Design Heuristics1. Select raw materials and chemical pathways to avoid storage and handling of hazardous

materials2. Use an excess of one reactant to completely consume the other reactant3. When nearly pure product are required eliminating inert species before the reaction

operation .If the separation is easily achievable. Do not do this when large exothermic heat is to be removed

4. Introduce purge streams for species that does not have an escape route5. Do not purge valuable or hazardous species 6. Recycle to extinction in reversible reactions7. For series reactions manipulate temperature and pressure to obtain better yield8. Consider reactive separation for reversible reactions9. Separate liquid mixtures using separators L-L extraction distillation est.10. Attempt to condense vapor with cooling water 11. Use 9 and 10 when you have a mixture of vapor and liquid12.

13.

14. to control high endothermic heat of reaction use ,excess reactant ,hot shot and inert diluents15. for small endothermic heat of reaction consider jacketed vessels or inter heater

To remove a highly-exothermic heat of reaction, consider the use of…

Heuristic 12:

excess reactant

cold shots.

an inert diluent

For less exothermic heats of reaction, circulate reactor fluid to an external cooler, or use a jacketed vessel or cooling coils. Also, consider the use of intercoolers.

Heuristic 13:

16. Cool vapor and then pump it avoid compressorsTutorial for high pressure separators and material and energy balance Tutorials

Property prediction methods

E?

R?

P?

Polar

RealElectrolyte

Pseudo & Real

Vacuum

Non-electrolyte

Braun K-10 or ideal

Chao-Seader,Grayson-Streed or Braun K-10

Peng-Robinson,Soave-Redlich-Kwong,Lee-Kesler-Plocker

Electrolyte NRTLOr Pizer

See Figure 2

Polarity

R? Real or pseudocomponents

P? Pressure

E? Electrolytes

All Non-polar

Estimating properties in Unisim Tutorial LV EQUILIBRIUM

Separation ProcessesAbsorbers and strippers

1. Calculate K

2. Calculate L min or V min

where:– Lin and Vin are the entering molar liquid and vapour flow rates, respectively.– (1 – fAK) is the fraction of the key component in the feed gas to be absorbed.– (1 – fSK) is the fraction of the key component in the feed liquid to be stripped.

P?

ij?

ij?

LL?P < 10 bar

P > 10 barPSRKPR or SRK with MHV2

Schwartentruber-RenonPR or SRK with WSPR or SRK with MHV2

UNIFAC and its extensions

UNIFAC LLE

PolarNon-electrolytes

No

Yes

Yes

LL?NoNo

Yes

Yes

NoWILSON, NRTL,UNIQUAC and their variances

NRTL, UNIQUACand their variances

LL? Liquid/Liquid

P? Pressure

ij? Interaction Parameters Available

K K=mole fraction of the key component in the gasmole fraction of the key component in the absorbent in equilibrium with the gas

Lmin=KKV in (1−φA K )

Vmin=Lin

K K(1−φS K )

3. Multiply L min or V min by 1.5 to get L or V4. Calculate Aek o Sek

AeK = L / KKVSeK = KKV/L

5. Calculate actual Number of stages N

6. Calculate fi A for other non key components

Tutorial Design of Absorbers

Design of Distillation columns

1. Assume a 99 mol % recovery of the light key in the distillate and the heavy key in the bottoms (unless more specific information is available).

2. Select the distillate and bottoms column pressures.

φ AK=AeK−1A

eK

N+1−1

φSK=SeK−1SeK

N+1−1

3. Estimate the number of equilibrium stages and reflux ratio by the FUG method (e.g., using Unisim’s “Shortcut Column”).

