mech Seal & Steam trap for better understanding
- 1. Presented by: Aditya Kumar, GEA (Mechanical) Ammonia-II Plant P. No.- 504661 Presentation on Mechanical Seal & Steam Trap
- 2. What is Shaft Seal ? The shaft seal is a sealing element which seals the rotating shaft of a centrifugal pump where it passes through the non-rotating pump casing. Shaft Seal reduces fluid leakage to atmosphere or the entry of air from outside to a certain level.
- 4. Types of Dynamic Seal LABYRINTH SEAL: It is a clearance type seal. There are no rubbing parts and always positive clearance is maintained between Stationary and rotating part. It is used in Turbine & Compressor. CARBON RING SEAL: Here carbon ring is used, which is in 3-4 parts and held together by means of spring and provide circulatory form. Generally clearance of 0.03-0.07mm is maintained between the carbon ring and rotor. This type of seal is used in Steam Turbine (Governor).
- 5. Types of Dynamic Seal GLAND PACKING: Packing directly touches the rotor and thereby power loss is very high. Here leakage rate is essential otherwise the packing will burn due to high temperature. Therefore this type of packing is used where minor leakage is allowed. As packing needs to be regularly changed ,equipment downtime is high. Generally reciprocating pumps have this type of seal. MECHANICAL SEAL: In this case there is no leakage .Also power loss is very less. Generally Centrifugal pump have this type of seal.
- 6. Mechanical Seal A Mechanical seal is a device which prevent leakage of fluids along rotating shafts. Primary seal face is at right angle to the axis of rotation between one stationary ring and one rotating ring. To minimize leakage. To prevent leakage of toxic fluid. O-Ring
- 7. API Standard The American Petroleum Institute is the largest U.S. trade association for the oil and natural gas industry. The American Petroleum Institute was founded on 20 March 1919. API Standards enhance the safety of industry operations, assure quality, help keep costs down, reduce waste, and minimize confusion. ASME is a construction codes (Dimension & Tolerances) that covers Design, Fabrication and construction issues While API code governs the continued operation, Inspection & Repairs. For eg. ASME Section VIII covers fabrication of Pressure Vessel but once the pressure vessel are put in service, API 510 takes place. According to a study from the U.S. Department of Commerce, one petrochemical manufacturer reduced costs by $2.5 million in one year by implementing an industry-developed risk-based inspection methodology for process equipment.
- 8. API 682 about Mechanical Seal Size of Shaft from 30 MM to 120 MM. Fluid temperature -30°C to 260°C and Pressure 0 Bar to 34.5 Bar. Flushing Connection on the gland plate shall be ¾” NPT and Vent & Drain connection shall be ½” or 3/8” NPT. The clearance between Shaft OD and shaft Sleeve bore shall be 0.025 to 0.075MM. Only Solid faces shall be used (Coated face are not allowed). The seal is to be tested in four different test fluids such as water, Propane, 20%NaOH and Mineral Oil. Dynamic test is required for minimum 100 hours at 3600 RPM and Static test shall be for 4 hours. For Dual Seal ,Each seal to be separately tested and Seal should have Minimum 3 years continuous running life.
- 9. Parts of Mechanical Seal A - Stationary face B - Rotating face C - Sleeve D - Gland Plate E - Stuffing box 1 - O-ring 2 - Dynamic O-ring 3 - Sleeve gasket 4 - Sealing interface 5 - Gland gasket
- 10. Sealing Points Of Mechanical Seal • Between the shaft and the sleeve. • Between the rotating component and the sleeve. • At the mating surfaces of the primary and mating rings. • Between the stationary component and the gland plate. • Between the gland plate and the stuffing box. IMPELLER SIDE DRIVE SIDE
- 11. Balance & Unbalance Seal The opening area or face area of the balanced seal is same as the unbalanced seal, but the closing area is maintained in proportion to the face area. As we reduce the closing area, the closing force also gets reduced. Thus, less heat gets generated, and we get extended life of the seal. The balance ratio is Ac/Ao. Seal Balance Ratio= (Db 2 – Di 2 ) / (Do 2 – Di 2 ) where Do is the seal face outside diameter; Di is the seal face inside diameter; Db is the balance diameter of the seal.
- 12. Balance & Unbalance Seal UNBALANCE SEAL In unbalance seal full value of the pressure sealed is exerted on sealing faces. Unbalance seal is used for low pressure application. Generally unbalance seal can be recommended up to 10 kg/sq.cm. BALANCE SEAL A step in sleeve is used to relieve the fluid pressure across seal face. For higher pressure only balanced seal is used. In case of balanced seal wear-tear is low & heat generation is less which ensures long life of seal. Generally 70-75% balancing is used.
