What are the effects of excessively high and low vacuum levels on turbine startup?
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Question: What are the effects of excessively high and low vacuum levels on the startup of a steam turbine? I hope fellow sailors will not hesitate to share their advice; thank you all~! !
With too high a vacuum and low exhaust pressure, the steam consumption for the same load decreases, resulting in better economic efficiency! By comparing the performance charts provided by the manufacturer regarding exhaust pressure and steam consumption, it can be seen that 1 Kpa has an impact on the amount of steam produced per ton; although this varies from one unit to another, an improvement in efficiency is certain. Conversely, the gas consumption increases. Additionally, during low-speed warming up, the vacuum level can be appropriately reduced; at the same speed, an increased exhaust pressure leads to higher steam consumption, thereby achieving a better warming effect!
At the beginning of startup, the vacuum level should not be too high; if it is too high, the amount of air intake will decrease, which affects the warming-up time and effectiveness, resulting in inadequate warming-up. Theoretically, for normal operation, a higher vacuum level is desirable as it helps to achieve maximum efficiency in the turbine. However, when the vacuum level is too high, higher quality materials are required for the turbine rotor and impeller, which makes it less economical. Therefore, I believe the vacuum level should be kept within a certain range – what could also be referred to as the optimal efficiency point
If the vacuum level is too high, the amount of steam entering will decrease, which affects the performance of the turbine； Too low a level will allow cold air to be drawn in through the shaft seal, affecting steam condensation. At the same time, the shaft seal is subjected to high thermal stress.
A high vacuum level means a low exhaust pressure at the final stage, right? Isn’t that better?
Based on my previous units, during startup the vacuum level should not be too low; as the speed increases and the amount of steam rises, the vacuum level is gradually reduced to the operating parameters
A low vacuum level results in better economic efficiency, but it increases shaft displacement; the condensate pump is prone to cavitation. A high vacuum level raises the temperature of the exhaust cylinder, leading to lower turbine efficiency.