LW Seal Gas System

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    01-Jan-2016

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<ul><li><p>L. W. Brittian Mechanical &amp; Electrical Instructor This is a short example of a training presentation developed for a specific piece of equipment. It is only one of many that I have developed for a multination company</p></li><li><p>Oil Free Screw Compressor Dry Gas Seal System</p></li><li><p>Part OneDry Gas Seal System</p></li><li><p>There are lots of things to tell you so lets get at it.Him? Thats Mole the gas molecule he is hunting a place to leak out.</p></li><li><p>IntroductionDescription.</p><p>Control and monitoring function.</p><p>Secondary labyrinth buffer.</p><p>Primary vent.</p><p>Secondary vent.</p><p>Checkout procedure.</p><p>System schematic drawings.</p></li><li><p>DescriptionInstalled in the GE oil free screw compressor.</p><p>Four shaft seals, one on each end of the two rotors.</p><p>Tandem type made by john crane.</p><p>Primary and secondary tungsten carbide rings.</p></li><li><p>DescriptionTwo mating rings.</p><p>Thin film of gas separates the two rings. </p><p>Pumping action created by design of tungsten rings.</p><p>Must have flow of clean gas to seal when shaft rotates.Full pressure breakdown occurs across. </p><p>Outboard secondary seal sees lower pressure, allows shutdown without process gas release into bearing cavities. </p></li><li><p>Control and Monitoring Function Primary buffer.</p><p>Filtered fuel gas feed to primary seal face.</p><p>Filters, 1 micron disposable coalescing elements.</p><p>Delta P monitors filter load.</p><p>0.25 bar (100 in H20) alarm setpoint.</p><p>A1-FCV 65703-33 suction end seals.</p></li><li><p>Control and Monitoring FunctionS1-FT-65703-31 discharge end seals.</p><p>PLC in UCP controls flow to suction end seals.</p><p>PLC signal from A1-PDT-65703-33 primary vent &amp; compressor suction. </p><p>PLC signal from a1-ft-65703-34 primary buffer gas flow suction end seals. Normal is one flow unit = 8ma.</p><p>Nitrogen gas supply backup @ 10 BarG. </p></li><li><p>Control and Monitoring Function Warning.Primary buffer gas supply to seals required anytime there is pressure in the process cavity of the compressor.</p><p>Failure to met this requirement could result in gas flow from inside the compressor across the primary seal faces and result in damage to the seal.</p></li><li><p>Secondary Labyrinth BufferInstrument air/separation buffer gas to outboard labyrinth seal.Separates dry gas seal from bearing cavity.Keeps lube oil vapor out of dry gas seals.Normal for instrument air/sep buffer gas exiting secondary vent and bearing housing.A1-PVC-65703-34 controls secondary buffer gas flow 1.38 BarG (20psig) to FCVs a1-fl-65703-37/38/40/41. 8.5 NCMH (300 SCFH) to each seal.A1-PT-65703-33 signal to PLC-UCP panel 1-MCP-8a low pressure alarm 4.0 BarG (58 PSIG).</p></li><li><p>Secondary Labyrinth BufferWarning.</p><p>Separation purge gas must be applied to before and during the operation of the lubrication system. This is required to avoid flooding of the dry gas seal with oil and subsequent seal failure. Failure to follow this procedure will void manufacturer's warranty.</p></li><li><p>Primary VentPrimary seal failure results in increase flow to primary vent.Alarm at 2 units, 250 mbar (11ma signal) increasing.Flow measured by A1-FT-65703-41B, A1-FST-65703-41A signal sent to PLC in unit safety panel (1-MCP-8B).</p><p>Trip when flow is 488 mbar (18.0 ma signal).</p><p>Primary vent back pressure un-controlled, typical 0.2 BarG (2.9 PSIG), max 2.5 BarG (36.3 psig).Positive pressure ensures positive gas flow across secondary seal face on each seal assembly.</p></li><li><p>Secondary VentVents small amounts of primary buffer gas, mostly secondary/instrument air to dedicated atmospheric vent with flame arrestor.</p><p>Not controlled, not monitored.</p></li><li><p>Checkout ProceduresSee also john crane installation manual.</p><p>Bench check PSI transmitters range calibrated per schematic values.Clean dry instrument air.3) bench check PSI transducers set proper range and outputs.4) primary buffer FCV operation per signal received.5) alarms and trips set per schematic.6) n.C. Valves indicated as solid.N.O. Valves indicated as outlined.All interconnecting piping complete and leak free.</p></li><li><p>System SchematicsGeneral SymbolsValve &amp; Instrument SymbolsWarning statement</p></li><li><p>System SchematicsDry gas SealsFilters</p></li><li><p>System Schematics</p></li><li><p>System Schematics</p></li><li><p>System Schematics</p></li><li><p>Part 2, Introduction To Dry Gas SealsIntroduction.Principals of operation.Installation guidelines.Operational guidelines.Maintenance.</p></li><li><p>Introduction ContinuedPrincipals of Operation for John Crain Type 28AT Bi-directional Tandem Seal Installed in a GE Oil Free Screw Compressor Model 165L4.Check the installation manual for the specific machine that you are working on for specific details, as this is material may not apply to the seals that your machine is equipped with.Provides information of value only information necessary for installation of theses seals.</p></li><li><p>Principals Of Operation</p><p>O RingsClosing springOutside or atmosphere side of the seal assemblyInside or process side of the seal</p></li><li><p>Principals Of Operation Continued</p><p>Sealing Dam WidthSpiral Grove cut into face of rotating ringRing rotation</p></li><li><p>Principals Of Operation Continued</p></li><li><p>Principals Of Operation ContinuedClosing Spring pressure</p><p>System PressureSystem breakdown pressure</p><p>Pressure generated by spiral groves in rotating ring face.