Monster Media 1996 #14/Monster Media No. 14 (April 1996) (Monster Media, Inc.).ISO/business/mixing10.zip/GASMIX.TXT

Text File | 1992-01-03 | 17KB | 378 lines

                   GAS MIXING DESIGN PROGRAM

                        INSTRUCTIONS


The Gas Mixing program is on disk with the name GASMIXER.EXE.
The other files on the disk called GAS3.PIC and GAS3.INP are also
necessary for the program to operate.  The file with the extension
.PIC are a file of screens used by the program that are read into
the high memory space of your computer during the initiation stage
of the program.  They must be present on the disk or in the
subdirectory of the computer that you use to initiate the operation
of this program.

The Gas Mixer program is started by inserting the disk into you A:
drive after you have booted up your computer.  Give the command at
the DOS prompt A:> GASMIXER and the program will begin.
The program should preferably be operated from a subdirectory on
your computers hard disk to maximize its preformance.

                      M A I N  M E N U

The Main menu for the Gas Mixing program will come on and present
you with alternate selections, to operate the program.  A new user
may wish to start by loading a file from the disk by using the
option 6 below.

The Disk related functions (Options 5,6,and 7) are identical to the
descriptions given in the Blending Program, except that, the
extension .GAS is added to all saved data files instead of .MIX.

Option 8 (New Case) will blank out all data in memory and permit a
new case to be entered from scratch.

Option E will exit the program.  You will be asked to confirm your
decision to quit to guard against accidental loss of data due to
key stroke error.

The Vessel Program (Option 1) is also identical to the program
provided with the Blending program and will not be described in the
following text.

The Liquid data is also essentially identical to the program
provided with the Blending program and will not be described;
except that provision was made to also input Surface Tension data.
Surface tension data is needed for gas bubble and hold up
correlations.

New data must be entered in the following order.  The Vessel data
must be entered first, followed by the Liquid properties then the
Gas properties, and finally the Agitator data.
                    G A S  P R O G R A M

The gas input program is selected by selecting Option 3 from the
Main Menu.  A data value must be entered for each data point
requested by the program.  Enter all data before F10 Key to
terminate input and calculate the gas property and bubbler results.

The following data are required as input.


                         INPUT  DATA

     Temperature   Deg F

     Henry's  Law constant  ( Atm/Lb-Mole Ft3)
          An optional window is provided in the program to
          calculate the Henry law constants from gas solubility
          data by pressing the F2 key.

     Compressibility Factor   usually 1.0

     Diffusivity of gas in solvent ( cm2/sec)
          Press the F1 key to calculate this if unknown.
          It is calculated by the method of Wilke and Chang as
          describe in section 14 of Perry's 4th Edition and in
          considerable detail in page 95 of Multiphase Chemical
          Reactor's -- Giannetto & Silveston.

     Psia - Outlet-  This is the operating pressure in the
          upper head, vapor space.  The pressure at the bottom
          sparger outlet will be calculated from the liquid head in
          the vessel.  The bottom sparger is assumed to be located
          at the bottom vessel tangent line.

     Mole % Reactant in the gas at the inlet (ie Sparger Outlet)
          and at the Outlet (upper head - vapor space)

     Lb-Moles/Hr (in and out)  This is the total gas rate to the
          reactor.  The sum of the gas reactants and inerts.

     Molecular Weight  of the gas in and out of the reactor.

                  CALCULATED GAS PROPERTIES

After the F10 key is pressed.  The program will proceed to
calculate the Inlet, Outlet and Log Mean Average values for the gas
properties as follows:

Lbs of Gas, Standard Cubic Feet/ Minute of Gas, Actual Cubic
Feet/Minute of Gas, Partial Pressure of the Reactant (psia),
Superficial Velocity of the gas in feet per second. ( This is the
Actual volume of the gas divided by the vessel cross sectional
area) , and finally the Gas energy transferred to the liquid by the
expanding gas in terms of BHP/ 1000 gallons.


                       BUBBLER RESULTS

The program calculates the key parameters of a bubbler reactor from
the liquid, gas and vessel properties.  A bubbler reactor is a
system without an agitator. All mixing is performed by the rising
gas bubbles.  The gas is assumed to be evenly dispersed across the
vessel cross section,and the Vessel is assumed to be vertical.

Hold Up Fraction -- The gas hold up fraction is calculated for the
Air Water system and is based upon a curve fit of the data
presented in Akita and Yoshita -- Jan 65  AIChE Journal.  This
method can be changed to the Method proposed by Hughmark that
incorporates the surface tension and specific gravity of the liquid
into the Holdup correlation.  In either case the Hold Up fraction
is principally a function of the gas superficial velocity.

Bubble Diameter -- The bubble diameter is based upon an assumed
size of 1/8 of and inch for the air/water system as recommended by
Fair.  This bubble size is then corrected for the specific gravity
and surface tension of the liquid according to Calderbank's
equation.

       Db = (0.125/12)*(Surf.Ten/72)^0.6*(SpGravity)^-0.2

The program will however not calculate or use a value less than 1/8
inch unless you override it.