- 13. Balance & Unbalance Seal
- 14. Component & Cartridge Seal A component seal consist of a separate rotating member and stationary seat that mount in a gland or housing. Since they are not preset, installation and maintenance are generally more difficult and require precise measurements during installation to prevent seal failure. The cartridge seal is an arrangement of seal components on a shaft sleeve and in a seal gland constituting a single unit that is usually assembled and pre-set at the factory i.e. cartridge type seals that are completely encased within secure housings. . Both bellows and spring-type seals can be cartridge-arranged if the pump stuffing box is large enough. cartridge type seals that are completely encased within secure housings. Further, non-cartridge type seals require precise measurements during installation to prevent seal failure.
- 15. Component & Cartridge Seal
- 16. Component type Mechanical Seal
- 17. Pusher Seal As the seal springs and other pressures in the stuffing box are exerted on the seal, closure of the seal faces is achieved. As the softer carbon face wears down, the rotating face must move to maintain face closure. The dynamic ‘O’ ring is designed to move axially (be pushed) along the shaft or sleeve. Rotating face Stationary Face Closing forces exerted on the seal faces • Used in low temp. services. • Used in light end services (ethylene, propane, methane, butane etc.). • ‘O’ ring secondary seals.
- 18. Non-Pusher Seal A non-pusher type seal consists of a bellows assembly. The bellows is a component that acts as both the load element (like a spring in a pusher type) and a secondary sealing element like an ‘O’ ring in a pusher type). Because the bellows prevents any leakage to the atmospheric side of the seal, and has a large clearance between itself and the shaft or sleeve it can move freely in the axial direction (no dynamic ‘O’ ring), reducing the potential for hang up. • Closing force supplied by bellows (no dynamic ’O’ ring) • Metal bellows use ‘grafoil’ secondary seals to handle high temperature
- 19. Single Seal & Multiple Seal Single seals use the pump's fluid as a lubricant, while double seals have a dedicated buffer or barrier liquid. A single mechanical seal consists of two very flat surfaces that are pressed together by a spring and slide against each other. Between these two surfaces is a fluid film generated by the pumped product. An absence of this fluid film (dry running of the pump) results in frictional heat and ultimate destruction of the mechanical seal. This fluid lubricates the seal faces and absorbs the heat generated from the associated friction, which crosses the seal faces as a liquid and vaporizes into the atmosphere. So, it's common practice to use a single mechanical seal if the pumped product poses little to no risk to the environment. A double mechanical seal consists of two seals arranged in a series. The inboard, or “primary seal” keeps the product contained within the pump housing. The outboard, or “secondary seal” prevents the flush liquid from leaking into the atmosphere.
- 20. Double Seal A double seal is an arrangement in which two mechanical seal are utilized face to face, back to back or in tandem (facing the same direction), allowing a barrier/buffer fluid or gas to be introduced between the two sets of seal faces. It has 2 Primary and 2 mating ring per seal with a barrier fluid between two seals. This type of seal is generally used for: 1. Flammable and toxic or otherwise dangerous fluids 2. Where seal face lubrication is required without diluting the pumped liquid.
- 21. Back to Back Double Seal Here two seals having back to back primary rings & mating rings are used at extreme ends. This arrangement is more suitable for sealing liquids at high vacuum. Lubrication of both the seal faces is done by barrier liquid at a pressure higher than pump pressure by 1 to 1.5 kg/sq.cm. In case of inboard seal failure the barrier fluid will mix with pumped liquid but pumped liquid will never leak out. So barrier fluid must be compatible with pumped liquid.
- 22. Double Tandem Seal Two seals in same direction facing fluid to be sealed & in series are used. Outer seal acts as a safety seal in case inner seal fails. Lubrication of inner seal is by pumping liquid itself & outer seal is lubricated by barrier fluid. Here barrier fluid pressure is less than pumping pressure. In case when inner seal fails, the pumped liquid will mix with barrier fluid but barrier fluid will never mix with pumped liquid. This type of seal is mostly used where hazardous fluid to be pumped. Eg. Tandem seal is used in Ammonia Pump P-3501A/B.
