Sthe Second - Copy (2)

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DESIGN OF SHELL AND TUBE HEAT

EXCHANGER UTILIZING FLUE GASESFROM CALCINERS (Second review)

VISHNU.R

REG No: ETAKCCT016

M-TECH(ICTM)

ROLL NO: 16

GEC THRISSUR

Internal Guide :Prof. Sunil .A.SAPME , Govt Engg College, Thrissur

External Guide: M.K PrabhakaranDeputy Chief Engineer (Mechanical), TTPL ,

Trivandrum


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Production Layout


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Concentration

Concentrator

Lute

Condenser

Vapor

Separator

Drum

Preheater

Overhead

Tank

Conc.

MeasuringTank

Steam

from

boiler

Steam

out

Vapor in

Vapor + Liquid

Liquor From Concentration

feed tank

140 gpl Ti02

190 gpl Ti02

Cooling Water

Vapor in

Precipitation

VaporRecycled


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GENERAL DESIGN CONSIDERATIONS

The general design considerations are categorized as

Selection of flow path

Construction codes

Tube bundle vibration

Testing / Performance Testing


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Selection of Flow Path

Tube side fluid :

More corrosive

Dirtier at higher pressures.

Shell Side Fluid :

Fluid of high viscosity

Gas.

Construction :

Least expensive is alloysteel with the tube side andcarbon steel on the shellside

Cleaning of inside of tubesis readily done than theexterior surfaces.

For gauge pressures inexcess of 2068 kPa for oneof the fluids, the lessexpensive construction hasthe high-pressure fluid inthe tubes.

Heat-exchanger shutdownsare most often caused byfouling, corrosion , anderosion.


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Construction Codes

Shelland Tube Heat Exchangers for General Refinery Services, API

Standard 660, 4th ed., 1982, is published by the American Petroleum

Institute to supplement both the TEMA Standards and the ASME

Code.

Standards of Tubular Exchanger Manufacturers Association, 6th ed.,1978 (commonly referred to as the TEMA Standards), serve tosupplement and define the ASME Code for all shell-and-tube-type heat-exchanger applications.

TEMA Class R design is for the generally severe requirements ofpetroleum and related processing applications. Equipment fabricated inaccordance with these standards is designed for safety and durabilityunder the rigorous service and maintenance conditions in suchapplications.


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TEMA Class C design is for the generally moderate

requirements of commercial and general process applications,

while TEMA Class B is for chemical process service.

Design pressures and temperatures for exchangers usually are

specified with a margin of safety beyond the conditions expectedin service. Design pressure is generally about 172 kPa (25

lbf/in2) greater than the maximum expected during operation or

at pump shutoff.

Design temperature is commonly 14C (25F) greater than the

maximum temperature in service.


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Tube Bundle Vibration

When plate baffled heat exchangers are designed for higher

flow rates and pressure drops , tube vibrations are found and

cause considerable damage to the equipment in service.

The most effective method of dealing with this problem is

the avoidance of cross flow by use of tube support baffles

which promote only longitudinal flow.


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Mechanism of Tube Vibration

Vortex SheddingThe vortex-shedding frequency ofthe fluid in cross-flow over thetubes may coincide with anatural frequency of the tubes

and excite large resonantvibration amplitudes.

FluidElastic CouplingFluid flowing over tubes causesthem to vibrate with a whirlingmotion. The mechanism of fluid-

elastic coupling occurs when acritical velocity is exceededand the vibration then becomesself-excited and grows inamplitude. This mechanismfrequently occurs in process heat

exchangers which suffervibration damage.

Pressure FluctuationsTurbulent pressure fluctuationswhich develop in the wake of acylinder or are carried to thecylinder from upstream may providea potential mechanism for tube

vibration. The tubes respond to theportion of the energy spectrum thatis close to their natural frequency.

Acoustic CouplingWhen the shell-side fluid is a low-density gas, acoustic resonance or

coupling develops when thestanding waves in the shell are inphase with vortex shedding from thetubes. The standing waves areperpendicular to the axis of thetubes and to the direction of cross-flow. Damage to the tubes is rare.However, the noise can be

extremely painful.


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Testing / Performance testing

Hydrostatic testing for emphasizing visual examination of tube

ends.

Leaking tubes.


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Internal-floating-head exchanger


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Constructional Details

FixedTube Sheet Heat Exchangers

Often used than any other type.

This construction requires tube sheet materials welded with

the shell. Any number of tube passes.

Shell side passes can be one to more. Shells with more than

two shell passes are very rare.

Clearance between baffles and shell.


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Expansion joints

Various types of expansion joints

are used to eliminate excessive

stresses caused by expansion. The

need for an expansion joint is afunction of both the amount of

differential expansion and the

cycling conditions to be expected

during operation.


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Tube Side Construction

Tube side header

The bonnet

Channel

Special high pressureclosures

Tube side passes

Tubes

Manufacturing tolerances

Tube joints

Rolled tube joints

Welded tube joints

Double tube sheet joints


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Shell side Construction

Shell sizes

Heat-exchanger shells are generally made from standard-

wall steel pipe in sizes up to 305-mm (12-in) diameter.

Shell Side arrangements One shell pass

Split flow

Double Split flow

Divided flow


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Pitch

It is the shortest distance between two adjacent tubes fora pattern.