The size of the bubbles has a major effect on the calculated Klas
and other data.  The user can override the size of the Sauter mean
Bubble diameter calculated by the program from the command line.
I do not suggest doing this unless you have experimental data.
Bubble sizes of less than 1/8 inch are not likely with most
systems.  You may however wish to make changes to this value to
determine the sensitivity of your design to the bubble size, or to
increase it to a higher value.

Liquid Height --  The Liquid height is calculated in inches above
the bottom vessel seam for both the clear liquid height and the
gassed volume.  You should check that your have provided enough
free volume in your vessel design to separate the gas.

Flow Regime -- This will be Quiescent if the average superficial
velocity is less than 0.2 ft/ sec.   Otherwise it will be
turbulent.  If the flow reqime is turbulent then the correlations
used in the bubbler reactor models have been extended beyond the
experimental data in the literature and may not be accurate.  There
is a higher level of risk in designing in this region.

Interfacial Area (Ft2/Ft3)  This is the total interfacial available
for mass transfer per cu. ft of volume.  The calculation of the
interfacial area is given by the following formula:

        Area = 12.0*6*HoldUp/Bubble Diamter

                 MASS TRANSFER COEFFICIENTS

The program calculates the Kga, Kla, rate of gas reaction per unit
volume and total LbMoles of gas reacted per hour for both the Air
Sulfite System and for the gas and liquid properties that describe
your system.  Essentially all the data presented for bubbler
reactors in the literature is based upon the Air Sulfite system.
This is also true for the agitated reactor correlations.

Kla Air-Water  This is calculated by the procedures recommended in
Fair's Article which in turn is based upon the Froessling Two-Film
model.  the equation is:

Kla = (12*Diff*Holdup)/(Bubble Diam)^2*[1+0.276*Nre^0.5*Scl^0.33]

     Where Nre = Bubble Reynolds Number
           Scl = visc liquid / (diffusivity * liq density)

This correlation was checked against the data presented in Akita
and Yoshita and it agrees over a wide data range.

The Kla for the specific system are calculated from the Kla of air
and water by multiplying the value by:

     [ Diff System / Diff Air water ] ^ 0.5

The values for Kga are calculated from the respective Kla's by with
values for the reactant average partial pressure and Henry law
constant.

     Kga Air/Water = Kla / 1.115*10^4
     Na  Air/Water = Kga * 0.12(ave pp atm)*1*10^-4
     Moles Air Reacted = Na * Liquid Volume in Ft3

For the Specified System
     Na = Kla(system) * (PPave in Atm) / Henry Constant
     Kga(system) = Na(system)*10^4 / (PPave in atm)

The following literature articles were used in the development of
this portion of the program.

     J.R. Fair  Chemical Engineering  July 3 and July 17 1967
     G.A. Hughmark I&EC Process Design and Development 1966
     Akita and Yoshida  AIChE Journal Jan 1965
     Shah and Deckwer AIChE Journal May 1982
     Tilton and Russell Chemical Engineering 1982

The interested user should obtain copies of these article to fully
understand the theory of bubble reactor design.  Shah and Deckwers
survey article lists all the major theory in this area.
               A G I T A T O R   P R O G R A M

The Agitator design program is addressed from the Main Menu after
the Gas data has been entered.  This program allows you to
calculate the improvement of the Mass transfer coefficients by the
use of an agitator.  The program is based upon the assumption that
only Rushton type ie Flat Blade disk turbines are used for the
bottom turbine.  They are generally considered the most effective
turbine for gas dispersion.  The upper turbines in the reactor can
be of different types.  You will have the option of using flat
blade, 45 degree axial, hydrofoil or propeller types for the upper
agitators.

                        AGITATOR BHP

The program data entry begins by requesting an input value for the
gassed BHP/1000 gallons to the lower agitator.  A window pops up
that will recommend a value based upon the gas rate specified in
the previous bubbler design program.  The Bhp/1000 gallons must
generally exceed the gas Bhp energy provided by the expanding gas
in order to be effective in dispersing the gas.  The lowest
effective value is the Flooding number.  The program will generally
select a value in the Moderate range.  The BHP/1000 gallons for
Uniform Distribution is the highest practical value.  Power Numbers
above this will not provide an increase in the  Process results,
since the gas will be completely and uniformly dispersed at this
value. The  BHP/1000 gallons values required for gas dispersion are
also a function of the Diameter of the Impeller to the Tank
diameter.  The Designer should normally select a value somewhat
above the Minimum Flooding value up to the Moderate range as given
by this entry screen.  This screen is addressable for changes from
the command line after data entry by pressing the 'B' {Bhp} key.

