All my life I've looked at words as though I were seeing them for the first time.”  (Ernest Hemingway)

 

NO CHOO CHOO BUT STILL A TRAIN

Preheat Exchanger Trains: A set of shell and tube heat exchangers connected by piping in which the same process stream is flowing while en route to being heated up or cooled down in a step-wise process.

The process streams that are heating up or cooling down the common process stream come from several sources in the processing plant.

Tank Farm: Cylindrically shaped tanks of varying sizes and duties located in an area that is remote from the processing area of an industrial complex.

Feedstocks, intermediate products, and final products in the liquid phase are stored in the tank farm.

Bullet and spherical shaped tanks store liquified gaseous products (gases like propane and butane that would be in the gaseous state were it not for being held under pressure).

On a day-to-day basis, Tank Farm Process Operators are busier than Process Unit Operators because the tank farm materials must constantly be moved around for just-in-time storage and just-in-time sales.

 

THE "BOX CARS" IN THE EXCHANGER TRAIN

Crude Oil Distillation Unit (CDU): The first processing unit in a fuels refinery that converts crude oil into motor fuel products.

The CDU uses distillation .... the physical separation of fluids by boiling point...to produce several hydrocarbon streams that fall into a range of boiling points.

These streams require more processing steps to be customer-ready.

The distillation process is as old as making alcohol and is not considered as technology difficult as catalytic processes.

However, the economical losses that result by erroneously fractionating a more valuable hydrocarbon into a less valuable hydrocarbon stream can never be recovered once the streams leave the Crude Tower.

Thus the Process Operators in the CDU have a greater impact on the profitability of a refinery than the Process Operators in charge of downstream processing units.

Desalter Preheat Exchanger Train:The Desalter Preheat Exchanger Train is a set of shell and tube heat exchangers arranged for series flow of crude through them. The crude oil is heated up via transferring the heat from several hot process streams that need to be cooled down.

Crude contains water (which may or may not be salty depending upon its production, post-production processing and transportation to the fuels refinery).

All water must be removed from crude prior to entering the Crude Distillation Tower which operates at 750 °F. Water rapidly vaporizes and expands at 750 °F. Failure to remove water would blow up the Crude Tower.

The process of desalting is completed in a vessel that is logically called a Desalter.

An electrostatic charge is sent through the Desalter. The charge lines up the water molecules with their oxygen charge on one side and charges from two hydrogen on the other.

In this aligned formation, the water molecules fall to the bottom of the Desalter, successfully separating the hydrocarbons in the oil from the water.

The oil fraction on the top continues to flow to the CDU Tower Feed Preheat Exchanger Train and the separated water on the bottom is sent to an Oily-Water Sewer.

The interface between the oil and water levels in the Desalter is the primary concern of Desalter operations.

The Desalter is an important example of Interface Level Control which will be featured in future PTOA Segments.

The oil and water that enter the Desalter have been heated to approximately 300 °F via heat exchanged while flowing through the Desalter Preheat Exchanger Train.

CDU Tower Feed Preheat Exchanger Train: The CDU Tower  Preheat Exchanger Train is a set of shell and tube heat exchangers arranged for series flow of crude through them. The crude oil is heated up via transferring the heat from several hot process streams that need to be cooled down.

Crude oil must attain a process temperature of 750 °F to be successfully distilled into fractions in the Crude Distillation Tower.

The CDU Tower Preheat Exchanger Train preheats the crude to approximately 500 °F by heat exchange.

A fired heater completes the heating process to achieve the 750 °F temperature required to distill the Crude Tower Feed in the CDU Tower.

 

HExes

2-pass Heat Exchanger=U Tube Bundle Heat Exchanger: A variety of shell and tube heat exchanger designs can be found in process industries.

The PTOA uses the typical U-tube bundle inside a shell for instructional purposes. The U tube structure is equivalent to stating the tube side flow has "2 passes through the exchanger."

(Generic) HEx Heater Symbol: A circle with an arrow pointing downward drawn over it. The PTOA logo features the symbol for a generic HEx heater.

(Generic) Hex Condenser Symbol: A circle with an arrow pointing upward drawn over it.

HExes: The written short hand for "shell and tube heat exchanger" that might be found in pass on notes or written procedures.

The term can also be used verbally when reviewing a PFD. However, more typically the heat exchangers are referred to by their tag names when discussing them.

Kettle-Type Reboiler Symbol:  A specific type of shell and tube heat exchanger whose symbol will be shown next to the bottom of a separating tower on a properly drawn PFD.

The shell of the reboiler is drawn with an enlarged area on the top side of the exchanger which illustrates that a vapor space above an established liquid level in the shell is accommodated.

The symbol will show heating media (steam) entering and exiting the exchanger as tube side flow.

The symbol will show one shell side inlet entering the bottom of the shell. This inlet will be drawn on the side nearest the channel head.

The symbol will show two shell side outlets:

• One of the shell side outlets is for the liquid product which is the desired product from the separation. This outlet will be drawn on the bottom of the shell and on the side furthest from the channel head.
• The second shell side outlet is for hot vapors that accrue above the liquid level and are returned to the separating tower via the top-side shell outlet.

Weir: A weir is a dam that allows a liquid level to accumulate to a defined level; without a weir the liquid would flow freely without establishing a level.

Liquid spills over the weir once the liquid level accumulates to a point that exceeds the height of the weir.

One use of weirs is building a liquid level in the shells of reboilers.

The spillover from the reboiler's shell-side weir is the desired liquid product that flows out of bottom-side shell outlet.

 

DIY ANSWERS!

No additional process industry jargon appeared in this PTOA segment.

This segment concluded process industry jargon related to shell and tube heat exchangers.

Upcoming PTOA segments featured jargon related o temperature-decreasing process industry equipment.

 

©2015 PTOA Segment 00054
PTOA Process Industry Jargon Recap 2-4

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