(3) Kettle Exchangers

Page-*What is Kettle Exchangers?

Page-*Outline of Kettle ExchangersBoiling regime is Pool Boiling.Internal liquid circulation occurs.A disengaged space is required to separate entrainment.TEMA-U or -T is commonly used as the rear-end to remove the tube bundle.Kettle exchangers is not recommended for wide-boiling range(*1) fluids because there is a potential of heavy comps. accumulation.(*1): Temperature difference between bubble and dew points is 11deg.C or more.

Page-*Kettle Exchangers SizingVG,VVG,HVG,MdropletNLL or Spillover LLThe kettle diameter is determined by the criterion that the actual vapor velocity is less than the maximum allowable velocity.These velocities are defined in the HTRI Design Manual.Entrainment ratios for kettle sizing are as follows: Steam generator = 0.001 liq-wt/vap-wt, Others = 0.01 liq-wt/vap-wtVG,V: Vertical vapor velocityVG,H: Horizontal vapor velocityVG,M: Average vapor velocity

Page-*Kettle Exchangers SizingFor clean service: 100% of vaporization to the feed liquid is possible. Thus, the overflow weir is not necessary.

For fouling service: Vaporization to the feed liquid is limited to 80vol%, so that 20vol% and more liquid is continuously drawn-off to remove the accumulated fouling material. In addition, the tube bundle should be covered with liquid securely. Thus, the overflow weir is provided.Vaporization percentageWithout overflow weirWith overflow weirWL,FWV,PWL,FWV,PWL,PVaporization= WV,P / WL,F= 1.0WL,F = WV,P+ WL,PVaporization= WV,P / WL,F

Page-*Kettle Exchangers SizingThe following values above the bundle as normal liquid level should be kept: - For general service: 50mm - For fouling service such as amine: 150mm

The liquid surface in the kettle is not stable by frothing. Thus, 75mm should be added to normal liquid level for kettle sizing. Xist uses 127mm above the tube bundle as default. Liquid height (H) above the top of tube bundleNLLSpillover LLWithout overflow weirWith overflow weirHH

Page-*Kettle Exchangers SizingBased on the equation in the HTRI Design Manual.The default entrainment ratio is 0.01 liq-wt/vap-wt.The calm liquid height is the same as the top of bundle.The froth height is 127mm above the top of bundle.Xists Sizing MethodKettle Dia.(ID)Bundle Dia.(OTL)Shell DIa.(ID)

Page-*Xist Input : Shell PanelSelect K, then Xist calculate thermal performance as pool boiling.Hot fluid location is Tubeside (Inside tubes)If the shell inside diameter is specified, the program calculates the bundle diameter. (recommend)

Page-*Xist Input : Reboiler PanelXist can calculate the kettle ID. However, the kettle ID should be sized by manual.The ratio of liquid level height and bundle diameter should be input if the liquid level is different from the default. It affects the internal circulation calculation.The entrainment ratio should be specified if that is different from the default and the kettle ID is determined by the program.Inlet pressure location: At inlet nozzle: Xist calculates pressure at the top of bundle At top of bundle: Xist calculates pressure at the bottom of bundle

Page-*Xist Input : Nozzle Location Panel (Inlet Nozzle)For single liquid phase, feed nozzle is located at Bottom.For high sub-cooled liquid, feed fluid should not be introduced to a vapor space. Because hammering would occur due to sudden volume decrease.For two-phase, feed nozzle should be placed at the side of shell and a vapor space of the kettle.

Page-*Various types of inletBaffleBaffleDistributorSlit at bottomBaffle TypeDistributor TypeFeed nozzle for two-phaseClosed-end pipeDistributor with slot holesClosed-end pipe

Page-*Outlet Vapor NozzlesVapor outlet nozzles should be positioned at the location corresponding to the middle of tube length to ensure equal vapor path length.As a rule of thumb, the number of outlet nozzle can be determined by the following equation rounded up to an integer: No. of nozzles = L/(5Db), L is bundle length, and Db indicates bundle diameter But the number of outlet nozzles should be determined by considering with the kettle ID.

Page-*Control Methods : Total VaporizerLCPCTotal Vaporizer : without the overflow weirVaporization to total feed liquid is 100%Feed rate is controlled by LIC.Pressure in the kettle is controlled by PIC, or is determined by the connected header.The holding time from LLL to HLL complies with BDM.HLLNLLTo header or K/O drumFeedLLL

Page-*Control Methods : Partial VaporizerLCVaporization to total feed liquid is less than 100%.Draw-off rate of product is controlled by LIC.The holding time from LLL to HLL in the product sump complies with BDM.The liquid surface is always kept above the top of tube bundle by the overflow weir.HLLLLLP1P2p,vHLLLLLP1P2p,vLCProductProductPartial Vaporizer : with the overflow weirP2 = P1+ p,vP2 = P1+ p,v

Page-*Xist Output / Kettle PerformanceConfirm Kettle Circulation Ratio > 1.0.If the circulation ratio is 1.0 or less, internal circulation may not occur. Internal fluid flow is close to pure cross flow as TEMA X-shell.Corrective measures to accomplish internal circulation are as follows: - To increase liquid head, the bundle length is shortened and the bundle diameter is enlarged. - Square pitch is applied to reduce pressure drop across the tube bundleShellside PerformanceFRCirculation Ratio = R/F

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Page-*Xist Output / VibrationTube vibration problem also occurs in the kettle.Engineers should check the results of vibration analysis, and determine the number of support plate.If the unsupported span of U-bend is longer than the TEMA criteria, use Xvib to analyze a tube vibration potential of U-bend. Because Xist can not analyze for U-bend.

Page-*PracticeKettle Type Chiller (Item Tag E-3133)Since the kettle side fluid is a boiling fluid, the physical properties for the actual mixture should be input. In this case, in order to minimize the intricate work, use property generator by VMG-Thermo in Xist.Tube side data shall be input manually. Use AKU type.Tube diameter, tube pitch and so on should be determined referring to the BD Manual. Consider liquid residence time for level control.The kettle ID should be sized by manual.