- 23. The Fluid Film In most mechanical seals the faces are kept lubricated by maintaining a thin film of fluid between the seal faces. This film can either come from the process fluid being pumped or from an external source. This is achieved by maintaining a precise gap between the faces that is large enough to allow in a small amounts of clean lubricating liquid but small enough to prevent contaminants from entering the gap between the seal faces. The gap between the faces on a typical seal is as little as 1 micron – 75 times narrower than a human hair. Because the gap is so tiny, particles are unable to enter otherwise damage the seal faces.
- 24. Seal Materials Carbon Graphite , Tungsten Carbide , Silicon Carbide , Ceramics , Rubber elastomers (Viton, PTFE, Neoprene) are the most common materials used in Mechanical Seals. Selection of material depends on operating temperature, pressure, corrosion resistance property & compatibility with pumped fluid . Carbon: It is compatible with most of the chemicals. It also has a good self lubricating properties for start up condition. Excellent heat transfer properties. Resin impregnated carbon which is generally used. Metal impregnated (normally antimony), used for high temp. application. Tungsten Carbide: It has outstanding wear resistant characteristics & high modulus of Elasticity. It is not suitable for high acidic liquids having Ph<4. Cobalt bonded generally used in many chemicals . Nickel bonded is generally used for BFW application and in refineries.
- 25. Seal Materials SILICON CARBIDE: It is corrosion resistant to most of the liquid except for highly alkaline liquids at high temp. First is resin bonded, used for high speed, high temp. applications due to its lower coefficient of friction & higher hardness. Second is alpha sintered and used for all general application. it has excellent abrasive resistance. CERAMIC: This is basically aluminum oxide. It has good abrasion resistance properties. But it can not take thermal shock, so it is used where temp. variation across the face is lower than 100o c .
- 26. Seal Materials ELASTOMERS: Here operating temp. is main criteria. The material must retain their flexibility at operating temp. And at the same time should be corrosion resistant. RUBBER ELASTOMERS: Usually viton, neoprene, etc are used. It’s compatibility with pumped fluid should be checked. GFT/PTFE ELASTOMERS: If rubber material is not compatible then these can be used. GFT(glass filled teflon) is capable of handling high temp. than PTFE(poly tetra flouro ethelene). sleeve wear is more with these materials than rubber. GRAFOIL PACKING: For higher temp. application where rubber/GFT packing are not suitable grafoil packing is used. But these can not be used in dynamic condition, hence can not be used in pusher type seal heads. this is the only packing used with metal bellows seals.
- 27. Face Flatness The mechanical seal faces are obviously the most critical sealing point of a mechanical seal assembly. The faces can be manufactured of different materials, one is typically carbon, while the other is usually a hard material. (i.e. Alox (Aluminum Oxide Ceramic), Tungsten Carbide, Silicon Carbide, etc.) In order for a seal to be achieved, the faces must be very flat. This is achieved by machining the faces, then lapping them to a fine finish. Flatness is measured in Light Bands. After lapping, the faces are placed on an Optical Flat, a clear glass surface where a monochromatic light is shined on the face. This single wavelength light will produce an image of rings or lines on the face. Each ring/line is One Light Band. Each light band is equivalent to .000011 or eleven millionths of an inch(.29μm). This refers to the variations in the surface of the face. On most face materials, one light band is found.
- 28. Face Flatness Surface flatness of the sliding faces Outer diameter of the sliding faces< 80 mm 2 light bands ( 0.58 μm) Outer diameter of the sliding faces > 80 mm 1 light band ( 0.29 μm) Sliding surface with imperfect flatness Perfectly flat surface
- 29. Internal recirculation from pump discharge to seal & use for clean pumpage only Recirculation from Pump discharge through a flow control orifice to the seal Recirculation from Pump discharge through a strainer & flow control orifice to the seal Recirculation from Pump seal chamber through a flow control orifice and back to the pump suction SEAL CHAMBER FOR PLAN 13 Flush is injected into the seal chamber from an external source Recirculation from Pump discharge through a cyclone separator delivering the clean fluid through seal cooler to seal chamber and fluid with solids back to pump suction API Seal Flush Plan
- 30. API Plan 52 & 62 (Quenching) LBI- Liquid Buffer Inlet, LBO- Liquid Buffer Outlet LSL- Level Switch Low LSH- Level Switch High PI- Pressure Indicator PS- Pressure Switch 6- Reservoir, 7- Make up Buffer Fluid F- Flush, V- Vent LI- Level Indicator
- 31. Causes of Seal Failure Dry running. Vaporization. Abrasives in product. Sludging. Bad fitments. Carbon ring erosion. Face distortion. O-ring extrusion. Spring distortion.
