Spray Gas Quench Design Considerations - BETE Fog Nozzle, Inc.
Spray Gas Quench Design Considerations - BETE Fog Nozzle, Inc. Spray Gas Quench Design Considerations - BETE Fog Nozzle, Inc.
Reliability ConsiderationsSystem reliability is influenced by manyfactors. Solids in the quench liquid areoften the root cause of the two mainfactors that cause system downtime,plugging, and erosion of nozzles.Solids in the quenching media maycause nozzle clogging. Plugging internalpassages of the spray nozzle leads tonon-uniform and inadequate gas cooling.It is important to select the correct nozzledesign and material of construction tomaximize free-passage, reduce cloggingand extend operating life. A strainersystem in the upstream piping can alsoprotect nozzles and maintain the nozzleperformance by preventing repair workand unnecessary equipment shut downs.the drop size. Wear and erosion of nozzlesdepends on process specific conditionssuch as; the velocity of the liquid, thehardness of the particles in the liquid andthe corrosive nature of the environment.Operational experience is frequently thebest guide to assessing if erosion is areasonable concern. Material selection isalso an important design factor tominimize nozzle wear and extend thesystem operating life. BETE has themanufacturing capability and engineeringexperience to assist you in selecting themost appropriate nozzle constructionmaterial to withstand the operatingenvironment.The second factor is the erosion ofinternal passages and nozzle outlet thatdistorts the spray pattern and increasesProcess controlThe process control of quench systemsmust be considered in the design phaseto achieve the optimal result. The quenchliquid flow is often controlled to achievea desired quench zone exit temperature.Instrumentation to monitor single-fluidnozzle pressure drop is frequently used.Two-fluid nozzles require a morethoughtful and deliberate approach tocontrol the atomizing gas and the liquidflow. One objective of nozzle control isto minimize the amount of atomizinggas (compressed air) and therefore,reduce the energy input to supply theatomizing media. Improved controlreduces operational cost and stabilizesthe system response to extremeconditions.Wet-wall conceptThe design of many wet wall quenchesinvolves little process control becausea constant liquid pressure is used tocontinually maintain the maximumrequired flow. This assures thequench spray system is always atpeak performance. Highly variable inletgas flows are robustly quenched with thissimple control approach. The measuredpressure drop is crosschecked with theexpected spray nozzle pressure dropbased on the measured flow. Thismeasurement is valuable to identifyany gross issues with the nozzles orflow measuring device. Control systemshave many conditions that need to beevaluated. The spray design must beable to manage the possible situationsgiven the combinations of flow pathsand range of flows.6PERFORMANCE THROUGH ENGINEERING
Dry-wall conceptSingle fluid nozzles are often used witha narrow range of gas throughput, andwhere multiple lances are used to managegreater turndown requirements. Thequench temperature control systemdetermines the flow rate of quenchliquid. Pressure drop control is used withmultiple lances to maintain a minimumpressure drop to assure the drop size issmaller than a predetermined value.Turndown to less than 75% of designis managed by controlling the flow tothe groups of nozzles to maintain therequired drop size, as described in thefirst example.Conventional flow control for two-fluidnozzles, shown in Figure 9, often usedin dry-wall quench systems providesexcellent and robust control. Numerouscontrol strategies can be implementedbased on overall system and processrequirements. The design of large-scalesystems with several second residencetime, should consider the gas transit timefrom the spray to sensor as lag-time ordead time between controller action andthe sensor response. This dead time variesdepending on throughput and inputtemperature. Numerous potential controlstrategies can be implemented based onoverall system requirements. One is afeed forward set point based on inlettemperature and mass flow. Multimodecontrollers using the combination of feedforwardand feedback provide additionalrobustness, but add complexity.Control of two-fluid nozzles is morecomplex than single-fluid nozzles;however, the range of operation is muchbroader. The myth is evaporation timeis controlled by constant drop size. Thereality is that under turndown conditionsthe gas residence time is longer andconsequently the drop size requiredcan be larger than in the maximum rateconditions. The flow control systemdescribed in Figure 10 can be used forinternal-mix or external-mix nozzle types.Internal-mix