minor II 1

EQUIPMENT COSTING

Here we will build the concepts and pursue the next step of determining equipment sizes, capacities, and costs. A well established method developed by Guthrie (1969) will then be used for costing the equipment.

Vessel Sizingvessels include flash drums, storage tanks, decanters

and some reactors. 1. Select vessel volume (V) based on a five-minute

liquid holdup time with an equal volume added for vapor flows. Thus, the formula is given by:

V = 2 [FL τ /ρL]

where FL =liquid flow rate leaving the vessel ρL = liquid density, and

τ = residence time, typically set to five minutes.

2. In addition, we make a few assumptions:• For general costing purposes, the aspect ratio, L/D will

be assumed to be four.• If diameter is greater than four feet (1.2 m) size unit

as a horizontal vessel. (This requires more space but less cost for structural support)

• As a safety factor choose the vessel (gauge) pressure to be 50% higher than the actual process pressure from the mass and energy balance.

• For the desired temperature range, we consider the required materials of construction as shown in Table.

Materials of Construction High Temperature Service

Tmax(oF) Steel950 Carbon steel (CS)

1150 502 stainless steels

1300 4 1 0 stainless steels ;330 stainless steel 1500 430, 446 stainless steels Stainless steels

(SS) (304,321,347,316) Hastelloy C, X Inconel2000 446 stainless steels Cast stainless, HC

Low Temperature ServiceT min (oF) Steel-50 Carbon steel (CS)-75 Nickel steel (A203) -320 Nickel steel (A353)-425 Stainless steels (SS) (302,304,310,347)

Guthrie Material and pressure factors for pressure vessels

MPF = Fm Fp

Shell Material Clad, F m Solid,Fm

Carbon Steel (CS) 1.00 1.00Stainless 316 (SS) 2.25 3.67Monel 3.89 6.34Titanium 4.23 7.89

Vessel Pressure (psig)

Up to 50 100 200 300 400 500 900 1000Fp 1.00 1.05 1.15 1.20 1.35 1.45 2.30 2.50

Heat Transfer EquipmentHeuristics for cost estimations• Consider the counter current, shell and tube heat

exchanger. • Again for sizing and costing, we need to observe the

design criteria for temperature and pressure (Prated = 1.5 Pactual) and observe the appropriate pressure and material factors in costing me exchanger

• Note that phase changes in heat exchangers lead to changes in V and need to be considered more carefully. In this case, we split the exchanger into serial units and calculate V and A for vapor media and for condensing media separately. Thus, the total area is given by: Atotal = Avap + Acon

• Finally, we choose 10,000 ft2 (or 1000 m2) as the maximum exchanger area.

Furnaces and Direct Fired HeatersHere the basic configuration for furnaces is given by a process heater

with a box or A-frame construction, carbon steel tubes, and a 500 psig design pressure. This includes complete field erection. The material and pressure factors for various types of furnaces.

Direct fired heaters is given by a process heater with cylindrical construction, carbon steel tubes, and a 500 psig design.

Guthrie Material and Pressure Factors for Direct Fired Heaters

MPF=Fm+Fp+Fd

Design Type Fd

Cylindrical 1.00 Dowtherm 1.33Vessel Pressure (psig)Up to 500 1000 1500Fp 0.00 0.15 0.20 Radiant Tube Material F m

Carbon Steel 0.00Chrome/Moly 0.45Stainless Steel 0.50

Similarly Guthrie’s factors for HEX and Furnaces are available in the literature

Guthrie Material and Pressure Factors for Heat ExchangerMPF=Fm(Fp+Fd)

Design Type Fd

Kettle reboiler 1.35Floating head 1.00U tube 0.85Fixed tube sheet 0.8

Vessel Pressure (psig)Up to 150 300 400 800 1000Fp 0.00 0.10 0.25 0.52 0.55

Shell/ Tube Material F m

Surface CS/CS CS/Brass CS/SS SS/SS CS/Monel(ft2)Upto 100 1.00 1.05 1.54 2.5 2.0100-500 1.00 1.10 1.78 3.1 2.3500-1000 1.00 1.15 2.25 3.26 2.51000-5000 1.00 1.30 2.81 3.75 3.1

Reactors• For reactor sizing we assume a given space velocity (s

per hr) based on a liquid or gas molar flowrate µ. Then we have:

s = 1/τ= µ (ρVcat)Ρ = molar density at standard temperature

and pressure (1 atm, 273 K) andVcat = volume of catalyst.

