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23 Cards in this Set
- Front
- Back
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Low Pressure Feedwater Heaters |
17th, 16th, 15th, and 13th Stage Feedwater Heaters |
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Intermediate Pressure Feedwater Heaters |
12th and 10th Stage Feedwater Heaters |
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High Pressure Feedwater Heater |
7th Stage Feedwater Heater |
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Which feedwater heaters have Reverse Current Valves? |
10th through 15th Stage Feedwater Heaters |
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How do the reverse current valves operate? |
In normal operation, and actuating arm is held in the disengaged position by a pneumatic power cylinder and air pressure from the turbine control system. When valve closure is required to protect the turbine, the disk will swing closed with normal check valve action. Possibility of failure to close is eliminated by the secondary closing force provided by spring action when the air pressure is exhausted by the turbine control system from the pneumatic power cylinder. Closure force of the reverse current valves is also actuated by a high contact on the feedwater heater level indicator. |
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What kind of valving does the 7th stage feedwater heater extraction line have? |
It contains an electric motor operated non return (stop-check) valve. The valve is designed with a full floating guided disk. When loss of steam flow through the valve, the disk is free to close by gravity. The disk may also be driven closed against full extraction pressure by the motor actuator. Operating signals for the motor actuator is received from an open-stop-close switch on the main control board. A contact on the 7th stage heater level indicator will also drive the check closed on excessively high level and the heater shell. |
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Which feedwater heater's extraction lines do not have valves or reverse current valves? |
17th and 16th Stage Feedwater Heaters |
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What type of level control instrumentation serves the feedwater heaters? |
Yarway level indicators are installed on the feedwater heaters to visually check the set point and operation of level control equipment. High and low level contacts on the indicators are employed to annunciate and caution the operator that recommended operating limits are being exceeded. Additional contacts on the level indicators perform various other functions automatically to maintain good control conditions. |
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What is the effect of a high level in a feedwater heater? |
Drips in the shell have risen and flooded the tubes in the steam condensing zone preventing heat transfer and reducing outlet temperature of the feedwater heater. |
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What is the effect of a low level in a feedwater heater? |
If the shell liquid level is too low, it will cause the steam to blow through the heater without transferring heat through the tubes to heat the feedwater. |
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Why do we have reverse current valves? |
To protect the turbine from reverse flow of steam or liquid flowing from the heater to the turbine. |
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What causes a reverse current valve to trip? |
• Loss of hydraulic oil pressure in the turbine generator.• Hi generator. • High level in the feedwater heater actuated by the heater level indicator. |
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Where do drips from the 12th Stage Feedwater Heater go? |
To the 12th Stage Feedwater Heater Drip Pump. The 12th stage drip pump takes suction from the 12th stage heater sub cooler and descharges into the boiler feed pumps suction line. |
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What could be the cause if the inlet and outlet temperature of the feedwater heater is the same? |
• High drip level in the heater preventing heat transfer to the tubes. • Low level in the heater causing steam to blow past the tubes without transferring heat. |
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What is special about the 7th Stage to 10th Stage drip regulatior? |
Closure of the 7th stage extraction steam motor operated valve by the control room switch will activate an air solenoid valve to supply 35 psi pressure to the head of the drip valve to the 10th stage heater preventing reverse flow. |
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During start up, what must be open on the feedwater heaters? |
The alternate drip valves (startup drains or dump valves) |
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What is the purpose of the drip valves? |
To directed the condensed drips from one heater to the next. 7th to 10th, 10th to 12th, 13th to 15th, 15th to 16th, 16th to 17th, and 12th goes to the 12th stage drip Pump to the suction line of the boiler feed pumps. |
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Pumps. Is the purpose of the alternate drip valves(startup valves or dump valves)? |
To direct the drips from the heaters to the condenser during startup or when the liquid level is rising in the heater and the normal drip valve cannot maintain proper liquid level. |
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Which extraction lines have 2 reverse current valves? |
12th and 13th stage extraction lines |
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Which extraction lines only have one reverse current valve? |
10th and 15th stage extraction lines |
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Which extractions lines do not have reverse current valves? |
7th, 16th, and 17th stage extraction lines. |
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Where do the turbine side and heater side drains on the extraction lines go to? |
The condenser |
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How do you take feedwater heater out of service? |
• Open FWH turbine side ext stm drain blk vlv • Close FWH heater side ext stm drain blk vlv. • Close FWH normal drip reg bypass blk vlv • Close FWH normal drip reg outlet blk vlv • Close extraction steam blk vlv • Open FWH feedwater bypass vlv • Close FWH feedwater inlet blk vlv • Close FWH feedwater outlet blk vlv • Close FWH vents to condenser • Open FWH feedwater inlet drain • Open FWH feedwater outlet drain • Open all remaining drains on FWH feedwater header • Close FWH alternate drip reg bypass vlv • Close FWH alternate drip reg outlet blk vlv • Open FWH steam side drain • Make sure heater is drained and cooled down • Remove chain and close FWH thermal relief blk vlv |
