HEAT EXCHANGERS Prepared by Bob Heaslip KESCO For Queens University CHEE 470 – Fall 2008 CONTENTS 1 INTRODUCTION TO HEAT EXCHANGERS .....................................................................................................................1 2 HEAT EXCHANGERS TYPES............................................................................................................................................3 2.1 DOUBLE PIPE HEAT EXCHANGERS......................................................................................................................4 2.2 HAIRPIN HEAT EXCHANGERS................................................................................................................................5 2.3 PLATE & FRAME HEAT EXCHANGERS.................................................................................................................6 2.4 SPIRAL PLATE HEAT EXCHANGERS....................................................................................................................8 2.5 SPIRAL TUBE & HELIFLOW HEAT EXCHANGERS...............................................................................................9 2.6 AIR COOLED HEAT EXCHANGERS......................................................................................................................10 3 TEMA TYPE SHELL & TUBE HEAT EXCHANGERS.....................................................................................................12 3.1 SHELL & TUBE HEAT EXCHANGER COMPONENTS.........................................................................................13 3.2 TUBES.......................................................................................................................................................................14 3.3 TUBE LAYOUT.........................................................................................................................................................16 3.3 TUBESHEETS..........................................................................................................................................................19 3.4 TEMA DESIGNATIONS...........................................................................................................................................19 3.5 SHELL.......................................................................................................................................................................21 3.6 BAFFLES..................................................................................................................................................................23 3.7 SHELL SIDE NOZZLES AND IMPINGEMENT PROTECTION.............................................................................25 3.8 TUBE SIDE CHANNELS..........................................................................................................................................26 4 SHELL & TUBE HEAT EXCHANGER ARRANGEMENTS ............................................................................................27 4.1 FLOATING HEAD HEAT EXCHANGERS...............................................................................................................27 4.2 FIXED TUBESHEET HEAT EXCHANGERS..........................................................................................................27 4.3 U-TUBE HEAT EXCHANGERS...............................................................................................................................28 4.4 HEAT EXCHANGER ORIENTATIONS...................................................................................................................28 5 SELECTION OF HEAT EXCHANGER TYPE & ORIENTATION....................................................................................30 5.1 SELECTION CHART................................................................................................................................................30 5.2 HEAT EXCHANGER TYPE.....................................................................................................................................31 5.3 FLUID PLACEMENT................................................................................................................................................31 5.4 SELECTION OF REBOILER TYPE & ORIENTATION...........................................................................................31 5.4 SELECTION OF CONDENSER TYPE & ORIENTATION......................................................................................35 6 SHELL & TUBE HEAT EXCHANGERS – THERMAL DESIGN .....................................................................................36 6.1 FILM THEORY OF HEAT TRANSFER...................................................................................................................36 6.2 AN OVERVIEW OF HEAT EXCHANGER CALCULATION PROCEDURES........................................................39 6.3 BASIC DATA REQUIRED FOR HEAT EXCHANGER CALCULATIONS.............................................................42 6.4 DETERMINATION OF DUTY, Q..............................................................................................................................43 6.5 TYPICAL OVERALL HEAT TRANSFER COEFFICIENTS....................................................................................45 6.6 TEMPERATURE DIFFERENCE, DT.......................................................................................................................46 6.7 METAL RESISTENCE IN TUBES, rw ......................................................................................................................50 6.9 FOULING RESISTENCES.......................................................................................................................................51 7. ESTIMATION OF FILM COEFFICIENTS .........................................................................................................................53 7.1 SENSIBLE HEAT TRANSFER TUBESIDE FILM COEFFICIENTS, hi..................................................................53 7.2 SENSIBLE HEAT TRANSFER SHELLSIDE FILM COEFFICIENTS, hi ................................................................58 7.3 CONDENSING FILM COEFFICIENTS....................................................................................................................61 7.4 VAPORIZERS AND REBOILERS...........................................................................................................................65 8. PRESSURE DROP.............................................................................................................................................................69 8.1 SHELL SIDE PRESSURE DROP...........................................................................................................................69 8.2 TUBE SIDE PRESSURE DROP..............................................................................................................................70 9 THERMAL DESIGN – OTHER TYPES OF EXCHANGERS...........................................................................................72 9.1 THERMAL DESIGN – PLATE & FRAME EXCHANGERS.....................................................................................72 9.2 THERMAL DESIGN – SPIRAL PLATE EXCHANGERS........................................................................................72 9.3 THERMAL DESIGN – DOUBLE PIPE & HAIR-PIN HEAT EXCHANGERS.........................................................72 9.4 THERMAL DESIGN – AIR COOLED HEAT EXCHANGERS................................................................................73 10 REFERENCES ...................................................................................................................................................................75 CHEE 470 Fall 2008 HEAT EXCHANGERS 1 INTRODUCTION TO HEAT EXCHANGERS Heat exchangers are used in many different services in a typical chemical plant. The following lists some of the services along with the common terms used to describe the heat exchangers services. Chiller An exchanger which uses a refrigerant to cool a fluid to a temperature below that which is achievable with water. Condenser Condenses a vapour or mixture of vapours either alone or in the presence of non-condensable gases. Cooler Cools liquids or gases normally using water. Exchanger Cools one fluid while heating the other fluid. Heater Imparts sensible heat to a liquid or gas by condensing steam or a heat transfer fluid. Reboiler Reboilers generate vapour to drive fractional distillation separation. The heating can be achieved via condensing a heat transfer fluid or sensible heat from a fluid. Thermosyphon Natural circulation of a boiling liquid is maintained by providing Reboiler sufficient head to provide circulation Forced A pump is used to circulate fluid through the reboiler Circulation Reboiler Superheater Heats a vapour to a temperature above it's boiling point Vaporizer A heat exchanger which vaporizes part or all of a liquid stream. 1 CHEE 470 Fall 2008 HEAT EXCHANGERS The preliminary Process Flow Diagram project indicates that many heat exchangers are required. The question is: what exchanger size, type and orientation is best for each service? The following sections describe the various types of exchangers and give guidelines for selection and design. 2 CHEE 470 Fall 2008 HEAT EXCHANGERS 2 HEAT EXCHANGERS TYPES There are several different styles of heat exchanger equipment in common use. These include: · Double pipe heat exchangers