4. Use Unisim’s Rigorous Column Solver to obtain a more accurate design of the number of stages and reflux ratio.

5. Calculate the plate efficiency (trayed column) or HETP (packed column).

6. Select the tray spacing (typically 2 ft.) and calculate the column height, H.

7. Compute the tower diameter, D, using Fair’s correlation for flooding velocity or Unisim’s Tray Sizing Utility.

Tutorial operating pressure for distillation columns Design of a distillation column with rigorous solver

Changes in column operations

Overall plate efficiency E0 is used to estimate actual number of trays

Tray sizing utility in Unisim instructions

Bubble point V.F = 0

Dew Point V.F = 1

Nactual=Nequilibrium

E0

1. Open your case study. If the green calculation light is not on, turn it on. 2. Click on Tools, Utilities, and add the tray sizing utility.3. Click on Select TS (tray section), click on a converged column (preferably a distillation column), Main

TS object, OK.4. Click on Add Section.5. Click on Design Specs. Hit F1. This should give you the help page for Setting Tray Sizing

specifications. Read this page carefully along with the information windows on the underlined green items. Click on each type of internals in item 7 and select that most suitable for your column. For item 8, you want to select the design mode to let this utility select optimal values. For sieve, valve & bubble-cap trays, note that the recommended number of flow paths and the tray spacing depend on the tower diameter. The tower diameter, in turn, depends on the number of flow paths, so you will probably have to iterate to achieve the recommended values.

6. Return to the Tray Sizing Specs page and enter any required values. This should cause the utility to calculate and converge. If weeping occurs in a sieve-tray column, switch to valve trays.

7. Click on Performance Results to see the calculated results. See also the Performance Plots. If necessary to reach recommended values (from help in 5 above), return to the Tray Sizing Specs page and make the required changes.

8. When you are satisfied with the results, from the Performance Results copy the column diameter, height, percent of flooding, and total pressure drop (bottom to top, Section Delta P). If you have used 100% column efficiency, to get the actual pressure difference you’ll have to divide by a realistic column efficiency and add a safety factor (see the heuristics listed above and Table 14.6 in the 7 th edition of Perry's Handbook). Return to the Column Design Connections page, and adjust either the top and/or bottom pressure to give the total pressure drop you’ve just determined. Return to the utility Performance Results. Note that the pressure drops and diameter(s) will have changed slightly.

9. Go to File, Print, and print out the first page (Tray Results) of the performance results.10. Click on Performance Plot, and print out plots of the Flow and Delta P.11. Compare the above results with those calculated using appropriate heuristics (e.g., % flooding,

diameter, height, height/diameter, pressure drop / tray, etc.). If you see any strong discrepancies, correct them in the Tray Sizing Utility Design Specs. If the height/diameter exceeds the value in heuristics, you will probably have to break the column into two parts. If you do this, make certain to account for the change in hydrostatic head for the liquid flowing between the two parts. (Draw a diagram to clarify your thinking.)

12. Make certain you have recorded the number of actual (not theoretical with 100%) trays, the top and bottom pressures, tower diameter and tower height, all corrected for tray efficiency and safety factor. You will need these to estimate the cost of installing and operating the column.

13. Repeat using the tray efficiency entered into the column calculations. Double-click on the column, enter the actual number of trays (without the safety factor) on the Design Connections page, and the efficiencies on Parameters Efficiencies. Make any changes required to get convergence.

14. Packed columns : Do NOT use tray efficiencies for packed columns. The height is equal to the number of trays times the HETP (Height Equivalent to a Theoretical Tray); this substitutes for the tray efficiency in tray columns. Add a safety factor to the height, say 10%.

Purchase costs of pressure vessels and separation towers (pg 573-579)

Cp = FMCV + CPL

CP = purchase cost of empty vessel including nozzles, manholes supports, platforms and ladders

Cv = Cost of empty vessel in carbon steel excluding platforms and ladders

FM = Material of construction factor.

