basic design concepts in process calculations
TRANSCRIPT
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CONCEPTS
IN PROCESS
CALCULATIONS
AZAS TEKNIK KIMIA (CHE100)
Oleh :
Aning Ayucitra
Semester Genap 2010/2011UKWMS
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Process & System..2
Definition ofprocess :
Operation or series of operations that cause a
physical or chemical change (or both) in a material or
mixture of materials Types of processes :
Physical or chemical
Batch, continuous, or semi-batch
Steady-state or transient
Process units : physical components constituting a
process
Process streams : materials entering & leaving a
process unit
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...contd
A block diagram for the following process system to make
instant coffee:
Roasted coffee beans are fed to a grinder, from which the
ground beans pass to a leaching unit in which the soluble
coffee is extracted with hot water to give a dilute coffeesolution. The residual wet solids are centrifuged to remove
the retained solution, which is mixed with the solution from
the leaching unit. The remaining solids are transported away
for agricultural use. The combined dilute coffee solution is fed
to a steam-heated evaporator to remove most of the water.
The concentrated coffee solution is dried in a spray drier in
which the remaining water is evaporated into a warm air
stream; the dried coffee powder product is collected for
packaging.
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...contd4
Grinder
Leaching
Unit
Centrifuge
Mixer Evaporator
Spray Drier
Roast coffee
beans
Ground
coffee beans
Hot
water
Dilute
solution
Water
Concentrated
solution
Residual
wet solids
Remaining solids
(to agricultural use)
WaterWarm
air
Concentrated
solution
Packaging
Dried coffee
powder
Product
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...contd
Definition ofsystem :
An arrangement of physical components in a process
connected or related to form or/and act as an entire unit
Can be constituted by 1 or more connected processunits
Physical systems : have well defined physical
boundaries between the systems and the surrounding
Open system, closed system, and isolated system Conceptual systems : arbitrarily defined with imaginary
boundary for purpose of process analysis
Can contain other physical systems within its boundary
control volume
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Definition ofsystem properties :
Quantities necessary to describe the state or condition of
a system
Extensive properties:
Dependent on extent (quantity) of system
E.g. weight, force, energy, flowrate
Intensive properties: Independent of the mass or size of system
E.g. Temperature, pressure, density, viscosity
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A mole is a certain number of molecules,
atoms, electrons, or other specified types of
particles
Symbol mol in the SI system :
The amount of a substance that contains as many
elementary entities (may be atoms, molecules,
ions, or other particles) as there are atoms 0.012kg of carbon 12
Composed of 6.02 x 1023 molecules
Designation : g mol
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MOLE UNIT
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To convert the number of moles to mass, use the molecular
weight the mass per mole :
g mol = mass in g / molecular weight
lb mol = mass in lb / molecular weight
or
mass in g = (mol.wt.)(g mol)
mass in lb = (mol.wt.)(lb mol)
Molecular weight of the compound is the sum of theweights of the atoms of which it is composed
MW of H2O = 2 H atoms + 1 O atom
= (2)(1.008) + (1)(16.000) = 18.02
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...contd
What is the molecular weight of acetic acid?
If a bucket holds 5.00 lb of K2SO4 (mol.wt. = ?), how many:
Pound moles of K2SO4 does it contain? Gram moles of K2SO4 does it contain?
How many pounds of CaO are in 10 g mol of CaO?
There is twice as much copper in 480 g of copper as there
is in 240 g of copper, but is there twice as much as copper
in 480 g of copper as there is silver in 240 g of silver?
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MASS & VOLUME
DENSITY
Ratio mass per unit volume
Units : kg/m3, g/cm3, lbm/ft3
Densities for liquids and solids do not changesignificantly at ordinary conditions with pressure, but dochange with temperature
SPECIFIC VOLUME The inverse of the density (= volume per unit mass or
unit amount of materials = 1/density)
Units : ?
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...contdSPECIFIC GRAVITY
Ratio of density of a substance to the density of a reference
substance at a specific condition
Reference substance : For liquids and solids : water at 4oC
For gases : air or other gases
In petroleum industry : oAPI
PROBLEM : Calculate the density of mercury in lbm/ft3. Specific gravity of mercury
at 20C is 13.546. Also calculate the volume in ft3 occupied by 215 kg
mercury.
Calculate the specific gravity of nitrogen gas at -10C and 14.7 PSI.
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MOLE & MASS FRACTION12
Mole fraction
The moles of a particular substance divided by
the total number of moles present
Mole fraction of A = (moles of A) / (total moles)
Mass (weight) fraction :
The mass of the substance divided by the totalmass of all the substances present
Mass fraction of A = (mass of A) / (total mass)
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PROBLEMS
1. An industrial-strenght drain cleaner contains 5.0
kg of water and 5.0 kg of NaOH. What are the
mass fraction and mole fraction of eachcomponent in the drain cleaner container?
2. Convert a salt concentration of 25 g/L in a
solution of density 1005 kg/m3 to a mass
fraction.
(hint: check all units)
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CONSENTRATIONS
The quantity of some solute per specified
amount of solvent, or solution, in a mixture of
two or more component
For example : Mass per unit volume
Moles per unit volume
Parts per million (ppm) and parts per billion (ppb) Others: molarity, normality
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PROBLEMS
The current OSHA 8 hour limit for HCN in air is 10.0ppm. A lethal dose of HCN in air (from Merck Index)is 300 mg/kg of air at room temperature. How manymg HCN/kg air is the 10.0 ppm? What fraction ofthe lethal dose is 10.0 ppm?
The mass rate of glucose and water in a solutionpumped into a fermenter are 0.15 lbm/hr and 1.25
lbm/hr respectively. Determine the mass fractionand (mass) concentration in g of glucose per L ofsolution. Assume that the density of the solution isthe same as water.
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A gaseous mixture contains 20 g of N2, 83 g of
O2, and 45 g of CO2.
Calculate:
the composition of the gas in mass fraction
the composition of the gas in mole fraction
the average molecular weight of the gas mixture
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CONVERSION OF UNITS17