ENERGY AUDIT
Pinpoint Areas where Energy
Efficiency can be Improved
DISTILLATION COLUMN
• Conventional Distillation Column vs Heat
Integrated Distillation Column
• In conventional column, rectification and
stripping section are at same pressure
• In HIDC, rectification section is at higher
pressure than stripping section steam
requirement decreases and hence energy
efficiency is improved
• Rectification and Stripping section are
connected by compressor and throttle valve
HIDC
Conventional column
STRIPPING
SECTION
RECTIFICATION
SECTION
Heat Integration of Reactor and
Distillation Column
COMPRESSOR
ORGANIC
VAPORS
FEED
HEAT
EXCHANGER
REACTOR
• Energy of Organic
vapors can be used
to preheat the feed
• Vapors are
compressed firstly to
increase their
bubble point
• These vapors are
feed of distillation
column
Process Description
• The reaction is between pivalic acid and
benzotrichloride. The reaction is exothermic
• Vapors which leave the reactor have to be condensed to
remove the HCl which is formed in the reactor before
feeding to Distillation Column.
• One of the ways for heat integration is to use heat
released by condensation of organic vapours for heating
of reactants and as a heating medium in reboiler. But the
problem is that the temperature required for heat transfer
fluid in reboiler and feed preheater should be in the
range of 210 0C – 240 0C while the organic vapour
condenses at 190 0C.
Heat Integration
• Organic vapours are pressurized so that its
bubble point rises to 2400C. The corresponding
pressure is found out to be 3 atm. Energy
requirement to compress vapours to 3 atm
pressure is 20 kJ/s.
• This forms vapors of temperature 3590C. It has
to be brought down to its bubble point. It is done
so by pre-heating the feed of the reactor using
finned tube heat exchanger. The saturated
vapours are then fed to the reboiler of the
distillation column
Energy Saving
• Steam requirement becomes zero after heat
integration
• Steam requirement before heat integration=
5000 tons i.e. Rs 50 lakhs per year
• Also there is saving of pumping 28.5m3/hr.
Pump Power = 4kW i.e. approx 2.6lakh.
• Compressor Duty (assuming 50%
compressor efficiency) = 40kW i.e. approx.
26 lakhs per year.
Increasing Efficiency in Heat
Exchanger
• Air Cooled Heat Exchangers: Low HTC so large
area and consume a lot of metal
• First Generation: Equilateral Pitch 63.5-67mm.
• Second Generation: Equilateral Pitch 58mm. Gives
Energy Saving of 8-10%
• Further instead of using equilateral pitch increase
the Longitudinal pitch and keep Transverse pitch
constant increases the energy efficiency by a further
10%.
• Also, addition of fins and ribs increases the surface
area which increases the energy efficiency
Pump Selection
• Centrifugal
• Positive Displacement
Advantages of centrifugal pumps:
• Very efficient
• Produce smooth and even flow
• Reliable with good service life
Systems requirement
Flow →
Pump sizing
• Pump must be
operated within 20%
of the maximum
efficiency value.
• Understanding of the
system requirement is
important parameter.
Case study
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•
•
•
•
•
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Flow rate of liquid: 1 m3/sec.
Head required : 46 m
Pump 1 operating efficiency: 81%
Pump 2 operating efficiency: 72%
Cost difference = Rs. 2.5 L
Reduction in power = 20 kW
Reduction in energy = 16000 kWh/yr.
Savings = Rs. 11.2 L
Thank You