Purchase cost of trays

CT = NTFNTFTTFTMCBT

CBT = base cost for sieve trays at a CE cost index of 500

NT = number of trays

FNT = factor depending on the number of trays

FTT = factor accounting for the type of tray

FTM = factor correcting for the material of construction

Purchase cost of packing

Cost of packings = VpCPK + CDR

VP = volume of the packing in ft3

CPK = installed cost of packing in $ per ft3

CDR = cost of high performance liquid distributors and redistributors

Total purchase cost

CTT=Cost of packings + CT + Cp

Atmospheric vessels

1. Calculate the design pressure, Pd (> operating pressure)

2. Calculate the design temperature (operating temperature + 50°F)

3. Calculate the maximum allowable stress, S, for the material of construction at the design temperature.

4. Calculate the shell wall thickness, tp, in the absence of corrosion, wind, and earthquake considerations.

5. For vertical vessels, calculate the additional thickness, tw, to withstand the wind load earthquake at the bottom of the column.

6. Calculate the average wall thickness, tV = tp + tw/2.

7. Add a corrosion allowance to tV to give tS.

8. Calculate the vessel weight, W, including the two heads, based on ts.

9. Calculate the empty vessel cost, CV (or read from chart)

10. Multiply CV by the material of construction factor, FM, and add the cost of platforms and ladders, CPL

Vacuum vessels

1. Calculate the design pressure, Pd (> operating pressure)

2. Calculate the design temperature (operating temperature + 50°F)

3. Calculate the modulus of elasticity, EM, for the material of construction at the design temperature.

4. Calculate the shell wall thickness, tV.

5. Add a corrosion allowance to tV to give tS.

6. Calculate the vessel weight, W, including the two heads, based on ts.

7. Calculate the empty vessel cost, CV (or read from chart)

8. Multiply CV by the material of construction factor, FM, and add the cost of platforms and ladders, CPL

Heat exchangersHeat transfer coefficient

ΔTm=ΔT LM=ΔT 1−ΔT 2

ln (ΔT 1/ΔT 2 )1

U clean= 1Udirty

−(R f , o+R f ,i )

where FT is a correction factor less than 1, which depends on two parameters, R and S.

use chart to determine Ft

Designing reboilers

• When steam is used for heating the reboiler, the entering steam must be specified as all vapor (vapour fraction = 1), and either P or T but not both.

• The exiting water should be specified as all liquid (vapor fraction 0) at a P slightly lower than the entering P (e.g., 1.5 psi lower).

• The steam flow rate should not be specified, as UniSim will calculate it from the heat required by the process stream and the change in specific enthalpy of the steam/water.

• Select a reasonable steam pressure or temperature. Steam is usually available at temperatures between 220 and 450ºF.

• Create a Fluid Package Basis for your desired heating fluid (e.g., ASME Steam) and make sure this basis is selected for the side of the heat exchanger where the heating fluid flows.

Designing Condensers

• When a condenser is cooled by water going to steam, the entering boiler feed water should be specified as all liquid (vapour fraction = 0) at a specified P or T but not both.

• The exiting steam should be specified as all vapor (vapour fraction = 1) at a slightly lower P (e.g., 1.5 psi lower).

ΔTm=FT ΔT LM for counter−current flow

S=T cold out−T cold inT hot in−Tcold in

R=T hot in−T hot outT cold out−T cold in

Q=UAFT ΔT LM

• When a condenser is cooled by a refrigerant, such as ethane or ammonia, the entering refrigerant should be specified as all liquid at a high pressure and the exiting refrigerant as all vapor at a much lower pressure. (See, for example, Perry's 7th page 11-77.)

• When cooling water is used for a condenser, specify T and P, but not the vapour fraction, since the cooling water is not saturated.

• Create a Fluid Package Basis for your desired cooling fluid (e.g., ASME Steam) and make sure this basis is selected for the side of the heat exchanger where the heating fluid flows.

