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 excha exchang nging ing heat, heat, of co cours urse… e……… …….. • Most importantly, importantly, to recover and reuse generated g enerated 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, 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 pressur e drop inside column
© PMTSB 2006
Heat exchangers How do they look like….. Reboilers
Figure 6.8: Various Various types of reboilers
© PMTSB 2006
Heat exchangers How do they work….. Reboilers Kettle type • Tube bundle inside an oversize shell which provides p rovides large vapor space above the bundle • This large vapor space is where liquid and gas phases are separated and then withdrawn withd rawn 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 circ ulate 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 s ame level as liquid level inside tower
© PMTSB 2006
Heat exchangers What are they for….. Evaporators • To remove solvent by vaporization from solids that th at 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, 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….. for….. exposed tube bundles bund les 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 go od 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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