KKA 3306 PROCESS AND PLANT DESIGN Lecture 7

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KKA 3306 - PROCESS AND PLANT DESIGN Lecture 7
By Robiah yunus Faculty of engineering Universiti
putra malaysia Serdang,43400 selangor.
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EQUIPMENT SIZING

• INTRODUCTION
• economic analysis of a process requires knowledge
  of capital and operating costs.
• capital costing is based on equipment sizes,
  capabilities and associated costs.
• In preliminary design, direct and non-iterative
  correlations are used in sizing of equipment
  units I.e. using Guthries method
• simplified sizing and costing are at 25 to 40
  level of accuracy

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EQUIPMENT SIZING PROCEDURES

• Vessel Sizing
• flash drums, storage tanks, decanters, selected
  reactors
• procedures
• calculate vessel volume (V)
• V 2 FL t/rL
• where FL liquid flow rate, t residence
  time (5 min) and rL liquid density
• length/diameter ratio, L/D 4
• If D gt 1.2 m, use horizontal vessel
• Pactual 1.5 times Pdesign
• Select materials based on max. operating
  temperature.

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EQUIPMENT SIZING PROCEDURES

• Heat Exchanger Sizing
• procedures
• calculate area, A
• A Q/UDTlm
• where Q heat duty, U heat transfer
  coefficient (Table 4.3) and DTlm is given by

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EQUIPMENT SIZING PROCEDURES

• Heat Exchanger Sizing
• Phase change operation
• if area, A is greater than 10000 ft2, use
  multiple heat exchangers.

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EQUIPMENT SIZING PROCEDURES

• Furnaces and Direct Fired Heaters
• For preliminary design, use Guthries method.
• Based on Material and Pressure Factor (MPF) (see
  Table 4.6)
• basic configurations
• a box or cylindrical construction with carbon
  steel tubes at 500 psig design pressure.

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EQUIPMENT SIZING PROCEDURES

• Reactors
• Determine the volume of reactor from
• V Vcat/(1-e) (e 0.5)
• s 1/t m / (r Vcat)
• Depending on reactor conditions, we may cost the
  reactor as either pressure vessel, heat
  exchangers or furnace based on its MPF.

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EQUIPMENT SIZING PROCEDURES

• Distillation Column
• Column Vessel Design parameters
• Height, diameter and number of trays
• Design of tray stacks - Guthries method
• based on MPF values ( Table 4.7)
• Use Fenske - Underwood-Gilliland methods to
  determine Theoretical R and N or
• Use Westerberg method

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Distillation Column Sizing

• Westerberg Method
• Determine Tray number and Reflux Ratio

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Distillation Column Sizing

• Empirical Method
• Minimum Number of Stages
• Fenske Equation
• Nm lnzlk/(1-zlk) /(1-zhk)/zhk/lnalk/hk
• ln xlk/xhkdis xhk/xlkbot /
  lnalk/hk
• Minimum Reflux
• Underwood
• Erbar-Maddox (Gilliland) Correlation

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Distillation Column Sizing

• Westerberg Method
• Calculate Column Diameter

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Distillation Column Sizing

• Westerberg Method
• 3) Determine Total Column Height
• Tray stack height (N - 1) x 0.6 m
• Extra feed space 1.5 m
• Disengagement Space 3.0 m
• Skirt height 1.5 m
• _____________________________________
• Total Height
• Nactual N /0.2
• 4) Calculate Qcond, Qreboiler

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EQUIPMENT SIZING PROCEDURES

• Absorption column
• Column Vessel Design parameters
• Height, diameter and number of trays
• The sizing procedures are similar to distillation
  with the exception of
• N - from Kremsers
• Nactual N /0.2
• Pumps - for pumping (P ) liquids
• Wth V DP
• Wb m DP/( r hp hm)

0.9
0.5
viscosity
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EQUIPMENT SIZING

• Compressors and Turbines
• Ideal compression work, W
• W m Hv(P2, T2) - Hv(P1, T1)
• For ideal gas,
• W mCP(T2 - T1) m(g/(g-1 )R (T2 - T1)
• but g CP / Cv and g 1.4 (Ideal)
• For an ideal, adiabatic isentropic compression
• T2 T1 (P2/P1) (g--1/g )
• W m(g/(g-1 )R T1(P2/P1) ((g-1)/ g)-1
• Wb W/ hc hm and hc 0.8
• hm 0.9 (electric)
• hm 0.8 (turbine)
• Maximum Wb 7.5 MW (actual)

