Saturday, January 10, 2009

Sealing Arangements for Casing


Gland seal systems are very important to main and auxiliary turbines. Turbine shafts must exit their casings in order to couple up or connect with the unit that the turbines drive (reduction gears, pumps, etc.) The main and auxiliary gland seal systems enable the turbine to be sealed where the shaft exits the casing; in effect keeping "air out and steam in."
The purpose of gland seal system is to prevent the leakage of air from the atmosphere into turbine casings and prevent the escape of steam from turbine casings into the atmosphere (see Figure 1).
Operation Overview
1. The pressure differential between the atmosphere and inside the main engine turbine casing will vary depending on ship's speed. Similarly, the differential between the atmosphere and inside the ship's service turbine generator (SSTG) turbine casing will vary depending on electrical load.

2. Labyrinths- Sets of labyrinth packing are employed along the turbine rotor where the rotor exits the turbine casing to maintain this pressure differential.
a. The labyrinths create many little chambers causing pressure drops along the shaft. The number of labyrinth sets depends greatly on the steam pressure possible in that area. Labyrinth packing alone will neither stop the flow of steam from the turbine nor prevent air flow into the turbine.
3. Gland Sealing Steam
a. The gland sealing system provides low pressure steam to the turbine gland in the final sets of labyrinth packing. This assists the labyrinth packing in sealing the turbine to prevent the entrance of air into the turbine, which would reduce or destroy the vacuum in the associated condenser. Excess pressure (excess gland seal) is removed by the gland seal unloader.
4. Gland Exhaust
a. Since there are times when steam escapes from the seals, a gland exhaust system is provided. The gland exhaust system consists of low pressure piping connected to the gland area between the last two outer sets of labyrinths which receives and prevents steam from escaping to the atmosphere. This system collects the steam and directs it to a condenser for further use in the steam plant.
C. Main Engine Gland Seal System Components.
1. The gland seal regulator (see Figure 2)

a. Senses system pressure on the outlet side of the regulator. The gland seal regulator valve reduces 150 psig auxiliary ("dry or wet" steam depending on the ship type) steam to gland seal system pressure of .5 to 2 psig. The valve begins to open at 2 psig and is fully open at .5 psig. The bypass valve allows the operator to maintain system pressure in the event the regulator valve is inoperable. (see Figure 1)
2. The Gland seal unloader valve (see Figure 3)

a. This valve senses the pressure of the gland seal supply piping. The unloader piping is wider in diameter than the regulator piping. The gland seal unloader "dumps" the excess gland seal piping pressure to the LP turbine exhaust trunk. The unloader begins to open at 2 psig, and is fully open at 3 psig. It has a handwheel to permit manual operation of the unloader to control gland seal system pressure during a loss of control air causality.
Piping system (see Figure 1)
a. The regulator supplies the gland seal header. This header has branch lines to each turbine gland area and a branch line to the unloader. The ahead throttle valve assembly and the astern throttle valve also have a connection to receive gland sealing steam. The reason is the same on the unloader- to prevent the possible introduction of air into the system. Any air entering the turbines or piping systems affect the vacuum in the main condenser.
b. On some ships, spectacle flanges are installed in the supply lines to the HP turbine glands to allow the gland seal and gland exhaust system to be isolated when singling up with the LP turbine operating.
c. Inputs to the gland seal system include the gland seal regulator, astern throttle leak-off, ahead throttle lifting rod leak-off, HP turbine forward and after gland leak-off, and main steam emergency throttle leak-off (on ships with singling up capabilities).
4. Main engine gland exhaust system
a. Steam leaking from the gland seal section of the shaft packing is drawn off by the gland exhaust system. Gland exhaust is drawn into the gland exhaust condenser section of the Main Engine Air Ejector.
b. The gland exhaust steam is then condensed and returned to the fresh water drain collecting tank. The air and non-condensable gases are drawn off by the gland exhaust fan.
5. Gland Seal steam system operation
a. The gland seal regulator supplies .5 to 2 psig steam to the glands in varying degrees as bells change on the main engine. When answering a low bell or all stop, the gland leak off is minimal, causing the regulator to supply the total gland sealing steam. As engine speed increases, the casing is pressurized and the increased gland leak off, along with the regulator, supplies all the gland sealing steam required by the system.
(1) As ship's speed increases, the main engine becomes self sealing. The gland seal regulator is fully shut and the unloader is functioning to maintain the system pressure between 2 3 psig, dumping the excess gland seal steam to the LP turbine exhaust trunk.
(2) As ship's speed slows, the gland seal system operates in reverse sequence. (see Figure 4,5,6)

D. SSTG Gland Seal System Components
1. These components are almost identical to the main engine gland sealing components. The major difference between the main and SSTG system is the size.
a. The Gland seal regulator
(1) Senses pressure on the drain pot (or manifold). The drain pot or manifold is similar to a header and acts as "collection area" for the system steam. This area allows for the sensing lines to accurately measure the system pressure. The valve functions by reducing 150 psig auxiliary steam to the system pressure of .5 2 psig.

