ETHANOL PRODUCER'S DATA BASE

Simplicity in Applied technology

HEURISTICS

 
 HEURISTIC 

 

  • Heuristic is the art and science of discovery and invention.
  • The word comes from the same Greek root as eureka, which means "I find".
  • A heuristic is a way of directing your attention fruitfully.
Wikipedia defines a heuristic as a method for helping in the solution of a problem, often informal. It is particularly used for a method that usually rapidly leads to a solution that is usually reasonably close to the best possible answer. Heuristics are rules of thumb, educated guesses, intuitive judgments or simply common sense.
In more precise terms, heuristics stand for strategies using readily accessible though loosely applicable information to control problem-solving in human beings and machine.
 

DISTILLATION TEMPERATURE

Defining the Boiling point of Water Ethanol Azeotrope

 

On a perfect day, at sea level, and with a constant atmospheric pressure of

101.32kPa, (14.7 Psi, 407.2” H2O, 29.92”Hg, 760Torr (mm Hg), 1,013mbar.)

Water boils at 212°F, Ethanol at 172.9°F, Azeotrope at 172.6°F
In distillation, the vaporizing temperature

of ethanol is critical in attaining high Proof, or purity.

  • We must consider all the above notions
  • To establish proper distillation temperature,
    • Yet this simple test before performing a distillation run
    • Will establish the exact boiling point of the water ethanol azeotrope..

 

1.     Fill a 5 quart pot with water, and place it on a burner, then bring it to a full boil.

2.     Using your distillation thermometer, read the boiling water temperature.

a.     Stem submerged half way, not touching sides or bottom.

b.     Wait for thermometer reading to stabilize.

3.     Note the reading:

a.     To  get  Ethanol  boiling temperature :  Multiply reading by 0.81556

b.     To get Azeotrope boiling temperature : Multiply reading by 0.81415

 Example:

Boiling water reads 210.5°F ( X 0.81556) = Ethanol  boils  at 171.67°F
Boiling water reads 210.5°F ( X 0.81415)=Azeotrope boils at 171.38°F


Therefore the temperature of the vapors will be maintained at exactly
171.4°F to 171.7°F throughout the distillation run for best performance

On that day, at that Elevation, for that atmospheric pressure, and this could change during a long distillation run...

So you would be advised to verify the proof of the Ethanol as it is processed, and adjust your still accordingly..

Since the vaporizing temperature is directly dependent on the atmospheric pressure, hence the elevation, this simple test will calibrate your still for near perfect runs every time…all the time.

DISTILLATION

Distillation usually is the most economical method of separating liquids, superior to extraction, adsorption, crystallization, or others. 

Column operating pressure is determined most often by the temperature of the available condensing medium, 100-120 F if cooling water; or by the maximum allowable reboiler temperature, 150 psig steam, 366 F.


Minimum reflux for binary mixtures is given by the following when separation is essentially complete (XD ~ 1) and D / F is the ratio of overhead product and feed rates: RmD/F = 1/( α-1), when feed is at the bubblepoint; (Rm + 1)D/F = α/(α-1), when feed is at the dewpoint.

A safety factor of 10% of the number of trays calculated by the best means is advisable.

Reflux pumps are made at least 25% oversize

>Peak efficiency of trays is at values of the vapor factor Fs = u(ρv)0.5 in the range 1.0-1.2 (ft/sec) (lb/cuft)0.5.

This range of Fs establishes the diameter of the tower.

>Roughly, linear velocities are 2 ft/sec at moderate pressures and 6 ft/sec in vacuum. 

The optimum value of the Kremser-Brown absorption factor

A = K(V / L) is in the range 1.25-2.0.

>Pressure drop per tray is of the order of 3 in. of water or 0.1 psi.

>Tray efficiencies for distillation of light hydrocarbons and aqueous solutions are 60-90%; and for stripping: 10-20%.

>Sieve trays have holes 0.25-0.50 in. dia, hole area being 10% of the active cross section.

>Valve trays have holes 1.5 in. dia each provided with a liftable cap, 12-14 caps/sqft of active cross section.

    >Valve trays usually are cheaper than sieve trays.

>Bubblecap trays are used only when a liquid level must be maintained at low turndown ratio; they can be designed for lower pressure drop than either sieve or valve trays.
>Weir heights are 2 in., weir lengths about 75% of tray diameter, liquid rate a maximum of about 8 gpm/in. of weir.

>Packings of random and structured materials suited especially to towers under 3 ft dia and where low pressure drop is desirable.

 

>The ratio of diameters of tower and packing should be at least 15, and a ratio of 20:1 is advisable.

Because of deformability, plastic packing is limited to a 10-15 inch depth unsupported, metal to 20-25 inch.

Liquid redistributors are needed every 5-10 tower diameters with pall rings but at least every 2 ft.

The number of liquid streams should be 2 in towers larger than 3 inch dia and more numerous if possible.
>Height equivalent to a theoretical plate (HETP) for vapor-liquid contacting is :

          5" For copper wool scrubbers 

          6" For structured mesh

          8" For 4 mm Raschig rings

          9" For 6 mm Raschig rings

        10" For 10 mm Marbles

>Packed towers should operate near 70% of the flooding rate given by the correlation of Sherwood, Lobo, et al.

Reflux drums usually are horizontal, with a liquid holdup of 5 min half full.

A takeoff pot for a second liquid phase, such as water in hydrocarbon systems, is sized for a linear velocity of that phase of 0.5 ft/sec.

For columns 3 inch dia, add 6 inch at the top for vapor disengagement and 8 inch at the bottom for liquid level and reboiler return.
 Limit the column height to about 7 ft max because of sealing space  considerations

Length to diameter ratio of the reflux column should be kept under 30.