What is the minimum steam inlet pressure for a turbine during operation?
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For back-pressure steam turbines, the medium-pressure steam inlet pressure is required to be maintained at no less than 3.0 MPa. However, today the steam inlet pressure of the turbine dropped to its lowest level ever recorded, at 2.58 MPA (while the steam temperature remained at 420 degrees). This situation lasted for about 20 minutes. Since the automatic protection system for the turbine’s steam inlet pressure was disabled, there was no automatic shutdown. At the lowest pressure, the turbine operated normally, with no fluctuations in speed, vibration, or displacement. I would like to ask the experts if they have encountered situations where a shutdown occurred due to low steam pressure, and what the steam pressure was at that time.
When the pressure is low, the valve is opened wider to maintain the unit’s set speed; if the pressure continues to drop, the speed also drops. If no adjustments are made, the unit will experience surge. If the pressure does not drop quickly enough, the load must be adjusted to keep the unit’s speed stable. If the pressure keeps falling, the only option is to reduce all loads and shut down the unit. This process requires strict monitoring of the steam temperature. Think about it carefully by yourself
This morning I specifically searched the Internet for information on this topic. Some sources state that the operating pressure for medium-pressure steam turbines is between 2.0 and 4.0; of course, the load must also be adjusted depending on the actual operating conditions.
If, as the pressure decreases and the temperature remains constant, the load also decreases accordingly, it is equivalent to operation at sliding parameters for a short period of time
If the pressure is low, the unit will definitely shut down; the unit is equipped with interlocks. As for at what pressure it shuts down, that depends on the set value. A gradual decrease in pressure, as long as it remains above the set value, seems to be fine, as everything is under automatic control. However, attention needs to be paid to the steam temperature to prevent liquid from being carried along in the steam. Incidentally, one of our companies’ Qingqi units operated at 18 kilograms of pressure for a short period of time, and seemed to function fine, but it’s still better to avoid such conditions
When designing a steam turbine, the maximum and minimum steam conditions specified by the buyer are taken into account. Within these ranges, the unit can maintain normal operation through control valves. If the steam parameters continue to decline, the turbine will operate at a reduced load, and its built-in protection system will trigger a shutdown of the unit
This post was last edited by eidl*ang on 2017-1-11 at 17:08. A low inlet steam pressure is not a mandatory interlock shutdown condition for the operation of the turbine. When the turbine control system is set to automatic mode, a decrease in steam pressure leads to an increase in steam consumption; as a result, the unit’s gas consumption rises and its efficiency drops. As long as the pressure is not too low, normal operation can be maintained. Of course, if the control valve is set to 100 and the speed continues to drop, attention should be paid to the risk of surge in the unit. Also, as the steam pressure decreases, the steam temperature changes; this temperature should not be lower than the saturated steam temperature at that corresponding pressure plus 40 degrees. This is how we control it.
Intake pressure is generally not a cause for shutdown; typically, the outlet backpressure of backpressure turbines is equipped with a shutdown interlock. When the inlet pressure is low, the control steam valve opens; once the speed reaches around 75%, there is no significant further increase. At this point, a large amount of steam entering can cause an increase in shaft displacement, preventing the speed from rising further and leading to surge in the compressor. Attention should also be paid to the degree of temperature drop – I have seen units continue to operate even when the temperature drops to 20 kilograms.
For medium-pressure steam turbines, the steam pressure must be maintained within the range of ±0.2 MPa of the design pressure; the maximum temperature shall not exceed the design temperature by more than 10°C, while the minimum temperature must not be lower than the design temperature by less than 15–20°C, otherwise it may cause damage to the operation of the equipment.
All the masters! For back-pressure medium-pressure steam turbines, what considerations underlie the interlock designed for a low steam outlet pressure?
As long as the temperature doesn’t drop, there’s no problem, but if the pressure decreases, increasing the steam supply is necessary to maintain the original load; avoid operating beyond the capacity limit to prevent the final stage blades from being overloaded