DESIGN SHELL AND TUBE HEAT EXCHANGER

MECHANICAL ENGINEERING TRAININGHEAT EXCHANGER/DESIGN SHELL AND TUBE HEAT EXCHANGER

AHEAT EXCHANGERis a piece of equipment built for efficientheat transferfrom one medium to anotherPURPOSECooling, Heating, Condensing, Boiling FEATURESVariety of Construction Many types of heat exchangers are available. Among them shell and Tube Heat Exchanger are most commonly used

INTRODUCTIONOVERVIEW HEAT EXCHANGERPRINCIPLE OF HEAT EXCHANGERHeat exchangers work because heat naturally flows from higher temperature to lower temperatures. Therefore if a hot fluid and a cold fluid are separated by a heat conducting surface heat can be transferred from the hot fluid to the cold fluid.

HEAT TRANSFERThe rate of heat flow at any point (kW/m2 of transfer surface) depends on:Heat transfer coefficient (U), itself a function of the properties of the fluids involved, fluid velocity, materials of construction, geometry and cleanliness of the exchangerTemperature difference between hot and cold streamsTotal heat transferred (Q) depends on:Heat transfer surface area (A)Heat transfer coefficient (U)Average temperature difference between the streams, strictly the log mean (TLM)Thus total heat transferred Q = UATLM

TYPE OF HEAT EXCHANGERShell & Tube Heat Exchanger

Air Cooled Heat Exchanger

Hairpin/Double Pipe Heat Exchanger

4. Compact Non Tubular Heat ExchangerPlate and frame heat exchanger (PHE)Gasketed and welded-plate heat exchangersMost PHE applications are liquid-liquid servicesGasket selection is one of the most critical and limiting factors in PHE usageWelded-And Brazed-plate Exchangersused for a great variety of designs for various applications from normal gasketed-plate exchanger services to air-preheater services on fired heaters or boilers.Spiral-plate Exchangers (SHE)The SHE is formed by rolling two strips of plate, with welded-on spacer studs, upon each other into clock-spring shape

Brazed-plate-fin Heat ExchangerBrazed-aluminum-plate-fin heat exchangers (or core exchangers or cold boxes) made up of a stack of rectangular sheets of aluminum separated by a wavy, usually perforated, aluminum fin.Plate-fin Tubular Exchangers (PFE)Spiral-tube Exchangers (STE)Graphite Heat ExchangersCascade CoolersBayonet-tube ExchangersETC

FUNCTION OF STHEEQUIPMENTFUNCTIONChillerCools a fluid to a temperature below that obtainable if water only were used as a coolant. It uses a refrigerant such as ammonia or Freon.CondenserCondenses a vapor or mixture of vapors, either alone or in the presence of a noncondensable gas.Partial condenserCondenses vapors at a point high enough to provide a temperature difference sufficient to preheat a cold stream of process fluid. This saves heat and eliminates the need for providing a separate preheater (using flame or steam).Final condenserCondenses the vapors to a final storage temperature of approximately 37.8C (100F). It uses water cooling, which means that the transferred heat islost to the process.CoolerCools liquids or gases by means of water.ExchangerPerforms a double function: (1) heats a cold fluid by (2) using a hot fluid which it cools. None of the transferred heat is lost.HeaterImparts sensible heat to a liquid or a gas by meansof condensing steam or Dowtherm. FUNCTION OF STHEEQUIPMENTFUNCTIONReboilerConnected to the bottom of a fractionating tower, it provides the reboil heat necessary for distillation. The heating medium may be either steam or a hot-process fluid.Thermosiphon reboilerNatural circulation of the boiling medium is obtained by maintaining sufficient liquid head to provide for circulation.Forced-circulation reboilerA pump is used to force liquid through the reboiler.Steam generatorGenerates steam for use elsewhere in the plant by using the available high-level heat in tar or a heavy oil.SuperheaterHeats a vapor above the saturation temperature.VaporizerA heater which vaporizes part of the liquid.Waste-heat boilerProduces steam; similar to steam generator, except that the heating medium is a hot gas or liquid produced in a chemical reaction.TEMA-STYLE SHELL AND TUBE HEAT EXCHANGERSTEMA TYPE STHE

NOMENCLATURE

PRINCIPAL TYPES OF CONSTRUCTIONFixed-Tube-Sheet Heat ExchangersThe tubesheets are welded to the shellNo limitation on the number of tube-side passes Tubes can completely fill the heat-exchanger shellTubes can be replacedSimple & low costShell side fouling < 0.00026m2K/W or shell side chemical cleaning is applicableExpansion joint required for T>60 deg Celsius

TYPE B-E-MU-Tube Heat ExchangerHigh temperature and pressure applicationHas no problem for thermal expansionThe number of tube holes in a given shell is less than that for a fixed-tube-sheet exchanger because of limitations on bending tubes of a very short radius

TYPE C-F-UPacked-Lantern-Ring ExchangerConstruction is the least costly of the straight-tube removable bundleThe shell- and tube-side fluids are each contained by separate rings of packing separated by a lantern ring and are installed at the floating tube sheet. The lantern ring is provided with weep holes. Any leakage passing the packing goes through the weep holes and then drops to the ground. Leakage at the packing will not result in mixing within the exchanger of the two fluids.The packed-lantern-ring construction is generally limited to design temperatures below 191C

TYPE A-J-WOutside-Packed Floating-Head ExchangerShell-side fluid is contained by rings of packing, which are compressed within a stuffing box by a packing follower ring.

TYPE A-E-PInternal Floating-Head ExchangerThe tube bundle is removable, and the floating tube sheet moves (or floats) to accommodate differential expansion between shell and tubes. The outer tube limit approaches the inside diameter of the gasket at the floating tube sheet. Clearances (between shell and OTL) are 29 mm (1-1/8 in) for pipe shells and 37 mm (1-7/16 in) for moderate diameter plate shells.

TYPE A-E-SPull-Through Floating-Head ExchangerConstruction is similar to that of the internal-floating-head split-backing ring exchanger except that the floating-head cover bolts directly to the floating tube sheet. The tube bundle can be withdrawn from the shell without removing either shell cover or floating-head cover. This feature reduces maintenance time during inspection and repair.TYPE A-K-T

Features of TEMA Shell-and-Tube-Type Exchangers