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Unit Operations in
Fertiliser Industry
I F F C O
INDIAN FARMERS FERTILISER COOPERATIVE LTD.
Sanjay Katheria
Process Engineering Section
Heat Transfer
Some Application of Heat
Transfer
Heat Transfer
Mode of Heat Transfer
- Conduction: Transfer of energy form more energetic particle of a
substance to the adjacent less energetic one.
- Convection: involves conduction and fluid motion
- Natural Convection
- Forced Convection
- Radiation: Transfer of energy in form of electromagnetic waves or
photons.
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Conduction
Steady State Conduction
Unsteady State Conduction
Fourier’s Law dq - kdt
dA dx
where A = area of isothermal surface
x = distance measured normally to surface
q = rate of heat flow across surface in direction normal to
surface
T= temperature
k = thermal conductivity
I F F C O
Thermal Resistance (R)
Heat Flow Through Composite Walls
R = R1 + R2 + R3
R1=L1/k1A, R2=L1/k2A, R3=L/k3A
Q = ∆T/R
Heat Flow Through Concentric Cylinders
Q = 2πk(T1 – T2)
ln(r1/r2)
Conduction
R1
k1
R3
k3
R2
k2
L1 L2 L3
A
R2
R1 T1
T2
I F F C O
Convection
Natural Convection
Forced Convection
Q = h*A*(T1 – T2), h = Film Coefficient i.e. Reciprocal
of heat transfer resistance
Hot Surface T1
Cold Fluid Warm Fluid
T2
Air
I F F C O
Radiation
Radiations are electromagnetic waves, do not require medium for transfer of energy
Blackbody: A perfect absorber and emitter of thermal radiation.
Stefan-Boltzman Law:
Wb = σ*T4
Wb = Total emissive power of a blackbody
σ = Stefan-Boltzman Constant
T = Absolute Temperature
I F F C O
Sun
Heat Exchanger Type of Heat Exchangers (Design)
Shell and Tube Heat Exchanger
Plate and Finned Heat Exchanger
Double Pipe Heat Exchanger
Type of Heat Exchangers (Flow)
Co-current Heat Exchanger
Counter Current Heat Exchanger
Cross Flow Heat Exchanger
I F F C O
Contd.. Log Mean Temperature Difference: The LMTD is a logarithmic
average of the temperature difference between the hot and cold
streams at each end of the exchanger. The larger the LMTD, the
more heat is transferred.
Overall Heat Transfer Coefficient: The LMTD is a logarithmic
average of the temperature difference between the hot and cold
streams at each end of the exchanger. The larger the LMTD, the
more heat is transferred.
Fouling Factor: Thermal resistance offered by the accumulation of
deposits on heat transfer surface.
Shell and Tube Heat Exchanger
Shell
Tubes
- Tube Layout
- Tube Pitch
- Outer Tube Limit
Baffles
- Segmented Baffles
- Baffle Spacing
- Baffle Cut
- Orifice Baffle
I F F C O
Plate & Frame Heat Exchanger
Tube Arrangement in Heat Exchanger
I F F C O
Finned
Tubes
I F F C O
I F F C O
Mass Transfer
Mass Transfer Operation
Distillation
Absorption
Stripping
I F F C O
Distillation
Vapor-Liquid Equilibrium
Ideal Solutions – Raoult’s Law
For an ideal solution, the equilibrium partial pressure p* of a constituent at a fixed temperature equals the product of its vapor pressure p when pure at a fixed temperature and its mole fraction in the liquid.
pA* = pAx pB
* = pBx
Relative Volatility/ Separation Factor
α =[ y*/(1-y*)] / [x/(1-x)]
α = 1.0 then no separation possible and larger the value of α above unity, the greater the degree of separatibility.
I F F C O
Continue..
Distillation: The function of distillation to separate, by vaporization, a liquid of miscible and volatile substance into its individual component or, in some cases into group of components.
- Atmospheric Distillation
- Vacuum Distillation
Flash Distillation: Flash is a single stage separation technique. A liquid mixture feed is pumped through a heater to raise the temperature and enthalpy of the mixture. It then flows through a valve and the pressure is reduced, causing the liquid to partially vaporize. Once the mixture enters a big enough volume, the liquid and vapor separate.
Batch Distillation
Azeaotropes: Constant-boiling mixture
I F F C O
Continue..
Continuous Distillation with Reflux
- Enriching/Rectifying Section
- Stripping Section
- Condenser
- Reboiler
- Plates
Azeotropic Distillation: A third component component some times
called and entrainer may be added to the binary mixture to form an
new low-boiling azeotrope with one of the original constituent,
whose volatility is such that it can easily be seperated from the other
original constituent.
Extractive Distillation: A third component, termed as a solvent, is
added which alters the relative volatility of the original constituent
and thus permitting the separation.
I F F C O
Figure 1: Continuous
fractionating column with
rectifying and stripping
sections.
I F F C O
Tray Design
Bubble Cap Tray
Sieve Tray
Design and Operating Characteristics
Number of Plates in the column
Diameter of the column
Heat input to reboiler
Heat output from condenser
Spacing between the plates
Type of Plate
Feed Location
Method of Ponchon and Savarit
Method of McCabe and Thiele
Minimum Reflux Ratio
Total Reflux
Minimum Number of Trays
I F F C O
Absorption
Solubility of a gas in a liquid
influenced by temperature and
pressure.
