7 - Hex

Unfired pressure vessel classifications Unfired Pressure Vessel

Drums

Storage vessel

Reactor

Columns

Separators

Exchangers

Surge drum

Atmospheric

Radial flow

Fractionation

Liquid-solid

Reboiler

Accumulator

Pressure

Axial flow

Distillation

Liquid-liquid

Evaporator

Catalyst drum

Radial & axial

Separation

Gas-liquid

Condenser

Resin & filter

Single bed

Gas-solid

Cooler

Storage

Multi bed

Filter

Plate

© PMTSB 2006

Heat exchangers What are they for….. • For exchanging heat, of course………. • Most importantly, to recover and reuse generated heat, rather than merely exchanging heat

© PMTSB 2006

Heat exchangers How do they work….. • By transferring the heat from a hot medium to another colder medium, without mixing the fluids • In most exchangers, heat is transferred by means of conduction through the fixed walls of the exchangers • This process relies on the thermal conductivity of a solid material and those of the fluids

© PMTSB 2006

Heat exchangers How do they work…..continued • When designing exchangers, consider the following;  Thermal conductivity of tubes  Corrosion resistance  Heating surface areas

 Turbulence of fluid must be as high as possible because thermal conductivity of fluid varies in direct proportion to the fluid turbulence  Fluid flow rate

© PMTSB 2006

Heat exchangers How do they work…..continued • Generally, the thermal conductivity of a substance is lower when it is in vapor phase or gas phase, than when it is in liquid phase

© PMTSB 2006

Heat exchangers How do they look like…..

Figure 6.1: Heat exchanger nomenclatures © PMTSB 2006

Heat exchangers How do they look like…..

Figure 6.1: Heat exchanger nomenclatures © PMTSB 2006

Heat exchangers How do they look like…..

Figure 6.2: Heat exchanger classifications, as per TEMA

© PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers • The most widely used type of exchangers • A bundle is enclosed inside a shell • Fluids never come into contact with each other

• Tubes are attached to tubesheet by welding, brazing, or rolling

© PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers Baffle plates • For causing the fluid flow inside the shell side to come into contact with as much tube surface as possible, hence more heat transfer will take place • They also provide support to the tubes

© PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers Fixed tubesheet • Both ends of the tube bundle are rigid – little expansion of the tubes • Used when temperature difference between two fluids is small

© PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers Fixed tubesheet

Figure 6.3: A fixed tube plate exchanger © PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers Floating head with removable bundle • Allows the floating tubesheet to be slipped into the shell for ease of installation and removal

Figure 6.4: An example of a floating head exchanger © PMTSB 2006

Heat exchangers How do they look like….. Shell & tube bundle exchangers U-tube exchanger • Allows large amount of tube expansion

Figure 6.5: An example of a U-tube heat exchanger © PMTSB 2006

Heat exchangers How do they look like….

Figure 6.6: Tube passes arrangements

© PMTSB 2006

Heat exchangers How do they look like….

Figure 6.7: An example of a tubesheet

© PMTSB 2006

Heat exchangers How do they work….. Reboilers • Installed at bottom of columns • Used to provide boilup for distillation and similar towers • They generate pressure required to push the vapor up the column • Vapor pressure generated must overcome pressure drop inside column

© PMTSB 2006

Heat exchangers How do they look like….. Reboilers

Figure 6.8: Various types of reboilers

© PMTSB 2006

Heat exchangers How do they work….. Reboilers Kettle type • Tube bundle inside an oversize shell which provides large vapor space above the bundle • This large vapor space is where liquid and gas phases are separated and then withdrawn separately

© PMTSB 2006

Heat exchangers How do they look like….. Reboilers Kettle type

Figure 6.9: A kettle type reboiler © PMTSB 2006

Heat exchangers How do they work….. Reboilers Thermosyphon • The fluid will circulate at a rate which the pressure losses in the system are just balanced by the available hydrostatic head • The driving force for circulation round the system is the difference in density of the cold liquid at the bottom column base and inlet piping, and the hot two-phase fluid in the upper exchanger tubes and outlet piping • Top tubesheet at same level as liquid level inside tower

© PMTSB 2006

Heat exchangers What are they for….. Evaporators • To remove solvent by vaporization from solids that are not soluble • Used to produce concentrated liquid

© PMTSB 2006

Heat exchangers How do they work….. Evaporators • Circulation of flow may be natural or forced with pumps • Forced circulation evaporators are for viscous and fouling services – but also more expensive • Most evaporators use natural circulation

© PMTSB 2006

Heat exchangers How do they look like….. Evaporators

Figure 6.10: A few types of evaporators © PMTSB 2006

Heat exchangers How do they look like….. Evaporators

Figure 6.11: Other examples of evaporators © PMTSB 2006

Heat exchangers What are they for….. Condensers • To reduce vapor temperature to the point of condensation i.e. vapor transforms into condensate

© PMTSB 2006

Heat exchangers How do they work….. Condensers • When freezing can occur, condensation is normally performed on the shell side to prevent clogging • When condensing mixtures whose lighter components are soluble in the condensate, tube side condensation is preferred because drainage is less complete and allows condensation to take place at higher temperatures

© PMTSB 2006

Heat exchangers How do they look like…..

Condensers

Figure 6.12: Various types of condenser

© PMTSB 2006

Heat exchangers How do they look like….. Condensers

Figure 6.13: A badly clogged seawater condenser © PMTSB 2006

Heat exchangers What are they for….. exposed tube bundles Air coolers • Cooler – when a hot fluid is cooled to a lower desired temperature by transfer of heat to water • Air cooler – when a hot fluid is cooled by air

© PMTSB 2006

Heat exchangers How do they work….. exposed tube bundles Air coolers • Since air is not as good as water in removing heat, the process of exchanging heat is further enhanced by installing fins outside the tubes • The process fluids flows through finned tubes and cooling air is blown across them with fans • Air cooler is easier to maintain than water cooler because air is not corrosive and unlikely to foul

© PMTSB 2006

Heat exchangers How do they look like….. exposed tube bundles Air coolers

Figure 6.14: Two types of air coolers

© PMTSB 2006

Heat exchangers How do they look like….. Plate heat exchangers

Figure 6.15: A plate heat exchanger being serviced © PMTSB 2006

Heat exchangers How do they look like….. Plate heat exchangers

Figure 6.16: A schematic of a plate heat exchanger

© PMTSB 2006

Heat exchangers How do they look like….. Plate heat exchangers

Figure 6.17: Fluid flow inside a plate heat exchanger © PMTSB 2006

Heat exchangers How do they look like…..

Figure 6.18: Various tube fins constructions

© PMTSB 2006

Heat exchangers How do they look like…..

Figure 6.19: Various tube fin attachment constructions © PMTSB 2006

End of PART B

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