</p></li><li><p>Principals Of Operation ContinuedForces interact and Reestablish Equilibrium</p></li><li><p>Principals Of Operation ContinuedForces interact and Reestablish Equilibrium</p></li><li><p>Installation GuidelinesA video clip was inserted that showed the removal of each of the parts from the wooden crate. Audio was provided to identify and describe each part</p></li><li><p>Installation Guidelines ContinuedCaution Related to a task that if not properly executed, could result in the seal functioning correctly. </p><p>WarningRelates to a procedure that if not correctly completed, damage to the seal cartridge could occur.</p></li><li><p>Installation Guidelines ContinuedThe manufacture recommends that of the four seals, the one for the thrust bearing end be installed first.Next they recommend that the thrust bearing be installed to hold the rotor shaft in position and aid in installing the coupling end seal cartridge.</p></li><li><p>Installation Guidelines ContinuedWarningThe rotor shafts must be centered in the compressors housing. The rotors must also be fixed with respect the its axial position while the seal cartridges are being installed.Check leading edge chamfers and the bore for burrs and sharp edges that could damage the seal.Confirm that nominal axial position is as specified on the project plans (HSP-1011967)</p></li><li><p>Installation Guidelines ContinuedInstallation is accomplished by following a series of steps listed on pages 6 thru 9 of the Users Manual for the Type 28 Series Seals.Dry gas seal hang up. Exercise to prevent. </p></li><li><p>Installation Guidelines ContinuedUsing manufactures original drawings aids in communication while reducing training development cost for the owner </p></li><li><p>Installation Guidelines Continued</p></li><li><p>Installation Guidelines Continued</p></li><li><p>Installation Guidelines Continued</p></li><li><p>Installation Guidelines ContinuedCompare this and the previous slide, one is color, the other black and white, both communicate well.</p></li><li><p>Operational GuidelinesSeal design description.</p><p>Gas quality.</p><p>Seal gas supply flow.</p><p>Leakage trends.</p><p>Reverse pressure.</p><p>Decompression.</p><p>Vibration.</p></li><li><p>Operational Guidelines ContinuedSeal design description.Buffer gas injected into cavity between inboard gas seal and inboard labyrinth to keep liquids and solids out.Also leaks past inboard gas seal into the cavity between inboard and outboard gas seals, to primary vent.Outboard gas seals seals leakage from inboard seal ad functions as safety seal in the event of inboard gas seal begins to leak excessively.</p></li><li><p>Operational Guidelines ContinuedSeal design description continued.Positive pressure differential buffer gas to separation labyrinth.Combined separation labyrinth and outboard seal leakage directed to secondary vent.Outboard labyrinth leakage vents to cavity between labyrinth and the bearing, to ensure separation of bearing oil and buffer gas.Primary seal leakage is monitored and recorded daily.</p></li><li><p>Operational Guidelines Continued</p><p>Gas Quality.Clean and Dry.Results in increased seal service life.As the moving components do not make physical contact, gas quality, or the lack of it can have either a positive or negative impact upon uptime.Computer animations such as this one can add a taste of humor to the training</p></li><li><p>Operational Guidelines Continued</p><p>Seal Gas Supply flow.An adequate supply of clean and dry gas will provide optimum seal performance. See seal gas schematics for correct pressures and volumes.</p></li><li><p>Operational Guidelines Continued</p><p>Leakage trends.Spikes in seal flow volume are to be anticipated, so long as alarms can be reset.Process variations will from time to time result in changes in seal leakage.Watch for trends, lower or higher can be a precursor to sealing problem.</p></li><li><p>Operational Guidelines Continued</p><p>Reverse pressure.Reverse pressure with the compressor off line, or in a static condition will result in increased static leakage.</p><p>Under dynamic conditions, can result in major damage to individual seal components.</p></li><li><p>Operational Guidelines Continued</p><p>Decompression.Explosive decompression damage results when seal o-rings absorb small amounts of gas within the o-rings materials, are subjected to rapid reductions in pressure. After such an event the o-ring looses it ability to form a tight seal.The manufacture recommends the decompression occur at a rate of no more than 118 PSIG per minute.</p></li><li><p>Operational Guidelines Continued</p><p>Vibration.This family of seals has been shown to be capable of withstanding vibration levels of 5 mills peak to peak.This value is well outside of the compressors operating limits.</p></li><li><p>MaintenanceCleaning, do not expose to oil.Storage.</p></li><li><p>Non-contact Dry Gas Seal Timeline1969 Spiral grove developmental research begins.1970 U.S. Patent issued to John Crane.1975 Spiral grove gas seal put in Turbo-expander service.1976 Pipeline Compressor installation.1984 Off-shore platforms and wet gas service.1987 Ethylene, Coker gas, Ammonia, Liquid methane pump.1991 Explosive decompression problems solved.1991 Applied to Gas turbines, Propylene refrigeration, Steam turbines.1992 Bi-directional grove developed.2000 Pressures up to 5,000 PSIG/350 Bars. </p></li><li><p>Non-contacting SealsEliminates heating effects of friction by non-contact between the seal faces.