Back-pressure steam turbine
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In a back-pressure turbine, when there is a sudden slight decrease in the gas volume at the turbine inlet, does the turbine speed increase or decrease?
The gas richness has decreased, probably due to a low reaction pressure. In this case, there are two options: either open the anti-surge valve of the atmospheric compressor, or reduce the speed of the compressor.
The speed of the turbine depends on the control mode of your compressor speed – whether it is automatic, manual, or semi-automatic. Being in different states means having different conditions. In manual mode, even if the inlet flow decreases suddenly by a small amount, the rotational speed remains unchanged; only the backflow momentum changes.
The rotation speed depends on the control method. For example, if you set it at 9000 RPM, there will be less rich gas at the inlet; the rotation speed will remain at 9000 RPM, but the mass flow rate of the fluid in circulation will be lower, and less steam will be required.
Can the amount of rich gas at the inlet affect the speed of the turbine? Very confused
It depends on the type of turbine; there are constant-speed and variable-speed types! The constant-speed type achieves balance by adjusting the amount of backflow motion, while the variable-speed type achieves balance by changing the rotation speed!
There are several possible interpretations of the original poster’s question: 1. The throttle valve is stuck and won’t move, resulting in a reduced amount of rich air entering; will the speed increase or decrease? 2. With the speed control on the DCS set to manual mode, and the amount of rich gas at the inlet reduced, will the speed increase or decrease? (Working principle of the speed control mechanism of a steam turbine: stabilizing the rotational speed or stabilizing the valve position of the speed control valve) 3. ……
The rotation speed does not change; it is adjusted based on the reaction pressure. When the amount of feed gas at the inlet decreases, the reaction pressure drops, and in such cases it is necessary to reduce the reaction speed or increase the counterforce in order to ensure the stable operation of the compressor
For example, at a speed of 8000 revolutions per minute, values such as 505 are used to control the operation; as the amount of rich gas decreases, the load on the compressor reduces. At this point, the valves remain unchanged, but the speed increases. The control system then takes action by closing the valves to maintain a constant speed. On the other hand, if reaction pressure control is used to prevent backflow, the backflow valve is opened to ensure stable reaction pressure
If you want to adjust the normal operating conditions of a turbine using its rotational speed, it is necessary to reduce that speed. In cases of a sudden decrease in speed, it is recommended to use counter-rotation for adjustment, or to combine both methods; it is not advisable to simply reduce the load significantly