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KKA 3306 PROCESS AND PLANT DESIGN Lecture 7

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3 types of operations; Adiabatic compression, Staged compression, Isothermal compression. ... when N =1, the equation reduces to adiabatic compression. When N ... – PowerPoint PPT presentation

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Title: KKA 3306 PROCESS AND PLANT DESIGN Lecture 7


1
KKA 3306 - PROCESS AND PLANT DESIGN Lecture 7
By Robiah yunus Faculty of engineering Universiti
putra malaysia Serdang,43400 selangor.
2
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

3
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.

4
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

5
EQUIPMENT SIZING PROCEDURES
  • Heat Exchanger Sizing
  • Phase change operation
  • if area, A is greater than 10000 ft2, use
    multiple heat exchangers.

6
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.

7
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.

8
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

9
Distillation Column Sizing
  • Westerberg Method
  • Determine Tray number and Reflux Ratio

10
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

11
Distillation Column Sizing
  • Westerberg Method
  • Calculate Column Diameter

12
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

13
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
14
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)

15
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

16
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 ?

17
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)

18
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

19
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.

20
EQUIPMENT SIZING
  • Refrigeration
  • Guidelines and Short Cut Model in Analyzing
    Multiple Cycles Refrigeration

21
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)

22
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

23
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)
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