Basic Design Concepts in Process Calculations

7/28/2019 Basic Design Concepts in Process Calculations

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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.

3


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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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...contd

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

7

MOLE UNIT


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...contd

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)

...contd13


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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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...contd

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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...contd

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

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Basic Design Concepts in Process Calculations