Tutorials heat exchangers

Purchase cost of heat exchangers (page 570-572)

Shell and tube

1. Calculate the base cost, CB, based on the tube outside surface area, A, using an equation or chart. Base case = ¾ or 1-in O.D., 16 BWG carbon steel tubes, 20 ft long, square or triangular pitch, carbon-steel shell, shell-side pressure up to 100 psig

2. The cost of a specific exchanger is then calculated from:

CP = FPFMFLCB

CB = base cost at a CE cost index of 500FP = pressure factor based on the shell-side pressureFM = materials of construction factorFL = tube length correction

Double pipe and

1. Calculate the base cost, CB, based on the outside surface area of the inner pipe, A, using an equation or chart. Base case = carbon-steel construction, pressure up to 600 psig

2. The cost of a specific exchanger is then calculated from:

CP = FPFMCB

CB = base cost at a CE cost index of 500FP = pressure factor based on the shell-side pressureFM = materials of construction factor

Reactors How to set up heating and cooling in Unisim

1. Enter all known conditions for the reaction kinetics, including the Catalyst Data on the Reactions Overall page and the tube diameter & wall thickness and void fraction on the Ratings page.

2. With the calculator turned off, guess values for Tube Volume and Length (do not specify the number of tubes) on the Ratings page, T & P for the process stream inlet & outlet. Turn the calculator on. If necessary, adjust these parameters to get a reasonable conversion.

3. Unspecify the exit pressure (or pressure drop). On the Design Parameters page click on the Ergun Equation button. If the pressure drop is too high, increase the reactor volume and/or decrease the tube length.

4. Turn off the calculator. Select a water-steam temperature corresponding to one of the standard steam pressure values, ~150oC, ~190 oC or ~253 oC . Enter this as the Inlet Temp on the Design Heat Transfer page. (The "Heat Medium" is actually the cooling medium, i.e. boiling water, and is on the shell side.) For Wall Heat Tran enter a reasonable value for boiling heat transfer (e.g., 200 Btu/h.ft2.oF). For tubes packed with solid catalyst particles, use an appropriate value such as ~200 kJ/h-m2-oC. For tubes containing only a fluid, use the default values for the Standard Tube Side Heat Transfer (A=1.6, B=0.51, C=1/3). (Alternately, you can use an equation shown in Table 17.18 in Walas.)

5. Turn on the calculator. When the calculations have converged, check the temperature profiles on the Performance Conditions Plot. If the coolant temperature varies significantly, increase the coolant flow and heat capacity until it is constant. If you find that this lowers the process temperature in the reactor too much, increase the initial coolant temperature to a higher standard steam pressure, even if this is higher than the process feed temperature.

6. When you are satisfied with the result, record the duty. This is the heat removed in formation of steam. Calculate the amount of steam produced by dividing the duty by the latent heat of evaporation of saturated water at this temperature.

How to make a plug-flow reactor isothermal, calculate yield, and prepare a case study with two independent variables

Setting the reactor outlet temperature equal to a specified inlet temperature

1. Reload a converged reactor into HYSYS.2. On the Design, Heat Transfer tab select Direct Q Value for the SS Duty Calculation Option. Select

either Heating or Cooling and name the energy stream. Leave the Duty unspecified (<empty>; for an adiabatic reactor this would be set to 0).

3. On the Worksheet Conditions tab set the outlet temperature equal to the inlet temperature.

Unfortunately, if the inlet temperature is changed the outlet temperature must be changed by hand in this method. To make the reactor automatically isothermal, use the following procedure:

1. On the pfd, double click on the reactor outlet stream. Unspecify the reactor product temperature.

2. Using the palette, insert a set (S) icon above the reactor.3. Double click on the set icon to open it. 4. On the Connections page, rename this object "Set isothermal" (without the quotation marks). Set

the Target Variable to the reactor product T and the Source the reactor feed.5. On the Parameters page, set the multiplier to 1 and the offset to 0.6. Close the Set menu and turn on the green calculate signal if it's not already on. The pfd should

quickly recalculate and converge.

Calculating the yield

1. Insert a spreadsheet into the pfd just below the reactor (see "help, index, spreadsheet, adding" for instructions on how to do this).

2. On the Connections page, rename the spreadsheet "Yield spreadsheet" or "yield calculator."3. Make cell A1 of the Imported Variables the molar flow rate of desired product in the reactor

effluent, A2 the molar flow rate of limiting reactant in the reactor feed, and A3 the flow rate of the limiting reactant in the reactor effluent.