two-fluid nozzles needspecial attention on controller tuningbecause of the interaction between thegas and liquid control loops. For example,a slight increase in the liquid flow in asystem with two independent mass flowcontrollers causes an increase in nozzleFTQuench LiquidQuench LiquidFTFTAtomizing GasFCFCFCStrainerPTStrainerSingle Fluid Quench Nozzle System ConfigurationFigure 9.PTCheck ValvePTTwo Fluid Quench Nozzle System ConfigurationFigure 10.pressure drop which in turn causes thegas control valve to open. These actionsresult in feedback to the liquid controlloop and ultimately overshoot of theliquid flow. The non-linear feedback cancause oscillatory behavior if the controllertuning parameters of the gas and liquidflows are not coordinated.Back flow prevention is critical ininternal-mix two-fluid nozzle piping toassure quench liquid does enter thecompressed air header. Several featureshave been incorporated into the systemas shown in Figure 13, recommendedmeasurements of the flow and nozzlepressure drop for both the gas andliquid streams.BETE Applications Engineering expertisecan reduce the initial and long term costof the quenching operation system.Process gasflowProcess gasflowFCFTPTControl ValveStrainerCheck ValveFlow Rate ControllerFlow Rate TransmitterPressure TransmitterSignal7PERFORMANCE THROUGH ENGINEERING
- Page 1 and 2: Spray Gas Quench Design Considerati
- Page 5: Spray NozzlesBecause of the wide va
- Page 9: Acid Gas QuenchA customer’s acid
Dry-wall conceptSingle fluid nozzles are often used witha narrow range of gas throughput, andwhere multiple lances are used to managegreater turndown requirements. Thequench temperature control systemdetermines the flow rate of quenchliquid. Pressure drop control is used withmultiple lances to maintain a minimumpressure drop to assure the drop size issmaller than a predetermined value.Turndown to less than 75% of designis managed by controlling the flow tothe groups of nozzles to maintain therequired drop size, as described in thefirst example.Conventional flow control for two-fluidnozzles, shown in Figure 9, often usedin dry-wall quench systems providesexcellent and robust control. Numerouscontrol strategies can be implementedbased on overall system and processrequirements. The design of large-scalesystems with several second residencetime, should consider the gas transit timefrom the spray to sensor as lag-time ordead time between controller action andthe sensor response. This dead time variesdepending on throughput and inputtemperature. Numerous potential controlstrategies can be implemented based onoverall system requirements. One is afeed forward set point based on inlettemperature and mass flow. Multimodecontrollers using the combination of feedforwardand feedback provide additionalrobustness, but add complexity.Control of two-fluid nozzles is morecomplex than single-fluid nozzles;however, the range of operation is muchbroader. The myth is evaporation timeis controlled by constant drop size. Thereality is that under turndown conditionsthe gas residence time is longer andconsequently the drop size requiredcan be larger than in the maximum rateconditions. The flow control systemdescribed in Figure 10 can be used forinternal-mix or external-mix nozzle types.Internal-mix two-fluid nozzles needspecial attention on controller tuningbecause of the interaction between thegas and liquid control loops. For example,a slight increase in the liquid flow in asystem with two independent mass flowcontrollers causes an increase in nozzleFT<strong>Quench</strong> Liquid<strong>Quench</strong> LiquidFTFTAtomizing <strong>Gas</strong>FCFCFCStrainerPTStrainerSingle Fluid <strong>Quench</strong> <strong>Nozzle</strong> System ConfigurationFigure 9.PTCheck ValvePTTwo Fluid <strong>Quench</strong> <strong>Nozzle</strong> System ConfigurationFigure 10.pressure drop which in turn causes thegas control valve to open. These actionsresult in feedback to the liquid controlloop and ultimately overshoot of theliquid flow. The non-linear feedback cancause oscillatory behavior if the controllertuning parameters of the gas and liquidflows are not coordinated.Back flow prevention is critical ininternal-mix two-fluid nozzle piping toassure quench liquid does enter thecompressed air header. Several featureshave been incorporated into the systemas shown in Figure 13, recommendedmeasurements of the flow and nozzlepressure drop for both the gas andliquid streams.<strong>BETE</strong> Applications Engineering expertisecan reduce the initial and long term costof the quenching operation system.Process gasflowProcess gasflowFCFTPTControl ValveStrainerCheck ValveFlow Rate ControllerFlow Rate TransmitterPressure TransmitterSignal7PERFORMANCE THROUGH ENGINEERING
Change language