FLOWING FLUID PROPERTIES THAT PREDICT FLUID BEHAVIOR … PART 3

I'm so heavyHeavy, heavy in your armsI'm so heavyHeavy, heavy in your arms

("Heavy in Your Arms," by Florence and the Machine, 2010)

THE 4 WAYS THAT THE HEAVINESS/LIGHTNESS OF FLUIDS
ARE REPRESENTED

Vegetable Oil, Rubbing Alcohol, and Lamp Oil are increasingly lighter than Water and float above it. Dawn Dish Soap, Karo Syrup, and Honey are progressively heavier than Water and sink below it.

In PTOA Segment #238, PTOA Readers and Students learned the first two of the four ways that the comparative heaviness/lightness of liquids are represented:

Density is the amount of fluid Mass per unit of specified Volume. Typical units of Fluid Density are Lbs/Ft³ in the USA and g/cc or Kg/M³ worldwide.
Specific Gravity is a dimensionless number which reveals the Relative Density of a liquid fluid to the basis of Water and the Relative Density of a gas fluid to the basis of Air.

This PTOA Segment focuses on two more ways that the heaviness/lightness of JUST LIQUIDS are represented in some industrial settings:

API Gravity for hydrocarbon liquids only.
Baume Gravity for water-based (aqueous) liquids.

API GRAVITY REVEALS THE HEAVINESS/LIGHTNESS OF HYDROCARBON LIQUIDS

Just like the physical properties of Density and Specific Gravity, the API Gravity is another way to gauge the relative heaviness/lightness of certain Liquids ... hydrocarbon Liquids.

API Gravity was developed by the American Petroleum Institute as a quick way to telegraph the heaviness/lightness of a crude oil when compared to a different crude oil. API Gravity is also used to assess the Relative Density of the several dozen hydrocarbon liquids that can be derived from crude oil ... however, API Gravity uses a different scale than Specific Gravity.

Guess what? Crude Unit Board Operators do not receive lab feedback in the form of ASTM Specific Gravity, but rather in terms of API Gravity. The API Gravity analysis and the "Temperature Distillation Range" of the Crude Unit liquid products inform the Board Operator if the desired products are being fractionated from the Crude Oil feedstock. For example, the feedback informs the Control Board Operator whether or not the heaviest components of Kerosine are being dropped into heavier diesel or if the lighter components of Kerosene are being distilled into lighter Gasoline.

Brilliant PTOA Readers and Students ... meaning those who have read the PTOA Segments in the intended, sequential order ... learned about the Exploration and Production (E&P) of crude oil and the refining of crude oil into fuels and petrochemicals way back in the PTOA Orientation.

The Crude Oil Trader in the USA would prefer a lighter, sweeter, low Tan Count Oil because this oil take less energy to convert into more valuable products.

Crude oil is made from plants and animals that that died many millions of years ago.

Since different types of plants and animals are found all over the globe, crude oils differ widely in their organic content. The components of crude oil are so unique that a crude oil analysis will reveal the original location of an oil that is spilled while in transit to a distant destination.

Specific Gravity was recently defined in PTOA Segment #238.

The definition/expression for API Gravity appears in the nearby box and reveals that the magnitude of API Gravity will always be inversely related to the magnitude of a hydrocarbon liquid's Specific Gravity.

Otherwise stated:

As the magnitude of a hydrocarbon liquid's Specific Gravity increases, the constant number 141.5 will be divided by a larger number and thus yield a smaller calculated API Gravity. And vice versa: as the Specific Gravity decreases, the constant number 141.5 will be divided by a smaller number and thus yield a greater calculated API Gravity.

API Gravity and Specific Gravity are inversely related. As the magnitude of API Gravity increases, the magnitude of Specific Gravity decreases, and vice versa.

When the API Gravity scale was invented, Water was assigned the value of "10" (as compared to "1" for Specific Gravity).

Tapis, a light, sweet Malaysian Crude Oil has an API of 45-47 and is very sweet with a sulfur content of just 0.04%. Brent Crude Oil is the benchmark for light oils in NW Europe but is still heavier than Tapis with an API=38 and more sour with a sulfur content of 0.37%. West Texas Intermediate (WTI) is the benchmark crude oil in the USA and has an API of 40 and a lower sulfur content than Brent at 0.24%.

The nearby graph illustrates the relationship of Specific Gravity (Y- Axis) to API Gravity (X-Axis).

Note that the "1"on the Specific Gravity (Y-Axis) correlates to the "10" on the API Gravity (X-Axis). This junction point represents the Specific Gravity and API Gravity of Water.

When the API Gravity of a hydrocarbon liquid is "greater than 10"... which infers the Specific Gravity of the hydrocarbon liquid is "less than 1" ... the hydrocarbon liquid is lighter than water and will float on top of water.

Therefore ...

A hydrocarbon liquid that is heavier than Water has an API Gravity "less than 10" and a Specific Gravity "greater than 1."

Uh-oh! Fred is confused!

Why is there an entirely different relative heaviness scale needed for liquid hydrocarbons?

Specific Gravity is still the most useful dimensionless number to compare the relative heaviness/lightness of very light hydrocarbon liquid mixtures and ditto for all gases (in that case, the basis is air at STP, of course).

However, Specific Gravity does not accurately capture the interaction of the various hydrocarbon liquids that comprise crude oils and crude oil fractions.

Fred, pretend you are a Crude Oil Trader. Your job is to buy crude oil at the lowest price possible to use as feedstock to your refinery or sell the crude oil that your Exploration and Production company produces for the highest price possible.

The API Gravity will instantly reveal how light or heavy the crude is. The crude's sulfur content, Viscosity, and API Gravity will reveal how much energy will be required to upgrade the crude oil into more valuable products.