• V is calculated based on the void fraction, f, of the catalyst (assume 50%).

• Depending on reactor conditions, we cost the reactor as a pressure vessel, heat exchanger, or furnace.

• Also, for these units use the appropriate material and pressure factors in Guthrie's method.

Distillation Columns• However, in order to cost the vessel, tray stack, and

heat exchangers, we first need to calculate the number of theoretical trays and the reflux ratio.

• Shortcut calculations for these can be performed through the Fenske equation (for minimum number of theoretical trays), the Underwood equation ( for minimum reflux ratio), and the Gilliland correlation that allows us to obtain the actual reflux ration and tray.

• We will start with a 24” tray spacing with carbon steel plate/sieve.

Guthrie Material and Pressure Factorsfor Tray Stacks

MPF = F m + Fs + Ft

Tray Type Ft

Grid (no downcomer) 0.0 Plate 0.0 Sieve 0.0 Valve or trough 0.4Bubble Cap 1.8 Koch Kascade 3.9

Tray Spacing, Fs

(inch) 24” 18” 12"Fs 1.4 2.2 1.0

Tray Material F m

Carbon Steel 0.0Stainless Steel 1.7 Monel 8.9

Absorbers:

Here the calculation procedure be same and NT will be calculated by using Kremer’s rule.•We use a very low efficiency 20%•We will use Guthurie’s data available for the costing of packing etc

Cost EstimationEquipment cost increases non-linearly with the

equipment size or capacity• For pressure vessels, for instance, the service capacity

depends on volume (V), while the cost depends on the weight (W) of the metal (proportional to surface area). For example, for a spherical vessel, we have:

V = π/6 D3 and W = ρM t (π D2)where t is the vessel thickness and ρM is the

metal density. In terms of volume, we have:D = (6V/π)l/3 and W = PM t (πl/3 (6V)2/3)

• with the vessel cost directly proportional to W = k V2/3.

• For cylindrical pressure vessels, we adopt a more general form used by Guthrie:

C= Co (L/Lo)α (D/Do)β

Correlations for pressure vessels are given in Table. Guthrie also considers separate correlations for storage vessels of various geometries.

• For preliminary design, we will only use the median data. Data for the correlations taken from Guthrie are given in Table. The cost data in Tables next two tables are given in terms of mid-1968 prices. In order to update these costs, we apply an update factor to account for inflation. The update factor is defined by:

UF = present cost index base cost index

Base Costs for Pressure Vessels

Equipment Type Co($) Lo(ft) Do(ft) α β MF2/MF4/MF6/MF8/MF1OVertical fabrication 1000 4.0 3.0 0.8 1.05 4.23/4.12/4.07/4.06/4.021≤D ≤ 10 ft,4 ≤ L ≤ 100ftHorizontal fabrication 690 4.0 3.0 0.78 0.98 3.18/3.06/3.01/2.99/2.961≤D ≤ 10 ft,4 ≤ L ≤ 100ft  Tray stacks 180 10.0 2.0 0.97 1.45 1.0/1.0/1.0/1.0/1.02≤D ≤ 10 ft,1 ≤ L ≤ 500ft

• MF2 Up to $200,000• MF4 $200,000 to

$400,000 • MF6 $400,000 to

$600,000 • MF8 $600,000 to

$800,000• MFI10 $800,000 to $1,000,000

Bare module cost is modified by the following factors:• Uninstalled cost = (BC) (MPF)• Installation = (BC) (MF) - BC = BC (MF - 1)• Total cost = BC (MPF + MF - 1)• Updated bare module cost = UF (BC) (MPF + MF - 1)

Finally, we do not treat contingency costs and indirect capital costs as Guthrie does. Instead for preliminary designs we apply overall indirect cost factors and a flat 25% contingency rate after all the equipment is costed.

Calculation of costs for a distillation column with condenser, reboiler and utility cost

• We have the following data:Column diameter = 0.82 m (2.7 ft.)Column height = 19.2 m (63 ft.)Tray Stack Height = 13.2 m (24 in. spacing)MOC= CS working pressure = 100 kPa

• we have F m and Fp as well as the MPF equal to 1.0. • Also using last table and formula C= Co (L/Lo)α

(D/Do)β we have an FOB cost (BC) of about $8350.

