Pinch Design Method Flashcards
The design must not transfer heat across the pinch by what 2 rule?
Process to process heat transfer
Inappropriate use of utilities
Above the pinch ______ can be used up to QHmin and below the pinch _______ ______ can be used up to QCmin.
Steam; cooling water
The ______ is the most constrained region of the problem and is what your design should start with.
Pinch
CPh <= CPc ______ the pinch
Above
CPh >= CPc _____ the pinch
Below
______ utility must not be used above the pinch.
Cold
Hot streams can be used on the cold streams ______ the pinch.
Above
Match hot streams to cold streams_______ the pinch
Above
Hot utility must not be used _____ the pitch
Below
It is essential to match cold streams _______ the pinch with a hot stream
Below
The number of units is an important criterion in the ______ _____
Capital cost
Keeping the number of units to a minimum can be achieved using the ____-______ _________.
Tick-off heuristic
Cooling water must not be used above the pinch, therefore, if there are ____ _____ above the pinch for which the pinch matches do not satisfy duties, additional process to process heat recovery is required.
Hot streams
If there are 3 hot streams and 2 cold streams, one of the hot streams cannot be cooled to the ______ temperature. The problem can be resolved by _______ a cold stream into two _______ branches.
Pinch; splitting; parallel
Sh <= Sc _____ the pinch
Above
If there had been a greater number of cold streams than hot streams in the design _____ the pinch, this would not have created a problem since _____ _____ can be used above the pinch.
Above; hot utility
Sh >= Sc _____ the pinch
Below
There is a degree of freedom in the design to choose the branch _____.
Flow rates
______ the utility pinch; high-pressure steam should be used and no low-pressure steam or cooling water.
Above
Between the utility pinch and process pinch _____ _____ steam should be used and no high - pressure steam or cooling water
Low pressure
Below the process pinch only _____ ____ should be used
Cooling water
Away from the pinch there is more flexibility and the ______ do not have to hold
Equalities
When trying splitting above the pinch start with cold streams with highest ________
Cp
What is the heat exchange between to process streams called?
Exchanger
A process stream is heated or cooled by a utility stream called a what?
Heater or cooler
When a process stream is completely vaporized it is called a
Vaporizer
A vaporizer that is associated with a distillation column is called a what?
Rebuilder
What is used to concentrate a solution
Evaporator
What do you use when heating is done by combustion?
Fired heater
What do we need when we want to design heat transfer equipment?
- duty
- stream conditions
- configuration
What do we need to solve heat transfer equipment design problems?
Physical properties, U (both h and k), Heat transport, overall resistance
What is the equation for heat transport?
Q=UAdeltaT
What is the equation for overall resistance?
R=1/(UA)
What is the most commonly used heat exchanger?
Shell and tube
What are advantages of shell and tube exchangers?
Large surface area in small volume
Good mechanical layout
Well established fabrication methods
Can be constructed from a wide variety of materials
Easily cleaned and maintained
Well established design procedures
What is the equation for heat transport for single phase streams with constant cp and no pressure effect on enthalpy?
Q=mass flowrate * heat capacity * delta T
What is the equation for heat flow when pure components are undergoing a phase change?
Q= mass flowrate times lamda
T-lines for counter-current flows do not what?
Cross
Lines should not approach each other too closely. Why?
As they approach, the area required for heat transfer goes to infinity
What is the closest approach called?
Pinch point
What is the heat transfer rate equation for single pass heat exchangers?
Q = UA((delta T2 - delta T1)/ln(delta T2/delta T1))
What are important assumptions made by the heat flow equation?
U is constant
No heat is lost to ambient environment
If FCph is greater than FCpc above the pinch point what should you do?
Split hot stream
Below the pinch point, if FCpc > FCph what should you do?
Split the cold stream
