Heat integration course _ Hanoi University of science and technology 2017Heat recovery and Heat exchange Basic concepts of heat exchange: Clearly, we will need to supply 180kW of steam h
Trang 1Lecture 2: Key concepts of Pinch Analysis
Do Xuan Truong
truong.doxuan@hust.edu.vn
Trang 2Heat recovery and Heat exchange
Basic concepts of heat exchange:
The feed, which starts cold and needs to be heated up, is
known as a cold stream
Conversely, the hot product which must be cooled down is
called a hot stream.
Trang 3Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
Basic concepts of heat exchange:
Clearly, we will need to supply 180kW of steam heating and 180kW of water cooling to operate the process
Trang 4Heat recovery and Heat exchange
Basic concepts of heat exchange:
Can we reduce energy consumption?
Yes; if we can recover some heat from the hot stream and use it to heat the cold stream in a heat exchanger, we will need less steam and water to satisfy the remaining duties.
Trang 5Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
Basic concepts of heat exchange:
1 The temperature–enthalpy diagram
Trang 6Heat recovery and Heat exchange
Basic concepts of heat exchange:
1 The temperature–enthalpy diagram
Trang 7Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
Basic concepts of heat exchange:
1 The temperature–enthalpy diagram
Trang 8Heat recovery and Heat
exchange
1 The temperature–enthalpy diagram
Trang 9Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
1 The temperature–enthalpy diagram
Trang 10Heat recovery and Heat exchange
The resulting T/H plot is a single curve representing all the hot streams, known as the hot
composite curve
A similar procedure gives a cold composite curve of all the cold streams in a problem
1 The temperature–enthalpy diagram
Trang 11Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
2 A targeting procedure: the “Problem Table” (Linnhoff and
Flower 1978)
Shifted temperatures, which are set at ½ ∆Tmin (5°C in
this example) below hot stream temperatures and ½ ∆Tmin
above cold stream temperatures.
Trang 12Heat recovery and Heat exchange
2 A targeting procedure: the “Problem Table” (Linnhoff and Flower
1978)
Trang 13Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
2 A targeting procedure: the “Problem Table” (Linnhoff and Flower
1978)
Trang 14Heat recovery and Heat exchange
2 A targeting procedure: the “Problem Table” (Linnhoff and
Flower 1978)
any heat available in interval i is hot enough to supply
any duty in interval i +1 Assuming that no heat is supplied to
the hottest interval 1 from hot utility, then the surplus of 60kW from
interval 1 is cascaded into interval 2.
Trang 15Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
2 A targeting procedure: the “Problem Table” (Linnhoff and
Flower 1978)
There it joins the 2.5kW surplus from interval 2, making 62.5kW to cascade into interval 3 Interval 3 has
a 82.5kW deficit, hence after accepting the 62.5kW it can
be regarded as passing on a 20kW deficit to interval 4
Interval 4 has a 75kW surplus and so passes on a 55kW
surplus to interval 5 Finally, the 15kW deficit in
interval 5 means that 40kW is the final cascaded energy to cold utility.
Trang 16Heat recovery and Heat exchange
Trang 17Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
Trang 18Heat recovery and Heat exchange
3 The pinch and its
Trang 19Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
five simple and effective
concepts:
● Targets: Once the composite curves and Problem Table are known,
we know
exactly how much external heating is unavoidably required
● The Pinch: Above the pinch the process needs external heating and
below the pinch it needs external cooling This tells us where to place
furnaces, steam heaters, coolers, etc It also tells us what site steam
services should be used and how we should recover heat from the
exhaust of steam and gas turbines.
● More in, more out: An off-target process requires more than the
● Trade-offs: A simple relationship exists between the number of
streams (process streams plus utilities) in a problem and the minimum number of heat
exchange “units” (i.e heaters, coolers and interchangers) A network which achieves the minimum energy targets, with the “heat source”
and “heat sink” sections separate, needs more units than if the pinch division had been
ignored This type of trade-off, between energy recovery and number of units,
adds to the traditional concept of a trade-off between energy and
surface area
3 The pinch and its
significance
Trang 20Heat recovery and Heat exchange
4 Heat exchanger network
design
Trang 21Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
4 Heat exchanger network
design
Trang 22Heat recovery and Heat exchange
4 Heat exchanger network design – above the pinch
Trang 23Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
4 Heat exchanger network design – above the pinch
Trang 24Heat recovery and Heat exchange
4 Heat exchanger network design – below the pinch
Trang 25Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
4 Heat exchanger network design
Trang 26Heat recovery and Heat exchange
4 Heat exchanger network design – Summary
Trang 27Heat integration course _ Hanoi University of science and technology 2017
Heat recovery and Heat exchange
4 Heat exchanger network design – Summary
Trang 28Heat recovery and Heat exchange
4 Heat exchanger network design – Summary