• The resulting module factor (MF) is 4.23 and the update factor is UF = 359/115 = 3.12

• The bare module cost (BMC) is then obtained from:BM(vessel) = UF (MF + MPF - 1) (BC) = $110,000

• The tray stack (bubble cap) is also calculated from table with L tray stack = (N-1) tray spacing (0.6 m or 24”)For N= 23 we have L= (23-1) 0.6 (2ft) = 13.2 m or 44 ft and D =

2.7 ft. (0.82 m) we have BC = $1150• Assuming bubble cap trays with 24" spacing, we have

MPF (Fs + F m + Ft) = 2.8We have the following cost:

BM(tray) = UF (MPF) (BC) = $ 10,000

The condenser can be sized and costed as follows. The overall heat transfer coefficients can be estimated from Guthurie’s

data and Perry's Handbook. For an acetone water (shell) 1 water (tube) system, we have U = 100 -

200 Btu/hr. ft2°F and we select U = (100) (5.678) = 567.8 W/m2 K. Tout = 319 K, Tin = 300K,

Also, we have:• ΔTlm = [(329 - 300) - (329 - 319)]/ In(29/10) = 17.8 K • Calculate A• A = Qc/ U ΔTlm = 122 m2 - 1300 ft2 < 10,000 ft2 (max.)

From data table, C = Co (S/So)

the base cost (BC) = $10,800 and for a floating head, carbon steel heat exchanger MPF = 1.0 and the module factor (MF) = 3.29.

Hence, the bare module cost is:• BMC = 3.12 (10800) (3.29) = $110700 ~ $111,000

• Sizing the reboiler first requires an overall heat transfer coefficient.

• For a water (shell) / steam (tube) system we have from data table, U = 250 - 400 Btu/hr ft2°F and we select U = 250 = 1420 W/m2 K. Also, ΔTlm = (459 - 385) = 74 K

• Calculate area:Areb = Qreb/U ΔTlm = 15.8 m2 = 170 ft2

• From data table, we have BC = $2900, MPF = 1.45 (for a slightly higher pressure and carbon steel kettle reboiler) and MF = 3.29.

• The resulting bare module cost becomes:BMC = (3.12) [(3.29 + 1.45 - 1) (2900)]

= $33,840 - 34,000

CostsVessel (19.2m x 0.78m) $ 110,000Tray stack (13.2m x 0.78m) $10,000Condenser $111,000Reboiler $34,000

• Total $265,000

Utility Costs $ 6,000/yr Cooling water Steam @ 150 sig $ 1,468,000/yr.

• Total $ 1,474,000/yr

Capital CostLang Factor Technique : Cost to build a major expansion to an existing

chemical plantCTM = FLang 1Σn Cp,i

Equipment module Costing• Factors Affecting : Equipment type, MOC, System Pressure• Use BARE MODULE COST: Use direct and indirect costs

CoBM = CP Fo

BM

To calculate FBM we have to know the value of FM and FP , both can be either calculated from the correlations or figures available

Estimate of actual BC for equipment

Five step algorithm1. Obtain the purchase cost, CP for the desired piece of

Equipment using suitable figure2. Find the material of construction factor, FM and pressure

factor, FP from appropriate figures and tables

3. Find BARE MODULE FACTOR, FoBM

4. Calculate the BARE MODULE COST, CoBM

5. Update the cost from CEPCI, 1996 to the present

Total Module Cost

• Total Module Cost: cost of small to moderate expansions or alterations to an existing facility

CTM = 1.18 1Σn COBM,i

Direct Cost Equipment free on board cost CP

Materials required for installation αM CM

Labor to install equipment and material CL = (CM + CP)αM

Total Direct CDE = CP + CM + CL = (1.0 + αM )(1.0+ αL)

Bare Module CBM= CDE + CIDE

Contingency fee Contingency Ccont = αCont CBM

Contractor fee Cfee = αCont CBM

Bare Module Cost Factor FBM= (1.0 + αM )( 1+ αL + αFIT + αLαO + α E)

Total Module = CTM = CBM + Ccont + CFee

Indirect CostFreight, insurance and taxes CFIT

Construction overhead CO

Contractor engineering expenses CE

CIDE = CFIT + CO + CE = (1.0 + αM )( αFIT + αLαO + α E)

Auxiliary facilitiesSite development CSite

Auxiliary building CAux

Offsite and Utilities Coff