L. W. Brittian Mechanical & 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

Dry Gas Seal System Oil Free Screw Compressor

Part One Dry Gas Seal System

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.

Introduction Description. Control and monitoring function. Secondary labyrinth buffer. Primary vent. Secondary vent. Checkout procedure. System schematic drawings.

Description Installed in the GE oil free screw compressor. Four shaft seals, one on each end of the two rotors. Tandem type made by john crane. Primary and secondary tungsten carbide rings.

Description Two mating rings. Thin film of gas separates the two rings. Pumping action created by design of tungsten rings. Must have flow of clean gas to seal when shaft rotates. Full pressure breakdown occurs across. Outboard secondary seal sees lower pressure, allows shutdown without process gas release into bearing cavities.

Control and Monitoring Function Primary buffer. Filtered fuel gas feed to primary seal face. Filters, 1 micron disposable coalescing elements. Delta P monitors filter load bar (100 in H20) alarm setpoint. A1-FCV suction end seals.

Control and Monitoring Function S1-FT discharge end seals. PLC in UCP controls flow to suction end seals. PLC signal from A1-PDT primary vent & compressor suction. PLC signal from a1-ft primary buffer gas flow suction end seals. Normal is one flow unit = 8ma. Nitrogen gas supply 10 BarG.

Control and Monitoring Function Warning. Primary buffer gas supply to seals required anytime there is pressure in the process cavity of the compressor. 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.

Secondary Labyrinth Buffer Instrument 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 controls secondary buffer gas flow 1.38 BarG (20psig) to FCVs a1-fl /38/40/ NCMH (300 SCFH) to each seal. A1-PT signal to PLC-UCP panel –1-MCP- 8a low pressure alarm 4.0 BarG (58 PSIG).

Secondary Labyrinth Buffer Warning. 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.

Primary Vent Primary seal failure results in increase flow to primary vent. Alarm at 2 units, 250 mbar (11ma signal) increasing. Flow measured by A1-FT B, A1-FST A signal sent to PLC in unit safety panel (1-MCP-8B). Trip when flow is 488 mbar (18.0 ma signal). 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.

Secondary Vent Vents small amounts of primary buffer gas, mostly secondary/instrument air to dedicated atmospheric vent with flame arrestor. Not controlled, not monitored.

Checkout Procedures See also john crane installation manual. 1)Bench check PSI transmitters range calibrated per schematic values. 2)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. 7)N.O. Valves indicated as outlined. 8)All interconnecting piping complete and leak free.

System Schematics General Symbols Valve & Instrument Symbols Warning statement

System Schematics Dry gas Seals Filters

System Schematics

Part 2, Introduction To Dry Gas Seals Introduction. Principals of operation. Installation guidelines. Operational guidelines. Maintenance.

Introduction Continued Principals 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.

Principals Of Operation O Rings Closing spring Outside or atmosphere side of the seal assembly Inside or process side of the seal

Principals Of Operation Continued Sealing Dam Width Spiral Grove cut into face of rotating ring Ring rotation

Principals Of Operation Continued

Closing Spring pressure System Pressure System breakdown pressure Pressure generated by spiral groves in rotating ring face.

Principals Of Operation Continued Forces interact and Reestablish Equilibrium

Principals Of Operation Continued Forces interact and Reestablish Equilibrium

Installation Guidelines A 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

Installation Guidelines Continued Caution Related to a task that if not properly executed, could result in the seal functioning correctly. Warning Relates to a procedure that if not correctly completed, damage to the seal cartridge could occur.

Installation Guidelines Continued The 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.

Installation Guidelines Continued Warning The 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 )

Installation Guidelines Continued Installation 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.

Installation Guidelines Continued Using manufactures original drawings aids in communication while reducing training development cost for the owner

Installation Guidelines Continued

Compare this and the previous slide, one is color, the other black and white, both communicate well.

Operational Guidelines Seal design description. Gas quality. Seal gas supply flow. Leakage trends. Reverse pressure. Decompression. Vibration.

Operational Guidelines Continued Seal 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.

Operational Guidelines Continued Seal 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.

Operational Guidelines Continued 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

Operational Guidelines Continued 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.

Operational Guidelines Continued 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.

Operational Guidelines Continued Reverse pressure. Reverse pressure with the compressor off line, or in a static condition will result in increased static leakage. Under dynamic conditions, can result in major damage to individual seal components.

Operational Guidelines Continued 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.

Operational Guidelines Continued 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.

Maintenance Cleaning, do not expose to oil. Storage.

Non-contact Dry Gas Seal Timeline 1969 Spiral grove developmental research begins U.S. Patent issued to John Crane Spiral grove gas seal put in Turbo-expander service Pipeline Compressor installation Off-shore platforms and wet gas service Ethylene, Coker gas, Ammonia, Liquid methane pump Explosive decompression problems solved Applied to Gas turbines, Propylene refrigeration, Steam turbines Bi-directional grove developed Pressures up to 5,000 PSIG/350 Bars.

Non-contacting Seals Eliminates heating effects of friction by non- contact between the seal faces. One seal face designed with a lift mechanism, faces float on cushion of gas. Spiral grove pressure build up at sealing dam provides resistance to flow, pressure also lifts sealing faces apart. Small gas flow across faces at to cool them. Opening and closing forces equal during operation.

Labyrinth Seals. Simple method of sealing a shaft. Series of knife edges. Clearance controlled to limit leakage. Pressure limit per knife edge typically 5 PSI. Non-hazardous gases vented to atmosphere. Hazardous gas duty, buffer gas at higher psi than process gas injected between labyrinth seals.

Summary Thirty + years, thousands of seals, millions of hours uptime. Throughout the world. Industrial standard. Centrifugal, and screw compressors, pumps, and turbo-expanders. Reduced mean time between maintenance (MTBTM). I can not leak out of this place

This completes our coverage of the Dry Gas Seal System.

Please push your chair under your desk. I need a break. Lets take a short break.

Credits Credits: 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.