2. The Gland seal unloading valve
a. Senses the pressure on the drain pot. The operating range is 2 3 psig, unloading excess gland seal pressure to the lower section of the turbine exhaust casing.
3. The piping system (see Figure 7)
a. Consists of piping to the forward and after glands from the drain pot or manifold. The inputs to the system are gland seal regulator, and the forward turbine bearing. At a 60% load on the generator, leakage from the forward end of the turbine (high pressure end) supplies the system, the regulator is closed and the unloader bleeds excess to the turbine exhaust trunk.
E. Gland Exhaust System
1. Steam leaking from the gland seal area of the shaft packing, steam leak off from the steam chest lift rods, and steam leak off from the trip throttle valve is drawn into the gland exhaust system and into the air ejector condenser.
2. The steam is condensed in the SSTG air ejector condenser. Air and non condensable gases are discharged to the atmosphere via the gland exhaust fan which maintains a slight vacuum on the auxiliary air ejector condenser.
F. Causes of System Failure
1. Since most gland seal regulators are air operated reducing valves, improper pressure settings on the air pilots for the regulating and unloading valves can cause system pressure to be too high or low, or both valves may be open at the same time. Ruptured diaphragms may occur in these air pilot controllers and air operated valves. Oil and water in the air lines to the pilots or air operated valves can cause erratic operation and deterioration of the rubber diaphragms. Upon loss of air pressure, both valves fail open and the unloader valve must be operated with the manual handwheel to control gland seal pressure.
2. Painted valve stems or improper packing installation can cause binding of the stem, restricting valve operation.
3. Improperly calibrated gages can cause the system to be improperly operated.
4. In the event of a jammed gland seal regulator, the operator should take control of gland seal pressure by using the regulator bypass valve.
G. Safety Precautions
1. Do not admit steam to the glands of an idle turbine, as varying degrees of corrosion, erosion, or a bowed rotor may result.
2. Ensure the gland seal system is in operation on the main engine before aligning the main engine air ejectors. This helps prevent dirt and debris from being drawn into the turbine glands.
3. Adjustment of components shall be conducted by qualified and knowledgeable personnel. When performing adjustments, careful coordination of involved personnel will minmize confusion of gage indication.

17 comments:

  1. I have a steam turbine 330 mw which if i operate at control valve set point of 345 mw causes the self sealing of hp ip and lp glands to fail and the auxilary sealing valve opens in auto. Why does this happen?

    ReplyDelete
  2. dear joseph
    the auxiliary steam is making up the gland sealing steam...if the ammount of sealin steam in the pockets is low, the aux steam will top up the required steam.
    when you increase steam demand to the turbine,the ammount of steam tapped to accommodate aux steam will be affected.normally aux steam is either supplied from its own aux boiler or tapped from main steam,pressure reduced, furthermore by adding etra steam to turbine,you will heat up the turbine,cooling steam from aux steam is required to redice the temperature difference between blades and casing.The turbine is designed to run own its manufactured range.By overloading it you tend to overheat.

    ReplyDelete
  3. to others please rephrase your question so that i can read and understand

    ReplyDelete
  4. Thanks allot for this articles it was a nice articles about steam seal, the promoter of silicon free high temperature sealant, polyurethane adhesives, thread locker and steam seals.

    ReplyDelete
  5. My cousin recommended this blog and she was totally right keep up the fantastic work!

    ReplyDelete
  6. How far out (max time)before a plant start up should you set seals? Why would you not want to set seals 10hrs before a start?

    Toshiba D11 Steam Turbine. GE 7H Gas Turbine.

    ReplyDelete
  7. Hello!
    We have problem with vacuum in the steam system!We checked almost all lines,retaided,retaped with special tape,main condenser is cleaned,vacuum pumps ok but sill vacuum only 680mmHg!Water temperature is 26 after Cel!Maybe it could bee a gland steam!On screen ir shows 0,1 bar, but on gland steam air regulator valve pressure ir adjusted 0,2 bar............and spill valve more than 0.2 bar but still is only 0.1 bar in the system!!What could be wrong???Maybe no water in constant level pot?Or air regulators have some error??!!

    ReplyDelete
  8. Application area, metal-to-metal joints
    BIRKOSIT - Dichtungskitt ®

    BIRKOSIT - Dichtungskitt ® Sealing Compound has been used for 50 years on Siemens turbines (product development 1952 with Siemens). Without the additional sealing of individual pressure areas using BIRKOSIT - Dichtungskitt ® the production imprecision or the distortion under loads are no longer evened out, which means that the turbine areas in the individual pressure areas become permeable under pressure. This means the turbine loses power, and can even lead to unplanned reconditioning.

    BIRKOSIT - Dichtungskitt ® is formulated to be practically inert in its standard applications in steam and gas turbines. It is, therefore, resistant to exposure to hot air, steam, water, light fuel oils and lubricants. By implication, it should be resistant to crude oil and natural gas.