- 32. Steam Trap A Steam Trap is a device used to discharge condensates and non-condensable gases with a negligible consumption or loss of live steam. The operation of a steam trap depends on the difference in properties between steam and condensate. It is an automatic valve capable of discharging condensate and trapping the steam. THE STEAM TRAPS CAN SENSED BETWEEN CONDENSATE AND STEAM IN FOLLOWING WAY. DIFFERENCE IN DENSITY (MECANICAL STEAM TRAP) DIFFERENCE IN TEMPRATURE (THERMOSTATIC STEAM TRAP) DIFFERENCE IN FLOW CHARACTERISTICS (THERMODYNAMIC STEAM TRAP)
- 33. Why Steam Trap is Necessary ? All the latent heat associated with steam is used. Condensate removal for pipe Capable of discharging air and other non-condensable gases. Water Hammering Corrosion Non-effective Heat Transfer
- 34. Mechanical Steam Trap & types Inverted Bucket Trap In Inverted Bucket steam traps, the bucket within the trap is attached to a lever that opens and closes the trap valve in response to the bucket’s motion. Ball Float trap: In ball float trap, as condensate enters the trap, the float attached to a lever becomes buoyant and moves the lever, causing the trap valve to open. The float responds to condensate flow, opening and closing the valve to compensate accordingly. Mechanical traps are steam traps that operate on the principle of specific gravity (specifically the difference in the specific gravities of water and steam). They will continuously pass massive volumes of condensate and are suitable for a large range of process applications.
- 35. Thermostatic Steam Trap Thermostatic trap remove condensate through the temperature difference of steam & Liquid phase (Condensate) i.e. it works on the difference in Enthalpy of Steam and Condensate. Balanced Pressure Trap: The Flexible sealed element expands and contracts lengthwise under the influence of internal & external Pressure. Liquid Expansion Trap: An oil filled element expands when heated to close the valve against the seat. The adjustment allows the temperature of the trap discharge to be altered between 60°C and 100°C. Bimetallic Expansion trap: Two metal having different coefficient of expansion are bonded together and heated the composite piece will take up a curved shape. This movement with changing temperature can be made to operate the valve of a steam trap.
- 36. Bimetallic Steam Trap The Bimetallic Steam Trap uses the Thermostatic principle of the unequal expansion of two metals (Bimetallic) at high temperatures to open and close the Condensate drain valve. When high-temperature Steam comes in, the Bimetal disk will heat and bend. Causes the stem to move upwards to close the valve, but if condensate water gets trapped in a steam trap, the condensate temperature will gradually decrease until the Bimetal disk comes back straight and causes the stem to slide down to open Valve.
- 37. Thermodynamic Steam Trap The thermodynamic trap is an extremely robust steam trap with a simple mode of operation. The trap operates by means of the dynamic effect of flash steam as it passes through the trap. The only moving part is the disc above the flat face inside the control chamber or cap. On start-up, incoming pressure raises the disc, and cool condensate plus air is immediately discharged from the inner ring, under the disc, and out through peripheral outlets. • Hot condensate flowing through the inlet passage into the chamber under the disc drops in pressure and releases flash steam moving at high velocity. This high velocity creates a low pressure area under the disc, drawing it towards its seat.
- 38. Selection of Steam Traps OPERATING CHARACTERISTICS PRESSURE AND TEMPERATURE LIMITS STEAM TRAP CAPACITY MATERIALS ADVERSE CONDITIONS
- 39. Steam Trap used in AMM-II Ball Float Steam Trap Make: M/s Spirax Thermodynamic Steam Trap Make: M/s Spirax Marshall Bimetallic Steam Trap Make: M/s Armstrong
- 40. Benefits of Effective Steam Trapping A healthy steam trap population allows condensate to be removed from the steam system effectively which means it can be re-used. We call this ‘condensate recovery’ and it saves energy and cost in a number of different ways: Reduced fuel costs: Normally, condensate will contain around 25% of the usable energy of the steam from which it came. Returning this to the boiler feed tank can save thousands of pounds per year in energy alone. Energy saving: Condensate returned to the feed tank reduces the need for boiler blowdown, which is used to reduce the concentration of dissolved solids in the boiler. This therefore reduces the energy lost from the boiler during the blowdown process. Reduced water charges: Returning and re-using condensate reduces the requirement for fresh replacement water. Reduced chemical treatment costs: Re-using as much condensate as possible minimises the need for costly chemicals to treat raw water. Reduced effluent costs: In many countries there are restrictions on releasing effluent at elevated temperatures so it must be cooled if discharged which incurs extra costs.
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