Cause it's all in my head.
I think about it over and over again.
I replay it over and over again.

("Over and Over Again," by Nelly & J. Bridges, 2004)

 

PTOA Segment 30: I HEAT UP.... I COOL DOWN

This PTOA segment introduced PTOA Readers and Students to shell and tube heat exchangers.

Shell and tube heat exchangers conserve energy by preheating a cooler process stream that must be hotter for continued processing via transferring the heat from a hotter process stream that must be cooler for continued processing.

An animated graphic created by Southern Exchanger Company (SHECO) was featured in this segment. This animated graphic clearly showed how the tube side flow entered an exchanger and flowed through a 2-pass bundle.

The shell side flow was clearly shown entering the shell inlet and then swirling around the baffles attached to the external side of the tube bundle before exiting the shell.

PTOA Readers and Students learned the hardware components of a 2-pass parallel-flow shell and tube heat exchanger.

 

PTOA Segment 31: OH SAY CAN YOU SEE? (NOPE!)

PTOA Readers and Students learned the generic ISA symbol for a shell and tube heat exchanger.

The clear circle represents shell side flow.The zig-zag line through the clear circle of the ISA symbol represents tube side flow.

The service duty of shell and tube heat exchangers are not obvious from looking at them.

PTOA Readers and Students were guided through determining the service duty of two shell and tube heat exchangers on a Benzene Plant PFD.

PTOA Readers and Students learned how to decode the service duty of shell and tube heat exchangers using hints given on the PFD.

PTOA Readers and Students were introduced to the utility known as "cooling water" which is generated specifically to remove heat from process streams.

 

PTOA Segment 32: DIY! (DO IT YOURSELF!)

PTOA Readers and Students were challenged to determine the service duty of four other Benzene Plant shell and tube heat exchangers on their own using their always-increasing knowledge of process industry technology.

PTOA Readers and Students decoded the service duty of the exchangers using hints from PFD equipment labels and their acquired knowledge regarding the purpose and function of "heaters," "coolers,"  "condensers" and "reboilers."

Additional decoding tools included understanding the  temperature-changing capabilities of steam and cooling water.

PTOA Readers and Students that completed the DIY exercise could righteously claim that they had experience interpreting a PFD solo.

This PTOA Segment concluded with a list of probable shell side and tube side process stream characteristics.

Corrosive, gooky, and high pressured process streams are best on the tube side.

Low pressure, mixed phase process streams, and streams that condense are best on the shell side.

Whenever in doubt, a Process Operator should consult the PFD or P&ID to expel any doubt as to which stream is being heated, which stream is being cooled, and which of the streams enters tube side or shell side.

 

PTOA Segment 33: NO CHOO CHOO BUT STILL A TRAIN

PTOA Readers and Students learned that shell and tube heat exchangers are often strung together in long "trains."

This PTOA Segment reiterated that attaining a process temperature needed to perform processing steps will always require purchasing fuel gas or natural gas for combustion.

The step that required a high process temperature is followed by processing steps that typically involve separating desired products from by-products or sending the process stream to storage. Either of these scenarios requires much lower process temperatures to be successful.

Thus, the typical processing plant design uses equipment to purposefully heat up a process stream and then other equipment to immediately cool down the process stream directly after completing the processing step that required the high process temperatures in the first place.

Ergo, to save money spent on fuel costs for fired heaters, energy is conserved by transferring the heat out of process streams that must be cooled with process streams that must be preheated.

Preheat exchanger trains perform these heat-conserving functions.

The temperature of a significant process stream is increased/decreased by absorbing/transferring heat from/into several different process streams that need to be cooled/heated in order to continue successful processing.

 

PTOA Segment 34: THE "BOX CARS" IN THE EXCHANGER TRAIN

This PTOA Segment provided experience reading a simplified exchanger-train PFD.

The longest exchanger train combination that PTOA Readers and Students are likely to encounter is the Desalter Preheat Train that precedes a Crude Distillation Unit (CDU) Feed Preheat Exchanger Train.

These preheat trains are found in every crude oil refinery.

The Crude Tower in a CDU separates crude oil into process streams that are refined into products like gasoline, diesel, and jet fuel in other plants at the refinery complex.

The temperature of the crude oil that flows into the Crude Tower must be at least 735 °F (391 °C) to make the separating process successful.

The Desalter and CDU Preheat Exchanger Trains greatly decrease the amount of fuel gas that would be needed to heat up the crude feed for a moderate-sized CDU Tower that processes 100,000 barrels of crude.

PTOA Readers and Students focussed on a Desalter and CDU Tower Feed Preheat Exchanger Train depicted in a simplified PFD.

Crude Oil was shown flowing out of storage in the tank farm at 114 deg F (45 deg C) and then flowing through seven sets of exchangers while being heated step-wise to 501 °F (261 °C) prior to entering a Crude Tower Feed fired heater.

The PFD showed how several process streams exchanged their heat with the crude process stream.

The process temperature of the crude increased step-wise as it flowed through each exchanger; the process temperature of each process stream that exchanged their heat with the crude left their respective heat exchanger at a significantly lower process temperature.

PTOA Readers and Students were once again challenged to determine the service duty of the last preheater in the CDU Preheat Exchanger Train by themselves.

 

PTOA Segment 35: HExes

The long phrase "shell and tube heat exchanger" was reduced to the industry jargon "HEx" in this PTOA segment.

PFD/P&ID HEx symbols for shell and tube HExes, reboilers and fin fan condensers were featured in a symbol chart.

Their respective symbols were studied to achieve a better understanding of how each icon depicts process flow.

PTOA Readers and Students recognized a generic ISA symbol for a HEx heater appears in the PTOA logo.

This PTOA segment concluded with a graphic of a Stripping Tower which depicted how the ISA symbols for a condenser and reboiler would appear on a PFD.

 

PTOA Segment 36: DIY ANSWERS!

This last PTOA introductory segment on shell and tube heat exchangers included the answers to the Do It Yourself Benzene PFD HEx analysis for E-103, E-104, E-105, and E-106.

The segment concluded with the answers regarding the service duty of E-7 in the CDU Tower Feed Preheat Exchanger Train.

PTOA Readers and Students were made aware that they had completed the focus on temperature-increasing and temperature-swapping process industry equipment.

The following PTOA segments would focus on temperature-decreasing process industry equipment.

 

©2015 PTOA Segment 00048
PTOA Deja Vu Review 2-3

 

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