Choice of solvent for absorption:
- Gas Solubility
- Volatility
- Corrosiveness
- Cost
- Viscosity
- Miscellaneaous: Nontoxic,
nonflammable and chemically
stable etc.
I F F C O
Continue..
Co-current Flow Absorption
Counter Current Flow Absorption
Loading: Occur because of higher gas/vapor flow rates.
Flooding: Flooding is brought about by excessive vapor flow,
causing liquid to be entrained in the column. Flooding is detected by
sharp increases in column differential pressure and significant
decrease in separation efficiency.
Weeping: This phenomenon is caused by low vapor flow. The
pressure exerted by the vapor is insufficient to hold up the liquid on
the tray. Therefore, liquid starts to leak through perforations.
Excessive weeping will lead to dumping.
Entrainment: Entrainment refers to the liquid carried by vapor up to
the tray above and is again caused by high vapor flow rates.
I F F C O
Desorption/Stripping
Recovery of absorbed gas from rich solvent.
Increase in temperature and reduction in pressure.
Absorption at high pressure then large amount of recovery can be done by simply flashing.
Stage wise operation
Inert gas or steam as stripping medium
Steam as preferred stripping medium as it can be condensed.
I F F C O
Fluid Flow Operations
Fluid Flow Operation
Newtonian (e.g. gases and most liquids)
non-Newtonian Fluids (e.g. sewage sludge)
Viscosity
I F F C O
Reynolds Number
Boundary Layer
Flow through Pipes
- Continuity Equation
- Bernoulli Equation
- Hagen-Poiseuille Equation
Friction Factor Chart
- Friction loss from expansion
- Friction loss from contraction
- Friction loss from fitting & valves
Continue..
I F F C O
I F F C O
I F F C O
Valves
Gate Valves
Plug Valve
Globe Valves
Ball Valve
Butterfly Valve
Needle Valve
Check Valves
I F F C O
Gate Valve Plug Valve Ball Valve
I F F C O
Globe Valve Butterfly Valve Check Valve
I F F C O
Pumps
Positive Displacement Pumps
- Reciprocating Pumps
- Rotary Pumps
I F F C O
Centrifugal Pumps
I F F C O
Pump
Capacity: Quantity of liquid discharge per unit of time
Head: The energy supplied to liquid per unit weight, obtained by
dividing the increase in pressure by liquid specific weight.
Power: The energy consumed by a pump per unit time for supplying
liquid energy in the form of pressure.
Efficiency: The ratio of the useful hydraulic work performed to the
actual work input.
Cavitations: Whenever the liquid pressure at pump suction drops
below the vapor pressure, liquid boiling occurs, and the vapor
bubble form. vapor bubbles may reduce or stop the liquid flow, as
well as damage the system.
Break Horse Power: The brake horsepower is the amount of real
horsepower going to the pump, not the horsepower used by the
motor.
I F F C O
NPSH
Net Positive Suction Head (NPSH): NPSH - can be expressed as
the difference between the Suction Head and the Liquids Vapor
Head.
Net Positive Suction Head (Required): In general determined
experimentally by the pump manufacturer in order to prevent
cavitation for safe and reliable operation of the pump.
Net Positive Suction Head (Available): Head made available the
suction system for the pump.
The available NPSHa of the system should always exceeded the
required NPSHr of the pump to avoid vaporization and cavitation of
the impellers eye.
I F F C O
Fan, Blower & Compressor
Fans: Large fans are usually centrifugal, operating on exactly the
same principle as centrifugal pumps. Low discharge head, from 5 to
60 in.
Blowers & Compressors:
- Adiabatic Compression
- Isothermal Compression
- Polytropic Compression
- Compression Ratio = pa/pb, pa, pb= inlet and outlet pressures
For blowers compressor ratio below 3 or 4 however for compressor
it can be more than 10.
I F F C O
Ejectors
A kind of vacuum pump that does not use moving is the jet ejectors,
in which the fluid to be moved is entrained in a high velocity stream
of second fluid.
Steam-jet Ejectors
I F F C O
Reaction Engineering
Reaction Engineering
I F F C O
Reaction Engineering
Elementary/ Non-elementary Reaction
Order of Reaction
Rate of Reaction: ri = [1/V][dNi/dt], V- volume, Nj- moles of jth
component and t - time
Rate Constant: k=k(t)
Conversion: X = [No– N]/No
Catalyst: To increase or decrease the rate of reaction
I F F C O
Reactors
Batch Reactors
Semi Batch Reactors
Continuous Steady State Reactors
- Tubular Reactors: Plug Flow Reactors and Packed Bed Reactors
- CSTR (Continuous Stirred Tank Reactors)
Batch
Reactor PFR CSTR
I F F C O
Batch Reactors
Constant Volume Batch Reactor
I F F C O
CSTR
I F F C O
Plug Flow Reactor
I F F C O
Solid Catalyzed Reaction
Role of catalyst and its working
Catalyst Poison
I F F C O
Packed Bed Catalytic Reactor
I F F C O
Thank You
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