                     TURBINE BLADE DATA

The Program is based upon the assumption that the agitator is a
Rushton type Flat blade disk turbine. The disk turbine can be
specified with an alternate number of blades and blade widths.  A
Window pops up to enable you the define the turbine.  The Default
values of 6 blades at a Blade width to diameter ratio of 0.2 is
given, but these values can be changed.  Blade Width ratio down to
0.125 can be used for high shear application.  The Sacrifice for
this is less circulation.  Blade widths above 0.2 do not yield a
process improvement.  The program will use the turbine blade
description to calculate the shear rates and the power requirements
of the turbine.  The turbine power number of the standard turbine
with 6 blades and a W/D blade ratio of 0.2 is 5.0.  The power
number is corrected for the number of blades by taking the ratio to
6 blades to the 0.8 power.  The Power Number is corrected for the
blade width by a linear relationship.

                   AGITATOR SUMMARY SCREEN

The program calculates the agitator results after the foregoing
data has been entered.  The program will size the diameter of the
required gas dispersion agitator based upon the desired BHP/1000
gallons.  The initial diameter will be approximately at an impeller
to tank diameter of 0.33 and the agitator RPM will be selected from
the standard AGMA speeds to get the closest match to the BHP/1000
gallon value selected.  The diameter and RPM can be altered from
the command line if values other than those selected by the design
section of this program are desired.

                 Mass Transfer Coefficients

The Kga,Kla, and Moles of gas reacted are calculated for the air
sulfite system as well as the specified system.  The values for the
Air Sulfite system are based upon the correlations presented by
OldShue in his book 'Fluid Mixing Technology' and from other
sources.  The Kga is a function of both the gas superficial
velocity and the gas energy in BHP/ 1000 gallons.  The Kga and Kla
of the specified system are calculated from the Air Sulfite data by
the diffusivities to the 0.5 power as discussed in the previous
section on the bubbler reactor models.

                       BOTTOM AGITATOR

The program calculates the following information for the bottom
agitator.  The BHP/1000 gallons for the flooded and for uniform
distribution.  The diameter of the turbine required for the
specified BHP/1000 gallons and the ratio of this diameter to the
diameter of the vessel.  The RPM selected is displayed and the
BHP/1000 gallons for both the gassed condition and the results in
liquid with no gas present.  The latter value is the BHP/1000
gallons if the selected agitator is operated without gas flow at
the selected RPM.  It is often more than twice the gas bhp /1000
gallon requirement since the presense of gas in the agitator will
severely reduce the liquid circulation and power dispersion.

The Gas Holdup ratio is based upon the correlation of Foust HC
Processing Nov 7 as follows:

  Holdup = 4.25*(BHp/1000gal)^0.47 *(Superficial Velocity)^0.53

If this formula gives a lower value then developed by the bubbler
model correlation in the previous section then the hold up for the
bubbler model is used.


The P/Po ratio is the power ratio of the gassed condition to the
pure liquid condtion.  This value was developed from correlations
provided in the Chemineer series in Chemical Engineering in 1976
and by Michel and Miller in AIChE Journal in May 1962.
The Torque in ft-lb is generated for the Bhp in the gassed
condition.  The Torque in liquid only is calculated by prorating
the torque gassed by the ratio of the liquid to the gassed BHP
requirements.

The gas Number is a number used in the calculations that is defined
as the ratio of the gas flow rate to the product of the rpm and
turbine diameter.

The gas mixing intensity number is a ratio used by Chemineer in
their Chemical Engineering Articles.

The Tip speed of the Agitator is calculated.


The pumping flow rates, Flow Number of the impeller, Agitator
Reynolds Number, Prandtl Number and the heat transfer coeffients
are calculated for both the lower and upper turbines.

The Shear both Max and Average are also calculated.  The average
shear is equal to the Maximum shear / 2.3.

Shear Max is calculated by the formula:
Shear = [9.7*RPS*(D/T)^0.3 ] / (W/D)   ratio of blades

The user is refered to R.L. Bowens article in Chemical Engineering
June 9 1986. For an excellent discussion of Shear sensitive systems
and how it is to be calculated.


                       UPPER AGITATOR
The upper agitator sizing calculations are started by selection of
the letter U from the command line.  The upper agitator selection
screens will come on and will request information on the type of
agitator and the number of agitators to be used in the upper
sections of the reactor.  You may select from the alternative of
Flat or Disk Blade Turbines, Axial 45 degree turbines, propeller or
hydrofoil designs.  The number of blades and the blade widths can
also be specified.  The computer will make recommendations on the
number of agitators to be used, but this can be overridden by the
user.   The agitator sizing will be based upon the agitator RPMs
selected for the lower agitator.  It is assumed that the upper
agitators and the lower gas dispersion agititor are on the same
shaft.  The Agitator RPM can only be changed from the lower
agitator command line.  The turbine diameters are limited to a
maximum size of 0.4 times the tank diameter for the computer sizing
calculations.  The diameter can however be specified at any value
from the commmand line.

This upper agitators are assumed to be located in the liquid bubble
swarm above the dispersing agitator.  Consequently, the amount of
gas entering the impeller is much less than the bottom agitator.
The power ratio is based upon the holdup value generate by the
bottom agitator.

The upper agitator calculation results include a summary of the
agitator Bhp's for both the gassed and liquid condition for the
number and type of agitators selected.  The same type of data are
calculated for the upper agitator as was presented for the lower
agitator including, flow pumping rates, and heat transfer
calculated values.