Sss

Steam Turbine Controls Consulting JOSEPH F. BYRD, JR., INC. PO Box 52 Dunn, NC 28335 PH: (910) 658-1291 [email protected] Steam Seal System When there is Vacuum inside the turbine (the LP casing and the HP casing at No Load), air will want to enter around the shaft. The Steam Seal System (SSS) prevents air from entering the turbine by applying 1.1 ATA steam through the Steam Seal Headed (SSH). To prevent SSH steam from blowing into the room, the slight vacuum of the Gland Steam Exhaust (GSE) pulls this steam along with a little air into the GSE. When there is Pressure inside the turbine (HP casing at Load), steam will want to escape from around the shaft. The SSS prevents steam from escaping by throttling it into the SSH. To prevent SSH steam from blowing into the room, the slight vacuum of the Gland Steam Exhaust (GSE) pulls this steam along with a little air into the GSE. Given the turbine internal steam temperature at the HP end will be higher, the throttled ~400 C SSH will be acceptable , However this SSH temperature would have too great of a mismatch with the metal temperatures at the LP end and thus de-super heating sprays are used to lower LP SSH steam to ~250 C. The “PID of Gland Sealing System” has been simplified for discussion. The “No Load” shows that Aux steam is provided through PCV391. This steam ~400C goes direct to HP seal, but the supply to the LP seal is through desuperheating spray DSH301 to lower temperature to ~250C. The “Full Load” shows that the HP steam blow-out into the SSH is supplying the sealing steam for the LP and the PCV391 closed. The position of PCV329 should be observed to close as the turbine load is increased. The design of your seals and their steam requirements would determine if it closes completely at high load. The higher sealing steam to the HP is due to the expected higher metal temperature of the turbine on that end. However, high temperature might cause warping during a cold startup. Another concern could be the heat from the turbine seal “cooking” the HP bearing oil deflector. A feature I have seen on steam seal systems is a relief valve to prevent the SSH pressure from increasing at high load from HP blow-by. A relief valve, (labeled “Unloader”) would dump the excessive steam seal steam at high load either to the condenser or a low pressure feed water heater □

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Steam Turbine Controls Consulting

JOSEPH F. BYRD, JR., INC. PO Box 52 Dunn, NC 28335 PH: (910) 658-1291 [email protected]

Steam Seal System When there is Vacuum inside the turbine (the LP casing and the HP casing at No Load), air will want to enter around the shaft. The Steam Seal System (SSS) prevents air from entering the turbine by applying 1.1 ATA steam through the Steam Seal Headed (SSH). To prevent SSH steam from blowing into the room, the slight vacuum of the Gland Steam Exhaust (GSE) pulls this steam along with a little air into the GSE.

When there is Pressure inside the turbine (HP casing at Load), steam will want to escape from around the shaft. The SSS prevents steam from escaping by throttling it into the SSH. To prevent SSH steam from blowing into the room, the slight vacuum of the Gland Steam Exhaust (GSE) pulls this steam along with a little air into the GSE.

Given the turbine internal steam temperature at the HP end will be higher, the throttled ~400 C SSH will be acceptable , However this SSH temperature would have too great of a mismatch with the metal temperatures at the LP end and thus de-super heating sprays are used to lower LP SSH steam to ~250 C. The “PID of Gland Sealing System” has been simplified for discussion. The “No Load” shows that Aux steam is provided through PCV391. This steam ~400C goes direct to HP seal, but the supply to the LP seal is through desuperheating spray DSH301 to lower temperature to ~250C. The “Full Load” shows that the HP steam blow-out into the SSH is supplying the sealing steam for the LP and the PCV391 closed. The position of PCV329 should be observed to close as the turbine load is increased. The design of your seals and their steam requirements would determine if it closes completely at high load. The higher sealing steam to the HP is due to the expected higher metal temperature of the turbine on that end. However, high temperature might cause warping during a cold startup. Another concern could be the heat from the turbine seal “cooking” the HP bearing oil deflector. A feature I have seen on steam seal systems is a relief valve to prevent the SSH pressure from increasing at high load from HP blow-by. A relief valve, (labeled “Unloader”) would dump the excessive steam seal steam at high load either to the condenser or a low pressure feed water heater

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