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Design Approach

The design approach of a shell and tube heat exchanger for this

thesis work has been subdivided into two as follows :

Service design

Mechanical designService design involves

Calculation of heat duty

Estimation of U

LMTD Estimation of Total heat transfer area

Decide Exchanger layout

Mechanical design involves the design of individual components

of a STHE.


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Service Design

Calculation of Mass flow rates of flue gases:

From the data collected such as manometer reading ,

temperatures , cd , area and further using temperature

relations and chemical properties of flue gases(eg: Specific

heat) in Perrys CEHB ,

The mass flow rate for exhaust gases was found to be 3.729

kg/s

Heat duty of flue gas : 575.64kW


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Mass flow rate of titanium di oxide:

From the calculated heat duty the mass flow rate of the

titanium di oxide was found to be 1.64 kg/s.

To check the design feasibility :

The aim is to evaporate the water from the titanium di

oxide mixture hence increase the specific gravity from

1.64 to 1.75

Analytically it was estimated that 0.14467 liters of water is

to be evaporated from 1 liter of Ti02 to reach the aim.

Also the heat required to vaporize the water content was

around 351.12kW , which is way lower than the actual

heat duty of the flue gas(575.64) . Hence the design was

confirmed feasible.


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Log Mean Temperature Difference

LMTD= 156.33oC

Total number of tubes needed : From the above collected data , and selecting OD 12

BWG tubes and selecting one inch triangular pitch( from

TEMA hand book) , the total number of tubes required is

1503. The tube side heat transfer coefficient is 68.592 W/m2 K

The shell side heat transfer coefficient is 10.366 W/m2 K


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The overall heat transfer coefficient (Uo) = 8.65 Wm2K

Heat transfer area requires : 459.7m2

The length of tubes : 6.096m

Actual heat transfer area : 548.06m2


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Mechanical Design (MS)

Shell side

Diameter= 1.067 m

Design pressure =

1.05atm

Design Temperature =

97oC

Shell thickness = 5mm

Nozzle thickness = 5mm Nozzle diameter =

125mm

Segmental baffles

25% cut transverse

baffles are used

Spacing = 400mm

Thickness = 6mm

Tube side design

Thickness of tubes =

3.404mm

Tube length : 6.09mm

Tube sheet thickness =

11.04mm

Channel(CS) = 10.55mm

Channel cover= 2mm


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Designed Heat Exchanger Specifications

Shell Side Tube Side

Material : Mild Steel Service fluid : Ti02 pulp

Corrosion allowance : 2mm No. of passes : 1

Service fluid : Flue gas Outside diameter : 19.05mm

No. of passes : 1 Inside diameter : 15.64

Shell diameter : 1067mm Wall thickness : 3.404mm

Inlet temperature : 300oC Tube length : 6.096m

Outlet temperature : 160oC Pitch (equilateral triangle) : 76mm

Segmental baffles : 25 % cut Number of tubes : 1503

Shell thickness : 5mm Inlet temperature : 30oC

Nozzle diameter : 125mm Outlet temperature : 30oC

Nozzle thickness : 5mm Nozzle thickness : 5mm

Baffle spacing : 400mm

Thickness of baffles : 6mm


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Possible flaws associated with analytical

calculations

Due to the large effect from other parameters such as designpressure/corrosion allowance, baffle cuts, seal strips, and soon, tube counts , tube passes etc. are to be used as estimatesonly. Exact tube counts are part of the design package of most

reputable exchanger design software and are normally used forthe final design.

Some of the prominent STHE design softwares are

Aspen One (Aspen Engineering Suite)

Aspen HYSYS/HTFS/HTFS+ (Aspen Engineering Suite),used mostly in Petrochemical Industries.

Chemcad 6/CC-Therm from Chemstations Inc.

Comsol multi-physics from Comsol Inc.


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ChemCad 6 / CC Therm Interface


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Chemcad CC-Therm Design Window

Flow sheet Heat Curve


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Proposed Block Diagrams For New

Concentration Unit

RotaryCalciner

Secondary blower

Primary blower

Combustion Chamber

Atomizing Blower

Concen

trator

Flue gas in

Flue gas out

TiO2 In

TiO2 Out

Cooling Tower

Electro Static Precipitator

Fume StackDraught Fan


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Proposed Block Diagram of New Concentration

Unit

Overhead Tank

ShellandTubeHe

at

Exchanger

(Concentrator)

VaporSeparator

Concentration

Measuring

tank

Condenser

Flue Gas in

Flue Gas Out

Aqueous TiO2

Conc. TiO2


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What else to be calculated ?

Final design using Chemcad CC-therm including rating of

HE.

Cost of proposed concentrator(STHE).

Cost of replaced equipment in concentration process.

New layout area.


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REFERENCES

Perrys Chemical Engineers Handbook , 1999 , The McGraw

Hills Companies Inc.

Standards of The Tubular Exchanger Manufacturers

Association , 1999 , ninth edition.

Design and Rating of Shell and Tube Heat Exchangers using

Chemcad , John Edwards , MNL 032A Issued 29 August 08,

Prepared by J.E. Edwards of P & I Design Ltd, Teesside, UK.


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THANK YOU

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