</p><p>One seal face designed with a lift mechanism, faces float on cushion of gas.</p><p>Spiral grove pressure build up at sealing dam provides resistance to flow, pressure also lifts sealing faces apart.</p><p>Small gas flow across faces at to cool them.</p><p>Opening and closing forces equal during operation.</p></li><li><p>Labyrinth Seals.Simple method of sealing a shaft.</p><p>Series of knife edges.</p><p>Clearance controlled to limit leakage.</p><p>Pressure limit per knife edge typically 5 PSI.</p><p>Non-hazardous gases vented to atmosphere.</p><p>Hazardous gas duty, buffer gas at higher psi than process gas injected between labyrinth seals.</p></li><li><p>SummaryThirty + years , thousands of seals, millions of hours uptime.</p><p>Throughout the world.</p><p>Industrial standard.</p><p>Centrifugal, and screw compressors, pumps, and turbo-expanders.</p><p>Reduced mean time between maintenance (MTBTM).</p><p>I can not leak out of this place</p></li><li><p>This completes our coverage of the Dry Gas Seal System.</p></li><li><p>Please push your chair under your desk.I need a break. Lets take a short break.</p></li><li><p>CreditsCredits: Working with original equipment manufactures, Engineering and Procurement and constructions firms and the projects owners training materials specific to the project can be quickly and economically developed using modern technology.</p><p>Welcome to class. Throughout this training, spaces such as this are provided for your in class notes. Should you have a question, write it down in the space provided so that you can ask it during the questions sessions.This portion of your training will cover the Dry Gas Seal System during part one. Part two will cover the Dry Gas Seal.In this training session we will review the methods used to keep lubrication oil out of the compressed process gas discharge stream and to keep the process gas from leaking out of the compressor. These are the main topics that we will review during this portion of the training.The GE compressor selected for this project has been provided with John Crane brand Dry Gas Seals. The sealing system also includes a seal gas system. We will cover details of the Seal gas system shortly.This complex shaft sealing system will be damaged by failure to follow the operating instructions. The gas used to provide primary buffer gas is the process gas. It is filtered through two sets of filters to ensure that only clean dry gas is supplied to the seals.</p><p>Periodically the filters will need to be changed, to facilitate this without shutting down the machine, two sets of duplex filters have been provided.</p><p>Filter load is indicated by the pressure drop across the filter assembly.An alarm will be annunciated when this pressure reaches 100 inches of water.</p><p>Flow control valve controls the flow of buffer gas to the suction end seals.A flow transmitter monitors flow from the discharge end seals.</p><p>In the event that adequate process gas is not available, a source of nitrogen gas pressure has been provided at a pressure of 10 BarG.Should process gas flow form the compressor into the seal cavity, this unfiltered gas could transport foreign objects that could easily damage the seals components.A source of instrument air is used to provide buffer gas to the outboard labyrinth seal. This gas helps to keep the oil vapor out of the dry gas seals.A pressure control valve controls this gas pressure to 20 PSIG (1.38 BarG)While a flow control provides 300 SCFH (8.5 NCM) to each seal.</p><p>Pressure is monitored at the unit control panel with a signal from a pressure transmitter.With many machines the first system started is the lubrication system. With this sealing system this can not be the case. Lubrication oil under pressure could flood the seal cavities, and potentially damaging the seals.In the event that the primary seal fails, there will be n increase in gas flow to the primary vent from the seal.The alarm is set at 250 mbar, while compressor trip is set at 488 mbar.Flow in the secondary vent is neither controlled or monitored as this is normally non-hazardous instrument air.Working with so many different processes and process machines it is very important if not necessary that checkout procedures be followed.You just can not remember every step every time. By developing the good habit of following the processes checklist, time and safety can be increased and maintenance time and expenses can be reduced.Before we begin reviewing the schematics for this systems, we would be wise to review a few of the many symbols used on theses schematics.</p><p>The engineers from time to time will will remind us not to make a common mistake by providing a warning note on the systems schematic, such as the one above.When beginning to review a new schematic it helps to begin by locating the main components, in this case we see the four seals and the two duplex seal gas filter assemblies. Highlighted on this sheet is the instrument air supply used as the separation buffer gas.Primary buffer gas flow has been highlighted on this sheet. In the space below write out the flow path of this gas t...</p></li></ul>

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