4. Click on the Spreadsheet tab. The values of the above three variables should be in black in their respective cells.

5. Click on cell A4. Set Variable Type to “unitless,” Variable to "yield," and enter the formula "=a1/(a2-a3)" in the bar just below Variable. This should result in placing the value of the yield in cell A4 in red. Make certain "Exportable" is checked.

6. Close the spreadsheet menu.

Preparing a case study with excess reactant and temperature as two independent variables

1. Open the Data Book.2. Add yield from the Yield spreadsheet to your list of Variables.3. Add a new Case Study entitled "Yield vs excess reactant & T," with the yield as the dependent

variable and the excess reactant flow rate and reactor temperature as independent variables.4. Select realistic bounds for the two independent variables. 5. Start the calculations and be patient while they are completed. Print out the resulting graph.

Tutorial Reactors

Pumps and compressorsDesign of Expanders and compressors

Work of a single stage per unit mass

W ad=γ

(γ−1 )RT1M [( P2

P1)

(γ−1 )γ −1]

The adiabatic discharge Temperature

where P1 = suction absolute pressureP2 = discharge absolute pressureT1 = suction temperature (K)g = Cp/Cv M = gas molar mass

For N stages assuming the gas is cooled back to original temp after each stage

where P2 / P1 = overall pressure ratio

T 2, ad=T 1( P2

P1 )(γ−1 )γ

W ad=Nγ

(γ−1 )RT1M [( P2

P1)

(γ−1 )Nγ −1]

T 2, ad=T 1( P2

P1 )(γ−1 )Nγ

The compressor efficiency, h, is given by:

The power required by a single stage

where PB = power, kWq0 = gas volumetric flow rate, std m3/s, evaluated at 0ºC and 100 kPa T1 = suction temperature, K

Tutorial Compressors

Pumps

Total fluid head H

Pump output or WHP

where Q = capacity (gallons/minutes) HT = total differential head (ft) r = density of the pumped liquid rw = density of water

η=Theoretical ( isentropic ) work Actual work

=Fluid powerTotal (brake) power

PB=0 .371T 1 γq0

(γ−1 ) η [(P2

P1)

(γ−1 )γ −1]

H=z+ Pρg

+ V2

2 g

WHP=QH T ρ

3960 ρw

Brake horse power BHP obtained from pump curves

Pump efficiency

Power can also be expressed by

where F = molar flow rate

v = molar volume

Tutorial Pumps

1

212 NNQQ

1

212 DDQQ

2

1

212

NNHH

2

1

212

DDHH

BHP=QHT ρ

3960ρwηP

ηP=WHPBHP

W=Fv (ΔP )

Costing

Compressors (pg565-570)

1. Calculate the base cost, CB, based on the consumed horsepower PC using an equation or chart.Base case = cast iron or carbon steel construction with electric motor drive

2. The cost of a specific compressor is then calculated from:

CP = FDFMCB

CB = Base cost at a CE cost index of 500FD = Drive type factor (FD = 1.15 for a steam turbine drive and FD = 1.25 for a gas turbine drive) FM = Materials of construction factor (FM = 2.5 for stainless steel and FM = 5.0 for nickel alloy

Pumps (pg 559-565)

Size factor S

Purchase cost

CP = FTFMCB

WhereCB = base cost at a CE cost index of 500FT = Type factor (Table 22.20 in Seider et al.)FM = materials of construction factor (table22.21 in Seider et al.)

Power consumed by pump motor

where Q = capacity (gal/min)

H = pump head (ft)

r = density of the pumped liquid (lbs/gal)

hP = pump fractional efficiency

hM = motor fractional efficiency

‘

S=Q (H )0 . 5

PC=WHPηPηM

=BHPηM

= QH ρ33 ,000ηP ηM

Purchase cost of motor

CP = FTCB

CB = base cost at a CE cost index of 500FT = Factor based on enclosure type and rpm (Table 22.22 in Seider et al.)