, and am greeted by the Devil himself, I will also feel quite at home. Once Satan realizes my vast experience in Sulfur Plants and Fired Heaters, I am confident he will enroll me in Hell’s Process Engineering Department.
Safety Note Hydrocarbon leaks in water cooling service can cause explosive mixtures to form below the distribution decks in cooling towers. Especially when cooling butane streams, this can, and has (Amoco Oil—Texas City), caused cooling towers to ignite. Check your cooling water outlets for combustible vapors perhaps once a month. The instrument that the operators use to issue vessel entry permits can be employed for this purpose. Vapors tend to accumulate beneath the distribution decks. Sludge buildup on these decks is another indication and result of hydrocarbon leaks into the cooling water return. Note From Author: If you have questions relating to this text or your work in general, please email me at [email protected].