DESIGN FINAL
A/B designation for pumps means
two pumps in parallel - one is a spare
Smaller (<10 m^3) HE's are
usually double pipe
Decision Variables
variables manipulated in order to max/min OF
When is a zones analysis needed in a heat exchanger
when a different heat transfer coefficient is required for different phases (heating liquid, boiling, heating vapor)
Cost for BFW
when steam added and when condensate not returned to boiler plant
How should battery limit symbols be integrated in a PFD
white side of half moods faces the process
Centrifugal Pump
"Constant Head" Pump Good for lower flows/ smaller pressure differences
Positive Displacement Pump
"Constant Volume" pump Good for large flows or pressure differences
Default Heat Exchanger
1-2 Shell and tube heat exchanger (1 shell pass, 2 tube passes)
Reason for running columns at high P
Decrease diameter + allow cooling water to be used in condenser
Mixing vapor and liquid stream
Discouraged because two-phase flow isn't well understood
Mixing liquids
Done in a mixing drum with level control to control outlet flowrate Usually done w/ recycle DO NOT mix vapor + liquid streams
What is the usual objective function in engineering
Econ
Boiling Regimes
Keep temp differences below 50°C
Design Specs for Steam
LPS: 5 barg saturated w/ credit MPS: 10 barg saturated w/ credit HPS: 41 barg, saturated Take credit for steam unless steam is lost in the process
Shell and Tube Parameters
More extreme temperature in the tubes, higher pressure in tubes, corrosive/fouling in tubes, condensing/boiling fluid in shell
Mixing streams
Must be at same pressure + will not be at design flowrates
If temp > 250°C
Need a fired heater
If temp < 40°C If temp > 400 °C
Need refrigerated water Need special MOC
NPSH
Net Positive Suction Head Available must be higher than required
Plotting Optimization should result in ______ curves
Smooth if all variables are continuous
A/B Designation for Pumps
Spare Equipment
Expected in a Design Report for a Stream Table
Stream Number Temp Pressure Vapor Frac Total Mass + Mole Flowrate Component Flowrate
Diagram for Heat Exchanger generated by Aspen
T-Q Diagram - make sure there is no temperature crossover
What is the meaning of T-905?
The fifth tower in unit 9
The best thermodynamic method
The one that fits the experimental data
T-Q Diagram
You cannot cool below boiling temp
What is SRK suitable for
moderate pressures, 1/2 Pcrit
What determines column pressure
temperatures of reboilers and condensers
Topoligical Optimization
changes in arrangement of process equipment - can unwanted by-products/equipment be eliminated?
Pumps are located near
ground level
Flash Separations
Single-state distillation
Desuperheater
Allows steam to be made any any temp
Cooling water
Available at 30°C
What is PR suitable for
Better than SRK for higher pressures
Typical Pipe Characteristics
Can be threaded Connected by fittings Schedule number (thiccness) Nominal Diameter, Outer Diameter
PFD Requirements
Equipment listed at the top Battery-limit symbols (Half moons) for Raw Materials and Products Flags not needed if all streams numbered Basic Control System Horizontal Lines Dominate Vertical Number Streams left to right Add arrows for equipment inlet and change in direction Utility Streams appreviated (lps,mps,hps,bfw,fg,cw,rw) Mixing Tanks ONLY for liquids Condenser shown as partial/total Reactors are vertical
How to account for Frictional Losses
Equivalent Length or Velocity head method
Reason for Large Reflux Ratio
Feed is dilute in more volatile component separation between boilers very close high distillate concentration needed reduce stage numbers
The main thing that can be adjusted in a chemical plant
Flowrate - by changing a valve
How to find tank volume from outlet flowrate
Fout * 10 min holdup * 2 (vapor space)
Typical Heat Transfer Trends
Gas heat transfer bad, liquid better, water better liquid (phase change is best)
General info about azeotropes
Ideal thermo never predicts them concerning polar and "associating" (?) molecules, electrolytes
Cavitation
If fluid is too close to vapor pressure at the pump inlet can cause long-term damage Pumps do not like suckin on vapes
How to increase NPSHa
Increase the heigh difference between the storage tank and pump entrance Increase the initial presusre Decrease the vapor pressure by decreasing the temperature Decrease pipe length Increase pipe diameter
Always ____ before _____
Pump before heating
What equipment should have basic control/ regulation systems
Pumps, tank levels, reactors (temp), valves
What cost must be included with a refrigerant
Refrigeration equipment
Objective Function in Optimization
The thing that is max/min'd
Reactor Requirements
Thermal fluid in cocurrent to minimize hot spots Heat exchanger area and reactor volume must be matched Conversion vs. Selectivity + Kinetics
Boiler Feed Water
Used to make steam
If Pressure < 1 atm or > 10 atm
Vacuum and large equipment More expensive for reinforcement
remedy to thicc column
decrease RR + increase pressure
high (>= 20) reflux ratio suggests
difficult separation
low (<= 20) reflux ratio suggests
easy separation
Reason for running columns at vacuum
ensure temp sensitive components don't degrade + so highest temp steam can be used
Feed location for DC
feed should be at tray with same temp + composition
Column feed pressure must be _____ than column pressure
greater
Correction factor for heat transfer rate in HE's
needed when close approach on T-Q diagram or for heat integration F =1 for constant-temp phase change
MUMNE for Heat Exchanger Integration
obtains minimum utility use config, and min number exchangers
Zoned Analysis needed for HE design when
phase change due to different heat transfer coefficients
Reasons for hot Spot in PFR
reaction is fastest at high reactant concentration, which is at reactor entrance rate of heat gen exceeds rate of heat removal
how to decrease column height
reduce trays + decrease tray spacing
Increasing R/Rmin does:
reduces trays increases reboiler and condenser duties increases dolumn diameter
Multiple shell passes needed in HE when
small approach temps + not needed with phase changes
