Relationship between steam consumption of the turbine, vacuum level, and exhaust temperature
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Our factory uses turbines to drive the compressors. Under normal load, the steam consumption is 30 tons. Recently, due to problems with the previous unit, the machine’s speed and pressure were reduced, and now the steam consumption has dropped to 10 tons. However, the exhaust temperature has risen sharply, from 50° to 100°, while the vacuum level remains unchanged. Experts, what could be the reason for this? ? ?
At low load operation, the humidity of the steam increases, causing the steam to not be cooled in the turbine; as a result, the temperature of the exhaust gas rises. This is my personal opinion; it’s not necessarily accurate, just for your reference
At low load, the steam is not fully utilized, resulting in significant reheat, which causes the temperature of the exhaust cylinder to rise.
After the unit slows down and its pressure is reduced, not only does the amount of steam used decrease, but the enthalpy drop of the steam within the turbine also becomes much smaller. In other words, under normal conditions, low-pressure steam at around 250°C can cause the rotor to do work, after which its temperature might drop to 100°C; further cooling by the surface cooler would then bring it down to around 50°C. But under these current operating conditions, the temperature of the steam after it drives the rotor might only drop to 150°C, with further cooling by the cooler resulting in a temperature of around 100°C! (When the vacuum level does not change much, its impact on the cooling effect of the surface cooler can be ignored.) This is just my personal opinion for reference only! :D
The main reason is low load and low steam throughput, which prevents the heat generated by blade aerodynamic friction from being dissipated; this problem is particularly pronounced in cases of pure condensing turbines.
Due to the low-load operation at this time, the amount of steam required is insufficient to remove the heat generated by friction as the turbine rotor rotates, which causes the temperature of the cylinder to rise!
You can figure it out by calculating the enthalpy of the steam.
The inlet pressure is low, the quality of the steam is poor, the capacity for performance is limited, and the exhaust temperature rises; this falls within the scope of the second law of thermodynamics —— for those who are just starting out
As a supplementary question, what is the exhaust humidity?
Reply to 8# kitesr: The quality of the inlet steam has not changed; consumption has decreased, which results in higher temperatures in the subsequent systems
Reply to 10# MYHAICHUAN: Could you please explain what is meant by \"reduced consumption\"? What is the relationship between it and the exhaust temperature?