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EQUIPMENT SIZING

• Staged Compressors.
• 3 types of operations Adiabatic compression,
  Staged compression, Isothermal compression.
• Staged compression is able to increase a desired
  gas pressure with less work by having
  inter-cooling after each compression stage

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EQUIPMENT SIZING

• Staged Compressors.
• For fixed number compressors ,N, minimum work
  occurs when all compression ratios are equal
• P1/P0 P2/P1 P3/P2 P4/P3 PN/PN-1
  (PN/P0)1/N
• Work required
• W m N (g/(g-1 ))R T0 (PN/P0)(g-1)/g N - 1
• when N 1, the equation reduces to adiabatic
  compression
• When N --gt?
• W m R T0 ln (PN/P0)
• Trade-off between work (operating cost) and
  compressor cost (capital cost), since as N ?, W ?

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EQUIPMENT SIZING

• Reciprocating Compressors.
• Reciprocating compressor perform work and
  pressure change through a piston and cylinder
  (change in volume)
• Best for low capacities and high changes in
  pressure.
• Work required
• W m (g/(g-1 ))R T0 (PN/P0)(g -1)/g - 1/
• 1 - ( c (PN/P0)1/g - 1
• where c V4/(V2 - V4)
• clearance factor (0.05 to 0.10)
• Compressor selection depends on gas flow rates
  and DP (Refer to Ulrich or Perrys handbook)

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EQUIPMENT SIZING

• Refrigeration
• If any process stream is to be below 300K,
  refrigeration is required.
• Refrigeration cycle and its phase diagram.
• COP Q/W , select COP 1.4
• Qc W Q 5/4 Q
• Some industrial applications require moderately
  low temperature which involves large temperature
  change. Hence it requires multiple cycles, N

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EQUIPMENT SIZING

• Refrigeration
• Rules in selecting refrigerant and cycle
  conditions
• Refrigerant , R must always be below its critical
  temperatures and pressures
• Tcond, max 0.98 TcR
• If cooling water is used as refrigerant, then
• Tcond, max gt TCW DTmin
• In the evaporator
• Tevap gt T boil,R
• Pevap gt 1 atm
• Choose DTmin around 5K for both condenser and
  evaporator.

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EQUIPMENT SIZING

• Refrigeration
• Guidelines and Short Cut Model in Analyzing
  Multiple Cycles Refrigeration

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EQUIPMENT COSTING

• Biegler, Grossman and Westerberg
• Process Equipment
• BC Co (S/So)a (Table 4.12)
• Cylindrical Pressure Vessel
• BC Co (L/Lo)a (D/Do)b (Table 4.11)
• Updated Bare Module Cost (BMC)
• BMC UF(BC)(MPF MF -1)
• UF Update Factor (CE Plant Index)
• Present Cost Index/Base Cost Index
• MPF From Equipment Sizing
• MF Module factor
• Fixed Capital BMC (10.250.4)

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EQUIPMENT COSTING

• Sinnot (Vol 6)
• Purchased Equipment Cost, PCE
• PCE BC (from graph) x MF x PF
• (Graphs 6.3 to 6.6)
• Updated PCE/Plant Cost
• Use Figure 6.1
• Fixed Capital Cost using Langs Factorial Method
• PPC PCE (1 ?1 ?2?3 . . . ?9)
• Fixed Capital (FCC) PPC (1 ?10
  ?11?12)
• Working Capital 10-20 of FCC
• Total Capital Investment FCC WCC

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ECONOMIC EVALUATION

• OPERATING/MANUFACTURING COSTS
• Fixed Costs (A)
• Maintenance 5-10 of FCC
• Operating Labor From ME
• Laboratory Costs 20-23 of Item 2
• Supervision 20 of Item 2
• Overheads 50 of Item 2
• Capital Charges 1 5 of FCC
• Local Taxes 2 of FCC
• Insurance 1 of FCC
• Royalties (License Fees) 1 of FCC
• Variable Costs (B)
• Raw Materials From ME
• Utilities From ME
• Other Materials 10
  of Item 1
• Shipping and packaging Negligible
• Direct Production Costs A B
• Indirect Production Costs C 0.25(AB)