Features of 330MW Steam Turbine
The 330MW steam turbine-generator adopted ALSTOM technology, by cooperation manufacturing of 330MW steam turbine-generator unit and auxiliary equipment, BSTG introduced advanced 330MW steam turbine-generator technology, including entire design, manufacture, installation, debugging, quality control and management. Comparing with other domestic 300MW steam turbine-generator, this type of 330MW unit has fallowing features：lower heat rate, startup quickly, flexible and reliable operations, long life time, excellent design, installation easy, adopting motor-driven feed water pump and the vertical type heaters.
Figure 1. 3-casing, 2-exhaust 330MW Steam Turbine
1、Lower heat rate
Based on the principle of “introducing advanced technique�? by many aspects comparison and type-selection, eventually BSTG introduced ALSTOM 330MW unit.
During cooperation manufacturing process, BSTG continue to absorb the technique improvement, especially IP module and HP module, and further improved turbine-generator thermal efficiency. In 1998 according to ASME PTC 6.1 standard. The approval heat rate test was made at Tai Zhou power plant 8 # unit. The result is 1838 kcal/kW·h（exhaust pressure is 4.5kPa�?lower than guarantee value 1851 kcal/kW·h .
2、Startup quickly
The steam turbine adopts IP Module startup mode, the technique originated from ALSTOM in the eighties of the twentieth century, then other famous company manufacture impulse-type turbine also adopted this technique.
The essential points for turbine startup is to control temperature difference between inlet steam and casing metal so that the thermal stress can be controlled in reasonable scope. Normally adopting HP module startup mode, HP rotor is heated first and its thermal stress is high. Therefore HP module startup mode will lead that casing heating time is more long and temperature rise is slow.
The steam turbine supplied by BSTG is equipped with HP and LP bypass and adopts IP module startup mode. Period from startup to carrying full load is following:
Cold startup 200 minutes
Warm startup (startup after a forty-hour shutdown) 80 minutes
Hot startup (startup after a nine-hour shutdown) 50 minutes
Extreme hot startup (after a one-hour shutdown) 35 minutes
Comparing with conventions HP module startup, the unit startup quickly, 20000 tons of fuel consumptions were saved in 30 years.
IP module startup mode have the following advantages.
(1) At cold startup, warm startup or hot startup, the steam at inlet of IP module always low pressure steam, for example, 330MW turbine adopts 1.5MPa low pressure steam. In this way, the steam heat exchange coefficient is little and IP rotor thermal stress level is low.
(2) At the initial stages of turbine startup, HP casing will be under vacuum by isolation, this not only prevents from HP rotor overheat but also warms up HP casing to prepare switch inlet steam from IP to HP.
(3) Switching inlet steam from IP casing to HP casing when IP module startup load reach 12%~15%, by this way, the inlet steam flow in HP casing is sufficient, which can ensure that the rotor and casing thermal stress level is low.
(4) Under cooperation of bypass system, this startup mode could ensure reasonable temperature distribution. Therefore, the thermal stress on IP module startup mode level will be more less than on HP module startup mode.
(5) According to ALSTOM stress and life wastage calculation, under warm startup and hot startup condition, each time life wastage is 0.009%, which more less than the life wastage on HP module startup mode, and under load step change condition (10%) , each time life wastage is only 0.009%. therefore, the unit life is very long and will exceed 30 years
3、Flexible and reliable operations
The steam turbine usually carries basic load. But also can carry pick to pick load. Even house-load without any time limitations.
Under cooperation of bypass system, the optimal load exchange rate could be put in practice, and ensure the unit safety. The unit can carry 345MW load on requiring the peak load, and the unit will permit to operate for long time on sliding pressure mode on requiring the low load at night, the scope of sliding pressure is from 35% to 91%.
At the same time, this unit has excellent load rejection performance, the unit is permitted to reject 100% load and rapidly switch into house-load operation.
4、Long life time
A life time of steam turbine depends on structure design, verying conditions and operation mode. IP startup mode facilitates extending life time of steam turbine. Usually the life time of the 330MW turbine is more than 30 years.
5、Excellent design
The turbine is a multi-stage, single-reheat impulse type. It comprises one HP module, one IP module and one LP module. Their structures have many features for example.
l The turbine casings are concentric multi-shell cylinders designed for an excellent thermal behavior to provide perfect tightness and a large operating flexibility (rapid startups and load changes).
l The high and narrow flanges of the casings with a low thermal inertia are designed. No preheating is required at startup and joint tightness is ensured in all conditions.
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Figure 2. HP module（left）�IP Module（right）inlet section drawing | The shaft diameter results from a compromise between, good mechanical behavior, good efficiency rating and good operational flexibility.
l The standard integral shroud blades for the HP, IP and first few LP stages, the blades of the last two LP stage differ from the other blades at the root and the tip They are provided with a fir-tree root which facilitates their assembly and disassembly while guaranteeing good vibration behavior in operation. The length of last stage blade is 902mm, so leaving velocity loss is lower.
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Figure 3. Control valve sealing structure | In the stop and control valves all the mating rubbing parts are either made from stellite or stessite coated for optimal sliding and tightness.
6、Installation easy
Assembled HP and IP module are directly delivered to site. It is not necessary to disassembly. So reducing two months of the period of installation.
Figure 4. completed HP module (left), IP module (right)
7、Adopting motor-driven feed water pump
Comparing with steam-turbine-driven, both proposals have a similar efficiency, but motor driven pump has following advantages:
l Simplify thermal dynamic system
l Reduce investment
l Operation easy
l Higher reliability
l Maintenance easy
8、The heater is designed in the vertical position in installation.
When the electric-driven water pump replaces the air-driven water pump, the space for the electric-driven water pump can be used for the vertical HP&LP heaters in the steam turbine hall. On the other side of the steam turbine the de-oxygen is positioned. Such layout has the following advantages:
l The space for the de-oxygen bay is reduced by 9m in width in building of the hall.
l The pipes for the 4 systems and re-heat system are shortened and therefore the investment is reduced.
l The pressure in the pipes is made fully used of and this helps reduce the coal consumption in power generation which is a considerable benefit to the customers.
9、Compact excitation.
Bearingless and brushless exciter giving shorter configuration and less maintenance.
10、Easy transportation.
No special wagon needed for transportation of generator stator, only 184tons, the lightest in 300MW class H2 cooled generator.
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