Quick Cooling System of Steam Turbine

12.1 Preparation prior to operation:

12.1.1 The quick cooling equipment is complete and useful.

12.1.2 Iron rust inside the heaters, gas collection tank and oil-water separator have been cleared out thoroughly that are treated for corrosion protection, the strainer is reliable through check which can ensure purity of air entering the turbine so as not to pollute the inside of turbine. Check and verify the drain in cylinder and related pipes are all discharged so as to prevent drain from dumping into the cylinder. Check if all metal temperature measurement points of cylinder are sound. Check if the indications of cylinder differential expansion, expansion, axial displacement and eccentricity, etc. are normal.

12.1.3 Operating of the safety valve of quick cooling equipment is reliable.

12.1.4 With the automatic control of heating air temperature that can control the temperature deviation within ±5℃ and alarm in case of exceeding the limit, the temperature and flow indicators and recorders are complete and useful.

12.1.5 Check if all valves of the quick cooling equipment and the system are in correct state.

12.1.6 Verify the circulating water system is put into operation and operating normally.

12.1.7 Verify the turning gear is put into operation and operating normally, shaft oscillation is not more than 0.07mm and the indications of instruments are normal.

12.1.8 Verify the condensate system is put into operation and operating normally;

normally.

12.1.10 The manhole on the steam side of condenser steam side is opened. Check if the drain valve before HP exhaust check valve is opened.

12.1.11 Only when the cylinder temperature decreases to below 350℃, it can put the quick cooling equipment into operation.

12.2 Monitoring of parameters in quick cooling process:

In order to ensure the mental temperature inside the turbine can decrease evenly in the process of quick-cooling after turbine shutdown so as to prevent overstress due to excessive cooling, rotor from bending and cylinder and welded junction from deforming, it must strictly monitor the changes in each point temperature, temperature difference between cylinder inner and outer wall, temperature difference between upper and lower cylinder, absolute expansion, differential expansion, axial deflection, rotor eccentricity, turning gear current, compressed air temperature and flow and electric heater current in the process of putting the quick cooling equipment of turbine into operation. The monitor control index of main parameters includes:

12.2.1 First stage metal temperature decreasing rate of HP cylinder is<5℃/h.

12.2.2 Carrier temperature decreasing rate of MP cylinder is<5℃/h.

12.2.3 Temperature difference between upper and lower cylinder of HP & MP cylinder is <42℃.

12.2.4 Indication of HP cylinder differential expansion is -2~+7.0 mm.

12.2.5 Indication of LP cylinder differential expansion is +6.5mm.

12.2.6 Rotor eccentricity is <0.076mm.

12.2.7 Turning gear current is normal.

12.2.8 Lubricating oil pressure is 0.12Mpa.

12.2.9 Cylinder expansion and contraction are smooth without sudden change 12.2.10 Control the compressed air flow within 25~80t/h.

12.2.11 After putt the quick cooling equipment of turbine into operation, , try to adopt no temperature difference and little flow mode as much as possible in the early stage of air supply, then slowly reduce the air temperature to keep the little temperature differences and increase the flow to observe the change in the cylinder’s temperature. Strictly control the cylinder’s air inlet temperature and ventilation quantity. In principle, keep stable for 30min every time of adjustment, if there is no change or great change, make readjustment. The outlet temperature of air heater shall decrease steadily without sudden change. When the air duct wall temperature of HP & MP cylinder is about 100℃ and the first stage metal temperature of HP cylinder decreases by less than 200 ℃, it may increase the ventilation quantity. When the first stage metal temperature of HP cylinder and No.1 stator carrier temperature of MP cylinder reach below 140 ℃ and do not

rise again obviously, it may end the forced ventilation. Close the air inlet valve and keep on turning for 30min to see if the temperature of all points rises again, if not, it may stop turning to start servicing.

12.3 Put-in of quick cooling equipment of turbine:

12.3.1 Put the LP cylinder spray of main machine into operation normally.

12.3.2 Slightly open the blowdown valve of oil-water separator and the drain valve of the gas collection tank.

12.3.3 Open the total valve of compressed air.

12.3.4 Put the heater into operation.

12.3.5 Open wide the primary valve and adjust the air inlet flow of secondary valve as putting the quick cooling equipment into operation. Slowly open the hand-operated air inlet valve of compressed air to HP & LP drain pipe.

