Steam turbine exhaust pipe temperature
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Why does the temperature of the steam turbine exhaust pipe rise at low speeds?
The turbine efficiency decreases, resulting in a reduction in the steam enthalpy drop; therefore, the exhaust steam temperature rises.
During low-speed warm-up, first, less work is done by the steam, resulting in a decrease in enthalpy; moreover, the high leakage rate of the main steam valve must also be taken into account； At the same time, if the vacuum level is too low, it will also result in an increased amount of sealed steam entering the cylinder, leading to a rapid rise in temperature. We have similar situations as well; usually, before the warming-up time is up, we decide whether to cross the critical point based on the temperature of the exhaust cylinder. After crossing that critical point, the temperature drops naturally.
At low speeds during warming up, the amount of air intake is limited, and the frictional heat generated cannot be dissipated; as a result, the exhaust temperature rises. Therefore, the warming-up period at low speeds should not be too long, with the exhaust temperature generally required to remain below 120 degrees Celsius!
During low-speed warm-up, the lower enthalpy drop results in a higher pressure at the exhaust side, and accordingly a higher temperature as well； At the same time, if there is shaft seal steam, it will also affect the exhaust temperature during low-speed warm-up.