    For placing your orders, please contact

    Project Sales Corporation, General Agency of A.I. Schulze, for marketing BIRKOSIT - Dichtungskitt ® in India
    28 Founta Plaza, Suryabagh, Visakhapatnam 530 020, AP, India; phone: +918912564393; fax: +918912590482

    http://india.birkosit.com

    Ordering Instructions:
    Product : BIRKOSIT DICHTUNGSKITT (SEALING COMPOUND)
    Make : AI SCHULZE, GERMANY
    Pack Size: 1 kg
    Price: Rs.4250 per KG
    Taxes: CST 2% extra against form C, else 14.5% extra
    Delivery FOR Destination through First Flight Courier/GATI
    MOQ: 10 kgs
    India Distributors: Project Sales Corporation, Visakhapatnam
    Country of Origin: Germany

    ReplyDelete
  9. Sole manufacturer and Distributor A.I. Schulze
    Chemotechnische Fabrik e.K.
    Project Sales Corporation
    General Agency of A.I. Schulze
    for marketing BIRKOSIT - Dichtungskitt ®
    in the India


    --------------------------------------------------------------------------------

    Product Data Sheet
    BIRKOSIT - Dichtungskitt ®
    for extreme conditions of temperature and pressure
    Description:

    BIRKOSIT is a single-component, paste luting agent / sealing compound for industrial use wherever conditions of temperature and pressure at smooth, plane sealing surfaces (butt joints) make extreme demands on the quality of the sealing compound.

    Product data sheet This applies, in particular, to the sealing
    of metallic joints: steam and gas turbines, compressors,
    pumps, housings, flange joints etc.

    Technical data:

    Temperature resistance:
    hot steam and air, hot and cold water, light fuel oils and lubricants, crude oil and natural gas at up to 900 °C.

    Pressure resistance:
    The excellent adhesion on sealing surfaces and butt joints guarantees a perfect seal up to 250 bar. The pressure resistance for flanges without sealing rings is up to 450 bar and even up to 550 bar for screw joints.

    Plastic deformation:
    is unlimited in its plastic workability so that, even under the most demanding conditions, the sealing film does not break. cf. temperature and pressure resistance.

    Application areas:
    Steam and gas turbines, power plants, gasworks and waterworks, oil refineries, smelting works, shipyards, paint and rubber manufacturing, chemical industry.

    Working recommendations:
    To be spread on the dry surfaces using a putty knife or rubber spatula. As the product doesn’t cure but slightly changes its consistence staying flexible and elastic, application on butt joints without time pressure is possible. And the product can be subjected immediately to working loads!
    A small amount of linseed oil varnish may be added to improve the spreading properties.

    Storage:
    Unlimited storage life when correctly stored. Its properties are stable and it is flexible in use. The tin should be properly closed when only a part of the contents is used.

    Packaging:
    BIRKOSIT is packed and supplied in special 1-kg tins. Its colour is reddish-brown. For further properties of the product, see the materials safety data sheet 91/155/EEC, changed 93/112/EC and the storage life certificate. State of October 2009.

    This issue of the product data sheet supersedes back issues.


    --------------------------------------------------------------------------------

    ReplyDelete
  10. BIRKOSIT - Dichtungskitt ®

    BIRKOSIT - Dichtungskitt ® Sealing Compound has been used for 50 years on turbines (product development 1952 with Siemens). Without the additional sealing of individual pressure areas using BIRKOSIT - Dichtungskitt ® the production imprecision or the distortion under loads are no longer evened out, which means that the turbine areas in the individual pressure areas become permeable under pressure. This means the turbine loses power, and can even lead to unplanned reconditioning.

    BIRKOSIT - Dichtungskitt ® is formulated to be practically inert in its standard applications in steam and gas turbines. It is, therefore, resistant to exposure to hot air, steam, water, light fuel oils and lubricants. By implication, it should be resistant to crude oil and natural gas.

    [main application]
    single-component, paste sealing compound for sealing between machined surfaces (joints between parts) in steam and gas turbines at temperatures up to 900 °C and pressures up to 250 bar.
    [other applications]
    can also be used for sealing between smooth surfaces in compressors, housings, pumps etc. and by extension, in valve glands and screw joints.

    [additional applications]
    All kinds of screwed metal flange pipe connections (independent of flange diameter and shape). Their operating conditions are characterized by water, steam, pressure, high temperature

    ReplyDelete
  11. what is a turbine steam pressure control?

    ReplyDelete
  12. what are the effect of overheating and overcooling of turbine casing

    ReplyDelete
  13. Can anyone tell me the advantages of pressure balanced gland segment please?

    ReplyDelete
  14. hi, can tell me why and how gland sealing of steam turbine temp. increse keeping pr. const.,& also auxulary staem team. const..And how control its temp.

    ReplyDelete
  15. The Steam turbine manufacturers company should be known for manufacturing best quality of industry specific and customized steam turbines.

    ReplyDelete
  16. Steam turbine manufacturers - Kessels is a leading Steam Turbine manufacturer in the range of 5 KW to 30 MW, providing the most reliable and efficient steam turbine solutions for over 25 years.

    ReplyDelete
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    ReplyDelete