12.3.6 Open gradually the air inlet valve wider and set the outlet temperature of air heater according to the decreasing of cylinder’s temperature, and control the temperature decreasing rate not exceed 5 /h.℃

12.3.7 Check if the exhaust temperature that shall not exceed 80 .℃

12.3.8 In the process of put-in, check if the temperature difference between upper and lower cylinder that shall not be more than 41 .℃

12.3. In the process of put-in, pay attention to the change in cylinder expansion, differential expansion and deflection.

12.3.10 Pay attention to the turning gear operating that is normal.

12.3.11 Keep various records.

12.3.12 If any abnormality, it shall stop air inlet of cylinder and report to the shift engineer.

12.4 Precautions in quick cooling operation:

12.4.1 Prior to forced cooling, purge the forced cooling system first up to standard and drain out the water depositing in the system pipe.

12.4.2 In the case where turning gear of turbine is not put into operation, it is absolutely prohibited to put the quick cooling equipment into operation; if so, stop the quick cooling system immediately after the turning gear tripping.

12.4.3 Put the electric heater into adjusting the outlet steam temperature to warm up the system pipe.

12.4.4 In the process of cooling, control the air inlet flow and outlet steam temperature strictly in accordance with the specified decreasing rate, intensify monitoring, make adjustment from time to time, control various parameters within permitted range and ensure safety of the unit.

12.4.5 In the process of forced cooling, it shall monitor and ensure normal operation of lubricating

system, if any system above stops, it shall stop forced cooling of turbine until the system recovers.

12.4.6 In the process of forced cooling, intensify the monitoring of the operation of service compressed air system at the same time.

12.4.7 In the process of cooling, if the decreasing rate difference between HP & MP cylinder temperature is high, it may adjust and control with each branch valve.

12.4.8 It must not interrupt the compressed air as putting the quick cooling equipment into operation so as to avoid dry heating of heater.

12.4.9 When the quick cooling equipment heater is in operation, pay attention to the operation of heater, if air compressor stops or compressed air interrupts, it shall stop inlet of compressed air and stop the quick cooling equipment.

12.4.10 When the quick cooling equipment is in operation, keep record of the turning gear current, exhaust cylinder temperature, governing stage metal temperature of turbine, MP carrier temperature, cylinder expansion, differential expansion, deflection and cylinder temperature, etc.

proper parameters once every half a hour.

12.4.11 In the process of quick cooling, it shall drain the water of steam-water separator, steam bleeding box and gas container of air compressor and clean the filter periodically to prevent oil and water dirty from entering the cylinder. Only in condition that the compressed air and flow are normal, can the heater be put in to operation and can air be supplied to the turbine after the air heater temperature becoming in accordance with the index. If discovering the air heater fails to control temperature, it shall close the air source to prevent cold water supplied to turbine.

Precautions and parameter requirements:

a. When the governing stage mental temperature is 350-300 , the temperature decreasing rate℃ shall be less than 3 /h and the temperature difference between hot air and mental shall be less℃ than 40 .℃

b. When the governing stage mental temperature is 300-250 , the temperature decreasing rate℃ shall be less than 4 /h and the temperature difference between hot air and mental shall be less℃ than 60 .℃

c. When the governing stage mental temperature is 250-200 , the temperature decreasing rate℃ shall be less than 5 /h and the temperature difference between hot air and mental shall be less℃ than 90 .℃

d. When the governing stage mental temperature is 200-150 , the temperature decreasing rate℃ shall be less than 5 /h and the temperature difference between hot air and mental shall be less℃

than 130 .℃

12.4.12 When air temperature exceeds the deviation or the electric heater loses power, it shall raise the alarm and interlock close the inlet valve to prevent cold air from entering and cooling the cylinder excessively, meanwhile cut off the power supply of heater to prevent the heater from dry heating.

12.5 Stop of quick cooling system

After finishing quick cooling, adjust the potentiometer to 0 point manually, stop the heater, open the power supply switch and continue to ventilate for 5~10 minutes, then close all valves. Slightly open of the blowdown valve to prevent air leak of air inlet valve from resulting in water entering the equipment.