Crude Oils can be classified:

Crude Oils from heaviest on the left to lightest on the right. Note that color cannot be used as a predictor of how light a crude oil is.

API Gravity greater than 31.1 = Light Crude Oil.
API Gravity range 22.3 to 31.1 = Medium Crude Oil.
API Gravity range 22.3 to 10 = Heavy Crude Oil.
API Gravity less than 10 = Extra Heavy Crude Oil.

This Vacuum Resid Crude Oil Analysis depicts a crude oil from which all the light gases and LPG, Gasoline feedstocks, Jet feedstocks, diesel feedstocks and heavy yet crackable oils have been removed. The API Gravity of 9.03 reveals this resid will sink in water. The Viscosity indicates this resid will not flow without heat traced process lines.

The Residual Oil from a Vacuum Unit Distillation Tower is an example of an Extra Heavy Crude Oil with an API Gravity less than 10.

All the light ends in the Crude Oil from which the Extra Heavy Crude Oil was derived have been removed via distillation. This fluid cannot be relied upon to flow without being heated.

BAUME GRAVITY
(pronounced "bawh-MAY" for the French dude who developed the scale)

Thank you ENGINEERING TOOLBOX for the graph that shows how the Baume Gravity (X Axis) is related to Specific Gravity (Y Axis).

Before the American Petroleum Institute developed the API Gravity for hydrocarbon liquids, the Baume Gravity was used to gauge the Relative Density of all liquids be they water-based (aka "aqueous based") or hydrocarbon-based.

Baume Gravity was discovered to be inaccurate with respect to measuring the relative heaviness of hydrocarbon liquids.

Baume Gravity is still used for non-hydrocarbon liquids.

A Baume Hydrometer reads in "degrees Baume" which can be referenced to a more conventionally understood Specific Gravity.

Typically, the industrial use of Baume Gravity is to measure the relative heaviness of the same liquid after that liquid has performed a task.

For example: Sulfuric Acid has an industrial use as a catalyst. The strength of the Sulfuric Acid wanes as the catalytic reactions occur and the Baume Gravity can reveal the changes in the Sulfuric Acid.

The industrial liquid called "Caustic" is used to neutralize acids (like HCl ...Hydrochloric Acid). Caustic can be blended to the strength needed as is indicated by Baume Gravity.

HOW ARE GRAVITIES MEASURED?

Determining the Specific Gravity of a Gas requires gas chromatography to breakdown the components of the gas.

How to Determine the Specific Gravity of a Gas

Determining the Specific Gravity of a gas is complicated!

A sample of the gas is sent to the laboratory. A correctly calibrated Gas Chromatograph reveals which gaseous compounds are in the gas and the volume percent of each gas.

Knowing the amount of each gas component within the tested gas and the Density of each gas component at STP makes it possible to calculate an averaged Density for the sampled gas. Next, dividing the tested gas's averaged Density by the Density of Air at STP yields the Specific Gravity of the sampled gas.

Fortunately, the math might be automatically performed by a smart chromatograph!

Note: The Schilling Specific Gravity apparatus and method can be used to determine the Specific Gravity of a gas in remote locations.

Determining Liquid Specific Gravity, API Gravity, and Baume Gravity

The determination of the Specific Gravity of a Liquid requires a Graduated Cylinder that contains the liquid being tested and a Hydrometer that is the correct type and has the correct measuring range.

For liquids, the process of determining Specific Gravity is so easy that Outside Process Operators can perform the task need be. A special-made Hydrometer and a graduated cylinder is all that is required.

A sample of the fluid is poured into the graduated cylinder and allowed to approach STP. The Hydrometer is carefully placed in the liquid and bobs around. Once the Hydrometer stops bobbing, the Specific Gravity, API Gravity, or degrees Baume Gravity are read at the liquid's top-level following the Hydrometer's instructions.

This is an API Gravity Hydrometer.

The correct apparatus is needed for an accurate measurement:

The ASTM Specific Gravity uses an ASTM Specific Gravity Hydrometer.
The API Gravity uses an API Hydrometer.
A Baume Gravity uses a Baume Hydrometer.

TAKE HOME MESSAGES: There are two methods to assess the relative heaviness of all Liquids and Gases: Density and Specific Gravity.

Specific Gravity is very useful determining the Relative Density of light hydrocarbon liquids and industrial gases.

The relative heaviness of hydrocarbon liquids can be determined via API Gravity. API Gravity reveals the ease of processing crude oils and the relative heaviness of the several dozen hydrocarbon liquids derived from crude oils.

API Gravity has an inverse relationship with Specific Gravity, a greater API infers a smaller Specific Gravity and vice versa.

On the API Gravity scale, Water is assigned the value of 10. An API Gravity less than 10 describes a hydrocarbon liquid which is heavier than water and will sink. An API Gravity greater than 10 describes a hydrocarbon liquid that is lighter than water and will float.

The relative heaviness of aqueous-based liquids can be determined via Baume Gravity. Typically, the industrial use of Baume Gravity is to assess how much the same liquid has chemically changed after the aqueous liquid has performed an industrial task. For example, "Caustic" is a chemical used to neutralize acid. The strength of acid needed to neutralize the strength of acid present can be determined by blending the "Caustic" to a specified Baume Gravity.

Determining the Specific Gravity of a gas is complicated; when accuracy is required gas chromatography technology is employed. A Shilling Apparatus could be used to determine the Specific Gravity of a gas if a gas chromatography lab is not accessible.

Determining the Specific Gravity, API Gravity, and Baume Gravity of liquids is much less complicated; only a specifically made Hydrometer and graduated cylinder are required.

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PV FLOWRATE FUNDAMENTALS FOCUS STUDY

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